[{"video_title": "The effects of mutations   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "So, today we're going to talk about the overall effects of a genetic mutation, and how mutations impact the affected organism as a whole. But first, I want to review the central dogma of molecular biology, and how genetic information in a cell is stored in the form of DNA, which is then transcribed to form RNA, which is then translated to form protein. Now nucleotides from DNA are transcribed to their complementary forms on RNA, which are then read as codons, or groups of three, to code for specific amino acids in a larger protein. Now if you mutate one of the nucleotides on DNA, like turning a thymine base into an adenine base, then that will affect the RNA sequence, and ultimately the protein that follows. So we say that mutations are generally mistakes in a cell's DNA that lead to abnormal protein production. So are mutations good, or are they bad? And what kind of effect do they have on the affected organism?"}, {"video_title": "The effects of mutations   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "Now if you mutate one of the nucleotides on DNA, like turning a thymine base into an adenine base, then that will affect the RNA sequence, and ultimately the protein that follows. So we say that mutations are generally mistakes in a cell's DNA that lead to abnormal protein production. So are mutations good, or are they bad? And what kind of effect do they have on the affected organism? Well there isn't really a good answer to this question at all, and there are many, many different types of mutations out there that can result in big structural changes, like the little pictures I've drawn out here, or may result in little subtle changes that might go completely unnoticed. It's very difficult to call a mutation good or bad though, since it really depends on a huge number of things, including the environment that the organism lives in. So let's look at an example of a good mutation."}, {"video_title": "The effects of mutations   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "And what kind of effect do they have on the affected organism? Well there isn't really a good answer to this question at all, and there are many, many different types of mutations out there that can result in big structural changes, like the little pictures I've drawn out here, or may result in little subtle changes that might go completely unnoticed. It's very difficult to call a mutation good or bad though, since it really depends on a huge number of things, including the environment that the organism lives in. So let's look at an example of a good mutation. So the bacteria Streptococcus pneumoniae is the bacteria that you typically see associated with pneumonia, and one of the more popular treatments for pneumonia is giving the infected person an antibiotic like penicillin, which would help kill all of the bacteria and get rid of the disease. But sometimes you can find some mutated Streptococcus bacteria that will have a special trait that makes them resistant to penicillin, and now penicillin won't kill them as easily as it'll kill the bacteria without the mutation. Now we call this a good mutation because the bacteria are living in a human host, where they're likely to encounter this deadly penicillin, and being resistant to antibiotics like penicillin would then be beneficial to the bacteria."}, {"video_title": "The effects of mutations   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "So let's look at an example of a good mutation. So the bacteria Streptococcus pneumoniae is the bacteria that you typically see associated with pneumonia, and one of the more popular treatments for pneumonia is giving the infected person an antibiotic like penicillin, which would help kill all of the bacteria and get rid of the disease. But sometimes you can find some mutated Streptococcus bacteria that will have a special trait that makes them resistant to penicillin, and now penicillin won't kill them as easily as it'll kill the bacteria without the mutation. Now we call this a good mutation because the bacteria are living in a human host, where they're likely to encounter this deadly penicillin, and being resistant to antibiotics like penicillin would then be beneficial to the bacteria. And just to clarify, I'm calling this a good mutation for the bacteria, not really for the human infected, since it'll be harder for them to get rid of the bacteria that are resistant to certain antibiotics. So now let's look at an example of a bad mutation. So the disease cystic fibrosis is usually caused by a mutation in the CFTR gene."}, {"video_title": "The effects of mutations   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "Now we call this a good mutation because the bacteria are living in a human host, where they're likely to encounter this deadly penicillin, and being resistant to antibiotics like penicillin would then be beneficial to the bacteria. And just to clarify, I'm calling this a good mutation for the bacteria, not really for the human infected, since it'll be harder for them to get rid of the bacteria that are resistant to certain antibiotics. So now let's look at an example of a bad mutation. So the disease cystic fibrosis is usually caused by a mutation in the CFTR gene. Now I'm not really going to go into detail about how this mutation actually hurts you, but I'll leave you with the idea that what it does is it makes the mucus that you'd find in a person's lungs really, really thick, which makes it really hard for people affected with the disease to breathe. So in general, we can say that the mutation causing cystic fibrosis would be a quote-unquote bad mutation. But mutations aren't strictly good or strictly bad."}, {"video_title": "The effects of mutations   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "So the disease cystic fibrosis is usually caused by a mutation in the CFTR gene. Now I'm not really going to go into detail about how this mutation actually hurts you, but I'll leave you with the idea that what it does is it makes the mucus that you'd find in a person's lungs really, really thick, which makes it really hard for people affected with the disease to breathe. So in general, we can say that the mutation causing cystic fibrosis would be a quote-unquote bad mutation. But mutations aren't strictly good or strictly bad. In fact, there are some mutations that can cause some favorable and some disadvantageous effects. Sickle cell disease results from a mutation in a protein called hemoglobin that you'd find in red blood cells. And this mutation turns hemoglobin into a much less functional form, which we'll call HBS."}, {"video_title": "The effects of mutations   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "But mutations aren't strictly good or strictly bad. In fact, there are some mutations that can cause some favorable and some disadvantageous effects. Sickle cell disease results from a mutation in a protein called hemoglobin that you'd find in red blood cells. And this mutation turns hemoglobin into a much less functional form, which we'll call HBS. And it's much less efficient at moving oxygen around the human body. But another effect of sickle cell disease is that it makes the diseased person less susceptible to malaria. Now malaria is a parasite that grows and multiplies in red blood cells and can have a lot of nasty effects on the host organism."}, {"video_title": "The effects of mutations   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "And this mutation turns hemoglobin into a much less functional form, which we'll call HBS. And it's much less efficient at moving oxygen around the human body. But another effect of sickle cell disease is that it makes the diseased person less susceptible to malaria. Now malaria is a parasite that grows and multiplies in red blood cells and can have a lot of nasty effects on the host organism. And the malaria parasite can't really grow as well in red blood cells that are affected with sickle cell disease. So in this case, the mutation associated with this disease has one bad effect, which is that the HBS isn't as good as carrying oxygen around the body, but also a good effect in that it makes it less likely that the diseased person will be affected by malaria, since they can't grow as well in the human's red blood cells. So what did we learn?"}, {"video_title": "The effects of mutations   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "Now malaria is a parasite that grows and multiplies in red blood cells and can have a lot of nasty effects on the host organism. And the malaria parasite can't really grow as well in red blood cells that are affected with sickle cell disease. So in this case, the mutation associated with this disease has one bad effect, which is that the HBS isn't as good as carrying oxygen around the body, but also a good effect in that it makes it less likely that the diseased person will be affected by malaria, since they can't grow as well in the human's red blood cells. So what did we learn? Well, first we learned that the effects of the mutation will usually, but not always, appear at the protein level. There are some exceptions to this rule. And second, we learned that genetic mutations can have advantageous, deleterious, or neutral effects depending on the type of mutation, the environment that the affected organism lives in, as well as a multitude of other factors."}, {"video_title": "Discussions of conditions for Hardy Weinberg   Biology   Khan Academy.mp3", "Sentence": "If P is the frequency of the blue allele, Q is the frequency of the brown allele, well, and if they're the only two versions, well, if you add the frequency of P of the blue plus the frequency of the brown, they're gonna add up to 100%, or one. And if you square both sides of this, you would get this expression right over here, and we talk about that this is the probability, or you could say the frequency of being a homozygous, homozygous for the blue. This is the probability of having two alleles for the brown. And then right here in the middle, this is the probability of being a heterozygote. And why is that? Well, because you could get a blue from your mom and a brown from your dad, or a blue from your dad and a brown from your mom. So there's two ways to get that PQ combination."}, {"video_title": "Discussions of conditions for Hardy Weinberg   Biology   Khan Academy.mp3", "Sentence": "And then right here in the middle, this is the probability of being a heterozygote. And why is that? Well, because you could get a blue from your mom and a brown from your dad, or a blue from your dad and a brown from your mom. So there's two ways to get that PQ combination. Now the key idea here is Hardy-Weinberg assumes a stable allele frequency. So let me write that really big. Because all of these other conditions that you might see are really like, well, what are all the different ways that you could somehow not have stable allele frequency?"}, {"video_title": "Discussions of conditions for Hardy Weinberg   Biology   Khan Academy.mp3", "Sentence": "So there's two ways to get that PQ combination. Now the key idea here is Hardy-Weinberg assumes a stable allele frequency. So let me write that really big. Because all of these other conditions that you might see are really like, well, what are all the different ways that you could somehow not have stable allele frequency? So let me write this down. Stable allele frequency. Stable allele frequency."}, {"video_title": "Discussions of conditions for Hardy Weinberg   Biology   Khan Academy.mp3", "Sentence": "Because all of these other conditions that you might see are really like, well, what are all the different ways that you could somehow not have stable allele frequency? So let me write this down. Stable allele frequency. Stable allele frequency. So a lot of times, there's a temptation to memorize a bunch of stuff. You might wanna do that, but the more important thing is to get the underlying idea. And the underlying idea is, well, will something somehow cause the allele frequency to be unstable?"}, {"video_title": "Discussions of conditions for Hardy Weinberg   Biology   Khan Academy.mp3", "Sentence": "Stable allele frequency. So a lot of times, there's a temptation to memorize a bunch of stuff. You might wanna do that, but the more important thing is to get the underlying idea. And the underlying idea is, well, will something somehow cause the allele frequency to be unstable? And actually, another way to say stable allele frequency is no evolution. No evolution. Evolution is a change in the heritable traits in a population, and that will include a change in allele frequency."}, {"video_title": "Discussions of conditions for Hardy Weinberg   Biology   Khan Academy.mp3", "Sentence": "And the underlying idea is, well, will something somehow cause the allele frequency to be unstable? And actually, another way to say stable allele frequency is no evolution. No evolution. Evolution is a change in the heritable traits in a population, and that will include a change in allele frequency. And if you think about the two ways that you could have a population evolving, well, you can have selection. So we're gonna assume no selection. Actually, there's more than two ways."}, {"video_title": "Discussions of conditions for Hardy Weinberg   Biology   Khan Academy.mp3", "Sentence": "Evolution is a change in the heritable traits in a population, and that will include a change in allele frequency. And if you think about the two ways that you could have a population evolving, well, you can have selection. So we're gonna assume no selection. Actually, there's more than two ways. You could have genetic engineering and all sorts of things. So we're gonna assume, but the mainstream ways, I guess you could say, we can assume no selection. We can assume no genetic drift."}, {"video_title": "Discussions of conditions for Hardy Weinberg   Biology   Khan Academy.mp3", "Sentence": "Actually, there's more than two ways. You could have genetic engineering and all sorts of things. So we're gonna assume, but the mainstream ways, I guess you could say, we can assume no selection. We can assume no genetic drift. Remember, selection is certain traits that make that organism more fit for that environment. Well, those traits are going to be more likely to be passed on. Genetic drift is random chance changes in the allele frequency."}, {"video_title": "Discussions of conditions for Hardy Weinberg   Biology   Khan Academy.mp3", "Sentence": "We can assume no genetic drift. Remember, selection is certain traits that make that organism more fit for that environment. Well, those traits are going to be more likely to be passed on. Genetic drift is random chance changes in the allele frequency. It could be due to small populations. It could be due to members of the population migrating or some type of bottleneck effect, some natural disaster that really gets you to that small population. So that's the big picture."}, {"video_title": "Discussions of conditions for Hardy Weinberg   Biology   Khan Academy.mp3", "Sentence": "Genetic drift is random chance changes in the allele frequency. It could be due to small populations. It could be due to members of the population migrating or some type of bottleneck effect, some natural disaster that really gets you to that small population. So that's the big picture. But given that big picture, I wanna dive deep into some of the assumptions that you might see in your biology class, just so you feel comfortable with them and you see that we're talking about the same thing. So the ones that I mentioned in that introductory video are no selection, and that's consistent with no evolution. I also talk about no net mutation, also consistent with no evolution."}, {"video_title": "Discussions of conditions for Hardy Weinberg   Biology   Khan Academy.mp3", "Sentence": "So that's the big picture. But given that big picture, I wanna dive deep into some of the assumptions that you might see in your biology class, just so you feel comfortable with them and you see that we're talking about the same thing. So the ones that I mentioned in that introductory video are no selection, and that's consistent with no evolution. I also talk about no net mutation, also consistent with no evolution. Once again, we don't wanna change the allele frequency. If there was net mutation, maybe some of those blue versions of the gene get a mutation, and they're now maybe a different version, or they're definitely not blue anymore, so the allele frequency would change. The reason why we care about large population is mainly for genetic drift."}, {"video_title": "Discussions of conditions for Hardy Weinberg   Biology   Khan Academy.mp3", "Sentence": "I also talk about no net mutation, also consistent with no evolution. Once again, we don't wanna change the allele frequency. If there was net mutation, maybe some of those blue versions of the gene get a mutation, and they're now maybe a different version, or they're definitely not blue anymore, so the allele frequency would change. The reason why we care about large population is mainly for genetic drift. If you have a very small population, just due to random chance, it's more likely that the allele frequencies can change appreciably. Now, other conditions that you will often see are things like random mating, that whether an orgasm has the blue or the brown version of the gene, that that doesn't make them any more or less desirable to a member of the opposite sex. And if you think about it, you might say, well, isn't that a form of selection?"}, {"video_title": "Discussions of conditions for Hardy Weinberg   Biology   Khan Academy.mp3", "Sentence": "The reason why we care about large population is mainly for genetic drift. If you have a very small population, just due to random chance, it's more likely that the allele frequencies can change appreciably. Now, other conditions that you will often see are things like random mating, that whether an orgasm has the blue or the brown version of the gene, that that doesn't make them any more or less desirable to a member of the opposite sex. And if you think about it, you might say, well, isn't that a form of selection? And you'd say, well, yes, it kind of is, but this is sometimes broken out as another way. Now, also, no migration, that you don't have, the population isn't growing by other organisms entering it or isn't shrinking by other organisms leaving, or there's not a mixing of population between two populations, and once again, it's all because we care about stable allele frequencies. Now, if we wanna go even further than that, and sometimes you will hear these types of things mentioned, although I just mentioned the five mainstream things, which all boil down to stable allele frequency, no evolution, no selection, no genetic drift, but sometimes we are assuming that we are dealing with diploid organisms, that you're getting one set of chromosomes from your mom, one set of chromosomes from your dad, or one version of an allele from your mom, one version of an allele from your dad, and you might say, well, how can you be other than diploid?"}, {"video_title": "Discussions of conditions for Hardy Weinberg   Biology   Khan Academy.mp3", "Sentence": "And if you think about it, you might say, well, isn't that a form of selection? And you'd say, well, yes, it kind of is, but this is sometimes broken out as another way. Now, also, no migration, that you don't have, the population isn't growing by other organisms entering it or isn't shrinking by other organisms leaving, or there's not a mixing of population between two populations, and once again, it's all because we care about stable allele frequencies. Now, if we wanna go even further than that, and sometimes you will hear these types of things mentioned, although I just mentioned the five mainstream things, which all boil down to stable allele frequency, no evolution, no selection, no genetic drift, but sometimes we are assuming that we are dealing with diploid organisms, that you're getting one set of chromosomes from your mom, one set of chromosomes from your dad, or one version of an allele from your mom, one version of an allele from your dad, and you might say, well, how can you be other than diploid? Well, you could be, there are tetraploid populations, especially this can happen in plants, or we could get two sets of chromosomes from your mom, two sets of chromosomes from your dad. We are assuming sexual reproduction, that we're not dealing with cloning, and or just budding, where you're just a copy of another organism from generation to generation. We're assuming that whether you are blue or brown, whether you have those versions, that that's not correlated with what sex you are."}, {"video_title": "Discussions of conditions for Hardy Weinberg   Biology   Khan Academy.mp3", "Sentence": "Now, if we wanna go even further than that, and sometimes you will hear these types of things mentioned, although I just mentioned the five mainstream things, which all boil down to stable allele frequency, no evolution, no selection, no genetic drift, but sometimes we are assuming that we are dealing with diploid organisms, that you're getting one set of chromosomes from your mom, one set of chromosomes from your dad, or one version of an allele from your mom, one version of an allele from your dad, and you might say, well, how can you be other than diploid? Well, you could be, there are tetraploid populations, especially this can happen in plants, or we could get two sets of chromosomes from your mom, two sets of chromosomes from your dad. We are assuming sexual reproduction, that we're not dealing with cloning, and or just budding, where you're just a copy of another organism from generation to generation. We're assuming that whether you are blue or brown, whether you have those versions, that that's not correlated with what sex you are. So allele frequency, allele frequency, same in all sexes, in all sexes, and we're assuming sexual reproduction. Once again, we're assuming one where there's only two sexes. So you could, if you were to think about, if you were to let your imagination go wild, you could imagine a lot of other constraints to put here, or other ways that the, where you could no longer have, apply the Hardy-Weinberg, where this is, we have two alleles, we're assuming sexual reproduction, diploid, you're getting a mom from your mom, from your dad, and just here are all the conditions that help us ensure that we have a stable allele frequency."}, {"video_title": "Discussions of conditions for Hardy Weinberg   Biology   Khan Academy.mp3", "Sentence": "We're assuming that whether you are blue or brown, whether you have those versions, that that's not correlated with what sex you are. So allele frequency, allele frequency, same in all sexes, in all sexes, and we're assuming sexual reproduction. Once again, we're assuming one where there's only two sexes. So you could, if you were to think about, if you were to let your imagination go wild, you could imagine a lot of other constraints to put here, or other ways that the, where you could no longer have, apply the Hardy-Weinberg, where this is, we have two alleles, we're assuming sexual reproduction, diploid, you're getting a mom from your mom, from your dad, and just here are all the conditions that help us ensure that we have a stable allele frequency. Now the one thing you're saying, okay, I can, you know, diploid, sexual reproduction, okay, but isn't, isn't, you know, isn't there always a chance for a little bit of genetic drift? Isn't there, you know, just the history of the world, is that we have this evolution? And the answer is yes."}, {"video_title": "Applications of DNA technologies   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "So what are some applications of DNA technology? Applications, DNA technology. Alright, well let's first look at medicine. So what are some applications of DNA technology in medicine? Well, one of the really big, the two big things where recombinant DNA technology was first used was to create insulin and human growth hormone. So before the advent of recombinant DNA technology, insulin and growth hormone were really, really hard to manufacture. You basically had to isolate it from another human and purify it and then give it to patients."}, {"video_title": "Applications of DNA technologies   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "So what are some applications of DNA technology in medicine? Well, one of the really big, the two big things where recombinant DNA technology was first used was to create insulin and human growth hormone. So before the advent of recombinant DNA technology, insulin and growth hormone were really, really hard to manufacture. You basically had to isolate it from another human and purify it and then give it to patients. But with recombinant DNA technology, you can basically just grow these proteins in E. coli. You can grow them and culture them in E. coli bacteria. So this really has changed the way that medicine is practiced and it's really helped a whole bunch of people."}, {"video_title": "Applications of DNA technologies   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "You basically had to isolate it from another human and purify it and then give it to patients. But with recombinant DNA technology, you can basically just grow these proteins in E. coli. You can grow them and culture them in E. coli bacteria. So this really has changed the way that medicine is practiced and it's really helped a whole bunch of people. So vaccines is another application of DNA technology. A while ago, vaccines were made by first denaturing the disease and then after the disease has been weakened, they would inject it into a human and they would hope that their immune system would be able to put up a fight against the weakened virus. And that way in the future, if they were infected with that virus, they would at least have some kind of immune response towards the virus."}, {"video_title": "Applications of DNA technologies   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "So this really has changed the way that medicine is practiced and it's really helped a whole bunch of people. So vaccines is another application of DNA technology. A while ago, vaccines were made by first denaturing the disease and then after the disease has been weakened, they would inject it into a human and they would hope that their immune system would be able to put up a fight against the weakened virus. And that way in the future, if they were infected with that virus, they would at least have some kind of immune response towards the virus. The problem with this was that the patient would sometimes get the disease because you're injecting a weak virus, but sometimes it wasn't weak enough. So with DNA technology, they can actually recreate the outer shell of the virus and inject that. So it's a lot more cost effective and it doesn't have the risk of actually causing the disease in the host."}, {"video_title": "Applications of DNA technologies   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "And that way in the future, if they were infected with that virus, they would at least have some kind of immune response towards the virus. The problem with this was that the patient would sometimes get the disease because you're injecting a weak virus, but sometimes it wasn't weak enough. So with DNA technology, they can actually recreate the outer shell of the virus and inject that. So it's a lot more cost effective and it doesn't have the risk of actually causing the disease in the host. So this is much safer and it is cheaper and it produces a better immune response. And so some vaccines that we actually use recombinant DNA technology to create include the Hep B virus and the herpes virus and malaria. So these are some applications of DNA technology in medicine."}, {"video_title": "Applications of DNA technologies   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "So it's a lot more cost effective and it doesn't have the risk of actually causing the disease in the host. So this is much safer and it is cheaper and it produces a better immune response. And so some vaccines that we actually use recombinant DNA technology to create include the Hep B virus and the herpes virus and malaria. So these are some applications of DNA technology in medicine. Another cool application of DNA technology is in solving crimes. So solving crimes, so in forensics. So there are parts of the genome known as non-coding regions of the genome."}, {"video_title": "Applications of DNA technologies   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "So these are some applications of DNA technology in medicine. Another cool application of DNA technology is in solving crimes. So solving crimes, so in forensics. So there are parts of the genome known as non-coding regions of the genome. And these regions can actually help forensic scientists identify specific individuals. So they can look at things like short tandem repeats, STRs. And these are basically short sequences of DNA, like two to six base pairs long."}, {"video_title": "Applications of DNA technologies   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "So there are parts of the genome known as non-coding regions of the genome. And these regions can actually help forensic scientists identify specific individuals. So they can look at things like short tandem repeats, STRs. And these are basically short sequences of DNA, like two to six base pairs long. And they're normally found in really high amounts. They're just these short repeats that are found in really high amounts and to varying degrees between different individuals. So they actually sequence these short tandem repeats."}, {"video_title": "Applications of DNA technologies   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "And these are basically short sequences of DNA, like two to six base pairs long. And they're normally found in really high amounts. They're just these short repeats that are found in really high amounts and to varying degrees between different individuals. So they actually sequence these short tandem repeats. They could identify specific individuals given a DNA sample. They can also look at mitochondrial DNA. So mitochondrial DNA is inherited from your mother and it's found in really high amounts within an individual cell."}, {"video_title": "Applications of DNA technologies   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "So they actually sequence these short tandem repeats. They could identify specific individuals given a DNA sample. They can also look at mitochondrial DNA. So mitochondrial DNA is inherited from your mother and it's found in really high amounts within an individual cell. So even if there's very little sample available, forensic scientists can analyze mitochondrial DNA in order to identify a potential suspect. Another technology that is used in forensic science is Y chromosome typing. So that's basically YSTR."}, {"video_title": "Applications of DNA technologies   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "So mitochondrial DNA is inherited from your mother and it's found in really high amounts within an individual cell. So even if there's very little sample available, forensic scientists can analyze mitochondrial DNA in order to identify a potential suspect. Another technology that is used in forensic science is Y chromosome typing. So that's basically YSTR. And this is looking at short tandem repeats found on the Y chromosome. And so DNA technology has helped scientists pick out individuals that have committed various crimes based on DNA samples that people that they were able to find. So agriculture is another field that has greatly benefited from recombinant DNA technology."}, {"video_title": "Applications of DNA technologies   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "So that's basically YSTR. And this is looking at short tandem repeats found on the Y chromosome. And so DNA technology has helped scientists pick out individuals that have committed various crimes based on DNA samples that people that they were able to find. So agriculture is another field that has greatly benefited from recombinant DNA technology. So, for example, scientists can now create plants that are crops that are resistant to insects and that are resistant to herbicides and can also delay ripening of the crop so that you can transport the crop from the farm to the store. So by doing this, you're basically able to create more crops to feed a growing population of individuals. And it also helps with the economy because then you've got farmers that are growing all their crops."}, {"video_title": "Endocytosis, phagocytosis, and pinocytosis   Biology   Khan Academy.mp3", "Sentence": "We have other videos where we talk about how small molecules or ions might be able to go through a cell's membrane in different ways, whether actively or passively, maybe facilitated in some way. What we want to talk about in this video is how we can do this for larger things. So we're going to focus on here is bulk, bulk transport, transport. So this first example, you could imagine this, this cell with this mauve or purple colored membrane is engulfing this big green thing, which is maybe a bacteria or something. And so you see that the membrane, let me make it very clear, this is inside, this is inside the cell, this is outside, outside the cell. And you can see the cellular membrane starts to wrap around this, I guess we can think of this as a bacteria. Then it fully wraps around, and then that membrane that was wrapping around the bacteria pinches off, and now the bacteria is inside of the cell, and it's wrapped by this membrane."}, {"video_title": "Endocytosis, phagocytosis, and pinocytosis   Biology   Khan Academy.mp3", "Sentence": "So this first example, you could imagine this, this cell with this mauve or purple colored membrane is engulfing this big green thing, which is maybe a bacteria or something. And so you see that the membrane, let me make it very clear, this is inside, this is inside the cell, this is outside, outside the cell. And you can see the cellular membrane starts to wrap around this, I guess we can think of this as a bacteria. Then it fully wraps around, and then that membrane that was wrapping around the bacteria pinches off, and now the bacteria is inside of the cell, and it's wrapped by this membrane. And this process, where you're engulfing these large things, we call this phagocytosis. So this is phago, phagocytosis. And the prefix, I guess you could say phago, comes from the Greek for to eat."}, {"video_title": "Endocytosis, phagocytosis, and pinocytosis   Biology   Khan Academy.mp3", "Sentence": "Then it fully wraps around, and then that membrane that was wrapping around the bacteria pinches off, and now the bacteria is inside of the cell, and it's wrapped by this membrane. And this process, where you're engulfing these large things, we call this phagocytosis. So this is phago, phagocytosis. And the prefix, I guess you could say phago, comes from the Greek for to eat. So this is literally about cell eating. And in many cases, this thing that is now in here, you could view this as the cell's food, this compartment that is holding this, in this case, bacteria, is going to transport it maybe to a lysosome so it can be processed and digested in some way. We would call this big compartment, this membrane-bound compartment, we would call this a food vacuole."}, {"video_title": "Endocytosis, phagocytosis, and pinocytosis   Biology   Khan Academy.mp3", "Sentence": "And the prefix, I guess you could say phago, comes from the Greek for to eat. So this is literally about cell eating. And in many cases, this thing that is now in here, you could view this as the cell's food, this compartment that is holding this, in this case, bacteria, is going to transport it maybe to a lysosome so it can be processed and digested in some way. We would call this big compartment, this membrane-bound compartment, we would call this a food vacuole. Food, food vacuole. Now, this scenario down here is similar but different. Over here I have the cell, which is, I see part of its membrane, and it's in magenta right over here."}, {"video_title": "Endocytosis, phagocytosis, and pinocytosis   Biology   Khan Academy.mp3", "Sentence": "We would call this big compartment, this membrane-bound compartment, we would call this a food vacuole. Food, food vacuole. Now, this scenario down here is similar but different. Over here I have the cell, which is, I see part of its membrane, and it's in magenta right over here. We can see the phospholipid bilayer. That's why I drew two lines for the membrane. And instead of engulfing a large particle or bacteria, it's just engulfing some fluid."}, {"video_title": "Endocytosis, phagocytosis, and pinocytosis   Biology   Khan Academy.mp3", "Sentence": "Over here I have the cell, which is, I see part of its membrane, and it's in magenta right over here. We can see the phospholipid bilayer. That's why I drew two lines for the membrane. And instead of engulfing a large particle or bacteria, it's just engulfing some fluid. It's engulfing some fluid. So you see it's starting to wrap around this section of fluid, wraps even more around this section of fluid, and then the membrane that was around it completely pinches off and goes into the cell. And I'm drawing all of these things in two dimensions, but this would actually be happening in three dimensions."}, {"video_title": "Endocytosis, phagocytosis, and pinocytosis   Biology   Khan Academy.mp3", "Sentence": "And instead of engulfing a large particle or bacteria, it's just engulfing some fluid. It's engulfing some fluid. So you see it's starting to wrap around this section of fluid, wraps even more around this section of fluid, and then the membrane that was around it completely pinches off and goes into the cell. And I'm drawing all of these things in two dimensions, but this would actually be happening in three dimensions. So this wouldn't just be a circle, this right over here would be a sphere. And this thing that has been pinched off and is now inside the cell, we call this a vesicle, which is just a general term for these membrane-bound compartments inside of cells. And this process where the cell has essentially drunk a bunch of fluid and the stuff that happens to be in the fluid, we call this pinocytosis."}, {"video_title": "Endocytosis, phagocytosis, and pinocytosis   Biology   Khan Academy.mp3", "Sentence": "And I'm drawing all of these things in two dimensions, but this would actually be happening in three dimensions. So this wouldn't just be a circle, this right over here would be a sphere. And this thing that has been pinched off and is now inside the cell, we call this a vesicle, which is just a general term for these membrane-bound compartments inside of cells. And this process where the cell has essentially drunk a bunch of fluid and the stuff that happens to be in the fluid, we call this pinocytosis. Pinocytosis. Pinocytosis. And pino comes from the Greek word to drink."}, {"video_title": "Endocytosis, phagocytosis, and pinocytosis   Biology   Khan Academy.mp3", "Sentence": "And this process where the cell has essentially drunk a bunch of fluid and the stuff that happens to be in the fluid, we call this pinocytosis. Pinocytosis. Pinocytosis. And pino comes from the Greek word to drink. And I'm always fascinated by word roots, and I'm not a linguistic expert here, but it's neat because even in languages I'm familiar with, like Hindi and Urdu, the word pina means to drink. So it's a, and maybe it's even related to the word pani, which is in those words, in those languages. I know all of these have a shared linguistic root, so it's always fascinating to see these, to see these linguistic connections."}, {"video_title": "Endocytosis, phagocytosis, and pinocytosis   Biology   Khan Academy.mp3", "Sentence": "And pino comes from the Greek word to drink. And I'm always fascinated by word roots, and I'm not a linguistic expert here, but it's neat because even in languages I'm familiar with, like Hindi and Urdu, the word pina means to drink. So it's a, and maybe it's even related to the word pani, which is in those words, in those languages. I know all of these have a shared linguistic root, so it's always fascinating to see these, to see these linguistic connections. So this is pinocytosis, where the cell is drinking, so to speak, but it's also getting the other stuff that's in that fluid. This is phagocytosis, the cell is eating. And those, these are both special cases of, I guess the more general term of engulfing in this way, which is called endocytosis."}, {"video_title": "Endocytosis, phagocytosis, and pinocytosis   Biology   Khan Academy.mp3", "Sentence": "I know all of these have a shared linguistic root, so it's always fascinating to see these, to see these linguistic connections. So this is pinocytosis, where the cell is drinking, so to speak, but it's also getting the other stuff that's in that fluid. This is phagocytosis, the cell is eating. And those, these are both special cases of, I guess the more general term of engulfing in this way, which is called endocytosis. Endo, endocytosis. So phagocytosis is a form of endocytosis, and pinocytosis is a form of endocytosis. Now the next question you might say is, okay, I can get that this happens, this can be observed under a microscope, but how does it happen?"}, {"video_title": "Endocytosis, phagocytosis, and pinocytosis   Biology   Khan Academy.mp3", "Sentence": "And those, these are both special cases of, I guess the more general term of engulfing in this way, which is called endocytosis. Endo, endocytosis. So phagocytosis is a form of endocytosis, and pinocytosis is a form of endocytosis. Now the next question you might say is, okay, I can get that this happens, this can be observed under a microscope, but how does it happen? How does the cell wrap around and pinch around? And like I say in a lot of videos, people think that we understand some of it, but this is not fully, fully understood. There's views that, well, the cytoskeleton must be involved in some way."}, {"video_title": "Endocytosis, phagocytosis, and pinocytosis   Biology   Khan Academy.mp3", "Sentence": "Now the next question you might say is, okay, I can get that this happens, this can be observed under a microscope, but how does it happen? How does the cell wrap around and pinch around? And like I say in a lot of videos, people think that we understand some of it, but this is not fully, fully understood. There's views that, well, the cytoskeleton must be involved in some way. It has to create space here for this thing to be able to pinch off and move in that direction. It maybe will help, actually, the cell's membrane wrap around in some way, but these are all areas of active research. How does this endocytosis actually occur?"}, {"video_title": "Molecular structure of RNA   Macromolecules   Biology   Khan Academy (3).mp3", "Sentence": "In fact, right depicted in front of us, we have two strands of DNA forming a double helix. And we can look at the telltale signs that this is DNA. And in particular, we can look at the five-carbon sugar on its backbone. We see, and let's actually number the carbons. This is one prime, two prime, three prime, four prime, five prime. We can see on the two-prime carbon, we don't have an oxygen attached to it. We don't have a hydroxyl group attached to it."}, {"video_title": "Molecular structure of RNA   Macromolecules   Biology   Khan Academy (3).mp3", "Sentence": "We see, and let's actually number the carbons. This is one prime, two prime, three prime, four prime, five prime. We can see on the two-prime carbon, we don't have an oxygen attached to it. We don't have a hydroxyl group attached to it. And because of that, we know that this is not ribose. This is deoxyribose. This right over here is deoxyribose."}, {"video_title": "Molecular structure of RNA   Macromolecules   Biology   Khan Academy (3).mp3", "Sentence": "We don't have a hydroxyl group attached to it. And because of that, we know that this is not ribose. This is deoxyribose. This right over here is deoxyribose. And these two are also deoxyribose. So that tells us that we have two strands of DNA, deoxyribonucleic acid. So let me write this down."}, {"video_title": "Molecular structure of RNA   Macromolecules   Biology   Khan Academy (3).mp3", "Sentence": "This right over here is deoxyribose. And these two are also deoxyribose. So that tells us that we have two strands of DNA, deoxyribonucleic acid. So let me write this down. This part of the chain, this is derived from a deoxyribose being attached to phosphate groups in a nitrogenous base. So deoxyribose. So what would we have to do if we wanted, instead of viewing this as two strands of DNA in a double helix formation, well, how would we have to rearrange, how would we have to edit the left-hand strand if instead we wanted to imagine that the left-hand strand is, say, messenger RNA being generated during transcription with a single strand of DNA here on the right?"}, {"video_title": "Molecular structure of RNA   Macromolecules   Biology   Khan Academy (3).mp3", "Sentence": "So let me write this down. This part of the chain, this is derived from a deoxyribose being attached to phosphate groups in a nitrogenous base. So deoxyribose. So what would we have to do if we wanted, instead of viewing this as two strands of DNA in a double helix formation, well, how would we have to rearrange, how would we have to edit the left-hand strand if instead we wanted to imagine that the left-hand strand is, say, messenger RNA being generated during transcription with a single strand of DNA here on the right? Well, to turn this into RNA, or to make it look like RNA, on the two prime carbon, well, we wanna turn the deoxyribose into just ribose, so we would wanna add a hydroxyl group right over here. So add a hydroxyl group over there. Actually, let me do that."}, {"video_title": "Molecular structure of RNA   Macromolecules   Biology   Khan Academy (3).mp3", "Sentence": "So what would we have to do if we wanted, instead of viewing this as two strands of DNA in a double helix formation, well, how would we have to rearrange, how would we have to edit the left-hand strand if instead we wanted to imagine that the left-hand strand is, say, messenger RNA being generated during transcription with a single strand of DNA here on the right? Well, to turn this into RNA, or to make it look like RNA, on the two prime carbon, well, we wanna turn the deoxyribose into just ribose, so we would wanna add a hydroxyl group right over here. So add a hydroxyl group over there. Actually, let me do that. Do the hydrogens in white. So add one hydroxyl group there. And I wanna do it on all the sugars on the left strand's backbone."}, {"video_title": "Molecular structure of RNA   Macromolecules   Biology   Khan Academy (3).mp3", "Sentence": "Actually, let me do that. Do the hydrogens in white. So add one hydroxyl group there. And I wanna do it on all the sugars on the left strand's backbone. If I want this to be a single strand of RNA, and RNA tends to be single-stranded. So oxygen and then a hydrogen. And so this hydroxyl, adding this hydroxyl group, instead of just having another hydrogen, just a hydrogen by itself over there, this tells us that this sugar is no longer deoxyribose."}, {"video_title": "Molecular structure of RNA   Macromolecules   Biology   Khan Academy (3).mp3", "Sentence": "And I wanna do it on all the sugars on the left strand's backbone. If I want this to be a single strand of RNA, and RNA tends to be single-stranded. So oxygen and then a hydrogen. And so this hydroxyl, adding this hydroxyl group, instead of just having another hydrogen, just a hydrogen by itself over there, this tells us that this sugar is no longer deoxyribose. This is ribose. So now we have ribose. We now have ribose in our backbone, which is a telltale sign that, well, at least now we have the backbone of RNA, ribonucleic acid, versus DNA, deoxyribonucleic acid."}, {"video_title": "Molecular structure of RNA   Macromolecules   Biology   Khan Academy (3).mp3", "Sentence": "And so this hydroxyl, adding this hydroxyl group, instead of just having another hydrogen, just a hydrogen by itself over there, this tells us that this sugar is no longer deoxyribose. This is ribose. So now we have ribose. We now have ribose in our backbone, which is a telltale sign that, well, at least now we have the backbone of RNA, ribonucleic acid, versus DNA, deoxyribonucleic acid. Now you might think we're done, but we're not quite done, because the nitrogenous bases on RNA are slightly different than the nitrogenous bases on DNA. On DNA, your nitrogenous bases are adenine, guanine, are adenine, guanine, and adenine and guanine are the two-ringed nitrogenous bases right over here. This is adenine, this is guanine."}, {"video_title": "Molecular structure of RNA   Macromolecules   Biology   Khan Academy (3).mp3", "Sentence": "We now have ribose in our backbone, which is a telltale sign that, well, at least now we have the backbone of RNA, ribonucleic acid, versus DNA, deoxyribonucleic acid. Now you might think we're done, but we're not quite done, because the nitrogenous bases on RNA are slightly different than the nitrogenous bases on DNA. On DNA, your nitrogenous bases are adenine, guanine, are adenine, guanine, and adenine and guanine are the two-ringed nitrogenous bases right over here. This is adenine, this is guanine. And you also have cytosine. Cytosine, I'm gonna do these all in different colors. Cytosine and thymine."}, {"video_title": "Molecular structure of RNA   Macromolecules   Biology   Khan Academy (3).mp3", "Sentence": "This is adenine, this is guanine. And you also have cytosine. Cytosine, I'm gonna do these all in different colors. Cytosine and thymine. I'm getting to the punchline too fast. And this right over here is cytosine, and this is thymine. And cytosine and thymine are single-ringed nitrogenous bases."}, {"video_title": "Molecular structure of RNA   Macromolecules   Biology   Khan Academy (3).mp3", "Sentence": "Cytosine and thymine. I'm getting to the punchline too fast. And this right over here is cytosine, and this is thymine. And cytosine and thymine are single-ringed nitrogenous bases. We call them pyrimidines, adenine and guanine. We call them purines. This is a little bit of a review."}, {"video_title": "Molecular structure of RNA   Macromolecules   Biology   Khan Academy (3).mp3", "Sentence": "And cytosine and thymine are single-ringed nitrogenous bases. We call them pyrimidines, adenine and guanine. We call them purines. This is a little bit of a review. In RNA, you still have adenine, you still have guanine, you still have cytosine, but instead of thymine, you have a very close relative of thymine, and that is uracil. So the way that this is drawn right now, this nitrogenous base, remember when we started this video, it was double-stranded DNA, this nitrogenous base right over here is thymine, and it bonds, it forms hydrogen bonds with adenine right over here. If I want to turn it into uracil, I just have to get rid of this methyl group right over here."}, {"video_title": "Molecular structure of RNA   Macromolecules   Biology   Khan Academy (3).mp3", "Sentence": "This is a little bit of a review. In RNA, you still have adenine, you still have guanine, you still have cytosine, but instead of thymine, you have a very close relative of thymine, and that is uracil. So the way that this is drawn right now, this nitrogenous base, remember when we started this video, it was double-stranded DNA, this nitrogenous base right over here is thymine, and it bonds, it forms hydrogen bonds with adenine right over here. If I want to turn it into uracil, I just have to get rid of this methyl group right over here. So if I just do this, if I just do this, and if I were to replace it with a hydrogen that is just implicitly bonded there, well now I'm dealing with uracil. So now I'm dealing with uracil. So you see that uracil and thymine are very close molecules, or they're very similar nitrogenous bases, and that's why they can play a very similar role."}, {"video_title": "Molecular structure of RNA   Macromolecules   Biology   Khan Academy (3).mp3", "Sentence": "If I want to turn it into uracil, I just have to get rid of this methyl group right over here. So if I just do this, if I just do this, and if I were to replace it with a hydrogen that is just implicitly bonded there, well now I'm dealing with uracil. So now I'm dealing with uracil. So you see that uracil and thymine are very close molecules, or they're very similar nitrogenous bases, and that's why they can play a very similar role. And it's still the case. And so what uracil pairs with, it pairs still with adenine, the same thing that thymine pairs with, and everything else is of course still the same. Now an interesting question, an interesting question is why uracil?"}, {"video_title": "Molecular structure of RNA   Macromolecules   Biology   Khan Academy (3).mp3", "Sentence": "So you see that uracil and thymine are very close molecules, or they're very similar nitrogenous bases, and that's why they can play a very similar role. And it's still the case. And so what uracil pairs with, it pairs still with adenine, the same thing that thymine pairs with, and everything else is of course still the same. Now an interesting question, an interesting question is why uracil? Why not thymine? Or you could say why thymine? Why not uracil?"}, {"video_title": "Molecular structure of RNA   Macromolecules   Biology   Khan Academy (3).mp3", "Sentence": "Now an interesting question, an interesting question is why uracil? Why not thymine? Or you could say why thymine? Why not uracil? And based on what I've read, it actually turns out that uracil is a little bit more error prone. It might be able to bond with other things when you're coding. It's a little bit less stable than thymine."}, {"video_title": "Molecular structure of RNA   Macromolecules   Biology   Khan Academy (3).mp3", "Sentence": "Why not uracil? And based on what I've read, it actually turns out that uracil is a little bit more error prone. It might be able to bond with other things when you're coding. It's a little bit less stable than thymine. And so uracil, uracil, uracil makes the RNA molecule, or actually makes the machinery of information transfer, it makes it less stable. It's a less stable, I guess, way to transfer information. And based on what I've read, in evolutionary history, RNA molecules, most people believe, predate DNA molecules."}, {"video_title": "Molecular structure of RNA   Macromolecules   Biology   Khan Academy (3).mp3", "Sentence": "It's a little bit less stable than thymine. And so uracil, uracil, uracil makes the RNA molecule, or actually makes the machinery of information transfer, it makes it less stable. It's a less stable, I guess, way to transfer information. And based on what I've read, in evolutionary history, RNA molecules, most people believe, predate DNA molecules. And then when you, so in the early stages you had a lot of change, and so uracil molecules were just fine, and there was a lot of errors and whatever else, but then once you had, I guess, information needed to be a little bit more persistent and a little less error prone, well then thymine helped stabilize, thymine helped stabilize things. There's also the view of, well why is uracil stuck around? Well RNA molecules, they have all of these roles in cells, messenger RNA molecules are taking information from the DNA and getting it transcribed, or getting it translated at the ribosome, but they shouldn't hang out forever."}, {"video_title": "Molecular structure of RNA   Macromolecules   Biology   Khan Academy (3).mp3", "Sentence": "And based on what I've read, in evolutionary history, RNA molecules, most people believe, predate DNA molecules. And then when you, so in the early stages you had a lot of change, and so uracil molecules were just fine, and there was a lot of errors and whatever else, but then once you had, I guess, information needed to be a little bit more persistent and a little less error prone, well then thymine helped stabilize, thymine helped stabilize things. There's also the view of, well why is uracil stuck around? Well RNA molecules, they have all of these roles in cells, messenger RNA molecules are taking information from the DNA and getting it transcribed, or getting it translated at the ribosome, but they shouldn't hang out forever. You actually want them to be somewhat unstable. So it's an interesting question to think about. Why do we have uracil instead of thymine?"}, {"video_title": "Molecular structure of RNA   Macromolecules   Biology   Khan Academy (3).mp3", "Sentence": "Well RNA molecules, they have all of these roles in cells, messenger RNA molecules are taking information from the DNA and getting it transcribed, or getting it translated at the ribosome, but they shouldn't hang out forever. You actually want them to be somewhat unstable. So it's an interesting question to think about. Why do we have uracil instead of thymine? Or why do we have thymine instead of uracil? But this is one of the telltale signs of, that we are now dealing with an RNA molecule. So now what we have on the left hand side, now all of this business, actually let me do this in a different color, all of this business, this strand, this strand right over here, we can now, the way it's drawn, we can now consider this an RNA molecule."}, {"video_title": "Molecular structure of RNA   Macromolecules   Biology   Khan Academy (3).mp3", "Sentence": "Why do we have uracil instead of thymine? Or why do we have thymine instead of uracil? But this is one of the telltale signs of, that we are now dealing with an RNA molecule. So now what we have on the left hand side, now all of this business, actually let me do this in a different color, all of this business, this strand, this strand right over here, we can now, the way it's drawn, we can now consider this an RNA molecule. And if we assume that this is happening during transcription, when a DNA molecule, where a single strand of DNA would want to replicate its information, then this over here would be mRNA, messenger, messenger RNA. And so what's going on here? Well, let's think about it."}, {"video_title": "Molecular structure of RNA   Macromolecules   Biology   Khan Academy (3).mp3", "Sentence": "So now what we have on the left hand side, now all of this business, actually let me do this in a different color, all of this business, this strand, this strand right over here, we can now, the way it's drawn, we can now consider this an RNA molecule. And if we assume that this is happening during transcription, when a DNA molecule, where a single strand of DNA would want to replicate its information, then this over here would be mRNA, messenger, messenger RNA. And so what's going on here? Well, let's think about it. This one, the way it's, the RNA, the messenger RNA, the way it's oriented, we have, if we go, we have phosphate group, then we go to five prime carbon, four prime, three prime, then phosphate group, then five prime, four prime, three prime, then phosphate group. So this is oriented five prime on top, three prime on the bottom. While this DNA molecule is oriented the other way."}, {"video_title": "Molecular structure of RNA   Macromolecules   Biology   Khan Academy (3).mp3", "Sentence": "Well, let's think about it. This one, the way it's, the RNA, the messenger RNA, the way it's oriented, we have, if we go, we have phosphate group, then we go to five prime carbon, four prime, three prime, then phosphate group, then five prime, four prime, three prime, then phosphate group. So this is oriented five prime on top, three prime on the bottom. While this DNA molecule is oriented the other way. This is a five prime carbon, this is a three prime carbon. So we have phosphate, three prime, five prime, phosphate. So we have three prime is on top, and five prime is on the bottom."}, {"video_title": "Molecular structure of RNA   Macromolecules   Biology   Khan Academy (3).mp3", "Sentence": "While this DNA molecule is oriented the other way. This is a five prime carbon, this is a three prime carbon. So we have phosphate, three prime, five prime, phosphate. So we have three prime is on top, and five prime is on the bottom. So if we wanted to think about what's happening, maybe using the symbols for the nitrogenous bases, we could say, all right, we have our mRNA molecule here, and this is its five prime end, and this is its three prime end. And then the first, the top nitrogenous base right over here, this is uracil. This is uracil."}, {"video_title": "Molecular structure of RNA   Macromolecules   Biology   Khan Academy (3).mp3", "Sentence": "So we have three prime is on top, and five prime is on the bottom. So if we wanted to think about what's happening, maybe using the symbols for the nitrogenous bases, we could say, all right, we have our mRNA molecule here, and this is its five prime end, and this is its three prime end. And then the first, the top nitrogenous base right over here, this is uracil. This is uracil. And then the second one over here, this is, sorry, over here, this is cytosine. So this is cytosine. This is cytosine right over here."}, {"video_title": "Molecular structure of RNA   Macromolecules   Biology   Khan Academy (3).mp3", "Sentence": "This is uracil. And then the second one over here, this is, sorry, over here, this is cytosine. So this is cytosine. This is cytosine right over here. And this is being transcribed from a DNA molecule, from this DNA molecule on the right-hand side. So this is DNA. And this DNA has an anti-parallel orientation."}, {"video_title": "Molecular structure of RNA   Macromolecules   Biology   Khan Academy (3).mp3", "Sentence": "This is cytosine right over here. And this is being transcribed from a DNA molecule, from this DNA molecule on the right-hand side. So this is DNA. And this DNA has an anti-parallel orientation. It's parallel, but it's kind of flipped over. The sugars are pointed in a different direction. So this is going from, this is the three prime end, this is the five prime end."}, {"video_title": "Molecular structure of RNA   Macromolecules   Biology   Khan Academy (3).mp3", "Sentence": "And this DNA has an anti-parallel orientation. It's parallel, but it's kind of flipped over. The sugars are pointed in a different direction. So this is going from, this is the three prime end, this is the five prime end. And we see that the uracil is hydrogen bonded to adenine. Adenine right over here. So adenine, and I'll draw dotted lines to show the hydrogen bonds."}, {"video_title": "Molecular structure of RNA   Macromolecules   Biology   Khan Academy (3).mp3", "Sentence": "So this is going from, this is the three prime end, this is the five prime end. And we see that the uracil is hydrogen bonded to adenine. Adenine right over here. So adenine, and I'll draw dotted lines to show the hydrogen bonds. And that the cytosine is hydrogen bonded to guanine. To guanine. So this right over here, that is guanine."}, {"video_title": "Molecular structure of RNA   Macromolecules   Biology   Khan Academy (3).mp3", "Sentence": "So adenine, and I'll draw dotted lines to show the hydrogen bonds. And that the cytosine is hydrogen bonded to guanine. To guanine. So this right over here, that is guanine. And actually I'll do the hydrogen bonds in white. So, you know, they are, actually there's multiple hydrogen bonds going on here. But just to be clear, this is mRNA, and on the right we have DNA."}, {"video_title": "Molecular structure of RNA   Macromolecules   Biology   Khan Academy (3).mp3", "Sentence": "So this right over here, that is guanine. And actually I'll do the hydrogen bonds in white. So, you know, they are, actually there's multiple hydrogen bonds going on here. But just to be clear, this is mRNA, and on the right we have DNA. And this could be happening during transcription. This could be happening during, I'm having trouble changing colors. This could be happening during transcription."}, {"video_title": "Molecular structure of RNA   Macromolecules   Biology   Khan Academy (3).mp3", "Sentence": "But just to be clear, this is mRNA, and on the right we have DNA. And this could be happening during transcription. This could be happening during, I'm having trouble changing colors. This could be happening during transcription. Now what are the types of RNAs out there? We've talked about this in other videos. Well you have messenger RNA, which is an important role in taking information from DNA and getting it eventually translated with the help of tRNAs and ribosomes."}, {"video_title": "Molecular structure of RNA   Macromolecules   Biology   Khan Academy (3).mp3", "Sentence": "This could be happening during transcription. Now what are the types of RNAs out there? We've talked about this in other videos. Well you have messenger RNA, which is an important role in taking information from DNA and getting it eventually translated with the help of tRNAs and ribosomes. And though I've just mentioned another type of RNA, and that's transfer RNA. So transfer RNA, tRNA. tRNA."}, {"video_title": "Molecular structure of RNA   Macromolecules   Biology   Khan Academy (3).mp3", "Sentence": "Well you have messenger RNA, which is an important role in taking information from DNA and getting it eventually translated with the help of tRNAs and ribosomes. And though I've just mentioned another type of RNA, and that's transfer RNA. So transfer RNA, tRNA. tRNA. And in the video, the overview video on transcription and translation, we talk about how tRNA does this. But it brings amino acids, it has amino acids attached at one end, and then it has anticodons on the other end that essentially pair, that pair with codon fragment or codons on the mRNA, and then that allows it to construct proteins. And this actually is, this right over here is a visualization of a tRNA molecule."}, {"video_title": "Molecular structure of RNA   Macromolecules   Biology   Khan Academy (3).mp3", "Sentence": "tRNA. And in the video, the overview video on transcription and translation, we talk about how tRNA does this. But it brings amino acids, it has amino acids attached at one end, and then it has anticodons on the other end that essentially pair, that pair with codon fragment or codons on the mRNA, and then that allows it to construct proteins. And this actually is, this right over here is a visualization of a tRNA molecule. So a lot of times when we think about DNA, we think about, okay, mRNA or RNA is an intermediary to be able to eventually translate it into proteins. And that is often the case, but sometimes you also just want the RNA itself. The RNA itself plays a role in the cell beyond just transmitting information."}, {"video_title": "Molecular structure of RNA   Macromolecules   Biology   Khan Academy (3).mp3", "Sentence": "And this actually is, this right over here is a visualization of a tRNA molecule. So a lot of times when we think about DNA, we think about, okay, mRNA or RNA is an intermediary to be able to eventually translate it into proteins. And that is often the case, but sometimes you also just want the RNA itself. The RNA itself plays a role in the cell beyond just transmitting information. And that's an example here with tRNA. And you can see it's interesting configuration where the amino acid will attach roughly in that area up there. And then you see the anticodon, the anticodon right down here in the bottom right."}, {"video_title": "Molecular structure of RNA   Macromolecules   Biology   Khan Academy (3).mp3", "Sentence": "The RNA itself plays a role in the cell beyond just transmitting information. And that's an example here with tRNA. And you can see it's interesting configuration where the amino acid will attach roughly in that area up there. And then you see the anticodon, the anticodon right down here in the bottom right. And different tRNA molecules will attach to different amino acids and they'll have different anticodons here. So this is another use for RNA. And then others include ribosomal RNA."}, {"video_title": "Molecular structure of RNA   Macromolecules   Biology   Khan Academy (3).mp3", "Sentence": "And then you see the anticodon, the anticodon right down here in the bottom right. And different tRNA molecules will attach to different amino acids and they'll have different anticodons here. So this is another use for RNA. And then others include ribosomal RNA. Ribosomal RNA. And they actually play a structural role in ribosomes, which is where translation occurs. And you also have things called microRNA."}, {"video_title": "Molecular structure of RNA   Macromolecules   Biology   Khan Academy (3).mp3", "Sentence": "And then others include ribosomal RNA. Ribosomal RNA. And they actually play a structural role in ribosomes, which is where translation occurs. And you also have things called microRNA. MicroRNA, which are short chains of RNA, which could be used to regulate the translation of other RNA molecules. So RNA, you know, DNA gets a lot of the attention, but RNA is really, really, really important. And a lot of people believe that RNA came first."}, {"video_title": "DNA cloning and recombinant DNA   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "And usually it's a piece of DNA that codes for something we care about. It is a gene that will express itself as a protein that we think is useful in some way. Now you might have also heard the term cloning in terms of the Clone Wars and Star Wars or Dolly the sheep, and that is a related idea. If you're cloning an animal or an organism, like a sheep, well then you are creating an animal that has the exact genetic material as the original animal. But when we talk about cloning and DNA cloning, we're talking about something a little bit simpler. Although as we'll see, it's still quite fascinating. It's identical copies of a piece of DNA."}, {"video_title": "DNA cloning and recombinant DNA   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "If you're cloning an animal or an organism, like a sheep, well then you are creating an animal that has the exact genetic material as the original animal. But when we talk about cloning and DNA cloning, we're talking about something a little bit simpler. Although as we'll see, it's still quite fascinating. It's identical copies of a piece of DNA. So how do we do that? Well let's say that this is a strand of DNA right over here, and I'm just drawing it as a line, but this is a double-stranded, and I'll just write it down, this is double-stranded. I don't want to have to take the trouble of keep drawing the multiple strands."}, {"video_title": "DNA cloning and recombinant DNA   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "It's identical copies of a piece of DNA. So how do we do that? Well let's say that this is a strand of DNA right over here, and I'm just drawing it as a line, but this is a double-stranded, and I'll just write it down, this is double-stranded. I don't want to have to take the trouble of keep drawing the multiple strands. Actually let me just draw, let me just try to draw the two strands just so we remind ourselves. So there we go, this is the double-stranded DNA, and let's say that this part of this DNA has a gene that we want to clone. We want to make copies of this right over here."}, {"video_title": "DNA cloning and recombinant DNA   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "I don't want to have to take the trouble of keep drawing the multiple strands. Actually let me just draw, let me just try to draw the two strands just so we remind ourselves. So there we go, this is the double-stranded DNA, and let's say that this part of this DNA has a gene that we want to clone. We want to make copies of this right over here. So gene to clone, gene to clone. Well the first thing we want to do is we want to cut this gene out somehow. And the way we do that is using restriction enzymes."}, {"video_title": "DNA cloning and recombinant DNA   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "We want to make copies of this right over here. So gene to clone, gene to clone. Well the first thing we want to do is we want to cut this gene out somehow. And the way we do that is using restriction enzymes. And there's a bunch of different restriction enzymes, and I personally find it fascinating that we as a civilization have gotten to the point that we can find and identify these enzymes, and we know at what points of DNA that they can cut, they recognize specific sequences, and then we can figure out, well which restriction enzyme should we use to cut out different pieces of DNA? But we have gotten to that point as a civilization. So we use restriction enzymes."}, {"video_title": "DNA cloning and recombinant DNA   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "And the way we do that is using restriction enzymes. And there's a bunch of different restriction enzymes, and I personally find it fascinating that we as a civilization have gotten to the point that we can find and identify these enzymes, and we know at what points of DNA that they can cut, they recognize specific sequences, and then we can figure out, well which restriction enzyme should we use to cut out different pieces of DNA? But we have gotten to that point as a civilization. So we use restriction enzymes. We might use one restriction enzyme, let me use a different color here, that latches on right over here and identifies the genetic sequence right over here and cuts right in the right place. So that might be a restriction enzyme right over there. And then you might use another restriction enzyme that identifies with the sequence at the other side that we want to cut."}, {"video_title": "DNA cloning and recombinant DNA   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "So we use restriction enzymes. We might use one restriction enzyme, let me use a different color here, that latches on right over here and identifies the genetic sequence right over here and cuts right in the right place. So that might be a restriction enzyme right over there. And then you might use another restriction enzyme that identifies with the sequence at the other side that we want to cut. So let me label these. These, those things right over there, those are restriction enzymes. Restriction enzymes."}, {"video_title": "DNA cloning and recombinant DNA   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "And then you might use another restriction enzyme that identifies with the sequence at the other side that we want to cut. So let me label these. These, those things right over there, those are restriction enzymes. Restriction enzymes. And so now you would have, after you apply the restriction enzymes, you will have just that gene. You might have a little bit left over on either side. But essentially you have cut out the gene."}, {"video_title": "DNA cloning and recombinant DNA   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "Restriction enzymes. And so now you would have, after you apply the restriction enzymes, you will have just that gene. You might have a little bit left over on either side. But essentially you have cut out the gene. You have used the restriction enzymes to cut out your gene. And then what you want to do is you want to paste it into what we will call a plasmid. And a plasmid is a piece of genetic material that sits outside of chromosomes but that can reproduce along, or that could, I guess we could say, can replicate along with the machinery of the, or the genetic machinery of the organism."}, {"video_title": "DNA cloning and recombinant DNA   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "But essentially you have cut out the gene. You have used the restriction enzymes to cut out your gene. And then what you want to do is you want to paste it into what we will call a plasmid. And a plasmid is a piece of genetic material that sits outside of chromosomes but that can reproduce along, or that could, I guess we could say, can replicate along with the machinery of the, or the genetic machinery of the organism. Or it could even express itself just like the genes of the organism that are in the chromosomes express themselves. So then, so this is where we cut, let me write this, we cut, we cut out the gene. And then we want to paste it, then we want to paste it into a plasmid."}, {"video_title": "DNA cloning and recombinant DNA   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "And a plasmid is a piece of genetic material that sits outside of chromosomes but that can reproduce along, or that could, I guess we could say, can replicate along with the machinery of the, or the genetic machinery of the organism. Or it could even express itself just like the genes of the organism that are in the chromosomes express themselves. So then, so this is where we cut, let me write this, we cut, we cut out the gene. And then we want to paste it, then we want to paste it into a plasmid. And plasmids tend to be circular DNA. So we will paste it into a plasmid. And in order for them to fit, there's oftentimes these overhangs over here."}, {"video_title": "DNA cloning and recombinant DNA   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "And then we want to paste it, then we want to paste it into a plasmid. And plasmids tend to be circular DNA. So we will paste it into a plasmid. And in order for them to fit, there's oftentimes these overhangs over here. So you might have an overhang over there. You might have an overhang over there. And so the plasmid that we're placing in might have complementary base pairs over the overhangs, which will allow it easier, it will become easier for them to react with each other if they have these overhangs."}, {"video_title": "DNA cloning and recombinant DNA   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "And in order for them to fit, there's oftentimes these overhangs over here. So you might have an overhang over there. You might have an overhang over there. And so the plasmid that we're placing in might have complementary base pairs over the overhangs, which will allow it easier, it will become easier for them to react with each other if they have these overhangs. So let me, we're pasting it into the plasmid. And this is amazing because obviously, DNA, this isn't stuff that we can like, you know, manipulate with our hands the way that we would copy and paste things with tape. You're making these solutions and you're applying the restriction enzymes."}, {"video_title": "DNA cloning and recombinant DNA   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "And so the plasmid that we're placing in might have complementary base pairs over the overhangs, which will allow it easier, it will become easier for them to react with each other if they have these overhangs. So let me, we're pasting it into the plasmid. And this is amazing because obviously, DNA, this isn't stuff that we can like, you know, manipulate with our hands the way that we would copy and paste things with tape. You're making these solutions and you're applying the restriction enzymes. The restriction enzymes are just in mass cutting these things. They're bumping in just the right way to cause this reaction to happen. Then you're taking those genes and then you're putting them with the plasmids that happen to have the right sequences at their ends so that they match up."}, {"video_title": "DNA cloning and recombinant DNA   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "You're making these solutions and you're applying the restriction enzymes. The restriction enzymes are just in mass cutting these things. They're bumping in just the right way to cause this reaction to happen. Then you're taking those genes and then you're putting them with the plasmids that happen to have the right sequences at their ends so that they match up. And then you also put in a bunch of DNA ligase, DNA ligase, to connect the backbones right over here. And we also saw DNA ligase when we studied replication. So that is DNA ligase, which you can think of it as helping to do, helping to do the pasting."}, {"video_title": "DNA cloning and recombinant DNA   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "Then you're taking those genes and then you're putting them with the plasmids that happen to have the right sequences at their ends so that they match up. And then you also put in a bunch of DNA ligase, DNA ligase, to connect the backbones right over here. And we also saw DNA ligase when we studied replication. So that is DNA ligase, which you can think of it as helping to do, helping to do the pasting. And so now we have this plasmid and we want to insert it into an organism that can make the copies for us. And an organism that's typically used is, or a type of organism is bacteria, and E. coli in particular. And so what we could do is, we could, let's say that we have a bunch of, let's say you have a vial right over here."}, {"video_title": "DNA cloning and recombinant DNA   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "So that is DNA ligase, which you can think of it as helping to do, helping to do the pasting. And so now we have this plasmid and we want to insert it into an organism that can make the copies for us. And an organism that's typically used is, or a type of organism is bacteria, and E. coli in particular. And so what we could do is, we could, let's say that we have a bunch of, let's say you have a vial right over here. You have a vial and it has a solution in it with a bunch of E. coli. A bunch of E. coli. And you actually wouldn't be able to see it visually."}, {"video_title": "DNA cloning and recombinant DNA   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "And so what we could do is, we could, let's say that we have a bunch of, let's say you have a vial right over here. You have a vial and it has a solution in it with a bunch of E. coli. A bunch of E. coli. And you actually wouldn't be able to see it visually. But there's E. coli in that solution. And then you would put your plasmids, which would be even harder to see, in that solution. And somehow we want the E. coli, we want the bacteria to take up the plasmid."}, {"video_title": "DNA cloning and recombinant DNA   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "And you actually wouldn't be able to see it visually. But there's E. coli in that solution. And then you would put your plasmids, which would be even harder to see, in that solution. And somehow we want the E. coli, we want the bacteria to take up the plasmid. And the technique that's typically done is giving some type of a shock to the system that makes the bacteria take up the plasmids. And the typical shock is a heat shock. And this isn't fully understood how the heat shock works, but it does."}, {"video_title": "DNA cloning and recombinant DNA   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "And somehow we want the E. coli, we want the bacteria to take up the plasmid. And the technique that's typically done is giving some type of a shock to the system that makes the bacteria take up the plasmids. And the typical shock is a heat shock. And this isn't fully understood how the heat shock works, but it does. And so people have been using this for some time. So if you have a bacteria, you have a bacteria right over here. It has its existing DNA."}, {"video_title": "DNA cloning and recombinant DNA   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "And this isn't fully understood how the heat shock works, but it does. And so people have been using this for some time. So if you have a bacteria, you have a bacteria right over here. It has its existing DNA. So this is its existing genetic material right over there. Let me label this. This is the bacteria."}, {"video_title": "DNA cloning and recombinant DNA   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "It has its existing DNA. So this is its existing genetic material right over there. Let me label this. This is the bacteria. You put it in the presence of our plasmids. So you put it in the presence of our plasmid and you apply the heat shock. And some of that bacteria is going to take in the plasmid."}, {"video_title": "DNA cloning and recombinant DNA   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "This is the bacteria. You put it in the presence of our plasmids. So you put it in the presence of our plasmid and you apply the heat shock. And some of that bacteria is going to take in the plasmid. It's going to take in the plasmid. And so just like that, it's going to take it in. And so what you then do is you place the solution that has your bacteria, some of which will have taken up the plasmid, and you put it, and then you try to grow the bacteria on a plate."}, {"video_title": "DNA cloning and recombinant DNA   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "And some of that bacteria is going to take in the plasmid. It's going to take in the plasmid. And so just like that, it's going to take it in. And so what you then do is you place the solution that has your bacteria, some of which will have taken up the plasmid, and you put it, and then you try to grow the bacteria on a plate. So let me draw that. So let me draw. So here we have a plate to grow our bacteria on."}, {"video_title": "DNA cloning and recombinant DNA   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "And so what you then do is you place the solution that has your bacteria, some of which will have taken up the plasmid, and you put it, and then you try to grow the bacteria on a plate. So let me draw that. So let me draw. So here we have a plate to grow our bacteria on. And it has nutrients right over here that bacteria can grow on. It has nutrients. It has nutrients."}, {"video_title": "DNA cloning and recombinant DNA   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "So here we have a plate to grow our bacteria on. And it has nutrients right over here that bacteria can grow on. It has nutrients. It has nutrients. And so you could say, okay, we'll put this here, and then a bunch of bacteria will just grow. So you would see things like this, which would be many, many, many, many cells of bacteria. There would be colonies of bacteria."}, {"video_title": "DNA cloning and recombinant DNA   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "It has nutrients. And so you could say, okay, we'll put this here, and then a bunch of bacteria will just grow. So you would see things like this, which would be many, many, many, many cells of bacteria. There would be colonies of bacteria. You could just let them grow. But there's a problem here. Because I mentioned some of the bacteria will take up the plasmids and some won't."}, {"video_title": "DNA cloning and recombinant DNA   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "There would be colonies of bacteria. You could just let them grow. But there's a problem here. Because I mentioned some of the bacteria will take up the plasmids and some won't. And so you won't know, hey, when this bacteria, when it keeps replicating, it might form one of these colonies. So this is a colony that you like. So this one is a good colony."}, {"video_title": "DNA cloning and recombinant DNA   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "Because I mentioned some of the bacteria will take up the plasmids and some won't. And so you won't know, hey, when this bacteria, when it keeps replicating, it might form one of these colonies. So this is a colony that you like. So this one is a good colony. Put a check mark there. But maybe this colony is formed by a initial bacteria or a set of bacteria that did not take up the plasmid. So it won't contain the actual gene in question."}, {"video_title": "DNA cloning and recombinant DNA   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "So this one is a good colony. Put a check mark there. But maybe this colony is formed by a initial bacteria or a set of bacteria that did not take up the plasmid. So it won't contain the actual gene in question. So you don't want that one. So how do you select for the bacteria that actually took up the plasmid? Well, what you do is, besides the gene that you care about, that you want to make copies of, you also place a gene for antibiotic resistance in your plasmid."}, {"video_title": "DNA cloning and recombinant DNA   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "So it won't contain the actual gene in question. So you don't want that one. So how do you select for the bacteria that actually took up the plasmid? Well, what you do is, besides the gene that you care about, that you want to make copies of, you also place a gene for antibiotic resistance in your plasmid. So now you have a gene for antibiotic resistance here. And so only the bacteria, and I think it's amazing that we as humanity are able to do these types of things, but now only the bacteria that have taken up the plasmid will have that antibiotic resistance. And so what you do is, in your nutrients, you put nutrients plus antibiotics, plus an antibiotic, antibiotic."}, {"video_title": "DNA cloning and recombinant DNA   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "Well, what you do is, besides the gene that you care about, that you want to make copies of, you also place a gene for antibiotic resistance in your plasmid. So now you have a gene for antibiotic resistance here. And so only the bacteria, and I think it's amazing that we as humanity are able to do these types of things, but now only the bacteria that have taken up the plasmid will have that antibiotic resistance. And so what you do is, in your nutrients, you put nutrients plus antibiotics, plus an antibiotic, antibiotic. And so this one will survive because it has that resistance. It has that gene that allows it to not be susceptible to the antibiotics. But these are not going to survive."}, {"video_title": "DNA cloning and recombinant DNA   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "And so what you do is, in your nutrients, you put nutrients plus antibiotics, plus an antibiotic, antibiotic. And so this one will survive because it has that resistance. It has that gene that allows it to not be susceptible to the antibiotics. But these are not going to survive. They're not even going to happen. They're not even going to grow because there's antibiotics mixed in with those nutrients. And so this is a pretty cool thing."}, {"video_title": "DNA cloning and recombinant DNA   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "But these are not going to survive. They're not even going to happen. They're not even going to grow because there's antibiotics mixed in with those nutrients. And so this is a pretty cool thing. You start with the gene that you cared about. You cut and pasted it into our plasmid. Let me write the labels down."}, {"video_title": "DNA cloning and recombinant DNA   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "And so this is a pretty cool thing. You start with the gene that you cared about. You cut and pasted it into our plasmid. Let me write the labels down. Into our plasmid that also contained a gene that gave antibiotic resistance to any bacteria that takes up the plasmid. You put these plasmids in the presence of the bacteria. You provide some type of a shock, maybe a heat shock, so that some of the bacteria takes it up."}, {"video_title": "DNA cloning and recombinant DNA   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "Let me write the labels down. Into our plasmid that also contained a gene that gave antibiotic resistance to any bacteria that takes up the plasmid. You put these plasmids in the presence of the bacteria. You provide some type of a shock, maybe a heat shock, so that some of the bacteria takes it up. And then the bacteria starts reproducing. And as it reproduces, it also is reproducing the plasmids. And because it has this antibiotic resistance, it is going to grow on this nutrient-antibiotic mixture, and the other bacteria that did not take up the plasmids are not going to grow."}, {"video_title": "DNA cloning and recombinant DNA   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "You provide some type of a shock, maybe a heat shock, so that some of the bacteria takes it up. And then the bacteria starts reproducing. And as it reproduces, it also is reproducing the plasmids. And because it has this antibiotic resistance, it is going to grow on this nutrient-antibiotic mixture, and the other bacteria that did not take up the plasmids are not going to grow. And so just like that, you can take this, you can take this colony right over here and put it into another solution or continue to grow it, and you will have multiple copies of that gene that are inside of that bacteria. Now the next question, and I'm oversimplifying things fairly dramatically, is well, how do you, you now have a bunch of bacteria that have a bunch of copies of that gene. How do you make use of it?"}, {"video_title": "DNA cloning and recombinant DNA   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "And because it has this antibiotic resistance, it is going to grow on this nutrient-antibiotic mixture, and the other bacteria that did not take up the plasmids are not going to grow. And so just like that, you can take this, you can take this colony right over here and put it into another solution or continue to grow it, and you will have multiple copies of that gene that are inside of that bacteria. Now the next question, and I'm oversimplifying things fairly dramatically, is well, how do you, you now have a bunch of bacteria that have a bunch of copies of that gene. How do you make use of it? Well, the bacteria themselves, let's say that gene is for something you want to manufacture, say insulin for diabetics. Well, you could actually use that bacteria's machiner. We use its reproductive machinery to keep replicating the genetic information, but you can also use its productive machinery, I guess you could say."}, {"video_title": "DNA cloning and recombinant DNA   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "How do you make use of it? Well, the bacteria themselves, let's say that gene is for something you want to manufacture, say insulin for diabetics. Well, you could actually use that bacteria's machiner. We use its reproductive machinery to keep replicating the genetic information, but you can also use its productive machinery, I guess you could say. It's going to express its existing DNA, but it can also express the genes that are on the plasmid. In fact, that's what gives its, that's what would give the bacteria its antibiotic resistance. But if this gene was, say, for insulin, well, then the bacteria will produce, will produce a bunch of insulin, a bunch of insulin molecules, which you might be able to use in some way."}, {"video_title": "Animal behavior foraging   Individuals and Society   MCAT   Khan Academy.mp3", "Sentence": "Because without this ability, the animal is not likely to be able to survive and reproduce. But this behavior is an interesting one because there's kind of a cost-benefit analysis that's associated with it. Obviously, an animal needs to be able to do it to survive, but going out and getting food can actually take up a lot of time and energy. So the animal needs to use energy in order to gain it. And so the goal with foraging is always to figure out how to get the highest energy yield while expending the least amount of energy doing it. And the term foraging actually refers to a bunch of different behaviors. For example, it can include looking for food, like this antelope right here who's eating grass."}, {"video_title": "Animal behavior foraging   Individuals and Society   MCAT   Khan Academy.mp3", "Sentence": "So the animal needs to use energy in order to gain it. And so the goal with foraging is always to figure out how to get the highest energy yield while expending the least amount of energy doing it. And the term foraging actually refers to a bunch of different behaviors. For example, it can include looking for food, like this antelope right here who's eating grass. But it can also include things like stalking prey, which we can see in this picture with a tiger chasing antelope. There are two main foraging strategies that an animal can use. And it's actually what we see the tiger doing in this picture right here, and that's solitary foraging."}, {"video_title": "Animal behavior foraging   Individuals and Society   MCAT   Khan Academy.mp3", "Sentence": "For example, it can include looking for food, like this antelope right here who's eating grass. But it can also include things like stalking prey, which we can see in this picture with a tiger chasing antelope. There are two main foraging strategies that an animal can use. And it's actually what we see the tiger doing in this picture right here, and that's solitary foraging. And actually, let me write that in orange to represent the tiger. So solitary foraging is exactly what it sounds like. It's when an animal looks for food by itself."}, {"video_title": "Animal behavior foraging   Individuals and Society   MCAT   Khan Academy.mp3", "Sentence": "And it's actually what we see the tiger doing in this picture right here, and that's solitary foraging. And actually, let me write that in orange to represent the tiger. So solitary foraging is exactly what it sounds like. It's when an animal looks for food by itself. The second type of foraging we see is group foraging, and that's what lions do, and so I'll write that in yellow here. And this is when animals look for food in groups. And one thing that's both good and bad about this strategy is that in this case, hunting would not only depend on your own behavior, but also the behavior of those around you."}, {"video_title": "Animal behavior foraging   Individuals and Society   MCAT   Khan Academy.mp3", "Sentence": "It's when an animal looks for food by itself. The second type of foraging we see is group foraging, and that's what lions do, and so I'll write that in yellow here. And this is when animals look for food in groups. And one thing that's both good and bad about this strategy is that in this case, hunting would not only depend on your own behavior, but also the behavior of those around you. And so this can actually lead to competition within a group, especially when resources are scarce. But there can also be many benefits to this strategy. When many animals are working together, it means that predators can take down larger prey or difficult, more aggressive prey."}, {"video_title": "Animal behavior foraging   Individuals and Society   MCAT   Khan Academy.mp3", "Sentence": "And one thing that's both good and bad about this strategy is that in this case, hunting would not only depend on your own behavior, but also the behavior of those around you. And so this can actually lead to competition within a group, especially when resources are scarce. But there can also be many benefits to this strategy. When many animals are working together, it means that predators can take down larger prey or difficult, more aggressive prey. So it can also be to the benefit of everyone in that group. Aside from looking at just strategies, another question that scientists typically have about foraging concerns how animals figure out how to do it in the first place. And obviously foraging behavior is probably driven strongly by genetics, but it turns out that information about foraging can also be gained through animal learning."}, {"video_title": "Exponential and logistic growth in populations    Ecology   Khan Academy.mp3", "Sentence": "Let's say that we're starting with a population of 1,000 rabbits, and we know that this population is growing at 10% per month. What I want to do is explore how that population will grow if it's growing 10% per month. So let's set up a little bit of a, let's set up a little table here, a little table. And on this left column, let's just say this is the number of months that have gone by, and on the right column, let's say this is the population. So we know from the information given to us that at zero months, we're starting off with 1,000 rabbits. Now let's think about what's going to happen after one month. Well, our population's going to grow by 10%, so we could take our population at the beginning of the month, and growing by 10%, that's the same thing as multiplying by 1.1."}, {"video_title": "Exponential and logistic growth in populations    Ecology   Khan Academy.mp3", "Sentence": "And on this left column, let's just say this is the number of months that have gone by, and on the right column, let's say this is the population. So we know from the information given to us that at zero months, we're starting off with 1,000 rabbits. Now let's think about what's going to happen after one month. Well, our population's going to grow by 10%, so we could take our population at the beginning of the month, and growing by 10%, that's the same thing as multiplying by 1.1. You have your original population, and then you grow it by 10%. One plus 10% is 1.1, so we can multiply it by 1.1. And that math we can do in our head, it is 1,100, or 1,100."}, {"video_title": "Exponential and logistic growth in populations    Ecology   Khan Academy.mp3", "Sentence": "Well, our population's going to grow by 10%, so we could take our population at the beginning of the month, and growing by 10%, that's the same thing as multiplying by 1.1. You have your original population, and then you grow it by 10%. One plus 10% is 1.1, so we can multiply it by 1.1. And that math we can do in our head, it is 1,100, or 1,100. But let's just write this as 1,000 times 1.1, not 1.5, times 1.1. Now let's think about what happens as we go to month two. Well, it's going to be the population that we started at the beginning of the month times 1.1 again."}, {"video_title": "Exponential and logistic growth in populations    Ecology   Khan Academy.mp3", "Sentence": "And that math we can do in our head, it is 1,100, or 1,100. But let's just write this as 1,000 times 1.1, not 1.5, times 1.1. Now let's think about what happens as we go to month two. Well, it's going to be the population that we started at the beginning of the month times 1.1 again. So it's going to be the population at the beginning of the month, which was that, which we have right over there. But then we're going to multiply by 1.1 again. Or we can just say that this is 1.1 squared."}, {"video_title": "Exponential and logistic growth in populations    Ecology   Khan Academy.mp3", "Sentence": "Well, it's going to be the population that we started at the beginning of the month times 1.1 again. So it's going to be the population at the beginning of the month, which was that, which we have right over there. But then we're going to multiply by 1.1 again. Or we can just say that this is 1.1 squared. And I think you see a pattern emerging. After another month, the population's going to be 1,000 times 1.1 to the third power. We're just going to multiply by 1.1 again."}, {"video_title": "Exponential and logistic growth in populations    Ecology   Khan Academy.mp3", "Sentence": "Or we can just say that this is 1.1 squared. And I think you see a pattern emerging. After another month, the population's going to be 1,000 times 1.1 to the third power. We're just going to multiply by 1.1 again. And so if you were to go n months into the future, well, you could see what's going to be. It's going to be 1,000 times, or being multiplied by 1.1 n times, or 1,000 times 1.1 to the nth power. And so we can set up an expression here."}, {"video_title": "Exponential and logistic growth in populations    Ecology   Khan Academy.mp3", "Sentence": "We're just going to multiply by 1.1 again. And so if you were to go n months into the future, well, you could see what's going to be. It's going to be 1,000 times, or being multiplied by 1.1 n times, or 1,000 times 1.1 to the nth power. And so we can set up an expression here. We could say, look, the population, let's say that the population is p. The population as a function of n, as a function of n, is going to be equal to our initial population, our initial population, times 1.1 to the nth power. And you might say, okay, well, this makes sense. It doesn't look like we're getting crazy numbers."}, {"video_title": "Exponential and logistic growth in populations    Ecology   Khan Academy.mp3", "Sentence": "And so we can set up an expression here. We could say, look, the population, let's say that the population is p. The population as a function of n, as a function of n, is going to be equal to our initial population, our initial population, times 1.1 to the nth power. And you might say, okay, well, this makes sense. It doesn't look like we're getting crazy numbers. But just for kicks, let's just think about what's going to happen in 10 years. So 10 years would be 120 months. So the population at the end of 120 months is going to be 1,000 times 1.1 to the 120th power."}, {"video_title": "Exponential and logistic growth in populations    Ecology   Khan Academy.mp3", "Sentence": "It doesn't look like we're getting crazy numbers. But just for kicks, let's just think about what's going to happen in 10 years. So 10 years would be 120 months. So the population at the end of 120 months is going to be 1,000 times 1.1 to the 120th power. And so let's, let me get a calculator out to do that. I cannot calculate 1.1 to the 120th power in my head. 1.1 to the 120th power is equal to that times our initial population."}, {"video_title": "Exponential and logistic growth in populations    Ecology   Khan Academy.mp3", "Sentence": "So the population at the end of 120 months is going to be 1,000 times 1.1 to the 120th power. And so let's, let me get a calculator out to do that. I cannot calculate 1.1 to the 120th power in my head. 1.1 to the 120th power is equal to that times our initial population. So times 1,000, one, two, three, is going to be equal to roughly 93 million rabbits. Let me write that down. So we started with 1,000, and we're going to have approximately 93 million rabbits."}, {"video_title": "Exponential and logistic growth in populations    Ecology   Khan Academy.mp3", "Sentence": "1.1 to the 120th power is equal to that times our initial population. So times 1,000, one, two, three, is going to be equal to roughly 93 million rabbits. Let me write that down. So we started with 1,000, and we're going to have approximately 93 million rabbits. 93 million, million rabbits. And so we grew by a factor of 93,000 over 10 years. So over another 10 years, we'd grow by 93,000 times this."}, {"video_title": "Exponential and logistic growth in populations    Ecology   Khan Academy.mp3", "Sentence": "So we started with 1,000, and we're going to have approximately 93 million rabbits. 93 million, million rabbits. And so we grew by a factor of 93,000 over 10 years. So over another 10 years, we'd grow by 93,000 times this. And so you quickly realize 10% per month is quite fast. And this might seem extremely fast, but this is actually not outlandish for a population of rabbits that are not limited by space, or predators, or food. And if you were to plot something like this out, if you were to plot the rabbit population with respect to time, you would see a graph that looks, let me draw it."}, {"video_title": "Exponential and logistic growth in populations    Ecology   Khan Academy.mp3", "Sentence": "So over another 10 years, we'd grow by 93,000 times this. And so you quickly realize 10% per month is quite fast. And this might seem extremely fast, but this is actually not outlandish for a population of rabbits that are not limited by space, or predators, or food. And if you were to plot something like this out, if you were to plot the rabbit population with respect to time, you would see a graph that looks, let me draw it. So this axis, it is time, say in months. And this axis, you have your population. You have your population."}, {"video_title": "Exponential and logistic growth in populations    Ecology   Khan Academy.mp3", "Sentence": "And if you were to plot something like this out, if you were to plot the rabbit population with respect to time, you would see a graph that looks, let me draw it. So this axis, it is time, say in months. And this axis, you have your population. You have your population. This type of function, or this type of equation, let me see, population, I, population, this is an exponential function. And so your population as a function of time is going to look like this. It's going to have this kind of hockey stick J shape right over here."}, {"video_title": "Exponential and logistic growth in populations    Ecology   Khan Academy.mp3", "Sentence": "You have your population. This type of function, or this type of equation, let me see, population, I, population, this is an exponential function. And so your population as a function of time is going to look like this. It's going to have this kind of hockey stick J shape right over here. And if you let these rabbits reproduce long enough, they would frankly take over the planet if they had enough food and if they had enough space to do it. But as you notice, I keep saying, if they have enough food and if they have enough space. The reality in the world is that there is not infinite food and infinite space, and it isn't the case that there are no predators or competition for resources."}, {"video_title": "Exponential and logistic growth in populations    Ecology   Khan Academy.mp3", "Sentence": "It's going to have this kind of hockey stick J shape right over here. And if you let these rabbits reproduce long enough, they would frankly take over the planet if they had enough food and if they had enough space to do it. But as you notice, I keep saying, if they have enough food and if they have enough space. The reality in the world is that there is not infinite food and infinite space, and it isn't the case that there are no predators or competition for resources. And so there is actually a maximum carrying capacity for a certain part of the environment for a certain type of species. And so what's more likely to happen, what we just described right over here is exponential growth. Exponential growth."}, {"video_title": "Exponential and logistic growth in populations    Ecology   Khan Academy.mp3", "Sentence": "The reality in the world is that there is not infinite food and infinite space, and it isn't the case that there are no predators or competition for resources. And so there is actually a maximum carrying capacity for a certain part of the environment for a certain type of species. And so what's more likely to happen, what we just described right over here is exponential growth. Exponential growth. And why is it called exponential growth? Well, you notice, we are growing by the input, which is time, is being thrown into our exponent. And so that is exponential growth."}, {"video_title": "Exponential and logistic growth in populations    Ecology   Khan Academy.mp3", "Sentence": "Exponential growth. And why is it called exponential growth? Well, you notice, we are growing by the input, which is time, is being thrown into our exponent. And so that is exponential growth. But obviously you can't have an infinite number of rabbits or you just can't grow forever. There is going to be some natural maximum carrying capacity that the environment can actually sustain. And so the actual growth that you would see, when the population is well below that carrying capacity, it's reasonable to model it with exponential growth."}, {"video_title": "Exponential and logistic growth in populations    Ecology   Khan Academy.mp3", "Sentence": "And so that is exponential growth. But obviously you can't have an infinite number of rabbits or you just can't grow forever. There is going to be some natural maximum carrying capacity that the environment can actually sustain. And so the actual growth that you would see, when the population is well below that carrying capacity, it's reasonable to model it with exponential growth. But as it gets closer and closer to that carrying capacity, it is going to asymptote up towards it. So it's gonna get up towards it, but not cross it. And that's just a model."}, {"video_title": "Exponential and logistic growth in populations    Ecology   Khan Academy.mp3", "Sentence": "And so the actual growth that you would see, when the population is well below that carrying capacity, it's reasonable to model it with exponential growth. But as it gets closer and closer to that carrying capacity, it is going to asymptote up towards it. So it's gonna get up towards it, but not cross it. And that's just a model. There are other situations where maybe it goes up to it and it crosses it and then it cycles around it. So these are all different ways of thinking about it. But the general idea is you wouldn't expect something to just grow unfettered forever."}, {"video_title": "Exponential and logistic growth in populations    Ecology   Khan Academy.mp3", "Sentence": "And that's just a model. There are other situations where maybe it goes up to it and it crosses it and then it cycles around it. So these are all different ways of thinking about it. But the general idea is you wouldn't expect something to just grow unfettered forever. Now this blue curve, which people often use to model populations, especially when they're thinking about the populations once they approach the environment's carrying capacity, this is this kind of S-shaped curve. That is considered, that's called logistic growth. And there is a logistic function that describes this, but you don't have to know it in the scope of a kind of an introductory biology."}, {"video_title": "Exponential and logistic growth in populations    Ecology   Khan Academy.mp3", "Sentence": "But the general idea is you wouldn't expect something to just grow unfettered forever. Now this blue curve, which people often use to model populations, especially when they're thinking about the populations once they approach the environment's carrying capacity, this is this kind of S-shaped curve. That is considered, that's called logistic growth. And there is a logistic function that describes this, but you don't have to know it in the scope of a kind of an introductory biology. There's a logistic growth and it's described by the logistic function. If you're curious about it, we do have videos on Khan Academy about logistic growth and also about exponential growth, and we go into a lot more detail on that. But the general idea here is when populations are not limited by their environment, by food, by resources, by space, they tend to grow exponentially."}, {"video_title": "Variation in a Species (3).mp3", "Sentence": "The whole process of natural selection is to some degree dependent on the idea of variation, that within any population of a species, you have some genetic variation. So for example, let's say I have a bunch of, well, this is the circle species. And one guy is that color, and then I've got a bunch more. Maybe some are that color. That's the same color. That one, and that one, and that one. And for whatever reason, sometimes there are no environmental factors that will predispose one of these guys to be able to survive and reproduce over the other."}, {"video_title": "Variation in a Species (3).mp3", "Sentence": "Maybe some are that color. That's the same color. That one, and that one, and that one. And for whatever reason, sometimes there are no environmental factors that will predispose one of these guys to be able to survive and reproduce over the other. But every now and then, there might be some environmental factor. And it makes maybe all of a sudden, this guy is more fit to reproduce. And so for whatever reason, this guy is able to reproduce more frequently, and these guys less frequently."}, {"video_title": "Variation in a Species (3).mp3", "Sentence": "And for whatever reason, sometimes there are no environmental factors that will predispose one of these guys to be able to survive and reproduce over the other. But every now and then, there might be some environmental factor. And it makes maybe all of a sudden, this guy is more fit to reproduce. And so for whatever reason, this guy is able to reproduce more frequently, and these guys less frequently. And some of them get killed or whatever, eaten by birds or they're just not able to reproduce for whatever reason. And then maybe these guys are something in between. And so over time, the frequency of the different traits you see in this population will change."}, {"video_title": "Variation in a Species (3).mp3", "Sentence": "And so for whatever reason, this guy is able to reproduce more frequently, and these guys less frequently. And some of them get killed or whatever, eaten by birds or they're just not able to reproduce for whatever reason. And then maybe these guys are something in between. And so over time, the frequency of the different traits you see in this population will change. And if they are drastic enough, maybe these guys start becoming dominant and start not liking these guys because they're so different or whatever else. We could see a lot of different reasons. This could eventually turn into a different species."}, {"video_title": "Variation in a Species (3).mp3", "Sentence": "And so over time, the frequency of the different traits you see in this population will change. And if they are drastic enough, maybe these guys start becoming dominant and start not liking these guys because they're so different or whatever else. We could see a lot of different reasons. This could eventually turn into a different species. Now, the obvious question is, what leads to this variation? In a population, what leads to this? In fact, even in our population, what leads to one person having dirty blonde hair, one person having brown hair, one person having black hair, and the spectrum of skin complexions and heights is pretty much infinite?"}, {"video_title": "Variation in a Species (3).mp3", "Sentence": "This could eventually turn into a different species. Now, the obvious question is, what leads to this variation? In a population, what leads to this? In fact, even in our population, what leads to one person having dirty blonde hair, one person having brown hair, one person having black hair, and the spectrum of skin complexions and heights is pretty much infinite? What causes that? And then one thing that I kind of point to, and we talked about this a little bit in the DNA video, is this notion of mutations. The DNA, we learned, is just a sequence of these bases."}, {"video_title": "Variation in a Species (3).mp3", "Sentence": "In fact, even in our population, what leads to one person having dirty blonde hair, one person having brown hair, one person having black hair, and the spectrum of skin complexions and heights is pretty much infinite? What causes that? And then one thing that I kind of point to, and we talked about this a little bit in the DNA video, is this notion of mutations. The DNA, we learned, is just a sequence of these bases. So adenine, guanine, let's say I got some thymine going, I have some more adenine, some cytosine. And that these code, if you have enough of these in a row, maybe you have a few hundred or a few thousands of these, these code for proteins or they code for things that control other proteins. But maybe you have a change in one of them."}, {"video_title": "Variation in a Species (3).mp3", "Sentence": "The DNA, we learned, is just a sequence of these bases. So adenine, guanine, let's say I got some thymine going, I have some more adenine, some cytosine. And that these code, if you have enough of these in a row, maybe you have a few hundred or a few thousands of these, these code for proteins or they code for things that control other proteins. But maybe you have a change in one of them. Maybe this cytosine, for whatever reason, becomes a guanine randomly. Or maybe these get deleted. And that would change the DNA."}, {"video_title": "Variation in a Species (3).mp3", "Sentence": "But maybe you have a change in one of them. Maybe this cytosine, for whatever reason, becomes a guanine randomly. Or maybe these get deleted. And that would change the DNA. But you can imagine, if I went to someone's computer code and just randomly started changing letters and randomly started inserting letters without really knowing what I'm doing, most of the time I'm going to break the computer program. Most of the time, the great majority of the time, this is going to go nowhere. For example, if I go into someone's computer program and if I just add a couple of spaces or something, that might not change their computer program."}, {"video_title": "Variation in a Species (3).mp3", "Sentence": "And that would change the DNA. But you can imagine, if I went to someone's computer code and just randomly started changing letters and randomly started inserting letters without really knowing what I'm doing, most of the time I'm going to break the computer program. Most of the time, the great majority of the time, this is going to go nowhere. For example, if I go into someone's computer program and if I just add a couple of spaces or something, that might not change their computer program. But if I start getting rid of semicolons and start changing numbers and all that, it'll probably make the computer program break. So it'll either do nothing or it'll actually kill the organisms most of the time. Mutations."}, {"video_title": "Variation in a Species (3).mp3", "Sentence": "For example, if I go into someone's computer program and if I just add a couple of spaces or something, that might not change their computer program. But if I start getting rid of semicolons and start changing numbers and all that, it'll probably make the computer program break. So it'll either do nothing or it'll actually kill the organisms most of the time. Mutations. Sometimes they might make the actual cell kind of go run amok and we'll do a whole maybe series of videos on cancer and that itself obviously would hurt the organism as a whole. Although if it occurs after the organism is reproduced, it might not be something that selects against the organism. But anyway, and it also wouldn't be passed on."}, {"video_title": "Variation in a Species (3).mp3", "Sentence": "Mutations. Sometimes they might make the actual cell kind of go run amok and we'll do a whole maybe series of videos on cancer and that itself obviously would hurt the organism as a whole. Although if it occurs after the organism is reproduced, it might not be something that selects against the organism. But anyway, and it also wouldn't be passed on. But anyway, I won't go too detailed into that. But the whole point is that mutations don't seem to be a satisfying source of variation. They could be a source or kind of contribute on the margin, but there must be something more profound than mutations that's creating the diversity even within, or maybe I should call the variation, even within a population."}, {"video_title": "Variation in a Species (3).mp3", "Sentence": "But anyway, and it also wouldn't be passed on. But anyway, I won't go too detailed into that. But the whole point is that mutations don't seem to be a satisfying source of variation. They could be a source or kind of contribute on the margin, but there must be something more profound than mutations that's creating the diversity even within, or maybe I should call the variation, even within a population. And the answer here is really, it's kind of right in front of us. It really addresses kind of one of the most fundamental things about biology. And it's so fundamental that a lot of people never even question why it is the way it is."}, {"video_title": "Variation in a Species (3).mp3", "Sentence": "They could be a source or kind of contribute on the margin, but there must be something more profound than mutations that's creating the diversity even within, or maybe I should call the variation, even within a population. And the answer here is really, it's kind of right in front of us. It really addresses kind of one of the most fundamental things about biology. And it's so fundamental that a lot of people never even question why it is the way it is. And that is sexual reproduction. And when I mean sexual reproduction, it's this notion that you have, and pretty much if you look at all organisms that have nucleuses, and we call those eukaryotes, maybe I'll do a whole video on eukaryotes versus prokaryotes. But it's the notion that if you look universally all the way from plants, not universally, but if you look at cells that have nucleuses, they almost universally have this phenomenon that you have males and you have females."}, {"video_title": "Variation in a Species (3).mp3", "Sentence": "And it's so fundamental that a lot of people never even question why it is the way it is. And that is sexual reproduction. And when I mean sexual reproduction, it's this notion that you have, and pretty much if you look at all organisms that have nucleuses, and we call those eukaryotes, maybe I'll do a whole video on eukaryotes versus prokaryotes. But it's the notion that if you look universally all the way from plants, not universally, but if you look at cells that have nucleuses, they almost universally have this phenomenon that you have males and you have females. In some organisms, an organism can be both a male and a female, but the common idea here is that all organisms kind of produce versions of their genetic material that mix with other organisms' version of their genetic material. If mutations were the only source of variation, then I could just butt off other cells. Maybe other cells would just butt off from me, and then randomly one cell might be a little bit different and whatever else."}, {"video_title": "Variation in a Species (3).mp3", "Sentence": "But it's the notion that if you look universally all the way from plants, not universally, but if you look at cells that have nucleuses, they almost universally have this phenomenon that you have males and you have females. In some organisms, an organism can be both a male and a female, but the common idea here is that all organisms kind of produce versions of their genetic material that mix with other organisms' version of their genetic material. If mutations were the only source of variation, then I could just butt off other cells. Maybe other cells would just butt off from me, and then randomly one cell might be a little bit different and whatever else. But that would, as we already talked about, most of the time we would have very little change, very little variation. And whatever variation does occur because of any kind of noise being introduced into this kind of butting process where I just replicate myself identically, most of the times it'll be negative. Most of the times it'll break the organism."}, {"video_title": "Variation in a Species (3).mp3", "Sentence": "Maybe other cells would just butt off from me, and then randomly one cell might be a little bit different and whatever else. But that would, as we already talked about, most of the time we would have very little change, very little variation. And whatever variation does occur because of any kind of noise being introduced into this kind of butting process where I just replicate myself identically, most of the times it'll be negative. Most of the times it'll break the organism. Now, when you have sexual reproduction, what happens? Well, you keep mixing and matching every possible combination of DNA in a species pool of DNA. Let me make this a little bit more concrete for you."}, {"video_title": "Variation in a Species (3).mp3", "Sentence": "Most of the times it'll break the organism. Now, when you have sexual reproduction, what happens? Well, you keep mixing and matching every possible combination of DNA in a species pool of DNA. Let me make this a little bit more concrete for you. So let me erase this horrible drawing I just did. So we all have, let me stick to humans because that's what we are. We have 23 pairs of chromosomes, and in each pair we have one chromosome from our mother and one chromosome from our father."}, {"video_title": "Variation in a Species (3).mp3", "Sentence": "Let me make this a little bit more concrete for you. So let me erase this horrible drawing I just did. So we all have, let me stick to humans because that's what we are. We have 23 pairs of chromosomes, and in each pair we have one chromosome from our mother and one chromosome from our father. So let me draw that. So I'll do my father's chromosomes in blue, so I have 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, and I'm running out of space. Let me do more here."}, {"video_title": "Variation in a Species (3).mp3", "Sentence": "We have 23 pairs of chromosomes, and in each pair we have one chromosome from our mother and one chromosome from our father. So let me draw that. So I'll do my father's chromosomes in blue, so I have 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, and I'm running out of space. Let me do more here. 16, 17, 18, 19, 20, 21, 22. And then I'll throw another one here that looks a little bit different. I'll throw one here that looks like a Y."}, {"video_title": "Variation in a Species (3).mp3", "Sentence": "Let me do more here. 16, 17, 18, 19, 20, 21, 22. And then I'll throw another one here that looks a little bit different. I'll throw one here that looks like a Y. And we'll talk more about the X's and the Y chromosomes. And I have 23 chromosomes from my mother. And not to be stereotypical, but maybe I'll do that in a more feminine color."}, {"video_title": "Variation in a Species (3).mp3", "Sentence": "I'll throw one here that looks like a Y. And we'll talk more about the X's and the Y chromosomes. And I have 23 chromosomes from my mother. And not to be stereotypical, but maybe I'll do that in a more feminine color. Let's see. So I have 23 chromosomes from my mother. 1, 2, I just have to draw 1, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23."}, {"video_title": "Variation in a Species (3).mp3", "Sentence": "And not to be stereotypical, but maybe I'll do that in a more feminine color. Let's see. So I have 23 chromosomes from my mother. 1, 2, I just have to draw 1, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23. So what's going on here? I have 23 from my mother. I have 23 from my father."}, {"video_title": "Variation in a Species (3).mp3", "Sentence": "1, 2, I just have to draw 1, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23. So what's going on here? I have 23 from my mother. I have 23 from my father. Now, each of these chromosomes, and I made them right next to each other. So for example, let me zoom in on one pair of these. So let's say we look at chromosome number 3."}, {"video_title": "Variation in a Species (3).mp3", "Sentence": "I have 23 from my father. Now, each of these chromosomes, and I made them right next to each other. So for example, let me zoom in on one pair of these. So let's say we look at chromosome number 3. So let me zoom in on chromosome number 3. I have one from my mother right here. And remember, actually maybe I'll do it this way."}, {"video_title": "Variation in a Species (3).mp3", "Sentence": "So let's say we look at chromosome number 3. So let me zoom in on chromosome number 3. I have one from my mother right here. And remember, actually maybe I'll do it this way. Remember, a chromosome is just a big, if you take the DNA, it just keeps wrapping around. It actually wraps around all these proteins and it creates the structure. But it's just a big, you see it like that, you're like, oh, maybe the DNA, no, but this could have millions of base pairs."}, {"video_title": "Variation in a Species (3).mp3", "Sentence": "And remember, actually maybe I'll do it this way. Remember, a chromosome is just a big, if you take the DNA, it just keeps wrapping around. It actually wraps around all these proteins and it creates the structure. But it's just a big, you see it like that, you're like, oh, maybe the DNA, no, but this could have millions of base pairs. So maybe it'll look something like that. It's a densely wrapped version of, well, it's a long string of DNA, and when it's normally drawn like this, which is not always the way it is, and we'll talk more about like that, they draw it as densely packed like that. So let's say that's from my mother and that's from my father."}, {"video_title": "Variation in a Species (3).mp3", "Sentence": "But it's just a big, you see it like that, you're like, oh, maybe the DNA, no, but this could have millions of base pairs. So maybe it'll look something like that. It's a densely wrapped version of, well, it's a long string of DNA, and when it's normally drawn like this, which is not always the way it is, and we'll talk more about like that, they draw it as densely packed like that. So let's say that's from my mother and that's from my father. Now, these are both, we call them, I'll call them, they're the same, let's call this chromosome 3. They're both chromosome 3. And what the idea is here is that I'm getting different traits from my father and from my mother."}, {"video_title": "Variation in a Species (3).mp3", "Sentence": "So let's say that's from my mother and that's from my father. Now, these are both, we call them, I'll call them, they're the same, let's call this chromosome 3. They're both chromosome 3. And what the idea is here is that I'm getting different traits from my father and from my mother. For example, and I'm doing a gross oversimplification here, but this is really to just give you the idea of what's going on. This chromosome 3, maybe it contains this trait for hair color. And maybe my father had, and I'll use my actual example, my father had very straight hair."}, {"video_title": "Variation in a Species (3).mp3", "Sentence": "And what the idea is here is that I'm getting different traits from my father and from my mother. For example, and I'm doing a gross oversimplification here, but this is really to just give you the idea of what's going on. This chromosome 3, maybe it contains this trait for hair color. And maybe my father had, and I'll use my actual example, my father had very straight hair. So let's say he had, some place on this chromosome, there is a gene for hair straightness. Let's say it's a little thing right there. And remember, that gene could be thousands of base pairs."}, {"video_title": "Variation in a Species (3).mp3", "Sentence": "And maybe my father had, and I'll use my actual example, my father had very straight hair. So let's say he had, some place on this chromosome, there is a gene for hair straightness. Let's say it's a little thing right there. And remember, that gene could be thousands of base pairs. But let's say this is hair straightness. So my father's version of that gene, or he had the allele for straightness. And remember, an allele is just a version of a gene."}, {"video_title": "Variation in a Species (3).mp3", "Sentence": "And remember, that gene could be thousands of base pairs. But let's say this is hair straightness. So my father's version of that gene, or he had the allele for straightness. And remember, an allele is just a version of a gene. So I'll call it the allele straight for straight hair. Now, this other chromosome that my mother gave me, this essentially, and there are exceptions, but for the most part, it codes for the same genes. And that's why I put them next to each other."}, {"video_title": "Variation in a Species (3).mp3", "Sentence": "And remember, an allele is just a version of a gene. So I'll call it the allele straight for straight hair. Now, this other chromosome that my mother gave me, this essentially, and there are exceptions, but for the most part, it codes for the same genes. And that's why I put them next to each other. So this will also have the gene for hair straightness or curliness. But my mom does happen to actually have curly hair. So she has the gene right there for curly hair."}, {"video_title": "Variation in a Species (3).mp3", "Sentence": "And that's why I put them next to each other. So this will also have the gene for hair straightness or curliness. But my mom does happen to actually have curly hair. So she has the gene right there for curly hair. So she has the version of the gene here is, let's see, allele curly. The gene just says, look, this is the gene for whether or not your hair is curly. Each version of the gene is called an allele."}, {"video_title": "Variation in a Species (3).mp3", "Sentence": "So she has the gene right there for curly hair. So she has the version of the gene here is, let's see, allele curly. The gene just says, look, this is the gene for whether or not your hair is curly. Each version of the gene is called an allele. Allele curly. Now, when I got both of these in my body, or in my cells, and this is in every cell of my body, every cell of my body except for, and we'll talk a little in a few seconds about my germ cells, but every cell other than the ones that I use for reproduction have this complete set of chromosomes in it, which I find amazing. But only certain chromosomes are, for example, these genes will be completely useless in my fingernails because all of a sudden, the straight and the curly don't matter that much."}, {"video_title": "Variation in a Species (3).mp3", "Sentence": "Each version of the gene is called an allele. Allele curly. Now, when I got both of these in my body, or in my cells, and this is in every cell of my body, every cell of my body except for, and we'll talk a little in a few seconds about my germ cells, but every cell other than the ones that I use for reproduction have this complete set of chromosomes in it, which I find amazing. But only certain chromosomes are, for example, these genes will be completely useless in my fingernails because all of a sudden, the straight and the curly don't matter that much. And I'm simplifying. Maybe they will on some other dimension. But let's say for simplicity, they won't matter in certain places."}, {"video_title": "Variation in a Species (3).mp3", "Sentence": "But only certain chromosomes are, for example, these genes will be completely useless in my fingernails because all of a sudden, the straight and the curly don't matter that much. And I'm simplifying. Maybe they will on some other dimension. But let's say for simplicity, they won't matter in certain places. So certain genes are expressed in certain parts of the body, but every one of your body cells, and we call those somatic cells, and we'll separate those from the sex cells or the germ cells that we'll talk about later. So this is my body cells. So this is the great majority of your cells."}, {"video_title": "Variation in a Species (3).mp3", "Sentence": "But let's say for simplicity, they won't matter in certain places. So certain genes are expressed in certain parts of the body, but every one of your body cells, and we call those somatic cells, and we'll separate those from the sex cells or the germ cells that we'll talk about later. So this is my body cells. So this is the great majority of your cells. And this is opposed to your germ cells. And the germ cells, I'll just write it here just so you get it clear, for a male, that's the sperm cells. And for a female, that's the egg cells or the ova."}, {"video_title": "Variation in a Species (3).mp3", "Sentence": "So this is the great majority of your cells. And this is opposed to your germ cells. And the germ cells, I'll just write it here just so you get it clear, for a male, that's the sperm cells. And for a female, that's the egg cells or the ova. But most of my cells have a complete collection of these. What I want to give you the idea is that for every trait, I essentially have two versions, one from my mother and one from my father. Now these right here are called homologous chromosomes."}, {"video_title": "Variation in a Species (3).mp3", "Sentence": "And for a female, that's the egg cells or the ova. But most of my cells have a complete collection of these. What I want to give you the idea is that for every trait, I essentially have two versions, one from my mother and one from my father. Now these right here are called homologous chromosomes. Chromosomes, homologous. What that means is every time you see the prefix homologous, or if you see like homo sapien, or even the word homosexual or homogeneous, it means same. You see that all the time."}, {"video_title": "Variation in a Species (3).mp3", "Sentence": "Now these right here are called homologous chromosomes. Chromosomes, homologous. What that means is every time you see the prefix homologous, or if you see like homo sapien, or even the word homosexual or homogeneous, it means same. You see that all the time. So homologous means that they're almost the same. They're coding for the most part the same set of genes, but they're not identical. They actually might code for slightly different versions of the same gene."}, {"video_title": "Variation in a Species (3).mp3", "Sentence": "You see that all the time. So homologous means that they're almost the same. They're coding for the most part the same set of genes, but they're not identical. They actually might code for slightly different versions of the same gene. So depending on what versions I get, what is actually expressed for me. So my genotype, let me introduce another word. And I'm overwhelming you with words here."}, {"video_title": "Variation in a Species (3).mp3", "Sentence": "They actually might code for slightly different versions of the same gene. So depending on what versions I get, what is actually expressed for me. So my genotype, let me introduce another word. And I'm overwhelming you with words here. So my genotype is exactly what alleles I have, what versions of the gene. So I got like the fifth version of the curly allele. There could be multiple versions of the curly allele in our gene pool."}, {"video_title": "Variation in a Species (3).mp3", "Sentence": "And I'm overwhelming you with words here. So my genotype is exactly what alleles I have, what versions of the gene. So I got like the fifth version of the curly allele. There could be multiple versions of the curly allele in our gene pool. And maybe I got some version of the straight allele. That is my genotype. My phenotype is what my hair really looks like."}, {"video_title": "Variation in a Species (3).mp3", "Sentence": "There could be multiple versions of the curly allele in our gene pool. And maybe I got some version of the straight allele. That is my genotype. My phenotype is what my hair really looks like. So for example, two people could have different genotypes with the same, but they might code for hair that looks pretty much the same. So it might have a very similar phenotype. So one phenotype can be represented by multiple genotypes."}, {"video_title": "Variation in a Species (3).mp3", "Sentence": "My phenotype is what my hair really looks like. So for example, two people could have different genotypes with the same, but they might code for hair that looks pretty much the same. So it might have a very similar phenotype. So one phenotype can be represented by multiple genotypes. So that's just one thing to think about. And we'll talk a lot about that in the future, but I just want to introduce you into that there. Now, I entered this whole discussion because I wanted to talk about variation."}, {"video_title": "Variation in a Species (3).mp3", "Sentence": "So one phenotype can be represented by multiple genotypes. So that's just one thing to think about. And we'll talk a lot about that in the future, but I just want to introduce you into that there. Now, I entered this whole discussion because I wanted to talk about variation. So how does variation happen? Well, what's going to happen when I, so first of all, well, let me put it this way. What's going to happen when I reproduce and I have a son?"}, {"video_title": "Variation in a Species (3).mp3", "Sentence": "Now, I entered this whole discussion because I wanted to talk about variation. So how does variation happen? Well, what's going to happen when I, so first of all, well, let me put it this way. What's going to happen when I reproduce and I have a son? Well, my contribution to my son is going to be a random collection of half of these genes. I'm going to contribute either one. For each homologous pair, I'm either going to contribute the one that I got from my mother or the one that I got from my father."}, {"video_title": "Variation in a Species (3).mp3", "Sentence": "What's going to happen when I reproduce and I have a son? Well, my contribution to my son is going to be a random collection of half of these genes. I'm going to contribute either one. For each homologous pair, I'm either going to contribute the one that I got from my mother or the one that I got from my father. So let's say that the sperm cell that went on to fertilize my wife's egg, it just happened to have, let's say it happened to have that one, that one, well, I could just pick one from each of these 23 sets. And you could say, well, how many combinations are there? Well, for every set, I can pick one of the two homologous chromosomes, and I'm going to do that 23 times."}, {"video_title": "Variation in a Species (3).mp3", "Sentence": "For each homologous pair, I'm either going to contribute the one that I got from my mother or the one that I got from my father. So let's say that the sperm cell that went on to fertilize my wife's egg, it just happened to have, let's say it happened to have that one, that one, well, I could just pick one from each of these 23 sets. And you could say, well, how many combinations are there? Well, for every set, I can pick one of the two homologous chromosomes, and I'm going to do that 23 times. 2 times 2 times 2, so it's 2 to the 23rd. So there's 22 to the 23 different versions that I can contribute to any son or daughter that I might have. We'll talk about how that happens when we talk about meiosis or mitosis."}, {"video_title": "Variation in a Species (3).mp3", "Sentence": "Well, for every set, I can pick one of the two homologous chromosomes, and I'm going to do that 23 times. 2 times 2 times 2, so it's 2 to the 23rd. So there's 22 to the 23 different versions that I can contribute to any son or daughter that I might have. We'll talk about how that happens when we talk about meiosis or mitosis. That when I generate my sperm cells, sperm cells are essentially, instead of having 23 pairs of chromosomes in sperm, you only have 23 chromosomes. So for example, I'll take one from each of those, and through the process of meiosis, which we'll go into, I'll generate a bunch of sperm cells. And each sperm cell will have one from each of these pairs, one version from each of those pairs."}, {"video_title": "Variation in a Species (3).mp3", "Sentence": "We'll talk about how that happens when we talk about meiosis or mitosis. That when I generate my sperm cells, sperm cells are essentially, instead of having 23 pairs of chromosomes in sperm, you only have 23 chromosomes. So for example, I'll take one from each of those, and through the process of meiosis, which we'll go into, I'll generate a bunch of sperm cells. And each sperm cell will have one from each of these pairs, one version from each of those pairs. So maybe for this chromosome, I get it from my dad. From the next chromosome, I get it from my mom. Then I donate a couple more from, I shouldn't have drawn them next to each other, I donate a couple more from my mom, then for the chromosome number 5, it comes from my dad, and so on and so forth."}, {"video_title": "Variation in a Species (3).mp3", "Sentence": "And each sperm cell will have one from each of these pairs, one version from each of those pairs. So maybe for this chromosome, I get it from my dad. From the next chromosome, I get it from my mom. Then I donate a couple more from, I shouldn't have drawn them next to each other, I donate a couple more from my mom, then for the chromosome number 5, it comes from my dad, and so on and so forth. But there's 2 to the 23rd combinations here, because there are 23 pairs that I'm collecting from. Now, my wife's egg is going to have the same situation. There are 2 to the 23 different combinations of DNA that she can contribute, just based on which of the homologous pairs she will contribute."}, {"video_title": "Variation in a Species (3).mp3", "Sentence": "Then I donate a couple more from, I shouldn't have drawn them next to each other, I donate a couple more from my mom, then for the chromosome number 5, it comes from my dad, and so on and so forth. But there's 2 to the 23rd combinations here, because there are 23 pairs that I'm collecting from. Now, my wife's egg is going to have the same situation. There are 2 to the 23 different combinations of DNA that she can contribute, just based on which of the homologous pairs she will contribute. So the possible combinations that just one couple can produce, and I'm using my life as an example, but you could use this, this applies to everything. This applies to every species that experiences sexual reproduction. So if I can give 2 to the 23rd combinations of DNA, and my wife can give 2 to the 23 combinations of DNA, then we can produce 2 to the 46th combinations."}, {"video_title": "Variation in a Species (3).mp3", "Sentence": "There are 2 to the 23 different combinations of DNA that she can contribute, just based on which of the homologous pairs she will contribute. So the possible combinations that just one couple can produce, and I'm using my life as an example, but you could use this, this applies to everything. This applies to every species that experiences sexual reproduction. So if I can give 2 to the 23rd combinations of DNA, and my wife can give 2 to the 23 combinations of DNA, then we can produce 2 to the 46th combinations. Now, just to give an idea of how large of a number this is, this is 12,000, roughly 12,000 times the number of human beings on the planet today. So there's a huge amount of variation that even one couple can produce. And if you thought that even that isn't enough, it turns out that amongst these homologous pairs, and we'll talk about when this happens in meiosis, you can actually have DNA recombination."}, {"video_title": "Variation in a Species (3).mp3", "Sentence": "So if I can give 2 to the 23rd combinations of DNA, and my wife can give 2 to the 23 combinations of DNA, then we can produce 2 to the 46th combinations. Now, just to give an idea of how large of a number this is, this is 12,000, roughly 12,000 times the number of human beings on the planet today. So there's a huge amount of variation that even one couple can produce. And if you thought that even that isn't enough, it turns out that amongst these homologous pairs, and we'll talk about when this happens in meiosis, you can actually have DNA recombination. And all that means is that when these homologous pairs during meiosis line up near each other, you can have this thing called crossover, where all of this DNA here crosses over and touches over here, and all of this DNA crosses over and touches over there. So all of this goes there, and all of this goes there. And what you end up with after the crossover is that one DNA, the one that came from my mom, or that I thought came from my mom, now has a chunk that came from my dad."}, {"video_title": "Variation in a Species (3).mp3", "Sentence": "And if you thought that even that isn't enough, it turns out that amongst these homologous pairs, and we'll talk about when this happens in meiosis, you can actually have DNA recombination. And all that means is that when these homologous pairs during meiosis line up near each other, you can have this thing called crossover, where all of this DNA here crosses over and touches over here, and all of this DNA crosses over and touches over there. So all of this goes there, and all of this goes there. And what you end up with after the crossover is that one DNA, the one that came from my mom, or that I thought came from my mom, now has a chunk that came from my dad. And the chunk that came from my dad now has a chunk that came from my mom. Let me do it in the right color. It came from my mom like that."}, {"video_title": "Variation in a Species (3).mp3", "Sentence": "And what you end up with after the crossover is that one DNA, the one that came from my mom, or that I thought came from my mom, now has a chunk that came from my dad. And the chunk that came from my dad now has a chunk that came from my mom. Let me do it in the right color. It came from my mom like that. And so that even increases the amount of variety even more. So you can almost now, instead of talking about the different chromosomes that you're contributing, where the chromosomes are each of these collections of DNA, you can almost go to the different combinations at the gene level. And now you can think about an almost infinite form of variation."}, {"video_title": "Variation in a Species (3).mp3", "Sentence": "It came from my mom like that. And so that even increases the amount of variety even more. So you can almost now, instead of talking about the different chromosomes that you're contributing, where the chromosomes are each of these collections of DNA, you can almost go to the different combinations at the gene level. And now you can think about an almost infinite form of variation. And you can think about all of the variation that might emerge when you start mixing and mashing different versions of the same gene in a population. And you don't just look at one gene. I mean, the reality is that genes by themselves very seldom code for a specific."}, {"video_title": "Variation in a Species (3).mp3", "Sentence": "And now you can think about an almost infinite form of variation. And you can think about all of the variation that might emerge when you start mixing and mashing different versions of the same gene in a population. And you don't just look at one gene. I mean, the reality is that genes by themselves very seldom code for a specific. You can very seldom look for one gene and say, oh, that is brown hair. Or look for one gene and say, oh, that's intelligence. Or that is how likable someone is."}, {"video_title": "Variation in a Species (3).mp3", "Sentence": "I mean, the reality is that genes by themselves very seldom code for a specific. You can very seldom look for one gene and say, oh, that is brown hair. Or look for one gene and say, oh, that's intelligence. Or that is how likable someone is. It's usually a whole set of genes interacting in an incredibly complicated way. Hair might be coded for by this whole set of genes on multiple chromosomes. And this might be coded for a whole set of genes on multiple chromosomes."}, {"video_title": "Variation in a Species (3).mp3", "Sentence": "Or that is how likable someone is. It's usually a whole set of genes interacting in an incredibly complicated way. Hair might be coded for by this whole set of genes on multiple chromosomes. And this might be coded for a whole set of genes on multiple chromosomes. And so then you can start thinking about all of the different combinations. And then all of a sudden, maybe some combination that never existed before all of a sudden emerges. And that's very successful."}, {"video_title": "Variation in a Species (3).mp3", "Sentence": "And this might be coded for a whole set of genes on multiple chromosomes. And so then you can start thinking about all of the different combinations. And then all of a sudden, maybe some combination that never existed before all of a sudden emerges. And that's very successful. But I'll leave you to think about it because maybe that combination might be passed on or it may not be passed on because of this recombination. But we'll talk more about that in the future. But I wanted to introduce this idea of sexual reproduction to you because this really is the main source of variation within a population."}, {"video_title": "Variation in a Species (3).mp3", "Sentence": "And that's very successful. But I'll leave you to think about it because maybe that combination might be passed on or it may not be passed on because of this recombination. But we'll talk more about that in the future. But I wanted to introduce this idea of sexual reproduction to you because this really is the main source of variation within a population. And it's kind of a philosophical idea because we almost take the idea of having males and females for granted because it's this universal idea. But I did a little reading on it. It turns out that this actually only emerged about 1.4 billion years ago."}, {"video_title": "Variation in a Species (3).mp3", "Sentence": "But I wanted to introduce this idea of sexual reproduction to you because this really is the main source of variation within a population. And it's kind of a philosophical idea because we almost take the idea of having males and females for granted because it's this universal idea. But I did a little reading on it. It turns out that this actually only emerged about 1.4 billion years ago. That this is almost a useful trait because once you introduce this level of variation, the natural selection can start. You can kind of say that when you have this more powerful form of variation than just pure mutations, and maybe you might have some primitive form of crossover before. But now that you have this sexual reproduction and you have this variation, natural selection can occur in a more efficient way so that species that were able to reproduce and essentially recombine their DNA and mix and match it in this way were able to produce more variety and were able to essentially be selected for the environment in a more efficient way."}, {"video_title": "Variation in a Species (3).mp3", "Sentence": "It turns out that this actually only emerged about 1.4 billion years ago. That this is almost a useful trait because once you introduce this level of variation, the natural selection can start. You can kind of say that when you have this more powerful form of variation than just pure mutations, and maybe you might have some primitive form of crossover before. But now that you have this sexual reproduction and you have this variation, natural selection can occur in a more efficient way so that species that were able to reproduce and essentially recombine their DNA and mix and match it in this way were able to produce more variety and were able to essentially be selected for the environment in a more efficient way. So they started to essentially outnumber the ones that couldn't. So it became a kind of a very universal trait. But you could have imagined a world, and there are science fiction books written about this, where you have three genders, where you have gender one, two, three."}, {"video_title": "Variation in a Species (3).mp3", "Sentence": "But now that you have this sexual reproduction and you have this variation, natural selection can occur in a more efficient way so that species that were able to reproduce and essentially recombine their DNA and mix and match it in this way were able to produce more variety and were able to essentially be selected for the environment in a more efficient way. So they started to essentially outnumber the ones that couldn't. So it became a kind of a very universal trait. But you could have imagined a world, and there are science fiction books written about this, where you have three genders, where you have gender one, two, three. You could have 10 genders. And it just happens to be that on Earth, this notion of having two genders turned out to be a very efficient and stable way of introducing variation into a population. So hopefully you found that interesting."}, {"video_title": "Flow of energy and matter through ecosystem    Ecology   Khan Academy.mp3", "Sentence": "And so the whole time that we go through this video, think about these two ideas. And then even after watching this video, look at ecosystems around yourself, even ones that you are part of, and think about how energy flows and how matter is recycled. So let's first think about energy. So the energy for most ecosystems originally comes from the sun. There are other sources of energy. You could think about even moonlight, but that essentially comes from the sun. But there's also geothermal energy, but the sun is the source of most energy for most ecosystems we can think of."}, {"video_title": "Flow of energy and matter through ecosystem    Ecology   Khan Academy.mp3", "Sentence": "So the energy for most ecosystems originally comes from the sun. There are other sources of energy. You could think about even moonlight, but that essentially comes from the sun. But there's also geothermal energy, but the sun is the source of most energy for most ecosystems we can think of. And how does the ecosystem make use of that energy? How does that get into, how does that get stored within the ecosystem, especially as biomass? Well, it starts with primary producers, which are usually going to be plants."}, {"video_title": "Flow of energy and matter through ecosystem    Ecology   Khan Academy.mp3", "Sentence": "But there's also geothermal energy, but the sun is the source of most energy for most ecosystems we can think of. And how does the ecosystem make use of that energy? How does that get into, how does that get stored within the ecosystem, especially as biomass? Well, it starts with primary producers, which are usually going to be plants. They can also be bacteria that are able to photosynthesize, that are able to take that energy and create biomolecules that store energy from it. And so these are primary producers, these plants in this diagram. Sometimes you'll see them referred to as autotrophs."}, {"video_title": "Flow of energy and matter through ecosystem    Ecology   Khan Academy.mp3", "Sentence": "Well, it starts with primary producers, which are usually going to be plants. They can also be bacteria that are able to photosynthesize, that are able to take that energy and create biomolecules that store energy from it. And so these are primary producers, these plants in this diagram. Sometimes you'll see them referred to as autotrophs. They are getting their own food from the sun, from this energy. And once again, how is that energy stored? Well, it's stored in these biological molecules."}, {"video_title": "Flow of energy and matter through ecosystem    Ecology   Khan Academy.mp3", "Sentence": "Sometimes you'll see them referred to as autotrophs. They are getting their own food from the sun, from this energy. And once again, how is that energy stored? Well, it's stored in these biological molecules. If you were to zoom in into the molecules in this plant, and this is a huge oversimplification, you'll see all these bonds between these carbons. And to make those bonds requires energy. And if you were to break those bonds, it could release energy."}, {"video_title": "Flow of energy and matter through ecosystem    Ecology   Khan Academy.mp3", "Sentence": "Well, it's stored in these biological molecules. If you were to zoom in into the molecules in this plant, and this is a huge oversimplification, you'll see all these bonds between these carbons. And to make those bonds requires energy. And if you were to break those bonds, it could release energy. And you might say, well, where did all these carbons come from that are in this tree? Well, the carbon is coming from the air. Our air has carbon dioxide in it."}, {"video_title": "Flow of energy and matter through ecosystem    Ecology   Khan Academy.mp3", "Sentence": "And if you were to break those bonds, it could release energy. And you might say, well, where did all these carbons come from that are in this tree? Well, the carbon is coming from the air. Our air has carbon dioxide in it. It has carbon dioxide, so those are the carbons. Maybe let me draw some oxygens. So two oxygens for every carbon."}, {"video_title": "Flow of energy and matter through ecosystem    Ecology   Khan Academy.mp3", "Sentence": "Our air has carbon dioxide in it. It has carbon dioxide, so those are the carbons. Maybe let me draw some oxygens. So two oxygens for every carbon. And the whole process of photosynthesis is all about fixing that carbon. Let me write that word down. We are fixing that carbon from a gaseous form, when it's part of carbon dioxide, into the structure of the plant, into the biological molecules of the plant."}, {"video_title": "Flow of energy and matter through ecosystem    Ecology   Khan Academy.mp3", "Sentence": "So two oxygens for every carbon. And the whole process of photosynthesis is all about fixing that carbon. Let me write that word down. We are fixing that carbon from a gaseous form, when it's part of carbon dioxide, into the structure of the plant, into the biological molecules of the plant. So it's storing that energy. Now, it's not a perfectly efficient process. Not all of the energy from the sun is going to be able to be stored."}, {"video_title": "Flow of energy and matter through ecosystem    Ecology   Khan Academy.mp3", "Sentence": "We are fixing that carbon from a gaseous form, when it's part of carbon dioxide, into the structure of the plant, into the biological molecules of the plant. So it's storing that energy. Now, it's not a perfectly efficient process. Not all of the energy from the sun is going to be able to be stored. Some of it is being reflected. Even the plant itself, as it goes, as it lives, as it reproduces, as its cells divide, some of that energy is used. And eventually, that energy is released as heat."}, {"video_title": "Flow of energy and matter through ecosystem    Ecology   Khan Academy.mp3", "Sentence": "Not all of the energy from the sun is going to be able to be stored. Some of it is being reflected. Even the plant itself, as it goes, as it lives, as it reproduces, as its cells divide, some of that energy is used. And eventually, that energy is released as heat. And you're gonna see this trend a lot in thermodynamic systems, that you are taking, you're going from one energy, you're using energy to do some work, but in the process, you are going to be producing heat. But this is just the beginning of our energy flow. Now we can think about how that energy now flows to the other actors in the ecosystem."}, {"video_title": "Flow of energy and matter through ecosystem    Ecology   Khan Academy.mp3", "Sentence": "And eventually, that energy is released as heat. And you're gonna see this trend a lot in thermodynamic systems, that you are taking, you're going from one energy, you're using energy to do some work, but in the process, you are going to be producing heat. But this is just the beginning of our energy flow. Now we can think about how that energy now flows to the other actors in the ecosystem. So the next phase, and this is a very simplified diagram or ecosystem that we're thinking about. Most ecosystems are far, far, far more complex. Let's think about the characters that would eat the plants, the characters that would eat the primary producers."}, {"video_title": "Flow of energy and matter through ecosystem    Ecology   Khan Academy.mp3", "Sentence": "Now we can think about how that energy now flows to the other actors in the ecosystem. So the next phase, and this is a very simplified diagram or ecosystem that we're thinking about. Most ecosystems are far, far, far more complex. Let's think about the characters that would eat the plants, the characters that would eat the primary producers. And we call the folks that eat the primary producers, we call them primary consumers. So this bunny or this squirrel right over here, they are primary, primary consumers. They consume the primary producers."}, {"video_title": "Flow of energy and matter through ecosystem    Ecology   Khan Academy.mp3", "Sentence": "Let's think about the characters that would eat the plants, the characters that would eat the primary producers. And we call the folks that eat the primary producers, we call them primary consumers. So this bunny or this squirrel right over here, they are primary, primary consumers. They consume the primary producers. And why do they consume them? Why does a bunny eat the grass? Well, because it gets energy from those bonds between, in the biological molecules, from those carbon bonds and other bonds."}, {"video_title": "Flow of energy and matter through ecosystem    Ecology   Khan Academy.mp3", "Sentence": "They consume the primary producers. And why do they consume them? Why does a bunny eat the grass? Well, because it gets energy from those bonds between, in the biological molecules, from those carbon bonds and other bonds. And it's able to use that energy to grow itself, to reproduce, to live, to run around. And it also stores some of that energy in its own biomass. And once again, this process is not very efficient."}, {"video_title": "Flow of energy and matter through ecosystem    Ecology   Khan Academy.mp3", "Sentence": "Well, because it gets energy from those bonds between, in the biological molecules, from those carbon bonds and other bonds. And it's able to use that energy to grow itself, to reproduce, to live, to run around. And it also stores some of that energy in its own biomass. And once again, this process is not very efficient. Going from one layer of trophy to another layer of trophy, you only have about 10%, 10% of the energy gets transferred or gets stored in the next, gets stored in the next layer. Why only 10%? Well, because not all of the plants get eaten."}, {"video_title": "Flow of energy and matter through ecosystem    Ecology   Khan Academy.mp3", "Sentence": "And once again, this process is not very efficient. Going from one layer of trophy to another layer of trophy, you only have about 10%, 10% of the energy gets transferred or gets stored in the next, gets stored in the next layer. Why only 10%? Well, because not all of the plants get eaten. The whole process of eating plants, digesting plants, some of the energy gets pooped out, because the primary consumer here, or the consumer, isn't able to get all of it out of the actual biological molecules. And so overall, it's an inefficient process. Now, we're not done yet."}, {"video_title": "Flow of energy and matter through ecosystem    Ecology   Khan Academy.mp3", "Sentence": "Well, because not all of the plants get eaten. The whole process of eating plants, digesting plants, some of the energy gets pooped out, because the primary consumer here, or the consumer, isn't able to get all of it out of the actual biological molecules. And so overall, it's an inefficient process. Now, we're not done yet. We still have energy stored in the biological molecules of this primary consumer that someone might be interested in. And we know that in many ecosystems, there are things that like to eat rabbits or even squirrels. And in this drawing, it will be this fox."}, {"video_title": "Flow of energy and matter through ecosystem    Ecology   Khan Academy.mp3", "Sentence": "Now, we're not done yet. We still have energy stored in the biological molecules of this primary consumer that someone might be interested in. And we know that in many ecosystems, there are things that like to eat rabbits or even squirrels. And in this drawing, it will be this fox. And this fox, because it eats primary consumers, we would call it a secondary consumer. A secondary consumer. And you could keep going on with this."}, {"video_title": "Flow of energy and matter through ecosystem    Ecology   Khan Academy.mp3", "Sentence": "And in this drawing, it will be this fox. And this fox, because it eats primary consumers, we would call it a secondary consumer. A secondary consumer. And you could keep going on with this. If there were some character out here, let's say there's some guy who likes to eat foxes, sets a knife in his hand that he uses to go after the foxes with. Well, so the fox could go to him. And once again, why is he eating foxes?"}, {"video_title": "Flow of energy and matter through ecosystem    Ecology   Khan Academy.mp3", "Sentence": "And you could keep going on with this. If there were some character out here, let's say there's some guy who likes to eat foxes, sets a knife in his hand that he uses to go after the foxes with. Well, so the fox could go to him. And once again, why is he eating foxes? Well, he wants that energy in that fox, and actually some of them, it's actually not just about molecules. We'll talk about matter in a second. He wants the energy and the matter from the fox to grow and live himself."}, {"video_title": "Flow of energy and matter through ecosystem    Ecology   Khan Academy.mp3", "Sentence": "And once again, why is he eating foxes? Well, he wants that energy in that fox, and actually some of them, it's actually not just about molecules. We'll talk about matter in a second. He wants the energy and the matter from the fox to grow and live himself. And so this character would be called a tertiary consumer. Tertiary consumer. And if there's no one who wants to eat him, well then he would be considered an apex consumer, an apex predator."}, {"video_title": "Flow of energy and matter through ecosystem    Ecology   Khan Academy.mp3", "Sentence": "He wants the energy and the matter from the fox to grow and live himself. And so this character would be called a tertiary consumer. Tertiary consumer. And if there's no one who wants to eat him, well then he would be considered an apex consumer, an apex predator. And these characters that eat other animals, we've talked about it before, they're called carnivores. But let me just say, he's the apex. And apex, we're really thinking about the top of the food chain."}, {"video_title": "Flow of energy and matter through ecosystem    Ecology   Khan Academy.mp3", "Sentence": "And if there's no one who wants to eat him, well then he would be considered an apex consumer, an apex predator. And these characters that eat other animals, we've talked about it before, they're called carnivores. But let me just say, he's the apex. And apex, we're really thinking about the top of the food chain. That's why that would be called an apex consumer or an apex predator. But we're not done yet. Because at some point, all of these characters, whether we're talking about the trees, the bunnies, the fox, this character who likes to eat foxes, they're going to die."}, {"video_title": "Flow of energy and matter through ecosystem    Ecology   Khan Academy.mp3", "Sentence": "And apex, we're really thinking about the top of the food chain. That's why that would be called an apex consumer or an apex predator. But we're not done yet. Because at some point, all of these characters, whether we're talking about the trees, the bunnies, the fox, this character who likes to eat foxes, they're going to die. And that energy just doesn't disappear. And in general, you're gonna see energy is conserved and it flows from one place to another. That energy is then going to be used by, it is going to be used by these characters right over here, which we call decomposers."}, {"video_title": "Flow of energy and matter through ecosystem    Ecology   Khan Academy.mp3", "Sentence": "Because at some point, all of these characters, whether we're talking about the trees, the bunnies, the fox, this character who likes to eat foxes, they're going to die. And that energy just doesn't disappear. And in general, you're gonna see energy is conserved and it flows from one place to another. That energy is then going to be used by, it is going to be used by these characters right over here, which we call decomposers. They can take all that leftover energy in that dead carcass or even in the poop and they can make use of it, once again, for them to live, for them to reproduce. And then by breaking that down, they can release a lot of those nutrients and the matter that's used, and once again, the matter is recycled, once again, to be used by the plants. So it creates this really nice cycle."}, {"video_title": "Flow of energy and matter through ecosystem    Ecology   Khan Academy.mp3", "Sentence": "That energy is then going to be used by, it is going to be used by these characters right over here, which we call decomposers. They can take all that leftover energy in that dead carcass or even in the poop and they can make use of it, once again, for them to live, for them to reproduce. And then by breaking that down, they can release a lot of those nutrients and the matter that's used, and once again, the matter is recycled, once again, to be used by the plants. So it creates this really nice cycle. And the important thing to realize is it comes in as light, that energy gets transferred as we go through the different layers of trophy. And it's not a completely efficient process and a lot of that energy, especially as we, as these organisms live and reproduce and run around, gets released as heat. Now, we focus a lot on the energy."}, {"video_title": "Flow of energy and matter through ecosystem    Ecology   Khan Academy.mp3", "Sentence": "So it creates this really nice cycle. And the important thing to realize is it comes in as light, that energy gets transferred as we go through the different layers of trophy. And it's not a completely efficient process and a lot of that energy, especially as we, as these organisms live and reproduce and run around, gets released as heat. Now, we focus a lot on the energy. Let's think a little bit about the matter. And I've already touched on it. But the matter is recycled."}, {"video_title": "Flow of energy and matter through ecosystem    Ecology   Khan Academy.mp3", "Sentence": "Now, we focus a lot on the energy. Let's think a little bit about the matter. And I've already touched on it. But the matter is recycled. There isn't, at least in the way we've set this up, there isn't a new matter that is entering or leaving these ecosystems or being magically created or magically destroyed. As I mentioned, when you look at a leaf on a plant growing or a tree growing or a leaf of grass growing, that matter isn't just coming out of nowhere. It's coming out of, it's just a different form or maybe the best way to put it, that matter was always there in the form of carbon dioxide."}, {"video_title": "Flow of energy and matter through ecosystem    Ecology   Khan Academy.mp3", "Sentence": "But the matter is recycled. There isn't, at least in the way we've set this up, there isn't a new matter that is entering or leaving these ecosystems or being magically created or magically destroyed. As I mentioned, when you look at a leaf on a plant growing or a tree growing or a leaf of grass growing, that matter isn't just coming out of nowhere. It's coming out of, it's just a different form or maybe the best way to put it, that matter was always there in the form of carbon dioxide. The plant is just using that energy from the sun to fix that carbon from a gas form into a solid form. And it's able to use that energy to form bonds between the carbons in these biological molecules that actually store energy. And the plant can use that energy to grow."}, {"video_title": "Flow of energy and matter through ecosystem    Ecology   Khan Academy.mp3", "Sentence": "It's coming out of, it's just a different form or maybe the best way to put it, that matter was always there in the form of carbon dioxide. The plant is just using that energy from the sun to fix that carbon from a gas form into a solid form. And it's able to use that energy to form bonds between the carbons in these biological molecules that actually store energy. And the plant can use that energy to grow. And as we've talked about, things that eat the plants or the things that eat the plants can use that energy. And as we talked before, the carbon dioxide comes in. These plants, and maybe this arrow might be a little bit misleading."}, {"video_title": "Flow of energy and matter through ecosystem    Ecology   Khan Academy.mp3", "Sentence": "And the plant can use that energy to grow. And as we've talked about, things that eat the plants or the things that eat the plants can use that energy. And as we talked before, the carbon dioxide comes in. These plants, and maybe this arrow might be a little bit misleading. So let me erase that for now. But we release oxygen, O2. That oxygen, and we've seen that as part of the photosynthesis process, that oxygen is used by the animals to metabolize these biological molecules."}, {"video_title": "Flow of energy and matter through ecosystem    Ecology   Khan Academy.mp3", "Sentence": "These plants, and maybe this arrow might be a little bit misleading. So let me erase that for now. But we release oxygen, O2. That oxygen, and we've seen that as part of the photosynthesis process, that oxygen is used by the animals to metabolize these biological molecules. We study that in biology and in respiration. And the matter itself, as we say, we have this carbon right over here. When it gets eaten, well then that becomes part of the biomolecules inside of this bunny."}, {"video_title": "Flow of energy and matter through ecosystem    Ecology   Khan Academy.mp3", "Sentence": "That oxygen, and we've seen that as part of the photosynthesis process, that oxygen is used by the animals to metabolize these biological molecules. We study that in biology and in respiration. And the matter itself, as we say, we have this carbon right over here. When it gets eaten, well then that becomes part of the biomolecules inside of this bunny. And when the bunny uses any of these biological molecules as a source of energy, so it's able to break those bonds through respiration, well then that carbon gets released in the form of carbon dioxide. So maybe this is a better way. And actually it was already drawn right over here."}, {"video_title": "Flow of energy and matter through ecosystem    Ecology   Khan Academy.mp3", "Sentence": "When it gets eaten, well then that becomes part of the biomolecules inside of this bunny. And when the bunny uses any of these biological molecules as a source of energy, so it's able to break those bonds through respiration, well then that carbon gets released in the form of carbon dioxide. So maybe this is a better way. And actually it was already drawn right over here. And so the important thing to realize is that energy is flowing, light from the sun comes in, all this action goes on, and then it gets released as heat on almost every step. But the matter itself, it's always been there. All of the atoms in our body on Earth, it's just constantly being recycled."}, {"video_title": "Flow of energy and matter through ecosystem    Ecology   Khan Academy.mp3", "Sentence": "And actually it was already drawn right over here. And so the important thing to realize is that energy is flowing, light from the sun comes in, all this action goes on, and then it gets released as heat on almost every step. But the matter itself, it's always been there. All of the atoms in our body on Earth, it's just constantly being recycled. It actually was generated inside of stars many, many billions of years ago. And we just keep reusing it over and over and over again. It gets recycled from one form to another."}, {"video_title": "Phylogenetic trees    Evolution   Khan Academy.mp3", "Sentence": "And if you put that into an evolutionary context, relatedness should be tied to how recent did two species share a common ancestor. And what we're going to try to do in this video is construct a tree for showing how different species evolved from common ancestors, and we're going to do it based on some of these observable traits that we see. But this is going to be a huge oversimplification. I'm only doing it with five species and five very simple traits. As we'll see or as we'll talk about in future videos, this can be done in a much more complex way, and that's what biologists would do. They would look at much more than five traits, and they would look at molecular evidence, molecular evidence in terms of protein differences, in terms of DNA differences, to really start to build out what we call a phylogenetic tree. So let me write this down."}, {"video_title": "Phylogenetic trees    Evolution   Khan Academy.mp3", "Sentence": "I'm only doing it with five species and five very simple traits. As we'll see or as we'll talk about in future videos, this can be done in a much more complex way, and that's what biologists would do. They would look at much more than five traits, and they would look at molecular evidence, molecular evidence in terms of protein differences, in terms of DNA differences, to really start to build out what we call a phylogenetic tree. So let me write this down. That's what we're going to create. Phylogenetic, genetic tree. Phylo comes from the Greek for group or kind or tribe, and then genetic comes related to the word genesis."}, {"video_title": "Phylogenetic trees    Evolution   Khan Academy.mp3", "Sentence": "So let me write this down. That's what we're going to create. Phylogenetic, genetic tree. Phylo comes from the Greek for group or kind or tribe, and then genetic comes related to the word genesis. How did these things come about? How did the different groups or tribes, or in this case, how did the different species come about? Well, when you're trying to make one of these trees, it's important to realize that this is a hypothesis, but you're, like always, trying to come up with the simplest hypothesis that can explain the observations that you actually see."}, {"video_title": "Phylogenetic trees    Evolution   Khan Academy.mp3", "Sentence": "Phylo comes from the Greek for group or kind or tribe, and then genetic comes related to the word genesis. How did these things come about? How did the different groups or tribes, or in this case, how did the different species come about? Well, when you're trying to make one of these trees, it's important to realize that this is a hypothesis, but you're, like always, trying to come up with the simplest hypothesis that can explain the observations that you actually see. And when we look at these, at least the species that we have listed here, it looks like there's one that is more different than all the other ones. The lamprey here does not have any of these five traits that we are observing, so this we would call the outgroup. The lamprey is the outgroup, and a lot of times when you need to construct a phylogenetic tree, they might provide you something with something that is clearly an outgroup."}, {"video_title": "Phylogenetic trees    Evolution   Khan Academy.mp3", "Sentence": "Well, when you're trying to make one of these trees, it's important to realize that this is a hypothesis, but you're, like always, trying to come up with the simplest hypothesis that can explain the observations that you actually see. And when we look at these, at least the species that we have listed here, it looks like there's one that is more different than all the other ones. The lamprey here does not have any of these five traits that we are observing, so this we would call the outgroup. The lamprey is the outgroup, and a lot of times when you need to construct a phylogenetic tree, they might provide you something with something that is clearly an outgroup. Here it doesn't have any of these observable traits. Sometimes if we're looking at genetic differences, it might have the largest number of genetic differences relative to everything else. And so it makes sense, the simplest hypothesis is its common ancestor is most distant into the past with everything else."}, {"video_title": "Phylogenetic trees    Evolution   Khan Academy.mp3", "Sentence": "The lamprey is the outgroup, and a lot of times when you need to construct a phylogenetic tree, they might provide you something with something that is clearly an outgroup. Here it doesn't have any of these observable traits. Sometimes if we're looking at genetic differences, it might have the largest number of genetic differences relative to everything else. And so it makes sense, the simplest hypothesis is its common ancestor is most distant into the past with everything else. And so let me start to draw this tree. So I am going to put deep into the past, so deep into the past, there is a branching out point where you have the common ancestor of the lamprey and everything else we see here. So eventually, that common ancestor, and there's many, many species along the way, and eventually we get a lamprey in present time."}, {"video_title": "Phylogenetic trees    Evolution   Khan Academy.mp3", "Sentence": "And so it makes sense, the simplest hypothesis is its common ancestor is most distant into the past with everything else. And so let me start to draw this tree. So I am going to put deep into the past, so deep into the past, there is a branching out point where you have the common ancestor of the lamprey and everything else we see here. So eventually, that common ancestor, and there's many, many species along the way, and eventually we get a lamprey in present time. In present time. And so the next thing to think about is, all right, well how did everything else end up branching? Well, what's common about everything else that maybe wasn't common about the lamprey?"}, {"video_title": "Phylogenetic trees    Evolution   Khan Academy.mp3", "Sentence": "So eventually, that common ancestor, and there's many, many species along the way, and eventually we get a lamprey in present time. In present time. And so the next thing to think about is, all right, well how did everything else end up branching? Well, what's common about everything else that maybe wasn't common about the lamprey? Well, one common thing is we see that everything else, at least that we have listed here, have jaws. And so it's reasonable to say, all right, we have this common ancestor, this between the lamprey and everything else at this branching point right over here. And then it branched off into multiple species, and one of those species must have evolved jaws."}, {"video_title": "Phylogenetic trees    Evolution   Khan Academy.mp3", "Sentence": "Well, what's common about everything else that maybe wasn't common about the lamprey? Well, one common thing is we see that everything else, at least that we have listed here, have jaws. And so it's reasonable to say, all right, we have this common ancestor, this between the lamprey and everything else at this branching point right over here. And then it branched off into multiple species, and one of those species must have evolved jaws. So let me put jaws right over here. So jaws right over there. And jaws, that's called, jaws are considered a derived trait."}, {"video_title": "Phylogenetic trees    Evolution   Khan Academy.mp3", "Sentence": "And then it branched off into multiple species, and one of those species must have evolved jaws. So let me put jaws right over here. So jaws right over there. And jaws, that's called, jaws are considered a derived trait. This ancestral species at this root did not have jaws, we're assuming, but at some point, they evolved and they stuck around because they proved to be favorable in certain environments. Or it could have even been things like genetic drift, who knows, but I'm guessing that it was favorable in certain environments. So let's see, let's see if we can classify everyone else."}, {"video_title": "Phylogenetic trees    Evolution   Khan Academy.mp3", "Sentence": "And jaws, that's called, jaws are considered a derived trait. This ancestral species at this root did not have jaws, we're assuming, but at some point, they evolved and they stuck around because they proved to be favorable in certain environments. Or it could have even been things like genetic drift, who knows, but I'm guessing that it was favorable in certain environments. So let's see, let's see if we can classify everyone else. So now out of the four, so let's actually cross out the lamprey just for simplification, since we've already classified that character. Now of everyone else, we've already thought about, everyone's got jaws, so now let's go to the next most common trait. So, and actually let me cross out the jaws too, just for, keep things simple."}, {"video_title": "Phylogenetic trees    Evolution   Khan Academy.mp3", "Sentence": "So let's see, let's see if we can classify everyone else. So now out of the four, so let's actually cross out the lamprey just for simplification, since we've already classified that character. Now of everyone else, we've already thought about, everyone's got jaws, so now let's go to the next most common trait. So, and actually let me cross out the jaws too, just for, keep things simple. So I can do that a little bit cleaner. So I'm gonna cross out the jaws. And now let's see, the most, the next most common trait is, are the lungs, but not every species that we have left has lungs."}, {"video_title": "Phylogenetic trees    Evolution   Khan Academy.mp3", "Sentence": "So, and actually let me cross out the jaws too, just for, keep things simple. So I can do that a little bit cleaner. So I'm gonna cross out the jaws. And now let's see, the most, the next most common trait is, are the lungs, but not every species that we have left has lungs. The sea bass does not have lungs. It does not breathe air the way that animals that live outside of the water breathe air. And so they, the next, the next point of divergence must be between the sea bass and everything that we have left over."}, {"video_title": "Phylogenetic trees    Evolution   Khan Academy.mp3", "Sentence": "And now let's see, the most, the next most common trait is, are the lungs, but not every species that we have left has lungs. The sea bass does not have lungs. It does not breathe air the way that animals that live outside of the water breathe air. And so they, the next, the next point of divergence must be between the sea bass and everything that we have left over. So let me draw that. So, and once again, I said must be, this is a hypothesis. I think it's a reasonable hypothesis."}, {"video_title": "Phylogenetic trees    Evolution   Khan Academy.mp3", "Sentence": "And so they, the next, the next point of divergence must be between the sea bass and everything that we have left over. So let me draw that. So, and once again, I said must be, this is a hypothesis. I think it's a reasonable hypothesis. So let me draw that. So this is the sea, sea bass. And there's a common ancestor between the sea bass and everything else, and the antelope, the bald eagle, and the alligator."}, {"video_title": "Phylogenetic trees    Evolution   Khan Academy.mp3", "Sentence": "I think it's a reasonable hypothesis. So let me draw that. So this is the sea, sea bass. And there's a common ancestor between the sea bass and everything else, and the antelope, the bald eagle, and the alligator. And at some point, that common ancestor diverged into multiple species, and one of those, one of those child species must have evolved lungs. So lungs must have evolved at some point. But we're assuming that that wasn't, that wasn't on this lineage for the sea bass."}, {"video_title": "Phylogenetic trees    Evolution   Khan Academy.mp3", "Sentence": "And there's a common ancestor between the sea bass and everything else, and the antelope, the bald eagle, and the alligator. And at some point, that common ancestor diverged into multiple species, and one of those, one of those child species must have evolved lungs. So lungs must have evolved at some point. But we're assuming that that wasn't, that wasn't on this lineage for the sea bass. And once again, I'm just trying to find the simplest explanation. There might have been some situation where maybe lungs evolved and then, de, or then went away at some point. You reverted to an ancestral form."}, {"video_title": "Phylogenetic trees    Evolution   Khan Academy.mp3", "Sentence": "But we're assuming that that wasn't, that wasn't on this lineage for the sea bass. And once again, I'm just trying to find the simplest explanation. There might have been some situation where maybe lungs evolved and then, de, or then went away at some point. You reverted to an ancestral form. But we like to go with the simplest explanation. This is a property that biologists will also often call parsimony. And actually, let me write this down."}, {"video_title": "Phylogenetic trees    Evolution   Khan Academy.mp3", "Sentence": "You reverted to an ancestral form. But we like to go with the simplest explanation. This is a property that biologists will also often call parsimony. And actually, let me write this down. Parsimony, which in everyday language means cheap. If someone tells you you're parsimonious, it's a nice sounding word, but it means that you are cheap. But parsimony in this context say, hey, we're trying to, we're trying to be cheap with complexity."}, {"video_title": "Phylogenetic trees    Evolution   Khan Academy.mp3", "Sentence": "And actually, let me write this down. Parsimony, which in everyday language means cheap. If someone tells you you're parsimonious, it's a nice sounding word, but it means that you are cheap. But parsimony in this context say, hey, we're trying to, we're trying to be cheap with complexity. We're trying to be as simple as possible in our explanation of what's going on. But anyway, let's go back to what we were doing. So we've already put into consideration, we have already talked about the sea bass here, and we have already talked about lungs."}, {"video_title": "Phylogenetic trees    Evolution   Khan Academy.mp3", "Sentence": "But parsimony in this context say, hey, we're trying to, we're trying to be cheap with complexity. We're trying to be as simple as possible in our explanation of what's going on. But anyway, let's go back to what we were doing. So we've already put into consideration, we have already talked about the sea bass here, and we have already talked about lungs. All right, so what do we have left? So we have to talk about the antelope, the bald eagle, the alligator, and gizzard, and fur. All right, it looks like the bald eagle and alligator have gizzard, the antelope has fur."}, {"video_title": "Phylogenetic trees    Evolution   Khan Academy.mp3", "Sentence": "So we've already put into consideration, we have already talked about the sea bass here, and we have already talked about lungs. All right, so what do we have left? So we have to talk about the antelope, the bald eagle, the alligator, and gizzard, and fur. All right, it looks like the bald eagle and alligator have gizzard, the antelope has fur. Oh, and actually, we haven't talked about the bald eagle and feathers as yet either. All right, so it is possible. So let's make the next thing between, well, we could do it this way."}, {"video_title": "Phylogenetic trees    Evolution   Khan Academy.mp3", "Sentence": "All right, it looks like the bald eagle and alligator have gizzard, the antelope has fur. Oh, and actually, we haven't talked about the bald eagle and feathers as yet either. All right, so it is possible. So let's make the next thing between, well, we could do it this way. And once again, I'm trying to do this in real time, something that seems, so let's make a branch here. And let's say that that is the branch for, let's say that's the branch for the bald eagle. Let's say B eagle."}, {"video_title": "Phylogenetic trees    Evolution   Khan Academy.mp3", "Sentence": "So let's make the next thing between, well, we could do it this way. And once again, I'm trying to do this in real time, something that seems, so let's make a branch here. And let's say that that is the branch for, let's say that's the branch for the bald eagle. Let's say B eagle. That's the branch for the bald eagle. Let's see if I can construct one that'll explain the differences between the bald eagle, the antelope, and the alligator. Well, the bald eagle and the alligator have something in common."}, {"video_title": "Phylogenetic trees    Evolution   Khan Academy.mp3", "Sentence": "Let's say B eagle. That's the branch for the bald eagle. Let's see if I can construct one that'll explain the differences between the bald eagle, the antelope, and the alligator. Well, the bald eagle and the alligator have something in common. They have a gizzard in common. So let me make a branching point, make them a little bit closer than the bald eagle is to the antelope. So let me do that."}, {"video_title": "Phylogenetic trees    Evolution   Khan Academy.mp3", "Sentence": "Well, the bald eagle and the alligator have something in common. They have a gizzard in common. So let me make a branching point, make them a little bit closer than the bald eagle is to the antelope. So let me do that. So let me put the alligator there. And then I'm gonna talk about when we get these derived traits. So that is the alligator."}, {"video_title": "Phylogenetic trees    Evolution   Khan Academy.mp3", "Sentence": "So let me do that. So let me put the alligator there. And then I'm gonna talk about when we get these derived traits. So that is the alligator. And obviously I could have written the alligator on this side and the bald eagle on that. So I could rotate at any one of these branching points. And then what we would have left is the antelope."}, {"video_title": "Phylogenetic trees    Evolution   Khan Academy.mp3", "Sentence": "So that is the alligator. And obviously I could have written the alligator on this side and the bald eagle on that. So I could rotate at any one of these branching points. And then what we would have left is the antelope. Now let's see if I can account for all of these derived traits. Antelope. All right, so we have the common ancestor of the sea bass, the bald eagle, the alligator, and the antelope right over here."}, {"video_title": "Phylogenetic trees    Evolution   Khan Academy.mp3", "Sentence": "And then what we would have left is the antelope. Now let's see if I can account for all of these derived traits. Antelope. All right, so we have the common ancestor of the sea bass, the bald eagle, the alligator, and the antelope right over here. We have a branching point. At some point, the lungs, where we are hypothesizing, evolve in this branch. And then this branch, well, let's say that this branch, this is the common ancestor between the antelope, alligator, and bald eagle."}, {"video_title": "Phylogenetic trees    Evolution   Khan Academy.mp3", "Sentence": "All right, so we have the common ancestor of the sea bass, the bald eagle, the alligator, and the antelope right over here. We have a branching point. At some point, the lungs, where we are hypothesizing, evolve in this branch. And then this branch, well, let's say that this branch, this is the common ancestor between the antelope, alligator, and bald eagle. And a common ancestor of the bald eagle and alligator, they have to get the gizzard. So let's put the gizzard down right over here. This is where the gizzard, this is our hypothesis."}, {"video_title": "Phylogenetic trees    Evolution   Khan Academy.mp3", "Sentence": "And then this branch, well, let's say that this branch, this is the common ancestor between the antelope, alligator, and bald eagle. And a common ancestor of the bald eagle and alligator, they have to get the gizzard. So let's put the gizzard down right over here. This is where the gizzard, this is our hypothesis. Do that same colors. So that's the gizzard. Gizzard right over there."}, {"video_title": "Phylogenetic trees    Evolution   Khan Academy.mp3", "Sentence": "This is where the gizzard, this is our hypothesis. Do that same colors. So that's the gizzard. Gizzard right over there. And so everything that descended from that ancestor that had the gizzard, well, they're going to have gizzards. That's what we're assuming. But once again, that can be lost."}, {"video_title": "Phylogenetic trees    Evolution   Khan Academy.mp3", "Sentence": "Gizzard right over there. And so everything that descended from that ancestor that had the gizzard, well, they're going to have gizzards. That's what we're assuming. But once again, that can be lost. This is a hypothesis. And so we have accounted for the gizzard. Let me cross that out."}, {"video_title": "Phylogenetic trees    Evolution   Khan Academy.mp3", "Sentence": "But once again, that can be lost. This is a hypothesis. And so we have accounted for the gizzard. Let me cross that out. So we have accounted for the gizzard. And so let's see, we have to account for the feathers. And the bald eagle is the only one that has feathers."}, {"video_title": "Phylogenetic trees    Evolution   Khan Academy.mp3", "Sentence": "Let me cross that out. So we have accounted for the gizzard. And so let's see, we have to account for the feathers. And the bald eagle is the only one that has feathers. So let me put that here. So at some point, you have a common ancestor of an alligator and a bald eagle. It branches off into multiple species, one of which gets a feather or gets feathers."}, {"video_title": "Phylogenetic trees    Evolution   Khan Academy.mp3", "Sentence": "And the bald eagle is the only one that has feathers. So let me put that here. So at some point, you have a common ancestor of an alligator and a bald eagle. It branches off into multiple species, one of which gets a feather or gets feathers. And once again, that could have branched off into many, many things, because we know that the bald eagle isn't the only species with feathers. But the bald eagle for sure is a species that has feathers. And let's see, so we've accounted for the feathers now."}, {"video_title": "Phylogenetic trees    Evolution   Khan Academy.mp3", "Sentence": "It branches off into multiple species, one of which gets a feather or gets feathers. And once again, that could have branched off into many, many things, because we know that the bald eagle isn't the only species with feathers. But the bald eagle for sure is a species that has feathers. And let's see, so we've accounted for the feathers now. Feathers. And now we just have to account for the fur, the fur of the antelope. And so we don't know where this could have happened."}, {"video_title": "Phylogenetic trees    Evolution   Khan Academy.mp3", "Sentence": "And let's see, so we've accounted for the feathers now. Feathers. And now we just have to account for the fur, the fur of the antelope. And so we don't know where this could have happened. We might want to look for more evidence to come up with a good hypothesis. But someplace along this right branch, we could put the fur. And so there you have it."}, {"video_title": "Phylogenetic trees    Evolution   Khan Academy.mp3", "Sentence": "And so we don't know where this could have happened. We might want to look for more evidence to come up with a good hypothesis. But someplace along this right branch, we could put the fur. And so there you have it. This is actually a reasonable phylogenetic tree. I practiced the practice of parsimony to come up with the simplest explanation. But there are more complicated explanations."}, {"video_title": "Phylogenetic trees    Evolution   Khan Academy.mp3", "Sentence": "And so there you have it. This is actually a reasonable phylogenetic tree. I practiced the practice of parsimony to come up with the simplest explanation. But there are more complicated explanations. And we don't know, some of those more complicated explanations could very well be true. But from this, we have a very quick and easy graphical representation of how related different species could be and where they share common ancestors. So a bald eagle and an alligator, based on this phylogenetic tree, we would say are more related than a bald eagle is to an antelope."}, {"video_title": "Phylogenetic trees    Evolution   Khan Academy.mp3", "Sentence": "But there are more complicated explanations. And we don't know, some of those more complicated explanations could very well be true. But from this, we have a very quick and easy graphical representation of how related different species could be and where they share common ancestors. So a bald eagle and an alligator, based on this phylogenetic tree, we would say are more related than a bald eagle is to an antelope. The bald eagle and the alligator have a more recent common ancestor right there than both of their common ancestors with the antelope. And that would make them more related. And if we were doing this for real, we would want to look at genetic evidence and look at the various proteins and say, okay, does that back this up?"}, {"video_title": "Endoplasmic reticulum and Golgi bodies   Biology   Khan Academy.mp3", "Sentence": "We've already talked about the process from going from DNA to messenger RNA, and we call that process transcription, and this occurs in the nucleus. And then that messenger RNA makes its way outside of the nucleus, and it attaches to a ribosome, and then it is translated into a protein. It is translated into a protein. And so you could say that this part right over here, this is happening as this is being facilitated by a ribosome, or it's happening at a ribosome. With that high-level overview, I now want to think a little bit in more detail about how this actually happens, or the structure of things where this happens inside of a cell. And so I'm going to now draw the nucleus in a little bit more detail so that we can really see what's happening on its membrane. So this right over here, this over here is the nucleus."}, {"video_title": "Endoplasmic reticulum and Golgi bodies   Biology   Khan Academy.mp3", "Sentence": "And so you could say that this part right over here, this is happening as this is being facilitated by a ribosome, or it's happening at a ribosome. With that high-level overview, I now want to think a little bit in more detail about how this actually happens, or the structure of things where this happens inside of a cell. And so I'm going to now draw the nucleus in a little bit more detail so that we can really see what's happening on its membrane. So this right over here, this over here is the nucleus. Actually, let me draw it like this. And instead of just drawing the nucleus with one single line, I'm going to draw it with two lines, because it's actually a double bilipid membrane. So this is one bilipid layer right over here, and then this is another one right over here."}, {"video_title": "Endoplasmic reticulum and Golgi bodies   Biology   Khan Academy.mp3", "Sentence": "So this right over here, this over here is the nucleus. Actually, let me draw it like this. And instead of just drawing the nucleus with one single line, I'm going to draw it with two lines, because it's actually a double bilipid membrane. So this is one bilipid layer right over here, and then this is another one right over here. And I'm obviously not drawing it to scale. I'm drawing it so that you can get a sense of things. So each of these lines that I'm drawing, if I were to zoom in on this, so if I were to zoom in on each of these lines, so let's zoom in."}, {"video_title": "Endoplasmic reticulum and Golgi bodies   Biology   Khan Academy.mp3", "Sentence": "So this is one bilipid layer right over here, and then this is another one right over here. And I'm obviously not drawing it to scale. I'm drawing it so that you can get a sense of things. So each of these lines that I'm drawing, if I were to zoom in on this, so if I were to zoom in on each of these lines, so let's zoom in. And if I got a box like that, you would see a bilipid layer. So a bilipid layer looks like this. You have the circle as a hydrophilic end, and those lines are the fatty hydrophobic ends."}, {"video_title": "Endoplasmic reticulum and Golgi bodies   Biology   Khan Academy.mp3", "Sentence": "So each of these lines that I'm drawing, if I were to zoom in on this, so if I were to zoom in on each of these lines, so let's zoom in. And if I got a box like that, you would see a bilipid layer. So a bilipid layer looks like this. You have the circle as a hydrophilic end, and those lines are the fatty hydrophobic ends. So that's our bilipid layer. So that's each of these lines that I have drawn. Each of them are a bilipid layer."}, {"video_title": "Endoplasmic reticulum and Golgi bodies   Biology   Khan Academy.mp3", "Sentence": "You have the circle as a hydrophilic end, and those lines are the fatty hydrophobic ends. So that's our bilipid layer. So that's each of these lines that I have drawn. Each of them are a bilipid layer. So the question is, well, how does the mRNA, obviously you have all this transcription going on. You have the DNA. You have the mRNA."}, {"video_title": "Endoplasmic reticulum and Golgi bodies   Biology   Khan Academy.mp3", "Sentence": "Each of them are a bilipid layer. So the question is, well, how does the mRNA, obviously you have all this transcription going on. You have the DNA. You have the mRNA. It's all in here, this big jumble of chromatin inside the nucleus. How does it make its way outside of this double bilipid layer? And the way it makes its way out is through nuclear pores."}, {"video_title": "Endoplasmic reticulum and Golgi bodies   Biology   Khan Academy.mp3", "Sentence": "You have the mRNA. It's all in here, this big jumble of chromatin inside the nucleus. How does it make its way outside of this double bilipid layer? And the way it makes its way out is through nuclear pores. So a nuclear pore is essentially a tunnel, and there are thousands of these, is a tunnel through this bilipid layer. And the tunnel is made up of a bunch of proteins. So this right over here, and this is kind of a cross section of it, but you could almost imagine it, if you're thinking of it in three dimensions, you would imagine a tunnel, a tunnel made out of proteins that goes through this double bilipid membrane."}, {"video_title": "Endoplasmic reticulum and Golgi bodies   Biology   Khan Academy.mp3", "Sentence": "And the way it makes its way out is through nuclear pores. So a nuclear pore is essentially a tunnel, and there are thousands of these, is a tunnel through this bilipid layer. And the tunnel is made up of a bunch of proteins. So this right over here, and this is kind of a cross section of it, but you could almost imagine it, if you're thinking of it in three dimensions, you would imagine a tunnel, a tunnel made out of proteins that goes through this double bilipid membrane. And so the mRNA can make its way out and get to a free ribosome and then be translated into a protein. But this right over here is not the complete picture, because when you translate a protein using a free ribosome, this is for proteins that are used inside the cell. So let me draw the entire cell right over here."}, {"video_title": "Endoplasmic reticulum and Golgi bodies   Biology   Khan Academy.mp3", "Sentence": "So this right over here, and this is kind of a cross section of it, but you could almost imagine it, if you're thinking of it in three dimensions, you would imagine a tunnel, a tunnel made out of proteins that goes through this double bilipid membrane. And so the mRNA can make its way out and get to a free ribosome and then be translated into a protein. But this right over here is not the complete picture, because when you translate a protein using a free ribosome, this is for proteins that are used inside the cell. So let me draw the entire cell right over here. So this is the cell. This right over here is the cytosol of the cell. And you might be sometimes confused with the term cytosol and cytoplasm."}, {"video_title": "Endoplasmic reticulum and Golgi bodies   Biology   Khan Academy.mp3", "Sentence": "So let me draw the entire cell right over here. So this is the cell. This right over here is the cytosol of the cell. And you might be sometimes confused with the term cytosol and cytoplasm. Cytosol is all the fluid between the organelles. Cytoplasm is everything that's inside the cell. So it's the cytosol and the organelles and the stuff inside the organelles is the cytoplasm."}, {"video_title": "Endoplasmic reticulum and Golgi bodies   Biology   Khan Academy.mp3", "Sentence": "And you might be sometimes confused with the term cytosol and cytoplasm. Cytosol is all the fluid between the organelles. Cytoplasm is everything that's inside the cell. So it's the cytosol and the organelles and the stuff inside the organelles is the cytoplasm. So cytoplasm is everything inside of the cell. Cytosol is just the fluid that's between the organelles. So anyway, the free ribosome over here, this translation is good for proteins used within the cell itself."}, {"video_title": "Endoplasmic reticulum and Golgi bodies   Biology   Khan Academy.mp3", "Sentence": "So it's the cytosol and the organelles and the stuff inside the organelles is the cytoplasm. So cytoplasm is everything inside of the cell. Cytosol is just the fluid that's between the organelles. So anyway, the free ribosome over here, this translation is good for proteins used within the cell itself. The proteins can then float around the cytosol and used in whichever way is appropriate. But how do you get protein outside of the cell or even inside the cellular membrane? Not within the cell, but embedded in the cell membrane or outside of the cell itself?"}, {"video_title": "Endoplasmic reticulum and Golgi bodies   Biology   Khan Academy.mp3", "Sentence": "So anyway, the free ribosome over here, this translation is good for proteins used within the cell itself. The proteins can then float around the cytosol and used in whichever way is appropriate. But how do you get protein outside of the cell or even inside the cellular membrane? Not within the cell, but embedded in the cell membrane or outside of the cell itself? And we know that cells communicate in all sorts of different ways. And they produce proteins for other cells or for use in the bloodstream or whatever it might be. And that's what we're going to focus on in this video."}, {"video_title": "Endoplasmic reticulum and Golgi bodies   Biology   Khan Academy.mp3", "Sentence": "Not within the cell, but embedded in the cell membrane or outside of the cell itself? And we know that cells communicate in all sorts of different ways. And they produce proteins for other cells or for use in the bloodstream or whatever it might be. And that's what we're going to focus on in this video. So contiguous with this what's called the perinuclear space right over here, so the space between these two membranes. So you have this perinuclear space between the inner and outer nuclear membrane. Let me just label that."}, {"video_title": "Endoplasmic reticulum and Golgi bodies   Biology   Khan Academy.mp3", "Sentence": "And that's what we're going to focus on in this video. So contiguous with this what's called the perinuclear space right over here, so the space between these two membranes. So you have this perinuclear space between the inner and outer nuclear membrane. Let me just label that. That's the inner nuclear membrane. That's the outer nuclear membrane. You could continue this outer nuclear membrane, and you get into these kind of flaps and folds and bulges."}, {"video_title": "Endoplasmic reticulum and Golgi bodies   Biology   Khan Academy.mp3", "Sentence": "Let me just label that. That's the inner nuclear membrane. That's the outer nuclear membrane. You could continue this outer nuclear membrane, and you get into these kind of flaps and folds and bulges. And this right over here is considered a separate organelle. So you get this thing that looks like this. And I'll just do it the best that I can draw it."}, {"video_title": "Endoplasmic reticulum and Golgi bodies   Biology   Khan Academy.mp3", "Sentence": "You could continue this outer nuclear membrane, and you get into these kind of flaps and folds and bulges. And this right over here is considered a separate organelle. So you get this thing that looks like this. And I'll just do it the best that I can draw it. And this right over here is called the endoplasmic reticulum. So this right here is endoplasmic reticulum, which I've always thought would be a good name for a band. And the endoplasmic reticulum is key for starting to produce and then later on package proteins that are used for that are either embedded in the cellular membrane or used outside of the cell itself."}, {"video_title": "Endoplasmic reticulum and Golgi bodies   Biology   Khan Academy.mp3", "Sentence": "And I'll just do it the best that I can draw it. And this right over here is called the endoplasmic reticulum. So this right here is endoplasmic reticulum, which I've always thought would be a good name for a band. And the endoplasmic reticulum is key for starting to produce and then later on package proteins that are used for that are either embedded in the cellular membrane or used outside of the cell itself. So how does that happen? Well, the endoplasmic reticulum really has two regions. It has the rough endoplasmic reticulum."}, {"video_title": "Endoplasmic reticulum and Golgi bodies   Biology   Khan Academy.mp3", "Sentence": "And the endoplasmic reticulum is key for starting to produce and then later on package proteins that are used for that are either embedded in the cellular membrane or used outside of the cell itself. So how does that happen? Well, the endoplasmic reticulum really has two regions. It has the rough endoplasmic reticulum. And the rough endoplasmic reticulum has a bunch of ribosomes. So that's a free ribosome right over here. This is an attached ribosome."}, {"video_title": "Endoplasmic reticulum and Golgi bodies   Biology   Khan Academy.mp3", "Sentence": "It has the rough endoplasmic reticulum. And the rough endoplasmic reticulum has a bunch of ribosomes. So that's a free ribosome right over here. This is an attached ribosome. These are ribosomes that are attached to the membrane of the endoplasmic reticulum. So this region where you have attached ribosomes right over here, that is the rough endoplasmic reticulum. I'll call it the rough ER for short, perhaps an even better name for a band."}, {"video_title": "Endoplasmic reticulum and Golgi bodies   Biology   Khan Academy.mp3", "Sentence": "This is an attached ribosome. These are ribosomes that are attached to the membrane of the endoplasmic reticulum. So this region where you have attached ribosomes right over here, that is the rough endoplasmic reticulum. I'll call it the rough ER for short, perhaps an even better name for a band. And then there's another region, which is a smooth endoplasmic reticulum. And the role that this plays in protein synthesis, or at least getting proteins ready for the outside of the cell, is you can have messenger RNA. Let me do that in that lighter green color."}, {"video_title": "Endoplasmic reticulum and Golgi bodies   Biology   Khan Academy.mp3", "Sentence": "I'll call it the rough ER for short, perhaps an even better name for a band. And then there's another region, which is a smooth endoplasmic reticulum. And the role that this plays in protein synthesis, or at least getting proteins ready for the outside of the cell, is you can have messenger RNA. Let me do that in that lighter green color. You can have messenger RNA find one of these ribosomes associated with the rough endoplasmic reticulum. And as the protein is translated, it won't be translated inside the cytosol. It'll be translated on the other side of the rough endoplasmic reticulum."}, {"video_title": "Endoplasmic reticulum and Golgi bodies   Biology   Khan Academy.mp3", "Sentence": "Let me do that in that lighter green color. You can have messenger RNA find one of these ribosomes associated with the rough endoplasmic reticulum. And as the protein is translated, it won't be translated inside the cytosol. It'll be translated on the other side of the rough endoplasmic reticulum. Or you could say on the inside of it, on the lumen, or in the lumen of the rough endoplasmic reticulum. Let me draw that a little bit better. So let's say that this right over here is the membrane of the endoplasmic reticulum."}, {"video_title": "Endoplasmic reticulum and Golgi bodies   Biology   Khan Academy.mp3", "Sentence": "It'll be translated on the other side of the rough endoplasmic reticulum. Or you could say on the inside of it, on the lumen, or in the lumen of the rough endoplasmic reticulum. Let me draw that a little bit better. So let's say that this right over here is the membrane of the endoplasmic reticulum. And then as a protein, or as an mRNA is being translated into protein, the ribosome can attach. And let's say that this right over here is the mRNA that is being translated. Let's say it's going in that direction right over here."}, {"video_title": "Endoplasmic reticulum and Golgi bodies   Biology   Khan Academy.mp3", "Sentence": "So let's say that this right over here is the membrane of the endoplasmic reticulum. And then as a protein, or as an mRNA is being translated into protein, the ribosome can attach. And let's say that this right over here is the mRNA that is being translated. Let's say it's going in that direction right over here. Here is the membrane of the ER. So ER membrane. This right over here, and actually the way I've drawn it right over here, this is just one bilipid layer."}, {"video_title": "Endoplasmic reticulum and Golgi bodies   Biology   Khan Academy.mp3", "Sentence": "Let's say it's going in that direction right over here. Here is the membrane of the ER. So ER membrane. This right over here, and actually the way I've drawn it right over here, this is just one bilipid layer. So let me just, I could draw it like this. I could do it like this. And this is actually, this bilipid layer is continuous."}, {"video_title": "Endoplasmic reticulum and Golgi bodies   Biology   Khan Academy.mp3", "Sentence": "This right over here, and actually the way I've drawn it right over here, this is just one bilipid layer. So let me just, I could draw it like this. I could do it like this. And this is actually, this bilipid layer is continuous. It's continuous with the outer nuclear membrane. So let me just make it like that so you get the picture. And then at some point in the translation process, the protein can be spit out on the inside."}, {"video_title": "Endoplasmic reticulum and Golgi bodies   Biology   Khan Academy.mp3", "Sentence": "And this is actually, this bilipid layer is continuous. It's continuous with the outer nuclear membrane. So let me just make it like that so you get the picture. And then at some point in the translation process, the protein can be spit out on the inside. As it's being translated, it can be spit out on the inside of the endoplasmic reticulum. So this is the lumen. This is the ER lumen right over here."}, {"video_title": "Endoplasmic reticulum and Golgi bodies   Biology   Khan Academy.mp3", "Sentence": "And then at some point in the translation process, the protein can be spit out on the inside. As it's being translated, it can be spit out on the inside of the endoplasmic reticulum. So this is the lumen. This is the ER lumen right over here. So we're inside the endoplasmic reticulum here. Here we're outside. Here we're outside in the cytosol."}, {"video_title": "Endoplasmic reticulum and Golgi bodies   Biology   Khan Academy.mp3", "Sentence": "This is the ER lumen right over here. So we're inside the endoplasmic reticulum here. Here we're outside. Here we're outside in the cytosol. So that way you get the protein now inside the ER, inside the endoplasmic reticulum. And it can travel through it. And at some point, it can bud off."}, {"video_title": "Endoplasmic reticulum and Golgi bodies   Biology   Khan Academy.mp3", "Sentence": "Here we're outside in the cytosol. So that way you get the protein now inside the ER, inside the endoplasmic reticulum. And it can travel through it. And at some point, it can bud off. So let's say, imagine the protein is right over here. And the smooth endoplasmic reticulum has many functions. And I won't get into all of the depth of how it's involved."}, {"video_title": "Endoplasmic reticulum and Golgi bodies   Biology   Khan Academy.mp3", "Sentence": "And at some point, it can bud off. So let's say, imagine the protein is right over here. And the smooth endoplasmic reticulum has many functions. And I won't get into all of the depth of how it's involved. But at some point, that protein can bud off. So let me draw a budding off protein. So let's say this is the membrane of the endoplasmic reticulum."}, {"video_title": "Endoplasmic reticulum and Golgi bodies   Biology   Khan Academy.mp3", "Sentence": "And I won't get into all of the depth of how it's involved. But at some point, that protein can bud off. So let me draw a budding off protein. So let's say this is the membrane of the endoplasmic reticulum. And a protein, let's say, ends up right over here. And then it can bud out. So it could go from that to that."}, {"video_title": "Endoplasmic reticulum and Golgi bodies   Biology   Khan Academy.mp3", "Sentence": "So let's say this is the membrane of the endoplasmic reticulum. And a protein, let's say, ends up right over here. And then it can bud out. So it could go from that to that. I think you see where this is going. And then it could go to something like this. It could go from this to something like this."}, {"video_title": "Endoplasmic reticulum and Golgi bodies   Biology   Khan Academy.mp3", "Sentence": "So it could go from that to that. I think you see where this is going. And then it could go to something like this. It could go from this to something like this. Now it has budded out. And when you have a protein, or really you have anything that's being transported around a cell with its own little mini membrane, we call this a vesicle. So now it'll bundle up."}, {"video_title": "Endoplasmic reticulum and Golgi bodies   Biology   Khan Academy.mp3", "Sentence": "It could go from this to something like this. Now it has budded out. And when you have a protein, or really you have anything that's being transported around a cell with its own little mini membrane, we call this a vesicle. So now it'll bundle up. And now it is a vesicle. Now this vesicle can then, let me draw some of these vesicles holding some proteins. So let me draw that."}, {"video_title": "Endoplasmic reticulum and Golgi bodies   Biology   Khan Academy.mp3", "Sentence": "So now it'll bundle up. And now it is a vesicle. Now this vesicle can then, let me draw some of these vesicles holding some proteins. So let me draw that. It can then go to the Golgi apparatus, which I'll draw in blue right over here as best as I can. So the Golgi apparatus. This is not, obviously, there could be better drawings of something like this."}, {"video_title": "Endoplasmic reticulum and Golgi bodies   Biology   Khan Academy.mp3", "Sentence": "So let me draw that. It can then go to the Golgi apparatus, which I'll draw in blue right over here as best as I can. So the Golgi apparatus. This is not, obviously, there could be better drawings of something like this. And then they can essentially do the reverse process. And they can attach themselves to the Golgi, oftentimes the Golgi body, named after Mr. Golgi, who discovered this. And then the proteins, once they get into the inside of the Golgi body, then they essentially go into a maturation process so that they're ready for transport outside of the cell or maybe to be embedded into the cellular membrane."}, {"video_title": "Endoplasmic reticulum and Golgi bodies   Biology   Khan Academy.mp3", "Sentence": "This is not, obviously, there could be better drawings of something like this. And then they can essentially do the reverse process. And they can attach themselves to the Golgi, oftentimes the Golgi body, named after Mr. Golgi, who discovered this. And then the proteins, once they get into the inside of the Golgi body, then they essentially go into a maturation process so that they're ready for transport outside of the cell or maybe to be embedded into the cellular membrane. So this right over here is the Golgi body, or a Golgi body, or a Golgi apparatus. Apparatus, or Golgi body. And then once they're done with that process, then this is kind of the fully manufactured protein ready to be used."}, {"video_title": "Endoplasmic reticulum and Golgi bodies   Biology   Khan Academy.mp3", "Sentence": "And then the proteins, once they get into the inside of the Golgi body, then they essentially go into a maturation process so that they're ready for transport outside of the cell or maybe to be embedded into the cellular membrane. So this right over here is the Golgi body, or a Golgi body, or a Golgi apparatus. Apparatus, or Golgi body. And then once they're done with that process, then this is kind of the fully manufactured protein ready to be used. And actually, maybe I'll make it a slightly different. Well, I'll just use that same color. This is the fully manufactured protein."}, {"video_title": "Cell cycle control   Cells   MCAT   Khan Academy (2).mp3", "Sentence": "Now the cell cycle is not a sort of thing that occurs in a very unchecked manner. There's actually a lot of regulation in play here. In fact, there are two key places that we have extensive regulation of the cell cycle. The first checkpoint is right here between the G1 and the S phase. So we regulate before we get to the point of DNA replication. The other major checkpoint is right here between G2 and the step where we jump right to mitosis. And there are a couple of proteins that regulate this process."}, {"video_title": "Cell cycle control   Cells   MCAT   Khan Academy (2).mp3", "Sentence": "The first checkpoint is right here between the G1 and the S phase. So we regulate before we get to the point of DNA replication. The other major checkpoint is right here between G2 and the step where we jump right to mitosis. And there are a couple of proteins that regulate this process. Two main ones are called cyclin-dependent kinases. So cyclin-dependent kinases, which as you may recall, a kinase is something that adds a phosphate group. So I'll put in parentheses, it'll plus a phosphate group."}, {"video_title": "Cell cycle control   Cells   MCAT   Khan Academy (2).mp3", "Sentence": "And there are a couple of proteins that regulate this process. Two main ones are called cyclin-dependent kinases. So cyclin-dependent kinases, which as you may recall, a kinase is something that adds a phosphate group. So I'll put in parentheses, it'll plus a phosphate group. And it'll add a phosphate group on other enzymes or proteins to either activate or inactivate them. And these cyclin-dependent kinases will work together with a protein you might be able to guess the name of, cyclins. Because what else would these kinases depend on?"}, {"video_title": "Cell cycle control   Cells   MCAT   Khan Academy (2).mp3", "Sentence": "So I'll put in parentheses, it'll plus a phosphate group. And it'll add a phosphate group on other enzymes or proteins to either activate or inactivate them. And these cyclin-dependent kinases will work together with a protein you might be able to guess the name of, cyclins. Because what else would these kinases depend on? So an important thing to notice is that these cyclin-dependent kinases or CDKs are always present. All the different types are always present in a cell, but their default form or their default function is for them to be inactive. And so they need to be activated by these cyclin proteins."}, {"video_title": "Cell cycle control   Cells   MCAT   Khan Academy (2).mp3", "Sentence": "Because what else would these kinases depend on? So an important thing to notice is that these cyclin-dependent kinases or CDKs are always present. All the different types are always present in a cell, but their default form or their default function is for them to be inactive. And so they need to be activated by these cyclin proteins. And the point of regulation here is that specific cyclins, so I'll write specific with just spec, so specific cyclins are made at specific times. And again, the reason why they're both so important is that when you have a cyclin-dependent kinase, it is only active when they are bound to a specific cyclin. It's at this point again that this guy is active."}, {"video_title": "Cell cycle control   Cells   MCAT   Khan Academy (2).mp3", "Sentence": "And so they need to be activated by these cyclin proteins. And the point of regulation here is that specific cyclins, so I'll write specific with just spec, so specific cyclins are made at specific times. And again, the reason why they're both so important is that when you have a cyclin-dependent kinase, it is only active when they are bound to a specific cyclin. It's at this point again that this guy is active. And the CDK is the business end of this complex. So that's the reason why in G1 you'll see the production of cyclins D and cyclin E. And from there you'll see CDK2 bound to your cyclin E, and at the same time you'll also have your CDK4 bound to your cyclin D. These activated kinases then, specifically the CDK4 cyclin D complex, will phosphorylate a protein called RB. So I'll draw just a little reaction over here where we add a phosphate group on our RB protein."}, {"video_title": "Cell cycle control   Cells   MCAT   Khan Academy (2).mp3", "Sentence": "It's at this point again that this guy is active. And the CDK is the business end of this complex. So that's the reason why in G1 you'll see the production of cyclins D and cyclin E. And from there you'll see CDK2 bound to your cyclin E, and at the same time you'll also have your CDK4 bound to your cyclin D. These activated kinases then, specifically the CDK4 cyclin D complex, will phosphorylate a protein called RB. So I'll draw just a little reaction over here where we add a phosphate group on our RB protein. So when RB is phosphorylated, it can't inhibit DNA replication like it usually is supposed to do. The phosphate group renders it inactive. And this is sort of the setup we have as we go further on in our cell cycle."}, {"video_title": "Cell cycle control   Cells   MCAT   Khan Academy (2).mp3", "Sentence": "So I'll draw just a little reaction over here where we add a phosphate group on our RB protein. So when RB is phosphorylated, it can't inhibit DNA replication like it usually is supposed to do. The phosphate group renders it inactive. And this is sort of the setup we have as we go further on in our cell cycle. In the S phase we have cyclin A produced. Cyclin A will complex again with CDK2 most directly to activate DNA replication. So it helps to activate DNA replication."}, {"video_title": "Cell cycle control   Cells   MCAT   Khan Academy (2).mp3", "Sentence": "And this is sort of the setup we have as we go further on in our cell cycle. In the S phase we have cyclin A produced. Cyclin A will complex again with CDK2 most directly to activate DNA replication. So it helps to activate DNA replication. And in a similar way we have cyclin B only produced in the G2 phase because the cyclin B CDK1 complex is able to activate, activate, what step do you think? Mitosis or cell division. So it's important to recognize that in order to pass these checkpoints, you need to have these cyclin proteins present so that they can go ahead and inhibit proteins that are blocking DNA synthesis or replication from occurring or so they can promote the production of proteins that are needed for mitosis."}, {"video_title": "DNA replication and RNA transcription and translation   Khan Academy.mp3", "Sentence": "And we're gonna focus on a conceptual level. I'm not gonna go into all of the, I guess you could say biochemical details. Really just give you the conceptual idea of what happens. So right over here, this could be a fragment of DNA. I have what I have, this is eight base pairs depicted. And just to be clear, we talked about this in the introductory video to DNA. DNA is much more than a handful of base pairs."}, {"video_title": "DNA replication and RNA transcription and translation   Khan Academy.mp3", "Sentence": "So right over here, this could be a fragment of DNA. I have what I have, this is eight base pairs depicted. And just to be clear, we talked about this in the introductory video to DNA. DNA is much more than a handful of base pairs. A DNA molecule can be tens of millions of base pairs long. So for example, this might be a section of a much longer molecule. So the much longer strand of DNA, and even there I'm probably not giving justice to it, but this might just be this very, very small section, right, let me just in a different color, this little section right over here zoomed in."}, {"video_title": "DNA replication and RNA transcription and translation   Khan Academy.mp3", "Sentence": "DNA is much more than a handful of base pairs. A DNA molecule can be tens of millions of base pairs long. So for example, this might be a section of a much longer molecule. So the much longer strand of DNA, and even there I'm probably not giving justice to it, but this might just be this very, very small section, right, let me just in a different color, this little section right over here zoomed in. So once again, it might be part of a molecule that has not seven or eight base pairs, but might have 70 million base pairs. So just like that. So just like that."}, {"video_title": "DNA replication and RNA transcription and translation   Khan Academy.mp3", "Sentence": "So the much longer strand of DNA, and even there I'm probably not giving justice to it, but this might just be this very, very small section, right, let me just in a different color, this little section right over here zoomed in. So once again, it might be part of a molecule that has not seven or eight base pairs, but might have 70 million base pairs. So just like that. So just like that. So let's understand what a molecular basis of heredity would need to do. Well first of all, it would need to be replicable. Or something, we would need to be able to replicate it."}, {"video_title": "DNA replication and RNA transcription and translation   Khan Academy.mp3", "Sentence": "So just like that. So let's understand what a molecular basis of heredity would need to do. Well first of all, it would need to be replicable. Or something, we would need to be able to replicate it. As a cell divides, the two new cells would want to have the same genetic material. So how does DNA replicate? And this process is called replication."}, {"video_title": "DNA replication and RNA transcription and translation   Khan Academy.mp3", "Sentence": "Or something, we would need to be able to replicate it. As a cell divides, the two new cells would want to have the same genetic material. So how does DNA replicate? And this process is called replication. So let me, replication, and we covered this in the introduction video as well, but it's nice to see the different processes next to each other. And replication, well you can imagine taking either, splitting these two sides of the ladder, and actually let's do that. So let me copy and paste."}, {"video_title": "DNA replication and RNA transcription and translation   Khan Academy.mp3", "Sentence": "And this process is called replication. So let me, replication, and we covered this in the introduction video as well, but it's nice to see the different processes next to each other. And replication, well you can imagine taking either, splitting these two sides of the ladder, and actually let's do that. So let me copy and paste. So if I take that side right over there, and so let me copy and then paste it. And then there we go. A little bit of it is dropping below the video, but I think that serves the purpose."}, {"video_title": "DNA replication and RNA transcription and translation   Khan Academy.mp3", "Sentence": "So let me copy and paste. So if I take that side right over there, and so let me copy and then paste it. And then there we go. A little bit of it is dropping below the video, but I think that serves the purpose. And then, and then let's copy and paste the other side. So let me select that. And then I copy, and then I paste."}, {"video_title": "DNA replication and RNA transcription and translation   Khan Academy.mp3", "Sentence": "A little bit of it is dropping below the video, but I think that serves the purpose. And then, and then let's copy and paste the other side. So let me select that. And then I copy, and then I paste. And it's just like that. And so you can imagine, if you were to split these, these, I guess you could call them two sides of the ladder, then either side could be used to construct the other side, and then you would have two strands, two identical strands of the DNA. And so let's see what that actually looks like."}, {"video_title": "DNA replication and RNA transcription and translation   Khan Academy.mp3", "Sentence": "And then I copy, and then I paste. And it's just like that. And so you can imagine, if you were to split these, these, I guess you could call them two sides of the ladder, then either side could be used to construct the other side, and then you would have two strands, two identical strands of the DNA. And so let's see what that actually looks like. So let me get my pen tool out now. Let me deselect this. Get the pen tool out."}, {"video_title": "DNA replication and RNA transcription and translation   Khan Academy.mp3", "Sentence": "And so let's see what that actually looks like. So let me get my pen tool out now. Let me deselect this. Get the pen tool out. It's a new tool I'm using, so let me make sure I'm doing it right. All right, so from this side, from this left side, or at least what we are looking at is the left side, you can then construct another right side based on this information. A always pairs with T, if we're talking about DNA."}, {"video_title": "DNA replication and RNA transcription and translation   Khan Academy.mp3", "Sentence": "Get the pen tool out. It's a new tool I'm using, so let me make sure I'm doing it right. All right, so from this side, from this left side, or at least what we are looking at is the left side, you can then construct another right side based on this information. A always pairs with T, if we're talking about DNA. So adenine pairs with thymine, just like that. Thymine pairs with adenine. Let me do that a little bit neater."}, {"video_title": "DNA replication and RNA transcription and translation   Khan Academy.mp3", "Sentence": "A always pairs with T, if we're talking about DNA. So adenine pairs with thymine, just like that. Thymine pairs with adenine. Let me do that a little bit neater. Thymine pairs with adenine. Guanine pairs with cytosine. That's cytosine."}, {"video_title": "DNA replication and RNA transcription and translation   Khan Academy.mp3", "Sentence": "Let me do that a little bit neater. Thymine pairs with adenine. Guanine pairs with cytosine. That's cytosine. Cytosine pairs with guanine, falling a little bit down here. And just like that, I was able to construct a new right-hand side using that left-hand side. So maybe I'll do the new, the new sugar phosphate backbone in yellow."}, {"video_title": "DNA replication and RNA transcription and translation   Khan Academy.mp3", "Sentence": "That's cytosine. Cytosine pairs with guanine, falling a little bit down here. And just like that, I was able to construct a new right-hand side using that left-hand side. So maybe I'll do the new, the new sugar phosphate backbone in yellow. And we can do the same thing here using the original right-hand side. So using the original right-hand side, once again, the Ts pair with the As, thymine, let me do that in that adenine's color. So we have an adenine and thymine, adenine and thymine, adenine and thymine."}, {"video_title": "DNA replication and RNA transcription and translation   Khan Academy.mp3", "Sentence": "So maybe I'll do the new, the new sugar phosphate backbone in yellow. And we can do the same thing here using the original right-hand side. So using the original right-hand side, once again, the Ts pair with the As, thymine, let me do that in that adenine's color. So we have an adenine and thymine, adenine and thymine, adenine and thymine. Thymine pairs with adenine, so thymine, adenine. Thymine, adenine. Guanine pairs with cytosine."}, {"video_title": "DNA replication and RNA transcription and translation   Khan Academy.mp3", "Sentence": "So we have an adenine and thymine, adenine and thymine, adenine and thymine. Thymine pairs with adenine, so thymine, adenine. Thymine, adenine. Guanine pairs with cytosine. Guanine, guanine, and then cytosine pairs with guanine. So cytosine, just like that. And so you can take half of each of this ladder and then you could use it to construct the other half, and what you've essentially done is you've replicated the actual DNA."}, {"video_title": "DNA replication and RNA transcription and translation   Khan Academy.mp3", "Sentence": "Guanine pairs with cytosine. Guanine, guanine, and then cytosine pairs with guanine. So cytosine, just like that. And so you can take half of each of this ladder and then you could use it to construct the other half, and what you've essentially done is you've replicated the actual DNA. And this is actually a kind of conceptual level of how replication is done before a cell divides and replicates, and then the entire cell duplicates itself. So that's replication. So the next thing you're probably thinking about, okay, well, you know, it's nice to be able to replicate yourself, but that's kind of useless if that information can't be used to define the organism in some way, to express what's actually happening."}, {"video_title": "DNA replication and RNA transcription and translation   Khan Academy.mp3", "Sentence": "And so you can take half of each of this ladder and then you could use it to construct the other half, and what you've essentially done is you've replicated the actual DNA. And this is actually a kind of conceptual level of how replication is done before a cell divides and replicates, and then the entire cell duplicates itself. So that's replication. So the next thing you're probably thinking about, okay, well, you know, it's nice to be able to replicate yourself, but that's kind of useless if that information can't be used to define the organism in some way, to express what's actually happening. And so let's think about how the genes in this DNA molecule are actually expressed. So I'll write this as expression. Expression."}, {"video_title": "DNA replication and RNA transcription and translation   Khan Academy.mp3", "Sentence": "So the next thing you're probably thinking about, okay, well, you know, it's nice to be able to replicate yourself, but that's kind of useless if that information can't be used to define the organism in some way, to express what's actually happening. And so let's think about how the genes in this DNA molecule are actually expressed. So I'll write this as expression. Expression. And actually, that actually warrants a little bit of a detour, because you hear sometimes the words DNA and chromosome and gene used somewhat interchangeably, and they are clearly related, but it's worth knowing what is what. So when you're talking about DNA, you're talking literally about this molecule here that has this sugar phosphate base and it has the sequence of base pairs, it's got this double helix structure, and so this whole thing, this could be a DNA molecule. Now, when you have a DNA molecule and it's packaged together with other molecules and proteins and kind of given a broader structure, then you're talking about a chromosome."}, {"video_title": "DNA replication and RNA transcription and translation   Khan Academy.mp3", "Sentence": "Expression. And actually, that actually warrants a little bit of a detour, because you hear sometimes the words DNA and chromosome and gene used somewhat interchangeably, and they are clearly related, but it's worth knowing what is what. So when you're talking about DNA, you're talking literally about this molecule here that has this sugar phosphate base and it has the sequence of base pairs, it's got this double helix structure, and so this whole thing, this could be a DNA molecule. Now, when you have a DNA molecule and it's packaged together with other molecules and proteins and kind of given a broader structure, then you're talking about a chromosome. And when you're talking about a gene, you're talking about a section of DNA that's used to express a certain trait, or actually, used to code for a certain type of protein. So for example, this whole thing could be a strand of DNA, but this part right over, let's say in orange, I'll do it, this part in orange right over here could be one gene. It might define, it could, this information for one gene, it could define a protein."}, {"video_title": "DNA replication and RNA transcription and translation   Khan Academy.mp3", "Sentence": "Now, when you have a DNA molecule and it's packaged together with other molecules and proteins and kind of given a broader structure, then you're talking about a chromosome. And when you're talking about a gene, you're talking about a section of DNA that's used to express a certain trait, or actually, used to code for a certain type of protein. So for example, this whole thing could be a strand of DNA, but this part right over, let's say in orange, I'll do it, this part in orange right over here could be one gene. It might define, it could, this information for one gene, it could define a protein. This one might, this section right over here could do, could be used to define another gene. And genes could be anywhere from several thousand base pairs long all the way up into the millions. And as we'll see, the way that a gene is expressed, the way we get from the information for that section of DNA into a protein, which is really how it's expressed, is through a related molecule to DNA, and that is RNA."}, {"video_title": "DNA replication and RNA transcription and translation   Khan Academy.mp3", "Sentence": "It might define, it could, this information for one gene, it could define a protein. This one might, this section right over here could do, could be used to define another gene. And genes could be anywhere from several thousand base pairs long all the way up into the millions. And as we'll see, the way that a gene is expressed, the way we get from the information for that section of DNA into a protein, which is really how it's expressed, is through a related molecule to DNA, and that is RNA. And actually, let me write this down. RNA, RNA. So RNA stands for ribonucleic acid."}, {"video_title": "DNA replication and RNA transcription and translation   Khan Academy.mp3", "Sentence": "And as we'll see, the way that a gene is expressed, the way we get from the information for that section of DNA into a protein, which is really how it's expressed, is through a related molecule to DNA, and that is RNA. And actually, let me write this down. RNA, RNA. So RNA stands for ribonucleic acid. Ribonucleic acid, let me write that down. Ribo, ribonucleic, nucleic acid. Nucleic acid."}, {"video_title": "DNA replication and RNA transcription and translation   Khan Academy.mp3", "Sentence": "So RNA stands for ribonucleic acid. Ribonucleic acid, let me write that down. Ribo, ribonucleic, nucleic acid. Nucleic acid. And so you might remember that DNA is deoxyribonucleic acid so the sugar backbone in RNA is a very similar molecule. Well, now it's got its oxy, it's not deoxyribonucleic acid, it's ribonucleic acid. The R, let me make it clear where the RNA comes from."}, {"video_title": "DNA replication and RNA transcription and translation   Khan Academy.mp3", "Sentence": "Nucleic acid. And so you might remember that DNA is deoxyribonucleic acid so the sugar backbone in RNA is a very similar molecule. Well, now it's got its oxy, it's not deoxyribonucleic acid, it's ribonucleic acid. The R, let me make it clear where the RNA comes from. The R is right over there, then you have the nucleic, that's the N, it's found, or, well, it's nucleic, and then it's A, acid, same reason why we called the DNA nucleic acid. So you have this RNA. So what role does this play as we are trying to express the information in this DNA?"}, {"video_title": "DNA replication and RNA transcription and translation   Khan Academy.mp3", "Sentence": "The R, let me make it clear where the RNA comes from. The R is right over there, then you have the nucleic, that's the N, it's found, or, well, it's nucleic, and then it's A, acid, same reason why we called the DNA nucleic acid. So you have this RNA. So what role does this play as we are trying to express the information in this DNA? Well, the DNA, especially if we're talking about cells with nuclei, the DNA sits there, but that information has to, for the most part, get outside of the nucleus in order to be expressed. And one of the functions that RNA plays is to be that messenger, that messenger between a certain section of DNA and kind of what goes on outside of the nucleus so that that can be translated into an actual protein. So the step that you go from DNA to mRNA, messenger RNA, is called transcription."}, {"video_title": "DNA replication and RNA transcription and translation   Khan Academy.mp3", "Sentence": "So what role does this play as we are trying to express the information in this DNA? Well, the DNA, especially if we're talking about cells with nuclei, the DNA sits there, but that information has to, for the most part, get outside of the nucleus in order to be expressed. And one of the functions that RNA plays is to be that messenger, that messenger between a certain section of DNA and kind of what goes on outside of the nucleus so that that can be translated into an actual protein. So the step that you go from DNA to mRNA, messenger RNA, is called transcription. Let me write that down. Transcription. Transcription."}, {"video_title": "DNA replication and RNA transcription and translation   Khan Academy.mp3", "Sentence": "So the step that you go from DNA to mRNA, messenger RNA, is called transcription. Let me write that down. Transcription. Transcription. Transcription. And what happens in transcription, let's go back to looking at one side of this, one side of this DNA molecule. So let's say you have that right over there."}, {"video_title": "DNA replication and RNA transcription and translation   Khan Academy.mp3", "Sentence": "Transcription. Transcription. And what happens in transcription, let's go back to looking at one side of this, one side of this DNA molecule. So let's say you have that right over there. Let me copy and paste it. So there we go. Actually, I didn't want to do that."}, {"video_title": "DNA replication and RNA transcription and translation   Khan Academy.mp3", "Sentence": "So let's say you have that right over there. Let me copy and paste it. So there we go. Actually, I didn't want to do that. I wanted the other side. So actually, I think I'm on the wrong, let me go back here. And so let me copy and then let me paste."}, {"video_title": "DNA replication and RNA transcription and translation   Khan Academy.mp3", "Sentence": "Actually, I didn't want to do that. I wanted the other side. So actually, I think I'm on the wrong, let me go back here. And so let me copy and then let me paste. There we go. So let's say you have, let's say that you have part of this DNA molecule, or you have one half of it, just like we did when we replicated it, but now we're not just trying to duplicate the DNA molecule, we're actually trying to create a corresponding mRNA molecule, at least for that section, that section of, at least for that gene. So this might be part of a gene that, actually, whoops, let me make sure I'm using the right tool."}, {"video_title": "DNA replication and RNA transcription and translation   Khan Academy.mp3", "Sentence": "And so let me copy and then let me paste. There we go. So let's say you have, let's say that you have part of this DNA molecule, or you have one half of it, just like we did when we replicated it, but now we're not just trying to duplicate the DNA molecule, we're actually trying to create a corresponding mRNA molecule, at least for that section, that section of, at least for that gene. So this might be part of a gene that, actually, whoops, let me make sure I'm using the right tool. This might be part of a gene that is, you know, this section of our DNA molecule right over there. And so transcription is a very similar conceptual idea where we're now going to construct a strand of RNA, and specifically mRNA, because it's going to take that information outside of the nucleus. And so it's very similar, except for when we're talking about RNA, adenine, instead of pairing with thymine, is now going to pair with uracil."}, {"video_title": "DNA replication and RNA transcription and translation   Khan Academy.mp3", "Sentence": "So this might be part of a gene that, actually, whoops, let me make sure I'm using the right tool. This might be part of a gene that is, you know, this section of our DNA molecule right over there. And so transcription is a very similar conceptual idea where we're now going to construct a strand of RNA, and specifically mRNA, because it's going to take that information outside of the nucleus. And so it's very similar, except for when we're talking about RNA, adenine, instead of pairing with thymine, is now going to pair with uracil. So let me write this down. So now you're gonna have adenine pairs not with thymine, but uracil. DNA has uracil instead of the thymine, but you're still going to have cytosine and guanine pairing."}, {"video_title": "DNA replication and RNA transcription and translation   Khan Academy.mp3", "Sentence": "And so it's very similar, except for when we're talking about RNA, adenine, instead of pairing with thymine, is now going to pair with uracil. So let me write this down. So now you're gonna have adenine pairs not with thymine, but uracil. DNA has uracil instead of the thymine, but you're still going to have cytosine and guanine pairing. So for the RNA, and in this case the mRNA, that's going to leave the nucleus, A is going to pair with U. U for uracil. So uracil, uracil, that's the base we're talking about. Let me write it down."}, {"video_title": "DNA replication and RNA transcription and translation   Khan Academy.mp3", "Sentence": "DNA has uracil instead of the thymine, but you're still going to have cytosine and guanine pairing. So for the RNA, and in this case the mRNA, that's going to leave the nucleus, A is going to pair with U. U for uracil. So uracil, uracil, that's the base we're talking about. Let me write it down. Uracil, uracil. Thymine is still going to pair with adenine. It's still going to pair with adenine."}, {"video_title": "DNA replication and RNA transcription and translation   Khan Academy.mp3", "Sentence": "Let me write it down. Uracil, uracil. Thymine is still going to pair with adenine. It's still going to pair with adenine. Just like that. Guanine's gonna pair with cytosine. Guanine, and cytosine, and cytosine's going to pair."}, {"video_title": "DNA replication and RNA transcription and translation   Khan Academy.mp3", "Sentence": "It's still going to pair with adenine. Just like that. Guanine's gonna pair with cytosine. Guanine, and cytosine, and cytosine's going to pair. Cytosine's going to pair with guanine. And so when you do that, now these two characters can detach, and now you have a single strand of RNA, and in this case messenger RNA, that has all the information on that section of DNA. And so now that thing can leave the nucleus, go attach to a ribosome, and we'll talk more about that in future videos, exactly how that's happened."}, {"video_title": "DNA replication and RNA transcription and translation   Khan Academy.mp3", "Sentence": "Guanine, and cytosine, and cytosine's going to pair. Cytosine's going to pair with guanine. And so when you do that, now these two characters can detach, and now you have a single strand of RNA, and in this case messenger RNA, that has all the information on that section of DNA. And so now that thing can leave the nucleus, go attach to a ribosome, and we'll talk more about that in future videos, exactly how that's happened. And then this code can be used to actually code for proteins. Now how does that happen? And that process is called translation."}, {"video_title": "DNA replication and RNA transcription and translation   Khan Academy.mp3", "Sentence": "And so now that thing can leave the nucleus, go attach to a ribosome, and we'll talk more about that in future videos, exactly how that's happened. And then this code can be used to actually code for proteins. Now how does that happen? And that process is called translation. So translation, translation, which is really taking this base pair sequence and turning it into an amino acid sequence. Proteins are made up of sequences of amino acids. So translation."}, {"video_title": "DNA replication and RNA transcription and translation   Khan Academy.mp3", "Sentence": "And that process is called translation. So translation, translation, which is really taking this base pair sequence and turning it into an amino acid sequence. Proteins are made up of sequences of amino acids. So translation. So let's take our mRNA, or this little section of our mRNA, and actually let me do it, let me draw it like this. Let me draw it like this. And let's see, I have, it is UAC, so it's gonna be UAC, then UU, then ACG, okay?"}, {"video_title": "DNA replication and RNA transcription and translation   Khan Academy.mp3", "Sentence": "So translation. So let's take our mRNA, or this little section of our mRNA, and actually let me do it, let me draw it like this. Let me draw it like this. And let's see, I have, it is UAC, so it's gonna be UAC, then UU, then ACG, okay? And then we have an A, let me make sure I change to the right color. We have an A there, and then we have this UUA, CG, all right? Now let me put a C right over there."}, {"video_title": "DNA replication and RNA transcription and translation   Khan Academy.mp3", "Sentence": "And let's see, I have, it is UAC, so it's gonna be UAC, then UU, then ACG, okay? And then we have an A, let me make sure I change to the right color. We have an A there, and then we have this UUA, CG, all right? Now let me put a C right over there. I'm just taking this and I'm writing it horizontally. I have a C here, not a G, it's a C. And then finally I have a G. And of course it'll keep going on and on and on. And what happens is, each sequence of three, and you have to be very careful where it starts, and so this is in some ways a delicate and surprising, but at the same time surprisingly robust process, every three of these bases code for a specific amino acid."}, {"video_title": "DNA replication and RNA transcription and translation   Khan Academy.mp3", "Sentence": "Now let me put a C right over there. I'm just taking this and I'm writing it horizontally. I have a C here, not a G, it's a C. And then finally I have a G. And of course it'll keep going on and on and on. And what happens is, each sequence of three, and you have to be very careful where it starts, and so this is in some ways a delicate and surprising, but at the same time surprisingly robust process, every three of these bases code for a specific amino acid. And so three bases together, so these bases right over here, I guess you could say this three-letter word or this three-letter sequence, that's called a codon, codon. And this is going to be the next codon, the next codon. And we actually haven't drawn the next codon after that because we need three bases to get to the next codon."}, {"video_title": "DNA replication and RNA transcription and translation   Khan Academy.mp3", "Sentence": "And what happens is, each sequence of three, and you have to be very careful where it starts, and so this is in some ways a delicate and surprising, but at the same time surprisingly robust process, every three of these bases code for a specific amino acid. And so three bases together, so these bases right over here, I guess you could say this three-letter word or this three-letter sequence, that's called a codon, codon. And this is going to be the next codon, the next codon. And we actually haven't drawn the next codon after that because we need three bases to get to the next codon. And how many possible codons do you have? Well, you have one of four bases and you have them in three different places, so you have four times four times four possible codon words, I guess you could say, and four times four times four is 64. So you have 64 possible codons, which is good because you have 20 possible amino acids."}, {"video_title": "DNA replication and RNA transcription and translation   Khan Academy.mp3", "Sentence": "And we actually haven't drawn the next codon after that because we need three bases to get to the next codon. And how many possible codons do you have? Well, you have one of four bases and you have them in three different places, so you have four times four times four possible codon words, I guess you could say, and four times four times four is 64. So you have 64 possible codons, which is good because you have 20 possible amino acids. So this is overkill and allows codons to be used for other purposes as well. And they also, you might have more than one codon coding for the same amino acid. So you have 64 possible codons, they need to code for 20 amino acids."}, {"video_title": "DNA replication and RNA transcription and translation   Khan Academy.mp3", "Sentence": "So you have 64 possible codons, which is good because you have 20 possible amino acids. So this is overkill and allows codons to be used for other purposes as well. And they also, you might have more than one codon coding for the same amino acid. So you have 64 possible codons, they need to code for 20 amino acids. And so this codon right over here, with the ribosome, and we'll talk more about how that happens, can code for, can code for, say, could code for amino acid one. So let me just write it here. This is amino acid one."}, {"video_title": "DNA replication and RNA transcription and translation   Khan Academy.mp3", "Sentence": "So you have 64 possible codons, they need to code for 20 amino acids. And so this codon right over here, with the ribosome, and we'll talk more about how that happens, can code for, can code for, say, could code for amino acid one. So let me just write it here. This is amino acid one. And actually this amino acid is brought to here. They're actually matched together by another type of RNA. This is mRNA we're talking about right over here."}, {"video_title": "DNA replication and RNA transcription and translation   Khan Academy.mp3", "Sentence": "This is amino acid one. And actually this amino acid is brought to here. They're actually matched together by another type of RNA. This is mRNA we're talking about right over here. This is mRNA, but there's another type of RNA called tRNA that essentially brings these two characters together. So the tRNA, and I'm just gonna, it's got some structure here, I'm not drawing it completely right, but it's going to match right over here where maybe it has an A, a U, and a G right over here. And on this end, it was attached to this amino acid, and so it matches them together."}, {"video_title": "DNA replication and RNA transcription and translation   Khan Academy.mp3", "Sentence": "This is mRNA we're talking about right over here. This is mRNA, but there's another type of RNA called tRNA that essentially brings these two characters together. So the tRNA, and I'm just gonna, it's got some structure here, I'm not drawing it completely right, but it's going to match right over here where maybe it has an A, a U, and a G right over here. And on this end, it was attached to this amino acid, and so it matches them together. And then you're gonna have another tRNA that might attach to amino acid two, which I will do in purple, amino acid two. And that just happens to coincide with, so it can complement right over here, so it attaches in the right place. So it's A, a U right over here, this tRNA."}, {"video_title": "DNA replication and RNA transcription and translation   Khan Academy.mp3", "Sentence": "And on this end, it was attached to this amino acid, and so it matches them together. And then you're gonna have another tRNA that might attach to amino acid two, which I will do in purple, amino acid two. And that just happens to coincide with, so it can complement right over here, so it attaches in the right place. So it's A, a U right over here, this tRNA. And so it'll construct the sequence of amino acids. And as you put these amino acids together, then you are actually constructing a protein. So a protein is essentially a bunch of, a sequence of these amino acids put together."}, {"video_title": "DNA replication and RNA transcription and translation   Khan Academy.mp3", "Sentence": "So it's A, a U right over here, this tRNA. And so it'll construct the sequence of amino acids. And as you put these amino acids together, then you are actually constructing a protein. So a protein is essentially a bunch of, a sequence of these amino acids put together. So a sequence of these amino acids put together. And these proteins are essentially the molecules that run life for the most part. Obviously, if you eat an animal, it's going to be made up of fat and sugars and proteins, but the proteins are the things that actually do a lot of the, whether they're enzymes, whether they're structural, the muscle is formed from proteins."}, {"video_title": "DNA replication and RNA transcription and translation   Khan Academy.mp3", "Sentence": "So a protein is essentially a bunch of, a sequence of these amino acids put together. So a sequence of these amino acids put together. And these proteins are essentially the molecules that run life for the most part. Obviously, if you eat an animal, it's going to be made up of fat and sugars and proteins, but the proteins are the things that actually do a lot of the, whether they're enzymes, whether they're structural, the muscle is formed from proteins. These are the things, and I'm just drawing a small segment of them. They could be thousands or more of these amino acids long. And they kind of form these incredibly complex shapes, and they have all of these functions."}, {"video_title": "Allele frequency.mp3", "Sentence": "What I want to do in this video is explore the idea of allele frequency. Allele frequency. And just as a reminder, an allele is a variant of a gene. You get a variant of a gene from your mother and you get another variant of the gene from the father. And so when we're talking about the allele, we're talking about that specific variant that you got from your mother or your father. And we've seen this before. But now let's dig a little bit deeper."}, {"video_title": "Allele frequency.mp3", "Sentence": "You get a variant of a gene from your mother and you get another variant of the gene from the father. And so when we're talking about the allele, we're talking about that specific variant that you got from your mother or your father. And we've seen this before. But now let's dig a little bit deeper. And to help us get our heads around this, we'll start with a fairly common model for this. And we're gonna think about eye color. And obviously this is a very large simplification."}, {"video_title": "Allele frequency.mp3", "Sentence": "But now let's dig a little bit deeper. And to help us get our heads around this, we'll start with a fairly common model for this. And we're gonna think about eye color. And obviously this is a very large simplification. But let's just assume that we have a population where there's only two variants of an eye color gene. Let's first assume there is an eye color gene and let's assume there's two variants. One variant, one allele for eye color, we'll use the shorthand capital B."}, {"video_title": "Allele frequency.mp3", "Sentence": "And obviously this is a very large simplification. But let's just assume that we have a population where there's only two variants of an eye color gene. Let's first assume there is an eye color gene and let's assume there's two variants. One variant, one allele for eye color, we'll use the shorthand capital B. Let's say that's the allele for brown. Brown eye color. And we're gonna assume that this one is dominant."}, {"video_title": "Allele frequency.mp3", "Sentence": "One variant, one allele for eye color, we'll use the shorthand capital B. Let's say that's the allele for brown. Brown eye color. And we're gonna assume that this one is dominant. It's dominant over the other allele. Now the other allele, we're gonna assume, is for blue eye color. And we'll represent that with a lowercase b."}, {"video_title": "Allele frequency.mp3", "Sentence": "And we're gonna assume that this one is dominant. It's dominant over the other allele. Now the other allele, we're gonna assume, is for blue eye color. And we'll represent that with a lowercase b. So that is blue eye color. And we're going to assume that this is recessive. So once again, this is review."}, {"video_title": "Allele frequency.mp3", "Sentence": "And we'll represent that with a lowercase b. So that is blue eye color. And we're going to assume that this is recessive. So once again, this is review. Someone who has one of the big B alleles, the brown alleles. It doesn't matter what their other allele is going to be because it's either gonna be another brown or it's going to be a blue. They're going to show brown eyes."}, {"video_title": "Allele frequency.mp3", "Sentence": "So once again, this is review. Someone who has one of the big B alleles, the brown alleles. It doesn't matter what their other allele is going to be because it's either gonna be another brown or it's going to be a blue. They're going to show brown eyes. So this is going to be brown eyes. And this is going to be brown eyes because the capital B is dominant. The only way to get blue eyes is to be, the only way to have blue eyes is to be a homozygote for the recessive allele."}, {"video_title": "Allele frequency.mp3", "Sentence": "They're going to show brown eyes. So this is going to be brown eyes. And this is going to be brown eyes because the capital B is dominant. The only way to get blue eyes is to be, the only way to have blue eyes is to be a homozygote for the recessive allele. And all of that, of course, is review. We've seen that before. But now let's think about allele frequency."}, {"video_title": "Allele frequency.mp3", "Sentence": "The only way to get blue eyes is to be, the only way to have blue eyes is to be a homozygote for the recessive allele. And all of that, of course, is review. We've seen that before. But now let's think about allele frequency. And to think about that, I'll set up a very artificially small population. So let's say our population has exactly two people in it. Population has exactly two people in it, person one and person two."}, {"video_title": "Allele frequency.mp3", "Sentence": "But now let's think about allele frequency. And to think about that, I'll set up a very artificially small population. So let's say our population has exactly two people in it. Population has exactly two people in it, person one and person two. And let's say we're able to look into their DNA and figure out their genotypes. So person one, let's say, has a capital B allele, has a brown allele and a blue allele. While person two has two blue alleles."}, {"video_title": "Allele frequency.mp3", "Sentence": "Population has exactly two people in it, person one and person two. And let's say we're able to look into their DNA and figure out their genotypes. So person one, let's say, has a capital B allele, has a brown allele and a blue allele. While person two has two blue alleles. Now given that we know the genotypes in this artificially small population, now we can start thinking about the allele frequencies or the frequencies of the different alleles. So what do you think is going to be the frequency, the frequency of the brown allele in this population? And I encourage you to pause this video and think about this on your own."}, {"video_title": "Allele frequency.mp3", "Sentence": "While person two has two blue alleles. Now given that we know the genotypes in this artificially small population, now we can start thinking about the allele frequencies or the frequencies of the different alleles. So what do you think is going to be the frequency, the frequency of the brown allele in this population? And I encourage you to pause this video and think about this on your own. So I'm assuming you've had a go at it. So you might be tempted to say, oh, well it looks like one out of two people have it, maybe it's 50%. But that wouldn't be the right way to think about allele frequencies."}, {"video_title": "Allele frequency.mp3", "Sentence": "And I encourage you to pause this video and think about this on your own. So I'm assuming you've had a go at it. So you might be tempted to say, oh, well it looks like one out of two people have it, maybe it's 50%. But that wouldn't be the right way to think about allele frequencies. And allele frequencies, you wanna dig a little bit deeper and look at the individual alleles. And when you look at that, you say, okay, there's four individual alleles in this population of, or there's four variants in this, or there's literally four chromosomes, I guess you could say, that are carrying that gene in this population. And out of them, one of them carry, one of them is the capital B, is the capital B allele."}, {"video_title": "Allele frequency.mp3", "Sentence": "But that wouldn't be the right way to think about allele frequencies. And allele frequencies, you wanna dig a little bit deeper and look at the individual alleles. And when you look at that, you say, okay, there's four individual alleles in this population of, or there's four variants in this, or there's literally four chromosomes, I guess you could say, that are carrying that gene in this population. And out of them, one of them carry, one of them is the capital B, is the capital B allele. And so we could say that that is going to be 0.25, or 25%. So once again, 20, 25% of the genes for eye color have the capital B allele, have the brown allele. Now we can do the same, we can ask ourselves the same question for the lowercase b allele."}, {"video_title": "Allele frequency.mp3", "Sentence": "And out of them, one of them carry, one of them is the capital B, is the capital B allele. And so we could say that that is going to be 0.25, or 25%. So once again, 20, 25% of the genes for eye color have the capital B allele, have the brown allele. Now we can do the same, we can ask ourselves the same question for the lowercase b allele. What fraction of the genes in this population are code for or represent the lowercase b, the blue allele? And once again, I encourage you to pause the video and think about it. Well, very similar idea."}, {"video_title": "Allele frequency.mp3", "Sentence": "Now we can do the same, we can ask ourselves the same question for the lowercase b allele. What fraction of the genes in this population are code for or represent the lowercase b, the blue allele? And once again, I encourage you to pause the video and think about it. Well, very similar idea. There's four genes in the population that are coding for eye color. Of them, one, two, three, one, two, three, code for or are the lowercase blue, are the lowercase blue allele. So that's 0.75, or 75%."}, {"video_title": "Allele frequency.mp3", "Sentence": "Well, very similar idea. There's four genes in the population that are coding for eye color. Of them, one, two, three, one, two, three, code for or are the lowercase blue, are the lowercase blue allele. So that's 0.75, or 75%. 75% of the genes code for the lowercase, the blue allele, while 25 are the brown, are the brown allele. And I really wanna hit this point home, how this is different than, say, the phenotype frequency. If I asked you in the population, if I asked you the percent of brown-eyed people, brown-eyed people, so now I'm talking about phenotype, what would that be?"}, {"video_title": "Allele frequency.mp3", "Sentence": "So that's 0.75, or 75%. 75% of the genes code for the lowercase, the blue allele, while 25 are the brown, are the brown allele. And I really wanna hit this point home, how this is different than, say, the phenotype frequency. If I asked you in the population, if I asked you the percent of brown-eyed people, brown-eyed people, so now I'm talking about phenotype, what would that be? Well, there's two people in the population, one of them is exhibiting brown eyes, so that's going to be 1.5. And similarly, if I were to ask you what is the percentage of people who are blue-eyed? That too would be 1.5."}, {"video_title": "Allele frequency.mp3", "Sentence": "If I asked you in the population, if I asked you the percent of brown-eyed people, brown-eyed people, so now I'm talking about phenotype, what would that be? Well, there's two people in the population, one of them is exhibiting brown eyes, so that's going to be 1.5. And similarly, if I were to ask you what is the percentage of people who are blue-eyed? That too would be 1.5. This person is one of the two people, they're exhibiting blue eyes. But allele frequency, we're digging deeper. We're looking at the genotypes, and we're saying, well, out of the four genes here, one of them is the big B allele, so that's 25%, so 25% of the gene population codes for, is the brown allele, and 75% is the blue allele."}, {"video_title": "Allele frequency.mp3", "Sentence": "That too would be 1.5. This person is one of the two people, they're exhibiting blue eyes. But allele frequency, we're digging deeper. We're looking at the genotypes, and we're saying, well, out of the four genes here, one of them is the big B allele, so that's 25%, so 25% of the gene population codes for, is the brown allele, and 75% is the blue allele. And this is really important to internalize, because once we internalize this, then as we'll see, the ideas in the Hardy-Weinberg principle start to make a lot of sense. And I'll do a little bit of foreshadowing. We can denote this, and this is just a convention that's often used, by the lowercase letter p, and we can use q, lowercase q, to denote the frequency."}, {"video_title": "Allele frequency.mp3", "Sentence": "We're looking at the genotypes, and we're saying, well, out of the four genes here, one of them is the big B allele, so that's 25%, so 25% of the gene population codes for, is the brown allele, and 75% is the blue allele. And this is really important to internalize, because once we internalize this, then as we'll see, the ideas in the Hardy-Weinberg principle start to make a lot of sense. And I'll do a little bit of foreshadowing. We can denote this, and this is just a convention that's often used, by the lowercase letter p, and we can use q, lowercase q, to denote the frequency. So p, lowercase p, is the frequency of the dominant allele, lowercase q, the frequency of the recessive allele. But what's true here? What's true of p, what's true, what's going to be true of p plus q?"}, {"video_title": "Allele frequency.mp3", "Sentence": "We can denote this, and this is just a convention that's often used, by the lowercase letter p, and we can use q, lowercase q, to denote the frequency. So p, lowercase p, is the frequency of the dominant allele, lowercase q, the frequency of the recessive allele. But what's true here? What's true of p, what's true, what's going to be true of p plus q? What's going to be, what's p plus q going to be equal to? And I encourage you to pause the video again, and think about that. What is this going to be equal to?"}, {"video_title": "Allele frequency.mp3", "Sentence": "What's true of p, what's true, what's going to be true of p plus q? What's going to be, what's p plus q going to be equal to? And I encourage you to pause the video again, and think about that. What is this going to be equal to? Well, when we started off, we said that there's only two potential, that's one of the assumptions we assumed. We assumed there's only two alleles in this population, and kind of the allele population for this, and this gene population for this trait. So the frequency of the dominant ones, plus the frequency of the recessive ones, well, everyone's gonna have one of those two, so if you add those two frequencies, it's going to have to add to 100%, 100%."}, {"video_title": "Allele frequency.mp3", "Sentence": "What is this going to be equal to? Well, when we started off, we said that there's only two potential, that's one of the assumptions we assumed. We assumed there's only two alleles in this population, and kind of the allele population for this, and this gene population for this trait. So the frequency of the dominant ones, plus the frequency of the recessive ones, well, everyone's gonna have one of those two, so if you add those two frequencies, it's going to have to add to 100%, 100%. And we see that there, 1 4th plus 3 4th is one, is one, or 100%, and 25% plus 75% is also 100%. So we could say p plus q is equal to 100%, or we could say that p plus q is equal to one, is equal to one. And so in the next video, we're gonna start from the seemingly fairly simple idea, to get to a richer and fairly neat idea that's expressed in the Hardy-Weinberg equation."}, {"video_title": "Fluid mosaic model of cell membranes   Biology   Khan Academy.mp3", "Sentence": "Well, if we were to look at a cell membrane, and just to be clear what we're looking at, if this is a cell right over here, if this is a cell, and this is its membrane, this is the membrane, it's kind of what keeps the cell, the inside of the cell separated from whatever is outside the cell, we're looking at a cross section of its surface. We're looking at a cross section of its surface. We're down here, down here, this is inside the cell, if we look at it relative to this diagram, this is inside the cell, and this is outside. This is outside. And when you zoom in, when you zoom in, this little part right over here, this is actually a phospholipid bilayer that forms it. And so when you hear that, you might say, well, what is a phospholipid? And that's a good question, because when you understand what a phospholipid is, it starts to make sense why it would form a bilayer like this, and why it's the basis for so many membranes in biological systems."}, {"video_title": "Fluid mosaic model of cell membranes   Biology   Khan Academy.mp3", "Sentence": "This is outside. And when you zoom in, when you zoom in, this little part right over here, this is actually a phospholipid bilayer that forms it. And so when you hear that, you might say, well, what is a phospholipid? And that's a good question, because when you understand what a phospholipid is, it starts to make sense why it would form a bilayer like this, and why it's the basis for so many membranes in biological systems. So this is indicative of a phospholipid. And as its name implies, and let me write that down, this is a phospholipid, it's a lipid that involves a phosphate group. And in general, the word lipid, and we have a whole video on lipids, means something that doesn't dissolve so well in water."}, {"video_title": "Fluid mosaic model of cell membranes   Biology   Khan Academy.mp3", "Sentence": "And that's a good question, because when you understand what a phospholipid is, it starts to make sense why it would form a bilayer like this, and why it's the basis for so many membranes in biological systems. So this is indicative of a phospholipid. And as its name implies, and let me write that down, this is a phospholipid, it's a lipid that involves a phosphate group. And in general, the word lipid, and we have a whole video on lipids, means something that doesn't dissolve so well in water. And that's true as the case of this phospholipid. You have these hydrocarbon tails that are coming from fatty acids. And so these hydrocarbon tails, they have no obvious charge or no obvious polarity."}, {"video_title": "Fluid mosaic model of cell membranes   Biology   Khan Academy.mp3", "Sentence": "And in general, the word lipid, and we have a whole video on lipids, means something that doesn't dissolve so well in water. And that's true as the case of this phospholipid. You have these hydrocarbon tails that are coming from fatty acids. And so these hydrocarbon tails, they have no obvious charge or no obvious polarity. We know that water's a polar molecule. That's what gives us its hydrogen bonds, and it's attracted to itself. But these don't have those, and so they're not going to be attracted to the water, and the water's not going to be attracted to them."}, {"video_title": "Fluid mosaic model of cell membranes   Biology   Khan Academy.mp3", "Sentence": "And so these hydrocarbon tails, they have no obvious charge or no obvious polarity. We know that water's a polar molecule. That's what gives us its hydrogen bonds, and it's attracted to itself. But these don't have those, and so they're not going to be attracted to the water, and the water's not going to be attracted to them. And so these tails are hydrophobic. So you have hydrophobic, hydrophobic tails. And these are really kind of the lipid part of the phospholipids."}, {"video_title": "Fluid mosaic model of cell membranes   Biology   Khan Academy.mp3", "Sentence": "But these don't have those, and so they're not going to be attracted to the water, and the water's not going to be attracted to them. And so these tails are hydrophobic. So you have hydrophobic, hydrophobic tails. And these are really kind of the lipid part of the phospholipids. And then you have the phosphate head. You have the phosphate head right over here. And as you can clearly see, this has some charge."}, {"video_title": "Fluid mosaic model of cell membranes   Biology   Khan Academy.mp3", "Sentence": "And these are really kind of the lipid part of the phospholipids. And then you have the phosphate head. You have the phosphate head right over here. And as you can clearly see, this has some charge. Charged molecules do well in polar substances like water. They're going to dissolve well. And so this part right over here is going to be hydrophilic."}, {"video_title": "Fluid mosaic model of cell membranes   Biology   Khan Academy.mp3", "Sentence": "And as you can clearly see, this has some charge. Charged molecules do well in polar substances like water. They're going to dissolve well. And so this part right over here is going to be hydrophilic. And actually, molecules that have a hydrophilic part and a hydrophobic part, there's a special word for them. Amphipathic, a word that I sometimes have trouble saying. So phospholipids are amphipathic, amphipathic, which means that they have both a hydrophilic end, a part that is attracted to water, and a hydrophobic end that is not attracted to water."}, {"video_title": "Fluid mosaic model of cell membranes   Biology   Khan Academy.mp3", "Sentence": "And so this part right over here is going to be hydrophilic. And actually, molecules that have a hydrophilic part and a hydrophobic part, there's a special word for them. Amphipathic, a word that I sometimes have trouble saying. So phospholipids are amphipathic, amphipathic, which means that they have both a hydrophilic end, a part that is attracted to water, and a hydrophobic end that is not attracted to water. And hopefully that starts to explain why they organize themselves in this way. Because you can imagine, the hydrophilic heads are going to want to be where the water is, which is going to be either outside the cell or inside the cells. And the tails are hydrophobic."}, {"video_title": "Fluid mosaic model of cell membranes   Biology   Khan Academy.mp3", "Sentence": "So phospholipids are amphipathic, amphipathic, which means that they have both a hydrophilic end, a part that is attracted to water, and a hydrophobic end that is not attracted to water. And hopefully that starts to explain why they organize themselves in this way. Because you can imagine, the hydrophilic heads are going to want to be where the water is, which is going to be either outside the cell or inside the cells. And the tails are hydrophobic. The water's going to go away from them, or they're going to go away from the water. And so they're just going to face each other, and they're going to be on the inside of the membrane. But the really cool thing is a structure like this, having this amphipathic molecule, allows things like these lipid bilayers, I should say, to form."}, {"video_title": "Fluid mosaic model of cell membranes   Biology   Khan Academy.mp3", "Sentence": "And the tails are hydrophobic. The water's going to go away from them, or they're going to go away from the water. And so they're just going to face each other, and they're going to be on the inside of the membrane. But the really cool thing is a structure like this, having this amphipathic molecule, allows things like these lipid bilayers, I should say, to form. And it's actually fascinating, we think, that if you go far back enough, even before life in cellular form formed, that you might have had phospholipids spontaneously forming these spheres of where you have a bilayer, a lipid bilayer. So you can imagine something, let me see if I drew a cross section. Let me see if I can draw it relatively neatly."}, {"video_title": "Fluid mosaic model of cell membranes   Biology   Khan Academy.mp3", "Sentence": "But the really cool thing is a structure like this, having this amphipathic molecule, allows things like these lipid bilayers, I should say, to form. And it's actually fascinating, we think, that if you go far back enough, even before life in cellular form formed, that you might have had phospholipids spontaneously forming these spheres of where you have a bilayer, a lipid bilayer. So you can imagine something, let me see if I drew a cross section. Let me see if I can draw it relatively neatly. So I think I'll draw half of it, just because you get, well, I'll draw the whole thing. Hopefully you get the idea. So that would be one layer of the phosphate heads facing the outside."}, {"video_title": "Fluid mosaic model of cell membranes   Biology   Khan Academy.mp3", "Sentence": "Let me see if I can draw it relatively neatly. So I think I'll draw half of it, just because you get, well, I'll draw the whole thing. Hopefully you get the idea. So that would be one layer of the phosphate heads facing the outside. This is the inner layer. And I'm doing a cross section right over here. And then you have your hydrophobic tails."}, {"video_title": "Fluid mosaic model of cell membranes   Biology   Khan Academy.mp3", "Sentence": "So that would be one layer of the phosphate heads facing the outside. This is the inner layer. And I'm doing a cross section right over here. And then you have your hydrophobic tails. So your hydrophobic tails, let me do that in a different color. So your hydrophobic tails, I think you get the picture. We have a bunch of hydrophobic tails on either end."}, {"video_title": "Fluid mosaic model of cell membranes   Biology   Khan Academy.mp3", "Sentence": "And then you have your hydrophobic tails. So your hydrophobic tails, let me do that in a different color. So your hydrophobic tails, I think you get the picture. We have a bunch of hydrophobic tails on either end. And then you could spontaneously form a structure like this which starts to feel like, hey, well, maybe there's a protocell forming. And obviously to actually have real life, you have to have some form of information that can be passed on. And you have to have some type of metabolism."}, {"video_title": "Fluid mosaic model of cell membranes   Biology   Khan Academy.mp3", "Sentence": "We have a bunch of hydrophobic tails on either end. And then you could spontaneously form a structure like this which starts to feel like, hey, well, maybe there's a protocell forming. And obviously to actually have real life, you have to have some form of information that can be passed on. And you have to have some type of metabolism. And the cell is living in all of the definitions of life. But at least this basic structure of the cellular membrane, you can imagine how it forms in a pre-life state even by virtue of amphipathic molecules like a phospholipid. So fair enough."}, {"video_title": "Fluid mosaic model of cell membranes   Biology   Khan Academy.mp3", "Sentence": "And you have to have some type of metabolism. And the cell is living in all of the definitions of life. But at least this basic structure of the cellular membrane, you can imagine how it forms in a pre-life state even by virtue of amphipathic molecules like a phospholipid. So fair enough. We're able to form this phospholipid bilayer. But what are all these other things that I have drawn here? Well, these are proteins."}, {"video_title": "Fluid mosaic model of cell membranes   Biology   Khan Academy.mp3", "Sentence": "So fair enough. We're able to form this phospholipid bilayer. But what are all these other things that I have drawn here? Well, these are proteins. And these are examples of, so this is a protein right over here. This is a protein. This is a protein."}, {"video_title": "Fluid mosaic model of cell membranes   Biology   Khan Academy.mp3", "Sentence": "Well, these are proteins. And these are examples of, so this is a protein right over here. This is a protein. This is a protein. And I just drew some kind of blobs to be indicative of the variety of proteins. But the important thing to realize is, is when you think of cells, there's all of this diversity. There's all of this complexity that is on or embedded inside of its membrane."}, {"video_title": "Fluid mosaic model of cell membranes   Biology   Khan Academy.mp3", "Sentence": "This is a protein. And I just drew some kind of blobs to be indicative of the variety of proteins. But the important thing to realize is, is when you think of cells, there's all of this diversity. There's all of this complexity that is on or embedded inside of its membrane. So instead of just thinking of it just kind of as a uniform phospholipid bilayer, there's all sorts of stuff. There's all sorts of stuff. Maybe if we view this as a cross section, there's all sorts of stuff embedded in it."}, {"video_title": "Fluid mosaic model of cell membranes   Biology   Khan Academy.mp3", "Sentence": "There's all of this complexity that is on or embedded inside of its membrane. So instead of just thinking of it just kind of as a uniform phospholipid bilayer, there's all sorts of stuff. There's all sorts of stuff. Maybe if we view this as a cross section, there's all sorts of stuff embedded in it. And we see it right over here in this diagram. You could say there's a mosaic of things embedded in it. A mosaic is a picture made up of a bunch of different components of all different colors."}, {"video_title": "Fluid mosaic model of cell membranes   Biology   Khan Academy.mp3", "Sentence": "Maybe if we view this as a cross section, there's all sorts of stuff embedded in it. And we see it right over here in this diagram. You could say there's a mosaic of things embedded in it. A mosaic is a picture made up of a bunch of different components of all different colors. And you can see that you have all different different components here, different types of proteins. You have proteins like this that go across the membrane. We call these transmembrane proteins."}, {"video_title": "Fluid mosaic model of cell membranes   Biology   Khan Academy.mp3", "Sentence": "A mosaic is a picture made up of a bunch of different components of all different colors. And you can see that you have all different different components here, different types of proteins. You have proteins like this that go across the membrane. We call these transmembrane proteins. They're a special class of integral proteins. You have integral proteins like this that might only interact with one part of the bilayer, while these kind of go across it. You have things like glycolipids."}, {"video_title": "Fluid mosaic model of cell membranes   Biology   Khan Academy.mp3", "Sentence": "We call these transmembrane proteins. They're a special class of integral proteins. You have integral proteins like this that might only interact with one part of the bilayer, while these kind of go across it. You have things like glycolipids. So this right over here, this is a glycolipid. Glycolipid, which is fascinating. It lodges itself in the membrane because it has this lipid end."}, {"video_title": "Fluid mosaic model of cell membranes   Biology   Khan Academy.mp3", "Sentence": "You have things like glycolipids. So this right over here, this is a glycolipid. Glycolipid, which is fascinating. It lodges itself in the membrane because it has this lipid end. So that's going to be hydrophobic. It's going to get along with all of the other hydrophobic things. But then it has an end that's really a, that's a chain of sugars."}, {"video_title": "Fluid mosaic model of cell membranes   Biology   Khan Academy.mp3", "Sentence": "It lodges itself in the membrane because it has this lipid end. So that's going to be hydrophobic. It's going to get along with all of the other hydrophobic things. But then it has an end that's really a, that's a chain of sugars. And that part is going to be hydrophilic. It's going to sit outside of the cell. And these chains of sugars, these are actually key for cell-cell recognition."}, {"video_title": "Fluid mosaic model of cell membranes   Biology   Khan Academy.mp3", "Sentence": "But then it has an end that's really a, that's a chain of sugars. And that part is going to be hydrophilic. It's going to sit outside of the cell. And these chains of sugars, these are actually key for cell-cell recognition. Our immune system uses these to differentiate between which cells are the ones that are actually from my body, the ones that I don't want to mess with, the ones I want to protect, and which cells are the ones that are foreign, the ones that I might want to attack. When people talk about blood type, they're talking about, well, what type of specific glycolipids do you have on certain, on cells? And there's all sorts of, and that's not all we're talking about when we talk about glycolipids as kind of a way for cells to be recognized or to be tagged in different ways."}, {"video_title": "Fluid mosaic model of cell membranes   Biology   Khan Academy.mp3", "Sentence": "And these chains of sugars, these are actually key for cell-cell recognition. Our immune system uses these to differentiate between which cells are the ones that are actually from my body, the ones that I don't want to mess with, the ones I want to protect, and which cells are the ones that are foreign, the ones that I might want to attack. When people talk about blood type, they're talking about, well, what type of specific glycolipids do you have on certain, on cells? And there's all sorts of, and that's not all we're talking about when we talk about glycolipids as kind of a way for cells to be recognized or to be tagged in different ways. So it's a fascinating thing that these chains of sugars can lead to such complex behavior, and frankly, such useful behavior from our point of view. But you don't just have, you don't just have sugar chains on lipids, you also have sugar chains on proteins. This right over here is an example of a glycoprotein."}, {"video_title": "Fluid mosaic model of cell membranes   Biology   Khan Academy.mp3", "Sentence": "And there's all sorts of, and that's not all we're talking about when we talk about glycolipids as kind of a way for cells to be recognized or to be tagged in different ways. So it's a fascinating thing that these chains of sugars can lead to such complex behavior, and frankly, such useful behavior from our point of view. But you don't just have, you don't just have sugar chains on lipids, you also have sugar chains on proteins. This right over here is an example of a glycoprotein. Glycoprotein. And as you can see, when you put all this stuff together, you get a mosaic. And I'm actually not even done there."}, {"video_title": "Fluid mosaic model of cell membranes   Biology   Khan Academy.mp3", "Sentence": "This right over here is an example of a glycoprotein. Glycoprotein. And as you can see, when you put all this stuff together, you get a mosaic. And I'm actually not even done there. You have things like cholesterol embedded. Cholesterol is a lipid, so it's gonna sit in the hydrophobic part of the membrane, and that actually helps with the fluidity of the membrane, making sure it's not too fluid or not too stiff. So this is cholesterol."}, {"video_title": "Fluid mosaic model of cell membranes   Biology   Khan Academy.mp3", "Sentence": "And I'm actually not even done there. You have things like cholesterol embedded. Cholesterol is a lipid, so it's gonna sit in the hydrophobic part of the membrane, and that actually helps with the fluidity of the membrane, making sure it's not too fluid or not too stiff. So this is cholesterol. Cholesterol right over there. So you see this mosaic of stuff, but what about the fluid part? And I just talked about cholesterol's value and making sure that it's just the right amount of fluidity."}, {"video_title": "Fluid mosaic model of cell membranes   Biology   Khan Academy.mp3", "Sentence": "So this is cholesterol. Cholesterol right over there. So you see this mosaic of stuff, but what about the fluid part? And I just talked about cholesterol's value and making sure that it's just the right amount of fluidity. What's neat about this is this isn't a rigid structure. If this thing were to be jostled around a little bit or maybe it would be plucked out somehow, the phospholipids would just spontaneously rearrange to fill in the gap. You can imagine these things are all flowing around, that this membrane actually has a consistency of oil or salad dressing."}, {"video_title": "Fluid mosaic model of cell membranes   Biology   Khan Academy.mp3", "Sentence": "And I just talked about cholesterol's value and making sure that it's just the right amount of fluidity. What's neat about this is this isn't a rigid structure. If this thing were to be jostled around a little bit or maybe it would be plucked out somehow, the phospholipids would just spontaneously rearrange to fill in the gap. You can imagine these things are all flowing around, that this membrane actually has a consistency of oil or salad dressing. So it isn't like a rubbery texture like you might imagine, or a membrane like a balloon. It's actually fluid. These things can move around, but even though it's fluid, it's good enough to separate the two environments, the environment inside the cell from the environment outside of the cell."}, {"video_title": "Water as a solvent   Water, acids, and bases   Biology   Khan Academy.mp3", "Sentence": "One end has a partially negative charge, and the other end has partially positive charges. And we talked about how this leads to hydrogen bonds. And we alluded to the fact that, hey, maybe these hydrogen bonds give us all sorts of neat properties of water. And what I want to talk about in this video is one of those very important properties, and that's water's ability to be a solvent. And this means that it's easy for certain things to be dissolved inside of water. And that's super important because that's how a lot of the chemistry occurs, by things getting dissolved in water and then interacting and bumping with other things. And this is actually what's happening inside of cells in the cytoplasm."}, {"video_title": "Water as a solvent   Water, acids, and bases   Biology   Khan Academy.mp3", "Sentence": "And what I want to talk about in this video is one of those very important properties, and that's water's ability to be a solvent. And this means that it's easy for certain things to be dissolved inside of water. And that's super important because that's how a lot of the chemistry occurs, by things getting dissolved in water and then interacting and bumping with other things. And this is actually what's happening inside of cells in the cytoplasm. The cytoplasm, which is mostly water, is a solvent which allows a bunch of interactions to happen between different types of molecules. But let's think about why water is a good solvent and what types of things it can dissolve easily and what types of things it might not be able to dissolve so easily. So the key feature that makes water a good solvent, or at least a good solvent for a large class of molecules, is its polarity."}, {"video_title": "Water as a solvent   Water, acids, and bases   Biology   Khan Academy.mp3", "Sentence": "And this is actually what's happening inside of cells in the cytoplasm. The cytoplasm, which is mostly water, is a solvent which allows a bunch of interactions to happen between different types of molecules. But let's think about why water is a good solvent and what types of things it can dissolve easily and what types of things it might not be able to dissolve so easily. So the key feature that makes water a good solvent, or at least a good solvent for a large class of molecules, is its polarity. If I were to take some sodium chloride, often known as table salt, if I were to take sodium NaCl, sodium chloride, the sodium and chloride are attracted by ionic bonds. The sodium right over here has a positive charge. It has an electron stripped from it."}, {"video_title": "Water as a solvent   Water, acids, and bases   Biology   Khan Academy.mp3", "Sentence": "So the key feature that makes water a good solvent, or at least a good solvent for a large class of molecules, is its polarity. If I were to take some sodium chloride, often known as table salt, if I were to take sodium NaCl, sodium chloride, the sodium and chloride are attracted by ionic bonds. The sodium right over here has a positive charge. It has an electron stripped from it. And the chloride has a... Let me write that in a different color. So the sodium has a positive charge because it has an electron stripped from it. And the chloride is an anion."}, {"video_title": "Water as a solvent   Water, acids, and bases   Biology   Khan Academy.mp3", "Sentence": "It has an electron stripped from it. And the chloride has a... Let me write that in a different color. So the sodium has a positive charge because it has an electron stripped from it. And the chloride is an anion. It has a negative charge. It is a negatively charged ion because it gains an extra electron. So they're attracted to each other."}, {"video_title": "Water as a solvent   Water, acids, and bases   Biology   Khan Academy.mp3", "Sentence": "And the chloride is an anion. It has a negative charge. It is a negatively charged ion because it gains an extra electron. So they're attracted to each other. This has a positive charge. This has a negative charge. This is called an ionic bond."}, {"video_title": "Water as a solvent   Water, acids, and bases   Biology   Khan Academy.mp3", "Sentence": "So they're attracted to each other. This has a positive charge. This has a negative charge. This is called an ionic bond. But if you put sodium chloride in water, something very interesting happens. This is something that we've all experienced. Take some table salt and put it in water and see what happens."}, {"video_title": "Water as a solvent   Water, acids, and bases   Biology   Khan Academy.mp3", "Sentence": "This is called an ionic bond. But if you put sodium chloride in water, something very interesting happens. This is something that we've all experienced. Take some table salt and put it in water and see what happens. It will dissolve. And why does it dissolve? Well, let's draw it out."}, {"video_title": "Water as a solvent   Water, acids, and bases   Biology   Khan Academy.mp3", "Sentence": "Take some table salt and put it in water and see what happens. It will dissolve. And why does it dissolve? Well, let's draw it out. So this is the sodium right over here. So that's the sodium. It has a positive charge."}, {"video_title": "Water as a solvent   Water, acids, and bases   Biology   Khan Academy.mp3", "Sentence": "Well, let's draw it out. So this is the sodium right over here. So that's the sodium. It has a positive charge. And then this is the chloride right over here. It has a negative charge. What's going to happen if you put it inside of the water?"}, {"video_title": "Water as a solvent   Water, acids, and bases   Biology   Khan Academy.mp3", "Sentence": "It has a positive charge. And then this is the chloride right over here. It has a negative charge. What's going to happen if you put it inside of the water? Let me do that negative charge in the green. What's going to happen when you put it inside of water? Well, you can imagine."}, {"video_title": "Water as a solvent   Water, acids, and bases   Biology   Khan Academy.mp3", "Sentence": "What's going to happen if you put it inside of the water? Let me do that negative charge in the green. What's going to happen when you put it inside of water? Well, you can imagine. The negative ends of the water molecules are going to be attracted to the sodium ion. So it's going to look something like this. So you have the oxygen."}, {"video_title": "Water as a solvent   Water, acids, and bases   Biology   Khan Academy.mp3", "Sentence": "Well, you can imagine. The negative ends of the water molecules are going to be attracted to the sodium ion. So it's going to look something like this. So you have the oxygen. So you have the oxygen. Oxygen. Oxygen."}, {"video_title": "Water as a solvent   Water, acids, and bases   Biology   Khan Academy.mp3", "Sentence": "So you have the oxygen. So you have the oxygen. Oxygen. Oxygen. Oxygen. Oxygen. I'm clearly not drawing things to scale, but this will just give you the idea."}, {"video_title": "Water as a solvent   Water, acids, and bases   Biology   Khan Academy.mp3", "Sentence": "Oxygen. Oxygen. Oxygen. I'm clearly not drawing things to scale, but this will just give you the idea. This end of the water molecule all has a partially negative charge. Partially negative charge. So it's going to be attracted to the positive sodium ion."}, {"video_title": "Water as a solvent   Water, acids, and bases   Biology   Khan Academy.mp3", "Sentence": "I'm clearly not drawing things to scale, but this will just give you the idea. This end of the water molecule all has a partially negative charge. Partially negative charge. So it's going to be attracted to the positive sodium ion. And then the hydrogen ends are going to have a partial positive charge. And then they're going to be repelled. They are going to be repelled from the positive sodium ion."}, {"video_title": "Water as a solvent   Water, acids, and bases   Biology   Khan Academy.mp3", "Sentence": "So it's going to be attracted to the positive sodium ion. And then the hydrogen ends are going to have a partial positive charge. And then they're going to be repelled. They are going to be repelled from the positive sodium ion. So it's going to look something like this. It's going to look something like this. You're going to have partial positive charge on the outside."}, {"video_title": "Water as a solvent   Water, acids, and bases   Biology   Khan Academy.mp3", "Sentence": "They are going to be repelled from the positive sodium ion. So it's going to look something like this. It's going to look something like this. You're going to have partial positive charge on the outside. Partial positive charge on the outside. And now these hydrogens over here, this will just interact with water the way that it would typically with the hydrogen bonding the molecules just flowing past each other. So the fact that the sodium ion here it's an ion."}, {"video_title": "Water as a solvent   Water, acids, and bases   Biology   Khan Academy.mp3", "Sentence": "You're going to have partial positive charge on the outside. Partial positive charge on the outside. And now these hydrogens over here, this will just interact with water the way that it would typically with the hydrogen bonding the molecules just flowing past each other. So the fact that the sodium ion here it's an ion. It has charge. It is able to dissolve in the water very easily because it is attracted to the partially negative ends of the water molecule. Now a similar thing is going to happen with the chloride ion."}, {"video_title": "Water as a solvent   Water, acids, and bases   Biology   Khan Academy.mp3", "Sentence": "So the fact that the sodium ion here it's an ion. It has charge. It is able to dissolve in the water very easily because it is attracted to the partially negative ends of the water molecule. Now a similar thing is going to happen with the chloride ion. And we call a negative ion an anion. So over here, and actually let me move it over a little bit so that I have some space. So the chloride anion let me move it over a little bit."}, {"video_title": "Water as a solvent   Water, acids, and bases   Biology   Khan Academy.mp3", "Sentence": "Now a similar thing is going to happen with the chloride ion. And we call a negative ion an anion. So over here, and actually let me move it over a little bit so that I have some space. So the chloride anion let me move it over a little bit. So right, maybe I'll move it over maybe I'll move it right over here. So the chloride anion let me see, I'm having trouble with my selection tool. Alright, so there we go."}, {"video_title": "Water as a solvent   Water, acids, and bases   Biology   Khan Academy.mp3", "Sentence": "So the chloride anion let me move it over a little bit. So right, maybe I'll move it over maybe I'll move it right over here. So the chloride anion let me see, I'm having trouble with my selection tool. Alright, so there we go. The chloride anion, it has a negative charge so it's going to be attracted to the positive end of the water molecules. So you can imagine something like this. So the hydrogen ends are going to be attracted to it."}, {"video_title": "Water as a solvent   Water, acids, and bases   Biology   Khan Academy.mp3", "Sentence": "Alright, so there we go. The chloride anion, it has a negative charge so it's going to be attracted to the positive end of the water molecules. So you can imagine something like this. So the hydrogen ends are going to be attracted to it. They have a partially positive charge. They have a partially positive charge. Of course you have the oxygen end that has a partially negative charge."}, {"video_title": "Water as a solvent   Water, acids, and bases   Biology   Khan Academy.mp3", "Sentence": "So the hydrogen ends are going to be attracted to it. They have a partially positive charge. They have a partially positive charge. Of course you have the oxygen end that has a partially negative charge. It has a partially negative charge. And I could draw more of these hydrogen, hydrogen attracted there. You have the oxygen over, let me do that I want to keep my colors consistent."}, {"video_title": "Water as a solvent   Water, acids, and bases   Biology   Khan Academy.mp3", "Sentence": "Of course you have the oxygen end that has a partially negative charge. It has a partially negative charge. And I could draw more of these hydrogen, hydrogen attracted there. You have the oxygen over, let me do that I want to keep my colors consistent. The oxygen right over there. You have the hydrogen. Once again, this isn't drawn to scale."}, {"video_title": "Water as a solvent   Water, acids, and bases   Biology   Khan Academy.mp3", "Sentence": "You have the oxygen over, let me do that I want to keep my colors consistent. The oxygen right over there. You have the hydrogen. Once again, this isn't drawn to scale. Hydrogen it is bonded to the oxygen. And so once again, you can form this, I guess you can almost imagine this shell of water molecules is going to be attracted to it. It's going to be attracted or I guess you could say the partially positive end which is where the hydrogen atoms are is what's going to be attracted to this negative ion."}, {"video_title": "Water as a solvent   Water, acids, and bases   Biology   Khan Academy.mp3", "Sentence": "Once again, this isn't drawn to scale. Hydrogen it is bonded to the oxygen. And so once again, you can form this, I guess you can almost imagine this shell of water molecules is going to be attracted to it. It's going to be attracted or I guess you could say the partially positive end which is where the hydrogen atoms are is what's going to be attracted to this negative ion. So this is partial positive over here. And then on the partially negative side outside of this shell, you can imagine it's just going to interact with the water just the way any water molecule would. And so it's going to be able to flow very easily."}, {"video_title": "Water as a solvent   Water, acids, and bases   Biology   Khan Academy.mp3", "Sentence": "It's going to be attracted or I guess you could say the partially positive end which is where the hydrogen atoms are is what's going to be attracted to this negative ion. So this is partial positive over here. And then on the partially negative side outside of this shell, you can imagine it's just going to interact with the water just the way any water molecule would. And so it's going to be able to flow very easily. So you probably see something interesting here. If something has charge if it's an ion or if something has some polarity it's very easy to dissolve it inside of water. And in this case, and just to have some terminology here in this case, water is the solvent so water is the solvent so the solvent is water and the thing that's being dissolved in the water, we call that a solute."}, {"video_title": "Water as a solvent   Water, acids, and bases   Biology   Khan Academy.mp3", "Sentence": "And so it's going to be able to flow very easily. So you probably see something interesting here. If something has charge if it's an ion or if something has some polarity it's very easy to dissolve it inside of water. And in this case, and just to have some terminology here in this case, water is the solvent so water is the solvent so the solvent is water and the thing that's being dissolved in the water, we call that a solute. So we call this the solute. So the sodium chloride that is, you could use sodium chloride as a solute or you could say that the sodium ions are solute and so are the chloride ions that is also you can consider to be the solute. And so you say, well what kind of things dissolve well?"}, {"video_title": "Water as a solvent   Water, acids, and bases   Biology   Khan Academy.mp3", "Sentence": "And in this case, and just to have some terminology here in this case, water is the solvent so water is the solvent so the solvent is water and the thing that's being dissolved in the water, we call that a solute. So we call this the solute. So the sodium chloride that is, you could use sodium chloride as a solute or you could say that the sodium ions are solute and so are the chloride ions that is also you can consider to be the solute. And so you say, well what kind of things dissolve well? Well things that have charge or that are polar. And things that are charged and polar and tend to dissolve well in water there's another word we use for them. We say that they are hydrophilic."}, {"video_title": "Water as a solvent   Water, acids, and bases   Biology   Khan Academy.mp3", "Sentence": "And so you say, well what kind of things dissolve well? Well things that have charge or that are polar. And things that are charged and polar and tend to dissolve well in water there's another word we use for them. We say that they are hydrophilic. So we could say that this right over here is hydrophilic. And if you look at the word roots, hydro is referring to water. So hydro is referring to water and philic means loving."}, {"video_title": "Water as a solvent   Water, acids, and bases   Biology   Khan Academy.mp3", "Sentence": "We say that they are hydrophilic. So we could say that this right over here is hydrophilic. And if you look at the word roots, hydro is referring to water. So hydro is referring to water and philic means loving. So this literally means water loving. Water loving. Hydrophilic."}, {"video_title": "Water as a solvent   Water, acids, and bases   Biology   Khan Academy.mp3", "Sentence": "So hydro is referring to water and philic means loving. So this literally means water loving. Water loving. Hydrophilic. And so you might be asking, ok everything we've talked about, we've seen water molecules, that's polar we're looking at charged ions, ok we can get that we can get why they would be hydrophilic, they can incorporate themselves well into the water. But what are examples of things that would not incorporate themselves well in the water? Well in general things that don't have charge or that aren't polar aren't going to be able to dissolve in water all that well."}, {"video_title": "Water as a solvent   Water, acids, and bases   Biology   Khan Academy.mp3", "Sentence": "Hydrophilic. And so you might be asking, ok everything we've talked about, we've seen water molecules, that's polar we're looking at charged ions, ok we can get that we can get why they would be hydrophilic, they can incorporate themselves well into the water. But what are examples of things that would not incorporate themselves well in the water? Well in general things that don't have charge or that aren't polar aren't going to be able to dissolve in water all that well. And a good example is hydrocarbons. So if you took some hexane, and hexane is a major constituent of car gasoline. So hexane, hex the prefix means six carbons."}, {"video_title": "Water as a solvent   Water, acids, and bases   Biology   Khan Academy.mp3", "Sentence": "Well in general things that don't have charge or that aren't polar aren't going to be able to dissolve in water all that well. And a good example is hydrocarbons. So if you took some hexane, and hexane is a major constituent of car gasoline. So hexane, hex the prefix means six carbons. So let's see one let me do this in another color. So we have one, two three, four, five six carbons. So one, two, three, four, five, six carbons."}, {"video_title": "Water as a solvent   Water, acids, and bases   Biology   Khan Academy.mp3", "Sentence": "So hexane, hex the prefix means six carbons. So let's see one let me do this in another color. So we have one, two three, four, five six carbons. So one, two, three, four, five, six carbons. And then all the other bonds are with hydrogens. So let me draw this as well as I can. Carbon at least typically forms four bonds."}, {"video_title": "Water as a solvent   Water, acids, and bases   Biology   Khan Academy.mp3", "Sentence": "So one, two, three, four, five, six carbons. And then all the other bonds are with hydrogens. So let me draw this as well as I can. Carbon at least typically forms four bonds. So hydrogen hydrogen, hydrogen, hydrogen hydrogen, hydrogen, hydrogen hydrogen, this right over here is hexane. This thing has no polarity to it. It doesn't form hydrogen bonds, it doesn't have any polarity."}, {"video_title": "Water as a solvent   Water, acids, and bases   Biology   Khan Academy.mp3", "Sentence": "Carbon at least typically forms four bonds. So hydrogen hydrogen, hydrogen, hydrogen hydrogen, hydrogen, hydrogen hydrogen, this right over here is hexane. This thing has no polarity to it. It doesn't form hydrogen bonds, it doesn't have any polarity. And so if you were to take hexane and throw it into water, it's not going to dissolve that well. It's actually going to kind of bead up. And you would see that if you actually threw some gasoline inside of water."}, {"video_title": "Water as a solvent   Water, acids, and bases   Biology   Khan Academy.mp3", "Sentence": "It doesn't form hydrogen bonds, it doesn't have any polarity. And so if you were to take hexane and throw it into water, it's not going to dissolve that well. It's actually going to kind of bead up. And you would see that if you actually threw some gasoline inside of water. So things like hexane we would call hydrophobic. Hydrophobic. So this right over here is hydrophobic."}, {"video_title": "Water as a solvent   Water, acids, and bases   Biology   Khan Academy.mp3", "Sentence": "And you would see that if you actually threw some gasoline inside of water. So things like hexane we would call hydrophobic. Hydrophobic. So this right over here is hydrophobic. Hydrophobic. It literally ball up to avoid getting in touch, to minimize its contact with the water. Because the water is attracted to itself and is not so attracted to this stuff right over here."}, {"video_title": "Water as a solvent   Water, acids, and bases   Biology   Khan Academy.mp3", "Sentence": "So this right over here is hydrophobic. Hydrophobic. It literally ball up to avoid getting in touch, to minimize its contact with the water. Because the water is attracted to itself and is not so attracted to this stuff right over here. And hydrophobic, you still have hydro meaning water. And then phobic means fearing. So this right over here is water fearing."}, {"video_title": "The RNA Origin of Life.mp3", "Sentence": "This is one of the most important questions humanity has ever posed, and the scientific answer is, we don't entirely know. You might think that cracking DNA's genetic code should have explained life's origins, and it definitely helped. Thanks to our understanding of DNA, we can map out the history of evolution all the way back to single-celled life. But that's where we're stuck. The problem is, DNA is a great way to store information, but it doesn't do much else. Cells rely on other molecules, like proteins, to replicate, grow, and survive. Proteins on the other hand, work great as molecular machines to keep cells alive and healthy, but they can't store information or copy themselves."}, {"video_title": "The RNA Origin of Life.mp3", "Sentence": "But that's where we're stuck. The problem is, DNA is a great way to store information, but it doesn't do much else. Cells rely on other molecules, like proteins, to replicate, grow, and survive. Proteins on the other hand, work great as molecular machines to keep cells alive and healthy, but they can't store information or copy themselves. They need DNA for that. So we have a chicken and egg problem. DNA needs proteins to function, and proteins need DNA to exist."}, {"video_title": "The RNA Origin of Life.mp3", "Sentence": "Proteins on the other hand, work great as molecular machines to keep cells alive and healthy, but they can't store information or copy themselves. They need DNA for that. So we have a chicken and egg problem. DNA needs proteins to function, and proteins need DNA to exist. So which came first? Which molecule made life possible? Well, there's a third type of molecule that may hold the answer, RNA."}, {"video_title": "The RNA Origin of Life.mp3", "Sentence": "DNA needs proteins to function, and proteins need DNA to exist. So which came first? Which molecule made life possible? Well, there's a third type of molecule that may hold the answer, RNA. Most scientists think that RNA came first because RNA can do two jobs, store information and perform various functions that keep cells alive. This idea, that RNA came first, is called the RNA world hypothesis. RNA world suggests that billions of years ago, in some primordial soup of molecules, a self-replicating RNA formed."}, {"video_title": "The RNA Origin of Life.mp3", "Sentence": "Well, there's a third type of molecule that may hold the answer, RNA. Most scientists think that RNA came first because RNA can do two jobs, store information and perform various functions that keep cells alive. This idea, that RNA came first, is called the RNA world hypothesis. RNA world suggests that billions of years ago, in some primordial soup of molecules, a self-replicating RNA formed. This may have happened in volcanic vents deep on the ocean floor, or perhaps clay clumps brought the necessary chemical building blocks together. Some scientists have even speculated that early RNAs formed on Mars and hitched a ride on an asteroid to our planet. One way or another, self-replicating RNAs emerged, multiplied, and evolved."}, {"video_title": "The RNA Origin of Life.mp3", "Sentence": "RNA world suggests that billions of years ago, in some primordial soup of molecules, a self-replicating RNA formed. This may have happened in volcanic vents deep on the ocean floor, or perhaps clay clumps brought the necessary chemical building blocks together. Some scientists have even speculated that early RNAs formed on Mars and hitched a ride on an asteroid to our planet. One way or another, self-replicating RNAs emerged, multiplied, and evolved. Over millions of years, they developed into a legion of molecular machines. These microscopic proto-life forms blossomed and competed. The best collections of code lived on, and the weaker ones died out."}, {"video_title": "The RNA Origin of Life.mp3", "Sentence": "One way or another, self-replicating RNAs emerged, multiplied, and evolved. Over millions of years, they developed into a legion of molecular machines. These microscopic proto-life forms blossomed and competed. The best collections of code lived on, and the weaker ones died out. Survival of the fittest was the name of the game. This competition for survival eventually led RNAs to evolve the ability to build strong, stable proteins, which excelled at carrying out complex biological processes. And somewhere along the line, some critical RNAs mutated into the familiar double helix of DNA."}, {"video_title": "The RNA Origin of Life.mp3", "Sentence": "The best collections of code lived on, and the weaker ones died out. Survival of the fittest was the name of the game. This competition for survival eventually led RNAs to evolve the ability to build strong, stable proteins, which excelled at carrying out complex biological processes. And somewhere along the line, some critical RNAs mutated into the familiar double helix of DNA. DNA became a stable archive of genetic information that stored blueprints for the most successful RNA and protein molecules. Life became more complex over trillions of tiny steps and happy accidents. And all the while, the RNA lineup grew, alongside lengthening genomes of DNA and complex proteins."}, {"video_title": "The RNA Origin of Life.mp3", "Sentence": "And somewhere along the line, some critical RNAs mutated into the familiar double helix of DNA. DNA became a stable archive of genetic information that stored blueprints for the most successful RNA and protein molecules. Life became more complex over trillions of tiny steps and happy accidents. And all the while, the RNA lineup grew, alongside lengthening genomes of DNA and complex proteins. And it's all still happening inside your body. RNAs have adapted to become the Swiss Army knives of our cells. Today, they can slice, dice, catalyze, build, destroy, code, replicate, and transform."}, {"video_title": "Functional groups   Properties of carbon   Biology   Khan Academy.mp3", "Sentence": "We spent some time talking about hydrocarbons, and hydrocarbons are interesting, especially if you want to combust things, if you want some fuel. But now we're going to make things a little bit more interesting by adding things to the hydrocarbons. And the things we're gonna add, we call functional groups. Functional groups. And my goal in this video is to give you an overview of the major functional groups that you might see attached to carbon backbones that make the molecules interesting biologically. Now the first one I will focus on is an OH group. So you have an OH attached to a carbon backbone over here."}, {"video_title": "Functional groups   Properties of carbon   Biology   Khan Academy.mp3", "Sentence": "Functional groups. And my goal in this video is to give you an overview of the major functional groups that you might see attached to carbon backbones that make the molecules interesting biologically. Now the first one I will focus on is an OH group. So you have an OH attached to a carbon backbone over here. It doesn't have to be attached to a carbon backbone. But the OH right over here, this is called a hydroxyl group. Hydroxyl group."}, {"video_title": "Functional groups   Properties of carbon   Biology   Khan Academy.mp3", "Sentence": "So you have an OH attached to a carbon backbone over here. It doesn't have to be attached to a carbon backbone. But the OH right over here, this is called a hydroxyl group. Hydroxyl group. And when it is attached to a carbon backbone, like this one is, then it turns the entire molecule into an alcohol. Alcohol. This is an alcohol."}, {"video_title": "Functional groups   Properties of carbon   Biology   Khan Academy.mp3", "Sentence": "Hydroxyl group. And when it is attached to a carbon backbone, like this one is, then it turns the entire molecule into an alcohol. Alcohol. This is an alcohol. And this one in particular, if you want the name, we have two carbons on its longest chain, and it is an alcohol. So we use the prefix eth for the two carbons. So let me write that down."}, {"video_title": "Functional groups   Properties of carbon   Biology   Khan Academy.mp3", "Sentence": "This is an alcohol. And this one in particular, if you want the name, we have two carbons on its longest chain, and it is an alcohol. So we use the prefix eth for the two carbons. So let me write that down. We're gonna use the prefix eth because we have two carbons here. And we're gonna say eth-anol. Now what are the properties here?"}, {"video_title": "Functional groups   Properties of carbon   Biology   Khan Academy.mp3", "Sentence": "So let me write that down. We're gonna use the prefix eth because we have two carbons here. And we're gonna say eth-anol. Now what are the properties here? Well you have oxygen, which is very electronegative, bonded to a hydrogen and to a carbon. But the oxygen's a lot more electronegative than the hydrogen. So you're going to have a partially negative charge at this end, away from the hydrogen, a partial positive charge at the hydrogen end."}, {"video_title": "Functional groups   Properties of carbon   Biology   Khan Academy.mp3", "Sentence": "Now what are the properties here? Well you have oxygen, which is very electronegative, bonded to a hydrogen and to a carbon. But the oxygen's a lot more electronegative than the hydrogen. So you're going to have a partially negative charge at this end, away from the hydrogen, a partial positive charge at the hydrogen end. And to a lesser degree at the carbon end too. But hydrogen is even less electronegative than even carbon. And so this one, so a hydroxyl group, they are polar."}, {"video_title": "Functional groups   Properties of carbon   Biology   Khan Academy.mp3", "Sentence": "So you're going to have a partially negative charge at this end, away from the hydrogen, a partial positive charge at the hydrogen end. And to a lesser degree at the carbon end too. But hydrogen is even less electronegative than even carbon. And so this one, so a hydroxyl group, they are polar. They are polar. And because they're polar, you can dissolve them into water. They are hydrophilic."}, {"video_title": "Functional groups   Properties of carbon   Biology   Khan Academy.mp3", "Sentence": "And so this one, so a hydroxyl group, they are polar. They are polar. And because they're polar, you can dissolve them into water. They are hydrophilic. They can form hydrogen bonds. So you can dissolve this. Now a similar functional group, or one that has somewhat similar properties, is right over here."}, {"video_title": "Functional groups   Properties of carbon   Biology   Khan Academy.mp3", "Sentence": "They are hydrophilic. They can form hydrogen bonds. So you can dissolve this. Now a similar functional group, or one that has somewhat similar properties, is right over here. And you might say, wait, why is this one similar? I have sulfur here instead of oxygen. But if you look at the periodic table, you will see that sulfur and oxygen both have six valence electrons."}, {"video_title": "Functional groups   Properties of carbon   Biology   Khan Academy.mp3", "Sentence": "Now a similar functional group, or one that has somewhat similar properties, is right over here. And you might say, wait, why is this one similar? I have sulfur here instead of oxygen. But if you look at the periodic table, you will see that sulfur and oxygen both have six valence electrons. They both would love nothing more than to grab or pretend to grab two other electrons. And this is why they tend to form two covalent bonds. And so this group right over here, which is called a sulfhydryl group, this is a sulfhydryl group."}, {"video_title": "Functional groups   Properties of carbon   Biology   Khan Academy.mp3", "Sentence": "But if you look at the periodic table, you will see that sulfur and oxygen both have six valence electrons. They both would love nothing more than to grab or pretend to grab two other electrons. And this is why they tend to form two covalent bonds. And so this group right over here, which is called a sulfhydryl group, this is a sulfhydryl group. It's kind of similar to a hydroxyl group, with the one difference that sulfur is electronegative, but it is less electronegative than oxygen. So you're still going to have a partially negative charge and a partially positive charge, but it's going to be less polar. So it's not quite as polar as if you had a hydroxyl group."}, {"video_title": "Functional groups   Properties of carbon   Biology   Khan Academy.mp3", "Sentence": "And so this group right over here, which is called a sulfhydryl group, this is a sulfhydryl group. It's kind of similar to a hydroxyl group, with the one difference that sulfur is electronegative, but it is less electronegative than oxygen. So you're still going to have a partially negative charge and a partially positive charge, but it's going to be less polar. So it's not quite as polar as if you had a hydroxyl group. Now when you have this sulfhydryl group, it's attached to, say, a carbon chain. And when I use this R right over here, when I have this R, this is just shorthand for carbon and a bunch of other stuff. I could have, if I wanted to generalize an alcohol right over here, I could have written R, and then I could have written the hydroxyl group, O, and then bond that to an H. So over here, this shorthand R would have been the shorthand for all of this business, all of this business right over here."}, {"video_title": "Functional groups   Properties of carbon   Biology   Khan Academy.mp3", "Sentence": "So it's not quite as polar as if you had a hydroxyl group. Now when you have this sulfhydryl group, it's attached to, say, a carbon chain. And when I use this R right over here, when I have this R, this is just shorthand for carbon and a bunch of other stuff. I could have, if I wanted to generalize an alcohol right over here, I could have written R, and then I could have written the hydroxyl group, O, and then bond that to an H. So over here, this shorthand R would have been the shorthand for all of this business, all of this business right over here. And so that's what we're doing over there. I'm not saying that this R is exactly this. It means it's some carbon backbone, and some carbons, hydrogens, and maybe other stuff, maybe even some other functional groups."}, {"video_title": "Functional groups   Properties of carbon   Biology   Khan Academy.mp3", "Sentence": "I could have, if I wanted to generalize an alcohol right over here, I could have written R, and then I could have written the hydroxyl group, O, and then bond that to an H. So over here, this shorthand R would have been the shorthand for all of this business, all of this business right over here. And so that's what we're doing over there. I'm not saying that this R is exactly this. It means it's some carbon backbone, and some carbons, hydrogens, and maybe other stuff, maybe even some other functional groups. But we're just focused on the sulfhydryl right over here. And so if you see something like this, you'd say, okay, yeah, this is still gonna be polar, but not quite as polar as if I were dealing with a hydroxyl group. Now over here, we have a more complex molecule, but this is a molecule that you run into probably on a daily basis."}, {"video_title": "Functional groups   Properties of carbon   Biology   Khan Academy.mp3", "Sentence": "It means it's some carbon backbone, and some carbons, hydrogens, and maybe other stuff, maybe even some other functional groups. But we're just focused on the sulfhydryl right over here. And so if you see something like this, you'd say, okay, yeah, this is still gonna be polar, but not quite as polar as if I were dealing with a hydroxyl group. Now over here, we have a more complex molecule, but this is a molecule that you run into probably on a daily basis. This is the sugar fructose. This is the sugar fructose. And this is when it is not in a ring."}, {"video_title": "Functional groups   Properties of carbon   Biology   Khan Academy.mp3", "Sentence": "Now over here, we have a more complex molecule, but this is a molecule that you run into probably on a daily basis. This is the sugar fructose. This is the sugar fructose. And this is when it is not in a ring. If you were to throw this into water, it'll readily form a ring. But when it's not in a ring form, you can recognize already the hydroxyl groups. You have a hydroxyl group on this carbon, you have a hydroxyl group on this carbon, hydroxyl group on this carbon, you have a hydroxyl group on that carbon, you have a hydroxyl group on this carbon, and then on this carbon, it's double bonded to an oxygen, we call this a carbonyl group."}, {"video_title": "Functional groups   Properties of carbon   Biology   Khan Academy.mp3", "Sentence": "And this is when it is not in a ring. If you were to throw this into water, it'll readily form a ring. But when it's not in a ring form, you can recognize already the hydroxyl groups. You have a hydroxyl group on this carbon, you have a hydroxyl group on this carbon, hydroxyl group on this carbon, you have a hydroxyl group on that carbon, you have a hydroxyl group on this carbon, and then on this carbon, it's double bonded to an oxygen, we call this a carbonyl group. This is a carbonyl. Carbonyl. A group, And this is actually how you would tell a sugar."}, {"video_title": "Functional groups   Properties of carbon   Biology   Khan Academy.mp3", "Sentence": "You have a hydroxyl group on this carbon, you have a hydroxyl group on this carbon, hydroxyl group on this carbon, you have a hydroxyl group on that carbon, you have a hydroxyl group on this carbon, and then on this carbon, it's double bonded to an oxygen, we call this a carbonyl group. This is a carbonyl. Carbonyl. A group, And this is actually how you would tell a sugar. It's like, look, especially when it's in a straight chain, all my carbons have one hydroxyl on them, except for this one, it has a carbonyl group. And one of the takeaways for a carbonyl group, we've already talked about oxygen being very electronegative, even more electronegative than carbon, it's double bonds, it's going to hog the electrons on the oxygen end, so you're gonna have a partially negative charge over here, partially positive charge over here, and so this one is also going to be polar, and in fact, the entire molecule is very polar, because it has all these hydroxyl groups on it as well, but this is also going to give it polarity here, and because this carbon has a slightly positive charge, it is susceptible to nucleophilic attack. And when you take organic chemistry, you'll see that things that wanna share, that have a predisposition to share their electrons in a bond, might wanna come and form a bond with this carbon, and maybe one of these electron pairs go back to this oxygen, maybe bond with something else."}, {"video_title": "Functional groups   Properties of carbon   Biology   Khan Academy.mp3", "Sentence": "A group, And this is actually how you would tell a sugar. It's like, look, especially when it's in a straight chain, all my carbons have one hydroxyl on them, except for this one, it has a carbonyl group. And one of the takeaways for a carbonyl group, we've already talked about oxygen being very electronegative, even more electronegative than carbon, it's double bonds, it's going to hog the electrons on the oxygen end, so you're gonna have a partially negative charge over here, partially positive charge over here, and so this one is also going to be polar, and in fact, the entire molecule is very polar, because it has all these hydroxyl groups on it as well, but this is also going to give it polarity here, and because this carbon has a slightly positive charge, it is susceptible to nucleophilic attack. And when you take organic chemistry, you'll see that things that wanna share, that have a predisposition to share their electrons in a bond, might wanna come and form a bond with this carbon, and maybe one of these electron pairs go back to this oxygen, maybe bond with something else. But we'll talk about that in the future when we study some organic chemistry mechanisms. The important thing to hear is just recognize, okay, I got some hydroxyl groups, hey, I got a carbonyl group right over here as well. Now this molecule, this is an amino acid, and you will see amino acids a lot when you study biology, and this has actually a couple of interesting groups on it."}, {"video_title": "Functional groups   Properties of carbon   Biology   Khan Academy.mp3", "Sentence": "And when you take organic chemistry, you'll see that things that wanna share, that have a predisposition to share their electrons in a bond, might wanna come and form a bond with this carbon, and maybe one of these electron pairs go back to this oxygen, maybe bond with something else. But we'll talk about that in the future when we study some organic chemistry mechanisms. The important thing to hear is just recognize, okay, I got some hydroxyl groups, hey, I got a carbonyl group right over here as well. Now this molecule, this is an amino acid, and you will see amino acids a lot when you study biology, and this has actually a couple of interesting groups on it. The first group of note is this stuff that I am circling in orange, because you have a carbon that is, you could say it's part of a carbonyl group, but it is also bound to a hydroxyl group. It is also bound to a hydroxyl group right over there. And when you have this configuration, where you have a carbon double bonded to an oxygen, and then single bonded to a hydroxyl group, we call this a carboxyl group."}, {"video_title": "Functional groups   Properties of carbon   Biology   Khan Academy.mp3", "Sentence": "Now this molecule, this is an amino acid, and you will see amino acids a lot when you study biology, and this has actually a couple of interesting groups on it. The first group of note is this stuff that I am circling in orange, because you have a carbon that is, you could say it's part of a carbonyl group, but it is also bound to a hydroxyl group. It is also bound to a hydroxyl group right over there. And when you have this configuration, where you have a carbon double bonded to an oxygen, and then single bonded to a hydroxyl group, we call this a carboxyl group. This is a carboxyl group. And one of the takeaways from this is that it is acidic, because this can readily give up the hydrogen proton. This oxygen, we already know oxygen likes to hog electrons, it can take up both of these electrons and become negative, and actually there's actually resonance here, because those electrons get shared throughout the group, and actually even potentially even beyond the group, but especially inside of the group, and then leaving the hydrogen proton."}, {"video_title": "Functional groups   Properties of carbon   Biology   Khan Academy.mp3", "Sentence": "And when you have this configuration, where you have a carbon double bonded to an oxygen, and then single bonded to a hydroxyl group, we call this a carboxyl group. This is a carboxyl group. And one of the takeaways from this is that it is acidic, because this can readily give up the hydrogen proton. This oxygen, we already know oxygen likes to hog electrons, it can take up both of these electrons and become negative, and actually there's actually resonance here, because those electrons get shared throughout the group, and actually even potentially even beyond the group, but especially inside of the group, and then leaving the hydrogen proton. So this can readily donate a hydrogen proton, so this is generally viewed as acidic. Now, this amino acid over here, it also, and this is where this name comes from, actually the acid comes from this carboxyl group, that's the acidic part, and then you have an amino group. You have an amino group."}, {"video_title": "Functional groups   Properties of carbon   Biology   Khan Academy.mp3", "Sentence": "This oxygen, we already know oxygen likes to hog electrons, it can take up both of these electrons and become negative, and actually there's actually resonance here, because those electrons get shared throughout the group, and actually even potentially even beyond the group, but especially inside of the group, and then leaving the hydrogen proton. So this can readily donate a hydrogen proton, so this is generally viewed as acidic. Now, this amino acid over here, it also, and this is where this name comes from, actually the acid comes from this carboxyl group, that's the acidic part, and then you have an amino group. You have an amino group. Right over here. And because it's involving nitrogen, this is the amino group. This is what gives the amino part of the name amino acid."}, {"video_title": "Functional groups   Properties of carbon   Biology   Khan Academy.mp3", "Sentence": "You have an amino group. Right over here. And because it's involving nitrogen, this is the amino group. This is what gives the amino part of the name amino acid. Amino acid. And this is actually generally basic, because nitrogen could, it has a lone pair, it has a lone pair of electrons right over here, and so it could use that lone pair to pick up, to form a bond with a hydrogen ion, to pick up a hydrogen ion. So under the right circumstances, it can form a bond with a hydrogen ion, which we know, a positive ion, which would just be a proton, and so it would have a positive charge."}, {"video_title": "Functional groups   Properties of carbon   Biology   Khan Academy.mp3", "Sentence": "This is what gives the amino part of the name amino acid. Amino acid. And this is actually generally basic, because nitrogen could, it has a lone pair, it has a lone pair of electrons right over here, and so it could use that lone pair to pick up, to form a bond with a hydrogen ion, to pick up a hydrogen ion. So under the right circumstances, it can form a bond with a hydrogen ion, which we know, a positive ion, which would just be a proton, and so it would have a positive charge. And so since it can sop up hydrogen ions, we can view this as the amino group as being basic. But this right over here is leucine, it's an amino acid, super important for muscle growth, but there you can appreciate. You have essentially a hydrocarbon chain, but it has a carboxyl group at this end, and an amino group right over here."}, {"video_title": "Functional groups   Properties of carbon   Biology   Khan Academy.mp3", "Sentence": "So under the right circumstances, it can form a bond with a hydrogen ion, which we know, a positive ion, which would just be a proton, and so it would have a positive charge. And so since it can sop up hydrogen ions, we can view this as the amino group as being basic. But this right over here is leucine, it's an amino acid, super important for muscle growth, but there you can appreciate. You have essentially a hydrocarbon chain, but it has a carboxyl group at this end, and an amino group right over here. And another thing that you'll sometimes people talk about is even hydrocarbon groups. For example, if you consider the main chain of this, and we could consider it either using this carbon or this carbon, but if we consider this to be the main chain of carbons, if we consider that to be the main chain of carbons, then we would consider this right over here to be a methyl group. Remember, the prefix meth refers to one carbon, so it's one carbon bonded to a bunch of hydrogens, to three hydrogens here, and so we would call this a methyl group."}, {"video_title": "Functional groups   Properties of carbon   Biology   Khan Academy.mp3", "Sentence": "You have essentially a hydrocarbon chain, but it has a carboxyl group at this end, and an amino group right over here. And another thing that you'll sometimes people talk about is even hydrocarbon groups. For example, if you consider the main chain of this, and we could consider it either using this carbon or this carbon, but if we consider this to be the main chain of carbons, if we consider that to be the main chain of carbons, then we would consider this right over here to be a methyl group. Remember, the prefix meth refers to one carbon, so it's one carbon bonded to a bunch of hydrogens, to three hydrogens here, and so we would call this a methyl group. And in general, if you have a hydrocarbon bonded to other hydrocarbon groups, these things are hydrophobic, so these things, there's nothing polar about them, and so they're not going to want to, at least these parts of the molecules are not going to naturally dissolve inside of water. Now the last group we're gonna focus on, and you're gonna see a lot of these, and especially in biology, you're gonna see it as part of ATP, you're gonna see it as the backbone of DNA, and that's phosphate groups. And this right over here, this right over here, is the phosphate group."}, {"video_title": "Functional groups   Properties of carbon   Biology   Khan Academy.mp3", "Sentence": "Remember, the prefix meth refers to one carbon, so it's one carbon bonded to a bunch of hydrogens, to three hydrogens here, and so we would call this a methyl group. And in general, if you have a hydrocarbon bonded to other hydrocarbon groups, these things are hydrophobic, so these things, there's nothing polar about them, and so they're not going to want to, at least these parts of the molecules are not going to naturally dissolve inside of water. Now the last group we're gonna focus on, and you're gonna see a lot of these, and especially in biology, you're gonna see it as part of ATP, you're gonna see it as the backbone of DNA, and that's phosphate groups. And this right over here, this right over here, is the phosphate group. I've drawn it bonded to a bunch of, kind of a group over here, who knows what it is, bunch of carbons, a bunch of other things, and then I've bonded it to two hydrogens, but it doesn't always have to be bound to hydrogens. But when it is bound to hydrogens like this, it's considered to be protonated, and so it can actually take up, it can actually hog these electrons and dump these hydrogens, and dump these hydrogens into a solution. So a phosphate group is considered to be acidic."}, {"video_title": "Functional groups   Properties of carbon   Biology   Khan Academy.mp3", "Sentence": "And this right over here, this right over here, is the phosphate group. I've drawn it bonded to a bunch of, kind of a group over here, who knows what it is, bunch of carbons, a bunch of other things, and then I've bonded it to two hydrogens, but it doesn't always have to be bound to hydrogens. But when it is bound to hydrogens like this, it's considered to be protonated, and so it can actually take up, it can actually hog these electrons and dump these hydrogens, and dump these hydrogens into a solution. So a phosphate group is considered to be acidic. It is considered, well, especially when it is protonated like this, it is considered to be acidic, because it can donate protons. So this is just an overview of a lot of the functional groups you will see throughout biology, and a lot of big, hairy, complex molecules. When you actually break it down, you say, okay, there's a hydrocarbon chain there, oh, I see a sugar there, I see a bunch of hydroxyls, and I have a carbonyl group, oh, I see an amine group, I see, or amino group, I see a carboxyl group."}, {"video_title": "Carbon as a building block of life   Properties of carbon   Biology   Khan Academy.mp3", "Sentence": "For example, this graphite right over here, this is one form carbon takes, very important when you're writing with a pencil, otherwise you wouldn't have any writing if you didn't have the graphite scraping onto your paper. And your paper is also, it's not pure carbon, but it has a lot of carbon in it. This right over here is a raw diamond, another form that carbon can take after a long period of time under intense pressure. But what you may or may not realize is that carbon is actually essential for life. In fact, life as we know it is carbon-based. So carbon-based life. When we look for signs of life, or at least life as we know it on other planets, we're looking for signs of carbon-based life."}, {"video_title": "Carbon as a building block of life   Properties of carbon   Biology   Khan Academy.mp3", "Sentence": "But what you may or may not realize is that carbon is actually essential for life. In fact, life as we know it is carbon-based. So carbon-based life. When we look for signs of life, or at least life as we know it on other planets, we're looking for signs of carbon-based life. And there might be other forms, other elements that form the backbone of life, but carbon is the only one that we have been able to observe. Now why is carbon so valuable for life? Why does it form the backbone of the molecules that make life possible?"}, {"video_title": "Carbon as a building block of life   Properties of carbon   Biology   Khan Academy.mp3", "Sentence": "When we look for signs of life, or at least life as we know it on other planets, we're looking for signs of carbon-based life. And there might be other forms, other elements that form the backbone of life, but carbon is the only one that we have been able to observe. Now why is carbon so valuable for life? Why does it form the backbone of the molecules that make life possible? Well it all comes down to where it sits in the periodic table and how many, and its atomic number and how it tends to bond with things. So this is why chemistry is important. So carbon we see over here has an atomic number of six, which by definition means it has six protons."}, {"video_title": "Carbon as a building block of life   Properties of carbon   Biology   Khan Academy.mp3", "Sentence": "Why does it form the backbone of the molecules that make life possible? Well it all comes down to where it sits in the periodic table and how many, and its atomic number and how it tends to bond with things. So this is why chemistry is important. So carbon we see over here has an atomic number of six, which by definition means it has six protons. So if I were to draw its nucleus, it would have one, two, three, four, five, six protons. And the most common isotope of carbon on Earth is carbon-12, which also has six neutrons. So let me draw that in this nucleus."}, {"video_title": "Carbon as a building block of life   Properties of carbon   Biology   Khan Academy.mp3", "Sentence": "So carbon we see over here has an atomic number of six, which by definition means it has six protons. So if I were to draw its nucleus, it would have one, two, three, four, five, six protons. And the most common isotope of carbon on Earth is carbon-12, which also has six neutrons. So let me draw that in this nucleus. One, two, three, four, five, six neutrons. And then neutral carbon's going to have six electrons. And so two of them are going to be in their innermost, in the first shell."}, {"video_title": "Carbon as a building block of life   Properties of carbon   Biology   Khan Academy.mp3", "Sentence": "So let me draw that in this nucleus. One, two, three, four, five, six neutrons. And then neutral carbon's going to have six electrons. And so two of them are going to be in their innermost, in the first shell. So that's two of them right over there. These are the inner shell, I guess you could say. So that's the first two electrons."}, {"video_title": "Carbon as a building block of life   Properties of carbon   Biology   Khan Academy.mp3", "Sentence": "And so two of them are going to be in their innermost, in the first shell. So that's two of them right over there. These are the inner shell, I guess you could say. So that's the first two electrons. And then you have four remaining in its outermost shell. And these four are considered valence electrons. These are the electrons that actually do the reacting."}, {"video_title": "Carbon as a building block of life   Properties of carbon   Biology   Khan Academy.mp3", "Sentence": "So that's the first two electrons. And then you have four remaining in its outermost shell. And these four are considered valence electrons. These are the electrons that actually do the reacting. And if any of this seems unfamiliar to you, I encourage you to watch the videos on Khan Academy on things like valence electrons. But this is a little bit of a review right over here. Carbon has four valence electrons."}, {"video_title": "Carbon as a building block of life   Properties of carbon   Biology   Khan Academy.mp3", "Sentence": "These are the electrons that actually do the reacting. And if any of this seems unfamiliar to you, I encourage you to watch the videos on Khan Academy on things like valence electrons. But this is a little bit of a review right over here. Carbon has four valence electrons. And valence electrons are the ones that do, or that tend to do, the reacting. And so I could, if I wanted to simplify this drawing over here, I could say, okay, carbon, and if I were to just draw its valence electrons, which is a typical thing to do, I could say carbon has one, two, three, four valence electrons. Now you might remember the octet rule that atoms tend to be more stable when they at least pretend that they're sharing or that they have eight electrons in their outermost shell."}, {"video_title": "Carbon as a building block of life   Properties of carbon   Biology   Khan Academy.mp3", "Sentence": "Carbon has four valence electrons. And valence electrons are the ones that do, or that tend to do, the reacting. And so I could, if I wanted to simplify this drawing over here, I could say, okay, carbon, and if I were to just draw its valence electrons, which is a typical thing to do, I could say carbon has one, two, three, four valence electrons. Now you might remember the octet rule that atoms tend to be more stable when they at least pretend that they're sharing or that they have eight electrons in their outermost shell. And so carbon can do that by forming four covalent bonds. For example, it could do that with hydrogens. This hydrogen over here has one valence electron."}, {"video_title": "Carbon as a building block of life   Properties of carbon   Biology   Khan Academy.mp3", "Sentence": "Now you might remember the octet rule that atoms tend to be more stable when they at least pretend that they're sharing or that they have eight electrons in their outermost shell. And so carbon can do that by forming four covalent bonds. For example, it could do that with hydrogens. This hydrogen over here has one valence electron. It actually only has one electron. Now the hydrogen feels good. It feels like it's sharing two electrons, filling its first shell."}, {"video_title": "Carbon as a building block of life   Properties of carbon   Biology   Khan Academy.mp3", "Sentence": "This hydrogen over here has one valence electron. It actually only has one electron. Now the hydrogen feels good. It feels like it's sharing two electrons, filling its first shell. Hydrogen's just trying to fill out the first shell, feel a little bit more like helium. And now this carbon says, oh, now I get to share this electron. And then carbon can do it again with another hydrogen."}, {"video_title": "Carbon as a building block of life   Properties of carbon   Biology   Khan Academy.mp3", "Sentence": "It feels like it's sharing two electrons, filling its first shell. Hydrogen's just trying to fill out the first shell, feel a little bit more like helium. And now this carbon says, oh, now I get to share this electron. And then carbon can do it again with another hydrogen. It can do it again with another hydrogen. And it can do it again with another hydrogen. So now carbon can feel like, hey, I'm sharing eight electrons."}, {"video_title": "Carbon as a building block of life   Properties of carbon   Biology   Khan Academy.mp3", "Sentence": "And then carbon can do it again with another hydrogen. It can do it again with another hydrogen. And it can do it again with another hydrogen. So now carbon can feel like, hey, I'm sharing eight electrons. And each of the hydrogens feel like, oh, look, I'm sharing two electrons. Everyone seems to be happy. Everyone seems to be stable."}, {"video_title": "Carbon as a building block of life   Properties of carbon   Biology   Khan Academy.mp3", "Sentence": "So now carbon can feel like, hey, I'm sharing eight electrons. And each of the hydrogens feel like, oh, look, I'm sharing two electrons. Everyone seems to be happy. Everyone seems to be stable. And this molecule right over here, this is methane. This is methane. And by definition, because it involves carbon, it is considered an organic molecule."}, {"video_title": "Carbon as a building block of life   Properties of carbon   Biology   Khan Academy.mp3", "Sentence": "Everyone seems to be stable. And this molecule right over here, this is methane. This is methane. And by definition, because it involves carbon, it is considered an organic molecule. It is considered an organic molecule. In fact, the whole field of organic chemistry is all about studying organic molecules, which are molecules that have carbon. Now, because this only has carbon and hydrogen in it, it is also considered to be a hydrocarbon."}, {"video_title": "Carbon as a building block of life   Properties of carbon   Biology   Khan Academy.mp3", "Sentence": "And by definition, because it involves carbon, it is considered an organic molecule. It is considered an organic molecule. In fact, the whole field of organic chemistry is all about studying organic molecules, which are molecules that have carbon. Now, because this only has carbon and hydrogen in it, it is also considered to be a hydrocarbon. Hydrocarbon. Hydrocarbon. And you might be familiar with things like gasoline being considered a hydrocarbon."}, {"video_title": "Carbon as a building block of life   Properties of carbon   Biology   Khan Academy.mp3", "Sentence": "Now, because this only has carbon and hydrogen in it, it is also considered to be a hydrocarbon. Hydrocarbon. Hydrocarbon. And you might be familiar with things like gasoline being considered a hydrocarbon. And it is indeed a hydrocarbon. In fact, gasoline, gasoline, and actually even methane could be used as fuel right over here. But, and typically, you could see these long chains of hydrocarbons."}, {"video_title": "Carbon as a building block of life   Properties of carbon   Biology   Khan Academy.mp3", "Sentence": "And you might be familiar with things like gasoline being considered a hydrocarbon. And it is indeed a hydrocarbon. In fact, gasoline, gasoline, and actually even methane could be used as fuel right over here. But, and typically, you could see these long chains of hydrocarbons. For example, you could have eight carbons form octane. You might be familiar with things like high octane fuel. So let's see, carbon two, three, four, five, six, seven, eight."}, {"video_title": "Carbon as a building block of life   Properties of carbon   Biology   Khan Academy.mp3", "Sentence": "But, and typically, you could see these long chains of hydrocarbons. For example, you could have eight carbons form octane. You might be familiar with things like high octane fuel. So let's see, carbon two, three, four, five, six, seven, eight. This is a hydrocarbon. It's octane because it has eight carbons, oct, octane. And all the other bonds, remember, carbon forms four bonds, or typically forms four bonds."}, {"video_title": "Carbon as a building block of life   Properties of carbon   Biology   Khan Academy.mp3", "Sentence": "So let's see, carbon two, three, four, five, six, seven, eight. This is a hydrocarbon. It's octane because it has eight carbons, oct, octane. And all the other bonds, remember, carbon forms four bonds, or typically forms four bonds. So now that carbon has four bonds. Now this carbon has four bonds. Now this carbon, two of them to hydrogen, two of them to carbon."}, {"video_title": "Carbon as a building block of life   Properties of carbon   Biology   Khan Academy.mp3", "Sentence": "And all the other bonds, remember, carbon forms four bonds, or typically forms four bonds. So now that carbon has four bonds. Now this carbon has four bonds. Now this carbon, two of them to hydrogen, two of them to carbon. Two to hydrogen, two to carbon. Hopefully this starts to give you an appreciation why carbon is so useful as a building block because it can form so many bonds with so many different structures. And these hydrocarbons, they can be chains or they can even form rings, they can form cycles."}, {"video_title": "Carbon as a building block of life   Properties of carbon   Biology   Khan Academy.mp3", "Sentence": "Now this carbon, two of them to hydrogen, two of them to carbon. Two to hydrogen, two to carbon. Hopefully this starts to give you an appreciation why carbon is so useful as a building block because it can form so many bonds with so many different structures. And these hydrocarbons, they can be chains or they can even form rings, they can form cycles. And in things like graphite and in diamond, carbons can form these lattice structures where carbon is bonding to more than two carbons more than two carbons in these three dimensional shapes. In these three dimensional shapes. And the shape, because it's forming three bonds, that carbon typically forms bonds in, these are called tetrahedral shapes, or tetrahedral bonding."}, {"video_title": "Carbon as a building block of life   Properties of carbon   Biology   Khan Academy.mp3", "Sentence": "And these hydrocarbons, they can be chains or they can even form rings, they can form cycles. And in things like graphite and in diamond, carbons can form these lattice structures where carbon is bonding to more than two carbons more than two carbons in these three dimensional shapes. In these three dimensional shapes. And the shape, because it's forming three bonds, that carbon typically forms bonds in, these are called tetrahedral shapes, or tetrahedral bonding. And when someone says tetrahedron, if someone says tetrahedron, they're talking about a, let me do this in a different color. So a tetrahedron is a three dimensional shape that has four sides, each of which are triangles. Each of which are triangles."}, {"video_title": "Carbon as a building block of life   Properties of carbon   Biology   Khan Academy.mp3", "Sentence": "And the shape, because it's forming three bonds, that carbon typically forms bonds in, these are called tetrahedral shapes, or tetrahedral bonding. And when someone says tetrahedron, if someone says tetrahedron, they're talking about a, let me do this in a different color. So a tetrahedron is a three dimensional shape that has four sides, each of which are triangles. Each of which are triangles. And so it would look like this. You could view it as a pyramid with a triangular base. A pyramid with a triangular base."}, {"video_title": "Carbon as a building block of life   Properties of carbon   Biology   Khan Academy.mp3", "Sentence": "Each of which are triangles. And so it would look like this. You could view it as a pyramid with a triangular base. A pyramid with a triangular base. And when carbon forms bonds, let's say in the case of this methane right over here, I'll draw the carbon in the middle as this yellow circle, then each of the hydrogens over here are going to be at the corners, or I guess you'd say the vertices of the tetrahedron. And so this is the tetrahedral shape that carbon is actually forming. And of course you have these covalent bonds right over here."}, {"video_title": "Carbon as a building block of life   Properties of carbon   Biology   Khan Academy.mp3", "Sentence": "A pyramid with a triangular base. And when carbon forms bonds, let's say in the case of this methane right over here, I'll draw the carbon in the middle as this yellow circle, then each of the hydrogens over here are going to be at the corners, or I guess you'd say the vertices of the tetrahedron. And so this is the tetrahedral shape that carbon is actually forming. And of course you have these covalent bonds right over here. Let me do this in a different color. You have these covalent bonds over here. And we could draw it like this."}, {"video_title": "Carbon as a building block of life   Properties of carbon   Biology   Khan Academy.mp3", "Sentence": "And of course you have these covalent bonds right over here. Let me do this in a different color. You have these covalent bonds over here. And we could draw it like this. We could draw these covalent bonds like this. That's one of them. Maybe that's this one over here."}, {"video_title": "Carbon as a building block of life   Properties of carbon   Biology   Khan Academy.mp3", "Sentence": "And we could draw it like this. We could draw these covalent bonds like this. That's one of them. Maybe that's this one over here. This one over here is right over here. These electrons are all just buzzing around. And then you have one over here."}, {"video_title": "Carbon as a building block of life   Properties of carbon   Biology   Khan Academy.mp3", "Sentence": "Maybe that's this one over here. This one over here is right over here. These electrons are all just buzzing around. And then you have one over here. And then you have one over here. So you might see methane sometimes just drawn like this. You might just see it drawn like this."}, {"video_title": "Carbon as a building block of life   Properties of carbon   Biology   Khan Academy.mp3", "Sentence": "And then you have one over here. And then you have one over here. So you might see methane sometimes just drawn like this. You might just see it drawn like this. But it's really forming a tetrahedral shape. Let me finish drawing it. So hydrogen, hydrogen, hydrogen, hydrogen, where each of these lines represents a pair of electrons."}, {"video_title": "Carbon as a building block of life   Properties of carbon   Biology   Khan Academy.mp3", "Sentence": "You might just see it drawn like this. But it's really forming a tetrahedral shape. Let me finish drawing it. So hydrogen, hydrogen, hydrogen, hydrogen, where each of these lines represents a pair of electrons. So you have eight electrons being shared in aggregate. But the actual shape is closer to this. Now I'm claiming to you that it's the backbone of life, or life as we know it."}, {"video_title": "Carbon as a building block of life   Properties of carbon   Biology   Khan Academy.mp3", "Sentence": "So hydrogen, hydrogen, hydrogen, hydrogen, where each of these lines represents a pair of electrons. So you have eight electrons being shared in aggregate. But the actual shape is closer to this. Now I'm claiming to you that it's the backbone of life, or life as we know it. And it's even the backbone of life as you are, life in the form of you. We've already talked about you being a majority water, and that's why if you look at the average human being, the average human being is going to be roughly, depends on how well hydrated you are and your stage of development, the average human being is going to be 65% oxygen by mass. So you're 2 3rds oxygen, and that's because of all of the water."}, {"video_title": "Carbon as a building block of life   Properties of carbon   Biology   Khan Academy.mp3", "Sentence": "Now I'm claiming to you that it's the backbone of life, or life as we know it. And it's even the backbone of life as you are, life in the form of you. We've already talked about you being a majority water, and that's why if you look at the average human being, the average human being is going to be roughly, depends on how well hydrated you are and your stage of development, the average human being is going to be 65% oxygen by mass. So you're 2 3rds oxygen, and that's because of all of the water. Water is H2O, and oxygen forms the bulk of the mass of the water molecule. But in second place comes carbon. In second place comes carbon."}, {"video_title": "Carbon as a building block of life   Properties of carbon   Biology   Khan Academy.mp3", "Sentence": "So you're 2 3rds oxygen, and that's because of all of the water. Water is H2O, and oxygen forms the bulk of the mass of the water molecule. But in second place comes carbon. In second place comes carbon. Carbon is approximately 18% of your body's mass. And this is because if you think about the non-fluid part, the non-liquid part of your body, there's a lot of carbon going on there. This right over here is a DNA molecule, and so these little gray areas, this is all carbon."}, {"video_title": "Carbon as a building block of life   Properties of carbon   Biology   Khan Academy.mp3", "Sentence": "In second place comes carbon. Carbon is approximately 18% of your body's mass. And this is because if you think about the non-fluid part, the non-liquid part of your body, there's a lot of carbon going on there. This right over here is a DNA molecule, and so these little gray areas, this is all carbon. This right over here, this right over here is hexokinase. I'm not gonna go into the details about what it does, but hexokinase is a protein, hexokinase, and the teal color that you see there, that is all carbon, that's all carbon. This right over here is glucose."}, {"video_title": "Carbon as a building block of life   Properties of carbon   Biology   Khan Academy.mp3", "Sentence": "This right over here is a DNA molecule, and so these little gray areas, this is all carbon. This right over here, this right over here is hexokinase. I'm not gonna go into the details about what it does, but hexokinase is a protein, hexokinase, and the teal color that you see there, that is all carbon, that's all carbon. This right over here is glucose. It's very sweet. It's an important way to regulate your body's energy. And the teal color, that is carbon."}, {"video_title": "Carbon as a building block of life   Properties of carbon   Biology   Khan Academy.mp3", "Sentence": "This right over here is glucose. It's very sweet. It's an important way to regulate your body's energy. And the teal color, that is carbon. This is ATP, often considered to be the molecular currency of energy in your body. And all the teal there, this is carbon. This is why a lot of, especially the non-water part of your body, is carbon."}, {"video_title": "Human activities that threaten biodiversity.mp3", "Sentence": "We're going to talk about something that we'll call local factors, as opposed to more global human effects. But before we go into some of those, we really need to talk about the fact that the human population is growing fast. In 2014, the estimate was just over 7 billion people on earth. Human population growth is exponential. The more people you have, the more reproduction you have going on. If you have more reproduction happening, then the curve on a graph of population versus time is going to get steeper and steeper and steeper, to the point where we're looking at about 9 billion people by the year 2050. It was Thomas Malthus in 1798 who came up with the concept of carrying capacity."}, {"video_title": "Human activities that threaten biodiversity.mp3", "Sentence": "Human population growth is exponential. The more people you have, the more reproduction you have going on. If you have more reproduction happening, then the curve on a graph of population versus time is going to get steeper and steeper and steeper, to the point where we're looking at about 9 billion people by the year 2050. It was Thomas Malthus in 1798 who came up with the concept of carrying capacity. Basically, he said that the earth can't indefinitely support an ever increasing human population. That's a concept that to us, I think, seems quite clear, but Malthus was a member of a social force at that time. Basically, the clergy that felt the earth was put here for humans to use and upon which we should go forth and multiply."}, {"video_title": "Human activities that threaten biodiversity.mp3", "Sentence": "It was Thomas Malthus in 1798 who came up with the concept of carrying capacity. Basically, he said that the earth can't indefinitely support an ever increasing human population. That's a concept that to us, I think, seems quite clear, but Malthus was a member of a social force at that time. Basically, the clergy that felt the earth was put here for humans to use and upon which we should go forth and multiply. But Malthus was among the first in recognizing that there was no way that human population could increase indefinitely without having some sort of an effect on the environment and the environment's ability to support us. The logic he used led him to the fact that based on the kind of farming he saw around him at the time, there would soon be so many people there wouldn't be enough to eat. Basically, the planet was going to check population growth through famine."}, {"video_title": "Human activities that threaten biodiversity.mp3", "Sentence": "Basically, the clergy that felt the earth was put here for humans to use and upon which we should go forth and multiply. But Malthus was among the first in recognizing that there was no way that human population could increase indefinitely without having some sort of an effect on the environment and the environment's ability to support us. The logic he used led him to the fact that based on the kind of farming he saw around him at the time, there would soon be so many people there wouldn't be enough to eat. Basically, the planet was going to check population growth through famine. He had seen famine, he knew what it was like, so the planet was going to take care of it if we didn't. In other words, we would exceed the planet's carrying capacity for human beings. The question arose, what actually is the carrying capacity of planet earth for humans?"}, {"video_title": "Human activities that threaten biodiversity.mp3", "Sentence": "Basically, the planet was going to check population growth through famine. He had seen famine, he knew what it was like, so the planet was going to take care of it if we didn't. In other words, we would exceed the planet's carrying capacity for human beings. The question arose, what actually is the carrying capacity of planet earth for humans? The answer is like most scientific replies, it depends. We haven't hit the Malthusian limit yet because of a very important thing, and that's human technology. The ability to come up with answers to problems that are facing us at almost every turn."}, {"video_title": "Human activities that threaten biodiversity.mp3", "Sentence": "The question arose, what actually is the carrying capacity of planet earth for humans? The answer is like most scientific replies, it depends. We haven't hit the Malthusian limit yet because of a very important thing, and that's human technology. The ability to come up with answers to problems that are facing us at almost every turn. In this case, the answers came through science and technology that increased food production. This made it possible for us to get back on the exponential population growth curve and escape Malthus' view of what the upper limits were. In fact, there are some estimates that suggest if we all did with less and lived at the lowest possible level for existence, earth could support an estimated 40 billion people."}, {"video_title": "Human activities that threaten biodiversity.mp3", "Sentence": "The ability to come up with answers to problems that are facing us at almost every turn. In this case, the answers came through science and technology that increased food production. This made it possible for us to get back on the exponential population growth curve and escape Malthus' view of what the upper limits were. In fact, there are some estimates that suggest if we all did with less and lived at the lowest possible level for existence, earth could support an estimated 40 billion people. But even if we were able to reach a carrying capacity of 40 billion, it would require sacrifices for all humans on earth, some more than others. It raises a huge question about the quality of life, which points out what's increasingly becoming the single most important fact about human population growth on earth today, that the world's wealthiest 16% of the people on earth use 80% of the available resources. The bottom line here, as I say, is that it's complicated."}, {"video_title": "Human activities that threaten biodiversity.mp3", "Sentence": "In fact, there are some estimates that suggest if we all did with less and lived at the lowest possible level for existence, earth could support an estimated 40 billion people. But even if we were able to reach a carrying capacity of 40 billion, it would require sacrifices for all humans on earth, some more than others. It raises a huge question about the quality of life, which points out what's increasingly becoming the single most important fact about human population growth on earth today, that the world's wealthiest 16% of the people on earth use 80% of the available resources. The bottom line here, as I say, is that it's complicated. We recognize that the human population is growing, we recognize that resource utilization is much higher in some countries than in others. But what I really want to do is circle back to our primary objective and examine what this really means for biodiversity. If you asked anyone, they'd say it's pretty clear that human population growth and resource utilization have huge effects not just on our social and economic well-being, but of course on biodiversity."}, {"video_title": "Human activities that threaten biodiversity.mp3", "Sentence": "The bottom line here, as I say, is that it's complicated. We recognize that the human population is growing, we recognize that resource utilization is much higher in some countries than in others. But what I really want to do is circle back to our primary objective and examine what this really means for biodiversity. If you asked anyone, they'd say it's pretty clear that human population growth and resource utilization have huge effects not just on our social and economic well-being, but of course on biodiversity. But how exactly? It translates into decreases in species richness. It's primarily through the loss of species richness that our greatest population growth effects are going to show up."}, {"video_title": "Human activities that threaten biodiversity.mp3", "Sentence": "If you asked anyone, they'd say it's pretty clear that human population growth and resource utilization have huge effects not just on our social and economic well-being, but of course on biodiversity. But how exactly? It translates into decreases in species richness. It's primarily through the loss of species richness that our greatest population growth effects are going to show up. If we simplify it, it's as fundamental as no two things can occupy the same place at the same time. That's what we're talking about. If a human is living in a given place, fewer native plants and animals can live there."}, {"video_title": "Human activities that threaten biodiversity.mp3", "Sentence": "It's primarily through the loss of species richness that our greatest population growth effects are going to show up. If we simplify it, it's as fundamental as no two things can occupy the same place at the same time. That's what we're talking about. If a human is living in a given place, fewer native plants and animals can live there. The details of how human population growth actually affects species richness are only now starting to be worked out. We don't have a lot of data yet. It's a huge, complex problem."}, {"video_title": "Human activities that threaten biodiversity.mp3", "Sentence": "If a human is living in a given place, fewer native plants and animals can live there. The details of how human population growth actually affects species richness are only now starting to be worked out. We don't have a lot of data yet. It's a huge, complex problem. One of the pioneering papers on this was published in 2003 by McKee and colleagues. They measured a number of factors in 114 different countries and what they discovered was that out of all the factors that they looked at, human population growth and species richness were tightly linked. In other words, if you were to slow population growth, that might be sufficient to stop drops in species richness."}, {"video_title": "Human activities that threaten biodiversity.mp3", "Sentence": "It's a huge, complex problem. One of the pioneering papers on this was published in 2003 by McKee and colleagues. They measured a number of factors in 114 different countries and what they discovered was that out of all the factors that they looked at, human population growth and species richness were tightly linked. In other words, if you were to slow population growth, that might be sufficient to stop drops in species richness. They suggested that all you need to know is population size. Plug this into the equation and you can figure out in a given place what effect it's going to have on biodiversity. Calculations show that the number of threatened species in an average nation is going to increase 7% by 2020 and 14% by 2050 just based on population growth alone."}, {"video_title": "Human activities that threaten biodiversity.mp3", "Sentence": "In other words, if you were to slow population growth, that might be sufficient to stop drops in species richness. They suggested that all you need to know is population size. Plug this into the equation and you can figure out in a given place what effect it's going to have on biodiversity. Calculations show that the number of threatened species in an average nation is going to increase 7% by 2020 and 14% by 2050 just based on population growth alone. That's a very simple relationship, but if you open up that box represented by the idea of population growth and unpack what it means, you're talking about lots of human-induced drops in biodiversity. And as usual, things get complicated. I'd say that there are seven major human-mediated causes of biodiversity loss."}, {"video_title": "Human activities that threaten biodiversity.mp3", "Sentence": "Calculations show that the number of threatened species in an average nation is going to increase 7% by 2020 and 14% by 2050 just based on population growth alone. That's a very simple relationship, but if you open up that box represented by the idea of population growth and unpack what it means, you're talking about lots of human-induced drops in biodiversity. And as usual, things get complicated. I'd say that there are seven major human-mediated causes of biodiversity loss. They can be grouped into two main categories, localized ones and global ones. The global causes we'll look at in separate videos, but for the localized ones, we're going to list four. Land use change, pollution, resource exploitation, and introduction of exotic species."}, {"video_title": "Human activities that threaten biodiversity.mp3", "Sentence": "I'd say that there are seven major human-mediated causes of biodiversity loss. They can be grouped into two main categories, localized ones and global ones. The global causes we'll look at in separate videos, but for the localized ones, we're going to list four. Land use change, pollution, resource exploitation, and introduction of exotic species. Of course, they overlap a little, but I think for the most part, these are good ways of unpacking our box of problems. Let's start with land use changes. These include things like habitat destruction and conversion of natural habitat to human use that isn't necessarily compatible with the organisms that are native there."}, {"video_title": "Human activities that threaten biodiversity.mp3", "Sentence": "Land use change, pollution, resource exploitation, and introduction of exotic species. Of course, they overlap a little, but I think for the most part, these are good ways of unpacking our box of problems. Let's start with land use changes. These include things like habitat destruction and conversion of natural habitat to human use that isn't necessarily compatible with the organisms that are native there. This includes crop monoculture that results in a very dramatic drop in species richness in a given habitat. When people think about habitat destruction and conversion, they think of slash and burn agriculture, destroying rainforest, plowing over stuff, or removing the tops of mountains to get out resources like coal, but there are ocean use changes too that I think we should not ignore. Think of coastal wetland loss and mangrove destruction."}, {"video_title": "Human activities that threaten biodiversity.mp3", "Sentence": "These include things like habitat destruction and conversion of natural habitat to human use that isn't necessarily compatible with the organisms that are native there. This includes crop monoculture that results in a very dramatic drop in species richness in a given habitat. When people think about habitat destruction and conversion, they think of slash and burn agriculture, destroying rainforest, plowing over stuff, or removing the tops of mountains to get out resources like coal, but there are ocean use changes too that I think we should not ignore. Think of coastal wetland loss and mangrove destruction. Urbanization is an enormous change in land use. More people need more homes and more places to work. That in turn requires an expansion of agricultural resources and the spread of those into environments that were previously untouched."}, {"video_title": "Human activities that threaten biodiversity.mp3", "Sentence": "Think of coastal wetland loss and mangrove destruction. Urbanization is an enormous change in land use. More people need more homes and more places to work. That in turn requires an expansion of agricultural resources and the spread of those into environments that were previously untouched. It's a very complex problem, as I say, but simply put, the more people you have, the less natural undeveloped habitat there's going to be. It's very easy to see how that's linked to a drop in biodiversity. The second local factor is pollution."}, {"video_title": "Human activities that threaten biodiversity.mp3", "Sentence": "That in turn requires an expansion of agricultural resources and the spread of those into environments that were previously untouched. It's a very complex problem, as I say, but simply put, the more people you have, the less natural undeveloped habitat there's going to be. It's very easy to see how that's linked to a drop in biodiversity. The second local factor is pollution. A lot had been done to bring the subject to people's attention to the point where we think about it as enormous disasters attached to super fun cleanup sites and such, but there are other more subtle ways of polluting the environment, which I think are worth thinking about when we talk about drops in biodiversity. For example, the degradation of local habitats through human activities that cause downstream effects, things like the leaching of harmful chemicals from mines into the water table. Waterborne pollutants can pop out in very unusual places and have really big downstream effects, if you'll excuse the pun, on the reproductive viability of organisms that happen to be in those places."}, {"video_title": "Human activities that threaten biodiversity.mp3", "Sentence": "The second local factor is pollution. A lot had been done to bring the subject to people's attention to the point where we think about it as enormous disasters attached to super fun cleanup sites and such, but there are other more subtle ways of polluting the environment, which I think are worth thinking about when we talk about drops in biodiversity. For example, the degradation of local habitats through human activities that cause downstream effects, things like the leaching of harmful chemicals from mines into the water table. Waterborne pollutants can pop out in very unusual places and have really big downstream effects, if you'll excuse the pun, on the reproductive viability of organisms that happen to be in those places. There are also dead zones in the ocean caused by nitrogen fertilizers that wash into rivers. Where the rivers flow into the sea, the nitrogen causes blooms of bacteria, which in turn use up the oxygen. Anything that tries to be active in an area where the oxygen is being used up by the bacteria, any oxygen requiring organism, that is pretty much any animal for example, is going to have a really hard time of it."}, {"video_title": "Human activities that threaten biodiversity.mp3", "Sentence": "Waterborne pollutants can pop out in very unusual places and have really big downstream effects, if you'll excuse the pun, on the reproductive viability of organisms that happen to be in those places. There are also dead zones in the ocean caused by nitrogen fertilizers that wash into rivers. Where the rivers flow into the sea, the nitrogen causes blooms of bacteria, which in turn use up the oxygen. Anything that tries to be active in an area where the oxygen is being used up by the bacteria, any oxygen requiring organism, that is pretty much any animal for example, is going to have a really hard time of it. These dead zones are now starting to be a little bit better understood and it's pretty clear that they're growing in size and in number in relation to population growth. Then there's the overall problem of waste disposal. Untreated sewage is a classic problem for biodiversity."}, {"video_title": "Human activities that threaten biodiversity.mp3", "Sentence": "Anything that tries to be active in an area where the oxygen is being used up by the bacteria, any oxygen requiring organism, that is pretty much any animal for example, is going to have a really hard time of it. These dead zones are now starting to be a little bit better understood and it's pretty clear that they're growing in size and in number in relation to population growth. Then there's the overall problem of waste disposal. Untreated sewage is a classic problem for biodiversity. It's not just, of course, human waste. It has to do with sometimes bizarre chemistry involved in the high-tech stuff that we're making now. We're talking about chemical compounds, including drugs and PCBs."}, {"video_title": "Human activities that threaten biodiversity.mp3", "Sentence": "Untreated sewage is a classic problem for biodiversity. It's not just, of course, human waste. It has to do with sometimes bizarre chemistry involved in the high-tech stuff that we're making now. We're talking about chemical compounds, including drugs and PCBs. There are lots of strange molecules that humans are producing and dumping. In some cases, you get these hormone mimics, simple compounds derived from prescription drugs and other man-made chemicals that get flushed into waterways. Hormone mimics act like naturally occurring hormones that control normal development of wild organisms, particularly water-living ones."}, {"video_title": "Human activities that threaten biodiversity.mp3", "Sentence": "We're talking about chemical compounds, including drugs and PCBs. There are lots of strange molecules that humans are producing and dumping. In some cases, you get these hormone mimics, simple compounds derived from prescription drugs and other man-made chemicals that get flushed into waterways. Hormone mimics act like naturally occurring hormones that control normal development of wild organisms, particularly water-living ones. Hormone mimics can also adversely affect their reproductive organs. There are many, many, many examples of this kind of pollution, one that people wouldn't necessarily think of. Another one that doesn't immediately occur to people is noise pollution."}, {"video_title": "Human activities that threaten biodiversity.mp3", "Sentence": "Hormone mimics act like naturally occurring hormones that control normal development of wild organisms, particularly water-living ones. Hormone mimics can also adversely affect their reproductive organs. There are many, many, many examples of this kind of pollution, one that people wouldn't necessarily think of. Another one that doesn't immediately occur to people is noise pollution. Birds in cities are reacting to noise levels. Even the organisms that are not being wiped out because of our expanding cities are starting to adapt to an urban environment by changing their behavior and reproductive patterns. And some of them just can't do it."}, {"video_title": "Human activities that threaten biodiversity.mp3", "Sentence": "Another one that doesn't immediately occur to people is noise pollution. Birds in cities are reacting to noise levels. Even the organisms that are not being wiped out because of our expanding cities are starting to adapt to an urban environment by changing their behavior and reproductive patterns. And some of them just can't do it. Noise can also be a major factor in marine mammal survival. Evidence suggests that sonar pollution interferes with the health of marine mammals. Patterns of reproduction can also be upset by our introduction of light pollution to places where there wasn't light before."}, {"video_title": "Human activities that threaten biodiversity.mp3", "Sentence": "And some of them just can't do it. Noise can also be a major factor in marine mammal survival. Evidence suggests that sonar pollution interferes with the health of marine mammals. Patterns of reproduction can also be upset by our introduction of light pollution to places where there wasn't light before. Sea turtle hatchlings can be impacted by artificial light heading toward it instead of the ocean when they hatch out of their nests on the beach. And bird strikes on buildings are greatly increased at night when the lights are left on. Let's look at the third local factor, resource exploitation."}, {"video_title": "Human activities that threaten biodiversity.mp3", "Sentence": "Patterns of reproduction can also be upset by our introduction of light pollution to places where there wasn't light before. Sea turtle hatchlings can be impacted by artificial light heading toward it instead of the ocean when they hatch out of their nests on the beach. And bird strikes on buildings are greatly increased at night when the lights are left on. Let's look at the third local factor, resource exploitation. This gets to the simple idea that humans are always using things from their environment. We are inextricably linked to that environment and we use up stuff. We always have."}, {"video_title": "Human activities that threaten biodiversity.mp3", "Sentence": "Let's look at the third local factor, resource exploitation. This gets to the simple idea that humans are always using things from their environment. We are inextricably linked to that environment and we use up stuff. We always have. We have to do that in order to stay alive. There are classic ways we use resources like hunting, cutting down forests for firewood and lumber. Where does the biodiversity go then?"}, {"video_title": "Human activities that threaten biodiversity.mp3", "Sentence": "We always have. We have to do that in order to stay alive. There are classic ways we use resources like hunting, cutting down forests for firewood and lumber. Where does the biodiversity go then? A big one for me as a marine scientist, of course, is fishing. We talk about the harvest of fish, but it's not really a gathering of what one sows. It's really a straight up removal of a resource as much as mining is."}, {"video_title": "Human activities that threaten biodiversity.mp3", "Sentence": "Where does the biodiversity go then? A big one for me as a marine scientist, of course, is fishing. We talk about the harvest of fish, but it's not really a gathering of what one sows. It's really a straight up removal of a resource as much as mining is. There are attempts to control overfishing, but to a large extent we often don't have enough data to know just what a sustainable amount of extraction is until it's too late. Before we were moved to action, for example, the cod fishery had collapsed on the Grand Banks of Newfoundland. Today we have no idea what the long-term effect of huge trawls scraping over the sea bottom will be."}, {"video_title": "Human activities that threaten biodiversity.mp3", "Sentence": "It's really a straight up removal of a resource as much as mining is. There are attempts to control overfishing, but to a large extent we often don't have enough data to know just what a sustainable amount of extraction is until it's too late. Before we were moved to action, for example, the cod fishery had collapsed on the Grand Banks of Newfoundland. Today we have no idea what the long-term effect of huge trawls scraping over the sea bottom will be. Now countries are pushing to fish more in the Antarctic, which is a problem because fish, like most things there, grow slowly in the cold Antarctic depths. The last local cause of reduction in species richness I want to mention is the introduction of exotic species and we'll talk about those in the next video. So just to bring it all back to this concept of carrying capacity, the emerging message is that if everyone on Earth can manage to do more with less, especially in places where we presently use up relatively so much more, we might be on track towards a more manageable carrying capacity for humans on Earth with a decent quality of life."}, {"video_title": "DNA   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "For example, someone might have told you, hey, you walk kind of like your dad, or your smile is kind of like your mom, or your eyes are like one of your uncles or your grandparents. And so there's always been this notion of inherited traits. But it wasn't until the 1800s that that started to be studied in a more scientific way with Gregor Mendel, the father of genetics. But even then, even Mendel, who was starting to understand the mechanisms of, or he was trying to understand how inheritance happens, and he even could start to breed certain types of things, even he didn't know exactly what was the molecular basis for inheritance. And the answer to that question wasn't figured out until fairly recent times, until the mid-20th century, not until the structure of DNA was established by Watson and Crick. And their work was based on the work of many others, especially folks like Rosalind Franklin, who essentially provided the bulk of the data for Watson and Crick's work, Maurice Wilkins, and many, many, many other folks. But it was really the structure of DNA that made people say, hey, that looks like the molecule that's storing the information."}, {"video_title": "DNA   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "But even then, even Mendel, who was starting to understand the mechanisms of, or he was trying to understand how inheritance happens, and he even could start to breed certain types of things, even he didn't know exactly what was the molecular basis for inheritance. And the answer to that question wasn't figured out until fairly recent times, until the mid-20th century, not until the structure of DNA was established by Watson and Crick. And their work was based on the work of many others, especially folks like Rosalind Franklin, who essentially provided the bulk of the data for Watson and Crick's work, Maurice Wilkins, and many, many, many other folks. But it was really the structure of DNA that made people say, hey, that looks like the molecule that's storing the information. And just to be clear, DNA wasn't discovered in 1953. DNA was discovered in the mid-1800s. It was this kind of, this molecule that was inside of nuclei, of cells, and for some time, people said, oh, maybe this could be a molecular basis of inheritance."}, {"video_title": "DNA   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "But it was really the structure of DNA that made people say, hey, that looks like the molecule that's storing the information. And just to be clear, DNA wasn't discovered in 1953. DNA was discovered in the mid-1800s. It was this kind of, this molecule that was inside of nuclei, of cells, and for some time, people said, oh, maybe this could be a molecular basis of inheritance. You know, you could imagine what you would need to be a molecular basis of inheritance. It would have to be a molecule or a series of molecules that could contain information, that could be replicated, that could be expressed in some way. But it wasn't until 1953, when this double helix structure of DNA was established that people said, hey, this looks like our molecule."}, {"video_title": "DNA   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "It was this kind of, this molecule that was inside of nuclei, of cells, and for some time, people said, oh, maybe this could be a molecular basis of inheritance. You know, you could imagine what you would need to be a molecular basis of inheritance. It would have to be a molecule or a series of molecules that could contain information, that could be replicated, that could be expressed in some way. But it wasn't until 1953, when this double helix structure of DNA was established that people said, hey, this looks like our molecule. So first, let's just talk about the structure here, and then actually we'll talk about where this name, DNA, deoxyribonucleic acid, comes from. And then we'll talk a little bit about why the structure lends itself well to something that stores information, that can replicate its information, and that could express its information. We might go in-depth on the expression of information in future videos."}, {"video_title": "DNA   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "But it wasn't until 1953, when this double helix structure of DNA was established that people said, hey, this looks like our molecule. So first, let's just talk about the structure here, and then actually we'll talk about where this name, DNA, deoxyribonucleic acid, comes from. And then we'll talk a little bit about why the structure lends itself well to something that stores information, that can replicate its information, and that could express its information. We might go in-depth on the expression of information in future videos. So this structure right over here, and this is a visual depiction of a DNA molecule, you can view this as kind of a twisted ladder. It has these two, I guess you could say, sides of the ladder that are twisted. That is one side right over there, and then it is another side."}, {"video_title": "DNA   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "We might go in-depth on the expression of information in future videos. So this structure right over here, and this is a visual depiction of a DNA molecule, you can view this as kind of a twisted ladder. It has these two, I guess you could say, sides of the ladder that are twisted. That is one side right over there, and then it is another side. There is another side right over here. And in between those two sides, or connecting those two sides of that twisted ladder, you have these rungs. And these rungs are actually where the information, the genetic information is, I guess you could say, stored in some way."}, {"video_title": "DNA   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "That is one side right over there, and then it is another side. There is another side right over here. And in between those two sides, or connecting those two sides of that twisted ladder, you have these rungs. And these rungs are actually where the information, the genetic information is, I guess you could say, stored in some way. Because these rungs, it's a sequence of different bases. And when I say bases, you might say, wait, this says acid, why are you saying bases right over here? Well, the word deoxyribonucleic acid comes from the fact that this backbone is made up of a combination of sugar and phosphate."}, {"video_title": "DNA   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "And these rungs are actually where the information, the genetic information is, I guess you could say, stored in some way. Because these rungs, it's a sequence of different bases. And when I say bases, you might say, wait, this says acid, why are you saying bases right over here? Well, the word deoxyribonucleic acid comes from the fact that this backbone is made up of a combination of sugar and phosphate. And the sugar that makes up the backbone is deoxyribose, so that's essentially the D in DNA. And then the phosphate group is acidic, and that's where you get the acid part of it. And nucleic is, hey, this was found in nuclei of cells."}, {"video_title": "DNA   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "Well, the word deoxyribonucleic acid comes from the fact that this backbone is made up of a combination of sugar and phosphate. And the sugar that makes up the backbone is deoxyribose, so that's essentially the D in DNA. And then the phosphate group is acidic, and that's where you get the acid part of it. And nucleic is, hey, this was found in nuclei of cells. It is nucleic acid, deoxyribonucleic acid. But it's not, it also, it is actually mildly acidic all in total, but for every acid, it actually also has a base. And that base, those bases form the rung of the ladders."}, {"video_title": "DNA   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "And nucleic is, hey, this was found in nuclei of cells. It is nucleic acid, deoxyribonucleic acid. But it's not, it also, it is actually mildly acidic all in total, but for every acid, it actually also has a base. And that base, those bases form the rung of the ladders. And actually, each rung is a pair of bases. And as I said, that's where the information is actually stored. Well, what am I talking about?"}, {"video_title": "DNA   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "And that base, those bases form the rung of the ladders. And actually, each rung is a pair of bases. And as I said, that's where the information is actually stored. Well, what am I talking about? Well, let me talk about the four different bases that make up the rungs of a DNA molecule. So you have adenine. And so, for example, this part right over here, this section of that rung might be adenine."}, {"video_title": "DNA   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "Well, what am I talking about? Well, let me talk about the four different bases that make up the rungs of a DNA molecule. So you have adenine. And so, for example, this part right over here, this section of that rung might be adenine. Maybe this right over here is adenine. This right over here. Remember, each of these rungs are made up by, it's a pair of bases."}, {"video_title": "DNA   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "And so, for example, this part right over here, this section of that rung might be adenine. Maybe this right over here is adenine. This right over here. Remember, each of these rungs are made up by, it's a pair of bases. And that might be adenine. Maybe this is adenine. And I could stop there."}, {"video_title": "DNA   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "Remember, each of these rungs are made up by, it's a pair of bases. And that might be adenine. Maybe this is adenine. And I could stop there. I'll do a little more adenine. Maybe that's adenine right over there. And adenine always pairs with the base thymine."}, {"video_title": "DNA   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "And I could stop there. I'll do a little more adenine. Maybe that's adenine right over there. And adenine always pairs with the base thymine. So let me write that down. So adenine pairs with thymine. Thymine."}, {"video_title": "DNA   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "And adenine always pairs with the base thymine. So let me write that down. So adenine pairs with thymine. Thymine. So if that's an adenine there, then this is going to be a thymine. If this is an adenine, then this is going to be a thymine. Or if I drew the thymine first, well, I'll say, okay, it's going to pair with the adenine."}, {"video_title": "DNA   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "Thymine. So if that's an adenine there, then this is going to be a thymine. If this is an adenine, then this is going to be a thymine. Or if I drew the thymine first, well, I'll say, okay, it's going to pair with the adenine. So this is going to be a thymine right over here. This is going to be a thymine. If I were to draw this, this would be a thymine right over here."}, {"video_title": "DNA   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "Or if I drew the thymine first, well, I'll say, okay, it's going to pair with the adenine. So this is going to be a thymine right over here. This is going to be a thymine. If I were to draw this, this would be a thymine right over here. Now, the other two bases, you have cytosine, which pairs with guanine, or guanine that pairs with cytosine. So guanine. And we're not going to go into the molecular structure of these bases just yet, although these are good names to know because they show up a lot and they really form kind of the code, your genetic code."}, {"video_title": "DNA   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "If I were to draw this, this would be a thymine right over here. Now, the other two bases, you have cytosine, which pairs with guanine, or guanine that pairs with cytosine. So guanine. And we're not going to go into the molecular structure of these bases just yet, although these are good names to know because they show up a lot and they really form kind of the code, your genetic code. So guanine pairs with cytosine. Guanine and cytosine. Cytosine."}, {"video_title": "DNA   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "And we're not going to go into the molecular structure of these bases just yet, although these are good names to know because they show up a lot and they really form kind of the code, your genetic code. So guanine pairs with cytosine. Guanine and cytosine. Cytosine. So actually, if this is, let's say there's some cytosine there, let's say cytosine right over here, maybe this is cytosine, maybe this is cytosine, maybe this is cytosine, this is cytosine, and maybe this is cytosine, then it always pairs with the guanine. If we're talking about, so let's see, this is guanine then, then this will be guanine, this is guanine, this is guanine, I actually didn't draw stuff here, but this is guanine, I didn't say what these could be, but these would be made of pairs of, they could be adenine-thymine pairs, and it could be adenine on either side or the thymine on either side, and they could be made of guanine-cytosine pairs, where the guanine or the cytosine is on either side. Actually, just to make it a little bit more complete, let me just color in the rungs here as best as I can."}, {"video_title": "DNA   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "Cytosine. So actually, if this is, let's say there's some cytosine there, let's say cytosine right over here, maybe this is cytosine, maybe this is cytosine, maybe this is cytosine, this is cytosine, and maybe this is cytosine, then it always pairs with the guanine. If we're talking about, so let's see, this is guanine then, then this will be guanine, this is guanine, this is guanine, I actually didn't draw stuff here, but this is guanine, I didn't say what these could be, but these would be made of pairs of, they could be adenine-thymine pairs, and it could be adenine on either side or the thymine on either side, and they could be made of guanine-cytosine pairs, where the guanine or the cytosine is on either side. Actually, just to make it a little bit more complete, let me just color in the rungs here as best as I can. So those are guanine, so they're gonna pair with cytosine, pair with cytosine, pair with cytosine. And when it's drawn this way, you might start to see how this is essentially a code, the order of which the bases are, I guess the order in which we have these, or the sequence of these bases essentially encode the information that make you you, and you could debate, well, how much of it is nature versus nurture, and when people say nature, you know, it's literally genetic, and that's an ongoing debate, but it does code for things like your hair color, when you see that your smile is similar to your parents. It is because that information, to a large degree, is encoded genetically."}, {"video_title": "DNA   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "Actually, just to make it a little bit more complete, let me just color in the rungs here as best as I can. So those are guanine, so they're gonna pair with cytosine, pair with cytosine, pair with cytosine. And when it's drawn this way, you might start to see how this is essentially a code, the order of which the bases are, I guess the order in which we have these, or the sequence of these bases essentially encode the information that make you you, and you could debate, well, how much of it is nature versus nurture, and when people say nature, you know, it's literally genetic, and that's an ongoing debate, but it does code for things like your hair color, when you see that your smile is similar to your parents. It is because that information, to a large degree, is encoded genetically. It affects a lot of what makes you you, and actually not even just within a species, but also across species. Humans have more genetic material in common with other humans than they do with, say, a plant, but all living creatures as we know them have genetic information. This is the basis by which they are passing down their actual traits."}, {"video_title": "DNA   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "It is because that information, to a large degree, is encoded genetically. It affects a lot of what makes you you, and actually not even just within a species, but also across species. Humans have more genetic material in common with other humans than they do with, say, a plant, but all living creatures as we know them have genetic information. This is the basis by which they are passing down their actual traits. Now, you might be saying, well, how much genetic information does a human being have? And the number will either disappoint you or you might find it mind-boggling. The human genome, and every species has a different number of base pairs, to a large degree correlated with how complex they are, although not always, but the human genome has six million, sorry, not six million, six billion."}, {"video_title": "DNA   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "This is the basis by which they are passing down their actual traits. Now, you might be saying, well, how much genetic information does a human being have? And the number will either disappoint you or you might find it mind-boggling. The human genome, and every species has a different number of base pairs, to a large degree correlated with how complex they are, although not always, but the human genome has six million, sorry, not six million, six billion. Six million would be disappointing. Even billion might be disappointing. Six billion base pairs."}, {"video_title": "DNA   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "The human genome, and every species has a different number of base pairs, to a large degree correlated with how complex they are, although not always, but the human genome has six million, sorry, not six million, six billion. Six million would be disappointing. Even billion might be disappointing. Six billion base pairs. Six billion base pairs. And when you have your full complement of chromosomes, and this is in most of the cells in your body, outside of your sex cells, the sperm or the egg cells, this is going to be spread over 46 chromosomes. 46 chromosomes, or I guess you could say 23 pair of chromosomes."}, {"video_title": "DNA   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "Six billion base pairs. Six billion base pairs. And when you have your full complement of chromosomes, and this is in most of the cells in your body, outside of your sex cells, the sperm or the egg cells, this is going to be spread over 46 chromosomes. 46 chromosomes, or I guess you could say 23 pair of chromosomes. So if you divide six billion by 46, you get a little over, on average, 100 million, I think it's 100 and something million base pairs per chromosome. And some chromosomes are longer, actually some of the longest are over 200 million, and some might be shorter. That's just on average."}, {"video_title": "DNA   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "46 chromosomes, or I guess you could say 23 pair of chromosomes. So if you divide six billion by 46, you get a little over, on average, 100 million, I think it's 100 and something million base pairs per chromosome. And some chromosomes are longer, actually some of the longest are over 200 million, and some might be shorter. That's just on average. Now, this number might, to some of you, might be exciting. You're like, oh, I thought I was a simple creature. I didn't know I was this complex."}, {"video_title": "DNA   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "That's just on average. Now, this number might, to some of you, might be exciting. You're like, oh, I thought I was a simple creature. I didn't know I was this complex. Six billion, that's a lot of base pairs. That feels like a lot of information. For others of you, it might not feel so great."}, {"video_title": "DNA   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "I didn't know I was this complex. Six billion, that's a lot of base pairs. That feels like a lot of information. For others of you, it might not feel so great. You might say, hey, wait, I could store this much information on a modern thumb drive or on a hard disk. I thought I was more unique than that. And of course, we all are special and unique, but you might say, oh, six billion base pairs, I thought I was infinitely complex and whatever else, and there's some arguments for that along some other directions."}, {"video_title": "DNA   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "For others of you, it might not feel so great. You might say, hey, wait, I could store this much information on a modern thumb drive or on a hard disk. I thought I was more unique than that. And of course, we all are special and unique, but you might say, oh, six billion base pairs, I thought I was infinitely complex and whatever else, and there's some arguments for that along some other directions. But this is the approximate length, I guess you could say, the approximate size of the actual human genome. And when we talk about chromosomes, and we'll talk about chromosomes in much more depth, imagine taking this zoomed in thing that you have right over here, and over here, I don't know how many we have, like one, two, three, four, five, six, seven, eight, nine, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19. We have about 20 base pairs depicted here."}, {"video_title": "DNA   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "And of course, we all are special and unique, but you might say, oh, six billion base pairs, I thought I was infinitely complex and whatever else, and there's some arguments for that along some other directions. But this is the approximate length, I guess you could say, the approximate size of the actual human genome. And when we talk about chromosomes, and we'll talk about chromosomes in much more depth, imagine taking this zoomed in thing that you have right over here, and over here, I don't know how many we have, like one, two, three, four, five, six, seven, eight, nine, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19. We have about 20 base pairs depicted here. Imagine if you had about 200 million of these base pairs, and then you were to take this thing and you were to kind of coil it up into that thing is a chromosome. Is a chromosome. And you're saying, wait, I have that much information in most of the cells of my body?"}, {"video_title": "DNA   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "We have about 20 base pairs depicted here. Imagine if you had about 200 million of these base pairs, and then you were to take this thing and you were to kind of coil it up into that thing is a chromosome. Is a chromosome. And you're saying, wait, I have that much information in most of the cells of my body? This thing must be incredibly compact. And if you said that, I would say, yes, you are correct. This, the radius, the radius of the DNA molecule is on the order of one nanometer."}, {"video_title": "DNA   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "And you're saying, wait, I have that much information in most of the cells of my body? This thing must be incredibly compact. And if you said that, I would say, yes, you are correct. This, the radius, the radius of the DNA molecule is on the order of one nanometer. One nanometer, which is a billionth of a meter. So you can start to assess kind of the scale of this thing. This is a very dense way to actually store information."}, {"video_title": "DNA   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "This, the radius, the radius of the DNA molecule is on the order of one nanometer. One nanometer, which is a billionth of a meter. So you can start to assess kind of the scale of this thing. This is a very dense way to actually store information. But just to have an appreciation of, and you might have seen it when I was coloring in, on why the structure lends itself to being able to replicate the information or even to be able to translate or express the information, let's think about if you were to take this ladder and you were to just kind of split all the base pairs. So you just have one half of them. So you essentially have half of the ladder."}, {"video_title": "DNA   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "This is a very dense way to actually store information. But just to have an appreciation of, and you might have seen it when I was coloring in, on why the structure lends itself to being able to replicate the information or even to be able to translate or express the information, let's think about if you were to take this ladder and you were to just kind of split all the base pairs. So you just have one half of them. So you essentially have half of the ladder. And so if you only have half of the ladder, you're able to construct the other half of the ladder. Let's take an example. Let's say, and I'll just use the first letter to abbreviate for each of these bases."}, {"video_title": "DNA   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "So you essentially have half of the ladder. And so if you only have half of the ladder, you're able to construct the other half of the ladder. Let's take an example. Let's say, and I'll just use the first letter to abbreviate for each of these bases. So let's say you have some, so let's say this is one of the, this is the sugar phosphate backbone right over here. So this could be one of the sides. And let's say there's some adenine, actually, let me do them in the right color."}, {"video_title": "DNA   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "Let's say, and I'll just use the first letter to abbreviate for each of these bases. So let's say you have some, so let's say this is one of the, this is the sugar phosphate backbone right over here. So this could be one of the sides. And let's say there's some adenine, actually, let me do them in the right color. So you've got some adenine, adenine, maybe some adenine right over here. Maybe there's an adenine there. Maybe you have some thymine, thymine, maybe thymine right over here."}, {"video_title": "DNA   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "And let's say there's some adenine, actually, let me do them in the right color. So you've got some adenine, adenine, maybe some adenine right over here. Maybe there's an adenine there. Maybe you have some thymine, thymine, maybe thymine right over here. Then you have some, you have some guanine, guanine, guanine. And then let's say you have some cytosine and you have some cytosine. So with just half of this ladder, I guess you could say, you're able to construct the other half."}, {"video_title": "DNA   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "Maybe you have some thymine, thymine, maybe thymine right over here. Then you have some, you have some guanine, guanine, guanine. And then let's say you have some cytosine and you have some cytosine. So with just half of this ladder, I guess you could say, you're able to construct the other half. And that's actually how DNA replicates. This ladder splits and then each of those two halves of that ladder are able to construct versions of the other half, or versions of the other half are able to be constructed on top of that half. So how does that happen?"}, {"video_title": "DNA   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "So with just half of this ladder, I guess you could say, you're able to construct the other half. And that's actually how DNA replicates. This ladder splits and then each of those two halves of that ladder are able to construct versions of the other half, or versions of the other half are able to be constructed on top of that half. So how does that happen? Well, it's based on how these bases pair. Adenine always pairs with thymine if we're talking about DNA. So if you have an A there, you're gonna have a T on this end, T on this end."}, {"video_title": "DNA   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "So how does that happen? Well, it's based on how these bases pair. Adenine always pairs with thymine if we're talking about DNA. So if you have an A there, you're gonna have a T on this end, T on this end. T's right all over here, T right over there. If you have a T on that end, you're gonna have an A right over there, A, A. If you have a G, a guanine on this side, you're gonna have a cytosine on the other side."}, {"video_title": "DNA   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "So if you have an A there, you're gonna have a T on this end, T on this end. T's right all over here, T right over there. If you have a T on that end, you're gonna have an A right over there, A, A. If you have a G, a guanine on this side, you're gonna have a cytosine on the other side. Cytosine, cytosine, cytosine. And if you have a cytosine, you're gonna have a guanine on the other side. And so hopefully that gives you an appreciation of how DNA can replicate itself."}, {"video_title": "DNA   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "If you have a G, a guanine on this side, you're gonna have a cytosine on the other side. Cytosine, cytosine, cytosine. And if you have a cytosine, you're gonna have a guanine on the other side. And so hopefully that gives you an appreciation of how DNA can replicate itself. And as we'll see also, how this information can be translated to other forms of either related molecules, but eventually to proteins. And just to kind of round out this video, to get a real visual sense of what the DNA molecule looks like, or I guess a different visual depiction from this, I found this animated, that animated GIF that, you know, if you haven't fully digested what a double helix looks like, this is it. And you see here, you see your sugar phosphate bases here."}, {"video_title": "DNA   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "And so hopefully that gives you an appreciation of how DNA can replicate itself. And as we'll see also, how this information can be translated to other forms of either related molecules, but eventually to proteins. And just to kind of round out this video, to get a real visual sense of what the DNA molecule looks like, or I guess a different visual depiction from this, I found this animated, that animated GIF that, you know, if you haven't fully digested what a double helix looks like, this is it. And you see here, you see your sugar phosphate bases here. You see kind of the sugars and phosphate, the sugars and the phosphates alternating along this backbone. And then the rungs of the latter are these base pairs. So this is one of the bases, that's the corresponding, I guess you could say partner."}, {"video_title": "Applying the Hardy-Weinberg equation   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "So let's stick with this idea, this simplification, that there's a gene for eye color, and it only comes with two variants. It has the dominant variant, which codes for brown eye color, and it has the recessive variant, which codes for blue eye color. So if either one of your alleles is this capital B, you're gonna have brown eyes. The only way to have blue eyes is to have lowercase, is to be homozygous for the recessive allele. Now let's say that in a population, it's a large population, one that meets all of the Hardy-Weinberg equilibrium assumptions, let's say that you were to observe that 9% of this population has blue eyes. So now we're talking about the phenotype. You can actually observe that they have blue eyes."}, {"video_title": "Applying the Hardy-Weinberg equation   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "The only way to have blue eyes is to have lowercase, is to be homozygous for the recessive allele. Now let's say that in a population, it's a large population, one that meets all of the Hardy-Weinberg equilibrium assumptions, let's say that you were to observe that 9% of this population has blue eyes. So now we're talking about the phenotype. You can actually observe that they have blue eyes. So based on this, can we figure out, can we figure out P, which is the frequency of the dominant allele, can we figure this out? And can we figure out Q, which is the frequency of the recessive allele, can we figure that out as well? And I encourage you to pause this video, and based on what we saw of the Hardy-Weinberg equation, can we figure these things out, given this information?"}, {"video_title": "Applying the Hardy-Weinberg equation   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "You can actually observe that they have blue eyes. So based on this, can we figure out, can we figure out P, which is the frequency of the dominant allele, can we figure this out? And can we figure out Q, which is the frequency of the recessive allele, can we figure that out as well? And I encourage you to pause this video, and based on what we saw of the Hardy-Weinberg equation, can we figure these things out, given this information? Well, let's revisit the Hardy-Weinberg equation. We've worked it out in a previous video, but I'll rewrite it right now. It says the allele frequency for the dominant, the dominant allele frequency squared plus two times the dominant allele frequency times the recessive allele frequency plus the recessive allele frequency squared is equal to one."}, {"video_title": "Applying the Hardy-Weinberg equation   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "And I encourage you to pause this video, and based on what we saw of the Hardy-Weinberg equation, can we figure these things out, given this information? Well, let's revisit the Hardy-Weinberg equation. We've worked it out in a previous video, but I'll rewrite it right now. It says the allele frequency for the dominant, the dominant allele frequency squared plus two times the dominant allele frequency times the recessive allele frequency plus the recessive allele frequency squared is equal to one. And we saw that this just comes from the idea that P plus Q is going to be equal to one. There's a 100% chance, if you were to randomly pick a gene, that it's one of these two, one of these two variants. Now, when we say 9% has blue eyes, what does that mean?"}, {"video_title": "Applying the Hardy-Weinberg equation   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "It says the allele frequency for the dominant, the dominant allele frequency squared plus two times the dominant allele frequency times the recessive allele frequency plus the recessive allele frequency squared is equal to one. And we saw that this just comes from the idea that P plus Q is going to be equal to one. There's a 100% chance, if you were to randomly pick a gene, that it's one of these two, one of these two variants. Now, when we say 9% has blue eyes, what does that mean? Well, the only way to have blue eyes is if your genotype is homozygous recessive, because if you have a capital B in here, then you're gonna have brown eyes. So we can say that 9% also has this genotype. Or you could say that the frequency in the population of this genotype is 9%."}, {"video_title": "Applying the Hardy-Weinberg equation   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "Now, when we say 9% has blue eyes, what does that mean? Well, the only way to have blue eyes is if your genotype is homozygous recessive, because if you have a capital B in here, then you're gonna have brown eyes. So we can say that 9% also has this genotype. Or you could say that the frequency in the population of this genotype is 9%. But we've already seen that's exactly, that's exactly what this term right over here is. That's this Q squared term. This is the probability, one way to think about it, of getting, of, this is the, Q, of course, is the frequency of the recessive allele."}, {"video_title": "Applying the Hardy-Weinberg equation   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "Or you could say that the frequency in the population of this genotype is 9%. But we've already seen that's exactly, that's exactly what this term right over here is. That's this Q squared term. This is the probability, one way to think about it, of getting, of, this is the, Q, of course, is the frequency of the recessive allele. Now, this is the, you could view this as the probability of getting two of the recessive alleles is going to be, if you're in your population, it's going to be 9%. So we could say Q squared is equal to 9%. Or another way to think about it, this term right over here is 9%, or 0.09, 0.09."}, {"video_title": "Applying the Hardy-Weinberg equation   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "This is the probability, one way to think about it, of getting, of, this is the, Q, of course, is the frequency of the recessive allele. Now, this is the, you could view this as the probability of getting two of the recessive alleles is going to be, if you're in your population, it's going to be 9%. So we could say Q squared is equal to 9%. Or another way to think about it, this term right over here is 9%, or 0.09, 0.09. That's what this, 9% has this genotype, that's what this tells us right over here. So then we can solve for Q. If Q squared, I'll write it as a decimal, 0.09, that means that Q is going to be the square root of 0.09, which is equal to 0.3."}, {"video_title": "Applying the Hardy-Weinberg equation   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "Or another way to think about it, this term right over here is 9%, or 0.09, 0.09. That's what this, 9% has this genotype, that's what this tells us right over here. So then we can solve for Q. If Q squared, I'll write it as a decimal, 0.09, that means that Q is going to be the square root of 0.09, which is equal to 0.3. So just like that, we were able to figure out the allele frequency of the recessive allele. 30%, and I could write that as a percentage, 0.3, or 30%, if you were looking at the genes in the population, 30% express our code for the recessive allele, or the recessive variant. And so based on that, we can figure out what percentage code for the dominant variant."}, {"video_title": "Applying the Hardy-Weinberg equation   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "If Q squared, I'll write it as a decimal, 0.09, that means that Q is going to be the square root of 0.09, which is equal to 0.3. So just like that, we were able to figure out the allele frequency of the recessive allele. 30%, and I could write that as a percentage, 0.3, or 30%, if you were looking at the genes in the population, 30% express our code for the recessive allele, or the recessive variant. And so based on that, we can figure out what percentage code for the dominant variant. The rest of the genes must code for the dominant one, because we're assuming there's only two of them. P plus Q equal 100%, or P plus Q is equal to one. So this must be 70%."}, {"video_title": "Applying the Hardy-Weinberg equation   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "And so based on that, we can figure out what percentage code for the dominant variant. The rest of the genes must code for the dominant one, because we're assuming there's only two of them. P plus Q equal 100%, or P plus Q is equal to one. So this must be 70%. So just based on that, we can kind of dig a little bit deeper here. So what is P squared? P squared is going to be 70% squared, or 0.7 squared."}, {"video_title": "Applying the Hardy-Weinberg equation   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "So this must be 70%. So just based on that, we can kind of dig a little bit deeper here. So what is P squared? P squared is going to be 70% squared, or 0.7 squared. So this right over here is 0.7 squared, which is 0.49. So one way to think about it is, based on this, and once again, a lot of simple equation, but these really neat ideas are starting to pop out of it. Based on just this information, we're now able to say that 49% of the population is going to have a genotype of capital B, capital B."}, {"video_title": "Applying the Hardy-Weinberg equation   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "P squared is going to be 70% squared, or 0.7 squared. So this right over here is 0.7 squared, which is 0.49. So one way to think about it is, based on this, and once again, a lot of simple equation, but these really neat ideas are starting to pop out of it. Based on just this information, we're now able to say that 49% of the population is going to have a genotype of capital B, capital B. They're gonna be homozygous dominant. And then we can figure out this right over here. Two times P times Q, that's going to be two times 0.7, times 0.7, times 0.3, times 0.3."}, {"video_title": "Applying the Hardy-Weinberg equation   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "Based on just this information, we're now able to say that 49% of the population is going to have a genotype of capital B, capital B. They're gonna be homozygous dominant. And then we can figure out this right over here. Two times P times Q, that's going to be two times 0.7, times 0.7, times 0.3, times 0.3. So let's see, that's going to be two times 0.21, so this is going to be, this right over here is going to be 0.42. Or another way to think about it is, 42% of this population is going to have the genotype uppercase B and lowercase b. And you see, they all add up."}, {"video_title": "Applying the Hardy-Weinberg equation   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "Two times P times Q, that's going to be two times 0.7, times 0.7, times 0.3, times 0.3. So let's see, that's going to be two times 0.21, so this is going to be, this right over here is going to be 0.42. Or another way to think about it is, 42% of this population is going to have the genotype uppercase B and lowercase b. And you see, they all add up. 49% plus 42% is 91%, plus 9% all adds up to one, all adds up to 100%. So you get a little bit of information here, and based on what we know about allele frequencies, making a few assumptions, we're able to get a lot more knowledge about this population. And this is actually very useful in real life."}, {"video_title": "Introduction to passive and active transport   High school biology   Khan Academy.mp3", "Sentence": "Let's say that you have decided to go canoeing and right over here, this is a top view of our river right here. This is our river and let's say that the current, the river is going towards the right. So there's two different directions. So there's two different directions that you could be canoeing in. You could imagine someone who is canoeing in the same direction as the current, so they are canoeing that way, and then you could imagine another person who's canoeing the other way. So someone who's canoeing upstream. This person is canoeing downstream, this person is canoeing upstream, so they are going in that direction."}, {"video_title": "Introduction to passive and active transport   High school biology   Khan Academy.mp3", "Sentence": "So there's two different directions that you could be canoeing in. You could imagine someone who is canoeing in the same direction as the current, so they are canoeing that way, and then you could imagine another person who's canoeing the other way. So someone who's canoeing upstream. This person is canoeing downstream, this person is canoeing upstream, so they are going in that direction. So pause this video and think about which person is going to have to expend more energy or which person is going to have to be more active and which person is going to be more passive. Well, yes, this wasn't an incredibly hard question. If you are going with the flow of current, as the person in yellow is here, they don't even have to take their paddles out."}, {"video_title": "Introduction to passive and active transport   High school biology   Khan Academy.mp3", "Sentence": "This person is canoeing downstream, this person is canoeing upstream, so they are going in that direction. So pause this video and think about which person is going to have to expend more energy or which person is going to have to be more active and which person is going to be more passive. Well, yes, this wasn't an incredibly hard question. If you are going with the flow of current, as the person in yellow is here, they don't even have to take their paddles out. They can just take a nap, and the boat will naturally go with the current. They would be, they could be just moving passively, while the person in blue here, they're gonna have to work really, really, really hard. They're gonna have to paddle some just to not even move to the right, and then even paddle even more to actually go against the current."}, {"video_title": "Introduction to passive and active transport   High school biology   Khan Academy.mp3", "Sentence": "If you are going with the flow of current, as the person in yellow is here, they don't even have to take their paddles out. They can just take a nap, and the boat will naturally go with the current. They would be, they could be just moving passively, while the person in blue here, they're gonna have to work really, really, really hard. They're gonna have to paddle some just to not even move to the right, and then even paddle even more to actually go against the current. So this person would have to be very active. And so this is really just a metaphor for what we're going to talk about now, and that's the idea in biology of active versus passive transport. So let's start with maybe the more pleasant one in either situation, and that is passive transport."}, {"video_title": "Introduction to passive and active transport   High school biology   Khan Academy.mp3", "Sentence": "They're gonna have to paddle some just to not even move to the right, and then even paddle even more to actually go against the current. So this person would have to be very active. And so this is really just a metaphor for what we're going to talk about now, and that's the idea in biology of active versus passive transport. So let's start with maybe the more pleasant one in either situation, and that is passive transport. So passive transport is when something goes with the gradient. So what do I mean by that? So you could have a concentration gradient."}, {"video_title": "Introduction to passive and active transport   High school biology   Khan Academy.mp3", "Sentence": "So let's start with maybe the more pleasant one in either situation, and that is passive transport. So passive transport is when something goes with the gradient. So what do I mean by that? So you could have a concentration gradient. So let's say that on, let's say I have a tube of some kind, and let's say it's filled with water, and dissolved in that water at this end of the tube, I have a high concentration of some molecule or something right over here, while on the right-hand side, I have a low concentration. So what do we think is going to happen? Well, these things are just going to naturally move around, and over time, they're gonna bounce their way so that after a little bit of time has passed, a lot of these things are just going to passively move to the right."}, {"video_title": "Introduction to passive and active transport   High school biology   Khan Academy.mp3", "Sentence": "So you could have a concentration gradient. So let's say that on, let's say I have a tube of some kind, and let's say it's filled with water, and dissolved in that water at this end of the tube, I have a high concentration of some molecule or something right over here, while on the right-hand side, I have a low concentration. So what do we think is going to happen? Well, these things are just going to naturally move around, and over time, they're gonna bounce their way so that after a little bit of time has passed, a lot of these things are just going to passively move to the right. And so at some point, you might have an equal concentration or roughly equal throughout this entire container. And so this movement along your concentration gradient, here you're moving from high concentration to low concentration, this would be passive transport. This is a concentration gradient that we're moving along."}, {"video_title": "Introduction to passive and active transport   High school biology   Khan Academy.mp3", "Sentence": "Well, these things are just going to naturally move around, and over time, they're gonna bounce their way so that after a little bit of time has passed, a lot of these things are just going to passively move to the right. And so at some point, you might have an equal concentration or roughly equal throughout this entire container. And so this movement along your concentration gradient, here you're moving from high concentration to low concentration, this would be passive transport. This is a concentration gradient that we're moving along. Let me write that down. This is our concentration gradient. But you could also have an electrical gradient."}, {"video_title": "Introduction to passive and active transport   High school biology   Khan Academy.mp3", "Sentence": "This is a concentration gradient that we're moving along. Let me write that down. This is our concentration gradient. But you could also have an electrical gradient. So let's take a similar type of container. Maybe it's filled with water. And on the left-hand side, imagine if you have a bunch of positive particles or molecules, and on the right, you have a bunch of negative particles or molecules."}, {"video_title": "Introduction to passive and active transport   High school biology   Khan Academy.mp3", "Sentence": "But you could also have an electrical gradient. So let's take a similar type of container. Maybe it's filled with water. And on the left-hand side, imagine if you have a bunch of positive particles or molecules, and on the right, you have a bunch of negative particles or molecules. Well, the positive ones repel each other, so do the negative ones, but the positives attract the negative, and the negative attract the positive. And so you would think that things would naturally move down their electrical gradient. The positives wanna go away from each other, and they are drawn to the negative."}, {"video_title": "Introduction to passive and active transport   High school biology   Khan Academy.mp3", "Sentence": "And on the left-hand side, imagine if you have a bunch of positive particles or molecules, and on the right, you have a bunch of negative particles or molecules. Well, the positive ones repel each other, so do the negative ones, but the positives attract the negative, and the negative attract the positive. And so you would think that things would naturally move down their electrical gradient. The positives wanna go away from each other, and they are drawn to the negative. Similarly, the negatives wanna get away from each other, and they are drawn to the positive. So whether you're talking about a concentration gradient or an electrical gradient, and sometimes you have a combination of both, an electrochemical gradient, when you're moving along with your gradient, you don't have to use any energy, that's known as passive transport. So no energy needed."}, {"video_title": "Introduction to passive and active transport   High school biology   Khan Academy.mp3", "Sentence": "The positives wanna go away from each other, and they are drawn to the negative. Similarly, the negatives wanna get away from each other, and they are drawn to the positive. So whether you're talking about a concentration gradient or an electrical gradient, and sometimes you have a combination of both, an electrochemical gradient, when you're moving along with your gradient, you don't have to use any energy, that's known as passive transport. So no energy needed. It's just going to happen naturally. Now, the opposite is the notion of active transport. Active transport."}, {"video_title": "Introduction to passive and active transport   High school biology   Khan Academy.mp3", "Sentence": "So no energy needed. It's just going to happen naturally. Now, the opposite is the notion of active transport. Active transport. And this is when you go against the gradient. So an active transport would be somehow, let's say you're in this situation right over here, somehow getting one of these particles, let me do it in that same color, somehow getting one of these particles, instead of moving to go in that direction, it will actually go against its gradient in that direction. Or another situation is, imagine if you have a positive particle right over here, instead of making it, instead of it naturally just going to that direction, somehow you make it go against its gradient, and you make it go closer to the other positive particles."}, {"video_title": "Introduction to passive and active transport   High school biology   Khan Academy.mp3", "Sentence": "Active transport. And this is when you go against the gradient. So an active transport would be somehow, let's say you're in this situation right over here, somehow getting one of these particles, let me do it in that same color, somehow getting one of these particles, instead of moving to go in that direction, it will actually go against its gradient in that direction. Or another situation is, imagine if you have a positive particle right over here, instead of making it, instead of it naturally just going to that direction, somehow you make it go against its gradient, and you make it go closer to the other positive particles. Well, this is going to require energy to do. And probably the most cited example, or the most common example that we're going to see in biology class of active transport is what's known as a sodium-potassium pump, which we will study in detail in other videos. But let's say that this thing that I'm drawing here in white, this is a cell membrane."}, {"video_title": "Introduction to passive and active transport   High school biology   Khan Academy.mp3", "Sentence": "Or another situation is, imagine if you have a positive particle right over here, instead of making it, instead of it naturally just going to that direction, somehow you make it go against its gradient, and you make it go closer to the other positive particles. Well, this is going to require energy to do. And probably the most cited example, or the most common example that we're going to see in biology class of active transport is what's known as a sodium-potassium pump, which we will study in detail in other videos. But let's say that this thing that I'm drawing here in white, this is a cell membrane. And I'm drawing these gaps for a reason. And what you have on the outside of the cell membrane, you have some potassium ions on the outside, but you have a lot more on the inside. So these are all potassium ions on the inside of your cell."}, {"video_title": "Introduction to passive and active transport   High school biology   Khan Academy.mp3", "Sentence": "But let's say that this thing that I'm drawing here in white, this is a cell membrane. And I'm drawing these gaps for a reason. And what you have on the outside of the cell membrane, you have some potassium ions on the outside, but you have a lot more on the inside. So these are all potassium ions on the inside of your cell. And then, so let me just write K plus, K plus, K plus, K plus, K plus. And you'll have some sodium ions on the inside of your cell, Na plus, but you have a lot more on the outside of your cell. And in general, the outside of your cell is going to have many more positive ions than the inside."}, {"video_title": "Introduction to passive and active transport   High school biology   Khan Academy.mp3", "Sentence": "So these are all potassium ions on the inside of your cell. And then, so let me just write K plus, K plus, K plus, K plus, K plus. And you'll have some sodium ions on the inside of your cell, Na plus, but you have a lot more on the outside of your cell. And in general, the outside of your cell is going to have many more positive ions than the inside. Maybe you already see where this is going. Na plus, Na plus, Na plus. I think you get the idea."}, {"video_title": "Introduction to passive and active transport   High school biology   Khan Academy.mp3", "Sentence": "And in general, the outside of your cell is going to have many more positive ions than the inside. Maybe you already see where this is going. Na plus, Na plus, Na plus. I think you get the idea. Na plus, Na plus. Now, if on this membrane, let's ignore this part right over here. If I just had a channel right over here that was open only to potassium, so only potassium can go through."}, {"video_title": "Introduction to passive and active transport   High school biology   Khan Academy.mp3", "Sentence": "I think you get the idea. Na plus, Na plus. Now, if on this membrane, let's ignore this part right over here. If I just had a channel right over here that was open only to potassium, so only potassium can go through. So only potassium can go through this channel right over here. What do you think is going to happen? Well, you would have passive transport."}, {"video_title": "Introduction to passive and active transport   High school biology   Khan Academy.mp3", "Sentence": "If I just had a channel right over here that was open only to potassium, so only potassium can go through. So only potassium can go through this channel right over here. What do you think is going to happen? Well, you would have passive transport. These positively charged potassiums right over here, they would go down their concentration gradient. There's more likely to have a potassium ion just bump in the right way just right over here so that it goes through the channel because there's just more potassiums out on the inside of the cell than there would be on the outside. And so this, this potassium's going down their concentration gradient from high concentration to low concentration through this channel, this would be passive transport."}, {"video_title": "Introduction to passive and active transport   High school biology   Khan Academy.mp3", "Sentence": "Well, you would have passive transport. These positively charged potassiums right over here, they would go down their concentration gradient. There's more likely to have a potassium ion just bump in the right way just right over here so that it goes through the channel because there's just more potassiums out on the inside of the cell than there would be on the outside. And so this, this potassium's going down their concentration gradient from high concentration to low concentration through this channel, this would be passive transport. Passive transport. But you could imagine there's also active transport. And that active transport is what pumps the sodium ions inside the cell outside of the cell even though it's not only against its concentration gradient, it's also against its electrical gradient."}, {"video_title": "Introduction to passive and active transport   High school biology   Khan Academy.mp3", "Sentence": "And so this, this potassium's going down their concentration gradient from high concentration to low concentration through this channel, this would be passive transport. Passive transport. But you could imagine there's also active transport. And that active transport is what pumps the sodium ions inside the cell outside of the cell even though it's not only against its concentration gradient, it's also against its electrical gradient. The outside's more positive, so you wouldn't think a positive ion would naturally go outside. And the outside has more sodiums than it does inside, but the sodium potassium pump still pumps those sodiums outside. And as I hinted at, it does this using energy."}, {"video_title": "Introduction to passive and active transport   High school biology   Khan Academy.mp3", "Sentence": "And that active transport is what pumps the sodium ions inside the cell outside of the cell even though it's not only against its concentration gradient, it's also against its electrical gradient. The outside's more positive, so you wouldn't think a positive ion would naturally go outside. And the outside has more sodiums than it does inside, but the sodium potassium pump still pumps those sodiums outside. And as I hinted at, it does this using energy. So you'll sometimes see a sodium potassium pump drawn like this. And once again, I'm not gonna go into depth on it. We have a whole video on it."}, {"video_title": "Introduction to passive and active transport   High school biology   Khan Academy.mp3", "Sentence": "And as I hinted at, it does this using energy. So you'll sometimes see a sodium potassium pump drawn like this. And once again, I'm not gonna go into depth on it. We have a whole video on it. But the general idea is is that the sodiums bind over here and then some ATP, which is the powerhouse of cells, which we will study in more depth later on in biology, it leverages its energy to change the shape of the proteins that make up the sodium potassium pump to then pump these sodiums outside of the cell. So it's gonna go from this shape and then it's just going to, you could view it as opening it up that way. The real enzymes look quite different, but that's the general idea."}, {"video_title": "Hormone concentration metabolism and negative feedback   NCLEX-RN   Khan Academy.mp3", "Sentence": "When we talk about the endocrine organs and the endocrine glands, and we talk about hormones flowing all throughout the body, it's pretty easy to develop this mental image of that process happening pretty haphazardly. And so you kind of imagine hormones just coursing all throughout the body, being fired at will and sent everywhere. But if you think about the effects of the endocrine glands, like in the adrenal gland, with the fight or flight hormones, it becomes pretty important that the effects being stimulated by these hormones be well-controlled, because our body's pretty sensitive to those effects. And so it turns out that the hormone concentration in our blood at any given time is pretty tightly controlled. And one of the ways that it's controlled is through this idea of metabolism and excretion. And so for every hormone that reaches its receptor, thousands more are swept up and removed by the body. And one of the ways that they're removed is through the liver."}, {"video_title": "Hormone concentration metabolism and negative feedback   NCLEX-RN   Khan Academy.mp3", "Sentence": "And so it turns out that the hormone concentration in our blood at any given time is pretty tightly controlled. And one of the ways that it's controlled is through this idea of metabolism and excretion. And so for every hormone that reaches its receptor, thousands more are swept up and removed by the body. And one of the ways that they're removed is through the liver. And the liver will metabolize extra hormones and turn them into bile, which is ultimately excreted in the digestive system. And another organ is the kidney. And you have two of these, and they're filtering your blood all of the time."}, {"video_title": "Hormone concentration metabolism and negative feedback   NCLEX-RN   Khan Academy.mp3", "Sentence": "And one of the ways that they're removed is through the liver. And the liver will metabolize extra hormones and turn them into bile, which is ultimately excreted in the digestive system. And another organ is the kidney. And you have two of these, and they're filtering your blood all of the time. And they're removing waste products from the blood through urine. And then some hormones are actually just broken down in the blood. And then the products of that breakdown flow into the liver or the kidneys."}, {"video_title": "Hormone concentration metabolism and negative feedback   NCLEX-RN   Khan Academy.mp3", "Sentence": "And you have two of these, and they're filtering your blood all of the time. And they're removing waste products from the blood through urine. And then some hormones are actually just broken down in the blood. And then the products of that breakdown flow into the liver or the kidneys. And then sometimes you can even sweat these hormones out. But the idea here is that all of the time, for all of the hormones reaching the receptors, a lot are just swept up and removed from the body. And another way that concentrations of hormones in the body are controlled are through feedback loops."}, {"video_title": "Hormone concentration metabolism and negative feedback   NCLEX-RN   Khan Academy.mp3", "Sentence": "And then the products of that breakdown flow into the liver or the kidneys. And then sometimes you can even sweat these hormones out. But the idea here is that all of the time, for all of the hormones reaching the receptors, a lot are just swept up and removed from the body. And another way that concentrations of hormones in the body are controlled are through feedback loops. And the majority of feedback loops are what we consider to be negative feedback loops. And the idea behind negative feedback loops is that conditions resulting from the hormone action suppress further release of those hormones. And that can be a pretty confusing idea."}, {"video_title": "Hormone concentration metabolism and negative feedback   NCLEX-RN   Khan Academy.mp3", "Sentence": "And another way that concentrations of hormones in the body are controlled are through feedback loops. And the majority of feedback loops are what we consider to be negative feedback loops. And the idea behind negative feedback loops is that conditions resulting from the hormone action suppress further release of those hormones. And that can be a pretty confusing idea. So I'm going to draw out an example. So we have the hypothalamus here. I'm going to draw it in."}, {"video_title": "Hormone concentration metabolism and negative feedback   NCLEX-RN   Khan Academy.mp3", "Sentence": "And that can be a pretty confusing idea. So I'm going to draw out an example. So we have the hypothalamus here. I'm going to draw it in. And I'll write it down. And the hypothalamus releases a hormone, thyroid-releasing hormone, so TRH. And it releases it, and it goes down to the pituitary gland, which I'll draw in, and right here."}, {"video_title": "Hormone concentration metabolism and negative feedback   NCLEX-RN   Khan Academy.mp3", "Sentence": "I'm going to draw it in. And I'll write it down. And the hypothalamus releases a hormone, thyroid-releasing hormone, so TRH. And it releases it, and it goes down to the pituitary gland, which I'll draw in, and right here. And in response to TRH, the pituitary gland releases thyroid-stimulating hormone, or TSH. And TSH goes down to the thyroid glands, which would be about right here. And the thyroid gland releases its hormones, T3, or triiodothyronine, and thyroxine."}, {"video_title": "Hormone concentration metabolism and negative feedback   NCLEX-RN   Khan Academy.mp3", "Sentence": "And it releases it, and it goes down to the pituitary gland, which I'll draw in, and right here. And in response to TRH, the pituitary gland releases thyroid-stimulating hormone, or TSH. And TSH goes down to the thyroid glands, which would be about right here. And the thyroid gland releases its hormones, T3, or triiodothyronine, and thyroxine. And these thyroid hormones travel all throughout the body in search of the receptors in order to, let's say, upregulate metabolism. That's one of the major jobs of the thyroid glands. And so here's where the idea becomes pretty cool, because some of the receptors are located on the pituitary gland and the hypothalamus."}, {"video_title": "Hormone concentration metabolism and negative feedback   NCLEX-RN   Khan Academy.mp3", "Sentence": "And the thyroid gland releases its hormones, T3, or triiodothyronine, and thyroxine. And these thyroid hormones travel all throughout the body in search of the receptors in order to, let's say, upregulate metabolism. That's one of the major jobs of the thyroid glands. And so here's where the idea becomes pretty cool, because some of the receptors are located on the pituitary gland and the hypothalamus. And as the thyroid hormones reach the pituitary and the hypothalamus, they signal the hypothalamus and pituitary gland to stop making their hormones. And the hypothalamus and pituitary glands see that we have enough thyroid hormones in the blood and that they don't need to make any anymore. And so this is a major way that the thyroid hormone levels in the body are controlled."}, {"video_title": "Hormone concentration metabolism and negative feedback   NCLEX-RN   Khan Academy.mp3", "Sentence": "And so here's where the idea becomes pretty cool, because some of the receptors are located on the pituitary gland and the hypothalamus. And as the thyroid hormones reach the pituitary and the hypothalamus, they signal the hypothalamus and pituitary gland to stop making their hormones. And the hypothalamus and pituitary glands see that we have enough thyroid hormones in the blood and that they don't need to make any anymore. And so this is a major way that the thyroid hormone levels in the body are controlled. And you might say, hey, that sounds a little bit redundant. I mean, if the hypothalamus can be turned off by the thyroid hormones and it's upstream from the pituitary gland, why does the pituitary gland even have to have these receptors? But the redundancy is really just a reflection of how important feedback control is and how important the concentration of hormones in the body is."}, {"video_title": "Introduction to Evolution and Natural Selection (2).mp3", "Sentence": "And that's the idea of evolution. And whenever we hear this word, I mean, even if we don't hear it in the biological context, we imagine that something is changing. It is evolving. And so when people use the word evolution in our everyday context, they think of this notion of change, that this is going to test my drawing ability. But you see an ape, bunt over. We've all seen this picture at the Natural Museum, and he's walking hunchback like that, and his head's bent down. And I'm doing my best."}, {"video_title": "Introduction to Evolution and Natural Selection (2).mp3", "Sentence": "And so when people use the word evolution in our everyday context, they think of this notion of change, that this is going to test my drawing ability. But you see an ape, bunt over. We've all seen this picture at the Natural Museum, and he's walking hunchback like that, and his head's bent down. And I'm doing my best. That's the ape. Maybe he's also wearing a hat. And then they show this picture where he slowly, slowly becomes more and more upright."}, {"video_title": "Introduction to Evolution and Natural Selection (2).mp3", "Sentence": "And I'm doing my best. That's the ape. Maybe he's also wearing a hat. And then they show this picture where he slowly, slowly becomes more and more upright. And eventually, he turns into some dude who's just walking on his way to work, also just as happy. And now he's walking completely upright. And it's some kind of implication that walking upright is better than not walking upright, et cetera, et cetera."}, {"video_title": "Introduction to Evolution and Natural Selection (2).mp3", "Sentence": "And then they show this picture where he slowly, slowly becomes more and more upright. And eventually, he turns into some dude who's just walking on his way to work, also just as happy. And now he's walking completely upright. And it's some kind of implication that walking upright is better than not walking upright, et cetera, et cetera. Oh, he doesn't have a tail anymore. Let me eliminate that. This guy does have a tail."}, {"video_title": "Introduction to Evolution and Natural Selection (2).mp3", "Sentence": "And it's some kind of implication that walking upright is better than not walking upright, et cetera, et cetera. Oh, he doesn't have a tail anymore. Let me eliminate that. This guy does have a tail. Let me do it in an appropriate width. This guy has a tail, so you're going to have to excuse my drawing skills. But we've all seen this."}, {"video_title": "Introduction to Evolution and Natural Selection (2).mp3", "Sentence": "This guy does have a tail. Let me do it in an appropriate width. This guy has a tail, so you're going to have to excuse my drawing skills. But we've all seen this. If you've ever gone to a natural history museum, they'll just make more and more upright apes. And eventually, you get to a human being. And it's this idea that the apes somehow changed into a human being."}, {"video_title": "Introduction to Evolution and Natural Selection (2).mp3", "Sentence": "But we've all seen this. If you've ever gone to a natural history museum, they'll just make more and more upright apes. And eventually, you get to a human being. And it's this idea that the apes somehow changed into a human being. And I've seen this in multiple contexts, even inside of biology classes and even the scientific community. They'll say, oh, the ape evolved into the human, or the ape evolved into the pre-human, the guy that almost stood upright. The guy that was a little bit hunched back, so he looked a little bit like an ape and a little bit like a human, and so on and so forth."}, {"video_title": "Introduction to Evolution and Natural Selection (2).mp3", "Sentence": "And it's this idea that the apes somehow changed into a human being. And I've seen this in multiple contexts, even inside of biology classes and even the scientific community. They'll say, oh, the ape evolved into the human, or the ape evolved into the pre-human, the guy that almost stood upright. The guy that was a little bit hunched back, so he looked a little bit like an ape and a little bit like a human, and so on and so forth. And I want to be very clear here. Even though this process did happen, that you did have creatures that over time accumulated changes that maybe their ancestors might have looked more like this, and eventually they looked more like this, there was no active process going on called evolution. It's not like the ape said, gee, I would like my kids to look more like this dude, so somehow I'm going to get my DNA to get enough changes to look more like this."}, {"video_title": "Introduction to Evolution and Natural Selection (2).mp3", "Sentence": "The guy that was a little bit hunched back, so he looked a little bit like an ape and a little bit like a human, and so on and so forth. And I want to be very clear here. Even though this process did happen, that you did have creatures that over time accumulated changes that maybe their ancestors might have looked more like this, and eventually they looked more like this, there was no active process going on called evolution. It's not like the ape said, gee, I would like my kids to look more like this dude, so somehow I'm going to get my DNA to get enough changes to look more like this. And it's not like the DNA knew. The DNA didn't say, hey, it is better to be walking than to be kind of hunched back like an ape, and so therefore, I am going to try to somehow spontaneously change into this dude. That's not what evolution is."}, {"video_title": "Introduction to Evolution and Natural Selection (2).mp3", "Sentence": "It's not like the ape said, gee, I would like my kids to look more like this dude, so somehow I'm going to get my DNA to get enough changes to look more like this. And it's not like the DNA knew. The DNA didn't say, hey, it is better to be walking than to be kind of hunched back like an ape, and so therefore, I am going to try to somehow spontaneously change into this dude. That's not what evolution is. It's not like some people imagine that maybe there's a tree, and on that tree there's a bunch of good fruit at the top of the tree. Maybe they're apples. And then maybe you have some type of cow-like creature, or maybe it's some type of horse-like creature that says, gee, I would like to get to those apples."}, {"video_title": "Introduction to Evolution and Natural Selection (2).mp3", "Sentence": "That's not what evolution is. It's not like some people imagine that maybe there's a tree, and on that tree there's a bunch of good fruit at the top of the tree. Maybe they're apples. And then maybe you have some type of cow-like creature, or maybe it's some type of horse-like creature that says, gee, I would like to get to those apples. And that just because they want to get there, maybe the next generation, they keep trying to raise their neck. And then after generation after generation, their necks get longer and longer, and eventually they turn into giraffes. That is not what evolution is, and that's not what it implies."}, {"video_title": "Introduction to Evolution and Natural Selection (2).mp3", "Sentence": "And then maybe you have some type of cow-like creature, or maybe it's some type of horse-like creature that says, gee, I would like to get to those apples. And that just because they want to get there, maybe the next generation, they keep trying to raise their neck. And then after generation after generation, their necks get longer and longer, and eventually they turn into giraffes. That is not what evolution is, and that's not what it implies. Although sometimes the everyday notion of the word seems to make us think that way. What evolution is, and actually this is the word that I prefer to use, it's natural selection. Natural selection, let me write that word down."}, {"video_title": "Introduction to Evolution and Natural Selection (2).mp3", "Sentence": "That is not what evolution is, and that's not what it implies. Although sometimes the everyday notion of the word seems to make us think that way. What evolution is, and actually this is the word that I prefer to use, it's natural selection. Natural selection, let me write that word down. And literally what it means is that in any population of living organisms, you're going to have some variation. And this is an important key word here. Variation just means, look, there's just some change."}, {"video_title": "Introduction to Evolution and Natural Selection (2).mp3", "Sentence": "Natural selection, let me write that word down. And literally what it means is that in any population of living organisms, you're going to have some variation. And this is an important key word here. Variation just means, look, there's just some change. If you look at the kids in your school, you'll see variation. Some people are tall, some people are short, some people have blonde hair, some people have black hair, so on and so forth. There's always variation."}, {"video_title": "Introduction to Evolution and Natural Selection (2).mp3", "Sentence": "Variation just means, look, there's just some change. If you look at the kids in your school, you'll see variation. Some people are tall, some people are short, some people have blonde hair, some people have black hair, so on and so forth. There's always variation. And what natural selection is, is this process that sometimes environmental factors will select for certain variations. Some variations might not matter at all, but some variations matter a lot. One example that's given in every biology book, but it really is interesting."}, {"video_title": "Introduction to Evolution and Natural Selection (2).mp3", "Sentence": "There's always variation. And what natural selection is, is this process that sometimes environmental factors will select for certain variations. Some variations might not matter at all, but some variations matter a lot. One example that's given in every biology book, but it really is interesting. I believe they're called the peppered moth, and this was pre-industrial revolution England. Most peppered moths, there was just this variation. Some of them were, I guess we could call them more peppered than others."}, {"video_title": "Introduction to Evolution and Natural Selection (2).mp3", "Sentence": "One example that's given in every biology book, but it really is interesting. I believe they're called the peppered moth, and this was pre-industrial revolution England. Most peppered moths, there was just this variation. Some of them were, I guess we could call them more peppered than others. So some of them might look like this. So it had spots like that. Some of them might have looked more like that."}, {"video_title": "Introduction to Evolution and Natural Selection (2).mp3", "Sentence": "Some of them were, I guess we could call them more peppered than others. So some of them might look like this. So it had spots like that. Some of them might have looked more like that. And of course, they had some black spots on them. And then some of them might have been, you know, just barely have any spots. You just have this natural variation."}, {"video_title": "Introduction to Evolution and Natural Selection (2).mp3", "Sentence": "Some of them might have looked more like that. And of course, they had some black spots on them. And then some of them might have been, you know, just barely have any spots. You just have this natural variation. Like you'd see in any population of animals, you'll see some variation in colors. Now, they were all happy probably for thousands of years, just this natural variation. It was a non-important trait for these peppered moths."}, {"video_title": "Introduction to Evolution and Natural Selection (2).mp3", "Sentence": "You just have this natural variation. Like you'd see in any population of animals, you'll see some variation in colors. Now, they were all happy probably for thousands of years, just this natural variation. It was a non-important trait for these peppered moths. But then all of a sudden, the Industrial Revolution happens in England, and all this soot gets released from all of these factories that are running these steam engines powered by coal. And so all of a sudden, a lot of the things that once were gray or white, for example, maybe some tree trunks. Let me draw some tree trunks."}, {"video_title": "Introduction to Evolution and Natural Selection (2).mp3", "Sentence": "It was a non-important trait for these peppered moths. But then all of a sudden, the Industrial Revolution happens in England, and all this soot gets released from all of these factories that are running these steam engines powered by coal. And so all of a sudden, a lot of the things that once were gray or white, for example, maybe some tree trunks. Let me draw some tree trunks. Maybe there were some tree trunks that used to look like this. Maybe some tree trunks used to look something like this. And a peppered moth would be pretty OK. And maybe there were some tree trunks that were pretty dark."}, {"video_title": "Introduction to Evolution and Natural Selection (2).mp3", "Sentence": "Let me draw some tree trunks. Maybe there were some tree trunks that used to look like this. Maybe some tree trunks used to look something like this. And a peppered moth would be pretty OK. And maybe there were some tree trunks that were pretty dark. But all of a sudden, the Industrial Revolution happens. Everything gets covered with soot from the coal being burned. And then all of a sudden, all the trees look like this."}, {"video_title": "Introduction to Evolution and Natural Selection (2).mp3", "Sentence": "And a peppered moth would be pretty OK. And maybe there were some tree trunks that were pretty dark. But all of a sudden, the Industrial Revolution happens. Everything gets covered with soot from the coal being burned. And then all of a sudden, all the trees look like this. They're just completely pitch black, or they're a lot darker than they were before. Now, all of a sudden, you've had a major change to these moths' environment. And you have to think, what is going to select for these moths?"}, {"video_title": "Introduction to Evolution and Natural Selection (2).mp3", "Sentence": "And then all of a sudden, all the trees look like this. They're just completely pitch black, or they're a lot darker than they were before. Now, all of a sudden, you've had a major change to these moths' environment. And you have to think, what is going to select for these moths? Well, one thing that might get these moths are birds and the ability of the birds to see the moths. So all of a sudden, if the environment became a lot blacker than it was before, you can guess what's going to happen. The birds are going to see this dude a lot easier than they're going to see this dude."}, {"video_title": "Introduction to Evolution and Natural Selection (2).mp3", "Sentence": "And you have to think, what is going to select for these moths? Well, one thing that might get these moths are birds and the ability of the birds to see the moths. So all of a sudden, if the environment became a lot blacker than it was before, you can guess what's going to happen. The birds are going to see this dude a lot easier than they're going to see this dude. Because this dude on a black background, he's going to be a lot harder to see. And it's not like the birds won't catch this guy. They'll catch all of them."}, {"video_title": "Introduction to Evolution and Natural Selection (2).mp3", "Sentence": "The birds are going to see this dude a lot easier than they're going to see this dude. Because this dude on a black background, he's going to be a lot harder to see. And it's not like the birds won't catch this guy. They'll catch all of them. But they're going to catch this guy a lot more frequently. So you can imagine what happens. If the birds start catching these guys before they can reproduce, or maybe while they're reproducing, what's going to happen?"}, {"video_title": "Introduction to Evolution and Natural Selection (2).mp3", "Sentence": "They'll catch all of them. But they're going to catch this guy a lot more frequently. So you can imagine what happens. If the birds start catching these guys before they can reproduce, or maybe while they're reproducing, what's going to happen? This guy, the darker dudes, are going to reproduce a lot more often. And all of a sudden, you're going to have a lot more moths that look like this. You're going to have a lot more of these dudes."}, {"video_title": "Introduction to Evolution and Natural Selection (2).mp3", "Sentence": "If the birds start catching these guys before they can reproduce, or maybe while they're reproducing, what's going to happen? This guy, the darker dudes, are going to reproduce a lot more often. And all of a sudden, you're going to have a lot more moths that look like this. You're going to have a lot more of these dudes. So what happened here? Was there any design, or was there any active change by any of the moths? I mean, it looks like a really smart thing to do, to become black, right?"}, {"video_title": "Introduction to Evolution and Natural Selection (2).mp3", "Sentence": "You're going to have a lot more of these dudes. So what happened here? Was there any design, or was there any active change by any of the moths? I mean, it looks like a really smart thing to do, to become black, right? Your surrounding became black, and you wait a couple of generations of these moths, and now all of a sudden, the moths are black. And you might say, wow, those moths are geniuses. They all somehow decided to evolve into black moths in order to hide from the birds more easily."}, {"video_title": "Introduction to Evolution and Natural Selection (2).mp3", "Sentence": "I mean, it looks like a really smart thing to do, to become black, right? Your surrounding became black, and you wait a couple of generations of these moths, and now all of a sudden, the moths are black. And you might say, wow, those moths are geniuses. They all somehow decided to evolve into black moths in order to hide from the birds more easily. But that's not what happened. You had a lot of variation in your peppered moth population. And what happened was that when everything turned darker and darker, these dudes right here, or dudettes, had a lot less success in reproducing."}, {"video_title": "Introduction to Evolution and Natural Selection (2).mp3", "Sentence": "They all somehow decided to evolve into black moths in order to hide from the birds more easily. But that's not what happened. You had a lot of variation in your peppered moth population. And what happened was that when everything turned darker and darker, these dudes right here, or dudettes, had a lot less success in reproducing. These guys just reproduced more and more and more. And these guys got eaten up before they were able to do, so maybe while they were reproducing, so that they couldn't produce as many offspring. And then this trait just became dominant."}, {"video_title": "Introduction to Evolution and Natural Selection (2).mp3", "Sentence": "And what happened was that when everything turned darker and darker, these dudes right here, or dudettes, had a lot less success in reproducing. These guys just reproduced more and more and more. And these guys got eaten up before they were able to do, so maybe while they were reproducing, so that they couldn't produce as many offspring. And then this trait just became dominant. And then the peppered moth just became, you can kind of view it as a black moth. Now you might say, OK, Sal, that's one example. I need more."}, {"video_title": "Introduction to Evolution and Natural Selection (2).mp3", "Sentence": "And then this trait just became dominant. And then the peppered moth just became, you can kind of view it as a black moth. Now you might say, OK, Sal, that's one example. I need more. This is natural selection. It's purported to apply to everything. It purports to explain why we evolved from basic bacteria, or maybe even self-replicating RNA, which I will talk about more in the future."}, {"video_title": "Introduction to Evolution and Natural Selection (2).mp3", "Sentence": "I need more. This is natural selection. It's purported to apply to everything. It purports to explain why we evolved from basic bacteria, or maybe even self-replicating RNA, which I will talk about more in the future. I need more evidence of this. I need to see it in real time. And the best example of this is really the flu."}, {"video_title": "Introduction to Evolution and Natural Selection (2).mp3", "Sentence": "It purports to explain why we evolved from basic bacteria, or maybe even self-replicating RNA, which I will talk about more in the future. I need more evidence of this. I need to see it in real time. And the best example of this is really the flu. And I'll do other videos in the future on what viruses are and how they replicate. And viruses are actually fascinating, because it's not even clear that they're alive. They're literally just little buckets of DNA and sometimes RNA, which we'll learn is genetic information."}, {"video_title": "Introduction to Evolution and Natural Selection (2).mp3", "Sentence": "And the best example of this is really the flu. And I'll do other videos in the future on what viruses are and how they replicate. And viruses are actually fascinating, because it's not even clear that they're alive. They're literally just little buckets of DNA and sometimes RNA, which we'll learn is genetic information. And they're just contained in these viral, these little protein containers that are these neat geometrical shapes. And that's all they are. They really don't have, you know, they're not like regular living organisms that actively move and that actively have metabolisms and all that."}, {"video_title": "Introduction to Evolution and Natural Selection (2).mp3", "Sentence": "They're literally just little buckets of DNA and sometimes RNA, which we'll learn is genetic information. And they're just contained in these viral, these little protein containers that are these neat geometrical shapes. And that's all they are. They really don't have, you know, they're not like regular living organisms that actively move and that actively have metabolisms and all that. What they do is they take that little DNA and they inject it into other things that can process it. And then they use that DNA to produce more viruses. But anyway, we could do a whole series of videos on viruses."}, {"video_title": "Introduction to Evolution and Natural Selection (2).mp3", "Sentence": "They really don't have, you know, they're not like regular living organisms that actively move and that actively have metabolisms and all that. What they do is they take that little DNA and they inject it into other things that can process it. And then they use that DNA to produce more viruses. But anyway, we could do a whole series of videos on viruses. But the flu is a virus. And what happens every year is you have a certain type of virus and they have some variation. And I'll just make the variation by, I don't know, how many dots they have."}, {"video_title": "Introduction to Evolution and Natural Selection (2).mp3", "Sentence": "But anyway, we could do a whole series of videos on viruses. But the flu is a virus. And what happens every year is you have a certain type of virus and they have some variation. And I'll just make the variation by, I don't know, how many dots they have. And they infect, let's say it's a human flu, they infect humans, and slowly our immune systems, which we can make a whole set of videos on as well, start to recognize the virus and are able to attack them before they can do a lot of damage. So now you can imagine what happens if, let's say that this is the current flu. Let me do all of them."}, {"video_title": "Introduction to Evolution and Natural Selection (2).mp3", "Sentence": "And I'll just make the variation by, I don't know, how many dots they have. And they infect, let's say it's a human flu, they infect humans, and slowly our immune systems, which we can make a whole set of videos on as well, start to recognize the virus and are able to attack them before they can do a lot of damage. So now you can imagine what happens if, let's say that this is the current flu. Let me do all of them. They all have these little two dots and that's how, and we'll talk in the future what these dots are and how they can be recognized, but let's say that's how our immune system recognize them. They start realizing, oh, any time I get this little green dude with two dots on it, that's not a good thing to have around, so I'm going to attack it in some way and destroy it before he infects my DNA and all the rest. And so you have a very strong natural selection once immune systems learn what this virus is, and we'll talk more about what learning means for an immune system, that they'll start attacking these guys."}, {"video_title": "Introduction to Evolution and Natural Selection (2).mp3", "Sentence": "Let me do all of them. They all have these little two dots and that's how, and we'll talk in the future what these dots are and how they can be recognized, but let's say that's how our immune system recognize them. They start realizing, oh, any time I get this little green dude with two dots on it, that's not a good thing to have around, so I'm going to attack it in some way and destroy it before he infects my DNA and all the rest. And so you have a very strong natural selection once immune systems learn what this virus is, and we'll talk more about what learning means for an immune system, that they'll start attacking these guys. But flu, you can kind of think of them as being tricky, but they're not really tricky. They're not sentient objects, but what they do do is they constantly change. So what you have is, in any flu population, you're always having a little bit of change."}, {"video_title": "Introduction to Evolution and Natural Selection (2).mp3", "Sentence": "And so you have a very strong natural selection once immune systems learn what this virus is, and we'll talk more about what learning means for an immune system, that they'll start attacking these guys. But flu, you can kind of think of them as being tricky, but they're not really tricky. They're not sentient objects, but what they do do is they constantly change. So what you have is, in any flu population, you're always having a little bit of change. So maybe the great majority of them have those two dots, but maybe every now and then one of them has one dot, one of them has three dots, and maybe that's just a random mutation. This just randomly happened. Maybe one in every million of these viruses have this only one dot instead of two dots."}, {"video_title": "Introduction to Evolution and Natural Selection (2).mp3", "Sentence": "So what you have is, in any flu population, you're always having a little bit of change. So maybe the great majority of them have those two dots, but maybe every now and then one of them has one dot, one of them has three dots, and maybe that's just a random mutation. This just randomly happened. Maybe one in every million of these viruses have this only one dot instead of two dots. But what's going to happen as soon as, let's say, the human immune system gets used to attacking the virus with the two red dots? Well, then this guy isn't going to have to compete with the other virus capsules for infecting people. He's going to have people's DNA all to himself."}, {"video_title": "Introduction to Evolution and Natural Selection (2).mp3", "Sentence": "Maybe one in every million of these viruses have this only one dot instead of two dots. But what's going to happen as soon as, let's say, the human immune system gets used to attacking the virus with the two red dots? Well, then this guy isn't going to have to compete with the other virus capsules for infecting people. He's going to have people's DNA all to himself. And so he or she or whatever you want to call this virus is then going to be more successful. So by next year's flu season, when people start sneezing and are able to spread it on doorknobs and whatever else again, this guy is going to be the new flu virus. So when you see this process of every year there's a new flu virus, that is evolution and natural selection in real time."}, {"video_title": "Introduction to Evolution and Natural Selection (2).mp3", "Sentence": "He's going to have people's DNA all to himself. And so he or she or whatever you want to call this virus is then going to be more successful. So by next year's flu season, when people start sneezing and are able to spread it on doorknobs and whatever else again, this guy is going to be the new flu virus. So when you see this process of every year there's a new flu virus, that is evolution and natural selection in real time. It is happening. It isn't this thing that only happens over eons and eons of time, although most of the substantial things that we see in our lives or even ourselves are based on these things that happened over eons and eons of time. But it happens on a yearly basis."}, {"video_title": "Introduction to Evolution and Natural Selection (2).mp3", "Sentence": "So when you see this process of every year there's a new flu virus, that is evolution and natural selection in real time. It is happening. It isn't this thing that only happens over eons and eons of time, although most of the substantial things that we see in our lives or even ourselves are based on these things that happened over eons and eons of time. But it happens on a yearly basis. Another example is if you think about antibiotics and bacteria. Bacteria are these little cells that move around. And we'll talk more about them."}, {"video_title": "Introduction to Evolution and Natural Selection (2).mp3", "Sentence": "But it happens on a yearly basis. Another example is if you think about antibiotics and bacteria. Bacteria are these little cells that move around. And we'll talk more about them. They actually are definitely living. They have metabolisms and whatever else. And this is just a nice note."}, {"video_title": "Introduction to Evolution and Natural Selection (2).mp3", "Sentence": "And we'll talk more about them. They actually are definitely living. They have metabolisms and whatever else. And this is just a nice note. When people talk about infections, it could either be a viral infection, which are these things that go and infect your DNA and then use your cell mechanisms to reproduce. Or it could be a bacterial infection, which are literally little cells that move around and they release toxins that make you sick and whatever else. So bacteria, these are what antibiotics kill."}, {"video_title": "Introduction to Evolution and Natural Selection (2).mp3", "Sentence": "And this is just a nice note. When people talk about infections, it could either be a viral infection, which are these things that go and infect your DNA and then use your cell mechanisms to reproduce. Or it could be a bacterial infection, which are literally little cells that move around and they release toxins that make you sick and whatever else. So bacteria, these are what antibiotics kill. They attack bacteria. They kill them. Now, you probably, if you know a couple of doctors or whatever, and you say, hey, I'm sick."}, {"video_title": "Introduction to Evolution and Natural Selection (2).mp3", "Sentence": "So bacteria, these are what antibiotics kill. They attack bacteria. They kill them. Now, you probably, if you know a couple of doctors or whatever, and you say, hey, I'm sick. I think I have a bacterial infection. Give me some antibiotics. A responsible doctor says, no, I won't give you antibiotics just willy-nilly, because what happens is the more antibiotics you use, you're more likely to create versions and I want to be very careful about the word create, because you're not actively creating them."}, {"video_title": "Introduction to Evolution and Natural Selection (2).mp3", "Sentence": "Now, you probably, if you know a couple of doctors or whatever, and you say, hey, I'm sick. I think I have a bacterial infection. Give me some antibiotics. A responsible doctor says, no, I won't give you antibiotics just willy-nilly, because what happens is the more antibiotics you use, you're more likely to create versions and I want to be very careful about the word create, because you're not actively creating them. But let's say, and let me finish my sentence, you're very likely to help select for antibiotic-resistant bacterias. Now, how does that work? So let's say that these are all bacteria and you have gazillions of them, right?"}, {"video_title": "Introduction to Evolution and Natural Selection (2).mp3", "Sentence": "A responsible doctor says, no, I won't give you antibiotics just willy-nilly, because what happens is the more antibiotics you use, you're more likely to create versions and I want to be very careful about the word create, because you're not actively creating them. But let's say, and let me finish my sentence, you're very likely to help select for antibiotic-resistant bacterias. Now, how does that work? So let's say that these are all bacteria and you have gazillions of them, right? And every now and then you get one that's slightly different. Now, in a population of bacteria, these all will make you equally sick, and this is just some random difference in the bacteria, maybe on its DNA some slight different changes happened, but whatever happened. These all are the kind of bacteria, you don't want to get a lot of them in your system."}, {"video_title": "Introduction to Evolution and Natural Selection (2).mp3", "Sentence": "So let's say that these are all bacteria and you have gazillions of them, right? And every now and then you get one that's slightly different. Now, in a population of bacteria, these all will make you equally sick, and this is just some random difference in the bacteria, maybe on its DNA some slight different changes happened, but whatever happened. These all are the kind of bacteria, you don't want to get a lot of them in your system. Your immune system can attack them and fight them off, but if you get a lot of them, they might kill you or make you sick or whatever else. Now, if everyone just starts using antibiotics when they're not sick or when they don't really need to in a life or death situation, you might have an antibiotic that is really good at killing the green bacteria. But what happens if you all of a sudden kill a lot of the green bacteria?"}, {"video_title": "Introduction to Evolution and Natural Selection (2).mp3", "Sentence": "These all are the kind of bacteria, you don't want to get a lot of them in your system. Your immune system can attack them and fight them off, but if you get a lot of them, they might kill you or make you sick or whatever else. Now, if everyone just starts using antibiotics when they're not sick or when they don't really need to in a life or death situation, you might have an antibiotic that is really good at killing the green bacteria. But what happens if you all of a sudden kill a lot of the green bacteria? Well, now the blue bacteria have the whole ecosystem that before it was competing with all these green dudes to get all the good stuff inside of your body, but now he's all alone, and now he can replicate willy-nilly. So now he's going to replicate willy-nilly. And this is, once again, it wasn't like there was any design, there was any intelligent process here that said, look, some bacteria said, I'm going to be a little bit smarter and design myself to resist this antibiotic threat."}, {"video_title": "Introduction to Evolution and Natural Selection (2).mp3", "Sentence": "But what happens if you all of a sudden kill a lot of the green bacteria? Well, now the blue bacteria have the whole ecosystem that before it was competing with all these green dudes to get all the good stuff inside of your body, but now he's all alone, and now he can replicate willy-nilly. So now he's going to replicate willy-nilly. And this is, once again, it wasn't like there was any design, there was any intelligent process here that said, look, some bacteria said, I'm going to be a little bit smarter and design myself to resist this antibiotic threat. No. There's just these random changes that happen, and mutations and viruses and bacteria happen frequently. And there are these random changes that happen."}, {"video_title": "Introduction to Evolution and Natural Selection (2).mp3", "Sentence": "And this is, once again, it wasn't like there was any design, there was any intelligent process here that said, look, some bacteria said, I'm going to be a little bit smarter and design myself to resist this antibiotic threat. No. There's just these random changes that happen, and mutations and viruses and bacteria happen frequently. And there are these random changes that happen. And this might be a one in a billion change. But all of a sudden, if you start killing off all of the people that it's competing with, this guy can start replicating really fast and then become the dominant bacteria. And then all of a sudden, that antibiotic that you had developed very carefully to destroy the green dudes is useless."}, {"video_title": "Introduction to Evolution and Natural Selection (2).mp3", "Sentence": "And there are these random changes that happen. And this might be a one in a billion change. But all of a sudden, if you start killing off all of the people that it's competing with, this guy can start replicating really fast and then become the dominant bacteria. And then all of a sudden, that antibiotic that you had developed very carefully to destroy the green dudes is useless. And you have this superbug. You might have heard the word superbug. That's what a superbug is."}, {"video_title": "Introduction to Evolution and Natural Selection (2).mp3", "Sentence": "And then all of a sudden, that antibiotic that you had developed very carefully to destroy the green dudes is useless. And you have this superbug. You might have heard the word superbug. That's what a superbug is. It's not like it designed itself somehow. It's just that we got very good at killing its competition, and so we allowed it to take over. And we can't kill it because all of the drugs were just good at killing its competition."}, {"video_title": "Introduction to Evolution and Natural Selection (2).mp3", "Sentence": "That's what a superbug is. It's not like it designed itself somehow. It's just that we got very good at killing its competition, and so we allowed it to take over. And we can't kill it because all of the drugs were just good at killing its competition. That these bacteria just keep mutating and keep mutating. And if we use these antibiotics a little bit too heavily, we'll always be selecting for the things that won't be affected by the antibiotics. Well, anyway, I think I've spoken long enough."}, {"video_title": "Introduction to Evolution and Natural Selection (2).mp3", "Sentence": "And we can't kill it because all of the drugs were just good at killing its competition. That these bacteria just keep mutating and keep mutating. And if we use these antibiotics a little bit too heavily, we'll always be selecting for the things that won't be affected by the antibiotics. Well, anyway, I think I've spoken long enough. But this is a fascinating, fascinating topic. And I really wanted to make this my very first video or lecture, if you will, on biology. Because if you really went to, you know, biology is the study of life, and we can talk about what life is, whether viruses are living, whatnot."}, {"video_title": "Introduction to Evolution and Natural Selection (2).mp3", "Sentence": "Well, anyway, I think I've spoken long enough. But this is a fascinating, fascinating topic. And I really wanted to make this my very first video or lecture, if you will, on biology. Because if you really went to, you know, biology is the study of life, and we can talk about what life is, whether viruses are living, whatnot. But if you really want to study living systems, you really can't make any assumptions other than natural selection. We could go to another planet where the creatures don't have DNA. Or maybe they have some other type of hereditary information stored in their cells."}, {"video_title": "Introduction to Evolution and Natural Selection (2).mp3", "Sentence": "Because if you really went to, you know, biology is the study of life, and we can talk about what life is, whether viruses are living, whatnot. But if you really want to study living systems, you really can't make any assumptions other than natural selection. We could go to another planet where the creatures don't have DNA. Or maybe they have some other type of hereditary information stored in their cells. Or they replicate some other way. Or they're not even carbon-based. Maybe they're silicon-based."}, {"video_title": "Introduction to Evolution and Natural Selection (2).mp3", "Sentence": "Or maybe they have some other type of hereditary information stored in their cells. Or they replicate some other way. Or they're not even carbon-based. Maybe they're silicon-based. And if we went to that type of a planet in order to study the biology on that planet, everything else we know about biology, about viruses and DNA, would be useless. But if we do understand this one concept of natural selection, that your environment will select. And there's no active process here."}, {"video_title": "Introduction to Evolution and Natural Selection (2).mp3", "Sentence": "Maybe they're silicon-based. And if we went to that type of a planet in order to study the biology on that planet, everything else we know about biology, about viruses and DNA, would be useless. But if we do understand this one concept of natural selection, that your environment will select. And there's no active process here. It's just random stuff happened. And they randomly select for random changes. And over large swaths of time, and these are unimaginably large swaths of time, those changes essentially accumulate and they might accumulate into fairly significant things."}, {"video_title": "Photosynthesis evolution   Cellular energetics   AP Biology   Khan Academy.mp3", "Sentence": "In this video, we are going to talk about the evolution of photosynthesis on Earth, because that's the only place that, at least so far, we're aware of photosynthesis occurring. I personally believe that it's occurring in many places in the universe, but we don't really know just yet. But first, a reminder of what photosynthesis even is. It's the process where organisms are able to take carbon dioxide in the atmosphere, in the presence of water, and then use the sun's energy, so sunlight, to then produce sugars, and I'll C6H12O6, and free oxygen, so O2. Now, the way I've written this chemical equation right over here, it hasn't balanced. So, see, I have six carbons here, so let me put a six out front there. But now, let's see, I have 12 hydrogens here."}, {"video_title": "Photosynthesis evolution   Cellular energetics   AP Biology   Khan Academy.mp3", "Sentence": "It's the process where organisms are able to take carbon dioxide in the atmosphere, in the presence of water, and then use the sun's energy, so sunlight, to then produce sugars, and I'll C6H12O6, and free oxygen, so O2. Now, the way I've written this chemical equation right over here, it hasn't balanced. So, see, I have six carbons here, so let me put a six out front there. But now, let's see, I have 12 hydrogens here. I only have two hydrogens here, so let me multiply this by six as well. And let's see, on the left-hand side, I have two oxygens times six is 12, plus another six oxygens, 18 oxygens. So I need 18 oxygens over here."}, {"video_title": "Photosynthesis evolution   Cellular energetics   AP Biology   Khan Academy.mp3", "Sentence": "But now, let's see, I have 12 hydrogens here. I only have two hydrogens here, so let me multiply this by six as well. And let's see, on the left-hand side, I have two oxygens times six is 12, plus another six oxygens, 18 oxygens. So I need 18 oxygens over here. I already have six right over here, so I'll need another 12 right over here, so I'll put a six out front, so I have balanced that. And it's important for you to realize that this is a really big deal. You would not exist without photosynthesis."}, {"video_title": "Photosynthesis evolution   Cellular energetics   AP Biology   Khan Academy.mp3", "Sentence": "So I need 18 oxygens over here. I already have six right over here, so I'll need another 12 right over here, so I'll put a six out front, so I have balanced that. And it's important for you to realize that this is a really big deal. You would not exist without photosynthesis. And I know what you're thinking. You don't photosynthesize things. But the things that you eat, or the things that you eat, the things that they eat, they do some sort of photosynthesis."}, {"video_title": "Photosynthesis evolution   Cellular energetics   AP Biology   Khan Academy.mp3", "Sentence": "You would not exist without photosynthesis. And I know what you're thinking. You don't photosynthesize things. But the things that you eat, or the things that you eat, the things that they eat, they do some sort of photosynthesis. At the end of the day, our energy is coming from the sun. Even if you're eating an animal, that animal might be eating another animal that eats a plant, and that plant is using the sun's energy and it's storing it in the form of carbon-based molecules, oftentimes sugars, and then when we eat these things, we are able to produce energy for them and do things like educational videos. But an interesting question is, where does this come from?"}, {"video_title": "Photosynthesis evolution   Cellular energetics   AP Biology   Khan Academy.mp3", "Sentence": "But the things that you eat, or the things that you eat, the things that they eat, they do some sort of photosynthesis. At the end of the day, our energy is coming from the sun. Even if you're eating an animal, that animal might be eating another animal that eats a plant, and that plant is using the sun's energy and it's storing it in the form of carbon-based molecules, oftentimes sugars, and then when we eat these things, we are able to produce energy for them and do things like educational videos. But an interesting question is, where does this come from? And a straightforward answer is, we don't have all the answers, but scientists have a reasonably good idea of where it probably came from. Today, we can observe cyanobacteria. This is what cyanobacteria looks like."}, {"video_title": "Photosynthesis evolution   Cellular energetics   AP Biology   Khan Academy.mp3", "Sentence": "But an interesting question is, where does this come from? And a straightforward answer is, we don't have all the answers, but scientists have a reasonably good idea of where it probably came from. Today, we can observe cyanobacteria. This is what cyanobacteria looks like. It is, like all bacteria, prokaryotic, and it is able to conduct photosynthesis. And scientists believe that organisms not too different from cyanobacteria, probably an ancestor of cyanobacteria, existed on Earth 2 1\u20442, 3 billion, maybe even older, maybe even further back in time, years ago. And that's early in Earth's history."}, {"video_title": "Photosynthesis evolution   Cellular energetics   AP Biology   Khan Academy.mp3", "Sentence": "This is what cyanobacteria looks like. It is, like all bacteria, prokaryotic, and it is able to conduct photosynthesis. And scientists believe that organisms not too different from cyanobacteria, probably an ancestor of cyanobacteria, existed on Earth 2 1\u20442, 3 billion, maybe even older, maybe even further back in time, years ago. And that's early in Earth's history. Earth has only been around for about 4 1\u20442 billion years. And that ancestor of cyanobacteria, like cyanobacteria, was able to take carbon dioxide in the atmosphere in the presence of water and produce oxygen. And even though this is bacteria and each of these organisms are very small, in aggregate, they can have a pretty significant impact."}, {"video_title": "Photosynthesis evolution   Cellular energetics   AP Biology   Khan Academy.mp3", "Sentence": "And that's early in Earth's history. Earth has only been around for about 4 1\u20442 billion years. And that ancestor of cyanobacteria, like cyanobacteria, was able to take carbon dioxide in the atmosphere in the presence of water and produce oxygen. And even though this is bacteria and each of these organisms are very small, in aggregate, they can have a pretty significant impact. For example, this is a cyanobacteria plume near Fiji, and you can see that these are pretty significant things that can be a significant contributor to oxygen in the atmosphere. And scientists believe that it was these ancestors of cyanobacteria that, as they evolved on Earth and started growing and growing and multiplying, that they started to affect Earth's atmosphere. So what you see in this chart right over here is our best sense of what the oxygen content in the atmosphere was if we go back in time."}, {"video_title": "Photosynthesis evolution   Cellular energetics   AP Biology   Khan Academy.mp3", "Sentence": "And even though this is bacteria and each of these organisms are very small, in aggregate, they can have a pretty significant impact. For example, this is a cyanobacteria plume near Fiji, and you can see that these are pretty significant things that can be a significant contributor to oxygen in the atmosphere. And scientists believe that it was these ancestors of cyanobacteria that, as they evolved on Earth and started growing and growing and multiplying, that they started to affect Earth's atmosphere. So what you see in this chart right over here is our best sense of what the oxygen content in the atmosphere was if we go back in time. And we can start to figure this out based by looking at rock samples that are very, very old, by looking at the fossil record, very, very old. So just so you understand what's going on here, this horizontal axis right over here, this is billions of years ago. This is one billion years ago, two billion years ago, three billion years ago, 3.8 billion years ago."}, {"video_title": "Photosynthesis evolution   Cellular energetics   AP Biology   Khan Academy.mp3", "Sentence": "So what you see in this chart right over here is our best sense of what the oxygen content in the atmosphere was if we go back in time. And we can start to figure this out based by looking at rock samples that are very, very old, by looking at the fossil record, very, very old. So just so you understand what's going on here, this horizontal axis right over here, this is billions of years ago. This is one billion years ago, two billion years ago, three billion years ago, 3.8 billion years ago. So it covers most of Earth's history. If you just wanna put things in context, humans, modern humans, have only been around for about two or 300,000 years, so we wouldn't even show up as a pixel on this diagram right over here. So we're going back into deep time."}, {"video_title": "Photosynthesis evolution   Cellular energetics   AP Biology   Khan Academy.mp3", "Sentence": "This is one billion years ago, two billion years ago, three billion years ago, 3.8 billion years ago. So it covers most of Earth's history. If you just wanna put things in context, humans, modern humans, have only been around for about two or 300,000 years, so we wouldn't even show up as a pixel on this diagram right over here. So we're going back into deep time. And scientists believe that the first photosynthetic organisms might have evolved approaching three billion years ago, although we're not exactly sure. And those organisms might have been producing oxygen from the photosynthesis, but it might have been absorbed by things like the ocean. But eventually, those organisms, probably these ancestors of cyanobacteria, became significant enough that the oxygen started pouring in the atmosphere."}, {"video_title": "Photosynthesis evolution   Cellular energetics   AP Biology   Khan Academy.mp3", "Sentence": "So we're going back into deep time. And scientists believe that the first photosynthetic organisms might have evolved approaching three billion years ago, although we're not exactly sure. And those organisms might have been producing oxygen from the photosynthesis, but it might have been absorbed by things like the ocean. But eventually, those organisms, probably these ancestors of cyanobacteria, became significant enough that the oxygen started pouring in the atmosphere. And we start to see that right over here, where before this point, the atmospheric oxygen was pretty close to 0%. And then right over here, at the great oxygenation event, I'll just call it GOE, all of a sudden, oxygen becomes a larger and larger percentage of the atmosphere. And these two lines represent two different estimates of what percentage of the atmosphere oxygen was at these various times."}, {"video_title": "Photosynthesis evolution   Cellular energetics   AP Biology   Khan Academy.mp3", "Sentence": "But eventually, those organisms, probably these ancestors of cyanobacteria, became significant enough that the oxygen started pouring in the atmosphere. And we start to see that right over here, where before this point, the atmospheric oxygen was pretty close to 0%. And then right over here, at the great oxygenation event, I'll just call it GOE, all of a sudden, oxygen becomes a larger and larger percentage of the atmosphere. And these two lines represent two different estimates of what percentage of the atmosphere oxygen was at these various times. And it grew all the way to modern times, where oxygen is roughly 20 or 21% of our atmosphere. And the reason why this is sometimes called an oxygen catastrophe is that there were a lot of anaerobic organisms that found oxygen poisonous, and so there was a great extinction event from all of this oxygen in the atmosphere. But it was not a catastrophe for what eventually would be us, because we are dependent not just on the sugars from photosynthesis, but we're also dependent on the oxygen from photosynthesis."}, {"video_title": "Photosynthesis evolution   Cellular energetics   AP Biology   Khan Academy.mp3", "Sentence": "And these two lines represent two different estimates of what percentage of the atmosphere oxygen was at these various times. And it grew all the way to modern times, where oxygen is roughly 20 or 21% of our atmosphere. And the reason why this is sometimes called an oxygen catastrophe is that there were a lot of anaerobic organisms that found oxygen poisonous, and so there was a great extinction event from all of this oxygen in the atmosphere. But it was not a catastrophe for what eventually would be us, because we are dependent not just on the sugars from photosynthesis, but we're also dependent on the oxygen from photosynthesis. We use this oxygen to conduct respiration. You can almost view respiration as a backwards process. You take your sugars, and in the presence of oxygen, you are able to extract that energy from those sugars so that we can live."}, {"video_title": "Photosynthesis evolution   Cellular energetics   AP Biology   Khan Academy.mp3", "Sentence": "But it was not a catastrophe for what eventually would be us, because we are dependent not just on the sugars from photosynthesis, but we're also dependent on the oxygen from photosynthesis. We use this oxygen to conduct respiration. You can almost view respiration as a backwards process. You take your sugars, and in the presence of oxygen, you are able to extract that energy from those sugars so that we can live. Now, an interesting question is, at what point did we go from these prokaryotic bacteria organisms to eukaryotic organisms that are able to perform photosynthesis, most notably plants? Well, this goes back to endosymbiosis theory. We have a whole other video on that, but it's this idea that the ancestors of the cyanobacteria might have lived in symbiosis with another eukaryotic cell where the cyanobacteria ancestor was able to harness light energy to produce sugars for the larger cell, and in return, the larger cell was able to give protection or nutrients."}, {"video_title": "Photosynthesis evolution   Cellular energetics   AP Biology   Khan Academy.mp3", "Sentence": "You take your sugars, and in the presence of oxygen, you are able to extract that energy from those sugars so that we can live. Now, an interesting question is, at what point did we go from these prokaryotic bacteria organisms to eukaryotic organisms that are able to perform photosynthesis, most notably plants? Well, this goes back to endosymbiosis theory. We have a whole other video on that, but it's this idea that the ancestors of the cyanobacteria might have lived in symbiosis with another eukaryotic cell where the cyanobacteria ancestor was able to harness light energy to produce sugars for the larger cell, and in return, the larger cell was able to give protection or nutrients. And so we believe, based on endosymbiosis theory, that chloroplasts, and right over here you see plant cells with visible chloroplasts in them, that chloroplasts are actually descendants of those ancestors of cyanobacteria. Cyanobacteria would be other descendants of them, but these are the ones that started to live in symbiosis with what would later become plant cells. And good evidence that these might have ancestors that used to live independently is that they have DNA that is very similar to the DNA of cyanobacteria."}, {"video_title": "Photosynthesis evolution   Cellular energetics   AP Biology   Khan Academy.mp3", "Sentence": "We have a whole other video on that, but it's this idea that the ancestors of the cyanobacteria might have lived in symbiosis with another eukaryotic cell where the cyanobacteria ancestor was able to harness light energy to produce sugars for the larger cell, and in return, the larger cell was able to give protection or nutrients. And so we believe, based on endosymbiosis theory, that chloroplasts, and right over here you see plant cells with visible chloroplasts in them, that chloroplasts are actually descendants of those ancestors of cyanobacteria. Cyanobacteria would be other descendants of them, but these are the ones that started to live in symbiosis with what would later become plant cells. And good evidence that these might have ancestors that used to live independently is that they have DNA that is very similar to the DNA of cyanobacteria. They have ribosomes, their own ribosomes, that are very similar to the ribosomes of cyanobacteria. And so like mitochondria, we believe chloroplasts originated as independent bacteria-like organisms and eventually were engulfed into eukaryotic cells. So I will leave you there."}, {"video_title": "Photosynthesis evolution   Cellular energetics   AP Biology   Khan Academy.mp3", "Sentence": "And good evidence that these might have ancestors that used to live independently is that they have DNA that is very similar to the DNA of cyanobacteria. They have ribosomes, their own ribosomes, that are very similar to the ribosomes of cyanobacteria. And so like mitochondria, we believe chloroplasts originated as independent bacteria-like organisms and eventually were engulfed into eukaryotic cells. So I will leave you there. Photosynthesis is a big deal, and it's really interesting to think about where it came from. It likely evolved on Earth many billions of years ago, probably close to three billion years ago. But around 2.3, 2.4 billion years ago, it fundamentally changed the planet where you had oxygen pouring into the atmosphere, killing a lot of organisms, but making it possible for many other organisms to live."}, {"video_title": "Introduction to metabolism anabolism and catabolism   Khan Academy.mp3", "Sentence": "And at its essence, we can call this metabolism. Metabolism. And this is the taking energy in different forms, breaking it down into its more fundamental components, and then building it up in ways that we would find useful, useful for energy, useful for structure, so that we can actually live our lives, we can grow, we can reproduce, we can respond to our surroundings. So as I just said, metabolism, and we're gonna go into a bunch of examples of this, metabolism at its heart is really two different processes. There's the breaking down of substances for energy or for structure, to get back to the building blocks, and we call that catabolism. Catabolism. So this is the breaking down of things."}, {"video_title": "Introduction to metabolism anabolism and catabolism   Khan Academy.mp3", "Sentence": "So as I just said, metabolism, and we're gonna go into a bunch of examples of this, metabolism at its heart is really two different processes. There's the breaking down of substances for energy or for structure, to get back to the building blocks, and we call that catabolism. Catabolism. So this is the breaking down of things. And then once we've broken down things, we're ready to rebuild them in ways that we would find useful. And we call this anabolism. Anabolism."}, {"video_title": "Introduction to metabolism anabolism and catabolism   Khan Academy.mp3", "Sentence": "So this is the breaking down of things. And then once we've broken down things, we're ready to rebuild them in ways that we would find useful. And we call this anabolism. Anabolism. Or anabolism. Anabolism, just like that. And one way to think about it is, imagine that someone had built something with Legos, and you wanna build something with Legos."}, {"video_title": "Introduction to metabolism anabolism and catabolism   Khan Academy.mp3", "Sentence": "Anabolism. Or anabolism. Anabolism, just like that. And one way to think about it is, imagine that someone had built something with Legos, and you wanna build something with Legos. Well, you could go to those Legos, and you'd wanna break it down, but not break it down too much, you wouldn't melt the plastic, you would break it down into the individual Lego pieces, and then you would build it back up into whatever shape that you actually cared about. And you might not actually have to even build it, break it down all the way to the basic Lego pieces, there might be structures in that first Lego castle that was constructed that you might find useful. So let's just think about how all of this gets started."}, {"video_title": "Introduction to metabolism anabolism and catabolism   Khan Academy.mp3", "Sentence": "And one way to think about it is, imagine that someone had built something with Legos, and you wanna build something with Legos. Well, you could go to those Legos, and you'd wanna break it down, but not break it down too much, you wouldn't melt the plastic, you would break it down into the individual Lego pieces, and then you would build it back up into whatever shape that you actually cared about. And you might not actually have to even build it, break it down all the way to the basic Lego pieces, there might be structures in that first Lego castle that was constructed that you might find useful. So let's just think about how all of this gets started. And what's exciting is that all of this got started, or gets started, from stars, from fusion reactions in stars. And this right over here is a picture of a star, a star that we are very familiar with, this is the sun. But you may or may not realize that the sun is only one of probably several stars that have been involved in life as we know it."}, {"video_title": "Introduction to metabolism anabolism and catabolism   Khan Academy.mp3", "Sentence": "So let's just think about how all of this gets started. And what's exciting is that all of this got started, or gets started, from stars, from fusion reactions in stars. And this right over here is a picture of a star, a star that we are very familiar with, this is the sun. But you may or may not realize that the sun is only one of probably several stars that have been involved in life as we know it. The sun is our most direct source of energy for most of life as we know it, there are some bacteria and things that are able to live off of vents at the bottom of the ocean because of the heat created. But the sun is our primary source of energy. But when I say that other stars might have been involved, including dead stars that existed billions of years ago, it's because the heavier elements that we're composed of, or that are around us in the environment, the carbon, the oxygen, we could just keep going, pretty much everything other than hydrogen, it was constructed in fusion reactions from hydrogen inside of stars."}, {"video_title": "Introduction to metabolism anabolism and catabolism   Khan Academy.mp3", "Sentence": "But you may or may not realize that the sun is only one of probably several stars that have been involved in life as we know it. The sun is our most direct source of energy for most of life as we know it, there are some bacteria and things that are able to live off of vents at the bottom of the ocean because of the heat created. But the sun is our primary source of energy. But when I say that other stars might have been involved, including dead stars that existed billions of years ago, it's because the heavier elements that we're composed of, or that are around us in the environment, the carbon, the oxygen, we could just keep going, pretty much everything other than hydrogen, it was constructed in fusion reactions from hydrogen inside of stars. So we really are made up of the remnants of stars. And so here we are, we're on Earth, Earth is all this condensed matter from four and a half billion years ago, probably some nearby supernova got all of this dust that was constructed in a previous star to coalesce in that way. And you have radiation, you have energy from the sun, and once again, that energy is coming from fusion reactions."}, {"video_title": "Introduction to metabolism anabolism and catabolism   Khan Academy.mp3", "Sentence": "But when I say that other stars might have been involved, including dead stars that existed billions of years ago, it's because the heavier elements that we're composed of, or that are around us in the environment, the carbon, the oxygen, we could just keep going, pretty much everything other than hydrogen, it was constructed in fusion reactions from hydrogen inside of stars. So we really are made up of the remnants of stars. And so here we are, we're on Earth, Earth is all this condensed matter from four and a half billion years ago, probably some nearby supernova got all of this dust that was constructed in a previous star to coalesce in that way. And you have radiation, you have energy from the sun, and once again, that energy is coming from fusion reactions. And it's fusing lighter elements into heavier elements. So the sun is also constructing more heavy elements. But that energy, that energy makes its way to the Earth."}, {"video_title": "Introduction to metabolism anabolism and catabolism   Khan Academy.mp3", "Sentence": "And you have radiation, you have energy from the sun, and once again, that energy is coming from fusion reactions. And it's fusing lighter elements into heavier elements. So the sun is also constructing more heavy elements. But that energy, that energy makes its way to the Earth. And you have organisms, like plants, that are able to use that energy to construct the material, the food, we could say, that is eventually going to get around to us. And so this process, you may or may not be familiar with it, this is photosynthesis. And we're going to go into a lot more detail."}, {"video_title": "Introduction to metabolism anabolism and catabolism   Khan Academy.mp3", "Sentence": "But that energy, that energy makes its way to the Earth. And you have organisms, like plants, that are able to use that energy to construct the material, the food, we could say, that is eventually going to get around to us. And so this process, you may or may not be familiar with it, this is photosynthesis. And we're going to go into a lot more detail. Synthesis. And as the word implies, photo, it's photosynthesis, it's making things out of light. And one thing I like to ask people when they are first exposed to photosynthesis, I was like, okay, we could see this grass growing, or we could see this wheat growing, or we could see a tree growing, but where is that material coming from?"}, {"video_title": "Introduction to metabolism anabolism and catabolism   Khan Academy.mp3", "Sentence": "And we're going to go into a lot more detail. Synthesis. And as the word implies, photo, it's photosynthesis, it's making things out of light. And one thing I like to ask people when they are first exposed to photosynthesis, I was like, okay, we could see this grass growing, or we could see this wheat growing, or we could see a tree growing, but where is that material coming from? And the most common answer is, oh, somehow it's coming from the ground, and there are some nutrients that are coming from the ground, but it's really all about fixing carbon. And you're going to hear about this a lot, especially as we talk about the carbon cycle. But you have carbon dioxide primarily in the air."}, {"video_title": "Introduction to metabolism anabolism and catabolism   Khan Academy.mp3", "Sentence": "And one thing I like to ask people when they are first exposed to photosynthesis, I was like, okay, we could see this grass growing, or we could see this wheat growing, or we could see a tree growing, but where is that material coming from? And the most common answer is, oh, somehow it's coming from the ground, and there are some nutrients that are coming from the ground, but it's really all about fixing carbon. And you're going to hear about this a lot, especially as we talk about the carbon cycle. But you have carbon dioxide primarily in the air. So you have carbon, you have, I'll just write it this way. So you have carbon dioxide in the air. And what photosynthesis allows these plants to do is take the carbon and that carbon dioxide and form bonds with it, turn it from its gas form into solid forms, into glucose molecules, and then use that glucose to build up cellulose and to build out other forms of starch and whatever else it might be."}, {"video_title": "Introduction to metabolism anabolism and catabolism   Khan Academy.mp3", "Sentence": "But you have carbon dioxide primarily in the air. So you have carbon, you have, I'll just write it this way. So you have carbon dioxide in the air. And what photosynthesis allows these plants to do is take the carbon and that carbon dioxide and form bonds with it, turn it from its gas form into solid forms, into glucose molecules, and then use that glucose to build up cellulose and to build out other forms of starch and whatever else it might be. So it's taking these molecules in the air, I'll just draw them as these little, it's taking these molecules that are in the air, and it's using the energy of the sun to fix them, to actually form bonds between the carbons and with other things. As we said, we're mostly carbon and hydrogen, we have some oxygen in there, but we're able to form these structures. Now, from there, other living organisms, and this is a huge oversimplification, it can involve bacteria, it can involve all sorts of things."}, {"video_title": "Introduction to metabolism anabolism and catabolism   Khan Academy.mp3", "Sentence": "And what photosynthesis allows these plants to do is take the carbon and that carbon dioxide and form bonds with it, turn it from its gas form into solid forms, into glucose molecules, and then use that glucose to build up cellulose and to build out other forms of starch and whatever else it might be. So it's taking these molecules in the air, I'll just draw them as these little, it's taking these molecules that are in the air, and it's using the energy of the sun to fix them, to actually form bonds between the carbons and with other things. As we said, we're mostly carbon and hydrogen, we have some oxygen in there, but we're able to form these structures. Now, from there, other living organisms, and this is a huge oversimplification, it can involve bacteria, it can involve all sorts of things. And just a reminder, even on that photosynthesis, it isn't just light and it isn't just the carbon dioxide, it also involves the water, and we talk about that. So you also have water involved. You also have the water involved."}, {"video_title": "Introduction to metabolism anabolism and catabolism   Khan Academy.mp3", "Sentence": "Now, from there, other living organisms, and this is a huge oversimplification, it can involve bacteria, it can involve all sorts of things. And just a reminder, even on that photosynthesis, it isn't just light and it isn't just the carbon dioxide, it also involves the water, and we talk about that. So you also have water involved. You also have the water involved. So you have the carbon dioxide, so CO2, light from the sun, and water. These things are able to grow, and nutrients from the earth. And then from that, you're able to construct things like, well, you can directly go to these plants that are taking energy from the sun and construct things like bread."}, {"video_title": "Introduction to metabolism anabolism and catabolism   Khan Academy.mp3", "Sentence": "You also have the water involved. So you have the carbon dioxide, so CO2, light from the sun, and water. These things are able to grow, and nutrients from the earth. And then from that, you're able to construct things like, well, you can directly go to these plants that are taking energy from the sun and construct things like bread. Or you have other animals that will eat things like the grass and then break them down in their own way, and they'll be assisted by bacteria, and then rebuild themselves up into a cow, into milk. And so what this cow is doing, it's metabolizing this grass. It's able to break it down, it's able to catabolize the various molecules in the grass and break them down into building blocks that can then be used to build up the cow, to build up milk, and whatever else."}, {"video_title": "Introduction to metabolism anabolism and catabolism   Khan Academy.mp3", "Sentence": "And then from that, you're able to construct things like, well, you can directly go to these plants that are taking energy from the sun and construct things like bread. Or you have other animals that will eat things like the grass and then break them down in their own way, and they'll be assisted by bacteria, and then rebuild themselves up into a cow, into milk. And so what this cow is doing, it's metabolizing this grass. It's able to break it down, it's able to catabolize the various molecules in the grass and break them down into building blocks that can then be used to build up the cow, to build up milk, and whatever else. And you might be saying, what are these types of molecules that we keep breaking down and then building back up? Well, you have carbohydrates. Carbohydrates."}, {"video_title": "Introduction to metabolism anabolism and catabolism   Khan Academy.mp3", "Sentence": "It's able to break it down, it's able to catabolize the various molecules in the grass and break them down into building blocks that can then be used to build up the cow, to build up milk, and whatever else. And you might be saying, what are these types of molecules that we keep breaking down and then building back up? Well, you have carbohydrates. Carbohydrates. And you're going to see most of the molecules that I'm about to talk about, frankly, all of them on the back of a nutritional package, because it tells you what's inside of it. What is your body going to metabolize when it eats that whatever's inside of the package? So carbohydrates, these are either simple sugars like glucose or fructose, or it could be polymers of the sugars, polysaccharides."}, {"video_title": "Introduction to metabolism anabolism and catabolism   Khan Academy.mp3", "Sentence": "Carbohydrates. And you're going to see most of the molecules that I'm about to talk about, frankly, all of them on the back of a nutritional package, because it tells you what's inside of it. What is your body going to metabolize when it eats that whatever's inside of the package? So carbohydrates, these are either simple sugars like glucose or fructose, or it could be polymers of the sugars, polysaccharides. It could be starches made up of many, many elements, or many, many multiples of these simple sugars. We could be talking about lipids. So fatty acids, we could be talking about cholesterols."}, {"video_title": "Introduction to metabolism anabolism and catabolism   Khan Academy.mp3", "Sentence": "So carbohydrates, these are either simple sugars like glucose or fructose, or it could be polymers of the sugars, polysaccharides. It could be starches made up of many, many elements, or many, many multiples of these simple sugars. We could be talking about lipids. So fatty acids, we could be talking about cholesterols. These are essential structures, and they're also essential for various metabolic pathways inside of all of life. Or it could be proteins. It could be proteins made up of amino acids."}, {"video_title": "Introduction to metabolism anabolism and catabolism   Khan Academy.mp3", "Sentence": "So fatty acids, we could be talking about cholesterols. These are essential structures, and they're also essential for various metabolic pathways inside of all of life. Or it could be proteins. It could be proteins made up of amino acids. Sometimes people say, the reason why you want the proteins is because it's made up of these amino acids. So you could break down these proteins and get the amino acids, and then build it up into new proteins. Proteins and amino acids."}, {"video_title": "Introduction to metabolism anabolism and catabolism   Khan Academy.mp3", "Sentence": "It could be proteins made up of amino acids. Sometimes people say, the reason why you want the proteins is because it's made up of these amino acids. So you could break down these proteins and get the amino acids, and then build it up into new proteins. Proteins and amino acids. And all of these things, they are found in things like in the foods we eat, which we will then consume. We will then metabolize. We will first catabolize them and break them down, and then we will use those building blocks to build it back up."}, {"video_title": "Introduction to metabolism anabolism and catabolism   Khan Academy.mp3", "Sentence": "Proteins and amino acids. And all of these things, they are found in things like in the foods we eat, which we will then consume. We will then metabolize. We will first catabolize them and break them down, and then we will use those building blocks to build it back up. And at the end of the day, these provide the structures that make our bodies what they are. They allow us to interact with our environment, and they provide energy. And that energy, at the end of the day, the true molecular currency for that energy is a molecule called ATP."}, {"video_title": "Introduction to metabolism anabolism and catabolism   Khan Academy.mp3", "Sentence": "We will first catabolize them and break them down, and then we will use those building blocks to build it back up. And at the end of the day, these provide the structures that make our bodies what they are. They allow us to interact with our environment, and they provide energy. And that energy, at the end of the day, the true molecular currency for that energy is a molecule called ATP. That's a molecule of ATP right over there. Adenosine triphosphate. And the key for ATP, why it is the molecular currency for energy, are the three phosphate groups."}, {"video_title": "Introduction to metabolism anabolism and catabolism   Khan Academy.mp3", "Sentence": "And that energy, at the end of the day, the true molecular currency for that energy is a molecule called ATP. That's a molecule of ATP right over there. Adenosine triphosphate. And the key for ATP, why it is the molecular currency for energy, are the three phosphate groups. So it has these three phosphate groups, and we have a whole video on it, or a whole series of videos on it, really. But the main key is that there's a lot of energy, especially between the, I guess on the last phosphate group. And this energy in that bond, as the phosphate group breaks off, it can release it to provide all sorts of life mechanisms, including being able to metabolize things."}, {"video_title": "Introduction to metabolism anabolism and catabolism   Khan Academy.mp3", "Sentence": "And the key for ATP, why it is the molecular currency for energy, are the three phosphate groups. So it has these three phosphate groups, and we have a whole video on it, or a whole series of videos on it, really. But the main key is that there's a lot of energy, especially between the, I guess on the last phosphate group. And this energy in that bond, as the phosphate group breaks off, it can release it to provide all sorts of life mechanisms, including being able to metabolize things. So ATP right over here, this is the currency of energy in life as we know it. And it's actually an interesting molecule because it's essentially, it's a piece of, if you were to just take this section of it right over here, it really is, it looks like a piece of RNA. It looks like you're taking a, you have the ribose, you have the adenine, you have a phosphate group, and it can actually be used to construct things like RNA and even DNA, beyond just being the molecular currency of energy."}, {"video_title": "Introduction to metabolism anabolism and catabolism   Khan Academy.mp3", "Sentence": "And this energy in that bond, as the phosphate group breaks off, it can release it to provide all sorts of life mechanisms, including being able to metabolize things. So ATP right over here, this is the currency of energy in life as we know it. And it's actually an interesting molecule because it's essentially, it's a piece of, if you were to just take this section of it right over here, it really is, it looks like a piece of RNA. It looks like you're taking a, you have the ribose, you have the adenine, you have a phosphate group, and it can actually be used to construct things like RNA and even DNA, beyond just being the molecular currency of energy. So it's fun to see how these pieces all fit together, how they can be broken up, and you see these patterns over and over again in biological systems. And these biological systems are really just made up of breaking down and building back up carbohydrates, lipids, including fatty acids, cholesterol, other things, and proteins slash amino acids. So this whole thing, look around you, look at your day, look at the things you're consuming, and you'll see this pattern over and over and over again."}, {"video_title": "Population regulation   Ecology   Khan Academy.mp3", "Sentence": "What I want to do in this video is think a little bit more about how populations can be regulated. And broadly speaking, we can think of the regulation of populations in two different categories. There's the regulation dependent on density, so density dependent regulation, density dependent, and then there's the type of regulation that isn't dependent on density, so we could call that density independent regulation. Independent, independent regulation. So first let's think about density dependent regulation. And let me draw a little chart here to help us visualize that. So let's say that that axis is the population."}, {"video_title": "Population regulation   Ecology   Khan Academy.mp3", "Sentence": "Independent, independent regulation. So first let's think about density dependent regulation. And let me draw a little chart here to help us visualize that. So let's say that that axis is the population. I'll say P for population. And let's say this axis is time, so T for time. In previous videos, we talked about a population, I like to use the example of rabbits, how it could grow exponentially."}, {"video_title": "Population regulation   Ecology   Khan Academy.mp3", "Sentence": "So let's say that that axis is the population. I'll say P for population. And let's say this axis is time, so T for time. In previous videos, we talked about a population, I like to use the example of rabbits, how it could grow exponentially. So if it's just growing a certain percent every month, that population will grow exponentially. But we can't expect that that will just happen forever. If rabbits just kept growing exponentially, it wouldn't take long for them to cover the surface of the Earth and then fill the universe, if in some ways they weren't limited by anything."}, {"video_title": "Population regulation   Ecology   Khan Academy.mp3", "Sentence": "In previous videos, we talked about a population, I like to use the example of rabbits, how it could grow exponentially. So if it's just growing a certain percent every month, that population will grow exponentially. But we can't expect that that will just happen forever. If rabbits just kept growing exponentially, it wouldn't take long for them to cover the surface of the Earth and then fill the universe, if in some ways they weren't limited by anything. But we know that they are limited by things. And so the environment only has a certain amount of carrying capacity. And we'll think a little bit about this carrying capacity in a second."}, {"video_title": "Population regulation   Ecology   Khan Academy.mp3", "Sentence": "If rabbits just kept growing exponentially, it wouldn't take long for them to cover the surface of the Earth and then fill the universe, if in some ways they weren't limited by anything. But we know that they are limited by things. And so the environment only has a certain amount of carrying capacity. And we'll think a little bit about this carrying capacity in a second. And what's determining the carrying capacity. And so as the density of the rabbits in a certain area get higher and higher and higher, well then the density dependent, let me use a different color, the density dependent factors start to play. The density dependent limiting factors."}, {"video_title": "Population regulation   Ecology   Khan Academy.mp3", "Sentence": "And we'll think a little bit about this carrying capacity in a second. And what's determining the carrying capacity. And so as the density of the rabbits in a certain area get higher and higher and higher, well then the density dependent, let me use a different color, the density dependent factors start to play. The density dependent limiting factors. And what could be some of these density dependent limiting factors that keep the population from going dramatically above the carrying capacity? Well, the most obvious one could be competition for resources competition for resources. And the one that might come to mind most clearly is food resources."}, {"video_title": "Population regulation   Ecology   Khan Academy.mp3", "Sentence": "The density dependent limiting factors. And what could be some of these density dependent limiting factors that keep the population from going dramatically above the carrying capacity? Well, the most obvious one could be competition for resources competition for resources. And the one that might come to mind most clearly is food resources. So this is actually a picture of Australia in the mid 1800s. And they had a bunny population problem. That rabbits were first introduced in order to have a little bit of hunting."}, {"video_title": "Population regulation   Ecology   Khan Academy.mp3", "Sentence": "And the one that might come to mind most clearly is food resources. So this is actually a picture of Australia in the mid 1800s. And they had a bunny population problem. That rabbits were first introduced in order to have a little bit of hunting. But then they reproduced like rabbits. And it was estimated that at some point you had over a billion rabbits that had populated the country. And that was, you might say, oh how cute."}, {"video_title": "Population regulation   Ecology   Khan Academy.mp3", "Sentence": "That rabbits were first introduced in order to have a little bit of hunting. But then they reproduced like rabbits. And it was estimated that at some point you had over a billion rabbits that had populated the country. And that was, you might say, oh how cute. But it was a huge problem. They were eating all of the, they were eating the farmable, they were eating crops, they were eating the grass that other types of livestock would graze on. So it was a huge infestation of rabbits."}, {"video_title": "Population regulation   Ecology   Khan Academy.mp3", "Sentence": "And that was, you might say, oh how cute. But it was a huge problem. They were eating all of the, they were eating the farmable, they were eating crops, they were eating the grass that other types of livestock would graze on. So it was a huge infestation of rabbits. And so you can imagine one competition for resources is just the grass itself. In this picture you can see that the land is barren. Maybe this happened because the rabbits ate all of the vegetation here."}, {"video_title": "Population regulation   Ecology   Khan Academy.mp3", "Sentence": "So it was a huge infestation of rabbits. And so you can imagine one competition for resources is just the grass itself. In this picture you can see that the land is barren. Maybe this happened because the rabbits ate all of the vegetation here. So competition for resources. One type of resource could be food. Another type of resource could be water."}, {"video_title": "Population regulation   Ecology   Khan Academy.mp3", "Sentence": "Maybe this happened because the rabbits ate all of the vegetation here. So competition for resources. One type of resource could be food. Another type of resource could be water. There might only be so much water to support organisms of a certain kind. And we're only, here we often talk about animals, but it could be plants, or it could be bacteria. It could be all sorts of organisms that we're talking about."}, {"video_title": "Population regulation   Ecology   Khan Academy.mp3", "Sentence": "Another type of resource could be water. There might only be so much water to support organisms of a certain kind. And we're only, here we often talk about animals, but it could be plants, or it could be bacteria. It could be all sorts of organisms that we're talking about. And if we're talking about plants, we could think about light. You could say, well what limits having an infinite number of plants in a certain area? Well, water will limit."}, {"video_title": "Population regulation   Ecology   Khan Academy.mp3", "Sentence": "It could be all sorts of organisms that we're talking about. And if we're talking about plants, we could think about light. You could say, well what limits having an infinite number of plants in a certain area? Well, water will limit. The nutrients in the soil will limit. But also access to light. You've seen pictures of a dense canopy in a rainforest."}, {"video_title": "Population regulation   Ecology   Khan Academy.mp3", "Sentence": "Well, water will limit. The nutrients in the soil will limit. But also access to light. You've seen pictures of a dense canopy in a rainforest. And the plants are trying to seek out whatever gap in the canopy they can find so that they can get some access to that light. Now there's other examples, and this wouldn't apply as much to, say, plants, but the idea of shelter. This might apply to humans, or to other types of animals that maybe need shelter in order to hide, or a place to reproduce, or whatever else."}, {"video_title": "Population regulation   Ecology   Khan Academy.mp3", "Sentence": "You've seen pictures of a dense canopy in a rainforest. And the plants are trying to seek out whatever gap in the canopy they can find so that they can get some access to that light. Now there's other examples, and this wouldn't apply as much to, say, plants, but the idea of shelter. This might apply to humans, or to other types of animals that maybe need shelter in order to hide, or a place to reproduce, or whatever else. So at some point, if the population density gets too high in a certain region, then these things are going to limit how dense the population can get, or frankly, just what the population actually is. And so that would lead, once again, we talked about this in a previous video, to this logistic curve right over here, where we just start approaching the carrying capacity. And it is possible that you could even go above the carrying capacity, and then you're kind of this very unstable situation, and then something happens, you go below it, then you go above it, and then below it, and then something like that."}, {"video_title": "Population regulation   Ecology   Khan Academy.mp3", "Sentence": "This might apply to humans, or to other types of animals that maybe need shelter in order to hide, or a place to reproduce, or whatever else. So at some point, if the population density gets too high in a certain region, then these things are going to limit how dense the population can get, or frankly, just what the population actually is. And so that would lead, once again, we talked about this in a previous video, to this logistic curve right over here, where we just start approaching the carrying capacity. And it is possible that you could even go above the carrying capacity, and then you're kind of this very unstable situation, and then something happens, you go below it, then you go above it, and then below it, and then something like that. But what are other density-dependent factors that we could think about? Well, another thing is, if you are a predator, when, say, the rabbits become this dense, it's much easier to start to pick them off, and it's much easier to get your lunch. And so predatory factors, or we could say predation."}, {"video_title": "Population regulation   Ecology   Khan Academy.mp3", "Sentence": "And it is possible that you could even go above the carrying capacity, and then you're kind of this very unstable situation, and then something happens, you go below it, then you go above it, and then below it, and then something like that. But what are other density-dependent factors that we could think about? Well, another thing is, if you are a predator, when, say, the rabbits become this dense, it's much easier to start to pick them off, and it's much easier to get your lunch. And so predatory factors, or we could say predation. Predation. Once a population gets large enough and dense enough, it might be the predators who could say, hey, we can start, it's way easier for us to get our lunch. Now, the other thing, that it might be a little less obvious, but when you have a high-density population, and there's examples of this in medieval times in Europe, and even in modern times today with human populations, but this happens with all organisms, is that when you become a dense population, there's more interaction, there's more contact, there's more sharing of resources like water, and so disease and parasites becomes an issue."}, {"video_title": "Population regulation   Ecology   Khan Academy.mp3", "Sentence": "And so predatory factors, or we could say predation. Predation. Once a population gets large enough and dense enough, it might be the predators who could say, hey, we can start, it's way easier for us to get our lunch. Now, the other thing, that it might be a little less obvious, but when you have a high-density population, and there's examples of this in medieval times in Europe, and even in modern times today with human populations, but this happens with all organisms, is that when you become a dense population, there's more interaction, there's more contact, there's more sharing of resources like water, and so disease and parasites becomes an issue. So let me write this down. Disease and parasites can spread much easier, and they're much more likely to start limiting the population. The thing that always comes to my mind is the plague in medieval times, where it was very easy to spread from one human to the next, or frankly, from rats to humans, and whatever else."}, {"video_title": "Population regulation   Ecology   Khan Academy.mp3", "Sentence": "Now, the other thing, that it might be a little less obvious, but when you have a high-density population, and there's examples of this in medieval times in Europe, and even in modern times today with human populations, but this happens with all organisms, is that when you become a dense population, there's more interaction, there's more contact, there's more sharing of resources like water, and so disease and parasites becomes an issue. So let me write this down. Disease and parasites can spread much easier, and they're much more likely to start limiting the population. The thing that always comes to my mind is the plague in medieval times, where it was very easy to spread from one human to the next, or frankly, from rats to humans, and whatever else. Now, the other thing, and this is maybe somewhat related to everything else we've talked about, is waste accumulation. So let me write this right over here. Waste."}, {"video_title": "Population regulation   Ecology   Khan Academy.mp3", "Sentence": "The thing that always comes to my mind is the plague in medieval times, where it was very easy to spread from one human to the next, or frankly, from rats to humans, and whatever else. Now, the other thing, and this is maybe somewhat related to everything else we've talked about, is waste accumulation. So let me write this right over here. Waste. If you have a really high-density population, and the waste is just everywhere, it could poison the water, it might poison sources of food, it might help the spread of disease and parasites. And once again, all of these things help define what the carrying capacity, how dense can a population get in a certain region. Now, you might say, well, maybe they don't have to stay in a region, maybe they can go and explore other places, and that's possible, and that's been the story for many different types of species."}, {"video_title": "Population regulation   Ecology   Khan Academy.mp3", "Sentence": "Waste. If you have a really high-density population, and the waste is just everywhere, it could poison the water, it might poison sources of food, it might help the spread of disease and parasites. And once again, all of these things help define what the carrying capacity, how dense can a population get in a certain region. Now, you might say, well, maybe they don't have to stay in a region, maybe they can go and explore other places, and that's possible, and that's been the story for many different types of species. Lemmings are famous for when their population gets dense in a certain area, groups of them start just running to start exploring other areas, sometimes running in directions that are not that good for them. So all of these are density-dependent factors, and a lot of these, as we just talked about, you could think of them as biotic factors. They're related to other living things around."}, {"video_title": "Population regulation   Ecology   Khan Academy.mp3", "Sentence": "Now, you might say, well, maybe they don't have to stay in a region, maybe they can go and explore other places, and that's possible, and that's been the story for many different types of species. Lemmings are famous for when their population gets dense in a certain area, groups of them start just running to start exploring other areas, sometimes running in directions that are not that good for them. So all of these are density-dependent factors, and a lot of these, as we just talked about, you could think of them as biotic factors. They're related to other living things around. The density-independent factors tend to be abiotic, they tend to not be related to living things. So the most common density-independent factor is natural disasters. So natural, natural disaster."}, {"video_title": "Population regulation   Ecology   Khan Academy.mp3", "Sentence": "They're related to other living things around. The density-independent factors tend to be abiotic, they tend to not be related to living things. So the most common density-independent factor is natural disasters. So natural, natural disaster. We have a picture here of a forest fire. The deer population here might not be in any way close to their carrying capacity, but despite that, the forest fire maybe might kill off a lot of the deer. Other natural disasters, you could have a flood, you could have a tsunami, you could have a meteorite coming from outer space, that happened to the dinosaurs, to just knock out huge populations."}, {"video_title": "Population regulation   Ecology   Khan Academy.mp3", "Sentence": "So natural, natural disaster. We have a picture here of a forest fire. The deer population here might not be in any way close to their carrying capacity, but despite that, the forest fire maybe might kill off a lot of the deer. Other natural disasters, you could have a flood, you could have a tsunami, you could have a meteorite coming from outer space, that happened to the dinosaurs, to just knock out huge populations. And so density-independent factors, you could have the population growing, and at just some random point, there's some density-independent factor. There's a forest fire, there's a flood, or something else, and then maybe the population grows from there and eventually gets closer to its carrying capacity. Who knows?"}, {"video_title": "Population regulation   Ecology   Khan Academy.mp3", "Sentence": "Other natural disasters, you could have a flood, you could have a tsunami, you could have a meteorite coming from outer space, that happened to the dinosaurs, to just knock out huge populations. And so density-independent factors, you could have the population growing, and at just some random point, there's some density-independent factor. There's a forest fire, there's a flood, or something else, and then maybe the population grows from there and eventually gets closer to its carrying capacity. Who knows? But the density-independent factors, once again, it's not related to where we are on this curve. It could happen at any time, and to some degree, they feel a little bit more random. Now, with all of this talk about carrying capacities and the different density-dependent factors, you might be thinking, well, what about human beings?"}, {"video_title": "Population regulation   Ecology   Khan Academy.mp3", "Sentence": "Who knows? But the density-independent factors, once again, it's not related to where we are on this curve. It could happen at any time, and to some degree, they feel a little bit more random. Now, with all of this talk about carrying capacities and the different density-dependent factors, you might be thinking, well, what about human beings? We are, for sure, a species, and so these same ideas apply to us. And so is there a natural carrying capacity for the environments that we are in? And there's a famous philosopher, scientist, Thomas Malthus, and I have a whole video on him, but he hypothesized that humanity had a very serious problem because our populations were growing exponentially, so this is population, this is time, and so he said, look, there's just a natural carrying capacity for human beings, and as human beings just kept growing exponentially, we would hit that carrying capacity, and the term for that carrying capacity in the case of human beings that Thomas Malthus set up, and there's a whole video on this, is the Malthusian limit, and he hypothesized that once we crossed it or approached it there would be all sorts of crises, that once you're at this carrying capacity there might not be enough food and then there might be a famine, or we go across it and then disease spreads a lot more, and so he was just applying these ideas of density-dependent factors to human populations and said, hey, this is not gonna be pleasant for humanity."}, {"video_title": "Cell membrane proteins   Cells   MCAT   Khan Academy.mp3", "Sentence": "In this video, we're going to explore membrane proteins. Did you know that the cell membrane can be composed up to 75% protein? So most cell membranes have about 50% or less protein. And proteins are there because the cell membrane uses proteins for pretty much everything that it does, all of these cell membrane processes that it performs. So just to remind us what a cell membrane actually is, a cell membrane is made up of little things that look like this, which are called phospholipids. And they come together and form what we call a lipid bilayer. So over here, I've pre-drawn a lipid bilayer."}, {"video_title": "Cell membrane proteins   Cells   MCAT   Khan Academy.mp3", "Sentence": "And proteins are there because the cell membrane uses proteins for pretty much everything that it does, all of these cell membrane processes that it performs. So just to remind us what a cell membrane actually is, a cell membrane is made up of little things that look like this, which are called phospholipids. And they come together and form what we call a lipid bilayer. So over here, I've pre-drawn a lipid bilayer. And it'll look something like this. It'll be made up of a lot of these small phospholipids that we've drawn above. And it'll make up our bilayer."}, {"video_title": "Cell membrane proteins   Cells   MCAT   Khan Academy.mp3", "Sentence": "So over here, I've pre-drawn a lipid bilayer. And it'll look something like this. It'll be made up of a lot of these small phospholipids that we've drawn above. And it'll make up our bilayer. So you can see that there are two layers of these phospholipids. Now, there's two major types of proteins in the cell membrane. The first can look something like this."}, {"video_title": "Cell membrane proteins   Cells   MCAT   Khan Academy.mp3", "Sentence": "And it'll make up our bilayer. So you can see that there are two layers of these phospholipids. Now, there's two major types of proteins in the cell membrane. The first can look something like this. And this can appear anywhere in the cell membrane. And there are usually quite a few of these throughout the entire cell. So this is what we call an integral protein."}, {"video_title": "Cell membrane proteins   Cells   MCAT   Khan Academy.mp3", "Sentence": "The first can look something like this. And this can appear anywhere in the cell membrane. And there are usually quite a few of these throughout the entire cell. So this is what we call an integral protein. You'll notice that it's called an integral protein because you can think of it like it's integrated throughout the entire membrane. Another type of protein that we might encounter might appear on top of the membrane. Occasionally, it might be slightly into the membrane."}, {"video_title": "Cell membrane proteins   Cells   MCAT   Khan Academy.mp3", "Sentence": "So this is what we call an integral protein. You'll notice that it's called an integral protein because you can think of it like it's integrated throughout the entire membrane. Another type of protein that we might encounter might appear on top of the membrane. Occasionally, it might be slightly into the membrane. And it can also rest on top of integral proteins. And this we call peripheral proteins. And the reason why we call it a peripheral protein is because it's on the peripheral, or the outside, of the cell membrane."}, {"video_title": "Cell membrane proteins   Cells   MCAT   Khan Academy.mp3", "Sentence": "Occasionally, it might be slightly into the membrane. And it can also rest on top of integral proteins. And this we call peripheral proteins. And the reason why we call it a peripheral protein is because it's on the peripheral, or the outside, of the cell membrane. The difference between peripheral and integral proteins is that integral proteins are really stuck inside the cell membrane. As you can see in this picture, the integral protein is really inside the membrane. And as a result, it'll be very difficult to remove."}, {"video_title": "Cell membrane proteins   Cells   MCAT   Khan Academy.mp3", "Sentence": "And the reason why we call it a peripheral protein is because it's on the peripheral, or the outside, of the cell membrane. The difference between peripheral and integral proteins is that integral proteins are really stuck inside the cell membrane. As you can see in this picture, the integral protein is really inside the membrane. And as a result, it'll be very difficult to remove. Peripheral proteins kind of attach and remove themselves from the cell membrane or from other proteins. They generally are there for different cell processes. So for example, a hormone might be a peripheral protein."}, {"video_title": "Cell membrane proteins   Cells   MCAT   Khan Academy.mp3", "Sentence": "And as a result, it'll be very difficult to remove. Peripheral proteins kind of attach and remove themselves from the cell membrane or from other proteins. They generally are there for different cell processes. So for example, a hormone might be a peripheral protein. And it might attach to the cell, make the cell do something, and then leave. Peripheral proteins can also exist inside the cell on the cell membrane. Another type of protein is extremely rare."}, {"video_title": "Cell membrane proteins   Cells   MCAT   Khan Academy.mp3", "Sentence": "So for example, a hormone might be a peripheral protein. And it might attach to the cell, make the cell do something, and then leave. Peripheral proteins can also exist inside the cell on the cell membrane. Another type of protein is extremely rare. And it can appear inside the cell membrane like that. And we call this a lipid-bound protein. Why might you think a lipid-bound protein is so difficult to find, so rare?"}, {"video_title": "Cell membrane proteins   Cells   MCAT   Khan Academy.mp3", "Sentence": "Another type of protein is extremely rare. And it can appear inside the cell membrane like that. And we call this a lipid-bound protein. Why might you think a lipid-bound protein is so difficult to find, so rare? Well, the reason why is because proteins are there to interact with the outside environment. And lipid-bound proteins are stuck on the interior of the cell membrane itself. So it can't really interact with the outside of the cell or the inside of the cell."}, {"video_title": "Cell membrane proteins   Cells   MCAT   Khan Academy.mp3", "Sentence": "Why might you think a lipid-bound protein is so difficult to find, so rare? Well, the reason why is because proteins are there to interact with the outside environment. And lipid-bound proteins are stuck on the interior of the cell membrane itself. So it can't really interact with the outside of the cell or the inside of the cell. So it doesn't really serve a big function in terms of the cell membrane performing its duties. We're going to spend a little bit of time talking about two types of integral proteins that are extremely important, because these two proteins are found all over the cell. And they help the cell maintain homeostasis, or balance."}, {"video_title": "Cell membrane proteins   Cells   MCAT   Khan Academy.mp3", "Sentence": "So it can't really interact with the outside of the cell or the inside of the cell. So it doesn't really serve a big function in terms of the cell membrane performing its duties. We're going to spend a little bit of time talking about two types of integral proteins that are extremely important, because these two proteins are found all over the cell. And they help the cell maintain homeostasis, or balance. The first type can look something like this. Again, this is an integral protein. What do you think this protein might be used for?"}, {"video_title": "Cell membrane proteins   Cells   MCAT   Khan Academy.mp3", "Sentence": "And they help the cell maintain homeostasis, or balance. The first type can look something like this. Again, this is an integral protein. What do you think this protein might be used for? This isn't two proteins. It's actually one protein with a hole through it. Well, this protein is actually used to allow things to pass through the cell."}, {"video_title": "Cell membrane proteins   Cells   MCAT   Khan Academy.mp3", "Sentence": "What do you think this protein might be used for? This isn't two proteins. It's actually one protein with a hole through it. Well, this protein is actually used to allow things to pass through the cell. We call this a channel protein. And like the name implies, there's a channel or hole inside the protein that lets things pass through. So for example, if there is some sort of ion, let's say this is an Na plus ion, a sodium ion, this is outside the cell."}, {"video_title": "Cell membrane proteins   Cells   MCAT   Khan Academy.mp3", "Sentence": "Well, this protein is actually used to allow things to pass through the cell. We call this a channel protein. And like the name implies, there's a channel or hole inside the protein that lets things pass through. So for example, if there is some sort of ion, let's say this is an Na plus ion, a sodium ion, this is outside the cell. And the cell at this point really needs these sodium ions to perform a really important process. So what the channel proteins do is they'll allow these outside extracellular ions into the cell. And normally, these sodium ions wouldn't be able to pass through the cell membrane just by themselves."}, {"video_title": "Cell membrane proteins   Cells   MCAT   Khan Academy.mp3", "Sentence": "So for example, if there is some sort of ion, let's say this is an Na plus ion, a sodium ion, this is outside the cell. And the cell at this point really needs these sodium ions to perform a really important process. So what the channel proteins do is they'll allow these outside extracellular ions into the cell. And normally, these sodium ions wouldn't be able to pass through the cell membrane just by themselves. These channel proteins allow our bodies to take in different materials from the outside environment into our cells. What they can also do is they can also do the reverse. So let's say your cell has way too much sodium, and it needs to get rid of it."}, {"video_title": "Cell membrane proteins   Cells   MCAT   Khan Academy.mp3", "Sentence": "And normally, these sodium ions wouldn't be able to pass through the cell membrane just by themselves. These channel proteins allow our bodies to take in different materials from the outside environment into our cells. What they can also do is they can also do the reverse. So let's say your cell has way too much sodium, and it needs to get rid of it. So channel proteins can start pumping these out. Channel proteins generally don't require energy. So there's no energy needed."}, {"video_title": "Cell membrane proteins   Cells   MCAT   Khan Academy.mp3", "Sentence": "So let's say your cell has way too much sodium, and it needs to get rid of it. So channel proteins can start pumping these out. Channel proteins generally don't require energy. So there's no energy needed. Sometimes we call energy ATP. And another thing that's special about channel proteins is you'll notice that it'll go with the concentration gradient. So out here, there's a lot."}, {"video_title": "Cell membrane proteins   Cells   MCAT   Khan Academy.mp3", "Sentence": "So there's no energy needed. Sometimes we call energy ATP. And another thing that's special about channel proteins is you'll notice that it'll go with the concentration gradient. So out here, there's a lot. And inside, there's very little. So it'll pump from where there's a lot of sodium into where there's very little. So it'll go what we call down a concentration gradient."}, {"video_title": "Cell membrane proteins   Cells   MCAT   Khan Academy.mp3", "Sentence": "So out here, there's a lot. And inside, there's very little. So it'll pump from where there's a lot of sodium into where there's very little. So it'll go what we call down a concentration gradient. Concentration gradient. The second type of very important integral protein is called a carrier protein. And like the name implies, it carries substances into the cell."}, {"video_title": "Cell membrane proteins   Cells   MCAT   Khan Academy.mp3", "Sentence": "So it'll go what we call down a concentration gradient. Concentration gradient. The second type of very important integral protein is called a carrier protein. And like the name implies, it carries substances into the cell. I kind of picture it like a baseball glove, like this. So if there's a molecule that's outside the cell, and the cell actually needs this molecule, so what the carrier protein will do is it'll actually protect this substance so that it can enter the cell safely. It can also do this in reverse."}, {"video_title": "Cell membrane proteins   Cells   MCAT   Khan Academy.mp3", "Sentence": "And like the name implies, it carries substances into the cell. I kind of picture it like a baseball glove, like this. So if there's a molecule that's outside the cell, and the cell actually needs this molecule, so what the carrier protein will do is it'll actually protect this substance so that it can enter the cell safely. It can also do this in reverse. It can take something inside the cell and pump it outside the cell. And this type of protein is really important because unlike channel proteins, carrier proteins can go against the concentration gradient. And this is really important because say your cell has a lot of chloride ions."}, {"video_title": "Cell membrane proteins   Cells   MCAT   Khan Academy.mp3", "Sentence": "It can also do this in reverse. It can take something inside the cell and pump it outside the cell. And this type of protein is really important because unlike channel proteins, carrier proteins can go against the concentration gradient. And this is really important because say your cell has a lot of chloride ions. And your body needs more to perform a certain process. So what your body can do is it can bring more chloride ions into your cell, even though your cell already has a lot of chloride ions. So carrier proteins can sometimes use energy or ATP."}, {"video_title": "Cell membrane proteins   Cells   MCAT   Khan Academy.mp3", "Sentence": "And this is really important because say your cell has a lot of chloride ions. And your body needs more to perform a certain process. So what your body can do is it can bring more chloride ions into your cell, even though your cell already has a lot of chloride ions. So carrier proteins can sometimes use energy or ATP. Finally, there's a type of protein that can exist on any of these that we've drawn here. And this is what we call a glycoprotein. So what a glycoprotein would look like is there will be a chain of sugars attached to a protein."}, {"video_title": "Cell membrane proteins   Cells   MCAT   Khan Academy.mp3", "Sentence": "So carrier proteins can sometimes use energy or ATP. Finally, there's a type of protein that can exist on any of these that we've drawn here. And this is what we call a glycoprotein. So what a glycoprotein would look like is there will be a chain of sugars attached to a protein. And it can be on integral proteins, peripheral proteins, channel proteins. Glycoproteins, you'll notice, have the prefix glyco, which means sugar. And basically, it's just sugar plus protein."}, {"video_title": "Cell membrane proteins   Cells   MCAT   Khan Academy.mp3", "Sentence": "So what a glycoprotein would look like is there will be a chain of sugars attached to a protein. And it can be on integral proteins, peripheral proteins, channel proteins. Glycoproteins, you'll notice, have the prefix glyco, which means sugar. And basically, it's just sugar plus protein. And the purpose of glycoproteins is that it's used in signaling. So it allows a cell to recognize another cell. So in summary, in this picture that we have drawn out of a cell membrane and several different proteins, we have two main classes of proteins."}, {"video_title": "Cell membrane proteins   Cells   MCAT   Khan Academy.mp3", "Sentence": "And basically, it's just sugar plus protein. And the purpose of glycoproteins is that it's used in signaling. So it allows a cell to recognize another cell. So in summary, in this picture that we have drawn out of a cell membrane and several different proteins, we have two main classes of proteins. We have peripheral proteins, which are on the outside of the cell. And they're really easy to remove. We have our integral proteins, which are stuck inside the cell and really tough to remove."}, {"video_title": "Cell membrane proteins   Cells   MCAT   Khan Academy.mp3", "Sentence": "So in summary, in this picture that we have drawn out of a cell membrane and several different proteins, we have two main classes of proteins. We have peripheral proteins, which are on the outside of the cell. And they're really easy to remove. We have our integral proteins, which are stuck inside the cell and really tough to remove. We have our lipid-bound proteins. We have channel proteins, which allow things to move through the cell by its concentration gradient. And it doesn't require energy."}, {"video_title": "Cell membrane proteins   Cells   MCAT   Khan Academy.mp3", "Sentence": "We have our integral proteins, which are stuck inside the cell and really tough to remove. We have our lipid-bound proteins. We have channel proteins, which allow things to move through the cell by its concentration gradient. And it doesn't require energy. And it doesn't require ATP. We have our carrier proteins, which are kind of like a baseball glove. It can take in a particular molecule and let it out inside the cell."}, {"video_title": "Cell membrane proteins   Cells   MCAT   Khan Academy.mp3", "Sentence": "And it doesn't require energy. And it doesn't require ATP. We have our carrier proteins, which are kind of like a baseball glove. It can take in a particular molecule and let it out inside the cell. Or it can do it in reverse. And these can sometimes use ATP. And what's special is they can go against the concentration gradient."}, {"video_title": "Cell membrane proteins   Cells   MCAT   Khan Academy.mp3", "Sentence": "It can take in a particular molecule and let it out inside the cell. Or it can do it in reverse. And these can sometimes use ATP. And what's special is they can go against the concentration gradient. And finally, we have glycoproteins, which really can be any of the proteins that we've drawn out. It's a sugar plus a protein. And it participates in signaling, so cells can recognize each other."}, {"video_title": "Biodiversity and extinction, then and now.mp3", "Sentence": "Species go extinct for a variety of natural reasons like meteor strikes, volcanic eruptions, natural climate shifts, movements of continents over geological eons, things that occur all the time without the involvement of humans. Therefore, scientists know there's a natural background rate of extinction that's estimated to be somewhere in the neighborhood of one to five extinctions a year, averaged over geologic time. This background rate exists because organisms are constantly being confronted by environmental changes. Some can deal with it, others can't. A major change has the potential result of an extinction. Even without a direct natural phenomenon that could kill individuals directly, a species could go extinct due to its inability to keep up with the competitors, predators, or parasites that are always influencing its local environment or changing the way that it interacts with its ecosystem. It's now estimated that the present extinction rate is somewhere between 1,000 to 10,000 times the background rate."}, {"video_title": "Biodiversity and extinction, then and now.mp3", "Sentence": "Some can deal with it, others can't. A major change has the potential result of an extinction. Even without a direct natural phenomenon that could kill individuals directly, a species could go extinct due to its inability to keep up with the competitors, predators, or parasites that are always influencing its local environment or changing the way that it interacts with its ecosystem. It's now estimated that the present extinction rate is somewhere between 1,000 to 10,000 times the background rate. And we also know the main reason for this. The reason is us. What I'd like to do here is frame this within nothing less than the entire history of life on Earth."}, {"video_title": "Biodiversity and extinction, then and now.mp3", "Sentence": "It's now estimated that the present extinction rate is somewhere between 1,000 to 10,000 times the background rate. And we also know the main reason for this. The reason is us. What I'd like to do here is frame this within nothing less than the entire history of life on Earth. Have extinctions of this magnitude happened before? And what can we learn from that? The answer is yes."}, {"video_title": "Biodiversity and extinction, then and now.mp3", "Sentence": "What I'd like to do here is frame this within nothing less than the entire history of life on Earth. Have extinctions of this magnitude happened before? And what can we learn from that? The answer is yes. There have been massive extinctions in the past, and we're now experiencing the highest rate of extinction since the last major mass extinction that occurred at the end of the Cretaceous, some 65 million years ago. This is the one that a lot of people, especially seven-year-olds, are familiar with because it ended the age of dinosaurs. This extinction was likely caused by effects that occurred after the impact of a large asteroid, which scientists like to call a bolide."}, {"video_title": "Biodiversity and extinction, then and now.mp3", "Sentence": "The answer is yes. There have been massive extinctions in the past, and we're now experiencing the highest rate of extinction since the last major mass extinction that occurred at the end of the Cretaceous, some 65 million years ago. This is the one that a lot of people, especially seven-year-olds, are familiar with because it ended the age of dinosaurs. This extinction was likely caused by effects that occurred after the impact of a large asteroid, which scientists like to call a bolide. So when you see the term bolide impact, you can tell your friends that that means basically kablooey. Some suggest that the smoking gun of this bolide impact is a huge crater 15 to 20 kilometers deep and over 170 kilometers across, buried deeply in sediments along the Yucatan Peninsula. This crater was made by a bolide about 10 kilometers across."}, {"video_title": "Biodiversity and extinction, then and now.mp3", "Sentence": "This extinction was likely caused by effects that occurred after the impact of a large asteroid, which scientists like to call a bolide. So when you see the term bolide impact, you can tell your friends that that means basically kablooey. Some suggest that the smoking gun of this bolide impact is a huge crater 15 to 20 kilometers deep and over 170 kilometers across, buried deeply in sediments along the Yucatan Peninsula. This crater was made by a bolide about 10 kilometers across. Events like this leave a physical, detectable mark in Earth's crust. Geologists use markers like this, along with other changes in the rocks, to give special names to specific periods, intervals of geologic time and history bounded by these markers. Names like Paleozoic, Cambrian, Carboniferous, Cenozoic, these are names of epochs, eras, periods, etc."}, {"video_title": "Biodiversity and extinction, then and now.mp3", "Sentence": "This crater was made by a bolide about 10 kilometers across. Events like this leave a physical, detectable mark in Earth's crust. Geologists use markers like this, along with other changes in the rocks, to give special names to specific periods, intervals of geologic time and history bounded by these markers. Names like Paleozoic, Cambrian, Carboniferous, Cenozoic, these are names of epochs, eras, periods, etc. in the history of the planet. Scientists ask if we are, right now, making an event that will be detectable millions of years from now in the geologic record. Some claim that we are, and that we should be calling this present epoch the Anthropocene."}, {"video_title": "Biodiversity and extinction, then and now.mp3", "Sentence": "Names like Paleozoic, Cambrian, Carboniferous, Cenozoic, these are names of epochs, eras, periods, etc. in the history of the planet. Scientists ask if we are, right now, making an event that will be detectable millions of years from now in the geologic record. Some claim that we are, and that we should be calling this present epoch the Anthropocene. Anthro for human, with cene being the suffix that we use to designate these epochs. So these scientists suggest that we signify a special epoch in the history of the Earth, an epoch marked by a new type of fossil evidence, such as plastics or some crusty carbon layer that indicates that we have left an indelible mark in the geology that will be preserved for eons. Right now, what can we learn from the past by looking at this big picture history of extinction on Earth?"}, {"video_title": "Biodiversity and extinction, then and now.mp3", "Sentence": "Some claim that we are, and that we should be calling this present epoch the Anthropocene. Anthro for human, with cene being the suffix that we use to designate these epochs. So these scientists suggest that we signify a special epoch in the history of the Earth, an epoch marked by a new type of fossil evidence, such as plastics or some crusty carbon layer that indicates that we have left an indelible mark in the geology that will be preserved for eons. Right now, what can we learn from the past by looking at this big picture history of extinction on Earth? We know that biodiversity is governed by a balancing act between speciation and extinction. Does biodiversity increase steadily with time? Has it reached an equilibrium limit?"}, {"video_title": "Biodiversity and extinction, then and now.mp3", "Sentence": "Right now, what can we learn from the past by looking at this big picture history of extinction on Earth? We know that biodiversity is governed by a balancing act between speciation and extinction. Does biodiversity increase steadily with time? Has it reached an equilibrium limit? Speciation is caused by one species splitting to give rise to two new species, each of those giving rise to two more, and so on. You'd expect the number of species to increase over time. However, that multiplication is offset by extinction."}, {"video_title": "Biodiversity and extinction, then and now.mp3", "Sentence": "Has it reached an equilibrium limit? Speciation is caused by one species splitting to give rise to two new species, each of those giving rise to two more, and so on. You'd expect the number of species to increase over time. However, that multiplication is offset by extinction. If you look at a graph of biodiversity over the history of our planet, you get something that looks like this. You can see that there is indeed an overall trend towards an increase in biodiversity, but you can also mark certain spots on this curve here, here, here, here, and here that indicate significant drops in biodiversity. These are known as major mass extinction events, times during which extraordinarily high numbers of species disappeared, times when the extinction rate was well above the background rate."}, {"video_title": "Biodiversity and extinction, then and now.mp3", "Sentence": "However, that multiplication is offset by extinction. If you look at a graph of biodiversity over the history of our planet, you get something that looks like this. You can see that there is indeed an overall trend towards an increase in biodiversity, but you can also mark certain spots on this curve here, here, here, here, and here that indicate significant drops in biodiversity. These are known as major mass extinction events, times during which extraordinarily high numbers of species disappeared, times when the extinction rate was well above the background rate. It's worth looking at these because they suggest some interesting and, I think, relevant reasons for why these extinctions happen. So I want to go into these in a little bit of detail. The first one, here, occurs at the Ordovician-Selurian boundary 440 to 450 million years ago."}, {"video_title": "Biodiversity and extinction, then and now.mp3", "Sentence": "These are known as major mass extinction events, times during which extraordinarily high numbers of species disappeared, times when the extinction rate was well above the background rate. It's worth looking at these because they suggest some interesting and, I think, relevant reasons for why these extinctions happen. So I want to go into these in a little bit of detail. The first one, here, occurs at the Ordovician-Selurian boundary 440 to 450 million years ago. What on Earth can we learn from something that happened so long ago? Well, for one thing, during this time, 60% of marine invertebrate species died out. These extinctions seem to be the result of effects caused by movement of the huge supercontinent that existed at that time, Gondwana."}, {"video_title": "Biodiversity and extinction, then and now.mp3", "Sentence": "The first one, here, occurs at the Ordovician-Selurian boundary 440 to 450 million years ago. What on Earth can we learn from something that happened so long ago? Well, for one thing, during this time, 60% of marine invertebrate species died out. These extinctions seem to be the result of effects caused by movement of the huge supercontinent that existed at that time, Gondwana. Sounds like a pretty interesting place, except that it moves slowly into the south polar region, with a consequent sea level fall as significant amounts of the planet's precipitation became tied up in snow and ice on Gondwana, rather than flowing back into the sea. And this change disrupted marine ecosystems along the continental shelf, resulting in extinctions, extinctions recorded as another marker in the fossil record. The second major extinction, here, occurred during the late Devonian period, about 374 million years ago."}, {"video_title": "Biodiversity and extinction, then and now.mp3", "Sentence": "These extinctions seem to be the result of effects caused by movement of the huge supercontinent that existed at that time, Gondwana. Sounds like a pretty interesting place, except that it moves slowly into the south polar region, with a consequent sea level fall as significant amounts of the planet's precipitation became tied up in snow and ice on Gondwana, rather than flowing back into the sea. And this change disrupted marine ecosystems along the continental shelf, resulting in extinctions, extinctions recorded as another marker in the fossil record. The second major extinction, here, occurred during the late Devonian period, about 374 million years ago. I'm amazed that scientists can get that precise, but they can. We now know that 50% of all the genera on Earth went extinct at this time. Think about that for a moment."}, {"video_title": "Biodiversity and extinction, then and now.mp3", "Sentence": "The second major extinction, here, occurred during the late Devonian period, about 374 million years ago. I'm amazed that scientists can get that precise, but they can. We now know that 50% of all the genera on Earth went extinct at this time. Think about that for a moment. We're not talking about species, we're talking about entire genera. And that means a lot of species. There's some thought that this was due to a bolide impact that occurred long before the one that wiped out the dinosaurs."}, {"video_title": "Biodiversity and extinction, then and now.mp3", "Sentence": "Think about that for a moment. We're not talking about species, we're talking about entire genera. And that means a lot of species. There's some thought that this was due to a bolide impact that occurred long before the one that wiped out the dinosaurs. But maybe not. Others think maybe it was oceanic volcanism, or some global cooling mechanism that we don't fully understand. Some suggest that it was due to a drop in speciation rate, rather than an increase in extinction rate."}, {"video_title": "Biodiversity and extinction, then and now.mp3", "Sentence": "There's some thought that this was due to a bolide impact that occurred long before the one that wiped out the dinosaurs. But maybe not. Others think maybe it was oceanic volcanism, or some global cooling mechanism that we don't fully understand. Some suggest that it was due to a drop in speciation rate, rather than an increase in extinction rate. And clearly, more research is needed here. The third of the big five extinction events, here, is something that occurred at the end of the Permian, between the Permian and Triassic periods, about 252 million years ago. This is sometimes known as the Great Dying, the biggest known extinction event, during which 96% of all marine and 70% of all terrestrial vertebrates died out."}, {"video_title": "Biodiversity and extinction, then and now.mp3", "Sentence": "Some suggest that it was due to a drop in speciation rate, rather than an increase in extinction rate. And clearly, more research is needed here. The third of the big five extinction events, here, is something that occurred at the end of the Permian, between the Permian and Triassic periods, about 252 million years ago. This is sometimes known as the Great Dying, the biggest known extinction event, during which 96% of all marine and 70% of all terrestrial vertebrates died out. It also appears that it's one of the few mass extinctions in which insects took a big hit. I guess it takes a lot to kill all those cockroaches. In total, 83% of all the genera on Earth disappeared."}, {"video_title": "Biodiversity and extinction, then and now.mp3", "Sentence": "This is sometimes known as the Great Dying, the biggest known extinction event, during which 96% of all marine and 70% of all terrestrial vertebrates died out. It also appears that it's one of the few mass extinctions in which insects took a big hit. I guess it takes a lot to kill all those cockroaches. In total, 83% of all the genera on Earth disappeared. The suggested reasons behind this mass extinction range all over the map, some people think it might have been one or more bolide impacts, or volcanism on a huge scale, possibly from a place called the Siberian Traps, where there were huge outpourings of lava, big fires going on, and all kinds of horrible things happening to the environment because of that volcanism. It could also have been a runaway greenhouse effect triggered by the sudden release of methane from the ocean floor. Methane can be stored by the activities of bacteria as something called methane clathrates in sediments of the ocean floor."}, {"video_title": "Biodiversity and extinction, then and now.mp3", "Sentence": "In total, 83% of all the genera on Earth disappeared. The suggested reasons behind this mass extinction range all over the map, some people think it might have been one or more bolide impacts, or volcanism on a huge scale, possibly from a place called the Siberian Traps, where there were huge outpourings of lava, big fires going on, and all kinds of horrible things happening to the environment because of that volcanism. It could also have been a runaway greenhouse effect triggered by the sudden release of methane from the ocean floor. Methane can be stored by the activities of bacteria as something called methane clathrates in sediments of the ocean floor. Geologic disturbance might be able to release these stores of clathrates, releasing huge amounts of the potent greenhouse gas, methane. Other people think that there might have been major sea level changes at the time due to overall climate changes. Increasing anoxic conditions, or lack of oxygen in the deep sea, or perhaps shifts in oceanic circulation patterns could be results of those climate changes."}, {"video_title": "Biodiversity and extinction, then and now.mp3", "Sentence": "Methane can be stored by the activities of bacteria as something called methane clathrates in sediments of the ocean floor. Geologic disturbance might be able to release these stores of clathrates, releasing huge amounts of the potent greenhouse gas, methane. Other people think that there might have been major sea level changes at the time due to overall climate changes. Increasing anoxic conditions, or lack of oxygen in the deep sea, or perhaps shifts in oceanic circulation patterns could be results of those climate changes. Or maybe a hellish convergence of all these things. I can easily imagine the volcanism causing earthquakes that would release methane clathrates and cause oceanic circulation changes, and so on and so forth. A cascade of disasters."}, {"video_title": "Biodiversity and extinction, then and now.mp3", "Sentence": "Increasing anoxic conditions, or lack of oxygen in the deep sea, or perhaps shifts in oceanic circulation patterns could be results of those climate changes. Or maybe a hellish convergence of all these things. I can easily imagine the volcanism causing earthquakes that would release methane clathrates and cause oceanic circulation changes, and so on and so forth. A cascade of disasters. The fourth major extinction occurred at the Triassic-Jurassic boundary, 201 million years ago. 34% of all marine genera died out, along with a whole bunch of terrestrial vertebrate groups, clearing the stage for the rise of the dinosaurs. Hooray!"}, {"video_title": "Biodiversity and extinction, then and now.mp3", "Sentence": "A cascade of disasters. The fourth major extinction occurred at the Triassic-Jurassic boundary, 201 million years ago. 34% of all marine genera died out, along with a whole bunch of terrestrial vertebrate groups, clearing the stage for the rise of the dinosaurs. Hooray! Where would all of our 5-10 year olds be if it weren't for the Triassic-Jurassic extinction? Statistical analysis suggests some complications in figuring out what the story is here, but a drop in speciation rather than an increase in extinction might have caused this drop in biodiversity, too. The fifth and possibly most famous of all the Big Five extinctions is the Cretaceous-Paleogene event 65 to 66 million years ago."}, {"video_title": "Biodiversity and extinction, then and now.mp3", "Sentence": "Hooray! Where would all of our 5-10 year olds be if it weren't for the Triassic-Jurassic extinction? Statistical analysis suggests some complications in figuring out what the story is here, but a drop in speciation rather than an increase in extinction might have caused this drop in biodiversity, too. The fifth and possibly most famous of all the Big Five extinctions is the Cretaceous-Paleogene event 65 to 66 million years ago. And we know the story. A kablooey, a bolide impact, with dinosaurs dying out in the aftermath, along with lots of other groups. About 75% of all known species went extinct, but this was followed by rapid recovery, giving way to what many scientists refer to as the modern biota, including the rise of mammals."}, {"video_title": "Biodiversity and extinction, then and now.mp3", "Sentence": "The fifth and possibly most famous of all the Big Five extinctions is the Cretaceous-Paleogene event 65 to 66 million years ago. And we know the story. A kablooey, a bolide impact, with dinosaurs dying out in the aftermath, along with lots of other groups. About 75% of all known species went extinct, but this was followed by rapid recovery, giving way to what many scientists refer to as the modern biota, including the rise of mammals. And I think we can learn something from that, too. Life is amazingly tenacious. For all the delicacy of an individual or a species, life recovered in impressive ways at least five different times."}, {"video_title": "Biodiversity and extinction, then and now.mp3", "Sentence": "About 75% of all known species went extinct, but this was followed by rapid recovery, giving way to what many scientists refer to as the modern biota, including the rise of mammals. And I think we can learn something from that, too. Life is amazingly tenacious. For all the delicacy of an individual or a species, life recovered in impressive ways at least five different times. Which leads to a fascinating question. What happens after a mass extinction? What are the contingencies, as evolutionists call them, that happen when ecosystems are suddenly opened up by the removal of many species?"}, {"video_title": "Biodiversity and extinction, then and now.mp3", "Sentence": "For all the delicacy of an individual or a species, life recovered in impressive ways at least five different times. Which leads to a fascinating question. What happens after a mass extinction? What are the contingencies, as evolutionists call them, that happen when ecosystems are suddenly opened up by the removal of many species? Who comes next? Who can take advantage of the changes in the openings? And how fast can all that happen?"}, {"video_title": "Biodiversity and extinction, then and now.mp3", "Sentence": "What are the contingencies, as evolutionists call them, that happen when ecosystems are suddenly opened up by the removal of many species? Who comes next? Who can take advantage of the changes in the openings? And how fast can all that happen? Those are difficult but very interesting and very relevant scientific questions. So there are lots of people working on them because, as I like to say, the past is where you came from. Without knowing where you came from, sometimes you can't know where you're going."}, {"video_title": "Biodiversity and extinction, then and now.mp3", "Sentence": "And how fast can all that happen? Those are difficult but very interesting and very relevant scientific questions. So there are lots of people working on them because, as I like to say, the past is where you came from. Without knowing where you came from, sometimes you can't know where you're going. And lots of the extinction causes I just described should sound a bit familiar, because they bring us back full circle to the beginning of this video in thinking about a sixth mass extinction during the Anthropocene. For the first time in the entire history of life on Earth, there's a mass extinction happening due to a single species, us. What's going to happen while this is going on and after it runs its present course?"}, {"video_title": "Biodiversity and extinction, then and now.mp3", "Sentence": "Without knowing where you came from, sometimes you can't know where you're going. And lots of the extinction causes I just described should sound a bit familiar, because they bring us back full circle to the beginning of this video in thinking about a sixth mass extinction during the Anthropocene. For the first time in the entire history of life on Earth, there's a mass extinction happening due to a single species, us. What's going to happen while this is going on and after it runs its present course? I hate to imagine a world without tigers or blue whales or sequoias or salmon, clams, coral reefs. But without them and the ecosystems that depend on them, our time is limited. We'll not only be the cause of a mass extinction, we'll be part of it."}, {"video_title": "Speed and precision of DNA replication   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "And that's the speed and the precision with which this is actually happening. As we talked about in that video, it feels pretty complex. You have this topoisomerase that's unwinding things, the helicase is unzipping it. Then you have the polymerase that can only go from the five prime to three prime direction. It needs a little primer to get started, but then it starts adding the nucleotides on the lagging strand. You have to have the RNA primer, but then it's going from, once again, from five prime to three prime. So you have these Okazaki fragments."}, {"video_title": "Speed and precision of DNA replication   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "Then you have the polymerase that can only go from the five prime to three prime direction. It needs a little primer to get started, but then it starts adding the nucleotides on the lagging strand. You have to have the RNA primer, but then it's going from, once again, from five prime to three prime. So you have these Okazaki fragments. And all of this craziness that's happening, and remember, these things don't have brains. These aren't computers. They don't know exactly where to go."}, {"video_title": "Speed and precision of DNA replication   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "So you have these Okazaki fragments. And all of this craziness that's happening, and remember, these things don't have brains. These aren't computers. They don't know exactly where to go. It's all because of the chemistry. They're all bumping into each other and reacting in just the right way to make this incredible thing happen. Now what I'm about to tell you is really going to boggle your mind because this is happening incredibly fast."}, {"video_title": "Speed and precision of DNA replication   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "They don't know exactly where to go. It's all because of the chemistry. They're all bumping into each other and reacting in just the right way to make this incredible thing happen. Now what I'm about to tell you is really going to boggle your mind because this is happening incredibly fast. DNA polymerase has been clocked, at least in E. coli, has a clock at approaching 1,000 base pairs per second. I think the number that I saw was 700-something base pairs per second. So polymerase, let me write this down."}, {"video_title": "Speed and precision of DNA replication   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "Now what I'm about to tell you is really going to boggle your mind because this is happening incredibly fast. DNA polymerase has been clocked, at least in E. coli, has a clock at approaching 1,000 base pairs per second. I think the number that I saw was 700-something base pairs per second. So polymerase, let me write this down. This is worth writing down because it's mind-boggling. It gives you a sense of just how amazing the machinery in your cells are. So it's been as high as, and it can change."}, {"video_title": "Speed and precision of DNA replication   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "So polymerase, let me write this down. This is worth writing down because it's mind-boggling. It gives you a sense of just how amazing the machinery in your cells are. So it's been as high as, and it can change. It can speed up and slow down, and that's actually been observed. But polymerase, as fast as, as fast as 700-plus base pairs per second. Base pairs per second."}, {"video_title": "Speed and precision of DNA replication   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "So it's been as high as, and it can change. It can speed up and slow down, and that's actually been observed. But polymerase, as fast as, as fast as 700-plus base pairs per second. Base pairs per second. So on this diagram, hey man, it's just zipping. It's just zipping along, at least from our perceptual frame of reference. A second seems like a very short amount of time to us, but on a molecular scale, these things are just bouncing around and just getting this stuff done."}, {"video_title": "Speed and precision of DNA replication   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "Base pairs per second. So on this diagram, hey man, it's just zipping. It's just zipping along, at least from our perceptual frame of reference. A second seems like a very short amount of time to us, but on a molecular scale, these things are just bouncing around and just getting this stuff done. Now the second thing that you might be wondering, okay, this is happening fast, but surely it has a lot of errors. Well, the first thing you might say, well, if it had a lot of errors, that would really not be good for biology because you always have DNA replicating throughout our lives, and at some point you just have so many errors that the cells wouldn't function anymore. And so lucky for us that this is actually a fairly precise process."}, {"video_title": "Speed and precision of DNA replication   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "A second seems like a very short amount of time to us, but on a molecular scale, these things are just bouncing around and just getting this stuff done. Now the second thing that you might be wondering, okay, this is happening fast, but surely it has a lot of errors. Well, the first thing you might say, well, if it had a lot of errors, that would really not be good for biology because you always have DNA replicating throughout our lives, and at some point you just have so many errors that the cells wouldn't function anymore. And so lucky for us that this is actually a fairly precise process. Even in the first pass of the polymerase, you have one mistake, you have one mistake, let me write this down because it's amazing, one mistake for every approximately 10 to the seventh. So this is 10 million nucleotides. And that might seem pretty accurate, but you've got to remember, we have billions of nucleotides in our DNA, so this would still introduce a lot of errors, but then there's proofreading that goes back and makes sure that those errors don't stick around."}, {"video_title": "Speed and precision of DNA replication   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "And so lucky for us that this is actually a fairly precise process. Even in the first pass of the polymerase, you have one mistake, you have one mistake, let me write this down because it's amazing, one mistake for every approximately 10 to the seventh. So this is 10 million nucleotides. And that might seem pretty accurate, but you've got to remember, we have billions of nucleotides in our DNA, so this would still introduce a lot of errors, but then there's proofreading that goes back and makes sure that those errors don't stick around. And so once all the proofreading takes place, it actually becomes one mistake, one mistake for every approximately 10 to the ninth nucleotide. So approximately, you can, we do this at an incredibly fast pace, as fast as 700 plus approaching 1,000 base pairs per second, and you have one error every billion nucleotides, especially after you go through these proofreading steps. And so it's incredibly fast, and it's incredibly precise."}, {"video_title": "Were Dinosaurs Undergoing Long-Term Decline Before Mass Extinction.mp3", "Sentence": "Why did they go extinct? When did they go extinct? And we know that dinosaurs went extinct about 65 million years ago, right at the end of the Cretaceous. We know there was a big asteroid that hit the planet at that time. We know there was massive volcanic eruptions going on at that time. But it's remained a bit of a mystery. Did one or both of those things cause dinosaurs to go extinct?"}, {"video_title": "Were Dinosaurs Undergoing Long-Term Decline Before Mass Extinction.mp3", "Sentence": "We know there was a big asteroid that hit the planet at that time. We know there was massive volcanic eruptions going on at that time. But it's remained a bit of a mystery. Did one or both of those things cause dinosaurs to go extinct? Or were there other factors involved? We have a paper coming out in Nature Communications on the dinosaur extinction and how dinosaurs were changing during those 10 to 12 million years right before their extinction. And this is a collaboration between myself and Mark Norell, my advisor here at the American Museum, and our colleagues Richard Butler and Albert Prieto Marquez in Munich."}, {"video_title": "Were Dinosaurs Undergoing Long-Term Decline Before Mass Extinction.mp3", "Sentence": "Did one or both of those things cause dinosaurs to go extinct? Or were there other factors involved? We have a paper coming out in Nature Communications on the dinosaur extinction and how dinosaurs were changing during those 10 to 12 million years right before their extinction. And this is a collaboration between myself and Mark Norell, my advisor here at the American Museum, and our colleagues Richard Butler and Albert Prieto Marquez in Munich. So what we've done with this project is we've looked specifically at dinosaur anatomy. There has been a lot of previous work on the dinosaur extinction over the last several decades. But what most people have done before is they've looked at species counts."}, {"video_title": "Were Dinosaurs Undergoing Long-Term Decline Before Mass Extinction.mp3", "Sentence": "And this is a collaboration between myself and Mark Norell, my advisor here at the American Museum, and our colleagues Richard Butler and Albert Prieto Marquez in Munich. So what we've done with this project is we've looked specifically at dinosaur anatomy. There has been a lot of previous work on the dinosaur extinction over the last several decades. But what most people have done before is they've looked at species counts. They've looked at dinosaur diversity in terms of how many species of dinosaurs there were and how that changed over time. What we do in this paper is that we take a completely different approach. So we're not as interested in the number of species as we are in the number of kinds."}, {"video_title": "Were Dinosaurs Undergoing Long-Term Decline Before Mass Extinction.mp3", "Sentence": "But what most people have done before is they've looked at species counts. They've looked at dinosaur diversity in terms of how many species of dinosaurs there were and how that changed over time. What we do in this paper is that we take a completely different approach. So we're not as interested in the number of species as we are in the number of kinds. What we've done is we've tried to tease that signal out to look at the physical difference among different dinosaur species, how that represents itself as one comes up to the terminal Cretaceous event. Our results show really that dinosaurs were in a state of flux during the final 12 million years before they went extinct. Some groups of dinosaurs, like the carnivorous dinosaurs and smaller species of plant eaters, were pretty steady in their evolution during those 12 million years before the extinction."}, {"video_title": "Were Dinosaurs Undergoing Long-Term Decline Before Mass Extinction.mp3", "Sentence": "So we're not as interested in the number of species as we are in the number of kinds. What we've done is we've tried to tease that signal out to look at the physical difference among different dinosaur species, how that represents itself as one comes up to the terminal Cretaceous event. Our results show really that dinosaurs were in a state of flux during the final 12 million years before they went extinct. Some groups of dinosaurs, like the carnivorous dinosaurs and smaller species of plant eaters, were pretty steady in their evolution during those 12 million years before the extinction. But other groups of dinosaurs, specifically the very large plant-eating dinosaurs, things like the Ceratopsians, like Triceratops, and also the duck-billed dinosaurs, these animals seem to have been undergoing a very long-term decline. We also found that different dinosaurs living in different parts of the world were changing in different ways. So dinosaurs living in North America generally seem to have been undergoing a decline in biodiversity, at least these large plant eaters, whereas those living in Asia seem to have actually been increasing."}, {"video_title": "Ionic bonds   Molecular and ionic compound structure and properties   AP Chemistry   Khan Academy.mp3", "Sentence": "We have thought about the number of electrons and protons and neutrons and the electron configuration of atoms. But atoms don't just operate in isolation. If that were the case, the whole universe, including us, would just be a bunch of atoms drifting around. What begins to be interesting is how the atoms actually interact with each other. And one of the most interesting forms of interaction is when they stick to each other in some way, shape, or form. And this sticking together of atoms is what we are going to study in this video. Another way to talk about it is how do atoms bond?"}, {"video_title": "Ionic bonds   Molecular and ionic compound structure and properties   AP Chemistry   Khan Academy.mp3", "Sentence": "What begins to be interesting is how the atoms actually interact with each other. And one of the most interesting forms of interaction is when they stick to each other in some way, shape, or form. And this sticking together of atoms is what we are going to study in this video. Another way to talk about it is how do atoms bond? Now, as we will see, there are several types of bonds, and it's really a spectrum. But let's just start with what I would consider one of the more extreme type of bonds. And to understand it, let's get a periodic table of elements out right over here."}, {"video_title": "Ionic bonds   Molecular and ionic compound structure and properties   AP Chemistry   Khan Academy.mp3", "Sentence": "Another way to talk about it is how do atoms bond? Now, as we will see, there are several types of bonds, and it's really a spectrum. But let's just start with what I would consider one of the more extreme type of bonds. And to understand it, let's get a periodic table of elements out right over here. So let's say that we are dealing with a group one element, let's say sodium right over here. What's interesting about group one elements is that they have one valence electron. If we want to visualize the valence electrons for, say, sodium, we could do it with what's known as a Lewis dot structure or a Lewis electron dot structure, sometimes just called a dot structure for short."}, {"video_title": "Ionic bonds   Molecular and ionic compound structure and properties   AP Chemistry   Khan Academy.mp3", "Sentence": "And to understand it, let's get a periodic table of elements out right over here. So let's say that we are dealing with a group one element, let's say sodium right over here. What's interesting about group one elements is that they have one valence electron. If we want to visualize the valence electrons for, say, sodium, we could do it with what's known as a Lewis dot structure or a Lewis electron dot structure, sometimes just called a dot structure for short. But because a neutral sodium has one valence electron, we would just draw that one valence electron like that. Now, let's go to the other end of the periodic table and say look at chlorine. Chlorine is a halogen."}, {"video_title": "Ionic bonds   Molecular and ionic compound structure and properties   AP Chemistry   Khan Academy.mp3", "Sentence": "If we want to visualize the valence electrons for, say, sodium, we could do it with what's known as a Lewis dot structure or a Lewis electron dot structure, sometimes just called a dot structure for short. But because a neutral sodium has one valence electron, we would just draw that one valence electron like that. Now, let's go to the other end of the periodic table and say look at chlorine. Chlorine is a halogen. Halogens have seven valence electrons. So chlorine's valence electrons would look like this. It has one, two, three, four, five, six, seven valence electrons."}, {"video_title": "Ionic bonds   Molecular and ionic compound structure and properties   AP Chemistry   Khan Academy.mp3", "Sentence": "Chlorine is a halogen. Halogens have seven valence electrons. So chlorine's valence electrons would look like this. It has one, two, three, four, five, six, seven valence electrons. And so you can imagine chlorine would love to get another electron in order to complete its outer shell. And we've also studied in other videos these atoms, these elements at the top right of the periodic table, which are not the noble gases, but especially the top of these halogens, things like oxygen, nitrogen, these are very electronegative. They like to pull electrons, hog electrons."}, {"video_title": "Ionic bonds   Molecular and ionic compound structure and properties   AP Chemistry   Khan Academy.mp3", "Sentence": "It has one, two, three, four, five, six, seven valence electrons. And so you can imagine chlorine would love to get another electron in order to complete its outer shell. And we've also studied in other videos these atoms, these elements at the top right of the periodic table, which are not the noble gases, but especially the top of these halogens, things like oxygen, nitrogen, these are very electronegative. They like to pull electrons, hog electrons. And so what do you think is going to happen when you put these characters together? This guy wants to lose the electrons and chlorine wants to gain an electron. Well, maybe the chlorine will take an electron from the sodium."}, {"video_title": "Ionic bonds   Molecular and ionic compound structure and properties   AP Chemistry   Khan Academy.mp3", "Sentence": "They like to pull electrons, hog electrons. And so what do you think is going to happen when you put these characters together? This guy wants to lose the electrons and chlorine wants to gain an electron. Well, maybe the chlorine will take an electron from the sodium. Now, in a real chemical reaction, you would have trillions of these and they're bouncing around and different things are happening. But just for simplicity, let's just imagine that these are the only two. And let's imagine that this chlorine is able to nab an electron from this sodium."}, {"video_title": "Ionic bonds   Molecular and ionic compound structure and properties   AP Chemistry   Khan Academy.mp3", "Sentence": "Well, maybe the chlorine will take an electron from the sodium. Now, in a real chemical reaction, you would have trillions of these and they're bouncing around and different things are happening. But just for simplicity, let's just imagine that these are the only two. And let's imagine that this chlorine is able to nab an electron from this sodium. So what is going to happen? Well, this sodium is then going to become positively charged, because it's going to lose an electron. And then the chlorine, the chlorine is now going to gain an electron."}, {"video_title": "Ionic bonds   Molecular and ionic compound structure and properties   AP Chemistry   Khan Academy.mp3", "Sentence": "And let's imagine that this chlorine is able to nab an electron from this sodium. So what is going to happen? Well, this sodium is then going to become positively charged, because it's going to lose an electron. And then the chlorine, the chlorine is now going to gain an electron. So it's going to become a chloride anion. Anion is a negative ion. It's a sodium cation, a positive ion."}, {"video_title": "Ionic bonds   Molecular and ionic compound structure and properties   AP Chemistry   Khan Academy.mp3", "Sentence": "And then the chlorine, the chlorine is now going to gain an electron. So it's going to become a chloride anion. Anion is a negative ion. It's a sodium cation, a positive ion. Ion means it's charged. And now it's a chloride anion. So it has the valence electrons that it had before."}, {"video_title": "Ionic bonds   Molecular and ionic compound structure and properties   AP Chemistry   Khan Academy.mp3", "Sentence": "It's a sodium cation, a positive ion. Ion means it's charged. And now it's a chloride anion. So it has the valence electrons that it had before. And then you could imagine that it gains one from the sodium. And now it has a negative charge. Now, what do we know about positively charged ions and negatively charged ions?"}, {"video_title": "Ionic bonds   Molecular and ionic compound structure and properties   AP Chemistry   Khan Academy.mp3", "Sentence": "So it has the valence electrons that it had before. And then you could imagine that it gains one from the sodium. And now it has a negative charge. Now, what do we know about positively charged ions and negatively charged ions? Well, opposites attract, Coulomb forces. So these two characters are going to be attracted to each other. Or another way to think of it, they're gonna stick together."}, {"video_title": "Ionic bonds   Molecular and ionic compound structure and properties   AP Chemistry   Khan Academy.mp3", "Sentence": "Now, what do we know about positively charged ions and negatively charged ions? Well, opposites attract, Coulomb forces. So these two characters are going to be attracted to each other. Or another way to think of it, they're gonna stick together. Or another way you could think about it, they are going to be bonded. And they will form a compound of sodium chloride. And notice, the whole compound here is neutral."}, {"video_title": "Ionic bonds   Molecular and ionic compound structure and properties   AP Chemistry   Khan Academy.mp3", "Sentence": "Or another way to think of it, they're gonna stick together. Or another way you could think about it, they are going to be bonded. And they will form a compound of sodium chloride. And notice, the whole compound here is neutral. It has a plus one charge for the sodium, a negative one charge for the chloride. But taken together, it is neutral because these are hanging out together. And this type of bond between ions, you might guess what it's called."}, {"video_title": "Introduction to nucleic acids and nucleotides   High school biology   Khan Academy (2).mp3", "Sentence": "We are now going to talk about what is perhaps the most important macromolecule in life, and that is known as nucleic acid. Now first of all, where does that name come from? Well, scientists first observed this in the nucleus of cells, and so that's where you get the nucleic part, and it has some acidic properties, and so that's where you get the acid part. And perhaps the most famous of the nucleic acids is deoxyribonucleic acid, or DNA for short, and we'll go into some depth in this as we go through our journey in biology, but you might already know that this is the molecule that stores our hereditary information. This DNA, to a large degree, makes you you, and it's known as a macromolecule, and we've talked about macromolecules in other videos. We've talked about carbohydrates, and we have talked about proteins, and DNA is a macromolecule because it can be made of many millions of atoms. Just to get a sense of it, you can see right over here the double helix of DNA, where you have one side of your helix right over there, and then another one right over here, and then you kind of have these rungs of this twisted ladder."}, {"video_title": "Introduction to nucleic acids and nucleotides   High school biology   Khan Academy (2).mp3", "Sentence": "And perhaps the most famous of the nucleic acids is deoxyribonucleic acid, or DNA for short, and we'll go into some depth in this as we go through our journey in biology, but you might already know that this is the molecule that stores our hereditary information. This DNA, to a large degree, makes you you, and it's known as a macromolecule, and we've talked about macromolecules in other videos. We've talked about carbohydrates, and we have talked about proteins, and DNA is a macromolecule because it can be made of many millions of atoms. Just to get a sense of it, you can see right over here the double helix of DNA, where you have one side of your helix right over there, and then another one right over here, and then you kind of have these rungs of this twisted ladder. A DNA molecule, let's say in the human genome, a chromosome, for example, is primarily a really long DNA molecule, and it can have on the order of 100 million rungs to this ladder. Now, another thing to appreciate, like many other macromolecules, DNA, or nucleic acids in general, they are polymers in that they are made up of building block molecules, and those building blocks for nucleic acids, and DNA is the most famous nucleic acid, and RNA, ribonucleic acid, would be a close second, but the building blocks of them are known as nucleotides. Nucleotides."}, {"video_title": "Introduction to nucleic acids and nucleotides   High school biology   Khan Academy (2).mp3", "Sentence": "Just to get a sense of it, you can see right over here the double helix of DNA, where you have one side of your helix right over there, and then another one right over here, and then you kind of have these rungs of this twisted ladder. A DNA molecule, let's say in the human genome, a chromosome, for example, is primarily a really long DNA molecule, and it can have on the order of 100 million rungs to this ladder. Now, another thing to appreciate, like many other macromolecules, DNA, or nucleic acids in general, they are polymers in that they are made up of building block molecules, and those building blocks for nucleic acids, and DNA is the most famous nucleic acid, and RNA, ribonucleic acid, would be a close second, but the building blocks of them are known as nucleotides. Nucleotides. And we see some examples of nucleotides right over here. This is deoxyadenosine monophosphate, which would be a nucleotide found in DNA. You can see the various parts of it."}, {"video_title": "Introduction to nucleic acids and nucleotides   High school biology   Khan Academy (2).mp3", "Sentence": "Nucleotides. And we see some examples of nucleotides right over here. This is deoxyadenosine monophosphate, which would be a nucleotide found in DNA. You can see the various parts of it. You have a phosphate group right over here. You have a five-carbon sugar, which in this case is ribose, and then you have what is known as a nitrogenous base, and why is it called nitrogenous? Well, those blue circles represent nitrogen, and we've seen this before."}, {"video_title": "Introduction to nucleic acids and nucleotides   High school biology   Khan Academy (2).mp3", "Sentence": "You can see the various parts of it. You have a phosphate group right over here. You have a five-carbon sugar, which in this case is ribose, and then you have what is known as a nitrogenous base, and why is it called nitrogenous? Well, those blue circles represent nitrogen, and we've seen this before. The grays are carbons, and the reds are oxygens, and the whites are hydrogens, and so this part of the molecule has some basic characteristics, while this phosphate group at the end, this has some acidic characteristics, and what happens is is they get stacked onto each other where the ribose phosphates alternate to form the backbone of this DNA molecule. You can see it right over here where you have a phosphate and a ribose and a phosphate and a ribose, and then you have the nitrogenous base forming part of the rung of the ladder. And the way that DNA stores information is every one of these nitrogenous bases right over here, this is adenine, it has a complementary nitrogenous base on the other to complete that rung of the ladder."}, {"video_title": "Introduction to nucleic acids and nucleotides   High school biology   Khan Academy (2).mp3", "Sentence": "Well, those blue circles represent nitrogen, and we've seen this before. The grays are carbons, and the reds are oxygens, and the whites are hydrogens, and so this part of the molecule has some basic characteristics, while this phosphate group at the end, this has some acidic characteristics, and what happens is is they get stacked onto each other where the ribose phosphates alternate to form the backbone of this DNA molecule. You can see it right over here where you have a phosphate and a ribose and a phosphate and a ribose, and then you have the nitrogenous base forming part of the rung of the ladder. And the way that DNA stores information is every one of these nitrogenous bases right over here, this is adenine, it has a complementary nitrogenous base on the other to complete that rung of the ladder. So adenine matches with thymine in DNA, and we'll see in future videos in RNA, it's a nitrogenous base known as uracil, and guanine matches with cytosine. Don't worry too much about this now. We'll go into some depth in this in future videos when we talk about DNA and how information is stored in it, but for the sake of this video, just appreciate that the monomer for a nucleic acid like DNA is a nucleotide, so monomer."}, {"video_title": "Introduction to nucleic acids and nucleotides   High school biology   Khan Academy (2).mp3", "Sentence": "And the way that DNA stores information is every one of these nitrogenous bases right over here, this is adenine, it has a complementary nitrogenous base on the other to complete that rung of the ladder. So adenine matches with thymine in DNA, and we'll see in future videos in RNA, it's a nitrogenous base known as uracil, and guanine matches with cytosine. Don't worry too much about this now. We'll go into some depth in this in future videos when we talk about DNA and how information is stored in it, but for the sake of this video, just appreciate that the monomer for a nucleic acid like DNA is a nucleotide, so monomer. And to be very clear, this would not be the only monomer. The analogous nucleotide in RNA, which stands for ribonucleic acid, would be adenosine monophosphate right over here. You can see the difference between the two, that we have an oxygen right over here and we don't have an oxygen right over here."}, {"video_title": "Introduction to nucleic acids and nucleotides   High school biology   Khan Academy (2).mp3", "Sentence": "We'll go into some depth in this in future videos when we talk about DNA and how information is stored in it, but for the sake of this video, just appreciate that the monomer for a nucleic acid like DNA is a nucleotide, so monomer. And to be very clear, this would not be the only monomer. The analogous nucleotide in RNA, which stands for ribonucleic acid, would be adenosine monophosphate right over here. You can see the difference between the two, that we have an oxygen right over here and we don't have an oxygen right over here. That's why this is called deoxy, and that's why it's deoxyribonucleic acid. You're missing one of those oxygens on your five-carbon sugar but adenine, as I mentioned, is not the only nitrogenous base. You could have a nucleotide where the nitrogenous base is thymine, and so once again, this looks very similar, but notice what is going on over here."}, {"video_title": "Introduction to nucleic acids and nucleotides   High school biology   Khan Academy (2).mp3", "Sentence": "You can see the difference between the two, that we have an oxygen right over here and we don't have an oxygen right over here. That's why this is called deoxy, and that's why it's deoxyribonucleic acid. You're missing one of those oxygens on your five-carbon sugar but adenine, as I mentioned, is not the only nitrogenous base. You could have a nucleotide where the nitrogenous base is thymine, and so once again, this looks very similar, but notice what is going on over here. You could have a nucleotide that looks like this. Once again, you have your five-carbon sugar here, you have your phosphate group, but the nitrogenous base here keeps on changing, and it's the order of these different nucleotides that actually encodes the information in DNA. Now, one question you might say is, well, look, if I have this part of the molecule that has basic characteristics, why is it considered an acid?"}, {"video_title": "Introduction to nucleic acids and nucleotides   High school biology   Khan Academy (2).mp3", "Sentence": "You could have a nucleotide where the nitrogenous base is thymine, and so once again, this looks very similar, but notice what is going on over here. You could have a nucleotide that looks like this. Once again, you have your five-carbon sugar here, you have your phosphate group, but the nitrogenous base here keeps on changing, and it's the order of these different nucleotides that actually encodes the information in DNA. Now, one question you might say is, well, look, if I have this part of the molecule that has basic characteristics, why is it considered an acid? Well, look at how this molecule is structured. The basic parts form the rungs of this ladder, so they're not going to be as reactive because they're really tied, they're closer to the inside of the molecule, while the acidic parts, the phosphate groups, are on the outside, so they're going to be more reactive, and so the molecule as a whole is going to have an acidic characteristic. I'm going to leave you there."}, {"video_title": "Evidence for evolution    Biology   Khan Academy (2).mp3", "Sentence": "We've done many videos on Khan Academy on evolution and natural selection, explaining them, but I thought I would do a video going a little bit more in depth in evidence for evolution and natural selection. And I'm starting with this quote, \"'Nothing in biology makes sense \"'except in light of evolution.'\" This is by Theodosia Dobzhansky, who's a famous biologist, he's passed away now. And what he's saying is absolutely true, and this is why it's so important to appreciate the evidence for evolution and natural selection, and to understand them, because before the theory of evolution, biology was just about observation and classification without having a cohesive narrative for how all of this came about. And since Darwin had come up with this theory in the mid-19th century, we've had far more tools to back it up beyond just the observations we had up until that point. We have our tools around dating in the fossil record, which gives us much more evidence. We have our tools of microbiology and genetics, which gives us even stronger evidence."}, {"video_title": "Evidence for evolution    Biology   Khan Academy (2).mp3", "Sentence": "And what he's saying is absolutely true, and this is why it's so important to appreciate the evidence for evolution and natural selection, and to understand them, because before the theory of evolution, biology was just about observation and classification without having a cohesive narrative for how all of this came about. And since Darwin had come up with this theory in the mid-19th century, we've had far more tools to back it up beyond just the observations we had up until that point. We have our tools around dating in the fossil record, which gives us much more evidence. We have our tools of microbiology and genetics, which gives us even stronger evidence. So a lot of times people say, oh, it's theory of evolution, is it just a theory? Well, it's about as strong as theories get. And without it, as Theodosia Dobzhansky said, biology as we know it, and all of the progress we've made in biology, frankly, wouldn't make any sense and probably would not have happened."}, {"video_title": "Evidence for evolution    Biology   Khan Academy (2).mp3", "Sentence": "We have our tools of microbiology and genetics, which gives us even stronger evidence. So a lot of times people say, oh, it's theory of evolution, is it just a theory? Well, it's about as strong as theories get. And without it, as Theodosia Dobzhansky said, biology as we know it, and all of the progress we've made in biology, frankly, wouldn't make any sense and probably would not have happened. Now, I'm going to broadly go into three types of evidence in this video for evolution and natural selection. The first is structural. And these are the types of things that folks like Darwin would have observed, that people have been observing in biology for a long time, but evolution and natural selection starts to make a lot more sense of it."}, {"video_title": "Evidence for evolution    Biology   Khan Academy (2).mp3", "Sentence": "And without it, as Theodosia Dobzhansky said, biology as we know it, and all of the progress we've made in biology, frankly, wouldn't make any sense and probably would not have happened. Now, I'm going to broadly go into three types of evidence in this video for evolution and natural selection. The first is structural. And these are the types of things that folks like Darwin would have observed, that people have been observing in biology for a long time, but evolution and natural selection starts to make a lot more sense of it. And here we're talking about the macro structure, things that we can, for the most part, observe with our eyes or with a very simple microscope. The next level is what we've learned, really over the last 100 or so years, at the micro level, in microbiology. Microbiology, and especially in genetics."}, {"video_title": "Evidence for evolution    Biology   Khan Academy (2).mp3", "Sentence": "And these are the types of things that folks like Darwin would have observed, that people have been observing in biology for a long time, but evolution and natural selection starts to make a lot more sense of it. And here we're talking about the macro structure, things that we can, for the most part, observe with our eyes or with a very simple microscope. The next level is what we've learned, really over the last 100 or so years, at the micro level, in microbiology. Microbiology, and especially in genetics. So this has really firmed up the theory of evolution. And then the last dimension we'll look at is direct observation. Direct observation."}, {"video_title": "Evidence for evolution    Biology   Khan Academy (2).mp3", "Sentence": "Microbiology, and especially in genetics. So this has really firmed up the theory of evolution. And then the last dimension we'll look at is direct observation. Direct observation. And this is really where it goes beyond a theory. We are seeing it happen. A lot of times people say, oh, it's a theory, it happened, the theory says it happened over tens of millions of years, but no one was around to really observe, even if we see a lot of evidence, no one knows if it for sure happened."}, {"video_title": "Evidence for evolution    Biology   Khan Academy (2).mp3", "Sentence": "Direct observation. And this is really where it goes beyond a theory. We are seeing it happen. A lot of times people say, oh, it's a theory, it happened, the theory says it happened over tens of millions of years, but no one was around to really observe, even if we see a lot of evidence, no one knows if it for sure happened. But if you're directly observing things, well, you know it's for sure happening. And as we'll see, evolution does not only occur over timescales of millions or tens of millions of years, it actually can occur, and we see it occurring all the time on scales well within a human observational capacity, within just a matter of months or years. So let's go through each of these."}, {"video_title": "Evidence for evolution    Biology   Khan Academy (2).mp3", "Sentence": "A lot of times people say, oh, it's a theory, it happened, the theory says it happened over tens of millions of years, but no one was around to really observe, even if we see a lot of evidence, no one knows if it for sure happened. But if you're directly observing things, well, you know it's for sure happening. And as we'll see, evolution does not only occur over timescales of millions or tens of millions of years, it actually can occur, and we see it occurring all the time on scales well within a human observational capacity, within just a matter of months or years. So let's go through each of these. So first let's talk about structural. And this is a very high-level overview. I encourage you to do more research on it."}, {"video_title": "Evidence for evolution    Biology   Khan Academy (2).mp3", "Sentence": "So let's go through each of these. So first let's talk about structural. And this is a very high-level overview. I encourage you to do more research on it. You will find loads and loads and loads of any type of this evidence. So the first thing I wanna talk about is homologous structures, homologous structures that you see throughout the biological world. Homologous, homologous structures."}, {"video_title": "Evidence for evolution    Biology   Khan Academy (2).mp3", "Sentence": "I encourage you to do more research on it. You will find loads and loads and loads of any type of this evidence. So the first thing I wanna talk about is homologous structures, homologous structures that you see throughout the biological world. Homologous, homologous structures. And the word homologous means things that have similar structures, similar position, similar ancestry, but not necessarily the exact same function. And here you see examples of a, well, as a human we would consider a forearm. You see the human forearm and wrist."}, {"video_title": "Evidence for evolution    Biology   Khan Academy (2).mp3", "Sentence": "Homologous, homologous structures. And the word homologous means things that have similar structures, similar position, similar ancestry, but not necessarily the exact same function. And here you see examples of a, well, as a human we would consider a forearm. You see the human forearm and wrist. And then you see the homologous structures in dogs and birds and whales. And even though this part of those animals have very different functions, a human does not walk on its hands for the most part. A dog does walk on its front legs."}, {"video_title": "Evidence for evolution    Biology   Khan Academy (2).mp3", "Sentence": "You see the human forearm and wrist. And then you see the homologous structures in dogs and birds and whales. And even though this part of those animals have very different functions, a human does not walk on its hands for the most part. A dog does walk on its front legs. A bird isn't walking at all. It's using them to flap its wings. And a whale, this is making up its actual fins."}, {"video_title": "Evidence for evolution    Biology   Khan Academy (2).mp3", "Sentence": "A dog does walk on its front legs. A bird isn't walking at all. It's using them to flap its wings. And a whale, this is making up its actual fins. It's using them to propel or to control their movement inside of the water. And even though they have these very, very different functions, and at first when you look at a human and a bird and a whale, on the outside they might look reasonably different. When you look at these bone structures, they are eerily similar, especially with the color-coded, especially color-coded the way it is."}, {"video_title": "Evidence for evolution    Biology   Khan Academy (2).mp3", "Sentence": "And a whale, this is making up its actual fins. It's using them to propel or to control their movement inside of the water. And even though they have these very, very different functions, and at first when you look at a human and a bird and a whale, on the outside they might look reasonably different. When you look at these bone structures, they are eerily similar, especially with the color-coded, especially color-coded the way it is. So these are, this is a very strong hint that maybe humans, dogs, birds, and whales share a common ancestor more recently in the past than say other animals or organisms, I should say, that don't have, whose structures aren't as homologous as these are right over here. And if you were independently trying to create structures for what each of these different species are doing, it's not obvious that you would have such homologous structures actually be involved. Now these are all species that exist today."}, {"video_title": "Evidence for evolution    Biology   Khan Academy (2).mp3", "Sentence": "When you look at these bone structures, they are eerily similar, especially with the color-coded, especially color-coded the way it is. So these are, this is a very strong hint that maybe humans, dogs, birds, and whales share a common ancestor more recently in the past than say other animals or organisms, I should say, that don't have, whose structures aren't as homologous as these are right over here. And if you were independently trying to create structures for what each of these different species are doing, it's not obvious that you would have such homologous structures actually be involved. Now these are all species that exist today. These are all species that exist on the planet at the same time. But we also see structural evidence by going into the fossil record. In the last few hundred years, or really in the last hundred years is where we've gotten really good at it, we've gotten good at looking at different layers of different layers of rock strata and being able to date them and saying, okay, that layer was laid down X million years ago."}, {"video_title": "Evidence for evolution    Biology   Khan Academy (2).mp3", "Sentence": "Now these are all species that exist today. These are all species that exist on the planet at the same time. But we also see structural evidence by going into the fossil record. In the last few hundred years, or really in the last hundred years is where we've gotten really good at it, we've gotten good at looking at different layers of different layers of rock strata and being able to date them and saying, okay, that layer was laid down X million years ago. That layer was laid down a little bit more recent. This one was even more recent. And then looking at fossils within that to say, okay, 20 million years ago, there were species around that looked like that."}, {"video_title": "Evidence for evolution    Biology   Khan Academy (2).mp3", "Sentence": "In the last few hundred years, or really in the last hundred years is where we've gotten really good at it, we've gotten good at looking at different layers of different layers of rock strata and being able to date them and saying, okay, that layer was laid down X million years ago. That layer was laid down a little bit more recent. This one was even more recent. And then looking at fossils within that to say, okay, 20 million years ago, there were species around that looked like that. And then 10 million years ago, there were species that looked like that. And one example is if you look at horse-like animals. So this is right over here."}, {"video_title": "Evidence for evolution    Biology   Khan Academy (2).mp3", "Sentence": "And then looking at fossils within that to say, okay, 20 million years ago, there were species around that looked like that. And then 10 million years ago, there were species that looked like that. And one example is if you look at horse-like animals. So this is right over here. We're talking about horses, zebras, donkeys, mules, things like that. The modern ones, well, this is their bone structure. But if you look at the fossil record from 12 to five million years ago, you see fossils that look like this."}, {"video_title": "Evidence for evolution    Biology   Khan Academy (2).mp3", "Sentence": "So this is right over here. We're talking about horses, zebras, donkeys, mules, things like that. The modern ones, well, this is their bone structure. But if you look at the fossil record from 12 to five million years ago, you see fossils that look like this. And they're very close. So you see, it's very believable that you see you could have evolution from this to that. But then you go further back, and once again, it seems like a very gradual process."}, {"video_title": "Evidence for evolution    Biology   Khan Academy (2).mp3", "Sentence": "But if you look at the fossil record from 12 to five million years ago, you see fossils that look like this. And they're very close. So you see, it's very believable that you see you could have evolution from this to that. But then you go further back, and once again, it seems like a very gradual process. And once again, this is happening over, these are from 12 to five million years ago, these are from 16 to 12 million years ago, these are from over 34 million years ago. And so you can see how this is happening at a very, very gradual pace. And the mechanism, and we go into some depth in other videos in Khan Academy, you have variation species, you have the environment selecting for it."}, {"video_title": "Evidence for evolution    Biology   Khan Academy (2).mp3", "Sentence": "But then you go further back, and once again, it seems like a very gradual process. And once again, this is happening over, these are from 12 to five million years ago, these are from 16 to 12 million years ago, these are from over 34 million years ago. And so you can see how this is happening at a very, very gradual pace. And the mechanism, and we go into some depth in other videos in Khan Academy, you have variation species, you have the environment selecting for it. The environment might change, or different things happen, so you have different forms of selection, different types of combinations sprout up, they're more suitable for their environment, they start to reproduce better, they become the dominant species, or they take over certain parts of a niche or an ecosystem. And so you have this change, this heritable change of traits over time. And so when you look at the fossil record, it makes a lot of sense that, okay, this is strong evidence for evolution, that the animals that we see today weren't just put on, just created all of a sudden, and haven't changed since then, that there's a constant change, and we can see it directly through the fossil record."}, {"video_title": "Evidence for evolution    Biology   Khan Academy (2).mp3", "Sentence": "And the mechanism, and we go into some depth in other videos in Khan Academy, you have variation species, you have the environment selecting for it. The environment might change, or different things happen, so you have different forms of selection, different types of combinations sprout up, they're more suitable for their environment, they start to reproduce better, they become the dominant species, or they take over certain parts of a niche or an ecosystem. And so you have this change, this heritable change of traits over time. And so when you look at the fossil record, it makes a lot of sense that, okay, this is strong evidence for evolution, that the animals that we see today weren't just put on, just created all of a sudden, and haven't changed since then, that there's a constant change, and we can see it directly through the fossil record. Now, the next point of evidence, I will put a bit of a caveat, because the gentleman who first created this, his name was Haeckel, he was a controversial figure, he had some spurious theories, and even this diagram that he created, it seems like he fudged a little bit of the drawings in order to make a stronger argument, but even with modern observations, these drawings are pretty close to being correct. And it's very, very compelling, it shows the embryonic development of a whole series of species, from a fish on the left, to a reptile, to birds, to mammals, and another mammal, to non-human mammals, and of course, to humans. And you can see at the early stages, they look eerily similar."}, {"video_title": "Evidence for evolution    Biology   Khan Academy (2).mp3", "Sentence": "And so when you look at the fossil record, it makes a lot of sense that, okay, this is strong evidence for evolution, that the animals that we see today weren't just put on, just created all of a sudden, and haven't changed since then, that there's a constant change, and we can see it directly through the fossil record. Now, the next point of evidence, I will put a bit of a caveat, because the gentleman who first created this, his name was Haeckel, he was a controversial figure, he had some spurious theories, and even this diagram that he created, it seems like he fudged a little bit of the drawings in order to make a stronger argument, but even with modern observations, these drawings are pretty close to being correct. And it's very, very compelling, it shows the embryonic development of a whole series of species, from a fish on the left, to a reptile, to birds, to mammals, and another mammal, to non-human mammals, and of course, to humans. And you can see at the early stages, they look eerily similar. In fact, you see proto-gill slits in all of these animals, which later differentiate into things that are more suitable for what that animal actually becomes. And Haeckel, he's the guy who coined ontogeny recapitulates phylogeny, which is a very fancy way of saying that your embryonic development is telling the story of the evolutionary past, which isn't true, but you'll even hear people quote that today. But his drawings and his observations, this is compelling evidence for life-sharing a common ancestry, coming from similar origins that got more and more different over time through the process of natural selection."}, {"video_title": "Evidence for evolution    Biology   Khan Academy (2).mp3", "Sentence": "And you can see at the early stages, they look eerily similar. In fact, you see proto-gill slits in all of these animals, which later differentiate into things that are more suitable for what that animal actually becomes. And Haeckel, he's the guy who coined ontogeny recapitulates phylogeny, which is a very fancy way of saying that your embryonic development is telling the story of the evolutionary past, which isn't true, but you'll even hear people quote that today. But his drawings and his observations, this is compelling evidence for life-sharing a common ancestry, coming from similar origins that got more and more different over time through the process of natural selection. So everything I've talked about so far has been kind of macro-structure, things we can observe. The next thing I'm gonna talk about is you can think about it as micro-structures or processes, and this is microbiology. Micro-biology."}, {"video_title": "Evidence for evolution    Biology   Khan Academy (2).mp3", "Sentence": "But his drawings and his observations, this is compelling evidence for life-sharing a common ancestry, coming from similar origins that got more and more different over time through the process of natural selection. So everything I've talked about so far has been kind of macro-structure, things we can observe. The next thing I'm gonna talk about is you can think about it as micro-structures or processes, and this is microbiology. Micro-biology. And biolo-biology. Microbiology. And the more we understand about microbiology, the more compelling case of evolution."}, {"video_title": "Evidence for evolution    Biology   Khan Academy (2).mp3", "Sentence": "Micro-biology. And biolo-biology. Microbiology. And the more we understand about microbiology, the more compelling case of evolution. Because when we look at even, you know, one, all life forms that we know, they involve DNA. How the DNA gets replicated and translated and transcribed is very similar from one life form to another. The idea of DNA going to, DNA coding for proteins, proteins that are made up of amino acids is something that we see throughout biology."}, {"video_title": "Evidence for evolution    Biology   Khan Academy (2).mp3", "Sentence": "And the more we understand about microbiology, the more compelling case of evolution. Because when we look at even, you know, one, all life forms that we know, they involve DNA. How the DNA gets replicated and translated and transcribed is very similar from one life form to another. The idea of DNA going to, DNA coding for proteins, proteins that are made up of amino acids is something that we see throughout biology. Amino acids, which once again, hints at a common ancestry. And not only are those molecular, and many of the very proteins, are very, very similar, more similar than if you looked at the macro level or even at the structural level between different species. And not just do they share these common micro-structures and processes, but the actual information stored in things like DNA also are very, very strong evidence for evolution."}, {"video_title": "Evidence for evolution    Biology   Khan Academy (2).mp3", "Sentence": "The idea of DNA going to, DNA coding for proteins, proteins that are made up of amino acids is something that we see throughout biology. Amino acids, which once again, hints at a common ancestry. And not only are those molecular, and many of the very proteins, are very, very similar, more similar than if you looked at the macro level or even at the structural level between different species. And not just do they share these common micro-structures and processes, but the actual information stored in things like DNA also are very, very strong evidence for evolution. So this is a picture, I got this from, I got this from the site, I should give proper credit, 23andme.com. But this, and you'll see other data like this that's very similar to this, which is how much genetic similarity do we have between different species? And these numbers tell us how much genetic similarity at a high level do we have with chimpanzees, mice, fruit flies, yeast, and plants."}, {"video_title": "Evidence for evolution    Biology   Khan Academy (2).mp3", "Sentence": "And not just do they share these common micro-structures and processes, but the actual information stored in things like DNA also are very, very strong evidence for evolution. So this is a picture, I got this from, I got this from the site, I should give proper credit, 23andme.com. But this, and you'll see other data like this that's very similar to this, which is how much genetic similarity do we have between different species? And these numbers tell us how much genetic similarity at a high level do we have with chimpanzees, mice, fruit flies, yeast, and plants. And the fact that we have 26% of our genes in common with yeast is mind-blowing. Because at a macro level, it doesn't seem like there's a lot in common with yeast. But when you get at a microbiological level, there's a good bit that's in common with yeast."}, {"video_title": "Evidence for evolution    Biology   Khan Academy (2).mp3", "Sentence": "And these numbers tell us how much genetic similarity at a high level do we have with chimpanzees, mice, fruit flies, yeast, and plants. And the fact that we have 26% of our genes in common with yeast is mind-blowing. Because at a macro level, it doesn't seem like there's a lot in common with yeast. But when you get at a microbiological level, there's a good bit that's in common with yeast. And chimpanzees, we do relate to them. Their facial expressions often feel eerily human, their behaviors often feel eerily human, but their genes show just how close to human beings they actually are. And this actually shows that even, you know, mice are way closer, if you looked at the entire tree of life, based on genetic evidence, things like mice and even fruit flies are awfully close to human beings, especially if you were to compare it to bacteria or plants."}, {"video_title": "Evidence for evolution    Biology   Khan Academy (2).mp3", "Sentence": "But when you get at a microbiological level, there's a good bit that's in common with yeast. And chimpanzees, we do relate to them. Their facial expressions often feel eerily human, their behaviors often feel eerily human, but their genes show just how close to human beings they actually are. And this actually shows that even, you know, mice are way closer, if you looked at the entire tree of life, based on genetic evidence, things like mice and even fruit flies are awfully close to human beings, especially if you were to compare it to bacteria or plants. But once again, you share all of these common processes, and the fact that we can now measure how far things are away allows us to create a very accurate tree of life, especially thinking about how far in the past we had evolutionary common ancestors. Now the last thing that I promised I would talk about is direct evidence. Direct evidence of evolution."}, {"video_title": "Evidence for evolution    Biology   Khan Academy (2).mp3", "Sentence": "And this actually shows that even, you know, mice are way closer, if you looked at the entire tree of life, based on genetic evidence, things like mice and even fruit flies are awfully close to human beings, especially if you were to compare it to bacteria or plants. But once again, you share all of these common processes, and the fact that we can now measure how far things are away allows us to create a very accurate tree of life, especially thinking about how far in the past we had evolutionary common ancestors. Now the last thing that I promised I would talk about is direct evidence. Direct evidence of evolution. And I talk about this in the first evolution video. But the direct evidence we see all the time with things like bacteria, where you have bacteria, let's say growing around, and we have antibiotics that we use in our body to kill bacteria. But the reason why many physicians and scientists will tell you don't overuse antibiotics is because the more you use it, it causes a very strong natural selection process for bacteria that are going to be resistant to that antibiotic."}, {"video_title": "Evidence for evolution    Biology   Khan Academy (2).mp3", "Sentence": "Direct evidence of evolution. And I talk about this in the first evolution video. But the direct evidence we see all the time with things like bacteria, where you have bacteria, let's say growing around, and we have antibiotics that we use in our body to kill bacteria. But the reason why many physicians and scientists will tell you don't overuse antibiotics is because the more you use it, it causes a very strong natural selection process for bacteria that are going to be resistant to that antibiotic. So if you keep using an antibiotic and the bacteria keep changing, there's more and more variation, well, you're gonna kill a lot of the bacteria, but if even one of them is resistant to that antibiotic that you use, well then all of its competition is gonna get killed, and so that drug-resistant superbug, it's often called, is going to be able to go nuts, and that antibiotic isn't going to be able to do anything. And if you look at science today, if you look at medicine today, this is kind of an arms race. You have this constant need to create new antibiotics because more and more bacteria are becoming drug-resistant."}, {"video_title": "Evidence for evolution    Biology   Khan Academy (2).mp3", "Sentence": "But the reason why many physicians and scientists will tell you don't overuse antibiotics is because the more you use it, it causes a very strong natural selection process for bacteria that are going to be resistant to that antibiotic. So if you keep using an antibiotic and the bacteria keep changing, there's more and more variation, well, you're gonna kill a lot of the bacteria, but if even one of them is resistant to that antibiotic that you use, well then all of its competition is gonna get killed, and so that drug-resistant superbug, it's often called, is going to be able to go nuts, and that antibiotic isn't going to be able to do anything. And if you look at science today, if you look at medicine today, this is kind of an arms race. You have this constant need to create new antibiotics because more and more bacteria are becoming drug-resistant. They're becoming what's often called superbugs, where they are resistant to the existing antibiotics. And this is evolution and natural selection happening on a human scale. You could also think about the flu virus, where every year, that vaccine for the flu virus, you gotta get a new one every year because the virus is changing."}, {"video_title": "Mutation as a source of variation   Gene expression and regulation   AP Biology   Khan Academy (2).mp3", "Sentence": "So if you have a population of circles, obviously a very simple model here, maybe some of these circles are that off-white color, maybe some of them are blue, and maybe some of them are this salmon color. For certain traits, your environment might make certain of them better for reproduction, better for survival, evading predators, better for finding food. And let's say these circles, for whatever reason, they're an environment where maybe being blue makes it a little bit easier to evade predators and a little bit easier to reproduce and find food. Well then, in the next generation, in the next generation, because the blue's more likely to be able to get to reproduction, because they weren't eaten, you're likely to have more blues. So let me draw a few more blues, and maybe a little bit less of the other ones, because they're also competing for resources amongst each other, at least in this model that I'm doing. And so over time, if this blue phenotype, remember, phenotype is the expressed trait that's actually observable versus the genotype, which is the underlying genetics, which is sometimes observable and sometimes not. But as you can see, if in this environment, blue seems to carry some advantage, even if it's a slight probabilistic advantage, over many generations, blue will start to dominate."}, {"video_title": "Mutation as a source of variation   Gene expression and regulation   AP Biology   Khan Academy (2).mp3", "Sentence": "Well then, in the next generation, in the next generation, because the blue's more likely to be able to get to reproduction, because they weren't eaten, you're likely to have more blues. So let me draw a few more blues, and maybe a little bit less of the other ones, because they're also competing for resources amongst each other, at least in this model that I'm doing. And so over time, if this blue phenotype, remember, phenotype is the expressed trait that's actually observable versus the genotype, which is the underlying genetics, which is sometimes observable and sometimes not. But as you can see, if in this environment, blue seems to carry some advantage, even if it's a slight probabilistic advantage, over many generations, blue will start to dominate. And so you start to see that evolution of this population to being more blue as a species. So you have these blue circles. So one way to think about it is you have variation in a species is really what natural selection is based off of certain variants might be more favorable than others."}, {"video_title": "Mutation as a source of variation   Gene expression and regulation   AP Biology   Khan Academy (2).mp3", "Sentence": "But as you can see, if in this environment, blue seems to carry some advantage, even if it's a slight probabilistic advantage, over many generations, blue will start to dominate. And so you start to see that evolution of this population to being more blue as a species. So you have these blue circles. So one way to think about it is you have variation in a species is really what natural selection is based off of certain variants might be more favorable than others. So that is what's really necessary for natural selection to fuel evolution, to fuel evolution. Now, a key question is, where does this variation in a population come from? And to think about that, we just have to remind ourselves where our phenotypes come from."}, {"video_title": "Mutation as a source of variation   Gene expression and regulation   AP Biology   Khan Academy (2).mp3", "Sentence": "So one way to think about it is you have variation in a species is really what natural selection is based off of certain variants might be more favorable than others. So that is what's really necessary for natural selection to fuel evolution, to fuel evolution. Now, a key question is, where does this variation in a population come from? And to think about that, we just have to remind ourselves where our phenotypes come from. How do these expressed traits get expressed? Well, in all the living organisms we're aware of, we have DNA. As human beings, we have 23 pair of chromosomes, and each chromosome you could view as just a very, very, very, very long strand of DNA, and sections of that DNA code for various traits."}, {"video_title": "Mutation as a source of variation   Gene expression and regulation   AP Biology   Khan Academy (2).mp3", "Sentence": "And to think about that, we just have to remind ourselves where our phenotypes come from. How do these expressed traits get expressed? Well, in all the living organisms we're aware of, we have DNA. As human beings, we have 23 pair of chromosomes, and each chromosome you could view as just a very, very, very, very long strand of DNA, and sections of that DNA code for various traits. And each of those sections that code for, say, a certain protein or a part of an enzyme, we call those things genes. We call those things genes. So we have multiple chromosomes."}, {"video_title": "Mutation as a source of variation   Gene expression and regulation   AP Biology   Khan Academy (2).mp3", "Sentence": "As human beings, we have 23 pair of chromosomes, and each chromosome you could view as just a very, very, very, very long strand of DNA, and sections of that DNA code for various traits. And each of those sections that code for, say, a certain protein or a part of an enzyme, we call those things genes. We call those things genes. So we have multiple chromosomes. We have 20, as human beings, different species have different number, but as human beings, we have 23 pair of chromosomes. Each chromosome you view as a long strand of DNA. Parts of that DNA code for specific genes."}, {"video_title": "Mutation as a source of variation   Gene expression and regulation   AP Biology   Khan Academy (2).mp3", "Sentence": "So we have multiple chromosomes. We have 20, as human beings, different species have different number, but as human beings, we have 23 pair of chromosomes. Each chromosome you view as a long strand of DNA. Parts of that DNA code for specific genes. And then if you were to zoom in, if you were to zoom in on those genes, you would see these nucleotide sequences. This is all a review. We've seen this in other videos, where you see your adenine, your guanine, your cytosine, your thymine, in order that carries the information that will eventually be coded into mRNA, which then gets coded into protein."}, {"video_title": "Mutation as a source of variation   Gene expression and regulation   AP Biology   Khan Academy (2).mp3", "Sentence": "Parts of that DNA code for specific genes. And then if you were to zoom in, if you were to zoom in on those genes, you would see these nucleotide sequences. This is all a review. We've seen this in other videos, where you see your adenine, your guanine, your cytosine, your thymine, in order that carries the information that will eventually be coded into mRNA, which then gets coded into protein. Now, there's two primary sources of variation. One source of variation is sexual reproduction. Sexual reproduction."}, {"video_title": "Mutation as a source of variation   Gene expression and regulation   AP Biology   Khan Academy (2).mp3", "Sentence": "We've seen this in other videos, where you see your adenine, your guanine, your cytosine, your thymine, in order that carries the information that will eventually be coded into mRNA, which then gets coded into protein. Now, there's two primary sources of variation. One source of variation is sexual reproduction. Sexual reproduction. Now, not all organisms reproduce sexually, but many of the ones that we know, including human beings, do. We're a male member of the species and a female member of the species. Each contribute a random half of their chromosomes to the next organism."}, {"video_title": "Mutation as a source of variation   Gene expression and regulation   AP Biology   Khan Academy (2).mp3", "Sentence": "Sexual reproduction. Now, not all organisms reproduce sexually, but many of the ones that we know, including human beings, do. We're a male member of the species and a female member of the species. Each contribute a random half of their chromosomes to the next organism. So one way to think about sexual reproduction is it keeps shuffling the different versions of the genes that you have in the population into different combinations of those versions of genes. And so that generates variation. But sexual reproduction by itself will not create new versions of genes, which we call alleles, or new genes entirely."}, {"video_title": "Mutation as a source of variation   Gene expression and regulation   AP Biology   Khan Academy (2).mp3", "Sentence": "Each contribute a random half of their chromosomes to the next organism. So one way to think about sexual reproduction is it keeps shuffling the different versions of the genes that you have in the population into different combinations of those versions of genes. And so that generates variation. But sexual reproduction by itself will not create new versions of genes, which we call alleles, or new genes entirely. And so the primary way that that happens is through mutations. And you might have guessed that we were going to talk about that, because I had this title up here. So another source of variation, and you could almost view this as a more fundamental one, because this would happen even in organisms that aren't reproducing sexually, is that over time, there could be just random mistakes."}, {"video_title": "Mutation as a source of variation   Gene expression and regulation   AP Biology   Khan Academy (2).mp3", "Sentence": "But sexual reproduction by itself will not create new versions of genes, which we call alleles, or new genes entirely. And so the primary way that that happens is through mutations. And you might have guessed that we were going to talk about that, because I had this title up here. So another source of variation, and you could almost view this as a more fundamental one, because this would happen even in organisms that aren't reproducing sexually, is that over time, there could be just random mistakes. There could be edits to these genes. And it could be a random, maybe this G gets turned into a C randomly. Or maybe this T and A gets cut out during the DNA replication process."}, {"video_title": "Mutation as a source of variation   Gene expression and regulation   AP Biology   Khan Academy (2).mp3", "Sentence": "So another source of variation, and you could almost view this as a more fundamental one, because this would happen even in organisms that aren't reproducing sexually, is that over time, there could be just random mistakes. There could be edits to these genes. And it could be a random, maybe this G gets turned into a C randomly. Or maybe this T and A gets cut out during the DNA replication process. These mutations, which are all about genotype, and let me make this very clear. So when we're looking at this sequence, we're thinking about genotype. Differences in genotype are not always obvious from expressed traits."}, {"video_title": "Mutation as a source of variation   Gene expression and regulation   AP Biology   Khan Academy (2).mp3", "Sentence": "Or maybe this T and A gets cut out during the DNA replication process. These mutations, which are all about genotype, and let me make this very clear. So when we're looking at this sequence, we're thinking about genotype. Differences in genotype are not always obvious from expressed traits. So sometimes they do change phenotype, or they're observable in phenotype. Sometimes they're not. But when they are observable in phenotype, as I just mentioned, many times it could be a negative change in phenotype, where it makes it less viable for that organism, or it's harder for them to survive and reproduce."}, {"video_title": "Mutation as a source of variation   Gene expression and regulation   AP Biology   Khan Academy (2).mp3", "Sentence": "Differences in genotype are not always obvious from expressed traits. So sometimes they do change phenotype, or they're observable in phenotype. Sometimes they're not. But when they are observable in phenotype, as I just mentioned, many times it could be a negative change in phenotype, where it makes it less viable for that organism, or it's harder for them to survive and reproduce. But every now and then, it could result in a variation in phenotype that is maybe neutral, or even confers some type of advantage. So it might have been a random mutation that somehow turned one of these white circles into a blue circle. And there might have been another mutation that turned a white circle into a square, and that just wasn't even viable as an organism."}, {"video_title": "Species.mp3", "Sentence": "And you can imagine there's no more obvious thing to classify than all of the living things around us, than all of the life that around us. So what I want to start talking about is how do we classify all of the life around us. And this is more often generally referred to taxonomy. But the most basic question you have when you look at all of the life around you, you start to see similarities between some of these living things. You see, obviously, this thing right over here is more similar to the things that look like it than it does to the grass behind it or to that tree. And so we start saying, well, maybe I should group this thing right over here into a group with other things like it. And that very most building block of how we classify all of the living things around us is putting them into buckets called species."}, {"video_title": "Species.mp3", "Sentence": "But the most basic question you have when you look at all of the life around you, you start to see similarities between some of these living things. You see, obviously, this thing right over here is more similar to the things that look like it than it does to the grass behind it or to that tree. And so we start saying, well, maybe I should group this thing right over here into a group with other things like it. And that very most building block of how we classify all of the living things around us is putting them into buckets called species. So for example, this is one particular animal, but we see other animals that seem to look like it. And so we say they're all part of the species of lions. And this animal, it's one animal, and there's other animals that have stripes, but some might be fatter or taller or skinnier or whatever else, darker or lighter."}, {"video_title": "Species.mp3", "Sentence": "And that very most building block of how we classify all of the living things around us is putting them into buckets called species. So for example, this is one particular animal, but we see other animals that seem to look like it. And so we say they're all part of the species of lions. And this animal, it's one animal, and there's other animals that have stripes, but some might be fatter or taller or skinnier or whatever else, darker or lighter. But we say they're similar enough that we call them all tigers. We call all the animals, even though they might be a little bit bigger or skinnier or fatter or lighter or darker, we call all of them that have this kind of, they look similar to this thing right over here, we would call this a donkey. We would call the things that we think are like this animal right here a horse."}, {"video_title": "Species.mp3", "Sentence": "And this animal, it's one animal, and there's other animals that have stripes, but some might be fatter or taller or skinnier or whatever else, darker or lighter. But we say they're similar enough that we call them all tigers. We call all the animals, even though they might be a little bit bigger or skinnier or fatter or lighter or darker, we call all of them that have this kind of, they look similar to this thing right over here, we would call this a donkey. We would call the things that we think are like this animal right here a horse. Now, that might seem like a pretty straightforward way to think about it. Oh, everything that looks kind of like this character right here is a lion. Anything that looks kind of like this character right here is a tiger."}, {"video_title": "Species.mp3", "Sentence": "We would call the things that we think are like this animal right here a horse. Now, that might seem like a pretty straightforward way to think about it. Oh, everything that looks kind of like this character right here is a lion. Anything that looks kind of like this character right here is a tiger. But that by itself is not a good enough definition for a species, things that look like each other or things that act like each other, because what we'll see is that there's some things that could be very different, at least in how they look or act, but are actually closely related, and we'll talk about what it means to be closely related. And then we can see things that look very similar, that they have similar structures or they have similar behavior, like for example, bats and birds, but they are actually all very, very distantly related. So we need a more exact definition for species than just things that look like each other or just things that act like each other."}, {"video_title": "Species.mp3", "Sentence": "Anything that looks kind of like this character right here is a tiger. But that by itself is not a good enough definition for a species, things that look like each other or things that act like each other, because what we'll see is that there's some things that could be very different, at least in how they look or act, but are actually closely related, and we'll talk about what it means to be closely related. And then we can see things that look very similar, that they have similar structures or they have similar behavior, like for example, bats and birds, but they are actually all very, very distantly related. So we need a more exact definition for species than just things that look like each other or just things that act like each other. And so the most typical definition for a species are animals that can interbreed, and when we say interbreed, literally they can produce offspring with each other, and the offspring are fertile, which means that the offspring can then further have babies, that they're not sterile, that they're capable of breeding with other animals and producing more offspring. And to show an example of this, this right here is a male lion. You find a male lion and a female lioness, and most of the time they will be able to have offspring, and those offspring can go and mate with other lions or lionesses, depending on their sex, and then they can have viable offspring."}, {"video_title": "Species.mp3", "Sentence": "So we need a more exact definition for species than just things that look like each other or just things that act like each other. And so the most typical definition for a species are animals that can interbreed, and when we say interbreed, literally they can produce offspring with each other, and the offspring are fertile, which means that the offspring can then further have babies, that they're not sterile, that they're capable of breeding with other animals and producing more offspring. And to show an example of this, this right here is a male lion. You find a male lion and a female lioness, and most of the time they will be able to have offspring, and those offspring can go and mate with other lions or lionesses, depending on their sex, and then they can have viable offspring. So it seems to work out pretty well for lions. Same thing is true of tigers. Now, it does turn out that if you get a male lion, if you have a male lion and a female tigress, they can breed, and they can produce offspring."}, {"video_title": "Species.mp3", "Sentence": "You find a male lion and a female lioness, and most of the time they will be able to have offspring, and those offspring can go and mate with other lions or lionesses, depending on their sex, and then they can have viable offspring. So it seems to work out pretty well for lions. Same thing is true of tigers. Now, it does turn out that if you get a male lion, if you have a male lion and a female tigress, they can breed, and they can produce offspring. And their offspring, which was made famous by Napoleon Dynamite, he was kind of fascinated by it, these are kind of fascinating animals, their offspring is called a liger. You get a male lion breeding with a female tiger, you produce a liger, which is a hybrid, it's a cross between a lion and a tiger, and they're fascinating animals. They're actually larger than either lions or tigers."}, {"video_title": "Species.mp3", "Sentence": "Now, it does turn out that if you get a male lion, if you have a male lion and a female tigress, they can breed, and they can produce offspring. And their offspring, which was made famous by Napoleon Dynamite, he was kind of fascinated by it, these are kind of fascinating animals, their offspring is called a liger. You get a male lion breeding with a female tiger, you produce a liger, which is a hybrid, it's a cross between a lion and a tiger, and they're fascinating animals. They're actually larger than either lions or tigers. They're the largest cats that we know of. But these ligers cannot be referred to as a separate species, or you can't say that lions and tigers are the same species, because even though they are able to interbreed, their offspring, for the most part, is not fertile, is not able to produce offspring. There have been one-off stories about ligers being mated with either a lion or tiger, but those are one-off stories."}, {"video_title": "Species.mp3", "Sentence": "They're actually larger than either lions or tigers. They're the largest cats that we know of. But these ligers cannot be referred to as a separate species, or you can't say that lions and tigers are the same species, because even though they are able to interbreed, their offspring, for the most part, is not fertile, is not able to produce offspring. There have been one-off stories about ligers being mated with either a lion or tiger, but those are one-off stories. In general, ligers can't interbreed, and in general this combination isn't going to produce offspring that can keep interbreeding or that are fertile. So that's why we say that lions and tigers are different species, and that liger, we wouldn't even call it a species at all, we would actually call it a hybrid between two species. Now the same thing is true, and actually you might be asking yourself, well, this was a male lion and a female tigress, what if we went the other way around?"}, {"video_title": "Species.mp3", "Sentence": "There have been one-off stories about ligers being mated with either a lion or tiger, but those are one-off stories. In general, ligers can't interbreed, and in general this combination isn't going to produce offspring that can keep interbreeding or that are fertile. So that's why we say that lions and tigers are different species, and that liger, we wouldn't even call it a species at all, we would actually call it a hybrid between two species. Now the same thing is true, and actually you might be asking yourself, well, this was a male lion and a female tigress, what if we went the other way around? What if we had a female lioness and a male tiger? In that case you would produce something else called a tiglon, I actually don't know how to pronounce that, and that is a different hybrid that has slightly different properties than a liger. So I encourage you to look up what a tiglon is."}, {"video_title": "Species.mp3", "Sentence": "Now the same thing is true, and actually you might be asking yourself, well, this was a male lion and a female tigress, what if we went the other way around? What if we had a female lioness and a male tiger? In that case you would produce something else called a tiglon, I actually don't know how to pronounce that, and that is a different hybrid that has slightly different properties than a liger. So I encourage you to look up what a tiglon is. Similarly, you give me a male donkey, and donkeys are clearly a species by themselves because if you give me a male donkey and a female donkey, they can reproduce, produce another donkey, and then that donkey can mate with other donkeys to produce more and more donkeys. So not only can a donkey interbreed with another donkey, but that product, that child donkey, can then keep interbreeding with other donkeys. Similarly, horses, they can interbreed and produce fertile offspring."}, {"video_title": "Species.mp3", "Sentence": "So I encourage you to look up what a tiglon is. Similarly, you give me a male donkey, and donkeys are clearly a species by themselves because if you give me a male donkey and a female donkey, they can reproduce, produce another donkey, and then that donkey can mate with other donkeys to produce more and more donkeys. So not only can a donkey interbreed with another donkey, but that product, that child donkey, can then keep interbreeding with other donkeys. Similarly, horses, they can interbreed and produce fertile offspring. But if you give me a male donkey and a female horse, they can mate and they can produce a mule. But once again, like the ligers, mules are not, at least as far as I know, mules cannot, they're not fertile. Mules cannot produce further offspring."}, {"video_title": "Species.mp3", "Sentence": "Similarly, horses, they can interbreed and produce fertile offspring. But if you give me a male donkey and a female horse, they can mate and they can produce a mule. But once again, like the ligers, mules are not, at least as far as I know, mules cannot, they're not fertile. Mules cannot produce further offspring. They cannot interbreed with each other. And because even though donkeys and horses can breed and produce mules, their offspring aren't fertile, we don't consider donkeys and horses part of the same species, and we would consider mules, like a liger or a tiglon, we would consider them a hybrid. So these are all hybrids, or we would call cross."}, {"video_title": "Species.mp3", "Sentence": "Mules cannot produce further offspring. They cannot interbreed with each other. And because even though donkeys and horses can breed and produce mules, their offspring aren't fertile, we don't consider donkeys and horses part of the same species, and we would consider mules, like a liger or a tiglon, we would consider them a hybrid. So these are all hybrids, or we would call cross. The word hybrid is used when you have two things, two different types that are somehow coming together, somehow having a combination. And once again, like the case with the tiglon, you might say, well, what if I had a female donkey and a male horse, and then you would actually produce something called a hinny, which similarly, which isn't as common as a mule, and people like to use mules, they're actually very good work animals because they have some of the good properties of both donkeys and horses. Hinnies are less common, but once again, it is possible, and they have different properties than mules."}, {"video_title": "Species.mp3", "Sentence": "So these are all hybrids, or we would call cross. The word hybrid is used when you have two things, two different types that are somehow coming together, somehow having a combination. And once again, like the case with the tiglon, you might say, well, what if I had a female donkey and a male horse, and then you would actually produce something called a hinny, which similarly, which isn't as common as a mule, and people like to use mules, they're actually very good work animals because they have some of the good properties of both donkeys and horses. Hinnies are less common, but once again, it is possible, and they have different properties than mules. And I do want to emphasize this idea, because when we started off, we just kind of tried to think about, well, how can we classify things, and we said, hey, maybe things that look and act similar we can call a species. But I want to show you where, and maybe things that look and act different, we shouldn't call them species. But I want to show you a very typical case, and one that's really all around us all the time, where this definition, animals that can interbreed and the offspring are fertile, really does seem to become much, much more important than just some notion of animals that look alike or animals that act the same."}, {"video_title": "Species.mp3", "Sentence": "Hinnies are less common, but once again, it is possible, and they have different properties than mules. And I do want to emphasize this idea, because when we started off, we just kind of tried to think about, well, how can we classify things, and we said, hey, maybe things that look and act similar we can call a species. But I want to show you where, and maybe things that look and act different, we shouldn't call them species. But I want to show you a very typical case, and one that's really all around us all the time, where this definition, animals that can interbreed and the offspring are fertile, really does seem to become much, much more important than just some notion of animals that look alike or animals that act the same. And the best example of that is with dogs. I said this is a very typical species here, because dogs, and I just took a sample of some of the different types of breeds of dogs, they can look very, very different. It's obvious."}, {"video_title": "Species.mp3", "Sentence": "But I want to show you a very typical case, and one that's really all around us all the time, where this definition, animals that can interbreed and the offspring are fertile, really does seem to become much, much more important than just some notion of animals that look alike or animals that act the same. And the best example of that is with dogs. I said this is a very typical species here, because dogs, and I just took a sample of some of the different types of breeds of dogs, they can look very, very different. It's obvious. Look at the difference between these dogs. For example, this little chihuahua here and this dog right over here, obviously, size-wise, they look and even how they act are much, much more different than maybe how this donkey would act relative to this horse or how this lion would act relative to this tigress. And they obviously look very different."}, {"video_title": "Species.mp3", "Sentence": "It's obvious. Look at the difference between these dogs. For example, this little chihuahua here and this dog right over here, obviously, size-wise, they look and even how they act are much, much more different than maybe how this donkey would act relative to this horse or how this lion would act relative to this tigress. And they obviously look very different. They have completely different sizes. But these two things actually can interbreed, although for these two in particular, it seems like the mechanics would get kind of difficult. Assuming they get over the mechanical hurdles, they could interbreed and produce fertile offspring."}, {"video_title": "Species.mp3", "Sentence": "And they obviously look very different. They have completely different sizes. But these two things actually can interbreed, although for these two in particular, it seems like the mechanics would get kind of difficult. Assuming they get over the mechanical hurdles, they could interbreed and produce fertile offspring. Same for these two characters. Same for these two characters over here. And because of that, even though all the different breeds of dogs, and most of this is really due to humans' doings of trying to breed for specific traits, even though they look so different and even though they act so different, because they can interbreed and they can produce fertile offspring, we consider all of these things to be members of the same species."}, {"video_title": "Cellular specialization (differentiation)   Cells   MCAT   Khan Academy.mp3", "Sentence": "So all of these really, really specialized cells like this muscle cell here, with its little contractile proteins, and this nerve cell here that can send signals, and this waterproof skin cell here, and this red blood cell that carries our oxygen, all of these came from these stem cells up here, which were completely unspecialized. So how does something like this happen? Well, it's actually pretty interesting. Let me first give you an analogy here. So just imagine a library, right? Like the one you used to go to when you were a teenager or something like that, and the one that you hopefully still go to. It has all the books you can imagine, right?"}, {"video_title": "Cellular specialization (differentiation)   Cells   MCAT   Khan Academy.mp3", "Sentence": "Let me first give you an analogy here. So just imagine a library, right? Like the one you used to go to when you were a teenager or something like that, and the one that you hopefully still go to. It has all the books you can imagine, right? But depending on which books you borrow and which books you read, you are changed. You end up knowing a totally different subset of stuff compared to someone who read different books than you, right? But all the books that you both read are still in this one library."}, {"video_title": "Cellular specialization (differentiation)   Cells   MCAT   Khan Academy.mp3", "Sentence": "It has all the books you can imagine, right? But depending on which books you borrow and which books you read, you are changed. You end up knowing a totally different subset of stuff compared to someone who read different books than you, right? But all the books that you both read are still in this one library. And there's actually a really similar system with our genes and with our DNA. So recall that inside the nucleus of each cell is your DNA. This is our library."}, {"video_title": "Cellular specialization (differentiation)   Cells   MCAT   Khan Academy.mp3", "Sentence": "But all the books that you both read are still in this one library. And there's actually a really similar system with our genes and with our DNA. So recall that inside the nucleus of each cell is your DNA. This is our library. This is our set of genetic instructions for building our entire body. And within our DNA library here, we have our books, which are segments of our DNA that we call genes. And genes give our cells specific instructions on how to make different kinds of proteins."}, {"video_title": "Cellular specialization (differentiation)   Cells   MCAT   Khan Academy.mp3", "Sentence": "This is our library. This is our set of genetic instructions for building our entire body. And within our DNA library here, we have our books, which are segments of our DNA that we call genes. And genes give our cells specific instructions on how to make different kinds of proteins. And having different proteins around, well, that changes the way our cells look, and it changes the way our cells act. So it gives our cells really different abilities. So, well, I mean, with the exception of the red blood cells, which lack nuclei, every single somatic cell in your body contains the exact same DNA."}, {"video_title": "Cellular specialization (differentiation)   Cells   MCAT   Khan Academy.mp3", "Sentence": "And genes give our cells specific instructions on how to make different kinds of proteins. And having different proteins around, well, that changes the way our cells look, and it changes the way our cells act. So it gives our cells really different abilities. So, well, I mean, with the exception of the red blood cells, which lack nuclei, every single somatic cell in your body contains the exact same DNA. Yet this muscle cell here, right, it looks and it acts differently to this neuron here. And that's because they're each reading different books in our DNA library. They're using different genes to make their proteins."}, {"video_title": "Cellular specialization (differentiation)   Cells   MCAT   Khan Academy.mp3", "Sentence": "So, well, I mean, with the exception of the red blood cells, which lack nuclei, every single somatic cell in your body contains the exact same DNA. Yet this muscle cell here, right, it looks and it acts differently to this neuron here. And that's because they're each reading different books in our DNA library. They're using different genes to make their proteins. And just a bit of terminology here, when a cell is actively using certain genes, it's said to be expressing those genes. And a gene being expressed is said to be turned on, and one not being expressed is turned off. So just keep that in mind."}, {"video_title": "Cellular specialization (differentiation)   Cells   MCAT   Khan Academy.mp3", "Sentence": "They're using different genes to make their proteins. And just a bit of terminology here, when a cell is actively using certain genes, it's said to be expressing those genes. And a gene being expressed is said to be turned on, and one not being expressed is turned off. So just keep that in mind. So why am I telling you all of this? Well, because in the end, it all relates to how our stem cells all the way up here end up differentiating into our specialized cells down here. So the bottom line is, in order to differentiate, to, for example, specialize into our muscle cell here, this stem cell up here turned on its muscle cell genes."}, {"video_title": "Cellular specialization (differentiation)   Cells   MCAT   Khan Academy.mp3", "Sentence": "So just keep that in mind. So why am I telling you all of this? Well, because in the end, it all relates to how our stem cells all the way up here end up differentiating into our specialized cells down here. So the bottom line is, in order to differentiate, to, for example, specialize into our muscle cell here, this stem cell up here turned on its muscle cell genes. So here's its DNA, and I'm highlighting its muscle cell genes that it turned on right now. And it also turned off some other genes. So by turning on its muscle cell genes, now proteins get made within the cell that changes how the cell looks."}, {"video_title": "Cellular specialization (differentiation)   Cells   MCAT   Khan Academy.mp3", "Sentence": "So the bottom line is, in order to differentiate, to, for example, specialize into our muscle cell here, this stem cell up here turned on its muscle cell genes. So here's its DNA, and I'm highlighting its muscle cell genes that it turned on right now. And it also turned off some other genes. So by turning on its muscle cell genes, now proteins get made within the cell that changes how the cell looks. See, now it's a bit elongated, right, this muscle cell here, and it also changes its functions. Now our muscle cell has contractile proteins in it to help it be a nice, useful muscle cell to help us move around, right? And our neuron here, our stem cell turned on its become a neuron genes here, right?"}, {"video_title": "Cellular specialization (differentiation)   Cells   MCAT   Khan Academy.mp3", "Sentence": "So by turning on its muscle cell genes, now proteins get made within the cell that changes how the cell looks. See, now it's a bit elongated, right, this muscle cell here, and it also changes its functions. Now our muscle cell has contractile proteins in it to help it be a nice, useful muscle cell to help us move around, right? And our neuron here, our stem cell turned on its become a neuron genes here, right? And it turned off some other ones, and then the cell started producing all the proteins it needed to turn into a neuron, like the proteins that would make it elongate like this and grow out these little spiky things up here called dendrites, okay? And let me also say that, remember, our stem cell up here was pluripotent. It could turn into any of our somatic adult body cells, but once it specialized into these mature cell types, these can't go on to differentiate into other cells, and they actually can't de-differentiate either."}, {"video_title": "Cellular specialization (differentiation)   Cells   MCAT   Khan Academy.mp3", "Sentence": "And our neuron here, our stem cell turned on its become a neuron genes here, right? And it turned off some other ones, and then the cell started producing all the proteins it needed to turn into a neuron, like the proteins that would make it elongate like this and grow out these little spiky things up here called dendrites, okay? And let me also say that, remember, our stem cell up here was pluripotent. It could turn into any of our somatic adult body cells, but once it specialized into these mature cell types, these can't go on to differentiate into other cells, and they actually can't de-differentiate either. They can't go backwards up to stem cells naturally, at least in us humans. So these cells stick around to form our bodies. So by now you must be wondering, well, what determines what genes in a given cell are turned on or off?"}, {"video_title": "Cellular specialization (differentiation)   Cells   MCAT   Khan Academy.mp3", "Sentence": "It could turn into any of our somatic adult body cells, but once it specialized into these mature cell types, these can't go on to differentiate into other cells, and they actually can't de-differentiate either. They can't go backwards up to stem cells naturally, at least in us humans. So these cells stick around to form our bodies. So by now you must be wondering, well, what determines what genes in a given cell are turned on or off? In other words, how in the heck does the cell know it's time to specialize into a different cell type? Well, it turns out that cells decide what they're going to grow up to be based on cues they get, and these cues can be from their internal environment, or the cues can come from their external environment, their outside environment. So let me just show you two major ways this can happen here, these cues."}, {"video_title": "Cellular specialization (differentiation)   Cells   MCAT   Khan Academy.mp3", "Sentence": "So by now you must be wondering, well, what determines what genes in a given cell are turned on or off? In other words, how in the heck does the cell know it's time to specialize into a different cell type? Well, it turns out that cells decide what they're going to grow up to be based on cues they get, and these cues can be from their internal environment, or the cues can come from their external environment, their outside environment. So let me just show you two major ways this can happen here, these cues. So in the development of lots of different organisms, us humans included, we start out with one cell, right, the zygote. And our zygote has these little proteins called transcription factors floating around in its cytoplasm. And also the precursors of these transcription factors are there too, little bits of mRNA."}, {"video_title": "Cellular specialization (differentiation)   Cells   MCAT   Khan Academy.mp3", "Sentence": "So let me just show you two major ways this can happen here, these cues. So in the development of lots of different organisms, us humans included, we start out with one cell, right, the zygote. And our zygote has these little proteins called transcription factors floating around in its cytoplasm. And also the precursors of these transcription factors are there too, little bits of mRNA. So two things to note. First, transcription factors will activate certain genes and turn them on, that's what transcription factors do. And second, notice that all these little transcription factors are clustered around in one area."}, {"video_title": "Cellular specialization (differentiation)   Cells   MCAT   Khan Academy.mp3", "Sentence": "And also the precursors of these transcription factors are there too, little bits of mRNA. So two things to note. First, transcription factors will activate certain genes and turn them on, that's what transcription factors do. And second, notice that all these little transcription factors are clustered around in one area. And this is important because when this zygote starts to divide, where do all these transcription factors end up? Well, like you see here, they only end up in the cells that divided off in that original region where they all were clustered around, right? So these cells up here don't have any, or don't have much."}, {"video_title": "Cellular specialization (differentiation)   Cells   MCAT   Khan Academy.mp3", "Sentence": "And second, notice that all these little transcription factors are clustered around in one area. And this is important because when this zygote starts to divide, where do all these transcription factors end up? Well, like you see here, they only end up in the cells that divided off in that original region where they all were clustered around, right? So these cells up here don't have any, or don't have much. And these cells down here have a whole heap of transcription factors. So now you can imagine that different genes will get activated in these different cells and that'll determine what each of these cells specializes into because now they're going to make different proteins. So this mechanism here is pretty appropriately called asymmetric segregation of cellular determinants."}, {"video_title": "Cellular specialization (differentiation)   Cells   MCAT   Khan Academy.mp3", "Sentence": "So these cells up here don't have any, or don't have much. And these cells down here have a whole heap of transcription factors. So now you can imagine that different genes will get activated in these different cells and that'll determine what each of these cells specializes into because now they're going to make different proteins. So this mechanism here is pretty appropriately called asymmetric segregation of cellular determinants. It's this big mouthful here, but you can, if we break it down here, you can see asymmetric because it really just refers to how these transcription factors are not symmetrically distributed among the daughter cells here. And this cellular determinants bit is just referring to the transcription factors or their precursors. So that's one way that cells can be made to specialize into different things, just having different transcription factors around."}, {"video_title": "Cellular specialization (differentiation)   Cells   MCAT   Khan Academy.mp3", "Sentence": "So this mechanism here is pretty appropriately called asymmetric segregation of cellular determinants. It's this big mouthful here, but you can, if we break it down here, you can see asymmetric because it really just refers to how these transcription factors are not symmetrically distributed among the daughter cells here. And this cellular determinants bit is just referring to the transcription factors or their precursors. So that's one way that cells can be made to specialize into different things, just having different transcription factors around. But the second way to specialization that I'll mention is called inductive signaling or just induction. And induction is kind of like really strong encouragement, almost like peer pressure, where one cell, or actually usually a group of cells, can induce another group of cells to differentiate by just using some signals. And the signals can be passed a few different ways."}, {"video_title": "Cellular specialization (differentiation)   Cells   MCAT   Khan Academy.mp3", "Sentence": "So that's one way that cells can be made to specialize into different things, just having different transcription factors around. But the second way to specialization that I'll mention is called inductive signaling or just induction. And induction is kind of like really strong encouragement, almost like peer pressure, where one cell, or actually usually a group of cells, can induce another group of cells to differentiate by just using some signals. And the signals can be passed a few different ways. So they can be passed by diffusion, they could be released from one group and just diffuse over to the other group where they'll bind receptors on the other groups and cause the cells over there to differentiate. Or the induction could be done by direct contact between cells. You can see these little surface proteins on each of these cells binding each other."}, {"video_title": "Cellular specialization (differentiation)   Cells   MCAT   Khan Academy.mp3", "Sentence": "And the signals can be passed a few different ways. So they can be passed by diffusion, they could be released from one group and just diffuse over to the other group where they'll bind receptors on the other groups and cause the cells over there to differentiate. Or the induction could be done by direct contact between cells. You can see these little surface proteins on each of these cells binding each other. That's direct contact. Or you could have signals pass through gap junctions, which are little connections, or actually I should say connexons, between cells that are connected. And that could induce the cell to specialize, the cell over here."}, {"video_title": "Cellular specialization (differentiation)   Cells   MCAT   Khan Academy.mp3", "Sentence": "You can see these little surface proteins on each of these cells binding each other. That's direct contact. Or you could have signals pass through gap junctions, which are little connections, or actually I should say connexons, between cells that are connected. And that could induce the cell to specialize, the cell over here. And I call this a connexon because in cellular biology, these proteins that make up part of a gap junction are collectively called a connexon. Anyway, induction is absolutely key in forming lots of our body parts. Like our limbs are formed partially through induction, and our ears and our eyes, and lots more of our body parts are formed through induction in development, in embryological development."}, {"video_title": "Cellular specialization (differentiation)   Cells   MCAT   Khan Academy.mp3", "Sentence": "And that could induce the cell to specialize, the cell over here. And I call this a connexon because in cellular biology, these proteins that make up part of a gap junction are collectively called a connexon. Anyway, induction is absolutely key in forming lots of our body parts. Like our limbs are formed partially through induction, and our ears and our eyes, and lots more of our body parts are formed through induction in development, in embryological development. So induction is really important in cell specialization. And so on that note, I'll just remind you, remember the goal here with the cytoplasmic determinants, those transcription factors I talked about earlier, and then all these signals that you get in induction, remember the goal is to get cells to change their gene expression, right? To flick on or flick off certain genes, which ultimately is what causes cells to differentiate into other, more specialized cells."}, {"video_title": "Uniporters, symporters and antiporters   Biology   Khan Academy.mp3", "Sentence": "And if you have a small enough molecule, let's say this is molecular oxygen, it's small, it doesn't have any charge, it has no polarity, that will be able to diffuse down its concentration gradient through the cellular membrane. But as we start to talk about things with more charge or things that might be larger, then we're going to need some help. Now the first type of help is just help to allow things to flow down their concentration gradient. And that we call facilitated diffusion. We have a whole video on facilitated diffusion. And one form of facilitated diffusion, hey, just open up a tunnel and let things flow down their concentration gradient. We saw that with the potassium ion channels, where potassium builds up on the inside of the cell because of the sodium-potassium pump."}, {"video_title": "Uniporters, symporters and antiporters   Biology   Khan Academy.mp3", "Sentence": "And that we call facilitated diffusion. We have a whole video on facilitated diffusion. And one form of facilitated diffusion, hey, just open up a tunnel and let things flow down their concentration gradient. We saw that with the potassium ion channels, where potassium builds up on the inside of the cell because of the sodium-potassium pump. Let me just be clear down here, this is the inside, this is the outside of the cell. But then these channels allow the potassium to flow down their concentration gradient. It's going to be put in check because of its charge and it's more positive outside, but we talk about that in other videos."}, {"video_title": "Uniporters, symporters and antiporters   Biology   Khan Academy.mp3", "Sentence": "We saw that with the potassium ion channels, where potassium builds up on the inside of the cell because of the sodium-potassium pump. Let me just be clear down here, this is the inside, this is the outside of the cell. But then these channels allow the potassium to flow down their concentration gradient. It's going to be put in check because of its charge and it's more positive outside, but we talk about that in other videos. But it's just a simple tunnel. Now sometimes that tunnel is gated. It's only going to be open if a certain trigger is hit."}, {"video_title": "Uniporters, symporters and antiporters   Biology   Khan Academy.mp3", "Sentence": "It's going to be put in check because of its charge and it's more positive outside, but we talk about that in other videos. But it's just a simple tunnel. Now sometimes that tunnel is gated. It's only going to be open if a certain trigger is hit. And we see that when we talk about signals going down a neuron, voltage-gated channels. Once the voltage hits a certain amount, then the channel opens and then the sodium that has a higher concentration outside can flow down its concentration gradient inside. But both of these, this is considered passive transport."}, {"video_title": "Uniporters, symporters and antiporters   Biology   Khan Academy.mp3", "Sentence": "It's only going to be open if a certain trigger is hit. And we see that when we talk about signals going down a neuron, voltage-gated channels. Once the voltage hits a certain amount, then the channel opens and then the sodium that has a higher concentration outside can flow down its concentration gradient inside. But both of these, this is considered passive transport. It's facilitated diffusion, passive transport. We're allowing things to flow down their concentration gradient. You can see here, the potassium is going in the direction of its concentration gradient."}, {"video_title": "Uniporters, symporters and antiporters   Biology   Khan Academy.mp3", "Sentence": "But both of these, this is considered passive transport. It's facilitated diffusion, passive transport. We're allowing things to flow down their concentration gradient. You can see here, the potassium is going in the direction of its concentration gradient. It's high concentration inside, low concentration outside. So we're allowing it to flow down the concentration gradient. Here the sodium is high concentration outside, low concentration inside."}, {"video_title": "Uniporters, symporters and antiporters   Biology   Khan Academy.mp3", "Sentence": "You can see here, the potassium is going in the direction of its concentration gradient. It's high concentration inside, low concentration outside. So we're allowing it to flow down the concentration gradient. Here the sodium is high concentration outside, low concentration inside. And this happened because of the sodium-potassium pump, but we're allowing it to now flow down its concentration gradient. Now let's talk about active transport. So passive transport doesn't require any energy to make this stuff happen."}, {"video_title": "Uniporters, symporters and antiporters   Biology   Khan Academy.mp3", "Sentence": "Here the sodium is high concentration outside, low concentration inside. And this happened because of the sodium-potassium pump, but we're allowing it to now flow down its concentration gradient. Now let's talk about active transport. So passive transport doesn't require any energy to make this stuff happen. It's just about things flowing down their gradient. In active transport, we're either directly using energy to make something go against its gradient, or we're using some energy from a previous active transport to help facilitate something else going against this gradient. So first let's talk about primary active transport, because this might be a little bit more easy to think about."}, {"video_title": "Uniporters, symporters and antiporters   Biology   Khan Academy.mp3", "Sentence": "So passive transport doesn't require any energy to make this stuff happen. It's just about things flowing down their gradient. In active transport, we're either directly using energy to make something go against its gradient, or we're using some energy from a previous active transport to help facilitate something else going against this gradient. So first let's talk about primary active transport, because this might be a little bit more easy to think about. And none of them are that daunting. And the best case of this, if we're talking about animal cells, is the sodium-potassium pump. The sodium-potassium pump, super important for establishing resting membrane voltage, I guess you could say, resting membrane potential."}, {"video_title": "Uniporters, symporters and antiporters   Biology   Khan Academy.mp3", "Sentence": "So first let's talk about primary active transport, because this might be a little bit more easy to think about. And none of them are that daunting. And the best case of this, if we're talking about animal cells, is the sodium-potassium pump. The sodium-potassium pump, super important for establishing resting membrane voltage, I guess you could say, resting membrane potential. But the concentration gradients that it establishes are also very important. The sodium, it establishes, it pumps sodium ions out of the cell against its concentration gradient. So we say the sodium ions already have a higher concentration outside, but it keeps pumping them out."}, {"video_title": "Uniporters, symporters and antiporters   Biology   Khan Academy.mp3", "Sentence": "The sodium-potassium pump, super important for establishing resting membrane voltage, I guess you could say, resting membrane potential. But the concentration gradients that it establishes are also very important. The sodium, it establishes, it pumps sodium ions out of the cell against its concentration gradient. So we say the sodium ions already have a higher concentration outside, but it keeps pumping them out. And to do that, it needs to use ATP. It breaks up ATP into ADP and a phosphate group. It hydrolyzes it."}, {"video_title": "Uniporters, symporters and antiporters   Biology   Khan Academy.mp3", "Sentence": "So we say the sodium ions already have a higher concentration outside, but it keeps pumping them out. And to do that, it needs to use ATP. It breaks up ATP into ADP and a phosphate group. It hydrolyzes it. And so that's why it's sometimes called an ATPase. It's an enzyme that helps break up ATP. But it uses that, and it uses that energy to pump sodium out of the cell and potassium into the cell."}, {"video_title": "Uniporters, symporters and antiporters   Biology   Khan Academy.mp3", "Sentence": "It hydrolyzes it. And so that's why it's sometimes called an ATPase. It's an enzyme that helps break up ATP. But it uses that, and it uses that energy to pump sodium out of the cell and potassium into the cell. And then as we'll see, that sodium that's pumped out of it, that kind of forms a potential energy because it starts to build a chemo-electrochemical gradient, which can later be used to power secondary active transport. We'll talk about that in a few seconds. Now this is in animal cells."}, {"video_title": "Uniporters, symporters and antiporters   Biology   Khan Academy.mp3", "Sentence": "But it uses that, and it uses that energy to pump sodium out of the cell and potassium into the cell. And then as we'll see, that sodium that's pumped out of it, that kind of forms a potential energy because it starts to build a chemo-electrochemical gradient, which can later be used to power secondary active transport. We'll talk about that in a few seconds. Now this is in animal cells. The analog in plant cells, fungi, protists, prokaryotes, is the proton ATPase or the proton pump, which does the same thing, but it does it, instead of doing it in two directions, it does it for protons. It pumps the protons out of the cell against their concentration gradient. So even though you have a higher concentration outside than inside, it'll continue to pump them out."}, {"video_title": "Uniporters, symporters and antiporters   Biology   Khan Academy.mp3", "Sentence": "Now this is in animal cells. The analog in plant cells, fungi, protists, prokaryotes, is the proton ATPase or the proton pump, which does the same thing, but it does it, instead of doing it in two directions, it does it for protons. It pumps the protons out of the cell against their concentration gradient. So even though you have a higher concentration outside than inside, it'll continue to pump them out. But to power it, it uses ATP to change its conformation in the right way. And so that's why this is often called a proton ATPase. This is called sodium potassium ATPase."}, {"video_title": "Uniporters, symporters and antiporters   Biology   Khan Academy.mp3", "Sentence": "So even though you have a higher concentration outside than inside, it'll continue to pump them out. But to power it, it uses ATP to change its conformation in the right way. And so that's why this is often called a proton ATPase. This is called sodium potassium ATPase. That's our friend, the sodium potassium pump. This is called proton ATPase. And you wouldn't see these in the same cell."}, {"video_title": "Uniporters, symporters and antiporters   Biology   Khan Academy.mp3", "Sentence": "This is called sodium potassium ATPase. That's our friend, the sodium potassium pump. This is called proton ATPase. And you wouldn't see these in the same cell. So maybe I'll draw a little line over here. This would be in plants, fungi, protists, things like that. This would be in animal cells."}, {"video_title": "Uniporters, symporters and antiporters   Biology   Khan Academy.mp3", "Sentence": "And you wouldn't see these in the same cell. So maybe I'll draw a little line over here. This would be in plants, fungi, protists, things like that. This would be in animal cells. But both of them are actively using energy. They're directly using ATP to transport things against their concentration gradient, which is why we call it active transport. Now, because you have these concentration gradients, or these electrochemical gradients are established, those can then be used to do other forms of active transport."}, {"video_title": "Uniporters, symporters and antiporters   Biology   Khan Academy.mp3", "Sentence": "This would be in animal cells. But both of them are actively using energy. They're directly using ATP to transport things against their concentration gradient, which is why we call it active transport. Now, because you have these concentration gradients, or these electrochemical gradients are established, those can then be used to do other forms of active transport. And that's what we call secondary active transport. So this right over here, this is my little depiction of a symporter. And this is a sodium glucose symporter."}, {"video_title": "Uniporters, symporters and antiporters   Biology   Khan Academy.mp3", "Sentence": "Now, because you have these concentration gradients, or these electrochemical gradients are established, those can then be used to do other forms of active transport. And that's what we call secondary active transport. So this right over here, this is my little depiction of a symporter. And this is a sodium glucose symporter. And what it does is it leverages the sodium flowing down its concentration gradient. And once again, that was established with the sodium potassium pump. So it's flowing down its concentration gradient, but it's leveraging that energy."}, {"video_title": "Uniporters, symporters and antiporters   Biology   Khan Academy.mp3", "Sentence": "And this is a sodium glucose symporter. And what it does is it leverages the sodium flowing down its concentration gradient. And once again, that was established with the sodium potassium pump. So it's flowing down its concentration gradient, but it's leveraging that energy. You can imagine kind of putting a little wheel under a waterfall to make it spin, to also make glucose, to transport glucose against its concentration gradient. So the glucose already has a, will have a high concentration gradient here, low over here, but it's transporting glucose against its concentration gradient. We talk about it in other videos."}, {"video_title": "Uniporters, symporters and antiporters   Biology   Khan Academy.mp3", "Sentence": "So it's flowing down its concentration gradient, but it's leveraging that energy. You can imagine kind of putting a little wheel under a waterfall to make it spin, to also make glucose, to transport glucose against its concentration gradient. So the glucose already has a, will have a high concentration gradient here, low over here, but it's transporting glucose against its concentration gradient. We talk about it in other videos. And then another example of secondary active transport is an antiporter or an exchanger. In the symporter or cotransporter, they're both going in the same direction, even though one is going with its concentration gradient, that's essentially powering it, and the other one is going against its concentration gradient, that's why it's active transport. With an exchanger, they're going in opposite directions."}, {"video_title": "Uniporters, symporters and antiporters   Biology   Khan Academy.mp3", "Sentence": "We talk about it in other videos. And then another example of secondary active transport is an antiporter or an exchanger. In the symporter or cotransporter, they're both going in the same direction, even though one is going with its concentration gradient, that's essentially powering it, and the other one is going against its concentration gradient, that's why it's active transport. With an exchanger, they're going in opposite directions. So you have the sodium calcium ion exchanger, and here the sodium is going down its concentration gradient, and that fuel's taking the calcium ions outside of the cell against its concentration gradient. So once again, anytime something is going against its concentration gradient, and once again, in this case, it's calcium, it's going to be active transport. But since the sodium ions, the sodium ions are going in a different direction than the calcium ions, we call this an antiporter, while this right over here is a cotransporter, a symporter."}, {"video_title": "Uniporters, symporters and antiporters   Biology   Khan Academy.mp3", "Sentence": "With an exchanger, they're going in opposite directions. So you have the sodium calcium ion exchanger, and here the sodium is going down its concentration gradient, and that fuel's taking the calcium ions outside of the cell against its concentration gradient. So once again, anytime something is going against its concentration gradient, and once again, in this case, it's calcium, it's going to be active transport. But since the sodium ions, the sodium ions are going in a different direction than the calcium ions, we call this an antiporter, while this right over here is a cotransporter, a symporter. Now you might say, hey, wait, isn't the sodium potassium pump, isn't this an antiporter? Things are going in different directions. And the difference is, both of these, this is primary active transport, and the sodium potassium pump, both of these things are going against their concentration gradient."}, {"video_title": "Uniporters, symporters and antiporters   Biology   Khan Academy.mp3", "Sentence": "But since the sodium ions, the sodium ions are going in a different direction than the calcium ions, we call this an antiporter, while this right over here is a cotransporter, a symporter. Now you might say, hey, wait, isn't the sodium potassium pump, isn't this an antiporter? Things are going in different directions. And the difference is, both of these, this is primary active transport, and the sodium potassium pump, both of these things are going against their concentration gradient. In a true antiporter, it's really secondary active transport. One of them is going with their concentration gradient, going down it, which is providing the energy to take the other thing against its concentration gradient. So anyway, hopefully this gives you a high-level overview of the various forms of transport, and it gives you more appreciation for how beautiful and intricate and mesmerizing cellular membranes and all the different things cells have to do actually are."}, {"video_title": "Antiparallel structure of DNA strands   Biology   Khan Academy (2).mp3", "Sentence": "And then you have a sugar. And then you have a phosphate group and then you have a sugar. And so I could draw the strand something like this. So phosphate and then we have a sugar. Whoops, let me just draw all the phosphates ahead of time. So you have the phosphates on that end and then you have the sugars. And you see the same thing on the other strand as well where we have phosphate, phosphate with a sugar, then another phosphate, then a sugar, then another phosphate."}, {"video_title": "Antiparallel structure of DNA strands   Biology   Khan Academy (2).mp3", "Sentence": "So phosphate and then we have a sugar. Whoops, let me just draw all the phosphates ahead of time. So you have the phosphates on that end and then you have the sugars. And you see the same thing on the other strand as well where we have phosphate, phosphate with a sugar, then another phosphate, then a sugar, then another phosphate. Let me circle the sugars as well. So you have a sugar there and then you have the sugar there as well. So on the other strand, it's also going to look like this."}, {"video_title": "Antiparallel structure of DNA strands   Biology   Khan Academy (2).mp3", "Sentence": "And you see the same thing on the other strand as well where we have phosphate, phosphate with a sugar, then another phosphate, then a sugar, then another phosphate. Let me circle the sugars as well. So you have a sugar there and then you have the sugar there as well. So on the other strand, it's also going to look like this. So let me draw the phosphates. I'm just abstracting them now. So the phosphate and then you have the sugars in between the phosphates."}, {"video_title": "Antiparallel structure of DNA strands   Biology   Khan Academy (2).mp3", "Sentence": "So on the other strand, it's also going to look like this. So let me draw the phosphates. I'm just abstracting them now. So the phosphate and then you have the sugars in between the phosphates. And what links them, you can think of them as the rungs on the ladder, these are the complementary nitrogenous bases. And the reason why we call them nitrogenous bases, I actually forgot to talk about in the last videos, is that these nitrogens are really electronegative and they can take up more hydrogen protons. They have an extra lone pair, the nitrogens have an extra lone pair that can be used up under the right conditions to potentially sop up more hydrogen protons."}, {"video_title": "Antiparallel structure of DNA strands   Biology   Khan Academy (2).mp3", "Sentence": "So the phosphate and then you have the sugars in between the phosphates. And what links them, you can think of them as the rungs on the ladder, these are the complementary nitrogenous bases. And the reason why we call them nitrogenous bases, I actually forgot to talk about in the last videos, is that these nitrogens are really electronegative and they can take up more hydrogen protons. They have an extra lone pair, the nitrogens have an extra lone pair that can be used up under the right conditions to potentially sop up more hydrogen protons. Now, a lot of people ask, well, if you have these nitrogenous bases here, why is DNA called an acid? Why is it called an acid? Well, the first thing is that the basic properties of the nitrogenous base are offset to a good degree based on the fact that they're able to hydrogen bond with each other."}, {"video_title": "Antiparallel structure of DNA strands   Biology   Khan Academy (2).mp3", "Sentence": "They have an extra lone pair, the nitrogens have an extra lone pair that can be used up under the right conditions to potentially sop up more hydrogen protons. Now, a lot of people ask, well, if you have these nitrogenous bases here, why is DNA called an acid? Why is it called an acid? Well, the first thing is that the basic properties of the nitrogenous base are offset to a good degree based on the fact that they're able to hydrogen bond with each other. And that's what actually forms these rungs, the rungs of the ladder when these complementary nitrogenous bases form these hydrogen bonds with each other. But even more, the reason why we call it an acid is the phosphate groups, when they're protonated, are acids. Now, the reason why we tend to draw them deprotonated is when they're so acidic that if you put them in a neutral solution, they're going to be deprotonated."}, {"video_title": "Antiparallel structure of DNA strands   Biology   Khan Academy (2).mp3", "Sentence": "Well, the first thing is that the basic properties of the nitrogenous base are offset to a good degree based on the fact that they're able to hydrogen bond with each other. And that's what actually forms these rungs, the rungs of the ladder when these complementary nitrogenous bases form these hydrogen bonds with each other. But even more, the reason why we call it an acid is the phosphate groups, when they're protonated, are acids. Now, the reason why we tend to draw them deprotonated is when they're so acidic that if you put them in a neutral solution, they're going to be deprotonated. So this is the form that you're more likely to find it in the nucleus of an actual cell once it's actually already deprotonated. But in general, phosphate groups are considered acidic. And if I were to draw kind of a more pure phosphate group, and I talked about this already in the last video, I would have it protonated, and so I wouldn't draw that negative charge like that."}, {"video_title": "Antiparallel structure of DNA strands   Biology   Khan Academy (2).mp3", "Sentence": "Now, the reason why we tend to draw them deprotonated is when they're so acidic that if you put them in a neutral solution, they're going to be deprotonated. So this is the form that you're more likely to find it in the nucleus of an actual cell once it's actually already deprotonated. But in general, phosphate groups are considered acidic. And if I were to draw kind of a more pure phosphate group, and I talked about this already in the last video, I would have it protonated, and so I wouldn't draw that negative charge like that. So that's just a review of last time. But let's actually, it doesn't mean just, since I already started abstracting it, let's abstract it further. So let's draw the nitrogenous bases a little bit."}, {"video_title": "Antiparallel structure of DNA strands   Biology   Khan Academy (2).mp3", "Sentence": "And if I were to draw kind of a more pure phosphate group, and I talked about this already in the last video, I would have it protonated, and so I wouldn't draw that negative charge like that. So that's just a review of last time. But let's actually, it doesn't mean just, since I already started abstracting it, let's abstract it further. So let's draw the nitrogenous bases a little bit. So I have thymine here, and I will do thymine in this green color. So this right over there is thymine. So this is attached to thymine."}, {"video_title": "Antiparallel structure of DNA strands   Biology   Khan Academy (2).mp3", "Sentence": "So let's draw the nitrogenous bases a little bit. So I have thymine here, and I will do thymine in this green color. So this right over there is thymine. So this is attached to thymine. And the complementary nitrogenous base to thymine is adenine, which I will do. Let's see, I'm running out of colors here. Let's see, adenine."}, {"video_title": "Antiparallel structure of DNA strands   Biology   Khan Academy (2).mp3", "Sentence": "So this is attached to thymine. And the complementary nitrogenous base to thymine is adenine, which I will do. Let's see, I'm running out of colors here. Let's see, adenine. I'll do this in an orange color. It's got so many nitrogens on it. So actually, so let me, so it actually should include that hydrogen right over there."}, {"video_title": "Antiparallel structure of DNA strands   Biology   Khan Academy (2).mp3", "Sentence": "Let's see, adenine. I'll do this in an orange color. It's got so many nitrogens on it. So actually, so let me, so it actually should include that hydrogen right over there. So this right over here is adenine. And they form, they have these hydrogen bonds between them right over here because they have partially negative and positive charges on either end that are attracted to each other. And then we go to this rung, one rung below it."}, {"video_title": "Antiparallel structure of DNA strands   Biology   Khan Academy (2).mp3", "Sentence": "So actually, so let me, so it actually should include that hydrogen right over there. So this right over here is adenine. And they form, they have these hydrogen bonds between them right over here because they have partially negative and positive charges on either end that are attracted to each other. And then we go to this rung, one rung below it. And what is going on? Well, let's see. We have, I really am running out of colors here."}, {"video_title": "Antiparallel structure of DNA strands   Biology   Khan Academy (2).mp3", "Sentence": "And then we go to this rung, one rung below it. And what is going on? Well, let's see. We have, I really am running out of colors here. We have this nitrogenous base is cytosine. This nitrogenous base right over here is cytosine. This nitrogenous base here is cytosine."}, {"video_title": "Antiparallel structure of DNA strands   Biology   Khan Academy (2).mp3", "Sentence": "We have, I really am running out of colors here. We have this nitrogenous base is cytosine. This nitrogenous base right over here is cytosine. This nitrogenous base here is cytosine. And it is paired up with guanine. It is paired up with guanine. I'll do guanine in this color."}, {"video_title": "Antiparallel structure of DNA strands   Biology   Khan Academy (2).mp3", "Sentence": "This nitrogenous base here is cytosine. And it is paired up with guanine. It is paired up with guanine. I'll do guanine in this color. So it is, it is paired up with guanine right over there. And we even saw this in the introductory video to DNA. Now, you might say, oh look, these two strands seem parallel to each other."}, {"video_title": "Antiparallel structure of DNA strands   Biology   Khan Academy (2).mp3", "Sentence": "I'll do guanine in this color. So it is, it is paired up with guanine right over there. And we even saw this in the introductory video to DNA. Now, you might say, oh look, these two strands seem parallel to each other. And in some ways that is true. But there might be something other, another interesting thing that you might have noticed is the direction in which they are oriented. I guess is the best way to phrase it."}, {"video_title": "Antiparallel structure of DNA strands   Biology   Khan Academy (2).mp3", "Sentence": "Now, you might say, oh look, these two strands seem parallel to each other. And in some ways that is true. But there might be something other, another interesting thing that you might have noticed is the direction in which they are oriented. I guess is the best way to phrase it. If we, and you especially see that when you focus in on the sugars. Notice the sugars over here, the deoxyriboses are the things that, or the parts of the nucleotide that come from deoxyribose. You see the oxygens on the top of the ribose, on the top of these five member rings."}, {"video_title": "Antiparallel structure of DNA strands   Biology   Khan Academy (2).mp3", "Sentence": "I guess is the best way to phrase it. If we, and you especially see that when you focus in on the sugars. Notice the sugars over here, the deoxyriboses are the things that, or the parts of the nucleotide that come from deoxyribose. You see the oxygens on the top of the ribose, on the top of these five member rings. The oxygen is on top. While on this side, the oxygen is on the bottom. And so they are actually in different orientations."}, {"video_title": "Antiparallel structure of DNA strands   Biology   Khan Academy (2).mp3", "Sentence": "You see the oxygens on the top of the ribose, on the top of these five member rings. The oxygen is on top. While on this side, the oxygen is on the bottom. And so they are actually in different orientations. Here the oxygen's pointing up. Here the oxygen is pointing down. And to get a little bit more concrete about that, we can number the carbons on the ribose to think about the directions and use those numbers of the carbons to describe the different directions."}, {"video_title": "Antiparallel structure of DNA strands   Biology   Khan Academy (2).mp3", "Sentence": "And so they are actually in different orientations. Here the oxygen's pointing up. Here the oxygen is pointing down. And to get a little bit more concrete about that, we can number the carbons on the ribose to think about the directions and use those numbers of the carbons to describe the different directions. So let's number our carbons. So when ribose, so this is, these are both ribose. We saw that in the molecular structure of DNA videos."}, {"video_title": "Antiparallel structure of DNA strands   Biology   Khan Academy (2).mp3", "Sentence": "And to get a little bit more concrete about that, we can number the carbons on the ribose to think about the directions and use those numbers of the carbons to describe the different directions. So let's number our carbons. So when ribose, so this is, these are both ribose. We saw that in the molecular structure of DNA videos. When we're talking about DNA, we're talking about deoxyribose. So it does not have, it does not have a, it does not, instead of having a hydroxyl group on the number two carbon, it just has a, it just has a hydrogen. So instead of having a hydroxyl group on the number two carbon, it just has a hydrogen."}, {"video_title": "Antiparallel structure of DNA strands   Biology   Khan Academy (2).mp3", "Sentence": "We saw that in the molecular structure of DNA videos. When we're talking about DNA, we're talking about deoxyribose. So it does not have, it does not have a, it does not, instead of having a hydroxyl group on the number two carbon, it just has a, it just has a hydrogen. So instead of having a hydroxyl group on the number two carbon, it just has a hydrogen. But let's actually number them. So this is the one prime carbon starting at the carbonyl group. Let me do that in a different color."}, {"video_title": "Antiparallel structure of DNA strands   Biology   Khan Academy (2).mp3", "Sentence": "So instead of having a hydroxyl group on the number two carbon, it just has a hydrogen. But let's actually number them. So this is the one prime carbon starting at the carbonyl group. Let me do that in a different color. So this is the one prime carbon. And I'm just numbering them starting at the carbonyl group. One prime, two prime, three prime, four prime, five prime."}, {"video_title": "Antiparallel structure of DNA strands   Biology   Khan Academy (2).mp3", "Sentence": "Let me do that in a different color. So this is the one prime carbon. And I'm just numbering them starting at the carbonyl group. One prime, two prime, three prime, four prime, five prime. And then when you look at it as a ring, this was the one prime. This is the two prime. This is the three prime."}, {"video_title": "Antiparallel structure of DNA strands   Biology   Khan Academy (2).mp3", "Sentence": "One prime, two prime, three prime, four prime, five prime. And then when you look at it as a ring, this was the one prime. This is the two prime. This is the three prime. This is the four prime. This is the five prime. Or if you were to number them on this diagram right over here, actually in the DNA molecule, this is the one prime."}, {"video_title": "Antiparallel structure of DNA strands   Biology   Khan Academy (2).mp3", "Sentence": "This is the three prime. This is the four prime. This is the five prime. Or if you were to number them on this diagram right over here, actually in the DNA molecule, this is the one prime. This is the two prime carbon. This is the three prime carbon. This is the four prime carbon."}, {"video_title": "Antiparallel structure of DNA strands   Biology   Khan Academy (2).mp3", "Sentence": "Or if you were to number them on this diagram right over here, actually in the DNA molecule, this is the one prime. This is the two prime carbon. This is the three prime carbon. This is the four prime carbon. And this is the five prime carbon. And so one way to think about it is we'll go phosphate group, and it's connected, it's connected with what we call phosphodiester linkages. Phosphodiester linkages, that's what's essentially allowing these backbones to link up."}, {"video_title": "Antiparallel structure of DNA strands   Biology   Khan Academy (2).mp3", "Sentence": "This is the four prime carbon. And this is the five prime carbon. And so one way to think about it is we'll go phosphate group, and it's connected, it's connected with what we call phosphodiester linkages. Phosphodiester linkages, that's what's essentially allowing these backbones to link up. But we're going from phosphate to five prime carbon to, and then through the sugar, we go to the three prime carbon, then we go to another phosphate, then we go to the five prime carbon. Let me label that. This is the five prime carbon."}, {"video_title": "Antiparallel structure of DNA strands   Biology   Khan Academy (2).mp3", "Sentence": "Phosphodiester linkages, that's what's essentially allowing these backbones to link up. But we're going from phosphate to five prime carbon to, and then through the sugar, we go to the three prime carbon, then we go to another phosphate, then we go to the five prime carbon. Let me label that. This is the five prime carbon. Then we go to the three prime carbon. And that just comes straight out of just numbering these, starting with the carbon that was the number one carbon, which went in a straight chain form. It's at the carbonyl, it's part of the carbonyl group."}, {"video_title": "Antiparallel structure of DNA strands   Biology   Khan Academy (2).mp3", "Sentence": "This is the five prime carbon. Then we go to the three prime carbon. And that just comes straight out of just numbering these, starting with the carbon that was the number one carbon, which went in a straight chain form. It's at the carbonyl, it's part of the carbonyl group. But you see we're going from five, we go phosphate, five prime, three prime, phosphate, five prime, three prime, phosphate. So one way to describe the orientation is saying, hey, we're going in the direction from five prime to three prime. So we could say, we could say that we're going from five prime, we're going from five prime to three prime that way, on the left-hand chain."}, {"video_title": "Antiparallel structure of DNA strands   Biology   Khan Academy (2).mp3", "Sentence": "It's at the carbonyl, it's part of the carbonyl group. But you see we're going from five, we go phosphate, five prime, three prime, phosphate, five prime, three prime, phosphate. So one way to describe the orientation is saying, hey, we're going in the direction from five prime to three prime. So we could say, we could say that we're going from five prime, we're going from five prime to three prime that way, on the left-hand chain. And what are we doing on the right-hand chain? Well, let's number them again. So this is the one prime carbon."}, {"video_title": "Antiparallel structure of DNA strands   Biology   Khan Academy (2).mp3", "Sentence": "So we could say, we could say that we're going from five prime, we're going from five prime to three prime that way, on the left-hand chain. And what are we doing on the right-hand chain? Well, let's number them again. So this is the one prime carbon. Now this thing, relative to this, is upside down, it's inverted. So one prime, two prime, three prime, four prime, five prime. I could do it up here."}, {"video_title": "Antiparallel structure of DNA strands   Biology   Khan Academy (2).mp3", "Sentence": "So this is the one prime carbon. Now this thing, relative to this, is upside down, it's inverted. So one prime, two prime, three prime, four prime, five prime. I could do it up here. One prime carbon, two prime carbon, three prime carbon, four prime carbon, five prime carbon. Here you're going from phosphate, three prime, five prime, phosphate, three prime, five prime, phosphate. So the way that the sugars are oriented, if you're going from top to bottom the way we're looking here, you're going from three prime to five prime."}, {"video_title": "Antiparallel structure of DNA strands   Biology   Khan Academy (2).mp3", "Sentence": "I could do it up here. One prime carbon, two prime carbon, three prime carbon, four prime carbon, five prime carbon. Here you're going from phosphate, three prime, five prime, phosphate, three prime, five prime, phosphate. So the way that the sugars are oriented, if you're going from top to bottom the way we're looking here, you're going from three prime to five prime. So on the right-hand side, you are, it's three prime, five prime. And so if you wanted to draw an arrow from five prime to three prime, you could look at it like that. And so you could say these are parallel, but since they are essentially oriented in, they're pointing in different directions, even though they're actually parallel, we would call the structure of DNA anti-parallel."}, {"video_title": "Antiparallel structure of DNA strands   Biology   Khan Academy (2).mp3", "Sentence": "So the way that the sugars are oriented, if you're going from top to bottom the way we're looking here, you're going from three prime to five prime. So on the right-hand side, you are, it's three prime, five prime. And so if you wanted to draw an arrow from five prime to three prime, you could look at it like that. And so you could say these are parallel, but since they are essentially oriented in, they're pointing in different directions, even though they're actually parallel, we would call the structure of DNA anti-parallel. So this would be an anti-parallel structure of DNA. So these two strands, they're complementary, they're defined by each other. The thymine bonds with the adenine, the cytosine bonds with the guanine, or they are attracted to each other through these hydrogen bonds, but the two backbones, they're pointed in different directions."}, {"video_title": "Antiparallel structure of DNA strands   Biology   Khan Academy (2).mp3", "Sentence": "And so you could say these are parallel, but since they are essentially oriented in, they're pointing in different directions, even though they're actually parallel, we would call the structure of DNA anti-parallel. So this would be an anti-parallel structure of DNA. So these two strands, they're complementary, they're defined by each other. The thymine bonds with the adenine, the cytosine bonds with the guanine, or they are attracted to each other through these hydrogen bonds, but the two backbones, they're pointed in different directions. Now another interesting thing to think about, since we're talking about the molecular structure of DNA, is how do these things form? How do these things know to orient in this way? And part of, what plays part of that role is the fact that these phosphate groups are negative."}, {"video_title": "Antiparallel structure of DNA strands   Biology   Khan Academy (2).mp3", "Sentence": "The thymine bonds with the adenine, the cytosine bonds with the guanine, or they are attracted to each other through these hydrogen bonds, but the two backbones, they're pointed in different directions. Now another interesting thing to think about, since we're talking about the molecular structure of DNA, is how do these things form? How do these things know to orient in this way? And part of, what plays part of that role is the fact that these phosphate groups are negative. So you think these things that have outright negative charge, they're gonna try to get as far away from each other as possible, and then when they, you know, they just keep kind of orienting, getting far away from each other, and these are long, these are very, very, very, very long molecules. In the introductory video to DNA, we talk about how long these chromosomes are, how many base pairs we actually have, and these are long molecules. So all of these phosphate groups on either strand, they want to get away from each other, and then these things want to, these things want to get close to each other because of the hydrogen bonds, and so that's what helps form this actual ladder structure."}, {"video_title": "Antiparallel structure of DNA strands   Biology   Khan Academy (2).mp3", "Sentence": "And part of, what plays part of that role is the fact that these phosphate groups are negative. So you think these things that have outright negative charge, they're gonna try to get as far away from each other as possible, and then when they, you know, they just keep kind of orienting, getting far away from each other, and these are long, these are very, very, very, very long molecules. In the introductory video to DNA, we talk about how long these chromosomes are, how many base pairs we actually have, and these are long molecules. So all of these phosphate groups on either strand, they want to get away from each other, and then these things want to, these things want to get close to each other because of the hydrogen bonds, and so that's what helps form this actual ladder structure. So DNA, fascinating molecule. We could speak for days about it. It's actually mind-blowing when you think about its implications for who we are."}, {"video_title": "Antiparallel structure of DNA strands   Biology   Khan Academy (2).mp3", "Sentence": "So all of these phosphate groups on either strand, they want to get away from each other, and then these things want to, these things want to get close to each other because of the hydrogen bonds, and so that's what helps form this actual ladder structure. So DNA, fascinating molecule. We could speak for days about it. It's actually mind-blowing when you think about its implications for who we are. But hopefully this gives you a better sense of what it is molecularly. Molecularly, I cannot say it. Molecularly."}, {"video_title": "Hypotonic, isotonic, and hypertonic solutions (tonicity)   Khan Academy.mp3", "Sentence": "And then I have the water molecules depicted by these blue circles. And then I have the solute inside of the solution, inside of the water solution, that we depict with these yellow circles. And I've clearly exaggerated the size of the water molecules and the solute particles relative to the size of the cell, but I did that so that we can visualize what's actually going on. Now we're going to assume that the cellular membrane, this phospholipid bilayer, is semipermeable, that it will allow water molecules to pass in and out. So a water molecule could go from the inside to the outside or from the outside to the inside. But we're gonna assume that it does not allow the passage of the solute particles. So that's why it's semipermeable, it's permeable to certain things, or we could say selectively permeable."}, {"video_title": "Hypotonic, isotonic, and hypertonic solutions (tonicity)   Khan Academy.mp3", "Sentence": "Now we're going to assume that the cellular membrane, this phospholipid bilayer, is semipermeable, that it will allow water molecules to pass in and out. So a water molecule could go from the inside to the outside or from the outside to the inside. But we're gonna assume that it does not allow the passage of the solute particles. So that's why it's semipermeable, it's permeable to certain things, or we could say selectively permeable. Now, what do we think is going to happen? Well, the first thing that you might observe is we have a lower concentration of solute on the outside than we have on the inside. So at any given moment in time, you will have some water molecules moving in just the right direction to go from the outside to the inside, and you will also have some water molecules that might be in just the right place to go from the inside to the outside."}, {"video_title": "Hypotonic, isotonic, and hypertonic solutions (tonicity)   Khan Academy.mp3", "Sentence": "So that's why it's semipermeable, it's permeable to certain things, or we could say selectively permeable. Now, what do we think is going to happen? Well, the first thing that you might observe is we have a lower concentration of solute on the outside than we have on the inside. So at any given moment in time, you will have some water molecules moving in just the right direction to go from the outside to the inside, and you will also have some water molecules that might be in just the right place to go from the inside to the outside. But what's more likely to happen, and what's going to happen more over a certain period of time? Well, the water molecules that are on the outside, and we talk about this in the osmosis video, they're going to be less obstructed by solute particles. If they happen to be, if this one happens to be moving in that direction, well, it's gonna make its way to the membrane and then maybe get through the membrane."}, {"video_title": "Hypotonic, isotonic, and hypertonic solutions (tonicity)   Khan Academy.mp3", "Sentence": "So at any given moment in time, you will have some water molecules moving in just the right direction to go from the outside to the inside, and you will also have some water molecules that might be in just the right place to go from the inside to the outside. But what's more likely to happen, and what's going to happen more over a certain period of time? Well, the water molecules that are on the outside, and we talk about this in the osmosis video, they're going to be less obstructed by solute particles. If they happen to be, if this one happens to be moving in that direction, well, it's gonna make its way to the membrane and then maybe get through the membrane. While something, maybe this, if this water molecule was moving in this direction, well, gee, it's gonna be obstructed now. Maybe this is bouncing back and it's gonna ricochet off of it. So the water molecules on the inside are more obstructed."}, {"video_title": "Hypotonic, isotonic, and hypertonic solutions (tonicity)   Khan Academy.mp3", "Sentence": "If they happen to be, if this one happens to be moving in that direction, well, it's gonna make its way to the membrane and then maybe get through the membrane. While something, maybe this, if this water molecule was moving in this direction, well, gee, it's gonna be obstructed now. Maybe this is bouncing back and it's gonna ricochet off of it. So the water molecules on the inside are more obstructed. They're less likely to be able to fully interact with the membrane or move in the right direction. They're being obstructed by these solute particles. So even though you're gonna have water molecules going back and forth, in a given period of time, you have a higher probability of more going in than going out."}, {"video_title": "Hypotonic, isotonic, and hypertonic solutions (tonicity)   Khan Academy.mp3", "Sentence": "So the water molecules on the inside are more obstructed. They're less likely to be able to fully interact with the membrane or move in the right direction. They're being obstructed by these solute particles. So even though you're gonna have water molecules going back and forth, in a given period of time, you have a higher probability of more going in than going out. And so you're going to have a net inflow, net inflow, inflow of H2O, of water molecules. Now, a situation like this, where we're talking about a cell and it's in a solution that has a lower concentration of solute, and it's important that we're talking about a solute that is not permeable, that is not allowed to go through the membrane. The membrane is not permeable to that solute."}, {"video_title": "Hypotonic, isotonic, and hypertonic solutions (tonicity)   Khan Academy.mp3", "Sentence": "So even though you're gonna have water molecules going back and forth, in a given period of time, you have a higher probability of more going in than going out. And so you're going to have a net inflow, net inflow, inflow of H2O, of water molecules. Now, a situation like this, where we're talking about a cell and it's in a solution that has a lower concentration of solute, and it's important that we're talking about a solute that is not permeable, that is not allowed to go through the membrane. The membrane is not permeable to that solute. We call this type of situation, this type of solution that the cell is immersed in, we call this a hypotonic solution. Hypotonic, hypotonic solution. And any time we're talking about hypotonic, or as we'll see, isotonic and hypertonic, we're talking about relative, we're talking about relative concentrations of solute that cannot get through some type of, that cannot get through some type of a membrane."}, {"video_title": "Hypotonic, isotonic, and hypertonic solutions (tonicity)   Khan Academy.mp3", "Sentence": "The membrane is not permeable to that solute. We call this type of situation, this type of solution that the cell is immersed in, we call this a hypotonic solution. Hypotonic, hypotonic solution. And any time we're talking about hypotonic, or as we'll see, isotonic and hypertonic, we're talking about relative, we're talking about relative concentrations of solute that cannot get through some type of, that cannot get through some type of a membrane. And the word hypo, you might have seen it in other things, it's a prefix that means less of something. So in this case, we have a lower concentration of solute in the solution than we have inside of the cell. And because of that, you're going to have osmosis, you're gonna have water molecules going from the inside, or you're gonna have water molecules going from the outside, I should say, to the inside."}, {"video_title": "Hypotonic, isotonic, and hypertonic solutions (tonicity)   Khan Academy.mp3", "Sentence": "And any time we're talking about hypotonic, or as we'll see, isotonic and hypertonic, we're talking about relative, we're talking about relative concentrations of solute that cannot get through some type of, that cannot get through some type of a membrane. And the word hypo, you might have seen it in other things, it's a prefix that means less of something. So in this case, we have a lower concentration of solute in the solution than we have inside of the cell. And because of that, you're going to have osmosis, you're gonna have water molecules going from the inside, or you're gonna have water molecules going from the outside, I should say, to the inside. And that's actually going to put pressure on the cell. The cell itself might expand, or it could even, if there's enough pressure, it might even explode. So now let's go to the next scenario."}, {"video_title": "Hypotonic, isotonic, and hypertonic solutions (tonicity)   Khan Academy.mp3", "Sentence": "And because of that, you're going to have osmosis, you're gonna have water molecules going from the inside, or you're gonna have water molecules going from the outside, I should say, to the inside. And that's actually going to put pressure on the cell. The cell itself might expand, or it could even, if there's enough pressure, it might even explode. So now let's go to the next scenario. In this scenario, we have roughly equal concentrations of solute on the outside and on the inside, at least I tried to draw them that way. So in this situation, the probability of a water molecule in a given period of time going from the outside to the inside, or from the inside to the outside, is going to be the same. And so you're not going to have any net inflow or net outflow, you're always gonna have water molecules going back and forth, but there's not gonna be any net inflow or outflow."}, {"video_title": "Hypotonic, isotonic, and hypertonic solutions (tonicity)   Khan Academy.mp3", "Sentence": "So now let's go to the next scenario. In this scenario, we have roughly equal concentrations of solute on the outside and on the inside, at least I tried to draw them that way. So in this situation, the probability of a water molecule in a given period of time going from the outside to the inside, or from the inside to the outside, is going to be the same. And so you're not going to have any net inflow or net outflow, you're always gonna have water molecules going back and forth, but there's not gonna be any net inflow or outflow. And so in this situation, so let's see, let me write, no net, no net flow. And this type of solution, where you have the same concentration of solute, in the solution as you do inside the cell, we would call this an isotonic, this is an isotonic solution, isotonic solution. And the prefix iso, which refers to things that are the same, it has the same concentration of solute."}, {"video_title": "Hypotonic, isotonic, and hypertonic solutions (tonicity)   Khan Academy.mp3", "Sentence": "And so you're not going to have any net inflow or net outflow, you're always gonna have water molecules going back and forth, but there's not gonna be any net inflow or outflow. And so in this situation, so let's see, let me write, no net, no net flow. And this type of solution, where you have the same concentration of solute, in the solution as you do inside the cell, we would call this an isotonic, this is an isotonic solution, isotonic solution. And the prefix iso, which refers to things that are the same, it has the same concentration of solute. And so you have no net inflow. So hypotonic solution, you have water molecules going into the cell, the cell expanding, kind of like a filling balloon. Isotonic solution, no net flow."}, {"video_title": "Hypotonic, isotonic, and hypertonic solutions (tonicity)   Khan Academy.mp3", "Sentence": "And the prefix iso, which refers to things that are the same, it has the same concentration of solute. And so you have no net inflow. So hypotonic solution, you have water molecules going into the cell, the cell expanding, kind of like a filling balloon. Isotonic solution, no net flow. And then of course, you can imagine in this last scenario, I have a higher concentration of solute on the outside than I have on the inside. And we can guess what's going to happen. So first, what would I call this?"}, {"video_title": "Hypotonic, isotonic, and hypertonic solutions (tonicity)   Khan Academy.mp3", "Sentence": "Isotonic solution, no net flow. And then of course, you can imagine in this last scenario, I have a higher concentration of solute on the outside than I have on the inside. And we can guess what's going to happen. So first, what would I call this? Well, I have more of something in the solution, so I would use the prefix hyper. I have more of it, more, hypertonic. This is a hypertonic solution."}, {"video_title": "Hypotonic, isotonic, and hypertonic solutions (tonicity)   Khan Academy.mp3", "Sentence": "So first, what would I call this? Well, I have more of something in the solution, so I would use the prefix hyper. I have more of it, more, hypertonic. This is a hypertonic solution. And once again, the water molecule, the solute can't go across the membrane, but the water molecules can. And you're gonna have water molecules going from the outside, going from the outside to the inside and from the inside to the outside. But the probability that the ones going from the, the ones on the inside are gonna be less obstructed to go out than the ones on the outside to go in."}, {"video_title": "Hypotonic, isotonic, and hypertonic solutions (tonicity)   Khan Academy.mp3", "Sentence": "This is a hypertonic solution. And once again, the water molecule, the solute can't go across the membrane, but the water molecules can. And you're gonna have water molecules going from the outside, going from the outside to the inside and from the inside to the outside. But the probability that the ones going from the, the ones on the inside are gonna be less obstructed to go out than the ones on the outside to go in. And so you're going to have a net outflow. You have a higher probability of things going from the inside to the outside than you do from things going from the outside to the inside because they're gonna be more obstructed. And so they're gonna be held back, I guess, in different ways."}, {"video_title": "Hypotonic, isotonic, and hypertonic solutions (tonicity)   Khan Academy.mp3", "Sentence": "But the probability that the ones going from the, the ones on the inside are gonna be less obstructed to go out than the ones on the outside to go in. And so you're going to have a net outflow. You have a higher probability of things going from the inside to the outside than you do from things going from the outside to the inside because they're gonna be more obstructed. And so they're gonna be held back, I guess, in different ways. So in this situation, you're gonna have, you're gonna have the water escape the cell and the cell actually might shrivel up. The cell, since it's gonna lose that pressure from the water, the cell itself might shrivel up in some way. And you can actually see this in actual living systems."}, {"video_title": "Hypotonic, isotonic, and hypertonic solutions (tonicity)   Khan Academy.mp3", "Sentence": "And so they're gonna be held back, I guess, in different ways. So in this situation, you're gonna have, you're gonna have the water escape the cell and the cell actually might shrivel up. The cell, since it's gonna lose that pressure from the water, the cell itself might shrivel up in some way. And you can actually see this in actual living systems. If you were to put a red blood cell into a hypotonic solution, the water's gonna rush into it and it's gonna look, it's gonna blow up, it's gonna, it's going to expand. And so it's gonna look like a overinflated red blood cell. In an isotonic solution, it's gonna look the way that we're used to seeing a red blood cell, actually having kind of that little divot in the middle area while over here, it's all going to expand."}, {"video_title": "Lac operon.mp3", "Sentence": "And it is part of E. coli's genome. And it is involved, and the lac right over here is referring to lactose. And so you can imagine that it codes for genes involved in the metabolism of lactose. And the word lactose might already be familiar to you. It is a sugar found in milk. Some of us, including myself, are lactose intolerant. I have trouble digesting lactose."}, {"video_title": "Lac operon.mp3", "Sentence": "And the word lactose might already be familiar to you. It is a sugar found in milk. Some of us, including myself, are lactose intolerant. I have trouble digesting lactose. So I have mixed feelings regarding this. But in general, for a cell to make use of it, it needs to be able to absorb the lactose. It needs to be able to split it up into simpler sugars that it can actually use for fuel."}, {"video_title": "Lac operon.mp3", "Sentence": "I have trouble digesting lactose. So I have mixed feelings regarding this. But in general, for a cell to make use of it, it needs to be able to absorb the lactose. It needs to be able to split it up into simpler sugars that it can actually use for fuel. And that is what the genes in the lac operon actually do code for. So just as an example, the lacZ gene right over here, this codes for an enzyme that helps cleave the lactose into simpler sugars. The lacY gene codes for an enzyme that allows for the absorption of lactose through cellular membranes."}, {"video_title": "Lac operon.mp3", "Sentence": "It needs to be able to split it up into simpler sugars that it can actually use for fuel. And that is what the genes in the lac operon actually do code for. So just as an example, the lacZ gene right over here, this codes for an enzyme that helps cleave the lactose into simpler sugars. The lacY gene codes for an enzyme that allows for the absorption of lactose through cellular membranes. LacA is a little bit more interesting and a little less understood, but the general idea here is all three of these are involved in the metabolism and the absorption of lactose. And it is an operon, so we have our promoter here where our RNA polymerase would attach. And I've also drawn some other sites."}, {"video_title": "Lac operon.mp3", "Sentence": "The lacY gene codes for an enzyme that allows for the absorption of lactose through cellular membranes. LacA is a little bit more interesting and a little less understood, but the general idea here is all three of these are involved in the metabolism and the absorption of lactose. And it is an operon, so we have our promoter here where our RNA polymerase would attach. And I've also drawn some other sites. I've drawn the operator right over here where you can imagine a repressor, and it is indeed the lac repressor could bind. And over here, this CAP site, or C-A-P site, CAP stands for catabolite activator protein. Catabolite, catabolite activator."}, {"video_title": "Lac operon.mp3", "Sentence": "And I've also drawn some other sites. I've drawn the operator right over here where you can imagine a repressor, and it is indeed the lac repressor could bind. And over here, this CAP site, or C-A-P site, CAP stands for catabolite activator protein. Catabolite, catabolite activator. Whoops. Acti, activator protein. Protein."}, {"video_title": "Lac operon.mp3", "Sentence": "Catabolite, catabolite activator. Whoops. Acti, activator protein. Protein. And so this is, you can imagine, where a protein called the catabolite activator protein can bind and perhaps be an activator. So with that out of the way, let's think about different scenarios. Let's think about a scenario, let's think about a scenario where the E. coli is an environment where there is no lactose."}, {"video_title": "Lac operon.mp3", "Sentence": "Protein. And so this is, you can imagine, where a protein called the catabolite activator protein can bind and perhaps be an activator. So with that out of the way, let's think about different scenarios. Let's think about a scenario, let's think about a scenario where the E. coli is an environment where there is no lactose. So what do you think should happen over here? And a lot of these things are very logical. If you just assume that a lot of biological organisms are quite stingy, they don't want to just waste resources."}, {"video_title": "Lac operon.mp3", "Sentence": "Let's think about a scenario, let's think about a scenario where the E. coli is an environment where there is no lactose. So what do you think should happen over here? And a lot of these things are very logical. If you just assume that a lot of biological organisms are quite stingy, they don't want to just waste resources. Well, if there's no lactose, well, why transcribe the genes that can be translated into enzymes for the metabolism of lactose? So if there's no lactose, you can almost view this as a default state right over here. You actually have the lac repressor protein being bound to the operator."}, {"video_title": "Lac operon.mp3", "Sentence": "If you just assume that a lot of biological organisms are quite stingy, they don't want to just waste resources. Well, if there's no lactose, well, why transcribe the genes that can be translated into enzymes for the metabolism of lactose? So if there's no lactose, you can almost view this as a default state right over here. You actually have the lac repressor protein being bound to the operator. So this is the lac repressor, lac repressor right over there. And so you won't be able to transcribe these things. The RNA polymerase, the RNA polymerase won't be able to get anything done."}, {"video_title": "Lac operon.mp3", "Sentence": "You actually have the lac repressor protein being bound to the operator. So this is the lac repressor, lac repressor right over there. And so you won't be able to transcribe these things. The RNA polymerase, the RNA polymerase won't be able to get anything done. No transcription is going to occur. So no lactose, no transcription. Transcription, which makes a lot of sense."}, {"video_title": "Lac operon.mp3", "Sentence": "The RNA polymerase, the RNA polymerase won't be able to get anything done. No transcription is going to occur. So no lactose, no transcription. Transcription, which makes a lot of sense. The bacteria, or the bacterium, singular, doesn't want to waste resources. So what do you think should happen if there is lactose? So I'll keep this up here so you can see it."}, {"video_title": "Lac operon.mp3", "Sentence": "Transcription, which makes a lot of sense. The bacteria, or the bacterium, singular, doesn't want to waste resources. So what do you think should happen if there is lactose? So I'll keep this up here so you can see it. So lactose present. Lactose, lactose present. Well, you can imagine, well, you don't want that repressor around anymore, and that is indeed what happens, is that you have an isomer of lactose called allolactose."}, {"video_title": "Lac operon.mp3", "Sentence": "So I'll keep this up here so you can see it. So lactose present. Lactose, lactose present. Well, you can imagine, well, you don't want that repressor around anymore, and that is indeed what happens, is that you have an isomer of lactose called allolactose. So if lactose is present, you're going to have also allolactose present right over here. And so that is allolactose, which can act as an inducer of transcription. And the way that it acts as an inducer is if it binds to the lac repressor, the lac repressor can no longer bind to the operator site."}, {"video_title": "Lac operon.mp3", "Sentence": "Well, you can imagine, well, you don't want that repressor around anymore, and that is indeed what happens, is that you have an isomer of lactose called allolactose. So if lactose is present, you're going to have also allolactose present right over here. And so that is allolactose, which can act as an inducer of transcription. And the way that it acts as an inducer is if it binds to the lac repressor, the lac repressor can no longer bind to the operator site. So when the allolactose is present, it will bind to the repressor, and then the repressor is going to leave the operator site. It's not going to be able to bind as well. And so let me draw that."}, {"video_title": "Lac operon.mp3", "Sentence": "And the way that it acts as an inducer is if it binds to the lac repressor, the lac repressor can no longer bind to the operator site. So when the allolactose is present, it will bind to the repressor, and then the repressor is going to leave the operator site. It's not going to be able to bind as well. And so let me draw that. So in this case, the operator, sorry, the repressor, I should say. The operator is where the repressor binds. So this is the repressor right over here."}, {"video_title": "Lac operon.mp3", "Sentence": "And so let me draw that. So in this case, the operator, sorry, the repressor, I should say. The operator is where the repressor binds. So this is the repressor right over here. You have some allolactose. Let me do that in white. You have some allolactose that has bound to it."}, {"video_title": "Lac operon.mp3", "Sentence": "So this is the repressor right over here. You have some allolactose. Let me do that in white. You have some allolactose that has bound to it. And because of that, it's not going to bind to the operator. And since it's not bound to the operator, well, now the RNA polymerase can actually transcribe these genes. And that's valuable because by transcribing these genes, we are going to be able to metabolize this lactose."}, {"video_title": "Lac operon.mp3", "Sentence": "You have some allolactose that has bound to it. And because of that, it's not going to bind to the operator. And since it's not bound to the operator, well, now the RNA polymerase can actually transcribe these genes. And that's valuable because by transcribing these genes, we are going to be able to metabolize this lactose. So lactose present, you have transcription. Transcription. Transcription occurs."}, {"video_title": "Lac operon.mp3", "Sentence": "And that's valuable because by transcribing these genes, we are going to be able to metabolize this lactose. So lactose present, you have transcription. Transcription. Transcription occurs. Now that's a very high-level simple view of the lac operon, but there's more involved because there's other sugars, in particular glucose, which is preferred by the cell. So, whoops, I'm moving the wrong part. There you go."}, {"video_title": "Lac operon.mp3", "Sentence": "Transcription occurs. Now that's a very high-level simple view of the lac operon, but there's more involved because there's other sugars, in particular glucose, which is preferred by the cell. So, whoops, I'm moving the wrong part. There you go. So let's think about what will happen in the presence of glucose and not in the presence of glucose. So let me write here. So glucose, glucose, and no, and no glucose."}, {"video_title": "Lac operon.mp3", "Sentence": "There you go. So let's think about what will happen in the presence of glucose and not in the presence of glucose. So let me write here. So glucose, glucose, and no, and no glucose. Actually, let me do it. Let me do it. Well, let me, I'll do no glucose first."}, {"video_title": "Lac operon.mp3", "Sentence": "So glucose, glucose, and no, and no glucose. Actually, let me do it. Let me do it. Well, let me, I'll do no glucose first. Let's say we have no glucose. And remember, glucose is preferred to lactose. Simpler sugar, if you have glucose around, why worry about the lactose?"}, {"video_title": "Lac operon.mp3", "Sentence": "Well, let me, I'll do no glucose first. Let's say we have no glucose. And remember, glucose is preferred to lactose. Simpler sugar, if you have glucose around, why worry about the lactose? And then here we have, we have glucose, we have glucose around. And we could talk about both of these, both of these situations in the presence of lactose or not in the presence of lactose, but if we don't have, if we don't have any lactose around, so we're not gonna have the allolactose around, and then you're just gonna have the repressor sit on the operator and you're not going to have any transcription. So you can, and that's going to be whether or not we have glucose."}, {"video_title": "Lac operon.mp3", "Sentence": "Simpler sugar, if you have glucose around, why worry about the lactose? And then here we have, we have glucose, we have glucose around. And we could talk about both of these, both of these situations in the presence of lactose or not in the presence of lactose, but if we don't have, if we don't have any lactose around, so we're not gonna have the allolactose around, and then you're just gonna have the repressor sit on the operator and you're not going to have any transcription. So you can, and that's going to be whether or not we have glucose. So I'm gonna think about no glucose, but we do have lactose plus lactose. And in here you have glucose plus, glucose plus lactose. Well, the lactose part, if we have lactose around, then we're going to have the allolactose around."}, {"video_title": "Lac operon.mp3", "Sentence": "So you can, and that's going to be whether or not we have glucose. So I'm gonna think about no glucose, but we do have lactose plus lactose. And in here you have glucose plus, glucose plus lactose. Well, the lactose part, if we have lactose around, then we're going to have the allolactose around. And we just covered this scenario. The allolactose binds, binds to the lac repressor, keeps the lac repressor from binding to the operator. And so you have, you have your RNA polymerase is able to actually perform the transcription."}, {"video_title": "Lac operon.mp3", "Sentence": "Well, the lactose part, if we have lactose around, then we're going to have the allolactose around. And we just covered this scenario. The allolactose binds, binds to the lac repressor, keeps the lac repressor from binding to the operator. And so you have, you have your RNA polymerase is able to actually perform the transcription. But that's not it. If you, in a situation with no glucose, you actually are going to also involve the capside. You're going to have an activator that's going to make this happen even more."}, {"video_title": "Lac operon.mp3", "Sentence": "And so you have, you have your RNA polymerase is able to actually perform the transcription. But that's not it. If you, in a situation with no glucose, you actually are going to also involve the capside. You're going to have an activator that's going to make this happen even more. Because if you don't have glucose around, man, you really need that lactose. And so what you have is something called, so let me draw this, the catabolite activator protein, right over here. The catabolite activator protein."}, {"video_title": "Lac operon.mp3", "Sentence": "You're going to have an activator that's going to make this happen even more. Because if you don't have glucose around, man, you really need that lactose. And so what you have is something called, so let me draw this, the catabolite activator protein, right over here. The catabolite activator protein. And in the presence of cyclic AMP, adenosine monophosphate, it's a derivative of ATP. And so this is that right over there. Cyclic AMP, you'll see that come up a lot in biology."}, {"video_title": "Lac operon.mp3", "Sentence": "The catabolite activator protein. And in the presence of cyclic AMP, adenosine monophosphate, it's a derivative of ATP. And so this is that right over there. Cyclic AMP, you'll see that come up a lot in biology. So this is the catabolite activator protein. In the presence of CAMP, and we'll talk about how cyclic AMP relates to glucose in a second. In that presence, it is going to bind to this, the capside."}, {"video_title": "Lac operon.mp3", "Sentence": "Cyclic AMP, you'll see that come up a lot in biology. So this is the catabolite activator protein. In the presence of CAMP, and we'll talk about how cyclic AMP relates to glucose in a second. In that presence, it is going to bind to this, the capside. And it is going to further activate the transcription. So in this situation, no glucose plus lactose, you're gonna have even more transcription. So let me write this down."}, {"video_title": "Lac operon.mp3", "Sentence": "In that presence, it is going to bind to this, the capside. And it is going to further activate the transcription. So in this situation, no glucose plus lactose, you're gonna have even more transcription. So let me write this down. Lots of transcription. Lots of trans, transcription. Lots of transcription."}, {"video_title": "Lac operon.mp3", "Sentence": "So let me write this down. Lots of transcription. Lots of trans, transcription. Lots of transcription. Now I know what you're probably asking. This is what I first asked myself when people told me about cyclic AMP. Well how does cyclic AMP relate to glucose?"}, {"video_title": "Lac operon.mp3", "Sentence": "Lots of transcription. Now I know what you're probably asking. This is what I first asked myself when people told me about cyclic AMP. Well how does cyclic AMP relate to glucose? Well I'm not gonna go into a huge amount of detail here. But what you need to know here, and it makes sense, is that if you have glucose, so let me write it this way. If you have high glucose, high glucose, I'm having trouble writing."}, {"video_title": "Lac operon.mp3", "Sentence": "Well how does cyclic AMP relate to glucose? Well I'm not gonna go into a huge amount of detail here. But what you need to know here, and it makes sense, is that if you have glucose, so let me write it this way. If you have high glucose, high glucose, I'm having trouble writing. High glucose, then that's going to inhibit the production of cyclic AMP. So low cyclic adenosine monophosphate. And if you have low glucose, or no glucose, it's like a tongue twister."}, {"video_title": "Lac operon.mp3", "Sentence": "If you have high glucose, high glucose, I'm having trouble writing. High glucose, then that's going to inhibit the production of cyclic AMP. So low cyclic adenosine monophosphate. And if you have low glucose, or no glucose, it's like a tongue twister. If you have low glucose, well you're not going to inhibit the creation of cyclic AMP. And so you're going to have high cyclic AMP. So if you have no glucose, or low glucose, we are in this scenario right over here."}, {"video_title": "Lac operon.mp3", "Sentence": "And if you have low glucose, or no glucose, it's like a tongue twister. If you have low glucose, well you're not going to inhibit the creation of cyclic AMP. And so you're going to have high cyclic AMP. So if you have no glucose, or low glucose, we are in this scenario right over here. You're going to have high, or higher concentrations of cyclic AMP, which can bind to the catabolite activator protein, which then acts as an activator to allow even more transcription of the lac operon. Which once again, why is that important? Well if there's no glucose or low glucose, you're really going to need that lactose."}, {"video_title": "Lac operon.mp3", "Sentence": "So if you have no glucose, or low glucose, we are in this scenario right over here. You're going to have high, or higher concentrations of cyclic AMP, which can bind to the catabolite activator protein, which then acts as an activator to allow even more transcription of the lac operon. Which once again, why is that important? Well if there's no glucose or low glucose, you're really going to need that lactose. You really want to transcribe these genes as much as possible. Now what about the situation where there is glucose and lactose? Well once again, if there is lactose, then you're going to have allolactose, which is going to be able to bind to the lac repressor."}, {"video_title": "Lac operon.mp3", "Sentence": "Well if there's no glucose or low glucose, you're really going to need that lactose. You really want to transcribe these genes as much as possible. Now what about the situation where there is glucose and lactose? Well once again, if there is lactose, then you're going to have allolactose, which is going to be able to bind to the lac repressor. And by it binding to the lac repressor, the lac repressor is not going to be able to bind to the operator. And so you do have, once again, the RNA polymerase is going to be able to transcribe. But because you have glucose present, because you have glucose present, you're going to have low, or, well I'll just write low, cyclic AMP."}, {"video_title": "Lac operon.mp3", "Sentence": "Well once again, if there is lactose, then you're going to have allolactose, which is going to be able to bind to the lac repressor. And by it binding to the lac repressor, the lac repressor is not going to be able to bind to the operator. And so you do have, once again, the RNA polymerase is going to be able to transcribe. But because you have glucose present, because you have glucose present, you're going to have low, or, well I'll just write low, cyclic AMP. And since you have low or no cyclic AMP around, well that cyclic AMP isn't going to be able to bind to the catabolite activator protein. And so the catabolite activator protein isn't going to be able to act as an activator. I know I'm using a lot of words multiple times."}, {"video_title": "Lac operon.mp3", "Sentence": "But because you have glucose present, because you have glucose present, you're going to have low, or, well I'll just write low, cyclic AMP. And since you have low or no cyclic AMP around, well that cyclic AMP isn't going to be able to bind to the catabolite activator protein. And so the catabolite activator protein isn't going to be able to act as an activator. I know I'm using a lot of words multiple times. And so it's not going to bond to the activator site, or to the cap site. And so you're going to have less transcription. Less transcription."}, {"video_title": "Lac operon.mp3", "Sentence": "I know I'm using a lot of words multiple times. And so it's not going to bond to the activator site, or to the cap site. And so you're going to have less transcription. Less transcription. Transcription. Which once again makes sense. You've got glucose and lactose around."}, {"video_title": "Lac operon.mp3", "Sentence": "Less transcription. Transcription. Which once again makes sense. You've got glucose and lactose around. The cell would prefer to use glucose. Simpler sugar. Why waste resources?"}, {"video_title": "Lac operon.mp3", "Sentence": "You've got glucose and lactose around. The cell would prefer to use glucose. Simpler sugar. Why waste resources? You have plenty of energy around. Just go straight to the glucose. But if you don't have glucose around, well then use more resources so that you can digest the lactose."}, {"video_title": "Biodiversity and natural selection (2).mp3", "Sentence": "And we could leave it at that. We could all go home because we're done. But that's not going to make much of a video. What we really want to ask ourselves is, what is that? What is evolution? And how does it result in biodiversity? I like to think of the study of evolution as following two fairly simple pathways."}, {"video_title": "Biodiversity and natural selection (2).mp3", "Sentence": "What we really want to ask ourselves is, what is that? What is evolution? And how does it result in biodiversity? I like to think of the study of evolution as following two fairly simple pathways. These paths are pattern and process. Both of these are not only fascinating areas of study, but are crucial in expanding our knowledge of how life originated and how it continues to evolve. The pattern pathway studies the shape of evolution itself by looking at relationships, relationships among organisms over time."}, {"video_title": "Biodiversity and natural selection (2).mp3", "Sentence": "I like to think of the study of evolution as following two fairly simple pathways. These paths are pattern and process. Both of these are not only fascinating areas of study, but are crucial in expanding our knowledge of how life originated and how it continues to evolve. The pattern pathway studies the shape of evolution itself by looking at relationships, relationships among organisms over time. And to do that, you need to create a diagram or structure that links these organisms in time, showing a branching sequence of relationships, much like a family tree or genealogy. These evolutionary trees record not only the relationships among the organisms, but the events that occurred over time that indicate why we think these different organisms are related. Organisms depicted by genealogical trees really are a subject all on their own called phylogenetic systematics."}, {"video_title": "Biodiversity and natural selection (2).mp3", "Sentence": "The pattern pathway studies the shape of evolution itself by looking at relationships, relationships among organisms over time. And to do that, you need to create a diagram or structure that links these organisms in time, showing a branching sequence of relationships, much like a family tree or genealogy. These evolutionary trees record not only the relationships among the organisms, but the events that occurred over time that indicate why we think these different organisms are related. Organisms depicted by genealogical trees really are a subject all on their own called phylogenetic systematics. But let's set that aside for a moment. The process path is maybe a slightly better way to start. We want to talk about the mechanisms of evolution, how it actually happens."}, {"video_title": "Biodiversity and natural selection (2).mp3", "Sentence": "Organisms depicted by genealogical trees really are a subject all on their own called phylogenetic systematics. But let's set that aside for a moment. The process path is maybe a slightly better way to start. We want to talk about the mechanisms of evolution, how it actually happens. These are the drivers of the diversity along the multitude of lineages that spring out, branching and branching up the tree, up the limbs of the tree of life. Darwin and even some of his predecessors understood this. They could see that things could change, that the pattern of life, this tree, existed, that evolution happened, and that the relationships among organisms could be traced by looking at features of those organisms and how they changed depending on where they were in the tree."}, {"video_title": "Biodiversity and natural selection (2).mp3", "Sentence": "We want to talk about the mechanisms of evolution, how it actually happens. These are the drivers of the diversity along the multitude of lineages that spring out, branching and branching up the tree, up the limbs of the tree of life. Darwin and even some of his predecessors understood this. They could see that things could change, that the pattern of life, this tree, existed, that evolution happened, and that the relationships among organisms could be traced by looking at features of those organisms and how they changed depending on where they were in the tree. They could see, for example, that the wings of birds, the front legs of mammals and reptiles, and in fact all the four-limbed animals, indicated that there was some common relationship there. There was a common lineage. But at the same time, you could have change among the branches within those lineages."}, {"video_title": "Biodiversity and natural selection (2).mp3", "Sentence": "They could see that things could change, that the pattern of life, this tree, existed, that evolution happened, and that the relationships among organisms could be traced by looking at features of those organisms and how they changed depending on where they were in the tree. They could see, for example, that the wings of birds, the front legs of mammals and reptiles, and in fact all the four-limbed animals, indicated that there was some common relationship there. There was a common lineage. But at the same time, you could have change among the branches within those lineages. You could get a change in the front leg to a wing or to a grasping arm. General patterns were evident in everything. But at the time, there wasn't a good understanding of the mechanisms, the processes that could explain how these obviously changing, yet related forms could come about."}, {"video_title": "Biodiversity and natural selection (2).mp3", "Sentence": "But at the same time, you could have change among the branches within those lineages. You could get a change in the front leg to a wing or to a grasping arm. General patterns were evident in everything. But at the time, there wasn't a good understanding of the mechanisms, the processes that could explain how these obviously changing, yet related forms could come about. Darwin and his contemporaries read a lot of stuff about variation, which was visible all around them. It could all be seen. They realized that not all the individuals in a species or even in a population were exact duplicates of each other."}, {"video_title": "Biodiversity and natural selection (2).mp3", "Sentence": "But at the time, there wasn't a good understanding of the mechanisms, the processes that could explain how these obviously changing, yet related forms could come about. Darwin and his contemporaries read a lot of stuff about variation, which was visible all around them. It could all be seen. They realized that not all the individuals in a species or even in a population were exact duplicates of each other. This was a surprise to some people, but the evidence was everywhere, even in things as simple as the speed of racehorses. If you didn't have variation in how fast horses could run, the races would be pretty boring. Races actually demonstrate how horses were chosen for variations in speed."}, {"video_title": "Biodiversity and natural selection (2).mp3", "Sentence": "They realized that not all the individuals in a species or even in a population were exact duplicates of each other. This was a surprise to some people, but the evidence was everywhere, even in things as simple as the speed of racehorses. If you didn't have variation in how fast horses could run, the races would be pretty boring. Races actually demonstrate how horses were chosen for variations in speed. Humans bred fast horses with each other to get even faster horses. And these horses were selected for being the fastest. And that's the key word, selection."}, {"video_title": "Biodiversity and natural selection (2).mp3", "Sentence": "Races actually demonstrate how horses were chosen for variations in speed. Humans bred fast horses with each other to get even faster horses. And these horses were selected for being the fastest. And that's the key word, selection. Darwin thought, hey, what if nature worked that way? What if nature selected organisms somehow? He noticed that the form and the physiology and the behavior of plants and animals varied within natural populations just as much as they did in domesticated populations of things like horses."}, {"video_title": "Biodiversity and natural selection (2).mp3", "Sentence": "And that's the key word, selection. Darwin thought, hey, what if nature worked that way? What if nature selected organisms somehow? He noticed that the form and the physiology and the behavior of plants and animals varied within natural populations just as much as they did in domesticated populations of things like horses. Darwin realized that what we're really talking about here are the beginnings of the understanding of the evolutionary mechanism behind evolution, natural selection. Natural selection means that some natural variants, some individuals with different form or physiology or behavior might be better at getting through life than others. Better, that is, at gathering food, staying away from predators, turning sunlight into usable energy, resisting wind, having good root systems."}, {"video_title": "Biodiversity and natural selection (2).mp3", "Sentence": "He noticed that the form and the physiology and the behavior of plants and animals varied within natural populations just as much as they did in domesticated populations of things like horses. Darwin realized that what we're really talking about here are the beginnings of the understanding of the evolutionary mechanism behind evolution, natural selection. Natural selection means that some natural variants, some individuals with different form or physiology or behavior might be better at getting through life than others. Better, that is, at gathering food, staying away from predators, turning sunlight into usable energy, resisting wind, having good root systems. In other words, fitting the circumstances of the environment and surviving. What Darwin was really saying is that fitness of an individual meant being better able to produce offspring that had traits like the parent, traits that would help the offspring be better suited to the conditions of their environment. This has been referred to as survival of the fittest."}, {"video_title": "Biodiversity and natural selection (2).mp3", "Sentence": "Better, that is, at gathering food, staying away from predators, turning sunlight into usable energy, resisting wind, having good root systems. In other words, fitting the circumstances of the environment and surviving. What Darwin was really saying is that fitness of an individual meant being better able to produce offspring that had traits like the parent, traits that would help the offspring be better suited to the conditions of their environment. This has been referred to as survival of the fittest. Actually, I prefer the phrase survival of the fitter because fittest implies that there's an endpoint, that there's a goal, but there isn't. It's all relative because there are so many compromises and trade-offs in being well suited to a place as complex as the natural world that organisms can never reach that perfect match in all respects. This process of the environment selecting variants that are better suited to that environment, no matter how complex, is called natural selection."}, {"video_title": "Biodiversity and natural selection (2).mp3", "Sentence": "This has been referred to as survival of the fittest. Actually, I prefer the phrase survival of the fitter because fittest implies that there's an endpoint, that there's a goal, but there isn't. It's all relative because there are so many compromises and trade-offs in being well suited to a place as complex as the natural world that organisms can never reach that perfect match in all respects. This process of the environment selecting variants that are better suited to that environment, no matter how complex, is called natural selection. And those traits that make the selected variants better able to survive and reproduce and pass on those traits to future generations are known as adaptations. For example, a wild population of redwood trees might have some individuals that attain greater heights than others, and this results in better exposure to sunlight on foggy days, enhancing their ability to make food by photosynthesis when a change in the environment, such as the fog rolling in, challenges the survival of shorter trees. This in turn not only increases their individual chances for survival, but it also makes available more energy to the taller redwoods to produce more seeds that carry this tallness trait into future generations."}, {"video_title": "Biodiversity and natural selection (2).mp3", "Sentence": "This process of the environment selecting variants that are better suited to that environment, no matter how complex, is called natural selection. And those traits that make the selected variants better able to survive and reproduce and pass on those traits to future generations are known as adaptations. For example, a wild population of redwood trees might have some individuals that attain greater heights than others, and this results in better exposure to sunlight on foggy days, enhancing their ability to make food by photosynthesis when a change in the environment, such as the fog rolling in, challenges the survival of shorter trees. This in turn not only increases their individual chances for survival, but it also makes available more energy to the taller redwoods to produce more seeds that carry this tallness trait into future generations. So you get natural selection for a tallness trait and an adaptation to an environment that can present changes. Of course, as I mentioned, these simplistic examples kind of skim over the fact that there's always a series of trade-offs in nature. We have to consider, for example, that taller trees might have more trouble getting moisture from the roots all the way up to the tips of those highest branches, or that they could be more exposed to storms that could knock them down, or maybe there's some other physiological cause that we might not even have thought of."}, {"video_title": "Biodiversity and natural selection (2).mp3", "Sentence": "This in turn not only increases their individual chances for survival, but it also makes available more energy to the taller redwoods to produce more seeds that carry this tallness trait into future generations. So you get natural selection for a tallness trait and an adaptation to an environment that can present changes. Of course, as I mentioned, these simplistic examples kind of skim over the fact that there's always a series of trade-offs in nature. We have to consider, for example, that taller trees might have more trouble getting moisture from the roots all the way up to the tips of those highest branches, or that they could be more exposed to storms that could knock them down, or maybe there's some other physiological cause that we might not even have thought of. All these factors are part of a complicated balance that optimizes life to a given environmental situation or set of competing, selective factors. Stuff happens. Life is never simple."}, {"video_title": "Biodiversity and natural selection (2).mp3", "Sentence": "We have to consider, for example, that taller trees might have more trouble getting moisture from the roots all the way up to the tips of those highest branches, or that they could be more exposed to storms that could knock them down, or maybe there's some other physiological cause that we might not even have thought of. All these factors are part of a complicated balance that optimizes life to a given environmental situation or set of competing, selective factors. Stuff happens. Life is never simple. To me, all these aspects come together to represent the great beauties of life, this constant interplay of processes that results in the complexity of biodiversity, what Darwin called grandeur in this view of life. The flip side of this selection coin is that individuals in a population can also be selected against because they're less well-adapted, sometimes because of susceptibility to diseases or simply by not being good at avoiding being eaten, something that keeps those individuals from being reproductively successful. You might have noticed by now that there's an important element to this story of variation, selection, and adaptation that's missing here."}, {"video_title": "Biodiversity and natural selection (2).mp3", "Sentence": "Life is never simple. To me, all these aspects come together to represent the great beauties of life, this constant interplay of processes that results in the complexity of biodiversity, what Darwin called grandeur in this view of life. The flip side of this selection coin is that individuals in a population can also be selected against because they're less well-adapted, sometimes because of susceptibility to diseases or simply by not being good at avoiding being eaten, something that keeps those individuals from being reproductively successful. You might have noticed by now that there's an important element to this story of variation, selection, and adaptation that's missing here. Darwin noticed it too, he was a very smart guy and he fully recognized that there had to be some way by which organisms could pass on those selected traits, those adaptations to their offspring. It wouldn't work otherwise. There had to be a way that the offspring of individuals that had been selected for could inherit the traits of their successful parents and ancestors."}, {"video_title": "Biodiversity and natural selection (2).mp3", "Sentence": "You might have noticed by now that there's an important element to this story of variation, selection, and adaptation that's missing here. Darwin noticed it too, he was a very smart guy and he fully recognized that there had to be some way by which organisms could pass on those selected traits, those adaptations to their offspring. It wouldn't work otherwise. There had to be a way that the offspring of individuals that had been selected for could inherit the traits of their successful parents and ancestors. In Darwin's day, there wasn't a good understanding of a mechanism for that. It was only much later that scientists discovered how information is stored in genetic material and passed on to offspring. Today, our detailed understanding of evolutionary processes is built on the discoveries of both Darwin and geneticists."}, {"video_title": "Biodiversity and natural selection (2).mp3", "Sentence": "There had to be a way that the offspring of individuals that had been selected for could inherit the traits of their successful parents and ancestors. In Darwin's day, there wasn't a good understanding of a mechanism for that. It was only much later that scientists discovered how information is stored in genetic material and passed on to offspring. Today, our detailed understanding of evolutionary processes is built on the discoveries of both Darwin and geneticists. Stepping back now to put it all together, we can see that for all this to work, several different things have to be going on. You have to have variation in nature among the members of a population. You have to have natural forces that can select for or against the enhanced reproduction of individuals who possess certain variations."}, {"video_title": "Biodiversity and natural selection (2).mp3", "Sentence": "Today, our detailed understanding of evolutionary processes is built on the discoveries of both Darwin and geneticists. Stepping back now to put it all together, we can see that for all this to work, several different things have to be going on. You have to have variation in nature among the members of a population. You have to have natural forces that can select for or against the enhanced reproduction of individuals who possess certain variations. And you have to have a mechanism by which those selected variations get passed on, inherited by offspring and their future generations. These simple concepts are essentially all you really need for evolution to happen. And from these basic principles, we get all the complicated interweavings and interactions among all the factors that become the underlying drivers of Earth's biodiversity."}, {"video_title": "Natural Selection and the Owl Butterfly.mp3", "Sentence": "But then once everything became soot-filled, all of a sudden, the dark moths were less likely to be caught by predators. And so all of the white moths were less likely to be able to reproduce successfully. So the black moth trait, or that variant, dominated. And then if you came a little bit later and you saw all the moths have turned black, it's like, oh, these moths are geniuses. They appear to have somehow engineered their way to stay camouflaged. And the point I was making there is that, look, that wasn't engineered or an explicit move on the part of the moths or the DNA. That that was just a natural byproduct of them having some variation, and some of that variation was selected for."}, {"video_title": "Natural Selection and the Owl Butterfly.mp3", "Sentence": "And then if you came a little bit later and you saw all the moths have turned black, it's like, oh, these moths are geniuses. They appear to have somehow engineered their way to stay camouflaged. And the point I was making there is that, look, that wasn't engineered or an explicit move on the part of the moths or the DNA. That that was just a natural byproduct of them having some variation, and some of that variation was selected for. So with that example, that was pretty simple, black or white. But what about more complicated things? So for example, here I have a couple of pictures of what's commonly called the owl butterfly."}, {"video_title": "Natural Selection and the Owl Butterfly.mp3", "Sentence": "That that was just a natural byproduct of them having some variation, and some of that variation was selected for. So with that example, that was pretty simple, black or white. But what about more complicated things? So for example, here I have a couple of pictures of what's commonly called the owl butterfly. And what's amazing here, and it's pretty obvious if I probably don't have to point out to you, is that its wing looks like half of an owl's eye. I mean, I can almost draw a beak here and draw another wing there, and you can imagine an owl staring at us. And here, too, I can imagine a beak here, and you would think an owl in there, too."}, {"video_title": "Natural Selection and the Owl Butterfly.mp3", "Sentence": "So for example, here I have a couple of pictures of what's commonly called the owl butterfly. And what's amazing here, and it's pretty obvious if I probably don't have to point out to you, is that its wing looks like half of an owl's eye. I mean, I can almost draw a beak here and draw another wing there, and you can imagine an owl staring at us. And here, too, I can imagine a beak here, and you would think an owl in there, too. And so the question is, how does something this good show up randomly? I mean, you could imagine, OK, little spots or black and white or gray, but how does something that looks so much like an eye generate randomly? Now, the answer is, well, there's a couple of answers."}, {"video_title": "Natural Selection and the Owl Butterfly.mp3", "Sentence": "And here, too, I can imagine a beak here, and you would think an owl in there, too. And so the question is, how does something this good show up randomly? I mean, you could imagine, OK, little spots or black and white or gray, but how does something that looks so much like an eye generate randomly? Now, the answer is, well, there's a couple of answers. One is, why does this eye exist, or this eye-like pattern, or this owl-like eyes pattern? And there, the jury's still out on that. I read a little bit about it on Wikipedia, and these are all of these images I got from Wikipedia."}, {"video_title": "Natural Selection and the Owl Butterfly.mp3", "Sentence": "Now, the answer is, well, there's a couple of answers. One is, why does this eye exist, or this eye-like pattern, or this owl-like eyes pattern? And there, the jury's still out on that. I read a little bit about it on Wikipedia, and these are all of these images I got from Wikipedia. And Wikipedia, they said, look, there's two competing theories here. One theory is that this, even though to us humans, the way we see things, it looks like an owl's eye, that this is actually a decoy. That this is, you know, when some predator is about to chase these, wants to eat one of these things, they kind of go for the thing that looks most substantive."}, {"video_title": "Natural Selection and the Owl Butterfly.mp3", "Sentence": "I read a little bit about it on Wikipedia, and these are all of these images I got from Wikipedia. And Wikipedia, they said, look, there's two competing theories here. One theory is that this, even though to us humans, the way we see things, it looks like an owl's eye, that this is actually a decoy. That this is, you know, when some predator is about to chase these, wants to eat one of these things, they kind of go for the thing that looks most substantive. So instead of going for the butterfly's body, which doesn't look that substantive, they go for the big black thing. They say, oh, that looks like it's protein-rich, and it'll be a good meal. So they try to snap and bite at that, and if they bite at that, sure, the guy's wings are going to be clipped a little bit, and it's going to suck, but the animal itself, the actual butterfly, would survive, and maybe it can repair its wings."}, {"video_title": "Natural Selection and the Owl Butterfly.mp3", "Sentence": "That this is, you know, when some predator is about to chase these, wants to eat one of these things, they kind of go for the thing that looks most substantive. So instead of going for the butterfly's body, which doesn't look that substantive, they go for the big black thing. They say, oh, that looks like it's protein-rich, and it'll be a good meal. So they try to snap and bite at that, and if they bite at that, sure, the guy's wings are going to be clipped a little bit, and it's going to suck, but the animal itself, the actual butterfly, would survive, and maybe it can repair its wings. I don't know the actual biology of the owl butterfly. That's one theory, and then the argument against that goes, well, no, if that was the case, then you'd want the black spot even further back along its, you know, you'd want the spot way far away from the body. You'd want it back here instead of right here, because there's still a chance if something chomps at this little black spot that it'll still get the abdomen of the butterfly."}, {"video_title": "Natural Selection and the Owl Butterfly.mp3", "Sentence": "So they try to snap and bite at that, and if they bite at that, sure, the guy's wings are going to be clipped a little bit, and it's going to suck, but the animal itself, the actual butterfly, would survive, and maybe it can repair its wings. I don't know the actual biology of the owl butterfly. That's one theory, and then the argument against that goes, well, no, if that was the case, then you'd want the black spot even further back along its, you know, you'd want the spot way far away from the body. You'd want it back here instead of right here, because there's still a chance if something chomps at this little black spot that it'll still get the abdomen of the butterfly. Now, the other theory as to why this exists, and you know, who knows, maybe it's a little bit of both. Maybe both of these are true. Maybe this offers two advantages."}, {"video_title": "Natural Selection and the Owl Butterfly.mp3", "Sentence": "You'd want it back here instead of right here, because there's still a chance if something chomps at this little black spot that it'll still get the abdomen of the butterfly. Now, the other theory as to why this exists, and you know, who knows, maybe it's a little bit of both. Maybe both of these are true. Maybe this offers two advantages. The other theory, and this is kind of the one that jumps out at us when we see this, hey, this looks like an owl, maybe this is to scare away the things that are likely to eat this dude. So maybe if, and it does turn out in my reading, that they are lizards that like to eat these type of butterflies. And those lizards probably don't like to be around birds or owls, because those owls eat them."}, {"video_title": "Natural Selection and the Owl Butterfly.mp3", "Sentence": "Maybe this offers two advantages. The other theory, and this is kind of the one that jumps out at us when we see this, hey, this looks like an owl, maybe this is to scare away the things that are likely to eat this dude. So maybe if, and it does turn out in my reading, that they are lizards that like to eat these type of butterflies. And those lizards probably don't like to be around birds or owls, because those owls eat them. So that might be deterrent. And then the other example they said is, look, they tend to be eaten by this lizard right here. This is what Wikipedia told me."}, {"video_title": "Natural Selection and the Owl Butterfly.mp3", "Sentence": "And those lizards probably don't like to be around birds or owls, because those owls eat them. So that might be deterrent. And then the other example they said is, look, they tend to be eaten by this lizard right here. This is what Wikipedia told me. And that this lizard tends to be eaten by this frog right there, and that the eyes of this butterfly are not too dissimilar to the eyes of this frog. And you know, we can debate whether or not that's the case. And if this was the predator we're trying to mimic, you could make an argument that maybe we would have had more green on our wing."}, {"video_title": "Natural Selection and the Owl Butterfly.mp3", "Sentence": "This is what Wikipedia told me. And that this lizard tends to be eaten by this frog right there, and that the eyes of this butterfly are not too dissimilar to the eyes of this frog. And you know, we can debate whether or not that's the case. And if this was the predator we're trying to mimic, you could make an argument that maybe we would have had more green on our wing. But that's not the point of this video. But it's a fun discussion to have as to what is useful about this eye. But let's have the question, how did that eye come about?"}, {"video_title": "Natural Selection and the Owl Butterfly.mp3", "Sentence": "And if this was the predator we're trying to mimic, you could make an argument that maybe we would have had more green on our wing. But that's not the point of this video. But it's a fun discussion to have as to what is useful about this eye. But let's have the question, how did that eye come about? And when I say that eye, I mean the pattern on that wing. What set of events allowed this to happen? Because when I described evolution, and we know that everything in our biological kingdom is just a set of proteins and then stuff that maybe the protein can't."}, {"video_title": "Natural Selection and the Owl Butterfly.mp3", "Sentence": "But let's have the question, how did that eye come about? And when I say that eye, I mean the pattern on that wing. What set of events allowed this to happen? Because when I described evolution, and we know that everything in our biological kingdom is just a set of proteins and then stuff that maybe the protein can't. But mainly protein. And that protein's all coded for by DNA. I'm going to do future videos on DNA."}, {"video_title": "Natural Selection and the Owl Butterfly.mp3", "Sentence": "Because when I described evolution, and we know that everything in our biological kingdom is just a set of proteins and then stuff that maybe the protein can't. But mainly protein. And that protein's all coded for by DNA. I'm going to do future videos on DNA. But DNA is just a sequence of base pairs. It's a sequence of these molecules. And we represent the adenine and guanine and then cytosine and thymine."}, {"video_title": "Natural Selection and the Owl Butterfly.mp3", "Sentence": "I'm going to do future videos on DNA. But DNA is just a sequence of base pairs. It's a sequence of these molecules. And we represent the adenine and guanine and then cytosine and thymine. And maybe you have a couple of adenines in a row and some guanine and thymine. And I'll do a lot more on this in the future. But the idea is, look, it's just coded for by this sequence of these molecules."}, {"video_title": "Natural Selection and the Owl Butterfly.mp3", "Sentence": "And we represent the adenine and guanine and then cytosine and thymine. And maybe you have a couple of adenines in a row and some guanine and thymine. And I'll do a lot more on this in the future. But the idea is, look, it's just coded for by this sequence of these molecules. How do you get a sequence? How do you go from a butterfly that has no eye to all of a sudden an eye that goes there? Obviously, just one change that happens from a random mutation, maybe that G turns into an A, or maybe this C and this T get deleted."}, {"video_title": "Natural Selection and the Owl Butterfly.mp3", "Sentence": "But the idea is, look, it's just coded for by this sequence of these molecules. How do you get a sequence? How do you go from a butterfly that has no eye to all of a sudden an eye that goes there? Obviously, just one change that happens from a random mutation, maybe that G turns into an A, or maybe this C and this T get deleted. So everything. That alone isn't going to develop this beautiful of a pattern or this useful of a pattern. So how do the random changes explain something that's this intricate?"}, {"video_title": "Natural Selection and the Owl Butterfly.mp3", "Sentence": "Obviously, just one change that happens from a random mutation, maybe that G turns into an A, or maybe this C and this T get deleted. So everything. That alone isn't going to develop this beautiful of a pattern or this useful of a pattern. So how do the random changes explain something that's this intricate? And this is my explanation. And obviously, I wasn't sitting there watching over the thousands or millions of years as these owl butterflies emerged. So this is just my theory of how natural selection does explain this type of phenomenon."}, {"video_title": "Natural Selection and the Owl Butterfly.mp3", "Sentence": "So how do the random changes explain something that's this intricate? And this is my explanation. And obviously, I wasn't sitting there watching over the thousands or millions of years as these owl butterflies emerged. So this is just my theory of how natural selection does explain this type of phenomenon. You have a world where you have, in some environment, you have butterflies. And their wings look like, let's say you have some butterflies that are generally like this. That's their wing."}, {"video_title": "Natural Selection and the Owl Butterfly.mp3", "Sentence": "So this is just my theory of how natural selection does explain this type of phenomenon. You have a world where you have, in some environment, you have butterflies. And their wings look like, let's say you have some butterflies that are generally like this. That's their wing. And it's a very bad drawing, but I think you get the idea. And there's just some general patterns. We've seen it before."}, {"video_title": "Natural Selection and the Owl Butterfly.mp3", "Sentence": "That's their wing. And it's a very bad drawing, but I think you get the idea. And there's just some general patterns. We've seen it before. There's variation. And the variation does show up from these little random changes in DNA. And I think we can all believe that, that most of these changes are kind of benign."}, {"video_title": "Natural Selection and the Owl Butterfly.mp3", "Sentence": "We've seen it before. There's variation. And the variation does show up from these little random changes in DNA. And I think we can all believe that, that most of these changes are kind of benign. Maybe they just set up differently where a little pattern will show up or a little speck of pigment will show up with a slightly different color. And we even see amongst these owl butterflies, there is variation. This dude's wing is different than that guy's wing, with the commonality that they do have these eye-looking shapes."}, {"video_title": "Natural Selection and the Owl Butterfly.mp3", "Sentence": "And I think we can all believe that, that most of these changes are kind of benign. Maybe they just set up differently where a little pattern will show up or a little speck of pigment will show up with a slightly different color. And we even see amongst these owl butterflies, there is variation. This dude's wing is different than that guy's wing, with the commonality that they do have these eye-looking shapes. And there's not just one. There's actually multiple. This guy has this other thing up here that looks interesting."}, {"video_title": "Natural Selection and the Owl Butterfly.mp3", "Sentence": "This dude's wing is different than that guy's wing, with the commonality that they do have these eye-looking shapes. And there's not just one. There's actually multiple. This guy has this other thing up here that looks interesting. And they have multiple things, but the one really noticeable feature is this eye-looking thing. So how do we go from this to an eye-looking thing? So the idea is you have some variation."}, {"video_title": "Natural Selection and the Owl Butterfly.mp3", "Sentence": "This guy has this other thing up here that looks interesting. And they have multiple things, but the one really noticeable feature is this eye-looking thing. So how do we go from this to an eye-looking thing? So the idea is you have some variation. One guy might look like that. Another guy or gal might, just randomly, their dot might be something like that. Another gal or guy, these wings are really badly drawn, but you get the idea."}, {"video_title": "Natural Selection and the Owl Butterfly.mp3", "Sentence": "So the idea is you have some variation. One guy might look like that. Another guy or gal might, just randomly, their dot might be something like that. Another gal or guy, these wings are really badly drawn, but you get the idea. This is the butterfly's antenna right there. That's its body. Another person's patterns, or butterfly's patterns, might look like this."}, {"video_title": "Natural Selection and the Owl Butterfly.mp3", "Sentence": "Another gal or guy, these wings are really badly drawn, but you get the idea. This is the butterfly's antenna right there. That's its body. Another person's patterns, or butterfly's patterns, might look like this. And so they're just random. But when they go into a certain environment, for whatever reason, maybe one of its predators, maybe that theory that these are supposed to look like eyes is true. And so actually, maybe this guy just has a random pattern here."}, {"video_title": "Natural Selection and the Owl Butterfly.mp3", "Sentence": "Another person's patterns, or butterfly's patterns, might look like this. And so they're just random. But when they go into a certain environment, for whatever reason, maybe one of its predators, maybe that theory that these are supposed to look like eyes is true. And so actually, maybe this guy just has a random pattern here. And so this guy, and I'm not saying that it's definitely better, they're both going to be found and killed by predators. But it's all probabilistic. Maybe this guy has a 1% less chance of getting a predator."}, {"video_title": "Natural Selection and the Owl Butterfly.mp3", "Sentence": "And so actually, maybe this guy just has a random pattern here. And so this guy, and I'm not saying that it's definitely better, they're both going to be found and killed by predators. But it's all probabilistic. Maybe this guy has a 1% less chance of getting a predator. Because when a predator just looks at them out of the corner of that eye, that little, really hazy region kind of looks like an eye. And a predator would be better off just not messing with it. And they'd rather go after the dude that looks like this."}, {"video_title": "Natural Selection and the Owl Butterfly.mp3", "Sentence": "Maybe this guy has a 1% less chance of getting a predator. Because when a predator just looks at them out of the corner of that eye, that little, really hazy region kind of looks like an eye. And a predator would be better off just not messing with it. And they'd rather go after the dude that looks like this. So it's just a slight probability. Now you might say, OK, what's 1% going to do? But when you compound that 1% over thousands and thousands of generations, all of a sudden, this trait might dominate."}, {"video_title": "Natural Selection and the Owl Butterfly.mp3", "Sentence": "And they'd rather go after the dude that looks like this. So it's just a slight probability. Now you might say, OK, what's 1% going to do? But when you compound that 1% over thousands and thousands of generations, all of a sudden, this trait might dominate. And because he's just going to be killed that less frequently. 1% less frequently. Now maybe this guy has a similar trait, but his spot is closer to the abdomen."}, {"video_title": "Natural Selection and the Owl Butterfly.mp3", "Sentence": "But when you compound that 1% over thousands and thousands of generations, all of a sudden, this trait might dominate. And because he's just going to be killed that less frequently. 1% less frequently. Now maybe this guy has a similar trait, but his spot is closer to the abdomen. And here it's a trade-off. Because maybe some predators get scared away by this concentration of pigment. And once again, I'm not saying that we're here yet."}, {"video_title": "Natural Selection and the Owl Butterfly.mp3", "Sentence": "Now maybe this guy has a similar trait, but his spot is closer to the abdomen. And here it's a trade-off. Because maybe some predators get scared away by this concentration of pigment. And once again, I'm not saying that we're here yet. We're not at this kind of very advanced, sophisticated pattern yet. We're at this random concentration of pigment that just shows up. So we see that people who have this concentration of pigment further away from their abdomen, they do well."}, {"video_title": "Natural Selection and the Owl Butterfly.mp3", "Sentence": "And once again, I'm not saying that we're here yet. We're not at this kind of very advanced, sophisticated pattern yet. We're at this random concentration of pigment that just shows up. So we see that people who have this concentration of pigment further away from their abdomen, they do well. But when it's too close, maybe some predators think that that's actually an insect and they want to eat it. So that's actually a bad trait. So what happens is this guy dominates."}, {"video_title": "Natural Selection and the Owl Butterfly.mp3", "Sentence": "So we see that people who have this concentration of pigment further away from their abdomen, they do well. But when it's too close, maybe some predators think that that's actually an insect and they want to eat it. So that's actually a bad trait. So what happens is this guy dominates. And so within this population, you start having a lot of variation, because he's more likely to pass on these traits. And I want to make that point very clear. This isn't what happens over the course of an animal's lifetime."}, {"video_title": "Natural Selection and the Owl Butterfly.mp3", "Sentence": "So what happens is this guy dominates. And so within this population, you start having a lot of variation, because he's more likely to pass on these traits. And I want to make that point very clear. This isn't what happens over the course of an animal's lifetime. It's not like if somehow I experience something, or at least our current theory, if I experience something, that I can somehow pass on that knowledge to my child. What it says is if my DNA just happens to have just some variation that happens to be more useful or more likely for me to survive to reproduction and for my children to survive, then that will start to dominate in the population. So then the population, you're going to have variations within that."}, {"video_title": "Natural Selection and the Owl Butterfly.mp3", "Sentence": "This isn't what happens over the course of an animal's lifetime. It's not like if somehow I experience something, or at least our current theory, if I experience something, that I can somehow pass on that knowledge to my child. What it says is if my DNA just happens to have just some variation that happens to be more useful or more likely for me to survive to reproduction and for my children to survive, then that will start to dominate in the population. So then the population, you're going to have variations within that. Maybe some guys, it's going to get a little bit look like that, maybe another one's going to look a little bit like that. Maybe there's some spots there. You can kind of view it as the variation is, quote unquote, exploring."}, {"video_title": "Natural Selection and the Owl Butterfly.mp3", "Sentence": "So then the population, you're going to have variations within that. Maybe some guys, it's going to get a little bit look like that, maybe another one's going to look a little bit like that. Maybe there's some spots there. You can kind of view it as the variation is, quote unquote, exploring. But I want to be very clear not to use any active verbs here, because this is all being done really as almost a common sense process, where everything changes. The changes that are most suited are the ones that are going to survive more frequently. And then the next generation is going to have more of that, and then you'll have variation within that change."}, {"video_title": "Natural Selection and the Owl Butterfly.mp3", "Sentence": "You can kind of view it as the variation is, quote unquote, exploring. But I want to be very clear not to use any active verbs here, because this is all being done really as almost a common sense process, where everything changes. The changes that are most suited are the ones that are going to survive more frequently. And then the next generation is going to have more of that, and then you'll have variation within that change. And then this one might be like that. And maybe this is the one. These were good compared to that, but now when you're competing amongst themselves, this one is able to reproduce 1% more than this guy or this guy."}, {"video_title": "Natural Selection and the Owl Butterfly.mp3", "Sentence": "And then the next generation is going to have more of that, and then you'll have variation within that change. And then this one might be like that. And maybe this is the one. These were good compared to that, but now when you're competing amongst themselves, this one is able to reproduce 1% more than this guy or this guy. So this guy becomes, and maybe it's some combination of all the above, and they mix and match. It's a hugely complex system. But then this guy represents most of the population."}, {"video_title": "Natural Selection and the Owl Butterfly.mp3", "Sentence": "These were good compared to that, but now when you're competing amongst themselves, this one is able to reproduce 1% more than this guy or this guy. So this guy becomes, and maybe it's some combination of all the above, and they mix and match. It's a hugely complex system. But then this guy represents most of the population. And when I say this guy, I'm saying this guy's genetic information, at least as which pertains to his wings. And then you get variation amongst that. Maybe some of it, they have a little small dot, and there's some dots around it."}, {"video_title": "Natural Selection and the Owl Butterfly.mp3", "Sentence": "But then this guy represents most of the population. And when I say this guy, I'm saying this guy's genetic information, at least as which pertains to his wings. And then you get variation amongst that. Maybe some of it, they have a little small dot, and there's some dots around it. Maybe it's like this. Maybe one of them digresses and goes back here, but then he has trouble competing, so he gets knocked out again. And then some other people have it back here."}, {"video_title": "Natural Selection and the Owl Butterfly.mp3", "Sentence": "Maybe some of it, they have a little small dot, and there's some dots around it. Maybe it's like this. Maybe one of them digresses and goes back here, but then he has trouble competing, so he gets knocked out again. And then some other people have it back here. I think you get the point. That this isn't happening overnight. These changes can be fairly incremental, but we're doing it over thousands of generations."}, {"video_title": "Natural Selection and the Owl Butterfly.mp3", "Sentence": "And then some other people have it back here. I think you get the point. That this isn't happening overnight. These changes can be fairly incremental, but we're doing it over thousands of generations. So when you're talking about thousands of generations, or even millions of generations, even a 1% advantage can be significant. And when you accumulate those variations over a large period of time, you can get to fairly intricate patterns like this. So I just wanted to explain that, because this is often used as, hey, sure, I can believe the butterfly moth, or I can even maybe believe the examples of the antibiotics and the bacteria or the flu."}, {"video_title": "Natural Selection and the Owl Butterfly.mp3", "Sentence": "These changes can be fairly incremental, but we're doing it over thousands of generations. So when you're talking about thousands of generations, or even millions of generations, even a 1% advantage can be significant. And when you accumulate those variations over a large period of time, you can get to fairly intricate patterns like this. So I just wanted to explain that, because this is often used as, hey, sure, I can believe the butterfly moth, or I can even maybe believe the examples of the antibiotics and the bacteria or the flu. I mean, because those are kind of real-time examples. But how does something this intricate show up? And I actually want to make a point here."}, {"video_title": "Natural Selection and the Owl Butterfly.mp3", "Sentence": "So I just wanted to explain that, because this is often used as, hey, sure, I can believe the butterfly moth, or I can even maybe believe the examples of the antibiotics and the bacteria or the flu. I mean, because those are kind of real-time examples. But how does something this intricate show up? And I actually want to make a point here. We think this is more intricate because we can relate to it in our everyday lives. But if you actually look at a structure of a bacteria and how it operates, or what a virus does to infiltrate an immune system or a cell, that's actually on a lot more levels, a lot more intricate than a design. In fact, the whole reason why I'm using this as an example is because this is a fairly simple example, as opposed to kind of explaining the metabolism of a certain type of bacteria and how that might change and how it might become immune to penicillin or whatever else."}, {"video_title": "Natural Selection and the Owl Butterfly.mp3", "Sentence": "And I actually want to make a point here. We think this is more intricate because we can relate to it in our everyday lives. But if you actually look at a structure of a bacteria and how it operates, or what a virus does to infiltrate an immune system or a cell, that's actually on a lot more levels, a lot more intricate than a design. In fact, the whole reason why I'm using this as an example is because this is a fairly simple example, as opposed to kind of explaining the metabolism of a certain type of bacteria and how that might change and how it might become immune to penicillin or whatever else. But I want to make this very clear that these very intricate things, they don't happen overnight. It's not like one butterfly was completely, one uniform hot pink color, and then all of a sudden they have a child whose wings looked just like this. No, it happens over large periods of time."}, {"video_title": "Natural Selection and the Owl Butterfly.mp3", "Sentence": "In fact, the whole reason why I'm using this as an example is because this is a fairly simple example, as opposed to kind of explaining the metabolism of a certain type of bacteria and how that might change and how it might become immune to penicillin or whatever else. But I want to make this very clear that these very intricate things, they don't happen overnight. It's not like one butterfly was completely, one uniform hot pink color, and then all of a sudden they have a child whose wings looked just like this. No, it happens over large periods of time. Although there might be some little weird hormonal change that does this, but I'm not going to go there. But that is possible. But I just want to make this point because I think the more examples we see, the more it'll kind of hit home that this is a passive process."}, {"video_title": "Natural Selection and the Owl Butterfly.mp3", "Sentence": "No, it happens over large periods of time. Although there might be some little weird hormonal change that does this, but I'm not going to go there. But that is possible. But I just want to make this point because I think the more examples we see, the more it'll kind of hit home that this is a passive process. We're not talking about these things happening overnight. And it's actually really interesting to kind of look at our world around us and look at ecosystems as they are today, and try to think really hard about how something came to be, what it's useful for, why it might have been selected for. For example, are things, are traits that occur after reproduction selected for?"}, {"video_title": "Natural Selection and the Owl Butterfly.mp3", "Sentence": "But I just want to make this point because I think the more examples we see, the more it'll kind of hit home that this is a passive process. We're not talking about these things happening overnight. And it's actually really interesting to kind of look at our world around us and look at ecosystems as they are today, and try to think really hard about how something came to be, what it's useful for, why it might have been selected for. For example, are things, are traits that occur after reproduction selected for? Well, probably not, unless they affect the reproduction of the next cycle. For example, you might say, oh, well, the trait to be nurturing after reproductive years, that's after reproductive years. No, but it helps your offspring reproduce."}, {"video_title": "Natural Selection and the Owl Butterfly.mp3", "Sentence": "For example, are things, are traits that occur after reproduction selected for? Well, probably not, unless they affect the reproduction of the next cycle. For example, you might say, oh, well, the trait to be nurturing after reproductive years, that's after reproductive years. No, but it helps your offspring reproduce. But we already see a lot of diseases, especially once we get beyond our reproductive and our child-rearing years. So once we get into our 50s and 60s, the incidences of diseases increases exponentially from when we're younger, and that's because they're no longer being selected for, because it no longer affects our ability to reproduce, because we've already reproduced, we've already raised our children so that they could reproduce. So anything that happens at that point is now not being selected for."}, {"video_title": "Comparing mitosis and meiosis   Cells   MCAT   Khan Academy.mp3", "Sentence": "Before we go in depth on meiosis, I want to do a very high level overview comparing mitosis to meiosis. So in mitosis, and this is all a review if you've watched the mitosis video. In mitosis, we start with a cell, we start with a cell that has a diploid number of chromosomes. I'll just write 2N to show it has the diploid number. For human beings, this would be 46 chromosomes. 46 for humans. You get 23 chromosomes from your mother, 23 chromosomes from your father, or you could say you have 23 homologous pairs, which leads to 46 chromosomes."}, {"video_title": "Comparing mitosis and meiosis   Cells   MCAT   Khan Academy.mp3", "Sentence": "I'll just write 2N to show it has the diploid number. For human beings, this would be 46 chromosomes. 46 for humans. You get 23 chromosomes from your mother, 23 chromosomes from your father, or you could say you have 23 homologous pairs, which leads to 46 chromosomes. Now after the process of mitosis happens, and you have your cytokinesis and all the rest, you end up with two cells that each have the same genetic information as the original. So you now have two cells that each have the diploid number of chromosomes. So 2N and 2N."}, {"video_title": "Comparing mitosis and meiosis   Cells   MCAT   Khan Academy.mp3", "Sentence": "You get 23 chromosomes from your mother, 23 chromosomes from your father, or you could say you have 23 homologous pairs, which leads to 46 chromosomes. Now after the process of mitosis happens, and you have your cytokinesis and all the rest, you end up with two cells that each have the same genetic information as the original. So you now have two cells that each have the diploid number of chromosomes. So 2N and 2N. And now each of these cells are just like this cell was. It can go through interphase again, and it grows, and it can replicate its DNA and its centrosomes, and grow some more, and then each of these can go through mitosis again. And this is actually how most of the cells in your body grow."}, {"video_title": "Comparing mitosis and meiosis   Cells   MCAT   Khan Academy.mp3", "Sentence": "So 2N and 2N. And now each of these cells are just like this cell was. It can go through interphase again, and it grows, and it can replicate its DNA and its centrosomes, and grow some more, and then each of these can go through mitosis again. And this is actually how most of the cells in your body grow. This is how you turn from a single cell organism into you, or for the most part, into you. So that is mitosis. And one way to think about it, it's a cycle."}, {"video_title": "Comparing mitosis and meiosis   Cells   MCAT   Khan Academy.mp3", "Sentence": "And this is actually how most of the cells in your body grow. This is how you turn from a single cell organism into you, or for the most part, into you. So that is mitosis. And one way to think about it, it's a cycle. After each of these things go through mitosis, they can then go through the entire cell cycle again. And let me write this a little bit neater. Mitosis."}, {"video_title": "Comparing mitosis and meiosis   Cells   MCAT   Khan Academy.mp3", "Sentence": "And one way to think about it, it's a cycle. After each of these things go through mitosis, they can then go through the entire cell cycle again. And let me write this a little bit neater. Mitosis. That S was a little bit hard to read. Now what happens in meiosis? What happens in meiosis?"}, {"video_title": "Comparing mitosis and meiosis   Cells   MCAT   Khan Academy.mp3", "Sentence": "Mitosis. That S was a little bit hard to read. Now what happens in meiosis? What happens in meiosis? I'll do that over here. In meiosis, something slightly different happens. And it happens in two phases."}, {"video_title": "Comparing mitosis and meiosis   Cells   MCAT   Khan Academy.mp3", "Sentence": "What happens in meiosis? I'll do that over here. In meiosis, something slightly different happens. And it happens in two phases. So you will start with a cell that has a diploid number of chromosomes. So you will start with a cell that has a diploid number of chromosomes. And in its interphase, it also replicates its DNA."}, {"video_title": "Comparing mitosis and meiosis   Cells   MCAT   Khan Academy.mp3", "Sentence": "And it happens in two phases. So you will start with a cell that has a diploid number of chromosomes. So you will start with a cell that has a diploid number of chromosomes. And in its interphase, it also replicates its DNA. And then it goes through something called meiosis I. And in meiosis I, what you end up with is two cells that now have a haploid number of chromosomes. So you end up with two cells."}, {"video_title": "Comparing mitosis and meiosis   Cells   MCAT   Khan Academy.mp3", "Sentence": "And in its interphase, it also replicates its DNA. And then it goes through something called meiosis I. And in meiosis I, what you end up with is two cells that now have a haploid number of chromosomes. So you end up with two cells. You now have two cells that each have a haploid number of chromosomes. So you have N, and you have N. So if we're talking about human beings, you have 46 chromosomes here, and now you have 23 chromosomes in this nucleus, and now you have 23 in this nucleus, but you're still not done. Then each of these will then go through a phase, which I'll talk about in a second, which is very similar to mitosis, which will duplicate this entire cell into two."}, {"video_title": "Comparing mitosis and meiosis   Cells   MCAT   Khan Academy.mp3", "Sentence": "So you end up with two cells. You now have two cells that each have a haploid number of chromosomes. So you have N, and you have N. So if we're talking about human beings, you have 46 chromosomes here, and now you have 23 chromosomes in this nucleus, and now you have 23 in this nucleus, but you're still not done. Then each of these will then go through a phase, which I'll talk about in a second, which is very similar to mitosis, which will duplicate this entire cell into two. So actually, let me do it like this. So now, this one, you're going to have four. You're going to have four cells that each have the haploid number of chromosomes."}, {"video_title": "Comparing mitosis and meiosis   Cells   MCAT   Khan Academy.mp3", "Sentence": "Then each of these will then go through a phase, which I'll talk about in a second, which is very similar to mitosis, which will duplicate this entire cell into two. So actually, let me do it like this. So now, this one, you're going to have four. You're going to have four cells that each have the haploid number of chromosomes. And they all don't necessarily have the same genetic information anymore. Because as we go through this first phase, right over here of meiosis, and this first phase where you go from diploid to haploid, right over here, this is called meiosis I, you're essentially splitting the homologous pairs. So this one might get some of the homologous, some of the ones that you originally got from your father, and some of the ones that you originally got from your mother."}, {"video_title": "Comparing mitosis and meiosis   Cells   MCAT   Khan Academy.mp3", "Sentence": "You're going to have four cells that each have the haploid number of chromosomes. And they all don't necessarily have the same genetic information anymore. Because as we go through this first phase, right over here of meiosis, and this first phase where you go from diploid to haploid, right over here, this is called meiosis I, you're essentially splitting the homologous pairs. So this one might get some of the homologous, some of the ones that you originally got from your father, and some of the ones that you originally got from your mother. Some of the ones that you originally got from your father, some of the ones that you originally got from your mother. They split randomly, but each homologous pairs out the homologous pair gets split up. And then in this phase, meiosis two, so this phase right over here is called meiosis two, it's very similar to mitosis, except you're now dealing with cells that start off with the haploid number."}, {"video_title": "Comparing mitosis and meiosis   Cells   MCAT   Khan Academy.mp3", "Sentence": "So this one might get some of the homologous, some of the ones that you originally got from your father, and some of the ones that you originally got from your mother. Some of the ones that you originally got from your father, some of the ones that you originally got from your mother. They split randomly, but each homologous pairs out the homologous pair gets split up. And then in this phase, meiosis two, so this phase right over here is called meiosis two, it's very similar to mitosis, except you're now dealing with cells that start off with the haploid number. And it's important to realize meiosis is not a cycle. These cells that you have over here, these are gametes. These are sex cells."}, {"video_title": "Comparing mitosis and meiosis   Cells   MCAT   Khan Academy.mp3", "Sentence": "And then in this phase, meiosis two, so this phase right over here is called meiosis two, it's very similar to mitosis, except you're now dealing with cells that start off with the haploid number. And it's important to realize meiosis is not a cycle. These cells that you have over here, these are gametes. These are sex cells. These are gametes. These can now be used in fertilization. If we're talking about, if you're male, this is happening in your testes, and these are going to be sperm cells."}, {"video_title": "Comparing mitosis and meiosis   Cells   MCAT   Khan Academy.mp3", "Sentence": "These are sex cells. These are gametes. These can now be used in fertilization. If we're talking about, if you're male, this is happening in your testes, and these are going to be sperm cells. If you are female, this is happening in your ovaries, and these are going to be egg cells. If you are a tree, this could be pollen, or it could be an ovule. So these are, but these are used for fertilization."}, {"video_title": "Comparing mitosis and meiosis   Cells   MCAT   Khan Academy.mp3", "Sentence": "If we're talking about, if you're male, this is happening in your testes, and these are going to be sperm cells. If you are female, this is happening in your ovaries, and these are going to be egg cells. If you are a tree, this could be pollen, or it could be an ovule. So these are, but these are used for fertilization. These will fuse together in sexual reproduction to get to a fertilized egg, which then can undergo mitosis to create an entirely new organism. So not a cycle here, although I guess once, these will find sex cells from another organism and fuse with them, and then those can turn into another organism, and I guess the whole circle of life starts again. But it's not the case with mitosis, where this could just keep on going and going and going."}, {"video_title": "Comparing mitosis and meiosis   Cells   MCAT   Khan Academy.mp3", "Sentence": "So these are, but these are used for fertilization. These will fuse together in sexual reproduction to get to a fertilized egg, which then can undergo mitosis to create an entirely new organism. So not a cycle here, although I guess once, these will find sex cells from another organism and fuse with them, and then those can turn into another organism, and I guess the whole circle of life starts again. But it's not the case with mitosis, where this could just keep on going and going and going. This cell is just like this cell, while these sex cells are different than this one right over here. Now, where does this happen in the body? And we've talked about this in previous videos."}, {"video_title": "Comparing mitosis and meiosis   Cells   MCAT   Khan Academy.mp3", "Sentence": "But it's not the case with mitosis, where this could just keep on going and going and going. This cell is just like this cell, while these sex cells are different than this one right over here. Now, where does this happen in the body? And we've talked about this in previous videos. These are the bulk of, these are your somatic cells right over here. These are the ones that make up the bulk of your body, somatic cells. And where is this happening?"}, {"video_title": "Comparing mitosis and meiosis   Cells   MCAT   Khan Academy.mp3", "Sentence": "And we've talked about this in previous videos. These are the bulk of, these are your somatic cells right over here. These are the ones that make up the bulk of your body, somatic cells. And where is this happening? Well, this is happening in germ cells. As we mentioned, if you're male, it's in your testes, and if you're female, it's in your ovaries. And germ cells actually can undergo mitosis to produce other germ cells that have a diploid number of chromosomes, or they can undergo meiosis in order to produce sperm or egg cells in order to produce gametes."}, {"video_title": "Regulation of transcription   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "The answer actually lies in the expression of that DNA, which genes are actively transcribed and which ones aren't. And there are several ways in which gene regulation occurs at the level of transcription, and so we're going to be talking about the main ones here. Now, let's draw out a hypothetical gene here, and associated with this gene is a sequence upstream, so towards the 3' region of the antisense strand, also called the template strand. And this sequence is called the promoter, and there's another sequence in between the promoter and the gene called the operator. The operator is the sequence of DNA to which a transcription factor protein can bind, and the promoter is the sequence of DNA to which the RNA polymerase binds to start transcription. Now, first off in prokaryotes, we have what are called general transcription factors, which are a class of proteins that bind to specific sites on DNA to activate transcription. General transcription factors plus RNA polymerase and another protein complex called the mediator multiple protein complex constitute the basic transcriptional apparatus, which positions RNA polymerase right at the start of a protein coding sequence or a gene and then releases the polymerase to transcribe the messenger RNA from that DNA template."}, {"video_title": "Regulation of transcription   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "And this sequence is called the promoter, and there's another sequence in between the promoter and the gene called the operator. The operator is the sequence of DNA to which a transcription factor protein can bind, and the promoter is the sequence of DNA to which the RNA polymerase binds to start transcription. Now, first off in prokaryotes, we have what are called general transcription factors, which are a class of proteins that bind to specific sites on DNA to activate transcription. General transcription factors plus RNA polymerase and another protein complex called the mediator multiple protein complex constitute the basic transcriptional apparatus, which positions RNA polymerase right at the start of a protein coding sequence or a gene and then releases the polymerase to transcribe the messenger RNA from that DNA template. Now, there's another type of DNA binding protein called activators, and these enhance the interaction between RNA polymerase and a particular promoter, encouraging the expression of the gene. Activators can do this by increasing the attraction of RNA polymerase for the promoter through interactions with subunits of the RNA polymerase or indirectly by changing the structure of the DNA. An example of an activator is the catabolite activator protein, or CAP, and this protein activates transcription of the lac operon in E. coli."}, {"video_title": "Regulation of transcription   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "General transcription factors plus RNA polymerase and another protein complex called the mediator multiple protein complex constitute the basic transcriptional apparatus, which positions RNA polymerase right at the start of a protein coding sequence or a gene and then releases the polymerase to transcribe the messenger RNA from that DNA template. Now, there's another type of DNA binding protein called activators, and these enhance the interaction between RNA polymerase and a particular promoter, encouraging the expression of the gene. Activators can do this by increasing the attraction of RNA polymerase for the promoter through interactions with subunits of the RNA polymerase or indirectly by changing the structure of the DNA. An example of an activator is the catabolite activator protein, or CAP, and this protein activates transcription of the lac operon in E. coli. In the case of the lac operon in E. coli, cyclic adenosine monophosphate, or C-AMP, is produced during glucose starvation. This C-AMP actually binds to the catabolite activator protein, or CAP, which causes a conformational change that allows the CAP protein to bind to a DNA site located adjacent to the promoter. And then this activator, the CAP, then makes a direct protein-to-protein interaction with RNA polymerase that recruits the RNA polymerase to the promoter."}, {"video_title": "Regulation of transcription   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "An example of an activator is the catabolite activator protein, or CAP, and this protein activates transcription of the lac operon in E. coli. In the case of the lac operon in E. coli, cyclic adenosine monophosphate, or C-AMP, is produced during glucose starvation. This C-AMP actually binds to the catabolite activator protein, or CAP, which causes a conformational change that allows the CAP protein to bind to a DNA site located adjacent to the promoter. And then this activator, the CAP, then makes a direct protein-to-protein interaction with RNA polymerase that recruits the RNA polymerase to the promoter. Now, enhancers are sites on the DNA that are bound to by activators in order to loop the DNA in a certain way that brings a specific promoter to the initiation complex. And as the name implies, this enhances transcription of the genes in a particular gene cluster. And while enhancers are usually what are called cis-acting, cis meaning the same or acting on the same chromosome, an enhancer doesn't necessarily need to be particularly close to the gene that it acts on, and sometimes it's not even located on the same chromosome."}, {"video_title": "Regulation of transcription   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "And then this activator, the CAP, then makes a direct protein-to-protein interaction with RNA polymerase that recruits the RNA polymerase to the promoter. Now, enhancers are sites on the DNA that are bound to by activators in order to loop the DNA in a certain way that brings a specific promoter to the initiation complex. And as the name implies, this enhances transcription of the genes in a particular gene cluster. And while enhancers are usually what are called cis-acting, cis meaning the same or acting on the same chromosome, an enhancer doesn't necessarily need to be particularly close to the gene that it acts on, and sometimes it's not even located on the same chromosome. Enhancers don't act on the promoter region itself, but are actually bound by activator proteins. And these activator proteins can interact with that mediator complex I mentioned earlier, which recruits RNA polymerase and the general transcription factors, which then can lead to transcription of the genes. So here I've drawn a little schematic of what it might look like to have the enhancer actually change the structure of the DNA so that the DNA is now looping around."}, {"video_title": "Regulation of transcription   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "And while enhancers are usually what are called cis-acting, cis meaning the same or acting on the same chromosome, an enhancer doesn't necessarily need to be particularly close to the gene that it acts on, and sometimes it's not even located on the same chromosome. Enhancers don't act on the promoter region itself, but are actually bound by activator proteins. And these activator proteins can interact with that mediator complex I mentioned earlier, which recruits RNA polymerase and the general transcription factors, which then can lead to transcription of the genes. So here I've drawn a little schematic of what it might look like to have the enhancer actually change the structure of the DNA so that the DNA is now looping around. Here you still have your promoter sequence, the operator sequence, the gene sequence, and the enhancer sequence. And having the DNA looped in such a way so that you could then recruit RNA polymerase, the transcription factors, the mediator protein complex, and then you have transcription begin of this gene here. Now let's talk about repressors."}, {"video_title": "Regulation of transcription   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "So here I've drawn a little schematic of what it might look like to have the enhancer actually change the structure of the DNA so that the DNA is now looping around. Here you still have your promoter sequence, the operator sequence, the gene sequence, and the enhancer sequence. And having the DNA looped in such a way so that you could then recruit RNA polymerase, the transcription factors, the mediator protein complex, and then you have transcription begin of this gene here. Now let's talk about repressors. Repressors are proteins that bind to the operator, impeding RNA polymerase's progress along the strand and thus impeding the expression of the gene. Now if an inducer, which is a molecule that initiates gene expression, is present, then it can actually interact with the repressor protein in such a way that causes it to detach from the operator. And then this frees up RNA polymerase to then transcribe the gene further down on the DNA strand."}, {"video_title": "Regulation of transcription   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "Now let's talk about repressors. Repressors are proteins that bind to the operator, impeding RNA polymerase's progress along the strand and thus impeding the expression of the gene. Now if an inducer, which is a molecule that initiates gene expression, is present, then it can actually interact with the repressor protein in such a way that causes it to detach from the operator. And then this frees up RNA polymerase to then transcribe the gene further down on the DNA strand. One example of a repressor protein is the repressor protein associated again with the lac operon operator, which prevents the transcription of genes used in lactose metabolism unless lactose, which is the inducer molecule, is present as an alternative energy source. Now silencers are regions of DNA that are bound by repressor proteins in order to silence gene expression. And this mechanism is very similar to that of the enhancer sequences that I just talked about."}, {"video_title": "Regulation of transcription   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "And then this frees up RNA polymerase to then transcribe the gene further down on the DNA strand. One example of a repressor protein is the repressor protein associated again with the lac operon operator, which prevents the transcription of genes used in lactose metabolism unless lactose, which is the inducer molecule, is present as an alternative energy source. Now silencers are regions of DNA that are bound by repressor proteins in order to silence gene expression. And this mechanism is very similar to that of the enhancer sequences that I just talked about. And similarly, silencers can be located several bases upstream or downstream from the actual promoter of the gene. And when a repressor protein binds to the silencer region of the DNA, RNA polymerase is prevented from binding to the promoter region. Now a few notes about the differences between prokaryotes and eukaryotes when it comes to transcriptional regulation."}, {"video_title": "Regulation of transcription   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "And this mechanism is very similar to that of the enhancer sequences that I just talked about. And similarly, silencers can be located several bases upstream or downstream from the actual promoter of the gene. And when a repressor protein binds to the silencer region of the DNA, RNA polymerase is prevented from binding to the promoter region. Now a few notes about the differences between prokaryotes and eukaryotes when it comes to transcriptional regulation. In prokaryotes, the regulation of transcription is really needed for the cell to be able to quickly adapt to the ever-changing outer environment that it is sitting in. The presence, the quantity, the type of nutrients actually determines which genes are expressed. And in order to do that, genes must be regulated in some sort of fashion."}, {"video_title": "Regulation of transcription   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "Now a few notes about the differences between prokaryotes and eukaryotes when it comes to transcriptional regulation. In prokaryotes, the regulation of transcription is really needed for the cell to be able to quickly adapt to the ever-changing outer environment that it is sitting in. The presence, the quantity, the type of nutrients actually determines which genes are expressed. And in order to do that, genes must be regulated in some sort of fashion. So a combination of activators, repressors, and rarely enhancers, at least in the case of prokaryotes, determines whether a gene is transcribed. In eukaryotes, transcriptional regulation tends to involve a combination of interactions between several transcription factors, which allows for a more sophisticated response to multiple conditions in the environment. And another major difference between eukaryotes and prokaryotes is the fact that eukaryotes have a nuclear envelope, which prevents the simultaneous transcription and translation of a particular gene, and this adds an extra spatial and temporal control of gene expression."}, {"video_title": "Breaking down photosynthesis stages.mp3", "Sentence": "The photo is referring to that it's going to use light somehow, and what's it going to do with that light energy? Well, it's going to synthesize something, and in particular, what it's going to synthesize, as we'll see, is sugar. So we are going to go from energy and light, let me just write light, light energy, and we're going to use that light energy to synthesize, to synthesize sugar. Very broadly speaking, obviously this is a very, very high-level overview, but light energy isn't the only input here. We're also going to need some water, and as we go into future videos, we'll see what that water is used for. It's actually a source of electrons to do this, to make use of that light energy, frankly. And we're also going to need, we're also going to need some carbon dioxide."}, {"video_title": "Breaking down photosynthesis stages.mp3", "Sentence": "Very broadly speaking, obviously this is a very, very high-level overview, but light energy isn't the only input here. We're also going to need some water, and as we go into future videos, we'll see what that water is used for. It's actually a source of electrons to do this, to make use of that light energy, frankly. And we're also going to need, we're also going to need some carbon dioxide. Really, as a source of carbons, because there's a lot of carbon in those sugars, we're essentially going to fix the carbon. We're going to take it from this carbon dioxide gas and we're going to incorporate it into organic molecules and eventually into the sugar. And sugar isn't the only output."}, {"video_title": "Breaking down photosynthesis stages.mp3", "Sentence": "And we're also going to need, we're also going to need some carbon dioxide. Really, as a source of carbons, because there's a lot of carbon in those sugars, we're essentially going to fix the carbon. We're going to take it from this carbon dioxide gas and we're going to incorporate it into organic molecules and eventually into the sugar. And sugar isn't the only output. Another byproduct of this process is molecular oxygen. Once you strip the, you strip a couple of electrons from the water and the hydrogen ions are stripped away from it as well, all you're left with is oxygen. And you do that twice, then you have O2 and you have molecular oxygen."}, {"video_title": "Breaking down photosynthesis stages.mp3", "Sentence": "And sugar isn't the only output. Another byproduct of this process is molecular oxygen. Once you strip the, you strip a couple of electrons from the water and the hydrogen ions are stripped away from it as well, all you're left with is oxygen. And you do that twice, then you have O2 and you have molecular oxygen. And this is a byproduct of photosynthesis, but you can imagine this is very important to life on Earth as we know it, in particular for us. We would have trouble breathing if this was not a byproduct of photosynthesis. Now what I'm going to do now is break this out into two stages."}, {"video_title": "Breaking down photosynthesis stages.mp3", "Sentence": "And you do that twice, then you have O2 and you have molecular oxygen. And this is a byproduct of photosynthesis, but you can imagine this is very important to life on Earth as we know it, in particular for us. We would have trouble breathing if this was not a byproduct of photosynthesis. Now what I'm going to do now is break this out into two stages. And these two stages, we can call the light-dependent reactions, light-dependent, dependent reactions. And then the second stage, I will call the Calvin cycle. Calvin, Calvin cycle."}, {"video_title": "Breaking down photosynthesis stages.mp3", "Sentence": "Now what I'm going to do now is break this out into two stages. And these two stages, we can call the light-dependent reactions, light-dependent, dependent reactions. And then the second stage, I will call the Calvin cycle. Calvin, Calvin cycle. And as the name implies, the light-dependent reactions are dependent on light. So what's happening here is we're gonna take light energy, light energy, plus we're gonna take the water as a source of electrons, and we're going to use these two things, we're gonna use these two things to produce, to produce, let me write this in another color, to produce ATP, from ADP. So we're gonna produce ATP, which is a store of energy."}, {"video_title": "Breaking down photosynthesis stages.mp3", "Sentence": "Calvin, Calvin cycle. And as the name implies, the light-dependent reactions are dependent on light. So what's happening here is we're gonna take light energy, light energy, plus we're gonna take the water as a source of electrons, and we're going to use these two things, we're gonna use these two things to produce, to produce, let me write this in another color, to produce ATP, from ADP. So we're gonna produce ATP, which is a store of energy. And we're also going to reduce NADP plus into NADPH, which has energy as a strong reducing agent. So this is what is happening, broadly speaking, in the light reactions. And then in the Calvin cycle, what we're gonna do is we're gonna take these products of the light-dependent reactions."}, {"video_title": "Breaking down photosynthesis stages.mp3", "Sentence": "So we're gonna produce ATP, which is a store of energy. And we're also going to reduce NADP plus into NADPH, which has energy as a strong reducing agent. So this is what is happening, broadly speaking, in the light reactions. And then in the Calvin cycle, what we're gonna do is we're gonna take these products of the light-dependent reactions. So we're gonna take our ATP and our NADPH, and we can use their energy in conjunction with some carbon dioxide, with some carbon dioxide, in order to produce, in order to produce sugar, in order to produce sugar. And let me see, have I got everything here? Oh, of course, I'm missing one of the byproducts of the light-dependent reactions, a very important one."}, {"video_title": "Breaking down photosynthesis stages.mp3", "Sentence": "And then in the Calvin cycle, what we're gonna do is we're gonna take these products of the light-dependent reactions. So we're gonna take our ATP and our NADPH, and we can use their energy in conjunction with some carbon dioxide, with some carbon dioxide, in order to produce, in order to produce sugar, in order to produce sugar. And let me see, have I got everything here? Oh, of course, I'm missing one of the byproducts of the light-dependent reactions, a very important one. I'm missing the molecular, the molecular oxygen. So once again, this is what makes up photosynthesis, but you can break it up into these two segments. Light-dependent reaction is using the energy from photons and light, along with electrons from the water, to produce, to store energy as ATP and NADPH, and it has oxygen, molecular oxygen, as a byproduct."}, {"video_title": "Breaking down photosynthesis stages.mp3", "Sentence": "Oh, of course, I'm missing one of the byproducts of the light-dependent reactions, a very important one. I'm missing the molecular, the molecular oxygen. So once again, this is what makes up photosynthesis, but you can break it up into these two segments. Light-dependent reaction is using the energy from photons and light, along with electrons from the water, to produce, to store energy as ATP and NADPH, and it has oxygen, molecular oxygen, as a byproduct. In order for it to get one molecular oxygen, you're gonna have to need two of these water molecules. And then, as we go into the Calvin cycle, we can take these, the ATP and the NADPH, along with some carbon dioxide, and we can use that to actually store our energy as actual sugar. And as we'll do in future videos, we'll go into more depth, and what exactly happens in these light-dependent reactions, and what exactly happens in the Calvin cycle."}, {"video_title": "Covalent bonds   Molecular and ionic compound structure and properties   AP Chemistry   Khan Academy.mp3", "Sentence": "Let's say we're dealing with two oxygen atoms. So let me draw one oxygen here. A neutral oxygen has eight electrons total, but six of them are in its outer shell. So it has one, two, three, four, five, six valence electrons. And the way that I arranged them is I paired them up last. So you have these two valence electrons that are not paired with another electron. And now let me draw another oxygen, and I'm going to do it with a different color so that we can keep track of the electrons."}, {"video_title": "Covalent bonds   Molecular and ionic compound structure and properties   AP Chemistry   Khan Academy.mp3", "Sentence": "So it has one, two, three, four, five, six valence electrons. And the way that I arranged them is I paired them up last. So you have these two valence electrons that are not paired with another electron. And now let me draw another oxygen, and I'm going to do it with a different color so that we can keep track of the electrons. So another oxygen right over there also has six valence electrons. One, two, three, four, five, six valence electrons. Now this oxygen on the left, in order to become more stable, it would love to somehow gain or maybe share two more electrons."}, {"video_title": "Covalent bonds   Molecular and ionic compound structure and properties   AP Chemistry   Khan Academy.mp3", "Sentence": "And now let me draw another oxygen, and I'm going to do it with a different color so that we can keep track of the electrons. So another oxygen right over there also has six valence electrons. One, two, three, four, five, six valence electrons. Now this oxygen on the left, in order to become more stable, it would love to somehow gain or maybe share two more electrons. And of course this oxygen on the right, it's still oxygen. It also would love to gain or share two more valence electrons so how could it do it? Well what if the oxygen on the left shared this electron and this electron with the oxygen on the right, and the oxygen on the right shared this electron and this electron with the oxygen on the left?"}, {"video_title": "Covalent bonds   Molecular and ionic compound structure and properties   AP Chemistry   Khan Academy.mp3", "Sentence": "Now this oxygen on the left, in order to become more stable, it would love to somehow gain or maybe share two more electrons. And of course this oxygen on the right, it's still oxygen. It also would love to gain or share two more valence electrons so how could it do it? Well what if the oxygen on the left shared this electron and this electron with the oxygen on the right, and the oxygen on the right shared this electron and this electron with the oxygen on the left? Well if they did that, you would have something that looks like this. You have your oxygen on the left, you have the oxygen on the right, and the way we show two electrons that are being shared, let's say these two electrons are being shared, is just a line like this. This shows that there are two electrons that are being shared by these two oxygens and let's say that these two electrons are also being shared."}, {"video_title": "Covalent bonds   Molecular and ionic compound structure and properties   AP Chemistry   Khan Academy.mp3", "Sentence": "Well what if the oxygen on the left shared this electron and this electron with the oxygen on the right, and the oxygen on the right shared this electron and this electron with the oxygen on the left? Well if they did that, you would have something that looks like this. You have your oxygen on the left, you have the oxygen on the right, and the way we show two electrons that are being shared, let's say these two electrons are being shared, is just a line like this. This shows that there are two electrons that are being shared by these two oxygens and let's say that these two electrons are also being shared. You would do that with a line like this and then we could draw the remainder of the valence electrons. This oxygen on the left had, outside of the electrons that are being shared, it had four more valence electrons, and then the oxygen on the right had four more valence electrons. One, two, three, four."}, {"video_title": "Covalent bonds   Molecular and ionic compound structure and properties   AP Chemistry   Khan Academy.mp3", "Sentence": "This shows that there are two electrons that are being shared by these two oxygens and let's say that these two electrons are also being shared. You would do that with a line like this and then we could draw the remainder of the valence electrons. This oxygen on the left had, outside of the electrons that are being shared, it had four more valence electrons, and then the oxygen on the right had four more valence electrons. One, two, three, four. Now what's interesting here is these shared electrons, these are going to cause these oxygens to stick together. If they don't stick together, these electrons aren't going to be shared. So what we have formed here is known as a covalent bond."}, {"video_title": "Covalent bonds   Molecular and ionic compound structure and properties   AP Chemistry   Khan Academy.mp3", "Sentence": "One, two, three, four. Now what's interesting here is these shared electrons, these are going to cause these oxygens to stick together. If they don't stick together, these electrons aren't going to be shared. So what we have formed here is known as a covalent bond. Covalent bond. And what's interesting is it allows both of these oxygens in some ways to be more stable. From the left oxygen's point of view, it had six valence electrons, but now it's able to share two more."}, {"video_title": "Covalent bonds   Molecular and ionic compound structure and properties   AP Chemistry   Khan Academy.mp3", "Sentence": "So what we have formed here is known as a covalent bond. Covalent bond. And what's interesting is it allows both of these oxygens in some ways to be more stable. From the left oxygen's point of view, it had six valence electrons, but now it's able to share two more. Remember, each of these bonds, each of these lines represent two electrons. So this oxygen could say, hey, I get to have one, two, three, four, six, eight electrons that I'm dealing with, and the same thing is going to be true of this oxygen on the right. Now there are some covalent bonds that are between not so equals."}, {"video_title": "Covalent bonds   Molecular and ionic compound structure and properties   AP Chemistry   Khan Academy.mp3", "Sentence": "From the left oxygen's point of view, it had six valence electrons, but now it's able to share two more. Remember, each of these bonds, each of these lines represent two electrons. So this oxygen could say, hey, I get to have one, two, three, four, six, eight electrons that I'm dealing with, and the same thing is going to be true of this oxygen on the right. Now there are some covalent bonds that are between not so equals. So for example, if we're talking about water, and if we're talking about how oxygen bonds with hydrogen. So if we have oxygen right over here, once again I can draw it six valence electrons. One, two, three, four, five, and let me just draw the sixth one right over there."}, {"video_title": "Covalent bonds   Molecular and ionic compound structure and properties   AP Chemistry   Khan Academy.mp3", "Sentence": "Now there are some covalent bonds that are between not so equals. So for example, if we're talking about water, and if we're talking about how oxygen bonds with hydrogen. So if we have oxygen right over here, once again I can draw it six valence electrons. One, two, three, four, five, and let me just draw the sixth one right over there. And if I have hydrogen, hydrogen has one valence electron. So let's say that's a hydrogen right over there with one valence electron, maybe another hydrogen right over there with one valence electron. Oxygen and hydrogen form covalent bonds."}, {"video_title": "Covalent bonds   Molecular and ionic compound structure and properties   AP Chemistry   Khan Academy.mp3", "Sentence": "One, two, three, four, five, and let me just draw the sixth one right over there. And if I have hydrogen, hydrogen has one valence electron. So let's say that's a hydrogen right over there with one valence electron, maybe another hydrogen right over there with one valence electron. Oxygen and hydrogen form covalent bonds. In fact, that is how water is formed. And so what would that look like? Well, it would look like this."}, {"video_title": "Covalent bonds   Molecular and ionic compound structure and properties   AP Chemistry   Khan Academy.mp3", "Sentence": "Oxygen and hydrogen form covalent bonds. In fact, that is how water is formed. And so what would that look like? Well, it would look like this. You have oxygen right over here. You have these two pairs of electrons that I keep drawing. And then this electron right over here could be shared with the hydrogen, and that hydrogen's electron could be shared with the oxygen."}, {"video_title": "Covalent bonds   Molecular and ionic compound structure and properties   AP Chemistry   Khan Academy.mp3", "Sentence": "Well, it would look like this. You have oxygen right over here. You have these two pairs of electrons that I keep drawing. And then this electron right over here could be shared with the hydrogen, and that hydrogen's electron could be shared with the oxygen. So that forms a covalent bond with this hydrogen. And then this electron from the oxygen can be shared with the hydrogen, and that electron from the hydrogen can be shared with the oxygen. And so that would form a covalent bond with that other hydrogen."}, {"video_title": "Covalent bonds   Molecular and ionic compound structure and properties   AP Chemistry   Khan Academy.mp3", "Sentence": "And then this electron right over here could be shared with the hydrogen, and that hydrogen's electron could be shared with the oxygen. So that forms a covalent bond with this hydrogen. And then this electron from the oxygen can be shared with the hydrogen, and that electron from the hydrogen can be shared with the oxygen. And so that would form a covalent bond with that other hydrogen. And now here, once again, oxygen can kind of pretend like it has eight valence electrons, two, four, six, eight. And the hydrogens can kind of pretend that it has two valence electrons. But the one difference here is that oxygen is a lot more electronegative than hydrogen."}, {"video_title": "Covalent bonds   Molecular and ionic compound structure and properties   AP Chemistry   Khan Academy.mp3", "Sentence": "And so that would form a covalent bond with that other hydrogen. And now here, once again, oxygen can kind of pretend like it has eight valence electrons, two, four, six, eight. And the hydrogens can kind of pretend that it has two valence electrons. But the one difference here is that oxygen is a lot more electronegative than hydrogen. It's to the right of hydrogen. It's in this top right corner outside of, other than the noble gases, that really like to hog electrons. So what do you think is going to happen here?"}, {"video_title": "Covalent bonds   Molecular and ionic compound structure and properties   AP Chemistry   Khan Academy.mp3", "Sentence": "But the one difference here is that oxygen is a lot more electronegative than hydrogen. It's to the right of hydrogen. It's in this top right corner outside of, other than the noble gases, that really like to hog electrons. So what do you think is going to happen here? Well, the electrons in each of these covalent bonds are going to hang out around the oxygen more often than around the hydrogen. So if the electrons spend more time around the oxygen, you're going to have, in general, more negative charge around the oxygen. And so you're going to have a partial negative charge on the oxygen end of the water molecule."}, {"video_title": "Covalent bonds   Molecular and ionic compound structure and properties   AP Chemistry   Khan Academy.mp3", "Sentence": "So what do you think is going to happen here? Well, the electrons in each of these covalent bonds are going to hang out around the oxygen more often than around the hydrogen. So if the electrons spend more time around the oxygen, you're going to have, in general, more negative charge around the oxygen. And so you're going to have a partial negative charge on the oxygen end of the water molecule. And then you're going to have partial positive charges on the hydrogen ends of the molecules. And in case you're curious, that little symbol I'm using for partial, that's the lowercase Greek letter delta, which is just the convention in chemistry. And so this type of covalent bond, because there is some polarity, one side has more charge than the other, this is known as a polar covalent bond."}, {"video_title": "Variation in a Species (4).mp3", "Sentence": "So for example, let's say I have a bunch of, well, this is the circle species. And one guy is that color, and then I've got a bunch more. Maybe some are that color. That's the same color. That one, and that one, and that one. And for whatever reason, sometimes there are no environmental factors that will predispose one of these guys to be able to survive and reproduce over the other. But every now and then, there might be some environmental factor."}, {"video_title": "Variation in a Species (4).mp3", "Sentence": "That's the same color. That one, and that one, and that one. And for whatever reason, sometimes there are no environmental factors that will predispose one of these guys to be able to survive and reproduce over the other. But every now and then, there might be some environmental factor. And it makes maybe all of a sudden, this guy is more fit to reproduce. And so for whatever reason, this guy is able to reproduce more frequently, and these guys less frequently. And some of them get killed or whatever, eaten by birds or they're just not able to reproduce for whatever reason."}, {"video_title": "Variation in a Species (4).mp3", "Sentence": "But every now and then, there might be some environmental factor. And it makes maybe all of a sudden, this guy is more fit to reproduce. And so for whatever reason, this guy is able to reproduce more frequently, and these guys less frequently. And some of them get killed or whatever, eaten by birds or they're just not able to reproduce for whatever reason. And then maybe these guys are something in between. And so over time, the frequency of the different traits you see in this population will change. And if they are drastic enough, maybe these guys start becoming dominant and start not liking these guys because they're so different or whatever else."}, {"video_title": "Variation in a Species (4).mp3", "Sentence": "And some of them get killed or whatever, eaten by birds or they're just not able to reproduce for whatever reason. And then maybe these guys are something in between. And so over time, the frequency of the different traits you see in this population will change. And if they are drastic enough, maybe these guys start becoming dominant and start not liking these guys because they're so different or whatever else. We could see a lot of different reasons. This could eventually turn into a different species. Now, the obvious question is, what leads to this variation?"}, {"video_title": "Variation in a Species (4).mp3", "Sentence": "And if they are drastic enough, maybe these guys start becoming dominant and start not liking these guys because they're so different or whatever else. We could see a lot of different reasons. This could eventually turn into a different species. Now, the obvious question is, what leads to this variation? In a population, what leads to this? In fact, even in our population, what leads to one person having dirty blonde hair, one person having brown hair, one person having black hair, and the spectrum of skin complexions and heights is pretty much infinite? What causes that?"}, {"video_title": "Variation in a Species (4).mp3", "Sentence": "Now, the obvious question is, what leads to this variation? In a population, what leads to this? In fact, even in our population, what leads to one person having dirty blonde hair, one person having brown hair, one person having black hair, and the spectrum of skin complexions and heights is pretty much infinite? What causes that? And then one thing that I kind of point to, and we talked about this a little bit in the DNA video, is this notion of mutations. The DNA, we learned, is just a sequence of these bases. So adenine, guanine, let's say I got some thymine going, I have some more adenine, some cytosine."}, {"video_title": "Variation in a Species (4).mp3", "Sentence": "What causes that? And then one thing that I kind of point to, and we talked about this a little bit in the DNA video, is this notion of mutations. The DNA, we learned, is just a sequence of these bases. So adenine, guanine, let's say I got some thymine going, I have some more adenine, some cytosine. And that these code, if you have enough of these in a row, maybe you have a few hundred or a few thousands of these, these code for proteins or they code for things that control other proteins. But maybe you have a change in one of them. Maybe this cytosine, for whatever reason, becomes a guanine randomly."}, {"video_title": "Variation in a Species (4).mp3", "Sentence": "So adenine, guanine, let's say I got some thymine going, I have some more adenine, some cytosine. And that these code, if you have enough of these in a row, maybe you have a few hundred or a few thousands of these, these code for proteins or they code for things that control other proteins. But maybe you have a change in one of them. Maybe this cytosine, for whatever reason, becomes a guanine randomly. Or maybe these get deleted. And that would change the DNA. But you can imagine, if I went to someone's computer code and just randomly started changing letters and randomly started inserting letters without really knowing what I'm doing, most of the time I'm going to break the computer program."}, {"video_title": "Variation in a Species (4).mp3", "Sentence": "Maybe this cytosine, for whatever reason, becomes a guanine randomly. Or maybe these get deleted. And that would change the DNA. But you can imagine, if I went to someone's computer code and just randomly started changing letters and randomly started inserting letters without really knowing what I'm doing, most of the time I'm going to break the computer program. Most of the time, the great majority of the time, this is going to go nowhere. For example, if I go into someone's computer program and if I just add a couple of spaces or something, that might not change their computer program. But if I start getting rid of semicolons and start changing numbers and all that, it'll probably make the computer program break."}, {"video_title": "Variation in a Species (4).mp3", "Sentence": "But you can imagine, if I went to someone's computer code and just randomly started changing letters and randomly started inserting letters without really knowing what I'm doing, most of the time I'm going to break the computer program. Most of the time, the great majority of the time, this is going to go nowhere. For example, if I go into someone's computer program and if I just add a couple of spaces or something, that might not change their computer program. But if I start getting rid of semicolons and start changing numbers and all that, it'll probably make the computer program break. So it'll either do nothing or it'll actually kill the organisms most of the time. Mutations. Sometimes they might make the actual cell kind of go run amok and we'll do a whole maybe series of videos on cancer and that itself obviously would hurt the organism as a whole."}, {"video_title": "Variation in a Species (4).mp3", "Sentence": "But if I start getting rid of semicolons and start changing numbers and all that, it'll probably make the computer program break. So it'll either do nothing or it'll actually kill the organisms most of the time. Mutations. Sometimes they might make the actual cell kind of go run amok and we'll do a whole maybe series of videos on cancer and that itself obviously would hurt the organism as a whole. Although if it occurs after the organism is reproduced, it might not be something that selects against the organism. But anyway, and it also wouldn't be passed on. But anyway, I won't go too detailed into that."}, {"video_title": "Variation in a Species (4).mp3", "Sentence": "Sometimes they might make the actual cell kind of go run amok and we'll do a whole maybe series of videos on cancer and that itself obviously would hurt the organism as a whole. Although if it occurs after the organism is reproduced, it might not be something that selects against the organism. But anyway, and it also wouldn't be passed on. But anyway, I won't go too detailed into that. But the whole point is that mutations don't seem to be a satisfying source of variation. They could be a source or kind of contribute on the margin, but there must be something more profound than mutations that's creating the diversity even within, or maybe I should call the variation, even within a population. And the answer here is really, it's kind of right in front of us."}, {"video_title": "Variation in a Species (4).mp3", "Sentence": "But anyway, I won't go too detailed into that. But the whole point is that mutations don't seem to be a satisfying source of variation. They could be a source or kind of contribute on the margin, but there must be something more profound than mutations that's creating the diversity even within, or maybe I should call the variation, even within a population. And the answer here is really, it's kind of right in front of us. It really addresses kind of one of the most fundamental things about biology. And it's so fundamental that a lot of people never even question why it is the way it is. And that is sexual reproduction."}, {"video_title": "Variation in a Species (4).mp3", "Sentence": "And the answer here is really, it's kind of right in front of us. It really addresses kind of one of the most fundamental things about biology. And it's so fundamental that a lot of people never even question why it is the way it is. And that is sexual reproduction. And when I mean sexual reproduction, it's this notion that you have, and pretty much if you look at all organisms that have nucleuses, and we call those eukaryotes, maybe I'll do a whole video on eukaryotes versus prokaryotes. But it's the notion that if you look universally all the way from plants, not universally, but if you look at cells that have nucleuses, they almost universally have this phenomenon that you have males and you have females. In some organisms, an organism can be both a male and a female, but the common idea here is that all organisms kind of produce versions of their genetic material that mix with other organisms' version of their genetic material."}, {"video_title": "Variation in a Species (4).mp3", "Sentence": "And that is sexual reproduction. And when I mean sexual reproduction, it's this notion that you have, and pretty much if you look at all organisms that have nucleuses, and we call those eukaryotes, maybe I'll do a whole video on eukaryotes versus prokaryotes. But it's the notion that if you look universally all the way from plants, not universally, but if you look at cells that have nucleuses, they almost universally have this phenomenon that you have males and you have females. In some organisms, an organism can be both a male and a female, but the common idea here is that all organisms kind of produce versions of their genetic material that mix with other organisms' version of their genetic material. If mutations were the only source of variation, then I could just butt off other cells. Maybe other cells would just butt off from me, and then randomly one cell might be a little bit different and whatever else. But that would, as we already talked about, most of the time we would have very little change, very little variation."}, {"video_title": "Variation in a Species (4).mp3", "Sentence": "In some organisms, an organism can be both a male and a female, but the common idea here is that all organisms kind of produce versions of their genetic material that mix with other organisms' version of their genetic material. If mutations were the only source of variation, then I could just butt off other cells. Maybe other cells would just butt off from me, and then randomly one cell might be a little bit different and whatever else. But that would, as we already talked about, most of the time we would have very little change, very little variation. And whatever variation does occur because of any kind of noise being introduced into this kind of butting process where I just replicate myself identically, most of the times it'll be negative. Most of the times it'll break the organism. Now, when you have sexual reproduction, what happens?"}, {"video_title": "Variation in a Species (4).mp3", "Sentence": "But that would, as we already talked about, most of the time we would have very little change, very little variation. And whatever variation does occur because of any kind of noise being introduced into this kind of butting process where I just replicate myself identically, most of the times it'll be negative. Most of the times it'll break the organism. Now, when you have sexual reproduction, what happens? Well, you keep mixing and matching every possible combination of DNA in a species pool of DNA. Let me make this a little bit more concrete for you. So let me erase this horrible drawing I just did."}, {"video_title": "Variation in a Species (4).mp3", "Sentence": "Now, when you have sexual reproduction, what happens? Well, you keep mixing and matching every possible combination of DNA in a species pool of DNA. Let me make this a little bit more concrete for you. So let me erase this horrible drawing I just did. So we all have, let me stick to humans because that's what we are. We have 23 pairs of chromosomes, and in each pair we have one chromosome from our mother and one chromosome from our father. So let me draw that."}, {"video_title": "Variation in a Species (4).mp3", "Sentence": "So let me erase this horrible drawing I just did. So we all have, let me stick to humans because that's what we are. We have 23 pairs of chromosomes, and in each pair we have one chromosome from our mother and one chromosome from our father. So let me draw that. So I'll do my father's chromosomes in blue, so I have 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, and I'm running out of space. Let me do more here. 16, 17, 18, 19, 20, 21, 22."}, {"video_title": "Variation in a Species (4).mp3", "Sentence": "So let me draw that. So I'll do my father's chromosomes in blue, so I have 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, and I'm running out of space. Let me do more here. 16, 17, 18, 19, 20, 21, 22. And then I'll throw another one here that looks a little bit different. I'll throw one here that looks like a Y. And we'll talk more about the X's and the Y chromosomes."}, {"video_title": "Variation in a Species (4).mp3", "Sentence": "16, 17, 18, 19, 20, 21, 22. And then I'll throw another one here that looks a little bit different. I'll throw one here that looks like a Y. And we'll talk more about the X's and the Y chromosomes. And I have 23 chromosomes from my mother. And not to be stereotypical, but maybe I'll do that in a more feminine color. Let's see."}, {"video_title": "Variation in a Species (4).mp3", "Sentence": "And we'll talk more about the X's and the Y chromosomes. And I have 23 chromosomes from my mother. And not to be stereotypical, but maybe I'll do that in a more feminine color. Let's see. So I have 23 chromosomes from my mother. 1, 2, I just have to draw 1, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23. So what's going on here?"}, {"video_title": "Variation in a Species (4).mp3", "Sentence": "Let's see. So I have 23 chromosomes from my mother. 1, 2, I just have to draw 1, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23. So what's going on here? I have 23 from my mother. I have 23 from my father. Now, each of these chromosomes, and I made them right next to each other."}, {"video_title": "Variation in a Species (4).mp3", "Sentence": "So what's going on here? I have 23 from my mother. I have 23 from my father. Now, each of these chromosomes, and I made them right next to each other. So for example, let me zoom in on one pair of these. So let's say we look at chromosome number 3. So let me zoom in on chromosome number 3."}, {"video_title": "Variation in a Species (4).mp3", "Sentence": "Now, each of these chromosomes, and I made them right next to each other. So for example, let me zoom in on one pair of these. So let's say we look at chromosome number 3. So let me zoom in on chromosome number 3. I have one from my mother right here. And remember, actually maybe I'll do it this way. Remember, a chromosome is just a big, if you take the DNA, it just keeps wrapping around."}, {"video_title": "Variation in a Species (4).mp3", "Sentence": "So let me zoom in on chromosome number 3. I have one from my mother right here. And remember, actually maybe I'll do it this way. Remember, a chromosome is just a big, if you take the DNA, it just keeps wrapping around. It actually wraps around all these proteins and it creates the structure. But it's just a big, you see it like that, you're like, oh, maybe the DNA, no, but this could have millions of base pairs. So maybe it'll look something like that."}, {"video_title": "Variation in a Species (4).mp3", "Sentence": "Remember, a chromosome is just a big, if you take the DNA, it just keeps wrapping around. It actually wraps around all these proteins and it creates the structure. But it's just a big, you see it like that, you're like, oh, maybe the DNA, no, but this could have millions of base pairs. So maybe it'll look something like that. It's a densely wrapped version of, well, it's a long string of DNA, and when it's normally drawn like this, which is not always the way it is, and we'll talk more about like that, they draw it as densely packed like that. So let's say that's from my mother and that's from my father. Now, these are both, we call them, I'll call them, they're the same, let's call this chromosome 3."}, {"video_title": "Variation in a Species (4).mp3", "Sentence": "So maybe it'll look something like that. It's a densely wrapped version of, well, it's a long string of DNA, and when it's normally drawn like this, which is not always the way it is, and we'll talk more about like that, they draw it as densely packed like that. So let's say that's from my mother and that's from my father. Now, these are both, we call them, I'll call them, they're the same, let's call this chromosome 3. They're both chromosome 3. And what the idea is here is that I'm getting different traits from my father and from my mother. For example, and I'm doing a gross oversimplification here, but this is really to just give you the idea of what's going on."}, {"video_title": "Variation in a Species (4).mp3", "Sentence": "Now, these are both, we call them, I'll call them, they're the same, let's call this chromosome 3. They're both chromosome 3. And what the idea is here is that I'm getting different traits from my father and from my mother. For example, and I'm doing a gross oversimplification here, but this is really to just give you the idea of what's going on. This chromosome 3, maybe it contains this trait for hair color. And maybe my father had, and I'll use my actual example, my father had very straight hair. So let's say he had, some place on this chromosome, there is a gene for hair straightness."}, {"video_title": "Variation in a Species (4).mp3", "Sentence": "For example, and I'm doing a gross oversimplification here, but this is really to just give you the idea of what's going on. This chromosome 3, maybe it contains this trait for hair color. And maybe my father had, and I'll use my actual example, my father had very straight hair. So let's say he had, some place on this chromosome, there is a gene for hair straightness. Let's say it's a little thing right there. And remember, that gene could be thousands of base pairs. But let's say this is hair straightness."}, {"video_title": "Variation in a Species (4).mp3", "Sentence": "So let's say he had, some place on this chromosome, there is a gene for hair straightness. Let's say it's a little thing right there. And remember, that gene could be thousands of base pairs. But let's say this is hair straightness. So my father's version of that gene, or he had the allele for straightness. And remember, an allele is just a version of a gene. So I'll call it the allele straight for straight hair."}, {"video_title": "Variation in a Species (4).mp3", "Sentence": "But let's say this is hair straightness. So my father's version of that gene, or he had the allele for straightness. And remember, an allele is just a version of a gene. So I'll call it the allele straight for straight hair. Now, this other chromosome that my mother gave me, this essentially, and there are exceptions, but for the most part, it codes for the same genes. And that's why I put them next to each other. So this will also have the gene for hair straightness or curliness."}, {"video_title": "Variation in a Species (4).mp3", "Sentence": "So I'll call it the allele straight for straight hair. Now, this other chromosome that my mother gave me, this essentially, and there are exceptions, but for the most part, it codes for the same genes. And that's why I put them next to each other. So this will also have the gene for hair straightness or curliness. But my mom does happen to actually have curly hair. So she has the gene right there for curly hair. So she has the version of the gene here is, let's see, allele curly."}, {"video_title": "Variation in a Species (4).mp3", "Sentence": "So this will also have the gene for hair straightness or curliness. But my mom does happen to actually have curly hair. So she has the gene right there for curly hair. So she has the version of the gene here is, let's see, allele curly. The gene just says, look, this is the gene for whether or not your hair is curly. Each version of the gene is called an allele. Allele curly."}, {"video_title": "Variation in a Species (4).mp3", "Sentence": "So she has the version of the gene here is, let's see, allele curly. The gene just says, look, this is the gene for whether or not your hair is curly. Each version of the gene is called an allele. Allele curly. Now, when I got both of these in my body, or in my cells, and this is in every cell of my body, every cell of my body except for, and we'll talk a little in a few seconds about my germ cells, but every cell other than the ones that I use for reproduction have this complete set of chromosomes in it, which I find amazing. But only certain chromosomes are, for example, these genes will be completely useless in my fingernails because all of a sudden, the straight and the curly don't matter that much. And I'm simplifying."}, {"video_title": "Variation in a Species (4).mp3", "Sentence": "Allele curly. Now, when I got both of these in my body, or in my cells, and this is in every cell of my body, every cell of my body except for, and we'll talk a little in a few seconds about my germ cells, but every cell other than the ones that I use for reproduction have this complete set of chromosomes in it, which I find amazing. But only certain chromosomes are, for example, these genes will be completely useless in my fingernails because all of a sudden, the straight and the curly don't matter that much. And I'm simplifying. Maybe they will on some other dimension. But let's say for simplicity, they won't matter in certain places. So certain genes are expressed in certain parts of the body, but every one of your body cells, and we call those somatic cells, and we'll separate those from the sex cells or the germ cells that we'll talk about later."}, {"video_title": "Variation in a Species (4).mp3", "Sentence": "And I'm simplifying. Maybe they will on some other dimension. But let's say for simplicity, they won't matter in certain places. So certain genes are expressed in certain parts of the body, but every one of your body cells, and we call those somatic cells, and we'll separate those from the sex cells or the germ cells that we'll talk about later. So this is my body cells. So this is the great majority of your cells. And this is opposed to your germ cells."}, {"video_title": "Variation in a Species (4).mp3", "Sentence": "So certain genes are expressed in certain parts of the body, but every one of your body cells, and we call those somatic cells, and we'll separate those from the sex cells or the germ cells that we'll talk about later. So this is my body cells. So this is the great majority of your cells. And this is opposed to your germ cells. And the germ cells, I'll just write it here just so you get it clear, for a male, that's the sperm cells. And for a female, that's the egg cells or the ova. But most of my cells have a complete collection of these."}, {"video_title": "Variation in a Species (4).mp3", "Sentence": "And this is opposed to your germ cells. And the germ cells, I'll just write it here just so you get it clear, for a male, that's the sperm cells. And for a female, that's the egg cells or the ova. But most of my cells have a complete collection of these. What I want to give you the idea is that for every trait, I essentially have two versions, one from my mother and one from my father. Now these right here are called homologous chromosomes. Chromosomes, homologous."}, {"video_title": "Variation in a Species (4).mp3", "Sentence": "But most of my cells have a complete collection of these. What I want to give you the idea is that for every trait, I essentially have two versions, one from my mother and one from my father. Now these right here are called homologous chromosomes. Chromosomes, homologous. What that means is every time you see the prefix homologous, or if you see like homo sapien, or even the word homosexual or homogeneous, it means same. You see that all the time. So homologous means that they're almost the same."}, {"video_title": "Variation in a Species (4).mp3", "Sentence": "Chromosomes, homologous. What that means is every time you see the prefix homologous, or if you see like homo sapien, or even the word homosexual or homogeneous, it means same. You see that all the time. So homologous means that they're almost the same. They're coding for the most part the same set of genes, but they're not identical. They actually might code for slightly different versions of the same gene. So depending on what versions I get, what is actually expressed for me."}, {"video_title": "Variation in a Species (4).mp3", "Sentence": "So homologous means that they're almost the same. They're coding for the most part the same set of genes, but they're not identical. They actually might code for slightly different versions of the same gene. So depending on what versions I get, what is actually expressed for me. So my genotype, let me introduce another word. And I'm overwhelming you with words here. So my genotype is exactly what alleles I have, what versions of the gene."}, {"video_title": "Variation in a Species (4).mp3", "Sentence": "So depending on what versions I get, what is actually expressed for me. So my genotype, let me introduce another word. And I'm overwhelming you with words here. So my genotype is exactly what alleles I have, what versions of the gene. So I got like the fifth version of the curly allele. There could be multiple versions of the curly allele in our gene pool. And maybe I got some version of the straight allele."}, {"video_title": "Variation in a Species (4).mp3", "Sentence": "So my genotype is exactly what alleles I have, what versions of the gene. So I got like the fifth version of the curly allele. There could be multiple versions of the curly allele in our gene pool. And maybe I got some version of the straight allele. That is my genotype. My phenotype is what my hair really looks like. So for example, two people could have different genotypes with the same, but they might code for hair that looks pretty much the same."}, {"video_title": "Variation in a Species (4).mp3", "Sentence": "And maybe I got some version of the straight allele. That is my genotype. My phenotype is what my hair really looks like. So for example, two people could have different genotypes with the same, but they might code for hair that looks pretty much the same. So it might have a very similar phenotype. So one phenotype can be represented by multiple genotypes. So that's just one thing to think about."}, {"video_title": "Variation in a Species (4).mp3", "Sentence": "So for example, two people could have different genotypes with the same, but they might code for hair that looks pretty much the same. So it might have a very similar phenotype. So one phenotype can be represented by multiple genotypes. So that's just one thing to think about. And we'll talk a lot about that in the future, but I just want to introduce you into that there. Now, I entered this whole discussion because I wanted to talk about variation. So how does variation happen?"}, {"video_title": "Variation in a Species (4).mp3", "Sentence": "So that's just one thing to think about. And we'll talk a lot about that in the future, but I just want to introduce you into that there. Now, I entered this whole discussion because I wanted to talk about variation. So how does variation happen? Well, what's going to happen when I, so first of all, well, let me put it this way. What's going to happen when I reproduce and I have a son? Well, my contribution to my son is going to be a random collection of half of these genes."}, {"video_title": "Variation in a Species (4).mp3", "Sentence": "So how does variation happen? Well, what's going to happen when I, so first of all, well, let me put it this way. What's going to happen when I reproduce and I have a son? Well, my contribution to my son is going to be a random collection of half of these genes. I'm going to contribute either one. For each homologous pair, I'm either going to contribute the one that I got from my mother or the one that I got from my father. So let's say that the sperm cell that went on to fertilize my wife's egg, it just happened to have, let's say it happened to have that one, that one, well, I could just pick one from each of these 23 sets."}, {"video_title": "Variation in a Species (4).mp3", "Sentence": "Well, my contribution to my son is going to be a random collection of half of these genes. I'm going to contribute either one. For each homologous pair, I'm either going to contribute the one that I got from my mother or the one that I got from my father. So let's say that the sperm cell that went on to fertilize my wife's egg, it just happened to have, let's say it happened to have that one, that one, well, I could just pick one from each of these 23 sets. And you could say, well, how many combinations are there? Well, for every set, I can pick one of the two homologous chromosomes, and I'm going to do that 23 times. 2 times 2 times 2, so it's 2 to the 23rd."}, {"video_title": "Variation in a Species (4).mp3", "Sentence": "So let's say that the sperm cell that went on to fertilize my wife's egg, it just happened to have, let's say it happened to have that one, that one, well, I could just pick one from each of these 23 sets. And you could say, well, how many combinations are there? Well, for every set, I can pick one of the two homologous chromosomes, and I'm going to do that 23 times. 2 times 2 times 2, so it's 2 to the 23rd. So there's 22 to the 23 different versions that I can contribute to any son or daughter that I might have. We'll talk about how that happens when we talk about meiosis or mitosis. That when I generate my sperm cells, sperm cells are essentially, instead of having 23 pairs of chromosomes in sperm, you only have 23 chromosomes."}, {"video_title": "Variation in a Species (4).mp3", "Sentence": "2 times 2 times 2, so it's 2 to the 23rd. So there's 22 to the 23 different versions that I can contribute to any son or daughter that I might have. We'll talk about how that happens when we talk about meiosis or mitosis. That when I generate my sperm cells, sperm cells are essentially, instead of having 23 pairs of chromosomes in sperm, you only have 23 chromosomes. So for example, I'll take one from each of those, and through the process of meiosis, which we'll go into, I'll generate a bunch of sperm cells. And each sperm cell will have one from each of these pairs, one version from each of those pairs. So maybe for this chromosome, I get it from my dad."}, {"video_title": "Variation in a Species (4).mp3", "Sentence": "That when I generate my sperm cells, sperm cells are essentially, instead of having 23 pairs of chromosomes in sperm, you only have 23 chromosomes. So for example, I'll take one from each of those, and through the process of meiosis, which we'll go into, I'll generate a bunch of sperm cells. And each sperm cell will have one from each of these pairs, one version from each of those pairs. So maybe for this chromosome, I get it from my dad. From the next chromosome, I get it from my mom. Then I donate a couple more from, I shouldn't have drawn them next to each other, I donate a couple more from my mom, then for the chromosome number 5, it comes from my dad, and so on and so forth. But there's 2 to the 23rd combinations here, because there are 23 pairs that I'm collecting from."}, {"video_title": "Variation in a Species (4).mp3", "Sentence": "So maybe for this chromosome, I get it from my dad. From the next chromosome, I get it from my mom. Then I donate a couple more from, I shouldn't have drawn them next to each other, I donate a couple more from my mom, then for the chromosome number 5, it comes from my dad, and so on and so forth. But there's 2 to the 23rd combinations here, because there are 23 pairs that I'm collecting from. Now, my wife's egg is going to have the same situation. There are 2 to the 23 different combinations of DNA that she can contribute, just based on which of the homologous pairs she will contribute. So the possible combinations that just one couple can produce, and I'm using my life as an example, but you could use this, this applies to everything."}, {"video_title": "Variation in a Species (4).mp3", "Sentence": "But there's 2 to the 23rd combinations here, because there are 23 pairs that I'm collecting from. Now, my wife's egg is going to have the same situation. There are 2 to the 23 different combinations of DNA that she can contribute, just based on which of the homologous pairs she will contribute. So the possible combinations that just one couple can produce, and I'm using my life as an example, but you could use this, this applies to everything. This applies to every species that experiences sexual reproduction. So if I can give 2 to the 23rd combinations of DNA, and my wife can give 2 to the 23 combinations of DNA, then we can produce 2 to the 46th combinations. Now, just to give an idea of how large of a number this is, this is 12,000, roughly 12,000 times the number of human beings on the planet today."}, {"video_title": "Variation in a Species (4).mp3", "Sentence": "So the possible combinations that just one couple can produce, and I'm using my life as an example, but you could use this, this applies to everything. This applies to every species that experiences sexual reproduction. So if I can give 2 to the 23rd combinations of DNA, and my wife can give 2 to the 23 combinations of DNA, then we can produce 2 to the 46th combinations. Now, just to give an idea of how large of a number this is, this is 12,000, roughly 12,000 times the number of human beings on the planet today. So there's a huge amount of variation that even one couple can produce. And if you thought that even that isn't enough, it turns out that amongst these homologous pairs, and we'll talk about when this happens in meiosis, you can actually have DNA recombination. And all that means is that when these homologous pairs during meiosis line up near each other, you can have this thing called crossover, where all of this DNA here crosses over and touches over here, and all of this DNA crosses over and touches over there."}, {"video_title": "Variation in a Species (4).mp3", "Sentence": "Now, just to give an idea of how large of a number this is, this is 12,000, roughly 12,000 times the number of human beings on the planet today. So there's a huge amount of variation that even one couple can produce. And if you thought that even that isn't enough, it turns out that amongst these homologous pairs, and we'll talk about when this happens in meiosis, you can actually have DNA recombination. And all that means is that when these homologous pairs during meiosis line up near each other, you can have this thing called crossover, where all of this DNA here crosses over and touches over here, and all of this DNA crosses over and touches over there. So all of this goes there, and all of this goes there. And what you end up with after the crossover is that one DNA, the one that came from my mom, or that I thought came from my mom, now has a chunk that came from my dad. And the chunk that came from my dad now has a chunk that came from my mom."}, {"video_title": "Variation in a Species (4).mp3", "Sentence": "And all that means is that when these homologous pairs during meiosis line up near each other, you can have this thing called crossover, where all of this DNA here crosses over and touches over here, and all of this DNA crosses over and touches over there. So all of this goes there, and all of this goes there. And what you end up with after the crossover is that one DNA, the one that came from my mom, or that I thought came from my mom, now has a chunk that came from my dad. And the chunk that came from my dad now has a chunk that came from my mom. Let me do it in the right color. It came from my mom like that. And so that even increases the amount of variety even more."}, {"video_title": "Variation in a Species (4).mp3", "Sentence": "And the chunk that came from my dad now has a chunk that came from my mom. Let me do it in the right color. It came from my mom like that. And so that even increases the amount of variety even more. So you can almost now, instead of talking about the different chromosomes that you're contributing, where the chromosomes are each of these collections of DNA, you can almost go to the different combinations at the gene level. And now you can think about an almost infinite form of variation. And you can think about all of the variation that might emerge when you start mixing and mashing different versions of the same gene in a population."}, {"video_title": "Variation in a Species (4).mp3", "Sentence": "And so that even increases the amount of variety even more. So you can almost now, instead of talking about the different chromosomes that you're contributing, where the chromosomes are each of these collections of DNA, you can almost go to the different combinations at the gene level. And now you can think about an almost infinite form of variation. And you can think about all of the variation that might emerge when you start mixing and mashing different versions of the same gene in a population. And you don't just look at one gene. I mean, the reality is that genes by themselves very seldom code for a specific. You can very seldom look for one gene and say, oh, that is brown hair."}, {"video_title": "Variation in a Species (4).mp3", "Sentence": "And you can think about all of the variation that might emerge when you start mixing and mashing different versions of the same gene in a population. And you don't just look at one gene. I mean, the reality is that genes by themselves very seldom code for a specific. You can very seldom look for one gene and say, oh, that is brown hair. Or look for one gene and say, oh, that's intelligence. Or that is how likable someone is. It's usually a whole set of genes interacting in an incredibly complicated way."}, {"video_title": "Variation in a Species (4).mp3", "Sentence": "You can very seldom look for one gene and say, oh, that is brown hair. Or look for one gene and say, oh, that's intelligence. Or that is how likable someone is. It's usually a whole set of genes interacting in an incredibly complicated way. Hair might be coded for by this whole set of genes on multiple chromosomes. And this might be coded for a whole set of genes on multiple chromosomes. And so then you can start thinking about all of the different combinations."}, {"video_title": "Variation in a Species (4).mp3", "Sentence": "It's usually a whole set of genes interacting in an incredibly complicated way. Hair might be coded for by this whole set of genes on multiple chromosomes. And this might be coded for a whole set of genes on multiple chromosomes. And so then you can start thinking about all of the different combinations. And then all of a sudden, maybe some combination that never existed before all of a sudden emerges. And that's very successful. But I'll leave you to think about it because maybe that combination might be passed on or it may not be passed on because of this recombination."}, {"video_title": "Variation in a Species (4).mp3", "Sentence": "And so then you can start thinking about all of the different combinations. And then all of a sudden, maybe some combination that never existed before all of a sudden emerges. And that's very successful. But I'll leave you to think about it because maybe that combination might be passed on or it may not be passed on because of this recombination. But we'll talk more about that in the future. But I wanted to introduce this idea of sexual reproduction to you because this really is the main source of variation within a population. And it's kind of a philosophical idea because we almost take the idea of having males and females for granted because it's this universal idea."}, {"video_title": "Variation in a Species (4).mp3", "Sentence": "But I'll leave you to think about it because maybe that combination might be passed on or it may not be passed on because of this recombination. But we'll talk more about that in the future. But I wanted to introduce this idea of sexual reproduction to you because this really is the main source of variation within a population. And it's kind of a philosophical idea because we almost take the idea of having males and females for granted because it's this universal idea. But I did a little reading on it. It turns out that this actually only emerged about 1.4 billion years ago. That this is almost a useful trait because once you introduce this level of variation, the natural selection can start."}, {"video_title": "Variation in a Species (4).mp3", "Sentence": "And it's kind of a philosophical idea because we almost take the idea of having males and females for granted because it's this universal idea. But I did a little reading on it. It turns out that this actually only emerged about 1.4 billion years ago. That this is almost a useful trait because once you introduce this level of variation, the natural selection can start. You can kind of say that when you have this more powerful form of variation than just pure mutations, and maybe you might have some primitive form of crossover before. But now that you have this sexual reproduction and you have this variation, natural selection can occur in a more efficient way so that species that were able to reproduce and essentially recombine their DNA and mix and match it in this way were able to produce more variety and were able to essentially be selected for the environment in a more efficient way. So they started to essentially outnumber the ones that couldn't."}, {"video_title": "Variation in a Species (4).mp3", "Sentence": "That this is almost a useful trait because once you introduce this level of variation, the natural selection can start. You can kind of say that when you have this more powerful form of variation than just pure mutations, and maybe you might have some primitive form of crossover before. But now that you have this sexual reproduction and you have this variation, natural selection can occur in a more efficient way so that species that were able to reproduce and essentially recombine their DNA and mix and match it in this way were able to produce more variety and were able to essentially be selected for the environment in a more efficient way. So they started to essentially outnumber the ones that couldn't. So it became a kind of a very universal trait. But you could have imagined a world, and there are science fiction books written about this, where you have three genders, where you have gender one, two, three. You could have 10 genders."}, {"video_title": "Variation in a Species (4).mp3", "Sentence": "So they started to essentially outnumber the ones that couldn't. So it became a kind of a very universal trait. But you could have imagined a world, and there are science fiction books written about this, where you have three genders, where you have gender one, two, three. You could have 10 genders. And it just happens to be that on Earth, this notion of having two genders turned out to be a very efficient and stable way of introducing variation into a population. So hopefully you found that interesting. In the next video, I'll go more into the detail of how exactly meiosis and mitosis works."}, {"video_title": "Thomas Hunt Morgan and fruit flies.mp3", "Sentence": "This was based on some observations of meiosis and seeing how chromosomes behaved, and they seemed to behave in analogous ways to some of these inheritable factors, but they really didn't have good cellular proof that chromosomes indeed were the location for these inheritable factors. And we don't really start to get that until we start looking at the work of Thomas Hunt Morgan. Now in 1908, he decides to study fruit flies. So why does he want to study fruit flies? Have you ever seen a fruit fly? They're very, very, very small, so you could actually put a ton of fruit flies in one jar. So that's convenient."}, {"video_title": "Thomas Hunt Morgan and fruit flies.mp3", "Sentence": "So why does he want to study fruit flies? Have you ever seen a fruit fly? They're very, very, very small, so you could actually put a ton of fruit flies in one jar. So that's convenient. You oftentimes don't think about the practical logistics of science, but you could put a lot in one jar. They were actually cheap, and that's another practical concern of science is you don't always have a lot of resources to do your work. And they had short lives, and they reproduced a lot."}, {"video_title": "Thomas Hunt Morgan and fruit flies.mp3", "Sentence": "So that's convenient. You oftentimes don't think about the practical logistics of science, but you could put a lot in one jar. They were actually cheap, and that's another practical concern of science is you don't always have a lot of resources to do your work. And they had short lives, and they reproduced a lot. So you could very quickly get many, many offspring in many, many generations if you wanted to study how the different traits were passed on or not passed on. And so he spent some time, he started this in 1908, working with the fruit flies, and he kept breeding them in search for some type of a mutant trait. In general, when you look at traits in a species, the wild type, let me write this down, the wild type is the one that's typically seen, while the mutant trait is something that seems unusual."}, {"video_title": "Thomas Hunt Morgan and fruit flies.mp3", "Sentence": "And they had short lives, and they reproduced a lot. So you could very quickly get many, many offspring in many, many generations if you wanted to study how the different traits were passed on or not passed on. And so he spent some time, he started this in 1908, working with the fruit flies, and he kept breeding them in search for some type of a mutant trait. In general, when you look at traits in a species, the wild type, let me write this down, the wild type is the one that's typically seen, while the mutant trait is something that seems unusual. And after two years, he finally discovers a mutant trait in his fruit flies. He finds a white-eyed male. So this is the white-eyed male right over here."}, {"video_title": "Thomas Hunt Morgan and fruit flies.mp3", "Sentence": "In general, when you look at traits in a species, the wild type, let me write this down, the wild type is the one that's typically seen, while the mutant trait is something that seems unusual. And after two years, he finally discovers a mutant trait in his fruit flies. He finds a white-eyed male. So this is the white-eyed male right over here. He says, okay, now this is interesting. Let me take this white-eyed male and begin to cross it with other, with, well, with the females. And you say, well, how does this actually occur?"}, {"video_title": "Thomas Hunt Morgan and fruit flies.mp3", "Sentence": "So this is the white-eyed male right over here. He says, okay, now this is interesting. Let me take this white-eyed male and begin to cross it with other, with, well, with the females. And you say, well, how does this actually occur? Well, what you do is you take a jar full of females and you put the white-eyed male in there, and then the crossing happens. And what was interesting was the inheritance pattern that he saw for this white-eyed trait, because you have the parent generation here, but then in the F1 generation, all of the females were red-eyed, and all of the males were red-eyed. And so just off of that first generation, it wasn't clear that anything interesting was going on."}, {"video_title": "Thomas Hunt Morgan and fruit flies.mp3", "Sentence": "And you say, well, how does this actually occur? Well, what you do is you take a jar full of females and you put the white-eyed male in there, and then the crossing happens. And what was interesting was the inheritance pattern that he saw for this white-eyed trait, because you have the parent generation here, but then in the F1 generation, all of the females were red-eyed, and all of the males were red-eyed. And so just off of that first generation, it wasn't clear that anything interesting was going on. But then when he crossed these to each other, and I know what some of y'all are thinking, wait, aren't they all brothers and sisters being crossed to each other? Well, yeah, they're probably half brothers and sisters if they came from different mothers, but some of them could have been brothers and sisters. But yes, that's what people are talking about when they're crossing the F1 generation."}, {"video_title": "Thomas Hunt Morgan and fruit flies.mp3", "Sentence": "And so just off of that first generation, it wasn't clear that anything interesting was going on. But then when he crossed these to each other, and I know what some of y'all are thinking, wait, aren't they all brothers and sisters being crossed to each other? Well, yeah, they're probably half brothers and sisters if they came from different mothers, but some of them could have been brothers and sisters. But yes, that's what people are talking about when they're crossing the F1 generation. But when they crossed these with each other, he saw a pretty interesting pattern. He saw a three to one ratio of red eyes to white eyes. So for every four fruit flies, he would see, let me underline these, he would see three red-eyed, and he would see one white-eyed."}, {"video_title": "Thomas Hunt Morgan and fruit flies.mp3", "Sentence": "But yes, that's what people are talking about when they're crossing the F1 generation. But when they crossed these with each other, he saw a pretty interesting pattern. He saw a three to one ratio of red eyes to white eyes. So for every four fruit flies, he would see, let me underline these, he would see three red-eyed, and he would see one white-eyed. So the white-eyed trait makes a reappearance, which in and of itself is interesting. It shows that this can be passed on genetically, and that's interesting because this was a mutant that just showed up after he did many, many, many, many, many generations of observations. But what was even more interesting about this three to one ratio, and that three to one is something that popped up a lot in Mendelian genetics."}, {"video_title": "Thomas Hunt Morgan and fruit flies.mp3", "Sentence": "So for every four fruit flies, he would see, let me underline these, he would see three red-eyed, and he would see one white-eyed. So the white-eyed trait makes a reappearance, which in and of itself is interesting. It shows that this can be passed on genetically, and that's interesting because this was a mutant that just showed up after he did many, many, many, many, many generations of observations. But what was even more interesting about this three to one ratio, and that three to one is something that popped up a lot in Mendelian genetics. But what was even more interesting was that he only observed, he only observed the white eyes in the males in this F2 generation, in this second generation of the crosses right over there. And so you're thinking, well, why is that a big deal? Well, he was a pretty astute guy, and he says, well, look, if I'm only seeing it in the males, and it's not like he only got four offspring, it was in the ratio, he might have had hundreds of them, but it was in the ratio of two red-eyed females for every one red-eyed male for every one white-eyed male."}, {"video_title": "Thomas Hunt Morgan and fruit flies.mp3", "Sentence": "But what was even more interesting about this three to one ratio, and that three to one is something that popped up a lot in Mendelian genetics. But what was even more interesting was that he only observed, he only observed the white eyes in the males in this F2 generation, in this second generation of the crosses right over there. And so you're thinking, well, why is that a big deal? Well, he was a pretty astute guy, and he says, well, look, if I'm only seeing it in the males, and it's not like he only got four offspring, it was in the ratio, he might have had hundreds of them, but it was in the ratio of two red-eyed females for every one red-eyed male for every one white-eyed male. And so across these hundreds in this generation, he only observed the white eyes on the males. And he said, hmm, maybe this is in some way related to the chromosome that determines sex. And so what he was able to do is say, well, let's just assume that it is."}, {"video_title": "Thomas Hunt Morgan and fruit flies.mp3", "Sentence": "Well, he was a pretty astute guy, and he says, well, look, if I'm only seeing it in the males, and it's not like he only got four offspring, it was in the ratio, he might have had hundreds of them, but it was in the ratio of two red-eyed females for every one red-eyed male for every one white-eyed male. And so across these hundreds in this generation, he only observed the white eyes on the males. And he said, hmm, maybe this is in some way related to the chromosome that determines sex. And so what he was able to do is say, well, let's just assume that it is. Let's assume that that trait, that mutant allele, that mutant variation of the gene for eye color, let's assume it's carried on the X chromosome. And so the genotype for that first mutant fly, that white-eyed male that he found, we could call it, and this is the notation that people typically use, because this is a gene that we're assuming sits on a, it's sex-linked, it sits on a sex chromosome, in this case the X chromosome. The way that you would specify the genotype of that white-eyed male is, well, on his X chromosome, he had the white variation, he had the white allele, the white variation of that gene, and then on his Y chromosome, he had no variation for that gene."}, {"video_title": "Thomas Hunt Morgan and fruit flies.mp3", "Sentence": "And so what he was able to do is say, well, let's just assume that it is. Let's assume that that trait, that mutant allele, that mutant variation of the gene for eye color, let's assume it's carried on the X chromosome. And so the genotype for that first mutant fly, that white-eyed male that he found, we could call it, and this is the notation that people typically use, because this is a gene that we're assuming sits on a, it's sex-linked, it sits on a sex chromosome, in this case the X chromosome. The way that you would specify the genotype of that white-eyed male is, well, on his X chromosome, he had the white variation, he had the white allele, the white variation of that gene, and then on his Y chromosome, he had no variation for that gene. So we assume that it's only contained on the, only on the X chromosome. You've probably heard of heterozygous or homozygous. Well, this is a case where you hemizygous, you only have a version of the allele on one of your two chromosomes, one of the two that you've gotten from each of your parents."}, {"video_title": "Thomas Hunt Morgan and fruit flies.mp3", "Sentence": "The way that you would specify the genotype of that white-eyed male is, well, on his X chromosome, he had the white variation, he had the white allele, the white variation of that gene, and then on his Y chromosome, he had no variation for that gene. So we assume that it's only contained on the, only on the X chromosome. You've probably heard of heterozygous or homozygous. Well, this is a case where you hemizygous, you only have a version of the allele on one of your two chromosomes, one of the two that you've gotten from each of your parents. So this would be the genotype right here of the white-eyed male. The genotype for the red-eyed female is specified by, so it's on the X chromosome, and the females have two X chromosomes, just like in the situation for humans. So on each of the X chromosomes, we assume that the females start off with the red allele."}, {"video_title": "Thomas Hunt Morgan and fruit flies.mp3", "Sentence": "Well, this is a case where you hemizygous, you only have a version of the allele on one of your two chromosomes, one of the two that you've gotten from each of your parents. So this would be the genotype right here of the white-eyed male. The genotype for the red-eyed female is specified by, so it's on the X chromosome, and the females have two X chromosomes, just like in the situation for humans. So on each of the X chromosomes, we assume that the females start off with the red allele. And the red allele, the notation is the W plus, W plus. And you might say, well, why don't we just use the letter R? Well, we could have, but the general convention in genetics is to use the letter of the first mutant type discovered for that gene, and then to use this little plus type for the wild type."}, {"video_title": "Thomas Hunt Morgan and fruit flies.mp3", "Sentence": "So on each of the X chromosomes, we assume that the females start off with the red allele. And the red allele, the notation is the W plus, W plus. And you might say, well, why don't we just use the letter R? Well, we could have, but the general convention in genetics is to use the letter of the first mutant type discovered for that gene, and then to use this little plus type for the wild type. So the wild type is the red eyes, and then W, which is the first mutant discovered for this gene, is the first mutant allele, that we do, so we name it after that white. So this is the white, the white allele, and these right here, these represent the red alleles. So these are the genotype of the red-eyed female."}, {"video_title": "Thomas Hunt Morgan and fruit flies.mp3", "Sentence": "Well, we could have, but the general convention in genetics is to use the letter of the first mutant type discovered for that gene, and then to use this little plus type for the wild type. So the wild type is the red eyes, and then W, which is the first mutant discovered for this gene, is the first mutant allele, that we do, so we name it after that white. So this is the white, the white allele, and these right here, these represent the red alleles. So these are the genotype of the red-eyed female. And so when you cross that first generation, well, the white-eyed male, he can either, if he's with the, he'll either produce sperm that have the X chromosome in it, which is going to contain the allele, or sperm that have the Y chromosome in it, which is not going to contain the allele. And the red-eyed female, well, they produce eggs either way, either which of these X chromosomes they contribute, they're both going to have the wild type allele. And we can see how this crosses."}, {"video_title": "Thomas Hunt Morgan and fruit flies.mp3", "Sentence": "So these are the genotype of the red-eyed female. And so when you cross that first generation, well, the white-eyed male, he can either, if he's with the, he'll either produce sperm that have the X chromosome in it, which is going to contain the allele, or sperm that have the Y chromosome in it, which is not going to contain the allele. And the red-eyed female, well, they produce eggs either way, either which of these X chromosomes they contribute, they're both going to have the wild type allele. And we can see how this crosses. You could get an X from both parents. If you get an X from both parents, you're going to be female, because you're going to be XX. And each of these females, since you got one wild type and one mutant type, and the wild type turns out to be dominant, they still show, their phenotype is still red eyes."}, {"video_title": "Thomas Hunt Morgan and fruit flies.mp3", "Sentence": "And we can see how this crosses. You could get an X from both parents. If you get an X from both parents, you're going to be female, because you're going to be XX. And each of these females, since you got one wild type and one mutant type, and the wild type turns out to be dominant, they still show, their phenotype is still red eyes. They still have red eyes. But now they are heterozygotes. They are carrying the white allele."}, {"video_title": "Thomas Hunt Morgan and fruit flies.mp3", "Sentence": "And each of these females, since you got one wild type and one mutant type, and the wild type turns out to be dominant, they still show, their phenotype is still red eyes. They still have red eyes. But now they are heterozygotes. They are carrying the white allele. Now the male offspring right over here, well, in order to be male, they got the Y chromosome from their dad. So they're not able to get that white allele. And they get the red, the wild type, from their mom."}, {"video_title": "Thomas Hunt Morgan and fruit flies.mp3", "Sentence": "They are carrying the white allele. Now the male offspring right over here, well, in order to be male, they got the Y chromosome from their dad. So they're not able to get that white allele. And they get the red, the wild type, from their mom. And you could see it here. And this is why all of the males in that first generation were red. They only got one copy of the allele from their wild type mother."}, {"video_title": "Thomas Hunt Morgan and fruit flies.mp3", "Sentence": "And they get the red, the wild type, from their mom. And you could see it here. And this is why all of the males in that first generation were red. They only got one copy of the allele from their wild type mother. But then what was interesting is the crosses that you see in that next generation. If you took these red-eyed females that we already established, these are all going to be heterozygotes. And so you could see they have the red allele and they have the white allele."}, {"video_title": "Thomas Hunt Morgan and fruit flies.mp3", "Sentence": "They only got one copy of the allele from their wild type mother. But then what was interesting is the crosses that you see in that next generation. If you took these red-eyed females that we already established, these are all going to be heterozygotes. And so you could see they have the red allele and they have the white allele. And you cross that with red-eyed males. You cross it with red-eyed males. What is going to happen?"}, {"video_title": "Thomas Hunt Morgan and fruit flies.mp3", "Sentence": "And so you could see they have the red allele and they have the white allele. And you cross that with red-eyed males. You cross it with red-eyed males. What is going to happen? Well, the females in this generation, in order to be female, you have to get an X from your mom and your dad. And so they get an X from their dad, which has the mutant, sorry, which has the wild type there, the dominant red allele. And so regardless of which one they got from their mom, they're still going to be red-eyed females."}, {"video_title": "Thomas Hunt Morgan and fruit flies.mp3", "Sentence": "What is going to happen? Well, the females in this generation, in order to be female, you have to get an X from your mom and your dad. And so they get an X from their dad, which has the mutant, sorry, which has the wild type there, the dominant red allele. And so regardless of which one they got from their mom, they're still going to be red-eyed females. Some of them might be homozygotes. Some of them might be heterozygotes. But now we see something interesting happening in the males."}, {"video_title": "Thomas Hunt Morgan and fruit flies.mp3", "Sentence": "And so regardless of which one they got from their mom, they're still going to be red-eyed females. Some of them might be homozygotes. Some of them might be heterozygotes. But now we see something interesting happening in the males. You could have heterozygote male flies here, where they got the X from, where they got the red X from their mom. Or you could get the hemizygous white-eyed males, where they got the white allele, the white X from their mom. And this is the exact observation that Morgan made."}, {"video_title": "Thomas Hunt Morgan and fruit flies.mp3", "Sentence": "But now we see something interesting happening in the males. You could have heterozygote male flies here, where they got the X from, where they got the red X from their mom. Or you could get the hemizygous white-eyed males, where they got the white allele, the white X from their mom. And this is the exact observation that Morgan made. So it was a very interesting thing that he was able to see. He started breeding these in 1908. He started breeding these flies in 1908."}, {"video_title": "Thomas Hunt Morgan and fruit flies.mp3", "Sentence": "And this is the exact observation that Morgan made. So it was a very interesting thing that he was able to see. He started breeding these in 1908. He started breeding these flies in 1908. It wasn't until a couple of years that he finally found that first mutant white-eyed male. And it was in 1910 and 1911 that he publishes these discoveries in Nature. And the reason why this is a big deal is he says, look, my observations are completely consistent with this eye trait, this gene, being on the X chromosome."}, {"video_title": "Thomas Hunt Morgan and fruit flies.mp3", "Sentence": "He started breeding these flies in 1908. It wasn't until a couple of years that he finally found that first mutant white-eyed male. And it was in 1910 and 1911 that he publishes these discoveries in Nature. And the reason why this is a big deal is he says, look, my observations are completely consistent with this eye trait, this gene, being on the X chromosome. So he was able to show a direct linkage between, in this case, sex chromosomes, and these heritable factors that Mendel first talked about. And he would go on, and his students that he worked with would go on to study this for many, many, many, many years. And he actually ends up getting a Nobel Prize for this work."}, {"video_title": "Thomas Hunt Morgan and fruit flies.mp3", "Sentence": "And the reason why this is a big deal is he says, look, my observations are completely consistent with this eye trait, this gene, being on the X chromosome. So he was able to show a direct linkage between, in this case, sex chromosomes, and these heritable factors that Mendel first talked about. And he would go on, and his students that he worked with would go on to study this for many, many, many, many years. And he actually ends up getting a Nobel Prize for this work. And this is a big deal, because he's finally able to draw pretty substantive connections between these heritable factors of Mendel, this theory of Bovary and Sutton, that maybe chromosomes have something to do with these inheritable factors. And he's showing that this is actually the case. These sex chromosomes seem to carry the trait, or in this particular case, the X sex chromosome seems to carry the gene for eye color in these fruit flies."}, {"video_title": "Cell cycle control   Cells   MCAT   Khan Academy.mp3", "Sentence": "In fact, there are two key places that we have extensive regulation of the cell cycle. The first checkpoint is right here between the G1 and the S phase. So we regulate before we get to the point of DNA replication. The other major checkpoint is right here between G2 and the step where we jump right to mitosis. And there are a couple of proteins that regulate this process. Two main ones are called cyclin-dependent kinases. So cyclin-dependent kinases, which as you may recall, a kinase is something that adds a phosphate group."}, {"video_title": "Cell cycle control   Cells   MCAT   Khan Academy.mp3", "Sentence": "The other major checkpoint is right here between G2 and the step where we jump right to mitosis. And there are a couple of proteins that regulate this process. Two main ones are called cyclin-dependent kinases. So cyclin-dependent kinases, which as you may recall, a kinase is something that adds a phosphate group. So I'll put in parentheses, it'll plus a phosphate group. And it'll add a phosphate group on other enzymes or proteins to either activate or inactivate them. And these cyclin-dependent kinases will work together with a protein you might be able to guess the name of, cyclins."}, {"video_title": "Cell cycle control   Cells   MCAT   Khan Academy.mp3", "Sentence": "So cyclin-dependent kinases, which as you may recall, a kinase is something that adds a phosphate group. So I'll put in parentheses, it'll plus a phosphate group. And it'll add a phosphate group on other enzymes or proteins to either activate or inactivate them. And these cyclin-dependent kinases will work together with a protein you might be able to guess the name of, cyclins. Because what else would these kinases depend on? So an important thing to notice is that these cyclin-dependent kinases or CDKs are always present. All the different types are always present in a cell, but their default form or their default function is for them to be inactive."}, {"video_title": "Cell cycle control   Cells   MCAT   Khan Academy.mp3", "Sentence": "And these cyclin-dependent kinases will work together with a protein you might be able to guess the name of, cyclins. Because what else would these kinases depend on? So an important thing to notice is that these cyclin-dependent kinases or CDKs are always present. All the different types are always present in a cell, but their default form or their default function is for them to be inactive. And so they need to be activated by these cyclin proteins. And the point of regulation here is that specific cyclins, so I'll write specific with just spec, so specific cyclins are made at specific times. And again, the reason why they're both so important is that when you have a cyclin-dependent kinase, it is only active when they are bound to a specific cyclin."}, {"video_title": "Cell cycle control   Cells   MCAT   Khan Academy.mp3", "Sentence": "All the different types are always present in a cell, but their default form or their default function is for them to be inactive. And so they need to be activated by these cyclin proteins. And the point of regulation here is that specific cyclins, so I'll write specific with just spec, so specific cyclins are made at specific times. And again, the reason why they're both so important is that when you have a cyclin-dependent kinase, it is only active when they are bound to a specific cyclin. It's at this point again that this guy is active. And the CDK is the business end of this complex. So that's the reason why in G1 you'll see the production of cyclins D and cyclin E. And from there you'll see CDK2 bound to your cyclin E, and at the same time you'll also have your CDK4 bound to your cyclin D. These activated kinases then, specifically the CDK4 cyclin D complex, will phosphorylate a protein called RB."}, {"video_title": "Cell cycle control   Cells   MCAT   Khan Academy.mp3", "Sentence": "And again, the reason why they're both so important is that when you have a cyclin-dependent kinase, it is only active when they are bound to a specific cyclin. It's at this point again that this guy is active. And the CDK is the business end of this complex. So that's the reason why in G1 you'll see the production of cyclins D and cyclin E. And from there you'll see CDK2 bound to your cyclin E, and at the same time you'll also have your CDK4 bound to your cyclin D. These activated kinases then, specifically the CDK4 cyclin D complex, will phosphorylate a protein called RB. So I'll draw just a little reaction over here where we add a phosphate group on our RB protein. So when RB is phosphorylated, it can't inhibit DNA replication like it usually is supposed to do. The phosphate group renders it inactive."}, {"video_title": "Cell cycle control   Cells   MCAT   Khan Academy.mp3", "Sentence": "So that's the reason why in G1 you'll see the production of cyclins D and cyclin E. And from there you'll see CDK2 bound to your cyclin E, and at the same time you'll also have your CDK4 bound to your cyclin D. These activated kinases then, specifically the CDK4 cyclin D complex, will phosphorylate a protein called RB. So I'll draw just a little reaction over here where we add a phosphate group on our RB protein. So when RB is phosphorylated, it can't inhibit DNA replication like it usually is supposed to do. The phosphate group renders it inactive. And this is sort of the setup we have as we go further on in our cell cycle. In the S phase we have cyclin A produced. Cyclin A will complex again with CDK2 most directly to activate DNA replication."}, {"video_title": "Cell cycle control   Cells   MCAT   Khan Academy.mp3", "Sentence": "The phosphate group renders it inactive. And this is sort of the setup we have as we go further on in our cell cycle. In the S phase we have cyclin A produced. Cyclin A will complex again with CDK2 most directly to activate DNA replication. So it helps to activate DNA replication. And in a similar way we have cyclin B only produced in the G2 phase because the cyclin B CDK1 complex is able to activate, activate, what step do you think? Mitosis or cell division."}, {"video_title": "Impact of mutations on translation into amino acids   High school biology   Khan Academy.mp3", "Sentence": "And the letters I'm going to use, these are the shorthands for the various nucleotide bases that make up a sequence of DNA. So let's say that I have some thymine, thymine, cytosine, guanine, cytosine, thymine, adenine, thymine, thymine, and let's throw another thymine in there. So that would be our sequence of DNA. And what would be the corresponding sequence of RNA that it would be transcribed into? If you remember this from previous videos, pause this video and try to figure that out. Well, the key thing to appreciate is if we're talking about base pairs in DNA, adenine pairs with thymine, cytosine pairs with guanine. But if we're talking about pairing into RNA, well then, instead of thymine in the RNA, you would have uracil."}, {"video_title": "Impact of mutations on translation into amino acids   High school biology   Khan Academy.mp3", "Sentence": "And what would be the corresponding sequence of RNA that it would be transcribed into? If you remember this from previous videos, pause this video and try to figure that out. Well, the key thing to appreciate is if we're talking about base pairs in DNA, adenine pairs with thymine, cytosine pairs with guanine. But if we're talking about pairing into RNA, well then, instead of thymine in the RNA, you would have uracil. So the RNA here is, well, the thymine in the DNA would correspond to an adenine in the RNA. Adenine, guanine, cytosine, guanine, adenine. And now since this is an RNA strand, instead of having a thymine right over here, this would be a uracil."}, {"video_title": "Impact of mutations on translation into amino acids   High school biology   Khan Academy.mp3", "Sentence": "But if we're talking about pairing into RNA, well then, instead of thymine in the RNA, you would have uracil. So the RNA here is, well, the thymine in the DNA would correspond to an adenine in the RNA. Adenine, guanine, cytosine, guanine, adenine. And now since this is an RNA strand, instead of having a thymine right over here, this would be a uracil. Adenine, adenine, adenine. So this process that we just did, this is transcription. Transcription, transcription."}, {"video_title": "Impact of mutations on translation into amino acids   High school biology   Khan Academy.mp3", "Sentence": "And now since this is an RNA strand, instead of having a thymine right over here, this would be a uracil. Adenine, adenine, adenine. So this process that we just did, this is transcription. Transcription, transcription. Transcription from DNA, DNA to RNA. Now the next step, if we're talking about the whole process of how does this information actually have an effect on the body is we're gonna go from the RNA and translate that into a protein. And the way we do that, we've seen this in previous videos, is every three of these bases, that's a codon, that it codes for a particular amino acid."}, {"video_title": "Impact of mutations on translation into amino acids   High school biology   Khan Academy.mp3", "Sentence": "Transcription, transcription. Transcription from DNA, DNA to RNA. Now the next step, if we're talking about the whole process of how does this information actually have an effect on the body is we're gonna go from the RNA and translate that into a protein. And the way we do that, we've seen this in previous videos, is every three of these bases, that's a codon, that it codes for a particular amino acid. Now to figure out what amino acid it codes for, we look at an amino acid translation table. And there's different types that you might see. This is the most typical type."}, {"video_title": "Impact of mutations on translation into amino acids   High school biology   Khan Academy.mp3", "Sentence": "And the way we do that, we've seen this in previous videos, is every three of these bases, that's a codon, that it codes for a particular amino acid. Now to figure out what amino acid it codes for, we look at an amino acid translation table. And there's different types that you might see. This is the most typical type. So the first base is A, second base is A, third base is G. First base A, second base A, we're in this cell, third base is G. And so that will code for the amino acid lysine. So we could write L-Y-S, short for lysine here. We could have also gotten that from a different type of translation table."}, {"video_title": "Impact of mutations on translation into amino acids   High school biology   Khan Academy.mp3", "Sentence": "This is the most typical type. So the first base is A, second base is A, third base is G. First base A, second base A, we're in this cell, third base is G. And so that will code for the amino acid lysine. So we could write L-Y-S, short for lysine here. We could have also gotten that from a different type of translation table. For example, you might see a circular one that looks like that. But we would have gotten the same result. A-A-G, start at the center, A-A-G codes for lysine."}, {"video_title": "Impact of mutations on translation into amino acids   High school biology   Khan Academy.mp3", "Sentence": "We could have also gotten that from a different type of translation table. For example, you might see a circular one that looks like that. But we would have gotten the same result. A-A-G, start at the center, A-A-G codes for lysine. Then the next codon, and if you're getting as excited about this as I am, I encourage you to pause this video and try to keep translating this. The next codon is C-G-A, C-G-A, arginine. C-G-A, arginine, arginine."}, {"video_title": "Impact of mutations on translation into amino acids   High school biology   Khan Academy.mp3", "Sentence": "A-A-G, start at the center, A-A-G codes for lysine. Then the next codon, and if you're getting as excited about this as I am, I encourage you to pause this video and try to keep translating this. The next codon is C-G-A, C-G-A, arginine. C-G-A, arginine, arginine. And then the next one is U-A-A, U-A-A. Well here they have this little black circular dot. What does that mean?"}, {"video_title": "Impact of mutations on translation into amino acids   High school biology   Khan Academy.mp3", "Sentence": "C-G-A, arginine, arginine. And then the next one is U-A-A, U-A-A. Well here they have this little black circular dot. What does that mean? Well that means stop codon. And sometimes they'll just write the word stop there. So this is stop."}, {"video_title": "Impact of mutations on translation into amino acids   High school biology   Khan Academy.mp3", "Sentence": "What does that mean? Well that means stop codon. And sometimes they'll just write the word stop there. So this is stop. There is not an amino acid called stop. This actually signals to, and this is happening in a ribosome, this is signaling for the translation process to stop. This is the end of our amino acid chain, of our polypeptide chain."}, {"video_title": "Impact of mutations on translation into amino acids   High school biology   Khan Academy.mp3", "Sentence": "So this is stop. There is not an amino acid called stop. This actually signals to, and this is happening in a ribosome, this is signaling for the translation process to stop. This is the end of our amino acid chain, of our polypeptide chain. And so we will stop right over there. But now let's do some interesting things. Let's think about situations where there are mutations, where some of these bases, maybe something gets inserted, maybe something gets deleted, maybe something gets swapped out."}, {"video_title": "Impact of mutations on translation into amino acids   High school biology   Khan Academy.mp3", "Sentence": "This is the end of our amino acid chain, of our polypeptide chain. And so we will stop right over there. But now let's do some interesting things. Let's think about situations where there are mutations, where some of these bases, maybe something gets inserted, maybe something gets deleted, maybe something gets swapped out. And so let's start with what's known as a point mutation. So let's say this C gets swapped out for an A. Well if that happened, then on the RNA strand, all of a sudden this would be a uracil."}, {"video_title": "Impact of mutations on translation into amino acids   High school biology   Khan Academy.mp3", "Sentence": "Let's think about situations where there are mutations, where some of these bases, maybe something gets inserted, maybe something gets deleted, maybe something gets swapped out. And so let's start with what's known as a point mutation. So let's say this C gets swapped out for an A. Well if that happened, then on the RNA strand, all of a sudden this would be a uracil. And if that is a uracil, this A-A-G would still be there, coding for lysine, but this second codon is now different. What would it now code for? Well C-U-A, C-U-A."}, {"video_title": "Impact of mutations on translation into amino acids   High school biology   Khan Academy.mp3", "Sentence": "Well if that happened, then on the RNA strand, all of a sudden this would be a uracil. And if that is a uracil, this A-A-G would still be there, coding for lysine, but this second codon is now different. What would it now code for? Well C-U-A, C-U-A. It'll now code for leucine instead of arginine. Leucine, L-E-U. This is fairly typical for a substitution mutation."}, {"video_title": "Impact of mutations on translation into amino acids   High school biology   Khan Academy.mp3", "Sentence": "Well C-U-A, C-U-A. It'll now code for leucine instead of arginine. Leucine, L-E-U. This is fairly typical for a substitution mutation. It might change a particular amino acid. But sometimes it could be more significant. For example, if this G was swapped out for an A, then this C on the RNA would then be a U, and then what would happen?"}, {"video_title": "Impact of mutations on translation into amino acids   High school biology   Khan Academy.mp3", "Sentence": "This is fairly typical for a substitution mutation. It might change a particular amino acid. But sometimes it could be more significant. For example, if this G was swapped out for an A, then this C on the RNA would then be a U, and then what would happen? Well this first codon would still code for lysine, but the second one would be U-G-A. U-G-A. Now all of a sudden it codes for a stop codon."}, {"video_title": "Impact of mutations on translation into amino acids   High school biology   Khan Academy.mp3", "Sentence": "For example, if this G was swapped out for an A, then this C on the RNA would then be a U, and then what would happen? Well this first codon would still code for lysine, but the second one would be U-G-A. U-G-A. Now all of a sudden it codes for a stop codon. And so the actual translation process would stop, which could be a very, very big deal if this DNA sequence, if the normal non-mutated polypeptide had to keep going on and on and on. Over here it just happened to have a stop codon next, but you can imagine if they had just another thousand codons before the end, but all of a sudden you had a point mutation to stop early, that would significantly affect the protein that it's coding for. Now another type of mutation that typically has a fairly significant effect is a frame shift mutation."}, {"video_title": "Impact of mutations on translation into amino acids   High school biology   Khan Academy.mp3", "Sentence": "Now all of a sudden it codes for a stop codon. And so the actual translation process would stop, which could be a very, very big deal if this DNA sequence, if the normal non-mutated polypeptide had to keep going on and on and on. Over here it just happened to have a stop codon next, but you can imagine if they had just another thousand codons before the end, but all of a sudden you had a point mutation to stop early, that would significantly affect the protein that it's coding for. Now another type of mutation that typically has a fairly significant effect is a frame shift mutation. And that's where something gets inserted or deleted and shifts everything. So for example, instead of the A being swapped in for the G, what if the A got inserted here? So then our sequence would look like this."}, {"video_title": "Impact of mutations on translation into amino acids   High school biology   Khan Academy.mp3", "Sentence": "Now another type of mutation that typically has a fairly significant effect is a frame shift mutation. And that's where something gets inserted or deleted and shifts everything. So for example, instead of the A being swapped in for the G, what if the A got inserted here? So then our sequence would look like this. T-T-C, and then we have A, and then you have G-C-T, G-C-T-A-T-T-T. So what just happened here, this was our original sequence, but the A got inserted here, it didn't replace the G, and so everything got shifted to the right. Now what are we coding for?"}, {"video_title": "Impact of mutations on translation into amino acids   High school biology   Khan Academy.mp3", "Sentence": "So then our sequence would look like this. T-T-C, and then we have A, and then you have G-C-T, G-C-T-A-T-T-T. So what just happened here, this was our original sequence, but the A got inserted here, it didn't replace the G, and so everything got shifted to the right. Now what are we coding for? Well when we transcribe to RNA, this will be A-A-G-U-C-G-A-U-A-A. And now this first codon still codes for lysine, we've seen that multiple times. But what about this second codon?"}, {"video_title": "Impact of mutations on translation into amino acids   High school biology   Khan Academy.mp3", "Sentence": "Now what are we coding for? Well when we transcribe to RNA, this will be A-A-G-U-C-G-A-U-A-A. And now this first codon still codes for lysine, we've seen that multiple times. But what about this second codon? The second codon over here, U-C-G, U-C-G, that's serine. U-C-G, that's serine. We got a different amino acid."}, {"video_title": "Impact of mutations on translation into amino acids   High school biology   Khan Academy.mp3", "Sentence": "But what about this second codon? The second codon over here, U-C-G, U-C-G, that's serine. U-C-G, that's serine. We got a different amino acid. And what's interesting is, it's not just that one amino acid is changing, we're gonna see that keeps happening. So now we have A-U-A, A-U-A. Here we have isoleucine, so isoleucine right over here, which is different than what we had before, we now don't have a stop codon anymore."}, {"video_title": "Impact of mutations on translation into amino acids   High school biology   Khan Academy.mp3", "Sentence": "We got a different amino acid. And what's interesting is, it's not just that one amino acid is changing, we're gonna see that keeps happening. So now we have A-U-A, A-U-A. Here we have isoleucine, so isoleucine right over here, which is different than what we had before, we now don't have a stop codon anymore. We would keep going on and on. And so you can imagine a frame shift mutation, where you either insert something or you take it out, so that the whole frame gets shifted, can have a dramatic impact on what it will transcribe and then translate for. Now lucky for us, even though mutations are always going on, there are many proofreading mechanisms in biological systems to make them less frequent than they otherwise would be."}, {"video_title": "Impact of mutations on translation into amino acids   High school biology   Khan Academy.mp3", "Sentence": "Here we have isoleucine, so isoleucine right over here, which is different than what we had before, we now don't have a stop codon anymore. We would keep going on and on. And so you can imagine a frame shift mutation, where you either insert something or you take it out, so that the whole frame gets shifted, can have a dramatic impact on what it will transcribe and then translate for. Now lucky for us, even though mutations are always going on, there are many proofreading mechanisms in biological systems to make them less frequent than they otherwise would be. And people are still understanding how these proofreading mechanisms fully happen. Another thing to appreciate is, we often associate a mutation as being equal to a bad thing. And oftentimes, it is a bad thing."}, {"video_title": "Impact of mutations on translation into amino acids   High school biology   Khan Academy.mp3", "Sentence": "Now lucky for us, even though mutations are always going on, there are many proofreading mechanisms in biological systems to make them less frequent than they otherwise would be. And people are still understanding how these proofreading mechanisms fully happen. Another thing to appreciate is, we often associate a mutation as being equal to a bad thing. And oftentimes, it is a bad thing. What used to be a functional protein may no longer be a functional protein, because the amino acids, the coding got stopped short, or there was a frame shift mutation, it's just coding for completely different things. So sometimes it could be very bad, and some diseases actually are caused by strange mutations like that that show up. Oftentimes, the mutation might not be a big deal."}, {"video_title": "Impact of mutations on translation into amino acids   High school biology   Khan Academy.mp3", "Sentence": "And oftentimes, it is a bad thing. What used to be a functional protein may no longer be a functional protein, because the amino acids, the coding got stopped short, or there was a frame shift mutation, it's just coding for completely different things. So sometimes it could be very bad, and some diseases actually are caused by strange mutations like that that show up. Oftentimes, the mutation might not be a big deal. Maybe something gets swapped out, maybe only one amino acid changes, and it doesn't really change the ability of the protein to do its job, in which case it doesn't matter. But every now and then, a mutation can actually be a good thing. In fact, we need the mutation in order to have variation in a population."}, {"video_title": "Impact of mutations on translation into amino acids   High school biology   Khan Academy.mp3", "Sentence": "Oftentimes, the mutation might not be a big deal. Maybe something gets swapped out, maybe only one amino acid changes, and it doesn't really change the ability of the protein to do its job, in which case it doesn't matter. But every now and then, a mutation can actually be a good thing. In fact, we need the mutation in order to have variation in a population. And variation is what natural selection and evolution run off. If you don't have variation, then you're not going to have different things that get selected in different environments, and you're not going to have that gradual change over time. So big picture, hopefully you got a better appreciation for how transcription and then translation, let me write that down, and then, so that's transcription from DNA to RNA, and then this is translation, translation from RNA to protein, to protein, to protein."}, {"video_title": "Non-coding RNA (ncRNA)   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "What is a non-coding RNA? Well, a non-coding RNA, or an NCRNA, as it is abbreviated, is a functional RNA molecule that actually skips this last step, and is not translated into a protein. In other words, they just go directly from transcription into an RNA molecule, and then go off to perform any number of vital functions within the cell. And there are many examples of non-coding RNAs, including microRNAs, ribosomal RNA, transfer RNA, the list goes on and on. And as we go through each of these different types and examples of non-coding RNAs, you'll start to see that there's sort of an emerging theme here, and that is that most of these non-coding RNAs participate in either transcription or translation in one capacity or another. So let's start off with microRNAs. MicroRNAs, or mRNAs, function in transcriptional and post-transcriptional regulation of gene expression, and they do this by base pairing with complementary sequences within mRNA or messenger RNA molecules."}, {"video_title": "Non-coding RNA (ncRNA)   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "And there are many examples of non-coding RNAs, including microRNAs, ribosomal RNA, transfer RNA, the list goes on and on. And as we go through each of these different types and examples of non-coding RNAs, you'll start to see that there's sort of an emerging theme here, and that is that most of these non-coding RNAs participate in either transcription or translation in one capacity or another. So let's start off with microRNAs. MicroRNAs, or mRNAs, function in transcriptional and post-transcriptional regulation of gene expression, and they do this by base pairing with complementary sequences within mRNA or messenger RNA molecules. And this usually results in gene silencing through translational repression or target degradation. In essence, the mRNA to which these microRNAs bind are prevented from being translated, or they are sent on a pathway for degradation. Now, the next set of non-coding RNAs that we'll be talking about are all involved in translation, the first of which is ribosomal RNA."}, {"video_title": "Non-coding RNA (ncRNA)   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "MicroRNAs, or mRNAs, function in transcriptional and post-transcriptional regulation of gene expression, and they do this by base pairing with complementary sequences within mRNA or messenger RNA molecules. And this usually results in gene silencing through translational repression or target degradation. In essence, the mRNA to which these microRNAs bind are prevented from being translated, or they are sent on a pathway for degradation. Now, the next set of non-coding RNAs that we'll be talking about are all involved in translation, the first of which is ribosomal RNA. Now, ribosomes are the cellular machinery used to translate mRNA into proteins, and it is made up of one type of RNA molecule, ribosomal RNA. Transfer RNAs are an adapter molecule that links the codons in an mRNA strand to the corresponding amino acids. And so this is another type of non-coding RNA that you'll see in translation."}, {"video_title": "Non-coding RNA (ncRNA)   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "Now, the next set of non-coding RNAs that we'll be talking about are all involved in translation, the first of which is ribosomal RNA. Now, ribosomes are the cellular machinery used to translate mRNA into proteins, and it is made up of one type of RNA molecule, ribosomal RNA. Transfer RNAs are an adapter molecule that links the codons in an mRNA strand to the corresponding amino acids. And so this is another type of non-coding RNA that you'll see in translation. The third type is called SNO-RNA, which stands for small nucleolar RNA, and it's a class of small RNA molecules that guide covalent modifications of ribosomal RNA, transfer RNA, and small nuclear RNAs, primarily through methylation, which is the addition of methyl groups, or pseudouridylation, which is the addition of an isomer of the nucleoside uridine. Now, another class of non-coding RNAs are the small nuclear RNAs, or SNRNAs, not to be confused with the SNO-RNAs, the small nucleolar RNAs that we just talked about. Now, small nuclear RNAs get their name from the fact that the average length of these RNA molecules is approximately 150 nucleotides, and their primary function is in the processing of pre-mRNA in the nucleus."}, {"video_title": "Non-coding RNA (ncRNA)   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "And so this is another type of non-coding RNA that you'll see in translation. The third type is called SNO-RNA, which stands for small nucleolar RNA, and it's a class of small RNA molecules that guide covalent modifications of ribosomal RNA, transfer RNA, and small nuclear RNAs, primarily through methylation, which is the addition of methyl groups, or pseudouridylation, which is the addition of an isomer of the nucleoside uridine. Now, another class of non-coding RNAs are the small nuclear RNAs, or SNRNAs, not to be confused with the SNO-RNAs, the small nucleolar RNAs that we just talked about. Now, small nuclear RNAs get their name from the fact that the average length of these RNA molecules is approximately 150 nucleotides, and their primary function is in the processing of pre-mRNA in the nucleus. They also aid in the regulation of transcription factors, or a particular RNA polymerase, RNA polymerase II, as well as maintaining telomeres, which are the regions of repetitive nucleotide sequences at the end of a chromatid, which protects the end of the chromosome from deterioration during chromosomal replication. Now, SNRNA can be associated with a set of specific proteins, and form complexes that are called small nuclear ribonucleoproteins, or SNRNPs, or sometimes people just call them SNRPs. And there is a special SNRP complex called the spliceosome made up of five small nuclear RNAs and over 150 proteins that is responsible for splicing or removing the introns contained in messenger RNA, which is a major step in the post-transcriptional modification that takes place in the nucleus of eukaryotes."}, {"video_title": "Membrane Receptors   Nervous system physiology   NCLEX-RN   Khan Academy.mp3", "Sentence": "In this video, we're going to talk a little bit about membrane receptors. Membrane receptors are really important because they are the things that actually allow our cells to communicate with the outside world. Without membrane receptors, our cells wouldn't be able to work together and they wouldn't be able to form the human body as we know it. A membrane receptor is essentially an integral protein that is embedded in the cell membrane that takes part in communication with the outside environment. For short, I'm just going to say it's an integral protein that communicates with the outside environment. The way membrane receptors work is that in our bodies, there are a bunch of these signaling molecules going around. We call these extracellular signaling molecules because they are outsider cells."}, {"video_title": "Membrane Receptors   Nervous system physiology   NCLEX-RN   Khan Academy.mp3", "Sentence": "A membrane receptor is essentially an integral protein that is embedded in the cell membrane that takes part in communication with the outside environment. For short, I'm just going to say it's an integral protein that communicates with the outside environment. The way membrane receptors work is that in our bodies, there are a bunch of these signaling molecules going around. We call these extracellular signaling molecules because they are outsider cells. Let's say this outside area is the extracellular portion. Let's say we have a pink signaling molecule. For the sake of diagramming, I'm going to say it looks like a triangle."}, {"video_title": "Membrane Receptors   Nervous system physiology   NCLEX-RN   Khan Academy.mp3", "Sentence": "We call these extracellular signaling molecules because they are outsider cells. Let's say this outside area is the extracellular portion. Let's say we have a pink signaling molecule. For the sake of diagramming, I'm going to say it looks like a triangle. In reality, signaling molecules do not look like triangles. Signaling molecules can be a variety of things. They can be ions or molecules, essentially, that bind to another chemical entity."}, {"video_title": "Membrane Receptors   Nervous system physiology   NCLEX-RN   Khan Academy.mp3", "Sentence": "For the sake of diagramming, I'm going to say it looks like a triangle. In reality, signaling molecules do not look like triangles. Signaling molecules can be a variety of things. They can be ions or molecules, essentially, that bind to another chemical entity. We also call these ligands. A ligand can be something like a neurotransmitter, a hormone, cell recognition molecules. What these can do is these can attach to our membrane receptors and trigger changes inside the cell."}, {"video_title": "Membrane Receptors   Nervous system physiology   NCLEX-RN   Khan Academy.mp3", "Sentence": "They can be ions or molecules, essentially, that bind to another chemical entity. We also call these ligands. A ligand can be something like a neurotransmitter, a hormone, cell recognition molecules. What these can do is these can attach to our membrane receptors and trigger changes inside the cell. I'm going to do the membrane receptors in a nice blue color. Remember we say they're integral proteins. Integral proteins are proteins that go through the entire cell membrane."}, {"video_title": "Membrane Receptors   Nervous system physiology   NCLEX-RN   Khan Academy.mp3", "Sentence": "What these can do is these can attach to our membrane receptors and trigger changes inside the cell. I'm going to do the membrane receptors in a nice blue color. Remember we say they're integral proteins. Integral proteins are proteins that go through the entire cell membrane. Let's say here we have our nice integral protein. What will happen, essentially, is this ligand will bind to our integral protein. This integral protein, which again appears in our cell membrane, will actually bind to that nice triangle-shaped ligand that we have, like this."}, {"video_title": "Membrane Receptors   Nervous system physiology   NCLEX-RN   Khan Academy.mp3", "Sentence": "Integral proteins are proteins that go through the entire cell membrane. Let's say here we have our nice integral protein. What will happen, essentially, is this ligand will bind to our integral protein. This integral protein, which again appears in our cell membrane, will actually bind to that nice triangle-shaped ligand that we have, like this. Now what we have is our ligand receptor complex. Just a fancy way of saying our ligand and our membrane receptor have bound. Once this happens, this can essentially tell the cell what to do."}, {"video_title": "Membrane Receptors   Nervous system physiology   NCLEX-RN   Khan Academy.mp3", "Sentence": "This integral protein, which again appears in our cell membrane, will actually bind to that nice triangle-shaped ligand that we have, like this. Now what we have is our ligand receptor complex. Just a fancy way of saying our ligand and our membrane receptor have bound. Once this happens, this can essentially tell the cell what to do. This can explain things like how hormones function, how our nerve impulses work, why our cells divide, cell death. It also explains why our cell allows certain things into the cell and other things not sometimes. In terms of a bigger real-world application, this is really critically important in designing pharmaceutical drugs."}, {"video_title": "Membrane Receptors   Nervous system physiology   NCLEX-RN   Khan Academy.mp3", "Sentence": "Once this happens, this can essentially tell the cell what to do. This can explain things like how hormones function, how our nerve impulses work, why our cells divide, cell death. It also explains why our cell allows certain things into the cell and other things not sometimes. In terms of a bigger real-world application, this is really critically important in designing pharmaceutical drugs. In fact, a very big percentage of pharmaceutical drugs actually target our membrane receptors. This is actually why some drugs can target specific cells. Some drugs might only target your liver, while other drugs might target your heart."}, {"video_title": "Membrane Receptors   Nervous system physiology   NCLEX-RN   Khan Academy.mp3", "Sentence": "In terms of a bigger real-world application, this is really critically important in designing pharmaceutical drugs. In fact, a very big percentage of pharmaceutical drugs actually target our membrane receptors. This is actually why some drugs can target specific cells. Some drugs might only target your liver, while other drugs might target your heart. The reason why is because different cells might actually have different receptors, and these receptors might bind different things. This whole process of binding and telling the cell what to do, we actually have a really special name for it. It's called signal transduction."}, {"video_title": "Membrane Receptors   Nervous system physiology   NCLEX-RN   Khan Academy.mp3", "Sentence": "Some drugs might only target your liver, while other drugs might target your heart. The reason why is because different cells might actually have different receptors, and these receptors might bind different things. This whole process of binding and telling the cell what to do, we actually have a really special name for it. It's called signal transduction. This is a process that we call signal transduction. What happens during signal transduction is an extracellular signal molecule, so this is our ligand, binds to our membrane receptor. These receptor proteins then cause an intracellular response."}, {"video_title": "Membrane Receptors   Nervous system physiology   NCLEX-RN   Khan Academy.mp3", "Sentence": "It's called signal transduction. This is a process that we call signal transduction. What happens during signal transduction is an extracellular signal molecule, so this is our ligand, binds to our membrane receptor. These receptor proteins then cause an intracellular response. After binding, there will be what's called an intracellular response. This receptor will bind to the protein, and this will cause the protein to actually change conformation, which then activates intracellular signaling proteins, so proteins on the intracellular side of the cell. This activates a cascade of protein signals that will alter the behavior of our cell."}, {"video_title": "Membrane Receptors   Nervous system physiology   NCLEX-RN   Khan Academy.mp3", "Sentence": "These receptor proteins then cause an intracellular response. After binding, there will be what's called an intracellular response. This receptor will bind to the protein, and this will cause the protein to actually change conformation, which then activates intracellular signaling proteins, so proteins on the intracellular side of the cell. This activates a cascade of protein signals that will alter the behavior of our cell. Sounds really complicated. Essentially, the way this works is we have an original signal, our ligand. This can be, again, a hormone, a neurotransmitter, something like that."}, {"video_title": "Membrane Receptors   Nervous system physiology   NCLEX-RN   Khan Academy.mp3", "Sentence": "This activates a cascade of protein signals that will alter the behavior of our cell. Sounds really complicated. Essentially, the way this works is we have an original signal, our ligand. This can be, again, a hormone, a neurotransmitter, something like that. This original signal is passed along. It'll bind to our protein, and that protein will tell other proteins inside the cell about what's going on. This signal is propagated throughout the cell, causing the cell to perform a specific function."}, {"video_title": "Membrane Receptors   Nervous system physiology   NCLEX-RN   Khan Academy.mp3", "Sentence": "This can be, again, a hormone, a neurotransmitter, something like that. This original signal is passed along. It'll bind to our protein, and that protein will tell other proteins inside the cell about what's going on. This signal is propagated throughout the cell, causing the cell to perform a specific function. You'll notice that in the diagram, we actually drew a really specific shape for our ligand. We chose a triangle. I chose a triangle because it's a little easier to draw, but this triangle actually fits right into the protein that I was drawing, which has an empty triangle space."}, {"video_title": "Membrane Receptors   Nervous system physiology   NCLEX-RN   Khan Academy.mp3", "Sentence": "This signal is propagated throughout the cell, causing the cell to perform a specific function. You'll notice that in the diagram, we actually drew a really specific shape for our ligand. We chose a triangle. I chose a triangle because it's a little easier to draw, but this triangle actually fits right into the protein that I was drawing, which has an empty triangle space. This is actually really important. Each specific receptor, so the thing that's missing a triangle, can only bind to a few types and often only one specific type of ligand. It can only bind that specific triangle-pinked ligand."}, {"video_title": "Membrane Receptors   Nervous system physiology   NCLEX-RN   Khan Academy.mp3", "Sentence": "I chose a triangle because it's a little easier to draw, but this triangle actually fits right into the protein that I was drawing, which has an empty triangle space. This is actually really important. Each specific receptor, so the thing that's missing a triangle, can only bind to a few types and often only one specific type of ligand. It can only bind that specific triangle-pinked ligand. Membrane receptors allow our body and cells to transfer information, and it can be very, very specific about it. This is important because when our body releases a hormone, it's kind of floating around in our entire bloodstream. How does our pancreas know that the hormone's intended for it?"}, {"video_title": "Membrane Receptors   Nervous system physiology   NCLEX-RN   Khan Academy.mp3", "Sentence": "It can only bind that specific triangle-pinked ligand. Membrane receptors allow our body and cells to transfer information, and it can be very, very specific about it. This is important because when our body releases a hormone, it's kind of floating around in our entire bloodstream. How does our pancreas know that the hormone's intended for it? How would our heart cells not react to it? This is why. The membrane receptors have a very specific preference for certain specific types of ligands."}, {"video_title": "Membrane Receptors   Nervous system physiology   NCLEX-RN   Khan Academy.mp3", "Sentence": "How does our pancreas know that the hormone's intended for it? How would our heart cells not react to it? This is why. The membrane receptors have a very specific preference for certain specific types of ligands. This is what we call our lock and key model. If we imagine our ligand as the key and our receptor protein as a lock, our receptor protein as a lock needs a very specific type of key in order to open it. Just like how our keychain, we might have a key to our mailbox and a key to our front door, maybe a key to our desk."}, {"video_title": "Membrane Receptors   Nervous system physiology   NCLEX-RN   Khan Academy.mp3", "Sentence": "The membrane receptors have a very specific preference for certain specific types of ligands. This is what we call our lock and key model. If we imagine our ligand as the key and our receptor protein as a lock, our receptor protein as a lock needs a very specific type of key in order to open it. Just like how our keychain, we might have a key to our mailbox and a key to our front door, maybe a key to our desk. Each of these keys does something different and opens a different lock. That's kind of how our cells work. I just want to make a note that this is a slightly outdated model."}, {"video_title": "Membrane Receptors   Nervous system physiology   NCLEX-RN   Khan Academy.mp3", "Sentence": "Just like how our keychain, we might have a key to our mailbox and a key to our front door, maybe a key to our desk. Each of these keys does something different and opens a different lock. That's kind of how our cells work. I just want to make a note that this is a slightly outdated model. Our updated model is actually what we call induced fit. These two concepts are very similar, but instead of saying that the ligands and the membrane receptors have very, very specific shape, induced fit brings a little more flexibility. It says the ligands and the membrane receptors can sometimes change conformations, kind of like how dough can be a little squishy so that they can fit each other."}, {"video_title": "Membrane Receptors   Nervous system physiology   NCLEX-RN   Khan Academy.mp3", "Sentence": "I just want to make a note that this is a slightly outdated model. Our updated model is actually what we call induced fit. These two concepts are very similar, but instead of saying that the ligands and the membrane receptors have very, very specific shape, induced fit brings a little more flexibility. It says the ligands and the membrane receptors can sometimes change conformations, kind of like how dough can be a little squishy so that they can fit each other. Overall, there are still a ton of new membrane receptors that are being discovered. As far as we know, we can group membrane receptors into three large groups. The first group we call ligand-gated ion channels."}, {"video_title": "Membrane Receptors   Nervous system physiology   NCLEX-RN   Khan Academy.mp3", "Sentence": "It says the ligands and the membrane receptors can sometimes change conformations, kind of like how dough can be a little squishy so that they can fit each other. Overall, there are still a ton of new membrane receptors that are being discovered. As far as we know, we can group membrane receptors into three large groups. The first group we call ligand-gated ion channels. The second group we call G-protein coupled receptors. Lastly, our third group we call enzyme-linked receptors. In summary, essentially we have really important membrane receptors in our cell membrane."}, {"video_title": "Membrane Receptors   Nervous system physiology   NCLEX-RN   Khan Academy.mp3", "Sentence": "The first group we call ligand-gated ion channels. The second group we call G-protein coupled receptors. Lastly, our third group we call enzyme-linked receptors. In summary, essentially we have really important membrane receptors in our cell membrane. These are integral proteins that allow our cells to communicate with the outside environment. The process in which these integral proteins work, these membrane receptors work, is that we have a ligand, which can be an ion or a molecule. It can bind to our integral protein, causing a process that we call signal transduction."}, {"video_title": "Membrane Receptors   Nervous system physiology   NCLEX-RN   Khan Academy.mp3", "Sentence": "In summary, essentially we have really important membrane receptors in our cell membrane. These are integral proteins that allow our cells to communicate with the outside environment. The process in which these integral proteins work, these membrane receptors work, is that we have a ligand, which can be an ion or a molecule. It can bind to our integral protein, causing a process that we call signal transduction. Signal transduction essentially means that our original signal, our ligand, is propagated throughout the cell as different proteins are activated, causing our intracellular response. Ligands and membrane receptors have a very specific fit. Only specific ligands can bind with specific membrane receptors."}, {"video_title": "Membrane Receptors   Nervous system physiology   NCLEX-RN   Khan Academy.mp3", "Sentence": "It can bind to our integral protein, causing a process that we call signal transduction. Signal transduction essentially means that our original signal, our ligand, is propagated throughout the cell as different proteins are activated, causing our intracellular response. Ligands and membrane receptors have a very specific fit. Only specific ligands can bind with specific membrane receptors. We call this lock and key. A more updated name for it is induced fit, in which the ligands and membrane receptors are a little more flexible, kind of like dough. They'll actually slightly alter conformations when they fit together."}, {"video_title": "Molecular structure of DNA   Macromolecules   Biology   Khan Academy.mp3", "Sentence": "But what I want to do in this video is dig a little bit deeper, actually get into the molecular structure of DNA. And just as a starting point, let's just remind ourselves what DNA stands for. I'm gonna write the different parts of the word in different colors. So it stands for deoxyribonucleic, ribonucleic, ribonucleic acid, ribonucleic acid. So I'm just gonna put this on the side. And now let's actually look at the molecular structure and how it relates to this actual name, deoxyribonucleic acid. So DNA is just a general term for nucleic acid."}, {"video_title": "Molecular structure of DNA   Macromolecules   Biology   Khan Academy.mp3", "Sentence": "So it stands for deoxyribonucleic, ribonucleic, ribonucleic acid, ribonucleic acid. So I'm just gonna put this on the side. And now let's actually look at the molecular structure and how it relates to this actual name, deoxyribonucleic acid. So DNA is just a general term for nucleic acid. And the term nucleic comes from the fact that it's found in the nucleus, it's found in the nucleus of eukaryotes. So that's where the nucleic comes from. And we'll talk about in a second why it's called an acid, but I'll wait on that."}, {"video_title": "Molecular structure of DNA   Macromolecules   Biology   Khan Academy.mp3", "Sentence": "So DNA is just a general term for nucleic acid. And the term nucleic comes from the fact that it's found in the nucleus, it's found in the nucleus of eukaryotes. So that's where the nucleic comes from. And we'll talk about in a second why it's called an acid, but I'll wait on that. And now each DNA molecule is made up of a chain of what we call nucleotides. So what we call nucleotides. So it's made up of nucleotides."}, {"video_title": "Molecular structure of DNA   Macromolecules   Biology   Khan Academy.mp3", "Sentence": "And we'll talk about in a second why it's called an acid, but I'll wait on that. And now each DNA molecule is made up of a chain of what we call nucleotides. So what we call nucleotides. So it's made up of nucleotides. So what does a nucleotide look like? Well, what I have right over here is I have two strands, I've zoomed in two strands of DNA. So you could view this side right over here as one of the, I guess you could say the backbones of one side of the ladder."}, {"video_title": "Molecular structure of DNA   Macromolecules   Biology   Khan Academy.mp3", "Sentence": "So it's made up of nucleotides. So what does a nucleotide look like? Well, what I have right over here is I have two strands, I've zoomed in two strands of DNA. So you could view this side right over here as one of the, I guess you could say the backbones of one side of the ladder. This is the other side of the ladder. And then each of these bridges, and I will talk about what molecules these are, these are kind of the rungs of the ladder. And a nucleotide, let me separate off a nucleotide."}, {"video_title": "Molecular structure of DNA   Macromolecules   Biology   Khan Academy.mp3", "Sentence": "So you could view this side right over here as one of the, I guess you could say the backbones of one side of the ladder. This is the other side of the ladder. And then each of these bridges, and I will talk about what molecules these are, these are kind of the rungs of the ladder. And a nucleotide, let me separate off a nucleotide. So a nucleotide would, so what I am coordinating off, what I am coordinating off right over here could be considered a nucleotide. So that's one nucleotide, and then it's connected to another. It's connected to another nucleotide, another nucleotide right over here."}, {"video_title": "Molecular structure of DNA   Macromolecules   Biology   Khan Academy.mp3", "Sentence": "And a nucleotide, let me separate off a nucleotide. So a nucleotide would, so what I am coordinating off, what I am coordinating off right over here could be considered a nucleotide. So that's one nucleotide, and then it's connected to another. It's connected to another nucleotide, another nucleotide right over here. And on the right-hand side, we have a nucleotide, we have a nucleotide right over there, and then, actually, I wanna do it, let me do it slightly different. We have a nucleotide right over here on the right side, and then right below that, we have another, we have another nucleotide, we have another nucleotide. So depicted here, we essentially have four nucleotides."}, {"video_title": "Molecular structure of DNA   Macromolecules   Biology   Khan Academy.mp3", "Sentence": "It's connected to another nucleotide, another nucleotide right over here. And on the right-hand side, we have a nucleotide, we have a nucleotide right over there, and then, actually, I wanna do it, let me do it slightly different. We have a nucleotide right over here on the right side, and then right below that, we have another, we have another nucleotide, we have another nucleotide. So depicted here, we essentially have four nucleotides. These two are on this left side of the ladder, these two are on the right side of the ladder. Now let's think about the different pieces of that nucleotide. So the one thing that might jump out at you is we have these phosphate groups."}, {"video_title": "Molecular structure of DNA   Macromolecules   Biology   Khan Academy.mp3", "Sentence": "So depicted here, we essentially have four nucleotides. These two are on this left side of the ladder, these two are on the right side of the ladder. Now let's think about the different pieces of that nucleotide. So the one thing that might jump out at you is we have these phosphate groups. So this is a phosphate group right over here, this is a phosphate group right over here. Each of these nucleotides have a phosphate group. So this is a phosphate group over here, and this is a phosphate group over here."}, {"video_title": "Molecular structure of DNA   Macromolecules   Biology   Khan Academy.mp3", "Sentence": "So the one thing that might jump out at you is we have these phosphate groups. So this is a phosphate group right over here, this is a phosphate group right over here. Each of these nucleotides have a phosphate group. So this is a phosphate group over here, and this is a phosphate group over here. Now the phosphate groups are actually what make DNA, or actually what make nucleic acid an acid. And you might say, wait, wait, the way you've drawn it, Sal, you have a negative charge. Something with a negative charge would attract protons, it would sop up protons."}, {"video_title": "Molecular structure of DNA   Macromolecules   Biology   Khan Academy.mp3", "Sentence": "So this is a phosphate group over here, and this is a phosphate group over here. Now the phosphate groups are actually what make DNA, or actually what make nucleic acid an acid. And you might say, wait, wait, the way you've drawn it, Sal, you have a negative charge. Something with a negative charge would attract protons, it would sop up protons. How can you call this an acid? This actually looks more basic. And the reason why DNA is typically drawn with these negative charges here is that it's so acidic, and if you put it into a neutral solution, it's actually going to lose its hydrogens."}, {"video_title": "Molecular structure of DNA   Macromolecules   Biology   Khan Academy.mp3", "Sentence": "Something with a negative charge would attract protons, it would sop up protons. How can you call this an acid? This actually looks more basic. And the reason why DNA is typically drawn with these negative charges here is that it's so acidic, and if you put it into a neutral solution, it's actually going to lose its hydrogens. Actually the DNA, if we actually want to be formal about it, the DNA molecules would actually have its phosphates protonated like this, but it so badly wants to lose these hydrogen protons, so it typically would be, let me draw it like this. Let me get rid of the negative charge just on this one. Whoops, just on this phosphate group over here."}, {"video_title": "Molecular structure of DNA   Macromolecules   Biology   Khan Academy.mp3", "Sentence": "And the reason why DNA is typically drawn with these negative charges here is that it's so acidic, and if you put it into a neutral solution, it's actually going to lose its hydrogens. Actually the DNA, if we actually want to be formal about it, the DNA molecules would actually have its phosphates protonated like this, but it so badly wants to lose these hydrogen protons, so it typically would be, let me draw it like this. Let me get rid of the negative charge just on this one. Whoops, just on this phosphate group over here. So if you get rid of the negative charge, and if this was bounded, this is bonded to a hydrogen, this so badly wants to grab these electrons. So this oxygen can grab these electrons, and then this hydrogen will just be grabbed by another water molecule or something, or so the proton will be let go. That's why we call it an acid."}, {"video_title": "Molecular structure of DNA   Macromolecules   Biology   Khan Academy.mp3", "Sentence": "Whoops, just on this phosphate group over here. So if you get rid of the negative charge, and if this was bounded, this is bonded to a hydrogen, this so badly wants to grab these electrons. So this oxygen can grab these electrons, and then this hydrogen will just be grabbed by another water molecule or something, or so the proton will be let go. That's why we call it an acid. So if it wasn't in a solution, it would have the hydrogens, but it would be very acidic. As soon as you put it into a neutral solution, it's going to lose those hydrogens. So the phosphate groups are what make it an acid, but it's confusing sometimes, because usually when you see it depicted, you see it with these negative charges, and that's because it has already lost its hydrogen protons."}, {"video_title": "Molecular structure of DNA   Macromolecules   Biology   Khan Academy.mp3", "Sentence": "That's why we call it an acid. So if it wasn't in a solution, it would have the hydrogens, but it would be very acidic. As soon as you put it into a neutral solution, it's going to lose those hydrogens. So the phosphate groups are what make it an acid, but it's confusing sometimes, because usually when you see it depicted, you see it with these negative charges, and that's because it has already lost its hydrogen protons. You're actually depicting the conjugate base here, but that's where it gets its acidic name from, because it starts protonated, or I guess in its acid form it's protonated, but it readily loses it, and so that's where it gets the name acid from. So each of these nucleotides, they have a phosphate group. Now the next thing you might notice, the next thing you might notice is, the next thing you might notice is this group right over here."}, {"video_title": "Molecular structure of DNA   Macromolecules   Biology   Khan Academy.mp3", "Sentence": "So the phosphate groups are what make it an acid, but it's confusing sometimes, because usually when you see it depicted, you see it with these negative charges, and that's because it has already lost its hydrogen protons. You're actually depicting the conjugate base here, but that's where it gets its acidic name from, because it starts protonated, or I guess in its acid form it's protonated, but it readily loses it, and so that's where it gets the name acid from. So each of these nucleotides, they have a phosphate group. Now the next thing you might notice, the next thing you might notice is, the next thing you might notice is this group right over here. It is a cycle, it is a ring, and it looks an awful lot like a sugar, and that's because it is a sugar. So this sugar is based on, it's a five-carbon sugar. What I have depicted here, this sugar, this is ribose."}, {"video_title": "Molecular structure of DNA   Macromolecules   Biology   Khan Academy.mp3", "Sentence": "Now the next thing you might notice, the next thing you might notice is, the next thing you might notice is this group right over here. It is a cycle, it is a ring, and it looks an awful lot like a sugar, and that's because it is a sugar. So this sugar is based on, it's a five-carbon sugar. What I have depicted here, this sugar, this is ribose. So this sugar right over here is ribose. This is when it's just as a straight chain, and like many sugars, it can take a cyclical form. Actually, it can take many different cyclical forms, but the one that's most typically described is when you have the, let me show you a number of the carbons, because carbon numbering is important when we talk about DNA."}, {"video_title": "Molecular structure of DNA   Macromolecules   Biology   Khan Academy.mp3", "Sentence": "What I have depicted here, this sugar, this is ribose. So this sugar right over here is ribose. This is when it's just as a straight chain, and like many sugars, it can take a cyclical form. Actually, it can take many different cyclical forms, but the one that's most typically described is when you have the, let me show you a number of the carbons, because carbon numbering is important when we talk about DNA. If we start at the carbonyl group right over here, we call that the one carbon, or the one prime carbon. One prime, two prime, three prime, four prime, and five prime. That's the five prime carbon."}, {"video_title": "Molecular structure of DNA   Macromolecules   Biology   Khan Academy.mp3", "Sentence": "Actually, it can take many different cyclical forms, but the one that's most typically described is when you have the, let me show you a number of the carbons, because carbon numbering is important when we talk about DNA. If we start at the carbonyl group right over here, we call that the one carbon, or the one prime carbon. One prime, two prime, three prime, four prime, and five prime. That's the five prime carbon. And so you form the cyclical form of ribose, is if you have the oxygen, you have the oxygen right over here on the four prime carbon, it uses one of its lone pairs, it uses one of its lone pairs to form a bond, to form a bond with, with the one prime, with the one prime carbon. And I drew it that way, because it kind of does bend, the whole molecule's going to have to bend that way to form this structure. And then when it forms that bond, the carbon can let go of one of these double bonds, and then that can, then the oxygen, the oxygen can use that, the oxygen can use those electrons to go grab a hydrogen proton from someplace, so to nab onto a hydrogen proton."}, {"video_title": "Molecular structure of DNA   Macromolecules   Biology   Khan Academy.mp3", "Sentence": "That's the five prime carbon. And so you form the cyclical form of ribose, is if you have the oxygen, you have the oxygen right over here on the four prime carbon, it uses one of its lone pairs, it uses one of its lone pairs to form a bond, to form a bond with, with the one prime, with the one prime carbon. And I drew it that way, because it kind of does bend, the whole molecule's going to have to bend that way to form this structure. And then when it forms that bond, the carbon can let go of one of these double bonds, and then that can, then the oxygen, the oxygen can use that, the oxygen can use those electrons to go grab a hydrogen proton from someplace, so to nab onto a hydrogen proton. So when it does that, you're in this form. And this form, just to be clear of what we're talking about, this is the one prime carbon, one prime, two prime, three prime, four prime, and five, five prime carbon. And where we see this bond, this is a one prime carbon, it was part of a carbonyl, now it lets go of one of those double bonds so that this oxygen can form a bond with a hydrogen proton, so it let go of a double bond there so that this could form a bond with a hydrogen proton."}, {"video_title": "Molecular structure of DNA   Macromolecules   Biology   Khan Academy.mp3", "Sentence": "And then when it forms that bond, the carbon can let go of one of these double bonds, and then that can, then the oxygen, the oxygen can use that, the oxygen can use those electrons to go grab a hydrogen proton from someplace, so to nab onto a hydrogen proton. So when it does that, you're in this form. And this form, just to be clear of what we're talking about, this is the one prime carbon, one prime, two prime, three prime, four prime, and five, five prime carbon. And where we see this bond, this is a one prime carbon, it was part of a carbonyl, now it lets go of one of those double bonds so that this oxygen can form a bond with a hydrogen proton, so it let go of a double bond there so that this could form a bond with a hydrogen proton. So this hydrogen proton is that hydrogen proton right over there, and this green, this green bond that gets formed between the four prime carbon and, or between the oxygen that's attached to the four prime carbon and the one prime carbon, that's this. That's this bond right over here. This oxygen is that oxygen right there."}, {"video_title": "Molecular structure of DNA   Macromolecules   Biology   Khan Academy.mp3", "Sentence": "And where we see this bond, this is a one prime carbon, it was part of a carbonyl, now it lets go of one of those double bonds so that this oxygen can form a bond with a hydrogen proton, so it let go of a double bond there so that this could form a bond with a hydrogen proton. So this hydrogen proton is that hydrogen proton right over there, and this green, this green bond that gets formed between the four prime carbon and, or between the oxygen that's attached to the four prime carbon and the one prime carbon, that's this. That's this bond right over here. This oxygen is that oxygen right there. Notice, this oxygen is bound to the four prime carbon, and now it's also bound to the one prime carbon. And it was also attached to a hydrogen, it was also attached to a hydrogen. that hydrogen is there, but then that could get nabbed up by another passing water molecule to become hydronium, so it can get lost."}, {"video_title": "Molecular structure of DNA   Macromolecules   Biology   Khan Academy.mp3", "Sentence": "This oxygen is that oxygen right there. Notice, this oxygen is bound to the four prime carbon, and now it's also bound to the one prime carbon. And it was also attached to a hydrogen, it was also attached to a hydrogen. that hydrogen is there, but then that could get nabbed up by another passing water molecule to become hydronium, so it can get lost. And you know, net-net, it grabs up a hydrogen proton right over here, and so it can lose a hydrogen proton right there, so it's not adding or losing net-net. And so you form this cyclical form. And the cyclical form right over here is very close to what we see in a DNA molecule."}, {"video_title": "Molecular structure of DNA   Macromolecules   Biology   Khan Academy.mp3", "Sentence": "that hydrogen is there, but then that could get nabbed up by another passing water molecule to become hydronium, so it can get lost. And you know, net-net, it grabs up a hydrogen proton right over here, and so it can lose a hydrogen proton right there, so it's not adding or losing net-net. And so you form this cyclical form. And the cyclical form right over here is very close to what we see in a DNA molecule. It's actually exactly what we would see in an RNA molecule, in ribonucleic acid. And so what do we think we're talking about when we say deoxyribonucleic acid? Well, you could start with, you have a ribose here, but if we got rid of one of the oxygen groups, and in particular, one of, well, actually, if we just got rid of one of the oxygens, we replace a hydroxyl with just a hydrogen, well, then you're gonna have deoxyribose."}, {"video_title": "Molecular structure of DNA   Macromolecules   Biology   Khan Academy.mp3", "Sentence": "And the cyclical form right over here is very close to what we see in a DNA molecule. It's actually exactly what we would see in an RNA molecule, in ribonucleic acid. And so what do we think we're talking about when we say deoxyribonucleic acid? Well, you could start with, you have a ribose here, but if we got rid of one of the oxygen groups, and in particular, one of, well, actually, if we just got rid of one of the oxygens, we replace a hydroxyl with just a hydrogen, well, then you're gonna have deoxyribose. And you see that over here. This five-member ring, you have four carbons right over here, it looks just like this. The hydrogens are implicit to the carbons."}, {"video_title": "Molecular structure of DNA   Macromolecules   Biology   Khan Academy.mp3", "Sentence": "Well, you could start with, you have a ribose here, but if we got rid of one of the oxygen groups, and in particular, one of, well, actually, if we just got rid of one of the oxygens, we replace a hydroxyl with just a hydrogen, well, then you're gonna have deoxyribose. And you see that over here. This five-member ring, you have four carbons right over here, it looks just like this. The hydrogens are implicit to the carbons. We've seen this multiple times. The carbons are at where these lines intersect, or I guess at the edges, or maybe, and also where these lines end right over there. But you see, this does not have an, this molecule, if we compare these two molecules, if we compare these two molecules over here, we see that this guy has an OH, and this guy implicitly just has, this guy has an OH and an H. This guy implicitly has just two hydrogens over here."}, {"video_title": "Molecular structure of DNA   Macromolecules   Biology   Khan Academy.mp3", "Sentence": "The hydrogens are implicit to the carbons. We've seen this multiple times. The carbons are at where these lines intersect, or I guess at the edges, or maybe, and also where these lines end right over there. But you see, this does not have an, this molecule, if we compare these two molecules, if we compare these two molecules over here, we see that this guy has an OH, and this guy implicitly just has, this guy has an OH and an H. This guy implicitly has just two hydrogens over here. So he's missing an oxygen. So this is deoxyribose. So deoxyribose, deoxyribose doesn't have this oxygen."}, {"video_title": "Molecular structure of DNA   Macromolecules   Biology   Khan Academy.mp3", "Sentence": "But you see, this does not have an, this molecule, if we compare these two molecules, if we compare these two molecules over here, we see that this guy has an OH, and this guy implicitly just has, this guy has an OH and an H. This guy implicitly has just two hydrogens over here. So he's missing an oxygen. So this is deoxyribose. So deoxyribose, deoxyribose doesn't have this oxygen. It does not have the oxygen on the two prime carbon. So this, if you get rid of that, this is deoxyribose. So let me circle that."}, {"video_title": "Molecular structure of DNA   Macromolecules   Biology   Khan Academy.mp3", "Sentence": "So deoxyribose, deoxyribose doesn't have this oxygen. It does not have the oxygen on the two prime carbon. So this, if you get rid of that, this is deoxyribose. So let me circle that. So what we're, this thing right over here, this thing right over here, that is deoxyribose. Deoxy, or it's based on deoxyribose, I guess before it bonded to these other constituents, you could consider this deoxyribose. And so that's where the deoxyribo comes from."}, {"video_title": "Molecular structure of DNA   Macromolecules   Biology   Khan Academy.mp3", "Sentence": "So let me circle that. So what we're, this thing right over here, this thing right over here, that is deoxyribose. Deoxy, or it's based on deoxyribose, I guess before it bonded to these other constituents, you could consider this deoxyribose. And so that's where the deoxyribo comes from. And then the last piece of it, the last piece of it is this chunk right over here. And these we call nitrogenous bases. So nitrogenous, nitrogenous, nitrogenous bases."}, {"video_title": "Molecular structure of DNA   Macromolecules   Biology   Khan Academy.mp3", "Sentence": "And so that's where the deoxyribo comes from. And then the last piece of it, the last piece of it is this chunk right over here. And these we call nitrogenous bases. So nitrogenous, nitrogenous, nitrogenous bases. And you can see we have different types of nitrogenous bases. This is a nitrogenous base. This is, this right over here, is a different nitrogenous base."}, {"video_title": "Molecular structure of DNA   Macromolecules   Biology   Khan Academy.mp3", "Sentence": "So nitrogenous, nitrogenous, nitrogenous bases. And you can see we have different types of nitrogenous bases. This is a nitrogenous base. This is, this right over here, is a different nitrogenous base. This right over here is another different nitrogenous base. Notice, this one only has one ring. This one has one ring."}, {"video_title": "Molecular structure of DNA   Macromolecules   Biology   Khan Academy.mp3", "Sentence": "This is, this right over here, is a different nitrogenous base. This right over here is another different nitrogenous base. Notice, this one only has one ring. This one has one ring. This one has two rings. This one over here has two rings. And we have different names for these nitrogenous bases."}, {"video_title": "Molecular structure of DNA   Macromolecules   Biology   Khan Academy.mp3", "Sentence": "This one has one ring. This one has two rings. This one over here has two rings. And we have different names for these nitrogenous bases. The ones with two rings, the general categorization, we call them purines. So nitrogenous bases, if you have two rings, you have two rings, we call them purines. as a general classification term."}, {"video_title": "Molecular structure of DNA   Macromolecules   Biology   Khan Academy.mp3", "Sentence": "And we have different names for these nitrogenous bases. The ones with two rings, the general categorization, we call them purines. So nitrogenous bases, if you have two rings, you have two rings, we call them purines. as a general classification term. Let me make sure, purines. And if you have one ring, maybe I'll just write it this way, one ring, one ring, we call these pyrimidines. Pyrimidines."}, {"video_title": "Molecular structure of DNA   Macromolecules   Biology   Khan Academy.mp3", "Sentence": "as a general classification term. Let me make sure, purines. And if you have one ring, maybe I'll just write it this way, one ring, one ring, we call these pyrimidines. Pyrimidines. Pyrimidines. We call these pyrimidines. And these particular, these two on the right, these two purines, this one up here, this is adenine."}, {"video_title": "Molecular structure of DNA   Macromolecules   Biology   Khan Academy.mp3", "Sentence": "Pyrimidines. Pyrimidines. We call these pyrimidines. And these particular, these two on the right, these two purines, this one up here, this is adenine. And we talk about how they pair in the overview video on DNA. But this one right over here is adenine, this nitrogenous base. This one over here is guanine."}, {"video_title": "Molecular structure of DNA   Macromolecules   Biology   Khan Academy.mp3", "Sentence": "And these particular, these two on the right, these two purines, this one up here, this is adenine. And we talk about how they pair in the overview video on DNA. But this one right over here is adenine, this nitrogenous base. This one over here is guanine. That is guanine. And then, over here, this single ring nitrogenous base, which makes it a pyrimidine, this is thymine. This right over here is thymine."}, {"video_title": "Molecular structure of DNA   Macromolecules   Biology   Khan Academy.mp3", "Sentence": "This one over here is guanine. That is guanine. And then, over here, this single ring nitrogenous base, which makes it a pyrimidine, this is thymine. This right over here is thymine. This is thymine. And then last but not least, if we're talking about DNA, when we go into RNA, we're also gonna talk about uracil. But when we talk about DNA, this one over here is cytosine."}, {"video_title": "Molecular structure of DNA   Macromolecules   Biology   Khan Academy.mp3", "Sentence": "This right over here is thymine. This is thymine. And then last but not least, if we're talking about DNA, when we go into RNA, we're also gonna talk about uracil. But when we talk about DNA, this one over here is cytosine. Cytosine. And you can see the way it's structured, that thymine is attracted to adenine, it bonds with adenine, and cytosine bonds with guanine. So how are they bonding?"}, {"video_title": "Molecular structure of DNA   Macromolecules   Biology   Khan Academy.mp3", "Sentence": "But when we talk about DNA, this one over here is cytosine. Cytosine. And you can see the way it's structured, that thymine is attracted to adenine, it bonds with adenine, and cytosine bonds with guanine. So how are they bonding? Well, the way that these nitrogenous bases form the rungs of the ladder, how they're drawn to each other, this is our good old friend hydrogen bonds. And this all comes out of the fact that nitrogen is quite electronegative, so when nitrogen is bound to a hydrogen, you're going to have a partially negative charge at the nitrogen. Let me do this in green."}, {"video_title": "Molecular structure of DNA   Macromolecules   Biology   Khan Academy.mp3", "Sentence": "So how are they bonding? Well, the way that these nitrogenous bases form the rungs of the ladder, how they're drawn to each other, this is our good old friend hydrogen bonds. And this all comes out of the fact that nitrogen is quite electronegative, so when nitrogen is bound to a hydrogen, you're going to have a partially negative charge at the nitrogen. Let me do this in green. You're gonna have a partial negative charge at the nitrogen and a partially positive charge at the hydrogen. And then oxygen, we've always talked about as being electronegative, so it has a partial negative charge. So the partial negative charge of this oxygen is gonna be attracted to the partial positive charge of this hydrogen, and so you're going to have, you're going to have a hydrogen bond."}, {"video_title": "Molecular structure of DNA   Macromolecules   Biology   Khan Academy.mp3", "Sentence": "Let me do this in green. You're gonna have a partial negative charge at the nitrogen and a partially positive charge at the hydrogen. And then oxygen, we've always talked about as being electronegative, so it has a partial negative charge. So the partial negative charge of this oxygen is gonna be attracted to the partial positive charge of this hydrogen, and so you're going to have, you're going to have a hydrogen bond. And that's the same thing that's gonna happen between this hydrogen, which is going, its electrons are being hogged by this nitrogen, and this nitrogen, which itself hogs electrons, so that forms a hydrogen bond. And then down here, you have a hydrogen that has a partially positive charge, because its electrons are being hogged, and then you have this oxygen with a partially negative charge. They're going to be attracted to each other."}, {"video_title": "Molecular structure of DNA   Macromolecules   Biology   Khan Academy.mp3", "Sentence": "So the partial negative charge of this oxygen is gonna be attracted to the partial positive charge of this hydrogen, and so you're going to have, you're going to have a hydrogen bond. And that's the same thing that's gonna happen between this hydrogen, which is going, its electrons are being hogged by this nitrogen, and this nitrogen, which itself hogs electrons, so that forms a hydrogen bond. And then down here, you have a hydrogen that has a partially positive charge, because its electrons are being hogged, and then you have this oxygen with a partially negative charge. They're going to be attracted to each other. That's a hydrogen bond. Same thing between this nitrogen and that hydrogen, and same thing between this oxygen and that hydrogen. And that's why cytosine and guanine pair up, and that's why thymine and adenine pair up, and we talk about that as well in the overview video of DNA."}, {"video_title": "Surface tension   States of matter and intermolecular forces   Chemistry   Khan Academy.mp3", "Sentence": "This is the air. These are some air molecules. Maybe they're nitrogen molecules. They're fairly far apart. In fact, in reality, they would be even more far apart than this. And then over here you have water molecules. We've seen this many times."}, {"video_title": "Surface tension   States of matter and intermolecular forces   Chemistry   Khan Academy.mp3", "Sentence": "They're fairly far apart. In fact, in reality, they would be even more far apart than this. And then over here you have water molecules. We've seen this many times. You have the oxygen atom, and it's bonded to two hydrogen atoms. And the oxygen atom likes to hog the electrons more. It's more electronegative, so you have a partially negative charge at this end and partially positive ends at this end."}, {"video_title": "Surface tension   States of matter and intermolecular forces   Chemistry   Khan Academy.mp3", "Sentence": "We've seen this many times. You have the oxygen atom, and it's bonded to two hydrogen atoms. And the oxygen atom likes to hog the electrons more. It's more electronegative, so you have a partially negative charge at this end and partially positive ends at this end. And that attraction between the partially positive ends and the partially negative ends, that's what gives water all sorts of neat properties. Those are the hydrogen bonds. Those are the hydrogen bonds that give water all sorts of neat properties and keep it in its liquid state at just standard temperature and pressure."}, {"video_title": "Surface tension   States of matter and intermolecular forces   Chemistry   Khan Academy.mp3", "Sentence": "It's more electronegative, so you have a partially negative charge at this end and partially positive ends at this end. And that attraction between the partially positive ends and the partially negative ends, that's what gives water all sorts of neat properties. Those are the hydrogen bonds. Those are the hydrogen bonds that give water all sorts of neat properties and keep it in its liquid state at just standard temperature and pressure. Now what I wanna think about is the surface in particular. And if you look at the surface of water, it might look completely smooth, but if you were to zoom in on a molecular level, you'll see that, well, it's just made up of these molecules. But roughly speaking, let's just say that this is roughly the surface of the water."}, {"video_title": "Surface tension   States of matter and intermolecular forces   Chemistry   Khan Academy.mp3", "Sentence": "Those are the hydrogen bonds that give water all sorts of neat properties and keep it in its liquid state at just standard temperature and pressure. Now what I wanna think about is the surface in particular. And if you look at the surface of water, it might look completely smooth, but if you were to zoom in on a molecular level, you'll see that, well, it's just made up of these molecules. But roughly speaking, let's just say that this is roughly the surface of the water. Now what's going on at the surface? Well, all of these molecules are interacting through hydrogen bonds. Let's say this molecule right over here, it has hydrogen bonds pulling on it upwards, up to this one, pulling in this way, pulling it downwards, pulling it in really, to some degree, almost every direction."}, {"video_title": "Surface tension   States of matter and intermolecular forces   Chemistry   Khan Academy.mp3", "Sentence": "But roughly speaking, let's just say that this is roughly the surface of the water. Now what's going on at the surface? Well, all of these molecules are interacting through hydrogen bonds. Let's say this molecule right over here, it has hydrogen bonds pulling on it upwards, up to this one, pulling in this way, pulling it downwards, pulling it in really, to some degree, almost every direction. And they all have their kinetic energy and they're bumping around, but they're flowing past each other. The hydrogen bonds are giving that cohesiveness. The molecules are attracted to each other."}, {"video_title": "Surface tension   States of matter and intermolecular forces   Chemistry   Khan Academy.mp3", "Sentence": "Let's say this molecule right over here, it has hydrogen bonds pulling on it upwards, up to this one, pulling in this way, pulling it downwards, pulling it in really, to some degree, almost every direction. And they all have their kinetic energy and they're bumping around, but they're flowing past each other. The hydrogen bonds are giving that cohesiveness. The molecules are attracted to each other. But if you look at the molecules on the surface, if you look at the ones on the surface, sure, they might have stuff pulling down on them, they might have stuff pulling them to the side, but they don't have anything pulling on them from above. And because of this, you could imagine that they're able to get a little bit more densely packed, that they're able to get a little closer to their neighbors, and this is what allows them to actually have a stronger, I guess you could say intermolecular force at the surface than you have within the body. And that causes a phenomenon known as surface tension."}, {"video_title": "Surface tension   States of matter and intermolecular forces   Chemistry   Khan Academy.mp3", "Sentence": "The molecules are attracted to each other. But if you look at the molecules on the surface, if you look at the ones on the surface, sure, they might have stuff pulling down on them, they might have stuff pulling them to the side, but they don't have anything pulling on them from above. And because of this, you could imagine that they're able to get a little bit more densely packed, that they're able to get a little closer to their neighbors, and this is what allows them to actually have a stronger, I guess you could say intermolecular force at the surface than you have within the body. And that causes a phenomenon known as surface tension. So you have stronger, you have kind of a deeper, and this is still just hydrogen bonds, but since they're not being pulled in other directions by upwards by the air, they're able to get a little bit more closely packed and a little bit tighter. And this we refer to as surface tension. Surface tension."}, {"video_title": "Surface tension   States of matter and intermolecular forces   Chemistry   Khan Academy.mp3", "Sentence": "And that causes a phenomenon known as surface tension. So you have stronger, you have kind of a deeper, and this is still just hydrogen bonds, but since they're not being pulled in other directions by upwards by the air, they're able to get a little bit more closely packed and a little bit tighter. And this we refer to as surface tension. Surface tension. And you have probably observed surface tension many, many, many times in your life in the form of, say, a water droplet. A water droplet, it's able to have this roughly round shape because all the little water molecules on the surface of the water droplet, and here the surface might even be on the bottom of the water droplet, they're more attracted to each other than they are to the surrounding air. So they're able to form this type of a shape."}, {"video_title": "Surface tension   States of matter and intermolecular forces   Chemistry   Khan Academy.mp3", "Sentence": "Surface tension. And you have probably observed surface tension many, many, many times in your life in the form of, say, a water droplet. A water droplet, it's able to have this roughly round shape because all the little water molecules on the surface of the water droplet, and here the surface might even be on the bottom of the water droplet, they're more attracted to each other than they are to the surrounding air. So they're able to form this type of a shape. You might have seen it if you go to a pond or a stream sometimes, so you see some still water, and say, let's say, let me do this in blue. So let's say that this is the surface of the water right over here. You might have seen insects that are able to walk on the surface of the water, and I'm not doing a great job at drawing the insects, they don't look exactly like that, but they can walk on the surface of the water."}, {"video_title": "Surface tension   States of matter and intermolecular forces   Chemistry   Khan Academy.mp3", "Sentence": "So they're able to form this type of a shape. You might have seen it if you go to a pond or a stream sometimes, so you see some still water, and say, let's say, let me do this in blue. So let's say that this is the surface of the water right over here. You might have seen insects that are able to walk on the surface of the water, and I'm not doing a great job at drawing the insects, they don't look exactly like that, but they can walk on the surface of the water. You might have seen, or you might have even tried to do something like put a paper clip on the water. And even though this thing is actually more dense than the water, and you might expect it to sink, but because of the surface tension, which really forms something of a film on the top of the water, the thing won't penetrate the surface, so the paper clip will float. Unless you were to push on it a little bit, and allow it to puncture the surface, and then it would actually sink, which is what you would expect, because it is actually denser."}, {"video_title": "Surface tension   States of matter and intermolecular forces   Chemistry   Khan Academy.mp3", "Sentence": "You might have seen insects that are able to walk on the surface of the water, and I'm not doing a great job at drawing the insects, they don't look exactly like that, but they can walk on the surface of the water. You might have seen, or you might have even tried to do something like put a paper clip on the water. And even though this thing is actually more dense than the water, and you might expect it to sink, but because of the surface tension, which really forms something of a film on the top of the water, the thing won't penetrate the surface, so the paper clip will float. Unless you were to push on it a little bit, and allow it to puncture the surface, and then it would actually sink, which is what you would expect, because it is actually denser. You'd even see this if you were to take a cup. If you were to take a cup, and you were to fill it all the way up to the rim, and then a little bit higher, it won't immediately overflow. It won't immediately overflow."}, {"video_title": "Surface tension   States of matter and intermolecular forces   Chemistry   Khan Academy.mp3", "Sentence": "Unless you were to push on it a little bit, and allow it to puncture the surface, and then it would actually sink, which is what you would expect, because it is actually denser. You'd even see this if you were to take a cup. If you were to take a cup, and you were to fill it all the way up to the rim, and then a little bit higher, it won't immediately overflow. It won't immediately overflow. If you're very careful, you'll see that you form a bulge here. And that bulge is because those individual water molecules are more attracted to each other than they are to the surrounding air. So that allows for something of a little bulge."}, {"video_title": "Surface tension   States of matter and intermolecular forces   Chemistry   Khan Academy.mp3", "Sentence": "It won't immediately overflow. If you're very careful, you'll see that you form a bulge here. And that bulge is because those individual water molecules are more attracted to each other than they are to the surrounding air. So that allows for something of a little bulge. Obviously, if you keep pouring water, at some point, they're just gonna start overflowing, because gravity's gonna take over, or gravity's gonna overwhelm the surface tension. But this bulge will actually form. So surface tension, it is really due to the cohesion of the water."}, {"video_title": "Endomembrane system   Structure of a cell   Biology   Khan Academy (2).mp3", "Sentence": "What I want to do in this video is give an overview of the endomembrane system in eukaryotic cells. Endomembrane system. And at a very high level, the endomembrane system is all of the membranes that interact with each other inside of a cell. So what membranes are we talking about? Well, you can start off by talking about the cell membrane itself. And all of these membranes, these have bilayers of phospholipids. Sometimes my brain malfunctions and I call them bilipid layers."}, {"video_title": "Endomembrane system   Structure of a cell   Biology   Khan Academy (2).mp3", "Sentence": "So what membranes are we talking about? Well, you can start off by talking about the cell membrane itself. And all of these membranes, these have bilayers of phospholipids. Sometimes my brain malfunctions and I call them bilipid layers. But these are bilayers of phospholipids. So if I were to zoom in right over here, if I were to zoom in right over there, that line, it really is a bilayer, a bilayer of phospholipids. So it would look like this."}, {"video_title": "Endomembrane system   Structure of a cell   Biology   Khan Academy (2).mp3", "Sentence": "Sometimes my brain malfunctions and I call them bilipid layers. But these are bilayers of phospholipids. So if I were to zoom in right over here, if I were to zoom in right over there, that line, it really is a bilayer, a bilayer of phospholipids. So it would look like this. So you have your hydrophilic heads pointing outwards and your hydrophobic tails pointing inwards. So hydrophilic heads pointing outwards, hydrophobic tails pointing inwards, and it keeps going. So you have, if we think of it from left to right, you have a layer of two, or you have a bilayer, I should say, of phospholipids."}, {"video_title": "Endomembrane system   Structure of a cell   Biology   Khan Academy (2).mp3", "Sentence": "So it would look like this. So you have your hydrophilic heads pointing outwards and your hydrophobic tails pointing inwards. So hydrophilic heads pointing outwards, hydrophobic tails pointing inwards, and it keeps going. So you have, if we think of it from left to right, you have a layer of two, or you have a bilayer, I should say, of phospholipids. That's going to be true of the cellular membrane. That's going to be true of the outer nuclear membrane. Right over here, we drew this one on the video on the endoplasmic reticulum."}, {"video_title": "Endomembrane system   Structure of a cell   Biology   Khan Academy (2).mp3", "Sentence": "So you have, if we think of it from left to right, you have a layer of two, or you have a bilayer, I should say, of phospholipids. That's going to be true of the cellular membrane. That's going to be true of the outer nuclear membrane. Right over here, we drew this one on the video on the endoplasmic reticulum. And so over here, you see these two membranes. You might say, okay, is this a bilayer? No, this is actually two bilayers."}, {"video_title": "Endomembrane system   Structure of a cell   Biology   Khan Academy (2).mp3", "Sentence": "Right over here, we drew this one on the video on the endoplasmic reticulum. And so over here, you see these two membranes. You might say, okay, is this a bilayer? No, this is actually two bilayers. So this membrane right over here has a phospholipid bilayer, and this membrane over here also has a phospholipid bilayer. This, the one, let me do this in another color, this one that I'm starting to trace in magenta, that's the outer membrane of the nuclear envelope, and it's continuous with the membrane of the endoplasmic reticulum, which I'm starting to highlight right over here. And then the one that I'm highlighting in this purple color, this is the inner membrane of the nuclear envelope."}, {"video_title": "Endomembrane system   Structure of a cell   Biology   Khan Academy (2).mp3", "Sentence": "No, this is actually two bilayers. So this membrane right over here has a phospholipid bilayer, and this membrane over here also has a phospholipid bilayer. This, the one, let me do this in another color, this one that I'm starting to trace in magenta, that's the outer membrane of the nuclear envelope, and it's continuous with the membrane of the endoplasmic reticulum, which I'm starting to highlight right over here. And then the one that I'm highlighting in this purple color, this is the inner membrane of the nuclear envelope. And all of this is part of the endomembrane system. So I've already started talking about the endoplasmic reticulum, and we go into some depth on that on the video on the endoplasmic reticulum and the Golgi apparatus, but it's also part of the endomembrane system. And the endoplasmic reticulum in particular can represent up to or even more than 50% of the membrane associated, the phospholipid membrane associated with the cell."}, {"video_title": "Endomembrane system   Structure of a cell   Biology   Khan Academy (2).mp3", "Sentence": "And then the one that I'm highlighting in this purple color, this is the inner membrane of the nuclear envelope. And all of this is part of the endomembrane system. So I've already started talking about the endoplasmic reticulum, and we go into some depth on that on the video on the endoplasmic reticulum and the Golgi apparatus, but it's also part of the endomembrane system. And the endoplasmic reticulum in particular can represent up to or even more than 50% of the membrane associated, the phospholipid membrane associated with the cell. And we've talked about what goes on in the lumen of the endoplasmic reticulum. So this area right over here, right over here, we've talked about what happens there. Proteins can get synthesized, actually other molecules like lipids can get synthesized there."}, {"video_title": "Endomembrane system   Structure of a cell   Biology   Khan Academy (2).mp3", "Sentence": "And the endoplasmic reticulum in particular can represent up to or even more than 50% of the membrane associated, the phospholipid membrane associated with the cell. And we've talked about what goes on in the lumen of the endoplasmic reticulum. So this area right over here, right over here, we've talked about what happens there. Proteins can get synthesized, actually other molecules like lipids can get synthesized there. They can, and then they can go to the smooth ER, and then the place where they can exit from the smooth ER, and we saw that in the video on the endoplasmic reticulum, how they can kind of bud out, we call this area, it's often called the transitional ER. So this area right over here, we would call the transitional endoplasmic reticulum. Transitional, transitional, transitional, transitional ER is this place where these proteins are being budded off, and they're budding off in vesicles."}, {"video_title": "Endomembrane system   Structure of a cell   Biology   Khan Academy (2).mp3", "Sentence": "Proteins can get synthesized, actually other molecules like lipids can get synthesized there. They can, and then they can go to the smooth ER, and then the place where they can exit from the smooth ER, and we saw that in the video on the endoplasmic reticulum, how they can kind of bud out, we call this area, it's often called the transitional ER. So this area right over here, we would call the transitional endoplasmic reticulum. Transitional, transitional, transitional, transitional ER is this place where these proteins are being budded off, and they're budding off in vesicles. So this is the transitional ER. And all vesicles are are little small compartments that have a membrane around it that things like a protein can be transported in. And not, you know, I don't want to beat a dead horse here, but all of these lines that I'm drawing, even though I drew it as a single line, these are phospholipid bilayers."}, {"video_title": "Endomembrane system   Structure of a cell   Biology   Khan Academy (2).mp3", "Sentence": "Transitional, transitional, transitional, transitional ER is this place where these proteins are being budded off, and they're budding off in vesicles. So this is the transitional ER. And all vesicles are are little small compartments that have a membrane around it that things like a protein can be transported in. And not, you know, I don't want to beat a dead horse here, but all of these lines that I'm drawing, even though I drew it as a single line, these are phospholipid bilayers. So the membrane might be different, the phospholipid bilayers might be different when we go from one piece of the membrane to another, but they all have that same general notion of having this bilayer of phospholipids. But just as a review, these proteins, they can emerge from the transitional ER, they can make their way to the Golgi apparatus, and we've already talked about how in the Golgi apparatus these proteins can be matured. And when I say being matured, there's a bunch of enzymes in here, there's a bunch of Golgi enzymes in here, that can do all sorts of things to the proteins, tag them."}, {"video_title": "Endomembrane system   Structure of a cell   Biology   Khan Academy (2).mp3", "Sentence": "And not, you know, I don't want to beat a dead horse here, but all of these lines that I'm drawing, even though I drew it as a single line, these are phospholipid bilayers. So the membrane might be different, the phospholipid bilayers might be different when we go from one piece of the membrane to another, but they all have that same general notion of having this bilayer of phospholipids. But just as a review, these proteins, they can emerge from the transitional ER, they can make their way to the Golgi apparatus, and we've already talked about how in the Golgi apparatus these proteins can be matured. And when I say being matured, there's a bunch of enzymes in here, there's a bunch of Golgi enzymes in here, that can do all sorts of things to the proteins, tag them. They can actually add saccharides to them so that they become glycoproteins. They can tag them so they can be used in the cellular membrane, or be used outside of the cellular membrane, or to be used other places in the cell. So for example, this protein right over here, it butted off as a vesicle, it makes its way to the Golgi apparatus."}, {"video_title": "Endomembrane system   Structure of a cell   Biology   Khan Academy (2).mp3", "Sentence": "And when I say being matured, there's a bunch of enzymes in here, there's a bunch of Golgi enzymes in here, that can do all sorts of things to the proteins, tag them. They can actually add saccharides to them so that they become glycoproteins. They can tag them so they can be used in the cellular membrane, or be used outside of the cellular membrane, or to be used other places in the cell. So for example, this protein right over here, it butted off as a vesicle, it makes its way to the Golgi apparatus. The membrane can then merge and dump the protein into the Golgi apparatus. From there it can be matured, it might turn into a glycoprotein, who knows what happens to it. And then it could butt off again, and then this protein that's now butted off, it could go to be embedded into the cellular membrane, the protein could be excreted from the cell, or it could go to other parts of the cell."}, {"video_title": "Endomembrane system   Structure of a cell   Biology   Khan Academy (2).mp3", "Sentence": "So for example, this protein right over here, it butted off as a vesicle, it makes its way to the Golgi apparatus. The membrane can then merge and dump the protein into the Golgi apparatus. From there it can be matured, it might turn into a glycoprotein, who knows what happens to it. And then it could butt off again, and then this protein that's now butted off, it could go to be embedded into the cellular membrane, the protein could be excreted from the cell, or it could go to other parts of the cell. Now those aren't everything I've just talked about, those aren't the only parts of the endomembrane system. You have things like vacuoles, which are membrane-bound organelles in a cell. In plant cells, a vacuole can be used for storage, it could be used for structure, vacuoles can get quite large, and they can actually give the structure of the actual plant."}, {"video_title": "Endomembrane system   Structure of a cell   Biology   Khan Academy (2).mp3", "Sentence": "And then it could butt off again, and then this protein that's now butted off, it could go to be embedded into the cellular membrane, the protein could be excreted from the cell, or it could go to other parts of the cell. Now those aren't everything I've just talked about, those aren't the only parts of the endomembrane system. You have things like vacuoles, which are membrane-bound organelles in a cell. In plant cells, a vacuole can be used for storage, it could be used for structure, vacuoles can get quite large, and they can actually give the structure of the actual plant. In animal cells, you might have something called a lysosome. A lysosome is a membrane-bound structure where essentially things go to, for the most part, be recycled or to be torn apart. So maybe something got packaged from someplace, this is some molecules over, let me do this in another color, you have some, and I drew that vesicle a little bit too big, but maybe this stuff needs to be destroyed, so this membrane is going to, it can then merge with that membrane and dump its contents in here, and this has a low pH, and it can actually break apart this stuff, and it can digest this stuff, and recycle it into its more constituent material."}, {"video_title": "Molecular structure of DNA   Macromolecules   Biology   Khan Academy (2).mp3", "Sentence": "We already have an overview video of DNA, and I encourage you to watch that first. But what I want to do in this video is dig a little bit deeper, actually get into the molecular structure of DNA. And just as a starting point, let's just remind ourselves what DNA stands for. I'm gonna write the different parts of the word in different colors. So it stands for deoxyribonucleic, ribonucleic, ribonucleic acid, ribonucleic acid. So I'm just gonna put this on the side. And now let's actually look at the molecular structure and how it relates to this actual name, deoxyribonucleic acid."}, {"video_title": "Molecular structure of DNA   Macromolecules   Biology   Khan Academy (2).mp3", "Sentence": "I'm gonna write the different parts of the word in different colors. So it stands for deoxyribonucleic, ribonucleic, ribonucleic acid, ribonucleic acid. So I'm just gonna put this on the side. And now let's actually look at the molecular structure and how it relates to this actual name, deoxyribonucleic acid. So DNA is just a general term for nucleic acid. And the term nucleic comes from the fact that it's found in the nucleus, it's found in the nucleus of eukaryotes. So that's where the nucleic comes from."}, {"video_title": "Molecular structure of DNA   Macromolecules   Biology   Khan Academy (2).mp3", "Sentence": "And now let's actually look at the molecular structure and how it relates to this actual name, deoxyribonucleic acid. So DNA is just a general term for nucleic acid. And the term nucleic comes from the fact that it's found in the nucleus, it's found in the nucleus of eukaryotes. So that's where the nucleic comes from. And we'll talk about in a second why it's called an acid, but I'll wait on that. And now each DNA molecule is made up of a chain of what we call nucleotides. So what we call nucleotides."}, {"video_title": "Molecular structure of DNA   Macromolecules   Biology   Khan Academy (2).mp3", "Sentence": "So that's where the nucleic comes from. And we'll talk about in a second why it's called an acid, but I'll wait on that. And now each DNA molecule is made up of a chain of what we call nucleotides. So what we call nucleotides. So it's made up of nucleotides. So what does a nucleotide look like? Well, what I have right over here is I have two strands, I've zoomed in two strands of DNA."}, {"video_title": "Molecular structure of DNA   Macromolecules   Biology   Khan Academy (2).mp3", "Sentence": "So what we call nucleotides. So it's made up of nucleotides. So what does a nucleotide look like? Well, what I have right over here is I have two strands, I've zoomed in two strands of DNA. So you could view this side right over here as one of the, I guess you could say the backbones of one side of the ladder. This is the other side of the ladder. And then each of these bridges, and I will talk about what molecules these are, these are kind of the rungs of the ladder."}, {"video_title": "Molecular structure of DNA   Macromolecules   Biology   Khan Academy (2).mp3", "Sentence": "Well, what I have right over here is I have two strands, I've zoomed in two strands of DNA. So you could view this side right over here as one of the, I guess you could say the backbones of one side of the ladder. This is the other side of the ladder. And then each of these bridges, and I will talk about what molecules these are, these are kind of the rungs of the ladder. And a nucleotide, let me separate off a nucleotide. So a nucleotide would, so what I am coordinating off, what I am coordinating off right over here could be considered a nucleotide. So that's one nucleotide, and then it's connected to another."}, {"video_title": "Molecular structure of DNA   Macromolecules   Biology   Khan Academy (2).mp3", "Sentence": "And then each of these bridges, and I will talk about what molecules these are, these are kind of the rungs of the ladder. And a nucleotide, let me separate off a nucleotide. So a nucleotide would, so what I am coordinating off, what I am coordinating off right over here could be considered a nucleotide. So that's one nucleotide, and then it's connected to another. It's connected to another nucleotide, another nucleotide right over here. And on the right-hand side, we have a nucleotide, we have a nucleotide right over there, and then, actually, I wanna do it, let me do it slightly different. We have a nucleotide right over here on the right side, and then right below that, we have another, we have another nucleotide, we have another nucleotide."}, {"video_title": "Molecular structure of DNA   Macromolecules   Biology   Khan Academy (2).mp3", "Sentence": "So that's one nucleotide, and then it's connected to another. It's connected to another nucleotide, another nucleotide right over here. And on the right-hand side, we have a nucleotide, we have a nucleotide right over there, and then, actually, I wanna do it, let me do it slightly different. We have a nucleotide right over here on the right side, and then right below that, we have another, we have another nucleotide, we have another nucleotide. So depicted here, we essentially have four nucleotides. These two are on this left side of the ladder, these two are on the right side of the ladder. Now let's think about the different pieces of that nucleotide."}, {"video_title": "Molecular structure of DNA   Macromolecules   Biology   Khan Academy (2).mp3", "Sentence": "We have a nucleotide right over here on the right side, and then right below that, we have another, we have another nucleotide, we have another nucleotide. So depicted here, we essentially have four nucleotides. These two are on this left side of the ladder, these two are on the right side of the ladder. Now let's think about the different pieces of that nucleotide. So the one thing that might jump out at you is we have these phosphate groups. So this is a phosphate group right over here, this is a phosphate group right over here. Each of these nucleotides have a phosphate group."}, {"video_title": "Molecular structure of DNA   Macromolecules   Biology   Khan Academy (2).mp3", "Sentence": "Now let's think about the different pieces of that nucleotide. So the one thing that might jump out at you is we have these phosphate groups. So this is a phosphate group right over here, this is a phosphate group right over here. Each of these nucleotides have a phosphate group. So this is a phosphate group over here, and this is a phosphate group over here. Now the phosphate groups are actually what make DNA, or actually what make nucleic acid an acid. And you might say, wait, wait, the way you've drawn it, Sal, you have a negative charge."}, {"video_title": "Molecular structure of DNA   Macromolecules   Biology   Khan Academy (2).mp3", "Sentence": "Each of these nucleotides have a phosphate group. So this is a phosphate group over here, and this is a phosphate group over here. Now the phosphate groups are actually what make DNA, or actually what make nucleic acid an acid. And you might say, wait, wait, the way you've drawn it, Sal, you have a negative charge. Something with a negative charge would attract protons, it would sop up protons. How can you call this an acid? This actually looks more basic."}, {"video_title": "Molecular structure of DNA   Macromolecules   Biology   Khan Academy (2).mp3", "Sentence": "And you might say, wait, wait, the way you've drawn it, Sal, you have a negative charge. Something with a negative charge would attract protons, it would sop up protons. How can you call this an acid? This actually looks more basic. And the reason why DNA is typically drawn with these negative charges here is that it's so acidic, and if you put it into a neutral solution, it's actually going to lose its hydrogens. Actually the DNA, if we actually want to be formal about it, the DNA molecules would actually have its phosphates protonated like this, but it so badly wants to lose these hydrogen protons, so it typically would be, let me draw it like this. Let me get rid of the negative charge just on this one."}, {"video_title": "Molecular structure of DNA   Macromolecules   Biology   Khan Academy (2).mp3", "Sentence": "This actually looks more basic. And the reason why DNA is typically drawn with these negative charges here is that it's so acidic, and if you put it into a neutral solution, it's actually going to lose its hydrogens. Actually the DNA, if we actually want to be formal about it, the DNA molecules would actually have its phosphates protonated like this, but it so badly wants to lose these hydrogen protons, so it typically would be, let me draw it like this. Let me get rid of the negative charge just on this one. Whoops, just on this phosphate group over here. So if you get rid of the negative charge, and if this was bounded, this is bonded to a hydrogen, this so badly wants to grab these electrons. So this oxygen can grab these electrons, and then this hydrogen will just be grabbed by another water molecule or something, or so the proton will be let go."}, {"video_title": "Molecular structure of DNA   Macromolecules   Biology   Khan Academy (2).mp3", "Sentence": "Let me get rid of the negative charge just on this one. Whoops, just on this phosphate group over here. So if you get rid of the negative charge, and if this was bounded, this is bonded to a hydrogen, this so badly wants to grab these electrons. So this oxygen can grab these electrons, and then this hydrogen will just be grabbed by another water molecule or something, or so the proton will be let go. That's why we call it an acid. So if it wasn't in a solution, it would have the hydrogens, but it would be very acidic. As soon as you put it into a neutral solution, it's going to lose those hydrogens."}, {"video_title": "Molecular structure of DNA   Macromolecules   Biology   Khan Academy (2).mp3", "Sentence": "So this oxygen can grab these electrons, and then this hydrogen will just be grabbed by another water molecule or something, or so the proton will be let go. That's why we call it an acid. So if it wasn't in a solution, it would have the hydrogens, but it would be very acidic. As soon as you put it into a neutral solution, it's going to lose those hydrogens. So the phosphate groups are what make it an acid, but it's confusing sometimes, because usually when you see it depicted, you see it with these negative charges, and that's because it has already lost its hydrogen protons. You're actually depicting the conjugate base here, but that's where it gets its acidic name from, because it starts protonated, or I guess in its acid form it's protonated, but it readily loses it, and so that's where it gets the name acid from. So each of these nucleotides, they have a phosphate group."}, {"video_title": "Molecular structure of DNA   Macromolecules   Biology   Khan Academy (2).mp3", "Sentence": "As soon as you put it into a neutral solution, it's going to lose those hydrogens. So the phosphate groups are what make it an acid, but it's confusing sometimes, because usually when you see it depicted, you see it with these negative charges, and that's because it has already lost its hydrogen protons. You're actually depicting the conjugate base here, but that's where it gets its acidic name from, because it starts protonated, or I guess in its acid form it's protonated, but it readily loses it, and so that's where it gets the name acid from. So each of these nucleotides, they have a phosphate group. Now the next thing you might notice, the next thing you might notice is, the next thing you might notice is this group right over here. It is a cycle, it is a ring, and it looks an awful lot like a sugar, and that's because it is a sugar. So this sugar is based on, it's a five-carbon sugar."}, {"video_title": "Molecular structure of DNA   Macromolecules   Biology   Khan Academy (2).mp3", "Sentence": "So each of these nucleotides, they have a phosphate group. Now the next thing you might notice, the next thing you might notice is, the next thing you might notice is this group right over here. It is a cycle, it is a ring, and it looks an awful lot like a sugar, and that's because it is a sugar. So this sugar is based on, it's a five-carbon sugar. What I have depicted here, this sugar, this is ribose. So this sugar right over here is ribose. This is when it's just as a straight chain, and like many sugars, it can take a cyclical form."}, {"video_title": "Molecular structure of DNA   Macromolecules   Biology   Khan Academy (2).mp3", "Sentence": "So this sugar is based on, it's a five-carbon sugar. What I have depicted here, this sugar, this is ribose. So this sugar right over here is ribose. This is when it's just as a straight chain, and like many sugars, it can take a cyclical form. Actually, it can take many different cyclical forms, but the one that's most typically described is when you have the, let me show you a number of the carbons, because carbon numbering is important when we talk about DNA. If we start at the carbonyl group right over here, we call that the one carbon, or the one prime carbon. One prime, two prime, three prime, four prime, and five prime."}, {"video_title": "Molecular structure of DNA   Macromolecules   Biology   Khan Academy (2).mp3", "Sentence": "This is when it's just as a straight chain, and like many sugars, it can take a cyclical form. Actually, it can take many different cyclical forms, but the one that's most typically described is when you have the, let me show you a number of the carbons, because carbon numbering is important when we talk about DNA. If we start at the carbonyl group right over here, we call that the one carbon, or the one prime carbon. One prime, two prime, three prime, four prime, and five prime. That's the five prime carbon. And so you form the cyclical form of ribose, is if you have the oxygen, you have the oxygen right over here on the four prime carbon, it uses one of its lone pairs, it uses one of its lone pairs to form a bond, to form a bond with, with the one prime, with the one prime carbon. And I drew it that way, because it kind of does bend, the whole molecule's going to have to bend that way to form this structure."}, {"video_title": "Molecular structure of DNA   Macromolecules   Biology   Khan Academy (2).mp3", "Sentence": "One prime, two prime, three prime, four prime, and five prime. That's the five prime carbon. And so you form the cyclical form of ribose, is if you have the oxygen, you have the oxygen right over here on the four prime carbon, it uses one of its lone pairs, it uses one of its lone pairs to form a bond, to form a bond with, with the one prime, with the one prime carbon. And I drew it that way, because it kind of does bend, the whole molecule's going to have to bend that way to form this structure. And then when it forms that bond, the carbon can let go of one of these double bonds, and then that can, then the oxygen, the oxygen can use that, the oxygen can use those electrons to go grab a hydrogen proton from someplace, so to nab onto a hydrogen proton. So when it does that, you're in this form. And this form, just to be clear of what we're talking about, this is the one prime carbon, one prime, two prime, three prime, four prime, and five, five prime carbon."}, {"video_title": "Molecular structure of DNA   Macromolecules   Biology   Khan Academy (2).mp3", "Sentence": "And I drew it that way, because it kind of does bend, the whole molecule's going to have to bend that way to form this structure. And then when it forms that bond, the carbon can let go of one of these double bonds, and then that can, then the oxygen, the oxygen can use that, the oxygen can use those electrons to go grab a hydrogen proton from someplace, so to nab onto a hydrogen proton. So when it does that, you're in this form. And this form, just to be clear of what we're talking about, this is the one prime carbon, one prime, two prime, three prime, four prime, and five, five prime carbon. And where we see this bond, this is a one prime carbon, it was part of a carbonyl, now it lets go of one of those double bonds so that this oxygen can form a bond with a hydrogen proton, so it let go of a double bond there so that this could form a bond with a hydrogen proton. So this hydrogen proton is that hydrogen proton right over there, and this green bond that gets formed between the four prime carbon or between the oxygen that's attached to the four prime carbon and the one prime carbon, that's this, that's this bond right over here. This oxygen is that oxygen right there, notice, this oxygen is bound to the four prime carbon, and now it's also bound to the one prime carbon."}, {"video_title": "Molecular structure of DNA   Macromolecules   Biology   Khan Academy (2).mp3", "Sentence": "And this form, just to be clear of what we're talking about, this is the one prime carbon, one prime, two prime, three prime, four prime, and five, five prime carbon. And where we see this bond, this is a one prime carbon, it was part of a carbonyl, now it lets go of one of those double bonds so that this oxygen can form a bond with a hydrogen proton, so it let go of a double bond there so that this could form a bond with a hydrogen proton. So this hydrogen proton is that hydrogen proton right over there, and this green bond that gets formed between the four prime carbon or between the oxygen that's attached to the four prime carbon and the one prime carbon, that's this, that's this bond right over here. This oxygen is that oxygen right there, notice, this oxygen is bound to the four prime carbon, and now it's also bound to the one prime carbon. And it was also attached to a hydrogen, It was also attached to a hydrogen, so that hydrogen is there. But then that could get nabbed up by another passing water molecule to become hydronium, so it can get lost. And net-net, it grabs up a hydrogen proton right over here, and so it can lose a hydrogen proton right there."}, {"video_title": "Molecular structure of DNA   Macromolecules   Biology   Khan Academy (2).mp3", "Sentence": "This oxygen is that oxygen right there, notice, this oxygen is bound to the four prime carbon, and now it's also bound to the one prime carbon. And it was also attached to a hydrogen, It was also attached to a hydrogen, so that hydrogen is there. But then that could get nabbed up by another passing water molecule to become hydronium, so it can get lost. And net-net, it grabs up a hydrogen proton right over here, and so it can lose a hydrogen proton right there. So it's not adding or losing net-net. And so you form this cyclical form. And the cyclical form right over here is very close to what we see in a DNA molecule."}, {"video_title": "Molecular structure of DNA   Macromolecules   Biology   Khan Academy (2).mp3", "Sentence": "And net-net, it grabs up a hydrogen proton right over here, and so it can lose a hydrogen proton right there. So it's not adding or losing net-net. And so you form this cyclical form. And the cyclical form right over here is very close to what we see in a DNA molecule. It's actually exactly what we would see in an RNA molecule, in ribonucleic acid. And so what do we think we're talking about when we say deoxyribonucleic acid? Well, you could start with, you have a ribose here, but if we got rid of one of the oxygen groups, and in particular, one of, well, actually, if we just got rid of one of the oxygens, we replace a hydroxyl with just a hydrogen, well, then you're gonna have deoxyribose."}, {"video_title": "Molecular structure of DNA   Macromolecules   Biology   Khan Academy (2).mp3", "Sentence": "And the cyclical form right over here is very close to what we see in a DNA molecule. It's actually exactly what we would see in an RNA molecule, in ribonucleic acid. And so what do we think we're talking about when we say deoxyribonucleic acid? Well, you could start with, you have a ribose here, but if we got rid of one of the oxygen groups, and in particular, one of, well, actually, if we just got rid of one of the oxygens, we replace a hydroxyl with just a hydrogen, well, then you're gonna have deoxyribose. And you see that over here. This five-member ring, you have four carbons right over here. It looks just like this."}, {"video_title": "Molecular structure of DNA   Macromolecules   Biology   Khan Academy (2).mp3", "Sentence": "Well, you could start with, you have a ribose here, but if we got rid of one of the oxygen groups, and in particular, one of, well, actually, if we just got rid of one of the oxygens, we replace a hydroxyl with just a hydrogen, well, then you're gonna have deoxyribose. And you see that over here. This five-member ring, you have four carbons right over here. It looks just like this. The hydrogens are implicit to the carbons. We've seen this multiple times. The carbons are at where these lines intersect, or I guess at the edges, or maybe, and also where these lines end right over there."}, {"video_title": "Molecular structure of DNA   Macromolecules   Biology   Khan Academy (2).mp3", "Sentence": "It looks just like this. The hydrogens are implicit to the carbons. We've seen this multiple times. The carbons are at where these lines intersect, or I guess at the edges, or maybe, and also where these lines end right over there. But you see, this does not have an, this molecule, if we compare these two molecules, if we compare these two molecules over here, we see that this guy has an OH, and this guy implicitly just has, this guy has an OH and an H. This guy implicitly has just two hydrogens over here. So he's missing an oxygen. So this is deoxyribose."}, {"video_title": "Molecular structure of DNA   Macromolecules   Biology   Khan Academy (2).mp3", "Sentence": "The carbons are at where these lines intersect, or I guess at the edges, or maybe, and also where these lines end right over there. But you see, this does not have an, this molecule, if we compare these two molecules, if we compare these two molecules over here, we see that this guy has an OH, and this guy implicitly just has, this guy has an OH and an H. This guy implicitly has just two hydrogens over here. So he's missing an oxygen. So this is deoxyribose. So deoxyribose doesn't have this oxygen. It does not have the oxygen on the two prime carbon. So this, if you get rid of that, this is deoxyribose."}, {"video_title": "Molecular structure of DNA   Macromolecules   Biology   Khan Academy (2).mp3", "Sentence": "So this is deoxyribose. So deoxyribose doesn't have this oxygen. It does not have the oxygen on the two prime carbon. So this, if you get rid of that, this is deoxyribose. So let me circle that. So what we're, this thing right over here, this thing right over here, that is deoxyribose. Deoxy, or it's based on deoxyribose, I guess before it bonded to these other constituents, you could consider this deoxyribose."}, {"video_title": "Molecular structure of DNA   Macromolecules   Biology   Khan Academy (2).mp3", "Sentence": "So this, if you get rid of that, this is deoxyribose. So let me circle that. So what we're, this thing right over here, this thing right over here, that is deoxyribose. Deoxy, or it's based on deoxyribose, I guess before it bonded to these other constituents, you could consider this deoxyribose. And so that's where the deoxyribo comes from. And then the last piece of it, the last piece of it is this chunk right over here. And these we call nitrogenous bases."}, {"video_title": "Molecular structure of DNA   Macromolecules   Biology   Khan Academy (2).mp3", "Sentence": "Deoxy, or it's based on deoxyribose, I guess before it bonded to these other constituents, you could consider this deoxyribose. And so that's where the deoxyribo comes from. And then the last piece of it, the last piece of it is this chunk right over here. And these we call nitrogenous bases. So nitrogenous, nitrogenous, nitrogenous bases. And you can see we have different types of nitrogenous bases. This is a nitrogenous base."}, {"video_title": "Molecular structure of DNA   Macromolecules   Biology   Khan Academy (2).mp3", "Sentence": "And these we call nitrogenous bases. So nitrogenous, nitrogenous, nitrogenous bases. And you can see we have different types of nitrogenous bases. This is a nitrogenous base. This right over here is a different nitrogenous base. This right over here is another different nitrogenous base. Notice this one only has one ring, this one has one ring."}, {"video_title": "Molecular structure of DNA   Macromolecules   Biology   Khan Academy (2).mp3", "Sentence": "This is a nitrogenous base. This right over here is a different nitrogenous base. This right over here is another different nitrogenous base. Notice this one only has one ring, this one has one ring. This one has two rings. This one over here has two rings. And we have different names for these nitrogenous bases."}, {"video_title": "Molecular structure of DNA   Macromolecules   Biology   Khan Academy (2).mp3", "Sentence": "Notice this one only has one ring, this one has one ring. This one has two rings. This one over here has two rings. And we have different names for these nitrogenous bases. The ones with two rings, the general categorization, we call them purines. So nitrogenous bases, if you have two rings, if you have two rings, we call them purines. That's a general classification term."}, {"video_title": "Molecular structure of DNA   Macromolecules   Biology   Khan Academy (2).mp3", "Sentence": "And we have different names for these nitrogenous bases. The ones with two rings, the general categorization, we call them purines. So nitrogenous bases, if you have two rings, if you have two rings, we call them purines. That's a general classification term. Let me make sure, purines. And if you have one ring, maybe I'll just write it this way, one ring, one ring, we call these pyrimidines. Pyrimidines."}, {"video_title": "Molecular structure of DNA   Macromolecules   Biology   Khan Academy (2).mp3", "Sentence": "That's a general classification term. Let me make sure, purines. And if you have one ring, maybe I'll just write it this way, one ring, one ring, we call these pyrimidines. Pyrimidines. Pyrimidines. We call these pyrimidines. And these particular, these two on the right, these two purines, this one up here, this is adenine."}, {"video_title": "Molecular structure of DNA   Macromolecules   Biology   Khan Academy (2).mp3", "Sentence": "Pyrimidines. Pyrimidines. We call these pyrimidines. And these particular, these two on the right, these two purines, this one up here, this is adenine. And we talk about how they pair in the overview video on DNA. But this one right over here is adenine, this nitrogenous base. This one over here is guanine."}, {"video_title": "Molecular structure of DNA   Macromolecules   Biology   Khan Academy (2).mp3", "Sentence": "And these particular, these two on the right, these two purines, this one up here, this is adenine. And we talk about how they pair in the overview video on DNA. But this one right over here is adenine, this nitrogenous base. This one over here is guanine. That is guanine. And then, over here, over here, this single ring, this single ring nitrogenous base, which makes it a pyrimidine, this is thymine. This right over here is thymine."}, {"video_title": "Molecular structure of DNA   Macromolecules   Biology   Khan Academy (2).mp3", "Sentence": "This one over here is guanine. That is guanine. And then, over here, over here, this single ring, this single ring nitrogenous base, which makes it a pyrimidine, this is thymine. This right over here is thymine. This is thymine. And then last but not least, if we're talking about DNA, when we go into RNA, we're also gonna talk about uracil. But when we talk about DNA, this one over here is cytosine."}, {"video_title": "Molecular structure of DNA   Macromolecules   Biology   Khan Academy (2).mp3", "Sentence": "This right over here is thymine. This is thymine. And then last but not least, if we're talking about DNA, when we go into RNA, we're also gonna talk about uracil. But when we talk about DNA, this one over here is cytosine. Cy, cytosine. And you can see the way it's structured, that thymine is attracted to adenine, it bonds with adenine, and cytosine bonds with guanine. So how are they bonding?"}, {"video_title": "Molecular structure of DNA   Macromolecules   Biology   Khan Academy (2).mp3", "Sentence": "But when we talk about DNA, this one over here is cytosine. Cy, cytosine. And you can see the way it's structured, that thymine is attracted to adenine, it bonds with adenine, and cytosine bonds with guanine. So how are they bonding? Well, the way that these nitrogenous bases form the rungs of the ladder, how they're drawn to each other, this is our good old friend hydrogen bonds. And this all comes out of the fact that nitrogen is quite electronegative, so when nitrogen is bound to a hydrogen, you're going to have a partially negative charge at the nitrogen. Let me do this in green."}, {"video_title": "Molecular structure of DNA   Macromolecules   Biology   Khan Academy (2).mp3", "Sentence": "So how are they bonding? Well, the way that these nitrogenous bases form the rungs of the ladder, how they're drawn to each other, this is our good old friend hydrogen bonds. And this all comes out of the fact that nitrogen is quite electronegative, so when nitrogen is bound to a hydrogen, you're going to have a partially negative charge at the nitrogen. Let me do this in green. You're gonna have a partial negative charge at the nitrogen and a partially positive charge at the hydrogen. And then oxygen, we've always talked about as being electronegative, so it has a partial negative charge. So the partial negative charge of this oxygen is going to be attracted to the partial positive charge of this hydrogen, and so you're going to have, you're going to have a hydrogen bond."}, {"video_title": "Molecular structure of DNA   Macromolecules   Biology   Khan Academy (2).mp3", "Sentence": "Let me do this in green. You're gonna have a partial negative charge at the nitrogen and a partially positive charge at the hydrogen. And then oxygen, we've always talked about as being electronegative, so it has a partial negative charge. So the partial negative charge of this oxygen is going to be attracted to the partial positive charge of this hydrogen, and so you're going to have, you're going to have a hydrogen bond. And the same thing is going to happen between this hydrogen, which is going, its electrons are being hogged by this nitrogen, and this nitrogen, which itself hogs electrons, so that forms a hydrogen bond. And then down here, you have a hydrogen that has a partially positive charge because its electrons are being hogged, and then you have this oxygen with a partially negative charge. They're going to be attracted to each other."}, {"video_title": "Molecular structure of DNA   Macromolecules   Biology   Khan Academy (2).mp3", "Sentence": "So the partial negative charge of this oxygen is going to be attracted to the partial positive charge of this hydrogen, and so you're going to have, you're going to have a hydrogen bond. And the same thing is going to happen between this hydrogen, which is going, its electrons are being hogged by this nitrogen, and this nitrogen, which itself hogs electrons, so that forms a hydrogen bond. And then down here, you have a hydrogen that has a partially positive charge because its electrons are being hogged, and then you have this oxygen with a partially negative charge. They're going to be attracted to each other. That's a hydrogen bond. Same thing between this nitrogen and that hydrogen, and same thing between this oxygen and that hydrogen. And that's why cytosine and guanine pair up, and that's why thymine and adenine pair up, and we talk about that as well in the overview video of DNA."}, {"video_title": "Pedigree for determining probability of exhibiting sex linked recessive trait   Khan Academy.mp3", "Sentence": "If it's colored in, that means that they exhibit the trait. In this case, it's colorblindness. So Bill exhibits colorblindness. His phenotype is colorblind, while Bonnie does not exhibit colorblindness. Colorblindness is an X-linked recessive trait. If Barbara is expecting another child, so this is Barbara right here, what is the probability that it will be colorblind? So pause this video and see if you can figure that out on your own."}, {"video_title": "Pedigree for determining probability of exhibiting sex linked recessive trait   Khan Academy.mp3", "Sentence": "His phenotype is colorblind, while Bonnie does not exhibit colorblindness. Colorblindness is an X-linked recessive trait. If Barbara is expecting another child, so this is Barbara right here, what is the probability that it will be colorblind? So pause this video and see if you can figure that out on your own. All right, now let's work through this together. So they're asking us about their next child here. What is the probability that it is going to be colorblind?"}, {"video_title": "Pedigree for determining probability of exhibiting sex linked recessive trait   Khan Academy.mp3", "Sentence": "So pause this video and see if you can figure that out on your own. All right, now let's work through this together. So they're asking us about their next child here. What is the probability that it is going to be colorblind? And to help us with that, we can try to figure out the genotypes of Tom and Barbara. So Tom is pretty straightforward. He is male, we know that because there's a square there."}, {"video_title": "Pedigree for determining probability of exhibiting sex linked recessive trait   Khan Academy.mp3", "Sentence": "What is the probability that it is going to be colorblind? And to help us with that, we can try to figure out the genotypes of Tom and Barbara. So Tom is pretty straightforward. He is male, we know that because there's a square there. So X, he has an X chromosome and he has a Y chromosome. And colorblindness is an X-linked recessive trait. And so let me just make clear what's going on."}, {"video_title": "Pedigree for determining probability of exhibiting sex linked recessive trait   Khan Academy.mp3", "Sentence": "He is male, we know that because there's a square there. So X, he has an X chromosome and he has a Y chromosome. And colorblindness is an X-linked recessive trait. And so let me just make clear what's going on. So I'll do lowercase c for colorblind, colorblind. And I could do a capital C for the dominant trait, which is not colorblind. But since they look so similar, I'll just use a plus for not colorblind, not colorblind."}, {"video_title": "Pedigree for determining probability of exhibiting sex linked recessive trait   Khan Academy.mp3", "Sentence": "And so let me just make clear what's going on. So I'll do lowercase c for colorblind, colorblind. And I could do a capital C for the dominant trait, which is not colorblind. But since they look so similar, I'll just use a plus for not colorblind, not colorblind. And so Tom, his phenotype, he is colorblind. And he only has one X chromosome where the colorblind, what the colorblind trait is linked to. And so that must have the recessive allele right over there."}, {"video_title": "Pedigree for determining probability of exhibiting sex linked recessive trait   Khan Academy.mp3", "Sentence": "But since they look so similar, I'll just use a plus for not colorblind, not colorblind. And so Tom, his phenotype, he is colorblind. And he only has one X chromosome where the colorblind, what the colorblind trait is linked to. And so that must have the recessive allele right over there. So this is Tom's genotype. But what about Barbara? Well, we know Barbara's going to have two X chromosomes because Barbara is female."}, {"video_title": "Pedigree for determining probability of exhibiting sex linked recessive trait   Khan Academy.mp3", "Sentence": "And so that must have the recessive allele right over there. So this is Tom's genotype. But what about Barbara? Well, we know Barbara's going to have two X chromosomes because Barbara is female. And we know that both of them can't be lowercase c because then Barbara would exhibit colorblindness. But how can we figure out her actual genotype? Well, we could look at her parents."}, {"video_title": "Pedigree for determining probability of exhibiting sex linked recessive trait   Khan Academy.mp3", "Sentence": "Well, we know Barbara's going to have two X chromosomes because Barbara is female. And we know that both of them can't be lowercase c because then Barbara would exhibit colorblindness. But how can we figure out her actual genotype? Well, we could look at her parents. So Bill over here is going to have the same genotype as Tom, at least with respect to colorblindness. He is male, so he has an X chromosome and a Y chromosome. And because he exhibits colorblindness, that X chromosome must have the recessive colorblind allele associated with it."}, {"video_title": "Pedigree for determining probability of exhibiting sex linked recessive trait   Khan Academy.mp3", "Sentence": "Well, we could look at her parents. So Bill over here is going to have the same genotype as Tom, at least with respect to colorblindness. He is male, so he has an X chromosome and a Y chromosome. And because he exhibits colorblindness, that X chromosome must have the recessive colorblind allele associated with it. Now Bonnie, we do not know. She will be XX, will have two X chromosomes. Like Barbara, we know that both of these can't have the recessive allele because then Bonnie would be filled in."}, {"video_title": "Pedigree for determining probability of exhibiting sex linked recessive trait   Khan Academy.mp3", "Sentence": "And because he exhibits colorblindness, that X chromosome must have the recessive colorblind allele associated with it. Now Bonnie, we do not know. She will be XX, will have two X chromosomes. Like Barbara, we know that both of these can't have the recessive allele because then Bonnie would be filled in. She would exhibit colorblindness. But we don't know whether she is a carrier or whether she isn't. But let's just think about where Barbara got her chromosomes from."}, {"video_title": "Pedigree for determining probability of exhibiting sex linked recessive trait   Khan Academy.mp3", "Sentence": "Like Barbara, we know that both of these can't have the recessive allele because then Bonnie would be filled in. She would exhibit colorblindness. But we don't know whether she is a carrier or whether she isn't. But let's just think about where Barbara got her chromosomes from. One of her X chromosomes comes from her father. And the other one comes from her mother. So if she got this X chromosome from her father, her father only has one X chromosome to give, the one that has the colorblind allele."}, {"video_title": "Pedigree for determining probability of exhibiting sex linked recessive trait   Khan Academy.mp3", "Sentence": "But let's just think about where Barbara got her chromosomes from. One of her X chromosomes comes from her father. And the other one comes from her mother. So if she got this X chromosome from her father, her father only has one X chromosome to give, the one that has the colorblind allele. So if this is from her father, it must have the colorblind allele here. And we know that the one from her mother does not have the colorblind allele because if it was like this, then Barbara would be colorblind, and she isn't. So we know that this must be a plus here."}, {"video_title": "Pedigree for determining probability of exhibiting sex linked recessive trait   Khan Academy.mp3", "Sentence": "So if she got this X chromosome from her father, her father only has one X chromosome to give, the one that has the colorblind allele. So if this is from her father, it must have the colorblind allele here. And we know that the one from her mother does not have the colorblind allele because if it was like this, then Barbara would be colorblind, and she isn't. So we know that this must be a plus here. It is the dominant non-colorblind allele. And so now we know both of their genotypes. And we can use those to then figure out the possible outcomes for their offspring."}, {"video_title": "Pedigree for determining probability of exhibiting sex linked recessive trait   Khan Academy.mp3", "Sentence": "So we know that this must be a plus here. It is the dominant non-colorblind allele. And so now we know both of their genotypes. And we can use those to then figure out the possible outcomes for their offspring. So for example, Tom can contribute a X chromosome that has a colorblind allele or a Y chromosome. And Barbara, right over here, can contribute an X chromosome that has a colorblind allele or an X chromosome that has the non-colorblind allele. Barbara is a carrier."}, {"video_title": "Pedigree for determining probability of exhibiting sex linked recessive trait   Khan Academy.mp3", "Sentence": "And we can use those to then figure out the possible outcomes for their offspring. So for example, Tom can contribute a X chromosome that has a colorblind allele or a Y chromosome. And Barbara, right over here, can contribute an X chromosome that has a colorblind allele or an X chromosome that has the non-colorblind allele. Barbara is a carrier. And so let me just draw a little Punnett square here. And so we have four possible outcomes for their children, and they're all equally likely. So you can get the X chromosome from Barbara that has a colorblind allele and the X chromosome from Tom that has the colorblind allele."}, {"video_title": "Pedigree for determining probability of exhibiting sex linked recessive trait   Khan Academy.mp3", "Sentence": "Barbara is a carrier. And so let me just draw a little Punnett square here. And so we have four possible outcomes for their children, and they're all equally likely. So you can get the X chromosome from Barbara that has a colorblind allele and the X chromosome from Tom that has the colorblind allele. You could have the X chromosome from Barbara with the colorblind allele and the Y chromosome from Tom. You could have the non-colorblind X chromosome, or the X chromosome that does not have the colorblind allele on it and get the colorblind X chromosome from Tom. Or you could have the non-colorblind X chromosome and the Y chromosome from the father."}, {"video_title": "Pedigree for determining probability of exhibiting sex linked recessive trait   Khan Academy.mp3", "Sentence": "So you can get the X chromosome from Barbara that has a colorblind allele and the X chromosome from Tom that has the colorblind allele. You could have the X chromosome from Barbara with the colorblind allele and the Y chromosome from Tom. You could have the non-colorblind X chromosome, or the X chromosome that does not have the colorblind allele on it and get the colorblind X chromosome from Tom. Or you could have the non-colorblind X chromosome and the Y chromosome from the father. So there's four equal scenarios. And so in how many of these scenarios is the offspring colorblind? Well, here we have a colorblind female."}, {"video_title": "Pedigree for determining probability of exhibiting sex linked recessive trait   Khan Academy.mp3", "Sentence": "Or you could have the non-colorblind X chromosome and the Y chromosome from the father. So there's four equal scenarios. And so in how many of these scenarios is the offspring colorblind? Well, here we have a colorblind female. She has two of the recessive alleles, so that female will be colorblind. This is a female carrier, but they will not show the phenotype of being colorblind. This over here is a colorblind male, has only one X chromosome, and it has the colorblind allele on it."}, {"video_title": "Pedigree for determining probability of exhibiting sex linked recessive trait   Khan Academy.mp3", "Sentence": "Well, here we have a colorblind female. She has two of the recessive alleles, so that female will be colorblind. This is a female carrier, but they will not show the phenotype of being colorblind. This over here is a colorblind male, has only one X chromosome, and it has the colorblind allele on it. And this is a non-colorblind male. So out of four equal outcomes, two of them have the offspring being colorblind. So two out of four, that would be a 50% probability that the offspring will be colorblind."}, {"video_title": "Oxidative phosphorylation and the electron transport chain   Khan Academy.mp3", "Sentence": "And NADH is the main character here, but there are other coenzymes that are involved, like coenzyme Q, and you see that right over here. And what I want to talk about in this video is the process by which we actually are able to produce ATP from the oxidation of these coenzymes. And that process is what we call oxidative phosphorylation. Oxidative, oxidative phosphorylation. Now the main player when we're talking about cellular respiration and oxidative phosphorylation is NADH. NADH in the process of being oxidized to NAD, so it gets oxidized to N, gets oxidized to NAD, which has a positive charge, I often call it NAD+, but let's think about what this has. If we just look at, if we just look at this reaction from the point of view of NADH being oxidized, remember, oxidation is losing electrons."}, {"video_title": "Oxidative phosphorylation and the electron transport chain   Khan Academy.mp3", "Sentence": "Oxidative, oxidative phosphorylation. Now the main player when we're talking about cellular respiration and oxidative phosphorylation is NADH. NADH in the process of being oxidized to NAD, so it gets oxidized to N, gets oxidized to NAD, which has a positive charge, I often call it NAD+, but let's think about what this has. If we just look at, if we just look at this reaction from the point of view of NADH being oxidized, remember, oxidation is losing electrons. So NAD+, and then you're gonna have plus a hydrogen proton, plus you're going to have two electrons, plus two electrons. So this is what's happening when NADH is being oxidized into NAD. So this is oxidation right over here."}, {"video_title": "Oxidative phosphorylation and the electron transport chain   Khan Academy.mp3", "Sentence": "If we just look at, if we just look at this reaction from the point of view of NADH being oxidized, remember, oxidation is losing electrons. So NAD+, and then you're gonna have plus a hydrogen proton, plus you're going to have two electrons, plus two electrons. So this is what's happening when NADH is being oxidized into NAD. So this is oxidation right over here. Let me do this in another color. So this is oxidation. And this process of oxidation, if these electrons get the appropriate acceptor molecule, it can release a lot of energy."}, {"video_title": "Oxidative phosphorylation and the electron transport chain   Khan Academy.mp3", "Sentence": "So this is oxidation right over here. Let me do this in another color. So this is oxidation. And this process of oxidation, if these electrons get the appropriate acceptor molecule, it can release a lot of energy. And the eventual acceptor of those electrons, and I can show the corresponding reduction reaction, is we have two electrons, two electrons, plus two hydrogen protons, or really just two protons. A hydrogen nucleus is just a proton. It doesn't have a neutron for the main isotope of hydrogen."}, {"video_title": "Oxidative phosphorylation and the electron transport chain   Khan Academy.mp3", "Sentence": "And this process of oxidation, if these electrons get the appropriate acceptor molecule, it can release a lot of energy. And the eventual acceptor of those electrons, and I can show the corresponding reduction reaction, is we have two electrons, two electrons, plus two hydrogen protons, or really just two protons. A hydrogen nucleus is just a proton. It doesn't have a neutron for the main isotope of hydrogen. So two protons plus half of an oxygen molecule, yielding, you put all of these three, all of these things together, I should say, and you are going to get a water molecule. So you can think of it as the oxygen being the final acceptor of the electrons. And oxygen likes to oxidize things."}, {"video_title": "Oxidative phosphorylation and the electron transport chain   Khan Academy.mp3", "Sentence": "It doesn't have a neutron for the main isotope of hydrogen. So two protons plus half of an oxygen molecule, yielding, you put all of these three, all of these things together, I should say, and you are going to get a water molecule. So you can think of it as the oxygen being the final acceptor of the electrons. And oxygen likes to oxidize things. That's where the whole word oxidation comes from. So here, or another way to think of it, oxygen likes to be reduced. It likes to hog electrons."}, {"video_title": "Oxidative phosphorylation and the electron transport chain   Khan Academy.mp3", "Sentence": "And oxygen likes to oxidize things. That's where the whole word oxidation comes from. So here, or another way to think of it, oxygen likes to be reduced. It likes to hog electrons. So this is oxygen is being reduced. Oxygen, oxygen reduced. So if you just directly transferred these electrons from our NADH to the oxygen, it would release a lot of energy, but it would release so much energy that you wouldn't be able to capture most of it."}, {"video_title": "Oxidative phosphorylation and the electron transport chain   Khan Academy.mp3", "Sentence": "It likes to hog electrons. So this is oxygen is being reduced. Oxygen, oxygen reduced. So if you just directly transferred these electrons from our NADH to the oxygen, it would release a lot of energy, but it would release so much energy that you wouldn't be able to capture most of it. You wouldn't be able to use it to actually do useful work. And so the process of oxidative phosphorylation is all about doing this in a series of steps. And we do it by transferring these electrons from one electron acceptor to another electron acceptor."}, {"video_title": "Oxidative phosphorylation and the electron transport chain   Khan Academy.mp3", "Sentence": "So if you just directly transferred these electrons from our NADH to the oxygen, it would release a lot of energy, but it would release so much energy that you wouldn't be able to capture most of it. You wouldn't be able to use it to actually do useful work. And so the process of oxidative phosphorylation is all about doing this in a series of steps. And we do it by transferring these electrons from one electron acceptor to another electron acceptor. And every time we do that, we release some energy. And then that energy can be, in a more controlled way, be used to actually do work. And in this case, that work is pumping hydrogen protons across a membrane, and then that gradient that forms can actually be used to generate ATP."}, {"video_title": "Oxidative phosphorylation and the electron transport chain   Khan Academy.mp3", "Sentence": "And we do it by transferring these electrons from one electron acceptor to another electron acceptor. And every time we do that, we release some energy. And then that energy can be, in a more controlled way, be used to actually do work. And in this case, that work is pumping hydrogen protons across a membrane, and then that gradient that forms can actually be used to generate ATP. So let's talk through it a little bit more. So we're gonna go, these electrons, they're gonna be transferred, and I won't go into all of the details. This is to just give you a high-level overview of it."}, {"video_title": "Oxidative phosphorylation and the electron transport chain   Khan Academy.mp3", "Sentence": "And in this case, that work is pumping hydrogen protons across a membrane, and then that gradient that forms can actually be used to generate ATP. So let's talk through it a little bit more. So we're gonna go, these electrons, they're gonna be transferred, and I won't go into all of the details. This is to just give you a high-level overview of it. They're going to be transferred to different acceptors, which then transfer it to another acceptor. So it might go to a coenzyme, coenzyme Q, and a cytochrome, cytochrome C, and it keeps going to different things, eventually, eventually getting to this state right over here where those electrons can be accepted by the oxygen to actually form the water. And in the process, every step of the way, energy is being released."}, {"video_title": "Oxidative phosphorylation and the electron transport chain   Khan Academy.mp3", "Sentence": "This is to just give you a high-level overview of it. They're going to be transferred to different acceptors, which then transfer it to another acceptor. So it might go to a coenzyme, coenzyme Q, and a cytochrome, cytochrome C, and it keeps going to different things, eventually, eventually getting to this state right over here where those electrons can be accepted by the oxygen to actually form the water. And in the process, every step of the way, energy is being released. Energy, energy is being released. And this energy, as we will see in a second, is being used to pump hydrogen protons across a membrane. And we're gonna use that gradient to actually drive the production of ATP."}, {"video_title": "Oxidative phosphorylation and the electron transport chain   Khan Academy.mp3", "Sentence": "And in the process, every step of the way, energy is being released. Energy, energy is being released. And this energy, as we will see in a second, is being used to pump hydrogen protons across a membrane. And we're gonna use that gradient to actually drive the production of ATP. So let's think about that a little bit more. So let's zoom in on a mitochondria. So this is mitochondria."}, {"video_title": "Oxidative phosphorylation and the electron transport chain   Khan Academy.mp3", "Sentence": "And we're gonna use that gradient to actually drive the production of ATP. So let's think about that a little bit more. So let's zoom in on a mitochondria. So this is mitochondria. Let's say that's our mitochondria. And let me draw the inner membrane. And then these folds in the inner membrane, the singular for them is crista."}, {"video_title": "Oxidative phosphorylation and the electron transport chain   Khan Academy.mp3", "Sentence": "So this is mitochondria. Let's say that's our mitochondria. And let me draw the inner membrane. And then these folds in the inner membrane, the singular for them is crista. If we're talking about pearl, it's cristae. So we have these folds in the inner membrane right over here. So just to be clear what's going on, this is the outer membrane, outer membrane."}, {"video_title": "Oxidative phosphorylation and the electron transport chain   Khan Academy.mp3", "Sentence": "And then these folds in the inner membrane, the singular for them is crista. If we're talking about pearl, it's cristae. So we have these folds in the inner membrane right over here. So just to be clear what's going on, this is the outer membrane, outer membrane. That is the inner membrane, inner membrane. The space between the outer and the inner membrane, the space right over here, that is the intermembrane space. Intermembrane, membrane space."}, {"video_title": "Oxidative phosphorylation and the electron transport chain   Khan Academy.mp3", "Sentence": "So just to be clear what's going on, this is the outer membrane, outer membrane. That is the inner membrane, inner membrane. The space between the outer and the inner membrane, the space right over here, that is the intermembrane space. Intermembrane, membrane space. And then the space inside the inner membrane, let me make sure you can read that space properly, this space over here, this is the matrix. This is the matrix. And that is the location of our citric acid cycle or our Krebs cycle."}, {"video_title": "Oxidative phosphorylation and the electron transport chain   Khan Academy.mp3", "Sentence": "Intermembrane, membrane space. And then the space inside the inner membrane, let me make sure you can read that space properly, this space over here, this is the matrix. This is the matrix. And that is the location of our citric acid cycle or our Krebs cycle. And I can symbolize that with this little cycle. You know, we have a cycle going on here. And so that's where the bulk of the NADH is being produced."}, {"video_title": "Oxidative phosphorylation and the electron transport chain   Khan Academy.mp3", "Sentence": "And that is the location of our citric acid cycle or our Krebs cycle. And I can symbolize that with this little cycle. You know, we have a cycle going on here. And so that's where the bulk of the NADH is being produced. Now we also talk about some other coenzymes. In some books or classes you might hear about FAD being reduced to FADH2, which can then be oxidized as part of oxidative phosphorylation. Other times people say, well, actually that's going to be attached to an enzyme."}, {"video_title": "Oxidative phosphorylation and the electron transport chain   Khan Academy.mp3", "Sentence": "And so that's where the bulk of the NADH is being produced. Now we also talk about some other coenzymes. In some books or classes you might hear about FAD being reduced to FADH2, which can then be oxidized as part of oxidative phosphorylation. Other times people say, well, actually that's going to be attached to an enzyme. And then that FADH2 is used to reduce coenzyme Q to produce QH2, and then that participates in oxidative phosphorylation. So you could think about either one of these. I'll focus on QH2."}, {"video_title": "Oxidative phosphorylation and the electron transport chain   Khan Academy.mp3", "Sentence": "Other times people say, well, actually that's going to be attached to an enzyme. And then that FADH2 is used to reduce coenzyme Q to produce QH2, and then that participates in oxidative phosphorylation. So you could think about either one of these. I'll focus on QH2. Well, we'll actually focus on NADH because it's all a similar process. FADH2 or QH2 enters a little bit later down this process, so they don't produce as much energy, but they still can be used to help produce ATP. But anyway, our citric acid cycle, which we have shown in previous videos, that occurring in the matrix, and now let me do a little zoom in here."}, {"video_title": "Oxidative phosphorylation and the electron transport chain   Khan Academy.mp3", "Sentence": "I'll focus on QH2. Well, we'll actually focus on NADH because it's all a similar process. FADH2 or QH2 enters a little bit later down this process, so they don't produce as much energy, but they still can be used to help produce ATP. But anyway, our citric acid cycle, which we have shown in previous videos, that occurring in the matrix, and now let me do a little zoom in here. Let me do a zoom in. So if I were to zoom in, let's say, let me just get a color that we can see. So if I were to zoom in right over there, let's show this fold in the inner membrane, and let's make it clear that this is, like all of these membranes, these are all phospholipid bilayers."}, {"video_title": "Oxidative phosphorylation and the electron transport chain   Khan Academy.mp3", "Sentence": "But anyway, our citric acid cycle, which we have shown in previous videos, that occurring in the matrix, and now let me do a little zoom in here. Let me do a zoom in. So if I were to zoom in, let's say, let me just get a color that we can see. So if I were to zoom in right over there, let's show this fold in the inner membrane, and let's make it clear that this is, like all of these membranes, these are all phospholipid bilayers. So let me draw, let me do the same color that I did in the actual diagram. So we have all these, we have a bilayer of phospholipids, and I'm clearly not drawing any of this stuff to scale. So, almost done."}, {"video_title": "Oxidative phosphorylation and the electron transport chain   Khan Academy.mp3", "Sentence": "So if I were to zoom in right over there, let's show this fold in the inner membrane, and let's make it clear that this is, like all of these membranes, these are all phospholipid bilayers. So let me draw, let me do the same color that I did in the actual diagram. So we have all these, we have a bilayer of phospholipids, and I'm clearly not drawing any of this stuff to scale. So, almost done. All right, just to make it clear. And you have these enzymes that go across the phospholipid bilayer, and these enzymes are, these protein complexes are actually what facilitate oxidative phosphorylation, and this chain of enzymes, this chain of proteins, is what we call the electron, or is what we call the electron transport chain. So let me draw that."}, {"video_title": "Oxidative phosphorylation and the electron transport chain   Khan Academy.mp3", "Sentence": "So, almost done. All right, just to make it clear. And you have these enzymes that go across the phospholipid bilayer, and these enzymes are, these protein complexes are actually what facilitate oxidative phosphorylation, and this chain of enzymes, this chain of proteins, is what we call the electron, or is what we call the electron transport chain. So let me draw that. So maybe this is one protein, and I'm just drawing them as kind of these abstract, abstract, and you could refer to the electron transport chain as either these proteins, or you could use this process of these electrons going from one acceptor to another, eventually making its way all the way to the oxygen. So that might be one protein. This is another protein right over here."}, {"video_title": "Oxidative phosphorylation and the electron transport chain   Khan Academy.mp3", "Sentence": "So let me draw that. So maybe this is one protein, and I'm just drawing them as kind of these abstract, abstract, and you could refer to the electron transport chain as either these proteins, or you could use this process of these electrons going from one acceptor to another, eventually making its way all the way to the oxygen. So that might be one protein. This is another protein right over here. And I'll just do a couple of them. This is really about a high-level overview. And what's happening, what's happening is as the, and this is just gonna be a very high-level simplification of it, as you have your, let's say initially, your NADH comes in, so your NADH comes in, and it donates the protons and the electrons, and then it becomes NAD+, so it just became oxidized."}, {"video_title": "Oxidative phosphorylation and the electron transport chain   Khan Academy.mp3", "Sentence": "This is another protein right over here. And I'll just do a couple of them. This is really about a high-level overview. And what's happening, what's happening is as the, and this is just gonna be a very high-level simplification of it, as you have your, let's say initially, your NADH comes in, so your NADH comes in, and it donates the protons and the electrons, and then it becomes NAD+, so it just became oxidized. Those electrons will go to an acceptor, which then get transferred to another acceptor, they get transferred to another acceptor, and it goes through this electron transport chain, and as that energy is released, that energy is used to pump hydrogen protons from the matrix. So this side right over here, the left side right over here, this is the matrix. This is where our citric acid cycle occurs."}, {"video_title": "Oxidative phosphorylation and the electron transport chain   Khan Academy.mp3", "Sentence": "And what's happening, what's happening is as the, and this is just gonna be a very high-level simplification of it, as you have your, let's say initially, your NADH comes in, so your NADH comes in, and it donates the protons and the electrons, and then it becomes NAD+, so it just became oxidized. Those electrons will go to an acceptor, which then get transferred to another acceptor, they get transferred to another acceptor, and it goes through this electron transport chain, and as that energy is released, that energy is used to pump hydrogen protons from the matrix. So this side right over here, the left side right over here, this is the matrix. This is where our citric acid cycle occurs. So we have protons being pumped out. So we have these protons being pumped out as we release energy, as we go from one electron acceptor to another electron acceptor. And so the electrons are going from higher energy states, and they're releasing energy as they go down this kind of, towards more and more electronegative things, and they feel more comfortable with the water than they felt with the NADH, and by doing so, by these electrons going down that gradient, I guess you could say, or maybe a better way from going from a higher energy state to a lower energy state, we are creating this proton gradient."}, {"video_title": "Oxidative phosphorylation and the electron transport chain   Khan Academy.mp3", "Sentence": "This is where our citric acid cycle occurs. So we have protons being pumped out. So we have these protons being pumped out as we release energy, as we go from one electron acceptor to another electron acceptor. And so the electrons are going from higher energy states, and they're releasing energy as they go down this kind of, towards more and more electronegative things, and they feel more comfortable with the water than they felt with the NADH, and by doing so, by these electrons going down that gradient, I guess you could say, or maybe a better way from going from a higher energy state to a lower energy state, we are creating this proton gradient. So the concentration of protons on the right side of this membrane, just to be clear where this is, this space right over here, this is right over there. That's the intermembrane space where the hydrogen proton concentration is building up. Now, this is stored energy because this is an electrochemical gradient."}, {"video_title": "Oxidative phosphorylation and the electron transport chain   Khan Academy.mp3", "Sentence": "And so the electrons are going from higher energy states, and they're releasing energy as they go down this kind of, towards more and more electronegative things, and they feel more comfortable with the water than they felt with the NADH, and by doing so, by these electrons going down that gradient, I guess you could say, or maybe a better way from going from a higher energy state to a lower energy state, we are creating this proton gradient. So the concentration of protons on the right side of this membrane, just to be clear where this is, this space right over here, this is right over there. That's the intermembrane space where the hydrogen proton concentration is building up. Now, this is stored energy because this is an electrochemical gradient. All this positive charge, they wanna get away from each other. They wanna go to this less positive matrix right over here. And also, just you have a higher concentration of hydrogens and just natural diffusion."}, {"video_title": "Oxidative phosphorylation and the electron transport chain   Khan Academy.mp3", "Sentence": "Now, this is stored energy because this is an electrochemical gradient. All this positive charge, they wanna get away from each other. They wanna go to this less positive matrix right over here. And also, just you have a higher concentration of hydrogens and just natural diffusion. They would wanna go down their concentration gradient into the matrix. There's less of the protons here. There's less of the protons in the matrix than there are in the intermembrane space."}, {"video_title": "Oxidative phosphorylation and the electron transport chain   Khan Academy.mp3", "Sentence": "And also, just you have a higher concentration of hydrogens and just natural diffusion. They would wanna go down their concentration gradient into the matrix. There's less of the protons here. There's less of the protons in the matrix than there are in the intermembrane space. And so, that's the opportunity to now take that energy and produce ATP with them. And the way that this happens, the way this happens, let me extend my membrane a little bit. That's a different color."}, {"video_title": "Oxidative phosphorylation and the electron transport chain   Khan Academy.mp3", "Sentence": "There's less of the protons in the matrix than there are in the intermembrane space. And so, that's the opportunity to now take that energy and produce ATP with them. And the way that this happens, the way this happens, let me extend my membrane a little bit. That's a different color. So let me extend my membrane a little bit, is using a protein called ATP synthase. It's actually a protein complex, I should say. So ATP synthase, really an enzyme."}, {"video_title": "Oxidative phosphorylation and the electron transport chain   Khan Academy.mp3", "Sentence": "That's a different color. So let me extend my membrane a little bit, is using a protein called ATP synthase. It's actually a protein complex, I should say. So ATP synthase, really an enzyme. And ATP synthase goes across, it's actually a fascinating molecule. I'll show a better diagram of it in a second. But your ATP synthase goes across the membrane."}, {"video_title": "Oxidative phosphorylation and the electron transport chain   Khan Academy.mp3", "Sentence": "So ATP synthase, really an enzyme. And ATP synthase goes across, it's actually a fascinating molecule. I'll show a better diagram of it in a second. But your ATP synthase goes across the membrane. It actually has a fairly mechanical structure where it has a bit of a housing and it has an axle in the housing. So it looks maybe something like this. And it actually has something, you can view this as a thing that maybe holds it together."}, {"video_title": "Oxidative phosphorylation and the electron transport chain   Khan Academy.mp3", "Sentence": "But your ATP synthase goes across the membrane. It actually has a fairly mechanical structure where it has a bit of a housing and it has an axle in the housing. So it looks maybe something like this. And it actually has something, you can view this as a thing that maybe holds it together. So it's going across the membrane. I'll show a better diagram of it in a second. So then of course the membrane continues on."}, {"video_title": "Oxidative phosphorylation and the electron transport chain   Khan Academy.mp3", "Sentence": "And it actually has something, you can view this as a thing that maybe holds it together. So it's going across the membrane. I'll show a better diagram of it in a second. So then of course the membrane continues on. Membrane continues on. And what happens is, it allows these hydrogen protons to flow down their electrochemical gradient. So these hydrogen protons go down and they actually cause the axle to spin."}, {"video_title": "Oxidative phosphorylation and the electron transport chain   Khan Academy.mp3", "Sentence": "So then of course the membrane continues on. Membrane continues on. And what happens is, it allows these hydrogen protons to flow down their electrochemical gradient. So these hydrogen protons go down and they actually cause the axle to spin. So maybe I'll draw it this way. They actually cause the axle to spin as they go down their electrochemical gradient. And as this axle spins, and this axle, it's not this smooth, it's not like it's made out of metal or something."}, {"video_title": "Oxidative phosphorylation and the electron transport chain   Khan Academy.mp3", "Sentence": "So these hydrogen protons go down and they actually cause the axle to spin. So maybe I'll draw it this way. They actually cause the axle to spin as they go down their electrochemical gradient. And as this axle spins, and this axle, it's not this smooth, it's not like it's made out of metal or something. It's made out of amino acids. So it's all bumpy and all the rest. So it looks something like this."}, {"video_title": "Oxidative phosphorylation and the electron transport chain   Khan Academy.mp3", "Sentence": "And as this axle spins, and this axle, it's not this smooth, it's not like it's made out of metal or something. It's made out of amino acids. So it's all bumpy and all the rest. So it looks something like this. And what happens is you have ADPs, you have ADPs that get lodged in here. So let's say that's an ADP. And then a phosphate group."}, {"video_title": "Oxidative phosphorylation and the electron transport chain   Khan Academy.mp3", "Sentence": "So it looks something like this. And what happens is you have ADPs, you have ADPs that get lodged in here. So let's say that's an ADP. And then a phosphate group. And there are actually three different sites where this can happen. So that's an ADP and a phosphate group. And there's another site that I'm not drawing."}, {"video_title": "Oxidative phosphorylation and the electron transport chain   Khan Academy.mp3", "Sentence": "And then a phosphate group. And there are actually three different sites where this can happen. So that's an ADP and a phosphate group. And there's another site that I'm not drawing. But as this thing rotates, it essentially keeps changing the conformation of the protein and jams the phosphate group into the ADP, which takes energy and locks them into place to form the ATP. And when they form the ATP, they no longer attach to the active site and they let go. So you have this, actually this mechanical motor."}, {"video_title": "Oxidative phosphorylation and the electron transport chain   Khan Academy.mp3", "Sentence": "And there's another site that I'm not drawing. But as this thing rotates, it essentially keeps changing the conformation of the protein and jams the phosphate group into the ADP, which takes energy and locks them into place to form the ATP. And when they form the ATP, they no longer attach to the active site and they let go. So you have this, actually this mechanical motor. You can view it as almost like a turbine, a water turbine. The water goes through it and that energy is used to generate electricity. Here, hydrogen protons go down their electrochemical gradient."}, {"video_title": "Oxidative phosphorylation and the electron transport chain   Khan Academy.mp3", "Sentence": "So you have this, actually this mechanical motor. You can view it as almost like a turbine, a water turbine. The water goes through it and that energy is used to generate electricity. Here, hydrogen protons go down their electrochemical gradient. That rotary motion is then used to jam phosphate groups onto ADPs to form ATPs. And so this is the actual ATP production going on. And to get a better appreciation for what's going on, this is going on in your body right now."}, {"video_title": "Oxidative phosphorylation and the electron transport chain   Khan Academy.mp3", "Sentence": "Here, hydrogen protons go down their electrochemical gradient. That rotary motion is then used to jam phosphate groups onto ADPs to form ATPs. And so this is the actual ATP production going on. And to get a better appreciation for what's going on, this is going on in your body right now. This is going on in my body. Otherwise, I wouldn't be able to talk. This is how I'm generating my energy."}, {"video_title": "Oxidative phosphorylation and the electron transport chain   Khan Academy.mp3", "Sentence": "And to get a better appreciation for what's going on, this is going on in your body right now. This is going on in my body. Otherwise, I wouldn't be able to talk. This is how I'm generating my energy. This is a more accurate depiction of ATP synthase right over here. And based on this diagram, this is our, this, let me make sure I'm, so this right over here, I'm having trouble, I'm having trouble drawing on this. Let me see if I can."}, {"video_title": "Oxidative phosphorylation and the electron transport chain   Khan Academy.mp3", "Sentence": "This is how I'm generating my energy. This is a more accurate depiction of ATP synthase right over here. And based on this diagram, this is our, this, let me make sure I'm, so this right over here, I'm having trouble, I'm having trouble drawing on this. Let me see if I can. So this part right over here, this area right over there, that's our intermembrane space. This right over here is our, this over here is our matrix. This membrane, this is a phospholipid bilayer."}, {"video_title": "Oxidative phosphorylation and the electron transport chain   Khan Academy.mp3", "Sentence": "Let me see if I can. So this part right over here, this area right over there, that's our intermembrane space. This right over here is our, this over here is our matrix. This membrane, this is a phospholipid bilayer. So if I wanted, I could draw the bilayer of phospholipids right over here. And this is our inner membrane, or we could say this is a fold in the inner membrane. This could be on our crista."}, {"video_title": "Oxidative phosphorylation and the electron transport chain   Khan Academy.mp3", "Sentence": "This membrane, this is a phospholipid bilayer. So if I wanted, I could draw the bilayer of phospholipids right over here. And this is our inner membrane, or we could say this is a fold in the inner membrane. This could be on our crista. And so the hydrogen protons, they build up in the intermembrane space because of the electron transport chain. And then they flow down, and then they flow down their electrochemical gradient, turn this rotor, and then they cause the creation of the ATPs over here. So you have ADP, ADP plus a phosphate group, and then you produce, and you produce your ATP."}, {"video_title": "Oxidative phosphorylation and the electron transport chain   Khan Academy.mp3", "Sentence": "This could be on our crista. And so the hydrogen protons, they build up in the intermembrane space because of the electron transport chain. And then they flow down, and then they flow down their electrochemical gradient, turn this rotor, and then they cause the creation of the ATPs over here. So you have ADP, ADP plus a phosphate group, and then you produce, and you produce your ATP. So this is fascinating. This is going on in the cells of your body. It's going on as you speak."}, {"video_title": "Oxidative phosphorylation and the electron transport chain   Khan Academy.mp3", "Sentence": "So you have ADP, ADP plus a phosphate group, and then you produce, and you produce your ATP. So this is fascinating. This is going on in the cells of your body. It's going on as you speak. It's not some abstract thing that is somehow separate from your reality. This is what is making your reality possible. So hopefully you get a nice appreciation for this."}, {"video_title": "Oxidative phosphorylation and the electron transport chain   Khan Academy.mp3", "Sentence": "It's going on as you speak. It's not some abstract thing that is somehow separate from your reality. This is what is making your reality possible. So hopefully you get a nice appreciation for this. I mean, we spent a lot of time talking about cellular respiration. We spent a lot of time talking about, okay, we can produce some ATPs directly through glycolysis and through the citric acid cycle. But mostly, most of the energy is because of the reduction of these coenzymes, and especially NAD to NADH."}, {"video_title": "Photosynthesis.mp3", "Sentence": "Frankly, if this process didn't occur, we probably wouldn't have life on Earth and I wouldn't be making this video for you because there would be no place for me to actually get food. And the process is called photosynthesis. And you're probably reasonably familiar with the idea. The whole idea is plants and actually bacteria and algae and other things. But we normally associate it with plants. Let me make it in very simple terms. So we normally associate it with plants."}, {"video_title": "Photosynthesis.mp3", "Sentence": "The whole idea is plants and actually bacteria and algae and other things. But we normally associate it with plants. Let me make it in very simple terms. So we normally associate it with plants. And it's the process that plants use, and you might have learned this when we were very young. It's the process that plants use to take carbon dioxide plus some water plus some, I'll do it in yellow, plus some sunlight and turn it into some sugars or some maybe carbohydrates or sugars plus oxygen. And obviously this has two very profound pieces to it for us as a living species."}, {"video_title": "Photosynthesis.mp3", "Sentence": "So we normally associate it with plants. And it's the process that plants use, and you might have learned this when we were very young. It's the process that plants use to take carbon dioxide plus some water plus some, I'll do it in yellow, plus some sunlight and turn it into some sugars or some maybe carbohydrates or sugars plus oxygen. And obviously this has two very profound pieces to it for us as a living species. One, we need carbohydrates or we need sugars in order to fuel our bodies. You saw that in the cellular respiration videos. We generate all of our ATP by performing cellular respiration on glucose, which is essentially a byproduct or a broken down carbohydrate."}, {"video_title": "Photosynthesis.mp3", "Sentence": "And obviously this has two very profound pieces to it for us as a living species. One, we need carbohydrates or we need sugars in order to fuel our bodies. You saw that in the cellular respiration videos. We generate all of our ATP by performing cellular respiration on glucose, which is essentially a byproduct or a broken down carbohydrate. It's the simplest one for us to process in cellular respiration. And then the second hugely important part is getting the oxygen. Once again, we need to breathe oxygen in order for us to break down glucose, in order to respire, in order to perform cellular respiration."}, {"video_title": "Photosynthesis.mp3", "Sentence": "We generate all of our ATP by performing cellular respiration on glucose, which is essentially a byproduct or a broken down carbohydrate. It's the simplest one for us to process in cellular respiration. And then the second hugely important part is getting the oxygen. Once again, we need to breathe oxygen in order for us to break down glucose, in order to respire, in order to perform cellular respiration. So these two things are key for life, especially for life that breathes oxygen. So this process, other than the fact that it's interesting, that there are organisms around us, mostly plants, that are able to harness actual sunlight. You have these fusion reactions in the sun 93 million miles away, and it's releasing these photons, and some small subset of those photons reach the surface of Earth."}, {"video_title": "Photosynthesis.mp3", "Sentence": "Once again, we need to breathe oxygen in order for us to break down glucose, in order to respire, in order to perform cellular respiration. So these two things are key for life, especially for life that breathes oxygen. So this process, other than the fact that it's interesting, that there are organisms around us, mostly plants, that are able to harness actual sunlight. You have these fusion reactions in the sun 93 million miles away, and it's releasing these photons, and some small subset of those photons reach the surface of Earth. They make their way through clouds and whatever else. And then these plants and bacteria and algae are able to harness that somehow and turn them into sugars that we can then eat, or maybe the cow eats them and we eat the cow if we're not vegetarians. We can then use that for energy, not that the cow is all carbohydrates, but this is essentially what is used as the fuel or the energy for all of the other important compounds that we eat."}, {"video_title": "Photosynthesis.mp3", "Sentence": "You have these fusion reactions in the sun 93 million miles away, and it's releasing these photons, and some small subset of those photons reach the surface of Earth. They make their way through clouds and whatever else. And then these plants and bacteria and algae are able to harness that somehow and turn them into sugars that we can then eat, or maybe the cow eats them and we eat the cow if we're not vegetarians. We can then use that for energy, not that the cow is all carbohydrates, but this is essentially what is used as the fuel or the energy for all of the other important compounds that we eat. This is where we get all of our fuel. So this is fuel for animals. Or if you eat a potato directly, you're directly getting your carbohydrates."}, {"video_title": "Photosynthesis.mp3", "Sentence": "We can then use that for energy, not that the cow is all carbohydrates, but this is essentially what is used as the fuel or the energy for all of the other important compounds that we eat. This is where we get all of our fuel. So this is fuel for animals. Or if you eat a potato directly, you're directly getting your carbohydrates. But anyway, this is a very simple notion of photosynthesis, but it's not incorrect. If you had to know one thing about photosynthesis, this would be it. But let's delve a little bit deeper and try to get into the guts of it and see if we can understand a little bit better how this actually happens."}, {"video_title": "Photosynthesis.mp3", "Sentence": "Or if you eat a potato directly, you're directly getting your carbohydrates. But anyway, this is a very simple notion of photosynthesis, but it's not incorrect. If you had to know one thing about photosynthesis, this would be it. But let's delve a little bit deeper and try to get into the guts of it and see if we can understand a little bit better how this actually happens. I find it amazing that somehow photons of sunlight are used to create these sugar molecules or these carbohydrates. So let's delve a little bit deeper. In general, we can write the general equation for photosynthesis."}, {"video_title": "Photosynthesis.mp3", "Sentence": "But let's delve a little bit deeper and try to get into the guts of it and see if we can understand a little bit better how this actually happens. I find it amazing that somehow photons of sunlight are used to create these sugar molecules or these carbohydrates. So let's delve a little bit deeper. In general, we can write the general equation for photosynthesis. I've almost written it here, but I'll write it a little bit more scientifically specific. You start off with some carbon dioxide. You add to that some water."}, {"video_title": "Photosynthesis.mp3", "Sentence": "In general, we can write the general equation for photosynthesis. I've almost written it here, but I'll write it a little bit more scientifically specific. You start off with some carbon dioxide. You add to that some water. And you add to that, instead of sunlight, I'm going to say photons. Because these are what really do excite the electrons in the chlorophyll that go down, and you'll see this process probably in this video, and we'll go in more detail in the next few videos. But that excited electron goes to a high energy state, and as it goes to a lower energy state, we're able to harness that energy to produce ATPs, and you'll see NADPHs, and those are used to produce carbohydrates, but we'll see that in a little bit."}, {"video_title": "Photosynthesis.mp3", "Sentence": "You add to that some water. And you add to that, instead of sunlight, I'm going to say photons. Because these are what really do excite the electrons in the chlorophyll that go down, and you'll see this process probably in this video, and we'll go in more detail in the next few videos. But that excited electron goes to a high energy state, and as it goes to a lower energy state, we're able to harness that energy to produce ATPs, and you'll see NADPHs, and those are used to produce carbohydrates, but we'll see that in a little bit. But the overview of photosynthesis, you start off with these constituents, and then you end up with a carbohydrate. And a carbohydrate could be glucose, doesn't have to be glucose. So the general way we can write a carbohydrate is CH2O, and we'll put an N over here, that we could have N multiples of these."}, {"video_title": "Photosynthesis.mp3", "Sentence": "But that excited electron goes to a high energy state, and as it goes to a lower energy state, we're able to harness that energy to produce ATPs, and you'll see NADPHs, and those are used to produce carbohydrates, but we'll see that in a little bit. But the overview of photosynthesis, you start off with these constituents, and then you end up with a carbohydrate. And a carbohydrate could be glucose, doesn't have to be glucose. So the general way we can write a carbohydrate is CH2O, and we'll put an N over here, that we could have N multiples of these. And normally your N will be at least 3. In the case of glucose, N is 6. You have 6 carbons, 12 hydrogens, and 6 oxygens."}, {"video_title": "Photosynthesis.mp3", "Sentence": "So the general way we can write a carbohydrate is CH2O, and we'll put an N over here, that we could have N multiples of these. And normally your N will be at least 3. In the case of glucose, N is 6. You have 6 carbons, 12 hydrogens, and 6 oxygens. So this is a general term for a carbohydrate, but you could have many multiples of that. You could have these long-chain carbohydrates. So you end up with a carbohydrate, and then you end up with some oxygen."}, {"video_title": "Photosynthesis.mp3", "Sentence": "You have 6 carbons, 12 hydrogens, and 6 oxygens. So this is a general term for a carbohydrate, but you could have many multiples of that. You could have these long-chain carbohydrates. So you end up with a carbohydrate, and then you end up with some oxygen. So this right here isn't so different than what I wrote up here in my first overview of how we always imagined photosynthesis in our heads. In order to make this equation balance, let's say I have N carbons here, so I need N carbons there. Let's see, I have 2N hydrogens here, right?"}, {"video_title": "Photosynthesis.mp3", "Sentence": "So you end up with a carbohydrate, and then you end up with some oxygen. So this right here isn't so different than what I wrote up here in my first overview of how we always imagined photosynthesis in our heads. In order to make this equation balance, let's say I have N carbons here, so I need N carbons there. Let's see, I have 2N hydrogens here, right? 2 hydrogens, and I have N there, so I need 2N hydrogens here. So I'll put an N out there, and let's see how many oxygens. I have 2N oxygens plus another N, so I have 3N oxygens."}, {"video_title": "Photosynthesis.mp3", "Sentence": "Let's see, I have 2N hydrogens here, right? 2 hydrogens, and I have N there, so I need 2N hydrogens here. So I'll put an N out there, and let's see how many oxygens. I have 2N oxygens plus another N, so I have 3N oxygens. Let's see, I have 1N, and let's see, put an N here, and then I have 2N, and I think this equation balances out. So this is a 30,000-foot view of what's going on in photosynthesis. But when you dig a little deeper, you'll see that this doesn't happen directly, that this happens through a bunch of steps that eventually gets us to the carbohydrate."}, {"video_title": "Photosynthesis.mp3", "Sentence": "I have 2N oxygens plus another N, so I have 3N oxygens. Let's see, I have 1N, and let's see, put an N here, and then I have 2N, and I think this equation balances out. So this is a 30,000-foot view of what's going on in photosynthesis. But when you dig a little deeper, you'll see that this doesn't happen directly, that this happens through a bunch of steps that eventually gets us to the carbohydrate. So in general, we can break down photosynthesis. I'll rewrite the word. We can break down photosynthesis."}, {"video_title": "Photosynthesis.mp3", "Sentence": "But when you dig a little deeper, you'll see that this doesn't happen directly, that this happens through a bunch of steps that eventually gets us to the carbohydrate. So in general, we can break down photosynthesis. I'll rewrite the word. We can break down photosynthesis. And we'll delve deeper into future videos, but I want to give you the overview first into 2 stages. We can call 1 the light reactions, or sometimes they're called the light-dependent reactions, and that actually would probably be a better way to write it. Let me write it like that."}, {"video_title": "Photosynthesis.mp3", "Sentence": "We can break down photosynthesis. And we'll delve deeper into future videos, but I want to give you the overview first into 2 stages. We can call 1 the light reactions, or sometimes they're called the light-dependent reactions, and that actually would probably be a better way to write it. Let me write it like that. Light-dependent means that they need light to occur. Light-dependent reactions. And then you have something called the dark reactions, and that's actually a bad name because it also occurs in the light."}, {"video_title": "Photosynthesis.mp3", "Sentence": "Let me write it like that. Light-dependent means that they need light to occur. Light-dependent reactions. And then you have something called the dark reactions, and that's actually a bad name because it also occurs in the light. Dark reactions. I wrote it in a slightly darker color. And the reason why I said it's a bad name is because it still occurs in the light."}, {"video_title": "Photosynthesis.mp3", "Sentence": "And then you have something called the dark reactions, and that's actually a bad name because it also occurs in the light. Dark reactions. I wrote it in a slightly darker color. And the reason why I said it's a bad name is because it still occurs in the light. But the reason why they probably called it the dark reaction is that you don't need light, or that part of photosynthesis isn't dependent on photons to occur. So a better term for it would have been light-independent reaction. So just to be clear, the light reactions actually need sunlight."}, {"video_title": "Photosynthesis.mp3", "Sentence": "And the reason why I said it's a bad name is because it still occurs in the light. But the reason why they probably called it the dark reaction is that you don't need light, or that part of photosynthesis isn't dependent on photons to occur. So a better term for it would have been light-independent reaction. So just to be clear, the light reactions actually need sunlight. They actually need photons for them to proceed. The dark reactions do not need photons for them to happen, although they do occur when the sun is out. They don't need those photons, but they need the byproducts from the light reaction to occur."}, {"video_title": "Photosynthesis.mp3", "Sentence": "So just to be clear, the light reactions actually need sunlight. They actually need photons for them to proceed. The dark reactions do not need photons for them to happen, although they do occur when the sun is out. They don't need those photons, but they need the byproducts from the light reaction to occur. So that's why it's called the light-independent reaction. They occur while the sun is out, but they don't need the sun. This needs the sun, so let me make it very clear."}, {"video_title": "Photosynthesis.mp3", "Sentence": "They don't need those photons, but they need the byproducts from the light reaction to occur. So that's why it's called the light-independent reaction. They occur while the sun is out, but they don't need the sun. This needs the sun, so let me make it very clear. So this requires sunlight. This requires photons. And let me just make a very brief overview of this."}, {"video_title": "Photosynthesis.mp3", "Sentence": "This needs the sun, so let me make it very clear. So this requires sunlight. This requires photons. And let me just make a very brief overview of this. This will maybe let us start building a scaffold from which we can dig deeper. So the light reactions need photons, and then it needs water. So water goes into the light reactions, and out of the other side of the light reactions, we end up with some molecular oxygen."}, {"video_title": "Photosynthesis.mp3", "Sentence": "And let me just make a very brief overview of this. This will maybe let us start building a scaffold from which we can dig deeper. So the light reactions need photons, and then it needs water. So water goes into the light reactions, and out of the other side of the light reactions, we end up with some molecular oxygen. So that's what happens in the light reactions, and I'm going to go much deeper on what actually occurs. And what the light reactions produce, it produces ATP, which we know is the cellular or the biological currency of energy. It produces ATP, and it produces NADPH."}, {"video_title": "Photosynthesis.mp3", "Sentence": "So water goes into the light reactions, and out of the other side of the light reactions, we end up with some molecular oxygen. So that's what happens in the light reactions, and I'm going to go much deeper on what actually occurs. And what the light reactions produce, it produces ATP, which we know is the cellular or the biological currency of energy. It produces ATP, and it produces NADPH. Now, when we studied cellular respiration, we saw the molecule NADH. NADPH is very similar. You just have this P there."}, {"video_title": "Photosynthesis.mp3", "Sentence": "It produces ATP, and it produces NADPH. Now, when we studied cellular respiration, we saw the molecule NADH. NADPH is very similar. You just have this P there. You just have this phosphate group there. But they really perform similar mechanisms. That when you have this agent right here, this molecule right here, is able to give away \u2013 let's think about what this means."}, {"video_title": "Photosynthesis.mp3", "Sentence": "You just have this P there. You just have this phosphate group there. But they really perform similar mechanisms. That when you have this agent right here, this molecule right here, is able to give away \u2013 let's think about what this means. It's able to give away this hydrogen and the electron associated with this hydrogen. So if you give away an electron to someone else, or someone else gains an electron, that something else is being reduced. Let me write that down."}, {"video_title": "Photosynthesis.mp3", "Sentence": "That when you have this agent right here, this molecule right here, is able to give away \u2013 let's think about what this means. It's able to give away this hydrogen and the electron associated with this hydrogen. So if you give away an electron to someone else, or someone else gains an electron, that something else is being reduced. Let me write that down. Good reminder. Oil rig. Oxidation is losing an electron."}, {"video_title": "Photosynthesis.mp3", "Sentence": "Let me write that down. Good reminder. Oil rig. Oxidation is losing an electron. Reduction is gaining an electron. Your charge is reduced when you gain an electron. It has a negative charge."}, {"video_title": "Photosynthesis.mp3", "Sentence": "Oxidation is losing an electron. Reduction is gaining an electron. Your charge is reduced when you gain an electron. It has a negative charge. So this is a reducing agent. It gets oxidized by losing the hydrogen and the electron with it. I have a whole discussion on the biological versus chemistry view of oxidation."}, {"video_title": "Photosynthesis.mp3", "Sentence": "It has a negative charge. So this is a reducing agent. It gets oxidized by losing the hydrogen and the electron with it. I have a whole discussion on the biological versus chemistry view of oxidation. But it's the same idea. When I lose a hydrogen, I also lose the ability to hog that hydrogen's electron. So this right here, when it reacts with other things, it's a reducing agent."}, {"video_title": "Photosynthesis.mp3", "Sentence": "I have a whole discussion on the biological versus chemistry view of oxidation. But it's the same idea. When I lose a hydrogen, I also lose the ability to hog that hydrogen's electron. So this right here, when it reacts with other things, it's a reducing agent. It gives away this hydrogen and the electron associated with it. So the other thing gets reduced. So this thing is a reducing agent."}, {"video_title": "Photosynthesis.mp3", "Sentence": "So this right here, when it reacts with other things, it's a reducing agent. It gives away this hydrogen and the electron associated with it. So the other thing gets reduced. So this thing is a reducing agent. What's useful about it is when this hydrogen, and especially the electron associated with that hydrogen, goes from the NADPH to, say, another molecule and goes to a lower energy state, that energy can be used in the dark reactions. We saw in cellular respiration the very similar molecule, NADH, that through the electron transport chain was able to help produce ATP. As it gave away its electrons and they went to lower energy states."}, {"video_title": "Photosynthesis.mp3", "Sentence": "So this thing is a reducing agent. What's useful about it is when this hydrogen, and especially the electron associated with that hydrogen, goes from the NADPH to, say, another molecule and goes to a lower energy state, that energy can be used in the dark reactions. We saw in cellular respiration the very similar molecule, NADH, that through the electron transport chain was able to help produce ATP. As it gave away its electrons and they went to lower energy states. But I don't want to confuse you too much. So the light reactions, you take in photons, you take in water, it spits out oxygen, and it spits out ATP and NADPH that can then be used in the dark reactions. And the dark reactions, for most plants we talk about, it's called the Calvin cycle."}, {"video_title": "Photosynthesis.mp3", "Sentence": "As it gave away its electrons and they went to lower energy states. But I don't want to confuse you too much. So the light reactions, you take in photons, you take in water, it spits out oxygen, and it spits out ATP and NADPH that can then be used in the dark reactions. And the dark reactions, for most plants we talk about, it's called the Calvin cycle. And I'll go into a lot more detail of what actually occurs in the Calvin cycle. But it takes in the ATP, the NADPH, and it produces, it doesn't directly produce glucose, it produces a, well you probably saw this, you could call it PGAL, you could call it G3P, these all stand for, let me write these down, this is phosphoglyceraldehyde, let me write that down, phosphoglyceraldehyde, my handwriting broke down, or you could call it glyceraldehyde 3-phosphate, let me write that down, glyceraldehyde 3-phosphate, same exact molecule, you can almost imagine it, this is a very gross oversimplification, is 3 carbons with a phosphate group attached to it. But this can then be used to produce other carbohydrates, including glucose."}, {"video_title": "Photosynthesis.mp3", "Sentence": "And the dark reactions, for most plants we talk about, it's called the Calvin cycle. And I'll go into a lot more detail of what actually occurs in the Calvin cycle. But it takes in the ATP, the NADPH, and it produces, it doesn't directly produce glucose, it produces a, well you probably saw this, you could call it PGAL, you could call it G3P, these all stand for, let me write these down, this is phosphoglyceraldehyde, let me write that down, phosphoglyceraldehyde, my handwriting broke down, or you could call it glyceraldehyde 3-phosphate, let me write that down, glyceraldehyde 3-phosphate, same exact molecule, you can almost imagine it, this is a very gross oversimplification, is 3 carbons with a phosphate group attached to it. But this can then be used to produce other carbohydrates, including glucose. If you have two of these, you can use those two to produce glucose. So let's just take a quick overview again, because this is super important, I'm going to make videos on the light reactions and the dark reactions, those will be the next two videos I make. So photosynthesis, you start with photons."}, {"video_title": "Photosynthesis.mp3", "Sentence": "But this can then be used to produce other carbohydrates, including glucose. If you have two of these, you can use those two to produce glucose. So let's just take a quick overview again, because this is super important, I'm going to make videos on the light reactions and the dark reactions, those will be the next two videos I make. So photosynthesis, you start with photons. Now all of these occur when the sun is out, but only the light reactions actually need the photons. The light reactions take photons, we're going to go into more detail on what actually occurs, and it takes in water, oxygen gets spit out, ATP and NADPH get spit out, which are then used by the dark reaction, or the Calvin Cycle, or the light independent reaction, because these still occur in the light, they just don't need photons, so they're the light independent reaction, and it uses that in conjunction, we'll talk about other molecules that are used in conjunction, oh, and I forgot a very important constituent of the dark reaction, it needs carbon dioxide, that's where you get your carbons to keep producing these phosphoglyceraldehydes, or glyceraldehyde 3-phosphate, so that's super important. It takes in the carbon dioxide, the products from the light reactions, and then uses that in the Calvin Cycle to produce this very simple building block of other carbohydrates, and if you remember from glycolysis, you might remember that this PGAL molecule, or this G3P, same thing, this was actually the first product when we split glucose in two, when we performed glycolysis, so now we're going the other way, we're building glucose so that we can split it later for energy."}, {"video_title": "Introduction to genetic engineering   Molecular genetics   High school biology   Khan Academy.mp3", "Sentence": "We didn't even know that genes were actually the mechanism of heredity until the middle of the 20th century, and the direct modification of genes for some purpose really didn't even start happening until the 1970s. But it's worth noting that human beings have been in some ways influencing the genetics of organisms for a very, very, very long time. For example, in nature, you have things that look like this, we call them wolves. But today in our lives, we also have things that look like this. Now these dogs did not come about naturally. They came about from many generations of breeding, of human beings taking things that started off looking like wolves or foxes and selecting for certain traits. They might have selected for traits that maybe they're small and they look more like puppies even when they're full grown, or traits that they are more docile, they're more likely to listen to what a human being says to do, or traits that they're good at killing rodents, or whatever else it might be, and over time, repeated selection of those traits led to what we see as these different breeds of dogs."}, {"video_title": "Introduction to genetic engineering   Molecular genetics   High school biology   Khan Academy.mp3", "Sentence": "But today in our lives, we also have things that look like this. Now these dogs did not come about naturally. They came about from many generations of breeding, of human beings taking things that started off looking like wolves or foxes and selecting for certain traits. They might have selected for traits that maybe they're small and they look more like puppies even when they're full grown, or traits that they are more docile, they're more likely to listen to what a human being says to do, or traits that they're good at killing rodents, or whatever else it might be, and over time, repeated selection of those traits led to what we see as these different breeds of dogs. So even though human beings were doing this for hundreds and thousands of years, they were influencing what DNA gets passed on from one generation to another. They didn't know about the actual genetic code, but it was a form of genetic manipulation nonetheless. Similarly, if you look into the plant kingdom, when you go to the store and you see that sweet apple, things like that might not have existed in the form that you see them today."}, {"video_title": "Introduction to genetic engineering   Molecular genetics   High school biology   Khan Academy.mp3", "Sentence": "They might have selected for traits that maybe they're small and they look more like puppies even when they're full grown, or traits that they are more docile, they're more likely to listen to what a human being says to do, or traits that they're good at killing rodents, or whatever else it might be, and over time, repeated selection of those traits led to what we see as these different breeds of dogs. So even though human beings were doing this for hundreds and thousands of years, they were influencing what DNA gets passed on from one generation to another. They didn't know about the actual genetic code, but it was a form of genetic manipulation nonetheless. Similarly, if you look into the plant kingdom, when you go to the store and you see that sweet apple, things like that might not have existed in the form that you see them today. It is very likely, in fact, most agricultural products, people might have found wild apples, and we could be talking thousands of years ago, they might have found wild apple trees. Let me draw a quick apple tree here. And they might have found that the apples were a little bit sour and small, and hard to eat and hard to digest, but over time, people selected the trees that had sweeter apples, that had larger apples, and made the conditions so that they were more likely to reproduce, so over time, you got larger and sweeter apples like the type that you see at your store."}, {"video_title": "Introduction to genetic engineering   Molecular genetics   High school biology   Khan Academy.mp3", "Sentence": "Similarly, if you look into the plant kingdom, when you go to the store and you see that sweet apple, things like that might not have existed in the form that you see them today. It is very likely, in fact, most agricultural products, people might have found wild apples, and we could be talking thousands of years ago, they might have found wild apple trees. Let me draw a quick apple tree here. And they might have found that the apples were a little bit sour and small, and hard to eat and hard to digest, but over time, people selected the trees that had sweeter apples, that had larger apples, and made the conditions so that they were more likely to reproduce, so over time, you got larger and sweeter apples like the type that you see at your store. And as I mentioned, most agricultural products that we have today are the result of hundreds or thousands of years of this type of breeding. So even though that might not be the formal definition of genetic engineering, which typically is referring to something like gene modification, which we've only been able to do in the last few decades, human beings have been doing some type of influence on organisms' DNA for a very, very long time. But with that said, in the last few decades, we've been able to become much, much more precise with influencing DNA through genetic engineering."}, {"video_title": "Introduction to genetic engineering   Molecular genetics   High school biology   Khan Academy.mp3", "Sentence": "And they might have found that the apples were a little bit sour and small, and hard to eat and hard to digest, but over time, people selected the trees that had sweeter apples, that had larger apples, and made the conditions so that they were more likely to reproduce, so over time, you got larger and sweeter apples like the type that you see at your store. And as I mentioned, most agricultural products that we have today are the result of hundreds or thousands of years of this type of breeding. So even though that might not be the formal definition of genetic engineering, which typically is referring to something like gene modification, which we've only been able to do in the last few decades, human beings have been doing some type of influence on organisms' DNA for a very, very long time. But with that said, in the last few decades, we've been able to become much, much more precise with influencing DNA through genetic engineering. In other videos, we'll go more detail about how that is done, but you have this idea of recombinant DNA, combinant DNA, where you could take genes from one organism and put them in another organism. And you might say, why is this useful? Well, let's say that there's a tree you wanna grow."}, {"video_title": "Introduction to genetic engineering   Molecular genetics   High school biology   Khan Academy.mp3", "Sentence": "But with that said, in the last few decades, we've been able to become much, much more precise with influencing DNA through genetic engineering. In other videos, we'll go more detail about how that is done, but you have this idea of recombinant DNA, combinant DNA, where you could take genes from one organism and put them in another organism. And you might say, why is this useful? Well, let's say that there's a tree you wanna grow. Let's say it's an apple tree. But it's very susceptible to a certain type of disease, and if that disease hits, you lose all of your crop. But what if you could insert into the DNA of that apple tree maybe a gene that makes it more resistant to that disease?"}, {"video_title": "Introduction to genetic engineering   Molecular genetics   High school biology   Khan Academy.mp3", "Sentence": "Well, let's say that there's a tree you wanna grow. Let's say it's an apple tree. But it's very susceptible to a certain type of disease, and if that disease hits, you lose all of your crop. But what if you could insert into the DNA of that apple tree maybe a gene that makes it more resistant to that disease? And this is what people actually do today. So they will insert, insert DNA, and it could be some pretty wild things. I've read stories about inserting insect DNA into a plant so that it will be more robust in some way or another."}, {"video_title": "Introduction to genetic engineering   Molecular genetics   High school biology   Khan Academy.mp3", "Sentence": "But what if you could insert into the DNA of that apple tree maybe a gene that makes it more resistant to that disease? And this is what people actually do today. So they will insert, insert DNA, and it could be some pretty wild things. I've read stories about inserting insect DNA into a plant so that it will be more robust in some way or another. Now, this idea of recombinant DNA and genetically modifying food, this is often known as a genetically modified organism, this is somewhat controversial. Many people say, hey, this is good. It allows us to produce more robust foods."}, {"video_title": "Introduction to genetic engineering   Molecular genetics   High school biology   Khan Academy.mp3", "Sentence": "I've read stories about inserting insect DNA into a plant so that it will be more robust in some way or another. Now, this idea of recombinant DNA and genetically modifying food, this is often known as a genetically modified organism, this is somewhat controversial. Many people say, hey, this is good. It allows us to produce more robust foods. In fact, part of this recombinant DNA, inserting DNA into something else, it might make it more nutritious. It might provide for more vitamins. But other people would argue that, hey, we don't know exactly what all the repercussions of what we're doing will happen."}, {"video_title": "Introduction to genetic engineering   Molecular genetics   High school biology   Khan Academy.mp3", "Sentence": "It allows us to produce more robust foods. In fact, part of this recombinant DNA, inserting DNA into something else, it might make it more nutritious. It might provide for more vitamins. But other people would argue that, hey, we don't know exactly what all the repercussions of what we're doing will happen. We might think it's helpful, but when you're taking DNA from one organism and putting it into another, how does that affect the nutrition or the long-lasting effects of eating that over time? So this is something for you to think about, and we're starting to go, when we start asking these questions, into the field of bioethics. As we have more and more control over the genome, and especially as we'll see the human genome, there's questions that we have to ask about, is it good or is it bad?"}, {"video_title": "Introduction to genetic engineering   Molecular genetics   High school biology   Khan Academy.mp3", "Sentence": "But other people would argue that, hey, we don't know exactly what all the repercussions of what we're doing will happen. We might think it's helpful, but when you're taking DNA from one organism and putting it into another, how does that affect the nutrition or the long-lasting effects of eating that over time? So this is something for you to think about, and we're starting to go, when we start asking these questions, into the field of bioethics. As we have more and more control over the genome, and especially as we'll see the human genome, there's questions that we have to ask about, is it good or is it bad? But going back to this idea of genetic engineering and recombinant DNA, other things that you could do is, you could, let's say that we need to produce insulin for diabetics. Well, maybe you can take a bacteria cell and insert into the bacteria cell the gene that helps produce for insulin. And then all of a sudden, that bacteria cell can become a human insulin-producing factory so that we could have more insulin for diabetics, that this insulin could then be harvested."}, {"video_title": "Introduction to genetic engineering   Molecular genetics   High school biology   Khan Academy.mp3", "Sentence": "As we have more and more control over the genome, and especially as we'll see the human genome, there's questions that we have to ask about, is it good or is it bad? But going back to this idea of genetic engineering and recombinant DNA, other things that you could do is, you could, let's say that we need to produce insulin for diabetics. Well, maybe you can take a bacteria cell and insert into the bacteria cell the gene that helps produce for insulin. And then all of a sudden, that bacteria cell can become a human insulin-producing factory so that we could have more insulin for diabetics, that this insulin could then be harvested. That is a use of recombinant DNA. And so we really are going into an interesting period in humanity. For many thousands of years, we were breeding things, but now we're learning to manipulate things at a very fine-grain level."}, {"video_title": "Introduction to genetic engineering   Molecular genetics   High school biology   Khan Academy.mp3", "Sentence": "And then all of a sudden, that bacteria cell can become a human insulin-producing factory so that we could have more insulin for diabetics, that this insulin could then be harvested. That is a use of recombinant DNA. And so we really are going into an interesting period in humanity. For many thousands of years, we were breeding things, but now we're learning to manipulate things at a very fine-grain level. And it makes us ask all sorts of questions. There are likely to be some very good things we can do, produce new medicines, produce more robust crops, but there are also questions about what are the side effects and the bioethics get really interesting when we start thinking about modifying the human genome itself. Because when you're modifying genetics, you're not just modifying one organism, you're modifying all of their offspring."}, {"video_title": "Introduction to genetic engineering   Molecular genetics   High school biology   Khan Academy.mp3", "Sentence": "For many thousands of years, we were breeding things, but now we're learning to manipulate things at a very fine-grain level. And it makes us ask all sorts of questions. There are likely to be some very good things we can do, produce new medicines, produce more robust crops, but there are also questions about what are the side effects and the bioethics get really interesting when we start thinking about modifying the human genome itself. Because when you're modifying genetics, you're not just modifying one organism, you're modifying all of their offspring. You're modifying the genes that exist in the gene pool. And so some very good arguments for modifying the human genome are correcting diseases, some things that could be very serious. But over time, people might say, hey, I wanna be a little bit taller, I want a certain hair color, I want straighter teeth, or they might say, I want a child who has this trait or that trait."}, {"video_title": "Introduced species and biodiversity.mp3", "Sentence": "Let's face it, if you take a bunch of beautiful flowers and plant them in your garden, you're increasing the biodiversity in your garden, right? You raise the species richness in your garden. But it's not a simple additive equation. It's more complicated than that. The term introduced species is synonymous with exotic species. The definition is any species that through the activities of humans is knowingly or accidentally transferred from its native habitat into one in which it doesn't naturally occur. An introduced species is the opposite of a native species, which is one that occurs in an area naturally, without human intervention."}, {"video_title": "Introduced species and biodiversity.mp3", "Sentence": "It's more complicated than that. The term introduced species is synonymous with exotic species. The definition is any species that through the activities of humans is knowingly or accidentally transferred from its native habitat into one in which it doesn't naturally occur. An introduced species is the opposite of a native species, which is one that occurs in an area naturally, without human intervention. Many introductions are intentional. We do it on purpose, and we've been doing that for a heck of a long time, probably ever since humans came onto the scene and realized that they could pick something up that was alive and bring it somewhere else to serve their purposes. From goats and pigs to cattle and crops."}, {"video_title": "Introduced species and biodiversity.mp3", "Sentence": "An introduced species is the opposite of a native species, which is one that occurs in an area naturally, without human intervention. Many introductions are intentional. We do it on purpose, and we've been doing that for a heck of a long time, probably ever since humans came onto the scene and realized that they could pick something up that was alive and bring it somewhere else to serve their purposes. From goats and pigs to cattle and crops. Mostly we transport organisms that will do some good for us through agricultural means. We've been introducing plants and animals to places where they weren't native for a long, long time. Usually when people think about introduced species, they're really thinking more about the accidental ones, the things that happened coincidentally alongside human activities."}, {"video_title": "Introduced species and biodiversity.mp3", "Sentence": "From goats and pigs to cattle and crops. Mostly we transport organisms that will do some good for us through agricultural means. We've been introducing plants and animals to places where they weren't native for a long, long time. Usually when people think about introduced species, they're really thinking more about the accidental ones, the things that happened coincidentally alongside human activities. When we introduce a species to a new area, everything that's living on, in, or with that species comes along with it. If you pick up a cow from one place and move it to another, it's going to bring along all the parasites that those cows normally deal with. I think people immediately picture images of rats streaming off the ships when they pull into some beautiful Tahitian paradise."}, {"video_title": "Introduced species and biodiversity.mp3", "Sentence": "Usually when people think about introduced species, they're really thinking more about the accidental ones, the things that happened coincidentally alongside human activities. When we introduce a species to a new area, everything that's living on, in, or with that species comes along with it. If you pick up a cow from one place and move it to another, it's going to bring along all the parasites that those cows normally deal with. I think people immediately picture images of rats streaming off the ships when they pull into some beautiful Tahitian paradise. Or the snakes that came into Guam with military movements during World War II. These animals are legendary in doing damage to native birds. They're very obvious ways that introduced organisms radically change biodiversity in a single place."}, {"video_title": "Introduced species and biodiversity.mp3", "Sentence": "I think people immediately picture images of rats streaming off the ships when they pull into some beautiful Tahitian paradise. Or the snakes that came into Guam with military movements during World War II. These animals are legendary in doing damage to native birds. They're very obvious ways that introduced organisms radically change biodiversity in a single place. There are so many other subtle ways that introductions happen and cause problems. The bottom line is that the world economy is hit with an annual cost of $1.4 trillion dealing with the negative impacts, obvious and not so obvious, of introduced species. That's a number I have a hard time wrapping my mind around."}, {"video_title": "Introduced species and biodiversity.mp3", "Sentence": "They're very obvious ways that introduced organisms radically change biodiversity in a single place. There are so many other subtle ways that introductions happen and cause problems. The bottom line is that the world economy is hit with an annual cost of $1.4 trillion dealing with the negative impacts, obvious and not so obvious, of introduced species. That's a number I have a hard time wrapping my mind around. If you had an extra $1.4 trillion to play around with, there's a lot of possibility to do some good in the world. Because humans have been introducing new species for a long time, the concept of native habitat is a little bit slippery. The human activities that caused the transfer can happen long before we recognize that it actually happened."}, {"video_title": "Introduced species and biodiversity.mp3", "Sentence": "That's a number I have a hard time wrapping my mind around. If you had an extra $1.4 trillion to play around with, there's a lot of possibility to do some good in the world. Because humans have been introducing new species for a long time, the concept of native habitat is a little bit slippery. The human activities that caused the transfer can happen long before we recognize that it actually happened. So that sometimes, the history of an introduction can be lost. When we aren't sure of the history, up until the point we are sure or have some reasonable evidence, we call those species cryptogenic. Crypto means hidden."}, {"video_title": "Introduced species and biodiversity.mp3", "Sentence": "The human activities that caused the transfer can happen long before we recognize that it actually happened. So that sometimes, the history of an introduction can be lost. When we aren't sure of the history, up until the point we are sure or have some reasonable evidence, we call those species cryptogenic. Crypto means hidden. Genic means origin. Solving the riddles of cryptogenic species underscores another reason why collections are so important. The only way to trace the origins of introductions is to know what was there beforehand."}, {"video_title": "Introduced species and biodiversity.mp3", "Sentence": "Crypto means hidden. Genic means origin. Solving the riddles of cryptogenic species underscores another reason why collections are so important. The only way to trace the origins of introductions is to know what was there beforehand. Collections can preserve that historical information, and collections made today establish baselines for future reference. If those collections are maintained in perpetuity, those baselines are going to be good 100 years from now or 1,000 years from now when we see a radically different and altered environment due to the introductions. So we can use collections to try and get answers to this problem."}, {"video_title": "Introduced species and biodiversity.mp3", "Sentence": "The only way to trace the origins of introductions is to know what was there beforehand. Collections can preserve that historical information, and collections made today establish baselines for future reference. If those collections are maintained in perpetuity, those baselines are going to be good 100 years from now or 1,000 years from now when we see a radically different and altered environment due to the introductions. So we can use collections to try and get answers to this problem. Not all species are, in fact, harmful. Actually they're not all harmful to us because the ones that we introduce on purpose are ones that are there for our benefit. Some introduced species can provide new food sources or even habitats for native species."}, {"video_title": "Introduced species and biodiversity.mp3", "Sentence": "So we can use collections to try and get answers to this problem. Not all species are, in fact, harmful. Actually they're not all harmful to us because the ones that we introduce on purpose are ones that are there for our benefit. Some introduced species can provide new food sources or even habitats for native species. Native species aren't always helpless and harmed. They can make use of some of the newcomers. Introduced grasses and corn, for example, are eaten by native species, and certain trees that have been introduced can serve as habitats for birds."}, {"video_title": "Introduced species and biodiversity.mp3", "Sentence": "Some introduced species can provide new food sources or even habitats for native species. Native species aren't always helpless and harmed. They can make use of some of the newcomers. Introduced grasses and corn, for example, are eaten by native species, and certain trees that have been introduced can serve as habitats for birds. Some introduced species live under our radar. We don't even know they're there, doing little perceivable damage to the ecosystem by reducing species richness. But some introduced species certainly go beyond just living peacefully alongside the natives."}, {"video_title": "Introduced species and biodiversity.mp3", "Sentence": "Introduced grasses and corn, for example, are eaten by native species, and certain trees that have been introduced can serve as habitats for birds. Some introduced species live under our radar. We don't even know they're there, doing little perceivable damage to the ecosystem by reducing species richness. But some introduced species certainly go beyond just living peacefully alongside the natives. They can do this because they have competitive advantages. They lack natural controls, such as the predators or diseases that keep them in check in their native habitats. Some invasive species are generalists, which means they can tolerate, reproduce rapidly, and thrive in a wide range of environmental conditions, allowing them to successfully compete with and overwhelm native populations."}, {"video_title": "Introduced species and biodiversity.mp3", "Sentence": "But some introduced species certainly go beyond just living peacefully alongside the natives. They can do this because they have competitive advantages. They lack natural controls, such as the predators or diseases that keep them in check in their native habitats. Some invasive species are generalists, which means they can tolerate, reproduce rapidly, and thrive in a wide range of environmental conditions, allowing them to successfully compete with and overwhelm native populations. When introduced species take over an environment at the expense of native species, they're known as invasive species. All invasive species are introduced, but not all introduced species are invasive. Here's an example of consequences for humans as well as for species richness."}, {"video_title": "Introduced species and biodiversity.mp3", "Sentence": "Some invasive species are generalists, which means they can tolerate, reproduce rapidly, and thrive in a wide range of environmental conditions, allowing them to successfully compete with and overwhelm native populations. When introduced species take over an environment at the expense of native species, they're known as invasive species. All invasive species are introduced, but not all introduced species are invasive. Here's an example of consequences for humans as well as for species richness. In 1992, an introduced species of comb jelly was found in the Black Sea. Comb jellies are weird, transparent, jellyfish-like forms with a voracious appetite for fish larvae and eggs. Within months, that single introduction resulted in the total collapse of the anchovy fishery in the Black Sea."}, {"video_title": "Introduced species and biodiversity.mp3", "Sentence": "Here's an example of consequences for humans as well as for species richness. In 1992, an introduced species of comb jelly was found in the Black Sea. Comb jellies are weird, transparent, jellyfish-like forms with a voracious appetite for fish larvae and eggs. Within months, that single introduction resulted in the total collapse of the anchovy fishery in the Black Sea. Comb jellies tolerated the conditions in the Black Sea, and their population exploded at the expense of the anchovies. The bottom line here is that introduced species can outcompete the natives for food, for space, and other resources. They alter the ecosystem's food webs, disturbing crucial elements and interactions that would otherwise contribute to healthy ecosystem function."}, {"video_title": "Introduced species and biodiversity.mp3", "Sentence": "Within months, that single introduction resulted in the total collapse of the anchovy fishery in the Black Sea. Comb jellies tolerated the conditions in the Black Sea, and their population exploded at the expense of the anchovies. The bottom line here is that introduced species can outcompete the natives for food, for space, and other resources. They alter the ecosystem's food webs, disturbing crucial elements and interactions that would otherwise contribute to healthy ecosystem function. The comb jelly is a good example of that. Sure, your species list for the Black Sea has gone up by one, but it destroyed all the anchovies. You have to take a species off the list."}, {"video_title": "Introduced species and biodiversity.mp3", "Sentence": "They alter the ecosystem's food webs, disturbing crucial elements and interactions that would otherwise contribute to healthy ecosystem function. The comb jelly is a good example of that. Sure, your species list for the Black Sea has gone up by one, but it destroyed all the anchovies. You have to take a species off the list. Plus, perhaps whatever else was eating the anchovies. And before you know it, because there's nothing for the comb jellies to eat anymore, they're gone too. So, not only have you not added a species, but in the end you've actually subtracted a whole bunch."}, {"video_title": "Introduced species and biodiversity.mp3", "Sentence": "You have to take a species off the list. Plus, perhaps whatever else was eating the anchovies. And before you know it, because there's nothing for the comb jellies to eat anymore, they're gone too. So, not only have you not added a species, but in the end you've actually subtracted a whole bunch. So invasive species are, ultimately, organisms that cause decreases in ecosystem function. That's another definition of invasives that we need to come to grips with. What's worse, invasives very seldom come by themselves."}, {"video_title": "Introduced species and biodiversity.mp3", "Sentence": "So, not only have you not added a species, but in the end you've actually subtracted a whole bunch. So invasive species are, ultimately, organisms that cause decreases in ecosystem function. That's another definition of invasives that we need to come to grips with. What's worse, invasives very seldom come by themselves. As I was saying with the cow example, they often come with new diseases, new parasites, new accompanying effects that we can hardly predict. Another good example of invasives are pathogens, something that we don't often consider as invasives. These include disease-causing organisms like fungi or bacteria and even viruses."}, {"video_title": "Introduced species and biodiversity.mp3", "Sentence": "What's worse, invasives very seldom come by themselves. As I was saying with the cow example, they often come with new diseases, new parasites, new accompanying effects that we can hardly predict. Another good example of invasives are pathogens, something that we don't often consider as invasives. These include disease-causing organisms like fungi or bacteria and even viruses. These are things that we also introduce to wild populations, and there are extinctions that come from that. In fact, in the past 500 years, we've directly caused the extinction of more than 100 species of birds, partly through the introduction of disease. And heck knows what damage we did to organisms that were depending on those birds."}, {"video_title": "Introduced species and biodiversity.mp3", "Sentence": "These include disease-causing organisms like fungi or bacteria and even viruses. These are things that we also introduce to wild populations, and there are extinctions that come from that. In fact, in the past 500 years, we've directly caused the extinction of more than 100 species of birds, partly through the introduction of disease. And heck knows what damage we did to organisms that were depending on those birds. In the forest realm, Dutch Elm Disease was something that, when I was growing up, was a huge thing, and actually it still is. In North America, Dutch Elm Disease left skeletal trees for miles and miles. When I was a kid growing up in Toronto in the 60s, 80% of the elms in the city were killed, and it was really sad."}, {"video_title": "Introduced species and biodiversity.mp3", "Sentence": "And heck knows what damage we did to organisms that were depending on those birds. In the forest realm, Dutch Elm Disease was something that, when I was growing up, was a huge thing, and actually it still is. In North America, Dutch Elm Disease left skeletal trees for miles and miles. When I was a kid growing up in Toronto in the 60s, 80% of the elms in the city were killed, and it was really sad. Those trees were not only gorgeous, they were very important lumber. Elm trees were a direct service to us in so many different ways, from producing shade to furniture. The fungus was introduced by bark beetles, some of which were native and some of which were introduced, both of which supported and co-evolved with the fungal pathogen, which could not be stopped."}, {"video_title": "Introduced species and biodiversity.mp3", "Sentence": "When I was a kid growing up in Toronto in the 60s, 80% of the elms in the city were killed, and it was really sad. Those trees were not only gorgeous, they were very important lumber. Elm trees were a direct service to us in so many different ways, from producing shade to furniture. The fungus was introduced by bark beetles, some of which were native and some of which were introduced, both of which supported and co-evolved with the fungal pathogen, which could not be stopped. This idea of being a generalist, the ability to reproduce and displace natives, the ability to become more abundant at the expense of other species, to introduce diseases, to proliferate in non-native habitats, that should sound pretty familiar, because that's us. In some ways, we are the ultimate invasive species. We don't just introduce ourselves, we are invasive."}, {"video_title": "Introduced species and biodiversity.mp3", "Sentence": "The fungus was introduced by bark beetles, some of which were native and some of which were introduced, both of which supported and co-evolved with the fungal pathogen, which could not be stopped. This idea of being a generalist, the ability to reproduce and displace natives, the ability to become more abundant at the expense of other species, to introduce diseases, to proliferate in non-native habitats, that should sound pretty familiar, because that's us. In some ways, we are the ultimate invasive species. We don't just introduce ourselves, we are invasive. The difference is that, unlike the comb jellies and the bark beetles and cows, we're capable of recognizing that fact and maybe mitigating our impact. We can look at the world and the problems and start thinking about ways to control invasives, to corral them, maybe to reduce their effects, and not introduce them in the first place. We have to, not just for moral reasons, I think, but because, ironically, and as we said earlier, the invasives that we're bringing with us, accidentally or on purpose, can do a lot of harm to species upon which we depend."}, {"video_title": "Passive transport and selective permeability   Biology   Khan Academy.mp3", "Sentence": "And the first type of transport of molecule across membranes that I'm going to talk about is transport that does not require energy. It's all about molecules moving down their concentration gradient. And that type of transport we call passive transport. Passive transport. So it does not require energy. It's really just about things moving down their concentration gradient. So down, let me write move down concentration gradient."}, {"video_title": "Passive transport and selective permeability   Biology   Khan Academy.mp3", "Sentence": "Passive transport. So it does not require energy. It's really just about things moving down their concentration gradient. So down, let me write move down concentration gradient. Move down concentration, concentration gradient. Now, if you have this cellular membrane, a lot of things might want to move down their concentration gradient, but this membrane is selectively permeable. It's going to be more or less permeable to different types of molecules."}, {"video_title": "Passive transport and selective permeability   Biology   Khan Academy.mp3", "Sentence": "So down, let me write move down concentration gradient. Move down concentration, concentration gradient. Now, if you have this cellular membrane, a lot of things might want to move down their concentration gradient, but this membrane is selectively permeable. It's going to be more or less permeable to different types of molecules. So let's think about these different types of molecules and think about how they might diffuse passively across the membrane. So if we have really small molecules, we can say, okay, they might be able to fit in the gaps between the hydrophilic heads, and maybe they might not be, and they might be able to fit between the gaps of the hydrophobic tails and get through. So being small is good."}, {"video_title": "Passive transport and selective permeability   Biology   Khan Academy.mp3", "Sentence": "It's going to be more or less permeable to different types of molecules. So let's think about these different types of molecules and think about how they might diffuse passively across the membrane. So if we have really small molecules, we can say, okay, they might be able to fit in the gaps between the hydrophilic heads, and maybe they might not be, and they might be able to fit between the gaps of the hydrophobic tails and get through. So being small is good. So small, if you're small, that aids transport, passive transport. It aids diffusion across the membrane. And in particular, it really helps to be small and non-charged."}, {"video_title": "Passive transport and selective permeability   Biology   Khan Academy.mp3", "Sentence": "So being small is good. So small, if you're small, that aids transport, passive transport. It aids diffusion across the membrane. And in particular, it really helps to be small and non-charged. Small and no charge. So examples of that could be things like carbon dioxide. So carbon dioxide, it's a small molecule."}, {"video_title": "Passive transport and selective permeability   Biology   Khan Academy.mp3", "Sentence": "And in particular, it really helps to be small and non-charged. Small and no charge. So examples of that could be things like carbon dioxide. So carbon dioxide, it's a small molecule. It doesn't have a charge. So carbon dioxide molecules, if I have a higher concentration on the outside, on the outside, actually let me do it the other way around. Let's say I have a higher concentration on the inside than I have on the outside."}, {"video_title": "Passive transport and selective permeability   Biology   Khan Academy.mp3", "Sentence": "So carbon dioxide, it's a small molecule. It doesn't have a charge. So carbon dioxide molecules, if I have a higher concentration on the outside, on the outside, actually let me do it the other way around. Let's say I have a higher concentration on the inside than I have on the outside. Well, just as we learned in the diffusion video, in a given amount of time, you're gonna have more carbon dioxide molecules interacting with the bottom, going from inside of the cell and interacting with the membrane than from the outside of the cell. And sure, they don't have any charge, so they're not gonna be particularly attracted to the hydrophilic head of our phospholipids, but they're also not going to be repelled by them. And they're gonna have more on the inside interacting with the membrane than the outside."}, {"video_title": "Passive transport and selective permeability   Biology   Khan Academy.mp3", "Sentence": "Let's say I have a higher concentration on the inside than I have on the outside. Well, just as we learned in the diffusion video, in a given amount of time, you're gonna have more carbon dioxide molecules interacting with the bottom, going from inside of the cell and interacting with the membrane than from the outside of the cell. And sure, they don't have any charge, so they're not gonna be particularly attracted to the hydrophilic head of our phospholipids, but they're also not going to be repelled by them. And they're gonna have more on the inside interacting with the membrane than the outside. And so since they're small, some of them are gonna be able to pass through, and they're also not going to be bothered by the hydrophobic tails. And they're gonna have things going both ways, but you're gonna have more going from the inside to the outside than from the outside to the inside. So they're gonna move along with their concentration gradient."}, {"video_title": "Passive transport and selective permeability   Biology   Khan Academy.mp3", "Sentence": "And they're gonna have more on the inside interacting with the membrane than the outside. And so since they're small, some of them are gonna be able to pass through, and they're also not going to be bothered by the hydrophobic tails. And they're gonna have things going both ways, but you're gonna have more going from the inside to the outside than from the outside to the inside. So they're gonna move along with their concentration gradient. So carbon dioxide can actually diffuse quite well across cellular membranes. Another molecule that can is molecular oxygen. Molecular oxygen can also diffuse quite well across cellular membranes."}, {"video_title": "Passive transport and selective permeability   Biology   Khan Academy.mp3", "Sentence": "So they're gonna move along with their concentration gradient. So carbon dioxide can actually diffuse quite well across cellular membranes. Another molecule that can is molecular oxygen. Molecular oxygen can also diffuse quite well across cellular membranes. So if I have a higher concentration of oxygen on the outside than I have on the inside, because it's small and it's non-charged, it's not gonna have problems. It's not gonna be particularly attracted to the hydrophilic heads, but they're small, and they're gonna be able to pass right between them. It's gonna be indifferent to them."}, {"video_title": "Passive transport and selective permeability   Biology   Khan Academy.mp3", "Sentence": "Molecular oxygen can also diffuse quite well across cellular membranes. So if I have a higher concentration of oxygen on the outside than I have on the inside, because it's small and it's non-charged, it's not gonna have problems. It's not gonna be particularly attracted to the hydrophilic heads, but they're small, and they're gonna be able to pass right between them. It's gonna be indifferent to them. And then it's gonna be able to pass through all these hydrophobic tails. And since you have a higher concentration on the outside than the inside, you're just going to have more in a given amount of time, more random interactions of the ones going in that direction than the ones going in that direction. So you would have a net inflow into the cells."}, {"video_title": "Passive transport and selective permeability   Biology   Khan Academy.mp3", "Sentence": "It's gonna be indifferent to them. And then it's gonna be able to pass through all these hydrophobic tails. And since you have a higher concentration on the outside than the inside, you're just going to have more in a given amount of time, more random interactions of the ones going in that direction than the ones going in that direction. So you would have a net inflow into the cells. So these things are going to be able to diffuse fairly, fairly, whoops, these things are gonna be able to diffuse fairly, fairly naturally. Now, and of course they are going to be obstructed by just the structure, by all of these molecules here that make up the actual cellular membrane, but they're going to be able to get through. Now, what about things that would have a lot of trouble getting through?"}, {"video_title": "Passive transport and selective permeability   Biology   Khan Academy.mp3", "Sentence": "So you would have a net inflow into the cells. So these things are going to be able to diffuse fairly, fairly, whoops, these things are gonna be able to diffuse fairly, fairly naturally. Now, and of course they are going to be obstructed by just the structure, by all of these molecules here that make up the actual cellular membrane, but they're going to be able to get through. Now, what about things that would have a lot of trouble getting through? So things that would have a lot of trouble getting through would be things like a sodium ion, a sodium ion, or a potassium, or a potassium ion. Why would they have trouble getting through? Well, let's just imagine."}, {"video_title": "Passive transport and selective permeability   Biology   Khan Academy.mp3", "Sentence": "Now, what about things that would have a lot of trouble getting through? So things that would have a lot of trouble getting through would be things like a sodium ion, a sodium ion, or a potassium, or a potassium ion. Why would they have trouble getting through? Well, let's just imagine. Let's say I have a higher concentration of sodium on the outside, on the outside, than I have on the inside. Well, they might be attracted to the hydrophilic heads here that have some charge, but there's no reason why they would then want to go any further. They're going to be attracted to the hydrophilic heads that have charge, and they're not going to, and the hydrophobic tails have nothing interesting for them."}, {"video_title": "Passive transport and selective permeability   Biology   Khan Academy.mp3", "Sentence": "Well, let's just imagine. Let's say I have a higher concentration of sodium on the outside, on the outside, than I have on the inside. Well, they might be attracted to the hydrophilic heads here that have some charge, but there's no reason why they would then want to go any further. They're going to be attracted to the hydrophilic heads that have charge, and they're not going to, and the hydrophobic tails have nothing interesting for them. They're gonna wanna maybe clump around the phosphate heads, but not be able to migrate all the way through. So things that have outright charge are gonna have trouble just passively diffusing. We'll see in future videos that there's other ways for them to get through."}, {"video_title": "Passive transport and selective permeability   Biology   Khan Academy.mp3", "Sentence": "They're going to be attracted to the hydrophilic heads that have charge, and they're not going to, and the hydrophobic tails have nothing interesting for them. They're gonna wanna maybe clump around the phosphate heads, but not be able to migrate all the way through. So things that have outright charge are gonna have trouble just passively diffusing. We'll see in future videos that there's other ways for them to get through. You have things like channel proteins, which essentially give them tunnels, and we'll talk more about that, but just naturally, natural diffusion is going to be hard for things like this. Now, what about things that are in between? What about things like water molecules?"}, {"video_title": "Passive transport and selective permeability   Biology   Khan Academy.mp3", "Sentence": "We'll see in future videos that there's other ways for them to get through. You have things like channel proteins, which essentially give them tunnels, and we'll talk more about that, but just naturally, natural diffusion is going to be hard for things like this. Now, what about things that are in between? What about things like water molecules? And water is incredibly important because cells are living in an aqueous environment. They're surrounded by water on the inside of the cell and the outside of the cell. And water is in between because it doesn't have an outright charge, but it has a partially water molecules, oxygen, two hydrogens."}, {"video_title": "Passive transport and selective permeability   Biology   Khan Academy.mp3", "Sentence": "What about things like water molecules? And water is incredibly important because cells are living in an aqueous environment. They're surrounded by water on the inside of the cell and the outside of the cell. And water is in between because it doesn't have an outright charge, but it has a partially water molecules, oxygen, two hydrogens. Oxygen likes to hog the electrons, has a partial negative charge on that end. The hydrogens have their electrons charged, have a partial positive, and a partial positive charge on that end. And we call these phosphate heads hydrophilic because they're attracted to water and water's attracted to it."}, {"video_title": "Passive transport and selective permeability   Biology   Khan Academy.mp3", "Sentence": "And water is in between because it doesn't have an outright charge, but it has a partially water molecules, oxygen, two hydrogens. Oxygen likes to hog the electrons, has a partial negative charge on that end. The hydrogens have their electrons charged, have a partial positive, and a partial positive charge on that end. And we call these phosphate heads hydrophilic because they're attracted to water and water's attracted to it. So the water molecules, the water molecules for sure are going to be attracted to the hydrophilic heads, but their charge isn't so strong, it isn't so strong that they can't, if you have enough interactions, a lot of them will be attracted, but some of them will actually make it through. The water molecule is small enough and its charge is not strong enough, I guess you could say. It has some polarity, but it's going to be able to make it through."}, {"video_title": "Passive transport and selective permeability   Biology   Khan Academy.mp3", "Sentence": "And we call these phosphate heads hydrophilic because they're attracted to water and water's attracted to it. So the water molecules, the water molecules for sure are going to be attracted to the hydrophilic heads, but their charge isn't so strong, it isn't so strong that they can't, if you have enough interactions, a lot of them will be attracted, but some of them will actually make it through. The water molecule is small enough and its charge is not strong enough, I guess you could say. It has some polarity, but it's going to be able to make it through. Not as easily as a carbon dioxide or the molecular oxygen, but it will be able to slowly diffuse through. And as we'll see, there's other ways that this can be facilitated, right, where the water can go through once again, these we'll see in future videos, things like aquaporins, the tunnels through the membrane so it doesn't have to deal with all of this business right over here. And of course, if you have really large molecules, if you had like a big, if you had a big honking protein right over here, this would have trouble."}, {"video_title": "Passive transport and selective permeability   Biology   Khan Academy.mp3", "Sentence": "It has some polarity, but it's going to be able to make it through. Not as easily as a carbon dioxide or the molecular oxygen, but it will be able to slowly diffuse through. And as we'll see, there's other ways that this can be facilitated, right, where the water can go through once again, these we'll see in future videos, things like aquaporins, the tunnels through the membrane so it doesn't have to deal with all of this business right over here. And of course, if you have really large molecules, if you had like a big, if you had a big honking protein right over here, this would have trouble. This would have trouble. It would have trouble even physically getting through the gaps, not to mention whether parts of it are hydrophobic or hydrophilic. So hopefully this gets you a sense of the types of things that can diffuse through a cellular membrane."}, {"video_title": "Cellular evidence of common ancestry   Natural selection   AP Biology   Khan Academy (2).mp3", "Sentence": "Perhaps the most mind-blowing idea in all of biology is the concept that all living things we know of, based on current evidence that we have, all originated from a common ancestor. So it doesn't matter whether we're talking about a simple bacterial cell, which actually in reality isn't so simple after all, a tree made up of trillions and trillions of cells, a hairy primate made up of trillions and trillions cells, or seemingly well-dressed agriculture kittens, which are also made of trillions and trillions of cells, that they all share a common ancestor. You might have seen things like these evolutionary trees. This is an example right over here. This is saying the same thing, that everything that we see in the world today, all living things, regardless of what domain they're in, and we would be a subset of animals right over here. There's so many animal species that they all share a common ancestor several billions of years ago. But you should be skeptical."}, {"video_title": "Cellular evidence of common ancestry   Natural selection   AP Biology   Khan Academy (2).mp3", "Sentence": "This is an example right over here. This is saying the same thing, that everything that we see in the world today, all living things, regardless of what domain they're in, and we would be a subset of animals right over here. There's so many animal species that they all share a common ancestor several billions of years ago. But you should be skeptical. We are scientists here. How do we believe this? What is the evidence for that?"}, {"video_title": "Cellular evidence of common ancestry   Natural selection   AP Biology   Khan Academy (2).mp3", "Sentence": "But you should be skeptical. We are scientists here. How do we believe this? What is the evidence for that? And one piece of evidence is by looking at the cellular level and look at commonalities amongst different groups and realize that it would be unlikely for them to develop independently of each other. For example, all life forms that we know of have DNA. They all have RNA."}, {"video_title": "Cellular evidence of common ancestry   Natural selection   AP Biology   Khan Academy (2).mp3", "Sentence": "What is the evidence for that? And one piece of evidence is by looking at the cellular level and look at commonalities amongst different groups and realize that it would be unlikely for them to develop independently of each other. For example, all life forms that we know of have DNA. They all have RNA. And it isn't just how they encode information. It's also processes, biochemical processes, that occur in the cells. They all have some form of glycolysis."}, {"video_title": "Cellular evidence of common ancestry   Natural selection   AP Biology   Khan Academy (2).mp3", "Sentence": "They all have RNA. And it isn't just how they encode information. It's also processes, biochemical processes, that occur in the cells. They all have some form of glycolysis. But this seems, and these aren't the only things that we've observed are common to all life forms. They're all based on cells as the basic units, which are bound by a membrane. And so in theory, these things, I guess, could have developed independently of each other without having a common ancestor."}, {"video_title": "Cellular evidence of common ancestry   Natural selection   AP Biology   Khan Academy (2).mp3", "Sentence": "They all have some form of glycolysis. But this seems, and these aren't the only things that we've observed are common to all life forms. They're all based on cells as the basic units, which are bound by a membrane. And so in theory, these things, I guess, could have developed independently of each other without having a common ancestor. But having a common ancestor is the best explanation of why we see these different processes. Some of these are quite complex or these different structures throughout life as we know it. And so you're saying, all right, I can maybe buy that, that there's this common ancestor right over here."}, {"video_title": "Cellular evidence of common ancestry   Natural selection   AP Biology   Khan Academy (2).mp3", "Sentence": "And so in theory, these things, I guess, could have developed independently of each other without having a common ancestor. But having a common ancestor is the best explanation of why we see these different processes. Some of these are quite complex or these different structures throughout life as we know it. And so you're saying, all right, I can maybe buy that, that there's this common ancestor right over here. But how do we construct this tree? How do we know when things branched off? Because some of these branches off of these trees, once again, these would have occurred hundreds of millions or billions of years ago, and none of us were around to observe that happening."}, {"video_title": "Cellular evidence of common ancestry   Natural selection   AP Biology   Khan Academy (2).mp3", "Sentence": "And so you're saying, all right, I can maybe buy that, that there's this common ancestor right over here. But how do we construct this tree? How do we know when things branched off? Because some of these branches off of these trees, once again, these would have occurred hundreds of millions or billions of years ago, and none of us were around to observe that happening. And once again, that goes to more structural evidence. So for example, amongst what we now classify as eukaryotes, so everything in this brown color, this branch of the tree right over here, we see that all of them have membrane-bound organelles. Membrane-bound organelles."}, {"video_title": "Cellular evidence of common ancestry   Natural selection   AP Biology   Khan Academy (2).mp3", "Sentence": "Because some of these branches off of these trees, once again, these would have occurred hundreds of millions or billions of years ago, and none of us were around to observe that happening. And once again, that goes to more structural evidence. So for example, amongst what we now classify as eukaryotes, so everything in this brown color, this branch of the tree right over here, we see that all of them have membrane-bound organelles. Membrane-bound organelles. These are things like a nucleus or mitochondria that we study in many other videos. They all have linear chromosomes. So in other groups in this tree of life, in this evolutionary tree, you might have circular chromosomes, but common to all eukaryotes are the linear chromosomes."}, {"video_title": "Cellular evidence of common ancestry   Natural selection   AP Biology   Khan Academy (2).mp3", "Sentence": "Membrane-bound organelles. These are things like a nucleus or mitochondria that we study in many other videos. They all have linear chromosomes. So in other groups in this tree of life, in this evolutionary tree, you might have circular chromosomes, but common to all eukaryotes are the linear chromosomes. And they all have chromosomes that contain introns. Introns are sequences of DNA that don't code for genes that will then code into proteins. And we're still exploring what the point of introns are, but the reason why all of these have been classified together is that they have these similarities."}, {"video_title": "Cellular evidence of common ancestry   Natural selection   AP Biology   Khan Academy (2).mp3", "Sentence": "So in other groups in this tree of life, in this evolutionary tree, you might have circular chromosomes, but common to all eukaryotes are the linear chromosomes. And they all have chromosomes that contain introns. Introns are sequences of DNA that don't code for genes that will then code into proteins. And we're still exploring what the point of introns are, but the reason why all of these have been classified together is that they have these similarities. And so we believe that they would have formed their own branch. And based on how similar things are, that's where we theorize when things might have branched off. And now that we have more sophisticated tools of sequencing DNA and RNA, we can look at how different those sequences are to construct more and more precise trees like this."}, {"video_title": "Introduction to Heredity.mp3", "Sentence": "Let me do this so they have a little brown-eyed baby here. And this is just something, I mean, there's obviously thousands of generations of human beings, and we've observed this. We've observed that kids look like their parents, that they inherit some traits, and that some traits seem to dominate other traits. And one example of that tends to be a darker pigmentation in maybe the hair or the eyes. Even if the other parent has light pigmentation, the darker one seems to dominate, or sometimes it actually ends up being a mix, and we've seen that all around us. Now this study of what gets passed on and how it gets passed on, it's much older than the study of DNA, which was really kind of discovered or became a big deal in the middle of the 20th century. This was studied a long time, and kind of the father of classical genetics and heredity is Gregor Mendel, who was actually a monk."}, {"video_title": "Introduction to Heredity.mp3", "Sentence": "And one example of that tends to be a darker pigmentation in maybe the hair or the eyes. Even if the other parent has light pigmentation, the darker one seems to dominate, or sometimes it actually ends up being a mix, and we've seen that all around us. Now this study of what gets passed on and how it gets passed on, it's much older than the study of DNA, which was really kind of discovered or became a big deal in the middle of the 20th century. This was studied a long time, and kind of the father of classical genetics and heredity is Gregor Mendel, who was actually a monk. And he would mess around with plants and cross them and see which traits got passed and which traits didn't get passed, and try to get an understanding of how traits are passed from one generation to another. So when we do this, when we study this classical genetics, I'm going to make a bunch of simplifying assumptions, because we know that most of these don't hold for most of our genes, but it'll give us a little bit of sense of how to predict what might happen in future generations. So the first simplifying assumption I'll make is that some traits have kind of this all or nothing property."}, {"video_title": "Introduction to Heredity.mp3", "Sentence": "This was studied a long time, and kind of the father of classical genetics and heredity is Gregor Mendel, who was actually a monk. And he would mess around with plants and cross them and see which traits got passed and which traits didn't get passed, and try to get an understanding of how traits are passed from one generation to another. So when we do this, when we study this classical genetics, I'm going to make a bunch of simplifying assumptions, because we know that most of these don't hold for most of our genes, but it'll give us a little bit of sense of how to predict what might happen in future generations. So the first simplifying assumption I'll make is that some traits have kind of this all or nothing property. And we know that a lot of traits don't. Let's say that they're in the world, and this is a gross oversimplification. Let's say for eye color, let's say that there are two alleles."}, {"video_title": "Introduction to Heredity.mp3", "Sentence": "So the first simplifying assumption I'll make is that some traits have kind of this all or nothing property. And we know that a lot of traits don't. Let's say that they're in the world, and this is a gross oversimplification. Let's say for eye color, let's say that there are two alleles. Now remember what an allele was. An allele is a specific version of a gene. So let's say that you could have blue eye color or you could have brown eye color."}, {"video_title": "Introduction to Heredity.mp3", "Sentence": "Let's say for eye color, let's say that there are two alleles. Now remember what an allele was. An allele is a specific version of a gene. So let's say that you could have blue eye color or you could have brown eye color. That we lived in a universe where someone could only have one of these two versions of the eye color gene. We know that eye color is far more complex than that. So this is just a simplification."}, {"video_title": "Introduction to Heredity.mp3", "Sentence": "So let's say that you could have blue eye color or you could have brown eye color. That we lived in a universe where someone could only have one of these two versions of the eye color gene. We know that eye color is far more complex than that. So this is just a simplification. And let me just make up another one. Let me say that, I don't know, maybe for tooth size, that's a trait you won't see in any traditional biology textbook. And let's say that there's one trait for big teeth, and that there's another allele for small teeth."}, {"video_title": "Introduction to Heredity.mp3", "Sentence": "So this is just a simplification. And let me just make up another one. Let me say that, I don't know, maybe for tooth size, that's a trait you won't see in any traditional biology textbook. And let's say that there's one trait for big teeth, and that there's another allele for small teeth. And I want to make very clear this distinction between a gene and an allele. I talked about Gregor Mendel, and he was doing this in the 1850s well before we knew what DNA was or what even chromosomes were and how DNA was passed on, et cetera. But let's go into the microbiology of it to understand the difference."}, {"video_title": "Introduction to Heredity.mp3", "Sentence": "And let's say that there's one trait for big teeth, and that there's another allele for small teeth. And I want to make very clear this distinction between a gene and an allele. I talked about Gregor Mendel, and he was doing this in the 1850s well before we knew what DNA was or what even chromosomes were and how DNA was passed on, et cetera. But let's go into the microbiology of it to understand the difference. So I have a chromosome. Let's say on some chromosome, let me pick some chromosome here, let's say I got that from my dad. And on this chromosome, there's some location here, we could call that the locus on this chromosome, that where the eye color gene is."}, {"video_title": "Introduction to Heredity.mp3", "Sentence": "But let's go into the microbiology of it to understand the difference. So I have a chromosome. Let's say on some chromosome, let me pick some chromosome here, let's say I got that from my dad. And on this chromosome, there's some location here, we could call that the locus on this chromosome, that where the eye color gene is. That's the location of the eye color gene. Now I have two chromosomes, one from my father and one from my mother. So let's say that this is the chromosome from my mother."}, {"video_title": "Introduction to Heredity.mp3", "Sentence": "And on this chromosome, there's some location here, we could call that the locus on this chromosome, that where the eye color gene is. That's the location of the eye color gene. Now I have two chromosomes, one from my father and one from my mother. So let's say that this is the chromosome from my mother. And we know that when they're normally in the cell, they aren't nice and neatly organized like this in a chromosome, but this is just to kind of show you the idea. And let's say these are homologous chromosomes, so they code for the same genes. So on this gene from my mother, on that same location or locus, there is also the eye color gene."}, {"video_title": "Introduction to Heredity.mp3", "Sentence": "So let's say that this is the chromosome from my mother. And we know that when they're normally in the cell, they aren't nice and neatly organized like this in a chromosome, but this is just to kind of show you the idea. And let's say these are homologous chromosomes, so they code for the same genes. So on this gene from my mother, on that same location or locus, there is also the eye color gene. Now I might have the same version of the gene, and I'm saying that there's only two versions of this gene in the world. Now if I have the same version of the gene, I'm going to make a little shorthand notation. I'm going to write big B, actually let me do it the other way."}, {"video_title": "Introduction to Heredity.mp3", "Sentence": "So on this gene from my mother, on that same location or locus, there is also the eye color gene. Now I might have the same version of the gene, and I'm saying that there's only two versions of this gene in the world. Now if I have the same version of the gene, I'm going to make a little shorthand notation. I'm going to write big B, actually let me do it the other way. I'm going to write little b for blue, and I'm going to write big B for brown. There's a situation where this could be a little b and this could be a big B. And then I could write that my genotype, my genotype, I have the allele, I have one big B for my mom and I have one small b for my dad."}, {"video_title": "Introduction to Heredity.mp3", "Sentence": "I'm going to write big B, actually let me do it the other way. I'm going to write little b for blue, and I'm going to write big B for brown. There's a situation where this could be a little b and this could be a big B. And then I could write that my genotype, my genotype, I have the allele, I have one big B for my mom and I have one small b for my dad. Each of these instances or ways that this gene is expressed is an allele. So these are two different alleles. Or versions of the same gene."}, {"video_title": "Introduction to Heredity.mp3", "Sentence": "And then I could write that my genotype, my genotype, I have the allele, I have one big B for my mom and I have one small b for my dad. Each of these instances or ways that this gene is expressed is an allele. So these are two different alleles. Or versions of the same gene. And when I have two different versions like this, one version from my mom, one version from my dad, I'm called a heterozygote or sometimes it's called a heterozygous genotype. And the genotype is the exact versions of the alleles I have. If I had, let's say, the lower case b, I had the blue eye gene from both parents."}, {"video_title": "Introduction to Heredity.mp3", "Sentence": "Or versions of the same gene. And when I have two different versions like this, one version from my mom, one version from my dad, I'm called a heterozygote or sometimes it's called a heterozygous genotype. And the genotype is the exact versions of the alleles I have. If I had, let's say, the lower case b, I had the blue eye gene from both parents. So let's say that I was lowercase b, lowercase b. Then I would have two identical alleles. Both of my parents gave me the same version of the gene."}, {"video_title": "Introduction to Heredity.mp3", "Sentence": "If I had, let's say, the lower case b, I had the blue eye gene from both parents. So let's say that I was lowercase b, lowercase b. Then I would have two identical alleles. Both of my parents gave me the same version of the gene. And in this case, I'm called, this genotype is homozygous. Or this is a homozygous genotype. Or I'm a homozygote for this trait."}, {"video_title": "Introduction to Heredity.mp3", "Sentence": "Both of my parents gave me the same version of the gene. And in this case, I'm called, this genotype is homozygous. Or this is a homozygous genotype. Or I'm a homozygote for this trait. Now you might say, Sal, this is fine. These are the traits that you have. This case, I have a brown from maybe my mom and a blue from my dad, in this case I have a blue from both my mom and dad."}, {"video_title": "Introduction to Heredity.mp3", "Sentence": "Or I'm a homozygote for this trait. Now you might say, Sal, this is fine. These are the traits that you have. This case, I have a brown from maybe my mom and a blue from my dad, in this case I have a blue from both my mom and dad. How do we know whether my eyes are going to be brown or blue? And the reality is that it's very complex. It's a whole mixture of things."}, {"video_title": "Introduction to Heredity.mp3", "Sentence": "This case, I have a brown from maybe my mom and a blue from my dad, in this case I have a blue from both my mom and dad. How do we know whether my eyes are going to be brown or blue? And the reality is that it's very complex. It's a whole mixture of things. But Mendel, he studied things that showed what we'll call dominance. Dominance. And this is the idea that one of these traits dominates the other."}, {"video_title": "Introduction to Heredity.mp3", "Sentence": "It's a whole mixture of things. But Mendel, he studied things that showed what we'll call dominance. Dominance. And this is the idea that one of these traits dominates the other. So a lot of people originally thought that eye color, especially blue eyes, was always dominated by the other trait. So we'll assume that here. But that's a gross oversimplification."}, {"video_title": "Introduction to Heredity.mp3", "Sentence": "And this is the idea that one of these traits dominates the other. So a lot of people originally thought that eye color, especially blue eyes, was always dominated by the other trait. So we'll assume that here. But that's a gross oversimplification. So let's say that brown eyes are dominant. Dominant. And blue are recessive."}, {"video_title": "Introduction to Heredity.mp3", "Sentence": "But that's a gross oversimplification. So let's say that brown eyes are dominant. Dominant. And blue are recessive. I wanted to do that in blue. And blue eyes are recessive. If this is the case, and this is a, as I've said repeatedly, this is a gross oversimplification."}, {"video_title": "Introduction to Heredity.mp3", "Sentence": "And blue are recessive. I wanted to do that in blue. And blue eyes are recessive. If this is the case, and this is a, as I've said repeatedly, this is a gross oversimplification. But if that is the case, then if I were to inherit this genotype, because brown eyes are dominant, remember I said the big B here represents brown eyes, and the lowercase B is recessive, all you're going to see for the person with this genotype is brown eyes. So let me do this here. Let me write this here."}, {"video_title": "Introduction to Heredity.mp3", "Sentence": "If this is the case, and this is a, as I've said repeatedly, this is a gross oversimplification. But if that is the case, then if I were to inherit this genotype, because brown eyes are dominant, remember I said the big B here represents brown eyes, and the lowercase B is recessive, all you're going to see for the person with this genotype is brown eyes. So let me do this here. Let me write this here. So genotype, and then I'll write phenotype. And genotype is the actual versions of the genes you have. And then the phenotypes are what's expressed, or what do you see?"}, {"video_title": "Introduction to Heredity.mp3", "Sentence": "Let me write this here. So genotype, and then I'll write phenotype. And genotype is the actual versions of the genes you have. And then the phenotypes are what's expressed, or what do you see? So phenotype. So if I get a brown eye gene from my dad, and I want to do it in brown, let me do it in brown so you don't get confused. So if I have a brown eye gene from my dad, and a blue eye gene from my mom, my color transitions aren't there."}, {"video_title": "Introduction to Heredity.mp3", "Sentence": "And then the phenotypes are what's expressed, or what do you see? So phenotype. So if I get a brown eye gene from my dad, and I want to do it in brown, let me do it in brown so you don't get confused. So if I have a brown eye gene from my dad, and a blue eye gene from my mom, my color transitions aren't there. A blue eye gene from my mom, because the brown eye is recessive, the brown eye allele is recessive. And I just said a brown eyed gene, but what I should say is the brown eyed version of the gene, which is the brown allele, or the blue eyed version of the gene from my mom, which is the blue allele. Since the brown allele is dominant, I wrote that up here, what's going to be expressed are brown eyes."}, {"video_title": "Introduction to Heredity.mp3", "Sentence": "So if I have a brown eye gene from my dad, and a blue eye gene from my mom, my color transitions aren't there. A blue eye gene from my mom, because the brown eye is recessive, the brown eye allele is recessive. And I just said a brown eyed gene, but what I should say is the brown eyed version of the gene, which is the brown allele, or the blue eyed version of the gene from my mom, which is the blue allele. Since the brown allele is dominant, I wrote that up here, what's going to be expressed are brown eyes. Now, let's say if I had it the other way. Let's say I got a blue eyed allele from my dad, and I get a brown eyed allele from my mom. Same thing, the phenotype is going to be brown eyes."}, {"video_title": "Introduction to Heredity.mp3", "Sentence": "Since the brown allele is dominant, I wrote that up here, what's going to be expressed are brown eyes. Now, let's say if I had it the other way. Let's say I got a blue eyed allele from my dad, and I get a brown eyed allele from my mom. Same thing, the phenotype is going to be brown eyes. Now, what if I get a brown eyed allele from both my mom and my dad? Let me see. I keep changing the shade of brown, but they're all supposed to be the same."}, {"video_title": "Introduction to Heredity.mp3", "Sentence": "Same thing, the phenotype is going to be brown eyes. Now, what if I get a brown eyed allele from both my mom and my dad? Let me see. I keep changing the shade of brown, but they're all supposed to be the same. So let's say I get two dominant brown eyed alleles from my mom and my dad. Then what are you going to see? Well, you could guess that."}, {"video_title": "Introduction to Heredity.mp3", "Sentence": "I keep changing the shade of brown, but they're all supposed to be the same. So let's say I get two dominant brown eyed alleles from my mom and my dad. Then what are you going to see? Well, you could guess that. I'm still going to see brown eyes. So there's only one last combination, because these are the only two types of alleles we might see in our population, although for most genes, there's more than two types, for example, there's blood types, there's four types of blood. But let's say that I get one blue allele from each of my parents, one from my dad, one from my mom."}, {"video_title": "Introduction to Heredity.mp3", "Sentence": "Well, you could guess that. I'm still going to see brown eyes. So there's only one last combination, because these are the only two types of alleles we might see in our population, although for most genes, there's more than two types, for example, there's blood types, there's four types of blood. But let's say that I get one blue allele from each of my parents, one from my dad, one from my mom. Then all of a sudden, this is a recessive trait, but there's nothing to dominate it. So all of a sudden, the phenotype will be blue eyes. And I want to repeat again, this isn't necessarily how the alleles for eye color work, but it's a nice simplification to maybe understand how heredity works."}, {"video_title": "Introduction to Heredity.mp3", "Sentence": "But let's say that I get one blue allele from each of my parents, one from my dad, one from my mom. Then all of a sudden, this is a recessive trait, but there's nothing to dominate it. So all of a sudden, the phenotype will be blue eyes. And I want to repeat again, this isn't necessarily how the alleles for eye color work, but it's a nice simplification to maybe understand how heredity works. And there are some traits that can be studied in this simple way. But what I wanted to do here is to show you that many different genotypes, so these are all different genotypes, they all coded for the same phenotype. So just by looking at someone's eye color, you didn't know exactly whether they were homozygous dominant."}, {"video_title": "Introduction to Heredity.mp3", "Sentence": "And I want to repeat again, this isn't necessarily how the alleles for eye color work, but it's a nice simplification to maybe understand how heredity works. And there are some traits that can be studied in this simple way. But what I wanted to do here is to show you that many different genotypes, so these are all different genotypes, they all coded for the same phenotype. So just by looking at someone's eye color, you didn't know exactly whether they were homozygous dominant. This would be homozygous dominant. Or whether they were heterozygotes. This is heterozygous right here."}, {"video_title": "Introduction to Heredity.mp3", "Sentence": "So just by looking at someone's eye color, you didn't know exactly whether they were homozygous dominant. This would be homozygous dominant. Or whether they were heterozygotes. This is heterozygous right here. These two right here are heterozygotes. These are also sometimes called hybrids. But the word hybrid is kind of overloaded."}, {"video_title": "Introduction to Heredity.mp3", "Sentence": "This is heterozygous right here. These two right here are heterozygotes. These are also sometimes called hybrids. But the word hybrid is kind of overloaded. It's used a lot. But in this context, it means that you've got different versions of the allele for that gene. So let's think a little bit about what's actually happening when my mom and my dad reproduced."}, {"video_title": "Introduction to Heredity.mp3", "Sentence": "But the word hybrid is kind of overloaded. It's used a lot. But in this context, it means that you've got different versions of the allele for that gene. So let's think a little bit about what's actually happening when my mom and my dad reproduced. So let's think of a couple of different scenarios. Let's say that they're both hybrids. My dad has the brown-eyed dominant allele, and he also has the blue-eyed recessive allele."}, {"video_title": "Introduction to Heredity.mp3", "Sentence": "So let's think a little bit about what's actually happening when my mom and my dad reproduced. So let's think of a couple of different scenarios. Let's say that they're both hybrids. My dad has the brown-eyed dominant allele, and he also has the blue-eyed recessive allele. And let's say my mom has the same thing. So brown-eyed dominant, and she also has the blue-eyed recessive allele. Now let's think about if these two people, before you see what my eye color is, if you said, look, I'm giving you what these two people's genotypes are."}, {"video_title": "Introduction to Heredity.mp3", "Sentence": "My dad has the brown-eyed dominant allele, and he also has the blue-eyed recessive allele. And let's say my mom has the same thing. So brown-eyed dominant, and she also has the blue-eyed recessive allele. Now let's think about if these two people, before you see what my eye color is, if you said, look, I'm giving you what these two people's genotypes are. And let me label them. This is the mom. I think this is the standard convention."}, {"video_title": "Introduction to Heredity.mp3", "Sentence": "Now let's think about if these two people, before you see what my eye color is, if you said, look, I'm giving you what these two people's genotypes are. And let me label them. This is the mom. I think this is the standard convention. And let's make this right here. This is the dad. What are the different genotypes that their children could have?"}, {"video_title": "Introduction to Heredity.mp3", "Sentence": "I think this is the standard convention. And let's make this right here. This is the dad. What are the different genotypes that their children could have? So let's say they reproduce. I'm going to draw a little grid here. So let me draw a grid."}, {"video_title": "Introduction to Heredity.mp3", "Sentence": "What are the different genotypes that their children could have? So let's say they reproduce. I'm going to draw a little grid here. So let me draw a grid. All right. So we know from our study of meiosis that, look, my mom has this gene on, let me draw the genes again. So there's a homologous pair."}, {"video_title": "Introduction to Heredity.mp3", "Sentence": "So let me draw a grid. All right. So we know from our study of meiosis that, look, my mom has this gene on, let me draw the genes again. So there's a homologous pair. This is one chromosome right here. That's another chromosome right there. On this chromosome in the homologous pair, there might be, at the eye color locus, there's the brown eye gene."}, {"video_title": "Introduction to Heredity.mp3", "Sentence": "So there's a homologous pair. This is one chromosome right here. That's another chromosome right there. On this chromosome in the homologous pair, there might be, at the eye color locus, there's the brown eye gene. And at this one, at the eye color locus, there's a blue eye gene. And similarly for my dad, when you look at that same chromosome in his cells, let me do them like this. So this is one chromosome there, and this is the other chromosome here."}, {"video_title": "Introduction to Heredity.mp3", "Sentence": "On this chromosome in the homologous pair, there might be, at the eye color locus, there's the brown eye gene. And at this one, at the eye color locus, there's a blue eye gene. And similarly for my dad, when you look at that same chromosome in his cells, let me do them like this. So this is one chromosome there, and this is the other chromosome here. When you look at that locus on this chromosome or that location, it has the brown-eyed allele for that gene, and on this one, it has the blue-eyed allele on this gene. And we learn from meiosis when the chromosomes, well, they replicate first, and so you have these two chromatids on a chromosome, but they line up in meiosis I during the metaphase. And we don't know which way they line up."}, {"video_title": "Introduction to Heredity.mp3", "Sentence": "So this is one chromosome there, and this is the other chromosome here. When you look at that locus on this chromosome or that location, it has the brown-eyed allele for that gene, and on this one, it has the blue-eyed allele on this gene. And we learn from meiosis when the chromosomes, well, they replicate first, and so you have these two chromatids on a chromosome, but they line up in meiosis I during the metaphase. And we don't know which way they line up. For example, my dad might give me this chromosome or might give me that chromosome, or my mom might give me that chromosome or might give me that chromosome. So I could have any of these combinations. So for example, if I get this chromosome from my mom and this chromosome from my dad, what is the genotype going to be for eye color?"}, {"video_title": "Introduction to Heredity.mp3", "Sentence": "And we don't know which way they line up. For example, my dad might give me this chromosome or might give me that chromosome, or my mom might give me that chromosome or might give me that chromosome. So I could have any of these combinations. So for example, if I get this chromosome from my mom and this chromosome from my dad, what is the genotype going to be for eye color? Well, it's going to be capital B and capital B. If I get this chromosome from my mom and this chromosome from my dad, what's it going to be? Well, I'm going to get the big B from my dad, and then I'm going to get the lowercase b from my mom."}, {"video_title": "Introduction to Heredity.mp3", "Sentence": "So for example, if I get this chromosome from my mom and this chromosome from my dad, what is the genotype going to be for eye color? Well, it's going to be capital B and capital B. If I get this chromosome from my mom and this chromosome from my dad, what's it going to be? Well, I'm going to get the big B from my dad, and then I'm going to get the lowercase b from my mom. So this is another possibility. Now, this is another possibility here where I get the brown-eyed allele from my mom, and I get the blue-eyed allele from my dad. And then there is a possibility that I get this chromosome from my dad and this chromosome from my mom."}, {"video_title": "Introduction to Heredity.mp3", "Sentence": "Well, I'm going to get the big B from my dad, and then I'm going to get the lowercase b from my mom. So this is another possibility. Now, this is another possibility here where I get the brown-eyed allele from my mom, and I get the blue-eyed allele from my dad. And then there is a possibility that I get this chromosome from my dad and this chromosome from my mom. So it's this situation. Now, what are the phenotypes going to be? Well, we've already seen that this one right here is going to be brown, that one's going to be brown, this one's going to be brown, but this one is going to be blue."}, {"video_title": "Introduction to Heredity.mp3", "Sentence": "And then there is a possibility that I get this chromosome from my dad and this chromosome from my mom. So it's this situation. Now, what are the phenotypes going to be? Well, we've already seen that this one right here is going to be brown, that one's going to be brown, this one's going to be brown, but this one is going to be blue. I already showed you this. But if I were to tell you ahead of time that, look, I have two people, they're both hybrids or they're both heterozygotes for eye color, and eye color has this recessive dominant situation, and they're both heterozygotes where they each have one brown allele and one blue allele, and they're going to have a child, what's the probability that the child has brown eyes? What's the probability?"}, {"video_title": "Introduction to Heredity.mp3", "Sentence": "Well, we've already seen that this one right here is going to be brown, that one's going to be brown, this one's going to be brown, but this one is going to be blue. I already showed you this. But if I were to tell you ahead of time that, look, I have two people, they're both hybrids or they're both heterozygotes for eye color, and eye color has this recessive dominant situation, and they're both heterozygotes where they each have one brown allele and one blue allele, and they're going to have a child, what's the probability that the child has brown eyes? What's the probability? Well, each of these scenarios are equally likely. There's four equal scenarios. So let's put that in the denominator."}, {"video_title": "Introduction to Heredity.mp3", "Sentence": "What's the probability? Well, each of these scenarios are equally likely. There's four equal scenarios. So let's put that in the denominator. Four equal scenarios. And how many of those scenarios end up with brown eyes? Well, it's 1, 2, 3."}, {"video_title": "Introduction to Heredity.mp3", "Sentence": "So let's put that in the denominator. Four equal scenarios. And how many of those scenarios end up with brown eyes? Well, it's 1, 2, 3. So the probability is 3 4ths, or it's a 75% probability. Same logic. What's the probability that these parents produce an offspring with blue eyes?"}, {"video_title": "Introduction to Heredity.mp3", "Sentence": "Well, it's 1, 2, 3. So the probability is 3 4ths, or it's a 75% probability. Same logic. What's the probability that these parents produce an offspring with blue eyes? Well, that's only one of the four equally likely possibilities. So blue eyes is only 25%. Now, what is the probability that they produce a heterozygote?"}, {"video_title": "Introduction to Heredity.mp3", "Sentence": "What's the probability that these parents produce an offspring with blue eyes? Well, that's only one of the four equally likely possibilities. So blue eyes is only 25%. Now, what is the probability that they produce a heterozygote? So what is the probability that they produce a heterozygous offspring? So now we're not looking at the phenotype anymore. We're looking at the genotype."}, {"video_title": "Introduction to Heredity.mp3", "Sentence": "Now, what is the probability that they produce a heterozygote? So what is the probability that they produce a heterozygous offspring? So now we're not looking at the phenotype anymore. We're looking at the genotype. So of these combinations, which are heterozygous? Well, this one is, because it's a hybrid. It has a mix of the two alleles."}, {"video_title": "Introduction to Heredity.mp3", "Sentence": "We're looking at the genotype. So of these combinations, which are heterozygous? Well, this one is, because it's a hybrid. It has a mix of the two alleles. And so is this one. So what's the probability? Well, there's four different combinations."}, {"video_title": "Introduction to Heredity.mp3", "Sentence": "It has a mix of the two alleles. And so is this one. So what's the probability? Well, there's four different combinations. All of those are equally likely, and two of them result in a heterozygote. So it's 2 4ths, or 1 half, or 50%. So using this Punnett square, and of course we had to make a lot of assumptions about the genes and whether one's dominant or one's recessive, we can start to make predictions about the probabilities of different outcomes."}, {"video_title": "Introduction to Heredity.mp3", "Sentence": "Well, there's four different combinations. All of those are equally likely, and two of them result in a heterozygote. So it's 2 4ths, or 1 half, or 50%. So using this Punnett square, and of course we had to make a lot of assumptions about the genes and whether one's dominant or one's recessive, we can start to make predictions about the probabilities of different outcomes. And as we'll see in future videos, you can actually even go backwards. You can say, hey, given that this couple had five kids with brown eyes, what's the probability that they're both heterozygous or something like that? So it's a really interesting area, even though it is a bit of oversimplification, but many traits, especially some of the things that Gregor Mendel studied, can be studied in this way."}, {"video_title": "Mitochondria   Structure of a cell   Biology   Khan Academy.mp3", "Sentence": "So let's just think about a cell, and not just any cell, but a eukaryotic cell. So that's the cellular membrane. And when people say a eukaryote or a eukaryotic cell, they most typically say, oh, that must have its nuclear DNA and a membrane-bound nucleus. And that would be true. So let's draw our membrane-bound nucleus. That's our nuclear membrane. You have your DNA in here."}, {"video_title": "Mitochondria   Structure of a cell   Biology   Khan Academy.mp3", "Sentence": "And that would be true. So let's draw our membrane-bound nucleus. That's our nuclear membrane. You have your DNA in here. So let's draw some DNA. But when we talk about eukaryotic cells, we're not just talking about a membrane-bound nucleus. We're also talking about other membrane-bound organelles."}, {"video_title": "Mitochondria   Structure of a cell   Biology   Khan Academy.mp3", "Sentence": "You have your DNA in here. So let's draw some DNA. But when we talk about eukaryotic cells, we're not just talking about a membrane-bound nucleus. We're also talking about other membrane-bound organelles. And a close second place for a membrane-bound structure that is very important to the cell would be the mitochondria. So let's draw some mitochondria right over here. So I'll talk a little bit more about what these little squiggly lines that I'm drawing inside of the mitochondria are."}, {"video_title": "Mitochondria   Structure of a cell   Biology   Khan Academy.mp3", "Sentence": "We're also talking about other membrane-bound organelles. And a close second place for a membrane-bound structure that is very important to the cell would be the mitochondria. So let's draw some mitochondria right over here. So I'll talk a little bit more about what these little squiggly lines that I'm drawing inside of the mitochondria are. This is actually a little bit more of a textbook visualization, as we'll learn in a few minutes or seconds that we now have more sophisticated visualizations of what's actually going on inside of a mitochondria. But we actually haven't answered all of our questions. But you might have already learned that my, so let me make it clear."}, {"video_title": "Mitochondria   Structure of a cell   Biology   Khan Academy.mp3", "Sentence": "So I'll talk a little bit more about what these little squiggly lines that I'm drawing inside of the mitochondria are. This is actually a little bit more of a textbook visualization, as we'll learn in a few minutes or seconds that we now have more sophisticated visualizations of what's actually going on inside of a mitochondria. But we actually haven't answered all of our questions. But you might have already learned that my, so let me make it clear. These are mitochondria. That's the plural. If we're just talking about one of them, we're talking about a mitochondrion."}, {"video_title": "Mitochondria   Structure of a cell   Biology   Khan Academy.mp3", "Sentence": "But you might have already learned that my, so let me make it clear. These are mitochondria. That's the plural. If we're just talking about one of them, we're talking about a mitochondrion. That's the singular of mitochondria. But you might have already learned sometime in your past or in another Khan Academy video that these are viewed as the ATP factories for cells. So let me write it this way."}, {"video_title": "Mitochondria   Structure of a cell   Biology   Khan Academy.mp3", "Sentence": "If we're just talking about one of them, we're talking about a mitochondrion. That's the singular of mitochondria. But you might have already learned sometime in your past or in another Khan Academy video that these are viewed as the ATP factories for cells. So let me write it this way. So ATP factories. And if you watch the videos on ATP or cellular respiration or other videos, I repeatedly talk about how ATP is really the currency for energy in the cell, that when it's in its ATP form, you have adenosine triphosphate. If you pop one of the phosphate groups off, you pop one of the P's off, it releases energy."}, {"video_title": "Mitochondria   Structure of a cell   Biology   Khan Academy.mp3", "Sentence": "So let me write it this way. So ATP factories. And if you watch the videos on ATP or cellular respiration or other videos, I repeatedly talk about how ATP is really the currency for energy in the cell, that when it's in its ATP form, you have adenosine triphosphate. If you pop one of the phosphate groups off, you pop one of the P's off, it releases energy. And that's what your body uses to do all sorts of things, from movement to thinking to all sorts of things that actually go on your body. So you can imagine mitochondria are really important for energy for when the cell has to do things. And that's why you'll find more mitochondria in things like muscle cells, things that have to use a lot of energy."}, {"video_title": "Mitochondria   Structure of a cell   Biology   Khan Academy.mp3", "Sentence": "If you pop one of the phosphate groups off, you pop one of the P's off, it releases energy. And that's what your body uses to do all sorts of things, from movement to thinking to all sorts of things that actually go on your body. So you can imagine mitochondria are really important for energy for when the cell has to do things. And that's why you'll find more mitochondria in things like muscle cells, things that have to use a lot of energy. Now before I get into the structure of mitochondria, I want to talk a little bit about its fascinating past. Because we think of cells as the most basic unit of life, and that is true. That comes straight out of cell theory."}, {"video_title": "Mitochondria   Structure of a cell   Biology   Khan Academy.mp3", "Sentence": "And that's why you'll find more mitochondria in things like muscle cells, things that have to use a lot of energy. Now before I get into the structure of mitochondria, I want to talk a little bit about its fascinating past. Because we think of cells as the most basic unit of life, and that is true. That comes straight out of cell theory. But it turns out the most prevalent theory of how mitochondria got into our cells is that at one time, the predecessors, the ancestors to our mitochondria were free, independent organisms, microorganisms. So they're descendant from bacteria-like microorganisms that might have been living on their own. And they were maybe really good at processing energy, or maybe they were even good at other things."}, {"video_title": "Mitochondria   Structure of a cell   Biology   Khan Academy.mp3", "Sentence": "That comes straight out of cell theory. But it turns out the most prevalent theory of how mitochondria got into our cells is that at one time, the predecessors, the ancestors to our mitochondria were free, independent organisms, microorganisms. So they're descendant from bacteria-like microorganisms that might have been living on their own. And they were maybe really good at processing energy, or maybe they were even good at other things. But at some point in the evolutionary past, they got ingested by the ancestors of our cells. And instead of just being engulfed and being torn to shreds and kind of being digested and eaten, it was like, hey, wait, if these things stick around, those cells are more likely to survive. Because they're able to help process glucose or help generate more energy out of things."}, {"video_title": "Mitochondria   Structure of a cell   Biology   Khan Academy.mp3", "Sentence": "And they were maybe really good at processing energy, or maybe they were even good at other things. But at some point in the evolutionary past, they got ingested by the ancestors of our cells. And instead of just being engulfed and being torn to shreds and kind of being digested and eaten, it was like, hey, wait, if these things stick around, those cells are more likely to survive. Because they're able to help process glucose or help generate more energy out of things. And so the cells that were able to kind of live in symbiosis have them kind of give a place for the mitochondria to live, or the pre-mitochondria, the ancestor mitochondria. Those survived. And then through kind of the processes of natural selection, this is what we now associate eukaryotic cells as having mitochondria in it."}, {"video_title": "Mitochondria   Structure of a cell   Biology   Khan Academy.mp3", "Sentence": "Because they're able to help process glucose or help generate more energy out of things. And so the cells that were able to kind of live in symbiosis have them kind of give a place for the mitochondria to live, or the pre-mitochondria, the ancestor mitochondria. Those survived. And then through kind of the processes of natural selection, this is what we now associate eukaryotic cells as having mitochondria in it. So I find this whole idea of one organism being inside of another organism in symbiosis, even at the cellular level, that's kind of mind-boggling. But anyway, I'll stop talking about that. And now let's just talk about the present."}, {"video_title": "Mitochondria   Structure of a cell   Biology   Khan Academy.mp3", "Sentence": "And then through kind of the processes of natural selection, this is what we now associate eukaryotic cells as having mitochondria in it. So I find this whole idea of one organism being inside of another organism in symbiosis, even at the cellular level, that's kind of mind-boggling. But anyway, I'll stop talking about that. And now let's just talk about the present. Let's talk about what the actual structure of mitochondria are. And I'll first draw kind of a simplified drawing of a mitochondrion. And I'm going to draw a cross-section."}, {"video_title": "Mitochondria   Structure of a cell   Biology   Khan Academy.mp3", "Sentence": "And now let's just talk about the present. Let's talk about what the actual structure of mitochondria are. And I'll first draw kind of a simplified drawing of a mitochondrion. And I'm going to draw a cross-section. So I'm going to draw a cross-section. So if we were to kind of cut it in half. So what I've drawn right over here, this would be its outer membrane."}, {"video_title": "Mitochondria   Structure of a cell   Biology   Khan Academy.mp3", "Sentence": "And I'm going to draw a cross-section. So I'm going to draw a cross-section. So if we were to kind of cut it in half. So what I've drawn right over here, this would be its outer membrane. This is the outer membrane right over here. Let me label that. Outer membrane."}, {"video_title": "Mitochondria   Structure of a cell   Biology   Khan Academy.mp3", "Sentence": "So what I've drawn right over here, this would be its outer membrane. This is the outer membrane right over here. Let me label that. Outer membrane. And all of these membranes that I'm going to draw, they're all going to be phospholipid bilayers. So if I were to zoom in right over here, we would see a bilayer of phospholipids. So you have your hydrophilic heads facing outwards."}, {"video_title": "Mitochondria   Structure of a cell   Biology   Khan Academy.mp3", "Sentence": "Outer membrane. And all of these membranes that I'm going to draw, they're all going to be phospholipid bilayers. So if I were to zoom in right over here, we would see a bilayer of phospholipids. So you have your hydrophilic heads facing outwards. And your hydrophobic tails facing inwards. So you see something just like that. So they're all phospholipid bilayers."}, {"video_title": "Mitochondria   Structure of a cell   Biology   Khan Academy.mp3", "Sentence": "So you have your hydrophilic heads facing outwards. And your hydrophobic tails facing inwards. So you see something just like that. So they're all phospholipid bilayers. But they aren't just phospholipids. All of these membranes, they have all sorts of proteins embedded. I mean, the cells are incredibly complex structures."}, {"video_title": "Mitochondria   Structure of a cell   Biology   Khan Academy.mp3", "Sentence": "So they're all phospholipid bilayers. But they aren't just phospholipids. All of these membranes, they have all sorts of proteins embedded. I mean, the cells are incredibly complex structures. But even organelles like mitochondria have a fascinating, I guess you'd say, substructure to them. They themselves have all sorts of interesting proteins, enzymes embedded in their membranes that are able to help regulate what's going on inside and outside of these organelles. And one of the proteins that you have in the outer membrane of mitochondria, they're called porins."}, {"video_title": "Mitochondria   Structure of a cell   Biology   Khan Academy.mp3", "Sentence": "I mean, the cells are incredibly complex structures. But even organelles like mitochondria have a fascinating, I guess you'd say, substructure to them. They themselves have all sorts of interesting proteins, enzymes embedded in their membranes that are able to help regulate what's going on inside and outside of these organelles. And one of the proteins that you have in the outer membrane of mitochondria, they're called porins. And porins aren't found only in mitochondria, but they're kind of tunnel proteins. They're structured. They kind of form a hole."}, {"video_title": "Mitochondria   Structure of a cell   Biology   Khan Academy.mp3", "Sentence": "And one of the proteins that you have in the outer membrane of mitochondria, they're called porins. And porins aren't found only in mitochondria, but they're kind of tunnel proteins. They're structured. They kind of form a hole. They form a hole in the outer membrane. So I'm trying the best. I'm drawing them the best that I can."}, {"video_title": "Mitochondria   Structure of a cell   Biology   Khan Academy.mp3", "Sentence": "They kind of form a hole. They form a hole in the outer membrane. So I'm trying the best. I'm drawing them the best that I can. These are porins. And what's interesting about porins is they don't allow large molecules to pass through passively. But small molecules, like sugars or ions, can pass passively through the porins."}, {"video_title": "Mitochondria   Structure of a cell   Biology   Khan Academy.mp3", "Sentence": "I'm drawing them the best that I can. These are porins. And what's interesting about porins is they don't allow large molecules to pass through passively. But small molecules, like sugars or ions, can pass passively through the porins. And so because of that, your ion concentration and your small molecule concentrations tend to be similar on either side of this membrane, on either side of this outer membrane. But that's not the only membrane involved in a mitochondrion. We also have an inner membrane."}, {"video_title": "Mitochondria   Structure of a cell   Biology   Khan Academy.mp3", "Sentence": "But small molecules, like sugars or ions, can pass passively through the porins. And so because of that, your ion concentration and your small molecule concentrations tend to be similar on either side of this membrane, on either side of this outer membrane. But that's not the only membrane involved in a mitochondrion. We also have an inner membrane. I'll do that in yellow. We also have an inner membrane. And I'm going to draw it with a textbook model first."}, {"video_title": "Mitochondria   Structure of a cell   Biology   Khan Academy.mp3", "Sentence": "We also have an inner membrane. I'll do that in yellow. We also have an inner membrane. And I'm going to draw it with a textbook model first. And then we'll talk a little bit about what, since we now think this model is not quite right. So we have this inner membrane. And this inner membrane has these folds in it to increase their surface area."}, {"video_title": "Mitochondria   Structure of a cell   Biology   Khan Academy.mp3", "Sentence": "And I'm going to draw it with a textbook model first. And then we'll talk a little bit about what, since we now think this model is not quite right. So we have this inner membrane. And this inner membrane has these folds in it to increase their surface area. And the surface area is really important for the inner membrane because that's where the processes of the electron transport chain occur across, essentially, these membranes. So you want this extra surface area so you can essentially have more of that going on. And these folds have a name."}, {"video_title": "Mitochondria   Structure of a cell   Biology   Khan Academy.mp3", "Sentence": "And this inner membrane has these folds in it to increase their surface area. And the surface area is really important for the inner membrane because that's where the processes of the electron transport chain occur across, essentially, these membranes. So you want this extra surface area so you can essentially have more of that going on. And these folds have a name. So if you're talking about one of them, if you're talking about one of these folds, you're talking about a crista. You are talking about a crista. But if you're talking about more than one of them, you would call that a cristae."}, {"video_title": "Mitochondria   Structure of a cell   Biology   Khan Academy.mp3", "Sentence": "And these folds have a name. So if you're talking about one of them, if you're talking about one of these folds, you're talking about a crista. You are talking about a crista. But if you're talking about more than one of them, you would call that a cristae. Sometimes I've seen the pronunciation of this is cristae. Cristae or cristae, that's plural for cristae. And these are just folds in the inner membrane."}, {"video_title": "Mitochondria   Structure of a cell   Biology   Khan Academy.mp3", "Sentence": "But if you're talking about more than one of them, you would call that a cristae. Sometimes I've seen the pronunciation of this is cristae. Cristae or cristae, that's plural for cristae. And these are just folds in the inner membrane. And once again, the inner membrane is also a phospholipid bilayer. Now, inside of the inner membrane, so between the outer membrane and the inner membrane, you could imagine what this is going to be called. That space is called the intermembrane space."}, {"video_title": "Mitochondria   Structure of a cell   Biology   Khan Academy.mp3", "Sentence": "And these are just folds in the inner membrane. And once again, the inner membrane is also a phospholipid bilayer. Now, inside of the inner membrane, so between the outer membrane and the inner membrane, you could imagine what this is going to be called. That space is called the intermembrane space. Not too creative of a name. And because of the porins, the small molecule concentration in the intermembrane space and outside of the mitochondria out in the cytosol, those concentrations are gonna be similar. But then the inner membrane does not have the porins in it."}, {"video_title": "Mitochondria   Structure of a cell   Biology   Khan Academy.mp3", "Sentence": "That space is called the intermembrane space. Not too creative of a name. And because of the porins, the small molecule concentration in the intermembrane space and outside of the mitochondria out in the cytosol, those concentrations are gonna be similar. But then the inner membrane does not have the porins in it. And so you can actually have a different concentration on either side. And that is essential for the electron transport chain. The electron transport chain really culminates with a hydrogen ion gradient being built between the two sides."}, {"video_title": "Mitochondria   Structure of a cell   Biology   Khan Academy.mp3", "Sentence": "But then the inner membrane does not have the porins in it. And so you can actually have a different concentration on either side. And that is essential for the electron transport chain. The electron transport chain really culminates with a hydrogen ion gradient being built between the two sides. And then they flow down that gradient through a protein called ATP synthase, which helps us synthesize ATB. But we'll talk more about that maybe in this video or in a future video. But let's finish talking about the different parts of a mitochondrion."}, {"video_title": "Mitochondria   Structure of a cell   Biology   Khan Academy.mp3", "Sentence": "The electron transport chain really culminates with a hydrogen ion gradient being built between the two sides. And then they flow down that gradient through a protein called ATP synthase, which helps us synthesize ATB. But we'll talk more about that maybe in this video or in a future video. But let's finish talking about the different parts of a mitochondrion. So inside the inner membrane, you have this area right over here is called the matrix. It's called, let me use this in a different color. This right, this is the matrix."}, {"video_title": "Mitochondria   Structure of a cell   Biology   Khan Academy.mp3", "Sentence": "But let's finish talking about the different parts of a mitochondrion. So inside the inner membrane, you have this area right over here is called the matrix. It's called, let me use this in a different color. This right, this is the matrix. And it's called the matrix because it actually has a much higher protein concentration. It's actually more viscous than the cytosol that would be outside of the mitochondria. So this right over here is the matrix."}, {"video_title": "Mitochondria   Structure of a cell   Biology   Khan Academy.mp3", "Sentence": "This right, this is the matrix. And it's called the matrix because it actually has a much higher protein concentration. It's actually more viscous than the cytosol that would be outside of the mitochondria. So this right over here is the matrix. And when we talk about cellular respiration, cellular respiration has many phases in it. We talk about glycolysis. Glycolysis is actually occurring in the cytosol."}, {"video_title": "Mitochondria   Structure of a cell   Biology   Khan Academy.mp3", "Sentence": "So this right over here is the matrix. And when we talk about cellular respiration, cellular respiration has many phases in it. We talk about glycolysis. Glycolysis is actually occurring in the cytosol. So let me, so glycolysis can occur in the cytosol. Glycolysis. But the other major phases of cellular respiration, when we talk about the citric acid cycle, also known as the Krebs cycle, that is occurring in the matrix."}, {"video_title": "Mitochondria   Structure of a cell   Biology   Khan Academy.mp3", "Sentence": "Glycolysis is actually occurring in the cytosol. So let me, so glycolysis can occur in the cytosol. Glycolysis. But the other major phases of cellular respiration, when we talk about the citric acid cycle, also known as the Krebs cycle, that is occurring in the matrix. So Krebs, Krebs cycle is occurring in the matrix. And then I said the electron transport chain, which is really what's responsible for producing the bulk of the ATP, that is happening through proteins that are straddling the inner membrane or straddling the cristae right over here. Now we're not just done, and probably one of the most fascinating parts about mitochondria, we said that we think that they are descendant from these ancient independent life forms."}, {"video_title": "Mitochondria   Structure of a cell   Biology   Khan Academy.mp3", "Sentence": "But the other major phases of cellular respiration, when we talk about the citric acid cycle, also known as the Krebs cycle, that is occurring in the matrix. So Krebs, Krebs cycle is occurring in the matrix. And then I said the electron transport chain, which is really what's responsible for producing the bulk of the ATP, that is happening through proteins that are straddling the inner membrane or straddling the cristae right over here. Now we're not just done, and probably one of the most fascinating parts about mitochondria, we said that we think that they are descendant from these ancient independent life forms. And in order to be an ancient independent life form, they would have to have some information, some way to actually transmit their genetic information. And it turns out mitochondria actually have their own genetic information. They have mitochondrial DNA."}, {"video_title": "Mitochondria   Structure of a cell   Biology   Khan Academy.mp3", "Sentence": "Now we're not just done, and probably one of the most fascinating parts about mitochondria, we said that we think that they are descendant from these ancient independent life forms. And in order to be an ancient independent life form, they would have to have some information, some way to actually transmit their genetic information. And it turns out mitochondria actually have their own genetic information. They have mitochondrial DNA. And they often don't just even have one copy of it, they have multiple copies of it. And they're in loops, very similar, very similar to bacterial DNA. In fact, they have a lot in common with bacterial DNA, and that's why we think that the ancestor to mitochondria that lived independently was probably a form of bacteria or related to bacteria in some way."}, {"video_title": "Mitochondria   Structure of a cell   Biology   Khan Academy.mp3", "Sentence": "They have mitochondrial DNA. And they often don't just even have one copy of it, they have multiple copies of it. And they're in loops, very similar, very similar to bacterial DNA. In fact, they have a lot in common with bacterial DNA, and that's why we think that the ancestor to mitochondria that lived independently was probably a form of bacteria or related to bacteria in some way. So this is, this right over there, that is the loop of mitochondrial DNA. So all of the DNA that's inside of you, the bulk of it, yes, it is in your nuclear DNA, but you still have a little bit of DNA in your mitochondria. And what's interesting is your mitochondrial DNA, your mitochondria are inherited essentially from your mother's side."}, {"video_title": "Mitochondria   Structure of a cell   Biology   Khan Academy.mp3", "Sentence": "In fact, they have a lot in common with bacterial DNA, and that's why we think that the ancestor to mitochondria that lived independently was probably a form of bacteria or related to bacteria in some way. So this is, this right over there, that is the loop of mitochondrial DNA. So all of the DNA that's inside of you, the bulk of it, yes, it is in your nuclear DNA, but you still have a little bit of DNA in your mitochondria. And what's interesting is your mitochondrial DNA, your mitochondria are inherited essentially from your mother's side. Because when an egg is fertilized, when an egg is fertilized, a human egg has tons of mitochondria in it. It has tons of mitochondria, and I'm obviously not drawing all of the things in the human egg, it obviously has a nucleus and all of that. The sperm has some mitochondria in it."}, {"video_title": "Mitochondria   Structure of a cell   Biology   Khan Academy.mp3", "Sentence": "And what's interesting is your mitochondrial DNA, your mitochondria are inherited essentially from your mother's side. Because when an egg is fertilized, when an egg is fertilized, a human egg has tons of mitochondria in it. It has tons of mitochondria, and I'm obviously not drawing all of the things in the human egg, it obviously has a nucleus and all of that. The sperm has some mitochondria in it. The sperm has some mitochondria in it. You can imagine it needs some energy to be able to win that very competitive fight to get to fertilize the egg. But the current theories are, well, most of that gets digested and dissolved once it gets into, once it actually gets into the egg."}, {"video_title": "Mitochondria   Structure of a cell   Biology   Khan Academy.mp3", "Sentence": "The sperm has some mitochondria in it. The sperm has some mitochondria in it. You can imagine it needs some energy to be able to win that very competitive fight to get to fertilize the egg. But the current theories are, well, most of that gets digested and dissolved once it gets into, once it actually gets into the egg. And anyway, the egg itself has way more mitochondria. So the mitochondria, the DNA in your mitochondria is from your mother, or is essentially from your mother's side. And that's actually used, mitochondrial DNA, when people talk about kind of an ancient eve or tracing back to having kind of one common mother, people are looking at the mitochondrial DNA."}, {"video_title": "Mitochondria   Structure of a cell   Biology   Khan Academy.mp3", "Sentence": "But the current theories are, well, most of that gets digested and dissolved once it gets into, once it actually gets into the egg. And anyway, the egg itself has way more mitochondria. So the mitochondria, the DNA in your mitochondria is from your mother, or is essentially from your mother's side. And that's actually used, mitochondrial DNA, when people talk about kind of an ancient eve or tracing back to having kind of one common mother, people are looking at the mitochondrial DNA. So it is actually quite, quite fascinating. Now I said a little bit earlier, and obviously it has its own DNA, and then because it has its own DNA, it's able to synthesize some of its own RNA, its own ribosomes, so it also has ribosomes here. But it doesn't synthesize all of the proteins that are sitting in mitochondria."}, {"video_title": "Mitochondria   Structure of a cell   Biology   Khan Academy.mp3", "Sentence": "And that's actually used, mitochondrial DNA, when people talk about kind of an ancient eve or tracing back to having kind of one common mother, people are looking at the mitochondrial DNA. So it is actually quite, quite fascinating. Now I said a little bit earlier, and obviously it has its own DNA, and then because it has its own DNA, it's able to synthesize some of its own RNA, its own ribosomes, so it also has ribosomes here. But it doesn't synthesize all of the proteins that are sitting in mitochondria. A lot of those are still synthesized by, or coded for by your nuclear DNA, and are actually synthesized outside of the mitochondria and then make their way into the mitochondria. But mitochondria are these fascinating, fascinating things. They're all, you know, they're these little creatures living in symbiosis in our cells, and they're able to replicate themselves."}, {"video_title": "Mitochondria   Structure of a cell   Biology   Khan Academy.mp3", "Sentence": "But it doesn't synthesize all of the proteins that are sitting in mitochondria. A lot of those are still synthesized by, or coded for by your nuclear DNA, and are actually synthesized outside of the mitochondria and then make their way into the mitochondria. But mitochondria are these fascinating, fascinating things. They're all, you know, they're these little creatures living in symbiosis in our cells, and they're able to replicate themselves. And I don't know, I find all of this mind-boggling. But anyway, I said that this was the textbook model, because it turns out, when you look at a, when you look at a micrograph, a picture of mitochondria, it seems to back up this textbook model of these folds, these cristae, cristae, just kind of folding in. But when we've been able to have more sophisticated visualizations, it actually turns out that it's not just these simple folds that the inner membrane essentially pokes into the matrix, and it turns out it has these little tunnels that connect the space inside of the cristae to the intermembrane space."}, {"video_title": "Mitochondria   Structure of a cell   Biology   Khan Academy.mp3", "Sentence": "They're all, you know, they're these little creatures living in symbiosis in our cells, and they're able to replicate themselves. And I don't know, I find all of this mind-boggling. But anyway, I said that this was the textbook model, because it turns out, when you look at a, when you look at a micrograph, a picture of mitochondria, it seems to back up this textbook model of these folds, these cristae, cristae, just kind of folding in. But when we've been able to have more sophisticated visualizations, it actually turns out that it's not just these simple folds that the inner membrane essentially pokes into the matrix, and it turns out it has these little tunnels that connect the space inside of the cristae to the intermembrane space. So I like to think about this, because it makes you realize, you know, we look in textbooks and we take these things like mitochondria for granted, like, oh yeah, of course, that's where the ATP factories are. But it's still an area for visualization research to fully understand exactly how they work, and even how they are structured, that this Baffle model, where you see these cristae kind of just coming in and out of the different sides, this is actually no longer the accepted model for the actual visualization, the structure of mitochondria, it's something more like this, something more where, you know, you have this cristae junction model, where you have, if I were to draw a cross section, where this is, I drew the outer membrane, the inner membrane, I'll just draw, has these little tunnels to the actual, into the space inside of the cristae, this is actually now the more accepted visualization. So I want you to appreciate that, you know, in biology, you read something in a textbook, you kind of say, oh, people have figured all this stuff out, but people are still thinking more about, well, how does this structure work, what is the actual structure, and then how does it actually let this organelle, this fascinating organelle, do all of the things that it needs to do."}, {"video_title": "Taxonomy and the Tree of Life.mp3", "Sentence": "So classifying, classifying organisms. And his real innovation, before he came about, people realized that you had species of animals, that lions had certain properties that made them all lions, that they could interbreed and things like that, that monkey or chimpanzees would all interbreed and that would be a separate species, and that polar bears were a separate species, and that humans were a separate species. But what he really brought to the table is he decided, well, let me just not just group animals into species, maybe I can group species into other categories, and that's where we get the genus from. You group similar species into a genus. And then he went even beyond that, because even the idea of grouping things into a genus dated back to the ancient Greeks. He said, well, why don't I group similar genuses together into orders, orders together into classes, and then classes together into kingdoms. So really what he did is he said, well, maybe I can classify, I can create a tree, I can create a tree of life, I can create a structure so we can really see how far apart any two organisms are."}, {"video_title": "Taxonomy and the Tree of Life.mp3", "Sentence": "You group similar species into a genus. And then he went even beyond that, because even the idea of grouping things into a genus dated back to the ancient Greeks. He said, well, why don't I group similar genuses together into orders, orders together into classes, and then classes together into kingdoms. So really what he did is he said, well, maybe I can classify, I can create a tree, I can create a tree of life, I can create a structure so we can really see how far apart any two organisms are. And that's why he's really the father of modern taxonomy. And he did not have many tools. All he could do is look at his powers of observation."}, {"video_title": "Taxonomy and the Tree of Life.mp3", "Sentence": "So really what he did is he said, well, maybe I can classify, I can create a tree, I can create a tree of life, I can create a structure so we can really see how far apart any two organisms are. And that's why he's really the father of modern taxonomy. And he did not have many tools. All he could do is look at his powers of observation. He said, okay, those kind of animals, they have fur or they reproduce in this way, or they lay eggs or they don't lay eggs, or they have spinal columns or they don't have spinal columns. So that's the best that he could do when he did his taxonomy. But since then, there's obviously been tons of innovations in how we perceive animals or the natural world and our tools for studying them."}, {"video_title": "Taxonomy and the Tree of Life.mp3", "Sentence": "All he could do is look at his powers of observation. He said, okay, those kind of animals, they have fur or they reproduce in this way, or they lay eggs or they don't lay eggs, or they have spinal columns or they don't have spinal columns. So that's the best that he could do when he did his taxonomy. But since then, there's obviously been tons of innovations in how we perceive animals or the natural world and our tools for studying them. So one thing that he did not know about is evolution, this idea of common ancestry. And between our understandings of evolution and our ability to look back at the fossil record, that helps us get more precise at figuring out which animals are related to which. We can see, do they have a common ancestor more recent or further back?"}, {"video_title": "Taxonomy and the Tree of Life.mp3", "Sentence": "But since then, there's obviously been tons of innovations in how we perceive animals or the natural world and our tools for studying them. So one thing that he did not know about is evolution, this idea of common ancestry. And between our understandings of evolution and our ability to look back at the fossil record, that helps us get more precise at figuring out which animals are related to which. We can see, do they have a common ancestor more recent or further back? And what even Charles Darwin didn't have, which we now use as a tool in taxonomy, is the genetic evidence. So now we don't even have to rely on the fossil record. We can look at the DNA of two species that exist today and see how similar is that DNA."}, {"video_title": "Taxonomy and the Tree of Life.mp3", "Sentence": "We can see, do they have a common ancestor more recent or further back? And what even Charles Darwin didn't have, which we now use as a tool in taxonomy, is the genetic evidence. So now we don't even have to rely on the fossil record. We can look at the DNA of two species that exist today and see how similar is that DNA. And that tells us how recently they branched apart if we were able to find it in the fossil record, or how recently in the past did these two species become two different species. Now, with that said, I do wanna make this clear. And this is something that I've always had a little bit, it was fuzzy for me the first time that I was exposed to this idea of taxonomy, is that taxonomy is as much an art as it's a science."}, {"video_title": "Taxonomy and the Tree of Life.mp3", "Sentence": "We can look at the DNA of two species that exist today and see how similar is that DNA. And that tells us how recently they branched apart if we were able to find it in the fossil record, or how recently in the past did these two species become two different species. Now, with that said, I do wanna make this clear. And this is something that I've always had a little bit, it was fuzzy for me the first time that I was exposed to this idea of taxonomy, is that taxonomy is as much an art as it's a science. And today, even to this day, people are debating about the best way to classify things. And what do you pay attention to? And DNA has been the best tool so far in giving us a more systematic, a more analytical way of deciding how close two animals are."}, {"video_title": "Taxonomy and the Tree of Life.mp3", "Sentence": "And this is something that I've always had a little bit, it was fuzzy for me the first time that I was exposed to this idea of taxonomy, is that taxonomy is as much an art as it's a science. And today, even to this day, people are debating about the best way to classify things. And what do you pay attention to? And DNA has been the best tool so far in giving us a more systematic, a more analytical way of deciding how close two animals are. But to a large degree, a lot of these categories, deciding where to divide along kingdom, phylum, class, order, family, tribe, these are somewhat arbitrary. These are just picked based on early taxonomists, including Carl Linnaeus, and saying, oh, this looks like a grouping right over here. But they could have grouped at a broader level or a deeper level."}, {"video_title": "Taxonomy and the Tree of Life.mp3", "Sentence": "And DNA has been the best tool so far in giving us a more systematic, a more analytical way of deciding how close two animals are. But to a large degree, a lot of these categories, deciding where to divide along kingdom, phylum, class, order, family, tribe, these are somewhat arbitrary. These are just picked based on early taxonomists, including Carl Linnaeus, and saying, oh, this looks like a grouping right over here. But they could have grouped at a broader level or a deeper level. So these things right over here are somewhat arbitrary. A more analytical way is just to see how much DNA you have in common, and then use that as a measure of how far apart two animals are. Or really, I should say, two species are, because this taxonomy doesn't even apply just to animals."}, {"video_title": "Taxonomy and the Tree of Life.mp3", "Sentence": "But they could have grouped at a broader level or a deeper level. So these things right over here are somewhat arbitrary. A more analytical way is just to see how much DNA you have in common, and then use that as a measure of how far apart two animals are. Or really, I should say, two species are, because this taxonomy doesn't even apply just to animals. It applies to plants and bacteria and archaea and all sorts of things. So it's actually a broader thing than just animals. Now, with that out of the way, what I thought would be fun, just so that we could really get a sense of where modern taxonomy is, where the field that was essentially fathered by Carl Linnaeus, where it is now, and use that to figure out where we humans fit into the big picture."}, {"video_title": "Taxonomy and the Tree of Life.mp3", "Sentence": "Or really, I should say, two species are, because this taxonomy doesn't even apply just to animals. It applies to plants and bacteria and archaea and all sorts of things. So it's actually a broader thing than just animals. Now, with that out of the way, what I thought would be fun, just so that we could really get a sense of where modern taxonomy is, where the field that was essentially fathered by Carl Linnaeus, where it is now, and use that to figure out where we humans fit into the big picture. And obviously, I'm drawing just a small fraction of the universe of the organisms that we even know about right now. But at least it frames the picture in terms of something we understand, in particular, us, in particular, humans. Now, our species, we call ourselves humans, but we're really Homo sapiens."}, {"video_title": "Taxonomy and the Tree of Life.mp3", "Sentence": "Now, with that out of the way, what I thought would be fun, just so that we could really get a sense of where modern taxonomy is, where the field that was essentially fathered by Carl Linnaeus, where it is now, and use that to figure out where we humans fit into the big picture. And obviously, I'm drawing just a small fraction of the universe of the organisms that we even know about right now. But at least it frames the picture in terms of something we understand, in particular, us, in particular, humans. Now, our species, we call ourselves humans, but we're really Homo sapiens. And the sapiens is the species part, and then Homo is the genus. And what I'm doing right over here is I'm saying, well, if Homo is the genus, what other species were inside of Homo? And the reality is, or at least as far as we know, there are no other living species inside of Homo that we've probably killed them all off, or maybe we interbreed with them somehow, which might have argued that maybe they weren't different species."}, {"video_title": "Taxonomy and the Tree of Life.mp3", "Sentence": "Now, our species, we call ourselves humans, but we're really Homo sapiens. And the sapiens is the species part, and then Homo is the genus. And what I'm doing right over here is I'm saying, well, if Homo is the genus, what other species were inside of Homo? And the reality is, or at least as far as we know, there are no other living species inside of Homo that we've probably killed them all off, or maybe we interbreed with them somehow, which might have argued that maybe they weren't different species. But more likely, they were competing in the same ecosystems and they became endangered species very quickly when they competed with our ancestors. But the most recent other species within the genus that we know about are the Neanderthals. And the formal term for their species is Neanderthalensis."}, {"video_title": "Taxonomy and the Tree of Life.mp3", "Sentence": "And the reality is, or at least as far as we know, there are no other living species inside of Homo that we've probably killed them all off, or maybe we interbreed with them somehow, which might have argued that maybe they weren't different species. But more likely, they were competing in the same ecosystems and they became endangered species very quickly when they competed with our ancestors. But the most recent other species within the genus that we know about are the Neanderthals. And the formal term for their species is Neanderthalensis. Now, if we go further up the tree of life, further up the taxonomy, and you'll sometimes see tribe mentioned, sometimes you won't. And we tend to get a little bit more granular the closer we get to humans. When we go further away in the tree of life, we get a little bit less granular sometimes, but that's not always the case as well."}, {"video_title": "Taxonomy and the Tree of Life.mp3", "Sentence": "And the formal term for their species is Neanderthalensis. Now, if we go further up the tree of life, further up the taxonomy, and you'll sometimes see tribe mentioned, sometimes you won't. And we tend to get a little bit more granular the closer we get to humans. When we go further away in the tree of life, we get a little bit less granular sometimes, but that's not always the case as well. You go a little bit further up and you get to Hominini, and I'm sure I'm mispronouncing some of this as well. But another species that's in Hominini that is not in Homo, and I'm definitely not listing all of them, and that's why I'm showing all of these other branches over here, is what we call the common chimpanzee. And their species name is, their genus is Pan, and their species is Troglodytes."}, {"video_title": "Taxonomy and the Tree of Life.mp3", "Sentence": "When we go further away in the tree of life, we get a little bit less granular sometimes, but that's not always the case as well. You go a little bit further up and you get to Hominini, and I'm sure I'm mispronouncing some of this as well. But another species that's in Hominini that is not in Homo, and I'm definitely not listing all of them, and that's why I'm showing all of these other branches over here, is what we call the common chimpanzee. And their species name is, their genus is Pan, and their species is Troglodytes. So you would refer to them as Pan-Troglodytes. And that's also another convention that Carl Linnaeus came up with, is that you refer to a particular species by its genus and then its species, and you capitalize the genus and you lowercase the species. So we're Homo sapiens, this is Homo neanderthalensis, this is Pan-Troglodytes, or often referred to as chimpanzees."}, {"video_title": "Taxonomy and the Tree of Life.mp3", "Sentence": "And their species name is, their genus is Pan, and their species is Troglodytes. So you would refer to them as Pan-Troglodytes. And that's also another convention that Carl Linnaeus came up with, is that you refer to a particular species by its genus and then its species, and you capitalize the genus and you lowercase the species. So we're Homo sapiens, this is Homo neanderthalensis, this is Pan-Troglodytes, or often referred to as chimpanzees. Now, if you go up one higher level of broadness on this tree of life, you then get to the family. And we are in the family Hominidae, and Hominidae, and I'm sure I'm mispronouncing it once again. But just to give you an example, so everything I've listed so far, everything I've talked about so far, are within this family."}, {"video_title": "Taxonomy and the Tree of Life.mp3", "Sentence": "So we're Homo sapiens, this is Homo neanderthalensis, this is Pan-Troglodytes, or often referred to as chimpanzees. Now, if you go up one higher level of broadness on this tree of life, you then get to the family. And we are in the family Hominidae, and Hominidae, and I'm sure I'm mispronouncing it once again. But just to give you an example, so everything I've listed so far, everything I've talked about so far, are within this family. And to show you an animal that is not in this family, you just have to look at the gorilla. And you could call it the Gorillini, the Gorillini gorilla, or G gorilla. That's its actual species name."}, {"video_title": "Taxonomy and the Tree of Life.mp3", "Sentence": "But just to give you an example, so everything I've listed so far, everything I've talked about so far, are within this family. And to show you an animal that is not in this family, you just have to look at the gorilla. And you could call it the Gorillini, the Gorillini gorilla, or G gorilla. That's its actual species name. And this family right over here, sometimes the common term is the great apes. The great apes. Now, you go one further level, and this is, the whole reason why I'm doing this, and I'm not by any means am I being exhaustive about the other species that are in that family, but that are not in our tribe."}, {"video_title": "Taxonomy and the Tree of Life.mp3", "Sentence": "That's its actual species name. And this family right over here, sometimes the common term is the great apes. The great apes. Now, you go one further level, and this is, the whole reason why I'm doing this, and I'm not by any means am I being exhaustive about the other species that are in that family, but that are not in our tribe. I'm just trying to give you a picture of, as we get further and further out, as we get further out of our tribe, our family, our order, we're getting to things where the common ancestry with human goes further and further back in time. The genetic similarities become more and more different. And even just the physical differences, if we look at it at a very superficial level, become more and more and more different."}, {"video_title": "Taxonomy and the Tree of Life.mp3", "Sentence": "Now, you go one further level, and this is, the whole reason why I'm doing this, and I'm not by any means am I being exhaustive about the other species that are in that family, but that are not in our tribe. I'm just trying to give you a picture of, as we get further and further out, as we get further out of our tribe, our family, our order, we're getting to things where the common ancestry with human goes further and further back in time. The genetic similarities become more and more different. And even just the physical differences, if we look at it at a very superficial level, become more and more and more different. So you get to even a broader category. This is where you get to the primates. And this is probably something that you might be somewhat familiar with."}, {"video_title": "Taxonomy and the Tree of Life.mp3", "Sentence": "And even just the physical differences, if we look at it at a very superficial level, become more and more and more different. So you get to even a broader category. This is where you get to the primates. And this is probably something that you might be somewhat familiar with. And the term primates is general, these animals that look like they either live in trees or rainforest, or they're descendant of things that live in trees, so they have these things that they can grasp things with. They're good at climbing, broadly, not all of them are. Humans are probably the worst primates when it comes to climbing, or one of the worst."}, {"video_title": "Taxonomy and the Tree of Life.mp3", "Sentence": "And this is probably something that you might be somewhat familiar with. And the term primates is general, these animals that look like they either live in trees or rainforest, or they're descendant of things that live in trees, so they have these things that they can grasp things with. They're good at climbing, broadly, not all of them are. Humans are probably the worst primates when it comes to climbing, or one of the worst. But that's the general classification, that's what we generally think of when we think of primates. And if we think of a primate that is not a great ape, you just have to think of a baboon. So this right here is a baboon."}, {"video_title": "Taxonomy and the Tree of Life.mp3", "Sentence": "Humans are probably the worst primates when it comes to climbing, or one of the worst. But that's the general classification, that's what we generally think of when we think of primates. And if we think of a primate that is not a great ape, you just have to think of a baboon. So this right here is a baboon. It is a primate, but it is not a great ape. It is probably descendant, some baboons actually don't live in trees, but all of them are probably descendant from things that first live in trees, and that's why their hands and their feet look the way they do. Now you get to even a broader level of classification."}, {"video_title": "Taxonomy and the Tree of Life.mp3", "Sentence": "So this right here is a baboon. It is a primate, but it is not a great ape. It is probably descendant, some baboons actually don't live in trees, but all of them are probably descendant from things that first live in trees, and that's why their hands and their feet look the way they do. Now you get to even a broader level of classification. You get to the mammals, and once again, probably something you're used to thinking about. Mammals are air-breathing animals. They tend to have fur or hair."}, {"video_title": "Taxonomy and the Tree of Life.mp3", "Sentence": "Now you get to even a broader level of classification. You get to the mammals, and once again, probably something you're used to thinking about. Mammals are air-breathing animals. They tend to have fur or hair. They tend to provide some form of milk for their young. They have active mammary glands. There's other things that we can talk about what makes a mammal."}, {"video_title": "Taxonomy and the Tree of Life.mp3", "Sentence": "They tend to have fur or hair. They tend to provide some form of milk for their young. They have active mammary glands. There's other things that we can talk about what makes a mammal. I'm not gonna go into the rigorous definition, but just to give you an example of a mammal that is not a primate, I could show you this polar bear right over here. This is a mammal that is not a primate, and I could do other things. I could show you a tiger, or I could show you a giraffe or a horse, and so by no stretch of the imagination am I being comprehensive."}, {"video_title": "Taxonomy and the Tree of Life.mp3", "Sentence": "There's other things that we can talk about what makes a mammal. I'm not gonna go into the rigorous definition, but just to give you an example of a mammal that is not a primate, I could show you this polar bear right over here. This is a mammal that is not a primate, and I could do other things. I could show you a tiger, or I could show you a giraffe or a horse, and so by no stretch of the imagination am I being comprehensive. But let's keep getting broader. Now let's go to the class, or we're already at the class of mammalia, now let's go to the phylum. And phylum we are, humans and all mammals, we are in the phylum chordates."}, {"video_title": "Taxonomy and the Tree of Life.mp3", "Sentence": "I could show you a tiger, or I could show you a giraffe or a horse, and so by no stretch of the imagination am I being comprehensive. But let's keep getting broader. Now let's go to the class, or we're already at the class of mammalia, now let's go to the phylum. And phylum we are, humans and all mammals, we are in the phylum chordates. And chordates, we're actually in the subphylum, which I didn't write here, vertebrates, which means we have a vertebra, we have a spinal column with a spinal cord in it. Chordates are a little bit more general. Chordates is a phylum where kind of the arrangement of where the mouth is, where the digestive organs, where the anus is, where the spinal column is, where the brains, where the eyes, where the mouth, they're kind of all in the same place."}, {"video_title": "Taxonomy and the Tree of Life.mp3", "Sentence": "And phylum we are, humans and all mammals, we are in the phylum chordates. And chordates, we're actually in the subphylum, which I didn't write here, vertebrates, which means we have a vertebra, we have a spinal column with a spinal cord in it. Chordates are a little bit more general. Chordates is a phylum where kind of the arrangement of where the mouth is, where the digestive organs, where the anus is, where the spinal column is, where the brains, where the eyes, where the mouth, they're kind of all in the same place. And if you think about it, everything I've listed here kind of has the same general structure. You have a spinal column, you have a brain, you have a mouth, then the mouth leads to some type of a digestive column, and at the end of it you have an anus over there, and you have eyes in front of the brain. And so this is a general way, and I'm not being very rigorous here, is how you describe a chordate."}, {"video_title": "Taxonomy and the Tree of Life.mp3", "Sentence": "Chordates is a phylum where kind of the arrangement of where the mouth is, where the digestive organs, where the anus is, where the spinal column is, where the brains, where the eyes, where the mouth, they're kind of all in the same place. And if you think about it, everything I've listed here kind of has the same general structure. You have a spinal column, you have a brain, you have a mouth, then the mouth leads to some type of a digestive column, and at the end of it you have an anus over there, and you have eyes in front of the brain. And so this is a general way, and I'm not being very rigorous here, is how you describe a chordate. And to show a chordate that is not a mammal, you would just have to think of fish or sharks. So this right over here, this right over here, let me make sure, let me, this right over here is a non-mammal chordate. This is a great white shark over here."}, {"video_title": "Taxonomy and the Tree of Life.mp3", "Sentence": "And so this is a general way, and I'm not being very rigorous here, is how you describe a chordate. And to show a chordate that is not a mammal, you would just have to think of fish or sharks. So this right over here, this right over here, let me make sure, let me, this right over here is a non-mammal chordate. This is a great white shark over here. Now let's go even broader, and as you'll see, now we're getting to things that are very, very not, very, very not human-like. So you go one step broader, now we're in Animalia, we're the kingdom of animals, and this is the broadest definition that, or the broadest category that Carl Linnaeus thought about. Well, actually, he did go into trees as well."}, {"video_title": "Taxonomy and the Tree of Life.mp3", "Sentence": "This is a great white shark over here. Now let's go even broader, and as you'll see, now we're getting to things that are very, very not, very, very not human-like. So you go one step broader, now we're in Animalia, we're the kingdom of animals, and this is the broadest definition that, or the broadest category that Carl Linnaeus thought about. Well, actually, he did go into trees as well. But when you think of the kingdom of animals, when you think of things that aren't chordates, you start going into things like insects, and you start going into things like jellyfish. If you go even broader, now we're talking about the domain. You go to eukarya, so these are all organisms that have cells, and inside those cells they have complex structures."}, {"video_title": "Taxonomy and the Tree of Life.mp3", "Sentence": "Well, actually, he did go into trees as well. But when you think of the kingdom of animals, when you think of things that aren't chordates, you start going into things like insects, and you start going into things like jellyfish. If you go even broader, now we're talking about the domain. You go to eukarya, so these are all organisms that have cells, and inside those cells they have complex structures. So if you're eukarya, you have cells with complex structures. If you're a prokarya, which you don't have complex structures inside your cell. But other eukarya that are not animals include things like plants."}, {"video_title": "Taxonomy and the Tree of Life.mp3", "Sentence": "You go to eukarya, so these are all organisms that have cells, and inside those cells they have complex structures. So if you're eukarya, you have cells with complex structures. If you're a prokarya, which you don't have complex structures inside your cell. But other eukarya that are not animals include things like plants. And obviously I'm giving no justice to this whole branch of the tree of life. It could be just as rich or richer than everything I've drawn over here. This is just a small fraction of the entire tree of life."}, {"video_title": "Taxonomy and the Tree of Life.mp3", "Sentence": "But other eukarya that are not animals include things like plants. And obviously I'm giving no justice to this whole branch of the tree of life. It could be just as rich or richer than everything I've drawn over here. This is just a small fraction of the entire tree of life. But let's go even broader than that. So if you go even broader than that, and you say, well, what's a kind of life form that isn't eukarya, that wouldn't have these more complex cell structures, these mitochondria in the cells, the cell nucleuses, then you just have to think about something like bacteria. And if you wanna go even broader, there's things like viruses that you can even debate whether they really even are life, because they are dependent on other life forms for their actual reproduction, but they do have genetic material like everything else."}, {"video_title": "Taxonomy and the Tree of Life.mp3", "Sentence": "This is just a small fraction of the entire tree of life. But let's go even broader than that. So if you go even broader than that, and you say, well, what's a kind of life form that isn't eukarya, that wouldn't have these more complex cell structures, these mitochondria in the cells, the cell nucleuses, then you just have to think about something like bacteria. And if you wanna go even broader, there's things like viruses that you can even debate whether they really even are life, because they are dependent on other life forms for their actual reproduction, but they do have genetic material like everything else. And that, to me, is kind of a mind-blowing idea. As different as a plant is, look at a house plant that's in your house right now, or the tree when you walk home, or bacteria, this jellyfish. There is a commonality in that we all have DNA, and that DNA, for the most part, replicates in a very, very, very similar way."}, {"video_title": "Taxonomy and the Tree of Life.mp3", "Sentence": "And if you wanna go even broader, there's things like viruses that you can even debate whether they really even are life, because they are dependent on other life forms for their actual reproduction, but they do have genetic material like everything else. And that, to me, is kind of a mind-blowing idea. As different as a plant is, look at a house plant that's in your house right now, or the tree when you walk home, or bacteria, this jellyfish. There is a commonality in that we all have DNA, and that DNA, for the most part, replicates in a very, very, very similar way. So it's actually crazy that we actually even are related, or that we even do have a common ancestor with some of these things. And then it even begs the question, well, what about things like viruses? Anyway, I'll leave you here, and I really just want to let you know that, kind of make sure you realize that this is a, it's definitely worth studying, because we understand where we fit in in kind of the universe of living things."}, {"video_title": "Cell membrane overview and fluid mosaic model   Cells   MCAT   Khan Academy.mp3", "Sentence": "In this video, we're going to explore a little bit about the cell membrane. So just as a little refresher, let's say this is a picture of our cell with a little tiny nucleus in the middle. Our cell membrane is what's on the outside of our cell. So our cell membrane is what protects our cell from a really harsh outside environment. If it weren't for the cell membrane, we wouldn't be alive today because there would be nothing to protect us from the outside world. So we're going to talk about the main three things that make up the cell membrane. The first, phospholipids, the second, cholesterol, and the third, proteins."}, {"video_title": "Cell membrane overview and fluid mosaic model   Cells   MCAT   Khan Academy.mp3", "Sentence": "So our cell membrane is what protects our cell from a really harsh outside environment. If it weren't for the cell membrane, we wouldn't be alive today because there would be nothing to protect us from the outside world. So we're going to talk about the main three things that make up the cell membrane. The first, phospholipids, the second, cholesterol, and the third, proteins. So the first one we're going to talk about, and this makes up the majority of what's in our cell membrane, are phospholipids. And just for the sake of time, I've pre-drawn a picture of the cell membrane here. And you'll notice that all of these individual pieces are phospholipids."}, {"video_title": "Cell membrane overview and fluid mosaic model   Cells   MCAT   Khan Academy.mp3", "Sentence": "The first, phospholipids, the second, cholesterol, and the third, proteins. So the first one we're going to talk about, and this makes up the majority of what's in our cell membrane, are phospholipids. And just for the sake of time, I've pre-drawn a picture of the cell membrane here. And you'll notice that all of these individual pieces are phospholipids. And a phospholipid looks like this. It has that polar head group, that polar phosphate group, and it has two fatty acid tails. And so this is the way that we normally represent what a phospholipid looks like."}, {"video_title": "Cell membrane overview and fluid mosaic model   Cells   MCAT   Khan Academy.mp3", "Sentence": "And you'll notice that all of these individual pieces are phospholipids. And a phospholipid looks like this. It has that polar head group, that polar phosphate group, and it has two fatty acid tails. And so this is the way that we normally represent what a phospholipid looks like. And in the cell membrane, you can see that these phospholipids are packed pretty closely, pretty tightly together all throughout the entire membrane. And we're looking at this membrane, this is kind of like a cross-section. You can imagine that we cut the membrane in half."}, {"video_title": "Cell membrane overview and fluid mosaic model   Cells   MCAT   Khan Academy.mp3", "Sentence": "And so this is the way that we normally represent what a phospholipid looks like. And in the cell membrane, you can see that these phospholipids are packed pretty closely, pretty tightly together all throughout the entire membrane. And we're looking at this membrane, this is kind of like a cross-section. You can imagine that we cut the membrane in half. So what we have here is actually what we call our phospholipid bilayer. And sometimes it's also called the lipid bilayer. The second thing that we can find in our membrane is cholesterol."}, {"video_title": "Cell membrane overview and fluid mosaic model   Cells   MCAT   Khan Academy.mp3", "Sentence": "You can imagine that we cut the membrane in half. So what we have here is actually what we call our phospholipid bilayer. And sometimes it's also called the lipid bilayer. The second thing that we can find in our membrane is cholesterol. Now, we often hear cholesterol in foods and cholesterol in our blood, and we think it's a bad thing. But in this case, cholesterol is actually very important for our cell membrane. And cholesterol looks like this."}, {"video_title": "Cell membrane overview and fluid mosaic model   Cells   MCAT   Khan Academy.mp3", "Sentence": "The second thing that we can find in our membrane is cholesterol. Now, we often hear cholesterol in foods and cholesterol in our blood, and we think it's a bad thing. But in this case, cholesterol is actually very important for our cell membrane. And cholesterol looks like this. And again, just for the sake of time, I've pre-drawn what cholesterol looks like. And you'll notice that cholesterol has a lot of rings, and this gives cholesterol a pretty stable structure. And what cholesterol does is cholesterol kind of inserts itself between phospholipids, kind of like that."}, {"video_title": "Cell membrane overview and fluid mosaic model   Cells   MCAT   Khan Academy.mp3", "Sentence": "And cholesterol looks like this. And again, just for the sake of time, I've pre-drawn what cholesterol looks like. And you'll notice that cholesterol has a lot of rings, and this gives cholesterol a pretty stable structure. And what cholesterol does is cholesterol kind of inserts itself between phospholipids, kind of like that. And the way I think about it is cholesterol is kind of like a buffer. It maintains the fluidity of our cell membranes. So as temperatures become lower, cholesterol will help increase the fluidity."}, {"video_title": "Cell membrane overview and fluid mosaic model   Cells   MCAT   Khan Academy.mp3", "Sentence": "And what cholesterol does is cholesterol kind of inserts itself between phospholipids, kind of like that. And the way I think about it is cholesterol is kind of like a buffer. It maintains the fluidity of our cell membranes. So as temperatures become lower, cholesterol will help increase the fluidity. And as temperatures become higher, cholesterol will help reduce the fluidity of the cell membrane. So cholesterol keeps our cell membrane in kind of a happy middle ground of fluidity. And the third thing that makes up our cell membrane are proteins."}, {"video_title": "Cell membrane overview and fluid mosaic model   Cells   MCAT   Khan Academy.mp3", "Sentence": "So as temperatures become lower, cholesterol will help increase the fluidity. And as temperatures become higher, cholesterol will help reduce the fluidity of the cell membrane. So cholesterol keeps our cell membrane in kind of a happy middle ground of fluidity. And the third thing that makes up our cell membrane are proteins. And proteins are actually a big one. And depending on the cell, some cells will actually have a significant amount of protein in the membrane. And so proteins can take two major forms."}, {"video_title": "Cell membrane overview and fluid mosaic model   Cells   MCAT   Khan Academy.mp3", "Sentence": "And the third thing that makes up our cell membrane are proteins. And proteins are actually a big one. And depending on the cell, some cells will actually have a significant amount of protein in the membrane. And so proteins can take two major forms. The first is you can have a protein that crosses the entire membrane. We call this an integral protein. We also can call this a transmembrane protein."}, {"video_title": "Cell membrane overview and fluid mosaic model   Cells   MCAT   Khan Academy.mp3", "Sentence": "And so proteins can take two major forms. The first is you can have a protein that crosses the entire membrane. We call this an integral protein. We also can call this a transmembrane protein. And this can occur throughout different areas of the cell, like that. And some proteins actually kind of sit on top of the membrane, like this. Or they might sit on another protein, like that."}, {"video_title": "Cell membrane overview and fluid mosaic model   Cells   MCAT   Khan Academy.mp3", "Sentence": "We also can call this a transmembrane protein. And this can occur throughout different areas of the cell, like that. And some proteins actually kind of sit on top of the membrane, like this. Or they might sit on another protein, like that. And these are what we call peripheral proteins. There are some very rare proteins that actually can go halfway through the membrane. And even rarer, there are occasionally a few proteins that actually can be found inside the cell membrane, like this, between the two phospholipids, inside our bilayer."}, {"video_title": "Cell membrane overview and fluid mosaic model   Cells   MCAT   Khan Academy.mp3", "Sentence": "Or they might sit on another protein, like that. And these are what we call peripheral proteins. There are some very rare proteins that actually can go halfway through the membrane. And even rarer, there are occasionally a few proteins that actually can be found inside the cell membrane, like this, between the two phospholipids, inside our bilayer. Now, proteins are a very big player in the function of cell membranes. They actually carry out nearly all of the membrane processes that we can think of. And the two biggest things that proteins do is, the first, they can actually act as receptors."}, {"video_title": "Cell membrane overview and fluid mosaic model   Cells   MCAT   Khan Academy.mp3", "Sentence": "And even rarer, there are occasionally a few proteins that actually can be found inside the cell membrane, like this, between the two phospholipids, inside our bilayer. Now, proteins are a very big player in the function of cell membranes. They actually carry out nearly all of the membrane processes that we can think of. And the two biggest things that proteins do is, the first, they can actually act as receptors. So the proteins can actually tell the cell what's going on in the outside world. They act as communication. And the second thing that proteins can do, which generally occur in transmembrane proteins, is that proteins can actually help transport molecules in and out of the cell."}, {"video_title": "Cell membrane overview and fluid mosaic model   Cells   MCAT   Khan Academy.mp3", "Sentence": "And the two biggest things that proteins do is, the first, they can actually act as receptors. So the proteins can actually tell the cell what's going on in the outside world. They act as communication. And the second thing that proteins can do, which generally occur in transmembrane proteins, is that proteins can actually help transport molecules in and out of the cell. So now that we know the function of proteins, why do you think proteins that are lipid-bound or bound within our lipid bilayer, like this one here, is so rare? Well, it's because if the role of proteins is primarily to act as receptors, to communicate with our outside world, or to act as transport, to allow things to go from the inside to the outside or the outside to the inside, the proteins that are kind of stuck in between don't really have a big role in our cell membrane. And lastly, there's one very important type of molecule that actually binds to our lipids or our proteins."}, {"video_title": "Cell membrane overview and fluid mosaic model   Cells   MCAT   Khan Academy.mp3", "Sentence": "And the second thing that proteins can do, which generally occur in transmembrane proteins, is that proteins can actually help transport molecules in and out of the cell. So now that we know the function of proteins, why do you think proteins that are lipid-bound or bound within our lipid bilayer, like this one here, is so rare? Well, it's because if the role of proteins is primarily to act as receptors, to communicate with our outside world, or to act as transport, to allow things to go from the inside to the outside or the outside to the inside, the proteins that are kind of stuck in between don't really have a big role in our cell membrane. And lastly, there's one very important type of molecule that actually binds to our lipids or our proteins. And these are carbohydrates. And we call these glyco for short. So they would be glycoproteins, or they might be glycolipids."}, {"video_title": "Cell membrane overview and fluid mosaic model   Cells   MCAT   Khan Academy.mp3", "Sentence": "And lastly, there's one very important type of molecule that actually binds to our lipids or our proteins. And these are carbohydrates. And we call these glyco for short. So they would be glycoproteins, or they might be glycolipids. And what these do is they play a big role in communication. So for example, it allows a cell to recognize another cell in our body. If they play a role in communication in cells recognizing other cells, where do you think these sugars would go?"}, {"video_title": "Cell membrane overview and fluid mosaic model   Cells   MCAT   Khan Academy.mp3", "Sentence": "So they would be glycoproteins, or they might be glycolipids. And what these do is they play a big role in communication. So for example, it allows a cell to recognize another cell in our body. If they play a role in communication in cells recognizing other cells, where do you think these sugars would go? Well, these sugars would mainly occur on the outside of our membrane. So they would kind of stick out on proteins. These would be glycoproteins."}, {"video_title": "Cell membrane overview and fluid mosaic model   Cells   MCAT   Khan Academy.mp3", "Sentence": "If they play a role in communication in cells recognizing other cells, where do you think these sugars would go? Well, these sugars would mainly occur on the outside of our membrane. So they would kind of stick out on proteins. These would be glycoproteins. And they can be on peripheral or integral proteins. Or they might stick out on lipids, like this. And these would be glycolipids."}, {"video_title": "Cell membrane overview and fluid mosaic model   Cells   MCAT   Khan Academy.mp3", "Sentence": "These would be glycoproteins. And they can be on peripheral or integral proteins. Or they might stick out on lipids, like this. And these would be glycolipids. Now this is a little confusing to look at. What we've just drawn is a cross-section of our cell membrane. But what if we were looking at the cell membrane from the outside, kind of like a top view?"}, {"video_title": "Cell membrane overview and fluid mosaic model   Cells   MCAT   Khan Academy.mp3", "Sentence": "And these would be glycolipids. Now this is a little confusing to look at. What we've just drawn is a cross-section of our cell membrane. But what if we were looking at the cell membrane from the outside, kind of like a top view? What would that look like? Well, again, for the sake of time, I've pre-drawn our phospholipids. So if we were looking at the cell membrane from the outside, looking onto the top of the cell membrane, all we would see are these head groups of our phospholipids."}, {"video_title": "Cell membrane overview and fluid mosaic model   Cells   MCAT   Khan Academy.mp3", "Sentence": "But what if we were looking at the cell membrane from the outside, kind of like a top view? What would that look like? Well, again, for the sake of time, I've pre-drawn our phospholipids. So if we were looking at the cell membrane from the outside, looking onto the top of the cell membrane, all we would see are these head groups of our phospholipids. We might see some cholesterol in between our cell membranes, like this. And we might see some larger proteins that are on top of our cell membrane, like this, scattered throughout our cell. And lastly, we might actually see some glycoproteins and glycolipids on the outside."}, {"video_title": "Cell membrane overview and fluid mosaic model   Cells   MCAT   Khan Academy.mp3", "Sentence": "So if we were looking at the cell membrane from the outside, looking onto the top of the cell membrane, all we would see are these head groups of our phospholipids. We might see some cholesterol in between our cell membranes, like this. And we might see some larger proteins that are on top of our cell membrane, like this, scattered throughout our cell. And lastly, we might actually see some glycoproteins and glycolipids on the outside. And these would attach themselves to our proteins and our phospholipids, like that. So from the top, this is what our cell membrane would look like. And you know something really special about this?"}, {"video_title": "Cell membrane overview and fluid mosaic model   Cells   MCAT   Khan Academy.mp3", "Sentence": "And lastly, we might actually see some glycoproteins and glycolipids on the outside. And these would attach themselves to our proteins and our phospholipids, like that. So from the top, this is what our cell membrane would look like. And you know something really special about this? This kind of looks like a piece of art. So if we think back to elementary school, where we had the project where we would put a lot of beans or different macaroni together to create a piece of art, this kind of reminds me of that. So this is actually what we call a mosaic."}, {"video_title": "Cell membrane overview and fluid mosaic model   Cells   MCAT   Khan Academy.mp3", "Sentence": "And you know something really special about this? This kind of looks like a piece of art. So if we think back to elementary school, where we had the project where we would put a lot of beans or different macaroni together to create a piece of art, this kind of reminds me of that. So this is actually what we call a mosaic. So scientists kind of thought the same thing. And so scientists actually named this model of the cell the fluid mosaic model. And so the mosaic portion of our cell can be described here."}, {"video_title": "Cell membrane overview and fluid mosaic model   Cells   MCAT   Khan Academy.mp3", "Sentence": "So this is actually what we call a mosaic. So scientists kind of thought the same thing. And so scientists actually named this model of the cell the fluid mosaic model. And so the mosaic portion of our cell can be described here. Again, you can see that there are a lot of different pieces, different colorful, different types of pieces, put together to create this beautiful cell membrane. But why did we call it fluid? Well, the reason we call the cell membrane fluid is because these pieces in our cell membrane can actually move around."}, {"video_title": "Cell membrane overview and fluid mosaic model   Cells   MCAT   Khan Academy.mp3", "Sentence": "And so the mosaic portion of our cell can be described here. Again, you can see that there are a lot of different pieces, different colorful, different types of pieces, put together to create this beautiful cell membrane. But why did we call it fluid? Well, the reason we call the cell membrane fluid is because these pieces in our cell membrane can actually move around. They're not set in stone. So the proteins and phospholipids in our cell membrane can move around, like that. This is why we call it fluid."}, {"video_title": "Cell membrane overview and fluid mosaic model   Cells   MCAT   Khan Academy.mp3", "Sentence": "Well, the reason we call the cell membrane fluid is because these pieces in our cell membrane can actually move around. They're not set in stone. So the proteins and phospholipids in our cell membrane can move around, like that. This is why we call it fluid. What would that look like if we look at the cell membrane from the top? Well, the movement is actually not two-dimensional, like just up and down or just left and right. It can actually go in a lot of different directions."}, {"video_title": "Cell membrane overview and fluid mosaic model   Cells   MCAT   Khan Academy.mp3", "Sentence": "This is why we call it fluid. What would that look like if we look at the cell membrane from the top? Well, the movement is actually not two-dimensional, like just up and down or just left and right. It can actually go in a lot of different directions. So our proteins can move all around the cell membrane, and so can our phospholipids. So again, this is what we call the fluid mosaic model. And just as a little bit of a fun fact, this was only really discovered in 1972."}, {"video_title": "Cell membrane overview and fluid mosaic model   Cells   MCAT   Khan Academy.mp3", "Sentence": "It can actually go in a lot of different directions. So our proteins can move all around the cell membrane, and so can our phospholipids. So again, this is what we call the fluid mosaic model. And just as a little bit of a fun fact, this was only really discovered in 1972. So it was only 40 years ago that we really figured out that our cell membrane was actually the fluid mosaic model. So in summary, our cell membrane is made up of three major things. The first are phospholipids."}, {"video_title": "Cell membrane overview and fluid mosaic model   Cells   MCAT   Khan Academy.mp3", "Sentence": "And just as a little bit of a fun fact, this was only really discovered in 1972. So it was only 40 years ago that we really figured out that our cell membrane was actually the fluid mosaic model. So in summary, our cell membrane is made up of three major things. The first are phospholipids. These make up the most of the cell membrane, and they're kind of like a basic building block for our cell membrane to exist. The second are cholesterol. Cholesterol is scattered randomly through our cell membrane, and it helps maintain the fluidity of the cell membrane."}, {"video_title": "Elemental building blocks of biological molecules   Chemistry of life   AP Biology   Khan Academy.mp3", "Sentence": "What we have here is just a small sample of the types of molecules that you will see in a biological system. At the top left right over here, you have an example of an amino acid. Amino acids are the building blocks of proteins. And if we were to take a look at what an amino acid is made up of, in this dark gray color, those are carbon atoms. In the white, you see hydrogen atoms. In the red, you see oxygen atoms. And this blue right over here, that is a nitrogen atom."}, {"video_title": "Elemental building blocks of biological molecules   Chemistry of life   AP Biology   Khan Academy.mp3", "Sentence": "And if we were to take a look at what an amino acid is made up of, in this dark gray color, those are carbon atoms. In the white, you see hydrogen atoms. In the red, you see oxygen atoms. And this blue right over here, that is a nitrogen atom. And as you can see, a lot of these elements keep showing up in these various molecules, especially carbon and hydrogen. But also, you see a lot of oxygen and nitrogen. And as we're about to see, phosphorus also pops up a lot."}, {"video_title": "Elemental building blocks of biological molecules   Chemistry of life   AP Biology   Khan Academy.mp3", "Sentence": "And this blue right over here, that is a nitrogen atom. And as you can see, a lot of these elements keep showing up in these various molecules, especially carbon and hydrogen. But also, you see a lot of oxygen and nitrogen. And as we're about to see, phosphorus also pops up a lot. Now, this isn't a comprehensive list. You'll also see other elements. But these tend to show up fairly frequently."}, {"video_title": "Elemental building blocks of biological molecules   Chemistry of life   AP Biology   Khan Academy.mp3", "Sentence": "And as we're about to see, phosphorus also pops up a lot. Now, this isn't a comprehensive list. You'll also see other elements. But these tend to show up fairly frequently. For example, this is a model of ATP, adenosine triphosphate. As we study biology, you'll see that it's often viewed as the currency of energy, the molecular currency of energy in biological systems. And once again, we see a lot of carbons in the dark gray."}, {"video_title": "Elemental building blocks of biological molecules   Chemistry of life   AP Biology   Khan Academy.mp3", "Sentence": "But these tend to show up fairly frequently. For example, this is a model of ATP, adenosine triphosphate. As we study biology, you'll see that it's often viewed as the currency of energy, the molecular currency of energy in biological systems. And once again, we see a lot of carbons in the dark gray. We see the hydrogens in this off-white color, or the light gray, I guess you could say. You see your oxygens again. Here, the nitrogen is in this light blue color."}, {"video_title": "Elemental building blocks of biological molecules   Chemistry of life   AP Biology   Khan Academy.mp3", "Sentence": "And once again, we see a lot of carbons in the dark gray. We see the hydrogens in this off-white color, or the light gray, I guess you could say. You see your oxygens again. Here, the nitrogen is in this light blue color. And then you see the phosphoruses right over there in that yellow color, phosphorous. This is a model of a triglyceride, often known as a fat molecule. Fat molecules are used for energy storage."}, {"video_title": "Elemental building blocks of biological molecules   Chemistry of life   AP Biology   Khan Academy.mp3", "Sentence": "Here, the nitrogen is in this light blue color. And then you see the phosphoruses right over there in that yellow color, phosphorous. This is a model of a triglyceride, often known as a fat molecule. Fat molecules are used for energy storage. And once again, you see many carbons in the dark gray. And then you see these hydrogens and then a few oxygens. This is a model of DNA, a small segment of DNA."}, {"video_title": "Elemental building blocks of biological molecules   Chemistry of life   AP Biology   Khan Academy.mp3", "Sentence": "Fat molecules are used for energy storage. And once again, you see many carbons in the dark gray. And then you see these hydrogens and then a few oxygens. This is a model of DNA, a small segment of DNA. And this is a much more complex molecule than the other ones we've seen. In fact, this could extend far beyond our screen in either direction. But once again, you see these same familiar elements."}, {"video_title": "Elemental building blocks of biological molecules   Chemistry of life   AP Biology   Khan Academy.mp3", "Sentence": "This is a model of DNA, a small segment of DNA. And this is a much more complex molecule than the other ones we've seen. In fact, this could extend far beyond our screen in either direction. But once again, you see these same familiar elements. You see the carbon in the dark gray, the hydrogen in that white color. You see the oxygens in the red, the nitrogens in the blue, and the phosphorous in the yellow. So the big takeaway here is that biological molecules tend to be made up of the same set of elemental building blocks."}, {"video_title": "Elemental building blocks of biological molecules   Chemistry of life   AP Biology   Khan Academy.mp3", "Sentence": "But once again, you see these same familiar elements. You see the carbon in the dark gray, the hydrogen in that white color. You see the oxygens in the red, the nitrogens in the blue, and the phosphorous in the yellow. So the big takeaway here is that biological molecules tend to be made up of the same set of elemental building blocks. And in fact, it isn't just at the elemental level. It can even be at the molecular level. For example, in ATP, you have what's known as a nitrogenous base right over here."}, {"video_title": "Elemental building blocks of biological molecules   Chemistry of life   AP Biology   Khan Academy.mp3", "Sentence": "So the big takeaway here is that biological molecules tend to be made up of the same set of elemental building blocks. And in fact, it isn't just at the elemental level. It can even be at the molecular level. For example, in ATP, you have what's known as a nitrogenous base right over here. You have a five-carbon sugar right over here. And you have three phosphate groups, or a triphosphate group. In DNA, you have something very similar."}, {"video_title": "Elemental building blocks of biological molecules   Chemistry of life   AP Biology   Khan Academy.mp3", "Sentence": "For example, in ATP, you have what's known as a nitrogenous base right over here. You have a five-carbon sugar right over here. And you have three phosphate groups, or a triphosphate group. In DNA, you have something very similar. The nitrogenous bases are hard to see. They're kind of the rungs of the ladder here. You have your five-carbon sugars, also hard to see."}, {"video_title": "Elemental building blocks of biological molecules   Chemistry of life   AP Biology   Khan Academy.mp3", "Sentence": "In DNA, you have something very similar. The nitrogenous bases are hard to see. They're kind of the rungs of the ladder here. You have your five-carbon sugars, also hard to see. And then you have these phosphates as well. In fact, the backbone of DNA is made up of these five-carbon sugars and these phosphates. Now, why do these elements keep showing up?"}, {"video_title": "Elemental building blocks of biological molecules   Chemistry of life   AP Biology   Khan Academy.mp3", "Sentence": "You have your five-carbon sugars, also hard to see. And then you have these phosphates as well. In fact, the backbone of DNA is made up of these five-carbon sugars and these phosphates. Now, why do these elements keep showing up? Well, these are elements that you will see a lot in Earth. For example, nitrogen makes up most of our atmosphere. We have a lot of water on the surface of our planet, which is made up of oxygen and hydrogen."}, {"video_title": "Elemental building blocks of biological molecules   Chemistry of life   AP Biology   Khan Academy.mp3", "Sentence": "Now, why do these elements keep showing up? Well, these are elements that you will see a lot in Earth. For example, nitrogen makes up most of our atmosphere. We have a lot of water on the surface of our planet, which is made up of oxygen and hydrogen. Carbon actually makes up a surprisingly small percentage of our atmosphere, about 0.04% of our atmosphere. But photosynthetic organisms, like plants, are good at fixing carbon and storing energy in carbon bonds. And when we eat those, those become part of our bodies."}, {"video_title": "Elemental building blocks of biological molecules   Chemistry of life   AP Biology   Khan Academy.mp3", "Sentence": "We have a lot of water on the surface of our planet, which is made up of oxygen and hydrogen. Carbon actually makes up a surprisingly small percentage of our atmosphere, about 0.04% of our atmosphere. But photosynthetic organisms, like plants, are good at fixing carbon and storing energy in carbon bonds. And when we eat those, those become part of our bodies. And just to get an appreciation of what we are made up of in terms of elements, we can look at this chart right over here, where we see that we are primarily made up of oxygen, percentage in body. And that's because we're primarily made up of water, and water is primarily oxygen. It also has hydrogen."}, {"video_title": "Elemental building blocks of biological molecules   Chemistry of life   AP Biology   Khan Academy.mp3", "Sentence": "And when we eat those, those become part of our bodies. And just to get an appreciation of what we are made up of in terms of elements, we can look at this chart right over here, where we see that we are primarily made up of oxygen, percentage in body. And that's because we're primarily made up of water, and water is primarily oxygen. It also has hydrogen. Now, second to oxygen is carbon. And then you see nitrogen, phosphorus. We, of course, have a lot of calcium."}, {"video_title": "Elemental building blocks of biological molecules   Chemistry of life   AP Biology   Khan Academy.mp3", "Sentence": "It also has hydrogen. Now, second to oxygen is carbon. And then you see nitrogen, phosphorus. We, of course, have a lot of calcium. Calcium, of course, used in bones, but it's also used for things like muscle contractions. And I could keep on going down this list, and you will see these other elements in your study of biology. But the big picture is, is that even though biological systems can get fairly complex, they're made up of similar building blocks."}, {"video_title": "Molecular structure of DNA   Macromolecules   Biology   Khan Academy (3).mp3", "Sentence": "But what I want to do in this video is dig a little bit deeper, actually get into the molecular structure of DNA. And just as a starting point, let's just remind ourselves what DNA stands for. I'm gonna write the different parts of the word in different colors. So it stands for deoxyribonucleic, ribonucleic, ribonucleic acid, ribonucleic acid. So I'm just gonna put this on the side. And now let's actually look at the molecular structure and how it relates to this actual name, deoxyribonucleic acid. So DNA is just a general term for nucleic acid."}, {"video_title": "Molecular structure of DNA   Macromolecules   Biology   Khan Academy (3).mp3", "Sentence": "So it stands for deoxyribonucleic, ribonucleic, ribonucleic acid, ribonucleic acid. So I'm just gonna put this on the side. And now let's actually look at the molecular structure and how it relates to this actual name, deoxyribonucleic acid. So DNA is just a general term for nucleic acid. And the term nucleic comes from the fact that it's found in the nucleus, it's found in the nucleus of eukaryotes. So that's where the nucleic comes from. And we'll talk about in a second why it's called an acid, but I'll wait on that."}, {"video_title": "Molecular structure of DNA   Macromolecules   Biology   Khan Academy (3).mp3", "Sentence": "So DNA is just a general term for nucleic acid. And the term nucleic comes from the fact that it's found in the nucleus, it's found in the nucleus of eukaryotes. So that's where the nucleic comes from. And we'll talk about in a second why it's called an acid, but I'll wait on that. And now each DNA molecule is made up of a chain of what we call nucleotides. So what we call nucleotides. So it's made up of nucleotides."}, {"video_title": "Molecular structure of DNA   Macromolecules   Biology   Khan Academy (3).mp3", "Sentence": "And we'll talk about in a second why it's called an acid, but I'll wait on that. And now each DNA molecule is made up of a chain of what we call nucleotides. So what we call nucleotides. So it's made up of nucleotides. So what does a nucleotide look like? Well, what I have right over here is I have two strands, I've zoomed in two strands of DNA. So you could view this side right over here as one of the, I guess you could say the backbones of one side of the ladder."}, {"video_title": "Molecular structure of DNA   Macromolecules   Biology   Khan Academy (3).mp3", "Sentence": "So it's made up of nucleotides. So what does a nucleotide look like? Well, what I have right over here is I have two strands, I've zoomed in two strands of DNA. So you could view this side right over here as one of the, I guess you could say the backbones of one side of the ladder. This is the other side of the ladder. And then each of these bridges, and I will talk about what molecules these are, these are kind of the rungs of the ladder. And a nucleotide, let me separate off a nucleotide."}, {"video_title": "Molecular structure of DNA   Macromolecules   Biology   Khan Academy (3).mp3", "Sentence": "So you could view this side right over here as one of the, I guess you could say the backbones of one side of the ladder. This is the other side of the ladder. And then each of these bridges, and I will talk about what molecules these are, these are kind of the rungs of the ladder. And a nucleotide, let me separate off a nucleotide. So a nucleotide would, so what I am coordinating off, what I am coordinating off right over here could be considered a nucleotide. So that's one nucleotide, and then it's connected to another. It's connected to another nucleotide, another nucleotide right over here."}, {"video_title": "Molecular structure of DNA   Macromolecules   Biology   Khan Academy (3).mp3", "Sentence": "And a nucleotide, let me separate off a nucleotide. So a nucleotide would, so what I am coordinating off, what I am coordinating off right over here could be considered a nucleotide. So that's one nucleotide, and then it's connected to another. It's connected to another nucleotide, another nucleotide right over here. And on the right-hand side, we have a nucleotide, we have a nucleotide right over there, and then, actually, I wanna do it, let me do it slightly different. We have a nucleotide right over here on the right side, and then right below that, we have another, we have another nucleotide, we have another nucleotide. So depicted here, we essentially have four nucleotides."}, {"video_title": "Molecular structure of DNA   Macromolecules   Biology   Khan Academy (3).mp3", "Sentence": "It's connected to another nucleotide, another nucleotide right over here. And on the right-hand side, we have a nucleotide, we have a nucleotide right over there, and then, actually, I wanna do it, let me do it slightly different. We have a nucleotide right over here on the right side, and then right below that, we have another, we have another nucleotide, we have another nucleotide. So depicted here, we essentially have four nucleotides. These two are on this left side of the ladder, these two are on the right side of the ladder. Now let's think about the different pieces of that nucleotide. So the one thing that might jump out at you is we have these phosphate groups."}, {"video_title": "Molecular structure of DNA   Macromolecules   Biology   Khan Academy (3).mp3", "Sentence": "So depicted here, we essentially have four nucleotides. These two are on this left side of the ladder, these two are on the right side of the ladder. Now let's think about the different pieces of that nucleotide. So the one thing that might jump out at you is we have these phosphate groups. So this is a phosphate group right over here, this is a phosphate group right over here. Each of these nucleotides have a phosphate group. So this is a phosphate group over here, and this is a phosphate group over here."}, {"video_title": "Molecular structure of DNA   Macromolecules   Biology   Khan Academy (3).mp3", "Sentence": "So the one thing that might jump out at you is we have these phosphate groups. So this is a phosphate group right over here, this is a phosphate group right over here. Each of these nucleotides have a phosphate group. So this is a phosphate group over here, and this is a phosphate group over here. Now the phosphate groups are actually what make DNA, or actually what make nucleic acid an acid. And you might say, wait, wait, the way you've drawn it, Sal, you have a negative charge. Something with a negative charge would attract protons, it would sop up protons."}, {"video_title": "Molecular structure of DNA   Macromolecules   Biology   Khan Academy (3).mp3", "Sentence": "So this is a phosphate group over here, and this is a phosphate group over here. Now the phosphate groups are actually what make DNA, or actually what make nucleic acid an acid. And you might say, wait, wait, the way you've drawn it, Sal, you have a negative charge. Something with a negative charge would attract protons, it would sop up protons. How can you call this an acid? This actually looks more basic. And the reason why DNA is typically drawn with these negative charges here is that it's so acidic, and if you put it into a neutral solution, it's actually going to lose its hydrogens."}, {"video_title": "Molecular structure of DNA   Macromolecules   Biology   Khan Academy (3).mp3", "Sentence": "Something with a negative charge would attract protons, it would sop up protons. How can you call this an acid? This actually looks more basic. And the reason why DNA is typically drawn with these negative charges here is that it's so acidic, and if you put it into a neutral solution, it's actually going to lose its hydrogens. Actually the DNA, if we actually want to be formal about it, the DNA molecules would actually have its phosphates protonated like this, but it so badly wants to lose these hydrogen protons, so it typically would be, let me draw it like this. Let me get rid of the negative charge just on this one. Whoops, just on this phosphate group over here."}, {"video_title": "Molecular structure of DNA   Macromolecules   Biology   Khan Academy (3).mp3", "Sentence": "And the reason why DNA is typically drawn with these negative charges here is that it's so acidic, and if you put it into a neutral solution, it's actually going to lose its hydrogens. Actually the DNA, if we actually want to be formal about it, the DNA molecules would actually have its phosphates protonated like this, but it so badly wants to lose these hydrogen protons, so it typically would be, let me draw it like this. Let me get rid of the negative charge just on this one. Whoops, just on this phosphate group over here. So if you get rid of the negative charge, and if this was bounded, this is bonded to a hydrogen, this so badly wants to grab these electrons. So this oxygen can grab these electrons, and then this hydrogen will just be grabbed by another water molecule or something, or so the proton will be let go. That's why we call it an acid."}, {"video_title": "Molecular structure of DNA   Macromolecules   Biology   Khan Academy (3).mp3", "Sentence": "Whoops, just on this phosphate group over here. So if you get rid of the negative charge, and if this was bounded, this is bonded to a hydrogen, this so badly wants to grab these electrons. So this oxygen can grab these electrons, and then this hydrogen will just be grabbed by another water molecule or something, or so the proton will be let go. That's why we call it an acid. So if it wasn't in a solution, it would have the hydrogens, but it would be very acidic. As soon as you put it into a neutral solution, it's going to lose those hydrogens. So the phosphate groups are what make it an acid, but it's confusing sometimes, because usually when you see it depicted, you see it with these negative charges, and that's because it has already lost its hydrogen protons."}, {"video_title": "Molecular structure of DNA   Macromolecules   Biology   Khan Academy (3).mp3", "Sentence": "That's why we call it an acid. So if it wasn't in a solution, it would have the hydrogens, but it would be very acidic. As soon as you put it into a neutral solution, it's going to lose those hydrogens. So the phosphate groups are what make it an acid, but it's confusing sometimes, because usually when you see it depicted, you see it with these negative charges, and that's because it has already lost its hydrogen protons. You're actually depicting the conjugate base here, but that's where it gets its acidic name from, because it starts protonated, or I guess in its acid form it's protonated, but it readily loses it, and so that's where it gets the name acid from. So each of these nucleotides, they have a phosphate group. Now the next thing you might notice, the next thing you might notice is, the next thing you might notice is this group right over here."}, {"video_title": "Molecular structure of DNA   Macromolecules   Biology   Khan Academy (3).mp3", "Sentence": "So the phosphate groups are what make it an acid, but it's confusing sometimes, because usually when you see it depicted, you see it with these negative charges, and that's because it has already lost its hydrogen protons. You're actually depicting the conjugate base here, but that's where it gets its acidic name from, because it starts protonated, or I guess in its acid form it's protonated, but it readily loses it, and so that's where it gets the name acid from. So each of these nucleotides, they have a phosphate group. Now the next thing you might notice, the next thing you might notice is, the next thing you might notice is this group right over here. It is a cycle, it is a ring, and it looks an awful lot like a sugar, and that's because it is a sugar. So this sugar is based on, it's a five-carbon sugar. What I have depicted here, this sugar, this is ribose."}, {"video_title": "Molecular structure of DNA   Macromolecules   Biology   Khan Academy (3).mp3", "Sentence": "Now the next thing you might notice, the next thing you might notice is, the next thing you might notice is this group right over here. It is a cycle, it is a ring, and it looks an awful lot like a sugar, and that's because it is a sugar. So this sugar is based on, it's a five-carbon sugar. What I have depicted here, this sugar, this is ribose. So this sugar right over here is ribose. This is when it's just as a straight chain, and like many sugars, it can take a cyclical form. Actually, it can take many different cyclical forms, but the one that's most typically described is when you have the, let me show you a number of the carbons, because carbon numbering is important when we talk about DNA."}, {"video_title": "Molecular structure of DNA   Macromolecules   Biology   Khan Academy (3).mp3", "Sentence": "What I have depicted here, this sugar, this is ribose. So this sugar right over here is ribose. This is when it's just as a straight chain, and like many sugars, it can take a cyclical form. Actually, it can take many different cyclical forms, but the one that's most typically described is when you have the, let me show you a number of the carbons, because carbon numbering is important when we talk about DNA. If we start at the carbonyl group right over here, we call that the one carbon, or the one prime carbon. One prime, two prime, three prime, four prime, and five prime. That's the five prime carbon."}, {"video_title": "Molecular structure of DNA   Macromolecules   Biology   Khan Academy (3).mp3", "Sentence": "Actually, it can take many different cyclical forms, but the one that's most typically described is when you have the, let me show you a number of the carbons, because carbon numbering is important when we talk about DNA. If we start at the carbonyl group right over here, we call that the one carbon, or the one prime carbon. One prime, two prime, three prime, four prime, and five prime. That's the five prime carbon. And so you form the cyclical form of ribose, is if you have the oxygen, you have the oxygen right over here on the four prime carbon, it uses one of its lone pairs, it uses one of its lone pairs to form a bond, to form a bond with, with the one prime, with the one prime carbon. And I drew it that way, because it kind of does bend, the whole molecule's going to have to bend that way to form this structure. And then when it forms that bond, the carbon can let go of one of these double bonds, and then that can, then the oxygen, the oxygen can use that, the oxygen can use those electrons to go grab a hydrogen proton from someplace, so to nab onto a hydrogen proton."}, {"video_title": "Molecular structure of DNA   Macromolecules   Biology   Khan Academy (3).mp3", "Sentence": "That's the five prime carbon. And so you form the cyclical form of ribose, is if you have the oxygen, you have the oxygen right over here on the four prime carbon, it uses one of its lone pairs, it uses one of its lone pairs to form a bond, to form a bond with, with the one prime, with the one prime carbon. And I drew it that way, because it kind of does bend, the whole molecule's going to have to bend that way to form this structure. And then when it forms that bond, the carbon can let go of one of these double bonds, and then that can, then the oxygen, the oxygen can use that, the oxygen can use those electrons to go grab a hydrogen proton from someplace, so to nab onto a hydrogen proton. So when it does that, you're in this form. And this form, just to be clear of what we're talking about, this is the one prime carbon, one prime, two prime, three prime, four prime, and five, five prime carbon. And where we see this bond, this is a one prime carbon, it was part of a carbonyl, now it lets go of one of those double bonds so that this oxygen can form a bond with a hydrogen proton, so it let go of a double bond there so that this could form a bond with a hydrogen proton."}, {"video_title": "Molecular structure of DNA   Macromolecules   Biology   Khan Academy (3).mp3", "Sentence": "And then when it forms that bond, the carbon can let go of one of these double bonds, and then that can, then the oxygen, the oxygen can use that, the oxygen can use those electrons to go grab a hydrogen proton from someplace, so to nab onto a hydrogen proton. So when it does that, you're in this form. And this form, just to be clear of what we're talking about, this is the one prime carbon, one prime, two prime, three prime, four prime, and five, five prime carbon. And where we see this bond, this is a one prime carbon, it was part of a carbonyl, now it lets go of one of those double bonds so that this oxygen can form a bond with a hydrogen proton, so it let go of a double bond there so that this could form a bond with a hydrogen proton. So this hydrogen proton is that hydrogen proton right over there, and this green bond that gets formed between the four prime carbon and, or between the oxygen that's attached to the four prime carbon and the one prime carbon, that's this, that's this bond right over here. This oxygen is that oxygen right there. Notice, this oxygen is bound to the four prime carbon, and now it's also bound to the one prime carbon."}, {"video_title": "Molecular structure of DNA   Macromolecules   Biology   Khan Academy (3).mp3", "Sentence": "And where we see this bond, this is a one prime carbon, it was part of a carbonyl, now it lets go of one of those double bonds so that this oxygen can form a bond with a hydrogen proton, so it let go of a double bond there so that this could form a bond with a hydrogen proton. So this hydrogen proton is that hydrogen proton right over there, and this green bond that gets formed between the four prime carbon and, or between the oxygen that's attached to the four prime carbon and the one prime carbon, that's this, that's this bond right over here. This oxygen is that oxygen right there. Notice, this oxygen is bound to the four prime carbon, and now it's also bound to the one prime carbon. And it was also attached to a hydrogen, It was also attached to a hydrogen, so that hydrogen is there. But then that could get nabbed up by another passing water molecule to become hydronium, so it can get lost. And net-net, it grabs up a hydrogen proton right over here, and so it can lose a hydrogen proton right there."}, {"video_title": "Molecular structure of DNA   Macromolecules   Biology   Khan Academy (3).mp3", "Sentence": "Notice, this oxygen is bound to the four prime carbon, and now it's also bound to the one prime carbon. And it was also attached to a hydrogen, It was also attached to a hydrogen, so that hydrogen is there. But then that could get nabbed up by another passing water molecule to become hydronium, so it can get lost. And net-net, it grabs up a hydrogen proton right over here, and so it can lose a hydrogen proton right there. So it's not adding or losing net-net. And so you form this cyclical form. And the cyclical form right over here is very close to what we see in a DNA molecule."}, {"video_title": "Molecular structure of DNA   Macromolecules   Biology   Khan Academy (3).mp3", "Sentence": "And net-net, it grabs up a hydrogen proton right over here, and so it can lose a hydrogen proton right there. So it's not adding or losing net-net. And so you form this cyclical form. And the cyclical form right over here is very close to what we see in a DNA molecule. It's actually exactly what we would see in an RNA molecule, in ribonucleic acid. And so what do we think we're talking about when we say deoxyribonucleic acid? Well, you could start with, you have a ribose here, but if we got rid of one of the oxygen groups, and in particular, one of, well, actually, if we just got rid of one of the oxygens, we replace a hydroxyl with just a hydrogen, well, then you're gonna have deoxyribose."}, {"video_title": "Molecular structure of DNA   Macromolecules   Biology   Khan Academy (3).mp3", "Sentence": "And the cyclical form right over here is very close to what we see in a DNA molecule. It's actually exactly what we would see in an RNA molecule, in ribonucleic acid. And so what do we think we're talking about when we say deoxyribonucleic acid? Well, you could start with, you have a ribose here, but if we got rid of one of the oxygen groups, and in particular, one of, well, actually, if we just got rid of one of the oxygens, we replace a hydroxyl with just a hydrogen, well, then you're gonna have deoxyribose. And you see that over here. This five-member ring, you have four carbons right over here. It looks just like this."}, {"video_title": "Molecular structure of DNA   Macromolecules   Biology   Khan Academy (3).mp3", "Sentence": "Well, you could start with, you have a ribose here, but if we got rid of one of the oxygen groups, and in particular, one of, well, actually, if we just got rid of one of the oxygens, we replace a hydroxyl with just a hydrogen, well, then you're gonna have deoxyribose. And you see that over here. This five-member ring, you have four carbons right over here. It looks just like this. The hydrogens are implicit to the carbons. We've seen this multiple times. The carbons are at where these lines intersect, or I guess at the edges, or maybe, and also where these lines end right over there."}, {"video_title": "Molecular structure of DNA   Macromolecules   Biology   Khan Academy (3).mp3", "Sentence": "It looks just like this. The hydrogens are implicit to the carbons. We've seen this multiple times. The carbons are at where these lines intersect, or I guess at the edges, or maybe, and also where these lines end right over there. But you see, this does not have an, this molecule, if we compare these two molecules, if we compare these two molecules over here, we see that this guy has an OH, and this guy implicitly just has, this guy has an OH and an H. This guy implicitly has just two hydrogens over here. So he's missing an oxygen. So this is deoxyribose."}, {"video_title": "Molecular structure of DNA   Macromolecules   Biology   Khan Academy (3).mp3", "Sentence": "The carbons are at where these lines intersect, or I guess at the edges, or maybe, and also where these lines end right over there. But you see, this does not have an, this molecule, if we compare these two molecules, if we compare these two molecules over here, we see that this guy has an OH, and this guy implicitly just has, this guy has an OH and an H. This guy implicitly has just two hydrogens over here. So he's missing an oxygen. So this is deoxyribose. So deoxyribose doesn't have this oxygen. It does not have the oxygen on the two prime carbon. So this, if you get rid of that, this is deoxyribose."}, {"video_title": "Molecular structure of DNA   Macromolecules   Biology   Khan Academy (3).mp3", "Sentence": "So this is deoxyribose. So deoxyribose doesn't have this oxygen. It does not have the oxygen on the two prime carbon. So this, if you get rid of that, this is deoxyribose. So let me circle that. So what we're, this thing right over here, this thing right over here, that is deoxyribose. Deoxy, or it's based on deoxyribose, I guess before it bonded to these other constituents, you could consider this deoxyribose."}, {"video_title": "Molecular structure of DNA   Macromolecules   Biology   Khan Academy (3).mp3", "Sentence": "So this, if you get rid of that, this is deoxyribose. So let me circle that. So what we're, this thing right over here, this thing right over here, that is deoxyribose. Deoxy, or it's based on deoxyribose, I guess before it bonded to these other constituents, you could consider this deoxyribose. And so that's where the deoxyribo comes from. And then the last piece of it, the last piece of it is this chunk right over here. And these we call nitrogenous bases."}, {"video_title": "Molecular structure of DNA   Macromolecules   Biology   Khan Academy (3).mp3", "Sentence": "Deoxy, or it's based on deoxyribose, I guess before it bonded to these other constituents, you could consider this deoxyribose. And so that's where the deoxyribo comes from. And then the last piece of it, the last piece of it is this chunk right over here. And these we call nitrogenous bases. So nitrogenous, nitrogenous, nitrogenous bases. And you can see we have different types of nitrogenous bases. This is a nitrogenous base."}, {"video_title": "Molecular structure of DNA   Macromolecules   Biology   Khan Academy (3).mp3", "Sentence": "And these we call nitrogenous bases. So nitrogenous, nitrogenous, nitrogenous bases. And you can see we have different types of nitrogenous bases. This is a nitrogenous base. This right over here is a different nitrogenous base. This right over here is another different nitrogenous base. Notice this one only has one ring, this one has one ring."}, {"video_title": "Molecular structure of DNA   Macromolecules   Biology   Khan Academy (3).mp3", "Sentence": "This is a nitrogenous base. This right over here is a different nitrogenous base. This right over here is another different nitrogenous base. Notice this one only has one ring, this one has one ring. This one has two rings. This one over here has two rings. And we have different names for these nitrogenous bases."}, {"video_title": "Molecular structure of DNA   Macromolecules   Biology   Khan Academy (3).mp3", "Sentence": "Notice this one only has one ring, this one has one ring. This one has two rings. This one over here has two rings. And we have different names for these nitrogenous bases. The ones with two rings, the general categorization, we call them purines. So nitrogenous bases, if you have two rings, if you have two rings, we call them purines, as a general classification term. Let me make sure, purines."}, {"video_title": "Molecular structure of DNA   Macromolecules   Biology   Khan Academy (3).mp3", "Sentence": "And we have different names for these nitrogenous bases. The ones with two rings, the general categorization, we call them purines. So nitrogenous bases, if you have two rings, if you have two rings, we call them purines, as a general classification term. Let me make sure, purines. And if you have one ring, maybe I'll just write it this way, one ring, one ring, we call these pyrimidines. Pyrimidines. Pyrimidines."}, {"video_title": "Molecular structure of DNA   Macromolecules   Biology   Khan Academy (3).mp3", "Sentence": "Let me make sure, purines. And if you have one ring, maybe I'll just write it this way, one ring, one ring, we call these pyrimidines. Pyrimidines. Pyrimidines. We call these pyrimidines. And these particular, these two on the right, these two purines, this one up here, this is adenine. And we talk about how they pair in the overview video on DNA."}, {"video_title": "Molecular structure of DNA   Macromolecules   Biology   Khan Academy (3).mp3", "Sentence": "Pyrimidines. We call these pyrimidines. And these particular, these two on the right, these two purines, this one up here, this is adenine. And we talk about how they pair in the overview video on DNA. But this one right over here is adenine, this nitrogenous base. This one over here is guanine. That is guanine."}, {"video_title": "Molecular structure of DNA   Macromolecules   Biology   Khan Academy (3).mp3", "Sentence": "And we talk about how they pair in the overview video on DNA. But this one right over here is adenine, this nitrogenous base. This one over here is guanine. That is guanine. And then, over here, this single ring nitrogenous base, which makes it a pyrimidine, this is thymine. This right over here is thymine. This is thymine."}, {"video_title": "Molecular structure of DNA   Macromolecules   Biology   Khan Academy (3).mp3", "Sentence": "That is guanine. And then, over here, this single ring nitrogenous base, which makes it a pyrimidine, this is thymine. This right over here is thymine. This is thymine. And then last but not least, if we're talking about DNA, when we go into RNA, we're also gonna talk about uracil. But when we talk about DNA, this one over here is cytosine. Cytosine."}, {"video_title": "Molecular structure of DNA   Macromolecules   Biology   Khan Academy (3).mp3", "Sentence": "This is thymine. And then last but not least, if we're talking about DNA, when we go into RNA, we're also gonna talk about uracil. But when we talk about DNA, this one over here is cytosine. Cytosine. And you can see the way it's structured, that thymine is attracted to adenine, it bonds with adenine, and cytosine bonds with guanine. So how are they bonding? Well, the way that these nitrogenous bases form the rungs of the ladder, how they're drawn to each other, this is our good old friend hydrogen bonds."}, {"video_title": "Molecular structure of DNA   Macromolecules   Biology   Khan Academy (3).mp3", "Sentence": "Cytosine. And you can see the way it's structured, that thymine is attracted to adenine, it bonds with adenine, and cytosine bonds with guanine. So how are they bonding? Well, the way that these nitrogenous bases form the rungs of the ladder, how they're drawn to each other, this is our good old friend hydrogen bonds. And this all comes out of the fact that nitrogen is quite electronegative, so when nitrogen is bound to a hydrogen, you're going to have a partially negative charge at the nitrogen. Let me do this in green. You're gonna have a partial negative charge at the nitrogen and a partially positive charge at the hydrogen."}, {"video_title": "Molecular structure of DNA   Macromolecules   Biology   Khan Academy (3).mp3", "Sentence": "Well, the way that these nitrogenous bases form the rungs of the ladder, how they're drawn to each other, this is our good old friend hydrogen bonds. And this all comes out of the fact that nitrogen is quite electronegative, so when nitrogen is bound to a hydrogen, you're going to have a partially negative charge at the nitrogen. Let me do this in green. You're gonna have a partial negative charge at the nitrogen and a partially positive charge at the hydrogen. And then oxygen, we've always talked about as being electronegative, so it has a partial negative charge. So the partial negative charge of this oxygen is going to be attracted to the partial positive charge of this hydrogen, and so you're going to have, you're going to have a hydrogen bond. And the same thing's going to happen between this hydrogen, which is going, its electrons are being hogged by this nitrogen, and this nitrogen, which itself hogs electrons, so that forms a hydrogen bond."}, {"video_title": "Molecular structure of DNA   Macromolecules   Biology   Khan Academy (3).mp3", "Sentence": "You're gonna have a partial negative charge at the nitrogen and a partially positive charge at the hydrogen. And then oxygen, we've always talked about as being electronegative, so it has a partial negative charge. So the partial negative charge of this oxygen is going to be attracted to the partial positive charge of this hydrogen, and so you're going to have, you're going to have a hydrogen bond. And the same thing's going to happen between this hydrogen, which is going, its electrons are being hogged by this nitrogen, and this nitrogen, which itself hogs electrons, so that forms a hydrogen bond. And then down here, you have a hydrogen that has a partially positive charge because its electrons are being hogged, and then you have this oxygen with a partially negative charge. They're going to be attracted to each other. That's a hydrogen bond."}, {"video_title": "Organelles in eukaryotic cells   Cells   High school biology   Khan Academy.mp3", "Sentence": "What we're going to do in this video is give ourselves a little bit of a tour of eukaryotic cells. And the first place to start is just to remind ourselves what it means for a cell to be eukaryotic. It means that inside the cell, there are membrane-bound organelles. Now what does that mean? Well, you could view it as sub-compartments within the cell, membrane-bound organelles. And in this video in particular, we're going to highlight some of these membrane-bound organelles that make the cells eukaryotic. So let's just start with some of the ingredients that we know is true of all cells."}, {"video_title": "Organelles in eukaryotic cells   Cells   High school biology   Khan Academy.mp3", "Sentence": "Now what does that mean? Well, you could view it as sub-compartments within the cell, membrane-bound organelles. And in this video in particular, we're going to highlight some of these membrane-bound organelles that make the cells eukaryotic. So let's just start with some of the ingredients that we know is true of all cells. So you'll have your cellular membrane here, a little bit big so that we have a lot of space to draw things in. So this is our cellular membrane. I'll do a nice shading so you appreciate that it'll actually be three-dimensional."}, {"video_title": "Organelles in eukaryotic cells   Cells   High school biology   Khan Academy.mp3", "Sentence": "So let's just start with some of the ingredients that we know is true of all cells. So you'll have your cellular membrane here, a little bit big so that we have a lot of space to draw things in. So this is our cellular membrane. I'll do a nice shading so you appreciate that it'll actually be three-dimensional. We see so many slices of cells that sometimes we forget that they are more spherical or that they have three-dimensional shape to them. They're not all spherical. They can have different shapes."}, {"video_title": "Organelles in eukaryotic cells   Cells   High school biology   Khan Academy.mp3", "Sentence": "I'll do a nice shading so you appreciate that it'll actually be three-dimensional. We see so many slices of cells that sometimes we forget that they are more spherical or that they have three-dimensional shape to them. They're not all spherical. They can have different shapes. Now all cells, and there are some exceptions that we've talked about in previous videos, I should say most cells will have some genetic information in them in the form of DNA. So that is our DNA right over there. Now one of the key characteristics of a eukaryotic cell is that that genetic information is going to be inside a membrane-bound organelle."}, {"video_title": "Organelles in eukaryotic cells   Cells   High school biology   Khan Academy.mp3", "Sentence": "They can have different shapes. Now all cells, and there are some exceptions that we've talked about in previous videos, I should say most cells will have some genetic information in them in the form of DNA. So that is our DNA right over there. Now one of the key characteristics of a eukaryotic cell is that that genetic information is going to be inside a membrane-bound organelle. And that membrane-bound organelle or the membrane that binds or that surrounds the DNA here, that is the nuclear membrane. So let me draw the nuclear membrane right over here. And I'll put some shading in to appreciate that that also is going to be in three dimensions around the DNA."}, {"video_title": "Organelles in eukaryotic cells   Cells   High school biology   Khan Academy.mp3", "Sentence": "Now one of the key characteristics of a eukaryotic cell is that that genetic information is going to be inside a membrane-bound organelle. And that membrane-bound organelle or the membrane that binds or that surrounds the DNA here, that is the nuclear membrane. So let me draw the nuclear membrane right over here. And I'll put some shading in to appreciate that that also is going to be in three dimensions around the DNA. And so that is the first membrane-bound organelle that we're going to discuss, the nucleus. Now the nucleus, it turns out, is connected to another membrane-bound organelle. And we're gonna study this in future videos."}, {"video_title": "Organelles in eukaryotic cells   Cells   High school biology   Khan Academy.mp3", "Sentence": "And I'll put some shading in to appreciate that that also is going to be in three dimensions around the DNA. And so that is the first membrane-bound organelle that we're going to discuss, the nucleus. Now the nucleus, it turns out, is connected to another membrane-bound organelle. And we're gonna study this in future videos. What right here, I'm drawing holes or pores in the nuclear membrane. And those pores connect to something, it's a very fancy word, called the endoplasmic reticulum. And the endoplasmic reticulum is essentially these layers of these membranes."}, {"video_title": "Organelles in eukaryotic cells   Cells   High school biology   Khan Academy.mp3", "Sentence": "And we're gonna study this in future videos. What right here, I'm drawing holes or pores in the nuclear membrane. And those pores connect to something, it's a very fancy word, called the endoplasmic reticulum. And the endoplasmic reticulum is essentially these layers of these membranes. So I'm gonna do my best job at trying to draw an endoplasmic reticulum. Imagine extending from these pores, going into a space that has these, really these layered membranes that have a lot of surface area. And I'm not gonna go all the way around this nucleus, but in many cells, it will go around all the way around the nucleus."}, {"video_title": "Organelles in eukaryotic cells   Cells   High school biology   Khan Academy.mp3", "Sentence": "And the endoplasmic reticulum is essentially these layers of these membranes. So I'm gonna do my best job at trying to draw an endoplasmic reticulum. Imagine extending from these pores, going into a space that has these, really these layered membranes that have a lot of surface area. And I'm not gonna go all the way around this nucleus, but in many cells, it will go around all the way around the nucleus. And this right over here, and this is just a rough diagram, that is our endoplasmic, endoplasmic, not splasmic, endoplasmic, endoplasmic reticulum, which I've mentioned in previous videos would be an excellent name for a band. And what goes on in the endoplasmic reticulum is when you are in the process of taking that genetic information from DNA, and as we talk about in other videos, it gets transcribed into mRNA, so that mRNA is now containing that information. That mRNA will make its way out of that nuclear membrane through one of these pores, and then make its way to a ribosome that is attached to the membrane of the endoplasmic reticulum."}, {"video_title": "Organelles in eukaryotic cells   Cells   High school biology   Khan Academy.mp3", "Sentence": "And I'm not gonna go all the way around this nucleus, but in many cells, it will go around all the way around the nucleus. And this right over here, and this is just a rough diagram, that is our endoplasmic, endoplasmic, not splasmic, endoplasmic, endoplasmic reticulum, which I've mentioned in previous videos would be an excellent name for a band. And what goes on in the endoplasmic reticulum is when you are in the process of taking that genetic information from DNA, and as we talk about in other videos, it gets transcribed into mRNA, so that mRNA is now containing that information. That mRNA will make its way out of that nuclear membrane through one of these pores, and then make its way to a ribosome that is attached to the membrane of the endoplasmic reticulum. And so that's a ribosome there. I'm gonna do a bunch of ribosomes. And so, as we've talked about in previous videos, the ribosomes are really where you take that genetic information from that mRNA, and then you translate it into a protein."}, {"video_title": "Organelles in eukaryotic cells   Cells   High school biology   Khan Academy.mp3", "Sentence": "That mRNA will make its way out of that nuclear membrane through one of these pores, and then make its way to a ribosome that is attached to the membrane of the endoplasmic reticulum. And so that's a ribosome there. I'm gonna do a bunch of ribosomes. And so, as we've talked about in previous videos, the ribosomes are really where you take that genetic information from that mRNA, and then you translate it into a protein. So the ribosomes are the protein synthesis, so let me label that. So this right over here is a ribosome. And some ribosomes might be attached to the endoplasmic reticulum."}, {"video_title": "Organelles in eukaryotic cells   Cells   High school biology   Khan Academy.mp3", "Sentence": "And so, as we've talked about in previous videos, the ribosomes are really where you take that genetic information from that mRNA, and then you translate it into a protein. So the ribosomes are the protein synthesis, so let me label that. So this right over here is a ribosome. And some ribosomes might be attached to the endoplasmic reticulum. Some of them might just be floating out here in the cytoplasm, so that would be a free ribosome. Free ribosome. And even from the point of view of the endoplasmic reticulum, the parts of the endoplasmic reticulum where you have ribosomes attached, this is known as rough endoplasmic reticulum."}, {"video_title": "Organelles in eukaryotic cells   Cells   High school biology   Khan Academy.mp3", "Sentence": "And some ribosomes might be attached to the endoplasmic reticulum. Some of them might just be floating out here in the cytoplasm, so that would be a free ribosome. Free ribosome. And even from the point of view of the endoplasmic reticulum, the parts of the endoplasmic reticulum where you have ribosomes attached, this is known as rough endoplasmic reticulum. It's the ribosomes that are making them rough. It looks that way in a microscope. So I'll say rough ER for endoplasmic reticulum for short."}, {"video_title": "Organelles in eukaryotic cells   Cells   High school biology   Khan Academy.mp3", "Sentence": "And even from the point of view of the endoplasmic reticulum, the parts of the endoplasmic reticulum where you have ribosomes attached, this is known as rough endoplasmic reticulum. It's the ribosomes that are making them rough. It looks that way in a microscope. So I'll say rough ER for endoplasmic reticulum for short. And then you also have parts of the endoplasmic reticulum where you do not have ribosomes attached, and because that looks smooth through our microscope, it has been called, you can imagine, smooth endoplasmic reticulum. There are things known as Golgi bodies. Once again, another fascinating name."}, {"video_title": "Organelles in eukaryotic cells   Cells   High school biology   Khan Academy.mp3", "Sentence": "So I'll say rough ER for endoplasmic reticulum for short. And then you also have parts of the endoplasmic reticulum where you do not have ribosomes attached, and because that looks smooth through our microscope, it has been called, you can imagine, smooth endoplasmic reticulum. There are things known as Golgi bodies. Once again, another fascinating name. Gotta love these names in biology. That look kind of like an endoplasmic reticulum, but detached from the nuclear membrane. So let's say it's something like that."}, {"video_title": "Organelles in eukaryotic cells   Cells   High school biology   Khan Academy.mp3", "Sentence": "Once again, another fascinating name. Gotta love these names in biology. That look kind of like an endoplasmic reticulum, but detached from the nuclear membrane. So let's say it's something like that. That's my best drawing there. That's a Golgi body. And these are really good at packaging molecules, even proteins that might have just been produced, and packaging them so that they can be used outside of the cell, for example."}, {"video_title": "Organelles in eukaryotic cells   Cells   High school biology   Khan Academy.mp3", "Sentence": "So let's say it's something like that. That's my best drawing there. That's a Golgi body. And these are really good at packaging molecules, even proteins that might have just been produced, and packaging them so that they can be used outside of the cell, for example. So, and we'll go into detail in other videos where a protein might go to the Golgi body, get a little envelope around it, get some little processing going on, and then make its way outside of a cell. Now, another, and this is maybe one of the most famous membrane-bound organelles outside of the nucleus, is what's known as the powerhouse of the cell, and that is the mitochondria. And so I'll do this mitochondria in magenta because that's a nice, powerful color."}, {"video_title": "Organelles in eukaryotic cells   Cells   High school biology   Khan Academy.mp3", "Sentence": "And these are really good at packaging molecules, even proteins that might have just been produced, and packaging them so that they can be used outside of the cell, for example. So, and we'll go into detail in other videos where a protein might go to the Golgi body, get a little envelope around it, get some little processing going on, and then make its way outside of a cell. Now, another, and this is maybe one of the most famous membrane-bound organelles outside of the nucleus, is what's known as the powerhouse of the cell, and that is the mitochondria. And so I'll do this mitochondria in magenta because that's a nice, powerful color. So mitochondria, and I love mitochondria because it's fascinating how they even came to be. Mitochondria actually have their own DNA, and all of your mitochondrial DNA comes from your mother, and so that's actually very interesting for tracing maternal lineage. But mitochondria, this is where your, I'm gonna say, let's see what we can see inside of this."}, {"video_title": "Organelles in eukaryotic cells   Cells   High school biology   Khan Academy.mp3", "Sentence": "And so I'll do this mitochondria in magenta because that's a nice, powerful color. So mitochondria, and I love mitochondria because it's fascinating how they even came to be. Mitochondria actually have their own DNA, and all of your mitochondrial DNA comes from your mother, and so that's actually very interesting for tracing maternal lineage. But mitochondria, this is where your, I'm gonna say, let's see what we can see inside of this. This is where your ATP is produced. This is your mitochondria. It's really the powerhouse of the cell."}, {"video_title": "Organelles in eukaryotic cells   Cells   High school biology   Khan Academy.mp3", "Sentence": "But mitochondria, this is where your, I'm gonna say, let's see what we can see inside of this. This is where your ATP is produced. This is your mitochondria. It's really the powerhouse of the cell. What's interesting about mitochondria is evolutionary biologists believe that the ancestors of mitochondria, because mitochondria have their own DNA, they might have been independent organisms, independent cells, and at some point in our evolutionary past, they started living in symbiosis inside of what would be the ancestors of our cells, and then over time, they became so codependent that they started to replicate together, and mitochondria, in fact, became part of these eukaryotic cells. Now, if this eukaryotic cell was a plant cell or maybe an algae cell, you would have something called chloroplasts there. We don't have them, because we don't have photosynthesis, but this is a chloroplast, and if you could see inside, you could see the little thylakoid stacks right over here."}, {"video_title": "Organelles in eukaryotic cells   Cells   High school biology   Khan Academy.mp3", "Sentence": "It's really the powerhouse of the cell. What's interesting about mitochondria is evolutionary biologists believe that the ancestors of mitochondria, because mitochondria have their own DNA, they might have been independent organisms, independent cells, and at some point in our evolutionary past, they started living in symbiosis inside of what would be the ancestors of our cells, and then over time, they became so codependent that they started to replicate together, and mitochondria, in fact, became part of these eukaryotic cells. Now, if this eukaryotic cell was a plant cell or maybe an algae cell, you would have something called chloroplasts there. We don't have them, because we don't have photosynthesis, but this is a chloroplast, and if you could see inside, you could see the little thylakoid stacks right over here. You could see the little thylakoids if you could see inside, and so this right over here is a chloroplast, chloroplast, and this would be plants and algae. Animals do not have these, and these are where you have your photosynthesis take place, photosynthesis. Now, there's also some other membrane-bound organelles that are maybe less famous than the mitochondria or the chloroplast or, for sure, the nucleus, and that might be something like a vacuole, and in plants, vacuoles tend to be very big."}, {"video_title": "Organelles in eukaryotic cells   Cells   High school biology   Khan Academy.mp3", "Sentence": "We don't have them, because we don't have photosynthesis, but this is a chloroplast, and if you could see inside, you could see the little thylakoid stacks right over here. You could see the little thylakoids if you could see inside, and so this right over here is a chloroplast, chloroplast, and this would be plants and algae. Animals do not have these, and these are where you have your photosynthesis take place, photosynthesis. Now, there's also some other membrane-bound organelles that are maybe less famous than the mitochondria or the chloroplast or, for sure, the nucleus, and that might be something like a vacuole, and in plants, vacuoles tend to be very big. I could draw it, you know, this is three-dimensional, so I'll draw it on top of some of what I've drawn before, so if a vacuole right over here, this is a, and a plant can be a fairly significant compartment inside. In fact, it can even give structure to the plant itself because it is so big, and it contains water and enzymes. It's viewed as a kind of a storage compartment, but it can also contain enzymes that help digest things, that help break things down so that they can be used in some way, so that is a vacuole, and they don't just exist in plants."}, {"video_title": "Organelles in eukaryotic cells   Cells   High school biology   Khan Academy.mp3", "Sentence": "Now, there's also some other membrane-bound organelles that are maybe less famous than the mitochondria or the chloroplast or, for sure, the nucleus, and that might be something like a vacuole, and in plants, vacuoles tend to be very big. I could draw it, you know, this is three-dimensional, so I'll draw it on top of some of what I've drawn before, so if a vacuole right over here, this is a, and a plant can be a fairly significant compartment inside. In fact, it can even give structure to the plant itself because it is so big, and it contains water and enzymes. It's viewed as a kind of a storage compartment, but it can also contain enzymes that help digest things, that help break things down so that they can be used in some way, so that is a vacuole, and they don't just exist in plants. They can also exist in animal cells, but in plant cells, they tend to be, they can be very, very, very visible. Now, something that is somewhat related to some of the function that a vacuole plays that are most associated with animal cells, but now there's evidence that they also exist in plant cells, is the idea of a lysosome, so a lysosome right over here, that also is a compartment, and it's going to contain a whole series of enzymes in it that is useful for lysing, you could say, that is useful for breaking down either waste products as the cell lives, or even foreign substances that might not be helpful for the cells, so it's gonna contain a bunch of enzymes, and it helps break down things. Now, I'll leave you there."}, {"video_title": "Organelles in eukaryotic cells   Cells   High school biology   Khan Academy.mp3", "Sentence": "It's viewed as a kind of a storage compartment, but it can also contain enzymes that help digest things, that help break things down so that they can be used in some way, so that is a vacuole, and they don't just exist in plants. They can also exist in animal cells, but in plant cells, they tend to be, they can be very, very, very visible. Now, something that is somewhat related to some of the function that a vacuole plays that are most associated with animal cells, but now there's evidence that they also exist in plant cells, is the idea of a lysosome, so a lysosome right over here, that also is a compartment, and it's going to contain a whole series of enzymes in it that is useful for lysing, you could say, that is useful for breaking down either waste products as the cell lives, or even foreign substances that might not be helpful for the cells, so it's gonna contain a bunch of enzymes, and it helps break down things. Now, I'll leave you there. These aren't all of the structures in eukaryotic cells, but these are enough of the structures so that you can appreciate that there are a lot of membrane-bound organelles in eukaryotic cells, and to be clear, even if I were to show all of the membrane-bound structures, that's not all the complexity of a cell. The big thing to appreciate is the cells are incredibly complex. There's all sorts of structures in here that help transport things, that move things around."}, {"video_title": "Organelles in eukaryotic cells   Cells   High school biology   Khan Academy.mp3", "Sentence": "Now, I'll leave you there. These aren't all of the structures in eukaryotic cells, but these are enough of the structures so that you can appreciate that there are a lot of membrane-bound organelles in eukaryotic cells, and to be clear, even if I were to show all of the membrane-bound structures, that's not all the complexity of a cell. The big thing to appreciate is the cells are incredibly complex. There's all sorts of structures in here that help transport things, that move things around. If you could shrink yourself down and look inside of a cell, it would look more complex than the most complex cities. There's all sorts of activities, things being moved around, shuttled around. The cell itself is replicating and copying things, and so this is just the beginning."}, {"video_title": "Retroviruses   Cells   MCAT   Khan Academy.mp3", "Sentence": "So that special case is called a retrovirus. So first, let's zoom in and take a look at some unique things about the retrovirus that make it different from other viruses. So first of all, it is an enveloped, single-stranded RNA virus. And inside of this envelope, it also carries three special proteins. And right now, just be aware that there are three special proteins. I'll talk about them more when we get to each step where they're important. So as you know, enveloped viruses can enter in one of two ways, either through tricking receptors, receptor-mediated endocytosis, or through direct fusion."}, {"video_title": "Retroviruses   Cells   MCAT   Khan Academy.mp3", "Sentence": "And inside of this envelope, it also carries three special proteins. And right now, just be aware that there are three special proteins. I'll talk about them more when we get to each step where they're important. So as you know, enveloped viruses can enter in one of two ways, either through tricking receptors, receptor-mediated endocytosis, or through direct fusion. And it just so happens that in our example, and we're talking here about the retrovirus HIV, this retrovirus will enter the cell with direct fusion. So now that this nucleocapsid is inside the cell, it actually has to undergo a step called uncoating, where this purple capsid is dissolved. Oh, we forgot about the protein, so let me redraw those in right now."}, {"video_title": "Retroviruses   Cells   MCAT   Khan Academy.mp3", "Sentence": "So as you know, enveloped viruses can enter in one of two ways, either through tricking receptors, receptor-mediated endocytosis, or through direct fusion. And it just so happens that in our example, and we're talking here about the retrovirus HIV, this retrovirus will enter the cell with direct fusion. So now that this nucleocapsid is inside the cell, it actually has to undergo a step called uncoating, where this purple capsid is dissolved. Oh, we forgot about the protein, so let me redraw those in right now. So these are the proteins that were originally inside of that capsid. So everything inside of that coat is released. And this is where the first special step occurs."}, {"video_title": "Retroviruses   Cells   MCAT   Khan Academy.mp3", "Sentence": "Oh, we forgot about the protein, so let me redraw those in right now. So these are the proteins that were originally inside of that capsid. So everything inside of that coat is released. And this is where the first special step occurs. So we're gonna say that this red protein is reverse transcriptase. So reverse transcriptase will hop on to the RNA, and it reverse transcribes the RNA, which means that, so it reads from 5' to 3' end, and you will form complementary DNA, shown here in pink. And the reason it's called reverse transcription is usually you take DNA to make RNA, but in this case, you take RNA to make DNA."}, {"video_title": "Retroviruses   Cells   MCAT   Khan Academy.mp3", "Sentence": "And this is where the first special step occurs. So we're gonna say that this red protein is reverse transcriptase. So reverse transcriptase will hop on to the RNA, and it reverse transcribes the RNA, which means that, so it reads from 5' to 3' end, and you will form complementary DNA, shown here in pink. And the reason it's called reverse transcription is usually you take DNA to make RNA, but in this case, you take RNA to make DNA. And because this is the complementary DNA strand, we call this cDNA, complementary. And then reverse transcriptase will work again on this same RNA to make another cDNA strand. Because it's the same exact code, it can recombine with the other cDNA strand to make a double-stranded DNA."}, {"video_title": "Retroviruses   Cells   MCAT   Khan Academy.mp3", "Sentence": "And the reason it's called reverse transcription is usually you take DNA to make RNA, but in this case, you take RNA to make DNA. And because this is the complementary DNA strand, we call this cDNA, complementary. And then reverse transcriptase will work again on this same RNA to make another cDNA strand. Because it's the same exact code, it can recombine with the other cDNA strand to make a double-stranded DNA. And so now what happens is you have integrase coming along. And let's make integrase blue. So integrase comes along, clips off each of the 3' ends."}, {"video_title": "Retroviruses   Cells   MCAT   Khan Academy.mp3", "Sentence": "Because it's the same exact code, it can recombine with the other cDNA strand to make a double-stranded DNA. And so now what happens is you have integrase coming along. And let's make integrase blue. So integrase comes along, clips off each of the 3' ends. So now these are slightly shorter on each end. And sorry, this is a bit hard to see because this strand's 3' end is over here. And while the first one is actually clearly labeled as this is the 3' end."}, {"video_title": "Retroviruses   Cells   MCAT   Khan Academy.mp3", "Sentence": "So integrase comes along, clips off each of the 3' ends. So now these are slightly shorter on each end. And sorry, this is a bit hard to see because this strand's 3' end is over here. And while the first one is actually clearly labeled as this is the 3' end. And by clipping off those 3' sections, they form these sticky ends because unpaired DNA wants to be paired, and integrase has suddenly removed that part. And you might be wondering what happens to this RNA, and what happens is that it actually gets degraded by normal ribonuclease. So that's no longer there."}, {"video_title": "Retroviruses   Cells   MCAT   Khan Academy.mp3", "Sentence": "And while the first one is actually clearly labeled as this is the 3' end. And by clipping off those 3' sections, they form these sticky ends because unpaired DNA wants to be paired, and integrase has suddenly removed that part. And you might be wondering what happens to this RNA, and what happens is that it actually gets degraded by normal ribonuclease. So that's no longer there. And integrase does exactly what it says. It will follow this path and integrate this HIV DNA into the host's DNA. And one thing I just want to very quickly mention is that if I had drawn this to be super accurate, this would need to have a nucleus around it because the HIV retrovirus infects human eukaryotic cells, which have a nucleus."}, {"video_title": "Retroviruses   Cells   MCAT   Khan Academy.mp3", "Sentence": "So that's no longer there. And integrase does exactly what it says. It will follow this path and integrate this HIV DNA into the host's DNA. And one thing I just want to very quickly mention is that if I had drawn this to be super accurate, this would need to have a nucleus around it because the HIV retrovirus infects human eukaryotic cells, which have a nucleus. So it actually will travel through the nuclear membrane to get to the genome. And here, integrase helps viral DNA integrate with the host, like its name, integrase, integrate. So just imagine this is all double-stranded, but just for simple drawing's sake, this will just be one line."}, {"video_title": "Retroviruses   Cells   MCAT   Khan Academy.mp3", "Sentence": "And one thing I just want to very quickly mention is that if I had drawn this to be super accurate, this would need to have a nucleus around it because the HIV retrovirus infects human eukaryotic cells, which have a nucleus. So it actually will travel through the nuclear membrane to get to the genome. And here, integrase helps viral DNA integrate with the host, like its name, integrase, integrate. So just imagine this is all double-stranded, but just for simple drawing's sake, this will just be one line. So this is viral DNA, and this is called the provirus stage. So you can see that this is similar to the lysogenic cycle that we talked about before. But unlike the regular lysogenic cycle, it's not dormant or latent."}, {"video_title": "Retroviruses   Cells   MCAT   Khan Academy.mp3", "Sentence": "So just imagine this is all double-stranded, but just for simple drawing's sake, this will just be one line. So this is viral DNA, and this is called the provirus stage. So you can see that this is similar to the lysogenic cycle that we talked about before. But unlike the regular lysogenic cycle, it's not dormant or latent. It actually does not have that repressor gene, that typical lysogenic viruses have. So it is actively transcribed whenever the host's DNA is transcribed. So since the host cell thinks this is normal DNA, it will make RNA."}, {"video_title": "Retroviruses   Cells   MCAT   Khan Academy.mp3", "Sentence": "But unlike the regular lysogenic cycle, it's not dormant or latent. It actually does not have that repressor gene, that typical lysogenic viruses have. So it is actively transcribed whenever the host's DNA is transcribed. So since the host cell thinks this is normal DNA, it will make RNA. And I just wanted to call this viral mRNA so you have an idea that the cell cannot tell that this mRNA shouldn't have happened. So this mRNA exits the nucleus, and these viral RNAs are now in the cytosol. Again, once this viral mRNA exits the nucleus and goes into the cytoplasm, it's just like any other RNA, and some of these will be translated into proteins, like the capsid proteins, and of course the three proteins that we began with, which are the reverse transcriptase, the integrase, and actually the last one we haven't yet mentioned is the protease."}, {"video_title": "Retroviruses   Cells   MCAT   Khan Academy.mp3", "Sentence": "So since the host cell thinks this is normal DNA, it will make RNA. And I just wanted to call this viral mRNA so you have an idea that the cell cannot tell that this mRNA shouldn't have happened. So this mRNA exits the nucleus, and these viral RNAs are now in the cytosol. Again, once this viral mRNA exits the nucleus and goes into the cytoplasm, it's just like any other RNA, and some of these will be translated into proteins, like the capsid proteins, and of course the three proteins that we began with, which are the reverse transcriptase, the integrase, and actually the last one we haven't yet mentioned is the protease. The green here is protease. And we're going to hold off a little bit on what protease does, but here it's formed. And you can see that you now have all of the parts that can self-assemble into new viruses."}, {"video_title": "Retroviruses   Cells   MCAT   Khan Academy.mp3", "Sentence": "Again, once this viral mRNA exits the nucleus and goes into the cytoplasm, it's just like any other RNA, and some of these will be translated into proteins, like the capsid proteins, and of course the three proteins that we began with, which are the reverse transcriptase, the integrase, and actually the last one we haven't yet mentioned is the protease. The green here is protease. And we're going to hold off a little bit on what protease does, but here it's formed. And you can see that you now have all of the parts that can self-assemble into new viruses. So again, all of these viruses that are formed will have the RNA, the reverse transcriptase, the integrase, and the protease. So you'll notice that these are actually missing one thing. They're missing their envelope."}, {"video_title": "Retroviruses   Cells   MCAT   Khan Academy.mp3", "Sentence": "And you can see that you now have all of the parts that can self-assemble into new viruses. So again, all of these viruses that are formed will have the RNA, the reverse transcriptase, the integrase, and the protease. So you'll notice that these are actually missing one thing. They're missing their envelope. And so they're called immature viruses. And unlike the typical lytic cycle, it doesn't just break open the membrane. In fact, it takes advantage of the membrane."}, {"video_title": "Retroviruses   Cells   MCAT   Khan Academy.mp3", "Sentence": "They're missing their envelope. And so they're called immature viruses. And unlike the typical lytic cycle, it doesn't just break open the membrane. In fact, it takes advantage of the membrane. And so these viruses will come along, and they will bud off. So this one will enter here, and this one will enter here. Oops, and that's missing a border, I just realized."}, {"video_title": "Retroviruses   Cells   MCAT   Khan Academy.mp3", "Sentence": "In fact, it takes advantage of the membrane. And so these viruses will come along, and they will bud off. So this one will enter here, and this one will enter here. Oops, and that's missing a border, I just realized. So there you go. And they will bud off, and that will be their envelope. And sorry, they're missing the proteins, and I'll just draw them in again."}, {"video_title": "Retroviruses   Cells   MCAT   Khan Academy.mp3", "Sentence": "Oops, and that's missing a border, I just realized. So there you go. And they will bud off, and that will be their envelope. And sorry, they're missing the proteins, and I'll just draw them in again. So again, these are still immature, right? And before they go on to infect other cells, they have to mature somehow. So what happens is that protease inside of here will cleave those other proteins to make sure that they're fully functional before the virus enters another cell and starts this cycle all over again."}, {"video_title": "Retroviruses   Cells   MCAT   Khan Academy.mp3", "Sentence": "And sorry, they're missing the proteins, and I'll just draw them in again. So again, these are still immature, right? And before they go on to infect other cells, they have to mature somehow. So what happens is that protease inside of here will cleave those other proteins to make sure that they're fully functional before the virus enters another cell and starts this cycle all over again. And so retroviruses replicating are a bit more complicated than traditional replication. So it's not just lysogenic or lytic. It actually has elements of both."}, {"video_title": "Molecular structure of RNA   Macromolecules   Biology   Khan Academy (2).mp3", "Sentence": "And we can look at the telltale signs that this is DNA. And in particular, we can look at the five-carbon sugar on its backbone. We see, and let's actually number the carbons. This is one prime, two prime, three prime, four prime, five prime. We can see on the two-prime carbon, we don't have an oxygen attached to it. We don't have a hydroxyl group attached to it. And because of that, we know that this is not ribose."}, {"video_title": "Molecular structure of RNA   Macromolecules   Biology   Khan Academy (2).mp3", "Sentence": "This is one prime, two prime, three prime, four prime, five prime. We can see on the two-prime carbon, we don't have an oxygen attached to it. We don't have a hydroxyl group attached to it. And because of that, we know that this is not ribose. This is deoxyribose. This right over here is deoxyribose. And these two are also deoxyribose."}, {"video_title": "Molecular structure of RNA   Macromolecules   Biology   Khan Academy (2).mp3", "Sentence": "And because of that, we know that this is not ribose. This is deoxyribose. This right over here is deoxyribose. And these two are also deoxyribose. So that tells us that we have two strands of DNA, deoxyribonucleic acid. So let me write this down. This part of the chain, this is derived from a deoxyribose being attached to phosphate groups in a nitrogenous base."}, {"video_title": "Molecular structure of RNA   Macromolecules   Biology   Khan Academy (2).mp3", "Sentence": "And these two are also deoxyribose. So that tells us that we have two strands of DNA, deoxyribonucleic acid. So let me write this down. This part of the chain, this is derived from a deoxyribose being attached to phosphate groups in a nitrogenous base. So deoxyribose. So what would we have to do if we wanted, instead of viewing this as two strands of DNA in a double helix formation, well, how would we have to rearrange, how would we have to edit the left-hand strand if instead we wanted to imagine that the left-hand strand is, say, messenger RNA being generated during transcription with a single strand of DNA here on the right? Well, to turn this into RNA, or to make it look like RNA, on the two prime carbon, well, we wanna turn the deoxyribose into just ribose, so we would wanna add a hydroxyl group right over here."}, {"video_title": "Molecular structure of RNA   Macromolecules   Biology   Khan Academy (2).mp3", "Sentence": "This part of the chain, this is derived from a deoxyribose being attached to phosphate groups in a nitrogenous base. So deoxyribose. So what would we have to do if we wanted, instead of viewing this as two strands of DNA in a double helix formation, well, how would we have to rearrange, how would we have to edit the left-hand strand if instead we wanted to imagine that the left-hand strand is, say, messenger RNA being generated during transcription with a single strand of DNA here on the right? Well, to turn this into RNA, or to make it look like RNA, on the two prime carbon, well, we wanna turn the deoxyribose into just ribose, so we would wanna add a hydroxyl group right over here. So add a hydroxyl group over there. Actually, let me do that. Do the hydrogens in white."}, {"video_title": "Molecular structure of RNA   Macromolecules   Biology   Khan Academy (2).mp3", "Sentence": "Well, to turn this into RNA, or to make it look like RNA, on the two prime carbon, well, we wanna turn the deoxyribose into just ribose, so we would wanna add a hydroxyl group right over here. So add a hydroxyl group over there. Actually, let me do that. Do the hydrogens in white. So add one hydroxyl group there. And I wanna do it on all the sugars on the left strand's backbone. If I want this to be a single strand of RNA, and RNA tends to be single-stranded."}, {"video_title": "Molecular structure of RNA   Macromolecules   Biology   Khan Academy (2).mp3", "Sentence": "Do the hydrogens in white. So add one hydroxyl group there. And I wanna do it on all the sugars on the left strand's backbone. If I want this to be a single strand of RNA, and RNA tends to be single-stranded. So oxygen and then a hydrogen. And so this hydroxyl, adding this hydroxyl group, instead of just having another hydrogen, just a hydrogen by itself over there, this tells us that this sugar is no longer deoxyribose. This is ribose."}, {"video_title": "Molecular structure of RNA   Macromolecules   Biology   Khan Academy (2).mp3", "Sentence": "If I want this to be a single strand of RNA, and RNA tends to be single-stranded. So oxygen and then a hydrogen. And so this hydroxyl, adding this hydroxyl group, instead of just having another hydrogen, just a hydrogen by itself over there, this tells us that this sugar is no longer deoxyribose. This is ribose. So now we have ribose. We now have ribose in our backbone, which is a telltale sign that, well, at least now we have the backbone of RNA, ribonucleic acid, versus DNA, deoxyribonucleic acid. Now you might think we're done, but we're not quite done, because the nitrogenous bases on RNA are slightly different than the nitrogenous bases on DNA."}, {"video_title": "Molecular structure of RNA   Macromolecules   Biology   Khan Academy (2).mp3", "Sentence": "This is ribose. So now we have ribose. We now have ribose in our backbone, which is a telltale sign that, well, at least now we have the backbone of RNA, ribonucleic acid, versus DNA, deoxyribonucleic acid. Now you might think we're done, but we're not quite done, because the nitrogenous bases on RNA are slightly different than the nitrogenous bases on DNA. On DNA, your nitrogenous bases are adenine, guanine, are adenine, guanine, and adenine and guanine are the two-ringed nitrogenous bases right over here. This is adenine, this is guanine. And you also have cytosine."}, {"video_title": "Molecular structure of RNA   Macromolecules   Biology   Khan Academy (2).mp3", "Sentence": "Now you might think we're done, but we're not quite done, because the nitrogenous bases on RNA are slightly different than the nitrogenous bases on DNA. On DNA, your nitrogenous bases are adenine, guanine, are adenine, guanine, and adenine and guanine are the two-ringed nitrogenous bases right over here. This is adenine, this is guanine. And you also have cytosine. Cytosine, I'm gonna do these all in different colors. Cytosine and thymine. I'm getting to the punchline too fast."}, {"video_title": "Molecular structure of RNA   Macromolecules   Biology   Khan Academy (2).mp3", "Sentence": "And you also have cytosine. Cytosine, I'm gonna do these all in different colors. Cytosine and thymine. I'm getting to the punchline too fast. And this right over here is cytosine, and this is thymine. And cytosine and thymine are single-ringed nitrogenous bases. We call them pyrimidines, adenine and guanine."}, {"video_title": "Molecular structure of RNA   Macromolecules   Biology   Khan Academy (2).mp3", "Sentence": "I'm getting to the punchline too fast. And this right over here is cytosine, and this is thymine. And cytosine and thymine are single-ringed nitrogenous bases. We call them pyrimidines, adenine and guanine. We call them purines. This is a little bit of a review. In RNA, you still have adenine, you still have guanine, you still have cytosine, but instead of thymine, you have a very close relative of thymine, and that is uracil."}, {"video_title": "Molecular structure of RNA   Macromolecules   Biology   Khan Academy (2).mp3", "Sentence": "We call them pyrimidines, adenine and guanine. We call them purines. This is a little bit of a review. In RNA, you still have adenine, you still have guanine, you still have cytosine, but instead of thymine, you have a very close relative of thymine, and that is uracil. So the way that this is drawn right now, this nitrogenous base, remember when we started this video, it was double-stranded DNA, this nitrogenous base right over here is thymine, and it bonds, it forms hydrogen bonds with adenine right over here. If I want to turn it into uracil, I just have to get rid of this methyl group right over here. So if I just do this, if I just do this, and if I were to replace it with a hydrogen that is just implicitly bonded there, well now I'm dealing with uracil."}, {"video_title": "Molecular structure of RNA   Macromolecules   Biology   Khan Academy (2).mp3", "Sentence": "In RNA, you still have adenine, you still have guanine, you still have cytosine, but instead of thymine, you have a very close relative of thymine, and that is uracil. So the way that this is drawn right now, this nitrogenous base, remember when we started this video, it was double-stranded DNA, this nitrogenous base right over here is thymine, and it bonds, it forms hydrogen bonds with adenine right over here. If I want to turn it into uracil, I just have to get rid of this methyl group right over here. So if I just do this, if I just do this, and if I were to replace it with a hydrogen that is just implicitly bonded there, well now I'm dealing with uracil. So now I'm dealing with uracil. So you see that uracil and thymine are very close molecules, or they're very similar nitrogenous bases, and that's why they can play a very similar role. And it's still the case."}, {"video_title": "Molecular structure of RNA   Macromolecules   Biology   Khan Academy (2).mp3", "Sentence": "So if I just do this, if I just do this, and if I were to replace it with a hydrogen that is just implicitly bonded there, well now I'm dealing with uracil. So now I'm dealing with uracil. So you see that uracil and thymine are very close molecules, or they're very similar nitrogenous bases, and that's why they can play a very similar role. And it's still the case. And so what uracil pairs with, it pairs still with adenine, the same thing that thymine pairs with, and everything else is of course still the same. Now an interesting question, an interesting question is why uracil? Why not thymine?"}, {"video_title": "Molecular structure of RNA   Macromolecules   Biology   Khan Academy (2).mp3", "Sentence": "And it's still the case. And so what uracil pairs with, it pairs still with adenine, the same thing that thymine pairs with, and everything else is of course still the same. Now an interesting question, an interesting question is why uracil? Why not thymine? Or you could say why thymine? Why not uracil? And based on what I've read, it actually turns out that uracil is a little bit more error prone."}, {"video_title": "Molecular structure of RNA   Macromolecules   Biology   Khan Academy (2).mp3", "Sentence": "Why not thymine? Or you could say why thymine? Why not uracil? And based on what I've read, it actually turns out that uracil is a little bit more error prone. It might be able to bond with other things when you're coding. It's a little bit less stable than thymine. And so uracil, uracil, uracil makes the RNA molecule, or actually makes the machinery of information transfer, it makes it less stable."}, {"video_title": "Molecular structure of RNA   Macromolecules   Biology   Khan Academy (2).mp3", "Sentence": "And based on what I've read, it actually turns out that uracil is a little bit more error prone. It might be able to bond with other things when you're coding. It's a little bit less stable than thymine. And so uracil, uracil, uracil makes the RNA molecule, or actually makes the machinery of information transfer, it makes it less stable. It's a less stable, I guess, way to transfer information. And based on what I've read, in evolutionary history, RNA molecules, most people believe, predate DNA molecules. And then when you, so in the early stages you had a lot of change, and so uracil molecules were just fine, and there was a lot of errors and whatever else, but then once you had, I guess, information needed to be a little bit more persistent and a little less error prone, well then thymine helped stabilize, thymine helped stabilize things."}, {"video_title": "Molecular structure of RNA   Macromolecules   Biology   Khan Academy (2).mp3", "Sentence": "And so uracil, uracil, uracil makes the RNA molecule, or actually makes the machinery of information transfer, it makes it less stable. It's a less stable, I guess, way to transfer information. And based on what I've read, in evolutionary history, RNA molecules, most people believe, predate DNA molecules. And then when you, so in the early stages you had a lot of change, and so uracil molecules were just fine, and there was a lot of errors and whatever else, but then once you had, I guess, information needed to be a little bit more persistent and a little less error prone, well then thymine helped stabilize, thymine helped stabilize things. There's also the view of, well why is uracil stuck around? Well RNA molecules, they have all of these roles in cells, messenger RNA molecules are taking information from the DNA and getting it transcribed, or getting it translated at the ribosome, but they shouldn't hang out forever. You actually want them to be somewhat unstable."}, {"video_title": "Molecular structure of RNA   Macromolecules   Biology   Khan Academy (2).mp3", "Sentence": "And then when you, so in the early stages you had a lot of change, and so uracil molecules were just fine, and there was a lot of errors and whatever else, but then once you had, I guess, information needed to be a little bit more persistent and a little less error prone, well then thymine helped stabilize, thymine helped stabilize things. There's also the view of, well why is uracil stuck around? Well RNA molecules, they have all of these roles in cells, messenger RNA molecules are taking information from the DNA and getting it transcribed, or getting it translated at the ribosome, but they shouldn't hang out forever. You actually want them to be somewhat unstable. So it's an interesting question to think about. Why do we have uracil instead of thymine? Or why do we have thymine instead of uracil?"}, {"video_title": "Molecular structure of RNA   Macromolecules   Biology   Khan Academy (2).mp3", "Sentence": "You actually want them to be somewhat unstable. So it's an interesting question to think about. Why do we have uracil instead of thymine? Or why do we have thymine instead of uracil? But this is one of the telltale signs of, that we are now dealing with an RNA molecule. So now what we have on the left hand side, now all of this business, actually let me do this in a different color, all of this business, this strand, this strand right over here, we can now, the way it's drawn, we can now consider this an RNA molecule. And if we assume that this is happening during transcription, when a DNA molecule, where a single strand of DNA would want to replicate its information, then this over here would be mRNA, messenger, messenger RNA."}, {"video_title": "Molecular structure of RNA   Macromolecules   Biology   Khan Academy (2).mp3", "Sentence": "Or why do we have thymine instead of uracil? But this is one of the telltale signs of, that we are now dealing with an RNA molecule. So now what we have on the left hand side, now all of this business, actually let me do this in a different color, all of this business, this strand, this strand right over here, we can now, the way it's drawn, we can now consider this an RNA molecule. And if we assume that this is happening during transcription, when a DNA molecule, where a single strand of DNA would want to replicate its information, then this over here would be mRNA, messenger, messenger RNA. And so what's going on here? Well, let's think about it. This one, the way it's, the RNA, the messenger RNA, the way it's oriented, we have, if we go, we have phosphate group, then we go to five prime carbon, four prime, three prime, then phosphate group, then five prime, four prime, three prime, then phosphate group."}, {"video_title": "Molecular structure of RNA   Macromolecules   Biology   Khan Academy (2).mp3", "Sentence": "And if we assume that this is happening during transcription, when a DNA molecule, where a single strand of DNA would want to replicate its information, then this over here would be mRNA, messenger, messenger RNA. And so what's going on here? Well, let's think about it. This one, the way it's, the RNA, the messenger RNA, the way it's oriented, we have, if we go, we have phosphate group, then we go to five prime carbon, four prime, three prime, then phosphate group, then five prime, four prime, three prime, then phosphate group. So this is oriented five prime on top, three prime on the bottom. While this DNA molecule is oriented the other way. This is a five prime carbon, this is a three prime carbon."}, {"video_title": "Molecular structure of RNA   Macromolecules   Biology   Khan Academy (2).mp3", "Sentence": "This one, the way it's, the RNA, the messenger RNA, the way it's oriented, we have, if we go, we have phosphate group, then we go to five prime carbon, four prime, three prime, then phosphate group, then five prime, four prime, three prime, then phosphate group. So this is oriented five prime on top, three prime on the bottom. While this DNA molecule is oriented the other way. This is a five prime carbon, this is a three prime carbon. So we have phosphate, three prime, five prime, phosphate. So we have three prime is on top, and five prime is on the bottom. So if we wanted to think about what's happening, maybe using the symbols for the nitrogenous bases, we could say, all right, we have our mRNA molecule here, and this is its five prime end, and this is its three prime end."}, {"video_title": "Molecular structure of RNA   Macromolecules   Biology   Khan Academy (2).mp3", "Sentence": "This is a five prime carbon, this is a three prime carbon. So we have phosphate, three prime, five prime, phosphate. So we have three prime is on top, and five prime is on the bottom. So if we wanted to think about what's happening, maybe using the symbols for the nitrogenous bases, we could say, all right, we have our mRNA molecule here, and this is its five prime end, and this is its three prime end. And then the first, the top nitrogenous base right over here, this is uracil. This is uracil. And then the second one over here, this is, sorry, over here, this is cytosine."}, {"video_title": "Molecular structure of RNA   Macromolecules   Biology   Khan Academy (2).mp3", "Sentence": "So if we wanted to think about what's happening, maybe using the symbols for the nitrogenous bases, we could say, all right, we have our mRNA molecule here, and this is its five prime end, and this is its three prime end. And then the first, the top nitrogenous base right over here, this is uracil. This is uracil. And then the second one over here, this is, sorry, over here, this is cytosine. So this is cytosine. This is cytosine right over here. And this is being transcribed from a DNA molecule, from this DNA molecule on the right-hand side."}, {"video_title": "Molecular structure of RNA   Macromolecules   Biology   Khan Academy (2).mp3", "Sentence": "And then the second one over here, this is, sorry, over here, this is cytosine. So this is cytosine. This is cytosine right over here. And this is being transcribed from a DNA molecule, from this DNA molecule on the right-hand side. So this is DNA. And this DNA has an anti-parallel orientation. It's parallel, but it's kind of flipped over."}, {"video_title": "Molecular structure of RNA   Macromolecules   Biology   Khan Academy (2).mp3", "Sentence": "And this is being transcribed from a DNA molecule, from this DNA molecule on the right-hand side. So this is DNA. And this DNA has an anti-parallel orientation. It's parallel, but it's kind of flipped over. The sugars are pointed in a different direction. So this is going from, this is the three prime end, this is the five prime end. And we see that the uracil is hydrogen bonded to adenine."}, {"video_title": "Molecular structure of RNA   Macromolecules   Biology   Khan Academy (2).mp3", "Sentence": "It's parallel, but it's kind of flipped over. The sugars are pointed in a different direction. So this is going from, this is the three prime end, this is the five prime end. And we see that the uracil is hydrogen bonded to adenine. Adenine right over here. So adenine, and I'll draw dotted lines to show the hydrogen bonds. And that the cytosine is hydrogen bonded to guanine."}, {"video_title": "Molecular structure of RNA   Macromolecules   Biology   Khan Academy (2).mp3", "Sentence": "And we see that the uracil is hydrogen bonded to adenine. Adenine right over here. So adenine, and I'll draw dotted lines to show the hydrogen bonds. And that the cytosine is hydrogen bonded to guanine. To guanine. So this right over here, that is guanine. And actually I'll do the hydrogen bonds in white."}, {"video_title": "Molecular structure of RNA   Macromolecules   Biology   Khan Academy (2).mp3", "Sentence": "And that the cytosine is hydrogen bonded to guanine. To guanine. So this right over here, that is guanine. And actually I'll do the hydrogen bonds in white. So, you know, they are, actually there's multiple hydrogen bonds going on here. But just to be clear, this is mRNA, and on the right we have DNA. And this could be happening during transcription."}, {"video_title": "Molecular structure of RNA   Macromolecules   Biology   Khan Academy (2).mp3", "Sentence": "And actually I'll do the hydrogen bonds in white. So, you know, they are, actually there's multiple hydrogen bonds going on here. But just to be clear, this is mRNA, and on the right we have DNA. And this could be happening during transcription. This could be happening during, I'm having trouble changing colors. This could be happening during transcription. Now what are the types of RNAs out there?"}, {"video_title": "Molecular structure of RNA   Macromolecules   Biology   Khan Academy (2).mp3", "Sentence": "And this could be happening during transcription. This could be happening during, I'm having trouble changing colors. This could be happening during transcription. Now what are the types of RNAs out there? We've talked about this in other videos. Well you have messenger RNA, which is an important role in taking information from DNA and getting it eventually translated with the help of tRNAs and ribosomes. And though I've just mentioned another type of RNA, and that's transfer RNA."}, {"video_title": "Molecular structure of RNA   Macromolecules   Biology   Khan Academy (2).mp3", "Sentence": "Now what are the types of RNAs out there? We've talked about this in other videos. Well you have messenger RNA, which is an important role in taking information from DNA and getting it eventually translated with the help of tRNAs and ribosomes. And though I've just mentioned another type of RNA, and that's transfer RNA. So transfer RNA, tRNA. tRNA. And in the video, the overview video on transcription and translation, we talk about how tRNA does this."}, {"video_title": "Molecular structure of RNA   Macromolecules   Biology   Khan Academy (2).mp3", "Sentence": "And though I've just mentioned another type of RNA, and that's transfer RNA. So transfer RNA, tRNA. tRNA. And in the video, the overview video on transcription and translation, we talk about how tRNA does this. But it brings amino acids, it has amino acids attached at one end, and then it has anticodons on the other end that essentially pair, that pair with codon fragment or codons on the mRNA, and then that allows it to construct proteins. And this actually is, this right over here is a visualization of a tRNA molecule. So a lot of times when we think about DNA, we think about, okay, mRNA or RNA is an intermediary to be able to eventually translate it into proteins."}, {"video_title": "Molecular structure of RNA   Macromolecules   Biology   Khan Academy (2).mp3", "Sentence": "And in the video, the overview video on transcription and translation, we talk about how tRNA does this. But it brings amino acids, it has amino acids attached at one end, and then it has anticodons on the other end that essentially pair, that pair with codon fragment or codons on the mRNA, and then that allows it to construct proteins. And this actually is, this right over here is a visualization of a tRNA molecule. So a lot of times when we think about DNA, we think about, okay, mRNA or RNA is an intermediary to be able to eventually translate it into proteins. And that is often the case, but sometimes you also just want the RNA itself. The RNA itself plays a role in the cell beyond just transmitting information. And that's an example here with tRNA."}, {"video_title": "Molecular structure of RNA   Macromolecules   Biology   Khan Academy (2).mp3", "Sentence": "So a lot of times when we think about DNA, we think about, okay, mRNA or RNA is an intermediary to be able to eventually translate it into proteins. And that is often the case, but sometimes you also just want the RNA itself. The RNA itself plays a role in the cell beyond just transmitting information. And that's an example here with tRNA. And you can see it's interesting configuration where the amino acid will attach roughly in that area up there. And then you see the anticodon, the anticodon right down here in the bottom right. And different tRNA molecules will attach to different amino acids and they'll have different anticodons here."}, {"video_title": "Molecular structure of RNA   Macromolecules   Biology   Khan Academy (2).mp3", "Sentence": "And that's an example here with tRNA. And you can see it's interesting configuration where the amino acid will attach roughly in that area up there. And then you see the anticodon, the anticodon right down here in the bottom right. And different tRNA molecules will attach to different amino acids and they'll have different anticodons here. So this is another use for RNA. And then others include ribosomal RNA. Ribosomal RNA."}, {"video_title": "Molecular structure of RNA   Macromolecules   Biology   Khan Academy (2).mp3", "Sentence": "And different tRNA molecules will attach to different amino acids and they'll have different anticodons here. So this is another use for RNA. And then others include ribosomal RNA. Ribosomal RNA. And they actually play a structural role in ribosomes, which is where translation occurs. And you also have things called microRNA. MicroRNA, which are short chains of RNA, which could be used to regulate the translation of other RNA molecules."}, {"video_title": "Molecular structure of RNA   Macromolecules   Biology   Khan Academy (2).mp3", "Sentence": "Ribosomal RNA. And they actually play a structural role in ribosomes, which is where translation occurs. And you also have things called microRNA. MicroRNA, which are short chains of RNA, which could be used to regulate the translation of other RNA molecules. So RNA, you know, DNA gets a lot of the attention, but RNA is really, really, really important. And a lot of people believe that RNA came first. And it's potential that the first life or pseudo-life ever was just self-replicating RNA molecules and that DNA eventually evolved from RNA, but RNA stuck around because it's still very useful."}, {"video_title": "Antiparallel structure of DNA strands   Biology   Khan Academy.mp3", "Sentence": "And then you have a sugar. And then you have a phosphate group and then you have a sugar. And so I could draw the strand something like this. So phosphate and then we have a sugar. Whoops, let me just draw all the phosphates ahead of time. So you have the phosphates on that end and then you have the sugars. And you see the same thing on the other strand as well where we have phosphate, phosphate with a sugar, then another phosphate, then a sugar, then another phosphate."}, {"video_title": "Antiparallel structure of DNA strands   Biology   Khan Academy.mp3", "Sentence": "So phosphate and then we have a sugar. Whoops, let me just draw all the phosphates ahead of time. So you have the phosphates on that end and then you have the sugars. And you see the same thing on the other strand as well where we have phosphate, phosphate with a sugar, then another phosphate, then a sugar, then another phosphate. Let me circle the sugars as well. So you have a sugar there and then you have the sugar there as well. So on the other strand, it's also going to look like this."}, {"video_title": "Antiparallel structure of DNA strands   Biology   Khan Academy.mp3", "Sentence": "And you see the same thing on the other strand as well where we have phosphate, phosphate with a sugar, then another phosphate, then a sugar, then another phosphate. Let me circle the sugars as well. So you have a sugar there and then you have the sugar there as well. So on the other strand, it's also going to look like this. So let me draw the phosphates. I'm just abstracting them now. So the phosphate and then you have the sugars in between the phosphates."}, {"video_title": "Antiparallel structure of DNA strands   Biology   Khan Academy.mp3", "Sentence": "So on the other strand, it's also going to look like this. So let me draw the phosphates. I'm just abstracting them now. So the phosphate and then you have the sugars in between the phosphates. And what links them, you can think of them as the rungs on the ladder, these are the complementary nitrogenous bases. And the reason why we call them nitrogenous bases, I actually forgot to talk about in the last videos, is that these nitrogens are really electronegative and they can take up more hydrogen protons. They have an extra lone pair, the nitrogens have an extra lone pair that can be used up under the right conditions to potentially sop up more hydrogen protons."}, {"video_title": "Antiparallel structure of DNA strands   Biology   Khan Academy.mp3", "Sentence": "So the phosphate and then you have the sugars in between the phosphates. And what links them, you can think of them as the rungs on the ladder, these are the complementary nitrogenous bases. And the reason why we call them nitrogenous bases, I actually forgot to talk about in the last videos, is that these nitrogens are really electronegative and they can take up more hydrogen protons. They have an extra lone pair, the nitrogens have an extra lone pair that can be used up under the right conditions to potentially sop up more hydrogen protons. Now, a lot of people ask, well, if you have these nitrogenous bases here, why is DNA called an acid? Why is it called an acid? Well, the first thing is that the basic properties of the nitrogenous base are offset to a good degree based on the fact that they're able to hydrogen bond with each other."}, {"video_title": "Antiparallel structure of DNA strands   Biology   Khan Academy.mp3", "Sentence": "They have an extra lone pair, the nitrogens have an extra lone pair that can be used up under the right conditions to potentially sop up more hydrogen protons. Now, a lot of people ask, well, if you have these nitrogenous bases here, why is DNA called an acid? Why is it called an acid? Well, the first thing is that the basic properties of the nitrogenous base are offset to a good degree based on the fact that they're able to hydrogen bond with each other. And that's what actually forms these rungs, the rungs of the ladder when these complementary nitrogenous bases form these hydrogen bonds with each other. But even more, the reason why we call it an acid is the phosphate groups, when they're protonated, are acids. Now, the reason why we tend to draw them deprotonated is when they're so acidic that if you put them in a neutral solution, they're going to be deprotonated."}, {"video_title": "Antiparallel structure of DNA strands   Biology   Khan Academy.mp3", "Sentence": "Well, the first thing is that the basic properties of the nitrogenous base are offset to a good degree based on the fact that they're able to hydrogen bond with each other. And that's what actually forms these rungs, the rungs of the ladder when these complementary nitrogenous bases form these hydrogen bonds with each other. But even more, the reason why we call it an acid is the phosphate groups, when they're protonated, are acids. Now, the reason why we tend to draw them deprotonated is when they're so acidic that if you put them in a neutral solution, they're going to be deprotonated. So this is the form that you're more likely to find it in the nucleus of an actual cell once it's actually already deprotonated. But in general, phosphate groups are considered acidic. And if I were to draw kind of a more pure phosphate group, and I talked about this already in the last video, I would have it protonated, and so I wouldn't draw that negative charge like that."}, {"video_title": "Antiparallel structure of DNA strands   Biology   Khan Academy.mp3", "Sentence": "Now, the reason why we tend to draw them deprotonated is when they're so acidic that if you put them in a neutral solution, they're going to be deprotonated. So this is the form that you're more likely to find it in the nucleus of an actual cell once it's actually already deprotonated. But in general, phosphate groups are considered acidic. And if I were to draw kind of a more pure phosphate group, and I talked about this already in the last video, I would have it protonated, and so I wouldn't draw that negative charge like that. So that's just a review of last time. But let's actually, it doesn't mean just, since I already started abstracting it, let's abstract it further. So let's draw the nitrogenous bases a little bit."}, {"video_title": "Antiparallel structure of DNA strands   Biology   Khan Academy.mp3", "Sentence": "And if I were to draw kind of a more pure phosphate group, and I talked about this already in the last video, I would have it protonated, and so I wouldn't draw that negative charge like that. So that's just a review of last time. But let's actually, it doesn't mean just, since I already started abstracting it, let's abstract it further. So let's draw the nitrogenous bases a little bit. So I have thymine here, and I will do thymine in this green color. So this right over there is thymine. So this is attached to thymine."}, {"video_title": "Antiparallel structure of DNA strands   Biology   Khan Academy.mp3", "Sentence": "So let's draw the nitrogenous bases a little bit. So I have thymine here, and I will do thymine in this green color. So this right over there is thymine. So this is attached to thymine. And the complementary nitrogenous base to thymine is adenine, which I will do. Let's see, I'm running out of colors here. Let's see, adenine."}, {"video_title": "Antiparallel structure of DNA strands   Biology   Khan Academy.mp3", "Sentence": "So this is attached to thymine. And the complementary nitrogenous base to thymine is adenine, which I will do. Let's see, I'm running out of colors here. Let's see, adenine. I'll do this in an orange color. It's got so many nitrogens on it. So actually, so let me, so it actually should include that hydrogen right over there."}, {"video_title": "Antiparallel structure of DNA strands   Biology   Khan Academy.mp3", "Sentence": "Let's see, adenine. I'll do this in an orange color. It's got so many nitrogens on it. So actually, so let me, so it actually should include that hydrogen right over there. So this right over here is adenine. And they form, they have these hydrogen bonds between them right over here because they have partially negative and positive charges on either end that are attracted to each other. And then we go to this rung, one rung below it."}, {"video_title": "Antiparallel structure of DNA strands   Biology   Khan Academy.mp3", "Sentence": "So actually, so let me, so it actually should include that hydrogen right over there. So this right over here is adenine. And they form, they have these hydrogen bonds between them right over here because they have partially negative and positive charges on either end that are attracted to each other. And then we go to this rung, one rung below it. And what is going on? Well, let's see. We have, I really am running out of colors here."}, {"video_title": "Antiparallel structure of DNA strands   Biology   Khan Academy.mp3", "Sentence": "And then we go to this rung, one rung below it. And what is going on? Well, let's see. We have, I really am running out of colors here. We have this nitrogenous base is cytosine. This nitrogenous base right over here is cytosine. This nitrogenous base here is cytosine."}, {"video_title": "Antiparallel structure of DNA strands   Biology   Khan Academy.mp3", "Sentence": "We have, I really am running out of colors here. We have this nitrogenous base is cytosine. This nitrogenous base right over here is cytosine. This nitrogenous base here is cytosine. And it is paired up with guanine. It is paired up with guanine. I'll do guanine in this color."}, {"video_title": "Antiparallel structure of DNA strands   Biology   Khan Academy.mp3", "Sentence": "This nitrogenous base here is cytosine. And it is paired up with guanine. It is paired up with guanine. I'll do guanine in this color. So it is, it is paired up with guanine right over there. And we even saw this in the introductory video to DNA. Now, you might say, oh look, these two strands seem parallel to each other."}, {"video_title": "Antiparallel structure of DNA strands   Biology   Khan Academy.mp3", "Sentence": "I'll do guanine in this color. So it is, it is paired up with guanine right over there. And we even saw this in the introductory video to DNA. Now, you might say, oh look, these two strands seem parallel to each other. And in some ways that is true. But there might be something other, another interesting thing that you might have noticed is the direction in which they are oriented. I guess is the best way to phrase it."}, {"video_title": "Antiparallel structure of DNA strands   Biology   Khan Academy.mp3", "Sentence": "Now, you might say, oh look, these two strands seem parallel to each other. And in some ways that is true. But there might be something other, another interesting thing that you might have noticed is the direction in which they are oriented. I guess is the best way to phrase it. If we, and you especially see that when you focus in on the sugars. Notice the sugars over here, the deoxyriboses are the things that, or the parts of the nucleotide that come from deoxyribose. You see the oxygens on the top of the ribose, on the top of these five member rings."}, {"video_title": "Antiparallel structure of DNA strands   Biology   Khan Academy.mp3", "Sentence": "I guess is the best way to phrase it. If we, and you especially see that when you focus in on the sugars. Notice the sugars over here, the deoxyriboses are the things that, or the parts of the nucleotide that come from deoxyribose. You see the oxygens on the top of the ribose, on the top of these five member rings. The oxygen is on top. While on this side, the oxygen is on the bottom. And so they are actually in different orientations."}, {"video_title": "Antiparallel structure of DNA strands   Biology   Khan Academy.mp3", "Sentence": "You see the oxygens on the top of the ribose, on the top of these five member rings. The oxygen is on top. While on this side, the oxygen is on the bottom. And so they are actually in different orientations. Here the oxygen's pointing up. Here the oxygen is pointing down. And to get a little bit more concrete about that, we can number the carbons on the ribose to think about the directions and use those numbers of the carbons to describe the different directions."}, {"video_title": "Antiparallel structure of DNA strands   Biology   Khan Academy.mp3", "Sentence": "And so they are actually in different orientations. Here the oxygen's pointing up. Here the oxygen is pointing down. And to get a little bit more concrete about that, we can number the carbons on the ribose to think about the directions and use those numbers of the carbons to describe the different directions. So let's number our carbons. So when ribose, so this is, these are both ribose. We saw that in the molecular structure of DNA videos."}, {"video_title": "Antiparallel structure of DNA strands   Biology   Khan Academy.mp3", "Sentence": "And to get a little bit more concrete about that, we can number the carbons on the ribose to think about the directions and use those numbers of the carbons to describe the different directions. So let's number our carbons. So when ribose, so this is, these are both ribose. We saw that in the molecular structure of DNA videos. When we're talking about DNA, we're talking about deoxyribose. So it does not have, it does not have a, it does not, instead of having a hydroxyl group on the number two carbon, it just has a, it just has a hydrogen. So instead of having a hydroxyl group on the number two carbon, it just has a hydrogen."}, {"video_title": "Antiparallel structure of DNA strands   Biology   Khan Academy.mp3", "Sentence": "We saw that in the molecular structure of DNA videos. When we're talking about DNA, we're talking about deoxyribose. So it does not have, it does not have a, it does not, instead of having a hydroxyl group on the number two carbon, it just has a, it just has a hydrogen. So instead of having a hydroxyl group on the number two carbon, it just has a hydrogen. But let's actually number them. So this is the one prime carbon starting at the carbonyl group. Let me do that in a different color."}, {"video_title": "Antiparallel structure of DNA strands   Biology   Khan Academy.mp3", "Sentence": "So instead of having a hydroxyl group on the number two carbon, it just has a hydrogen. But let's actually number them. So this is the one prime carbon starting at the carbonyl group. Let me do that in a different color. So this is the one prime carbon. And I'm just numbering them starting at the carbonyl group. One prime, two prime, three prime, four prime, five prime."}, {"video_title": "Antiparallel structure of DNA strands   Biology   Khan Academy.mp3", "Sentence": "Let me do that in a different color. So this is the one prime carbon. And I'm just numbering them starting at the carbonyl group. One prime, two prime, three prime, four prime, five prime. And then when you look at it as a ring, this was the one prime. This is the two prime. This is the three prime."}, {"video_title": "Antiparallel structure of DNA strands   Biology   Khan Academy.mp3", "Sentence": "One prime, two prime, three prime, four prime, five prime. And then when you look at it as a ring, this was the one prime. This is the two prime. This is the three prime. This is the four prime. This is the five prime. Or if you were to number them on this diagram right over here, actually in the DNA molecule, this is the one prime."}, {"video_title": "Antiparallel structure of DNA strands   Biology   Khan Academy.mp3", "Sentence": "This is the three prime. This is the four prime. This is the five prime. Or if you were to number them on this diagram right over here, actually in the DNA molecule, this is the one prime. This is the two prime carbon. This is the three prime carbon. This is the four prime carbon."}, {"video_title": "Antiparallel structure of DNA strands   Biology   Khan Academy.mp3", "Sentence": "Or if you were to number them on this diagram right over here, actually in the DNA molecule, this is the one prime. This is the two prime carbon. This is the three prime carbon. This is the four prime carbon. And this is the five prime carbon. And so one way to think about it is we'll go phosphate group, and it's connected, it's connected with what we call phosphodiester linkages. Phosphodiester linkages, that's what's essentially allowing these backbones to link up."}, {"video_title": "Antiparallel structure of DNA strands   Biology   Khan Academy.mp3", "Sentence": "This is the four prime carbon. And this is the five prime carbon. And so one way to think about it is we'll go phosphate group, and it's connected, it's connected with what we call phosphodiester linkages. Phosphodiester linkages, that's what's essentially allowing these backbones to link up. But we're going from phosphate to five prime carbon to, and then through the sugar, we go to the three prime carbon, then we go to another phosphate, then we go to the five prime carbon. Let me label that. This is the five prime carbon."}, {"video_title": "Antiparallel structure of DNA strands   Biology   Khan Academy.mp3", "Sentence": "Phosphodiester linkages, that's what's essentially allowing these backbones to link up. But we're going from phosphate to five prime carbon to, and then through the sugar, we go to the three prime carbon, then we go to another phosphate, then we go to the five prime carbon. Let me label that. This is the five prime carbon. Then we go to the three prime carbon. And that just comes straight out of just numbering these, starting with the carbon that was the number one carbon, which went in a straight chain form. It's at the carbonyl, it's part of the carbonyl group."}, {"video_title": "Antiparallel structure of DNA strands   Biology   Khan Academy.mp3", "Sentence": "This is the five prime carbon. Then we go to the three prime carbon. And that just comes straight out of just numbering these, starting with the carbon that was the number one carbon, which went in a straight chain form. It's at the carbonyl, it's part of the carbonyl group. But you see we're going from five, we go phosphate, five prime, three prime, phosphate, five prime, three prime, phosphate. So one way to describe the orientation is saying, hey, we're going in the direction from five prime to three prime. So we could say, we could say that we're going from five prime, we're going from five prime to three prime that way, on the left-hand chain."}, {"video_title": "Antiparallel structure of DNA strands   Biology   Khan Academy.mp3", "Sentence": "It's at the carbonyl, it's part of the carbonyl group. But you see we're going from five, we go phosphate, five prime, three prime, phosphate, five prime, three prime, phosphate. So one way to describe the orientation is saying, hey, we're going in the direction from five prime to three prime. So we could say, we could say that we're going from five prime, we're going from five prime to three prime that way, on the left-hand chain. And what are we doing on the right-hand chain? Well, let's number them again. So this is the one prime carbon."}, {"video_title": "Antiparallel structure of DNA strands   Biology   Khan Academy.mp3", "Sentence": "So we could say, we could say that we're going from five prime, we're going from five prime to three prime that way, on the left-hand chain. And what are we doing on the right-hand chain? Well, let's number them again. So this is the one prime carbon. Now this thing, relative to this, is upside down, it's inverted. So one prime, two prime, three prime, four prime, five prime. I could do it up here."}, {"video_title": "Antiparallel structure of DNA strands   Biology   Khan Academy.mp3", "Sentence": "So this is the one prime carbon. Now this thing, relative to this, is upside down, it's inverted. So one prime, two prime, three prime, four prime, five prime. I could do it up here. One prime carbon, two prime carbon, three prime carbon, four prime carbon, five prime carbon. Here you're going from phosphate, three prime, five prime, phosphate, three prime, five prime, phosphate. So the way that the sugars are oriented, if you're going from top to bottom the way we're looking here, you're going from three prime to five prime."}, {"video_title": "Antiparallel structure of DNA strands   Biology   Khan Academy.mp3", "Sentence": "I could do it up here. One prime carbon, two prime carbon, three prime carbon, four prime carbon, five prime carbon. Here you're going from phosphate, three prime, five prime, phosphate, three prime, five prime, phosphate. So the way that the sugars are oriented, if you're going from top to bottom the way we're looking here, you're going from three prime to five prime. So on the right-hand side, you are, it's three prime, five prime. And so if you wanted to draw an arrow from five prime to three prime, you could look at it like that. And so you could say these are parallel, but since they are essentially oriented in, they're pointing in different directions, even though they're actually parallel, we would call the structure of DNA anti-parallel."}, {"video_title": "Antiparallel structure of DNA strands   Biology   Khan Academy.mp3", "Sentence": "So the way that the sugars are oriented, if you're going from top to bottom the way we're looking here, you're going from three prime to five prime. So on the right-hand side, you are, it's three prime, five prime. And so if you wanted to draw an arrow from five prime to three prime, you could look at it like that. And so you could say these are parallel, but since they are essentially oriented in, they're pointing in different directions, even though they're actually parallel, we would call the structure of DNA anti-parallel. So this would be an anti-parallel structure of DNA. So these two strands, they're complementary, they're defined by each other. The thymine bonds with the adenine, the cytosine bonds with the guanine, or they are attracted to each other through these hydrogen bonds, but the two backbones, they're pointed in different directions."}, {"video_title": "Antiparallel structure of DNA strands   Biology   Khan Academy.mp3", "Sentence": "And so you could say these are parallel, but since they are essentially oriented in, they're pointing in different directions, even though they're actually parallel, we would call the structure of DNA anti-parallel. So this would be an anti-parallel structure of DNA. So these two strands, they're complementary, they're defined by each other. The thymine bonds with the adenine, the cytosine bonds with the guanine, or they are attracted to each other through these hydrogen bonds, but the two backbones, they're pointed in different directions. Now another interesting thing to think about, since we're talking about the molecular structure of DNA, is how do these things form? How do these things know to orient in this way? And part of, what plays part of that role is the fact that these phosphate groups are negative."}, {"video_title": "Antiparallel structure of DNA strands   Biology   Khan Academy.mp3", "Sentence": "The thymine bonds with the adenine, the cytosine bonds with the guanine, or they are attracted to each other through these hydrogen bonds, but the two backbones, they're pointed in different directions. Now another interesting thing to think about, since we're talking about the molecular structure of DNA, is how do these things form? How do these things know to orient in this way? And part of, what plays part of that role is the fact that these phosphate groups are negative. So you think these things that have outright negative charge, they're gonna try to get as far away from each other as possible, and then when they, you know, they just keep kind of orienting, getting far away from each other, and these are long, these are very, very, very, very long molecules. In the introductory video to DNA, we talk about how long these chromosomes are, how many base pairs we actually have, and these are long molecules. So all of these phosphate groups on either strand, they want to get away from each other, and then these things want to, these things want to get close to each other because of the hydrogen bonds, and so that's what helps form this actual ladder structure."}, {"video_title": "Antiparallel structure of DNA strands   Biology   Khan Academy.mp3", "Sentence": "And part of, what plays part of that role is the fact that these phosphate groups are negative. So you think these things that have outright negative charge, they're gonna try to get as far away from each other as possible, and then when they, you know, they just keep kind of orienting, getting far away from each other, and these are long, these are very, very, very, very long molecules. In the introductory video to DNA, we talk about how long these chromosomes are, how many base pairs we actually have, and these are long molecules. So all of these phosphate groups on either strand, they want to get away from each other, and then these things want to, these things want to get close to each other because of the hydrogen bonds, and so that's what helps form this actual ladder structure. So DNA, fascinating molecule. We could speak for days about it. It's actually mind-blowing when you think about its implications for who we are."}, {"video_title": "Antiparallel structure of DNA strands   Biology   Khan Academy.mp3", "Sentence": "So all of these phosphate groups on either strand, they want to get away from each other, and then these things want to, these things want to get close to each other because of the hydrogen bonds, and so that's what helps form this actual ladder structure. So DNA, fascinating molecule. We could speak for days about it. It's actually mind-blowing when you think about its implications for who we are. But hopefully this gives you a better sense of what it is molecularly. Molecularly, I cannot say it. Molecularly."}, {"video_title": "Interactions between populations    Ecology   Khan Academy.mp3", "Sentence": "And in particular in this video, we're gonna focus on the interactions between those populations, the interactions between the different species. The technical term for that is interspecific interactions. I like to just say interactions between species. Now the first one that is often thought about is the notion of competition, competition. And this is when different populations, different species, are competing for the same resources. You can imagine a forest where you have different populations of plants that are competing for sunlight, that are competing for water, that are competing for nutrients in the soil. Even in this picture right over here, this is a picture of a community."}, {"video_title": "Interactions between populations    Ecology   Khan Academy.mp3", "Sentence": "Now the first one that is often thought about is the notion of competition, competition. And this is when different populations, different species, are competing for the same resources. You can imagine a forest where you have different populations of plants that are competing for sunlight, that are competing for water, that are competing for nutrients in the soil. Even in this picture right over here, this is a picture of a community. All of these different populations of fish and other things, sea anemones and coral, they are sharing this same region, and many of them could be in competition with each other. They might be going after the same food, or they might be going after the same shelter someplace. And oftentimes when people are talking about these interspecies or interspecific interactions, you'll see something like this, a minus slash minus, or a negative sign slash a negative sign."}, {"video_title": "Interactions between populations    Ecology   Khan Academy.mp3", "Sentence": "Even in this picture right over here, this is a picture of a community. All of these different populations of fish and other things, sea anemones and coral, they are sharing this same region, and many of them could be in competition with each other. They might be going after the same food, or they might be going after the same shelter someplace. And oftentimes when people are talking about these interspecies or interspecific interactions, you'll see something like this, a minus slash minus, or a negative sign slash a negative sign. And that means that this type of interaction, when you have two species or two populations that are in competition with each other, the more that you have of one, it's going to have a negative effect on the other, and vice versa. If I'm a plant, and if I'm in competition with another plant, and that one's taking my light, and if there's more of it taking my light, that's gonna have a negative impact on me, and vice versa. If I'm in competition with you, and we eat the same thing, the more of me that there's around eating your food, that's gonna have a negative impact on you, and vice versa."}, {"video_title": "Interactions between populations    Ecology   Khan Academy.mp3", "Sentence": "And oftentimes when people are talking about these interspecies or interspecific interactions, you'll see something like this, a minus slash minus, or a negative sign slash a negative sign. And that means that this type of interaction, when you have two species or two populations that are in competition with each other, the more that you have of one, it's going to have a negative effect on the other, and vice versa. If I'm a plant, and if I'm in competition with another plant, and that one's taking my light, and if there's more of it taking my light, that's gonna have a negative impact on me, and vice versa. If I'm in competition with you, and we eat the same thing, the more of me that there's around eating your food, that's gonna have a negative impact on you, and vice versa. So the next form of interspecific interaction, or interaction between species, is predation. Is predation. This is when one population likes to eat another population."}, {"video_title": "Interactions between populations    Ecology   Khan Academy.mp3", "Sentence": "If I'm in competition with you, and we eat the same thing, the more of me that there's around eating your food, that's gonna have a negative impact on you, and vice versa. So the next form of interspecific interaction, or interaction between species, is predation. Is predation. This is when one population likes to eat another population. And you might often associate predation with pictures like this that you see on television shows, on documentaries, you see a cheetah hunting, it looks like a cheetah hunting a gazelle, or a deer of some kind. Actually, it says right here, it's a young bushback. And this is predation."}, {"video_title": "Interactions between populations    Ecology   Khan Academy.mp3", "Sentence": "This is when one population likes to eat another population. And you might often associate predation with pictures like this that you see on television shows, on documentaries, you see a cheetah hunting, it looks like a cheetah hunting a gazelle, or a deer of some kind. Actually, it says right here, it's a young bushback. And this is predation. But this is not the only form of predation. This picture here of the goat eating grass, this is also predation. It's not quite as bloody and as violent, but it is still predation."}, {"video_title": "Interactions between populations    Ecology   Khan Academy.mp3", "Sentence": "And this is predation. But this is not the only form of predation. This picture here of the goat eating grass, this is also predation. It's not quite as bloody and as violent, but it is still predation. Because you have one species eating another species. In this case, you have this animal, the goat, that is eating the grass. And this type of predation, this specific type of predation, is called herbivory."}, {"video_title": "Interactions between populations    Ecology   Khan Academy.mp3", "Sentence": "It's not quite as bloody and as violent, but it is still predation. Because you have one species eating another species. In this case, you have this animal, the goat, that is eating the grass. And this type of predation, this specific type of predation, is called herbivory. Herbivory. But it is a type of predation. So we could say predation slash herbivory."}, {"video_title": "Interactions between populations    Ecology   Khan Academy.mp3", "Sentence": "And this type of predation, this specific type of predation, is called herbivory. Herbivory. But it is a type of predation. So we could say predation slash herbivory. Let me do a little slash here. Slash herbivory, which is a special case of predation. And you'll often see a plus slash minus."}, {"video_title": "Interactions between populations    Ecology   Khan Academy.mp3", "Sentence": "So we could say predation slash herbivory. Let me do a little slash here. Slash herbivory, which is a special case of predation. And you'll often see a plus slash minus. The more of, let's say, this species that you have, the species that is being eaten, it's going to benefit the predator. But the more of the predator that you have, it's going to have a negative effect on the actual prey. Now the next types of interactions are ones where you have long-term, fairly intimate interactions."}, {"video_title": "Interactions between populations    Ecology   Khan Academy.mp3", "Sentence": "And you'll often see a plus slash minus. The more of, let's say, this species that you have, the species that is being eaten, it's going to benefit the predator. But the more of the predator that you have, it's going to have a negative effect on the actual prey. Now the next types of interactions are ones where you have long-term, fairly intimate interactions. Where you have organisms that often time live with each other or even on each other. And this general term of organisms that have these long-term, intimate interactions is symbiosis. Symbiosis."}, {"video_title": "Interactions between populations    Ecology   Khan Academy.mp3", "Sentence": "Now the next types of interactions are ones where you have long-term, fairly intimate interactions. Where you have organisms that often time live with each other or even on each other. And this general term of organisms that have these long-term, intimate interactions is symbiosis. Symbiosis. Now in everyday language, when people talk about symbiosis, they're often talking about organisms that really benefit each other. But technically, symbiosis isn't just about benefiting each other. It could be that they're even hurting each other in some way or that maybe one benefits while the other one really doesn't care."}, {"video_title": "Interactions between populations    Ecology   Khan Academy.mp3", "Sentence": "Symbiosis. Now in everyday language, when people talk about symbiosis, they're often talking about organisms that really benefit each other. But technically, symbiosis isn't just about benefiting each other. It could be that they're even hurting each other in some way or that maybe one benefits while the other one really doesn't care. And so there's several types of symbiosis. The first that we could talk about is parasitism. Para, parasitism."}, {"video_title": "Interactions between populations    Ecology   Khan Academy.mp3", "Sentence": "It could be that they're even hurting each other in some way or that maybe one benefits while the other one really doesn't care. And so there's several types of symbiosis. The first that we could talk about is parasitism. Para, parasitism. And this looks a lot like predation. Where the more, the more, the parasite benefits the more of the host that there is. But the host is actually hurt by the parasite."}, {"video_title": "Interactions between populations    Ecology   Khan Academy.mp3", "Sentence": "Para, parasitism. And this looks a lot like predation. Where the more, the more, the parasite benefits the more of the host that there is. But the host is actually hurt by the parasite. And there's all sorts of examples of parasitism. We have right over here a zoomed in picture of a louse. So why is this parasitism?"}, {"video_title": "Interactions between populations    Ecology   Khan Academy.mp3", "Sentence": "But the host is actually hurt by the parasite. And there's all sorts of examples of parasitism. We have right over here a zoomed in picture of a louse. So why is this parasitism? Well, if this louse, I should say, so this is parasitism. Parasitism. And we would call this right, the louse here, a parasite, parasitism."}, {"video_title": "Interactions between populations    Ecology   Khan Academy.mp3", "Sentence": "So why is this parasitism? Well, if this louse, I should say, so this is parasitism. Parasitism. And we would call this right, the louse here, a parasite, parasitism. And this benefits by living in your hair because that's where it gets its food from. It can lay, or living on your scalp, it gets your food by sucking your blood. It can also lay eggs in your hair."}, {"video_title": "Interactions between populations    Ecology   Khan Academy.mp3", "Sentence": "And we would call this right, the louse here, a parasite, parasitism. And this benefits by living in your hair because that's where it gets its food from. It can lay, or living on your scalp, it gets your food by sucking your blood. It can also lay eggs in your hair. In some ways you could view it as almost shelter from the rest of the environment. But it's negative for you. It'll make you itchy."}, {"video_title": "Interactions between populations    Ecology   Khan Academy.mp3", "Sentence": "It can also lay eggs in your hair. In some ways you could view it as almost shelter from the rest of the environment. But it's negative for you. It'll make you itchy. It is taking your blood. It is uncomfortable. And so parasitism, once again, it's good for the parasite."}, {"video_title": "Interactions between populations    Ecology   Khan Academy.mp3", "Sentence": "It'll make you itchy. It is taking your blood. It is uncomfortable. And so parasitism, once again, it's good for the parasite. Just like predation is good for the predator. But not so good for the host in the case of parasitism. Now you have another situation where it is benefiting both sides."}, {"video_title": "Interactions between populations    Ecology   Khan Academy.mp3", "Sentence": "And so parasitism, once again, it's good for the parasite. Just like predation is good for the predator. But not so good for the host in the case of parasitism. Now you have another situation where it is benefiting both sides. And that is called mutualism. Mutualism, let me do that in a different color. So mutualism."}, {"video_title": "Interactions between populations    Ecology   Khan Academy.mp3", "Sentence": "Now you have another situation where it is benefiting both sides. And that is called mutualism. Mutualism, let me do that in a different color. So mutualism. This is where both sides benefit. And oftentimes when people talk about symbiosis, they're really talking about mutualism, which is a specific type of symbiosis where both species, where both animals, organisms benefit. They don't have to just be animals."}, {"video_title": "Interactions between populations    Ecology   Khan Academy.mp3", "Sentence": "So mutualism. This is where both sides benefit. And oftentimes when people talk about symbiosis, they're really talking about mutualism, which is a specific type of symbiosis where both species, where both animals, organisms benefit. They don't have to just be animals. This is an example of mutualism right here. Let me do that in a color you can see. So this is mutualism."}, {"video_title": "Interactions between populations    Ecology   Khan Academy.mp3", "Sentence": "They don't have to just be animals. This is an example of mutualism right here. Let me do that in a color you can see. So this is mutualism. Where you have a clownfish living within a sea anemone, the sea anemone is providing the clownfish shelter while the clownfish is keeping away other fish that might eat that sea anemone. So they are both benefiting from that interaction. And so that is mutualism."}, {"video_title": "Interactions between populations    Ecology   Khan Academy.mp3", "Sentence": "So this is mutualism. Where you have a clownfish living within a sea anemone, the sea anemone is providing the clownfish shelter while the clownfish is keeping away other fish that might eat that sea anemone. So they are both benefiting from that interaction. And so that is mutualism. Now you have another category where one species is benefiting and the other one is maybe a little bit more indifferent. So one species is benefiting and then the other one, well, maybe it is a little bit indifferent. And we call that commensalism."}, {"video_title": "Interactions between populations    Ecology   Khan Academy.mp3", "Sentence": "And so that is mutualism. Now you have another category where one species is benefiting and the other one is maybe a little bit more indifferent. So one species is benefiting and then the other one, well, maybe it is a little bit indifferent. And we call that commensalism. Commensalism. And once again, there's many examples of commensalism. This right here is a picture of bacteria living on your skin."}, {"video_title": "Interactions between populations    Ecology   Khan Academy.mp3", "Sentence": "And we call that commensalism. Commensalism. And once again, there's many examples of commensalism. This right here is a picture of bacteria living on your skin. And you do have bacteria living on your skin right now. Except, it's actually, well, oftentimes it's a good thing. Sometimes it's mutualism, that it's providing protection from harmful bacteria."}, {"video_title": "Interactions between populations    Ecology   Khan Academy.mp3", "Sentence": "This right here is a picture of bacteria living on your skin. And you do have bacteria living on your skin right now. Except, it's actually, well, oftentimes it's a good thing. Sometimes it's mutualism, that it's providing protection from harmful bacteria. But sometimes the bacteria is surely benefiting. It's living off of nutrients on your skin. The skin is its habitat."}, {"video_title": "Interactions between populations    Ecology   Khan Academy.mp3", "Sentence": "Sometimes it's mutualism, that it's providing protection from harmful bacteria. But sometimes the bacteria is surely benefiting. It's living off of nutrients on your skin. The skin is its habitat. But oftentimes it doesn't really have an impact on you. Now commensalism, let me write this down. Commensalism, oftentimes the more that we study it and the more that we understand it, we realize that actually maybe the host actually is benefiting, in which it is mutualism."}, {"video_title": "Interactions between populations    Ecology   Khan Academy.mp3", "Sentence": "The skin is its habitat. But oftentimes it doesn't really have an impact on you. Now commensalism, let me write this down. Commensalism, oftentimes the more that we study it and the more that we understand it, we realize that actually maybe the host actually is benefiting, in which it is mutualism. Or maybe the host actually is getting hurt, in which case it is parasitism. So oftentimes commensalism isn't completely neutral for the host. It could go either way."}, {"video_title": "Interactions between populations    Ecology   Khan Academy.mp3", "Sentence": "Commensalism, oftentimes the more that we study it and the more that we understand it, we realize that actually maybe the host actually is benefiting, in which it is mutualism. Or maybe the host actually is getting hurt, in which case it is parasitism. So oftentimes commensalism isn't completely neutral for the host. It could go either way. And so these are all the different types of interactions. So I encourage you, look around you, look at the world around you. And don't just limit yourself to animals."}, {"video_title": "Interactions between populations    Ecology   Khan Academy.mp3", "Sentence": "It could go either way. And so these are all the different types of interactions. So I encourage you, look around you, look at the world around you. And don't just limit yourself to animals. Think about bacteria. Think about plants. And think about, within a habitat, what are all of the different interspecies interactions and how you might wanna classify them."}, {"video_title": "How Did All Dinosaurs Except Birds Go Extinct.mp3", "Sentence": "In fact, that there's no doubt that at the time that dinosaurs went extinct, a large meteorite or asteroid hit the planet somewhere off the Yucatan Peninsula in Mexico. However, directly tying this event to the disappearance of the terrestrial fauna is very difficult. And that's just because our sample is so small. There's only a couple of places in the world where both dinosaur fossils as well as evidence of the impact are preserved. Both of those are in western North America. So we don't know whether it was an instantaneous event. We don't know whether the dinosaurs in the southern hemisphere held on for millions of years afterwards."}, {"video_title": "How Did All Dinosaurs Except Birds Go Extinct.mp3", "Sentence": "There's only a couple of places in the world where both dinosaur fossils as well as evidence of the impact are preserved. Both of those are in western North America. So we don't know whether it was an instantaneous event. We don't know whether the dinosaurs in the southern hemisphere held on for millions of years afterwards. We just don't have the record to be able to determine that. One thing we do know, though, is that certainly that the non-bird dinosaurs appear to be becoming more and more rare, less common as you approach the time when the meteorite hit about 65.4 million years ago. So that it's not like everything was going great and then you just had this massive cataclysmic event and everything disappeared."}, {"video_title": "How Did All Dinosaurs Except Birds Go Extinct.mp3", "Sentence": "We don't know whether the dinosaurs in the southern hemisphere held on for millions of years afterwards. We just don't have the record to be able to determine that. One thing we do know, though, is that certainly that the non-bird dinosaurs appear to be becoming more and more rare, less common as you approach the time when the meteorite hit about 65.4 million years ago. So that it's not like everything was going great and then you just had this massive cataclysmic event and everything disappeared. We know that stuff was changing, stuff was changing quickly. At the same time, there was a huge amount of volcanic activity, especially from places in western India. And interestingly enough, this coincides with around the time of the asteroid impact."}, {"video_title": "How Did All Dinosaurs Except Birds Go Extinct.mp3", "Sentence": "So that it's not like everything was going great and then you just had this massive cataclysmic event and everything disappeared. We know that stuff was changing, stuff was changing quickly. At the same time, there was a huge amount of volcanic activity, especially from places in western India. And interestingly enough, this coincides with around the time of the asteroid impact. So many paleontologists feel that it was a combination of factors, maybe both asteroids and volcanoes, that did the non-bird dinosaurs in. And I should emphasize, not just the non-avian or non-bird dinosaurs, but many, many other animals and plants. In fact, we estimate that maybe as much as 75% of all the species that lived on the earth at that time went extinct during this very dramatic event."}, {"video_title": "Loss of cell cycle control in cancer   Cells   MCAT   Khan Academy.mp3", "Sentence": "So control, control of the cell cycle occurs on a higher level with a couple of key proteins in addition to RB. One of the main proteins we talk about that regulate on a very high level is P53. It's even got a nickname. It's the guardian of the genome, the guardian of the genome. It's so important actually that Science Magazine called it the molecule of the year in 1993. Theobromine, the main molecule that's in chocolate hasn't even gotten this honor yet. So it shows you how important P53 is."}, {"video_title": "Loss of cell cycle control in cancer   Cells   MCAT   Khan Academy.mp3", "Sentence": "It's the guardian of the genome, the guardian of the genome. It's so important actually that Science Magazine called it the molecule of the year in 1993. Theobromine, the main molecule that's in chocolate hasn't even gotten this honor yet. So it shows you how important P53 is. It's more important than chocolate. P53 will bind DNA directly to produce proteins that block the progression of the cell cycle. One of those proteins include P21."}, {"video_title": "Loss of cell cycle control in cancer   Cells   MCAT   Khan Academy.mp3", "Sentence": "So it shows you how important P53 is. It's more important than chocolate. P53 will bind DNA directly to produce proteins that block the progression of the cell cycle. One of those proteins include P21. P21 will function to inhibit CDK. And so the CDK will not be able to activate DNA replication or activate mitosis. RB is another protein that's associated with the function of P53."}, {"video_title": "Loss of cell cycle control in cancer   Cells   MCAT   Khan Academy.mp3", "Sentence": "One of those proteins include P21. P21 will function to inhibit CDK. And so the CDK will not be able to activate DNA replication or activate mitosis. RB is another protein that's associated with the function of P53. And these proteins are considered tumor suppressor genes. So RB is a protein that's produced from a tumor suppressor gene just like P53. So I'll write that down over here."}, {"video_title": "Loss of cell cycle control in cancer   Cells   MCAT   Khan Academy.mp3", "Sentence": "RB is another protein that's associated with the function of P53. And these proteins are considered tumor suppressor genes. So RB is a protein that's produced from a tumor suppressor gene just like P53. So I'll write that down over here. These proteins are considered tumor suppressor genes. Tumor suppressor genes. They're made from tumor suppressor genes, I should rather say."}, {"video_title": "Loss of cell cycle control in cancer   Cells   MCAT   Khan Academy.mp3", "Sentence": "So I'll write that down over here. These proteins are considered tumor suppressor genes. Tumor suppressor genes. They're made from tumor suppressor genes, I should rather say. These proteins are made from tumor suppressor genes, which are important to have because if they're defected or if they have a mutation in them that makes them have loss of function, so that's an important term, defected or if they have a loss of function, loss of function, what ends up happening is that you tend to get, you tend to get cancer. Cancer, which I think you and I can both agree is not a good thing to have. So it's very important to have tumor suppressor genes."}, {"video_title": "Loss of cell cycle control in cancer   Cells   MCAT   Khan Academy.mp3", "Sentence": "They're made from tumor suppressor genes, I should rather say. These proteins are made from tumor suppressor genes, which are important to have because if they're defected or if they have a mutation in them that makes them have loss of function, so that's an important term, defected or if they have a loss of function, loss of function, what ends up happening is that you tend to get, you tend to get cancer. Cancer, which I think you and I can both agree is not a good thing to have. So it's very important to have tumor suppressor genes. And to illustrate how important that is, if you look at P53, greater than 50% of tumors have a defect in P53. RB got its name because a defect in RB would lead to a tumor of the eye known as retinoblastoma, which is why these two proteins are considered tumor suppressor genes. P21 is very unusual in that it doesn't actually lead to cancer when it's defected."}, {"video_title": "Loss of cell cycle control in cancer   Cells   MCAT   Khan Academy.mp3", "Sentence": "So it's very important to have tumor suppressor genes. And to illustrate how important that is, if you look at P53, greater than 50% of tumors have a defect in P53. RB got its name because a defect in RB would lead to a tumor of the eye known as retinoblastoma, which is why these two proteins are considered tumor suppressor genes. P21 is very unusual in that it doesn't actually lead to cancer when it's defected. Instead, scientists have found that mice, mice that are without P21 have the ability to regenerate their limbs. How weird is that? P21 lack causes the ability to regenerate their limbs, their arms and legs."}, {"video_title": "Loss of cell cycle control in cancer   Cells   MCAT   Khan Academy.mp3", "Sentence": "P21 is very unusual in that it doesn't actually lead to cancer when it's defected. Instead, scientists have found that mice, mice that are without P21 have the ability to regenerate their limbs. How weird is that? P21 lack causes the ability to regenerate their limbs, their arms and legs. So we're all still trying to figure out exactly how some of these key proteins work. But it's important to understand that tumor suppressor genes are essential for making sure that we regulate the cell cycle so we don't just go to the divide, divide, divide phase. We wanna make sure that we divide when it's appropriate, when a cell is ready to, or if it's even a cell that's supposed to divide in the first place."}, {"video_title": "Origins of life    Biology   Khan Academy.mp3", "Sentence": "We have many videos on Khan Academy on things like evolution, natural selection. We think we have a fairly solid understanding of how life can evolve to give us the variety, the diversity, and the complexity that we've seen around us but it still leaves unanswered a very fundamental question and this might be the biggest question known to us and that is the origins of life. How did life first emerge, at least on Earth, and that even starts to lead to other questions about is there life outside of this planet and what could it be like? And so let's start with what we actually know and I'm gonna start with a timeline. So let's go one billion years ago, let's go two billion years ago, three billion years ago, four billion years ago. So this is now. And once again, we're talking about a billion years ago."}, {"video_title": "Origins of life    Biology   Khan Academy.mp3", "Sentence": "And so let's start with what we actually know and I'm gonna start with a timeline. So let's go one billion years ago, let's go two billion years ago, three billion years ago, four billion years ago. So this is now. And once again, we're talking about a billion years ago. You'll sometimes see the abbreviation BYA, billion years ago, which is an unfathomable amount of time going into the past. But we know that Earth, along with the rest of the solar system, was formed around 4.6, 4.6 billion years ago. So that's when Earth was formed."}, {"video_title": "Origins of life    Biology   Khan Academy.mp3", "Sentence": "And once again, we're talking about a billion years ago. You'll sometimes see the abbreviation BYA, billion years ago, which is an unfathomable amount of time going into the past. But we know that Earth, along with the rest of the solar system, was formed around 4.6, 4.6 billion years ago. So that's when Earth was formed. And right at 4.6, or even, you know, you wait a casual 100 million years after that, 4.5 billion years ago, we believe that Earth wasn't very suitable for even very simple life to form. And that's because the solar system was a crazy place. You had collisions of all scales happening all of the time."}, {"video_title": "Origins of life    Biology   Khan Academy.mp3", "Sentence": "So that's when Earth was formed. And right at 4.6, or even, you know, you wait a casual 100 million years after that, 4.5 billion years ago, we believe that Earth wasn't very suitable for even very simple life to form. And that's because the solar system was a crazy place. You had collisions of all scales happening all of the time. The moon itself was formed from the collision of two planet-sized objects. One, kind of, you call it the proto-Earth and another planet-sized object, and they collided and then they started to spin around and one part became the moon, it was tidally linked with the Earth. But you can imagine, that's not an environment where it would be easy for life to form."}, {"video_title": "Origins of life    Biology   Khan Academy.mp3", "Sentence": "You had collisions of all scales happening all of the time. The moon itself was formed from the collision of two planet-sized objects. One, kind of, you call it the proto-Earth and another planet-sized object, and they collided and then they started to spin around and one part became the moon, it was tidally linked with the Earth. But you can imagine, that's not an environment where it would be easy for life to form. And even once the moon was formed, you had a heavy bombardment of things in the solar system. The solar system was a messy place. It took a long time for the stability that we now observe out there."}, {"video_title": "Origins of life    Biology   Khan Academy.mp3", "Sentence": "But you can imagine, that's not an environment where it would be easy for life to form. And even once the moon was formed, you had a heavy bombardment of things in the solar system. The solar system was a messy place. It took a long time for the stability that we now observe out there. And so that continued, we believe, until about 3.9 billion years ago, which is the earliest that we currently think that Earth might have been suitable for life. Before that, there might have been pockets where the bombardment stops and maybe some type of primitive life might have formed, but then it would have gone away with the heavy bombardment, but who knows? Maybe they could have survived that somehow, but that's the current mainstream belief."}, {"video_title": "Origins of life    Biology   Khan Academy.mp3", "Sentence": "It took a long time for the stability that we now observe out there. And so that continued, we believe, until about 3.9 billion years ago, which is the earliest that we currently think that Earth might have been suitable for life. Before that, there might have been pockets where the bombardment stops and maybe some type of primitive life might have formed, but then it would have gone away with the heavy bombardment, but who knows? Maybe they could have survived that somehow, but that's the current mainstream belief. The other thing we know is that we see fossil evidence for life 3.5 billion years ago. And these are stromatolites, this fossil evidence, microorganisms, they form these structures that actually continue to be formed today, these types of structures continue to be formed today. And although it might not feel like microorganisms are complex life, when you think about what has to happen within a microorganism, they are actually incredibly complex, especially if you compare them to very simple non-living organisms."}, {"video_title": "Origins of life    Biology   Khan Academy.mp3", "Sentence": "Maybe they could have survived that somehow, but that's the current mainstream belief. The other thing we know is that we see fossil evidence for life 3.5 billion years ago. And these are stromatolites, this fossil evidence, microorganisms, they form these structures that actually continue to be formed today, these types of structures continue to be formed today. And although it might not feel like microorganisms are complex life, when you think about what has to happen within a microorganism, they are actually incredibly complex, especially if you compare them to very simple non-living organisms. So our current belief is, well, some place in this region, life must have arisen on Earth. But that still doesn't, even if we were able to answer that question, oh, it was exactly 3.7 billion years ago was the first time that some RNA decided to, well, not decided, or ended up getting the right confirmation so it could replicate itself in some way, even if we know that date, it still leaves unanswered maybe the more interesting question, which is the how. The how is really, at least to me, more interesting than the when."}, {"video_title": "Origins of life    Biology   Khan Academy.mp3", "Sentence": "And although it might not feel like microorganisms are complex life, when you think about what has to happen within a microorganism, they are actually incredibly complex, especially if you compare them to very simple non-living organisms. So our current belief is, well, some place in this region, life must have arisen on Earth. But that still doesn't, even if we were able to answer that question, oh, it was exactly 3.7 billion years ago was the first time that some RNA decided to, well, not decided, or ended up getting the right confirmation so it could replicate itself in some way, even if we know that date, it still leaves unanswered maybe the more interesting question, which is the how. The how is really, at least to me, more interesting than the when. And to the how question, there's a couple of layers on it. The first is, well, let's just start with the most simple molecules that we would have expected to find on early Earth. Here's some examples of it right over here."}, {"video_title": "Origins of life    Biology   Khan Academy.mp3", "Sentence": "The how is really, at least to me, more interesting than the when. And to the how question, there's a couple of layers on it. The first is, well, let's just start with the most simple molecules that we would have expected to find on early Earth. Here's some examples of it right over here. This is H2O, or more commonly known as water. Right over here is CO2, more commonly known as carbon, that's a little hard to see, let me do a lighter color. So we have carbon dioxide right over here."}, {"video_title": "Origins of life    Biology   Khan Academy.mp3", "Sentence": "Here's some examples of it right over here. This is H2O, or more commonly known as water. Right over here is CO2, more commonly known as carbon, that's a little hard to see, let me do a lighter color. So we have carbon dioxide right over here. Here we have molecular nitrogen, you have some ammonia, you have some phosphate. These are, and many other of the elements that we see on Earth today, they might have been available in that early Earth, but how do they form, at least even the next step up, which is the slightly more complex, or actually a good bit more complex, organic molecules. And when people talk about organic molecules, they might be talking about things like this."}, {"video_title": "Origins of life    Biology   Khan Academy.mp3", "Sentence": "So we have carbon dioxide right over here. Here we have molecular nitrogen, you have some ammonia, you have some phosphate. These are, and many other of the elements that we see on Earth today, they might have been available in that early Earth, but how do they form, at least even the next step up, which is the slightly more complex, or actually a good bit more complex, organic molecules. And when people talk about organic molecules, they might be talking about things like this. These are amino acids. These are the building blocks of proteins. Amino acids, you see over here, nucleotides."}, {"video_title": "Origins of life    Biology   Khan Academy.mp3", "Sentence": "And when people talk about organic molecules, they might be talking about things like this. These are amino acids. These are the building blocks of proteins. Amino acids, you see over here, nucleotides. These are the building blocks of RNA, DNA, other things. And so the first question is, and these aren't the only simple organic molecules, you could think about sugars, and all sorts of other things. But the question is, is it realistic?"}, {"video_title": "Origins of life    Biology   Khan Academy.mp3", "Sentence": "Amino acids, you see over here, nucleotides. These are the building blocks of RNA, DNA, other things. And so the first question is, and these aren't the only simple organic molecules, you could think about sugars, and all sorts of other things. But the question is, is it realistic? Do we at least understand how we can go from these very simple molecules up here to these more complex, often called organic molecules? And the simple answer is we now have a lot of evidence that this is doable, that you can go from these things to these things abiotically, without the presence of life. You'll hear that word abiotic a lot."}, {"video_title": "Origins of life    Biology   Khan Academy.mp3", "Sentence": "But the question is, is it realistic? Do we at least understand how we can go from these very simple molecules up here to these more complex, often called organic molecules? And the simple answer is we now have a lot of evidence that this is doable, that you can go from these things to these things abiotically, without the presence of life. You'll hear that word abiotic a lot. Think about it, antibiotic, you're killing life, you're killing bacteria, abiotic, that is without life. And the points of evidence that we now have are, we believe, and we've seen evidence, that there's amino acids and organic molecules related to them on comets, meteorites, on other planets, that they formed spontaneously in space, once again, without the presence of life there. We've even been able to form amino acids and other molecules like this from these more simple elements in the laboratory."}, {"video_title": "Origins of life    Biology   Khan Academy.mp3", "Sentence": "You'll hear that word abiotic a lot. Think about it, antibiotic, you're killing life, you're killing bacteria, abiotic, that is without life. And the points of evidence that we now have are, we believe, and we've seen evidence, that there's amino acids and organic molecules related to them on comets, meteorites, on other planets, that they formed spontaneously in space, once again, without the presence of life there. We've even been able to form amino acids and other molecules like this from these more simple elements in the laboratory. The most famous experiment there is the Miller and Urey experiment. This was in the 1950s, where they were able to show, with some energy, they provided a spark. You could imagine that in the early Earth, it could have been from lightning."}, {"video_title": "Origins of life    Biology   Khan Academy.mp3", "Sentence": "We've even been able to form amino acids and other molecules like this from these more simple elements in the laboratory. The most famous experiment there is the Miller and Urey experiment. This was in the 1950s, where they were able to show, with some energy, they provided a spark. You could imagine that in the early Earth, it could have been from lightning. And they tried to set up a mix of gases that they believed was similar to the atmospheric mix in the early Earth, which didn't have much oxygen in the atmosphere then. We needed life to actually start to produce some of that oxygen. And even though today we think that they probably didn't have the mix of gases right, they did do something significant."}, {"video_title": "Origins of life    Biology   Khan Academy.mp3", "Sentence": "You could imagine that in the early Earth, it could have been from lightning. And they tried to set up a mix of gases that they believed was similar to the atmospheric mix in the early Earth, which didn't have much oxygen in the atmosphere then. We needed life to actually start to produce some of that oxygen. And even though today we think that they probably didn't have the mix of gases right, they did do something significant. They were able to show that with that mix of gases, at least they thought were in that atmosphere, and some energy being added to that system, that they were able to form some of these organic molecules. So we should feel pretty good that at least this first step is doable. Now the next question is, well, these organic molecules by themselves, that's not life."}, {"video_title": "Origins of life    Biology   Khan Academy.mp3", "Sentence": "And even though today we think that they probably didn't have the mix of gases right, they did do something significant. They were able to show that with that mix of gases, at least they thought were in that atmosphere, and some energy being added to that system, that they were able to form some of these organic molecules. So we should feel pretty good that at least this first step is doable. Now the next question is, well, these organic molecules by themselves, that's not life. In fact, these aren't even the most complex molecules that are, we believe, essential for life. Proteins are where things start to get really interesting. And a protein, a protein, proteins are one of the places."}, {"video_title": "Origins of life    Biology   Khan Academy.mp3", "Sentence": "Now the next question is, well, these organic molecules by themselves, that's not life. In fact, these aren't even the most complex molecules that are, we believe, essential for life. Proteins are where things start to get really interesting. And a protein, a protein, proteins are one of the places. A protein might have thousands of amino acids, thousands of amino, amino acids. Things like DNA and RNA, also we believe essential for life, or at least life as we know it, could be made up of tens of millions of nucleotides for one DNA molecule. So for example, this is just a small part of a DNA molecule, but you can already see much, much more complex than what we see over here."}, {"video_title": "Origins of life    Biology   Khan Academy.mp3", "Sentence": "And a protein, a protein, proteins are one of the places. A protein might have thousands of amino acids, thousands of amino, amino acids. Things like DNA and RNA, also we believe essential for life, or at least life as we know it, could be made up of tens of millions of nucleotides for one DNA molecule. So for example, this is just a small part of a DNA molecule, but you can already see much, much more complex than what we see over here. And there too, we have evidence that you can go from the amino acids to the proteins, or you can go from the nucleotides to the DNA without the presence of life, that these things can happen spontaneously if you have the right context, the right energy available. Some people believe, or it's been observed, that if you have the right surfaces, that these molecules can be organized in the right way to form these more complex things. Now I know what you're thinking, all right, proteins are really cool, DNA, RNA is really cool, but then how does that become life?"}, {"video_title": "Origins of life    Biology   Khan Academy.mp3", "Sentence": "So for example, this is just a small part of a DNA molecule, but you can already see much, much more complex than what we see over here. And there too, we have evidence that you can go from the amino acids to the proteins, or you can go from the nucleotides to the DNA without the presence of life, that these things can happen spontaneously if you have the right context, the right energy available. Some people believe, or it's been observed, that if you have the right surfaces, that these molecules can be organized in the right way to form these more complex things. Now I know what you're thinking, all right, proteins are really cool, DNA, RNA is really cool, but then how does that become life? At what point would we start carrying around, well that was a proto-life form. And this is where we really get into the area of the unknown because we don't know. And there's a couple of hypotheses out there."}, {"video_title": "Origins of life    Biology   Khan Academy.mp3", "Sentence": "Now I know what you're thinking, all right, proteins are really cool, DNA, RNA is really cool, but then how does that become life? At what point would we start carrying around, well that was a proto-life form. And this is where we really get into the area of the unknown because we don't know. And there's a couple of hypotheses out there. One of them is called the RNA world hypothesis. I'll write that down, RNA world hypothesis. And this is the idea that the first proto-life was self-replicating RNA molecules."}, {"video_title": "Origins of life    Biology   Khan Academy.mp3", "Sentence": "And there's a couple of hypotheses out there. One of them is called the RNA world hypothesis. I'll write that down, RNA world hypothesis. And this is the idea that the first proto-life was self-replicating RNA molecules. And the reason why people tend to focus in on RNA a little bit more than DNA is that even in cells today, RNA doesn't just store information, it can actually play a role as a catalyst when you think about things like tRNA and you think about ribosomal RNA. And so maybe some of that first proto-life was RNA, that information that replicated itself and catalyzed the replication of itself. Maybe it somehow got organized into membrane-bound structures so it could separate, so you had environments that were separated from the outside world."}, {"video_title": "Origins of life    Biology   Khan Academy.mp3", "Sentence": "And this is the idea that the first proto-life was self-replicating RNA molecules. And the reason why people tend to focus in on RNA a little bit more than DNA is that even in cells today, RNA doesn't just store information, it can actually play a role as a catalyst when you think about things like tRNA and you think about ribosomal RNA. And so maybe some of that first proto-life was RNA, that information that replicated itself and catalyzed the replication of itself. Maybe it somehow got organized into membrane-bound structures so it could separate, so you had environments that were separated from the outside world. But the simple answer is we don't know. Another mainstream hypothesis is the metabolism first hypothesis. Metabolism, metabolism first."}, {"video_title": "Origins of life    Biology   Khan Academy.mp3", "Sentence": "Maybe it somehow got organized into membrane-bound structures so it could separate, so you had environments that were separated from the outside world. But the simple answer is we don't know. Another mainstream hypothesis is the metabolism first hypothesis. Metabolism, metabolism first. And this is the idea that a lot of basic pathways that you might study in say a biochemistry book, that these were kind of first just happening in, well, all of this could have been happening in this primordial soup where you had these organic molecules and in the right conditions, maybe around heat vents and whatever else. But the metabolism first is that some of these mechanisms that we now study in biochemistry, these might have happened outside of a cell or outside of life and they just kept creating more and more complexity. But at some point, these things started happening in kind of self-organizing membrane-bound structures."}, {"video_title": "Origins of life    Biology   Khan Academy.mp3", "Sentence": "Metabolism, metabolism first. And this is the idea that a lot of basic pathways that you might study in say a biochemistry book, that these were kind of first just happening in, well, all of this could have been happening in this primordial soup where you had these organic molecules and in the right conditions, maybe around heat vents and whatever else. But the metabolism first is that some of these mechanisms that we now study in biochemistry, these might have happened outside of a cell or outside of life and they just kept creating more and more complexity. But at some point, these things started happening in kind of self-organizing membrane-bound structures. Maybe there's some kind of combination of the two. The simple answer is we just don't know. But there's some fascinating clues even if we observe current biology."}, {"video_title": "Animal communication   Individuals and Society   MCAT   Khan Academy.mp3", "Sentence": "So, first of all, we rely on language. So, we use it to communicate our ideas, thoughts, and feelings, and also to respond to the ideas, thoughts, and feelings of others. We also use a bunch of non-verbal cues. So, we smile when we're happy, we frown when we're sad, we can tell if the people around us are anxious or angry. And we also use visual cues. So, if I painted every room in my house black and blasted metallic all day, I would be sending out different signals, different cues about myself, than if I was to paint every room in my house pink and cover everything in posters of ballerinas and unicorns. And other animals, besides humans, have ways of communicating as well, maybe not with language per se, but with lots of different non-verbal cues and visual cues, as well as many other types of communication that aren't used by humans."}, {"video_title": "Animal communication   Individuals and Society   MCAT   Khan Academy.mp3", "Sentence": "So, we smile when we're happy, we frown when we're sad, we can tell if the people around us are anxious or angry. And we also use visual cues. So, if I painted every room in my house black and blasted metallic all day, I would be sending out different signals, different cues about myself, than if I was to paint every room in my house pink and cover everything in posters of ballerinas and unicorns. And other animals, besides humans, have ways of communicating as well, maybe not with language per se, but with lots of different non-verbal cues and visual cues, as well as many other types of communication that aren't used by humans. And while we'll go over all of those different types of communications in a separate video, I wanted to take a little bit of time to talk about why animals communicate and why this is necessary. So, one question we might want to ask is, who are animals communicating with? So, some species of animals might use different types of vocalization to communicate with members of the same species."}, {"video_title": "Animal communication   Individuals and Society   MCAT   Khan Academy.mp3", "Sentence": "And other animals, besides humans, have ways of communicating as well, maybe not with language per se, but with lots of different non-verbal cues and visual cues, as well as many other types of communication that aren't used by humans. And while we'll go over all of those different types of communications in a separate video, I wanted to take a little bit of time to talk about why animals communicate and why this is necessary. So, one question we might want to ask is, who are animals communicating with? So, some species of animals might use different types of vocalization to communicate with members of the same species. But animals can also communicate with other animals that are not in their species. So, for example, some types of frogs use really bright colors to signal that they're toxic, which will let other animals know not to eat them. And of course, animals can also communicate with humans."}, {"video_title": "Animal communication   Individuals and Society   MCAT   Khan Academy.mp3", "Sentence": "So, some species of animals might use different types of vocalization to communicate with members of the same species. But animals can also communicate with other animals that are not in their species. So, for example, some types of frogs use really bright colors to signal that they're toxic, which will let other animals know not to eat them. And of course, animals can also communicate with humans. Every morning, my cats let me know when it's time for me to wake up and feed them, or at least when they feel that I should wake up and feed them. But there's also auto-communication. So, animals can also use communication to give information to themselves, and that's kind of a trickier one, but I think the best example might be bats and echolocation."}, {"video_title": "Animal communication   Individuals and Society   MCAT   Khan Academy.mp3", "Sentence": "And of course, animals can also communicate with humans. Every morning, my cats let me know when it's time for me to wake up and feed them, or at least when they feel that I should wake up and feed them. But there's also auto-communication. So, animals can also use communication to give information to themselves, and that's kind of a trickier one, but I think the best example might be bats and echolocation. So, bats send out a signal, and then when that signal bounces back, they're able to gain information about the things in their environment. All right, so animals can use communication to give information to themselves, to members of their same species, and also members of other species. But what type of information are these animals trying to convey?"}, {"video_title": "Animal communication   Individuals and Society   MCAT   Khan Academy.mp3", "Sentence": "So, animals can also use communication to give information to themselves, and that's kind of a trickier one, but I think the best example might be bats and echolocation. So, bats send out a signal, and then when that signal bounces back, they're able to gain information about the things in their environment. All right, so animals can use communication to give information to themselves, to members of their same species, and also members of other species. But what type of information are these animals trying to convey? What is the main function of animal communication? Well, the first one would be mating rituals. Animals can produce a multitude of signals as a way to attract the opposite sex."}, {"video_title": "Animal communication   Individuals and Society   MCAT   Khan Academy.mp3", "Sentence": "But what type of information are these animals trying to convey? What is the main function of animal communication? Well, the first one would be mating rituals. Animals can produce a multitude of signals as a way to attract the opposite sex. Some are really brightly colored, others do complicated dances, and some do specific verbal calls. Animals also use communication to proclaim ownership or territory, or to defend territory. So, basically, it's a way of telling other animals to back off."}, {"video_title": "Animal communication   Individuals and Society   MCAT   Khan Academy.mp3", "Sentence": "Animals can produce a multitude of signals as a way to attract the opposite sex. Some are really brightly colored, others do complicated dances, and some do specific verbal calls. Animals also use communication to proclaim ownership or territory, or to defend territory. So, basically, it's a way of telling other animals to back off. And I had birds as pets in my house when I was growing up, and my birds were extremely kind. They would sit on your shoulder, they would try to eat all of your food, and they were just generally really social. But when they laid eggs, they got really territorial."}, {"video_title": "Animal communication   Individuals and Society   MCAT   Khan Academy.mp3", "Sentence": "So, basically, it's a way of telling other animals to back off. And I had birds as pets in my house when I was growing up, and my birds were extremely kind. They would sit on your shoulder, they would try to eat all of your food, and they were just generally really social. But when they laid eggs, they got really territorial. I mean, they would basically try to take your finger off if you got too close to them. Another function of animal communication is food communication. So, signaling to other animals where they can find food."}, {"video_title": "Animal communication   Individuals and Society   MCAT   Khan Academy.mp3", "Sentence": "But when they laid eggs, they got really territorial. I mean, they would basically try to take your finger off if you got too close to them. Another function of animal communication is food communication. So, signaling to other animals where they can find food. There's also alarm calls, or cases where animals will try to warn others about the presence of a predator. Animals can also use communication as a way to signal dominance and submission. So, for example, after dogs fight, they might adapt different stances to indicate who came out on top."}, {"video_title": "Animal communication   Individuals and Society   MCAT   Khan Academy.mp3", "Sentence": "So, signaling to other animals where they can find food. There's also alarm calls, or cases where animals will try to warn others about the presence of a predator. Animals can also use communication as a way to signal dominance and submission. So, for example, after dogs fight, they might adapt different stances to indicate who came out on top. But one thing I want to make sure to say before we actually go into really talking about all of the different ways that animals can use to communicate, is that I want to say that while it's clear that animals do communicate both with each other and with us as humans, we need to be really careful that we don't put too much thought into this. We need to be careful not to anthropomorphize, or attribute too many human characteristics to non-human animals. So we can try to interpret and try to ascribe meaning to the actions of animals, but we can never really be certain that we are correct because we can't really ask the animals what they mean."}, {"video_title": "Animal communication   Individuals and Society   MCAT   Khan Academy.mp3", "Sentence": "So, for example, after dogs fight, they might adapt different stances to indicate who came out on top. But one thing I want to make sure to say before we actually go into really talking about all of the different ways that animals can use to communicate, is that I want to say that while it's clear that animals do communicate both with each other and with us as humans, we need to be really careful that we don't put too much thought into this. We need to be careful not to anthropomorphize, or attribute too many human characteristics to non-human animals. So we can try to interpret and try to ascribe meaning to the actions of animals, but we can never really be certain that we are correct because we can't really ask the animals what they mean. So, my cats sleep with me at night, and they usually sit with me when I'm on the couch. And I would like to assume that it's because they love me and want to be with me, but it's possible that they're also only trying to keep physical contact with me because I produce a lot of body heat. And that it is that motivation, rather than love, that explains my cats' behaviors."}, {"video_title": "Cell membrane introduction   Cells   MCAT   Khan Academy.mp3", "Sentence": "Well, the reason is because we actually have a very important structure that prevents this from happening. This is what we call the cell membrane. The cell membrane is what's on the outside of a cell. So if we have a very basic picture of a cell here with a little nucleus on the inside, this pink outside layer is what we call the cell membrane. The cell membrane can protect our cell from the outside environment. And it can determine what can enter and leave our cell. This is a property that we call semi-permeability."}, {"video_title": "Cell membrane introduction   Cells   MCAT   Khan Academy.mp3", "Sentence": "So if we have a very basic picture of a cell here with a little nucleus on the inside, this pink outside layer is what we call the cell membrane. The cell membrane can protect our cell from the outside environment. And it can determine what can enter and leave our cell. This is a property that we call semi-permeability. It is somewhat permeable. Some things can enter, while other things cannot. So since this is such an important part of our cell, in fact, it's one of the reasons why we can actually survive in the world."}, {"video_title": "Cell membrane introduction   Cells   MCAT   Khan Academy.mp3", "Sentence": "This is a property that we call semi-permeability. It is somewhat permeable. Some things can enter, while other things cannot. So since this is such an important part of our cell, in fact, it's one of the reasons why we can actually survive in the world. So what actually makes up this structure? Well, the main building block of a cell membrane are what we call phospholipids. There are other substances that make up our cell membrane."}, {"video_title": "Cell membrane introduction   Cells   MCAT   Khan Academy.mp3", "Sentence": "So since this is such an important part of our cell, in fact, it's one of the reasons why we can actually survive in the world. So what actually makes up this structure? Well, the main building block of a cell membrane are what we call phospholipids. There are other substances that make up our cell membrane. But the most important building block are phospholipids. And so phospholipids have three major components. The first is a phosphate head group."}, {"video_title": "Cell membrane introduction   Cells   MCAT   Khan Academy.mp3", "Sentence": "There are other substances that make up our cell membrane. But the most important building block are phospholipids. And so phospholipids have three major components. The first is a phosphate head group. The second is a glycerol backbone. And the third are two fatty acid tails. So the way we draw this is we give the phosphate head group kind of like a head."}, {"video_title": "Cell membrane introduction   Cells   MCAT   Khan Academy.mp3", "Sentence": "The first is a phosphate head group. The second is a glycerol backbone. And the third are two fatty acid tails. So the way we draw this is we give the phosphate head group kind of like a head. It's a circle. And two fatty acid tails hang down from it, kind of like strings on a balloon. So the way I kind of remember this is a phospholipid looks like a balloon, but with two strings."}, {"video_title": "Cell membrane introduction   Cells   MCAT   Khan Academy.mp3", "Sentence": "So the way we draw this is we give the phosphate head group kind of like a head. It's a circle. And two fatty acid tails hang down from it, kind of like strings on a balloon. So the way I kind of remember this is a phospholipid looks like a balloon, but with two strings. Now, where's our glycerol backbone? Well, our glycerol backbone is actually what it sounds like. It's what holds the fatty acid tails to our phosphate head."}, {"video_title": "Cell membrane introduction   Cells   MCAT   Khan Academy.mp3", "Sentence": "So the way I kind of remember this is a phospholipid looks like a balloon, but with two strings. Now, where's our glycerol backbone? Well, our glycerol backbone is actually what it sounds like. It's what holds the fatty acid tails to our phosphate head. It's the backbone of this molecule. So it's usually not drawn in the picture. But just remember that it's there."}, {"video_title": "Cell membrane introduction   Cells   MCAT   Khan Academy.mp3", "Sentence": "It's what holds the fatty acid tails to our phosphate head. It's the backbone of this molecule. So it's usually not drawn in the picture. But just remember that it's there. And it holds our two fatty acid tails to our phosphate head group. So this structure actually has a very interesting property. Up here, this head group is actually hydrophilic, or polar."}, {"video_title": "Cell membrane introduction   Cells   MCAT   Khan Academy.mp3", "Sentence": "But just remember that it's there. And it holds our two fatty acid tails to our phosphate head group. So this structure actually has a very interesting property. Up here, this head group is actually hydrophilic, or polar. So hydrophilic means that it's water loving. This phosphate head group will do whatever it can to get to water. It loves water."}, {"video_title": "Cell membrane introduction   Cells   MCAT   Khan Academy.mp3", "Sentence": "Up here, this head group is actually hydrophilic, or polar. So hydrophilic means that it's water loving. This phosphate head group will do whatever it can to get to water. It loves water. But these fatty acid tails, because they're very, very long carbon chains, this is hydrophobic. I remember hydrophobic because a phobic, or phobia, is fearing. So hydro is water."}, {"video_title": "Cell membrane introduction   Cells   MCAT   Khan Academy.mp3", "Sentence": "It loves water. But these fatty acid tails, because they're very, very long carbon chains, this is hydrophobic. I remember hydrophobic because a phobic, or phobia, is fearing. So hydro is water. So it's water fearing. These two fatty acids will do whatever it can to get away from water. A molecule that has both of these things together is what we call an anthropathic molecule."}, {"video_title": "Cell membrane introduction   Cells   MCAT   Khan Academy.mp3", "Sentence": "So hydro is water. So it's water fearing. These two fatty acids will do whatever it can to get away from water. A molecule that has both of these things together is what we call an anthropathic molecule. It means that the molecule has a hydrophobic section and a hydrophilic section. So in water, what would this do? So let's say we put a ton of these molecules in water."}, {"video_title": "Cell membrane introduction   Cells   MCAT   Khan Academy.mp3", "Sentence": "A molecule that has both of these things together is what we call an anthropathic molecule. It means that the molecule has a hydrophobic section and a hydrophilic section. So in water, what would this do? So let's say we put a ton of these molecules in water. Once in water, the hydrophobic heads want to be as close to water as possible. But the tails don't. So what will happen is these phosphate groups are going to cluster together, while the tails try to shield themselves away from water."}, {"video_title": "Cell membrane introduction   Cells   MCAT   Khan Academy.mp3", "Sentence": "So let's say we put a ton of these molecules in water. Once in water, the hydrophobic heads want to be as close to water as possible. But the tails don't. So what will happen is these phosphate groups are going to cluster together, while the tails try to shield themselves away from water. But since this is a substance that's in water, water is going to be down here too. So this will actually form a really unique structure. Because the fatty acid tails are going to start grouping like this."}, {"video_title": "Cell membrane introduction   Cells   MCAT   Khan Academy.mp3", "Sentence": "So what will happen is these phosphate groups are going to cluster together, while the tails try to shield themselves away from water. But since this is a substance that's in water, water is going to be down here too. So this will actually form a really unique structure. Because the fatty acid tails are going to start grouping like this. And the phospholipids are going to be kind of upside down, so that the phosphate head groups can be close to water, while this inside section can be hydrophobic and away from water. This is what we call a phospholipid bilayer. This is the basic structure of a cell membrane."}, {"video_title": "Cell membrane introduction   Cells   MCAT   Khan Academy.mp3", "Sentence": "Because the fatty acid tails are going to start grouping like this. And the phospholipids are going to be kind of upside down, so that the phosphate head groups can be close to water, while this inside section can be hydrophobic and away from water. This is what we call a phospholipid bilayer. This is the basic structure of a cell membrane. And like we mentioned, this inside section is going to be hydrophobic. So now we have this structure that looks kind of like this. We call this our phospholipid bilayer, or lipid bilayer for short."}, {"video_title": "Cell membrane introduction   Cells   MCAT   Khan Academy.mp3", "Sentence": "This is the basic structure of a cell membrane. And like we mentioned, this inside section is going to be hydrophobic. So now we have this structure that looks kind of like this. We call this our phospholipid bilayer, or lipid bilayer for short. But doesn't this section here also interact with water? How can this structure be like this if this section here still touches water? And we know that the fatty acid tails don't want to touch water."}, {"video_title": "Cell membrane introduction   Cells   MCAT   Khan Academy.mp3", "Sentence": "We call this our phospholipid bilayer, or lipid bilayer for short. But doesn't this section here also interact with water? How can this structure be like this if this section here still touches water? And we know that the fatty acid tails don't want to touch water. Well, in a cell in real life, what actually happens is we end up with the structure that forms a circle like this. Now this is a fairly crudely drawn picture. In a cell, this wall is actually pretty thin compared to the entire body."}, {"video_title": "Cell membrane introduction   Cells   MCAT   Khan Academy.mp3", "Sentence": "And we know that the fatty acid tails don't want to touch water. Well, in a cell in real life, what actually happens is we end up with the structure that forms a circle like this. Now this is a fairly crudely drawn picture. In a cell, this wall is actually pretty thin compared to the entire body. So you'll notice that this water here doesn't become a problem anymore. Because in our actual cells, water can be on the outside and on the inside. And no matter where this cell membrane touches water, it's always going to be the phosphate head groups that are hydrophilic, that are seeking out water."}, {"video_title": "Cell membrane introduction   Cells   MCAT   Khan Academy.mp3", "Sentence": "In a cell, this wall is actually pretty thin compared to the entire body. So you'll notice that this water here doesn't become a problem anymore. Because in our actual cells, water can be on the outside and on the inside. And no matter where this cell membrane touches water, it's always going to be the phosphate head groups that are hydrophilic, that are seeking out water. And inside the cell membrane, we actually have a hydrophobic section. So moving on to a new picture, we mentioned before that the cell membrane is semipermeable. And we're going to explore that a little bit more."}, {"video_title": "Cell membrane introduction   Cells   MCAT   Khan Academy.mp3", "Sentence": "And no matter where this cell membrane touches water, it's always going to be the phosphate head groups that are hydrophilic, that are seeking out water. And inside the cell membrane, we actually have a hydrophobic section. So moving on to a new picture, we mentioned before that the cell membrane is semipermeable. And we're going to explore that a little bit more. So I've taken the liberty of pre-drawing a very long picture of a cell membrane. So as we mentioned, the cell membrane is actually a sphere that surrounds our cell. For the sake of this lesson, we're going to draw it out in a straight line."}, {"video_title": "Cell membrane introduction   Cells   MCAT   Khan Academy.mp3", "Sentence": "And we're going to explore that a little bit more. So I've taken the liberty of pre-drawing a very long picture of a cell membrane. So as we mentioned, the cell membrane is actually a sphere that surrounds our cell. For the sake of this lesson, we're going to draw it out in a straight line. And we're going to say that this can be the outside environment, or the extracellular. And this can be the inside, or the intracellular. So you'll notice that the cell membrane has these phospholipids packed really closely together."}, {"video_title": "Cell membrane introduction   Cells   MCAT   Khan Academy.mp3", "Sentence": "For the sake of this lesson, we're going to draw it out in a straight line. And we're going to say that this can be the outside environment, or the extracellular. And this can be the inside, or the intracellular. So you'll notice that the cell membrane has these phospholipids packed really closely together. So usually, small molecules are what can pass through the cell. Another property of the cell membrane that we've discussed is that this inside section right here is really hydrophobic. So generally, small, nonpolar molecules can pass through our cell membrane."}, {"video_title": "Cell membrane introduction   Cells   MCAT   Khan Academy.mp3", "Sentence": "So you'll notice that the cell membrane has these phospholipids packed really closely together. So usually, small molecules are what can pass through the cell. Another property of the cell membrane that we've discussed is that this inside section right here is really hydrophobic. So generally, small, nonpolar molecules can pass through our cell membrane. This is what we call passive diffusion. So what is a good example of a small, nonpolar molecule? Well, the most common type of small, nonpolar molecule tend to be gases, things like O2, for example, or CO2."}, {"video_title": "Cell membrane introduction   Cells   MCAT   Khan Academy.mp3", "Sentence": "So generally, small, nonpolar molecules can pass through our cell membrane. This is what we call passive diffusion. So what is a good example of a small, nonpolar molecule? Well, the most common type of small, nonpolar molecule tend to be gases, things like O2, for example, or CO2. These are things that surround us every single day. And our cell, in a sense, breathes these molecules in and out of our cell. So gases can very easily pass through our cell membrane."}, {"video_title": "Cell membrane introduction   Cells   MCAT   Khan Academy.mp3", "Sentence": "Well, the most common type of small, nonpolar molecule tend to be gases, things like O2, for example, or CO2. These are things that surround us every single day. And our cell, in a sense, breathes these molecules in and out of our cell. So gases can very easily pass through our cell membrane. And it's very fast. They are small, and they are nonpolar. So what else does our cell interact with every single day?"}, {"video_title": "Cell membrane introduction   Cells   MCAT   Khan Academy.mp3", "Sentence": "So gases can very easily pass through our cell membrane. And it's very fast. They are small, and they are nonpolar. So what else does our cell interact with every single day? Well, the most common one is water. So water is actually a pretty small molecule, and it's polar. So something else that's similar to water is ethanol."}, {"video_title": "Cell membrane introduction   Cells   MCAT   Khan Academy.mp3", "Sentence": "So what else does our cell interact with every single day? Well, the most common one is water. So water is actually a pretty small molecule, and it's polar. So something else that's similar to water is ethanol. This is like alcohol that we can drink. So how do these interact with our cell membrane? Well, we said that the cell membrane likes small molecules."}, {"video_title": "Cell membrane introduction   Cells   MCAT   Khan Academy.mp3", "Sentence": "So something else that's similar to water is ethanol. This is like alcohol that we can drink. So how do these interact with our cell membrane? Well, we said that the cell membrane likes small molecules. So these can actually pass through our cell membrane. But our cell membrane prefers nonpolar molecules. So these are actually going to pass through really slowly."}, {"video_title": "Cell membrane introduction   Cells   MCAT   Khan Academy.mp3", "Sentence": "Well, we said that the cell membrane likes small molecules. So these can actually pass through our cell membrane. But our cell membrane prefers nonpolar molecules. So these are actually going to pass through really slowly. And they can pass through because they're so tiny that they can kind of sneak by, but pretty slowly because this very hydrophobic region is still not going to like having water in there. So if we have small polar molecules, what about something that is large but nonpolar, like benzene? Well, benzene can actually pass through our cell membrane."}, {"video_title": "Cell membrane introduction   Cells   MCAT   Khan Academy.mp3", "Sentence": "So these are actually going to pass through really slowly. And they can pass through because they're so tiny that they can kind of sneak by, but pretty slowly because this very hydrophobic region is still not going to like having water in there. So if we have small polar molecules, what about something that is large but nonpolar, like benzene? Well, benzene can actually pass through our cell membrane. Even though it's large, it's nonpolar. So it's going to get along really well with that hydrophobic region in our cell membrane. But it's going to pass very slowly."}, {"video_title": "Cell membrane introduction   Cells   MCAT   Khan Academy.mp3", "Sentence": "Well, benzene can actually pass through our cell membrane. Even though it's large, it's nonpolar. So it's going to get along really well with that hydrophobic region in our cell membrane. But it's going to pass very slowly. Now, as a little bit of a fun fact, benzene used to be used in labs for students and researchers to wash their hands. Scientists actually found out that benzene can pass through our cell membrane and cause harm to our cells. What about something that is large and polar?"}, {"video_title": "Cell membrane introduction   Cells   MCAT   Khan Academy.mp3", "Sentence": "But it's going to pass very slowly. Now, as a little bit of a fun fact, benzene used to be used in labs for students and researchers to wash their hands. Scientists actually found out that benzene can pass through our cell membrane and cause harm to our cells. What about something that is large and polar? Well, a molecule like this would be sugar or glucose. Glucose actually cannot pass through our cell. It's large and it's polar."}, {"video_title": "Cell membrane introduction   Cells   MCAT   Khan Academy.mp3", "Sentence": "What about something that is large and polar? Well, a molecule like this would be sugar or glucose. Glucose actually cannot pass through our cell. It's large and it's polar. It's the complete opposite of what the cell membrane allows to pass through the cell. So glucose will have to be absorbed by our cells through other means. But it cannot pass through the cell membrane."}, {"video_title": "Cell membrane introduction   Cells   MCAT   Khan Academy.mp3", "Sentence": "It's large and it's polar. It's the complete opposite of what the cell membrane allows to pass through the cell. So glucose will have to be absorbed by our cells through other means. But it cannot pass through the cell membrane. What about charged molecules? These are also all over the place. What's an example of a charged molecule?"}, {"video_title": "Cell membrane introduction   Cells   MCAT   Khan Academy.mp3", "Sentence": "But it cannot pass through the cell membrane. What about charged molecules? These are also all over the place. What's an example of a charged molecule? Well, something like a chloride ion, a sodium ion, or any sort of ion. Another pretty common charged molecule are actually amino acids. And since these are charged, they're so incredibly polar or charged that they also cannot pass through."}, {"video_title": "Cell membrane introduction   Cells   MCAT   Khan Academy.mp3", "Sentence": "What's an example of a charged molecule? Well, something like a chloride ion, a sodium ion, or any sort of ion. Another pretty common charged molecule are actually amino acids. And since these are charged, they're so incredibly polar or charged that they also cannot pass through. So in summary, our cell membrane protects our cells and determines what enters and leaves, a property that we call semipermeability. And this cell membrane is made up of a whole bunch of phospholipids put together. Since our cell membrane has a very large hydrophobic region, it prefers nonpolar molecules."}, {"video_title": "Organelles in eukaryotic cells   Cells   High school biology   Khan Academy (2).mp3", "Sentence": "What we're going to do in this video is give ourselves a little bit of a tour of eukaryotic cells. And the first place to start is just to remind ourselves what it means for a cell to be eukaryotic. It means that inside the cell, there are membrane-bound organelles. Now what does that mean? Well, you could view it as sub-compartments within the cell, membrane-bound organelles. And in this video in particular, we're going to highlight some of these membrane-bound organelles that make the cells eukaryotic. So let's just start with some of the ingredients that we know is true of all cells."}, {"video_title": "Organelles in eukaryotic cells   Cells   High school biology   Khan Academy (2).mp3", "Sentence": "Now what does that mean? Well, you could view it as sub-compartments within the cell, membrane-bound organelles. And in this video in particular, we're going to highlight some of these membrane-bound organelles that make the cells eukaryotic. So let's just start with some of the ingredients that we know is true of all cells. So you'll have your cellular membrane here, a little bit big so that we have a lot of space to draw things in. So this is our cellular membrane. I'll do a nice shading so you appreciate that it'll actually be three-dimensional."}, {"video_title": "Organelles in eukaryotic cells   Cells   High school biology   Khan Academy (2).mp3", "Sentence": "So let's just start with some of the ingredients that we know is true of all cells. So you'll have your cellular membrane here, a little bit big so that we have a lot of space to draw things in. So this is our cellular membrane. I'll do a nice shading so you appreciate that it'll actually be three-dimensional. We see so many slices of cells that sometimes we forget that they are more spherical or that they have three-dimensional shape to them. They're not all spherical. They can have different shapes."}, {"video_title": "Organelles in eukaryotic cells   Cells   High school biology   Khan Academy (2).mp3", "Sentence": "I'll do a nice shading so you appreciate that it'll actually be three-dimensional. We see so many slices of cells that sometimes we forget that they are more spherical or that they have three-dimensional shape to them. They're not all spherical. They can have different shapes. Now all cells, and there are some exceptions that we've talked about in previous videos, I should say most cells will have some genetic information in them in the form of DNA. So that is our DNA right over there. Now one of the key characteristics of a eukaryotic cell is that that genetic information is going to be inside a membrane-bound organelle."}, {"video_title": "Organelles in eukaryotic cells   Cells   High school biology   Khan Academy (2).mp3", "Sentence": "They can have different shapes. Now all cells, and there are some exceptions that we've talked about in previous videos, I should say most cells will have some genetic information in them in the form of DNA. So that is our DNA right over there. Now one of the key characteristics of a eukaryotic cell is that that genetic information is going to be inside a membrane-bound organelle. And that membrane-bound organelle or the membrane that binds or that surrounds the DNA here, that is the nuclear membrane. So let me draw the nuclear membrane right over here. And I'll put some shading in to appreciate that that also is going to be in three dimensions around the DNA."}, {"video_title": "Organelles in eukaryotic cells   Cells   High school biology   Khan Academy (2).mp3", "Sentence": "Now one of the key characteristics of a eukaryotic cell is that that genetic information is going to be inside a membrane-bound organelle. And that membrane-bound organelle or the membrane that binds or that surrounds the DNA here, that is the nuclear membrane. So let me draw the nuclear membrane right over here. And I'll put some shading in to appreciate that that also is going to be in three dimensions around the DNA. And so that is the first membrane-bound organelle that we're going to discuss, the nucleus. Now the nucleus, it turns out, is connected to another membrane-bound organelle. And we're gonna study this in future videos."}, {"video_title": "Organelles in eukaryotic cells   Cells   High school biology   Khan Academy (2).mp3", "Sentence": "And I'll put some shading in to appreciate that that also is going to be in three dimensions around the DNA. And so that is the first membrane-bound organelle that we're going to discuss, the nucleus. Now the nucleus, it turns out, is connected to another membrane-bound organelle. And we're gonna study this in future videos. What right here, I'm drawing holes or pores in the nuclear membrane. And those pores connect to something, it's a very fancy word, called the endoplasmic reticulum. And the endoplasmic reticulum is essentially these layers of these membranes."}, {"video_title": "Organelles in eukaryotic cells   Cells   High school biology   Khan Academy (2).mp3", "Sentence": "And we're gonna study this in future videos. What right here, I'm drawing holes or pores in the nuclear membrane. And those pores connect to something, it's a very fancy word, called the endoplasmic reticulum. And the endoplasmic reticulum is essentially these layers of these membranes. So I'm gonna do my best job at trying to draw an endoplasmic reticulum. Imagine extending from these pores, going into a space that has these, really these layered membranes that have a lot of surface area. And I'm not gonna go all the way around this nucleus, but in many cells, it will go around all the way around the nucleus."}, {"video_title": "Organelles in eukaryotic cells   Cells   High school biology   Khan Academy (2).mp3", "Sentence": "And the endoplasmic reticulum is essentially these layers of these membranes. So I'm gonna do my best job at trying to draw an endoplasmic reticulum. Imagine extending from these pores, going into a space that has these, really these layered membranes that have a lot of surface area. And I'm not gonna go all the way around this nucleus, but in many cells, it will go around all the way around the nucleus. And this right over here, and this is just a rough diagram, that is our endoplasmic, endoplasmic, not splasmic, endoplasmic, endoplasmic reticulum, which I've mentioned in previous videos would be an excellent name for a band. And what goes on in the endoplasmic reticulum is when you are in the process of taking that genetic information from DNA, and as we talk about in other videos, it gets transcribed into mRNA, so that mRNA is now containing that information. That mRNA will make its way out of that nuclear membrane through one of these pores, and then make its way to a ribosome that is attached to the membrane of the endoplasmic reticulum."}, {"video_title": "Organelles in eukaryotic cells   Cells   High school biology   Khan Academy (2).mp3", "Sentence": "And I'm not gonna go all the way around this nucleus, but in many cells, it will go around all the way around the nucleus. And this right over here, and this is just a rough diagram, that is our endoplasmic, endoplasmic, not splasmic, endoplasmic, endoplasmic reticulum, which I've mentioned in previous videos would be an excellent name for a band. And what goes on in the endoplasmic reticulum is when you are in the process of taking that genetic information from DNA, and as we talk about in other videos, it gets transcribed into mRNA, so that mRNA is now containing that information. That mRNA will make its way out of that nuclear membrane through one of these pores, and then make its way to a ribosome that is attached to the membrane of the endoplasmic reticulum. And so that's a ribosome there. I'm gonna do a bunch of ribosomes. And so, as we've talked about in previous videos, the ribosomes are really where you take that genetic information from that mRNA, and then you translate it into a protein."}, {"video_title": "Organelles in eukaryotic cells   Cells   High school biology   Khan Academy (2).mp3", "Sentence": "That mRNA will make its way out of that nuclear membrane through one of these pores, and then make its way to a ribosome that is attached to the membrane of the endoplasmic reticulum. And so that's a ribosome there. I'm gonna do a bunch of ribosomes. And so, as we've talked about in previous videos, the ribosomes are really where you take that genetic information from that mRNA, and then you translate it into a protein. So the ribosomes are the protein synthesis, so let me label that. So this right over here is a ribosome. And some ribosomes might be attached to the endoplasmic reticulum."}, {"video_title": "Organelles in eukaryotic cells   Cells   High school biology   Khan Academy (2).mp3", "Sentence": "And so, as we've talked about in previous videos, the ribosomes are really where you take that genetic information from that mRNA, and then you translate it into a protein. So the ribosomes are the protein synthesis, so let me label that. So this right over here is a ribosome. And some ribosomes might be attached to the endoplasmic reticulum. Some of them might just be floating out here in the cytoplasm, so that would be a free ribosome. Free ribosome. And even from the point of view of the endoplasmic reticulum, the parts of the endoplasmic reticulum where you have ribosomes attached, this is known as rough endoplasmic reticulum."}, {"video_title": "Organelles in eukaryotic cells   Cells   High school biology   Khan Academy (2).mp3", "Sentence": "And some ribosomes might be attached to the endoplasmic reticulum. Some of them might just be floating out here in the cytoplasm, so that would be a free ribosome. Free ribosome. And even from the point of view of the endoplasmic reticulum, the parts of the endoplasmic reticulum where you have ribosomes attached, this is known as rough endoplasmic reticulum. It's the ribosomes that are making them rough. It looks that way in a microscope. So I'll say rough ER for endoplasmic reticulum for short."}, {"video_title": "Organelles in eukaryotic cells   Cells   High school biology   Khan Academy (2).mp3", "Sentence": "And even from the point of view of the endoplasmic reticulum, the parts of the endoplasmic reticulum where you have ribosomes attached, this is known as rough endoplasmic reticulum. It's the ribosomes that are making them rough. It looks that way in a microscope. So I'll say rough ER for endoplasmic reticulum for short. And then you also have parts of the endoplasmic reticulum where you do not have ribosomes attached, and because that looks smooth through our microscope, it has been called, you can imagine, smooth endoplasmic reticulum. There are things known as Golgi bodies. Once again, another fascinating name."}, {"video_title": "Organelles in eukaryotic cells   Cells   High school biology   Khan Academy (2).mp3", "Sentence": "So I'll say rough ER for endoplasmic reticulum for short. And then you also have parts of the endoplasmic reticulum where you do not have ribosomes attached, and because that looks smooth through our microscope, it has been called, you can imagine, smooth endoplasmic reticulum. There are things known as Golgi bodies. Once again, another fascinating name. Gotta love these names in biology. That look kind of like an endoplasmic reticulum, but detached from the nuclear membrane. So let's say it's something like that."}, {"video_title": "Organelles in eukaryotic cells   Cells   High school biology   Khan Academy (2).mp3", "Sentence": "Once again, another fascinating name. Gotta love these names in biology. That look kind of like an endoplasmic reticulum, but detached from the nuclear membrane. So let's say it's something like that. That's my best drawing there. That's a Golgi body. And these are really good at packaging molecules, even proteins that might have just been produced, and packaging them so that they can be used outside of the cell, for example."}, {"video_title": "Organelles in eukaryotic cells   Cells   High school biology   Khan Academy (2).mp3", "Sentence": "So let's say it's something like that. That's my best drawing there. That's a Golgi body. And these are really good at packaging molecules, even proteins that might have just been produced, and packaging them so that they can be used outside of the cell, for example. So, and we'll go into detail in other videos where a protein might go to the Golgi body, get a little envelope around it, get some little processing going on, and then make its way outside of a cell. Now, another, and this is maybe one of the most famous membrane-bound organelles outside of the nucleus, is what's known as the powerhouse of the cell, and that is the mitochondria. And so I'll do this mitochondria in magenta because that's a nice, powerful color."}, {"video_title": "Organelles in eukaryotic cells   Cells   High school biology   Khan Academy (2).mp3", "Sentence": "And these are really good at packaging molecules, even proteins that might have just been produced, and packaging them so that they can be used outside of the cell, for example. So, and we'll go into detail in other videos where a protein might go to the Golgi body, get a little envelope around it, get some little processing going on, and then make its way outside of a cell. Now, another, and this is maybe one of the most famous membrane-bound organelles outside of the nucleus, is what's known as the powerhouse of the cell, and that is the mitochondria. And so I'll do this mitochondria in magenta because that's a nice, powerful color. So mitochondria, and I love mitochondria because it's fascinating how they even came to be. Mitochondria actually have their own DNA, and all of your mitochondrial DNA comes from your mother, and so that's actually very interesting for tracing maternal lineage. But mitochondria, this is where your, I'm gonna say, let's see what we can see inside of this."}, {"video_title": "Organelles in eukaryotic cells   Cells   High school biology   Khan Academy (2).mp3", "Sentence": "And so I'll do this mitochondria in magenta because that's a nice, powerful color. So mitochondria, and I love mitochondria because it's fascinating how they even came to be. Mitochondria actually have their own DNA, and all of your mitochondrial DNA comes from your mother, and so that's actually very interesting for tracing maternal lineage. But mitochondria, this is where your, I'm gonna say, let's see what we can see inside of this. This is where your ATP is produced. This is your mitochondria. It's really the powerhouse of the cell."}, {"video_title": "Organelles in eukaryotic cells   Cells   High school biology   Khan Academy (2).mp3", "Sentence": "But mitochondria, this is where your, I'm gonna say, let's see what we can see inside of this. This is where your ATP is produced. This is your mitochondria. It's really the powerhouse of the cell. What's interesting about mitochondria is evolutionary biologists believe that the ancestors of mitochondria, because mitochondria have their own DNA, they might have been independent organisms, independent cells, and at some point in our evolutionary past, they started living in symbiosis inside of what would be the ancestors of our cells, and then over time, they became so codependent that they started to replicate together, and mitochondria, in fact, became part of these eukaryotic cells. Now, if this eukaryotic cell was a plant cell or maybe an algae cell, you would have something called chloroplasts there. We don't have them, because we don't have photosynthesis, but this is a chloroplast, and if you could see inside, you could see the little thylakoid stacks right over here."}, {"video_title": "Organelles in eukaryotic cells   Cells   High school biology   Khan Academy (2).mp3", "Sentence": "It's really the powerhouse of the cell. What's interesting about mitochondria is evolutionary biologists believe that the ancestors of mitochondria, because mitochondria have their own DNA, they might have been independent organisms, independent cells, and at some point in our evolutionary past, they started living in symbiosis inside of what would be the ancestors of our cells, and then over time, they became so codependent that they started to replicate together, and mitochondria, in fact, became part of these eukaryotic cells. Now, if this eukaryotic cell was a plant cell or maybe an algae cell, you would have something called chloroplasts there. We don't have them, because we don't have photosynthesis, but this is a chloroplast, and if you could see inside, you could see the little thylakoid stacks right over here. You could see the little thylakoids if you could see inside, and so this right over here is a chloroplast, chloroplast, and this would be plants and algae. Animals do not have these, and these are where you have your photosynthesis take place, photosynthesis. Now, there's also some other membrane-bound organelles that are maybe less famous than the mitochondria or the chloroplast or, for sure, the nucleus, and that might be something like a vacuole, and in plants, vacuoles tend to be very big."}, {"video_title": "Organelles in eukaryotic cells   Cells   High school biology   Khan Academy (2).mp3", "Sentence": "We don't have them, because we don't have photosynthesis, but this is a chloroplast, and if you could see inside, you could see the little thylakoid stacks right over here. You could see the little thylakoids if you could see inside, and so this right over here is a chloroplast, chloroplast, and this would be plants and algae. Animals do not have these, and these are where you have your photosynthesis take place, photosynthesis. Now, there's also some other membrane-bound organelles that are maybe less famous than the mitochondria or the chloroplast or, for sure, the nucleus, and that might be something like a vacuole, and in plants, vacuoles tend to be very big. I could draw it, you know, this is three-dimensional, so I'll draw it on top of some of what I've drawn before, so if a vacuole right over here, this is a, and a plant can be a fairly significant compartment inside. In fact, it can even give structure to the plant itself because it is so big, and it contains water and enzymes. It's viewed as a kind of a storage compartment, but it can also contain enzymes that help digest things, that help break things down so that they can be used in some way, so that is a vacuole, and they don't just exist in plants."}, {"video_title": "Organelles in eukaryotic cells   Cells   High school biology   Khan Academy (2).mp3", "Sentence": "Now, there's also some other membrane-bound organelles that are maybe less famous than the mitochondria or the chloroplast or, for sure, the nucleus, and that might be something like a vacuole, and in plants, vacuoles tend to be very big. I could draw it, you know, this is three-dimensional, so I'll draw it on top of some of what I've drawn before, so if a vacuole right over here, this is a, and a plant can be a fairly significant compartment inside. In fact, it can even give structure to the plant itself because it is so big, and it contains water and enzymes. It's viewed as a kind of a storage compartment, but it can also contain enzymes that help digest things, that help break things down so that they can be used in some way, so that is a vacuole, and they don't just exist in plants. They can also exist in animal cells, but in plant cells, they tend to be, they can be very, very, very visible. Now, something that is somewhat related to some of the function that a vacuole plays that are most associated with animal cells, but now there's evidence that they also exist in plant cells, is the idea of a lysosome, so a lysosome right over here, that also is a compartment, and it's going to contain a whole series of enzymes in it that is useful for lysing, you could say, that is useful for breaking down either waste products as the cell lives, or even foreign substances that might not be helpful for the cells, so it's gonna contain a bunch of enzymes, and it helps break down things. Now, I'll leave you there."}, {"video_title": "Organelles in eukaryotic cells   Cells   High school biology   Khan Academy (2).mp3", "Sentence": "It's viewed as a kind of a storage compartment, but it can also contain enzymes that help digest things, that help break things down so that they can be used in some way, so that is a vacuole, and they don't just exist in plants. They can also exist in animal cells, but in plant cells, they tend to be, they can be very, very, very visible. Now, something that is somewhat related to some of the function that a vacuole plays that are most associated with animal cells, but now there's evidence that they also exist in plant cells, is the idea of a lysosome, so a lysosome right over here, that also is a compartment, and it's going to contain a whole series of enzymes in it that is useful for lysing, you could say, that is useful for breaking down either waste products as the cell lives, or even foreign substances that might not be helpful for the cells, so it's gonna contain a bunch of enzymes, and it helps break down things. Now, I'll leave you there. These aren't all of the structures in eukaryotic cells, but these are enough of the structures so that you can appreciate that there are a lot of membrane-bound organelles in eukaryotic cells, and to be clear, even if I were to show all of the membrane-bound structures, that's not all the complexity of a cell. The big thing to appreciate is the cells are incredibly complex. There's all sorts of structures in here that help transport things, that move things around."}, {"video_title": "Organelles in eukaryotic cells   Cells   High school biology   Khan Academy (2).mp3", "Sentence": "Now, I'll leave you there. These aren't all of the structures in eukaryotic cells, but these are enough of the structures so that you can appreciate that there are a lot of membrane-bound organelles in eukaryotic cells, and to be clear, even if I were to show all of the membrane-bound structures, that's not all the complexity of a cell. The big thing to appreciate is the cells are incredibly complex. There's all sorts of structures in here that help transport things, that move things around. If you could shrink yourself down and look inside of a cell, it would look more complex than the most complex cities. There's all sorts of activities, things being moved around, shuttled around. The cell itself is replicating and copying things, and so this is just the beginning."}, {"video_title": "Discovering the tree of life   California Academy of Sciences.mp3", "Sentence": "Here we want to really focus on the latter and talk about evolutionary lineages, something that I live and breathe in my own scientific research. The study of evolutionary lineages is nothing less than analyzing biodiversity over time. We always want to know where did biodiversity come from, where is it going, and what is the role of humans in the future of these patterns. Lineages allow us to look at the evolutionary history of different species. So the study of evolutionary lineages is also the study of the tree of life. Scientists use that tree metaphor to depict actual relationships among organismal groups in a branching diagram. But how do you make that diagram?"}, {"video_title": "Discovering the tree of life   California Academy of Sciences.mp3", "Sentence": "Lineages allow us to look at the evolutionary history of different species. So the study of evolutionary lineages is also the study of the tree of life. Scientists use that tree metaphor to depict actual relationships among organismal groups in a branching diagram. But how do you make that diagram? What do you need to know that will allow us to assemble that tree of life? What we are talking about is a science known as phylogenetic systematics. Phylogenetic patterns are made up of characters, features you can observe in organisms."}, {"video_title": "Discovering the tree of life   California Academy of Sciences.mp3", "Sentence": "But how do you make that diagram? What do you need to know that will allow us to assemble that tree of life? What we are talking about is a science known as phylogenetic systematics. Phylogenetic patterns are made up of characters, features you can observe in organisms. Sounds pretty simple, but what it really means is that a unique feature of an organism represents a unique event in the evolutionary history of that organism, an event that marks the first appearance of that feature. And if you look at several organisms and list the unique features of those organisms, you are actually looking at the unique events in their histories that tell you something about their relationships. This is because these events can be shared with other organisms."}, {"video_title": "Discovering the tree of life   California Academy of Sciences.mp3", "Sentence": "Phylogenetic patterns are made up of characters, features you can observe in organisms. Sounds pretty simple, but what it really means is that a unique feature of an organism represents a unique event in the evolutionary history of that organism, an event that marks the first appearance of that feature. And if you look at several organisms and list the unique features of those organisms, you are actually looking at the unique events in their histories that tell you something about their relationships. This is because these events can be shared with other organisms. If they are shared, their histories are shared. In other words, the species are related. Think about sea urchins, for example."}, {"video_title": "Discovering the tree of life   California Academy of Sciences.mp3", "Sentence": "This is because these events can be shared with other organisms. If they are shared, their histories are shared. In other words, the species are related. Think about sea urchins, for example. Who wouldn't want to think about sea urchins? They're pretty neat animals. They have long spines, nice rounded bodies supporting those spines."}, {"video_title": "Discovering the tree of life   California Academy of Sciences.mp3", "Sentence": "Think about sea urchins, for example. Who wouldn't want to think about sea urchins? They're pretty neat animals. They have long spines, nice rounded bodies supporting those spines. But did you know that sand dollars are basically flat sea urchins that have adapted to life on the beach? Which I think is pretty nice work if you can get it. So if sand dollars are sea urchins, can we identify some evolutionary novelty that joins all the sand dollars together to the exclusion of all other types of sea urchins?"}, {"video_title": "Discovering the tree of life   California Academy of Sciences.mp3", "Sentence": "They have long spines, nice rounded bodies supporting those spines. But did you know that sand dollars are basically flat sea urchins that have adapted to life on the beach? Which I think is pretty nice work if you can get it. So if sand dollars are sea urchins, can we identify some evolutionary novelty that joins all the sand dollars together to the exclusion of all other types of sea urchins? Can we put them together in a single lineage? Here's our sea urchin and here is our sand dollar. But here's another type of sand dollar."}, {"video_title": "Discovering the tree of life   California Academy of Sciences.mp3", "Sentence": "So if sand dollars are sea urchins, can we identify some evolutionary novelty that joins all the sand dollars together to the exclusion of all other types of sea urchins? Can we put them together in a single lineage? Here's our sea urchin and here is our sand dollar. But here's another type of sand dollar. The obvious feature that links these two guys is that they are, as we said, really flat. But no other sea urchins are flat like this. That's a character that uniquely connects all of the sand dollars together to the exclusion of all other sea urchins."}, {"video_title": "Discovering the tree of life   California Academy of Sciences.mp3", "Sentence": "But here's another type of sand dollar. The obvious feature that links these two guys is that they are, as we said, really flat. But no other sea urchins are flat like this. That's a character that uniquely connects all of the sand dollars together to the exclusion of all other sea urchins. A feature that's arisen only once in the evolutionary history of the sea urchins that led to the sand dollars. The suggestion is that these two guys share common ancestry, a common history, because right at this point, they evolved this characteristic of being flat. With the sand dollar group, all of which we now know share common ancestry, you can have further elaborations on this flat form."}, {"video_title": "Discovering the tree of life   California Academy of Sciences.mp3", "Sentence": "That's a character that uniquely connects all of the sand dollars together to the exclusion of all other sea urchins. A feature that's arisen only once in the evolutionary history of the sea urchins that led to the sand dollars. The suggestion is that these two guys share common ancestry, a common history, because right at this point, they evolved this characteristic of being flat. With the sand dollar group, all of which we now know share common ancestry, you can have further elaborations on this flat form. For example, some will have weird holes through their bodies that also represent unique evolutionary events within the sand dollar grouping. And this is another critical thing to recognize about the tree of life. Every group is nested or included within another group."}, {"video_title": "Discovering the tree of life   California Academy of Sciences.mp3", "Sentence": "With the sand dollar group, all of which we now know share common ancestry, you can have further elaborations on this flat form. For example, some will have weird holes through their bodies that also represent unique evolutionary events within the sand dollar grouping. And this is another critical thing to recognize about the tree of life. Every group is nested or included within another group. Nature is a hierarchy that can be represented by these branching diagrams, diagrams known as cladograms or phylogenetic trees. But things can be really complicated. We know that there are some 250 living species of sand dollars and over 750 extinct fossil species."}, {"video_title": "Discovering the tree of life   California Academy of Sciences.mp3", "Sentence": "Every group is nested or included within another group. Nature is a hierarchy that can be represented by these branching diagrams, diagrams known as cladograms or phylogenetic trees. But things can be really complicated. We know that there are some 250 living species of sand dollars and over 750 extinct fossil species. We also know there's a single phylogenetic tree for sand dollars showing how they're all related one to another. But we don't know the precise shape, the branching order, also known as the topology of that tree. Each subgrouping can be supported by a unique evolutionary novelty or even several if you have lots of data."}, {"video_title": "Discovering the tree of life   California Academy of Sciences.mp3", "Sentence": "We know that there are some 250 living species of sand dollars and over 750 extinct fossil species. We also know there's a single phylogenetic tree for sand dollars showing how they're all related one to another. But we don't know the precise shape, the branching order, also known as the topology of that tree. Each subgrouping can be supported by a unique evolutionary novelty or even several if you have lots of data. The aim is to best arrange all the unique characters to resolve or support all of the relationships. Ultimately, the idea is to make a branch point for every single one of the relationships so we can document the unique evolutionary events or characters among all the species being studied. One thing that emerges from all of this is the simple fact that some species have appeared on earth more recently than others."}, {"video_title": "Discovering the tree of life   California Academy of Sciences.mp3", "Sentence": "Each subgrouping can be supported by a unique evolutionary novelty or even several if you have lots of data. The aim is to best arrange all the unique characters to resolve or support all of the relationships. Ultimately, the idea is to make a branch point for every single one of the relationships so we can document the unique evolutionary events or characters among all the species being studied. One thing that emerges from all of this is the simple fact that some species have appeared on earth more recently than others. You can read this from the topology of the tree when you realize that there's a time axis along here, oldest to most recent. The important thing is the relative branching order, the topology of the tree. This branch point occurred before that one and that branch point occurred before both of those."}, {"video_title": "Discovering the tree of life   California Academy of Sciences.mp3", "Sentence": "One thing that emerges from all of this is the simple fact that some species have appeared on earth more recently than others. You can read this from the topology of the tree when you realize that there's a time axis along here, oldest to most recent. The important thing is the relative branching order, the topology of the tree. This branch point occurred before that one and that branch point occurred before both of those. But let's face it, with 10 million species on earth, the tree of life can get pretty complicated, which is why it takes a lot of data and a lot of studies to place as accurately as possible each group of organisms on that big tree. So for phylogenetic systematics, you need to use a computer, taking lots and lots of character data, coding character traits for every species in your analysis and feeding that into a computer program. There are mathematical processes to produce trees that can be tested and tested again with new characters with the aim of arriving at the most supportable hypothesis for the topology of the tree."}, {"video_title": "Discovering the tree of life   California Academy of Sciences.mp3", "Sentence": "This branch point occurred before that one and that branch point occurred before both of those. But let's face it, with 10 million species on earth, the tree of life can get pretty complicated, which is why it takes a lot of data and a lot of studies to place as accurately as possible each group of organisms on that big tree. So for phylogenetic systematics, you need to use a computer, taking lots and lots of character data, coding character traits for every species in your analysis and feeding that into a computer program. There are mathematical processes to produce trees that can be tested and tested again with new characters with the aim of arriving at the most supportable hypothesis for the topology of the tree. Sometimes these new characters can lead to changes in the branching order of the tree. And there's something relatively new on the scene to help phylogeneticists test these hypotheses of relationships. And that, of course, is DNA."}, {"video_title": "Discovering the tree of life   California Academy of Sciences.mp3", "Sentence": "There are mathematical processes to produce trees that can be tested and tested again with new characters with the aim of arriving at the most supportable hypothesis for the topology of the tree. Sometimes these new characters can lead to changes in the branching order of the tree. And there's something relatively new on the scene to help phylogeneticists test these hypotheses of relationships. And that, of course, is DNA. Evolutionary pathways and novel features are recorded just as much in DNA as they might be in the physical traits of an organism that you can see with your eyes. Phylogeneticists rely more and more on the analysis of large amounts of molecular data to develop trees. With the grand view of these trees in hand, you get an even more powerful way of looking at how evolution happens."}, {"video_title": "Discovering the tree of life   California Academy of Sciences.mp3", "Sentence": "And that, of course, is DNA. Evolutionary pathways and novel features are recorded just as much in DNA as they might be in the physical traits of an organism that you can see with your eyes. Phylogeneticists rely more and more on the analysis of large amounts of molecular data to develop trees. With the grand view of these trees in hand, you get an even more powerful way of looking at how evolution happens. You can actually read life's history book, which I think is one of the most exciting things you can possibly do in this field of study. For example, in the case of the sand dollars, I can explore why they got flat or why they have these bizarre holes in them. Using the tree to tell a story of evolution."}, {"video_title": "Discovering the tree of life   California Academy of Sciences.mp3", "Sentence": "With the grand view of these trees in hand, you get an even more powerful way of looking at how evolution happens. You can actually read life's history book, which I think is one of the most exciting things you can possibly do in this field of study. For example, in the case of the sand dollars, I can explore why they got flat or why they have these bizarre holes in them. Using the tree to tell a story of evolution. It's what I live for in my science. One of the first ever cladograms appeared in the work of none other than Charles Darwin, who recognized the importance of evolutionary trees. I always think of old Chuck when I think of this grand picture of life, this grand picture of biodiversity, and how trees show that."}, {"video_title": "Volume of a sphere   Perimeter, area, and volume   Geometry   Khan Academy.mp3", "Sentence": "Find the volume of a sphere with a diameter of 14 centimeters. So if I have a sphere, so this isn't just a circle, this is a sphere, you could view it as a globe of some kind, so I'm going to shade it a little bit so you can tell that it's three dimensional. They're giving us the diameter, so if we go from one side of the sphere straight through the center of it, so we're imagining that we can see through the sphere, and we go straight through the centimeter, that distance right over there is 14 centimeters. Now, to find the volume of a sphere, we prove this, or you will see a proof for this later when you learn calculus, but the formula for the volume of a sphere is volume is equal to 4 thirds pi r cubed, where r is the radius of the sphere. So they've given us the diameter, and just like for circles, the radius of the sphere is half of the diameter. So in this example, our radius is going to be 7 centimeters. In fact, the sphere itself is a set of all points in three dimensions that is exactly the radius away from the center."}, {"video_title": "Volume of a sphere   Perimeter, area, and volume   Geometry   Khan Academy.mp3", "Sentence": "Now, to find the volume of a sphere, we prove this, or you will see a proof for this later when you learn calculus, but the formula for the volume of a sphere is volume is equal to 4 thirds pi r cubed, where r is the radius of the sphere. So they've given us the diameter, and just like for circles, the radius of the sphere is half of the diameter. So in this example, our radius is going to be 7 centimeters. In fact, the sphere itself is a set of all points in three dimensions that is exactly the radius away from the center. But with that out of the way, let's just apply this radius being 7 centimeters to this formula right over here. So we're going to have a volume is equal to 4 thirds pi times 7 centimeters to the third power. So I'll do that in that pink color."}, {"video_title": "Volume of a sphere   Perimeter, area, and volume   Geometry   Khan Academy.mp3", "Sentence": "In fact, the sphere itself is a set of all points in three dimensions that is exactly the radius away from the center. But with that out of the way, let's just apply this radius being 7 centimeters to this formula right over here. So we're going to have a volume is equal to 4 thirds pi times 7 centimeters to the third power. So I'll do that in that pink color. So times 7 centimeters to the third power. And since it already involves pi, and you can approximate pi with 3.14, some people even approximate it with 22 over 7, but we'll actually just get the calculator out to get the exact value for this volume. So this is going to be, so my volume is going to be 4 divided by 3, and then I don't want to just put a pi there, because that might interpret it as 4 divided by 3 pi."}, {"video_title": "Volume of a sphere   Perimeter, area, and volume   Geometry   Khan Academy.mp3", "Sentence": "So I'll do that in that pink color. So times 7 centimeters to the third power. And since it already involves pi, and you can approximate pi with 3.14, some people even approximate it with 22 over 7, but we'll actually just get the calculator out to get the exact value for this volume. So this is going to be, so my volume is going to be 4 divided by 3, and then I don't want to just put a pi there, because that might interpret it as 4 divided by 3 pi. So 4 divided by 3 times pi times 7 to the third power. In order of operations, it'll do the exponent before it does the multiplication, so this should work out. And the units are going to be in centimeters cubed, or cubic centimeters."}, {"video_title": "Volume of a sphere   Perimeter, area, and volume   Geometry   Khan Academy.mp3", "Sentence": "So this is going to be, so my volume is going to be 4 divided by 3, and then I don't want to just put a pi there, because that might interpret it as 4 divided by 3 pi. So 4 divided by 3 times pi times 7 to the third power. In order of operations, it'll do the exponent before it does the multiplication, so this should work out. And the units are going to be in centimeters cubed, or cubic centimeters. So we get 1436, they don't tell us what to round it to, so I'll just round it to the nearest tenth. 1436.8, so this is equal to 1436.8 centimeters cubed. And we're done."}, {"video_title": "Introduction to cellular respiration   Cellular respiration   Biology   Khan Academy.mp3", "Sentence": "At the end of the day, most of what we eat, or at least carbohydrates, end up as glucose in the future videos. I'll talk about how we derive energy from fats or proteins. But cellular respiration, let's go from glucose to energy and some other byproducts. And to be a little bit more specific about it, let me write the chemical reaction right here. So the chemical formula for glucose, you're going to have 6 carbons, 12 hydrogens, and 6 oxygens. So that's your glucose right there. So if you had 1 mole of glucose, let me write that."}, {"video_title": "Introduction to cellular respiration   Cellular respiration   Biology   Khan Academy.mp3", "Sentence": "And to be a little bit more specific about it, let me write the chemical reaction right here. So the chemical formula for glucose, you're going to have 6 carbons, 12 hydrogens, and 6 oxygens. So that's your glucose right there. So if you had 1 mole of glucose, let me write that. That's your glucose right there. And then to that 1 mole of glucose, if you had 6 moles of molecular oxygen running around the cell, then, and this is kind of a gross simplification for cellular respiration. I think you're going to appreciate over the course of the next few videos that one can get as involved into this mechanism as possible."}, {"video_title": "Introduction to cellular respiration   Cellular respiration   Biology   Khan Academy.mp3", "Sentence": "So if you had 1 mole of glucose, let me write that. That's your glucose right there. And then to that 1 mole of glucose, if you had 6 moles of molecular oxygen running around the cell, then, and this is kind of a gross simplification for cellular respiration. I think you're going to appreciate over the course of the next few videos that one can get as involved into this mechanism as possible. I think it's nice to get the big picture. But if you give me some glucose, if you have 1 mole of glucose and 6 moles of oxygen, through the process of cellular respiration, and so I'm just writing it as kind of a big black box right now. Let me pick a nice color."}, {"video_title": "Introduction to cellular respiration   Cellular respiration   Biology   Khan Academy.mp3", "Sentence": "I think you're going to appreciate over the course of the next few videos that one can get as involved into this mechanism as possible. I think it's nice to get the big picture. But if you give me some glucose, if you have 1 mole of glucose and 6 moles of oxygen, through the process of cellular respiration, and so I'm just writing it as kind of a big black box right now. Let me pick a nice color. So this is cellular respiration, which we'll see is quite involved. But I guess anything can be, if you want to be particular enough about it. Through cellular respiration, we're going to produce 6 moles of carbon dioxide, 6 moles of water, and, and this is the key, this is the super important part, and we're going to produce energy."}, {"video_title": "Introduction to cellular respiration   Cellular respiration   Biology   Khan Academy.mp3", "Sentence": "Let me pick a nice color. So this is cellular respiration, which we'll see is quite involved. But I guess anything can be, if you want to be particular enough about it. Through cellular respiration, we're going to produce 6 moles of carbon dioxide, 6 moles of water, and, and this is the key, this is the super important part, and we're going to produce energy. We're going to produce energy. And this is the energy that can be used to do useful work, to heat our bodies, to provide electrical impulses in our brains, whatever energy, especially a human body needs, but it's not just humans, it's provided by this cellular respiration mechanism. And when you say energy, you might say, hey, Sal, in the last video, didn't you just, well, if that was the last video you watched, you probably saw that I said that ATP is the energy currency for biological systems."}, {"video_title": "Introduction to cellular respiration   Cellular respiration   Biology   Khan Academy.mp3", "Sentence": "Through cellular respiration, we're going to produce 6 moles of carbon dioxide, 6 moles of water, and, and this is the key, this is the super important part, and we're going to produce energy. We're going to produce energy. And this is the energy that can be used to do useful work, to heat our bodies, to provide electrical impulses in our brains, whatever energy, especially a human body needs, but it's not just humans, it's provided by this cellular respiration mechanism. And when you say energy, you might say, hey, Sal, in the last video, didn't you just, well, if that was the last video you watched, you probably saw that I said that ATP is the energy currency for biological systems. And so you might say, hey, well, it looks like glucose is the energy currency for biological systems. And to some degree, both answers would be correct, but to just see how it kind of fits together is that the process of cellular respiration, it does produce energy directly, but that energy is used to produce ATP. So if I were to break down this energy portion of cellular respiration right there, some of it would just be heat, it just warms up the cell, and then some of it is used, and this is what the textbooks will tell you, the textbooks will say it produces 38 ATPs that can be more readily used by cells to contract muscles or generate nerve impulses or do whatever else, or grow or divide or whatever else the cell might need."}, {"video_title": "Introduction to cellular respiration   Cellular respiration   Biology   Khan Academy.mp3", "Sentence": "And when you say energy, you might say, hey, Sal, in the last video, didn't you just, well, if that was the last video you watched, you probably saw that I said that ATP is the energy currency for biological systems. And so you might say, hey, well, it looks like glucose is the energy currency for biological systems. And to some degree, both answers would be correct, but to just see how it kind of fits together is that the process of cellular respiration, it does produce energy directly, but that energy is used to produce ATP. So if I were to break down this energy portion of cellular respiration right there, some of it would just be heat, it just warms up the cell, and then some of it is used, and this is what the textbooks will tell you, the textbooks will say it produces 38 ATPs that can be more readily used by cells to contract muscles or generate nerve impulses or do whatever else, or grow or divide or whatever else the cell might need. So really cellular respiration, to say it produces energy, a little disingenuous. It's really the process of taking glucose and producing ATPs with maybe heat as a byproduct, but it's probably nice to have that heat around. We need to be reasonably warm in order for our cells to operate correctly."}, {"video_title": "Introduction to cellular respiration   Cellular respiration   Biology   Khan Academy.mp3", "Sentence": "So if I were to break down this energy portion of cellular respiration right there, some of it would just be heat, it just warms up the cell, and then some of it is used, and this is what the textbooks will tell you, the textbooks will say it produces 38 ATPs that can be more readily used by cells to contract muscles or generate nerve impulses or do whatever else, or grow or divide or whatever else the cell might need. So really cellular respiration, to say it produces energy, a little disingenuous. It's really the process of taking glucose and producing ATPs with maybe heat as a byproduct, but it's probably nice to have that heat around. We need to be reasonably warm in order for our cells to operate correctly. So the whole point is really to go from glucose, from one mole of glucose, and the textbooks will tell you, to 38 ATPs. And the reality is this is in kind of the ideal circumstances that you'll produce 38 ATPs. I was reading up about it a little bit before doing this video."}, {"video_title": "Introduction to cellular respiration   Cellular respiration   Biology   Khan Academy.mp3", "Sentence": "We need to be reasonably warm in order for our cells to operate correctly. So the whole point is really to go from glucose, from one mole of glucose, and the textbooks will tell you, to 38 ATPs. And the reality is this is in kind of the ideal circumstances that you'll produce 38 ATPs. I was reading up about it a little bit before doing this video. And the reality is, depending on the efficiency of the cell in performing cellular respiration, it'll probably be more on the order of 29 to 30 ATPs, but there's a huge variation here and people are really still studying this idea. But this is all cellular respiration is. In the next few videos we're going to break it down into its kind of constituent parts, and I'm going to introduce them to you right now just so you kind of realize that these are parts of cellular respiration."}, {"video_title": "Introduction to cellular respiration   Cellular respiration   Biology   Khan Academy.mp3", "Sentence": "I was reading up about it a little bit before doing this video. And the reality is, depending on the efficiency of the cell in performing cellular respiration, it'll probably be more on the order of 29 to 30 ATPs, but there's a huge variation here and people are really still studying this idea. But this is all cellular respiration is. In the next few videos we're going to break it down into its kind of constituent parts, and I'm going to introduce them to you right now just so you kind of realize that these are parts of cellular respiration. The first stage is called glycolysis, which literally means breaking up glucose. And just so you know, this part, the gly for glucose, or the glyco for glucose, really. And then lysis means to break up."}, {"video_title": "Introduction to cellular respiration   Cellular respiration   Biology   Khan Academy.mp3", "Sentence": "In the next few videos we're going to break it down into its kind of constituent parts, and I'm going to introduce them to you right now just so you kind of realize that these are parts of cellular respiration. The first stage is called glycolysis, which literally means breaking up glucose. And just so you know, this part, the gly for glucose, or the glyco for glucose, really. And then lysis means to break up. When you saw hydrolysis, it means using water to break up a molecule. Glycolysis means we're going to be breaking up glucose. And in case you care about things like word origins, glucose comes from the gluk part of glucose."}, {"video_title": "Introduction to cellular respiration   Cellular respiration   Biology   Khan Academy.mp3", "Sentence": "And then lysis means to break up. When you saw hydrolysis, it means using water to break up a molecule. Glycolysis means we're going to be breaking up glucose. And in case you care about things like word origins, glucose comes from the gluk part of glucose. It comes from Greek for sweet, and glucose is indeed sweet. And then all sugars, we put this ose ending, so that just means sugar. So you might think it's kind of a redundant statement to say sweet sugar, but there are some sugars that aren't sweet."}, {"video_title": "Introduction to cellular respiration   Cellular respiration   Biology   Khan Academy.mp3", "Sentence": "And in case you care about things like word origins, glucose comes from the gluk part of glucose. It comes from Greek for sweet, and glucose is indeed sweet. And then all sugars, we put this ose ending, so that just means sugar. So you might think it's kind of a redundant statement to say sweet sugar, but there are some sugars that aren't sweet. For example, lactose. You know, milk, it might be a little bit, but when you actually digest lactose, then you can turn it into an actual sweet sugar, but it doesn't taste sweet like glucose or fructose or sucrose would taste. But anyway, that's an aside."}, {"video_title": "Introduction to cellular respiration   Cellular respiration   Biology   Khan Academy.mp3", "Sentence": "So you might think it's kind of a redundant statement to say sweet sugar, but there are some sugars that aren't sweet. For example, lactose. You know, milk, it might be a little bit, but when you actually digest lactose, then you can turn it into an actual sweet sugar, but it doesn't taste sweet like glucose or fructose or sucrose would taste. But anyway, that's an aside. But the first step of cellular respiration is glycolysis, breaking up of glucose. And what it does is it breaks up the glucose from a 6-carbon molecule. So it literally takes it from a 6-carbon molecule."}, {"video_title": "Introduction to cellular respiration   Cellular respiration   Biology   Khan Academy.mp3", "Sentence": "But anyway, that's an aside. But the first step of cellular respiration is glycolysis, breaking up of glucose. And what it does is it breaks up the glucose from a 6-carbon molecule. So it literally takes it from a 6-carbon molecule. Let me draw it like this. A 6-carbon molecule that looks like this. And it's actually a cycle."}, {"video_title": "Introduction to cellular respiration   Cellular respiration   Biology   Khan Academy.mp3", "Sentence": "So it literally takes it from a 6-carbon molecule. Let me draw it like this. A 6-carbon molecule that looks like this. And it's actually a cycle. Let me show you what glucose actually looks like. This is glucose right here. And notice you have 1, 2, 3, 4, 5, 6 carbons."}, {"video_title": "Introduction to cellular respiration   Cellular respiration   Biology   Khan Academy.mp3", "Sentence": "And it's actually a cycle. Let me show you what glucose actually looks like. This is glucose right here. And notice you have 1, 2, 3, 4, 5, 6 carbons. I got this off of Wikipedia. Just look up glucose and you can see this diagram if you want to kind of see the details. Where you can see I have 6 carbons, 6 oxygens."}, {"video_title": "Introduction to cellular respiration   Cellular respiration   Biology   Khan Academy.mp3", "Sentence": "And notice you have 1, 2, 3, 4, 5, 6 carbons. I got this off of Wikipedia. Just look up glucose and you can see this diagram if you want to kind of see the details. Where you can see I have 6 carbons, 6 oxygens. That's 1, 2, 3, 4, 5, 6. And then all of these little small blue things are my hydrogen. So that's what glucose actually looks like."}, {"video_title": "Introduction to cellular respiration   Cellular respiration   Biology   Khan Academy.mp3", "Sentence": "Where you can see I have 6 carbons, 6 oxygens. That's 1, 2, 3, 4, 5, 6. And then all of these little small blue things are my hydrogen. So that's what glucose actually looks like. But the process of glycolysis, you're essentially just taking, I'm writing it out as a kind of a string, but you could imagine it as a chain. And it has oxygens and hydrogens added to it, to each of these carbons. But it has a carbon backbone and it breaks that carbon backbone into 2."}, {"video_title": "Introduction to cellular respiration   Cellular respiration   Biology   Khan Academy.mp3", "Sentence": "So that's what glucose actually looks like. But the process of glycolysis, you're essentially just taking, I'm writing it out as a kind of a string, but you could imagine it as a chain. And it has oxygens and hydrogens added to it, to each of these carbons. But it has a carbon backbone and it breaks that carbon backbone into 2. That's what glycolysis does right there. So you've kind of lysed the glucose in each of these things. And I haven't drawn all the other stuff that's added onto that."}, {"video_title": "Introduction to cellular respiration   Cellular respiration   Biology   Khan Academy.mp3", "Sentence": "But it has a carbon backbone and it breaks that carbon backbone into 2. That's what glycolysis does right there. So you've kind of lysed the glucose in each of these things. And I haven't drawn all the other stuff that's added onto that. These things are all bonded with other things. With oxygens and hydrogens, whatever. But each of these 3 carbon backbone molecules are called pyruvate."}, {"video_title": "Introduction to cellular respiration   Cellular respiration   Biology   Khan Academy.mp3", "Sentence": "And I haven't drawn all the other stuff that's added onto that. These things are all bonded with other things. With oxygens and hydrogens, whatever. But each of these 3 carbon backbone molecules are called pyruvate. We'll go into a lot more detail on that. But by glycolysis, it by itself generates, well, it needs 2 ATPs. So it needs 2 ATPs."}, {"video_title": "Introduction to cellular respiration   Cellular respiration   Biology   Khan Academy.mp3", "Sentence": "But each of these 3 carbon backbone molecules are called pyruvate. We'll go into a lot more detail on that. But by glycolysis, it by itself generates, well, it needs 2 ATPs. So it needs 2 ATPs. And it generates 4 ATPs. So net-net, on a net basis, it generates 2, let me write this in a different color, it generates 2 net ATP. So that's the first stage."}, {"video_title": "Introduction to cellular respiration   Cellular respiration   Biology   Khan Academy.mp3", "Sentence": "So it needs 2 ATPs. And it generates 4 ATPs. So net-net, on a net basis, it generates 2, let me write this in a different color, it generates 2 net ATP. So that's the first stage. And this can occur completely in the absence of oxygen. I'll do a whole video on glycolysis in the future. Then these byproducts, they get re-engineered a little bit and then they enter into what's called the Krebs cycle."}, {"video_title": "Introduction to cellular respiration   Cellular respiration   Biology   Khan Academy.mp3", "Sentence": "So that's the first stage. And this can occur completely in the absence of oxygen. I'll do a whole video on glycolysis in the future. Then these byproducts, they get re-engineered a little bit and then they enter into what's called the Krebs cycle. They enter what's called the Krebs cycle, which generates another 2 ATP. And then, and this is kind of the interesting point, there's another process that you can kind of say happens after the Krebs cycle, but we're in a cell and everything is bumping into everything all of the time. But it's normally kind of viewed to be after glycolysis in the Krebs cycle."}, {"video_title": "Introduction to cellular respiration   Cellular respiration   Biology   Khan Academy.mp3", "Sentence": "Then these byproducts, they get re-engineered a little bit and then they enter into what's called the Krebs cycle. They enter what's called the Krebs cycle, which generates another 2 ATP. And then, and this is kind of the interesting point, there's another process that you can kind of say happens after the Krebs cycle, but we're in a cell and everything is bumping into everything all of the time. But it's normally kind of viewed to be after glycolysis in the Krebs cycle. So this requires oxygen. So let me be clear, glycolysis, this first step, no oxygen required or doesn't need oxygen. It can occur with oxygen or without it."}, {"video_title": "Introduction to cellular respiration   Cellular respiration   Biology   Khan Academy.mp3", "Sentence": "But it's normally kind of viewed to be after glycolysis in the Krebs cycle. So this requires oxygen. So let me be clear, glycolysis, this first step, no oxygen required or doesn't need oxygen. It can occur with oxygen or without it. Oxygen not needed. Or you could say this is called an anaerobic process. This is the anaerobic part of the respiration."}, {"video_title": "Introduction to cellular respiration   Cellular respiration   Biology   Khan Academy.mp3", "Sentence": "It can occur with oxygen or without it. Oxygen not needed. Or you could say this is called an anaerobic process. This is the anaerobic part of the respiration. Let me write that down too. Anaerobic. Maybe I'll write it down here."}, {"video_title": "Introduction to cellular respiration   Cellular respiration   Biology   Khan Academy.mp3", "Sentence": "This is the anaerobic part of the respiration. Let me write that down too. Anaerobic. Maybe I'll write it down here. Glycolysis, since it doesn't need oxygen, we can say it's anaerobic. You might be familiar with the idea of aerobic exercise. The whole idea of aerobic exercise is to make you breathe hard because you need a lot of oxygen to do aerobic exercises."}, {"video_title": "Introduction to cellular respiration   Cellular respiration   Biology   Khan Academy.mp3", "Sentence": "Maybe I'll write it down here. Glycolysis, since it doesn't need oxygen, we can say it's anaerobic. You might be familiar with the idea of aerobic exercise. The whole idea of aerobic exercise is to make you breathe hard because you need a lot of oxygen to do aerobic exercises. So anaerobic means you don't need oxygen. Aerobic means it needs oxygen. Anaerobic means the opposite."}, {"video_title": "Introduction to cellular respiration   Cellular respiration   Biology   Khan Academy.mp3", "Sentence": "The whole idea of aerobic exercise is to make you breathe hard because you need a lot of oxygen to do aerobic exercises. So anaerobic means you don't need oxygen. Aerobic means it needs oxygen. Anaerobic means the opposite. You don't need oxygen. So glycolysis, anaerobic, and it produces two ATPs net. And then you go to the Krebs cycle."}, {"video_title": "Introduction to cellular respiration   Cellular respiration   Biology   Khan Academy.mp3", "Sentence": "Anaerobic means the opposite. You don't need oxygen. So glycolysis, anaerobic, and it produces two ATPs net. And then you go to the Krebs cycle. There's a little bit of setup involved here, and we'll do the detail of that in the future. But then you move over to the Krebs cycle, which is aerobic. It requires oxygen to be around."}, {"video_title": "Introduction to cellular respiration   Cellular respiration   Biology   Khan Academy.mp3", "Sentence": "And then you go to the Krebs cycle. There's a little bit of setup involved here, and we'll do the detail of that in the future. But then you move over to the Krebs cycle, which is aerobic. It requires oxygen to be around. And then this produces two ATPs. And then this is the part that, frankly, when I first learned it confused me a lot. But I'll just write it in order the way it's traditionally wrote."}, {"video_title": "Introduction to cellular respiration   Cellular respiration   Biology   Khan Academy.mp3", "Sentence": "It requires oxygen to be around. And then this produces two ATPs. And then this is the part that, frankly, when I first learned it confused me a lot. But I'll just write it in order the way it's traditionally wrote. Then you have something called, we're using the same colors too much, you have something called the electron transport chain. And this part gets credit for producing the bulk of the ATPs. 34 ATPs."}, {"video_title": "Introduction to cellular respiration   Cellular respiration   Biology   Khan Academy.mp3", "Sentence": "But I'll just write it in order the way it's traditionally wrote. Then you have something called, we're using the same colors too much, you have something called the electron transport chain. And this part gets credit for producing the bulk of the ATPs. 34 ATPs. And this is also aerobic. It requires oxygen. So you can see, if you had no oxygen, if the cells weren't getting enough oxygen, you can produce a little bit of energy."}, {"video_title": "Introduction to cellular respiration   Cellular respiration   Biology   Khan Academy.mp3", "Sentence": "34 ATPs. And this is also aerobic. It requires oxygen. So you can see, if you had no oxygen, if the cells weren't getting enough oxygen, you can produce a little bit of energy. But it's nowhere near as much as you can produce once you have the oxygen. And actually, when you start running out of oxygen, this can't proceed forward. So what happens is some of these byproducts of glycolysis, instead of going into the Krebs cycle and the electron transport chain where they need oxygen, instead they go through a side process called fermentation."}, {"video_title": "Introduction to cellular respiration   Cellular respiration   Biology   Khan Academy.mp3", "Sentence": "So you can see, if you had no oxygen, if the cells weren't getting enough oxygen, you can produce a little bit of energy. But it's nowhere near as much as you can produce once you have the oxygen. And actually, when you start running out of oxygen, this can't proceed forward. So what happens is some of these byproducts of glycolysis, instead of going into the Krebs cycle and the electron transport chain where they need oxygen, instead they go through a side process called fermentation. For some organisms, this process of fermentation takes your byproducts of glycolysis and literally produces alcohol. That's where alcohol comes from. That's called alcohol fermentation."}, {"video_title": "Introduction to cellular respiration   Cellular respiration   Biology   Khan Academy.mp3", "Sentence": "So what happens is some of these byproducts of glycolysis, instead of going into the Krebs cycle and the electron transport chain where they need oxygen, instead they go through a side process called fermentation. For some organisms, this process of fermentation takes your byproducts of glycolysis and literally produces alcohol. That's where alcohol comes from. That's called alcohol fermentation. And we, as human beings, I guess fortunately or unfortunately, our muscles do not directly produce alcohol. They produce lactic acid. So we do lactic acid fermentation."}, {"video_title": "Introduction to cellular respiration   Cellular respiration   Biology   Khan Academy.mp3", "Sentence": "That's called alcohol fermentation. And we, as human beings, I guess fortunately or unfortunately, our muscles do not directly produce alcohol. They produce lactic acid. So we do lactic acid fermentation. Let me write that down. Lactic acid. That's humans and probably other mammals."}, {"video_title": "Introduction to cellular respiration   Cellular respiration   Biology   Khan Academy.mp3", "Sentence": "So we do lactic acid fermentation. Let me write that down. Lactic acid. That's humans and probably other mammals. Humans. But other things like yeast will do alcohol fermentation. So this is when you don't have oxygen."}, {"video_title": "Introduction to cellular respiration   Cellular respiration   Biology   Khan Academy.mp3", "Sentence": "That's humans and probably other mammals. Humans. But other things like yeast will do alcohol fermentation. So this is when you don't have oxygen. It's actually this lactic acid that if I were to sprint really hard and not be able to get enough oxygen, that my muscles start to ache because this lactic acid starts to build up. But that's just a side thing. If we have oxygen, we can move to the Krebs cycle, get our two ATPs, and then go on to the electron transport chain and produce 34 ATPs, which is really the bulk of what happens in respiration."}, {"video_title": "Introduction to cellular respiration   Cellular respiration   Biology   Khan Academy.mp3", "Sentence": "So this is when you don't have oxygen. It's actually this lactic acid that if I were to sprint really hard and not be able to get enough oxygen, that my muscles start to ache because this lactic acid starts to build up. But that's just a side thing. If we have oxygen, we can move to the Krebs cycle, get our two ATPs, and then go on to the electron transport chain and produce 34 ATPs, which is really the bulk of what happens in respiration. Now I kind of said this as an aside. To some degree, this isn't fair. Because while these guys are operating, they're also producing these other molecules."}, {"video_title": "Introduction to cellular respiration   Cellular respiration   Biology   Khan Academy.mp3", "Sentence": "If we have oxygen, we can move to the Krebs cycle, get our two ATPs, and then go on to the electron transport chain and produce 34 ATPs, which is really the bulk of what happens in respiration. Now I kind of said this as an aside. To some degree, this isn't fair. Because while these guys are operating, they're also producing these other molecules. Or they're not producing them entirely, but what they're doing is they're taking, and I know it gets complicated here. But I think over the course of the next few videos, we'll get an intuition for it. In these two parts of the reaction, glycolysis and the Krebs cycle, we're constantly taking NAD, I'll write it as NAD plus, and we're adding hydrogens to it to form NADH."}, {"video_title": "Introduction to cellular respiration   Cellular respiration   Biology   Khan Academy.mp3", "Sentence": "Because while these guys are operating, they're also producing these other molecules. Or they're not producing them entirely, but what they're doing is they're taking, and I know it gets complicated here. But I think over the course of the next few videos, we'll get an intuition for it. In these two parts of the reaction, glycolysis and the Krebs cycle, we're constantly taking NAD, I'll write it as NAD plus, and we're adding hydrogens to it to form NADH. And this actually happens for one molecule of glucose, this happens to 10 NADs or 10 NAD pluses to become NADHs. And those are actually what drive the electron transport chain, and I'll talk a lot more about it and kind of how that happens and why is energy being derived and how is this an oxidative reaction and all of that and what's getting oxidized and what's being reduced. But I just wanted to give due credit."}, {"video_title": "Introduction to cellular respiration   Cellular respiration   Biology   Khan Academy.mp3", "Sentence": "In these two parts of the reaction, glycolysis and the Krebs cycle, we're constantly taking NAD, I'll write it as NAD plus, and we're adding hydrogens to it to form NADH. And this actually happens for one molecule of glucose, this happens to 10 NADs or 10 NAD pluses to become NADHs. And those are actually what drive the electron transport chain, and I'll talk a lot more about it and kind of how that happens and why is energy being derived and how is this an oxidative reaction and all of that and what's getting oxidized and what's being reduced. But I just wanted to give due credit. These guys aren't just producing two ATPs in each of these stages. They're also producing, actually, combined 10 NADHs, which each produce three ATPs in an ideal situation, the electron transport chain. And they're also doing it to this other molecule, FAD, which is very similar, but they're producing FADH."}, {"video_title": "Introduction to cellular respiration   Cellular respiration   Biology   Khan Academy.mp3", "Sentence": "But I just wanted to give due credit. These guys aren't just producing two ATPs in each of these stages. They're also producing, actually, combined 10 NADHs, which each produce three ATPs in an ideal situation, the electron transport chain. And they're also doing it to this other molecule, FAD, which is very similar, but they're producing FADH. Now I know all of this is very complicated. I'll make videos on this in the future. But the important thing to remember is cellular respiration, all it is, is taking glucose and kind of repackaging the energy in glucose and repackaging it in the form of, your textbooks will tell you, 38 ATPs."}, {"video_title": "Introduction to cellular respiration   Cellular respiration   Biology   Khan Academy.mp3", "Sentence": "And they're also doing it to this other molecule, FAD, which is very similar, but they're producing FADH. Now I know all of this is very complicated. I'll make videos on this in the future. But the important thing to remember is cellular respiration, all it is, is taking glucose and kind of repackaging the energy in glucose and repackaging it in the form of, your textbooks will tell you, 38 ATPs. And if you're taking an exam, that's a good number to write. It tends to, in reality, be a smaller number. It's also going to produce heat."}, {"video_title": "Introduction to cellular respiration   Cellular respiration   Biology   Khan Academy.mp3", "Sentence": "But the important thing to remember is cellular respiration, all it is, is taking glucose and kind of repackaging the energy in glucose and repackaging it in the form of, your textbooks will tell you, 38 ATPs. And if you're taking an exam, that's a good number to write. It tends to, in reality, be a smaller number. It's also going to produce heat. Actually, most of it is going to be heat. But 38 ATPs, and it does it through three stages. The first stage is glycolysis, where you're just literally splitting the glucose into two."}, {"video_title": "Introduction to cellular respiration   Cellular respiration   Biology   Khan Academy.mp3", "Sentence": "It's also going to produce heat. Actually, most of it is going to be heat. But 38 ATPs, and it does it through three stages. The first stage is glycolysis, where you're just literally splitting the glucose into two. You're generating some ATPs. But the more important thing is you're generating some NADHs that are going to be used later in the electron transport chain. Then those byproducts are split even more in the Kreb cycle, directly producing two ATPs."}, {"video_title": "Introduction to nucleic acids and nucleotides   High school biology   Khan Academy.mp3", "Sentence": "We are now going to talk about what is perhaps the most important macromolecule in life, and that is known as nucleic acid. Now first of all, where does that name come from? Well, scientists first observed this in the nucleus of cells, and so that's where you get the nucleic part, and it has some acidic properties, and so that's where you get the acid part. And perhaps the most famous of the nucleic acids is deoxyribonucleic acid, or DNA for short, and we'll go into some depth in this as we go through our journey in biology, but you might already know that this is the molecule that stores our hereditary information. This DNA, to a large degree, makes you you, and it's known as a macromolecule, and we've talked about macromolecules in other videos. We've talked about carbohydrates, and we have talked about proteins, and DNA is a macromolecule because it can be made of many millions of atoms. Just to get a sense of it, you can see right over here the double helix of DNA, where you have one side of your helix right over there, and then another one right over here, and then you kind of have these rungs of this twisted ladder."}, {"video_title": "Introduction to nucleic acids and nucleotides   High school biology   Khan Academy.mp3", "Sentence": "And perhaps the most famous of the nucleic acids is deoxyribonucleic acid, or DNA for short, and we'll go into some depth in this as we go through our journey in biology, but you might already know that this is the molecule that stores our hereditary information. This DNA, to a large degree, makes you you, and it's known as a macromolecule, and we've talked about macromolecules in other videos. We've talked about carbohydrates, and we have talked about proteins, and DNA is a macromolecule because it can be made of many millions of atoms. Just to get a sense of it, you can see right over here the double helix of DNA, where you have one side of your helix right over there, and then another one right over here, and then you kind of have these rungs of this twisted ladder. A DNA molecule, let's say in the human genome, a chromosome, for example, is primarily a really long DNA molecule, and it can have on the order of 100 million rungs to this ladder. Now, another thing to appreciate, like many other macromolecules, DNA, or nucleic acids in general, they are polymers in that they are made up of building block molecules, and those building blocks for nucleic acids, and DNA is the most famous nucleic acid, and RNA, ribonucleic acid, would be a close second, but the building blocks of them are known as nucleotides. Nucleotides."}, {"video_title": "Introduction to nucleic acids and nucleotides   High school biology   Khan Academy.mp3", "Sentence": "Just to get a sense of it, you can see right over here the double helix of DNA, where you have one side of your helix right over there, and then another one right over here, and then you kind of have these rungs of this twisted ladder. A DNA molecule, let's say in the human genome, a chromosome, for example, is primarily a really long DNA molecule, and it can have on the order of 100 million rungs to this ladder. Now, another thing to appreciate, like many other macromolecules, DNA, or nucleic acids in general, they are polymers in that they are made up of building block molecules, and those building blocks for nucleic acids, and DNA is the most famous nucleic acid, and RNA, ribonucleic acid, would be a close second, but the building blocks of them are known as nucleotides. Nucleotides. And we see some examples of nucleotides right over here. This is deoxyadenosine monophosphate, which would be a nucleotide found in DNA. You can see the various parts of it."}, {"video_title": "Introduction to nucleic acids and nucleotides   High school biology   Khan Academy.mp3", "Sentence": "Nucleotides. And we see some examples of nucleotides right over here. This is deoxyadenosine monophosphate, which would be a nucleotide found in DNA. You can see the various parts of it. You have a phosphate group right over here. You have a five-carbon sugar, which in this case is ribose, and then you have what is known as a nitrogenous base, and why is it called nitrogenous? Well, those blue circles represent nitrogen, and we've seen this before."}, {"video_title": "Introduction to nucleic acids and nucleotides   High school biology   Khan Academy.mp3", "Sentence": "You can see the various parts of it. You have a phosphate group right over here. You have a five-carbon sugar, which in this case is ribose, and then you have what is known as a nitrogenous base, and why is it called nitrogenous? Well, those blue circles represent nitrogen, and we've seen this before. The grays are carbons, and the reds are oxygens, and the whites are hydrogens, and so this part of the molecule has some basic characteristics, while this phosphate group at the end, this has some acidic characteristics, and what happens is is they get stacked onto each other where the ribose phosphates alternate to form the backbone of this DNA molecule. You can see it right over here where you have a phosphate and a ribose and a phosphate and a ribose, and then you have the nitrogenous base forming part of the rung of the ladder. And the way that DNA stores information is every one of these nitrogenous bases right over here, this is adenine, it has a complementary nitrogenous base on the other to complete that rung of the ladder."}, {"video_title": "Introduction to nucleic acids and nucleotides   High school biology   Khan Academy.mp3", "Sentence": "Well, those blue circles represent nitrogen, and we've seen this before. The grays are carbons, and the reds are oxygens, and the whites are hydrogens, and so this part of the molecule has some basic characteristics, while this phosphate group at the end, this has some acidic characteristics, and what happens is is they get stacked onto each other where the ribose phosphates alternate to form the backbone of this DNA molecule. You can see it right over here where you have a phosphate and a ribose and a phosphate and a ribose, and then you have the nitrogenous base forming part of the rung of the ladder. And the way that DNA stores information is every one of these nitrogenous bases right over here, this is adenine, it has a complementary nitrogenous base on the other to complete that rung of the ladder. So adenine matches with thymine in DNA, and we'll see in future videos in RNA, it's a nitrogenous base known as uracil, and guanine matches with cytosine. Don't worry too much about this now. We'll go into some depth in this in future videos when we talk about DNA and how information is stored in it, but for the sake of this video, just appreciate that the monomer for a nucleic acid like DNA is a nucleotide, so monomer."}, {"video_title": "Introduction to nucleic acids and nucleotides   High school biology   Khan Academy.mp3", "Sentence": "And the way that DNA stores information is every one of these nitrogenous bases right over here, this is adenine, it has a complementary nitrogenous base on the other to complete that rung of the ladder. So adenine matches with thymine in DNA, and we'll see in future videos in RNA, it's a nitrogenous base known as uracil, and guanine matches with cytosine. Don't worry too much about this now. We'll go into some depth in this in future videos when we talk about DNA and how information is stored in it, but for the sake of this video, just appreciate that the monomer for a nucleic acid like DNA is a nucleotide, so monomer. And to be very clear, this would not be the only monomer. The analogous nucleotide in RNA, which stands for ribonucleic acid, would be adenosine monophosphate right over here. You can see the difference between the two, that we have an oxygen right over here and we don't have an oxygen right over here."}, {"video_title": "Introduction to nucleic acids and nucleotides   High school biology   Khan Academy.mp3", "Sentence": "We'll go into some depth in this in future videos when we talk about DNA and how information is stored in it, but for the sake of this video, just appreciate that the monomer for a nucleic acid like DNA is a nucleotide, so monomer. And to be very clear, this would not be the only monomer. The analogous nucleotide in RNA, which stands for ribonucleic acid, would be adenosine monophosphate right over here. You can see the difference between the two, that we have an oxygen right over here and we don't have an oxygen right over here. That's why this is called deoxy, and that's why it's deoxyribonucleic acid. You're missing one of those oxygens on your five-carbon sugar but adenine, as I mentioned, is not the only nitrogenous base. You could have a nucleotide where the nitrogenous base is thymine, and so once again, this looks very similar, but notice what is going on over here."}, {"video_title": "Introduction to nucleic acids and nucleotides   High school biology   Khan Academy.mp3", "Sentence": "You can see the difference between the two, that we have an oxygen right over here and we don't have an oxygen right over here. That's why this is called deoxy, and that's why it's deoxyribonucleic acid. You're missing one of those oxygens on your five-carbon sugar but adenine, as I mentioned, is not the only nitrogenous base. You could have a nucleotide where the nitrogenous base is thymine, and so once again, this looks very similar, but notice what is going on over here. You could have a nucleotide that looks like this. Once again, you have your five-carbon sugar here, you have your phosphate group, but the nitrogenous base here keeps on changing, and it's the order of these different nucleotides that actually encodes the information in DNA. Now, one question you might say is, well, look, if I have this part of the molecule that has basic characteristics, why is it considered an acid?"}, {"video_title": "Introduction to nucleic acids and nucleotides   High school biology   Khan Academy.mp3", "Sentence": "You could have a nucleotide where the nitrogenous base is thymine, and so once again, this looks very similar, but notice what is going on over here. You could have a nucleotide that looks like this. Once again, you have your five-carbon sugar here, you have your phosphate group, but the nitrogenous base here keeps on changing, and it's the order of these different nucleotides that actually encodes the information in DNA. Now, one question you might say is, well, look, if I have this part of the molecule that has basic characteristics, why is it considered an acid? Well, look at how this molecule is structured. The basic parts form the rungs of this ladder, so they're not going to be as reactive because they're really tied, they're closer to the inside of the molecule, while the acidic parts, the phosphate groups, are on the outside, so they're going to be more reactive, and so the molecule as a whole is going to have an acidic characteristic. I'm going to leave you there."}, {"video_title": "New localities lead to new biodiversity.mp3", "Sentence": "For this video, I want to focus on the idea of dispersal, how the ranges of species can change and how this can affect biodiversity over time. As we've seen elsewhere, the classic model, called the vicarian's model, proposes that a mother species can be split into daughter species when barriers arise from changes in geology or climate or habitat, sometimes all three at the same time. These barriers can lead to divergences resulting in speciation through the restriction of gene flow. However, what we'd like to focus on here is that there's another way to really accentuate the effects of restricted gene flow, and that's something called dispersal. This is basically the way that species of plants, animals, and other organisms expand their ranges, their distributions on Earth, through movements of individuals that increase the sizes of the ranges of populations and therefore the ranges of the species themselves. Dispersal can also lead to speciation. Species like plants that have a rooted-to-the-ground or sedentary habit, like I sometimes have when there's a hockey game on, even plants have dispersal stages in the form of seeds that can be distributed in air or in water or even in and on other organisms."}, {"video_title": "New localities lead to new biodiversity.mp3", "Sentence": "However, what we'd like to focus on here is that there's another way to really accentuate the effects of restricted gene flow, and that's something called dispersal. This is basically the way that species of plants, animals, and other organisms expand their ranges, their distributions on Earth, through movements of individuals that increase the sizes of the ranges of populations and therefore the ranges of the species themselves. Dispersal can also lead to speciation. Species like plants that have a rooted-to-the-ground or sedentary habit, like I sometimes have when there's a hockey game on, even plants have dispersal stages in the form of seeds that can be distributed in air or in water or even in and on other organisms. Bird migration is an obvious dispersal mechanism. Bird movements can easily result in the establishment of new populations of a species where they didn't exist before. But did you know that spiders can also disperse through something called ballooning?"}, {"video_title": "New localities lead to new biodiversity.mp3", "Sentence": "Species like plants that have a rooted-to-the-ground or sedentary habit, like I sometimes have when there's a hockey game on, even plants have dispersal stages in the form of seeds that can be distributed in air or in water or even in and on other organisms. Bird migration is an obvious dispersal mechanism. Bird movements can easily result in the establishment of new populations of a species where they didn't exist before. But did you know that spiders can also disperse through something called ballooning? Young spiders especially can release fine silk threads that are caught by the wind, carrying the spider aloft and to new territories. There are many other examples of dispersal. The spores of fungi that blow in the wind and get up my nose and give me allergies, or a sneeze full of bacteria or viruses."}, {"video_title": "New localities lead to new biodiversity.mp3", "Sentence": "But did you know that spiders can also disperse through something called ballooning? Young spiders especially can release fine silk threads that are caught by the wind, carrying the spider aloft and to new territories. There are many other examples of dispersal. The spores of fungi that blow in the wind and get up my nose and give me allergies, or a sneeze full of bacteria or viruses. Even that's a dispersal technique that has evolved among microbes that increases their ranges during cold and flu season. Things like corals, sea urchins, and snails also disperse. Mostly they do this during the earliest stages of their lives, drifting through the water as little larvae."}, {"video_title": "New localities lead to new biodiversity.mp3", "Sentence": "The spores of fungi that blow in the wind and get up my nose and give me allergies, or a sneeze full of bacteria or viruses. Even that's a dispersal technique that has evolved among microbes that increases their ranges during cold and flu season. Things like corals, sea urchins, and snails also disperse. Mostly they do this during the earliest stages of their lives, drifting through the water as little larvae. These larvae can be carried significant distances and when they eventually settle down on the substrate and metamorphose or change from the juvenile dispersing stage into a small version of the more sedentary adult, they establish new populations and expand the species ranges. Organisms or pieces and mats of vegetation that wash into the ocean from land can harbor terrestrial organisms that go along for the ride and are taken out to sea. They may drift to new places to live and if they land and are successful, this can result in the establishment of a new population."}, {"video_title": "New localities lead to new biodiversity.mp3", "Sentence": "Mostly they do this during the earliest stages of their lives, drifting through the water as little larvae. These larvae can be carried significant distances and when they eventually settle down on the substrate and metamorphose or change from the juvenile dispersing stage into a small version of the more sedentary adult, they establish new populations and expand the species ranges. Organisms or pieces and mats of vegetation that wash into the ocean from land can harbor terrestrial organisms that go along for the ride and are taken out to sea. They may drift to new places to live and if they land and are successful, this can result in the establishment of a new population. All these events in nature make it worth asking, what happens at the end of these Olympian journeys, these organismal odysseys? If the conditions are right and the organisms can continue to survive, a new population can be established in a new place. The ability to survive and reproduce in this new place is key."}, {"video_title": "New localities lead to new biodiversity.mp3", "Sentence": "They may drift to new places to live and if they land and are successful, this can result in the establishment of a new population. All these events in nature make it worth asking, what happens at the end of these Olympian journeys, these organismal odysseys? If the conditions are right and the organisms can continue to survive, a new population can be established in a new place. The ability to survive and reproduce in this new place is key. In the case of sexual species, individuals need to be carrying viable young when they arrive or find a member of the opposite sex with which to produce new generations. If you think of a coconut, which can travel hundreds of miles floating in the ocean, washing up on a bare lava shore, it's going to have a much harder time of it than if it washes up on a sandy beach. In other words, the conditions have to be right for the establishment of a new population."}, {"video_title": "New localities lead to new biodiversity.mp3", "Sentence": "The ability to survive and reproduce in this new place is key. In the case of sexual species, individuals need to be carrying viable young when they arrive or find a member of the opposite sex with which to produce new generations. If you think of a coconut, which can travel hundreds of miles floating in the ocean, washing up on a bare lava shore, it's going to have a much harder time of it than if it washes up on a sandy beach. In other words, the conditions have to be right for the establishment of a new population. In general, the greater the distance between a new population and the original population, the more likely the gene flow will be restricted between the two populations and the more likely the two populations will diverge from each other. And this takes us to the idea of isolation. Isolation can be very obvious on islands, but it's interesting to remember that not all islands have to be in the middle of a body of water."}, {"video_title": "New localities lead to new biodiversity.mp3", "Sentence": "In other words, the conditions have to be right for the establishment of a new population. In general, the greater the distance between a new population and the original population, the more likely the gene flow will be restricted between the two populations and the more likely the two populations will diverge from each other. And this takes us to the idea of isolation. Isolation can be very obvious on islands, but it's interesting to remember that not all islands have to be in the middle of a body of water. You can have isolation among oases in a desert, for example. You can have isolation on the tops of mountains or in the valleys between the mountains. Or you can have isolation in a fragment of rainforest that's surrounded by extensively clear-cut land."}, {"video_title": "New localities lead to new biodiversity.mp3", "Sentence": "Isolation can be very obvious on islands, but it's interesting to remember that not all islands have to be in the middle of a body of water. You can have isolation among oases in a desert, for example. You can have isolation on the tops of mountains or in the valleys between the mountains. Or you can have isolation in a fragment of rainforest that's surrounded by extensively clear-cut land. And these habitat islands can exhibit the same principles of isolation and restriction of gene flow that influence speciation. Amazing patterns of speciation can emerge in all of these systems because there are some pretty basic rules that emerge logically from thinking about islands, dispersal, and isolation, leading to an entire field of study known as island biogeography. One of these rules is that islands can be harder or easier to get to depending on how far away they are."}, {"video_title": "New localities lead to new biodiversity.mp3", "Sentence": "Or you can have isolation in a fragment of rainforest that's surrounded by extensively clear-cut land. And these habitat islands can exhibit the same principles of isolation and restriction of gene flow that influence speciation. Amazing patterns of speciation can emerge in all of these systems because there are some pretty basic rules that emerge logically from thinking about islands, dispersal, and isolation, leading to an entire field of study known as island biogeography. One of these rules is that islands can be harder or easier to get to depending on how far away they are. This is known as the distance factor. Second, the longer the island has been in existence, the more likely it is that organisms have already arrived there and the longer they have had to diverge from their parent population. That's the time factor."}, {"video_title": "New localities lead to new biodiversity.mp3", "Sentence": "One of these rules is that islands can be harder or easier to get to depending on how far away they are. This is known as the distance factor. Second, the longer the island has been in existence, the more likely it is that organisms have already arrived there and the longer they have had to diverge from their parent population. That's the time factor. A third concept is that the smaller the island, the less likely it is for a species to get there in the first place. That would be called the area factor. Fourthly, diverse environmental conditions on an island can enhance the island's biodiversity because there's a greater chance that the right climate, the right ecological resources will be present."}, {"video_title": "New localities lead to new biodiversity.mp3", "Sentence": "That's the time factor. A third concept is that the smaller the island, the less likely it is for a species to get there in the first place. That would be called the area factor. Fourthly, diverse environmental conditions on an island can enhance the island's biodiversity because there's a greater chance that the right climate, the right ecological resources will be present. And we can refer to this as the habitat factor. A fifth logical rule concerns the location of the island with respect to things like currents and winds that allow new energy in the form of nutrients to flow into the system, supporting ecosystem functions or increasing or decreasing the likelihood of new colonizers arriving. And I would call that the flow factor."}, {"video_title": "New localities lead to new biodiversity.mp3", "Sentence": "Fourthly, diverse environmental conditions on an island can enhance the island's biodiversity because there's a greater chance that the right climate, the right ecological resources will be present. And we can refer to this as the habitat factor. A fifth logical rule concerns the location of the island with respect to things like currents and winds that allow new energy in the form of nutrients to flow into the system, supporting ecosystem functions or increasing or decreasing the likelihood of new colonizers arriving. And I would call that the flow factor. A sixth factor is just chance and random events that also play a big role. I'm not sure there's a name for that one, so I'm calling it the serendipity factor. An example of that might be a freak storm that carries organisms with it."}, {"video_title": "New localities lead to new biodiversity.mp3", "Sentence": "And I would call that the flow factor. A sixth factor is just chance and random events that also play a big role. I'm not sure there's a name for that one, so I'm calling it the serendipity factor. An example of that might be a freak storm that carries organisms with it. You might think of other factors or tweaks to these basic rules. For example, if you throw in the fact that organisms differ greatly in their ability to disperse, you have a rich and complicated overlay of things influencing the biodiversity on any particular island and why that biodiversity can be so different from one island to the next. Here's a simplified graph that illustrates a couple of these factors."}, {"video_title": "New localities lead to new biodiversity.mp3", "Sentence": "An example of that might be a freak storm that carries organisms with it. You might think of other factors or tweaks to these basic rules. For example, if you throw in the fact that organisms differ greatly in their ability to disperse, you have a rich and complicated overlay of things influencing the biodiversity on any particular island and why that biodiversity can be so different from one island to the next. Here's a simplified graph that illustrates a couple of these factors. You've got basically two sets of curves. One set refers to how close or far an island might be to the mainland and how that affects the rate of colonization. And the other set refers to whether the islands are large or small and how that's related to the rate or probability of extinction."}, {"video_title": "New localities lead to new biodiversity.mp3", "Sentence": "Here's a simplified graph that illustrates a couple of these factors. You've got basically two sets of curves. One set refers to how close or far an island might be to the mainland and how that affects the rate of colonization. And the other set refers to whether the islands are large or small and how that's related to the rate or probability of extinction. The horizontal axis represents increasing species richness. So you have a couple of interesting and important intersection points that mark the lower richness of a small distant island compared to that of a large nearby island. This graph incorporates a couple of other things."}, {"video_title": "New localities lead to new biodiversity.mp3", "Sentence": "And the other set refers to whether the islands are large or small and how that's related to the rate or probability of extinction. The horizontal axis represents increasing species richness. So you have a couple of interesting and important intersection points that mark the lower richness of a small distant island compared to that of a large nearby island. This graph incorporates a couple of other things. One is the balancing of colonization and extinction. The more crowded the island becomes, the more likely it is that extinctions will happen. It also summarizes the idea that large islands close to the mainland's source of new populations, places like, say, Madagascar, will have lots and lots of species."}, {"video_title": "New localities lead to new biodiversity.mp3", "Sentence": "This graph incorporates a couple of other things. One is the balancing of colonization and extinction. The more crowded the island becomes, the more likely it is that extinctions will happen. It also summarizes the idea that large islands close to the mainland's source of new populations, places like, say, Madagascar, will have lots and lots of species. But remember that on a big island like Madagascar, we have the habitat factor too. Populations can disperse on the island itself, find new habitats, encounter new barriers, and all kinds of new species can arise. And if you look at what's going on in Madagascar, that's definitely true."}, {"video_title": "New localities lead to new biodiversity.mp3", "Sentence": "It also summarizes the idea that large islands close to the mainland's source of new populations, places like, say, Madagascar, will have lots and lots of species. But remember that on a big island like Madagascar, we have the habitat factor too. Populations can disperse on the island itself, find new habitats, encounter new barriers, and all kinds of new species can arise. And if you look at what's going on in Madagascar, that's definitely true. Madagascar has lots of endemics, species that arose there and nowhere else. Also, the geologic evidence is strong that Madagascar broke free from Africa in the past, carrying with it subsets of species that existed on Africa and then continued to diverge and evolve on Madagascar. In contrast, consider the Galapagos."}, {"video_title": "New localities lead to new biodiversity.mp3", "Sentence": "And if you look at what's going on in Madagascar, that's definitely true. Madagascar has lots of endemics, species that arose there and nowhere else. Also, the geologic evidence is strong that Madagascar broke free from Africa in the past, carrying with it subsets of species that existed on Africa and then continued to diverge and evolve on Madagascar. In contrast, consider the Galapagos. This archipelago of islands is relatively far from any mainland and sprung up there through volcanism. These remote islands had almost no life on them when they first appeared. There were fewer species arriving there, but because of the multitude of islands within the archipelago, there is subsequent speciation of populations that make it to one island and then island hop from there."}, {"video_title": "New localities lead to new biodiversity.mp3", "Sentence": "In contrast, consider the Galapagos. This archipelago of islands is relatively far from any mainland and sprung up there through volcanism. These remote islands had almost no life on them when they first appeared. There were fewer species arriving there, but because of the multitude of islands within the archipelago, there is subsequent speciation of populations that make it to one island and then island hop from there. Lots of island groups illustrate these ideas. Hawaii and the Philippines, for example, in any of those island groupings, you can see all of these overlapping factors at work. It's a grand and beautiful view, I think, of how islands can foster the formation of new species."}, {"video_title": "New localities lead to new biodiversity.mp3", "Sentence": "There were fewer species arriving there, but because of the multitude of islands within the archipelago, there is subsequent speciation of populations that make it to one island and then island hop from there. Lots of island groups illustrate these ideas. Hawaii and the Philippines, for example, in any of those island groupings, you can see all of these overlapping factors at work. It's a grand and beautiful view, I think, of how islands can foster the formation of new species. But the graph can also tell you something about why so many island species are in such trouble. The island biogeography curves summarize that as well because we've got this word in there, extinction. Many island populations are vulnerable to extinction."}, {"video_title": "New localities lead to new biodiversity.mp3", "Sentence": "It's a grand and beautiful view, I think, of how islands can foster the formation of new species. But the graph can also tell you something about why so many island species are in such trouble. The island biogeography curves summarize that as well because we've got this word in there, extinction. Many island populations are vulnerable to extinction. I've been talking about all of this with no humans involved, but if you put humans in the equation, drop them into that island ecosystem, who's to say what the dimensions of the effects will be down the road? How do the curves get changed by human activity? What happens to the extinction curves?"}, {"video_title": "New localities lead to new biodiversity.mp3", "Sentence": "Many island populations are vulnerable to extinction. I've been talking about all of this with no humans involved, but if you put humans in the equation, drop them into that island ecosystem, who's to say what the dimensions of the effects will be down the road? How do the curves get changed by human activity? What happens to the extinction curves? How steep will they be? How big are the effects that humans have on these systems of endemic species? Scientists who try to gather data to make these curves more precisely understood also know that these human effects can be big, especially on islands."}, {"video_title": "Facilitated diffusion   Membranes and transport   Biology   Khan Academy.mp3", "Sentence": "And we talked about how small, non-charged, non-polar molecules would actually have the easiest time, things like carbon dioxide or molecular oxygen, would have the easiest time diffusing through the cellular membrane. They are small enough to kind of get through the little gaps here, and then since they have no charge or polarity, they're going to be fairly indifferent as they pass through. And then we talked about in between, you have things like water molecules, which are small enough to pass through the gaps, but they have some polarity, so they're not going to be able to get through super easily, but they will be able to seep through. And then we talked about things that would have a tough time and that's charged particles. Because charged particles, and we have some ions right over here, sodium ion, a potassium ion, even though these are fairly small, they're going to interact a lot with the phosphate heads right over here with this charge, which is going to make it hard for them to actually penetrate through the membrane. What I want to talk about in this video is still passive transport. Remember, passive transport is about not using energy."}, {"video_title": "Facilitated diffusion   Membranes and transport   Biology   Khan Academy.mp3", "Sentence": "And then we talked about things that would have a tough time and that's charged particles. Because charged particles, and we have some ions right over here, sodium ion, a potassium ion, even though these are fairly small, they're going to interact a lot with the phosphate heads right over here with this charge, which is going to make it hard for them to actually penetrate through the membrane. What I want to talk about in this video is still passive transport. Remember, passive transport is about not using energy. It's about moving down the concentration gradient, but we're going to talk about ways that passive transport can happen a little bit easier for some of these molecules over here. And that's because their transport, their passive transport, is going to be facilitated. So what we're going to talk about in this video, let me figure out a place where I can write it, is facilitated diffusion."}, {"video_title": "Facilitated diffusion   Membranes and transport   Biology   Khan Academy.mp3", "Sentence": "Remember, passive transport is about not using energy. It's about moving down the concentration gradient, but we're going to talk about ways that passive transport can happen a little bit easier for some of these molecules over here. And that's because their transport, their passive transport, is going to be facilitated. So what we're going to talk about in this video, let me figure out a place where I can write it, is facilitated diffusion. Let me write that down. Facilitated diffusion. So the last video was just straight up diffusion."}, {"video_title": "Facilitated diffusion   Membranes and transport   Biology   Khan Academy.mp3", "Sentence": "So what we're going to talk about in this video, let me figure out a place where I can write it, is facilitated diffusion. Let me write that down. Facilitated diffusion. So the last video was just straight up diffusion. Now we're going to talk about facilitating it. So what do you think, if you were trying to engineer something that would make it easy for these types of molecules, either a water molecule or an ion, to move down its concentration gradient, what would you do? Well, you might say, well, if I didn't have to mess with all of this, you know, all the hydrophilic heads and then the hydrophobic tails and then the hydrophilic heads here, well, that would make it pretty easy to move down your diffusion gradient."}, {"video_title": "Facilitated diffusion   Membranes and transport   Biology   Khan Academy.mp3", "Sentence": "So the last video was just straight up diffusion. Now we're going to talk about facilitating it. So what do you think, if you were trying to engineer something that would make it easy for these types of molecules, either a water molecule or an ion, to move down its concentration gradient, what would you do? Well, you might say, well, if I didn't have to mess with all of this, you know, all the hydrophilic heads and then the hydrophobic tails and then the hydrophilic heads here, well, that would make it pretty easy to move down your diffusion gradient. And that's exactly what has emerged in nature. Essentially, it just tunnels through, tunnels through the membrane. And so one form of facilitated diffusion can happen through what we call channel proteins."}, {"video_title": "Facilitated diffusion   Membranes and transport   Biology   Khan Academy.mp3", "Sentence": "Well, you might say, well, if I didn't have to mess with all of this, you know, all the hydrophilic heads and then the hydrophobic tails and then the hydrophilic heads here, well, that would make it pretty easy to move down your diffusion gradient. And that's exactly what has emerged in nature. Essentially, it just tunnels through, tunnels through the membrane. And so one form of facilitated diffusion can happen through what we call channel proteins. Let me write this in orange for no good reason. Channel, channel, channel proteins. Channel proteins."}, {"video_title": "Facilitated diffusion   Membranes and transport   Biology   Khan Academy.mp3", "Sentence": "And so one form of facilitated diffusion can happen through what we call channel proteins. Let me write this in orange for no good reason. Channel, channel, channel proteins. Channel proteins. And an example of a channel protein might be this one right over here. And maybe this one is specialized for being a channel for water. And so we would call this, this particular one we could call an aquaporin."}, {"video_title": "Facilitated diffusion   Membranes and transport   Biology   Khan Academy.mp3", "Sentence": "Channel proteins. And an example of a channel protein might be this one right over here. And maybe this one is specialized for being a channel for water. And so we would call this, this particular one we could call an aquaporin. Aqua, aquaporin, which is just a channel protein for water. And so you see it has this hole on top. And let's say you had more water molecules outside the cell than you have inside the cell."}, {"video_title": "Facilitated diffusion   Membranes and transport   Biology   Khan Academy.mp3", "Sentence": "And so we would call this, this particular one we could call an aquaporin. Aqua, aquaporin, which is just a channel protein for water. And so you see it has this hole on top. And let's say you had more water molecules outside the cell than you have inside the cell. And you wanted to move down its concentration gradient. Or maybe just you have a higher concentration of solute here, and so we're going to have osmosis occurring. So the water molecules are gonna, they're more likely to come, they're more likely to come from the outside to the inside than from the inside to the outside."}, {"video_title": "Facilitated diffusion   Membranes and transport   Biology   Khan Academy.mp3", "Sentence": "And let's say you had more water molecules outside the cell than you have inside the cell. And you wanted to move down its concentration gradient. Or maybe just you have a higher concentration of solute here, and so we're going to have osmosis occurring. So the water molecules are gonna, they're more likely to come, they're more likely to come from the outside to the inside than from the inside to the outside. And so you could have water molecules going there. They don't even have to really mess with the membrane. They're just gonna go through this aquaporin and then come out on the inside of the cell."}, {"video_title": "Facilitated diffusion   Membranes and transport   Biology   Khan Academy.mp3", "Sentence": "So the water molecules are gonna, they're more likely to come, they're more likely to come from the outside to the inside than from the inside to the outside. And so you could have water molecules going there. They don't even have to really mess with the membrane. They're just gonna go through this aquaporin and then come out on the inside of the cell. And you have similar channel proteins for ions. So this might be one for ions. And so let's say that this is a sodium, these are sodium ions right over here."}, {"video_title": "Facilitated diffusion   Membranes and transport   Biology   Khan Academy.mp3", "Sentence": "They're just gonna go through this aquaporin and then come out on the inside of the cell. And you have similar channel proteins for ions. So this might be one for ions. And so let's say that this is a sodium, these are sodium ions right over here. They're charged. They would have trouble getting through. But this channel protein might be specific to them and allows them, it allows them to go through."}, {"video_title": "Facilitated diffusion   Membranes and transport   Biology   Khan Academy.mp3", "Sentence": "And so let's say that this is a sodium, these are sodium ions right over here. They're charged. They would have trouble getting through. But this channel protein might be specific to them and allows them, it allows them to go through. And as we'll see when you study things like neurons, we'll see that these channel proteins, especially for ions, are incredibly important for amplifying an electrical signal down, or a chemo-electrical signal, I guess I could say. And they can also be gated. They can also open and close depending on the different conditions that are in different parts of the cell."}, {"video_title": "Facilitated diffusion   Membranes and transport   Biology   Khan Academy.mp3", "Sentence": "But this channel protein might be specific to them and allows them, it allows them to go through. And as we'll see when you study things like neurons, we'll see that these channel proteins, especially for ions, are incredibly important for amplifying an electrical signal down, or a chemo-electrical signal, I guess I could say. And they can also be gated. They can also open and close depending on the different conditions that are in different parts of the cell. So these channel proteins, they could just be open, or they could be open and closed, gated, based on different conditions, which you can see, that's actually key to what happens in nerve cells that we'll see in future videos. Now another type of facilitated diffusion can occur through what we call carrier proteins. Carrier proteins."}, {"video_title": "Facilitated diffusion   Membranes and transport   Biology   Khan Academy.mp3", "Sentence": "They can also open and close depending on the different conditions that are in different parts of the cell. So these channel proteins, they could just be open, or they could be open and closed, gated, based on different conditions, which you can see, that's actually key to what happens in nerve cells that we'll see in future videos. Now another type of facilitated diffusion can occur through what we call carrier proteins. Carrier proteins. And I wanna be clear. While I'm gonna talk about carrier proteins, but people are still studying exactly how they work. But the view is, okay, let me just draw the membrane here."}, {"video_title": "Facilitated diffusion   Membranes and transport   Biology   Khan Academy.mp3", "Sentence": "Carrier proteins. And I wanna be clear. While I'm gonna talk about carrier proteins, but people are still studying exactly how they work. But the view is, okay, let me just draw the membrane here. Let me draw, let me draw a membrane. I'm gonna do a carrier protein. I'm gonna draw a carrier protein in the membrane."}, {"video_title": "Facilitated diffusion   Membranes and transport   Biology   Khan Academy.mp3", "Sentence": "But the view is, okay, let me just draw the membrane here. Let me draw, let me draw a membrane. I'm gonna do a carrier protein. I'm gonna draw a carrier protein in the membrane. So this is a cross-section of, this is of my membrane, my phospholipid bilayer here. Almost done. And then a carrier protein, and the way I'm gonna draw it isn't exactly how a carrier protein would actually look, but it would hopefully give you the right idea."}, {"video_title": "Facilitated diffusion   Membranes and transport   Biology   Khan Academy.mp3", "Sentence": "I'm gonna draw a carrier protein in the membrane. So this is a cross-section of, this is of my membrane, my phospholipid bilayer here. Almost done. And then a carrier protein, and the way I'm gonna draw it isn't exactly how a carrier protein would actually look, but it would hopefully give you the right idea. So maybe it's like this. Maybe it's like this. And if things wanna move down their concentration gradient, let's say you have a higher concentration above, and I'm just gonna say some arbitrary particle has a higher concentration above than it does below, they can actually attach potentially, or kind of get into a compartment over here, and then that would trigger the carrier protein to change its shape so that, and let me see if I can draw its changed shape well."}, {"video_title": "Facilitated diffusion   Membranes and transport   Biology   Khan Academy.mp3", "Sentence": "And then a carrier protein, and the way I'm gonna draw it isn't exactly how a carrier protein would actually look, but it would hopefully give you the right idea. So maybe it's like this. Maybe it's like this. And if things wanna move down their concentration gradient, let's say you have a higher concentration above, and I'm just gonna say some arbitrary particle has a higher concentration above than it does below, they can actually attach potentially, or kind of get into a compartment over here, and then that would trigger the carrier protein to change its shape so that, and let me see if I can draw its changed shape well. So it could change its shape. So this is when it's taking stuff from above, and then when it sees that, hey, I've got stuff here, it can, let me, it can change its shape to look something like this. So it could kind of flip around."}, {"video_title": "Facilitated diffusion   Membranes and transport   Biology   Khan Academy.mp3", "Sentence": "And if things wanna move down their concentration gradient, let's say you have a higher concentration above, and I'm just gonna say some arbitrary particle has a higher concentration above than it does below, they can actually attach potentially, or kind of get into a compartment over here, and then that would trigger the carrier protein to change its shape so that, and let me see if I can draw its changed shape well. So it could change its shape. So this is when it's taking stuff from above, and then when it sees that, hey, I've got stuff here, it can, let me, it can change its shape to look something like this. So it could kind of flip around. Let me get the other tool. It could, whoops, really having trouble with my tools today. All right."}, {"video_title": "Facilitated diffusion   Membranes and transport   Biology   Khan Academy.mp3", "Sentence": "So it could kind of flip around. Let me get the other tool. It could, whoops, really having trouble with my tools today. All right. All right, it could flip around like this. So before it was open to the top, but now it could flip around, and the stuff that it just collected from the top could be dumped inside, inside the cell. And once again, this is passive transport because it's all about things moving down their concentration gradient."}, {"video_title": "Facilitated diffusion   Membranes and transport   Biology   Khan Academy.mp3", "Sentence": "All right. All right, it could flip around like this. So before it was open to the top, but now it could flip around, and the stuff that it just collected from the top could be dumped inside, inside the cell. And once again, this is passive transport because it's all about things moving down their concentration gradient. If there was no cellular membrane here, these things would have moved in this direction. You would have had more things moving in this direction in a given amount of time than you would have had things going in the opposite direction, but the cellular membrane was getting in the way, but then this carrier membrane can facilitate that passive transport. It can facilitate the actual diffusion."}, {"video_title": "Artificial selection and domestication   Natural selection   AP Biology   Khan Academy.mp3", "Sentence": "Although, in, for example, the case of this character and this character, the mechanics could get quite difficult. But an interesting question is, is where do dogs come from, and why do we have these seemingly specialized breeds amongst dogs? You might have things like a Rottweiler that's better for protection. You might have things like Terriers that have been specialized to maybe go after rodents. You have things like Border Collies that are good at herding other types of animals. The simple answer is, through artificial selection and domestication. Remember, in any population of a species, there's variation in that species."}, {"video_title": "Artificial selection and domestication   Natural selection   AP Biology   Khan Academy.mp3", "Sentence": "You might have things like Terriers that have been specialized to maybe go after rodents. You have things like Border Collies that are good at herding other types of animals. The simple answer is, through artificial selection and domestication. Remember, in any population of a species, there's variation in that species. And when we talked about natural selection, that's where the environment might select for certain of those variants. Certain of those variants might make it a little bit easier to survive or reproduce, and then those would predominate, and that's how evolution happens. Artificial selection and domestication is where humans take matters into their own hands."}, {"video_title": "Artificial selection and domestication   Natural selection   AP Biology   Khan Academy.mp3", "Sentence": "Remember, in any population of a species, there's variation in that species. And when we talked about natural selection, that's where the environment might select for certain of those variants. Certain of those variants might make it a little bit easier to survive or reproduce, and then those would predominate, and that's how evolution happens. Artificial selection and domestication is where humans take matters into their own hands. And instead of waiting for nature to do things, they are the selection factor. They pick which of the species get to reproduce and which ones don't. And when you have that type of artificial selection, the change can happen much, much faster."}, {"video_title": "Artificial selection and domestication   Natural selection   AP Biology   Khan Academy.mp3", "Sentence": "Artificial selection and domestication is where humans take matters into their own hands. And instead of waiting for nature to do things, they are the selection factor. They pick which of the species get to reproduce and which ones don't. And when you have that type of artificial selection, the change can happen much, much faster. Breeding is essentially artificial selection. So dogs like this, and all the dogs we know of, had ancestors that looked like this, that looked like a wolf, that were a wolf. And what we theorize is that the early stages of some wolves eventually evolving into dogs might have been more traditional natural selection, where tens of thousands of years ago, our hunter-gatherer ancestors, as they hunted and gathering, they might have left over food here or there."}, {"video_title": "Artificial selection and domestication   Natural selection   AP Biology   Khan Academy.mp3", "Sentence": "And when you have that type of artificial selection, the change can happen much, much faster. Breeding is essentially artificial selection. So dogs like this, and all the dogs we know of, had ancestors that looked like this, that looked like a wolf, that were a wolf. And what we theorize is that the early stages of some wolves eventually evolving into dogs might have been more traditional natural selection, where tens of thousands of years ago, our hunter-gatherer ancestors, as they hunted and gathering, they might have left over food here or there. And some of the wolves that just happened to be the variants that were a little bit more comfortable getting close to humans might have benefited from being able to get some of that leftover food, being able to get some of the remains that the human beings left behind. But then over time, human beings probably realized that, hey, these wolves are useful to have around. Maybe they provide some form of protection."}, {"video_title": "Artificial selection and domestication   Natural selection   AP Biology   Khan Academy.mp3", "Sentence": "And what we theorize is that the early stages of some wolves eventually evolving into dogs might have been more traditional natural selection, where tens of thousands of years ago, our hunter-gatherer ancestors, as they hunted and gathering, they might have left over food here or there. And some of the wolves that just happened to be the variants that were a little bit more comfortable getting close to humans might have benefited from being able to get some of that leftover food, being able to get some of the remains that the human beings left behind. But then over time, human beings probably realized that, hey, these wolves are useful to have around. Maybe they provide some form of protection. Maybe over time, they started breeding the wolves. So the wolves that were especially friendly, the wolves that were especially good at a certain task, say protection, or going after some type of an animal, or retrieving things, they allowed those to reproduce together, and over time, over tens of thousands of years, we went from wolves to dogs. And even once we had dogs, the breeding got even more specialized."}, {"video_title": "Artificial selection and domestication   Natural selection   AP Biology   Khan Academy.mp3", "Sentence": "Maybe they provide some form of protection. Maybe over time, they started breeding the wolves. So the wolves that were especially friendly, the wolves that were especially good at a certain task, say protection, or going after some type of an animal, or retrieving things, they allowed those to reproduce together, and over time, over tens of thousands of years, we went from wolves to dogs. And even once we had dogs, the breeding got even more specialized. As I mentioned, things like border collies, this was many years, many generations of breeding where sheep herders might have selected dogs that were good at herding sheep, that terriers came from dogs that were good at going after rodents, things like rottweilers or dogs, breeding the dogs that were especially good at providing protection or defense. And it isn't just dogs that are products of artificial selection and domestication. Pretty much any animal that you might see on, say, a farm would be the product of artificial selection and domestication."}, {"video_title": "Artificial selection and domestication   Natural selection   AP Biology   Khan Academy.mp3", "Sentence": "And even once we had dogs, the breeding got even more specialized. As I mentioned, things like border collies, this was many years, many generations of breeding where sheep herders might have selected dogs that were good at herding sheep, that terriers came from dogs that were good at going after rodents, things like rottweilers or dogs, breeding the dogs that were especially good at providing protection or defense. And it isn't just dogs that are products of artificial selection and domestication. Pretty much any animal that you might see on, say, a farm would be the product of artificial selection and domestication. A wild pig looks like this, while the ones that you would see on a farm look like that, and once again, they would have selected for things like docility, things where they're less aggressive and they're easier to take care of. And artificial selection and domestication does not apply just to animals. Pretty much anything you might see in the produce section of your supermarket is the product of artificial selection and domestication."}, {"video_title": "Allele frequency (2).mp3", "Sentence": "Allele frequency. And just as a reminder, an allele is a variant of a gene. You get a variant of a gene from your mother and you get another variant of the gene from the father. And so when we're talking about the allele, we're talking about that specific variant that you got from your mother or your father. And we've seen this before. But now let's dig a little bit deeper. And to help us get our heads around this, we'll start with a fairly common model for this."}, {"video_title": "Allele frequency (2).mp3", "Sentence": "And so when we're talking about the allele, we're talking about that specific variant that you got from your mother or your father. And we've seen this before. But now let's dig a little bit deeper. And to help us get our heads around this, we'll start with a fairly common model for this. And we're gonna think about eye color. And obviously this is a very large simplification. But let's just assume that we have a population where there's only two variants of an eye color gene."}, {"video_title": "Allele frequency (2).mp3", "Sentence": "And to help us get our heads around this, we'll start with a fairly common model for this. And we're gonna think about eye color. And obviously this is a very large simplification. But let's just assume that we have a population where there's only two variants of an eye color gene. Let's first assume there is an eye color gene and let's assume there's two variants. One variant, one allele for eye color, we'll use the shorthand capital B. Let's say that's the allele for brown."}, {"video_title": "Allele frequency (2).mp3", "Sentence": "But let's just assume that we have a population where there's only two variants of an eye color gene. Let's first assume there is an eye color gene and let's assume there's two variants. One variant, one allele for eye color, we'll use the shorthand capital B. Let's say that's the allele for brown. Brown eye color. And we're gonna assume that this one is dominant. It's dominant over the other allele."}, {"video_title": "Allele frequency (2).mp3", "Sentence": "Let's say that's the allele for brown. Brown eye color. And we're gonna assume that this one is dominant. It's dominant over the other allele. Now the other allele, we're gonna assume, is for blue eye color. And we'll represent that with a lowercase b. So that is blue eye color."}, {"video_title": "Allele frequency (2).mp3", "Sentence": "It's dominant over the other allele. Now the other allele, we're gonna assume, is for blue eye color. And we'll represent that with a lowercase b. So that is blue eye color. And we're going to assume that this is recessive. So once again, this is review. Someone who has one of the big B alleles, the brown alleles."}, {"video_title": "Allele frequency (2).mp3", "Sentence": "So that is blue eye color. And we're going to assume that this is recessive. So once again, this is review. Someone who has one of the big B alleles, the brown alleles. It doesn't matter what their other allele is going to be because it's either gonna be another brown or it's going to be a blue. They're going to show brown eyes. So this is going to be brown eyes."}, {"video_title": "Allele frequency (2).mp3", "Sentence": "Someone who has one of the big B alleles, the brown alleles. It doesn't matter what their other allele is going to be because it's either gonna be another brown or it's going to be a blue. They're going to show brown eyes. So this is going to be brown eyes. And this is going to be brown eyes because the capital B is dominant. The only way to get blue eyes is to be, the only way to have blue eyes is to be a homozygote for the recessive allele. And all of that, of course, is review."}, {"video_title": "Allele frequency (2).mp3", "Sentence": "So this is going to be brown eyes. And this is going to be brown eyes because the capital B is dominant. The only way to get blue eyes is to be, the only way to have blue eyes is to be a homozygote for the recessive allele. And all of that, of course, is review. We've seen that before. But now let's think about allele frequency. And to think about that, I'll set up a very artificially small population."}, {"video_title": "Allele frequency (2).mp3", "Sentence": "And all of that, of course, is review. We've seen that before. But now let's think about allele frequency. And to think about that, I'll set up a very artificially small population. So let's say our population has exactly two people in it. Population has exactly two people in it, person one and person two. And let's say we're able to look into their DNA and figure out their genotypes."}, {"video_title": "Allele frequency (2).mp3", "Sentence": "And to think about that, I'll set up a very artificially small population. So let's say our population has exactly two people in it. Population has exactly two people in it, person one and person two. And let's say we're able to look into their DNA and figure out their genotypes. So person one, let's say, has a capital B allele, has a brown allele and a blue allele. While person two has two blue alleles. Now given that we know the genotypes in this artificially small population, now we can start thinking about the allele frequencies or the frequencies of the different alleles."}, {"video_title": "Allele frequency (2).mp3", "Sentence": "And let's say we're able to look into their DNA and figure out their genotypes. So person one, let's say, has a capital B allele, has a brown allele and a blue allele. While person two has two blue alleles. Now given that we know the genotypes in this artificially small population, now we can start thinking about the allele frequencies or the frequencies of the different alleles. So what do you think is going to be the frequency, the frequency of the brown allele in this population? And I encourage you to pause this video and think about this on your own. So I'm assuming you've had a go at it."}, {"video_title": "Allele frequency (2).mp3", "Sentence": "Now given that we know the genotypes in this artificially small population, now we can start thinking about the allele frequencies or the frequencies of the different alleles. So what do you think is going to be the frequency, the frequency of the brown allele in this population? And I encourage you to pause this video and think about this on your own. So I'm assuming you've had a go at it. So you might be tempted to say, oh, well it looks like one out of two people have it, maybe it's 50%. But that wouldn't be the right way to think about allele frequencies. And allele frequencies, you wanna dig a little bit deeper and look at the individual alleles."}, {"video_title": "Allele frequency (2).mp3", "Sentence": "So I'm assuming you've had a go at it. So you might be tempted to say, oh, well it looks like one out of two people have it, maybe it's 50%. But that wouldn't be the right way to think about allele frequencies. And allele frequencies, you wanna dig a little bit deeper and look at the individual alleles. And when you look at that, you say, okay, there's four individual alleles in this population of, or there's four variants in this, or there's literally four chromosomes, I guess you could say, that are carrying that gene in this population. And out of them, one of them carry, one of them is the capital B, is the capital B allele. And so we could say that that is going to be 0.25, or 25%."}, {"video_title": "Allele frequency (2).mp3", "Sentence": "And allele frequencies, you wanna dig a little bit deeper and look at the individual alleles. And when you look at that, you say, okay, there's four individual alleles in this population of, or there's four variants in this, or there's literally four chromosomes, I guess you could say, that are carrying that gene in this population. And out of them, one of them carry, one of them is the capital B, is the capital B allele. And so we could say that that is going to be 0.25, or 25%. So once again, 20, 25% of the genes for eye color have the capital B allele, have the brown allele. Now we can do the same, we can ask ourselves the same question for the lowercase b allele. What fraction of the genes in this population are code for or represent the lowercase b, the blue allele?"}, {"video_title": "Allele frequency (2).mp3", "Sentence": "And so we could say that that is going to be 0.25, or 25%. So once again, 20, 25% of the genes for eye color have the capital B allele, have the brown allele. Now we can do the same, we can ask ourselves the same question for the lowercase b allele. What fraction of the genes in this population are code for or represent the lowercase b, the blue allele? And once again, I encourage you to pause the video and think about it. Well, very similar idea. There's four genes in the population that are coding for eye color."}, {"video_title": "Allele frequency (2).mp3", "Sentence": "What fraction of the genes in this population are code for or represent the lowercase b, the blue allele? And once again, I encourage you to pause the video and think about it. Well, very similar idea. There's four genes in the population that are coding for eye color. Of them, one, two, three, one, two, three, code for or are the lowercase blue, are the lowercase blue allele. So that's 0.75, or 75%. 75% of the genes code for the lowercase, the blue allele, while 25 are the brown, are the brown allele."}, {"video_title": "Allele frequency (2).mp3", "Sentence": "There's four genes in the population that are coding for eye color. Of them, one, two, three, one, two, three, code for or are the lowercase blue, are the lowercase blue allele. So that's 0.75, or 75%. 75% of the genes code for the lowercase, the blue allele, while 25 are the brown, are the brown allele. And I really wanna hit this point home, how this is different than, say, the phenotype frequency. If I asked you in the population, if I asked you the percent of brown-eyed people, brown-eyed people, so now I'm talking about phenotype, what would that be? Well, there's two people in the population, one of them is exhibiting brown eyes, so that's going to be 1.5."}, {"video_title": "Allele frequency (2).mp3", "Sentence": "75% of the genes code for the lowercase, the blue allele, while 25 are the brown, are the brown allele. And I really wanna hit this point home, how this is different than, say, the phenotype frequency. If I asked you in the population, if I asked you the percent of brown-eyed people, brown-eyed people, so now I'm talking about phenotype, what would that be? Well, there's two people in the population, one of them is exhibiting brown eyes, so that's going to be 1.5. And similarly, if I were to ask you what is the percentage of people who are blue-eyed? That too would be 1.5. This person is one of the two people, they're exhibiting blue eyes."}, {"video_title": "Allele frequency (2).mp3", "Sentence": "Well, there's two people in the population, one of them is exhibiting brown eyes, so that's going to be 1.5. And similarly, if I were to ask you what is the percentage of people who are blue-eyed? That too would be 1.5. This person is one of the two people, they're exhibiting blue eyes. But allele frequency, we're digging deeper. We're looking at the genotypes, and we're saying, well, out of the four genes here, one of them is the big B allele, so that's 25%, so 25% of the gene population codes for, is the brown allele, and 75% is the blue allele. And this is really important to internalize, because once we internalize this, then as we'll see, the ideas in the Hardy-Weinberg principle start to make a lot of sense."}, {"video_title": "Allele frequency (2).mp3", "Sentence": "This person is one of the two people, they're exhibiting blue eyes. But allele frequency, we're digging deeper. We're looking at the genotypes, and we're saying, well, out of the four genes here, one of them is the big B allele, so that's 25%, so 25% of the gene population codes for, is the brown allele, and 75% is the blue allele. And this is really important to internalize, because once we internalize this, then as we'll see, the ideas in the Hardy-Weinberg principle start to make a lot of sense. And I'll do a little bit of foreshadowing. We can denote this, and this is just a convention that's often used, by the lowercase letter p, and we can use q, lowercase q, to denote the frequency. So p, lowercase p, is the frequency of the dominant allele, lowercase q, the frequency of the recessive allele."}, {"video_title": "Allele frequency (2).mp3", "Sentence": "And this is really important to internalize, because once we internalize this, then as we'll see, the ideas in the Hardy-Weinberg principle start to make a lot of sense. And I'll do a little bit of foreshadowing. We can denote this, and this is just a convention that's often used, by the lowercase letter p, and we can use q, lowercase q, to denote the frequency. So p, lowercase p, is the frequency of the dominant allele, lowercase q, the frequency of the recessive allele. But what's true here? What's true of p, what's true, what's going to be true of p plus q? What's going to be, what's p plus q going to be equal to?"}, {"video_title": "Allele frequency (2).mp3", "Sentence": "So p, lowercase p, is the frequency of the dominant allele, lowercase q, the frequency of the recessive allele. But what's true here? What's true of p, what's true, what's going to be true of p plus q? What's going to be, what's p plus q going to be equal to? And I encourage you to pause the video again, and think about that. What is this going to be equal to? Well, when we started off, we said that there's only two potential, that's one of the assumptions we assumed."}, {"video_title": "Allele frequency (2).mp3", "Sentence": "What's going to be, what's p plus q going to be equal to? And I encourage you to pause the video again, and think about that. What is this going to be equal to? Well, when we started off, we said that there's only two potential, that's one of the assumptions we assumed. We assumed there's only two alleles in this population, and kind of the allele population for this, and this gene population for this trait. So the frequency of the dominant ones, plus the frequency of the recessive ones, well, everyone's gonna have one of those two, so if you add those two frequencies, it's going to have to add to 100%, 100%. And we see that there, 1 4th plus 3 4th is one, is one, or 100%, and 25% plus 75% is also 100%."}, {"video_title": "Variation in a Species (2).mp3", "Sentence": "The whole process of natural selection is to some degree dependent on the idea of variation, that within any population of a species, you have some genetic variation. So for example, let's say I have a bunch of, well, this is the circle species. And one guy is that color, and then I've got a bunch more. Maybe some are that color. That's the same color. That one, and that one, and that one. And for whatever reason, sometimes there are no environmental factors that will predispose one of these guys to be able to survive and reproduce over the other."}, {"video_title": "Variation in a Species (2).mp3", "Sentence": "Maybe some are that color. That's the same color. That one, and that one, and that one. And for whatever reason, sometimes there are no environmental factors that will predispose one of these guys to be able to survive and reproduce over the other. But every now and then, there might be some environmental factor. And it makes maybe all of a sudden, this guy is more fit to reproduce. And so for whatever reason, this guy is able to reproduce more frequently, and these guys less frequently."}, {"video_title": "Variation in a Species (2).mp3", "Sentence": "And for whatever reason, sometimes there are no environmental factors that will predispose one of these guys to be able to survive and reproduce over the other. But every now and then, there might be some environmental factor. And it makes maybe all of a sudden, this guy is more fit to reproduce. And so for whatever reason, this guy is able to reproduce more frequently, and these guys less frequently. And some of them get killed or whatever, eaten by birds or they're just not able to reproduce for whatever reason. And then maybe these guys are something in between. And so over time, the frequency of the different traits you see in this population will change."}, {"video_title": "Variation in a Species (2).mp3", "Sentence": "And so for whatever reason, this guy is able to reproduce more frequently, and these guys less frequently. And some of them get killed or whatever, eaten by birds or they're just not able to reproduce for whatever reason. And then maybe these guys are something in between. And so over time, the frequency of the different traits you see in this population will change. And if they are drastic enough, maybe these guys start becoming dominant and start not liking these guys because they're so different or whatever else. We could see a lot of different reasons. This could eventually turn into a different species."}, {"video_title": "Variation in a Species (2).mp3", "Sentence": "And so over time, the frequency of the different traits you see in this population will change. And if they are drastic enough, maybe these guys start becoming dominant and start not liking these guys because they're so different or whatever else. We could see a lot of different reasons. This could eventually turn into a different species. Now, the obvious question is, what leads to this variation? In a population, what leads to this? In fact, even in our population, what leads to one person having dirty blonde hair, one person having brown hair, one person having black hair, and the spectrum of skin complexions and heights is pretty much infinite?"}, {"video_title": "Variation in a Species (2).mp3", "Sentence": "This could eventually turn into a different species. Now, the obvious question is, what leads to this variation? In a population, what leads to this? In fact, even in our population, what leads to one person having dirty blonde hair, one person having brown hair, one person having black hair, and the spectrum of skin complexions and heights is pretty much infinite? What causes that? And then one thing that I kind of point to, and we talked about this a little bit in the DNA video, is this notion of mutations. The DNA, we learned, is just a sequence of these bases."}, {"video_title": "Variation in a Species (2).mp3", "Sentence": "In fact, even in our population, what leads to one person having dirty blonde hair, one person having brown hair, one person having black hair, and the spectrum of skin complexions and heights is pretty much infinite? What causes that? And then one thing that I kind of point to, and we talked about this a little bit in the DNA video, is this notion of mutations. The DNA, we learned, is just a sequence of these bases. So adenine, guanine, let's say I got some thymine going, I have some more adenine, some cytosine. And that these code, if you have enough of these in a row, maybe you have a few hundred or a few thousands of these, these code for proteins or they code for things that control other proteins. But maybe you have a change in one of them."}, {"video_title": "Variation in a Species (2).mp3", "Sentence": "The DNA, we learned, is just a sequence of these bases. So adenine, guanine, let's say I got some thymine going, I have some more adenine, some cytosine. And that these code, if you have enough of these in a row, maybe you have a few hundred or a few thousands of these, these code for proteins or they code for things that control other proteins. But maybe you have a change in one of them. Maybe this cytosine, for whatever reason, becomes a guanine randomly. Or maybe these get deleted. And that would change the DNA."}, {"video_title": "Variation in a Species (2).mp3", "Sentence": "But maybe you have a change in one of them. Maybe this cytosine, for whatever reason, becomes a guanine randomly. Or maybe these get deleted. And that would change the DNA. But you can imagine, if I went to someone's computer code and just randomly started changing letters and randomly started inserting letters without really knowing what I'm doing, most of the time I'm going to break the computer program. Most of the time, the great majority of the time, this is going to go nowhere. For example, if I go into someone's computer program and if I just add a couple of spaces or something, that might not change their computer program."}, {"video_title": "Variation in a Species (2).mp3", "Sentence": "And that would change the DNA. But you can imagine, if I went to someone's computer code and just randomly started changing letters and randomly started inserting letters without really knowing what I'm doing, most of the time I'm going to break the computer program. Most of the time, the great majority of the time, this is going to go nowhere. For example, if I go into someone's computer program and if I just add a couple of spaces or something, that might not change their computer program. But if I start getting rid of semicolons and start changing numbers and all that, it'll probably make the computer program break. So it'll either do nothing or it'll actually kill the organisms most of the time. Mutations."}, {"video_title": "Variation in a Species (2).mp3", "Sentence": "For example, if I go into someone's computer program and if I just add a couple of spaces or something, that might not change their computer program. But if I start getting rid of semicolons and start changing numbers and all that, it'll probably make the computer program break. So it'll either do nothing or it'll actually kill the organisms most of the time. Mutations. Sometimes they might make the actual cell kind of go run amok and we'll do a whole maybe series of videos on cancer and that itself obviously would hurt the organism as a whole. Although if it occurs after the organism is reproduced, it might not be something that selects against the organism. But anyway, and it also wouldn't be passed on."}, {"video_title": "Variation in a Species (2).mp3", "Sentence": "Mutations. Sometimes they might make the actual cell kind of go run amok and we'll do a whole maybe series of videos on cancer and that itself obviously would hurt the organism as a whole. Although if it occurs after the organism is reproduced, it might not be something that selects against the organism. But anyway, and it also wouldn't be passed on. But anyway, I won't go too detailed into that. But the whole point is that mutations don't seem to be a satisfying source of variation. They could be a source or kind of contribute on the margin, but there must be something more profound than mutations that's creating the diversity even within, or maybe I should call the variation, even within a population."}, {"video_title": "Variation in a Species (2).mp3", "Sentence": "But anyway, and it also wouldn't be passed on. But anyway, I won't go too detailed into that. But the whole point is that mutations don't seem to be a satisfying source of variation. They could be a source or kind of contribute on the margin, but there must be something more profound than mutations that's creating the diversity even within, or maybe I should call the variation, even within a population. And the answer here is really, it's kind of right in front of us. It really addresses kind of one of the most fundamental things about biology. And it's so fundamental that a lot of people never even question why it is the way it is."}, {"video_title": "Variation in a Species (2).mp3", "Sentence": "They could be a source or kind of contribute on the margin, but there must be something more profound than mutations that's creating the diversity even within, or maybe I should call the variation, even within a population. And the answer here is really, it's kind of right in front of us. It really addresses kind of one of the most fundamental things about biology. And it's so fundamental that a lot of people never even question why it is the way it is. And that is sexual reproduction. And when I mean sexual reproduction, it's this notion that you have, and pretty much if you look at all organisms that have nucleuses, and we call those eukaryotes, maybe I'll do a whole video on eukaryotes versus prokaryotes. But it's the notion that if you look universally all the way from plants, not universally, but if you look at cells that have nucleuses, they almost universally have this phenomenon that you have males and you have females."}, {"video_title": "Variation in a Species (2).mp3", "Sentence": "And it's so fundamental that a lot of people never even question why it is the way it is. And that is sexual reproduction. And when I mean sexual reproduction, it's this notion that you have, and pretty much if you look at all organisms that have nucleuses, and we call those eukaryotes, maybe I'll do a whole video on eukaryotes versus prokaryotes. But it's the notion that if you look universally all the way from plants, not universally, but if you look at cells that have nucleuses, they almost universally have this phenomenon that you have males and you have females. In some organisms, an organism can be both a male and a female, but the common idea here is that all organisms kind of produce versions of their genetic material that mix with other organisms' version of their genetic material. If mutations were the only source of variation, then I could just butt off other cells. Maybe other cells would just butt off from me, and then randomly one cell might be a little bit different and whatever else."}, {"video_title": "Variation in a Species (2).mp3", "Sentence": "But it's the notion that if you look universally all the way from plants, not universally, but if you look at cells that have nucleuses, they almost universally have this phenomenon that you have males and you have females. In some organisms, an organism can be both a male and a female, but the common idea here is that all organisms kind of produce versions of their genetic material that mix with other organisms' version of their genetic material. If mutations were the only source of variation, then I could just butt off other cells. Maybe other cells would just butt off from me, and then randomly one cell might be a little bit different and whatever else. But that would, as we already talked about, most of the time we would have very little change, very little variation. And whatever variation does occur because of any kind of noise being introduced into this kind of butting process where I just replicate myself identically, most of the times it'll be negative. Most of the times it'll break the organism."}, {"video_title": "Variation in a Species (2).mp3", "Sentence": "Maybe other cells would just butt off from me, and then randomly one cell might be a little bit different and whatever else. But that would, as we already talked about, most of the time we would have very little change, very little variation. And whatever variation does occur because of any kind of noise being introduced into this kind of butting process where I just replicate myself identically, most of the times it'll be negative. Most of the times it'll break the organism. Now, when you have sexual reproduction, what happens? Well, you keep mixing and matching every possible combination of DNA in a species pool of DNA. Let me make this a little bit more concrete for you."}, {"video_title": "Variation in a Species (2).mp3", "Sentence": "Most of the times it'll break the organism. Now, when you have sexual reproduction, what happens? Well, you keep mixing and matching every possible combination of DNA in a species pool of DNA. Let me make this a little bit more concrete for you. So let me erase this horrible drawing I just did. So we all have, let me stick to humans because that's what we are. We have 23 pairs of chromosomes, and in each pair we have one chromosome from our mother and one chromosome from our father."}, {"video_title": "Variation in a Species (2).mp3", "Sentence": "Let me make this a little bit more concrete for you. So let me erase this horrible drawing I just did. So we all have, let me stick to humans because that's what we are. We have 23 pairs of chromosomes, and in each pair we have one chromosome from our mother and one chromosome from our father. So let me draw that. So I'll do my father's chromosomes in blue, so I have 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, and I'm running out of space. Let me do more here."}, {"video_title": "Variation in a Species (2).mp3", "Sentence": "We have 23 pairs of chromosomes, and in each pair we have one chromosome from our mother and one chromosome from our father. So let me draw that. So I'll do my father's chromosomes in blue, so I have 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, and I'm running out of space. Let me do more here. 16, 17, 18, 19, 20, 21, 22. And then I'll throw another one here that looks a little bit different. I'll throw one here that looks like a Y."}, {"video_title": "Variation in a Species (2).mp3", "Sentence": "Let me do more here. 16, 17, 18, 19, 20, 21, 22. And then I'll throw another one here that looks a little bit different. I'll throw one here that looks like a Y. And we'll talk more about the X's and the Y chromosomes. And I have 23 chromosomes from my mother. And not to be stereotypical, but maybe I'll do that in a more feminine color."}, {"video_title": "Variation in a Species (2).mp3", "Sentence": "I'll throw one here that looks like a Y. And we'll talk more about the X's and the Y chromosomes. And I have 23 chromosomes from my mother. And not to be stereotypical, but maybe I'll do that in a more feminine color. Let's see. So I have 23 chromosomes from my mother. 1, 2, I just have to draw 1, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23."}, {"video_title": "Variation in a Species (2).mp3", "Sentence": "And not to be stereotypical, but maybe I'll do that in a more feminine color. Let's see. So I have 23 chromosomes from my mother. 1, 2, I just have to draw 1, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23. So what's going on here? I have 23 from my mother. I have 23 from my father."}, {"video_title": "Variation in a Species (2).mp3", "Sentence": "1, 2, I just have to draw 1, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23. So what's going on here? I have 23 from my mother. I have 23 from my father. Now, each of these chromosomes, and I made them right next to each other. So for example, let me zoom in on one pair of these. So let's say we look at chromosome number 3."}, {"video_title": "Variation in a Species (2).mp3", "Sentence": "I have 23 from my father. Now, each of these chromosomes, and I made them right next to each other. So for example, let me zoom in on one pair of these. So let's say we look at chromosome number 3. So let me zoom in on chromosome number 3. I have one from my mother right here. And remember, actually maybe I'll do it this way."}, {"video_title": "Variation in a Species (2).mp3", "Sentence": "So let's say we look at chromosome number 3. So let me zoom in on chromosome number 3. I have one from my mother right here. And remember, actually maybe I'll do it this way. Remember, a chromosome is just a big, if you take the DNA, it just keeps wrapping around. It actually wraps around all these proteins and it creates the structure. But it's just a big, you see it like that, you're like, oh, maybe the DNA, no, but this could have millions of base pairs."}, {"video_title": "Variation in a Species (2).mp3", "Sentence": "And remember, actually maybe I'll do it this way. Remember, a chromosome is just a big, if you take the DNA, it just keeps wrapping around. It actually wraps around all these proteins and it creates the structure. But it's just a big, you see it like that, you're like, oh, maybe the DNA, no, but this could have millions of base pairs. So maybe it'll look something like that. It's a densely wrapped version of, well, it's a long string of DNA, and when it's normally drawn like this, which is not always the way it is, and we'll talk more about like that, they draw it as densely packed like that. So let's say that's from my mother and that's from my father."}, {"video_title": "Variation in a Species (2).mp3", "Sentence": "But it's just a big, you see it like that, you're like, oh, maybe the DNA, no, but this could have millions of base pairs. So maybe it'll look something like that. It's a densely wrapped version of, well, it's a long string of DNA, and when it's normally drawn like this, which is not always the way it is, and we'll talk more about like that, they draw it as densely packed like that. So let's say that's from my mother and that's from my father. Now, these are both, we call them, I'll call them, they're the same, let's call this chromosome 3. They're both chromosome 3. And what the idea is here is that I'm getting different traits from my father and from my mother."}, {"video_title": "Variation in a Species (2).mp3", "Sentence": "So let's say that's from my mother and that's from my father. Now, these are both, we call them, I'll call them, they're the same, let's call this chromosome 3. They're both chromosome 3. And what the idea is here is that I'm getting different traits from my father and from my mother. For example, and I'm doing a gross oversimplification here, but this is really to just give you the idea of what's going on. This chromosome 3, maybe it contains this trait for hair color. And maybe my father had, and I'll use my actual example, my father had very straight hair."}, {"video_title": "Variation in a Species (2).mp3", "Sentence": "And what the idea is here is that I'm getting different traits from my father and from my mother. For example, and I'm doing a gross oversimplification here, but this is really to just give you the idea of what's going on. This chromosome 3, maybe it contains this trait for hair color. And maybe my father had, and I'll use my actual example, my father had very straight hair. So let's say he had, some place on this chromosome, there is a gene for hair straightness. Let's say it's a little thing right there. And remember, that gene could be thousands of base pairs."}, {"video_title": "Variation in a Species (2).mp3", "Sentence": "And maybe my father had, and I'll use my actual example, my father had very straight hair. So let's say he had, some place on this chromosome, there is a gene for hair straightness. Let's say it's a little thing right there. And remember, that gene could be thousands of base pairs. But let's say this is hair straightness. So my father's version of that gene, or he had the allele for straightness. And remember, an allele is just a version of a gene."}, {"video_title": "Variation in a Species (2).mp3", "Sentence": "And remember, that gene could be thousands of base pairs. But let's say this is hair straightness. So my father's version of that gene, or he had the allele for straightness. And remember, an allele is just a version of a gene. So I'll call it the allele straight for straight hair. Now, this other chromosome that my mother gave me, this essentially, and there are exceptions, but for the most part, it codes for the same genes. And that's why I put them next to each other."}, {"video_title": "Variation in a Species (2).mp3", "Sentence": "And remember, an allele is just a version of a gene. So I'll call it the allele straight for straight hair. Now, this other chromosome that my mother gave me, this essentially, and there are exceptions, but for the most part, it codes for the same genes. And that's why I put them next to each other. So this will also have the gene for hair straightness or curliness. But my mom does happen to actually have curly hair. So she has the gene right there for curly hair."}, {"video_title": "Variation in a Species (2).mp3", "Sentence": "And that's why I put them next to each other. So this will also have the gene for hair straightness or curliness. But my mom does happen to actually have curly hair. So she has the gene right there for curly hair. So she has the version of the gene here is, let's see, allele curly. The gene just says, look, this is the gene for whether or not your hair is curly. Each version of the gene is called an allele."}, {"video_title": "Variation in a Species (2).mp3", "Sentence": "So she has the gene right there for curly hair. So she has the version of the gene here is, let's see, allele curly. The gene just says, look, this is the gene for whether or not your hair is curly. Each version of the gene is called an allele. Allele curly. Now, when I got both of these in my body, or in my cells, and this is in every cell of my body, every cell of my body except for, and we'll talk a little in a few seconds about my germ cells, but every cell other than the ones that I use for reproduction have this complete set of chromosomes in it, which I find amazing. But only certain chromosomes are, for example, these genes will be completely useless in my fingernails because all of a sudden, the straight and the curly don't matter that much."}, {"video_title": "Variation in a Species (2).mp3", "Sentence": "Each version of the gene is called an allele. Allele curly. Now, when I got both of these in my body, or in my cells, and this is in every cell of my body, every cell of my body except for, and we'll talk a little in a few seconds about my germ cells, but every cell other than the ones that I use for reproduction have this complete set of chromosomes in it, which I find amazing. But only certain chromosomes are, for example, these genes will be completely useless in my fingernails because all of a sudden, the straight and the curly don't matter that much. And I'm simplifying. Maybe they will on some other dimension. But let's say for simplicity, they won't matter in certain places."}, {"video_title": "Variation in a Species (2).mp3", "Sentence": "But only certain chromosomes are, for example, these genes will be completely useless in my fingernails because all of a sudden, the straight and the curly don't matter that much. And I'm simplifying. Maybe they will on some other dimension. But let's say for simplicity, they won't matter in certain places. So certain genes are expressed in certain parts of the body, but every one of your body cells, and we call those somatic cells, and we'll separate those from the sex cells or the germ cells that we'll talk about later. So this is my body cells. So this is the great majority of your cells."}, {"video_title": "Variation in a Species (2).mp3", "Sentence": "But let's say for simplicity, they won't matter in certain places. So certain genes are expressed in certain parts of the body, but every one of your body cells, and we call those somatic cells, and we'll separate those from the sex cells or the germ cells that we'll talk about later. So this is my body cells. So this is the great majority of your cells. And this is opposed to your germ cells. And the germ cells, I'll just write it here just so you get it clear, for a male, that's the sperm cells. And for a female, that's the egg cells or the ova."}, {"video_title": "Variation in a Species (2).mp3", "Sentence": "So this is the great majority of your cells. And this is opposed to your germ cells. And the germ cells, I'll just write it here just so you get it clear, for a male, that's the sperm cells. And for a female, that's the egg cells or the ova. But most of my cells have a complete collection of these. What I want to give you the idea is that for every trait, I essentially have two versions, one from my mother and one from my father. Now these right here are called homologous chromosomes."}, {"video_title": "Variation in a Species (2).mp3", "Sentence": "And for a female, that's the egg cells or the ova. But most of my cells have a complete collection of these. What I want to give you the idea is that for every trait, I essentially have two versions, one from my mother and one from my father. Now these right here are called homologous chromosomes. Chromosomes, homologous. What that means is every time you see the prefix homologous, or if you see like homo sapien, or even the word homosexual or homogeneous, it means same. You see that all the time."}, {"video_title": "Variation in a Species (2).mp3", "Sentence": "Now these right here are called homologous chromosomes. Chromosomes, homologous. What that means is every time you see the prefix homologous, or if you see like homo sapien, or even the word homosexual or homogeneous, it means same. You see that all the time. So homologous means that they're almost the same. They're coding for the most part the same set of genes, but they're not identical. They actually might code for slightly different versions of the same gene."}, {"video_title": "Variation in a Species (2).mp3", "Sentence": "You see that all the time. So homologous means that they're almost the same. They're coding for the most part the same set of genes, but they're not identical. They actually might code for slightly different versions of the same gene. So depending on what versions I get, what is actually expressed for me. So my genotype, let me introduce another word. And I'm overwhelming you with words here."}, {"video_title": "Variation in a Species (2).mp3", "Sentence": "They actually might code for slightly different versions of the same gene. So depending on what versions I get, what is actually expressed for me. So my genotype, let me introduce another word. And I'm overwhelming you with words here. So my genotype is exactly what alleles I have, what versions of the gene. So I got like the fifth version of the curly allele. There could be multiple versions of the curly allele in our gene pool."}, {"video_title": "Variation in a Species (2).mp3", "Sentence": "And I'm overwhelming you with words here. So my genotype is exactly what alleles I have, what versions of the gene. So I got like the fifth version of the curly allele. There could be multiple versions of the curly allele in our gene pool. And maybe I got some version of the straight allele. That is my genotype. My phenotype is what my hair really looks like."}, {"video_title": "Variation in a Species (2).mp3", "Sentence": "There could be multiple versions of the curly allele in our gene pool. And maybe I got some version of the straight allele. That is my genotype. My phenotype is what my hair really looks like. So for example, two people could have different genotypes with the same, but they might code for hair that looks pretty much the same. So it might have a very similar phenotype. So one phenotype can be represented by multiple genotypes."}, {"video_title": "Variation in a Species (2).mp3", "Sentence": "My phenotype is what my hair really looks like. So for example, two people could have different genotypes with the same, but they might code for hair that looks pretty much the same. So it might have a very similar phenotype. So one phenotype can be represented by multiple genotypes. So that's just one thing to think about. And we'll talk a lot about that in the future, but I just want to introduce you into that there. Now, I entered this whole discussion because I wanted to talk about variation."}, {"video_title": "Variation in a Species (2).mp3", "Sentence": "So one phenotype can be represented by multiple genotypes. So that's just one thing to think about. And we'll talk a lot about that in the future, but I just want to introduce you into that there. Now, I entered this whole discussion because I wanted to talk about variation. So how does variation happen? Well, what's going to happen when I, so first of all, well, let me put it this way. What's going to happen when I reproduce and I have a son?"}, {"video_title": "Variation in a Species (2).mp3", "Sentence": "Now, I entered this whole discussion because I wanted to talk about variation. So how does variation happen? Well, what's going to happen when I, so first of all, well, let me put it this way. What's going to happen when I reproduce and I have a son? Well, my contribution to my son is going to be a random collection of half of these genes. I'm going to contribute either one. For each homologous pair, I'm either going to contribute the one that I got from my mother or the one that I got from my father."}, {"video_title": "Variation in a Species (2).mp3", "Sentence": "What's going to happen when I reproduce and I have a son? Well, my contribution to my son is going to be a random collection of half of these genes. I'm going to contribute either one. For each homologous pair, I'm either going to contribute the one that I got from my mother or the one that I got from my father. So let's say that the sperm cell that went on to fertilize my wife's egg, it just happened to have, let's say it happened to have that one, that one, well, I could just pick one from each of these 23 sets. And you could say, well, how many combinations are there? Well, for every set, I can pick one of the two homologous chromosomes, and I'm going to do that 23 times."}, {"video_title": "Variation in a Species (2).mp3", "Sentence": "For each homologous pair, I'm either going to contribute the one that I got from my mother or the one that I got from my father. So let's say that the sperm cell that went on to fertilize my wife's egg, it just happened to have, let's say it happened to have that one, that one, well, I could just pick one from each of these 23 sets. And you could say, well, how many combinations are there? Well, for every set, I can pick one of the two homologous chromosomes, and I'm going to do that 23 times. 2 times 2 times 2, so it's 2 to the 23rd. So there's 22 to the 23 different versions that I can contribute to any son or daughter that I might have. We'll talk about how that happens when we talk about meiosis or mitosis."}, {"video_title": "Variation in a Species (2).mp3", "Sentence": "Well, for every set, I can pick one of the two homologous chromosomes, and I'm going to do that 23 times. 2 times 2 times 2, so it's 2 to the 23rd. So there's 22 to the 23 different versions that I can contribute to any son or daughter that I might have. We'll talk about how that happens when we talk about meiosis or mitosis. That when I generate my sperm cells, sperm cells are essentially, instead of having 23 pairs of chromosomes in sperm, you only have 23 chromosomes. So for example, I'll take one from each of those, and through the process of meiosis, which we'll go into, I'll generate a bunch of sperm cells. And each sperm cell will have one from each of these pairs, one version from each of those pairs."}, {"video_title": "Variation in a Species (2).mp3", "Sentence": "We'll talk about how that happens when we talk about meiosis or mitosis. That when I generate my sperm cells, sperm cells are essentially, instead of having 23 pairs of chromosomes in sperm, you only have 23 chromosomes. So for example, I'll take one from each of those, and through the process of meiosis, which we'll go into, I'll generate a bunch of sperm cells. And each sperm cell will have one from each of these pairs, one version from each of those pairs. So maybe for this chromosome, I get it from my dad. From the next chromosome, I get it from my mom. Then I donate a couple more from, I shouldn't have drawn them next to each other, I donate a couple more from my mom, then for the chromosome number 5, it comes from my dad, and so on and so forth."}, {"video_title": "Variation in a Species (2).mp3", "Sentence": "And each sperm cell will have one from each of these pairs, one version from each of those pairs. So maybe for this chromosome, I get it from my dad. From the next chromosome, I get it from my mom. Then I donate a couple more from, I shouldn't have drawn them next to each other, I donate a couple more from my mom, then for the chromosome number 5, it comes from my dad, and so on and so forth. But there's 2 to the 23rd combinations here, because there are 23 pairs that I'm collecting from. Now, my wife's egg is going to have the same situation. There are 2 to the 23 different combinations of DNA that she can contribute, just based on which of the homologous pairs she will contribute."}, {"video_title": "Variation in a Species (2).mp3", "Sentence": "Then I donate a couple more from, I shouldn't have drawn them next to each other, I donate a couple more from my mom, then for the chromosome number 5, it comes from my dad, and so on and so forth. But there's 2 to the 23rd combinations here, because there are 23 pairs that I'm collecting from. Now, my wife's egg is going to have the same situation. There are 2 to the 23 different combinations of DNA that she can contribute, just based on which of the homologous pairs she will contribute. So the possible combinations that just one couple can produce, and I'm using my life as an example, but you could use this, this applies to everything. This applies to every species that experiences sexual reproduction. So if I can give 2 to the 23rd combinations of DNA, and my wife can give 2 to the 23 combinations of DNA, then we can produce 2 to the 46th combinations."}, {"video_title": "Variation in a Species (2).mp3", "Sentence": "There are 2 to the 23 different combinations of DNA that she can contribute, just based on which of the homologous pairs she will contribute. So the possible combinations that just one couple can produce, and I'm using my life as an example, but you could use this, this applies to everything. This applies to every species that experiences sexual reproduction. So if I can give 2 to the 23rd combinations of DNA, and my wife can give 2 to the 23 combinations of DNA, then we can produce 2 to the 46th combinations. Now, just to give an idea of how large of a number this is, this is 12,000, roughly 12,000 times the number of human beings on the planet today. So there's a huge amount of variation that even one couple can produce. And if you thought that even that isn't enough, it turns out that amongst these homologous pairs, and we'll talk about when this happens in meiosis, you can actually have DNA recombination."}, {"video_title": "Variation in a Species (2).mp3", "Sentence": "So if I can give 2 to the 23rd combinations of DNA, and my wife can give 2 to the 23 combinations of DNA, then we can produce 2 to the 46th combinations. Now, just to give an idea of how large of a number this is, this is 12,000, roughly 12,000 times the number of human beings on the planet today. So there's a huge amount of variation that even one couple can produce. And if you thought that even that isn't enough, it turns out that amongst these homologous pairs, and we'll talk about when this happens in meiosis, you can actually have DNA recombination. And all that means is that when these homologous pairs during meiosis line up near each other, you can have this thing called crossover, where all of this DNA here crosses over and touches over here, and all of this DNA crosses over and touches over there. So all of this goes there, and all of this goes there. And what you end up with after the crossover is that one DNA, the one that came from my mom, or that I thought came from my mom, now has a chunk that came from my dad."}, {"video_title": "Variation in a Species (2).mp3", "Sentence": "And if you thought that even that isn't enough, it turns out that amongst these homologous pairs, and we'll talk about when this happens in meiosis, you can actually have DNA recombination. And all that means is that when these homologous pairs during meiosis line up near each other, you can have this thing called crossover, where all of this DNA here crosses over and touches over here, and all of this DNA crosses over and touches over there. So all of this goes there, and all of this goes there. And what you end up with after the crossover is that one DNA, the one that came from my mom, or that I thought came from my mom, now has a chunk that came from my dad. And the chunk that came from my dad now has a chunk that came from my mom. Let me do it in the right color. It came from my mom like that."}, {"video_title": "Variation in a Species (2).mp3", "Sentence": "And what you end up with after the crossover is that one DNA, the one that came from my mom, or that I thought came from my mom, now has a chunk that came from my dad. And the chunk that came from my dad now has a chunk that came from my mom. Let me do it in the right color. It came from my mom like that. And so that even increases the amount of variety even more. So you can almost now, instead of talking about the different chromosomes that you're contributing, where the chromosomes are each of these collections of DNA, you can almost go to the different combinations at the gene level. And now you can think about an almost infinite form of variation."}, {"video_title": "Variation in a Species (2).mp3", "Sentence": "It came from my mom like that. And so that even increases the amount of variety even more. So you can almost now, instead of talking about the different chromosomes that you're contributing, where the chromosomes are each of these collections of DNA, you can almost go to the different combinations at the gene level. And now you can think about an almost infinite form of variation. And you can think about all of the variation that might emerge when you start mixing and mashing different versions of the same gene in a population. And you don't just look at one gene. I mean, the reality is that genes by themselves very seldom code for a specific."}, {"video_title": "Variation in a Species (2).mp3", "Sentence": "And now you can think about an almost infinite form of variation. And you can think about all of the variation that might emerge when you start mixing and mashing different versions of the same gene in a population. And you don't just look at one gene. I mean, the reality is that genes by themselves very seldom code for a specific. You can very seldom look for one gene and say, oh, that is brown hair. Or look for one gene and say, oh, that's intelligence. Or that is how likable someone is."}, {"video_title": "Variation in a Species (2).mp3", "Sentence": "I mean, the reality is that genes by themselves very seldom code for a specific. You can very seldom look for one gene and say, oh, that is brown hair. Or look for one gene and say, oh, that's intelligence. Or that is how likable someone is. It's usually a whole set of genes interacting in an incredibly complicated way. Hair might be coded for by this whole set of genes on multiple chromosomes. And this might be coded for a whole set of genes on multiple chromosomes."}, {"video_title": "Variation in a Species (2).mp3", "Sentence": "Or that is how likable someone is. It's usually a whole set of genes interacting in an incredibly complicated way. Hair might be coded for by this whole set of genes on multiple chromosomes. And this might be coded for a whole set of genes on multiple chromosomes. And so then you can start thinking about all of the different combinations. And then all of a sudden, maybe some combination that never existed before all of a sudden emerges. And that's very successful."}, {"video_title": "Variation in a Species (2).mp3", "Sentence": "And this might be coded for a whole set of genes on multiple chromosomes. And so then you can start thinking about all of the different combinations. And then all of a sudden, maybe some combination that never existed before all of a sudden emerges. And that's very successful. But I'll leave you to think about it because maybe that combination might be passed on or it may not be passed on because of this recombination. But we'll talk more about that in the future. But I wanted to introduce this idea of sexual reproduction to you because this really is the main source of variation within a population."}, {"video_title": "Variation in a Species (2).mp3", "Sentence": "And that's very successful. But I'll leave you to think about it because maybe that combination might be passed on or it may not be passed on because of this recombination. But we'll talk more about that in the future. But I wanted to introduce this idea of sexual reproduction to you because this really is the main source of variation within a population. And it's kind of a philosophical idea because we almost take the idea of having males and females for granted because it's this universal idea. But I did a little reading on it. It turns out that this actually only emerged about 1.4 billion years ago."}, {"video_title": "Variation in a Species (2).mp3", "Sentence": "But I wanted to introduce this idea of sexual reproduction to you because this really is the main source of variation within a population. And it's kind of a philosophical idea because we almost take the idea of having males and females for granted because it's this universal idea. But I did a little reading on it. It turns out that this actually only emerged about 1.4 billion years ago. That this is almost a useful trait because once you introduce this level of variation, the natural selection can start. You can kind of say that when you have this more powerful form of variation than just pure mutations, and maybe you might have some primitive form of crossover before. But now that you have this sexual reproduction and you have this variation, natural selection can occur in a more efficient way so that species that were able to reproduce and essentially recombine their DNA and mix and match it in this way were able to produce more variety and were able to essentially be selected for the environment in a more efficient way."}, {"video_title": "Variation in a Species (2).mp3", "Sentence": "It turns out that this actually only emerged about 1.4 billion years ago. That this is almost a useful trait because once you introduce this level of variation, the natural selection can start. You can kind of say that when you have this more powerful form of variation than just pure mutations, and maybe you might have some primitive form of crossover before. But now that you have this sexual reproduction and you have this variation, natural selection can occur in a more efficient way so that species that were able to reproduce and essentially recombine their DNA and mix and match it in this way were able to produce more variety and were able to essentially be selected for the environment in a more efficient way. So they started to essentially outnumber the ones that couldn't. So it became a kind of a very universal trait. But you could have imagined a world, and there are science fiction books written about this, where you have three genders, where you have gender one, two, three."}, {"video_title": "Variation in a Species (2).mp3", "Sentence": "But now that you have this sexual reproduction and you have this variation, natural selection can occur in a more efficient way so that species that were able to reproduce and essentially recombine their DNA and mix and match it in this way were able to produce more variety and were able to essentially be selected for the environment in a more efficient way. So they started to essentially outnumber the ones that couldn't. So it became a kind of a very universal trait. But you could have imagined a world, and there are science fiction books written about this, where you have three genders, where you have gender one, two, three. You could have 10 genders. And it just happens to be that on Earth, this notion of having two genders turned out to be a very efficient and stable way of introducing variation into a population. So hopefully you found that interesting."}, {"video_title": "Overview of cellular respiration   Cellular respiration   Biology   Khan Academy.mp3", "Sentence": "And it can be a pretty involved process, and even the way I'm going to do it, as messy as it looks, it's going to be cleaner than actually what goes on inside of your cells and other organism cells, because I'm going to show clearly from going from glucose and then see how we can produce ATP through glycolysis and the Krebs cycle and oxidative phosphorylation, but in reality, all sorts of molecules can jump in at different parts of the chain and then jump out at different parts of the chain to go along other pathways. But I'll show kind of the traditional narrative. So we're going to start off, for this narrative, we're going to start off with glucose. We have a six-carbon chain right over here, and we have the process of glycolysis, which is occurring in the cytosol of our cells. So if this is the cell right over here, you can imagine, well, the glycolysis could be occurring right over there. And that process of glycolysis is essentially splitting up this six-carbon glucose molecule into two three-carbon molecules, and these three carbon molecules, and we go into detail in another video, we call these pyruvate. And in the process of doing so, and this is, I guess you could say, the point of glycolysis, we're able to, on a net basis, produce two ATPs."}, {"video_title": "Overview of cellular respiration   Cellular respiration   Biology   Khan Academy.mp3", "Sentence": "We have a six-carbon chain right over here, and we have the process of glycolysis, which is occurring in the cytosol of our cells. So if this is the cell right over here, you can imagine, well, the glycolysis could be occurring right over there. And that process of glycolysis is essentially splitting up this six-carbon glucose molecule into two three-carbon molecules, and these three carbon molecules, and we go into detail in another video, we call these pyruvate. And in the process of doing so, and this is, I guess you could say, the point of glycolysis, we're able to, on a net basis, produce two ATPs. We actually produce four, but we have to use two. So on a net basis, we produce two ATPs, and I'm going to keep a little table here to keep track. So we produce two ATPs, and we are also, we're also in the process of that, we reduce two NAD molecules to NADH."}, {"video_title": "Overview of cellular respiration   Cellular respiration   Biology   Khan Academy.mp3", "Sentence": "And in the process of doing so, and this is, I guess you could say, the point of glycolysis, we're able to, on a net basis, produce two ATPs. We actually produce four, but we have to use two. So on a net basis, we produce two ATPs, and I'm going to keep a little table here to keep track. So we produce two ATPs, and we are also, we're also in the process of that, we reduce two NAD molecules to NADH. Remember, reduction is gaining of electrons. And you see over here, this is positively charged, this is neutrally charged, it essentially gains a hydride. So this is reduction."}, {"video_title": "Overview of cellular respiration   Cellular respiration   Biology   Khan Academy.mp3", "Sentence": "So we produce two ATPs, and we are also, we're also in the process of that, we reduce two NAD molecules to NADH. Remember, reduction is gaining of electrons. And you see over here, this is positively charged, this is neutrally charged, it essentially gains a hydride. So this is reduction. And if we go all the way through the pathway, all the way to oxidative phosphorylation, the electron transport chain, these NADHs, the reduced form of NAD, they can be then oxidized to provide, and in doing so, more energy is provided to produce even more ATPs, but we'll get to that. So you're also going to get two NADHs. Two NADHs get produced."}, {"video_title": "Overview of cellular respiration   Cellular respiration   Biology   Khan Academy.mp3", "Sentence": "So this is reduction. And if we go all the way through the pathway, all the way to oxidative phosphorylation, the electron transport chain, these NADHs, the reduced form of NAD, they can be then oxidized to provide, and in doing so, more energy is provided to produce even more ATPs, but we'll get to that. So you're also going to get two NADHs. Two NADHs get produced. Now at that point, you could kind of think of it as a little bit of a decision point. If there's no oxygen around, or if you're the type of organism that doesn't want to continue for some reason with cellular respiration or doesn't know how, this pyruvate can be used for fermentation. And we have videos on fermentation, lactic acid fermentation, alcohol fermentation."}, {"video_title": "Overview of cellular respiration   Cellular respiration   Biology   Khan Academy.mp3", "Sentence": "Two NADHs get produced. Now at that point, you could kind of think of it as a little bit of a decision point. If there's no oxygen around, or if you're the type of organism that doesn't want to continue for some reason with cellular respiration or doesn't know how, this pyruvate can be used for fermentation. And we have videos on fermentation, lactic acid fermentation, alcohol fermentation. And fermentation is all about using the pyruvates to oxidize your NADH back into NAD so it can be reused again for glycolysis. So even though the NADH has energy that could be eventually converted to ATP, and even though the pyruvates have energy that could eventually be converted into ATP, when you do fermentation, you kind of give up on that and you just view them as waste projects and you use the pyruvate to convert the NADH back into NAD and then glycolysis can occur again. But let's assume we're not going to go down the fermentation pathway, and we're going to continue with traditional aerobic cellular respiration using oxygen."}, {"video_title": "Overview of cellular respiration   Cellular respiration   Biology   Khan Academy.mp3", "Sentence": "And we have videos on fermentation, lactic acid fermentation, alcohol fermentation. And fermentation is all about using the pyruvates to oxidize your NADH back into NAD so it can be reused again for glycolysis. So even though the NADH has energy that could be eventually converted to ATP, and even though the pyruvates have energy that could eventually be converted into ATP, when you do fermentation, you kind of give up on that and you just view them as waste projects and you use the pyruvate to convert the NADH back into NAD and then glycolysis can occur again. But let's assume we're not going to go down the fermentation pathway, and we're going to continue with traditional aerobic cellular respiration using oxygen. Well, the next thing that's going to happen is that the carboxyl group, and everything I'm going to show now, it's going to happen for each of these pyruvates. So you can imagine these things all happening twice. So I'm going to multiply a bunch of things times two."}, {"video_title": "Overview of cellular respiration   Cellular respiration   Biology   Khan Academy.mp3", "Sentence": "But let's assume we're not going to go down the fermentation pathway, and we're going to continue with traditional aerobic cellular respiration using oxygen. Well, the next thing that's going to happen is that the carboxyl group, and everything I'm going to show now, it's going to happen for each of these pyruvates. So you can imagine these things all happening twice. So I'm going to multiply a bunch of things times two. But what happens in the next step is this carboxyl group, this carboxyl group is stripped off of the pyruvate and it essentially is going to be released as carbon dioxide. So this is our carbon dioxide being released here. And then the rest of our pyruvate, which is essentially an acetyl group, that latches on to coenzyme A."}, {"video_title": "Overview of cellular respiration   Cellular respiration   Biology   Khan Academy.mp3", "Sentence": "So I'm going to multiply a bunch of things times two. But what happens in the next step is this carboxyl group, this carboxyl group is stripped off of the pyruvate and it essentially is going to be released as carbon dioxide. So this is our carbon dioxide being released here. And then the rest of our pyruvate, which is essentially an acetyl group, that latches on to coenzyme A. And you'll hear a lot about coenzyme A. Sometimes they'll write just coA like this. Sometimes they'll do coA and then the sulfur bonded to the hydrogen."}, {"video_title": "Overview of cellular respiration   Cellular respiration   Biology   Khan Academy.mp3", "Sentence": "And then the rest of our pyruvate, which is essentially an acetyl group, that latches on to coenzyme A. And you'll hear a lot about coenzyme A. Sometimes they'll write just coA like this. Sometimes they'll do coA and then the sulfur bonded to the hydrogen. And the reason why they'll draw the sulfur part is because the sulfur is what bonds with the acetyl group right over here. So you have the carbon dioxide being released and then the acetyl group bonding with that sulfur. And by doing that you form acetyl coA."}, {"video_title": "Overview of cellular respiration   Cellular respiration   Biology   Khan Academy.mp3", "Sentence": "Sometimes they'll do coA and then the sulfur bonded to the hydrogen. And the reason why they'll draw the sulfur part is because the sulfur is what bonds with the acetyl group right over here. So you have the carbon dioxide being released and then the acetyl group bonding with that sulfur. And by doing that you form acetyl coA. And acetyl coA, just so you know, you only see three letters here, but this is actually a fairly involved molecule. This is actually a picture of acetyl coA. I know it's really small, but hopefully you appreciate it's a more involved molecule that the acetyl group that we're talking about is just this part right over here."}, {"video_title": "Overview of cellular respiration   Cellular respiration   Biology   Khan Academy.mp3", "Sentence": "And by doing that you form acetyl coA. And acetyl coA, just so you know, you only see three letters here, but this is actually a fairly involved molecule. This is actually a picture of acetyl coA. I know it's really small, but hopefully you appreciate it's a more involved molecule that the acetyl group that we're talking about is just this part right over here. And it's a coenzyme. It's really acting to transfer that acetyl group. And we'll see that in a second."}, {"video_title": "Overview of cellular respiration   Cellular respiration   Biology   Khan Academy.mp3", "Sentence": "I know it's really small, but hopefully you appreciate it's a more involved molecule that the acetyl group that we're talking about is just this part right over here. And it's a coenzyme. It's really acting to transfer that acetyl group. And we'll see that in a second. But it's also fun to look at these molecules because once again we see these patterns over and over again in biology or biochemistry. So acetyl coA, you have an adenine right over here. It's hard to see, but you have a ribose and you also have two phosphate groups."}, {"video_title": "Overview of cellular respiration   Cellular respiration   Biology   Khan Academy.mp3", "Sentence": "And we'll see that in a second. But it's also fun to look at these molecules because once again we see these patterns over and over again in biology or biochemistry. So acetyl coA, you have an adenine right over here. It's hard to see, but you have a ribose and you also have two phosphate groups. So this end of the acetyl coA is essentially an ADP. But it's used as a coenzyme. Everything that I'm talking about, this is all going to be facilitated by enzymes and the enzymes will have cofactors, coenzymes, if we're talking about organic cofactors, that are going to help facilitate things along."}, {"video_title": "Overview of cellular respiration   Cellular respiration   Biology   Khan Academy.mp3", "Sentence": "It's hard to see, but you have a ribose and you also have two phosphate groups. So this end of the acetyl coA is essentially an ADP. But it's used as a coenzyme. Everything that I'm talking about, this is all going to be facilitated by enzymes and the enzymes will have cofactors, coenzymes, if we're talking about organic cofactors, that are going to help facilitate things along. And as we see, the acetyl group joins on to the coenzyme A, forming acetyl coA. But that's just a temporary attachment. The acetyl coA is essentially going to transfer the acetyl group over to, and now we're going to enter into the citric acid cycle."}, {"video_title": "Overview of cellular respiration   Cellular respiration   Biology   Khan Academy.mp3", "Sentence": "Everything that I'm talking about, this is all going to be facilitated by enzymes and the enzymes will have cofactors, coenzymes, if we're talking about organic cofactors, that are going to help facilitate things along. And as we see, the acetyl group joins on to the coenzyme A, forming acetyl coA. But that's just a temporary attachment. The acetyl coA is essentially going to transfer the acetyl group over to, and now we're going to enter into the citric acid cycle. It's going to transfer these two carbons over to oxaloacetic acid to form citric acid. So it's going to transfer these two carbons to this one, two, three, four carbon molecule to form a one, two, three, four, five, six carbon molecule. Now before we go into the depths of the citric acid cycle, I want to make sure that I don't lose track of my accounting, because even that step right over here where we decarboxylated the pyruvate, we went from pyruvate to acetyl coA, that also reduced some NAD to NADH."}, {"video_title": "Overview of cellular respiration   Cellular respiration   Biology   Khan Academy.mp3", "Sentence": "The acetyl coA is essentially going to transfer the acetyl group over to, and now we're going to enter into the citric acid cycle. It's going to transfer these two carbons over to oxaloacetic acid to form citric acid. So it's going to transfer these two carbons to this one, two, three, four carbon molecule to form a one, two, three, four, five, six carbon molecule. Now before we go into the depths of the citric acid cycle, I want to make sure that I don't lose track of my accounting, because even that step right over here where we decarboxylated the pyruvate, we went from pyruvate to acetyl coA, that also reduced some NAD to NADH. Now this is going to happen once for each pyruvate, but all the accounting we're going to say is for one glucose molecule. So for one glucose molecule, it's going to happen for each of the pyruvates. So this is going to be times two."}, {"video_title": "Overview of cellular respiration   Cellular respiration   Biology   Khan Academy.mp3", "Sentence": "Now before we go into the depths of the citric acid cycle, I want to make sure that I don't lose track of my accounting, because even that step right over here where we decarboxylated the pyruvate, we went from pyruvate to acetyl coA, that also reduced some NAD to NADH. Now this is going to happen once for each pyruvate, but all the accounting we're going to say is for one glucose molecule. So for one glucose molecule, it's going to happen for each of the pyruvates. So this is going to be times two. So we're going to produce two NADHs in this step going from pyruvate to acetyl coA. Now the bulk of, I guess you could say, the catabolism of the carbons or the things that are eventually going to produce our ATPs are going to happen in what we call the citric acid or the Krebs cycle. It's called the citric acid cycle because when we transferred the acetyl group from the coenzyme A to the oxaloacetic acid, we formed citric acid."}, {"video_title": "Overview of cellular respiration   Cellular respiration   Biology   Khan Academy.mp3", "Sentence": "So this is going to be times two. So we're going to produce two NADHs in this step going from pyruvate to acetyl coA. Now the bulk of, I guess you could say, the catabolism of the carbons or the things that are eventually going to produce our ATPs are going to happen in what we call the citric acid or the Krebs cycle. It's called the citric acid cycle because when we transferred the acetyl group from the coenzyme A to the oxaloacetic acid, we formed citric acid. And citric acid, this is the thing that you have in lemons or orange juice. It is this molecule right over here. And the citric acid cycle, and it's also called the Krebs cycle, when you first learn it, it seems very, very complex, and some could argue that it is quite complex, but I'm just going to give you an overview of what's going on."}, {"video_title": "Overview of cellular respiration   Cellular respiration   Biology   Khan Academy.mp3", "Sentence": "It's called the citric acid cycle because when we transferred the acetyl group from the coenzyme A to the oxaloacetic acid, we formed citric acid. And citric acid, this is the thing that you have in lemons or orange juice. It is this molecule right over here. And the citric acid cycle, and it's also called the Krebs cycle, when you first learn it, it seems very, very complex, and some could argue that it is quite complex, but I'm just going to give you an overview of what's going on. The citric acid, once again, six carbon, it keeps getting broken down through multiple steps, and I'm really not showing all of the detail here, all the way back to oxaloacetic acid, where then it can accept the two carbons again. And just to be clear, once the two carbons are released by the coenzyme A, then that coenzyme A can be used again to decarboxylate some pyruvate. So there's a bunch of cycles going on."}, {"video_title": "Overview of cellular respiration   Cellular respiration   Biology   Khan Academy.mp3", "Sentence": "And the citric acid cycle, and it's also called the Krebs cycle, when you first learn it, it seems very, very complex, and some could argue that it is quite complex, but I'm just going to give you an overview of what's going on. The citric acid, once again, six carbon, it keeps getting broken down through multiple steps, and I'm really not showing all of the detail here, all the way back to oxaloacetic acid, where then it can accept the two carbons again. And just to be clear, once the two carbons are released by the coenzyme A, then that coenzyme A can be used again to decarboxylate some pyruvate. So there's a bunch of cycles going on. But the important takeaway is as we go through the citric acid cycle, as we go from one intermediary to the next, we keep reducing NAD to NADH. In fact, we do this three times for each cycle of the citric acid cycle. But remember, we're going to do this for each acetyl-CoA, for each pyruvate."}, {"video_title": "Overview of cellular respiration   Cellular respiration   Biology   Khan Academy.mp3", "Sentence": "So there's a bunch of cycles going on. But the important takeaway is as we go through the citric acid cycle, as we go from one intermediary to the next, we keep reducing NAD to NADH. In fact, we do this three times for each cycle of the citric acid cycle. But remember, we're going to do this for each acetyl-CoA, for each pyruvate. So all of this stuff is going to happen twice. So we're going to go through it twice for each original glucose molecule. So here we have one, two, three NADHs being produced, but since we're going to go through it twice, and we're going to do the accounting for the original glucose molecule, we could say that we have six NADs get reduced to NADH."}, {"video_title": "Overview of cellular respiration   Cellular respiration   Biology   Khan Academy.mp3", "Sentence": "But remember, we're going to do this for each acetyl-CoA, for each pyruvate. So all of this stuff is going to happen twice. So we're going to go through it twice for each original glucose molecule. So here we have one, two, three NADHs being produced, but since we're going to go through it twice, and we're going to do the accounting for the original glucose molecule, we could say that we have six NADs get reduced to NADH. Now you also, in the process, as you're breaking down, going from the six-carbon molecule to a four-carbon molecule, you're releasing carbon as carbon dioxide. And you also have traditionally GDP being converted into GTP, or sometimes ADP converted to ATP, but functionally it's equivalent to ATP either way. So we could also say that we're going to directly, remember we're going to do all of this stuff twice."}, {"video_title": "Overview of cellular respiration   Cellular respiration   Biology   Khan Academy.mp3", "Sentence": "So here we have one, two, three NADHs being produced, but since we're going to go through it twice, and we're going to do the accounting for the original glucose molecule, we could say that we have six NADs get reduced to NADH. Now you also, in the process, as you're breaking down, going from the six-carbon molecule to a four-carbon molecule, you're releasing carbon as carbon dioxide. And you also have traditionally GDP being converted into GTP, or sometimes ADP converted to ATP, but functionally it's equivalent to ATP either way. So we could also say that we're going to directly, remember we're going to do all of this stuff twice. So we could say that two, I'll just say two ATPs to make it simple. We could say GTP, but I'll say two ATPs, because once again, this happens once in each cycle, but we're going to do two cycles for each glucose. And then we have this other coenzyme right over here, FAD."}, {"video_title": "Overview of cellular respiration   Cellular respiration   Biology   Khan Academy.mp3", "Sentence": "So we could also say that we're going to directly, remember we're going to do all of this stuff twice. So we could say that two, I'll just say two ATPs to make it simple. We could say GTP, but I'll say two ATPs, because once again, this happens once in each cycle, but we're going to do two cycles for each glucose. And then we have this other coenzyme right over here, FAD. That gets reduced to FADH2, but that stays covalently attached to the enzymes that are facilitating it. So eventually that's being used to reduce coenzyme Q to QH2. So I'm just going to write the QH2 here, but once again you're going to get two of these."}, {"video_title": "Overview of cellular respiration   Cellular respiration   Biology   Khan Academy.mp3", "Sentence": "And then we have this other coenzyme right over here, FAD. That gets reduced to FADH2, but that stays covalently attached to the enzymes that are facilitating it. So eventually that's being used to reduce coenzyme Q to QH2. So I'm just going to write the QH2 here, but once again you're going to get two of these. So two QH2s. Now let's think about what the net product over here is going to be. And to think about it, we should just, I'll do a little bit of a shorthand, we'll go into more detail in future videos, is these coenzymes, the NADH, the QH2, these are going to be oxidized during oxidative phosphorylation and the electron transport chain to create a proton gradient across the inner membrane of mitochondria."}, {"video_title": "Overview of cellular respiration   Cellular respiration   Biology   Khan Academy.mp3", "Sentence": "So I'm just going to write the QH2 here, but once again you're going to get two of these. So two QH2s. Now let's think about what the net product over here is going to be. And to think about it, we should just, I'll do a little bit of a shorthand, we'll go into more detail in future videos, is these coenzymes, the NADH, the QH2, these are going to be oxidized during oxidative phosphorylation and the electron transport chain to create a proton gradient across the inner membrane of mitochondria. We're going to go into much more detail in the future, but that proton gradient is going to be used to produce more ATP. And one way to think about it is each NADH is going to produce, and I've seen a count, and it depends on the efficiency and where the NADH is actually going to be produced, but it's going to produce anywhere between two and three ATPs. Each of the reduced coenzyme Qs, so the QH2, that's going to each produce about one and a half ATPs."}, {"video_title": "Overview of cellular respiration   Cellular respiration   Biology   Khan Academy.mp3", "Sentence": "And to think about it, we should just, I'll do a little bit of a shorthand, we'll go into more detail in future videos, is these coenzymes, the NADH, the QH2, these are going to be oxidized during oxidative phosphorylation and the electron transport chain to create a proton gradient across the inner membrane of mitochondria. We're going to go into much more detail in the future, but that proton gradient is going to be used to produce more ATP. And one way to think about it is each NADH is going to produce, and I've seen a count, and it depends on the efficiency and where the NADH is actually going to be produced, but it's going to produce anywhere between two and three ATPs. Each of the reduced coenzyme Qs, so the QH2, that's going to each produce about one and a half ATPs. And people are still getting a good handle on exactly how this is happening. It depends on the efficiency of the cell and what the cell is actually trying to do. So using these ranges, actually I'll say one and a half to two, one and a half to two ATPs, and these are approximate numbers."}, {"video_title": "Overview of cellular respiration   Cellular respiration   Biology   Khan Academy.mp3", "Sentence": "Each of the reduced coenzyme Qs, so the QH2, that's going to each produce about one and a half ATPs. And people are still getting a good handle on exactly how this is happening. It depends on the efficiency of the cell and what the cell is actually trying to do. So using these ranges, actually I'll say one and a half to two, one and a half to two ATPs, and these are approximate numbers. So let's think about what our total accounting is. So if we just count up the ATP or the GTPs, we're going to get two there and two there. So we're going to have four direct or very close to direct ATPs, net being created."}, {"video_title": "Overview of cellular respiration   Cellular respiration   Biology   Khan Academy.mp3", "Sentence": "So using these ranges, actually I'll say one and a half to two, one and a half to two ATPs, and these are approximate numbers. So let's think about what our total accounting is. So if we just count up the ATP or the GTPs, we're going to get two there and two there. So we're going to have four direct or very close to direct ATPs, net being created. And then how many NADHs? We have two, four, and then we add six, we have 10 NADHs. And then we have two of the coenzyme Qs, two QH2s."}, {"video_title": "Overview of cellular respiration   Cellular respiration   Biology   Khan Academy.mp3", "Sentence": "So we're going to have four direct or very close to direct ATPs, net being created. And then how many NADHs? We have two, four, and then we add six, we have 10 NADHs. And then we have two of the coenzyme Qs, two QH2s. So that's going to be four ATPs. This is going to be between 20 and 30 NADHs, sorry, 20 and 30 ATPs. And then this is going to be three to four ATPs."}, {"video_title": "Overview of cellular respiration   Cellular respiration   Biology   Khan Academy.mp3", "Sentence": "And then we have two of the coenzyme Qs, two QH2s. So that's going to be four ATPs. This is going to be between 20 and 30 NADHs, sorry, 20 and 30 ATPs. And then this is going to be three to four ATPs. So if you add them all together, if you add the low ends of the range, you get, let's see, 20 plus three plus four, that's 27 ATPs. And the high end of the range, let's see, you have four plus 30 plus four, you have 38 ATPs. And 38 ATPs is currently considered to be kind of a theoretical maximum, but when we actually observe things in cells, it looks like it comes out at around 29 to 30 ATPs."}, {"video_title": "Overview of cellular respiration   Cellular respiration   Biology   Khan Academy.mp3", "Sentence": "And then this is going to be three to four ATPs. So if you add them all together, if you add the low ends of the range, you get, let's see, 20 plus three plus four, that's 27 ATPs. And the high end of the range, let's see, you have four plus 30 plus four, you have 38 ATPs. And 38 ATPs is currently considered to be kind of a theoretical maximum, but when we actually observe things in cells, it looks like it comes out at around 29 to 30 ATPs. And once again, it depends what the cell's trying to do, the type of cells and the type of efficiency. But all of this is happening through cellular respiration. And just to get a better sense of where all of this is occurring, where all of this is occurring, we said glycolysis is occurring in the cytosol, the citric acid cycle, this is occurring in the matrix of the mitochondria, so this space right over here, that is the citric acid cycle and that little magenta space that I've drawn, so that's the matrix, the video on mitochondria, we go into much more detail on that."}, {"video_title": "Overview of cellular respiration   Cellular respiration   Biology   Khan Academy.mp3", "Sentence": "And 38 ATPs is currently considered to be kind of a theoretical maximum, but when we actually observe things in cells, it looks like it comes out at around 29 to 30 ATPs. And once again, it depends what the cell's trying to do, the type of cells and the type of efficiency. But all of this is happening through cellular respiration. And just to get a better sense of where all of this is occurring, where all of this is occurring, we said glycolysis is occurring in the cytosol, the citric acid cycle, this is occurring in the matrix of the mitochondria, so this space right over here, that is the citric acid cycle and that little magenta space that I've drawn, so that's the matrix, the video on mitochondria, we go into much more detail on that. And then the actual conversion of these coenzymes, the electron transport chain, that's occurring across the membrane of the crista. And the crista are these folds, these kind of inner membrane folds of our mitochondria. So it's occurring across the membranes of these, actually the plural is cristae, crista is the singular of the cristae."}, {"video_title": "Variation in a Species.mp3", "Sentence": "So for example, let's say I have a bunch of, well, this is the circle species. And one guy is that color, and then I've got a bunch more. Maybe some are that color. That's the same color. That one, and that one, and that one. And for whatever reason, sometimes there are no environmental factors that will predispose one of these guys to be able to survive and reproduce over the other. But every now and then, there might be some environmental factor."}, {"video_title": "Variation in a Species.mp3", "Sentence": "That's the same color. That one, and that one, and that one. And for whatever reason, sometimes there are no environmental factors that will predispose one of these guys to be able to survive and reproduce over the other. But every now and then, there might be some environmental factor. And it makes maybe all of a sudden, this guy is more fit to reproduce. And so for whatever reason, this guy is able to reproduce more frequently, and these guys less frequently. And some of them get killed or whatever, eaten by birds or they're just not able to reproduce for whatever reason."}, {"video_title": "Variation in a Species.mp3", "Sentence": "But every now and then, there might be some environmental factor. And it makes maybe all of a sudden, this guy is more fit to reproduce. And so for whatever reason, this guy is able to reproduce more frequently, and these guys less frequently. And some of them get killed or whatever, eaten by birds or they're just not able to reproduce for whatever reason. And then maybe these guys are something in between. And so over time, the frequency of the different traits you see in this population will change. And if they are drastic enough, maybe these guys start becoming dominant and start not liking these guys because they're so different or whatever else."}, {"video_title": "Variation in a Species.mp3", "Sentence": "And some of them get killed or whatever, eaten by birds or they're just not able to reproduce for whatever reason. And then maybe these guys are something in between. And so over time, the frequency of the different traits you see in this population will change. And if they are drastic enough, maybe these guys start becoming dominant and start not liking these guys because they're so different or whatever else. We could see a lot of different reasons. This could eventually turn into a different species. Now, the obvious question is, what leads to this variation?"}, {"video_title": "Variation in a Species.mp3", "Sentence": "And if they are drastic enough, maybe these guys start becoming dominant and start not liking these guys because they're so different or whatever else. We could see a lot of different reasons. This could eventually turn into a different species. Now, the obvious question is, what leads to this variation? In a population, what leads to this? In fact, even in our population, what leads to one person having dirty blonde hair, one person having brown hair, one person having black hair, and the spectrum of skin complexions and heights is pretty much infinite? What causes that?"}, {"video_title": "Variation in a Species.mp3", "Sentence": "Now, the obvious question is, what leads to this variation? In a population, what leads to this? In fact, even in our population, what leads to one person having dirty blonde hair, one person having brown hair, one person having black hair, and the spectrum of skin complexions and heights is pretty much infinite? What causes that? And then one thing that I kind of point to, and we talked about this a little bit in the DNA video, is this notion of mutations. The DNA, we learned, is just a sequence of these bases. So adenine, guanine, let's say I got some thymine going, I have some more adenine, some cytosine."}, {"video_title": "Variation in a Species.mp3", "Sentence": "What causes that? And then one thing that I kind of point to, and we talked about this a little bit in the DNA video, is this notion of mutations. The DNA, we learned, is just a sequence of these bases. So adenine, guanine, let's say I got some thymine going, I have some more adenine, some cytosine. And that these code, if you have enough of these in a row, maybe you have a few hundred or a few thousands of these, these code for proteins or they code for things that control other proteins. But maybe you have a change in one of them. Maybe this cytosine, for whatever reason, becomes a guanine randomly."}, {"video_title": "Variation in a Species.mp3", "Sentence": "So adenine, guanine, let's say I got some thymine going, I have some more adenine, some cytosine. And that these code, if you have enough of these in a row, maybe you have a few hundred or a few thousands of these, these code for proteins or they code for things that control other proteins. But maybe you have a change in one of them. Maybe this cytosine, for whatever reason, becomes a guanine randomly. Or maybe these get deleted. And that would change the DNA. But you can imagine, if I went to someone's computer code and just randomly started changing letters and randomly started inserting letters without really knowing what I'm doing, most of the time I'm going to break the computer program."}, {"video_title": "Variation in a Species.mp3", "Sentence": "Maybe this cytosine, for whatever reason, becomes a guanine randomly. Or maybe these get deleted. And that would change the DNA. But you can imagine, if I went to someone's computer code and just randomly started changing letters and randomly started inserting letters without really knowing what I'm doing, most of the time I'm going to break the computer program. Most of the time, the great majority of the time, this is going to go nowhere. For example, if I go into someone's computer program and if I just add a couple of spaces or something, that might not change their computer program. But if I start getting rid of semicolons and start changing numbers and all that, it'll probably make the computer program break."}, {"video_title": "Variation in a Species.mp3", "Sentence": "But you can imagine, if I went to someone's computer code and just randomly started changing letters and randomly started inserting letters without really knowing what I'm doing, most of the time I'm going to break the computer program. Most of the time, the great majority of the time, this is going to go nowhere. For example, if I go into someone's computer program and if I just add a couple of spaces or something, that might not change their computer program. But if I start getting rid of semicolons and start changing numbers and all that, it'll probably make the computer program break. So it'll either do nothing or it'll actually kill the organisms most of the time. Mutations. Sometimes they might make the actual cell kind of go run amok and we'll do a whole maybe series of videos on cancer and that itself obviously would hurt the organism as a whole."}, {"video_title": "Variation in a Species.mp3", "Sentence": "But if I start getting rid of semicolons and start changing numbers and all that, it'll probably make the computer program break. So it'll either do nothing or it'll actually kill the organisms most of the time. Mutations. Sometimes they might make the actual cell kind of go run amok and we'll do a whole maybe series of videos on cancer and that itself obviously would hurt the organism as a whole. Although if it occurs after the organism is reproduced, it might not be something that selects against the organism. But anyway, and it also wouldn't be passed on. But anyway, I won't go too detailed into that."}, {"video_title": "Variation in a Species.mp3", "Sentence": "Sometimes they might make the actual cell kind of go run amok and we'll do a whole maybe series of videos on cancer and that itself obviously would hurt the organism as a whole. Although if it occurs after the organism is reproduced, it might not be something that selects against the organism. But anyway, and it also wouldn't be passed on. But anyway, I won't go too detailed into that. But the whole point is that mutations don't seem to be a satisfying source of variation. They could be a source or kind of contribute on the margin, but there must be something more profound than mutations that's creating the diversity even within, or maybe I should call the variation, even within a population. And the answer here is really, it's kind of right in front of us."}, {"video_title": "Variation in a Species.mp3", "Sentence": "But anyway, I won't go too detailed into that. But the whole point is that mutations don't seem to be a satisfying source of variation. They could be a source or kind of contribute on the margin, but there must be something more profound than mutations that's creating the diversity even within, or maybe I should call the variation, even within a population. And the answer here is really, it's kind of right in front of us. It really addresses kind of one of the most fundamental things about biology. And it's so fundamental that a lot of people never even question why it is the way it is. And that is sexual reproduction."}, {"video_title": "Variation in a Species.mp3", "Sentence": "And the answer here is really, it's kind of right in front of us. It really addresses kind of one of the most fundamental things about biology. And it's so fundamental that a lot of people never even question why it is the way it is. And that is sexual reproduction. And when I mean sexual reproduction, it's this notion that you have, and pretty much if you look at all organisms that have nucleuses, and we call those eukaryotes, maybe I'll do a whole video on eukaryotes versus prokaryotes. But it's the notion that if you look universally all the way from plants, not universally, but if you look at cells that have nucleuses, they almost universally have this phenomenon that you have males and you have females. In some organisms, an organism can be both a male and a female, but the common idea here is that all organisms kind of produce versions of their genetic material that mix with other organisms' version of their genetic material."}, {"video_title": "Variation in a Species.mp3", "Sentence": "And that is sexual reproduction. And when I mean sexual reproduction, it's this notion that you have, and pretty much if you look at all organisms that have nucleuses, and we call those eukaryotes, maybe I'll do a whole video on eukaryotes versus prokaryotes. But it's the notion that if you look universally all the way from plants, not universally, but if you look at cells that have nucleuses, they almost universally have this phenomenon that you have males and you have females. In some organisms, an organism can be both a male and a female, but the common idea here is that all organisms kind of produce versions of their genetic material that mix with other organisms' version of their genetic material. If mutations were the only source of variation, then I could just butt off other cells. Maybe other cells would just butt off from me, and then randomly one cell might be a little bit different and whatever else. But that would, as we already talked about, most of the time we would have very little change, very little variation."}, {"video_title": "Variation in a Species.mp3", "Sentence": "In some organisms, an organism can be both a male and a female, but the common idea here is that all organisms kind of produce versions of their genetic material that mix with other organisms' version of their genetic material. If mutations were the only source of variation, then I could just butt off other cells. Maybe other cells would just butt off from me, and then randomly one cell might be a little bit different and whatever else. But that would, as we already talked about, most of the time we would have very little change, very little variation. And whatever variation does occur because of any kind of noise being introduced into this kind of butting process where I just replicate myself identically, most of the times it'll be negative. Most of the times it'll break the organism. Now, when you have sexual reproduction, what happens?"}, {"video_title": "Variation in a Species.mp3", "Sentence": "But that would, as we already talked about, most of the time we would have very little change, very little variation. And whatever variation does occur because of any kind of noise being introduced into this kind of butting process where I just replicate myself identically, most of the times it'll be negative. Most of the times it'll break the organism. Now, when you have sexual reproduction, what happens? Well, you keep mixing and matching every possible combination of DNA in a species pool of DNA. Let me make this a little bit more concrete for you. So let me erase this horrible drawing I just did."}, {"video_title": "Variation in a Species.mp3", "Sentence": "Now, when you have sexual reproduction, what happens? Well, you keep mixing and matching every possible combination of DNA in a species pool of DNA. Let me make this a little bit more concrete for you. So let me erase this horrible drawing I just did. So we all have, let me stick to humans because that's what we are. We have 23 pairs of chromosomes, and in each pair we have one chromosome from our mother and one chromosome from our father. So let me draw that."}, {"video_title": "Variation in a Species.mp3", "Sentence": "So let me erase this horrible drawing I just did. So we all have, let me stick to humans because that's what we are. We have 23 pairs of chromosomes, and in each pair we have one chromosome from our mother and one chromosome from our father. So let me draw that. So I'll do my father's chromosomes in blue, so I have 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, and I'm running out of space. Let me do more here. 16, 17, 18, 19, 20, 21, 22."}, {"video_title": "Variation in a Species.mp3", "Sentence": "So let me draw that. So I'll do my father's chromosomes in blue, so I have 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, and I'm running out of space. Let me do more here. 16, 17, 18, 19, 20, 21, 22. And then I'll throw another one here that looks a little bit different. I'll throw one here that looks like a Y. And we'll talk more about the X's and the Y chromosomes."}, {"video_title": "Variation in a Species.mp3", "Sentence": "16, 17, 18, 19, 20, 21, 22. And then I'll throw another one here that looks a little bit different. I'll throw one here that looks like a Y. And we'll talk more about the X's and the Y chromosomes. And I have 23 chromosomes from my mother. And not to be stereotypical, but maybe I'll do that in a more feminine color. Let's see."}, {"video_title": "Variation in a Species.mp3", "Sentence": "And we'll talk more about the X's and the Y chromosomes. And I have 23 chromosomes from my mother. And not to be stereotypical, but maybe I'll do that in a more feminine color. Let's see. So I have 23 chromosomes from my mother. 1, 2, I just have to draw 1, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23. So what's going on here?"}, {"video_title": "Variation in a Species.mp3", "Sentence": "Let's see. So I have 23 chromosomes from my mother. 1, 2, I just have to draw 1, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23. So what's going on here? I have 23 from my mother. I have 23 from my father. Now, each of these chromosomes, and I made them right next to each other."}, {"video_title": "Variation in a Species.mp3", "Sentence": "So what's going on here? I have 23 from my mother. I have 23 from my father. Now, each of these chromosomes, and I made them right next to each other. So for example, let me zoom in on one pair of these. So let's say we look at chromosome number 3. So let me zoom in on chromosome number 3."}, {"video_title": "Variation in a Species.mp3", "Sentence": "Now, each of these chromosomes, and I made them right next to each other. So for example, let me zoom in on one pair of these. So let's say we look at chromosome number 3. So let me zoom in on chromosome number 3. I have one from my mother right here. And remember, actually maybe I'll do it this way. Remember, a chromosome is just a big, if you take the DNA, it just keeps wrapping around."}, {"video_title": "Variation in a Species.mp3", "Sentence": "So let me zoom in on chromosome number 3. I have one from my mother right here. And remember, actually maybe I'll do it this way. Remember, a chromosome is just a big, if you take the DNA, it just keeps wrapping around. It actually wraps around all these proteins and it creates the structure. But it's just a big, you see it like that, you're like, oh, maybe the DNA, no, but this could have millions of base pairs. So maybe it'll look something like that."}, {"video_title": "Variation in a Species.mp3", "Sentence": "Remember, a chromosome is just a big, if you take the DNA, it just keeps wrapping around. It actually wraps around all these proteins and it creates the structure. But it's just a big, you see it like that, you're like, oh, maybe the DNA, no, but this could have millions of base pairs. So maybe it'll look something like that. It's a densely wrapped version of, well, it's a long string of DNA, and when it's normally drawn like this, which is not always the way it is, and we'll talk more about like that, they draw it as densely packed like that. So let's say that's from my mother and that's from my father. Now, these are both, we call them, I'll call them, they're the same, let's call this chromosome 3."}, {"video_title": "Variation in a Species.mp3", "Sentence": "So maybe it'll look something like that. It's a densely wrapped version of, well, it's a long string of DNA, and when it's normally drawn like this, which is not always the way it is, and we'll talk more about like that, they draw it as densely packed like that. So let's say that's from my mother and that's from my father. Now, these are both, we call them, I'll call them, they're the same, let's call this chromosome 3. They're both chromosome 3. And what the idea is here is that I'm getting different traits from my father and from my mother. For example, and I'm doing a gross oversimplification here, but this is really to just give you the idea of what's going on."}, {"video_title": "Variation in a Species.mp3", "Sentence": "Now, these are both, we call them, I'll call them, they're the same, let's call this chromosome 3. They're both chromosome 3. And what the idea is here is that I'm getting different traits from my father and from my mother. For example, and I'm doing a gross oversimplification here, but this is really to just give you the idea of what's going on. This chromosome 3, maybe it contains this trait for hair color. And maybe my father had, and I'll use my actual example, my father had very straight hair. So let's say he had, some place on this chromosome, there is a gene for hair straightness."}, {"video_title": "Variation in a Species.mp3", "Sentence": "For example, and I'm doing a gross oversimplification here, but this is really to just give you the idea of what's going on. This chromosome 3, maybe it contains this trait for hair color. And maybe my father had, and I'll use my actual example, my father had very straight hair. So let's say he had, some place on this chromosome, there is a gene for hair straightness. Let's say it's a little thing right there. And remember, that gene could be thousands of base pairs. But let's say this is hair straightness."}, {"video_title": "Variation in a Species.mp3", "Sentence": "So let's say he had, some place on this chromosome, there is a gene for hair straightness. Let's say it's a little thing right there. And remember, that gene could be thousands of base pairs. But let's say this is hair straightness. So my father's version of that gene, or he had the allele for straightness. And remember, an allele is just a version of a gene. So I'll call it the allele straight for straight hair."}, {"video_title": "Variation in a Species.mp3", "Sentence": "But let's say this is hair straightness. So my father's version of that gene, or he had the allele for straightness. And remember, an allele is just a version of a gene. So I'll call it the allele straight for straight hair. Now, this other chromosome that my mother gave me, this essentially, and there are exceptions, but for the most part, it codes for the same genes. And that's why I put them next to each other. So this will also have the gene for hair straightness or curliness."}, {"video_title": "Variation in a Species.mp3", "Sentence": "So I'll call it the allele straight for straight hair. Now, this other chromosome that my mother gave me, this essentially, and there are exceptions, but for the most part, it codes for the same genes. And that's why I put them next to each other. So this will also have the gene for hair straightness or curliness. But my mom does happen to actually have curly hair. So she has the gene right there for curly hair. So she has the version of the gene here is, let's see, allele curly."}, {"video_title": "Variation in a Species.mp3", "Sentence": "So this will also have the gene for hair straightness or curliness. But my mom does happen to actually have curly hair. So she has the gene right there for curly hair. So she has the version of the gene here is, let's see, allele curly. The gene just says, look, this is the gene for whether or not your hair is curly. Each version of the gene is called an allele. Allele curly."}, {"video_title": "Variation in a Species.mp3", "Sentence": "So she has the version of the gene here is, let's see, allele curly. The gene just says, look, this is the gene for whether or not your hair is curly. Each version of the gene is called an allele. Allele curly. Now, when I got both of these in my body, or in my cells, and this is in every cell of my body, every cell of my body except for, and we'll talk a little in a few seconds about my germ cells, but every cell other than the ones that I use for reproduction have this complete set of chromosomes in it, which I find amazing. But only certain chromosomes are, for example, these genes will be completely useless in my fingernails because all of a sudden, the straight and the curly don't matter that much. And I'm simplifying."}, {"video_title": "Variation in a Species.mp3", "Sentence": "Allele curly. Now, when I got both of these in my body, or in my cells, and this is in every cell of my body, every cell of my body except for, and we'll talk a little in a few seconds about my germ cells, but every cell other than the ones that I use for reproduction have this complete set of chromosomes in it, which I find amazing. But only certain chromosomes are, for example, these genes will be completely useless in my fingernails because all of a sudden, the straight and the curly don't matter that much. And I'm simplifying. Maybe they will on some other dimension. But let's say for simplicity, they won't matter in certain places. So certain genes are expressed in certain parts of the body, but every one of your body cells, and we call those somatic cells, and we'll separate those from the sex cells or the germ cells that we'll talk about later."}, {"video_title": "Variation in a Species.mp3", "Sentence": "And I'm simplifying. Maybe they will on some other dimension. But let's say for simplicity, they won't matter in certain places. So certain genes are expressed in certain parts of the body, but every one of your body cells, and we call those somatic cells, and we'll separate those from the sex cells or the germ cells that we'll talk about later. So this is my body cells. So this is the great majority of your cells. And this is opposed to your germ cells."}, {"video_title": "Variation in a Species.mp3", "Sentence": "So certain genes are expressed in certain parts of the body, but every one of your body cells, and we call those somatic cells, and we'll separate those from the sex cells or the germ cells that we'll talk about later. So this is my body cells. So this is the great majority of your cells. And this is opposed to your germ cells. And the germ cells, I'll just write it here just so you get it clear, for a male, that's the sperm cells. And for a female, that's the egg cells or the ova. But most of my cells have a complete collection of these."}, {"video_title": "Variation in a Species.mp3", "Sentence": "And this is opposed to your germ cells. And the germ cells, I'll just write it here just so you get it clear, for a male, that's the sperm cells. And for a female, that's the egg cells or the ova. But most of my cells have a complete collection of these. What I want to give you the idea is that for every trait, I essentially have two versions, one from my mother and one from my father. Now these right here are called homologous chromosomes. Chromosomes, homologous."}, {"video_title": "Variation in a Species.mp3", "Sentence": "But most of my cells have a complete collection of these. What I want to give you the idea is that for every trait, I essentially have two versions, one from my mother and one from my father. Now these right here are called homologous chromosomes. Chromosomes, homologous. What that means is every time you see the prefix homologous, or if you see like homo sapien, or even the word homosexual or homogeneous, it means same. You see that all the time. So homologous means that they're almost the same."}, {"video_title": "Variation in a Species.mp3", "Sentence": "Chromosomes, homologous. What that means is every time you see the prefix homologous, or if you see like homo sapien, or even the word homosexual or homogeneous, it means same. You see that all the time. So homologous means that they're almost the same. They're coding for the most part the same set of genes, but they're not identical. They actually might code for slightly different versions of the same gene. So depending on what versions I get, what is actually expressed for me."}, {"video_title": "Variation in a Species.mp3", "Sentence": "So homologous means that they're almost the same. They're coding for the most part the same set of genes, but they're not identical. They actually might code for slightly different versions of the same gene. So depending on what versions I get, what is actually expressed for me. So my genotype, let me introduce another word. And I'm overwhelming you with words here. So my genotype is exactly what alleles I have, what versions of the gene."}, {"video_title": "Variation in a Species.mp3", "Sentence": "So depending on what versions I get, what is actually expressed for me. So my genotype, let me introduce another word. And I'm overwhelming you with words here. So my genotype is exactly what alleles I have, what versions of the gene. So I got like the fifth version of the curly allele. There could be multiple versions of the curly allele in our gene pool. And maybe I got some version of the straight allele."}, {"video_title": "Variation in a Species.mp3", "Sentence": "So my genotype is exactly what alleles I have, what versions of the gene. So I got like the fifth version of the curly allele. There could be multiple versions of the curly allele in our gene pool. And maybe I got some version of the straight allele. That is my genotype. My phenotype is what my hair really looks like. So for example, two people could have different genotypes with the same, but they might code for hair that looks pretty much the same."}, {"video_title": "Variation in a Species.mp3", "Sentence": "And maybe I got some version of the straight allele. That is my genotype. My phenotype is what my hair really looks like. So for example, two people could have different genotypes with the same, but they might code for hair that looks pretty much the same. So it might have a very similar phenotype. So one phenotype can be represented by multiple genotypes. So that's just one thing to think about."}, {"video_title": "Variation in a Species.mp3", "Sentence": "So for example, two people could have different genotypes with the same, but they might code for hair that looks pretty much the same. So it might have a very similar phenotype. So one phenotype can be represented by multiple genotypes. So that's just one thing to think about. And we'll talk a lot about that in the future, but I just want to introduce you into that there. Now, I entered this whole discussion because I wanted to talk about variation. So how does variation happen?"}, {"video_title": "Variation in a Species.mp3", "Sentence": "So that's just one thing to think about. And we'll talk a lot about that in the future, but I just want to introduce you into that there. Now, I entered this whole discussion because I wanted to talk about variation. So how does variation happen? Well, what's going to happen when I, so first of all, well, let me put it this way. What's going to happen when I reproduce and I have a son? Well, my contribution to my son is going to be a random collection of half of these genes."}, {"video_title": "Variation in a Species.mp3", "Sentence": "So how does variation happen? Well, what's going to happen when I, so first of all, well, let me put it this way. What's going to happen when I reproduce and I have a son? Well, my contribution to my son is going to be a random collection of half of these genes. I'm going to contribute either one. For each homologous pair, I'm either going to contribute the one that I got from my mother or the one that I got from my father. So let's say that the sperm cell that went on to fertilize my wife's egg, it just happened to have, let's say it happened to have that one, that one, well, I could just pick one from each of these 23 sets."}, {"video_title": "Variation in a Species.mp3", "Sentence": "Well, my contribution to my son is going to be a random collection of half of these genes. I'm going to contribute either one. For each homologous pair, I'm either going to contribute the one that I got from my mother or the one that I got from my father. So let's say that the sperm cell that went on to fertilize my wife's egg, it just happened to have, let's say it happened to have that one, that one, well, I could just pick one from each of these 23 sets. And you could say, well, how many combinations are there? Well, for every set, I can pick one of the two homologous chromosomes, and I'm going to do that 23 times. 2 times 2 times 2, so it's 2 to the 23rd."}, {"video_title": "Variation in a Species.mp3", "Sentence": "So let's say that the sperm cell that went on to fertilize my wife's egg, it just happened to have, let's say it happened to have that one, that one, well, I could just pick one from each of these 23 sets. And you could say, well, how many combinations are there? Well, for every set, I can pick one of the two homologous chromosomes, and I'm going to do that 23 times. 2 times 2 times 2, so it's 2 to the 23rd. So there's 22 to the 23 different versions that I can contribute to any son or daughter that I might have. We'll talk about how that happens when we talk about meiosis or mitosis. That when I generate my sperm cells, sperm cells are essentially, instead of having 23 pairs of chromosomes in sperm, you only have 23 chromosomes."}, {"video_title": "Variation in a Species.mp3", "Sentence": "2 times 2 times 2, so it's 2 to the 23rd. So there's 22 to the 23 different versions that I can contribute to any son or daughter that I might have. We'll talk about how that happens when we talk about meiosis or mitosis. That when I generate my sperm cells, sperm cells are essentially, instead of having 23 pairs of chromosomes in sperm, you only have 23 chromosomes. So for example, I'll take one from each of those, and through the process of meiosis, which we'll go into, I'll generate a bunch of sperm cells. And each sperm cell will have one from each of these pairs, one version from each of those pairs. So maybe for this chromosome, I get it from my dad."}, {"video_title": "Variation in a Species.mp3", "Sentence": "That when I generate my sperm cells, sperm cells are essentially, instead of having 23 pairs of chromosomes in sperm, you only have 23 chromosomes. So for example, I'll take one from each of those, and through the process of meiosis, which we'll go into, I'll generate a bunch of sperm cells. And each sperm cell will have one from each of these pairs, one version from each of those pairs. So maybe for this chromosome, I get it from my dad. From the next chromosome, I get it from my mom. Then I donate a couple more from, I shouldn't have drawn them next to each other, I donate a couple more from my mom, then for the chromosome number 5, it comes from my dad, and so on and so forth. But there's 2 to the 23rd combinations here, because there are 23 pairs that I'm collecting from."}, {"video_title": "Variation in a Species.mp3", "Sentence": "So maybe for this chromosome, I get it from my dad. From the next chromosome, I get it from my mom. Then I donate a couple more from, I shouldn't have drawn them next to each other, I donate a couple more from my mom, then for the chromosome number 5, it comes from my dad, and so on and so forth. But there's 2 to the 23rd combinations here, because there are 23 pairs that I'm collecting from. Now, my wife's egg is going to have the same situation. There are 2 to the 23 different combinations of DNA that she can contribute, just based on which of the homologous pairs she will contribute. So the possible combinations that just one couple can produce, and I'm using my life as an example, but you could use this, this applies to everything."}, {"video_title": "Variation in a Species.mp3", "Sentence": "But there's 2 to the 23rd combinations here, because there are 23 pairs that I'm collecting from. Now, my wife's egg is going to have the same situation. There are 2 to the 23 different combinations of DNA that she can contribute, just based on which of the homologous pairs she will contribute. So the possible combinations that just one couple can produce, and I'm using my life as an example, but you could use this, this applies to everything. This applies to every species that experiences sexual reproduction. So if I can give 2 to the 23rd combinations of DNA, and my wife can give 2 to the 23 combinations of DNA, then we can produce 2 to the 46th combinations. Now, just to give an idea of how large of a number this is, this is 12,000, roughly 12,000 times the number of human beings on the planet today."}, {"video_title": "Variation in a Species.mp3", "Sentence": "So the possible combinations that just one couple can produce, and I'm using my life as an example, but you could use this, this applies to everything. This applies to every species that experiences sexual reproduction. So if I can give 2 to the 23rd combinations of DNA, and my wife can give 2 to the 23 combinations of DNA, then we can produce 2 to the 46th combinations. Now, just to give an idea of how large of a number this is, this is 12,000, roughly 12,000 times the number of human beings on the planet today. So there's a huge amount of variation that even one couple can produce. And if you thought that even that isn't enough, it turns out that amongst these homologous pairs, and we'll talk about when this happens in meiosis, you can actually have DNA recombination. And all that means is that when these homologous pairs during meiosis line up near each other, you can have this thing called crossover, where all of this DNA here crosses over and touches over here, and all of this DNA crosses over and touches over there."}, {"video_title": "Variation in a Species.mp3", "Sentence": "Now, just to give an idea of how large of a number this is, this is 12,000, roughly 12,000 times the number of human beings on the planet today. So there's a huge amount of variation that even one couple can produce. And if you thought that even that isn't enough, it turns out that amongst these homologous pairs, and we'll talk about when this happens in meiosis, you can actually have DNA recombination. And all that means is that when these homologous pairs during meiosis line up near each other, you can have this thing called crossover, where all of this DNA here crosses over and touches over here, and all of this DNA crosses over and touches over there. So all of this goes there, and all of this goes there. And what you end up with after the crossover is that one DNA, the one that came from my mom, or that I thought came from my mom, now has a chunk that came from my dad. And the chunk that came from my dad now has a chunk that came from my mom."}, {"video_title": "Variation in a Species.mp3", "Sentence": "And all that means is that when these homologous pairs during meiosis line up near each other, you can have this thing called crossover, where all of this DNA here crosses over and touches over here, and all of this DNA crosses over and touches over there. So all of this goes there, and all of this goes there. And what you end up with after the crossover is that one DNA, the one that came from my mom, or that I thought came from my mom, now has a chunk that came from my dad. And the chunk that came from my dad now has a chunk that came from my mom. Let me do it in the right color. It came from my mom like that. And so that even increases the amount of variety even more."}, {"video_title": "Variation in a Species.mp3", "Sentence": "And the chunk that came from my dad now has a chunk that came from my mom. Let me do it in the right color. It came from my mom like that. And so that even increases the amount of variety even more. So you can almost now, instead of talking about the different chromosomes that you're contributing, where the chromosomes are each of these collections of DNA, you can almost go to the different combinations at the gene level. And now you can think about an almost infinite form of variation. And you can think about all of the variation that might emerge when you start mixing and mashing different versions of the same gene in a population."}, {"video_title": "Variation in a Species.mp3", "Sentence": "And so that even increases the amount of variety even more. So you can almost now, instead of talking about the different chromosomes that you're contributing, where the chromosomes are each of these collections of DNA, you can almost go to the different combinations at the gene level. And now you can think about an almost infinite form of variation. And you can think about all of the variation that might emerge when you start mixing and mashing different versions of the same gene in a population. And you don't just look at one gene. I mean, the reality is that genes by themselves very seldom code for a specific. You can very seldom look for one gene and say, oh, that is brown hair."}, {"video_title": "Variation in a Species.mp3", "Sentence": "And you can think about all of the variation that might emerge when you start mixing and mashing different versions of the same gene in a population. And you don't just look at one gene. I mean, the reality is that genes by themselves very seldom code for a specific. You can very seldom look for one gene and say, oh, that is brown hair. Or look for one gene and say, oh, that's intelligence. Or that is how likable someone is. It's usually a whole set of genes interacting in an incredibly complicated way."}, {"video_title": "Variation in a Species.mp3", "Sentence": "You can very seldom look for one gene and say, oh, that is brown hair. Or look for one gene and say, oh, that's intelligence. Or that is how likable someone is. It's usually a whole set of genes interacting in an incredibly complicated way. Hair might be coded for by this whole set of genes on multiple chromosomes. And this might be coded for a whole set of genes on multiple chromosomes. And so then you can start thinking about all of the different combinations."}, {"video_title": "Variation in a Species.mp3", "Sentence": "It's usually a whole set of genes interacting in an incredibly complicated way. Hair might be coded for by this whole set of genes on multiple chromosomes. And this might be coded for a whole set of genes on multiple chromosomes. And so then you can start thinking about all of the different combinations. And then all of a sudden, maybe some combination that never existed before all of a sudden emerges. And that's very successful. But I'll leave you to think about it because maybe that combination might be passed on or it may not be passed on because of this recombination."}, {"video_title": "Variation in a Species.mp3", "Sentence": "And so then you can start thinking about all of the different combinations. And then all of a sudden, maybe some combination that never existed before all of a sudden emerges. And that's very successful. But I'll leave you to think about it because maybe that combination might be passed on or it may not be passed on because of this recombination. But we'll talk more about that in the future. But I wanted to introduce this idea of sexual reproduction to you because this really is the main source of variation within a population. And it's kind of a philosophical idea because we almost take the idea of having males and females for granted because it's this universal idea."}, {"video_title": "Variation in a Species.mp3", "Sentence": "But I'll leave you to think about it because maybe that combination might be passed on or it may not be passed on because of this recombination. But we'll talk more about that in the future. But I wanted to introduce this idea of sexual reproduction to you because this really is the main source of variation within a population. And it's kind of a philosophical idea because we almost take the idea of having males and females for granted because it's this universal idea. But I did a little reading on it. It turns out that this actually only emerged about 1.4 billion years ago. That this is almost a useful trait because once you introduce this level of variation, the natural selection can start."}, {"video_title": "Variation in a Species.mp3", "Sentence": "And it's kind of a philosophical idea because we almost take the idea of having males and females for granted because it's this universal idea. But I did a little reading on it. It turns out that this actually only emerged about 1.4 billion years ago. That this is almost a useful trait because once you introduce this level of variation, the natural selection can start. You can kind of say that when you have this more powerful form of variation than just pure mutations, and maybe you might have some primitive form of crossover before. But now that you have this sexual reproduction and you have this variation, natural selection can occur in a more efficient way so that species that were able to reproduce and essentially recombine their DNA and mix and match it in this way were able to produce more variety and were able to essentially be selected for the environment in a more efficient way. So they started to essentially outnumber the ones that couldn't."}, {"video_title": "Variation in a Species.mp3", "Sentence": "That this is almost a useful trait because once you introduce this level of variation, the natural selection can start. You can kind of say that when you have this more powerful form of variation than just pure mutations, and maybe you might have some primitive form of crossover before. But now that you have this sexual reproduction and you have this variation, natural selection can occur in a more efficient way so that species that were able to reproduce and essentially recombine their DNA and mix and match it in this way were able to produce more variety and were able to essentially be selected for the environment in a more efficient way. So they started to essentially outnumber the ones that couldn't. So it became a kind of a very universal trait. But you could have imagined a world, and there are science fiction books written about this, where you have three genders, where you have gender one, two, three. You could have 10 genders."}, {"video_title": "Variation in a Species.mp3", "Sentence": "So they started to essentially outnumber the ones that couldn't. So it became a kind of a very universal trait. But you could have imagined a world, and there are science fiction books written about this, where you have three genders, where you have gender one, two, three. You could have 10 genders. And it just happens to be that on Earth, this notion of having two genders turned out to be a very efficient and stable way of introducing variation into a population. So hopefully you found that interesting. In the next video, I'll go more into the detail of how exactly meiosis and mitosis works."}, {"video_title": "Example of signal transduction pathway.mp3", "Sentence": "It might tell, it might activate some genes, it might change the metabolism of the cell in some ways, and this signal that goes from the receptor into the cell to make the cell behave in some way, we call that signal transduction. We call it transduction. Signal transduction. And in a previous video, I was kind of hand-wavy about it, and you might have been saying, well, how does a signal actually go into the cell? How does it actually move through the cell, and how does it actually make things happen? And what I want to do in this video is, I'm not going to go into all of the details, but I'm going to give you an appreciation for how transduction can actually occur. And hopefully it'll also give you appreciation for how complex biological systems, including you and me, and even each of our individual cells, actually are."}, {"video_title": "Example of signal transduction pathway.mp3", "Sentence": "And in a previous video, I was kind of hand-wavy about it, and you might have been saying, well, how does a signal actually go into the cell? How does it actually move through the cell, and how does it actually make things happen? And what I want to do in this video is, I'm not going to go into all of the details, but I'm going to give you an appreciation for how transduction can actually occur. And hopefully it'll also give you appreciation for how complex biological systems, including you and me, and even each of our individual cells, actually are. So this pathway that we're seeing up here, and you can see that there's a bunch of pathways that all kind of work together and overlap in terms of the enzymes and the proteins that are involved. This, as the diagram calls it, is the classical MAP kinase pathway. And if you're wondering, what does MAP kinase stand for, and oftentimes people will just say MAPK or M-A-P-K, it stands for mitogen, M for mitogen, mitogen-activated protein kinases."}, {"video_title": "Example of signal transduction pathway.mp3", "Sentence": "And hopefully it'll also give you appreciation for how complex biological systems, including you and me, and even each of our individual cells, actually are. So this pathway that we're seeing up here, and you can see that there's a bunch of pathways that all kind of work together and overlap in terms of the enzymes and the proteins that are involved. This, as the diagram calls it, is the classical MAP kinase pathway. And if you're wondering, what does MAP kinase stand for, and oftentimes people will just say MAPK or M-A-P-K, it stands for mitogen, M for mitogen, mitogen-activated protein kinases. And you might be saying, well, what does mitogen, what does mitogen mean? Well, mitogen refers to things that cause cells to mitose, to actually go into mitosis, to start replicating themselves. Now, what is, so mitogen-activated, so this pathway's going to be activated by a mitogen, mitogen-activated protein kinase."}, {"video_title": "Example of signal transduction pathway.mp3", "Sentence": "And if you're wondering, what does MAP kinase stand for, and oftentimes people will just say MAPK or M-A-P-K, it stands for mitogen, M for mitogen, mitogen-activated protein kinases. And you might be saying, well, what does mitogen, what does mitogen mean? Well, mitogen refers to things that cause cells to mitose, to actually go into mitosis, to start replicating themselves. Now, what is, so mitogen-activated, so this pathway's going to be activated by a mitogen, mitogen-activated protein kinase. Well, a protein kinase, a kinase, and we've seen kinases multiple times, they're involved in many, many, many biological mechanisms. These are general term for enzymes that help take a higher energy phosphate, or especially I should say a higher energy bond, or a phosphate part of an ATP or a GTP, and transfers them to different molecules. And as they transfer them to different molecules, it's able to leverage that energy to actually facilitate some type of a mechanism."}, {"video_title": "Example of signal transduction pathway.mp3", "Sentence": "Now, what is, so mitogen-activated, so this pathway's going to be activated by a mitogen, mitogen-activated protein kinase. Well, a protein kinase, a kinase, and we've seen kinases multiple times, they're involved in many, many, many biological mechanisms. These are general term for enzymes that help take a higher energy phosphate, or especially I should say a higher energy bond, or a phosphate part of an ATP or a GTP, and transfers them to different molecules. And as they transfer them to different molecules, it's able to leverage that energy to actually facilitate some type of a mechanism. Now, as I said, I'm not gonna go into all of the details here, this is actually quite complex, but I wanna make a little bit sense of it. And we're actually gonna talk about a few proteins and a few enzymes that are actually fairly important to modern biological research. So what you have right over here, I'll start with this molecule right over here, this is the ligand, this is the ligand, it's going to be released by some other part of the biological system from some other cell."}, {"video_title": "Example of signal transduction pathway.mp3", "Sentence": "And as they transfer them to different molecules, it's able to leverage that energy to actually facilitate some type of a mechanism. Now, as I said, I'm not gonna go into all of the details here, this is actually quite complex, but I wanna make a little bit sense of it. And we're actually gonna talk about a few proteins and a few enzymes that are actually fairly important to modern biological research. So what you have right over here, I'll start with this molecule right over here, this is the ligand, this is the ligand, it's going to be released by some other part of the biological system from some other cell. And this EGF, this stands for epidermal growth factor. And the 1986 Nobel Prize in Medicine was actually given for the discovery of EGF, of epidermal growth factor. Now this is going to be the ligand, this is essentially what's, you know, when this attaches or when this binds to a receptor, that's going to cause the signal to be transduced, you're gonna have the transduction going into the cell."}, {"video_title": "Example of signal transduction pathway.mp3", "Sentence": "So what you have right over here, I'll start with this molecule right over here, this is the ligand, this is the ligand, it's going to be released by some other part of the biological system from some other cell. And this EGF, this stands for epidermal growth factor. And the 1986 Nobel Prize in Medicine was actually given for the discovery of EGF, of epidermal growth factor. Now this is going to be the ligand, this is essentially what's, you know, when this attaches or when this binds to a receptor, that's going to cause the signal to be transduced, you're gonna have the transduction going into the cell. And so you can imagine, it's going to bind to this membrane receptor, and so EGFR literally stands for epidermal growth factor receptor. EGF receptor. And it's part of this protein complex, and once this binds, it's able to help activate, it's able to help activate RAS right over here."}, {"video_title": "Example of signal transduction pathway.mp3", "Sentence": "Now this is going to be the ligand, this is essentially what's, you know, when this attaches or when this binds to a receptor, that's going to cause the signal to be transduced, you're gonna have the transduction going into the cell. And so you can imagine, it's going to bind to this membrane receptor, and so EGFR literally stands for epidermal growth factor receptor. EGF receptor. And it's part of this protein complex, and once this binds, it's able to help activate, it's able to help activate RAS right over here. And RAS, and once again, you know, all of these names, they have these interesting histories associated with them. This stands for rat sarcoma. Rat sarcoma, and sarcomas are cancers in certain tissues in the body."}, {"video_title": "Example of signal transduction pathway.mp3", "Sentence": "And it's part of this protein complex, and once this binds, it's able to help activate, it's able to help activate RAS right over here. And RAS, and once again, you know, all of these names, they have these interesting histories associated with them. This stands for rat sarcoma. Rat sarcoma, and sarcomas are cancers in certain tissues in the body. And it was first discovered associated with certain cancers, that rats that had certain sarcomas, that they were able to see that there were mutations in the genes that produced the RAS protein. And because of those mutations, the RAS protein, that the enzymes associated with it, were in their activated mode. And because they were in their activated mode, this mechanism was kind of overactive, and any of the stop signals weren't actually happening."}, {"video_title": "Example of signal transduction pathway.mp3", "Sentence": "Rat sarcoma, and sarcomas are cancers in certain tissues in the body. And it was first discovered associated with certain cancers, that rats that had certain sarcomas, that they were able to see that there were mutations in the genes that produced the RAS protein. And because of those mutations, the RAS protein, that the enzymes associated with it, were in their activated mode. And because they were in their activated mode, this mechanism was kind of overactive, and any of the stop signals weren't actually happening. And so you can imagine a mechanism right over here that is about cell differentiation. That if this mechanism proceeds, it's eventually going to tell the DNA, some portions of the DNA, especially the portions of the DNA that are involved with DNA replication, with cell division, with mitosis, those are gonna go crazy. And that's exactly what happens in cancer."}, {"video_title": "Example of signal transduction pathway.mp3", "Sentence": "And because they were in their activated mode, this mechanism was kind of overactive, and any of the stop signals weren't actually happening. And so you can imagine a mechanism right over here that is about cell differentiation. That if this mechanism proceeds, it's eventually going to tell the DNA, some portions of the DNA, especially the portions of the DNA that are involved with DNA replication, with cell division, with mitosis, those are gonna go crazy. And that's exactly what happens in cancer. So this pathway is actually a very important pathway in cancer, and you see, you know, right over here, you actually see the MAP kinase. It's often called, or was originally called ERK, which is extracellular signal regulated kinase. But this is an incredibly important pathway to cancer researchers, and they actively are looking for different types of drugs, different types of molecules that can downregulate this type of pathway."}, {"video_title": "Example of signal transduction pathway.mp3", "Sentence": "And that's exactly what happens in cancer. So this pathway is actually a very important pathway in cancer, and you see, you know, right over here, you actually see the MAP kinase. It's often called, or was originally called ERK, which is extracellular signal regulated kinase. But this is an incredibly important pathway to cancer researchers, and they actively are looking for different types of drugs, different types of molecules that can downregulate this type of pathway. So the whole point of this video, once again, I'm not going into all of the details on the MAP kinase pathway, but it's to give you an appreciation for how complex transduction is. You have this cascade of the signal, which is really this phosphate groups originally transferred from a GTP going to the, going to the RAS, and it keeps cascading down all the way until you actually have the DNA being told to, or you start activating, you start activating mechanisms where the DNA is going to start replicating, and then the cell itself is going to proliferate and differentiate. And that's, when it goes crazy, and this needs to happen in practically every cells in our body, but there's all sorts of, there's all sorts of kind of factors that keep it from going crazy."}, {"video_title": "DNA sequencing   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "Have you ever wondered how we sequence DNA? Well, let's just take a quick look at DNA sequencing. So, we're going to break down DNA sequencing into three different steps. So the first step is you take the sample of DNA that you're interested in sequencing, and you basically use PCR to amplify the sample. So, by using PCR in order to amplify the sample, you're able to generate lots and lots of DNA fragments. So, the next thing that you do is normally in PCR you have to add nucleotides. You have to give the growing strand the substrate from which it can grow."}, {"video_title": "DNA sequencing   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "So the first step is you take the sample of DNA that you're interested in sequencing, and you basically use PCR to amplify the sample. So, by using PCR in order to amplify the sample, you're able to generate lots and lots of DNA fragments. So, the next thing that you do is normally in PCR you have to add nucleotides. You have to give the growing strand the substrate from which it can grow. So normally you add in regular deoxynucleotides, and those look something like this. You've got an OH group here, you've got an H group here, you have a base, and then you've got a carbon group, and oxygen, hydrogen. So this is what a normal nucleotide looks like."}, {"video_title": "DNA sequencing   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "You have to give the growing strand the substrate from which it can grow. So normally you add in regular deoxynucleotides, and those look something like this. You've got an OH group here, you've got an H group here, you have a base, and then you've got a carbon group, and oxygen, hydrogen. So this is what a normal nucleotide looks like. But, interspersed in the PCR, what you also want to add is you want to add in something known as a dideoxynucleotide. So a dideoxynucleotide looks something like this. It's basically exactly the same thing, but it only has a hydrogen here."}, {"video_title": "DNA sequencing   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "So this is what a normal nucleotide looks like. But, interspersed in the PCR, what you also want to add is you want to add in something known as a dideoxynucleotide. So a dideoxynucleotide looks something like this. It's basically exactly the same thing, but it only has a hydrogen here. So this oxygen is removed. And what that basically does is if this dideoxynucleotide, we can abbreviate DDNTP, if this incorporates into the growing strand, since there's no oxygen group here, the strand can no longer elongate. So you basically have termination of strand elongation as soon as this DDNTP incorporates."}, {"video_title": "DNA sequencing   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "It's basically exactly the same thing, but it only has a hydrogen here. So this oxygen is removed. And what that basically does is if this dideoxynucleotide, we can abbreviate DDNTP, if this incorporates into the growing strand, since there's no oxygen group here, the strand can no longer elongate. So you basically have termination of strand elongation as soon as this DDNTP incorporates. So what you can do is you can actually fluorescently label the different dideoxynucleotides. So for example, we've got, so for example, we have four different options. So we can label all the G's blue, we can label all the A's red, all the T's green, and all the C's orange."}, {"video_title": "DNA sequencing   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "So you basically have termination of strand elongation as soon as this DDNTP incorporates. So what you can do is you can actually fluorescently label the different dideoxynucleotides. So for example, we've got, so for example, we have four different options. So we can label all the G's blue, we can label all the A's red, all the T's green, and all the C's orange. And so basically what you have is you have these dideoxynucleotides with different fluorescent labels getting incorporated into the growing strand. And since PCR is able to amplify, create millions and millions of DNA fragments, you can basically, what you can do is you'll have strands of different lengths. So let's just kind of look at an example."}, {"video_title": "DNA sequencing   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "So we can label all the G's blue, we can label all the A's red, all the T's green, and all the C's orange. And so basically what you have is you have these dideoxynucleotides with different fluorescent labels getting incorporated into the growing strand. And since PCR is able to amplify, create millions and millions of DNA fragments, you can basically, what you can do is you'll have strands of different lengths. So let's just kind of look at an example. So let's imagine that we've got nucleotide being incorporated here, a regular nucleotide, and then another one incorporated here, and then another one, and then just randomly all of a sudden we have a dideoxynucleotide being incorporated here. And this would stop elongation of the strand. So you'd have a DNA strand that's just four nucleotides long."}, {"video_title": "DNA sequencing   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "So let's just kind of look at an example. So let's imagine that we've got nucleotide being incorporated here, a regular nucleotide, and then another one incorporated here, and then another one, and then just randomly all of a sudden we have a dideoxynucleotide being incorporated here. And this would stop elongation of the strand. So you'd have a DNA strand that's just four nucleotides long. And after another round of PCR, what we might have is we might have one, two, three, four, five, six, it's just growing, it's growing, it's growing, and then all of a sudden, whoa, what happened? You've got a dideoxynucleotide being incorporated. And so basically you just do this, and after you've got millions of samples, you'll eventually be able to have something that looks like this."}, {"video_title": "DNA sequencing   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "So you'd have a DNA strand that's just four nucleotides long. And after another round of PCR, what we might have is we might have one, two, three, four, five, six, it's just growing, it's growing, it's growing, and then all of a sudden, whoa, what happened? You've got a dideoxynucleotide being incorporated. And so basically you just do this, and after you've got millions of samples, you'll eventually be able to have something that looks like this. You'll have maybe just one regular nucleotide, and you've got a dideoxynucleotide incorporated. Or you might have maybe, let's say, two of them. So you'll have two, and then you've got a, let's use this color, so you've got a dideoxynucleotide."}, {"video_title": "DNA sequencing   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "And so basically you just do this, and after you've got millions of samples, you'll eventually be able to have something that looks like this. You'll have maybe just one regular nucleotide, and you've got a dideoxynucleotide incorporated. Or you might have maybe, let's say, two of them. So you'll have two, and then you've got a, let's use this color, so you've got a dideoxynucleotide. So what you can basically do is you can see that you have strands, and they're elongating, and different strands are terminated at different points by a dideoxynucleotide. And so basically, the next step is you use gel electrophoresis, electrophoresis, in order to separate the strands by size. So when you run all the different fragments on a gel, it'll separate them by size."}, {"video_title": "DNA sequencing   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "So you'll have two, and then you've got a, let's use this color, so you've got a dideoxynucleotide. So what you can basically do is you can see that you have strands, and they're elongating, and different strands are terminated at different points by a dideoxynucleotide. And so basically, the next step is you use gel electrophoresis, electrophoresis, in order to separate the strands by size. So when you run all the different fragments on a gel, it'll separate them by size. And then you can just have a computer go in and analyze all the fluorescent labels. So if it sees here that you've got this blue fluorescent light, then it knows that the second nucleotide in the sequence is a G. So it'll say G. And then it'll look here, and it'll say, okay, well this is a C. It'll look here, it'll say we have another G, and so on and so forth. And basically, the computer is able to, by reading these fluorescent labels, these fluorescent tags, it's able to give you a DNA sequence."}, {"video_title": "DNA   Biomolecules   MCAT   Khan Academy (3).mp3", "Sentence": "For example, someone might have told you, hey, you walk kind of like your dad, or your smile is kind of like your mom, or your eyes are like one of your uncles or your grandparents. And so there's always been this notion of inherited traits. But it wasn't until the 1800s that that started to be studied in a more scientific way with Gregor Mendel, the father of genetics. But even then, even Mendel, who was starting to understand the mechanisms of, or he was trying to understand how inheritance happens, and he even could start to breed certain types of things, even he didn't know exactly what was the molecular basis for inheritance. And the answer to that question wasn't figured out until fairly recent times, until the mid-20th century, not until the structure of DNA was established by Watson and Crick. And their work was based on the work of many others, especially folks like Rosalind Franklin, who essentially provided the bulk of the data for Watson and Crick's work, Maurice Wilkins, and many, many, many other folks. But it was really the structure of DNA that made people say, hey, that looks like the molecule that's storing the information."}, {"video_title": "DNA   Biomolecules   MCAT   Khan Academy (3).mp3", "Sentence": "But even then, even Mendel, who was starting to understand the mechanisms of, or he was trying to understand how inheritance happens, and he even could start to breed certain types of things, even he didn't know exactly what was the molecular basis for inheritance. And the answer to that question wasn't figured out until fairly recent times, until the mid-20th century, not until the structure of DNA was established by Watson and Crick. And their work was based on the work of many others, especially folks like Rosalind Franklin, who essentially provided the bulk of the data for Watson and Crick's work, Maurice Wilkins, and many, many, many other folks. But it was really the structure of DNA that made people say, hey, that looks like the molecule that's storing the information. And just to be clear, DNA wasn't discovered in 1953. DNA was discovered in the mid-1800s. It was this kind of, this molecule that was inside of nuclei, of cells, and for some time, people said, oh, maybe this could be a molecular basis of inheritance."}, {"video_title": "DNA   Biomolecules   MCAT   Khan Academy (3).mp3", "Sentence": "But it was really the structure of DNA that made people say, hey, that looks like the molecule that's storing the information. And just to be clear, DNA wasn't discovered in 1953. DNA was discovered in the mid-1800s. It was this kind of, this molecule that was inside of nuclei, of cells, and for some time, people said, oh, maybe this could be a molecular basis of inheritance. You know, you could imagine what you would need to be a molecular basis of inheritance. It would have to be a molecule or a series of molecules that could contain information, that could be replicated, that could be expressed in some way. But it wasn't until 1953, when this double helix structure of DNA was established that people said, hey, this looks like our molecule."}, {"video_title": "DNA   Biomolecules   MCAT   Khan Academy (3).mp3", "Sentence": "It was this kind of, this molecule that was inside of nuclei, of cells, and for some time, people said, oh, maybe this could be a molecular basis of inheritance. You know, you could imagine what you would need to be a molecular basis of inheritance. It would have to be a molecule or a series of molecules that could contain information, that could be replicated, that could be expressed in some way. But it wasn't until 1953, when this double helix structure of DNA was established that people said, hey, this looks like our molecule. So first, let's just talk about the structure here, and then actually we'll talk about where this name, DNA, deoxyribonucleic acid, comes from. And then we'll talk a little bit about why the structure lends itself well to something that stores information, that can replicate its information, and that could express its information. We might go in-depth on the expression of information in future videos."}, {"video_title": "DNA   Biomolecules   MCAT   Khan Academy (3).mp3", "Sentence": "But it wasn't until 1953, when this double helix structure of DNA was established that people said, hey, this looks like our molecule. So first, let's just talk about the structure here, and then actually we'll talk about where this name, DNA, deoxyribonucleic acid, comes from. And then we'll talk a little bit about why the structure lends itself well to something that stores information, that can replicate its information, and that could express its information. We might go in-depth on the expression of information in future videos. So this structure right over here, and this is a visual depiction of a DNA molecule, you can view this as kind of a twisted ladder. It has these two, I guess you could say, sides of the ladder that are twisted. That is one side right over there, and then it is another side."}, {"video_title": "DNA   Biomolecules   MCAT   Khan Academy (3).mp3", "Sentence": "We might go in-depth on the expression of information in future videos. So this structure right over here, and this is a visual depiction of a DNA molecule, you can view this as kind of a twisted ladder. It has these two, I guess you could say, sides of the ladder that are twisted. That is one side right over there, and then it is another side. There is another side right over here. And in between those two sides, or connecting those two sides of that twisted ladder, you have these rungs. And these rungs are actually where the information, the genetic information is, I guess you could say, stored in some way."}, {"video_title": "DNA   Biomolecules   MCAT   Khan Academy (3).mp3", "Sentence": "That is one side right over there, and then it is another side. There is another side right over here. And in between those two sides, or connecting those two sides of that twisted ladder, you have these rungs. And these rungs are actually where the information, the genetic information is, I guess you could say, stored in some way. Because these rungs, it's a sequence of different bases. And when I say bases, you might say, wait, this says acid, why are you saying bases right over here? Well, the word deoxyribonucleic acid comes from the fact that this backbone is made up of a combination of sugar and phosphate."}, {"video_title": "DNA   Biomolecules   MCAT   Khan Academy (3).mp3", "Sentence": "And these rungs are actually where the information, the genetic information is, I guess you could say, stored in some way. Because these rungs, it's a sequence of different bases. And when I say bases, you might say, wait, this says acid, why are you saying bases right over here? Well, the word deoxyribonucleic acid comes from the fact that this backbone is made up of a combination of sugar and phosphate. And the sugar that makes up the backbone is deoxyribose, so that's essentially the D in DNA. And then the phosphate group is acidic, and that's where you get the acid part of it. And nucleic is, hey, this was found in nuclei of cells."}, {"video_title": "DNA   Biomolecules   MCAT   Khan Academy (3).mp3", "Sentence": "Well, the word deoxyribonucleic acid comes from the fact that this backbone is made up of a combination of sugar and phosphate. And the sugar that makes up the backbone is deoxyribose, so that's essentially the D in DNA. And then the phosphate group is acidic, and that's where you get the acid part of it. And nucleic is, hey, this was found in nuclei of cells. It is nucleic acid, deoxyribonucleic acid. But it's not, it also, it is actually mildly acidic all in total, but for every acid, it actually also has a base. And that base, those bases form the rung of the ladders."}, {"video_title": "DNA   Biomolecules   MCAT   Khan Academy (3).mp3", "Sentence": "And nucleic is, hey, this was found in nuclei of cells. It is nucleic acid, deoxyribonucleic acid. But it's not, it also, it is actually mildly acidic all in total, but for every acid, it actually also has a base. And that base, those bases form the rung of the ladders. And actually, each rung is a pair of bases. And as I said, that's where the information is actually stored. Well, what am I talking about?"}, {"video_title": "DNA   Biomolecules   MCAT   Khan Academy (3).mp3", "Sentence": "And that base, those bases form the rung of the ladders. And actually, each rung is a pair of bases. And as I said, that's where the information is actually stored. Well, what am I talking about? Well, let me talk about the four different bases that make up the rungs of a DNA molecule. So you have adenine. And so, for example, this part right over here, this section of that rung might be adenine."}, {"video_title": "DNA   Biomolecules   MCAT   Khan Academy (3).mp3", "Sentence": "Well, what am I talking about? Well, let me talk about the four different bases that make up the rungs of a DNA molecule. So you have adenine. And so, for example, this part right over here, this section of that rung might be adenine. Maybe this right over here is adenine. This right over here. Remember, each of these rungs are made up by, it's a pair of bases."}, {"video_title": "DNA   Biomolecules   MCAT   Khan Academy (3).mp3", "Sentence": "And so, for example, this part right over here, this section of that rung might be adenine. Maybe this right over here is adenine. This right over here. Remember, each of these rungs are made up by, it's a pair of bases. And that might be adenine. Maybe this is adenine. And I could stop there."}, {"video_title": "DNA   Biomolecules   MCAT   Khan Academy (3).mp3", "Sentence": "Remember, each of these rungs are made up by, it's a pair of bases. And that might be adenine. Maybe this is adenine. And I could stop there. I'll do a little more adenine. Maybe that's adenine right over there. And adenine always pairs with the base thymine."}, {"video_title": "DNA   Biomolecules   MCAT   Khan Academy (3).mp3", "Sentence": "And I could stop there. I'll do a little more adenine. Maybe that's adenine right over there. And adenine always pairs with the base thymine. So let me write that down. So adenine pairs with thymine. Thymine."}, {"video_title": "DNA   Biomolecules   MCAT   Khan Academy (3).mp3", "Sentence": "And adenine always pairs with the base thymine. So let me write that down. So adenine pairs with thymine. Thymine. So if that's an adenine there, then this is going to be a thymine. If this is an adenine, then this is going to be a thymine. Or if I drew the thymine first, well, I'll say, okay, it's going to pair with the adenine."}, {"video_title": "DNA   Biomolecules   MCAT   Khan Academy (3).mp3", "Sentence": "Thymine. So if that's an adenine there, then this is going to be a thymine. If this is an adenine, then this is going to be a thymine. Or if I drew the thymine first, well, I'll say, okay, it's going to pair with the adenine. So this is going to be a thymine right over here. This is going to be a thymine. If I were to draw this, this would be a thymine right over here."}, {"video_title": "DNA   Biomolecules   MCAT   Khan Academy (3).mp3", "Sentence": "Or if I drew the thymine first, well, I'll say, okay, it's going to pair with the adenine. So this is going to be a thymine right over here. This is going to be a thymine. If I were to draw this, this would be a thymine right over here. Now, the other two bases, you have cytosine, which pairs with guanine, or guanine that pairs with cytosine. So guanine. And we're not going to go into the molecular structure of these bases just yet, although these are good names to know because they show up a lot and they really form kind of the code, your genetic code."}, {"video_title": "DNA   Biomolecules   MCAT   Khan Academy (3).mp3", "Sentence": "If I were to draw this, this would be a thymine right over here. Now, the other two bases, you have cytosine, which pairs with guanine, or guanine that pairs with cytosine. So guanine. And we're not going to go into the molecular structure of these bases just yet, although these are good names to know because they show up a lot and they really form kind of the code, your genetic code. So guanine pairs with cytosine. Guanine and cytosine. Cytosine."}, {"video_title": "DNA   Biomolecules   MCAT   Khan Academy (3).mp3", "Sentence": "And we're not going to go into the molecular structure of these bases just yet, although these are good names to know because they show up a lot and they really form kind of the code, your genetic code. So guanine pairs with cytosine. Guanine and cytosine. Cytosine. So actually, if this is, let's say there's some cytosine there, let's say cytosine right over here, maybe this is cytosine, maybe this is cytosine, maybe this is cytosine, this is cytosine, and maybe this is cytosine, then it always pairs with the guanine. If we're talking about, so let's see, this is guanine then, then this will be guanine, this is guanine, this is guanine, I actually didn't draw stuff here, but this is guanine, I didn't say what these could be, but these would be made of pairs of, they could be adenine-thymine pairs, and it could be adenine on either side or the thymine on either side, and they could be made of guanine-cytosine pairs, where the guanine or the cytosine is on either side. Actually, just to make it a little bit more complete, let me just color in the rungs here as best as I can."}, {"video_title": "DNA   Biomolecules   MCAT   Khan Academy (3).mp3", "Sentence": "Cytosine. So actually, if this is, let's say there's some cytosine there, let's say cytosine right over here, maybe this is cytosine, maybe this is cytosine, maybe this is cytosine, this is cytosine, and maybe this is cytosine, then it always pairs with the guanine. If we're talking about, so let's see, this is guanine then, then this will be guanine, this is guanine, this is guanine, I actually didn't draw stuff here, but this is guanine, I didn't say what these could be, but these would be made of pairs of, they could be adenine-thymine pairs, and it could be adenine on either side or the thymine on either side, and they could be made of guanine-cytosine pairs, where the guanine or the cytosine is on either side. Actually, just to make it a little bit more complete, let me just color in the rungs here as best as I can. So those are guanine, so they're gonna pair with cytosine, pair with cytosine, pair with cytosine. And when it's drawn this way, you might start to see how this is essentially a code, the order of which the bases are, I guess the order in which we have these, or the sequence of these bases essentially encode the information that make you you, and you could debate, well, how much of it is nature versus nurture, and when people say nature, you know, it's literally genetic, and that's an ongoing debate, but it does code for things like your hair color, when you see that your smile is similar to your parents. It is because that information, to a large degree, is encoded genetically."}, {"video_title": "DNA   Biomolecules   MCAT   Khan Academy (3).mp3", "Sentence": "Actually, just to make it a little bit more complete, let me just color in the rungs here as best as I can. So those are guanine, so they're gonna pair with cytosine, pair with cytosine, pair with cytosine. And when it's drawn this way, you might start to see how this is essentially a code, the order of which the bases are, I guess the order in which we have these, or the sequence of these bases essentially encode the information that make you you, and you could debate, well, how much of it is nature versus nurture, and when people say nature, you know, it's literally genetic, and that's an ongoing debate, but it does code for things like your hair color, when you see that your smile is similar to your parents. It is because that information, to a large degree, is encoded genetically. It affects a lot of what makes you you, and actually not even just within a species, but also across species. Humans have more genetic material in common with other humans than they do with, say, a plant, but all living creatures as we know them have genetic information. This is the basis by which they are passing down their actual traits."}, {"video_title": "DNA   Biomolecules   MCAT   Khan Academy (3).mp3", "Sentence": "It is because that information, to a large degree, is encoded genetically. It affects a lot of what makes you you, and actually not even just within a species, but also across species. Humans have more genetic material in common with other humans than they do with, say, a plant, but all living creatures as we know them have genetic information. This is the basis by which they are passing down their actual traits. Now, you might be saying, well, how much genetic information does a human being have? And the number will either disappoint you or you might find it mind-boggling. The human genome, and every species has a different number of base pairs, to a large degree correlated with how complex they are, although not always, but the human genome has six million, sorry, not six million, six billion."}, {"video_title": "DNA   Biomolecules   MCAT   Khan Academy (3).mp3", "Sentence": "This is the basis by which they are passing down their actual traits. Now, you might be saying, well, how much genetic information does a human being have? And the number will either disappoint you or you might find it mind-boggling. The human genome, and every species has a different number of base pairs, to a large degree correlated with how complex they are, although not always, but the human genome has six million, sorry, not six million, six billion. Six million would be disappointing. Even billion might be disappointing. Six billion base pairs."}, {"video_title": "DNA   Biomolecules   MCAT   Khan Academy (3).mp3", "Sentence": "The human genome, and every species has a different number of base pairs, to a large degree correlated with how complex they are, although not always, but the human genome has six million, sorry, not six million, six billion. Six million would be disappointing. Even billion might be disappointing. Six billion base pairs. Six billion base pairs. And when you have your full complement of chromosomes, and this is in most of the cells in your body, outside of your sex cells, the sperm or the egg cells, this is going to be spread over 46 chromosomes. 46 chromosomes, or I guess you could say 23 pair of chromosomes."}, {"video_title": "DNA   Biomolecules   MCAT   Khan Academy (3).mp3", "Sentence": "Six billion base pairs. Six billion base pairs. And when you have your full complement of chromosomes, and this is in most of the cells in your body, outside of your sex cells, the sperm or the egg cells, this is going to be spread over 46 chromosomes. 46 chromosomes, or I guess you could say 23 pair of chromosomes. So if you divide six billion by 46, you get a little over, on average, 100 million, I think it's 100 and something million base pairs per chromosome. And some chromosomes are longer, actually some of the longest are over 200 million, and some might be shorter. That's just on average."}, {"video_title": "DNA   Biomolecules   MCAT   Khan Academy (3).mp3", "Sentence": "46 chromosomes, or I guess you could say 23 pair of chromosomes. So if you divide six billion by 46, you get a little over, on average, 100 million, I think it's 100 and something million base pairs per chromosome. And some chromosomes are longer, actually some of the longest are over 200 million, and some might be shorter. That's just on average. Now, this number might, to some of you, might be exciting. You're like, oh, I thought I was a simple creature. I didn't know I was this complex."}, {"video_title": "DNA   Biomolecules   MCAT   Khan Academy (3).mp3", "Sentence": "That's just on average. Now, this number might, to some of you, might be exciting. You're like, oh, I thought I was a simple creature. I didn't know I was this complex. Six billion, that's a lot of base pairs. That feels like a lot of information. For others of you, it might not feel so great."}, {"video_title": "DNA   Biomolecules   MCAT   Khan Academy (3).mp3", "Sentence": "I didn't know I was this complex. Six billion, that's a lot of base pairs. That feels like a lot of information. For others of you, it might not feel so great. You might say, hey, wait, I could store this much information on a modern thumb drive or on a hard disk. I thought I was more unique than that. And of course, we all are special and unique, but you might say, oh, six billion base pairs, I thought I was infinitely complex and whatever else, and there's some arguments for that along some other directions."}, {"video_title": "DNA   Biomolecules   MCAT   Khan Academy (3).mp3", "Sentence": "For others of you, it might not feel so great. You might say, hey, wait, I could store this much information on a modern thumb drive or on a hard disk. I thought I was more unique than that. And of course, we all are special and unique, but you might say, oh, six billion base pairs, I thought I was infinitely complex and whatever else, and there's some arguments for that along some other directions. But this is the approximate length, I guess you could say, the approximate size of the actual human genome. And when we talk about chromosomes, and we'll talk about chromosomes in much more depth, imagine taking this zoomed in thing that you have right over here, and over here, I don't know how many we have, like one, two, three, four, five, six, seven, eight, nine, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19. We have about 20 base pairs depicted here."}, {"video_title": "DNA   Biomolecules   MCAT   Khan Academy (3).mp3", "Sentence": "And of course, we all are special and unique, but you might say, oh, six billion base pairs, I thought I was infinitely complex and whatever else, and there's some arguments for that along some other directions. But this is the approximate length, I guess you could say, the approximate size of the actual human genome. And when we talk about chromosomes, and we'll talk about chromosomes in much more depth, imagine taking this zoomed in thing that you have right over here, and over here, I don't know how many we have, like one, two, three, four, five, six, seven, eight, nine, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19. We have about 20 base pairs depicted here. Imagine if you had about 200 million of these base pairs, and then you were to take this thing and you were to kind of coil it up into that thing is a chromosome. Is a chromosome. And you're saying, wait, I have that much information in most of the cells of my body?"}, {"video_title": "DNA   Biomolecules   MCAT   Khan Academy (3).mp3", "Sentence": "We have about 20 base pairs depicted here. Imagine if you had about 200 million of these base pairs, and then you were to take this thing and you were to kind of coil it up into that thing is a chromosome. Is a chromosome. And you're saying, wait, I have that much information in most of the cells of my body? This thing must be incredibly compact. And if you said that, I would say, yes, you are correct. This, the radius, the radius of the DNA molecule is on the order of one nanometer."}, {"video_title": "DNA   Biomolecules   MCAT   Khan Academy (3).mp3", "Sentence": "And you're saying, wait, I have that much information in most of the cells of my body? This thing must be incredibly compact. And if you said that, I would say, yes, you are correct. This, the radius, the radius of the DNA molecule is on the order of one nanometer. One nanometer, which is a billionth of a meter. So you can start to assess kind of the scale of this thing. This is a very dense way to actually store information."}, {"video_title": "DNA   Biomolecules   MCAT   Khan Academy (3).mp3", "Sentence": "This, the radius, the radius of the DNA molecule is on the order of one nanometer. One nanometer, which is a billionth of a meter. So you can start to assess kind of the scale of this thing. This is a very dense way to actually store information. But just to have an appreciation of, and you might have seen it when I was coloring in, on why the structure lends itself to being able to replicate the information or even to be able to translate or express the information, let's think about if you were to take this ladder and you were to just kind of split all the base pairs. So you just have one half of them. So you essentially have half of the ladder."}, {"video_title": "DNA   Biomolecules   MCAT   Khan Academy (3).mp3", "Sentence": "This is a very dense way to actually store information. But just to have an appreciation of, and you might have seen it when I was coloring in, on why the structure lends itself to being able to replicate the information or even to be able to translate or express the information, let's think about if you were to take this ladder and you were to just kind of split all the base pairs. So you just have one half of them. So you essentially have half of the ladder. And so if you only have half of the ladder, you're able to construct the other half of the ladder. Let's take an example. Let's say, and I'll just use the first letter to abbreviate for each of these bases."}, {"video_title": "DNA   Biomolecules   MCAT   Khan Academy (3).mp3", "Sentence": "So you essentially have half of the ladder. And so if you only have half of the ladder, you're able to construct the other half of the ladder. Let's take an example. Let's say, and I'll just use the first letter to abbreviate for each of these bases. So let's say you have some, so let's say this is one of the, this is the sugar phosphate backbone right over here. So this could be one of the sides. And let's say there's some adenine, actually, let me do them in the right color."}, {"video_title": "DNA   Biomolecules   MCAT   Khan Academy (3).mp3", "Sentence": "Let's say, and I'll just use the first letter to abbreviate for each of these bases. So let's say you have some, so let's say this is one of the, this is the sugar phosphate backbone right over here. So this could be one of the sides. And let's say there's some adenine, actually, let me do them in the right color. So you've got some adenine, adenine, maybe some adenine right over here. Maybe there's an adenine there. Maybe you have some thymine, thymine, maybe thymine right over here."}, {"video_title": "DNA   Biomolecules   MCAT   Khan Academy (3).mp3", "Sentence": "And let's say there's some adenine, actually, let me do them in the right color. So you've got some adenine, adenine, maybe some adenine right over here. Maybe there's an adenine there. Maybe you have some thymine, thymine, maybe thymine right over here. Then you have some, you have some guanine, guanine, guanine. And then let's say you have some cytosine and you have some cytosine. So with just half of this ladder, I guess you could say, you're able to construct the other half."}, {"video_title": "DNA   Biomolecules   MCAT   Khan Academy (3).mp3", "Sentence": "Maybe you have some thymine, thymine, maybe thymine right over here. Then you have some, you have some guanine, guanine, guanine. And then let's say you have some cytosine and you have some cytosine. So with just half of this ladder, I guess you could say, you're able to construct the other half. And that's actually how DNA replicates. This ladder splits and then each of those two halves of that ladder are able to construct versions of the other half, or versions of the other half are able to be constructed on top of that half. So how does that happen?"}, {"video_title": "DNA   Biomolecules   MCAT   Khan Academy (3).mp3", "Sentence": "So with just half of this ladder, I guess you could say, you're able to construct the other half. And that's actually how DNA replicates. This ladder splits and then each of those two halves of that ladder are able to construct versions of the other half, or versions of the other half are able to be constructed on top of that half. So how does that happen? Well, it's based on how these bases pair. Adenine always pairs with thymine if we're talking about DNA. So if you have an A there, you're gonna have a T on this end, T on this end."}, {"video_title": "DNA   Biomolecules   MCAT   Khan Academy (3).mp3", "Sentence": "So how does that happen? Well, it's based on how these bases pair. Adenine always pairs with thymine if we're talking about DNA. So if you have an A there, you're gonna have a T on this end, T on this end. T's right all over here, T right over there. If you have a T on that end, you're gonna have an A right over there, A, A. If you have a G, a guanine on this side, you're gonna have a cytosine on the other side."}, {"video_title": "DNA   Biomolecules   MCAT   Khan Academy (3).mp3", "Sentence": "So if you have an A there, you're gonna have a T on this end, T on this end. T's right all over here, T right over there. If you have a T on that end, you're gonna have an A right over there, A, A. If you have a G, a guanine on this side, you're gonna have a cytosine on the other side. Cytosine, cytosine, cytosine. And if you have a cytosine, you're gonna have a guanine on the other side. And so hopefully that gives you an appreciation of how DNA can replicate itself."}, {"video_title": "DNA   Biomolecules   MCAT   Khan Academy (3).mp3", "Sentence": "If you have a G, a guanine on this side, you're gonna have a cytosine on the other side. Cytosine, cytosine, cytosine. And if you have a cytosine, you're gonna have a guanine on the other side. And so hopefully that gives you an appreciation of how DNA can replicate itself. And as we'll see also, how this information can be translated to other forms of either related molecules, but eventually to proteins. And just to kind of round out this video, to get a real visual sense of what the DNA molecule looks like, or I guess a different visual depiction from this, I found this animated, that animated GIF that, you know, if you haven't fully digested what a double helix looks like, this is it. And you see here, you see your sugar phosphate bases here."}, {"video_title": "DNA   Biomolecules   MCAT   Khan Academy (3).mp3", "Sentence": "And so hopefully that gives you an appreciation of how DNA can replicate itself. And as we'll see also, how this information can be translated to other forms of either related molecules, but eventually to proteins. And just to kind of round out this video, to get a real visual sense of what the DNA molecule looks like, or I guess a different visual depiction from this, I found this animated, that animated GIF that, you know, if you haven't fully digested what a double helix looks like, this is it. And you see here, you see your sugar phosphate bases here. You see kind of the sugars and phosphate, the sugars and the phosphates alternating along this backbone. And then the rungs of the latter are these base pairs. So this is one of the bases, that's the corresponding, I guess you could say partner."}, {"video_title": "Hydrogen bonding in water   Water, acids, and bases   Biology   Khan Academy.mp3", "Sentence": "I don't think it's any secret to anyone that water is essential to life. Most of the biological, or actually frankly, all of the significant biological processes in your body are dependent on water, and are probably occurring inside of water. When you think of the cells in your body, and the cytoplasm inside of your cells, that is mainly water. In fact, me, who is talking to you right now, I am 60 to 70% water. You can think of me as kind of this big bag of water that I'm making a video right now. It's not just human beings that need water. Life as we know it is dependent on water."}, {"video_title": "Hydrogen bonding in water   Water, acids, and bases   Biology   Khan Academy.mp3", "Sentence": "In fact, me, who is talking to you right now, I am 60 to 70% water. You can think of me as kind of this big bag of water that I'm making a video right now. It's not just human beings that need water. Life as we know it is dependent on water. That's why when we have the search for signs of life on other planets, we're always looking for signs of water. Maybe life can occur in other types of substances, but water is essential to life as we know it. To understand why water is so special, let's start to understand the structure of water, and how it interacts with itself."}, {"video_title": "Hydrogen bonding in water   Water, acids, and bases   Biology   Khan Academy.mp3", "Sentence": "Life as we know it is dependent on water. That's why when we have the search for signs of life on other planets, we're always looking for signs of water. Maybe life can occur in other types of substances, but water is essential to life as we know it. To understand why water is so special, let's start to understand the structure of water, and how it interacts with itself. Water, as you probably already know, is made up of one oxygen atom, and two hydrogen atoms. And two hydrogen atoms. That's why we call it H2O."}, {"video_title": "Hydrogen bonding in water   Water, acids, and bases   Biology   Khan Academy.mp3", "Sentence": "To understand why water is so special, let's start to understand the structure of water, and how it interacts with itself. Water, as you probably already know, is made up of one oxygen atom, and two hydrogen atoms. And two hydrogen atoms. That's why we call it H2O. H2O. They are bonded with covalent bonds. Covalent bonds, each of these bonds, this is a pair of electrons, that both of these atoms get to pretend like they have."}, {"video_title": "Hydrogen bonding in water   Water, acids, and bases   Biology   Khan Academy.mp3", "Sentence": "That's why we call it H2O. H2O. They are bonded with covalent bonds. Covalent bonds, each of these bonds, this is a pair of electrons, that both of these atoms get to pretend like they have. You have these two pairs. You might be saying, why did I draw the two hydrogens on this end? Why didn't I draw them on opposite sides of the oxygen?"}, {"video_title": "Hydrogen bonding in water   Water, acids, and bases   Biology   Khan Academy.mp3", "Sentence": "Covalent bonds, each of these bonds, this is a pair of electrons, that both of these atoms get to pretend like they have. You have these two pairs. You might be saying, why did I draw the two hydrogens on this end? Why didn't I draw them on opposite sides of the oxygen? That's because oxygen also has two lone electron pairs. Two lone electron pairs. And these things are always repelling each other."}, {"video_title": "Hydrogen bonding in water   Water, acids, and bases   Biology   Khan Academy.mp3", "Sentence": "Why didn't I draw them on opposite sides of the oxygen? That's because oxygen also has two lone electron pairs. Two lone electron pairs. And these things are always repelling each other. The electrons are repelling from each other. And so, in reality, if we were looking at it three dimensions, the oxygen molecule is kind of a tetrahedral shape. I could try to, let me try to draw it a little bit."}, {"video_title": "Hydrogen bonding in water   Water, acids, and bases   Biology   Khan Academy.mp3", "Sentence": "And these things are always repelling each other. The electrons are repelling from each other. And so, in reality, if we were looking at it three dimensions, the oxygen molecule is kind of a tetrahedral shape. I could try to, let me try to draw it a little bit. So if this is the oxygen right over here, then you would have, you could have maybe one lone pair of electrons. I'll draw just a little green circle there. Another lone pair of electrons back here."}, {"video_title": "Hydrogen bonding in water   Water, acids, and bases   Biology   Khan Academy.mp3", "Sentence": "I could try to, let me try to draw it a little bit. So if this is the oxygen right over here, then you would have, you could have maybe one lone pair of electrons. I'll draw just a little green circle there. Another lone pair of electrons back here. Then you have the covalent bond. You have the covalent bond to one hydrogen atom. One hydrogen atom right over there."}, {"video_title": "Hydrogen bonding in water   Water, acids, and bases   Biology   Khan Academy.mp3", "Sentence": "Another lone pair of electrons back here. Then you have the covalent bond. You have the covalent bond to one hydrogen atom. One hydrogen atom right over there. And then you have the covalent bond, then you have the covalent bond to the other hydrogen atom. And so you see it forms this tetrahedral shape. It's pretty close to a tetrahedron."}, {"video_title": "Hydrogen bonding in water   Water, acids, and bases   Biology   Khan Academy.mp3", "Sentence": "One hydrogen atom right over there. And then you have the covalent bond, then you have the covalent bond to the other hydrogen atom. And so you see it forms this tetrahedral shape. It's pretty close to a tetrahedron. Just like this. But the key is that the hydrogens are on one end of the molecule. This is, we're gonna see, very, very important to the unique properties or to what gives water its special properties."}, {"video_title": "Hydrogen bonding in water   Water, acids, and bases   Biology   Khan Academy.mp3", "Sentence": "It's pretty close to a tetrahedron. Just like this. But the key is that the hydrogens are on one end of the molecule. This is, we're gonna see, very, very important to the unique properties or to what gives water its special properties. Now one thing to realize is, you know, it's very, in chemistry, we draw these electrons very neatly, these dots up here. We draw these covalent bonds very neatly. But that's not the way that it actually works."}, {"video_title": "Hydrogen bonding in water   Water, acids, and bases   Biology   Khan Academy.mp3", "Sentence": "This is, we're gonna see, very, very important to the unique properties or to what gives water its special properties. Now one thing to realize is, you know, it's very, in chemistry, we draw these electrons very neatly, these dots up here. We draw these covalent bonds very neatly. But that's not the way that it actually works. Electrons are jumping around constantly. They're buzzing around. It's actually much more of a, even when you think about electrons, it's more of a probability of where you might find them."}, {"video_title": "Hydrogen bonding in water   Water, acids, and bases   Biology   Khan Academy.mp3", "Sentence": "But that's not the way that it actually works. Electrons are jumping around constantly. They're buzzing around. It's actually much more of a, even when you think about electrons, it's more of a probability of where you might find them. And so instead of thinking of these electrons as definitely here or definitely in these bonds, they're actually more of in this cloud around the different atoms. They're in this cloud that kind of describes a probability of where you might find them as they buzz and they jump around. And what's interesting about water is oxygen is extremely electronegative."}, {"video_title": "Hydrogen bonding in water   Water, acids, and bases   Biology   Khan Academy.mp3", "Sentence": "It's actually much more of a, even when you think about electrons, it's more of a probability of where you might find them. And so instead of thinking of these electrons as definitely here or definitely in these bonds, they're actually more of in this cloud around the different atoms. They're in this cloud that kind of describes a probability of where you might find them as they buzz and they jump around. And what's interesting about water is oxygen is extremely electronegative. So oxygen, that's oxygen, that's oxygen. It is extremely electronegative. It's one of the more electronegative elements we know of."}, {"video_title": "Hydrogen bonding in water   Water, acids, and bases   Biology   Khan Academy.mp3", "Sentence": "And what's interesting about water is oxygen is extremely electronegative. So oxygen, that's oxygen, that's oxygen. It is extremely electronegative. It's one of the more electronegative elements we know of. It's definitely way more electronegative than hydrogen. And you might be saying, well Sal, what does it mean to be electronegative? Well, electronegative is just a fancy way of saying that it hogs electrons."}, {"video_title": "Hydrogen bonding in water   Water, acids, and bases   Biology   Khan Academy.mp3", "Sentence": "It's one of the more electronegative elements we know of. It's definitely way more electronegative than hydrogen. And you might be saying, well Sal, what does it mean to be electronegative? Well, electronegative is just a fancy way of saying that it hogs electrons. Hogs electrons. It likes to keep electrons for itself. Hogs electrons."}, {"video_title": "Hydrogen bonding in water   Water, acids, and bases   Biology   Khan Academy.mp3", "Sentence": "Well, electronegative is just a fancy way of saying that it hogs electrons. Hogs electrons. It likes to keep electrons for itself. Hogs electrons. So that's what's going on. Oxygen likes to keep the electrons more around itself than the partners that it's bonding with. So even in these covalent bonds, you say, hey, we're supposed to be sharing these electrons."}, {"video_title": "Hydrogen bonding in water   Water, acids, and bases   Biology   Khan Academy.mp3", "Sentence": "Hogs electrons. So that's what's going on. Oxygen likes to keep the electrons more around itself than the partners that it's bonding with. So even in these covalent bonds, you say, hey, we're supposed to be sharing these electrons. Oxygen says, well, I still want them to spend a little bit more time with me. And so they actually do spend more time on the side without the hydrogens than they do around the hydrogens. And you could imagine what this is going to do."}, {"video_title": "Hydrogen bonding in water   Water, acids, and bases   Biology   Khan Academy.mp3", "Sentence": "So even in these covalent bonds, you say, hey, we're supposed to be sharing these electrons. Oxygen says, well, I still want them to spend a little bit more time with me. And so they actually do spend more time on the side without the hydrogens than they do around the hydrogens. And you could imagine what this is going to do. This is going to form a partial negative charge at the, I guess you could say the non-hydrogen end, the end that has, well I guess this top end, the way I've drawn it right over here. And this Greek letter delta, this is to signify a partial charge. And it's a partial negative charge."}, {"video_title": "Hydrogen bonding in water   Water, acids, and bases   Biology   Khan Academy.mp3", "Sentence": "And you could imagine what this is going to do. This is going to form a partial negative charge at the, I guess you could say the non-hydrogen end, the end that has, well I guess this top end, the way I've drawn it right over here. And this Greek letter delta, this is to signify a partial charge. And it's a partial negative charge. Because electrons are negative. And then over here, since you have a slight deficiency of electrons, because they're spending so much time around the oxygen, it forms a partial positive charge, partial positive charge right over there. So right when you just look at one, one water molecule, that doesn't seem so interesting."}, {"video_title": "Hydrogen bonding in water   Water, acids, and bases   Biology   Khan Academy.mp3", "Sentence": "And it's a partial negative charge. Because electrons are negative. And then over here, since you have a slight deficiency of electrons, because they're spending so much time around the oxygen, it forms a partial positive charge, partial positive charge right over there. So right when you just look at one, one water molecule, that doesn't seem so interesting. But it becomes really interesting when you look at many water molecules interacting together. So let me draw another water molecule right over here. So it's oxygen."}, {"video_title": "Hydrogen bonding in water   Water, acids, and bases   Biology   Khan Academy.mp3", "Sentence": "So right when you just look at one, one water molecule, that doesn't seem so interesting. But it becomes really interesting when you look at many water molecules interacting together. So let me draw another water molecule right over here. So it's oxygen. You have two hydrogens. And then you have the bonds between them. You have a partially negative charge there, partially positive charge on that end."}, {"video_title": "Hydrogen bonding in water   Water, acids, and bases   Biology   Khan Academy.mp3", "Sentence": "So it's oxygen. You have two hydrogens. And then you have the bonds between them. You have a partially negative charge there, partially positive charge on that end. And so you can imagine the partial, the side that has a partially negative charge is going to be attracted to the side that has a partially positive charge. And that attraction, that between these two, this is called a hydrogen bond. So that right over there is called a hydrogen bond."}, {"video_title": "Hydrogen bonding in water   Water, acids, and bases   Biology   Khan Academy.mp3", "Sentence": "You have a partially negative charge there, partially positive charge on that end. And so you can imagine the partial, the side that has a partially negative charge is going to be attracted to the side that has a partially positive charge. And that attraction, that between these two, this is called a hydrogen bond. So that right over there is called a hydrogen bond. And this is key to the behavior of water. And we're going to see that in future videos. All the different ways that hydrogen bonds give water its unique characteristics."}, {"video_title": "Hydrogen bonding in water   Water, acids, and bases   Biology   Khan Academy.mp3", "Sentence": "So that right over there is called a hydrogen bond. And this is key to the behavior of water. And we're going to see that in future videos. All the different ways that hydrogen bonds give water its unique characteristics. Hydrogen bonds are weaker than covalent bonds, but they're strong enough to give water that kind of nice fluid nature when we're thinking about kind of normal, where you'd say normal temperatures and pressures. This nice fluid nature. It allows these things to be attracted to each other, to have some cohesion, but also to break and reform and flow past each other."}, {"video_title": "Hydrogen bonding in water   Water, acids, and bases   Biology   Khan Academy.mp3", "Sentence": "All the different ways that hydrogen bonds give water its unique characteristics. Hydrogen bonds are weaker than covalent bonds, but they're strong enough to give water that kind of nice fluid nature when we're thinking about kind of normal, where you'd say normal temperatures and pressures. This nice fluid nature. It allows these things to be attracted to each other, to have some cohesion, but also to break and reform and flow past each other. So you can imagine another hydrogen bond with another water molecule, another water molecule right over here. So put my hydrogens over there. Put my hydrogens here."}, {"video_title": "Hydrogen bonding in water   Water, acids, and bases   Biology   Khan Academy.mp3", "Sentence": "It allows these things to be attracted to each other, to have some cohesion, but also to break and reform and flow past each other. So you can imagine another hydrogen bond with another water molecule, another water molecule right over here. So put my hydrogens over there. Put my hydrogens here. Bonds, partial negative, partial positive right over there. And so we'll see in future videos, hydrogen bonds, key for water flowing past itself, key for its properties to, its ability to take in heat, key for its ability to regulate temperature, key for its abilities why lakes don't freeze over, it's key for some of its properties around evaporative cooling and surface tension and adhesion and cohesion. And we'll see that."}, {"video_title": "Noncompetitive inhibition   Energy and enzymes   Biology   Khan Academy.mp3", "Sentence": "In the video on competitive inhibition, we saw that competitive inhibition is all about a substrate or potential substrate, an inhibitor competing for the enzyme. And whoever gets there first gets the enzyme. If the inhibitor gets there first, then the substrate isn't able to bind, and of course, no reaction is catalyzed. If the substrate is able to get there first, then the inhibitor isn't able to bind, and the reaction does get catalyzed. Now, the inhibitor and the substrate, they both might compete for the active site, if we're talking about competitive inhibition. But you also have allosteric competitive inhibition, where they're still trying to compete for the enzyme. Whoever gets there first gets the enzyme, but the inhibitor doesn't necessarily bind at the active site."}, {"video_title": "Noncompetitive inhibition   Energy and enzymes   Biology   Khan Academy.mp3", "Sentence": "If the substrate is able to get there first, then the inhibitor isn't able to bind, and the reaction does get catalyzed. Now, the inhibitor and the substrate, they both might compete for the active site, if we're talking about competitive inhibition. But you also have allosteric competitive inhibition, where they're still trying to compete for the enzyme. Whoever gets there first gets the enzyme, but the inhibitor doesn't necessarily bind at the active site. They bind at an allosteric site, but it's the same idea. If the inhibitor gets to the allosteric site before the substrate gets to the active site, then the conformation of the protein changes so that the active site, you know, it changes a little bit. Something like, let me draw in that same color."}, {"video_title": "Noncompetitive inhibition   Energy and enzymes   Biology   Khan Academy.mp3", "Sentence": "Whoever gets there first gets the enzyme, but the inhibitor doesn't necessarily bind at the active site. They bind at an allosteric site, but it's the same idea. If the inhibitor gets to the allosteric site before the substrate gets to the active site, then the conformation of the protein changes so that the active site, you know, it changes a little bit. Something like, let me draw in that same color. It changes, the conformation of the protein changes a little bit, and then the actual intended substrate isn't able to bind. If the intended substrate binds, then that changes the conformation a little bit at the allosteric site, and then the inhibitor isn't able to bind. So if that's competitive inhibition, where there's like, who gets to the enzyme first, what is non-competitive inhibition all about?"}, {"video_title": "Noncompetitive inhibition   Energy and enzymes   Biology   Khan Academy.mp3", "Sentence": "Something like, let me draw in that same color. It changes, the conformation of the protein changes a little bit, and then the actual intended substrate isn't able to bind. If the intended substrate binds, then that changes the conformation a little bit at the allosteric site, and then the inhibitor isn't able to bind. So if that's competitive inhibition, where there's like, who gets to the enzyme first, what is non-competitive inhibition all about? Well, let's draw that. So non-competitive inhibition. So non-competitive, competitive inhibition."}, {"video_title": "Noncompetitive inhibition   Energy and enzymes   Biology   Khan Academy.mp3", "Sentence": "So if that's competitive inhibition, where there's like, who gets to the enzyme first, what is non-competitive inhibition all about? Well, let's draw that. So non-competitive inhibition. So non-competitive, competitive inhibition. And the big picture here is that they can both bind. Whether one binds to the enzyme doesn't affect whether the other binds. So let's talk about it a little bit."}, {"video_title": "Noncompetitive inhibition   Energy and enzymes   Biology   Khan Academy.mp3", "Sentence": "So non-competitive, competitive inhibition. And the big picture here is that they can both bind. Whether one binds to the enzyme doesn't affect whether the other binds. So let's talk about it a little bit. So this is my enzyme. That's my enzyme right over there. And what we have happening, of course, is if the substrate's able to get to the active site, then of course the reaction is going to be catalyzed."}, {"video_title": "Noncompetitive inhibition   Energy and enzymes   Biology   Khan Academy.mp3", "Sentence": "So let's talk about it a little bit. So this is my enzyme. That's my enzyme right over there. And what we have happening, of course, is if the substrate's able to get to the active site, then of course the reaction is going to be catalyzed. And we saw that up here. Substrate binds to the active site, and then the reaction is catalyzed. In this case, the substrate got broken up into two other molecules."}, {"video_title": "Noncompetitive inhibition   Energy and enzymes   Biology   Khan Academy.mp3", "Sentence": "And what we have happening, of course, is if the substrate's able to get to the active site, then of course the reaction is going to be catalyzed. And we saw that up here. Substrate binds to the active site, and then the reaction is catalyzed. In this case, the substrate got broken up into two other molecules. But in non-competitive inhibition, what happens is the substrate can bind, and so can an inhibitor. And so can an inhibitor. And the inhibitor can bind in an allosteric site."}, {"video_title": "Noncompetitive inhibition   Energy and enzymes   Biology   Khan Academy.mp3", "Sentence": "In this case, the substrate got broken up into two other molecules. But in non-competitive inhibition, what happens is the substrate can bind, and so can an inhibitor. And so can an inhibitor. And the inhibitor can bind in an allosteric site. So this is our inhibitor right over here. The inhibitor can bind at an allosteric site. And when they're both bound, notice they're not competing for the enzyme."}, {"video_title": "Noncompetitive inhibition   Energy and enzymes   Biology   Khan Academy.mp3", "Sentence": "And the inhibitor can bind in an allosteric site. So this is our inhibitor right over here. The inhibitor can bind at an allosteric site. And when they're both bound, notice they're not competing for the enzyme. They both can be on the enzyme. This character can bind to the enzyme whether or not the substrate is there. But if this guy binds to the enzyme, the substrate can still bind to the enzyme, but now the reaction isn't going to proceed."}, {"video_title": "Noncompetitive inhibition   Energy and enzymes   Biology   Khan Academy.mp3", "Sentence": "And when they're both bound, notice they're not competing for the enzyme. They both can be on the enzyme. This character can bind to the enzyme whether or not the substrate is there. But if this guy binds to the enzyme, the substrate can still bind to the enzyme, but now the reaction isn't going to proceed. So now the reaction is going to look like this. So let me, so now there's not going to be any reaction. If this happens, the only option is is that they both unbind."}, {"video_title": "Noncompetitive inhibition   Energy and enzymes   Biology   Khan Academy.mp3", "Sentence": "But if this guy binds to the enzyme, the substrate can still bind to the enzyme, but now the reaction isn't going to proceed. So now the reaction is going to look like this. So let me, so now there's not going to be any reaction. If this happens, the only option is is that they both unbind. So now this character is just going to leave the active site. No reaction, no reaction has been catalyzed. So it just prevented anything from happening."}, {"video_title": "Noncompetitive inhibition   Energy and enzymes   Biology   Khan Academy.mp3", "Sentence": "If this happens, the only option is is that they both unbind. So now this character is just going to leave the active site. No reaction, no reaction has been catalyzed. So it just prevented anything from happening. And maybe this guy, this guy leaves as well. And the way I showed this non-competitive inhibition, I showed it happening at an allosteric site. The inhibitor attaching at an allosteric site."}, {"video_title": "Noncompetitive inhibition   Energy and enzymes   Biology   Khan Academy.mp3", "Sentence": "So it just prevented anything from happening. And maybe this guy, this guy leaves as well. And the way I showed this non-competitive inhibition, I showed it happening at an allosteric site. The inhibitor attaching at an allosteric site. But it actually doesn't even have to be the same case as long as it does not prevent the, as long as it can actually bind close to or even at the active site, as long as it does not prevent the substrate from binding to the active site. So you can even have a situation like this. So you can even have a situation like this."}, {"video_title": "Noncompetitive inhibition   Energy and enzymes   Biology   Khan Academy.mp3", "Sentence": "The inhibitor attaching at an allosteric site. But it actually doesn't even have to be the same case as long as it does not prevent the, as long as it can actually bind close to or even at the active site, as long as it does not prevent the substrate from binding to the active site. So you can even have a situation like this. So you can even have a situation like this. This is the one that's typically given for non-competitive inhibition where you have the inhibitor binding at an allosteric site. But the idea here is that they're not competing. Both of them can bind to the enzyme."}, {"video_title": "Noncompetitive inhibition   Energy and enzymes   Biology   Khan Academy.mp3", "Sentence": "So you can even have a situation like this. This is the one that's typically given for non-competitive inhibition where you have the inhibitor binding at an allosteric site. But the idea here is that they're not competing. Both of them can bind to the enzyme. If one of them binds first, then the other one can still bind. If the substrate binds first, then the inhibitor can still bind. If the inhibitor binds first, then the substrate can still bind."}, {"video_title": "Noncompetitive inhibition   Energy and enzymes   Biology   Khan Academy.mp3", "Sentence": "Both of them can bind to the enzyme. If one of them binds first, then the other one can still bind. If the substrate binds first, then the inhibitor can still bind. If the inhibitor binds first, then the substrate can still bind. But the reaction is not going to be catalyzed. But you can even have a situation, you can even have a situation where the inhibitor and the substrate can both bind in or around the active site. So that's the inhibitor, and then this is our substrate."}, {"video_title": "Noncompetitive inhibition   Energy and enzymes   Biology   Khan Academy.mp3", "Sentence": "If the inhibitor binds first, then the substrate can still bind. But the reaction is not going to be catalyzed. But you can even have a situation, you can even have a situation where the inhibitor and the substrate can both bind in or around the active site. So that's the inhibitor, and then this is our substrate. This is the substrate. But once again, this reaction is not going to occur. We have non-competitive inhibition."}, {"video_title": "Noncompetitive inhibition   Energy and enzymes   Biology   Khan Academy.mp3", "Sentence": "So that's the inhibitor, and then this is our substrate. This is the substrate. But once again, this reaction is not going to occur. We have non-competitive inhibition. They're not competing for the thing. They can both bind to it. Whether they can bind isn't dependent on whether the other one is bound."}, {"video_title": "Noncompetitive inhibition   Energy and enzymes   Biology   Khan Academy.mp3", "Sentence": "We have non-competitive inhibition. They're not competing for the thing. They can both bind to it. Whether they can bind isn't dependent on whether the other one is bound. But if the inhibitor is there, then it's not going to allow the reaction to actually be catalyzed, as opposed to competitive inhibition. Whoever gets to the enzyme first gets the enzyme. Hopefully that clarifies things."}, {"video_title": "Hydrolysis   Macromolecules   Biology   Khan Academy.mp3", "Sentence": "But then you could keep going, and you could form longer chains of glucose molecules. And these things, where you take a monosaccharide, glucose is the most common example of that, and you create chains of these, we call these polysaccharides. Polysaccharides. This is a polysaccharide. And there's all sorts of interesting examples of polysaccharides all around you, especially polysaccharides of glucose, or things that are derived from glucose. This right here, this is a bowl of mashed potatoes, which is mostly starch, which is mainly just chains of glucose. So this right over here, let me do that in a color that's actually visible."}, {"video_title": "Hydrolysis   Macromolecules   Biology   Khan Academy.mp3", "Sentence": "This is a polysaccharide. And there's all sorts of interesting examples of polysaccharides all around you, especially polysaccharides of glucose, or things that are derived from glucose. This right here, this is a bowl of mashed potatoes, which is mostly starch, which is mainly just chains of glucose. So this right over here, let me do that in a color that's actually visible. So that is starch. That is starch. The shell of a lot of insects, and things like lobsters, and the wings of these insects right over here, that's made of something called chitin."}, {"video_title": "Hydrolysis   Macromolecules   Biology   Khan Academy.mp3", "Sentence": "So this right over here, let me do that in a color that's actually visible. So that is starch. That is starch. The shell of a lot of insects, and things like lobsters, and the wings of these insects right over here, that's made of something called chitin. And chitin is also a polysaccharide. It's made of chains of, essentially a modification of glucose, chains of that. That's chitin right over there."}, {"video_title": "Hydrolysis   Macromolecules   Biology   Khan Academy.mp3", "Sentence": "The shell of a lot of insects, and things like lobsters, and the wings of these insects right over here, that's made of something called chitin. And chitin is also a polysaccharide. It's made of chains of, essentially a modification of glucose, chains of that. That's chitin right over there. Very similar to starch in our muscles, we have glycogen, which is our store of energy, in our muscles. You have cellulose, which is actually probably all around you right now. Cellulose are things like, let me write this down, because this is something that is all around you, and you don't even realize it."}, {"video_title": "Hydrolysis   Macromolecules   Biology   Khan Academy.mp3", "Sentence": "That's chitin right over there. Very similar to starch in our muscles, we have glycogen, which is our store of energy, in our muscles. You have cellulose, which is actually probably all around you right now. Cellulose are things like, let me write this down, because this is something that is all around you, and you don't even realize it. Cellulose, this is what constitutes things like paper, and wood. It's involved in the cell walls of plants. This right over here is a picture of cotton, cotton in its natural form."}, {"video_title": "Hydrolysis   Macromolecules   Biology   Khan Academy.mp3", "Sentence": "Cellulose are things like, let me write this down, because this is something that is all around you, and you don't even realize it. Cellulose, this is what constitutes things like paper, and wood. It's involved in the cell walls of plants. This right over here is a picture of cotton, cotton in its natural form. And cotton is actually one of the purest forms of cellulose. It's roughly 90% cellulose. And if you take a zoom in on a cotton fiber, or actually a fiber of cellulose, you will see chains of glucose molecules."}, {"video_title": "Hydrolysis   Macromolecules   Biology   Khan Academy.mp3", "Sentence": "This right over here is a picture of cotton, cotton in its natural form. And cotton is actually one of the purest forms of cellulose. It's roughly 90% cellulose. And if you take a zoom in on a cotton fiber, or actually a fiber of cellulose, you will see chains of glucose molecules. So you see this right over here, that is a glucose molecule. Then you see another glucose molecule, and this chain has been formed through dehydration synthesis. And the difference between starch and cellulose, or the main difference in terms of how this bonding has, with starch, the glucose molecules just keep forming the way that you saw in the video in dehydration synthesis, while in cellulose, they get flipped over."}, {"video_title": "Hydrolysis   Macromolecules   Biology   Khan Academy.mp3", "Sentence": "And if you take a zoom in on a cotton fiber, or actually a fiber of cellulose, you will see chains of glucose molecules. So you see this right over here, that is a glucose molecule. Then you see another glucose molecule, and this chain has been formed through dehydration synthesis. And the difference between starch and cellulose, or the main difference in terms of how this bonding has, with starch, the glucose molecules just keep forming the way that you saw in the video in dehydration synthesis, while in cellulose, they get flipped over. So you can see here, this oxygen is pointing that way, this oxygen is pointing that way, that oxygen is pointing that way. And you can look up more about cellulose, but it's really interesting. What gives it its structure are these hydrogen bonds that form between the partially negative, very electronegative oxygens on one strand, and the partially positive hydrogens on another strand."}, {"video_title": "Hydrolysis   Macromolecules   Biology   Khan Academy.mp3", "Sentence": "And the difference between starch and cellulose, or the main difference in terms of how this bonding has, with starch, the glucose molecules just keep forming the way that you saw in the video in dehydration synthesis, while in cellulose, they get flipped over. So you can see here, this oxygen is pointing that way, this oxygen is pointing that way, that oxygen is pointing that way. And you can look up more about cellulose, but it's really interesting. What gives it its structure are these hydrogen bonds that form between the partially negative, very electronegative oxygens on one strand, and the partially positive hydrogens on another strand. And that's actually what give its structure. So really, really interesting things, these polysaccharides. But a question is, how do you actually break these things down?"}, {"video_title": "Hydrolysis   Macromolecules   Biology   Khan Academy.mp3", "Sentence": "What gives it its structure are these hydrogen bonds that form between the partially negative, very electronegative oxygens on one strand, and the partially positive hydrogens on another strand. And that's actually what give its structure. So really, really interesting things, these polysaccharides. But a question is, how do you actually break these things down? If I were to eat these mashed potatoes, how do I eventually turn this thing into glucose so I can use it for energy? And the way that that happens, is through hydrolysis. And you can break down this word, the hydro, this is, if you see hydro, the prefix hydro, that's a good clue that it has something to do with water."}, {"video_title": "Hydrolysis   Macromolecules   Biology   Khan Academy.mp3", "Sentence": "But a question is, how do you actually break these things down? If I were to eat these mashed potatoes, how do I eventually turn this thing into glucose so I can use it for energy? And the way that that happens, is through hydrolysis. And you can break down this word, the hydro, this is, if you see hydro, the prefix hydro, that's a good clue that it has something to do with water. And then if you see lysis, if you're lysing something, this means that you're gonna break it down. So this is breaking down something using water. And that's exactly what happens with hydrolysis."}, {"video_title": "Hydrolysis   Macromolecules   Biology   Khan Academy.mp3", "Sentence": "And you can break down this word, the hydro, this is, if you see hydro, the prefix hydro, that's a good clue that it has something to do with water. And then if you see lysis, if you're lysing something, this means that you're gonna break it down. So this is breaking down something using water. And that's exactly what happens with hydrolysis. If you have this polysaccharide, and let's say we, let's throw a water molecule in there, we are going to add up, this water molecule is going to be able to break, it's going to be able to break one of these bonds. So we might end up with something like, we would end up, this chain could keep going in both directions, but we could end up with something that looks like this. With, that looks something, that looks something like that."}, {"video_title": "Hydrolysis   Macromolecules   Biology   Khan Academy.mp3", "Sentence": "And that's exactly what happens with hydrolysis. If you have this polysaccharide, and let's say we, let's throw a water molecule in there, we are going to add up, this water molecule is going to be able to break, it's going to be able to break one of these bonds. So we might end up with something like, we would end up, this chain could keep going in both directions, but we could end up with something that looks like this. With, that looks something, that looks something like that. So half of this water molecule gets broken up essentially to break this bond. It's the opposite of dehydration synthesis. So let's see if we can understand, get an overview of exactly how that happens."}, {"video_title": "Hydrolysis   Macromolecules   Biology   Khan Academy.mp3", "Sentence": "With, that looks something, that looks something like that. So half of this water molecule gets broken up essentially to break this bond. It's the opposite of dehydration synthesis. So let's see if we can understand, get an overview of exactly how that happens. So this right over here, this is a, this is a maltose, this is maltose right over here, it's disaccharide, it's just two glucose molecules attached to each other. If we kept doing this, if this kept going, if this guy had a bond to another glucose molecule and this guy had a bond to another glucose molecule, then we'd be dealing with starch or we could be dealing with glycogen. If this was flipped over in the chain and they kept flipping over and over, then we could be talking about cellulose."}, {"video_title": "Hydrolysis   Macromolecules   Biology   Khan Academy.mp3", "Sentence": "So let's see if we can understand, get an overview of exactly how that happens. So this right over here, this is a, this is a maltose, this is maltose right over here, it's disaccharide, it's just two glucose molecules attached to each other. If we kept doing this, if this kept going, if this guy had a bond to another glucose molecule and this guy had a bond to another glucose molecule, then we'd be dealing with starch or we could be dealing with glycogen. If this was flipped over in the chain and they kept flipping over and over, then we could be talking about cellulose. But let's just think about how this, the mechanism, the mechanism by which this bond can actually be broken. And it's really just the reverse of dehydration, the reverse of dehydration synthesis. So we can, this is just gonna be an overview of it."}, {"video_title": "Hydrolysis   Macromolecules   Biology   Khan Academy.mp3", "Sentence": "If this was flipped over in the chain and they kept flipping over and over, then we could be talking about cellulose. But let's just think about how this, the mechanism, the mechanism by which this bond can actually be broken. And it's really just the reverse of dehydration, the reverse of dehydration synthesis. So we can, this is just gonna be an overview of it. So we could start, this oxygen right over here, it's got two, it's got two lone pairs. There's always a chance that if it bumps into something in just the right way, it could nab, it could nab a hydrogen proton that is just sitting out there, that is just sitting out there in the fluid. We're assuming that this is happening in an aqueous solution."}, {"video_title": "Hydrolysis   Macromolecules   Biology   Khan Academy.mp3", "Sentence": "So we can, this is just gonna be an overview of it. So we could start, this oxygen right over here, it's got two, it's got two lone pairs. There's always a chance that if it bumps into something in just the right way, it could nab, it could nab a hydrogen proton that is just sitting out there, that is just sitting out there in the fluid. We're assuming that this is happening in an aqueous solution. It's happening in water. So it could just grab a hydrogen proton from maybe a passing hydronium molecule. And so if it does that, it would form, it would form, it would form a covalent bond and have a positive charge."}, {"video_title": "Hydrolysis   Macromolecules   Biology   Khan Academy.mp3", "Sentence": "We're assuming that this is happening in an aqueous solution. It's happening in water. So it could just grab a hydrogen proton from maybe a passing hydronium molecule. And so if it does that, it would form, it would form, it would form a covalent bond and have a positive charge. And now relative to actually both carbons, but let's focus on this carbon right over here. This guy would be what we call in organic chemistry a good leaving group, a good leaving group. So these electrons, these electrons, the oxygen might wanna just take these back because hey, it's got a positive charge, oxygen is really electronegative."}, {"video_title": "Hydrolysis   Macromolecules   Biology   Khan Academy.mp3", "Sentence": "And so if it does that, it would form, it would form, it would form a covalent bond and have a positive charge. And now relative to actually both carbons, but let's focus on this carbon right over here. This guy would be what we call in organic chemistry a good leaving group, a good leaving group. So these electrons, these electrons, the oxygen might wanna just take these back because hey, it's got a positive charge, oxygen is really electronegative. And so if things just bump in exactly the right way, if things interact in exactly the right way, you might have another water molecule. And this is where that extra water molecule is valuable in our hydrolysis. So let's say this is just another water molecule just passing by in exactly the right way."}, {"video_title": "Hydrolysis   Macromolecules   Biology   Khan Academy.mp3", "Sentence": "So these electrons, these electrons, the oxygen might wanna just take these back because hey, it's got a positive charge, oxygen is really electronegative. And so if things just bump in exactly the right way, if things interact in exactly the right way, you might have another water molecule. And this is where that extra water molecule is valuable in our hydrolysis. So let's say this is just another water molecule just passing by in exactly the right way. This could form, this could form a bond, this could form a bond with that carbon right over there. And just as it forms a bond with that carbon, the carbon says, okay, I'm getting to share some other electrons, let me let go of these electrons. So let's go of these electrons."}, {"video_title": "Hydrolysis   Macromolecules   Biology   Khan Academy.mp3", "Sentence": "So let's say this is just another water molecule just passing by in exactly the right way. This could form, this could form a bond, this could form a bond with that carbon right over there. And just as it forms a bond with that carbon, the carbon says, okay, I'm getting to share some other electrons, let me let go of these electrons. So let's go of these electrons. And then what do you have left? Well, we can go over here. And so now this carbon has, let me color code it."}, {"video_title": "Hydrolysis   Macromolecules   Biology   Khan Academy.mp3", "Sentence": "So let's go of these electrons. And then what do you have left? Well, we can go over here. And so now this carbon has, let me color code it. So this bond that was just forming, that is this bond, that is this bond right over here. This oxygen, this oxygen is this oxygen right over there. It actually has another hydrogen attached to it, so let me do that."}, {"video_title": "Hydrolysis   Macromolecules   Biology   Khan Academy.mp3", "Sentence": "And so now this carbon has, let me color code it. So this bond that was just forming, that is this bond, that is this bond right over here. This oxygen, this oxygen is this oxygen right over there. It actually has another hydrogen attached to it, so let me do that. So right when it makes the bond, it'll have a positive charge. And then this bond, this bond right over here goes back to this oxygen. This oxygen right over here is that oxygen right over there."}, {"video_title": "Hydrolysis   Macromolecules   Biology   Khan Academy.mp3", "Sentence": "It actually has another hydrogen attached to it, so let me do that. So right when it makes the bond, it'll have a positive charge. And then this bond, this bond right over here goes back to this oxygen. This oxygen right over here is that oxygen right over there. Now, when it started off, this guy grabbed a, this guy, well, and this guy, and this, let me, actually, and this hydrogen proton that it grabbed, I've shown in orange, that's this one. That's this one right over here. That's that one right over here."}, {"video_title": "Hydrolysis   Macromolecules   Biology   Khan Academy.mp3", "Sentence": "This oxygen right over here is that oxygen right over there. Now, when it started off, this guy grabbed a, this guy, well, and this guy, and this, let me, actually, and this hydrogen proton that it grabbed, I've shown in orange, that's this one. That's this one right over here. That's that one right over here. Now, this one grabbed a hydrogen proton, and now this one can actually give back a hydrogen proton to the solution. So if a water molecule passing by can just grab this hydrogen proton and then become a hydronium molecule. And so it took a hydrogen proton, it's giving it back."}, {"video_title": "Hydrolysis   Macromolecules   Biology   Khan Academy.mp3", "Sentence": "That's that one right over here. Now, this one grabbed a hydrogen proton, and now this one can actually give back a hydrogen proton to the solution. So if a water molecule passing by can just grab this hydrogen proton and then become a hydronium molecule. And so it took a hydrogen proton, it's giving it back. And so what we are left with, but it took up this water molecule right over here to break the bond. And so this is a positive charge. It could be a passing hydronium molecule, and then it'll just hand it off to that."}, {"video_title": "Hydrolysis   Macromolecules   Biology   Khan Academy.mp3", "Sentence": "And so it took a hydrogen proton, it's giving it back. And so what we are left with, but it took up this water molecule right over here to break the bond. And so this is a positive charge. It could be a passing hydronium molecule, and then it'll just hand it off to that. And there you have it. We have two standalone glucose molecules right over there. We have broken the bond."}, {"video_title": "Hydrolysis   Macromolecules   Biology   Khan Academy.mp3", "Sentence": "It could be a passing hydronium molecule, and then it'll just hand it off to that. And there you have it. We have two standalone glucose molecules right over there. We have broken the bond. And these could be parts of chains, in which case we've just broken the chain. Or if we're just dealing with maltose, now we've broken it down into the individual glucose molecules. And the example here is with glucose, but it could have been the case, or with maltose, and it could have been the case with sucrose, where we break sucrose down using hydrolysis into a glucose molecule and a fructose molecule."}, {"video_title": "Introduction to cilia, flagella and pseudopodia   Cells   High school biology   Khan Academy.mp3", "Sentence": "So this right over here is a picture of the amoeba Chaos carolinensi. And what you see here is a projection coming off from the main part of the cell. And this is called a pseudopod, which is referring to it being a false foot. The pod is coming from the same root word as podiatry, which is referring to the foot. And what I really want you to appreciate, this is used by amoeba either to move around or it could be even used to attack something that it wants to engulf. And think about what it might take to be able to do this, to be able to grow this type of a pseudofoot, this type of a false foot. You need all sorts of microstructures in here that will extend or contract as necessary."}, {"video_title": "Introduction to cilia, flagella and pseudopodia   Cells   High school biology   Khan Academy.mp3", "Sentence": "The pod is coming from the same root word as podiatry, which is referring to the foot. And what I really want you to appreciate, this is used by amoeba either to move around or it could be even used to attack something that it wants to engulf. And think about what it might take to be able to do this, to be able to grow this type of a pseudofoot, this type of a false foot. You need all sorts of microstructures in here that will extend or contract as necessary. And think about the machinery that you need to do that. And so the key realization is sometimes we just imagine cells as these bags of fluid with a few things floating around. But they're these incredibly complex structures."}, {"video_title": "Introduction to cilia, flagella and pseudopodia   Cells   High school biology   Khan Academy.mp3", "Sentence": "You need all sorts of microstructures in here that will extend or contract as necessary. And think about the machinery that you need to do that. And so the key realization is sometimes we just imagine cells as these bags of fluid with a few things floating around. But they're these incredibly complex structures. And biologists even today don't fully understand how everything works and they're studying how these things actually come to be. Now another structure that you will often see on unicellular organisms that either help them move around or even help move other things around are cilia. So this right over here is a picture of Oxytricha triflax, which is a unicellular organism."}, {"video_title": "Introduction to cilia, flagella and pseudopodia   Cells   High school biology   Khan Academy.mp3", "Sentence": "But they're these incredibly complex structures. And biologists even today don't fully understand how everything works and they're studying how these things actually come to be. Now another structure that you will often see on unicellular organisms that either help them move around or even help move other things around are cilia. So this right over here is a picture of Oxytricha triflax, which is a unicellular organism. It's a eukaryote. And you can clearly see these projections from its body here, these hair-like structures. Remember, this is a unicellular organism."}, {"video_title": "Introduction to cilia, flagella and pseudopodia   Cells   High school biology   Khan Academy.mp3", "Sentence": "So this right over here is a picture of Oxytricha triflax, which is a unicellular organism. It's a eukaryote. And you can clearly see these projections from its body here, these hair-like structures. Remember, this is a unicellular organism. If we were to, it's actually a fairly, it's a decent-sized one, that would be about, something like that would be about 30 micrometers right over there or 30 millionths of a meter or 30 thousandths of a millimeter. So small by our scale, but it's actually pretty big on the scale of it being a cell. And once again, these cilia tend to move in unison to either allow the microorganism to move around or sometimes they're used to move other things around."}, {"video_title": "Introduction to cilia, flagella and pseudopodia   Cells   High school biology   Khan Academy.mp3", "Sentence": "Remember, this is a unicellular organism. If we were to, it's actually a fairly, it's a decent-sized one, that would be about, something like that would be about 30 micrometers right over there or 30 millionths of a meter or 30 thousandths of a millimeter. So small by our scale, but it's actually pretty big on the scale of it being a cell. And once again, these cilia tend to move in unison to either allow the microorganism to move around or sometimes they're used to move other things around. For example, the cells that line your lungs will have cilia that are used to move things up or down, to move some of the saliva or any particles that are in there. Now, Oxytricha triflax is particularly interesting as a eukaryote because it doesn't just have one nucleus. It can have two nuclei."}, {"video_title": "Introduction to cilia, flagella and pseudopodia   Cells   High school biology   Khan Academy.mp3", "Sentence": "And once again, these cilia tend to move in unison to either allow the microorganism to move around or sometimes they're used to move other things around. For example, the cells that line your lungs will have cilia that are used to move things up or down, to move some of the saliva or any particles that are in there. Now, Oxytricha triflax is particularly interesting as a eukaryote because it doesn't just have one nucleus. It can have two nuclei. And within the nucleus, its DNA can be extremely fragmented. Most organisms have a reasonable number of chromosomes. Human beings have 23 pair."}, {"video_title": "Introduction to cilia, flagella and pseudopodia   Cells   High school biology   Khan Academy.mp3", "Sentence": "It can have two nuclei. And within the nucleus, its DNA can be extremely fragmented. Most organisms have a reasonable number of chromosomes. Human beings have 23 pair. That's actually a fairly large number. Oxytricha triflax could have thousands of chromosomes. And what's really interesting about Oxytricha triflax is how it mates."}, {"video_title": "Introduction to cilia, flagella and pseudopodia   Cells   High school biology   Khan Academy.mp3", "Sentence": "Human beings have 23 pair. That's actually a fairly large number. Oxytricha triflax could have thousands of chromosomes. And what's really interesting about Oxytricha triflax is how it mates. When it is under stress, it will merge with another Oxytricha triflax. And instead of producing another offspring, they mingle their DNA together. So by mating, they change each other's genetic makeup, which is fascinating."}, {"video_title": "Introduction to cilia, flagella and pseudopodia   Cells   High school biology   Khan Academy.mp3", "Sentence": "And what's really interesting about Oxytricha triflax is how it mates. When it is under stress, it will merge with another Oxytricha triflax. And instead of producing another offspring, they mingle their DNA together. So by mating, they change each other's genetic makeup, which is fascinating. And depending on your perspective, highly romantic. Now, another related idea is instead of having many cilia, some unicellular organisms will just have one large thing that looks like a tail that they can whip around to move. So this right over here is a commonly studied green algae."}, {"video_title": "Introduction to cilia, flagella and pseudopodia   Cells   High school biology   Khan Academy.mp3", "Sentence": "So by mating, they change each other's genetic makeup, which is fascinating. And depending on your perspective, highly romantic. Now, another related idea is instead of having many cilia, some unicellular organisms will just have one large thing that looks like a tail that they can whip around to move. So this right over here is a commonly studied green algae. It's called Chlamydomonas. And you can see very clearly here, this flagellum, this tail-like structure. And this is extremely thin."}, {"video_title": "Introduction to cilia, flagella and pseudopodia   Cells   High school biology   Khan Academy.mp3", "Sentence": "So this right over here is a commonly studied green algae. It's called Chlamydomonas. And you can see very clearly here, this flagellum, this tail-like structure. And this is extremely thin. We're seeing it under a very powerful microscope right over here. But just to get a sense of scale, a micrometer here would be about that. So the width of this flagellum, flagellum would be the singular."}, {"video_title": "Introduction to cilia, flagella and pseudopodia   Cells   High school biology   Khan Academy.mp3", "Sentence": "And this is extremely thin. We're seeing it under a very powerful microscope right over here. But just to get a sense of scale, a micrometer here would be about that. So the width of this flagellum, flagellum would be the singular. If we're talking about many of these, we would say flagella. This is about 1 1\u20444 of a micrometer. Another way of thinking about it, you could put 4,000 of these side by side, and you would have the width of a millimeter."}, {"video_title": "Introduction to cilia, flagella and pseudopodia   Cells   High school biology   Khan Academy.mp3", "Sentence": "So the width of this flagellum, flagellum would be the singular. If we're talking about many of these, we would say flagella. This is about 1 1\u20444 of a micrometer. Another way of thinking about it, you could put 4,000 of these side by side, and you would have the width of a millimeter. So extremely, extremely small. But once again, it really is amazing that these what seem like simple organisms to us are actually quite complex. There's a whole study of how these flagella move around, how the cell can spin it around so it allows it to move."}, {"video_title": "Introduction to cilia, flagella and pseudopodia   Cells   High school biology   Khan Academy.mp3", "Sentence": "Another way of thinking about it, you could put 4,000 of these side by side, and you would have the width of a millimeter. So extremely, extremely small. But once again, it really is amazing that these what seem like simple organisms to us are actually quite complex. There's a whole study of how these flagella move around, how the cell can spin it around so it allows it to move. If you were to actually decompose what's going on in this part of the cell, it's actually quite complex. It's biological machinery going on. So once again, these cells are not these just bags of just a few things floating around."}, {"video_title": "Enzymes   Energy and enzymes   Biology   Khan Academy.mp3", "Sentence": "And the phosphorylation of glucose is an example of that. And we go into some detail into that on the video on coupled reactions, and I think we actually call that the phosphorylation of glucose-6-phosphate. But it's super important because by putting the phosphate group on a glucose, it's ready to be the input to a whole series of biological mechanisms. It allows the glucose to be tagged, so it's going to be hard for it to escape the cell again. And it's a fairly straightforward mechanism where you have a lone pair of electrons on this hydroxyl group right over here. And then it attempts to, if it's in the right configuration, it can form a bond with the phosphorus in the phosphate group. Now the reason why it doesn't happen on its own, even though it's energetically favorable, once you form the bond, you have electrons that are going to be able to go into a lower energy state."}, {"video_title": "Enzymes   Energy and enzymes   Biology   Khan Academy.mp3", "Sentence": "It allows the glucose to be tagged, so it's going to be hard for it to escape the cell again. And it's a fairly straightforward mechanism where you have a lone pair of electrons on this hydroxyl group right over here. And then it attempts to, if it's in the right configuration, it can form a bond with the phosphorus in the phosphate group. Now the reason why it doesn't happen on its own, even though it's energetically favorable, once you form the bond, you have electrons that are going to be able to go into a lower energy state. So it has a negative delta G. If this is the molecules before the reaction, this is how much free energy they have before the reaction. After the reaction, they have less free energy. They have been able to release energy."}, {"video_title": "Enzymes   Energy and enzymes   Biology   Khan Academy.mp3", "Sentence": "Now the reason why it doesn't happen on its own, even though it's energetically favorable, once you form the bond, you have electrons that are going to be able to go into a lower energy state. So it has a negative delta G. If this is the molecules before the reaction, this is how much free energy they have before the reaction. After the reaction, they have less free energy. They have been able to release energy. So this is something that we would consider to be spontaneous. But for the reaction to happen, you need a little bit of energy to be put into the system. We call this our activation energy."}, {"video_title": "Enzymes   Energy and enzymes   Biology   Khan Academy.mp3", "Sentence": "They have been able to release energy. So this is something that we would consider to be spontaneous. But for the reaction to happen, you need a little bit of energy to be put into the system. We call this our activation energy. And you might say, well, why is that? Well, we have electrons that want to form a bond with this phosphorus, but this phosphorus is surrounded by negative charges. This oxygen right over here has a negative charge."}, {"video_title": "Enzymes   Energy and enzymes   Biology   Khan Academy.mp3", "Sentence": "We call this our activation energy. And you might say, well, why is that? Well, we have electrons that want to form a bond with this phosphorus, but this phosphorus is surrounded by negative charges. This oxygen right over here has a negative charge. This oxygen right over here has a negative charge. And as you can imagine, electrons don't like being around other electrons, like charges repel each other. So in order for this reaction to occur, or for it to occur more frequently, it has to be catalyzed."}, {"video_title": "Enzymes   Energy and enzymes   Biology   Khan Academy.mp3", "Sentence": "This oxygen right over here has a negative charge. This oxygen right over here has a negative charge. And as you can imagine, electrons don't like being around other electrons, like charges repel each other. So in order for this reaction to occur, or for it to occur more frequently, it has to be catalyzed. A catalyst is anything that makes a reaction happen faster, or even allows the reaction to happen at all. And when we talk about catalysts in biological systems, we're typically talking about enzymes. Enzymes."}, {"video_title": "Enzymes   Energy and enzymes   Biology   Khan Academy.mp3", "Sentence": "So in order for this reaction to occur, or for it to occur more frequently, it has to be catalyzed. A catalyst is anything that makes a reaction happen faster, or even allows the reaction to happen at all. And when we talk about catalysts in biological systems, we're typically talking about enzymes. Enzymes. And the way that an enzyme might catalyze this reaction, we actually talk about it when we talk about coupled reactions, is well, maybe it can provide some positive charges. It can provide some positive charges around these negative charges to pull them further away, to create space, so that you can actually have the reaction proceed. And so what an enzyme would do, it would make this curve, instead of having this hump on it, the curve would look more like this, so that the reaction can just proceed."}, {"video_title": "Enzymes   Energy and enzymes   Biology   Khan Academy.mp3", "Sentence": "Enzymes. And the way that an enzyme might catalyze this reaction, we actually talk about it when we talk about coupled reactions, is well, maybe it can provide some positive charges. It can provide some positive charges around these negative charges to pull them further away, to create space, so that you can actually have the reaction proceed. And so what an enzyme would do, it would make this curve, instead of having this hump on it, the curve would look more like this, so that the reaction can just proceed. But what are these enzymes? These things that can, you know, maybe it could place some interesting charge that can allow the reaction to happen a certain way. It might bend the molecules in a certain way to expose some bonds."}, {"video_title": "Enzymes   Energy and enzymes   Biology   Khan Academy.mp3", "Sentence": "And so what an enzyme would do, it would make this curve, instead of having this hump on it, the curve would look more like this, so that the reaction can just proceed. But what are these enzymes? These things that can, you know, maybe it could place some interesting charge that can allow the reaction to happen a certain way. It might bend the molecules in a certain way to expose some bonds. It might have a more acidic or basic environment that might be more favorable for the reaction. What are these seemingly magical things? Well, at a very high level, they tend to be these protein complexes, plus or minus a few other things."}, {"video_title": "Enzymes   Energy and enzymes   Biology   Khan Academy.mp3", "Sentence": "It might bend the molecules in a certain way to expose some bonds. It might have a more acidic or basic environment that might be more favorable for the reaction. What are these seemingly magical things? Well, at a very high level, they tend to be these protein complexes, plus or minus a few other things. So you can view them as proteins, and you know, maybe sometimes there'll be multiple polypeptide chains put together. They might have some other ions associated with them. But for the most part, they are proteins."}, {"video_title": "Enzymes   Energy and enzymes   Biology   Khan Academy.mp3", "Sentence": "Well, at a very high level, they tend to be these protein complexes, plus or minus a few other things. So you can view them as proteins, and you know, maybe sometimes there'll be multiple polypeptide chains put together. They might have some other ions associated with them. But for the most part, they are proteins. And the molecules that are going to react, that are going to bind to the proteins, we call these the substrates. So these, in this reaction right here, the glucose and the ATP, these are going to be the substrates. So you can imagine, you can imagine the enzyme that does this, and the general term for the enzyme that helps phosphorylate a sugar molecule like this, we call it a hexokinase."}, {"video_title": "Enzymes   Energy and enzymes   Biology   Khan Academy.mp3", "Sentence": "But for the most part, they are proteins. And the molecules that are going to react, that are going to bind to the proteins, we call these the substrates. So these, in this reaction right here, the glucose and the ATP, these are going to be the substrates. So you can imagine, you can imagine the enzyme that does this, and the general term for the enzyme that helps phosphorylate a sugar molecule like this, we call it a hexokinase. So it might be this crazy-looking protein. We're going to take better looks at this in a few moments. But the ATP, the ATP might bind to it right over there."}, {"video_title": "Enzymes   Energy and enzymes   Biology   Khan Academy.mp3", "Sentence": "So you can imagine, you can imagine the enzyme that does this, and the general term for the enzyme that helps phosphorylate a sugar molecule like this, we call it a hexokinase. So it might be this crazy-looking protein. We're going to take better looks at this in a few moments. But the ATP, the ATP might bind to it right over there. ATP is one of the substrates. And then the glucose might bind to it right over there. And so the two substrates bind, and the area where all of this is going on, we call that the active site."}, {"video_title": "Enzymes   Energy and enzymes   Biology   Khan Academy.mp3", "Sentence": "But the ATP, the ATP might bind to it right over there. ATP is one of the substrates. And then the glucose might bind to it right over there. And so the two substrates bind, and the area where all of this is going on, we call that the active site. So the active site, because that's where all the action is. The active site. And often when you have the substrates bind, they are able to interact with the protein to make the fit even stronger, to make it even more suitable for the reaction to take place."}, {"video_title": "Enzymes   Energy and enzymes   Biology   Khan Academy.mp3", "Sentence": "And so the two substrates bind, and the area where all of this is going on, we call that the active site. So the active site, because that's where all the action is. The active site. And often when you have the substrates bind, they are able to interact with the protein to make the fit even stronger, to make it even more suitable for the reaction to take place. And so the whole protein might bend a little bit to kind of lock these two in place a little bit more, and we call that induced fit. Induced fit. And so where would these positive charges come from?"}, {"video_title": "Enzymes   Energy and enzymes   Biology   Khan Academy.mp3", "Sentence": "And often when you have the substrates bind, they are able to interact with the protein to make the fit even stronger, to make it even more suitable for the reaction to take place. And so the whole protein might bend a little bit to kind of lock these two in place a little bit more, and we call that induced fit. Induced fit. And so where would these positive charges come from? Well, these would be things that are the side chains of the different amino acids on the polypeptide chain, on the protein. And it could even be other ions that get involved. In fact, in particular, to facilitate the phosphorylation of glucose, a magnesium ion might be involved to help draw some positive charge away."}, {"video_title": "Enzymes   Energy and enzymes   Biology   Khan Academy.mp3", "Sentence": "And so where would these positive charges come from? Well, these would be things that are the side chains of the different amino acids on the polypeptide chain, on the protein. And it could even be other ions that get involved. In fact, in particular, to facilitate the phosphorylation of glucose, a magnesium ion might be involved to help draw some positive charge away. But there's other positively charged groups that help draw a charge away so that the reaction is more likely to occur. So that's what enzymes are. And they tend to be optimally working in certain pH environments or at certain temperatures."}, {"video_title": "Enzymes   Energy and enzymes   Biology   Khan Academy.mp3", "Sentence": "In fact, in particular, to facilitate the phosphorylation of glucose, a magnesium ion might be involved to help draw some positive charge away. But there's other positively charged groups that help draw a charge away so that the reaction is more likely to occur. So that's what enzymes are. And they tend to be optimally working in certain pH environments or at certain temperatures. In general, higher temperatures allow more interactions, things are bumping around more. But if temperatures get a little bit too high, the protein or the enzyme might stop working. It might denature."}, {"video_title": "Enzymes   Energy and enzymes   Biology   Khan Academy.mp3", "Sentence": "And they tend to be optimally working in certain pH environments or at certain temperatures. In general, higher temperatures allow more interactions, things are bumping around more. But if temperatures get a little bit too high, the protein or the enzyme might stop working. It might denature. It might lose its actual structure. And what I want to now give you an appreciation for is how beautiful and complex these structures are. And you should appreciate what I'm showing you."}, {"video_title": "Enzymes   Energy and enzymes   Biology   Khan Academy.mp3", "Sentence": "It might denature. It might lose its actual structure. And what I want to now give you an appreciation for is how beautiful and complex these structures are. And you should appreciate what I'm showing you. These are in your cells. These are in your, you know, look at your hand. Look at, you know, everything around you."}, {"video_title": "Enzymes   Energy and enzymes   Biology   Khan Academy.mp3", "Sentence": "And you should appreciate what I'm showing you. These are in your cells. These are in your, you know, look at your hand. Look at, you know, everything around you. There's a lot of this stuff going on inside of you. So hopefully it gives an appreciation for the complexity of you as a biological system, but frankly, all biological systems. So this right over here, this is a visualization of a hexokinase, one variety of it."}, {"video_title": "Enzymes   Energy and enzymes   Biology   Khan Academy.mp3", "Sentence": "Look at, you know, everything around you. There's a lot of this stuff going on inside of you. So hopefully it gives an appreciation for the complexity of you as a biological system, but frankly, all biological systems. So this right over here, this is a visualization of a hexokinase, one variety of it. And just to get a sense of scale, this is a glucose molecule. And this right over here is an ATP. And so they will bind."}, {"video_title": "Enzymes   Energy and enzymes   Biology   Khan Academy.mp3", "Sentence": "So this right over here, this is a visualization of a hexokinase, one variety of it. And just to get a sense of scale, this is a glucose molecule. And this right over here is an ATP. And so they will bind. These are the two substrates. They will bind at the active site. You might have the induced fit where this fits around it."}, {"video_title": "Enzymes   Energy and enzymes   Biology   Khan Academy.mp3", "Sentence": "And so they will bind. These are the two substrates. They will bind at the active site. You might have the induced fit where this fits around it. It draws some charge away. It might bend the molecules in a certain way so that they're more likely to interact, bring these things close together. And so you're going to have the reaction occur."}, {"video_title": "Enzymes   Energy and enzymes   Biology   Khan Academy.mp3", "Sentence": "You might have the induced fit where this fits around it. It draws some charge away. It might bend the molecules in a certain way so that they're more likely to interact, bring these things close together. And so you're going to have the reaction occur. And then once the reaction occurs, they're not going to want to bind to the substrates anymore. I guess you could say the products at that point. And then they're going to let go of them."}, {"video_title": "Enzymes   Energy and enzymes   Biology   Khan Academy.mp3", "Sentence": "And so you're going to have the reaction occur. And then once the reaction occurs, they're not going to want to bind to the substrates anymore. I guess you could say the products at that point. And then they're going to let go of them. And then the enzyme hasn't changed. And that's an important property of an enzyme. It's not like it just has one use and it goes away."}, {"video_title": "Enzymes   Energy and enzymes   Biology   Khan Academy.mp3", "Sentence": "And then they're going to let go of them. And then the enzyme hasn't changed. And that's an important property of an enzyme. It's not like it just has one use and it goes away. It can keep doing this over and over and over again. One enzyme will do this many, many, many, many, many times in its actual life. And so now what I want to show you is a little three-dimensional visualization that I got from a website."}, {"video_title": "Enzymes   Energy and enzymes   Biology   Khan Academy.mp3", "Sentence": "It's not like it just has one use and it goes away. It can keep doing this over and over and over again. One enzyme will do this many, many, many, many, many times in its actual life. And so now what I want to show you is a little three-dimensional visualization that I got from a website. So let me go get that. I'll go ahead and pause my recording so I could get this little simulation or this model. And this is actually a hexokinase as well."}, {"video_title": "Enzymes   Energy and enzymes   Biology   Khan Academy.mp3", "Sentence": "And so now what I want to show you is a little three-dimensional visualization that I got from a website. So let me go get that. I'll go ahead and pause my recording so I could get this little simulation or this model. And this is actually a hexokinase as well. And hexokinases come in a bunch of different varieties. But this is a pretty neat thing to look at. And this has been visualized differently."}, {"video_title": "Enzymes   Energy and enzymes   Biology   Khan Academy.mp3", "Sentence": "And this is actually a hexokinase as well. And hexokinases come in a bunch of different varieties. But this is a pretty neat thing to look at. And this has been visualized differently. When you look up protein images on the web or anywhere, you'll see them sometimes with these ball and stick models. Sometimes you'll see them in these space-filling models. Sometimes you'll see them with this kind of, where you see the various structures."}, {"video_title": "Enzymes   Energy and enzymes   Biology   Khan Academy.mp3", "Sentence": "And this has been visualized differently. When you look up protein images on the web or anywhere, you'll see them sometimes with these ball and stick models. Sometimes you'll see them in these space-filling models. Sometimes you'll see them with this kind of, where you see the various structures. You notice the alpha helices here that we studied when we talked about protein structures. And you can also see some beta sheets. But this gives you an appreciation of the binding sites and how these things might interact."}, {"video_title": "Enzymes   Energy and enzymes   Biology   Khan Academy.mp3", "Sentence": "Sometimes you'll see them with this kind of, where you see the various structures. You notice the alpha helices here that we studied when we talked about protein structures. And you can also see some beta sheets. But this gives you an appreciation of the binding sites and how these things might interact. This right over here, that is a molecule of ATP. And then right next to it, I believe, if I'm looking at that right, that is a molecule of glucose. And notice they have bound, they are the two substrates, they have bound at the active site."}, {"video_title": "Enzymes   Energy and enzymes   Biology   Khan Academy.mp3", "Sentence": "But this gives you an appreciation of the binding sites and how these things might interact. This right over here, that is a molecule of ATP. And then right next to it, I believe, if I'm looking at that right, that is a molecule of glucose. And notice they have bound, they are the two substrates, they have bound at the active site. And now they can interact with each other. The enzyme, the hexokinase in this case, can help facilitate the reaction that we care about, the phosphorylation of glucose. So hopefully images like this and like this give you an appreciation for how complex and how beautiful these things actually are."}, {"video_title": "Endomembrane system   Structure of a cell   Biology   Khan Academy.mp3", "Sentence": "And at a very high level, the endomembrane system is all of the membranes that interact with each other inside of a cell. So what membranes are we talking about? Well, you can start off by talking about the cell membrane itself. And all of these membranes, these have bilayers of phospholipids. Sometimes my brain malfunctions and I call them bilipid layers. But these are bilayers of phospholipids. So if I were to zoom in right over here, if I were to zoom in right over there, that line, it really is a bilayer, a bilayer of phospholipids."}, {"video_title": "Endomembrane system   Structure of a cell   Biology   Khan Academy.mp3", "Sentence": "And all of these membranes, these have bilayers of phospholipids. Sometimes my brain malfunctions and I call them bilipid layers. But these are bilayers of phospholipids. So if I were to zoom in right over here, if I were to zoom in right over there, that line, it really is a bilayer, a bilayer of phospholipids. So it would look like this. So you have your hydrophilic heads pointing outwards and your hydrophobic tails pointing inwards. So hydrophilic heads pointing outwards, hydrophobic tails pointing inwards, and it keeps going."}, {"video_title": "Endomembrane system   Structure of a cell   Biology   Khan Academy.mp3", "Sentence": "So if I were to zoom in right over here, if I were to zoom in right over there, that line, it really is a bilayer, a bilayer of phospholipids. So it would look like this. So you have your hydrophilic heads pointing outwards and your hydrophobic tails pointing inwards. So hydrophilic heads pointing outwards, hydrophobic tails pointing inwards, and it keeps going. So you have, if we think of it from left to right, you have a layer of two, or you have a bilayer, I should say, of phospholipids. That's going to be true of the cellular membrane. That's going to be true of the outer nuclear membrane."}, {"video_title": "Endomembrane system   Structure of a cell   Biology   Khan Academy.mp3", "Sentence": "So hydrophilic heads pointing outwards, hydrophobic tails pointing inwards, and it keeps going. So you have, if we think of it from left to right, you have a layer of two, or you have a bilayer, I should say, of phospholipids. That's going to be true of the cellular membrane. That's going to be true of the outer nuclear membrane. Right over here, we drew this one on the video on the endoplasmic reticulum. And so over here, you see these two membranes. You might say, okay, is this a bilayer?"}, {"video_title": "Endomembrane system   Structure of a cell   Biology   Khan Academy.mp3", "Sentence": "That's going to be true of the outer nuclear membrane. Right over here, we drew this one on the video on the endoplasmic reticulum. And so over here, you see these two membranes. You might say, okay, is this a bilayer? No, this is actually two bilayers. So this membrane right over here has a phospholipid bilayer, and this membrane over here also has a phospholipid bilayer. This, the one, let me do this in another color, this one that I'm starting to trace in magenta, that's the outer membrane of the nuclear envelope, and it's continuous with the membrane of the endoplasmic reticulum, which I'm starting to highlight right over here."}, {"video_title": "Endomembrane system   Structure of a cell   Biology   Khan Academy.mp3", "Sentence": "You might say, okay, is this a bilayer? No, this is actually two bilayers. So this membrane right over here has a phospholipid bilayer, and this membrane over here also has a phospholipid bilayer. This, the one, let me do this in another color, this one that I'm starting to trace in magenta, that's the outer membrane of the nuclear envelope, and it's continuous with the membrane of the endoplasmic reticulum, which I'm starting to highlight right over here. And then the one that I'm highlighting in this purple color, this is the inner membrane of the nuclear envelope. And all of this is part of the endomembrane system. So I've already started talking about the endoplasmic reticulum, and we go into some depth on that on the video on the endoplasmic reticulum and the Golgi apparatus, but it's also part of the endomembrane system."}, {"video_title": "Endomembrane system   Structure of a cell   Biology   Khan Academy.mp3", "Sentence": "This, the one, let me do this in another color, this one that I'm starting to trace in magenta, that's the outer membrane of the nuclear envelope, and it's continuous with the membrane of the endoplasmic reticulum, which I'm starting to highlight right over here. And then the one that I'm highlighting in this purple color, this is the inner membrane of the nuclear envelope. And all of this is part of the endomembrane system. So I've already started talking about the endoplasmic reticulum, and we go into some depth on that on the video on the endoplasmic reticulum and the Golgi apparatus, but it's also part of the endomembrane system. And the endoplasmic reticulum in particular can represent up to or even more than 50% of the membrane associated, the phospholipid membrane associated with the cell. And we've talked about what goes on in the lumen of the endoplasmic reticulum. So this area right over here, right over here, we've talked about what happens there."}, {"video_title": "Endomembrane system   Structure of a cell   Biology   Khan Academy.mp3", "Sentence": "So I've already started talking about the endoplasmic reticulum, and we go into some depth on that on the video on the endoplasmic reticulum and the Golgi apparatus, but it's also part of the endomembrane system. And the endoplasmic reticulum in particular can represent up to or even more than 50% of the membrane associated, the phospholipid membrane associated with the cell. And we've talked about what goes on in the lumen of the endoplasmic reticulum. So this area right over here, right over here, we've talked about what happens there. Proteins can get synthesized, actually other molecules like lipids can get synthesized there. They can, and then they can go to the smooth ER, and then the place where they can exit from the smooth ER, and we saw that in the video on the endoplasmic reticulum, how they can kind of bud out, we call this area, it's often called the transitional ER. So this area right over here, we would call the transitional endoplasmic reticulum."}, {"video_title": "Endomembrane system   Structure of a cell   Biology   Khan Academy.mp3", "Sentence": "So this area right over here, right over here, we've talked about what happens there. Proteins can get synthesized, actually other molecules like lipids can get synthesized there. They can, and then they can go to the smooth ER, and then the place where they can exit from the smooth ER, and we saw that in the video on the endoplasmic reticulum, how they can kind of bud out, we call this area, it's often called the transitional ER. So this area right over here, we would call the transitional endoplasmic reticulum. Transitional, transitional, transitional, transitional ER is this place where these proteins are being budded off, and they're budding off in vesicles. So this is the transitional ER. And all vesicles are are little small compartments that have a membrane around it that things like a protein can be transported in."}, {"video_title": "Endomembrane system   Structure of a cell   Biology   Khan Academy.mp3", "Sentence": "So this area right over here, we would call the transitional endoplasmic reticulum. Transitional, transitional, transitional, transitional ER is this place where these proteins are being budded off, and they're budding off in vesicles. So this is the transitional ER. And all vesicles are are little small compartments that have a membrane around it that things like a protein can be transported in. And not, you know, I don't want to beat a dead horse here, but all of these lines that I'm drawing, even though I drew it as a single line, these are phospholipid bilayers. So the membrane might be different, the phospholipid bilayers might be different when we go from one piece of the membrane to another, but they all have that same general notion of having this bilayer of phospholipids. But just as a review, these proteins, they can emerge from the transitional ER, they can make their way to the Golgi apparatus, and we've already talked about how in the Golgi apparatus these proteins can be matured."}, {"video_title": "Endomembrane system   Structure of a cell   Biology   Khan Academy.mp3", "Sentence": "And all vesicles are are little small compartments that have a membrane around it that things like a protein can be transported in. And not, you know, I don't want to beat a dead horse here, but all of these lines that I'm drawing, even though I drew it as a single line, these are phospholipid bilayers. So the membrane might be different, the phospholipid bilayers might be different when we go from one piece of the membrane to another, but they all have that same general notion of having this bilayer of phospholipids. But just as a review, these proteins, they can emerge from the transitional ER, they can make their way to the Golgi apparatus, and we've already talked about how in the Golgi apparatus these proteins can be matured. And when I say being matured, there's a bunch of enzymes in here, there's a bunch of Golgi enzymes in here, that can do all sorts of things to the proteins, tag them. They can actually add saccharides to them so that they become glycoproteins. They can tag them so they can be used in the cellular membrane, or be used outside of the cellular membrane, or to be used other places in the cell."}, {"video_title": "Endomembrane system   Structure of a cell   Biology   Khan Academy.mp3", "Sentence": "But just as a review, these proteins, they can emerge from the transitional ER, they can make their way to the Golgi apparatus, and we've already talked about how in the Golgi apparatus these proteins can be matured. And when I say being matured, there's a bunch of enzymes in here, there's a bunch of Golgi enzymes in here, that can do all sorts of things to the proteins, tag them. They can actually add saccharides to them so that they become glycoproteins. They can tag them so they can be used in the cellular membrane, or be used outside of the cellular membrane, or to be used other places in the cell. So for example, this protein right over here, it butted off as a vesicle, it makes its way to the Golgi apparatus. The membrane can then merge and dump the protein into the Golgi apparatus. From there it can be matured, it might turn into a glycoprotein, who knows what happens to it."}, {"video_title": "Endomembrane system   Structure of a cell   Biology   Khan Academy.mp3", "Sentence": "They can tag them so they can be used in the cellular membrane, or be used outside of the cellular membrane, or to be used other places in the cell. So for example, this protein right over here, it butted off as a vesicle, it makes its way to the Golgi apparatus. The membrane can then merge and dump the protein into the Golgi apparatus. From there it can be matured, it might turn into a glycoprotein, who knows what happens to it. And then it could butt off again, and then this protein that's now butted off, it could go to be embedded into the cellular membrane, the protein could be excreted from the cell, or it could go to other parts of the cell. Now those aren't everything I've just talked about, those aren't the only parts of the endomembrane system. You have things like vacuoles, which are membrane-bound organelles in a cell."}, {"video_title": "Endomembrane system   Structure of a cell   Biology   Khan Academy.mp3", "Sentence": "From there it can be matured, it might turn into a glycoprotein, who knows what happens to it. And then it could butt off again, and then this protein that's now butted off, it could go to be embedded into the cellular membrane, the protein could be excreted from the cell, or it could go to other parts of the cell. Now those aren't everything I've just talked about, those aren't the only parts of the endomembrane system. You have things like vacuoles, which are membrane-bound organelles in a cell. In plant cells, a vacuole can be used for storage, it could be used for structure, vacuoles can get quite large, and they can actually give the structure of the actual plant. In animal cells, you might have something called a lysosome. A lysosome is a membrane-bound structure where essentially things go to, for the most part, be recycled or to be torn apart."}, {"video_title": "Endomembrane system   Structure of a cell   Biology   Khan Academy.mp3", "Sentence": "You have things like vacuoles, which are membrane-bound organelles in a cell. In plant cells, a vacuole can be used for storage, it could be used for structure, vacuoles can get quite large, and they can actually give the structure of the actual plant. In animal cells, you might have something called a lysosome. A lysosome is a membrane-bound structure where essentially things go to, for the most part, be recycled or to be torn apart. So maybe something got packaged from someplace, this is some molecules over, let me do this in another color, you have some, and I drew that vesicle a little bit too big, but maybe this stuff needs to be destroyed, so this membrane is going to, it can then merge with that membrane and dump its contents in here, and this has a low pH, and it can actually break apart this stuff, and it can digest this stuff, and recycle it into its more constituent material. So all of this is part of the endomembrane system. So once again, I hope it gives you an appreciation for how complex and on a lot of levels beautiful cells can be."}, {"video_title": "Endosymbiosis theory   Cell structure and function   AP Biology   Khan Academy.mp3", "Sentence": "For example, here is a diagram of a chloroplast that are found in plant or algal cells. And we know that this is where the photosynthesis takes place. But what's really interesting, above and beyond that, is that it seems that chloroplasts have a lot of the machinery necessary for being a prokaryotic cell on its own. We don't see it acting on its own, but it has its own DNA. It has ribosomes, which we know are the site where we go from messenger RNA to protein. Similarly, another interesting membrane-bound organelle that we see in eukaryotic cells, and this would include even animal cells and the cells in your and my bodies, are mitochondria. And mitochondria are often viewed as the energy factories of eukaryotic cells, where we can leverage oxygen in order to produce ATP."}, {"video_title": "Endosymbiosis theory   Cell structure and function   AP Biology   Khan Academy.mp3", "Sentence": "We don't see it acting on its own, but it has its own DNA. It has ribosomes, which we know are the site where we go from messenger RNA to protein. Similarly, another interesting membrane-bound organelle that we see in eukaryotic cells, and this would include even animal cells and the cells in your and my bodies, are mitochondria. And mitochondria are often viewed as the energy factories of eukaryotic cells, where we can leverage oxygen in order to produce ATP. And like chloroplasts, mitochondria has its own DNA. It also has mitochondrial ribosomes. Here are some just diagrams of how mitochondria might look inside of a larger eukaryotic cell."}, {"video_title": "Endosymbiosis theory   Cell structure and function   AP Biology   Khan Academy.mp3", "Sentence": "And mitochondria are often viewed as the energy factories of eukaryotic cells, where we can leverage oxygen in order to produce ATP. And like chloroplasts, mitochondria has its own DNA. It also has mitochondrial ribosomes. Here are some just diagrams of how mitochondria might look inside of a larger eukaryotic cell. And so evolutionary biologists, for many decades, looked at this and said, well, why do these things exist? Why do they almost look like prokaryotic cells on their own? And there's even examples of prokaryotic cells, independent prokaryotic bacteria, that live in symbiosis inside of other cells, and they look an awful lot like mitochondria and chloroplasts."}, {"video_title": "Endosymbiosis theory   Cell structure and function   AP Biology   Khan Academy.mp3", "Sentence": "Here are some just diagrams of how mitochondria might look inside of a larger eukaryotic cell. And so evolutionary biologists, for many decades, looked at this and said, well, why do these things exist? Why do they almost look like prokaryotic cells on their own? And there's even examples of prokaryotic cells, independent prokaryotic bacteria, that live in symbiosis inside of other cells, and they look an awful lot like mitochondria and chloroplasts. And so if we fast forward to the 1960s, someone named Lynn Margulis comes on the scene with endosymbiosis theory. And her view is that these membrane-bound organelles like mitochondria and chloroplasts, if we go deep into our evolutionary past, say 2 1\u20442 billion years ago, their ancestors were actually independent prokaryotic organisms that could produce energy aerobically or using oxygen. And precursors to what we would consider today to be modern eukaryotic cells that might have already had some membrane-bound structures like a nucleus and maybe some other things, that they could only metabolize things anaerobically."}, {"video_title": "Endosymbiosis theory   Cell structure and function   AP Biology   Khan Academy.mp3", "Sentence": "And there's even examples of prokaryotic cells, independent prokaryotic bacteria, that live in symbiosis inside of other cells, and they look an awful lot like mitochondria and chloroplasts. And so if we fast forward to the 1960s, someone named Lynn Margulis comes on the scene with endosymbiosis theory. And her view is that these membrane-bound organelles like mitochondria and chloroplasts, if we go deep into our evolutionary past, say 2 1\u20442 billion years ago, their ancestors were actually independent prokaryotic organisms that could produce energy aerobically or using oxygen. And precursors to what we would consider today to be modern eukaryotic cells that might have already had some membrane-bound structures like a nucleus and maybe some other things, that they could only metabolize things anaerobically. They couldn't leverage oxygen. While these other characters could leverage oxygen, and then they could have become symbionts, where the one that could leverage oxygen to produce more energy would get engulfed into the larger cell, and that larger cell is able to provide nutrients and protection, while the smaller cell that's engulfed inside of it is able to better metabolize the nutrients and leverage oxygen to produce more energy. And that over time, this symbiotic relationship became even more connected so that the smaller organism could not operate by itself, that it lost some of its DNA that was necessary to act independently, and some of it might have gotten incorporated into the DNA of the larger cell."}, {"video_title": "Endosymbiosis theory   Cell structure and function   AP Biology   Khan Academy.mp3", "Sentence": "And precursors to what we would consider today to be modern eukaryotic cells that might have already had some membrane-bound structures like a nucleus and maybe some other things, that they could only metabolize things anaerobically. They couldn't leverage oxygen. While these other characters could leverage oxygen, and then they could have become symbionts, where the one that could leverage oxygen to produce more energy would get engulfed into the larger cell, and that larger cell is able to provide nutrients and protection, while the smaller cell that's engulfed inside of it is able to better metabolize the nutrients and leverage oxygen to produce more energy. And that over time, this symbiotic relationship became even more connected so that the smaller organism could not operate by itself, that it lost some of its DNA that was necessary to act independently, and some of it might have gotten incorporated into the DNA of the larger cell. And those smaller organisms are what eventually evolved into what we consider today to be mitochondria. This is a fascinating theory, and it's actually been proven out. When Lynn Margulis first published this in the late 1960s, she wasn't taken that seriously."}, {"video_title": "Endosymbiosis theory   Cell structure and function   AP Biology   Khan Academy.mp3", "Sentence": "And that over time, this symbiotic relationship became even more connected so that the smaller organism could not operate by itself, that it lost some of its DNA that was necessary to act independently, and some of it might have gotten incorporated into the DNA of the larger cell. And those smaller organisms are what eventually evolved into what we consider today to be mitochondria. This is a fascinating theory, and it's actually been proven out. When Lynn Margulis first published this in the late 1960s, she wasn't taken that seriously. But in the decades since, it's been validated as we've looked at the DNA structures of mitochondria and chloroplasts, that this actually is the most likely theory of how they emerged in our cells. And so it's just a fascinating glimpse of evolution in general. We talk a lot about natural selection and the role of variation and mutations, but Lynn Margulis introduces another idea that could catalyze evolution, and that's that of symbiosis."}, {"video_title": "Scale of cells   Structure of a cell   Biology   Khan Academy.mp3", "Sentence": "When we study science, it's natural to just categorize a whole series of things as just being really, really unimaginably small. So when people say, hey, atomic scale, or molecular scale, or protein, or a cell, you often just group that together and say, oh, those are really, really, really, really small things. But what I want to do in this video is get an appreciation that even though all the things I just mentioned are really small, there's actually a huge difference in the sizes of those things. And hopefully that'll give us an appreciation for how complex something like a cell can be, how it can have all of this machinery, how it can actually be a living organism, or part of a living organism. And so at this scale, this is my little rendering, my drawing of a water molecule. You have the oxygen atom right over here in this purplish color, and then you have two hydrogen molecules bonded to it. And this is going to be roughly 0.275 nanometers."}, {"video_title": "Scale of cells   Structure of a cell   Biology   Khan Academy.mp3", "Sentence": "And hopefully that'll give us an appreciation for how complex something like a cell can be, how it can have all of this machinery, how it can actually be a living organism, or part of a living organism. And so at this scale, this is my little rendering, my drawing of a water molecule. You have the oxygen atom right over here in this purplish color, and then you have two hydrogen molecules bonded to it. And this is going to be roughly 0.275 nanometers. And just to remind ourselves, a nanometer is a billionth of a meter. And just to get an appreciation of that, so let me, so this is one billionth, one billionth, one billionth of a, one billionth of a meter. That's a nanometer."}, {"video_title": "Scale of cells   Structure of a cell   Biology   Khan Academy.mp3", "Sentence": "And this is going to be roughly 0.275 nanometers. And just to remind ourselves, a nanometer is a billionth of a meter. And just to get an appreciation of that, so let me, so this is one billionth, one billionth, one billionth of a, one billionth of a meter. That's a nanometer. And if you want to even attempt to visualize that, that would be a millionth of a millimeter. So one, let me write this. One millionth, one millionth of a millimeter."}, {"video_title": "Scale of cells   Structure of a cell   Biology   Khan Academy.mp3", "Sentence": "That's a nanometer. And if you want to even attempt to visualize that, that would be a millionth of a millimeter. So one, let me write this. One millionth, one millionth of a millimeter. And I actually like using this one, because a millimeter is about as small as I can on a reasonable basis visualize. But it's a millionth of that, so this definitely goes well beyond at least my capabilities of visualization. So that would be the diameter, or the width of a water molecule."}, {"video_title": "Scale of cells   Structure of a cell   Biology   Khan Academy.mp3", "Sentence": "One millionth, one millionth of a millimeter. And I actually like using this one, because a millimeter is about as small as I can on a reasonable basis visualize. But it's a millionth of that, so this definitely goes well beyond at least my capabilities of visualization. So that would be the diameter, or the width of a water molecule. But now let's go to the next scale up. We've talked a lot about proteins, and this is our friend, this right over here is our friend hemoglobin. And just so you get a sense of scale, the width of hemoglobin is going to be about five nanometers, or five billionths of a meter."}, {"video_title": "Scale of cells   Structure of a cell   Biology   Khan Academy.mp3", "Sentence": "So that would be the diameter, or the width of a water molecule. But now let's go to the next scale up. We've talked a lot about proteins, and this is our friend, this right over here is our friend hemoglobin. And just so you get a sense of scale, the width of hemoglobin is going to be about five nanometers, or five billionths of a meter. Now that seems super small, so in some ways it's okay to categorize that into your super small part of the brain. But it's good to appreciate this is much larger than a water molecule. If a water molecule were on this scale, I pre-drew it, this little thing over here, that's my attempt at drawing a water molecule at this same scale."}, {"video_title": "Scale of cells   Structure of a cell   Biology   Khan Academy.mp3", "Sentence": "And just so you get a sense of scale, the width of hemoglobin is going to be about five nanometers, or five billionths of a meter. Now that seems super small, so in some ways it's okay to categorize that into your super small part of the brain. But it's good to appreciate this is much larger than a water molecule. If a water molecule were on this scale, I pre-drew it, this little thing over here, that's my attempt at drawing a water molecule at this same scale. So even when you go from something like a water molecule to a protein, you're already going dramatically up in size, and dramatically up in complexity. And we've talked a lot about protein structure, how they can take on all these interesting shapes, and do fairly surprising and complex things inside of biological systems. But now let's go the next scale up."}, {"video_title": "Scale of cells   Structure of a cell   Biology   Khan Academy.mp3", "Sentence": "If a water molecule were on this scale, I pre-drew it, this little thing over here, that's my attempt at drawing a water molecule at this same scale. So even when you go from something like a water molecule to a protein, you're already going dramatically up in size, and dramatically up in complexity. And we've talked a lot about protein structure, how they can take on all these interesting shapes, and do fairly surprising and complex things inside of biological systems. But now let's go the next scale up. And the next scale up, I'm going to go to a virus. And what I've attempted to draw here, this is a fairly well-known virus, this is HIV. And it's actually one of the larger viruses, and its diameter is roughly 120 nanometers."}, {"video_title": "Scale of cells   Structure of a cell   Biology   Khan Academy.mp3", "Sentence": "But now let's go the next scale up. And the next scale up, I'm going to go to a virus. And what I've attempted to draw here, this is a fairly well-known virus, this is HIV. And it's actually one of the larger viruses, and its diameter is roughly 120 nanometers. So if we were to draw this hemoglobin protein at the same scale as we've drawn this virus, this thing right over here would be the hemoglobin protein, and we wouldn't even be able to see the water molecule at this scale right over here. But this is still really, really small. This is 120 billionths of a meter."}, {"video_title": "Scale of cells   Structure of a cell   Biology   Khan Academy.mp3", "Sentence": "And it's actually one of the larger viruses, and its diameter is roughly 120 nanometers. So if we were to draw this hemoglobin protein at the same scale as we've drawn this virus, this thing right over here would be the hemoglobin protein, and we wouldn't even be able to see the water molecule at this scale right over here. But this is still really, really small. This is 120 billionths of a meter. So this is still unimaginably small. But now let's go up to the next scale. So this creepy picture right over here, this is a T cell."}, {"video_title": "Scale of cells   Structure of a cell   Biology   Khan Academy.mp3", "Sentence": "This is 120 billionths of a meter. So this is still unimaginably small. But now let's go up to the next scale. So this creepy picture right over here, this is a T cell. This is a depiction, this is a, if you want to see the whole thing, that is a T cell right over here. This is a T cell. And this creepy picture, all the blue, that's the T cell."}, {"video_title": "Scale of cells   Structure of a cell   Biology   Khan Academy.mp3", "Sentence": "So this creepy picture right over here, this is a T cell. This is a depiction, this is a, if you want to see the whole thing, that is a T cell right over here. This is a T cell. And this creepy picture, all the blue, that's the T cell. And what you see in yellow, that's the HIV virus emerging, taking advantage of this T cell. So that's why it's so creepy. It's using that cell's machinery to reproduce itself."}, {"video_title": "Scale of cells   Structure of a cell   Biology   Khan Academy.mp3", "Sentence": "And this creepy picture, all the blue, that's the T cell. And what you see in yellow, that's the HIV virus emerging, taking advantage of this T cell. So that's why it's so creepy. It's using that cell's machinery to reproduce itself. But you immediately see on this picture how small the HIV virus is compared to the actual T cell. Each of these small little things, each of these small things is an HIV virus, which we already saw is a lot bigger than something like a hemoglobin protein. And so a hemoglobin protein, you wouldn't even be able to, you know, on this scale, maybe it would be a pixel, if that."}, {"video_title": "Scale of cells   Structure of a cell   Biology   Khan Academy.mp3", "Sentence": "It's using that cell's machinery to reproduce itself. But you immediately see on this picture how small the HIV virus is compared to the actual T cell. Each of these small little things, each of these small things is an HIV virus, which we already saw is a lot bigger than something like a hemoglobin protein. And so a hemoglobin protein, you wouldn't even be able to, you know, on this scale, maybe it would be a pixel, if that. And on a similar scale as this T cell, you have things like red blood cells. And this is actually a comparison, a side by side. This is using an electron, this is using an electron microscope."}, {"video_title": "Scale of cells   Structure of a cell   Biology   Khan Academy.mp3", "Sentence": "And so a hemoglobin protein, you wouldn't even be able to, you know, on this scale, maybe it would be a pixel, if that. And on a similar scale as this T cell, you have things like red blood cells. And this is actually a comparison, a side by side. This is using an electron, this is using an electron microscope. You see a red blood cell right over here, and you see a T cell. They're roughly on the same size, or at least the same order of magnitude size. And a red blood cell is going to be six to eight micrometers wide."}, {"video_title": "Scale of cells   Structure of a cell   Biology   Khan Academy.mp3", "Sentence": "This is using an electron, this is using an electron microscope. You see a red blood cell right over here, and you see a T cell. They're roughly on the same size, or at least the same order of magnitude size. And a red blood cell is going to be six to eight micrometers wide. So this is six to eight millionths of a meter. So if we were to, just take seven as the average, seven millionths, seven millionths of a meter. Over here we're talking about a millionth of a millimeter."}, {"video_title": "Scale of cells   Structure of a cell   Biology   Khan Academy.mp3", "Sentence": "And a red blood cell is going to be six to eight micrometers wide. So this is six to eight millionths of a meter. So if we were to, just take seven as the average, seven millionths, seven millionths of a meter. Over here we're talking about a millionth of a millimeter. Now we're talking about seven millionths of a meter. And just to get an appreciation for size, we already compared the virus, the HIV virus, to this cell. We're seeing it directly as they emerge from this cell."}, {"video_title": "Scale of cells   Structure of a cell   Biology   Khan Academy.mp3", "Sentence": "Over here we're talking about a millionth of a millimeter. Now we're talking about seven millionths of a meter. And just to get an appreciation for size, we already compared the virus, the HIV virus, to this cell. We're seeing it directly as they emerge from this cell. But each of these red blood cells are going to contain roughly 280 million hemoglobin molecules. So let me write, so there's going to be 200, each of these, there's going to be 280 million of these. So 280 million, that's not, million, million hemoglobins in each one of these."}, {"video_title": "Scale of cells   Structure of a cell   Biology   Khan Academy.mp3", "Sentence": "We're seeing it directly as they emerge from this cell. But each of these red blood cells are going to contain roughly 280 million hemoglobin molecules. So let me write, so there's going to be 200, each of these, there's going to be 280 million of these. So 280 million, that's not, million, million hemoglobins in each one of these. So hopefully this starts to give you an appreciation for, even though we categorize cells as these unimaginably small things, they're actually far larger, they're ginormous compared to things even like large, even proteins, and especially when you think of things on the molecular or the atomic scale. And that's why cells are so interesting. They actually have a lot of complexity to them."}, {"video_title": "Scale of cells   Structure of a cell   Biology   Khan Academy.mp3", "Sentence": "So 280 million, that's not, million, million hemoglobins in each one of these. So hopefully this starts to give you an appreciation for, even though we categorize cells as these unimaginably small things, they're actually far larger, they're ginormous compared to things even like large, even proteins, and especially when you think of things on the molecular or the atomic scale. And that's why cells are so interesting. They actually have a lot of complexity to them. But just to have an appreciation also for how small cells are, even though we've just described these red blood cells and these T cells, there's these, you know, there's these kind of worlds unto themselves, they're these incredibly complex things. If I were to draw the width of a human hair on this screen right now, relative to the scale of these red blood cells, it would be about as wide as this video. So from, if I were to draw a human hair, it would go from there roughly to there."}, {"video_title": "Scale of cells   Structure of a cell   Biology   Khan Academy.mp3", "Sentence": "They actually have a lot of complexity to them. But just to have an appreciation also for how small cells are, even though we've just described these red blood cells and these T cells, there's these, you know, there's these kind of worlds unto themselves, they're these incredibly complex things. If I were to draw the width of a human hair on this screen right now, relative to the scale of these red blood cells, it would be about as wide as this video. So from, if I were to draw a human hair, it would go from there roughly to there. There's actually a lot of variance in the width of a human hair. But the width of a human hair would be just about like that if you looked at the scale of, if you looked at the scale of this picture right over here. If you looked at these scales, it would be much, much, much, much bigger."}, {"video_title": "Scale of cells   Structure of a cell   Biology   Khan Academy.mp3", "Sentence": "So from, if I were to draw a human hair, it would go from there roughly to there. There's actually a lot of variance in the width of a human hair. But the width of a human hair would be just about like that if you looked at the scale of, if you looked at the scale of this picture right over here. If you looked at these scales, it would be much, much, much, much bigger. And I encourage you, you know, we can think, oh, okay, width of a human hair. Pluck a hair out, look at it, put it on a piece of paper. It's hard to even discern the width, but we're saying that that width compared to these red blood cells would actually be the entire width of the screen."}, {"video_title": "Pedigree for determining probability of exhibiting sex linked recessive trait   Khan Academy (2).mp3", "Sentence": "And we see this here, the standard convention is a square is male, circle is female. If it's colored in, that means that they exhibit the trait. In this case, it's colorblindness. So Bill exhibits colorblindness. His phenotype is colorblind, while Bonnie does not exhibit colorblindness. Colorblindness is an X-linked recessive trait. If Barbara is expecting another child, so this is Barbara right here, what is the probability that it will be colorblind?"}, {"video_title": "Pedigree for determining probability of exhibiting sex linked recessive trait   Khan Academy (2).mp3", "Sentence": "So Bill exhibits colorblindness. His phenotype is colorblind, while Bonnie does not exhibit colorblindness. Colorblindness is an X-linked recessive trait. If Barbara is expecting another child, so this is Barbara right here, what is the probability that it will be colorblind? So pause this video and see if you can figure that out on your own. All right, now let's work through this together. So they're asking us about their next child here."}, {"video_title": "Pedigree for determining probability of exhibiting sex linked recessive trait   Khan Academy (2).mp3", "Sentence": "If Barbara is expecting another child, so this is Barbara right here, what is the probability that it will be colorblind? So pause this video and see if you can figure that out on your own. All right, now let's work through this together. So they're asking us about their next child here. What is the probability that it is going to be colorblind? And to help us with that, we can try to figure out the genotypes of Tom and Barbara. So Tom is pretty straightforward."}, {"video_title": "Pedigree for determining probability of exhibiting sex linked recessive trait   Khan Academy (2).mp3", "Sentence": "So they're asking us about their next child here. What is the probability that it is going to be colorblind? And to help us with that, we can try to figure out the genotypes of Tom and Barbara. So Tom is pretty straightforward. He is male, we know that because there's a square there. So X, he has an X chromosome and he has a Y chromosome. And colorblindness is an X-linked recessive trait."}, {"video_title": "Pedigree for determining probability of exhibiting sex linked recessive trait   Khan Academy (2).mp3", "Sentence": "So Tom is pretty straightforward. He is male, we know that because there's a square there. So X, he has an X chromosome and he has a Y chromosome. And colorblindness is an X-linked recessive trait. And so let me just make clear what's going on. So I'll do lowercase c for colorblind, colorblind. And I could do a capital C for the dominant trait, which is not colorblind."}, {"video_title": "Pedigree for determining probability of exhibiting sex linked recessive trait   Khan Academy (2).mp3", "Sentence": "And colorblindness is an X-linked recessive trait. And so let me just make clear what's going on. So I'll do lowercase c for colorblind, colorblind. And I could do a capital C for the dominant trait, which is not colorblind. But since they look so similar, I'll just use a plus for not colorblind, not colorblind. And so Tom, his phenotype, he is colorblind. And he only has one X chromosome where the colorblind, what the colorblind trait is linked to."}, {"video_title": "Pedigree for determining probability of exhibiting sex linked recessive trait   Khan Academy (2).mp3", "Sentence": "And I could do a capital C for the dominant trait, which is not colorblind. But since they look so similar, I'll just use a plus for not colorblind, not colorblind. And so Tom, his phenotype, he is colorblind. And he only has one X chromosome where the colorblind, what the colorblind trait is linked to. And so that must have the recessive allele right over there. So this is Tom's genotype. But what about Barbara?"}, {"video_title": "Pedigree for determining probability of exhibiting sex linked recessive trait   Khan Academy (2).mp3", "Sentence": "And he only has one X chromosome where the colorblind, what the colorblind trait is linked to. And so that must have the recessive allele right over there. So this is Tom's genotype. But what about Barbara? Well, we know Barbara's going to have two X chromosomes because Barbara is female. And we know that both of them can't be lowercase c because then Barbara would exhibit colorblindness. But how can we figure out her actual genotype?"}, {"video_title": "Pedigree for determining probability of exhibiting sex linked recessive trait   Khan Academy (2).mp3", "Sentence": "But what about Barbara? Well, we know Barbara's going to have two X chromosomes because Barbara is female. And we know that both of them can't be lowercase c because then Barbara would exhibit colorblindness. But how can we figure out her actual genotype? Well, we could look at her parents. So Bill over here is going to have the same genotype as Tom, at least with respect to colorblindness. He is male, so he has an X chromosome and a Y chromosome."}, {"video_title": "Pedigree for determining probability of exhibiting sex linked recessive trait   Khan Academy (2).mp3", "Sentence": "But how can we figure out her actual genotype? Well, we could look at her parents. So Bill over here is going to have the same genotype as Tom, at least with respect to colorblindness. He is male, so he has an X chromosome and a Y chromosome. And because he exhibits colorblindness, that X chromosome must have the recessive colorblind allele associated with it. Now Bonnie, we do not know. She will be XX, will have two X chromosomes."}, {"video_title": "Pedigree for determining probability of exhibiting sex linked recessive trait   Khan Academy (2).mp3", "Sentence": "He is male, so he has an X chromosome and a Y chromosome. And because he exhibits colorblindness, that X chromosome must have the recessive colorblind allele associated with it. Now Bonnie, we do not know. She will be XX, will have two X chromosomes. Like Barbara, we know that both of these can't have the recessive allele because then Bonnie would be filled in. She would exhibit colorblindness. But we don't know whether she is a carrier or whether she isn't."}, {"video_title": "Pedigree for determining probability of exhibiting sex linked recessive trait   Khan Academy (2).mp3", "Sentence": "She will be XX, will have two X chromosomes. Like Barbara, we know that both of these can't have the recessive allele because then Bonnie would be filled in. She would exhibit colorblindness. But we don't know whether she is a carrier or whether she isn't. But let's just think about where Barbara got her chromosomes from. One of her X chromosomes comes from her father. And the other one comes from her mother."}, {"video_title": "Pedigree for determining probability of exhibiting sex linked recessive trait   Khan Academy (2).mp3", "Sentence": "But we don't know whether she is a carrier or whether she isn't. But let's just think about where Barbara got her chromosomes from. One of her X chromosomes comes from her father. And the other one comes from her mother. So if she got this X chromosome from her father, her father only has one X chromosome to give, the one that has the colorblind allele. So if this is from her father, it must have the colorblind allele here. And we know that the one from her mother does not have the colorblind allele because if it was like this, then Barbara would be colorblind, and she isn't."}, {"video_title": "Pedigree for determining probability of exhibiting sex linked recessive trait   Khan Academy (2).mp3", "Sentence": "And the other one comes from her mother. So if she got this X chromosome from her father, her father only has one X chromosome to give, the one that has the colorblind allele. So if this is from her father, it must have the colorblind allele here. And we know that the one from her mother does not have the colorblind allele because if it was like this, then Barbara would be colorblind, and she isn't. So we know that this must be a plus here. It is the dominant non-colorblind allele. And so now we know both of their genotypes."}, {"video_title": "Pedigree for determining probability of exhibiting sex linked recessive trait   Khan Academy (2).mp3", "Sentence": "And we know that the one from her mother does not have the colorblind allele because if it was like this, then Barbara would be colorblind, and she isn't. So we know that this must be a plus here. It is the dominant non-colorblind allele. And so now we know both of their genotypes. And we can use those to then figure out the possible outcomes for their offspring. So for example, Tom can contribute a X chromosome that has a colorblind allele or a Y chromosome. And Barbara, right over here, can contribute an X chromosome that has a colorblind allele or an X chromosome that has the non-colorblind allele."}, {"video_title": "Pedigree for determining probability of exhibiting sex linked recessive trait   Khan Academy (2).mp3", "Sentence": "And so now we know both of their genotypes. And we can use those to then figure out the possible outcomes for their offspring. So for example, Tom can contribute a X chromosome that has a colorblind allele or a Y chromosome. And Barbara, right over here, can contribute an X chromosome that has a colorblind allele or an X chromosome that has the non-colorblind allele. Barbara is a carrier. And so let me just draw a little Punnett square here. And so we have four possible outcomes for their children, and they're all equally likely."}, {"video_title": "Pedigree for determining probability of exhibiting sex linked recessive trait   Khan Academy (2).mp3", "Sentence": "And Barbara, right over here, can contribute an X chromosome that has a colorblind allele or an X chromosome that has the non-colorblind allele. Barbara is a carrier. And so let me just draw a little Punnett square here. And so we have four possible outcomes for their children, and they're all equally likely. So you can get the X chromosome from Barbara that has a colorblind allele and the X chromosome from Tom that has the colorblind allele. You could have the X chromosome from Barbara with the colorblind allele and the Y chromosome from Tom. You could have the non-colorblind X chromosome, or the X chromosome that does not have the colorblind allele on it and get the colorblind X chromosome from Tom."}, {"video_title": "Pedigree for determining probability of exhibiting sex linked recessive trait   Khan Academy (2).mp3", "Sentence": "And so we have four possible outcomes for their children, and they're all equally likely. So you can get the X chromosome from Barbara that has a colorblind allele and the X chromosome from Tom that has the colorblind allele. You could have the X chromosome from Barbara with the colorblind allele and the Y chromosome from Tom. You could have the non-colorblind X chromosome, or the X chromosome that does not have the colorblind allele on it and get the colorblind X chromosome from Tom. Or you could have the non-colorblind X chromosome and the Y chromosome from the father. So there's four equal scenarios. And so in how many of these scenarios is the offspring colorblind?"}, {"video_title": "Pedigree for determining probability of exhibiting sex linked recessive trait   Khan Academy (2).mp3", "Sentence": "You could have the non-colorblind X chromosome, or the X chromosome that does not have the colorblind allele on it and get the colorblind X chromosome from Tom. Or you could have the non-colorblind X chromosome and the Y chromosome from the father. So there's four equal scenarios. And so in how many of these scenarios is the offspring colorblind? Well, here we have a colorblind female. She has two of the recessive alleles, so that female will be colorblind. This is a female carrier, but they will not show the phenotype of being colorblind."}, {"video_title": "Pedigree for determining probability of exhibiting sex linked recessive trait   Khan Academy (2).mp3", "Sentence": "And so in how many of these scenarios is the offspring colorblind? Well, here we have a colorblind female. She has two of the recessive alleles, so that female will be colorblind. This is a female carrier, but they will not show the phenotype of being colorblind. This over here is a colorblind male, has only one X chromosome, and it has the colorblind allele on it. And this is a non-colorblind male. So out of four equal outcomes, two of them have the offspring being colorblind."}, {"video_title": "Genetic drift, bottleneck effect and founder effect   Biology   Khan Academy.mp3", "Sentence": "And a lot of times you'll hear people say evolution and natural selection really in the same breath. But what we want to make a little bit clearer in this video is that natural selection is one mechanism of evolution, and it's the one most talked about because it is viewed as the primary mechanism, natural selection. But what we're gonna talk about in this video is another mechanism called genetic drift. So there's natural selection and there is genetic drift. Now we've done many videos on natural selection, but it's this idea that you have variation in a population, you have different heritable traits, I'm gonna depict those with different colors here. We have a population of living circles here, and they could come in blue or maybe magenta, maybe they come in another variation too, maybe there is yellow circles. And natural selection is all about which of these traits are most fit for the environment so that they can reproduce."}, {"video_title": "Genetic drift, bottleneck effect and founder effect   Biology   Khan Academy.mp3", "Sentence": "So there's natural selection and there is genetic drift. Now we've done many videos on natural selection, but it's this idea that you have variation in a population, you have different heritable traits, I'm gonna depict those with different colors here. We have a population of living circles here, and they could come in blue or maybe magenta, maybe they come in another variation too, maybe there is yellow circles. And natural selection is all about which of these traits are most fit for the environment so that they can reproduce. So there might be something about being, say, blue, that allows those circles to reproduce faster or to be less likely to be caught by predators or to be able to stalk prey better. And so even if they're only slightly more likely to reproduce, over time, over many generations, their numbers will increase and dominate and the other numbers are less likely, are less likely to, or the other trait is less likely to survive, and so we will have this natural selection for that blue trait. So this is all about traits being the fittest traits."}, {"video_title": "Genetic drift, bottleneck effect and founder effect   Biology   Khan Academy.mp3", "Sentence": "And natural selection is all about which of these traits are most fit for the environment so that they can reproduce. So there might be something about being, say, blue, that allows those circles to reproduce faster or to be less likely to be caught by predators or to be able to stalk prey better. And so even if they're only slightly more likely to reproduce, over time, over many generations, their numbers will increase and dominate and the other numbers are less likely, are less likely to, or the other trait is less likely to survive, and so we will have this natural selection for that blue trait. So this is all about traits being the fittest traits. Now, genetic drift is also change in heritable traits of a population over generations, but it's not about the traits that are most fit for an environment are the ones that necessarily survive. Genetic drift is really about random, random, random changes, random changes. And a good example of that I have right over here that we got from, I'll give proper credit, this is from OpenStacks College Biology, and this shows how genetic drift could happen."}, {"video_title": "Genetic drift, bottleneck effect and founder effect   Biology   Khan Academy.mp3", "Sentence": "So this is all about traits being the fittest traits. Now, genetic drift is also change in heritable traits of a population over generations, but it's not about the traits that are most fit for an environment are the ones that necessarily survive. Genetic drift is really about random, random, random changes, random changes. And a good example of that I have right over here that we got from, I'll give proper credit, this is from OpenStacks College Biology, and this shows how genetic drift could happen. So right over here, I'm showing a very small population of, we have a population of 10 rabbits and we have the gene for color and we have two versions of that gene, or we could call them two alleles. You have the capital B version and you have the lowercase b, and capital B is dominant. This is, we're just kind of a very Mendelian example that we're showing here."}, {"video_title": "Genetic drift, bottleneck effect and founder effect   Biology   Khan Academy.mp3", "Sentence": "And a good example of that I have right over here that we got from, I'll give proper credit, this is from OpenStacks College Biology, and this shows how genetic drift could happen. So right over here, I'm showing a very small population of, we have a population of 10 rabbits and we have the gene for color and we have two versions of that gene, or we could call them two alleles. You have the capital B version and you have the lowercase b, and capital B is dominant. This is, we're just kind of a very Mendelian example that we're showing here. And so if you have two lowercase, if you have two of the lowercase genes, two of the white alleles, you're going to be white. If you have two of the brown alleles, the capital Bs, you're going to be brown, and if you're a heterozygote, you're still going to be brown. So as you can see here, there are several heterozygotes in this fairly small population."}, {"video_title": "Genetic drift, bottleneck effect and founder effect   Biology   Khan Academy.mp3", "Sentence": "This is, we're just kind of a very Mendelian example that we're showing here. And so if you have two lowercase, if you have two of the lowercase genes, two of the white alleles, you're going to be white. If you have two of the brown alleles, the capital Bs, you're going to be brown, and if you're a heterozygote, you're still going to be brown. So as you can see here, there are several heterozygotes in this fairly small population. But if you just count the capital Bs versus the lowercase bs, you see that we have an equal amount of each. And so the frequency, if you were to pick a random allele from this population, you're just as likely to pick a capital B than a lowercase b. Even though the phenotype, you see a lot more brown, but these six brown here have both the uppercase B and lowercase b."}, {"video_title": "Genetic drift, bottleneck effect and founder effect   Biology   Khan Academy.mp3", "Sentence": "So as you can see here, there are several heterozygotes in this fairly small population. But if you just count the capital Bs versus the lowercase bs, you see that we have an equal amount of each. And so the frequency, if you were to pick a random allele from this population, you're just as likely to pick a capital B than a lowercase b. Even though the phenotype, you see a lot more brown, but these six brown here have both the uppercase B and lowercase b. Now let's say they're in a population where whether you're brown or whether you are white, it confers no advantage. There's no more likelihood of surviving and reproducing if you're brown than white. But just by chance, by pure random chance, the five bunnies on the top are the ones that are able to reproduce, and the five bunnies on the bottom are not the ones that are able to reproduce."}, {"video_title": "Genetic drift, bottleneck effect and founder effect   Biology   Khan Academy.mp3", "Sentence": "Even though the phenotype, you see a lot more brown, but these six brown here have both the uppercase B and lowercase b. Now let's say they're in a population where whether you're brown or whether you are white, it confers no advantage. There's no more likelihood of surviving and reproducing if you're brown than white. But just by chance, by pure random chance, the five bunnies on the top are the ones that are able to reproduce, and the five bunnies on the bottom are not the ones that are able to reproduce. And you might be saying, hey, why did I pick those top five? I didn't pick them, I'm just giving an example. It could have been the bottom five."}, {"video_title": "Genetic drift, bottleneck effect and founder effect   Biology   Khan Academy.mp3", "Sentence": "But just by chance, by pure random chance, the five bunnies on the top are the ones that are able to reproduce, and the five bunnies on the bottom are not the ones that are able to reproduce. And you might be saying, hey, why did I pick those top five? I didn't pick them, I'm just giving an example. It could have been the bottom five. It could have been only these two, or the only two white ones were the ones that were able to reproduce. It's by pure random chance, or it could be because of traits that are unrelated to the alleles that we are talking about. But from the point of view of these alleles, it looks like random chance."}, {"video_title": "Genetic drift, bottleneck effect and founder effect   Biology   Khan Academy.mp3", "Sentence": "It could have been the bottom five. It could have been only these two, or the only two white ones were the ones that were able to reproduce. It's by pure random chance, or it could be because of traits that are unrelated to the alleles that we are talking about. But from the point of view of these alleles, it looks like random chance. And so in the next generation, in the next generation, those five rabbits reproduce, and you could have a situation like this. And just by random chance, as you can see, the capital B allele frequency has increased from 50% of the alleles in the population to 70%. And then it could be another random chance."}, {"video_title": "Genetic drift, bottleneck effect and founder effect   Biology   Khan Academy.mp3", "Sentence": "But from the point of view of these alleles, it looks like random chance. And so in the next generation, in the next generation, those five rabbits reproduce, and you could have a situation like this. And just by random chance, as you can see, the capital B allele frequency has increased from 50% of the alleles in the population to 70%. And then it could be another random chance. And I'm not saying this is necessarily going to happen. It could happen the other way. It could happen even though that first randomness happened."}, {"video_title": "Genetic drift, bottleneck effect and founder effect   Biology   Khan Academy.mp3", "Sentence": "And then it could be another random chance. And I'm not saying this is necessarily going to happen. It could happen the other way. It could happen even though that first randomness happened. Maybe now all of a sudden, this white rabbit is able to reproduce a lot, but maybe not. Maybe these two brown rabbits that are homozygous for the dominant trait are able to reproduce. And once again, it has nothing to do with fitness."}, {"video_title": "Genetic drift, bottleneck effect and founder effect   Biology   Khan Academy.mp3", "Sentence": "It could happen even though that first randomness happened. Maybe now all of a sudden, this white rabbit is able to reproduce a lot, but maybe not. Maybe these two brown rabbits that are homozygous for the dominant trait are able to reproduce. And once again, it has nothing to do with fitness. And so they're able to reproduce, and then all of a sudden, the white allele has been, is completely gone from the environment. And the reason why this happened isn't because the white allele somehow makes the bunnies less fit. In fact, it might have even conferred a little bit of an advantage."}, {"video_title": "Genetic drift, bottleneck effect and founder effect   Biology   Khan Academy.mp3", "Sentence": "And once again, it has nothing to do with fitness. And so they're able to reproduce, and then all of a sudden, the white allele has been, is completely gone from the environment. And the reason why this happened isn't because the white allele somehow makes the bunnies less fit. In fact, it might have even conferred a little bit of an advantage. It might have been a, from the environment that the bunnies are in point of view, it might have even been a better trait, but because of random chance, it disappears from the population. And the general idea with the genetic drift, so once again, just to compare, natural selection, you're selecting, or the environment is selecting traits that are more favorable for reproduction, while genetic drift is random changes, random changes in reproduction of the population. Now, as you can imagine, I just gave an example with 10 bunnies."}, {"video_title": "Genetic drift, bottleneck effect and founder effect   Biology   Khan Academy.mp3", "Sentence": "In fact, it might have even conferred a little bit of an advantage. It might have been a, from the environment that the bunnies are in point of view, it might have even been a better trait, but because of random chance, it disappears from the population. And the general idea with the genetic drift, so once again, just to compare, natural selection, you're selecting, or the environment is selecting traits that are more favorable for reproduction, while genetic drift is random changes, random changes in reproduction of the population. Now, as you can imagine, I just gave an example with 10 bunnies. And what I just described is much more likely to happen with small populations. So much more likely, more likely with, with small populations. If I, and we have videos on statistics on Khan Academy, but the likelihood of this happening with 10 bunnies versus the likelihood of what I just described happening with 10 million bunnies is very different."}, {"video_title": "Genetic drift, bottleneck effect and founder effect   Biology   Khan Academy.mp3", "Sentence": "Now, as you can imagine, I just gave an example with 10 bunnies. And what I just described is much more likely to happen with small populations. So much more likely, more likely with, with small populations. If I, and we have videos on statistics on Khan Academy, but the likelihood of this happening with 10 bunnies versus the likelihood of what I just described happening with 10 million bunnies is very different. It's much more likely to happen with a small population. So a lot of the contexts of genetic drift are when people talk about small populations. In fact, many times biologists are worried about small populations, specifically because of genetic drift."}, {"video_title": "Genetic drift, bottleneck effect and founder effect   Biology   Khan Academy.mp3", "Sentence": "If I, and we have videos on statistics on Khan Academy, but the likelihood of this happening with 10 bunnies versus the likelihood of what I just described happening with 10 million bunnies is very different. It's much more likely to happen with a small population. So a lot of the contexts of genetic drift are when people talk about small populations. In fact, many times biologists are worried about small populations, specifically because of genetic drift. For random reasons, you could have less diversity, less variation in your population, and even favorable traits could be selected for by random chance. Now, there's two types of genetic drift that are often called out that cause extreme reductions in population and significantly reduce the populations. One is called the bottleneck effect."}, {"video_title": "Genetic drift, bottleneck effect and founder effect   Biology   Khan Academy.mp3", "Sentence": "In fact, many times biologists are worried about small populations, specifically because of genetic drift. For random reasons, you could have less diversity, less variation in your population, and even favorable traits could be selected for by random chance. Now, there's two types of genetic drift that are often called out that cause extreme reductions in population and significantly reduce the populations. One is called the bottleneck effect. Let me write this down. So the bottleneck, the bottleneck effect. And then the other is called the founder effect."}, {"video_title": "Genetic drift, bottleneck effect and founder effect   Biology   Khan Academy.mp3", "Sentence": "One is called the bottleneck effect. Let me write this down. So the bottleneck, the bottleneck effect. And then the other is called the founder effect. Do that over here. The founder, founder effect. And they are both, they are both ideas where you have significant reduction in population for slightly different reasons."}, {"video_title": "Genetic drift, bottleneck effect and founder effect   Biology   Khan Academy.mp3", "Sentence": "And then the other is called the founder effect. Do that over here. The founder, founder effect. And they are both, they are both ideas where you have significant reduction in population for slightly different reasons. Bottleneck effect is you have some major disaster or event that kills off a lot of the population. So only a little bit of the population is able to survive. And the reason why it's called bottleneck is imagine if you had a bottle here."}, {"video_title": "Genetic drift, bottleneck effect and founder effect   Biology   Khan Academy.mp3", "Sentence": "And they are both, they are both ideas where you have significant reduction in population for slightly different reasons. Bottleneck effect is you have some major disaster or event that kills off a lot of the population. So only a little bit of the population is able to survive. And the reason why it's called bottleneck is imagine if you had a bottle here. If you had a bottle here, and I don't know, inside of that bottle you had marbles of different colors. So you have some yellow marbles, you have some magenta marbles, you have some, I don't know, blue marbles. These are the colors that I tend to be using."}, {"video_title": "Genetic drift, bottleneck effect and founder effect   Biology   Khan Academy.mp3", "Sentence": "And the reason why it's called bottleneck is imagine if you had a bottle here. If you had a bottle here, and I don't know, inside of that bottle you had marbles of different colors. So you have some yellow marbles, you have some magenta marbles, you have some, I don't know, blue marbles. These are the colors that I tend to be using. You have some blue marbles. So you have a lot of variation in your original population. But if you think about pouring them out of a bottle, maybe somehow there's some major disaster and only two of these survive."}, {"video_title": "Genetic drift, bottleneck effect and founder effect   Biology   Khan Academy.mp3", "Sentence": "These are the colors that I tend to be using. You have some blue marbles. So you have a lot of variation in your original population. But if you think about pouring them out of a bottle, maybe somehow there's some major disaster and only two of these survive. Or let's say only four of these survive. And so you could view that as, well what are the marbles that are getting poured out of the bottle? It's really just a metaphor."}, {"video_title": "Genetic drift, bottleneck effect and founder effect   Biology   Khan Academy.mp3", "Sentence": "But if you think about pouring them out of a bottle, maybe somehow there's some major disaster and only two of these survive. Or let's say only four of these survive. And so you could view that as, well what are the marbles that are getting poured out of the bottle? It's really just a metaphor. Obviously we're not putting populations of things in bottles. But after that disaster, only a handful survive and they might not have any traits that are in any way more desirable or more fit for the environment than everything else, but they just by random chance because of this disaster, they are the ones that survived. And so all of a sudden you have a massive reduction not only in the population, but also in the variation in that population."}, {"video_title": "Genetic drift, bottleneck effect and founder effect   Biology   Khan Academy.mp3", "Sentence": "It's really just a metaphor. Obviously we're not putting populations of things in bottles. But after that disaster, only a handful survive and they might not have any traits that are in any way more desirable or more fit for the environment than everything else, but they just by random chance because of this disaster, they are the ones that survived. And so all of a sudden you have a massive reduction not only in the population, but also in the variation in that population. And many alleles might have even disappeared and so you have an extreme form of genetic drift actually occurring. Another example is founder effect. Which is the same idea of a population becoming very small, but the founder effect isn't because of a natural disaster."}, {"video_title": "Genetic drift, bottleneck effect and founder effect   Biology   Khan Academy.mp3", "Sentence": "And so all of a sudden you have a massive reduction not only in the population, but also in the variation in that population. And many alleles might have even disappeared and so you have an extreme form of genetic drift actually occurring. Another example is founder effect. Which is the same idea of a population becoming very small, but the founder effect isn't because of a natural disaster. It's let's say you had a population once again. You have a lot of different alleles in that population. You have a lot of variation."}, {"video_title": "Genetic drift, bottleneck effect and founder effect   Biology   Khan Academy.mp3", "Sentence": "Which is the same idea of a population becoming very small, but the founder effect isn't because of a natural disaster. It's let's say you had a population once again. You have a lot of different alleles in that population. You have a lot of variation. You have a lot of variation in that population. Let me just keep coloring it. You have a lot of variation in this population."}, {"video_title": "Genetic drift, bottleneck effect and founder effect   Biology   Khan Academy.mp3", "Sentence": "You have a lot of variation. You have a lot of variation in that population. Let me just keep coloring it. You have a lot of variation in this population. And let's say that they're all hanging out in their region and maybe they are surrounded by mountains. I'm just making this up as I go. But let's say a couple of these blue characters were out walking one day and they maybe get separated from the rest of their population."}, {"video_title": "Genetic drift, bottleneck effect and founder effect   Biology   Khan Academy.mp3", "Sentence": "You have a lot of variation in this population. And let's say that they're all hanging out in their region and maybe they are surrounded by mountains. I'm just making this up as I go. But let's say a couple of these blue characters were out walking one day and they maybe get separated from the rest of their population. Maybe they discover a little undiscovered mountain pass and they go settle a new population someplace. So that's why it's called the founder effect. These are the founders of a new population."}, {"video_title": "Genetic drift, bottleneck effect and founder effect   Biology   Khan Academy.mp3", "Sentence": "But let's say a couple of these blue characters were out walking one day and they maybe get separated from the rest of their population. Maybe they discover a little undiscovered mountain pass and they go settle a new population someplace. So that's why it's called the founder effect. These are the founders of a new population. And once again, by random chance, they just have a lot less variation. They're a smaller population and they happen to be disproportionately or all blue in this case. And so now this population is going to, one, a few you might have already had, just the process of this was genetic drift where you have many alleles will have disappeared because you have such a small population of blues here."}, {"video_title": "Genetic drift, bottleneck effect and founder effect   Biology   Khan Academy.mp3", "Sentence": "These are the founders of a new population. And once again, by random chance, they just have a lot less variation. They're a smaller population and they happen to be disproportionately or all blue in this case. And so now this population is going to, one, a few you might have already had, just the process of this was genetic drift where you have many alleles will have disappeared because you have such a small population of blues here. And also because you have a small population, you're likely to have even more genetic drift. So it's a really interesting thing to think about. Evolution and natural selection are often talked about hand in hand, but natural selection isn't the only mechanism of evolution."}, {"video_title": "Conceptual overview of light dependent reactions.mp3", "Sentence": "We've seen in previous videos that photosynthesis can be broken down into the light-dependent reactions and the Calvin Cycle. And the light-dependent reactions is where we take light as an input along with water, and we'll see the water is actually a source of electrons, and we can use that to store energy in the form of ATP and NADPH, and as a byproduct, we produce molecular oxygen, which is very important for us to breathe. And then that ATP and that NADPH can be used in the Calvin Cycle along with carbon dioxide to actually synthesize sugar. What we're gonna focus on in this video are the light-dependent reactions. How does this process right here work? And to help us think about this, we are going to zoom in onto a thylakoid membrane. So this is a thylakoid right over here sitting inside of the chloroplast."}, {"video_title": "Conceptual overview of light dependent reactions.mp3", "Sentence": "What we're gonna focus on in this video are the light-dependent reactions. How does this process right here work? And to help us think about this, we are going to zoom in onto a thylakoid membrane. So this is a thylakoid right over here sitting inside of the chloroplast. And if we zoom in on its membrane, we see it's a phospholipid bilayer, like many membranes that we see in biology. And at first glance, this might seem like a very complex diagram, and that's because it is a complex diagram, and you will often see things like this in your biology textbooks, and it can be very intimidating. These proteins and molecules and complexes have very complicated-sounding names, but the general idea of what's going on is you'll hopefully find pretty straightforward."}, {"video_title": "Conceptual overview of light dependent reactions.mp3", "Sentence": "So this is a thylakoid right over here sitting inside of the chloroplast. And if we zoom in on its membrane, we see it's a phospholipid bilayer, like many membranes that we see in biology. And at first glance, this might seem like a very complex diagram, and that's because it is a complex diagram, and you will often see things like this in your biology textbooks, and it can be very intimidating. These proteins and molecules and complexes have very complicated-sounding names, but the general idea of what's going on is you'll hopefully find pretty straightforward. You have the energy from light, photons from light, are going to either directly or indirectly excite electrons. Those excited electrons, they're in a high-energy state, they're going to be transferred from one molecule to another, and they're going to go to lower-energy states. That's what allows those transfers to be spontaneous, for them to actually occur."}, {"video_title": "Conceptual overview of light dependent reactions.mp3", "Sentence": "These proteins and molecules and complexes have very complicated-sounding names, but the general idea of what's going on is you'll hopefully find pretty straightforward. You have the energy from light, photons from light, are going to either directly or indirectly excite electrons. Those excited electrons, they're in a high-energy state, they're going to be transferred from one molecule to another, and they're going to go to lower-energy states. That's what allows those transfers to be spontaneous, for them to actually occur. They're going from a high-energy state to a lower-energy state. The electrons are getting more and more and more comfortable, and some of that energy that's released as the electron goes from a high-energy state to a lower-energy state is used to pump hydrogen ions, hydrogen ions across the membrane, from the outside of the membrane in the stroma to the inside of the membrane, to within the thylakoid lumen. So you are building, so you're building a hydrogen ion concentration gradient, concentration, concentration gradient, where you have a higher concentration inside than you have outside."}, {"video_title": "Conceptual overview of light dependent reactions.mp3", "Sentence": "That's what allows those transfers to be spontaneous, for them to actually occur. They're going from a high-energy state to a lower-energy state. The electrons are getting more and more and more comfortable, and some of that energy that's released as the electron goes from a high-energy state to a lower-energy state is used to pump hydrogen ions, hydrogen ions across the membrane, from the outside of the membrane in the stroma to the inside of the membrane, to within the thylakoid lumen. So you are building, so you're building a hydrogen ion concentration gradient, concentration, concentration gradient, where you have a higher concentration inside than you have outside. And this by itself, this concentration gradient, as we'll see, can be used to fuel the production of ATP by ATP synthase, that those hydrogen ions want to get back out. They want to go down their concentration gradient, and as they go back out through the ATP synthase, it essentially turns that motor that can jam the phosphate group onto ADP to produce ATP. So one way to think about it, this is producing a hydrogen ion gradient, so we could do it this way."}, {"video_title": "Conceptual overview of light dependent reactions.mp3", "Sentence": "So you are building, so you're building a hydrogen ion concentration gradient, concentration, concentration gradient, where you have a higher concentration inside than you have outside. And this by itself, this concentration gradient, as we'll see, can be used to fuel the production of ATP by ATP synthase, that those hydrogen ions want to get back out. They want to go down their concentration gradient, and as they go back out through the ATP synthase, it essentially turns that motor that can jam the phosphate group onto ADP to produce ATP. So one way to think about it, this is producing a hydrogen ion gradient, so we could do it this way. We could say H plus gradient, which is then being used to produce the actual ATP. Now, the electrons going from a high-energy state to a lower-energy state in this part of the light-dependent reactions, that by itself isn't the only thing that is contributing to the hydrogen ion concentration gradient. Once that electron gets donated, you might say, well, how does it get replaced?"}, {"video_title": "Conceptual overview of light dependent reactions.mp3", "Sentence": "So one way to think about it, this is producing a hydrogen ion gradient, so we could do it this way. We could say H plus gradient, which is then being used to produce the actual ATP. Now, the electrons going from a high-energy state to a lower-energy state in this part of the light-dependent reactions, that by itself isn't the only thing that is contributing to the hydrogen ion concentration gradient. Once that electron gets donated, you might say, well, how does it get replaced? Well, the thing that's doing the donating, the thing that eventually gets excited and donates that electron, it's a chlorophyll A variation called P680. P680 is referring to, the P stands for pigment, 680 stands for 680 nanometers, the wavelength of light that it absorbs best. And so when it gets excited, it becomes, you'll see the notation often of P680 star."}, {"video_title": "Conceptual overview of light dependent reactions.mp3", "Sentence": "Once that electron gets donated, you might say, well, how does it get replaced? Well, the thing that's doing the donating, the thing that eventually gets excited and donates that electron, it's a chlorophyll A variation called P680. P680 is referring to, the P stands for pigment, 680 stands for 680 nanometers, the wavelength of light that it absorbs best. And so when it gets excited, it becomes, you'll see the notation often of P680 star. That's when it has an excited electron. And then after it gives away its electron, it becomes P680, P680 with a positive charge. And this P680, we could call it P680 plus right over here, or maybe a P680 ion, this is actually a very strong oxidizing agent."}, {"video_title": "Conceptual overview of light dependent reactions.mp3", "Sentence": "And so when it gets excited, it becomes, you'll see the notation often of P680 star. That's when it has an excited electron. And then after it gives away its electron, it becomes P680, P680 with a positive charge. And this P680, we could call it P680 plus right over here, or maybe a P680 ion, this is actually a very strong oxidizing agent. One of the strongest, if not the strongest, that we know in biological systems. And so it really likes to grab electrons from other things. And the thing that is around that it can grab electrons from is actually water."}, {"video_title": "Conceptual overview of light dependent reactions.mp3", "Sentence": "And this P680, we could call it P680 plus right over here, or maybe a P680 ion, this is actually a very strong oxidizing agent. One of the strongest, if not the strongest, that we know in biological systems. And so it really likes to grab electrons from other things. And the thing that is around that it can grab electrons from is actually water. And so this is such a strong oxidizing agent that it can essentially oxidize the oxygen in water. And oxygen is itself, I mean, oxidizing is named after oxygen because oxygen is such a strong, it's so electronegative, it's such a strong, it's the thing that's normally doing the oxidizing. So anyway, it grabs its electrons, once it gets this P680 plus, grabs an electron from water."}, {"video_title": "Conceptual overview of light dependent reactions.mp3", "Sentence": "And the thing that is around that it can grab electrons from is actually water. And so this is such a strong oxidizing agent that it can essentially oxidize the oxygen in water. And oxygen is itself, I mean, oxidizing is named after oxygen because oxygen is such a strong, it's so electronegative, it's such a strong, it's the thing that's normally doing the oxidizing. So anyway, it grabs its electrons, once it gets this P680 plus, grabs an electron from water. And then the water essentially falls apart. So you're left just with the oxygen and then the hydrogen ions. And so those hydrogen ions also contribute, those hydrogen ions also contribute to the increased hydrogen ion concentration on the inside."}, {"video_title": "Conceptual overview of light dependent reactions.mp3", "Sentence": "So anyway, it grabs its electrons, once it gets this P680 plus, grabs an electron from water. And then the water essentially falls apart. So you're left just with the oxygen and then the hydrogen ions. And so those hydrogen ions also contribute, those hydrogen ions also contribute to the increased hydrogen ion concentration on the inside. And this is where we get, this is where we get the oxygen byproduct right over here. Here we have one half of an O2, so if you do this twice, you're going to have a molecular oxygen. So so far, we've talked about how the oxygen gets produced, we've talked about how the ATP gets produced, what about the NADPH?"}, {"video_title": "Conceptual overview of light dependent reactions.mp3", "Sentence": "And so those hydrogen ions also contribute, those hydrogen ions also contribute to the increased hydrogen ion concentration on the inside. And this is where we get, this is where we get the oxygen byproduct right over here. Here we have one half of an O2, so if you do this twice, you're going to have a molecular oxygen. So so far, we've talked about how the oxygen gets produced, we've talked about how the ATP gets produced, what about the NADPH? Well, we started our process in photosystem II. You might say, why is it called photosystem II if that's where we start? Well, it's actually that's because that's the second photosystem to be discovered."}, {"video_title": "Conceptual overview of light dependent reactions.mp3", "Sentence": "So so far, we've talked about how the oxygen gets produced, we've talked about how the ATP gets produced, what about the NADPH? Well, we started our process in photosystem II. You might say, why is it called photosystem II if that's where we start? Well, it's actually that's because that's the second photosystem to be discovered. You might say, what is a photosystem? Well, these photosystems and complexes, they're combinations of proteins and molecules. And photosystem in particular has chlorophyll and variations of chlorophyll and pigment molecules that are responsive to light, that are very easy, that have electrons that can get excited by light."}, {"video_title": "Conceptual overview of light dependent reactions.mp3", "Sentence": "Well, it's actually that's because that's the second photosystem to be discovered. You might say, what is a photosystem? Well, these photosystems and complexes, they're combinations of proteins and molecules. And photosystem in particular has chlorophyll and variations of chlorophyll and pigment molecules that are responsive to light, that are very easy, that have electrons that can get excited by light. And they can transfer that energy back down to the P680 chlorophyll A pair, which then can have its electron excited, and then it can give that to an acceptor molecule, and then it can go to lower, lower energy states and pump those hydrogen ions out. But that's not the entire light-dependent reactions. That electron can eventually make its way over to photosystem I, and why is it called photosystem I?"}, {"video_title": "Conceptual overview of light dependent reactions.mp3", "Sentence": "And photosystem in particular has chlorophyll and variations of chlorophyll and pigment molecules that are responsive to light, that are very easy, that have electrons that can get excited by light. And they can transfer that energy back down to the P680 chlorophyll A pair, which then can have its electron excited, and then it can give that to an acceptor molecule, and then it can go to lower, lower energy states and pump those hydrogen ions out. But that's not the entire light-dependent reactions. That electron can eventually make its way over to photosystem I, and why is it called photosystem I? Well, it's because the first one that was discovered. In photosystem I, there's another chlorophyll A pair called P700, and that's because it optimally absorbs light of a wavelength of 700 nanometers. And you have something similar that happens, that light can either directly or indirectly excite its electron, and then that electron, as it goes to a lower energy level, it goes from one molecule to another, it can be used to reduce NAD plus into NADPH."}, {"video_title": "Conceptual overview of light dependent reactions.mp3", "Sentence": "That electron can eventually make its way over to photosystem I, and why is it called photosystem I? Well, it's because the first one that was discovered. In photosystem I, there's another chlorophyll A pair called P700, and that's because it optimally absorbs light of a wavelength of 700 nanometers. And you have something similar that happens, that light can either directly or indirectly excite its electron, and then that electron, as it goes to a lower energy level, it goes from one molecule to another, it can be used to reduce NAD plus into NADPH. And so that's where the NADPH comes from. And then once again, once the P700 has given its electron, it wants an electron, and well, it can get that from the electron that's been going from lower to lower and lower energy states that's essentially been making its way from, you can conceptualize it as the electron that's been making its way from photosystem II. And so that's why you'll often see these diagrams."}, {"video_title": "Conceptual overview of light dependent reactions.mp3", "Sentence": "And you have something similar that happens, that light can either directly or indirectly excite its electron, and then that electron, as it goes to a lower energy level, it goes from one molecule to another, it can be used to reduce NAD plus into NADPH. And so that's where the NADPH comes from. And then once again, once the P700 has given its electron, it wants an electron, and well, it can get that from the electron that's been going from lower to lower and lower energy states that's essentially been making its way from, you can conceptualize it as the electron that's been making its way from photosystem II. And so that's why you'll often see these diagrams. Lights come in, electron gets excited, it goes to lower and lower energy states. As it's doing that, it's being transferred from one molecule to another, being facilitated by enzymes. That energy, part of that energy is being used to transfer hydrogen ions into the thylakoid lumen, into the interior."}, {"video_title": "Conceptual overview of light dependent reactions.mp3", "Sentence": "And so that's why you'll often see these diagrams. Lights come in, electron gets excited, it goes to lower and lower energy states. As it's doing that, it's being transferred from one molecule to another, being facilitated by enzymes. That energy, part of that energy is being used to transfer hydrogen ions into the thylakoid lumen, into the interior. Then in photosystem I, you have another excitation event. That thing that got excited can grab that electron that went to lower and lower energy states, and its excited electron can once again be transferred from one molecule to another in order to fuel or provide the energy for NADP plus being converted into NADPH. And once again, the whole idea of the hydrogen ion concentration increasing here can fuel ATP synthase, which allows us to jam a phosphate onto ADP to produce ATP."}, {"video_title": "Conceptual overview of light dependent reactions.mp3", "Sentence": "That energy, part of that energy is being used to transfer hydrogen ions into the thylakoid lumen, into the interior. Then in photosystem I, you have another excitation event. That thing that got excited can grab that electron that went to lower and lower energy states, and its excited electron can once again be transferred from one molecule to another in order to fuel or provide the energy for NADP plus being converted into NADPH. And once again, the whole idea of the hydrogen ion concentration increasing here can fuel ATP synthase, which allows us to jam a phosphate onto ADP to produce ATP. So that is where we actually get all of these things, and the byproduct, of course, is our oxygen. And if you wanted to see that same idea, but kind of just thinking from an energetic point of view, without all the complexity of seeing the physical components involved, you see it right over here, where you have light energy comes, excites the electrons. Once the P680 has given that electron away, it wants an electron really badly."}, {"video_title": "Conceptual overview of light dependent reactions.mp3", "Sentence": "And once again, the whole idea of the hydrogen ion concentration increasing here can fuel ATP synthase, which allows us to jam a phosphate onto ADP to produce ATP. So that is where we actually get all of these things, and the byproduct, of course, is our oxygen. And if you wanted to see that same idea, but kind of just thinking from an energetic point of view, without all the complexity of seeing the physical components involved, you see it right over here, where you have light energy comes, excites the electrons. Once the P680 has given that electron away, it wants an electron really badly. It gets it from the water. And then as that electron goes to lower and lower and lower energy states, it can eventually be grabbed by P700 that has given away its an electron. And then that electron that was excited at P700 by once again more light energy, that can be transferred from one molecule to another to fuel the creation of NADPH."}, {"video_title": "Polymerase chain reaction (PCR)   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "Why have you done PCR? PCR was kind of the mainstay of my graduate project, where I built all sorts of different recombinant DNA molecules, and used them to learn things about plants. And so what does PCR in particular do? PCR basically makes you a lot of copies of a particular fragment of DNA that you're interested in. And so how does that, like why would you need to make a lot of copies of a particular fragment of DNA? So you might want to be making lots of copies so that you can clone it into a plasmid, and then do some other experiments with it. That's a big use."}, {"video_title": "Polymerase chain reaction (PCR)   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "PCR basically makes you a lot of copies of a particular fragment of DNA that you're interested in. And so how does that, like why would you need to make a lot of copies of a particular fragment of DNA? So you might want to be making lots of copies so that you can clone it into a plasmid, and then do some other experiments with it. That's a big use. So when we talked about cloning, and we're talking about sticking a fragment of DNA inside of a plasmid, it's not like you're just sticking one fragment into one plasmid. You're doing that with many, so you need a lot of fragments of DNA. Exactly, that is exactly it."}, {"video_title": "Polymerase chain reaction (PCR)   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "That's a big use. So when we talked about cloning, and we're talking about sticking a fragment of DNA inside of a plasmid, it's not like you're just sticking one fragment into one plasmid. You're doing that with many, so you need a lot of fragments of DNA. Exactly, that is exactly it. And you might start with a very small sample of DNA. And so you just really need to, where else would you have to do PCR? PCR is used a lot in forensics."}, {"video_title": "Polymerase chain reaction (PCR)   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "Exactly, that is exactly it. And you might start with a very small sample of DNA. And so you just really need to, where else would you have to do PCR? PCR is used a lot in forensics. It's also used a lot in medical diagnostics. So this could actually be your DNA that was being checked to see if you have a gene that would predispose you to a particular condition. All sorts of really practical applications."}, {"video_title": "Polymerase chain reaction (PCR)   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "PCR is used a lot in forensics. It's also used a lot in medical diagnostics. So this could actually be your DNA that was being checked to see if you have a gene that would predispose you to a particular condition. All sorts of really practical applications. Because it's hard to identify just one, one fragment of that gene. So you'd want to make copies, or as they say, amplify it, so that you could run it in gels and stuff and see how all of those molecules, how big they are or something like that. Exactly, if you were just looking in your DNA pulled out of your cell, that would be a needle in a haystack."}, {"video_title": "Polymerase chain reaction (PCR)   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "All sorts of really practical applications. Because it's hard to identify just one, one fragment of that gene. So you'd want to make copies, or as they say, amplify it, so that you could run it in gels and stuff and see how all of those molecules, how big they are or something like that. Exactly, if you were just looking in your DNA pulled out of your cell, that would be a needle in a haystack. So this is how you can really zoom in and look at just the thing you need to see. Okay, so you've drawn some diagrams here, and I actually have never done a PCR, but you have, so I'm going to tell you how I understand it happening, and then you tell me if this makes sense. So what you drew over here, this is double-stranded DNA, and this could have been from a sample of someone's hair or whatever else."}, {"video_title": "Polymerase chain reaction (PCR)   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "Exactly, if you were just looking in your DNA pulled out of your cell, that would be a needle in a haystack. So this is how you can really zoom in and look at just the thing you need to see. Okay, so you've drawn some diagrams here, and I actually have never done a PCR, but you have, so I'm going to tell you how I understand it happening, and then you tell me if this makes sense. So what you drew over here, this is double-stranded DNA, and this could have been from a sample of someone's hair or whatever else. And let's say we want to replicate or make many, many copies of a fragment of this. And so let's say the fragment that we really care about is the fragment roughly from there to there, this part, is what we want to make, we want to make multiple copies of. And so this first step, denaturation, I have trouble pronouncing things."}, {"video_title": "Polymerase chain reaction (PCR)   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "So what you drew over here, this is double-stranded DNA, and this could have been from a sample of someone's hair or whatever else. And let's say we want to replicate or make many, many copies of a fragment of this. And so let's say the fragment that we really care about is the fragment roughly from there to there, this part, is what we want to make, we want to make multiple copies of. And so this first step, denaturation, I have trouble pronouncing things. It's a weird word. It's a weird word. You have 96 degrees Celsius, so this is almost at the boiling point, so it's quite hot, and that separates the two strands."}, {"video_title": "Polymerase chain reaction (PCR)   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "And so this first step, denaturation, I have trouble pronouncing things. It's a weird word. It's a weird word. You have 96 degrees Celsius, so this is almost at the boiling point, so it's quite hot, and that separates the two strands. Precisely. And so once they're separated, then you can cool things down, although this still isn't that cool, 55 degrees Celsius would be very uncomfortable. But you would cool it down to this, and then these primers show up."}, {"video_title": "Polymerase chain reaction (PCR)   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "You have 96 degrees Celsius, so this is almost at the boiling point, so it's quite hot, and that separates the two strands. Precisely. And so once they're separated, then you can cool things down, although this still isn't that cool, 55 degrees Celsius would be very uncomfortable. But you would cool it down to this, and then these primers show up. And so one thing to remind ourselves is this process is happening inside of a test tube or in a big solution. So you heat it up, the DNA, the two strands separate, and do you just have this primer lying around? So the primer is something that you've ordered from a company and you've ordered a lot of it."}, {"video_title": "Polymerase chain reaction (PCR)   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "But you would cool it down to this, and then these primers show up. And so one thing to remind ourselves is this process is happening inside of a test tube or in a big solution. So you heat it up, the DNA, the two strands separate, and do you just have this primer lying around? So the primer is something that you've ordered from a company and you've ordered a lot of it. So you put in a ton of primer in your reaction so that there's a really good chance that when you get to this step here called annealing, that a primer is going to bind to many of your pieces of DNA. So this is our solution. Is this all happening in water?"}, {"video_title": "Polymerase chain reaction (PCR)   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "So the primer is something that you've ordered from a company and you've ordered a lot of it. So you put in a ton of primer in your reaction so that there's a really good chance that when you get to this step here called annealing, that a primer is going to bind to many of your pieces of DNA. So this is our solution. Is this all happening in water? Water with some salts and stuff floating around, yeah. Okay, so we have our solution right over here. You'd put whatever your initial DNA sample is in there, and once again, it's a very small amount."}, {"video_title": "Polymerase chain reaction (PCR)   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "Is this all happening in water? Water with some salts and stuff floating around, yeah. Okay, so we have our solution right over here. You'd put whatever your initial DNA sample is in there, and once again, it's a very small amount. You'd put a lot of that primer, so you'd want to put that in a lot of surplus. Let me do that in this magenta color. You obviously wouldn't see it in real life."}, {"video_title": "Polymerase chain reaction (PCR)   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "You'd put whatever your initial DNA sample is in there, and once again, it's a very small amount. You'd put a lot of that primer, so you'd want to put that in a lot of surplus. Let me do that in this magenta color. You obviously wouldn't see it in real life. It would just all dissolve. It would just look like a drop of liquid. It would look like, but for visualization, you put a lot of primer, and so you heat it up, the DNA strands separate, and then when you cool it back down, this primer's going to be specific to the ends of the region that you want to copy."}, {"video_title": "Polymerase chain reaction (PCR)   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "You obviously wouldn't see it in real life. It would just all dissolve. It would just look like a drop of liquid. It would look like, but for visualization, you put a lot of primer, and so you heat it up, the DNA strands separate, and then when you cool it back down, this primer's going to be specific to the ends of the region that you want to copy. Exactly. And so when you order online or wherever that you want a certain primer, you're going to pick the sequence of that primer to be specific to the regions you want to copy. Exactly, that's super important."}, {"video_title": "Polymerase chain reaction (PCR)   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "It would look like, but for visualization, you put a lot of primer, and so you heat it up, the DNA strands separate, and then when you cool it back down, this primer's going to be specific to the ends of the region that you want to copy. Exactly. And so when you order online or wherever that you want a certain primer, you're going to pick the sequence of that primer to be specific to the regions you want to copy. Exactly, that's super important. Okay, and so when you cool it back down, the primer attaches, and then you heat it back up, not quite to the 96 degrees Celsius, but to the 72 degrees Celsius, where you extend those, and I'm assuming since it's called polymerase chain reaction, that this is where the polymerase is involved. That is exactly where the polymerase comes in. So the polymerase is what is actually extending this, and is it, so I'll just draw a polymerase enzyme right over there doing the extending, and is it any type of polymerase enzyme?"}, {"video_title": "Polymerase chain reaction (PCR)   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "Exactly, that's super important. Okay, and so when you cool it back down, the primer attaches, and then you heat it back up, not quite to the 96 degrees Celsius, but to the 72 degrees Celsius, where you extend those, and I'm assuming since it's called polymerase chain reaction, that this is where the polymerase is involved. That is exactly where the polymerase comes in. So the polymerase is what is actually extending this, and is it, so I'll just draw a polymerase enzyme right over there doing the extending, and is it any type of polymerase enzyme? Could I just take the polymerase from my cells and throw it in there? So you actually need a special polymerase because you need one that is going to be pretty heat resistant. So as you were mentioning, even the cool step of this process is not something that your body would want to be hanging out in."}, {"video_title": "Polymerase chain reaction (PCR)   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "So the polymerase is what is actually extending this, and is it, so I'll just draw a polymerase enzyme right over there doing the extending, and is it any type of polymerase enzyme? Could I just take the polymerase from my cells and throw it in there? So you actually need a special polymerase because you need one that is going to be pretty heat resistant. So as you were mentioning, even the cool step of this process is not something that your body would want to be hanging out in. So the polymerase is actually from a really heat-tolerant microorganism. And what is that? It's called a TAC polymerase?"}, {"video_title": "Polymerase chain reaction (PCR)   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "So as you were mentioning, even the cool step of this process is not something that your body would want to be hanging out in. So the polymerase is actually from a really heat-tolerant microorganism. And what is that? It's called a TAC polymerase? Thermophilus aquaticus, I think? Makes quite a mouthful. And they found it at heated vents, this organism that is able to stand these high temperatures."}, {"video_title": "Polymerase chain reaction (PCR)   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "It's called a TAC polymerase? Thermophilus aquaticus, I think? Makes quite a mouthful. And they found it at heated vents, this organism that is able to stand these high temperatures. But that, I guess, leads to another question. Why do you have to heat it up to begin with? I guess just to separate the two strands?"}, {"video_title": "Polymerase chain reaction (PCR)   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "And they found it at heated vents, this organism that is able to stand these high temperatures. But that, I guess, leads to another question. Why do you have to heat it up to begin with? I guess just to separate the two strands? That's really the key reason. You just have to get them apart. You don't have an enzyme to do it the way you might in a cell, so heat does the trick."}, {"video_title": "Polymerase chain reaction (PCR)   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "I guess just to separate the two strands? That's really the key reason. You just have to get them apart. You don't have an enzyme to do it the way you might in a cell, so heat does the trick. Okay, so I get it. So this is one step. I'm guessing I'm getting at least the polymerase part of the PCR, where you heat it up, the strands separate, then you have all of this extra primer there."}, {"video_title": "Polymerase chain reaction (PCR)   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "You don't have an enzyme to do it the way you might in a cell, so heat does the trick. Okay, so I get it. So this is one step. I'm guessing I'm getting at least the polymerase part of the PCR, where you heat it up, the strands separate, then you have all of this extra primer there. The primer, because there's so much primer, the primer's much more likely to bind to at least at this part of the sequence than for these two strands to get back together at this point. And then you have the polymerase, the TAC polymerase in particular. And you would have added that at the beginning, you know, the TAC polymerase."}, {"video_title": "Polymerase chain reaction (PCR)   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "I'm guessing I'm getting at least the polymerase part of the PCR, where you heat it up, the strands separate, then you have all of this extra primer there. The primer, because there's so much primer, the primer's much more likely to bind to at least at this part of the sequence than for these two strands to get back together at this point. And then you have the polymerase, the TAC polymerase in particular. And you would have added that at the beginning, you know, the TAC polymerase. I guess I'll put it in this, I'll do it in a yellow color. So you would also put all that TAC polymerase in there. And once again, these things aren't robots."}, {"video_title": "Polymerase chain reaction (PCR)   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "And you would have added that at the beginning, you know, the TAC polymerase. I guess I'll put it in this, I'll do it in a yellow color. So you would also put all that TAC polymerase in there. And once again, these things aren't robots. They don't know exactly what they need to do. They just bump into things in the right way and react in the right way. And then you would also have to add a bunch of nucleotides."}, {"video_title": "Polymerase chain reaction (PCR)   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "And once again, these things aren't robots. They don't know exactly what they need to do. They just bump into things in the right way and react in the right way. And then you would also have to add a bunch of nucleotides. Yes, absolutely. Your reaction is not going to work if you forget the nucleotides. So the TAC polymerase, when you heat it back up again after the primers have been attached, is going to start adding all of these nucleotides."}, {"video_title": "Polymerase chain reaction (PCR)   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "And then you would also have to add a bunch of nucleotides. Yes, absolutely. Your reaction is not going to work if you forget the nucleotides. So the TAC polymerase, when you heat it back up again after the primers have been attached, is going to start adding all of these nucleotides. And what, do you just wait a certain amount of time or will it just keep going on forever? It'll keep going on for a while. Usually you do pick the length of that step to match how much time you expect the polymerase to need to complete your fragment."}, {"video_title": "Polymerase chain reaction (PCR)   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "So the TAC polymerase, when you heat it back up again after the primers have been attached, is going to start adding all of these nucleotides. And what, do you just wait a certain amount of time or will it just keep going on forever? It'll keep going on for a while. Usually you do pick the length of that step to match how much time you expect the polymerase to need to complete your fragment. But it kind of will stop, either it'll fall off or it'll stop when you go on to the next step. Okay, so this, I get this is so far. So, so far we have, after one cycle, let me, what you've written here, after one cycle we would have doubled at least that part, that part of the sequence that we care about."}, {"video_title": "Polymerase chain reaction (PCR)   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "Usually you do pick the length of that step to match how much time you expect the polymerase to need to complete your fragment. But it kind of will stop, either it'll fall off or it'll stop when you go on to the next step. Okay, so this, I get this is so far. So, so far we have, after one cycle, let me, what you've written here, after one cycle we would have doubled at least that part, that part of the sequence that we care about. Although we might even have, we might have copied even beyond that sequence. So where does the chain reaction come into this? So I guess you can interpret chain reaction in two ways."}, {"video_title": "Polymerase chain reaction (PCR)   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "So, so far we have, after one cycle, let me, what you've written here, after one cycle we would have doubled at least that part, that part of the sequence that we care about. Although we might even have, we might have copied even beyond that sequence. So where does the chain reaction come into this? So I guess you can interpret chain reaction in two ways. And one is, that's sort of what the polymerase does, is it, you know, adds things to make a chain. But there's actually even more of a chain reaction dimension here. And that's that we're actually getting this kind of exponential process going on."}, {"video_title": "Polymerase chain reaction (PCR)   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "So I guess you can interpret chain reaction in two ways. And one is, that's sort of what the polymerase does, is it, you know, adds things to make a chain. But there's actually even more of a chain reaction dimension here. And that's that we're actually getting this kind of exponential process going on. So you do it one cycle, you get to this situation right here. You heat it up, the strands separate, you cool it down, the primers attach, you heat it up again, the Taq polymerase does its job. And like all polymerase, it goes from the five prime to the three prime direction."}, {"video_title": "Polymerase chain reaction (PCR)   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "And that's that we're actually getting this kind of exponential process going on. So you do it one cycle, you get to this situation right here. You heat it up, the strands separate, you cool it down, the primers attach, you heat it up again, the Taq polymerase does its job. And like all polymerase, it goes from the five prime to the three prime direction. We talked about in that in the application. So now you have two strands. But now, since all of that stuff is in that solution, you can just keep, you can heat it up again."}, {"video_title": "Polymerase chain reaction (PCR)   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "And like all polymerase, it goes from the five prime to the three prime direction. We talked about in that in the application. So now you have two strands. But now, since all of that stuff is in that solution, you can just keep, you can heat it up again. Now each of, now these two strands can turn into, or these two, these two double strands can now turn into four single strands. Then you can cool it down again. Now they get primers attached to them."}, {"video_title": "Polymerase chain reaction (PCR)   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "But now, since all of that stuff is in that solution, you can just keep, you can heat it up again. Now each of, now these two strands can turn into, or these two, these two double strands can now turn into four single strands. Then you can cool it down again. Now they get primers attached to them. And they're still the same primer because we still care about the same sequence. And then that can keep, and so now you go from one to two to four. And so you keep repeating this."}, {"video_title": "Polymerase chain reaction (PCR)   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "Now they get primers attached to them. And they're still the same primer because we still care about the same sequence. And then that can keep, and so now you go from one to two to four. And so you keep repeating this. And so how many times would it be typical for you to repeat this cycle? So like 35 might be a pretty typical number of cycles to do. It depends a little what you're doing."}, {"video_title": "Polymerase chain reaction (PCR)   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "And so you keep repeating this. And so how many times would it be typical for you to repeat this cycle? So like 35 might be a pretty typical number of cycles to do. It depends a little what you're doing. But you're gonna do it a lot of times. And so if you do this 35 times, I mean each time you're multiplying by two. So it's gonna be two to the 35th power, which is well over a billion times."}, {"video_title": "Polymerase chain reaction (PCR)   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "It depends a little what you're doing. But you're gonna do it a lot of times. And so if you do this 35 times, I mean each time you're multiplying by two. So it's gonna be two to the 35th power, which is well over a billion times. So, and how long would that take? You've done this before. Um, depends on the length of your fragment, but usually like two to three hours."}, {"video_title": "Polymerase chain reaction (PCR)   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "So it's gonna be two to the 35th power, which is well over a billion times. So, and how long would that take? You've done this before. Um, depends on the length of your fragment, but usually like two to three hours. So in two to three hours, you can start with one fragment and get into the billions. If it's perfectly efficient, which I wish it always were, but you usually get quite a few pieces made. And one thing that I was, that I've always wondered when I first learned about this, and I'd like to go into a lab and do this with you, is, is, okay, I get that you have your primer and then the, and then the, the polymerase is just going to extend it like that."}, {"video_title": "Polymerase chain reaction (PCR)   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "Um, depends on the length of your fragment, but usually like two to three hours. So in two to three hours, you can start with one fragment and get into the billions. If it's perfectly efficient, which I wish it always were, but you usually get quite a few pieces made. And one thing that I was, that I've always wondered when I first learned about this, and I'd like to go into a lab and do this with you, is, is, okay, I get that you have your primer and then the, and then the, the polymerase is just going to extend it like that. But I was like, well, it's, you know, it's going to be, how does it know where to stop? And you explained, well, on that first pass, it might not know where to stop. But then when you start going in the other direction, it's going to, so over here, and when it goes in the other direction, it's gonna hit a, it's going to hit a, it's not going to have anything else to copy."}, {"video_title": "Polymerase chain reaction (PCR)   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "And one thing that I was, that I've always wondered when I first learned about this, and I'd like to go into a lab and do this with you, is, is, okay, I get that you have your primer and then the, and then the, the polymerase is just going to extend it like that. But I was like, well, it's, you know, it's going to be, how does it know where to stop? And you explained, well, on that first pass, it might not know where to stop. But then when you start going in the other direction, it's going to, so over here, and when it goes in the other direction, it's gonna hit a, it's going to hit a, it's not going to have anything else to copy. Exactly. And so then you're, so most of the, of the billions of molecules that you produce are going to be both ends, kind of a nice clean cut. The vast, vast majority, exactly."}, {"video_title": "ATP synthase   Cellular energetics   AP Biology   Khan Academy.mp3", "Sentence": "And you might be able to predict from its name what it does. It synthesizes ATP. Now you've probably seen it before. We saw it when we looked at respiration, or you will see it when you look at respiration, which is going on in most of the cells of your body. And you also see it when you study photosynthesis. The general thing that it does is, is it sits across a phospholipid membrane, and through other processes, you will have hydrogen ion concentration increase on one side of the membrane, have a higher hydrogen ion concentration on one side than on the other side. You still might have a few over here."}, {"video_title": "ATP synthase   Cellular energetics   AP Biology   Khan Academy.mp3", "Sentence": "We saw it when we looked at respiration, or you will see it when you look at respiration, which is going on in most of the cells of your body. And you also see it when you study photosynthesis. The general thing that it does is, is it sits across a phospholipid membrane, and through other processes, you will have hydrogen ion concentration increase on one side of the membrane, have a higher hydrogen ion concentration on one side than on the other side. You still might have a few over here. And a hydrogen ion is essentially a proton. So on this side of the membrane, it'll be more positive, so there will be a electromotive force to go to the other side. And also, you just have a higher concentration, so there's a chemical gradient, a concentration gradient, where if there's some way for these protons to get to this side, they would wanna get there."}, {"video_title": "ATP synthase   Cellular energetics   AP Biology   Khan Academy.mp3", "Sentence": "You still might have a few over here. And a hydrogen ion is essentially a proton. So on this side of the membrane, it'll be more positive, so there will be a electromotive force to go to the other side. And also, you just have a higher concentration, so there's a chemical gradient, a concentration gradient, where if there's some way for these protons to get to this side, they would wanna get there. So there's an electrochemical gradient that they would wanna go down. And ATP synthase provides a channel for those protons. But as those protons travel through the ATP synthase, they turn this part of it, which drives this axle, and then this axle nudges these parts of the protein so that they jam together an ADP with a phosphate group to produce ATP."}, {"video_title": "ATP synthase   Cellular energetics   AP Biology   Khan Academy.mp3", "Sentence": "And also, you just have a higher concentration, so there's a chemical gradient, a concentration gradient, where if there's some way for these protons to get to this side, they would wanna get there. So there's an electrochemical gradient that they would wanna go down. And ATP synthase provides a channel for those protons. But as those protons travel through the ATP synthase, they turn this part of it, which drives this axle, and then this axle nudges these parts of the protein so that they jam together an ADP with a phosphate group to produce ATP. So down here, going into this part of the complex, you'll have an ADP and a phosphate group. And then that rotation force that's provided by that electrochemical gradient, that then produces our ATP. And that's going to be the case both in respiration, which occurs in the mitochondria, and in photosynthesis, which occur in chloroplasts."}, {"video_title": "ATP synthase   Cellular energetics   AP Biology   Khan Academy.mp3", "Sentence": "But as those protons travel through the ATP synthase, they turn this part of it, which drives this axle, and then this axle nudges these parts of the protein so that they jam together an ADP with a phosphate group to produce ATP. So down here, going into this part of the complex, you'll have an ADP and a phosphate group. And then that rotation force that's provided by that electrochemical gradient, that then produces our ATP. And that's going to be the case both in respiration, which occurs in the mitochondria, and in photosynthesis, which occur in chloroplasts. Now, there's a few differences. In mitochondria, the hydrogen ions, these protons, the concentration builds up in the intermembrane space right over here because of the electron transport change. And we studied that in other videos."}, {"video_title": "ATP synthase   Cellular energetics   AP Biology   Khan Academy.mp3", "Sentence": "And that's going to be the case both in respiration, which occurs in the mitochondria, and in photosynthesis, which occur in chloroplasts. Now, there's a few differences. In mitochondria, the hydrogen ions, these protons, the concentration builds up in the intermembrane space right over here because of the electron transport change. And we studied that in other videos. And then the protons travel through the ATP synthase. You can see a little mini version right over here. You could imagine that what we see really big, that is a blown-up version of this part of the mitochondria."}, {"video_title": "ATP synthase   Cellular energetics   AP Biology   Khan Academy.mp3", "Sentence": "And we studied that in other videos. And then the protons travel through the ATP synthase. You can see a little mini version right over here. You could imagine that what we see really big, that is a blown-up version of this part of the mitochondria. And this, of course, is not to scale. So in the case of a mitochondria, this would be the inner membrane. Right over here would be the intermembrane space between the inner and the outer membrane, intermembrane space."}, {"video_title": "ATP synthase   Cellular energetics   AP Biology   Khan Academy.mp3", "Sentence": "You could imagine that what we see really big, that is a blown-up version of this part of the mitochondria. And this, of course, is not to scale. So in the case of a mitochondria, this would be the inner membrane. Right over here would be the intermembrane space between the inner and the outer membrane, intermembrane space. And right over here would be the matrix of the mitochondria. And so as the protons go through, they're able to produce ATP in the matrix. Now, in chloroplasts, the hydrogen protons build up inside the thylakoids, which are these parts of the chloroplast."}, {"video_title": "ATP synthase   Cellular energetics   AP Biology   Khan Academy.mp3", "Sentence": "Right over here would be the intermembrane space between the inner and the outer membrane, intermembrane space. And right over here would be the matrix of the mitochondria. And so as the protons go through, they're able to produce ATP in the matrix. Now, in chloroplasts, the hydrogen protons build up inside the thylakoids, which are these parts of the chloroplast. That space inside the thylakoids, often called the thylakoid space, sometimes called the lumen, that proton buildup inside the thylakoids happens because of the light reactions, the first phase of photosynthesis. But then those protons will travel through the thylakoid membrane to this area, which is known as the stroma in chloroplasts, and they produce the ATP in the stroma. But then the ATP is used in the second phase of photosynthesis to synthesize carbohydrates, which is, you could use one of the end products of photosynthesis."}, {"video_title": "ATP synthase   Cellular energetics   AP Biology   Khan Academy.mp3", "Sentence": "Now, in chloroplasts, the hydrogen protons build up inside the thylakoids, which are these parts of the chloroplast. That space inside the thylakoids, often called the thylakoid space, sometimes called the lumen, that proton buildup inside the thylakoids happens because of the light reactions, the first phase of photosynthesis. But then those protons will travel through the thylakoid membrane to this area, which is known as the stroma in chloroplasts, and they produce the ATP in the stroma. But then the ATP is used in the second phase of photosynthesis to synthesize carbohydrates, which is, you could use one of the end products of photosynthesis. So the big takeaway of this video is, one, ATP synthase is incredibly cool. If you look up on the internet, you can find some simulations that show ATP synthase and how it acts like a motor to jam the phosphate group to the ADP to produce ATP. And ATP synthase in mitochondria and chloroplasts are remarkably similar, although they sit in different parts of these organelles."}, {"video_title": "Exocytosis   Membranes and transport   Biology   Khan Academy.mp3", "Sentence": "And to understand how this works, it's really the reverse of endocytosis, we're going to go and produce some proteins in the endoplasmic reticulum. This is our classic example. Those proteins are then going to bud off in their own little vesicles, which then merge with the Golgi apparatus, where they are further processed. So they're processed in the Golgi apparatus right over here. And then eventually they're going to bud off of the Golgi apparatus in new vesicles, and those vesicles are going to make their way over to the cell's outer membrane, the plasma membrane, and the membranes of the vesicles are going to merge with the membrane of the cell, and in doing so, they're going to release their contents. And this is classic exocytosis. There are other cases where maybe it merges partially, releases the contents, and then buds back."}, {"video_title": "Exocytosis   Membranes and transport   Biology   Khan Academy.mp3", "Sentence": "So they're processed in the Golgi apparatus right over here. And then eventually they're going to bud off of the Golgi apparatus in new vesicles, and those vesicles are going to make their way over to the cell's outer membrane, the plasma membrane, and the membranes of the vesicles are going to merge with the membrane of the cell, and in doing so, they're going to release their contents. And this is classic exocytosis. There are other cases where maybe it merges partially, releases the contents, and then buds back. It's called the kiss-and-run method of exocytosis, but the classic one is it merges with the membrane. We can look at this membrane. After the vesicle's membrane has merged with the plasma membrane, the membrane might look like this."}, {"video_title": "Exocytosis   Membranes and transport   Biology   Khan Academy.mp3", "Sentence": "There are other cases where maybe it merges partially, releases the contents, and then buds back. It's called the kiss-and-run method of exocytosis, but the classic one is it merges with the membrane. We can look at this membrane. After the vesicle's membrane has merged with the plasma membrane, the membrane might look like this. It might look like this. So if the vesicle, let me do the vesicle's membrane in orange. The vesicle's membrane is that in orange."}, {"video_title": "Exocytosis   Membranes and transport   Biology   Khan Academy.mp3", "Sentence": "After the vesicle's membrane has merged with the plasma membrane, the membrane might look like this. It might look like this. So if the vesicle, let me do the vesicle's membrane in orange. The vesicle's membrane is that in orange. Well, now it has merged like this, and it has released its contents. It has released the protein to be used someplace else, someplace else in the body. And I want to be clear, this membrane, and I've talked about it many times in many other videos, even though I've drawn it as one line right over here, this is going to be, this is going to be a phospholipid bilayer."}, {"video_title": "Exocytosis   Membranes and transport   Biology   Khan Academy.mp3", "Sentence": "The vesicle's membrane is that in orange. Well, now it has merged like this, and it has released its contents. It has released the protein to be used someplace else, someplace else in the body. And I want to be clear, this membrane, and I've talked about it many times in many other videos, even though I've drawn it as one line right over here, this is going to be, this is going to be a phospholipid bilayer. So if we were to zoom in, if we were to zoom in, it would look like this. It's a phospholipid bilayer. So these are some of the phospholipids that were part of the original, or part of the original membrane."}, {"video_title": "Exocytosis   Membranes and transport   Biology   Khan Academy.mp3", "Sentence": "And I want to be clear, this membrane, and I've talked about it many times in many other videos, even though I've drawn it as one line right over here, this is going to be, this is going to be a phospholipid bilayer. So if we were to zoom in, if we were to zoom in, it would look like this. It's a phospholipid bilayer. So these are some of the phospholipids that were part of the original, or part of the original membrane. And then we also, in my little box, I get some of the ones that are part of, or that were part of the vesicle that was holding that protein, that were part of the vesicle that was holding the protein. So I really want to stress, I want to really stress these lines that I'm drawing, these are bilayers of phospholipids. And all of these lines, these membranes that you see, these are all bilayers of phospholipids, just to make sure that we are visualizing this correct."}, {"video_title": "Exocytosis   Membranes and transport   Biology   Khan Academy.mp3", "Sentence": "So these are some of the phospholipids that were part of the original, or part of the original membrane. And then we also, in my little box, I get some of the ones that are part of, or that were part of the vesicle that was holding that protein, that were part of the vesicle that was holding the protein. So I really want to stress, I want to really stress these lines that I'm drawing, these are bilayers of phospholipids. And all of these lines, these membranes that you see, these are all bilayers of phospholipids, just to make sure that we are visualizing this correct. And that's what exocytosis is. And one thing that I find interesting is when you first learn about it, you see a diagram like this, and you just assume, okay, well these bubbles of these membranes, they just randomly must float eventually to the membrane where they get merged, and then they release their contents. But it actually isn't that chaotic."}, {"video_title": "Exocytosis   Membranes and transport   Biology   Khan Academy.mp3", "Sentence": "And all of these lines, these membranes that you see, these are all bilayers of phospholipids, just to make sure that we are visualizing this correct. And that's what exocytosis is. And one thing that I find interesting is when you first learn about it, you see a diagram like this, and you just assume, okay, well these bubbles of these membranes, they just randomly must float eventually to the membrane where they get merged, and then they release their contents. But it actually isn't that chaotic. They actually can sit on tracks. So they actually can sit on tracks. Remember, we talk about the cytoskeleton, which isn't drawn enough, probably because it makes drawings really messy."}, {"video_title": "Exocytosis   Membranes and transport   Biology   Khan Academy.mp3", "Sentence": "But it actually isn't that chaotic. They actually can sit on tracks. So they actually can sit on tracks. Remember, we talk about the cytoskeleton, which isn't drawn enough, probably because it makes drawings really messy. But whenever we think about a cell, there's all this structure to it. There's all this structure to it. Microtubules, microfilaments, intermediate filaments, all of these things over here that not only provide structure to the cell, but they can be used to transport."}, {"video_title": "Exocytosis   Membranes and transport   Biology   Khan Academy.mp3", "Sentence": "Remember, we talk about the cytoskeleton, which isn't drawn enough, probably because it makes drawings really messy. But whenever we think about a cell, there's all this structure to it. There's all this structure to it. Microtubules, microfilaments, intermediate filaments, all of these things over here that not only provide structure to the cell, but they can be used to transport. And these vesicles, these vesicles can actually ride, can actually ride on these structures. And you could actually have motor protons, motor, not protons, motor proteins that are using ATP to actively push the vesicle containing its contents. So this is kind of a transportation."}, {"video_title": "Exocytosis   Membranes and transport   Biology   Khan Academy.mp3", "Sentence": "Microtubules, microfilaments, intermediate filaments, all of these things over here that not only provide structure to the cell, but they can be used to transport. And these vesicles, these vesicles can actually ride, can actually ride on these structures. And you could actually have motor protons, motor, not protons, motor proteins that are using ATP to actively push the vesicle containing its contents. So this is kind of a transportation. It's really like a factory to push them towards the membrane so that they can be released. So whenever I think about it, it's fascinating, because I always talk about these cells being a universe unto themselves. And they aren't just these blobs."}, {"video_title": "Exocytosis   Membranes and transport   Biology   Khan Academy.mp3", "Sentence": "So this is kind of a transportation. It's really like a factory to push them towards the membrane so that they can be released. So whenever I think about it, it's fascinating, because I always talk about these cells being a universe unto themselves. And they aren't just these blobs. They have all of these structures. There's all of these proteins that are, really, at an unbelievably small scale, able to do these fairly intricate processes. So what I just showed you, once again, this is classic exocytosis."}, {"video_title": "Exocytosis   Membranes and transport   Biology   Khan Academy.mp3", "Sentence": "And they aren't just these blobs. They have all of these structures. There's all of these proteins that are, really, at an unbelievably small scale, able to do these fairly intricate processes. So what I just showed you, once again, this is classic exocytosis. You'll see it when you have proteins, lipids being produced by the cell that need to be released somehow. They're also famously used in neurons at when they want, when you want the chemical signal, when you go from one neuron to another, you have exocytosis of neurotransmitters that will trigger the next neuron. So these are very, very important processes."}, {"video_title": "Diffusion and osmosis   Membranes and transport   Biology   Khan Academy.mp3", "Sentence": "So hopefully we can make some headway. So a good place to start, let's just imagine that I have some type of container here. Let's say that's my container. And inside of that container, I have a bunch of water molecules. They're all rubbing against each other. It's in its liquid form. This is liquid water."}, {"video_title": "Diffusion and osmosis   Membranes and transport   Biology   Khan Academy.mp3", "Sentence": "And inside of that container, I have a bunch of water molecules. They're all rubbing against each other. It's in its liquid form. This is liquid water. And then inside of the water molecules, I have some sugar molecules. Maybe I'll do sugar in this pink color. So I have a bunch of sugar molecules right here."}, {"video_title": "Diffusion and osmosis   Membranes and transport   Biology   Khan Academy.mp3", "Sentence": "This is liquid water. And then inside of the water molecules, I have some sugar molecules. Maybe I'll do sugar in this pink color. So I have a bunch of sugar molecules right here. I have many, many more water molecules, though. I want to make that clear. I have many, many more water molecules in this container we're dealing with."}, {"video_title": "Diffusion and osmosis   Membranes and transport   Biology   Khan Academy.mp3", "Sentence": "So I have a bunch of sugar molecules right here. I have many, many more water molecules, though. I want to make that clear. I have many, many more water molecules in this container we're dealing with. Now, in this type of situation, we call the thing that there is more of the solvent. So in this case, there's more water molecules. And you can literally just view more as the number of molecules."}, {"video_title": "Diffusion and osmosis   Membranes and transport   Biology   Khan Academy.mp3", "Sentence": "I have many, many more water molecules in this container we're dealing with. Now, in this type of situation, we call the thing that there is more of the solvent. So in this case, there's more water molecules. And you can literally just view more as the number of molecules. I'm not going to go into a whole discussion of moles and all of that, because you may or may not have been exposed to that yet. But just imagine whatever there's more of, that we're going to call the solvent. So in this case, water is the solvent."}, {"video_title": "Diffusion and osmosis   Membranes and transport   Biology   Khan Academy.mp3", "Sentence": "And you can literally just view more as the number of molecules. I'm not going to go into a whole discussion of moles and all of that, because you may or may not have been exposed to that yet. But just imagine whatever there's more of, that we're going to call the solvent. So in this case, water is the solvent. And whatever there is less of, so the more water is the solvent, and in this case, that is the sugar, that is considered the solute. So the sugar, it doesn't have to be sugar. It could be any molecule that there's less of than the water in this case."}, {"video_title": "Diffusion and osmosis   Membranes and transport   Biology   Khan Academy.mp3", "Sentence": "So in this case, water is the solvent. And whatever there is less of, so the more water is the solvent, and in this case, that is the sugar, that is considered the solute. So the sugar, it doesn't have to be sugar. It could be any molecule that there's less of than the water in this case. Sugar is the solute. And we say that the sugar has been dissolved into the water. And this whole thing right here, the combination of the water and the sugar molecules, we call a solution."}, {"video_title": "Diffusion and osmosis   Membranes and transport   Biology   Khan Academy.mp3", "Sentence": "It could be any molecule that there's less of than the water in this case. Sugar is the solute. And we say that the sugar has been dissolved into the water. And this whole thing right here, the combination of the water and the sugar molecules, we call a solution. We call this whole thing a solution. And a solution has a solvent and a solute. The solvent is water."}, {"video_title": "Diffusion and osmosis   Membranes and transport   Biology   Khan Academy.mp3", "Sentence": "And this whole thing right here, the combination of the water and the sugar molecules, we call a solution. We call this whole thing a solution. And a solution has a solvent and a solute. The solvent is water. That's the thing doing the dissolving. And the thing that is dissolved is the sugar. That's the solute."}, {"video_title": "Diffusion and osmosis   Membranes and transport   Biology   Khan Academy.mp3", "Sentence": "The solvent is water. That's the thing doing the dissolving. And the thing that is dissolved is the sugar. That's the solute. Now all of this may or may not be review for you, but I'm doing it for a reason. Because I want to talk about the idea of diffusion. And the idea is actually pretty straightforward."}, {"video_title": "Diffusion and osmosis   Membranes and transport   Biology   Khan Academy.mp3", "Sentence": "That's the solute. Now all of this may or may not be review for you, but I'm doing it for a reason. Because I want to talk about the idea of diffusion. And the idea is actually pretty straightforward. If I have, let's say the same container. Let me do a slightly different container here, just to talk about diffusion. We'll go back to water and sugar, especially back to water, but let's say we have a container here."}, {"video_title": "Diffusion and osmosis   Membranes and transport   Biology   Khan Academy.mp3", "Sentence": "And the idea is actually pretty straightforward. If I have, let's say the same container. Let me do a slightly different container here, just to talk about diffusion. We'll go back to water and sugar, especially back to water, but let's say we have a container here. And let's say it just has some air particles in it. It could be anything, oxygen or carbon dioxide. So let me just draw a couple of air molecules here."}, {"video_title": "Diffusion and osmosis   Membranes and transport   Biology   Khan Academy.mp3", "Sentence": "We'll go back to water and sugar, especially back to water, but let's say we have a container here. And let's say it just has some air particles in it. It could be anything, oxygen or carbon dioxide. So let me just draw a couple of air molecules here. So let's say that that is a gaseous, just for the sake of argument, oxygen. So each of this is an O2. Each of those, right?"}, {"video_title": "Diffusion and osmosis   Membranes and transport   Biology   Khan Academy.mp3", "Sentence": "So let me just draw a couple of air molecules here. So let's say that that is a gaseous, just for the sake of argument, oxygen. So each of this is an O2. Each of those, right? And let's say that this is the current configuration, that all of this is a vacuum here. And that there's some temperature. So these water molecules, they have some type of kinetic energy, they're moving in some type of random directions right there."}, {"video_title": "Diffusion and osmosis   Membranes and transport   Biology   Khan Academy.mp3", "Sentence": "Each of those, right? And let's say that this is the current configuration, that all of this is a vacuum here. And that there's some temperature. So these water molecules, they have some type of kinetic energy, they're moving in some type of random directions right there. So my question is, what is going to happen? What is going to happen in this type of container? Well, any of these guys are going to be randomly bumping into each other."}, {"video_title": "Diffusion and osmosis   Membranes and transport   Biology   Khan Academy.mp3", "Sentence": "So these water molecules, they have some type of kinetic energy, they're moving in some type of random directions right there. So my question is, what is going to happen? What is going to happen in this type of container? Well, any of these guys are going to be randomly bumping into each other. They're more likely to bump into things in this down left direction than they are in the upright direction. So if this guy was happening to go in this down left direction, he's going to bump into something and then ricochet into the upright direction. But in the upright direction, there's nothing to bounce into."}, {"video_title": "Diffusion and osmosis   Membranes and transport   Biology   Khan Academy.mp3", "Sentence": "Well, any of these guys are going to be randomly bumping into each other. They're more likely to bump into things in this down left direction than they are in the upright direction. So if this guy was happening to go in this down left direction, he's going to bump into something and then ricochet into the upright direction. But in the upright direction, there's nothing to bounce into. So in general, everything is moving in random directions, but you're more likely to be able to move in the rightward direction. When you go to the left, you're more likely to bump into something. So it's almost common sense."}, {"video_title": "Diffusion and osmosis   Membranes and transport   Biology   Khan Academy.mp3", "Sentence": "But in the upright direction, there's nothing to bounce into. So in general, everything is moving in random directions, but you're more likely to be able to move in the rightward direction. When you go to the left, you're more likely to bump into something. So it's almost common sense. Over time, if you just let this system come to some type of equilibrium, and I'm not going to go into detail on what that means. You can watch the thermodynamics videos if you'd like to see that. You'll eventually see the container will look something like this."}, {"video_title": "Diffusion and osmosis   Membranes and transport   Biology   Khan Academy.mp3", "Sentence": "So it's almost common sense. Over time, if you just let this system come to some type of equilibrium, and I'm not going to go into detail on what that means. You can watch the thermodynamics videos if you'd like to see that. You'll eventually see the container will look something like this. I can't guarantee it. There's some probability it would actually stay like this. But very likely that those five particles are going to get relatively spread out."}, {"video_title": "Diffusion and osmosis   Membranes and transport   Biology   Khan Academy.mp3", "Sentence": "You'll eventually see the container will look something like this. I can't guarantee it. There's some probability it would actually stay like this. But very likely that those five particles are going to get relatively spread out. This is diffusion. And so it's really just the spreading of particles or molecules from high concentration to low concentration areas. In this case, the molecules are going to spread in that direction, from a high concentration to low concentration area."}, {"video_title": "Diffusion and osmosis   Membranes and transport   Biology   Khan Academy.mp3", "Sentence": "But very likely that those five particles are going to get relatively spread out. This is diffusion. And so it's really just the spreading of particles or molecules from high concentration to low concentration areas. In this case, the molecules are going to spread in that direction, from a high concentration to low concentration area. Now you're saying, Sal, what is concentration? And there's many ways to measure concentration. And you can go into molarity and molality and all of that."}, {"video_title": "Diffusion and osmosis   Membranes and transport   Biology   Khan Academy.mp3", "Sentence": "In this case, the molecules are going to spread in that direction, from a high concentration to low concentration area. Now you're saying, Sal, what is concentration? And there's many ways to measure concentration. And you can go into molarity and molality and all of that. But the very simple idea is, how much of that particle do you have per unit space? So here you have a lot of those particles per unit space. And here you have very few of those particles per unit space."}, {"video_title": "Diffusion and osmosis   Membranes and transport   Biology   Khan Academy.mp3", "Sentence": "And you can go into molarity and molality and all of that. But the very simple idea is, how much of that particle do you have per unit space? So here you have a lot of those particles per unit space. And here you have very few of those particles per unit space. So this is a high concentration, and that's a low concentration. So you can imagine other experiments like this. You could imagine a solution like, let's do something like this."}, {"video_title": "Diffusion and osmosis   Membranes and transport   Biology   Khan Academy.mp3", "Sentence": "And here you have very few of those particles per unit space. So this is a high concentration, and that's a low concentration. So you can imagine other experiments like this. You could imagine a solution like, let's do something like this. Let's say I have two containers. Let's go back to the solution situation. So this was a gas, but I started off with that example."}, {"video_title": "Diffusion and osmosis   Membranes and transport   Biology   Khan Academy.mp3", "Sentence": "You could imagine a solution like, let's do something like this. Let's say I have two containers. Let's go back to the solution situation. So this was a gas, but I started off with that example. So let's stay with that example. Let's say that I have a door right there that's larger than either the water or the sugar molecules. On either side, I have a bunch of water molecules on either side, so I have a lot of water molecules."}, {"video_title": "Diffusion and osmosis   Membranes and transport   Biology   Khan Academy.mp3", "Sentence": "So this was a gas, but I started off with that example. So let's stay with that example. Let's say that I have a door right there that's larger than either the water or the sugar molecules. On either side, I have a bunch of water molecules on either side, so I have a lot of water molecules. I just had water molecules here. They're all bouncing around in random directions. And so the odds of a water molecule going this way equivalent to odds of a water molecule going that way, assuming that both sides have the same level of water molecule, otherwise the pressures would be different."}, {"video_title": "Diffusion and osmosis   Membranes and transport   Biology   Khan Academy.mp3", "Sentence": "On either side, I have a bunch of water molecules on either side, so I have a lot of water molecules. I just had water molecules here. They're all bouncing around in random directions. And so the odds of a water molecule going this way equivalent to odds of a water molecule going that way, assuming that both sides have the same level of water molecule, otherwise the pressures would be different. So let's say that the top of this is the same as the top of this. So there's no more pressure going in one direction or another. So if for whatever reason a bunch more water molecules were going in the rightward direction, then all of a sudden this would fill up with more water, and we know that that isn't likely to occur."}, {"video_title": "Diffusion and osmosis   Membranes and transport   Biology   Khan Academy.mp3", "Sentence": "And so the odds of a water molecule going this way equivalent to odds of a water molecule going that way, assuming that both sides have the same level of water molecule, otherwise the pressures would be different. So let's say that the top of this is the same as the top of this. So there's no more pressure going in one direction or another. So if for whatever reason a bunch more water molecules were going in the rightward direction, then all of a sudden this would fill up with more water, and we know that that isn't likely to occur. So this is just a solution, or this is just two containers of water. Now let's put some solute in it. Let's dissolve some solute in it."}, {"video_title": "Diffusion and osmosis   Membranes and transport   Biology   Khan Academy.mp3", "Sentence": "So if for whatever reason a bunch more water molecules were going in the rightward direction, then all of a sudden this would fill up with more water, and we know that that isn't likely to occur. So this is just a solution, or this is just two containers of water. Now let's put some solute in it. Let's dissolve some solute in it. Let's say we do all the dissolving on the left-hand side, so we put some sugar molecules on the left-hand side, and these are small enough to fit through this little pipe. That's one assumption that I'm making. So what's going to happen?"}, {"video_title": "Diffusion and osmosis   Membranes and transport   Biology   Khan Academy.mp3", "Sentence": "Let's dissolve some solute in it. Let's say we do all the dissolving on the left-hand side, so we put some sugar molecules on the left-hand side, and these are small enough to fit through this little pipe. That's one assumption that I'm making. So what's going to happen? All of these things have some type of kinetic energy. They're all bouncing around. Well, over time, the water is going back and forth."}, {"video_title": "Diffusion and osmosis   Membranes and transport   Biology   Khan Academy.mp3", "Sentence": "So what's going to happen? All of these things have some type of kinetic energy. They're all bouncing around. Well, over time, the water is going back and forth. This water molecule might go that way, that water molecule might go that way, but they net each other out. But over time, one of these big sugar molecules will be going in just the right direction to go through, maybe this guy, instead of going in that direction, he starts off going in that direction. He goes just through this tunnel connecting the two containers, and he'll end up there."}, {"video_title": "Diffusion and osmosis   Membranes and transport   Biology   Khan Academy.mp3", "Sentence": "Well, over time, the water is going back and forth. This water molecule might go that way, that water molecule might go that way, but they net each other out. But over time, one of these big sugar molecules will be going in just the right direction to go through, maybe this guy, instead of going in that direction, he starts off going in that direction. He goes just through this tunnel connecting the two containers, and he'll end up there. And this guy will still be bouncing around. There's some probability he goes back, but there's still more sugar particles here than there. So still there's more probability that one of these guys will go to that side, than one of these guys will go to that side."}, {"video_title": "Diffusion and osmosis   Membranes and transport   Biology   Khan Academy.mp3", "Sentence": "He goes just through this tunnel connecting the two containers, and he'll end up there. And this guy will still be bouncing around. There's some probability he goes back, but there's still more sugar particles here than there. So still there's more probability that one of these guys will go to that side, than one of these guys will go to that side. So you can imagine if you're doing this with gazillions of particles, I'm only doing it with four, over time, the particles will have spread out so that their concentrations are roughly equal. So that maybe you'll have two here over time. But when you're only dealing with three or four or five particles, there's some probability it doesn't happen."}, {"video_title": "Diffusion and osmosis   Membranes and transport   Biology   Khan Academy.mp3", "Sentence": "So still there's more probability that one of these guys will go to that side, than one of these guys will go to that side. So you can imagine if you're doing this with gazillions of particles, I'm only doing it with four, over time, the particles will have spread out so that their concentrations are roughly equal. So that maybe you'll have two here over time. But when you're only dealing with three or four or five particles, there's some probability it doesn't happen. But when you're doing it with a gazillion and they're super small, it's a very, very, very high likelihood. But anyway, this whole process, we went from a container of high concentration to a container of low concentration. And the particles would have spread from the low concentration container to the high concentration container."}, {"video_title": "Diffusion and osmosis   Membranes and transport   Biology   Khan Academy.mp3", "Sentence": "But when you're only dealing with three or four or five particles, there's some probability it doesn't happen. But when you're doing it with a gazillion and they're super small, it's a very, very, very high likelihood. But anyway, this whole process, we went from a container of high concentration to a container of low concentration. And the particles would have spread from the low concentration container to the high concentration container. So they diffused. This is diffusion. And just so that we learn some other words that tend to be used with the idea of diffusion, when we started off, this had a higher concentration."}, {"video_title": "Diffusion and osmosis   Membranes and transport   Biology   Khan Academy.mp3", "Sentence": "And the particles would have spread from the low concentration container to the high concentration container. So they diffused. This is diffusion. And just so that we learn some other words that tend to be used with the idea of diffusion, when we started off, this had a higher concentration. The left-hand side container had higher concentration. It's all relative, right? It's only higher than this guy."}, {"video_title": "Diffusion and osmosis   Membranes and transport   Biology   Khan Academy.mp3", "Sentence": "And just so that we learn some other words that tend to be used with the idea of diffusion, when we started off, this had a higher concentration. The left-hand side container had higher concentration. It's all relative, right? It's only higher than this guy. Higher concentration. And this right here had a lower concentration. And there are words for these things."}, {"video_title": "Diffusion and osmosis   Membranes and transport   Biology   Khan Academy.mp3", "Sentence": "It's only higher than this guy. Higher concentration. And this right here had a lower concentration. And there are words for these things. This solution with a high concentration is called a hypertonic solution. Let me write that in yellow. Hypertonic solution."}, {"video_title": "Diffusion and osmosis   Membranes and transport   Biology   Khan Academy.mp3", "Sentence": "And there are words for these things. This solution with a high concentration is called a hypertonic solution. Let me write that in yellow. Hypertonic solution. Hyper, in general, meaning having a lot of something, having too much of something. And this lower concentration is hypotonic. Lower concentration."}, {"video_title": "Diffusion and osmosis   Membranes and transport   Biology   Khan Academy.mp3", "Sentence": "Hypertonic solution. Hyper, in general, meaning having a lot of something, having too much of something. And this lower concentration is hypotonic. Lower concentration. You might have heard maybe one of your relatives, if they haven't had a meal in a while, say, I'm hypoglycemic. That means that they're feeling lightheaded. There's not enough sugar in their bloodstream and they want to pass out, so they want a meal."}, {"video_title": "Diffusion and osmosis   Membranes and transport   Biology   Khan Academy.mp3", "Sentence": "Lower concentration. You might have heard maybe one of your relatives, if they haven't had a meal in a while, say, I'm hypoglycemic. That means that they're feeling lightheaded. There's not enough sugar in their bloodstream and they want to pass out, so they want a meal. If you just had a candy bar, maybe you're hyperglycemic, or maybe you're just hyper in general. So these are just good prefixes to know. But hypertonic, you have a lot of the solute, so you have high concentration."}, {"video_title": "Diffusion and osmosis   Membranes and transport   Biology   Khan Academy.mp3", "Sentence": "There's not enough sugar in their bloodstream and they want to pass out, so they want a meal. If you just had a candy bar, maybe you're hyperglycemic, or maybe you're just hyper in general. So these are just good prefixes to know. But hypertonic, you have a lot of the solute, so you have high concentration. And then in hypotonic, not too much of the solute, so you have a low concentration. These are good words to know. So in general, if there's no barriers to the diffusion, like we had here, you will have the solute go from a high concentration, or hypertonic solution, if they can travel, to a hypotonic solution, to a hypo, where the concentration is lower."}, {"video_title": "Diffusion and osmosis   Membranes and transport   Biology   Khan Academy.mp3", "Sentence": "But hypertonic, you have a lot of the solute, so you have high concentration. And then in hypotonic, not too much of the solute, so you have a low concentration. These are good words to know. So in general, if there's no barriers to the diffusion, like we had here, you will have the solute go from a high concentration, or hypertonic solution, if they can travel, to a hypotonic solution, to a hypo, where the concentration is lower. Now, let's do an interesting experiment here. We've talked about diffusion, and so far we've been talking about the diffusion of the solute. And in general, and this is not always the case, if you want to be as general as possible, the solute is whatever you have less of, the solvent is whatever you have more of."}, {"video_title": "Diffusion and osmosis   Membranes and transport   Biology   Khan Academy.mp3", "Sentence": "So in general, if there's no barriers to the diffusion, like we had here, you will have the solute go from a high concentration, or hypertonic solution, if they can travel, to a hypotonic solution, to a hypo, where the concentration is lower. Now, let's do an interesting experiment here. We've talked about diffusion, and so far we've been talking about the diffusion of the solute. And in general, and this is not always the case, if you want to be as general as possible, the solute is whatever you have less of, the solvent is whatever you have more of. And the most common solvent tends to be water. But it doesn't have to be water. It could be some type of alcohol, it could be mercury, it could be a whole set of molecules, but water in most biological or chemical systems tends to be the most typical solvent."}, {"video_title": "Diffusion and osmosis   Membranes and transport   Biology   Khan Academy.mp3", "Sentence": "And in general, and this is not always the case, if you want to be as general as possible, the solute is whatever you have less of, the solvent is whatever you have more of. And the most common solvent tends to be water. But it doesn't have to be water. It could be some type of alcohol, it could be mercury, it could be a whole set of molecules, but water in most biological or chemical systems tends to be the most typical solvent. It's what other things are dissolved into. But what happens if we have a tunnel where the solute is too big to travel, but water is small enough to travel? So let's think about that situation."}, {"video_title": "Diffusion and osmosis   Membranes and transport   Biology   Khan Academy.mp3", "Sentence": "It could be some type of alcohol, it could be mercury, it could be a whole set of molecules, but water in most biological or chemical systems tends to be the most typical solvent. It's what other things are dissolved into. But what happens if we have a tunnel where the solute is too big to travel, but water is small enough to travel? So let's think about that situation. In order to think about it, I'm going to do something interesting. Let's say we have a container here. Let's say we have, actually I won't even draw a container."}, {"video_title": "Diffusion and osmosis   Membranes and transport   Biology   Khan Academy.mp3", "Sentence": "So let's think about that situation. In order to think about it, I'm going to do something interesting. Let's say we have a container here. Let's say we have, actually I won't even draw a container. Let's just say we have an outside environment that has a bunch of water. This is the outside environment. And then you have some type of membrane."}, {"video_title": "Diffusion and osmosis   Membranes and transport   Biology   Khan Academy.mp3", "Sentence": "Let's say we have, actually I won't even draw a container. Let's just say we have an outside environment that has a bunch of water. This is the outside environment. And then you have some type of membrane. Water can go in and out of this membrane. So it's semi-permeable. Well, it's permeable to water, but the solute cannot go through the membrane."}, {"video_title": "Diffusion and osmosis   Membranes and transport   Biology   Khan Academy.mp3", "Sentence": "And then you have some type of membrane. Water can go in and out of this membrane. So it's semi-permeable. Well, it's permeable to water, but the solute cannot go through the membrane. So let's say that the solute is sugar. So we have water on the outside and also inside the membrane. So these are little small water molecules."}, {"video_title": "Diffusion and osmosis   Membranes and transport   Biology   Khan Academy.mp3", "Sentence": "Well, it's permeable to water, but the solute cannot go through the membrane. So let's say that the solute is sugar. So we have water on the outside and also inside the membrane. So these are little small water molecules. This is a membrane right here. And let's say that we have some sugar molecules. I'm just picking on sugar."}, {"video_title": "Diffusion and osmosis   Membranes and transport   Biology   Khan Academy.mp3", "Sentence": "So these are little small water molecules. This is a membrane right here. And let's say that we have some sugar molecules. I'm just picking on sugar. It could have been anything. So we have some sugar molecules here that are just a little bit bigger. Or they could be a lot bigger, actually."}, {"video_title": "Diffusion and osmosis   Membranes and transport   Biology   Khan Academy.mp3", "Sentence": "I'm just picking on sugar. It could have been anything. So we have some sugar molecules here that are just a little bit bigger. Or they could be a lot bigger, actually. They're a lot bigger than water molecules. So you have a bunch of, and I only draw four, but you have a gazillion of them. But you have that much more water molecules."}, {"video_title": "Diffusion and osmosis   Membranes and transport   Biology   Khan Academy.mp3", "Sentence": "Or they could be a lot bigger, actually. They're a lot bigger than water molecules. So you have a bunch of, and I only draw four, but you have a gazillion of them. But you have that much more water molecules. I'm just trying to show you have more water molecules than sugar molecules. And this membrane is semi-permeable. Permeable means that it allows things to pass."}, {"video_title": "Diffusion and osmosis   Membranes and transport   Biology   Khan Academy.mp3", "Sentence": "But you have that much more water molecules. I'm just trying to show you have more water molecules than sugar molecules. And this membrane is semi-permeable. Permeable means that it allows things to pass. Semi-permeable means it's not completely permeable. So semi-permeable in this context, I'm saying I allow water to pass through the membrane. So water can pass."}, {"video_title": "Diffusion and osmosis   Membranes and transport   Biology   Khan Academy.mp3", "Sentence": "Permeable means that it allows things to pass. Semi-permeable means it's not completely permeable. So semi-permeable in this context, I'm saying I allow water to pass through the membrane. So water can pass. But sugar cannot. Sugar is too large. And the reason why in this case is because the sugar molecule is too big."}, {"video_title": "Diffusion and osmosis   Membranes and transport   Biology   Khan Academy.mp3", "Sentence": "So water can pass. But sugar cannot. Sugar is too large. And the reason why in this case is because the sugar molecule is too big. So if we were to zoom in on the actual membrane itself, maybe the membrane looks like this. I'm going to zoom in on this membrane. So it has little holes in the membrane, just like that."}, {"video_title": "Diffusion and osmosis   Membranes and transport   Biology   Khan Academy.mp3", "Sentence": "And the reason why in this case is because the sugar molecule is too big. So if we were to zoom in on the actual membrane itself, maybe the membrane looks like this. I'm going to zoom in on this membrane. So it has little holes in the membrane, just like that. And maybe the water molecules are about that size, so they can go through those holes. So the water molecules can go back and forth through the holes. But the sugar molecules are about that big, so they cannot go through that hole."}, {"video_title": "Diffusion and osmosis   Membranes and transport   Biology   Khan Academy.mp3", "Sentence": "So it has little holes in the membrane, just like that. And maybe the water molecules are about that size, so they can go through those holes. So the water molecules can go back and forth through the holes. But the sugar molecules are about that big, so they cannot go through that hole. They're too big for this opening right here to go back and forth between them. Now, what do you think is going to happen in this situation? So first of all, let's use our terminology."}, {"video_title": "Diffusion and osmosis   Membranes and transport   Biology   Khan Academy.mp3", "Sentence": "But the sugar molecules are about that big, so they cannot go through that hole. They're too big for this opening right here to go back and forth between them. Now, what do you think is going to happen in this situation? So first of all, let's use our terminology. Remember, sugar is our solute. Water is our solvent. Semi-permeable membrane."}, {"video_title": "Diffusion and osmosis   Membranes and transport   Biology   Khan Academy.mp3", "Sentence": "So first of all, let's use our terminology. Remember, sugar is our solute. Water is our solvent. Semi-permeable membrane. Which side of the membrane has a higher or lower concentration of solute? Well, the inside does. The inside is hypertonic."}, {"video_title": "Diffusion and osmosis   Membranes and transport   Biology   Khan Academy.mp3", "Sentence": "Semi-permeable membrane. Which side of the membrane has a higher or lower concentration of solute? Well, the inside does. The inside is hypertonic. The outside has a lower concentration. So it's hypotonic out here. Lower concentration of solute."}, {"video_title": "Diffusion and osmosis   Membranes and transport   Biology   Khan Academy.mp3", "Sentence": "The inside is hypertonic. The outside has a lower concentration. So it's hypotonic out here. Lower concentration of solute. Now, if these openings were big enough, based on what we just talked about, these guys are bouncing around. Water is traveling in either direction. And equal probability, or actually I'm going to talk about that in a second."}, {"video_title": "Diffusion and osmosis   Membranes and transport   Biology   Khan Academy.mp3", "Sentence": "Lower concentration of solute. Now, if these openings were big enough, based on what we just talked about, these guys are bouncing around. Water is traveling in either direction. And equal probability, or actually I'm going to talk about that in a second. If everything was wide open, it would be equal probability. But if it was wide open, these guys eventually would bounce their ways over to this side, and you'd probably end up with equal concentrations eventually. And so you would have your traditional diffusion, where high concentration of solute to low concentration of solute."}, {"video_title": "Diffusion and osmosis   Membranes and transport   Biology   Khan Academy.mp3", "Sentence": "And equal probability, or actually I'm going to talk about that in a second. If everything was wide open, it would be equal probability. But if it was wide open, these guys eventually would bounce their ways over to this side, and you'd probably end up with equal concentrations eventually. And so you would have your traditional diffusion, where high concentration of solute to low concentration of solute. But in this case, these guys, they can't fit through the hole. Only water can go back and forth. If these guys were not here, water would have an equal likelihood of going in this direction as they would be going in that direction."}, {"video_title": "Diffusion and osmosis   Membranes and transport   Biology   Khan Academy.mp3", "Sentence": "And so you would have your traditional diffusion, where high concentration of solute to low concentration of solute. But in this case, these guys, they can't fit through the hole. Only water can go back and forth. If these guys were not here, water would have an equal likelihood of going in this direction as they would be going in that direction. A completely equal likelihood. But because these guys are on the right-hand side of, or in this case, on the inside of our membrane, this is our inside of our membrane zoomed up, it's less likely, because these guys might be in the approach position of the holes. It's that slightly less likely for water to be in the approach position for the holes."}, {"video_title": "Diffusion and osmosis   Membranes and transport   Biology   Khan Academy.mp3", "Sentence": "If these guys were not here, water would have an equal likelihood of going in this direction as they would be going in that direction. A completely equal likelihood. But because these guys are on the right-hand side of, or in this case, on the inside of our membrane, this is our inside of our membrane zoomed up, it's less likely, because these guys might be in the approach position of the holes. It's that slightly less likely for water to be in the approach position for the holes. So it's actually more probable that water could enter than water exit. And I want to make that very clear. If these sugar molecules were not here, obviously it's equally likely for water to go in either direction."}, {"video_title": "Diffusion and osmosis   Membranes and transport   Biology   Khan Academy.mp3", "Sentence": "It's that slightly less likely for water to be in the approach position for the holes. So it's actually more probable that water could enter than water exit. And I want to make that very clear. If these sugar molecules were not here, obviously it's equally likely for water to go in either direction. Now that these sugar molecules are there, these sugar molecules might be on the right-hand side. They might be blocking, I guess the best way to think about it is blocking the approach to the hole. They'll never be able to go through the hole themselves, and they might not even be blocking the hole."}, {"video_title": "Diffusion and osmosis   Membranes and transport   Biology   Khan Academy.mp3", "Sentence": "If these sugar molecules were not here, obviously it's equally likely for water to go in either direction. Now that these sugar molecules are there, these sugar molecules might be on the right-hand side. They might be blocking, I guess the best way to think about it is blocking the approach to the hole. They'll never be able to go through the hole themselves, and they might not even be blocking the hole. But they're going in some random direction. So if a water molecule was approaching, it's all probabilistic and we're dealing with gazillions of molecules. It's that much more likely to be blocked to get outside."}, {"video_title": "Diffusion and osmosis   Membranes and transport   Biology   Khan Academy.mp3", "Sentence": "They'll never be able to go through the hole themselves, and they might not even be blocking the hole. But they're going in some random direction. So if a water molecule was approaching, it's all probabilistic and we're dealing with gazillions of molecules. It's that much more likely to be blocked to get outside. But the water molecules from the outside, there's nothing blocking them to get in. So you're going to have a flow of water inside. So in this situation, with a semipermeable membrane, you're going to have water, you're going to have a net inward flow of water."}, {"video_title": "Diffusion and osmosis   Membranes and transport   Biology   Khan Academy.mp3", "Sentence": "It's that much more likely to be blocked to get outside. But the water molecules from the outside, there's nothing blocking them to get in. So you're going to have a flow of water inside. So in this situation, with a semipermeable membrane, you're going to have water, you're going to have a net inward flow of water. And so this is kind of interesting. We have the solvent flowing from a hypotonic situation to a hypertonic solution. But it's only hypotonic in the solute."}, {"video_title": "Diffusion and osmosis   Membranes and transport   Biology   Khan Academy.mp3", "Sentence": "So in this situation, with a semipermeable membrane, you're going to have water, you're going to have a net inward flow of water. And so this is kind of interesting. We have the solvent flowing from a hypotonic situation to a hypertonic solution. But it's only hypotonic in the solute. That's when you talk about the solute. And it's only hypertonic when you talk about the solute. But water, if you flip it the other way, if you view sugar as the solvent, then you could say we're going from a high concentration of water to a low concentration of water."}, {"video_title": "Diffusion and osmosis   Membranes and transport   Biology   Khan Academy.mp3", "Sentence": "But it's only hypotonic in the solute. That's when you talk about the solute. And it's only hypertonic when you talk about the solute. But water, if you flip it the other way, if you view sugar as the solvent, then you could say we're going from a high concentration of water to a low concentration of water. I don't want to confuse you too much. This is what tends to confuse people. But just think about what's going to happen."}, {"video_title": "Diffusion and osmosis   Membranes and transport   Biology   Khan Academy.mp3", "Sentence": "But water, if you flip it the other way, if you view sugar as the solvent, then you could say we're going from a high concentration of water to a low concentration of water. I don't want to confuse you too much. This is what tends to confuse people. But just think about what's going to happen. No matter what, in what situation, the solution is going to do what it can to try to equilibrate the concentration, to make the concentrations on both sides as close as possible. And it's not just some magic. It's not like the solution knows."}, {"video_title": "Diffusion and osmosis   Membranes and transport   Biology   Khan Academy.mp3", "Sentence": "But just think about what's going to happen. No matter what, in what situation, the solution is going to do what it can to try to equilibrate the concentration, to make the concentrations on both sides as close as possible. And it's not just some magic. It's not like the solution knows. It's all based on probabilities and these things bumping around. But in this situation, water is more likely to flow into the container. So it's actually going to go from the hypotonic side, when we talk about low concentration of solute, to the side that has high concentrations of solute, of sugar."}, {"video_title": "Diffusion and osmosis   Membranes and transport   Biology   Khan Academy.mp3", "Sentence": "It's not like the solution knows. It's all based on probabilities and these things bumping around. But in this situation, water is more likely to flow into the container. So it's actually going to go from the hypotonic side, when we talk about low concentration of solute, to the side that has high concentrations of solute, of sugar. And actually, if this thing is stretchable, more water will keep flowing in. And this membrane will stretch out. But we won't go into too much detail here."}, {"video_title": "Diffusion and osmosis   Membranes and transport   Biology   Khan Academy.mp3", "Sentence": "So it's actually going to go from the hypotonic side, when we talk about low concentration of solute, to the side that has high concentrations of solute, of sugar. And actually, if this thing is stretchable, more water will keep flowing in. And this membrane will stretch out. But we won't go into too much detail here. But this idea of water, of the solvent, if in this case, water is the solvent, of water as a solvent diffusing through a semipermeable membrane, this is called osmosis. You've probably heard learning by osmosis. You know, if you put a book against your head, maybe it'll just seep into your brain."}, {"video_title": "Diffusion and osmosis   Membranes and transport   Biology   Khan Academy.mp3", "Sentence": "But we won't go into too much detail here. But this idea of water, of the solvent, if in this case, water is the solvent, of water as a solvent diffusing through a semipermeable membrane, this is called osmosis. You've probably heard learning by osmosis. You know, if you put a book against your head, maybe it'll just seep into your brain. Same idea. That's where the word comes from. This idea of water seeping through membranes to try to make concentrations more equal."}, {"video_title": "Diffusion and osmosis   Membranes and transport   Biology   Khan Academy.mp3", "Sentence": "You know, if you put a book against your head, maybe it'll just seep into your brain. Same idea. That's where the word comes from. This idea of water seeping through membranes to try to make concentrations more equal. So if you say, well, you see I have high concentration here, low concentration here. If there was no membrane here, these big molecules would exit. But because there's this semipermeable membrane here, they can't."}, {"video_title": "Diffusion and osmosis   Membranes and transport   Biology   Khan Academy.mp3", "Sentence": "This idea of water seeping through membranes to try to make concentrations more equal. So if you say, well, you see I have high concentration here, low concentration here. If there was no membrane here, these big molecules would exit. But because there's this semipermeable membrane here, they can't. So the system, just probabilistically, no magic here, more water will enter to try to equilibrate the concentration. And eventually, if maybe there's a few molecules out here, not as high concentration here, eventually if everything was allowed to happen fully, you'll get to the point where you have just as high a concentration on this side as you have on the right-hand side, because this right-hand side is going to fill with water and also probably become a larger volume. And then once again, the probabilities of a water molecule going to the right and to the left will be the same, and you'll get to some type of equilibrium."}, {"video_title": "Diffusion and osmosis   Membranes and transport   Biology   Khan Academy.mp3", "Sentence": "But because there's this semipermeable membrane here, they can't. So the system, just probabilistically, no magic here, more water will enter to try to equilibrate the concentration. And eventually, if maybe there's a few molecules out here, not as high concentration here, eventually if everything was allowed to happen fully, you'll get to the point where you have just as high a concentration on this side as you have on the right-hand side, because this right-hand side is going to fill with water and also probably become a larger volume. And then once again, the probabilities of a water molecule going to the right and to the left will be the same, and you'll get to some type of equilibrium. But I want to make it very clear. Diffusion is the idea of any particle going from higher concentration and spreading into a region that has a lower concentration and kind of just spreading out. Osmosis is the diffusion of water."}, {"video_title": "Elements and atoms   Atoms, compounds, and ions   Chemistry   Khan Academy.mp3", "Sentence": "We humans have known for thousands of years, just looking at our environment around us, that there are different substances. And these different substances tend to have different properties. And not only do they have different properties, one might reflect light in a certain way or not reflect light, or be a certain color, or at a certain temperature be liquid, or a gas, or be a solid. But we also start to observe how they react with each other in certain circumstances. And here's pictures of some of these substances. This right here is carbon. And this is in its graphite form."}, {"video_title": "Elements and atoms   Atoms, compounds, and ions   Chemistry   Khan Academy.mp3", "Sentence": "But we also start to observe how they react with each other in certain circumstances. And here's pictures of some of these substances. This right here is carbon. And this is in its graphite form. This right here is lead. This right here is gold. And all of the ones that I've shown pictures of here, and I got them all from this website right over there, all of these are in their solid form."}, {"video_title": "Elements and atoms   Atoms, compounds, and ions   Chemistry   Khan Academy.mp3", "Sentence": "And this is in its graphite form. This right here is lead. This right here is gold. And all of the ones that I've shown pictures of here, and I got them all from this website right over there, all of these are in their solid form. But we also know that it looks like there's certain types of air and certain types of air particles. And depending on what type of air particles you're looking at, whether it is carbon, or oxygen, or nitrogen, that seems to have different types of properties. Or there are other things that can be liquid."}, {"video_title": "Elements and atoms   Atoms, compounds, and ions   Chemistry   Khan Academy.mp3", "Sentence": "And all of the ones that I've shown pictures of here, and I got them all from this website right over there, all of these are in their solid form. But we also know that it looks like there's certain types of air and certain types of air particles. And depending on what type of air particles you're looking at, whether it is carbon, or oxygen, or nitrogen, that seems to have different types of properties. Or there are other things that can be liquid. Or even if you raise the temperature high enough on these things, if you raise the temperature high enough on gold or lead, you could get a liquid. Or if you burn this carbon, you can get it to a gaseous state, you can release it into the atmosphere, you can break its structure. So these are things that humanity has observed for thousands of years."}, {"video_title": "Elements and atoms   Atoms, compounds, and ions   Chemistry   Khan Academy.mp3", "Sentence": "Or there are other things that can be liquid. Or even if you raise the temperature high enough on these things, if you raise the temperature high enough on gold or lead, you could get a liquid. Or if you burn this carbon, you can get it to a gaseous state, you can release it into the atmosphere, you can break its structure. So these are things that humanity has observed for thousands of years. But it leads to a natural question that used to be a philosophical question, but now we can answer it a little bit better. And that question is, if you keep breaking down this carbon into smaller and smaller chunks, is there some smallest chunk, some smallest unit of this stuff, of this substance, that still has the properties of carbon? And if you were to somehow break that down even further, somehow you would lose the properties of the carbon."}, {"video_title": "Elements and atoms   Atoms, compounds, and ions   Chemistry   Khan Academy.mp3", "Sentence": "So these are things that humanity has observed for thousands of years. But it leads to a natural question that used to be a philosophical question, but now we can answer it a little bit better. And that question is, if you keep breaking down this carbon into smaller and smaller chunks, is there some smallest chunk, some smallest unit of this stuff, of this substance, that still has the properties of carbon? And if you were to somehow break that down even further, somehow you would lose the properties of the carbon. And the answer is, there is. And so just to get our terminology, we call these different substances, these pure substances that have these specific properties at certain temperatures and react in certain ways, we call them elements. Carbon is an element."}, {"video_title": "Elements and atoms   Atoms, compounds, and ions   Chemistry   Khan Academy.mp3", "Sentence": "And if you were to somehow break that down even further, somehow you would lose the properties of the carbon. And the answer is, there is. And so just to get our terminology, we call these different substances, these pure substances that have these specific properties at certain temperatures and react in certain ways, we call them elements. Carbon is an element. Lead is an element. Gold is an element. You might say that water is an element."}, {"video_title": "Elements and atoms   Atoms, compounds, and ions   Chemistry   Khan Academy.mp3", "Sentence": "Carbon is an element. Lead is an element. Gold is an element. You might say that water is an element. And in history, people have referred to water as an element. But now we know that water is made up of more basic elements. It's made of oxygen and of hydrogen."}, {"video_title": "Elements and atoms   Atoms, compounds, and ions   Chemistry   Khan Academy.mp3", "Sentence": "You might say that water is an element. And in history, people have referred to water as an element. But now we know that water is made up of more basic elements. It's made of oxygen and of hydrogen. And all of our elements are listed here in the periodic table of elements. C stands for carbon. I'm just going through the ones that are very relevant to humanity, but over time you'll probably familiarize yourself with all of these."}, {"video_title": "Elements and atoms   Atoms, compounds, and ions   Chemistry   Khan Academy.mp3", "Sentence": "It's made of oxygen and of hydrogen. And all of our elements are listed here in the periodic table of elements. C stands for carbon. I'm just going through the ones that are very relevant to humanity, but over time you'll probably familiarize yourself with all of these. This is oxygen. This is nitrogen. This is silicon."}, {"video_title": "Elements and atoms   Atoms, compounds, and ions   Chemistry   Khan Academy.mp3", "Sentence": "I'm just going through the ones that are very relevant to humanity, but over time you'll probably familiarize yourself with all of these. This is oxygen. This is nitrogen. This is silicon. This is, Au is gold. This is lead. And that most basic unit of any of these elements is the atom."}, {"video_title": "Elements and atoms   Atoms, compounds, and ions   Chemistry   Khan Academy.mp3", "Sentence": "This is silicon. This is, Au is gold. This is lead. And that most basic unit of any of these elements is the atom. So if you were to keep digging in and keep taking smaller and smaller chunks of this, eventually you would get to a carbon atom. Do the same thing over here. Eventually you would get to a gold atom."}, {"video_title": "Elements and atoms   Atoms, compounds, and ions   Chemistry   Khan Academy.mp3", "Sentence": "And that most basic unit of any of these elements is the atom. So if you were to keep digging in and keep taking smaller and smaller chunks of this, eventually you would get to a carbon atom. Do the same thing over here. Eventually you would get to a gold atom. You did the same thing over here. Eventually you'd get some, this little small, for lack of a better word, particle that you would call a lead atom. And you wouldn't be able to break that down anymore and still call that lead, for it to still have the properties of lead."}, {"video_title": "Elements and atoms   Atoms, compounds, and ions   Chemistry   Khan Academy.mp3", "Sentence": "Eventually you would get to a gold atom. You did the same thing over here. Eventually you'd get some, this little small, for lack of a better word, particle that you would call a lead atom. And you wouldn't be able to break that down anymore and still call that lead, for it to still have the properties of lead. And just to give you an idea, and this is really something that I have trouble imagining, is that atoms are unbelievably small, really unimaginably small. So for example, carbon. My hair is also made out of carbon."}, {"video_title": "Elements and atoms   Atoms, compounds, and ions   Chemistry   Khan Academy.mp3", "Sentence": "And you wouldn't be able to break that down anymore and still call that lead, for it to still have the properties of lead. And just to give you an idea, and this is really something that I have trouble imagining, is that atoms are unbelievably small, really unimaginably small. So for example, carbon. My hair is also made out of carbon. In fact, most of me is made out of carbon. In fact, most of all living things are made out of carbon. And so if you took my hair, and so my hair is carbon, my hair is mostly carbon."}, {"video_title": "Elements and atoms   Atoms, compounds, and ions   Chemistry   Khan Academy.mp3", "Sentence": "My hair is also made out of carbon. In fact, most of me is made out of carbon. In fact, most of all living things are made out of carbon. And so if you took my hair, and so my hair is carbon, my hair is mostly carbon. So if you took my hair right over here, and my hair isn't yellow, but it contrasts nicely with the black, my hair is black, but if I did that you wouldn't be able to see it on the screen. But if you took my hair here, and I were to ask you how many carbon atoms wide is my hair? What is the diameter?"}, {"video_title": "Elements and atoms   Atoms, compounds, and ions   Chemistry   Khan Academy.mp3", "Sentence": "And so if you took my hair, and so my hair is carbon, my hair is mostly carbon. So if you took my hair right over here, and my hair isn't yellow, but it contrasts nicely with the black, my hair is black, but if I did that you wouldn't be able to see it on the screen. But if you took my hair here, and I were to ask you how many carbon atoms wide is my hair? What is the diameter? So if you took a cross section of my hair, not the length, the width of my hair, and said how many carbon atoms wide is that, and you might guess, oh, Sal already told me they're very small, so maybe there's 1,000 carbon atoms there, or 10,000 or 100,000. I would say no. There are 1,000,000 carbon atoms, or you could string 1,000,000 carbon atoms across the width of the average human hair."}, {"video_title": "Elements and atoms   Atoms, compounds, and ions   Chemistry   Khan Academy.mp3", "Sentence": "What is the diameter? So if you took a cross section of my hair, not the length, the width of my hair, and said how many carbon atoms wide is that, and you might guess, oh, Sal already told me they're very small, so maybe there's 1,000 carbon atoms there, or 10,000 or 100,000. I would say no. There are 1,000,000 carbon atoms, or you could string 1,000,000 carbon atoms across the width of the average human hair. And that's obviously an approximation. It's not exactly 1,000,000, but that gives you a sense of how small an atom is. You know, pluck a hair out of your head, and just imagine putting a million things next to each other across the hair."}, {"video_title": "Elements and atoms   Atoms, compounds, and ions   Chemistry   Khan Academy.mp3", "Sentence": "There are 1,000,000 carbon atoms, or you could string 1,000,000 carbon atoms across the width of the average human hair. And that's obviously an approximation. It's not exactly 1,000,000, but that gives you a sense of how small an atom is. You know, pluck a hair out of your head, and just imagine putting a million things next to each other across the hair. Not the length of the hair, the width of the hair. It's even hard to see the width of a hair, and there would be a million carbon atoms just going along it. Now, it would be pretty cool in and of itself that we do know that there is this most basic building block of carbon, this most basic building block of any element."}, {"video_title": "Elements and atoms   Atoms, compounds, and ions   Chemistry   Khan Academy.mp3", "Sentence": "You know, pluck a hair out of your head, and just imagine putting a million things next to each other across the hair. Not the length of the hair, the width of the hair. It's even hard to see the width of a hair, and there would be a million carbon atoms just going along it. Now, it would be pretty cool in and of itself that we do know that there is this most basic building block of carbon, this most basic building block of any element. But what's even neater is that those basic building blocks are related to each other. A carbon atom is made up of even more fundamental particles. A gold atom is made up of even more fundamental particles."}, {"video_title": "Elements and atoms   Atoms, compounds, and ions   Chemistry   Khan Academy.mp3", "Sentence": "Now, it would be pretty cool in and of itself that we do know that there is this most basic building block of carbon, this most basic building block of any element. But what's even neater is that those basic building blocks are related to each other. A carbon atom is made up of even more fundamental particles. A gold atom is made up of even more fundamental particles. And they're actually defined by the arrangement of those fundamental particles. And if you were to change the number of fundamental particles you have, you could change the properties of the element, how it would react, or you could even change the element itself. And just to understand it a little bit better, let's talk about those fundamental elements."}, {"video_title": "Elements and atoms   Atoms, compounds, and ions   Chemistry   Khan Academy.mp3", "Sentence": "A gold atom is made up of even more fundamental particles. And they're actually defined by the arrangement of those fundamental particles. And if you were to change the number of fundamental particles you have, you could change the properties of the element, how it would react, or you could even change the element itself. And just to understand it a little bit better, let's talk about those fundamental elements. So you have the proton. And the proton is actually the defining the number of protons in the nucleus of an atom. And I'll talk about the nucleus in a second."}, {"video_title": "Elements and atoms   Atoms, compounds, and ions   Chemistry   Khan Academy.mp3", "Sentence": "And just to understand it a little bit better, let's talk about those fundamental elements. So you have the proton. And the proton is actually the defining the number of protons in the nucleus of an atom. And I'll talk about the nucleus in a second. That is what defines the element. So this is what defines an element. When you look at the periodic table right here, they're actually written in order of atomic number."}, {"video_title": "Elements and atoms   Atoms, compounds, and ions   Chemistry   Khan Academy.mp3", "Sentence": "And I'll talk about the nucleus in a second. That is what defines the element. So this is what defines an element. When you look at the periodic table right here, they're actually written in order of atomic number. And the atomic number is literally just the number of protons in the element. So by definition, hydrogen has one proton. Helium has two protons."}, {"video_title": "Elements and atoms   Atoms, compounds, and ions   Chemistry   Khan Academy.mp3", "Sentence": "When you look at the periodic table right here, they're actually written in order of atomic number. And the atomic number is literally just the number of protons in the element. So by definition, hydrogen has one proton. Helium has two protons. Carbon has six protons. You cannot have carbon with seven protons. If you did, it would be nitrogen."}, {"video_title": "Elements and atoms   Atoms, compounds, and ions   Chemistry   Khan Academy.mp3", "Sentence": "Helium has two protons. Carbon has six protons. You cannot have carbon with seven protons. If you did, it would be nitrogen. It would not be carbon anymore. Oxygen has eight protons. If somehow you were to add another proton to there, it wouldn't be oxygen anymore."}, {"video_title": "Elements and atoms   Atoms, compounds, and ions   Chemistry   Khan Academy.mp3", "Sentence": "If you did, it would be nitrogen. It would not be carbon anymore. Oxygen has eight protons. If somehow you were to add another proton to there, it wouldn't be oxygen anymore. It would be fluorine. So it defines the element. And the atomic number, the number of protons, and remember, that's the number that's written right at the top here for each of these elements in the periodic table, the number of protons is equal to the atomic number."}, {"video_title": "Elements and atoms   Atoms, compounds, and ions   Chemistry   Khan Academy.mp3", "Sentence": "If somehow you were to add another proton to there, it wouldn't be oxygen anymore. It would be fluorine. So it defines the element. And the atomic number, the number of protons, and remember, that's the number that's written right at the top here for each of these elements in the periodic table, the number of protons is equal to the atomic number. And they put that number up here because that is the defining characteristic of an element. The other two constituents of an atom, I guess we could call it that way, are the electron and the neutron. And the model you can start to build in your head, and this model as we go through chemistry, it'll get a little bit more abstract and really hard to conceptualize."}, {"video_title": "Elements and atoms   Atoms, compounds, and ions   Chemistry   Khan Academy.mp3", "Sentence": "And the atomic number, the number of protons, and remember, that's the number that's written right at the top here for each of these elements in the periodic table, the number of protons is equal to the atomic number. And they put that number up here because that is the defining characteristic of an element. The other two constituents of an atom, I guess we could call it that way, are the electron and the neutron. And the model you can start to build in your head, and this model as we go through chemistry, it'll get a little bit more abstract and really hard to conceptualize. But one way to think about it is you have the protons and the neutrons that are at the center of the atom. They're the nucleus of the atom. So for example, carbon we know has six protons."}, {"video_title": "Elements and atoms   Atoms, compounds, and ions   Chemistry   Khan Academy.mp3", "Sentence": "And the model you can start to build in your head, and this model as we go through chemistry, it'll get a little bit more abstract and really hard to conceptualize. But one way to think about it is you have the protons and the neutrons that are at the center of the atom. They're the nucleus of the atom. So for example, carbon we know has six protons. So one, two, three, four, five, six. Carbon-12, which is a version of carbon, will also have six neutrons. You can have versions of carbon that have a different number of neutrons."}, {"video_title": "Elements and atoms   Atoms, compounds, and ions   Chemistry   Khan Academy.mp3", "Sentence": "So for example, carbon we know has six protons. So one, two, three, four, five, six. Carbon-12, which is a version of carbon, will also have six neutrons. You can have versions of carbon that have a different number of neutrons. So the neutrons can change, the electrons can change, you can still have the same element. The protons can't change. If you change the protons, you've got a different element."}, {"video_title": "Elements and atoms   Atoms, compounds, and ions   Chemistry   Khan Academy.mp3", "Sentence": "You can have versions of carbon that have a different number of neutrons. So the neutrons can change, the electrons can change, you can still have the same element. The protons can't change. If you change the protons, you've got a different element. So let me draw a carbon-12 nucleus. So one, two, three, four, five, six. So this right here is the nucleus of carbon-12."}, {"video_title": "Elements and atoms   Atoms, compounds, and ions   Chemistry   Khan Academy.mp3", "Sentence": "If you change the protons, you've got a different element. So let me draw a carbon-12 nucleus. So one, two, three, four, five, six. So this right here is the nucleus of carbon-12. And sometimes it'll be written like this, and sometimes they'll actually write the number of protons as well. And the reason why we write it carbon-12, I counted out six neutrons, is that you could view this as the total number of one way to view it, and we'll get a little bit nuanced in the future, is that this is the total number of protons and neutrons inside of its nucleus. And this carbon, by definition, has an atomic number of six, but we can rewrite it here just so that we can remind ourselves."}, {"video_title": "Elements and atoms   Atoms, compounds, and ions   Chemistry   Khan Academy.mp3", "Sentence": "So this right here is the nucleus of carbon-12. And sometimes it'll be written like this, and sometimes they'll actually write the number of protons as well. And the reason why we write it carbon-12, I counted out six neutrons, is that you could view this as the total number of one way to view it, and we'll get a little bit nuanced in the future, is that this is the total number of protons and neutrons inside of its nucleus. And this carbon, by definition, has an atomic number of six, but we can rewrite it here just so that we can remind ourselves. So at the center of a carbon atom, we have this nucleus. And carbon-12 will have six protons and six neutrons. Another version of carbon, carbon-14, will still have six protons, but then it would have eight neutrons."}, {"video_title": "Elements and atoms   Atoms, compounds, and ions   Chemistry   Khan Academy.mp3", "Sentence": "And this carbon, by definition, has an atomic number of six, but we can rewrite it here just so that we can remind ourselves. So at the center of a carbon atom, we have this nucleus. And carbon-12 will have six protons and six neutrons. Another version of carbon, carbon-14, will still have six protons, but then it would have eight neutrons. So the number of neutrons can change. But this is carbon-12 right over here. And if carbon-12 is neutral, and I'll give a little nuance on this word in a second as well, if it is neutral, it'll also have six electrons."}, {"video_title": "Elements and atoms   Atoms, compounds, and ions   Chemistry   Khan Academy.mp3", "Sentence": "Another version of carbon, carbon-14, will still have six protons, but then it would have eight neutrons. So the number of neutrons can change. But this is carbon-12 right over here. And if carbon-12 is neutral, and I'll give a little nuance on this word in a second as well, if it is neutral, it'll also have six electrons. So let me draw those six electrons. One, two, three, four, five, six. And one way, and this is maybe the first order way of thinking about the relationship between the electrons and the nucleus, is that you can imagine the electrons are kind of moving around, buzzing around this nucleus."}, {"video_title": "Elements and atoms   Atoms, compounds, and ions   Chemistry   Khan Academy.mp3", "Sentence": "And if carbon-12 is neutral, and I'll give a little nuance on this word in a second as well, if it is neutral, it'll also have six electrons. So let me draw those six electrons. One, two, three, four, five, six. And one way, and this is maybe the first order way of thinking about the relationship between the electrons and the nucleus, is that you can imagine the electrons are kind of moving around, buzzing around this nucleus. One model is you could kind of think of them as orbiting around the nucleus, but that's not quite right. They don't orbit the way that a planet, say, orbits around the sun. But that's a good starting point."}, {"video_title": "Elements and atoms   Atoms, compounds, and ions   Chemistry   Khan Academy.mp3", "Sentence": "And one way, and this is maybe the first order way of thinking about the relationship between the electrons and the nucleus, is that you can imagine the electrons are kind of moving around, buzzing around this nucleus. One model is you could kind of think of them as orbiting around the nucleus, but that's not quite right. They don't orbit the way that a planet, say, orbits around the sun. But that's a good starting point. Another way is they're kind of jumping around the nucleus, or they're buzzing around the nucleus. And that's just because reality just gets very strange at this level, and we'll actually have to go into quantum physics to really understand what the electron is doing. But a first mental model in your head is that the center of this atom, of this carbon-12 atom, you have this nucleus right over there."}, {"video_title": "Elements and atoms   Atoms, compounds, and ions   Chemistry   Khan Academy.mp3", "Sentence": "But that's a good starting point. Another way is they're kind of jumping around the nucleus, or they're buzzing around the nucleus. And that's just because reality just gets very strange at this level, and we'll actually have to go into quantum physics to really understand what the electron is doing. But a first mental model in your head is that the center of this atom, of this carbon-12 atom, you have this nucleus right over there. And these electrons are jumping around this nucleus. And the reason why these electrons don't just go off away from this nucleus, why they're kind of bound to this nucleus and they form part of this atom, is that protons have a positive charge and electrons have a negative charge. And it's one of these properties of these fundamental particles."}, {"video_title": "Elements and atoms   Atoms, compounds, and ions   Chemistry   Khan Academy.mp3", "Sentence": "But a first mental model in your head is that the center of this atom, of this carbon-12 atom, you have this nucleus right over there. And these electrons are jumping around this nucleus. And the reason why these electrons don't just go off away from this nucleus, why they're kind of bound to this nucleus and they form part of this atom, is that protons have a positive charge and electrons have a negative charge. And it's one of these properties of these fundamental particles. When you start thinking about, well, what is a charge fundamentally, other than a label, and it starts to get kind of deep. But the one thing that we know when we talk about electromagnetic force is that unlike charges attract each other. So the best way to think about it is protons and electrons, because they have different charges, they attract each other."}, {"video_title": "Elements and atoms   Atoms, compounds, and ions   Chemistry   Khan Academy.mp3", "Sentence": "And it's one of these properties of these fundamental particles. When you start thinking about, well, what is a charge fundamentally, other than a label, and it starts to get kind of deep. But the one thing that we know when we talk about electromagnetic force is that unlike charges attract each other. So the best way to think about it is protons and electrons, because they have different charges, they attract each other. Neutrons are neutral. So they're really just sitting here inside of the nucleus. And they do affect the properties on some level for some atoms of certain elements."}, {"video_title": "Elements and atoms   Atoms, compounds, and ions   Chemistry   Khan Academy.mp3", "Sentence": "So the best way to think about it is protons and electrons, because they have different charges, they attract each other. Neutrons are neutral. So they're really just sitting here inside of the nucleus. And they do affect the properties on some level for some atoms of certain elements. But the reason why we have the electrons not just flying off on their own is because they are attracted. They are attracted towards the nucleus. And they also have an unbelievably high velocity."}, {"video_title": "Elements and atoms   Atoms, compounds, and ions   Chemistry   Khan Academy.mp3", "Sentence": "And they do affect the properties on some level for some atoms of certain elements. But the reason why we have the electrons not just flying off on their own is because they are attracted. They are attracted towards the nucleus. And they also have an unbelievably high velocity. It's actually hard for, and we start touching once again on a very strange part of physics, once we start talking about what an electron actually is doing. But it has enough, I guess you could say it's jumping around enough that it doesn't want to just fall into the nucleus, I guess is one way of thinking about it. And so I mentioned carbon-12 right over here, defined by the number of protons."}, {"video_title": "Elements and atoms   Atoms, compounds, and ions   Chemistry   Khan Academy.mp3", "Sentence": "And they also have an unbelievably high velocity. It's actually hard for, and we start touching once again on a very strange part of physics, once we start talking about what an electron actually is doing. But it has enough, I guess you could say it's jumping around enough that it doesn't want to just fall into the nucleus, I guess is one way of thinking about it. And so I mentioned carbon-12 right over here, defined by the number of protons. Oxygen would be defined by having eight protons. But once again, electrons can interact with other electrons, or they can be taken away by other atoms. And that actually forms a lot of our understanding of chemistry."}, {"video_title": "Elements and atoms   Atoms, compounds, and ions   Chemistry   Khan Academy.mp3", "Sentence": "And so I mentioned carbon-12 right over here, defined by the number of protons. Oxygen would be defined by having eight protons. But once again, electrons can interact with other electrons, or they can be taken away by other atoms. And that actually forms a lot of our understanding of chemistry. It's based on how many electrons an atom has, or a certain element has, and how those electrons are configured, and how the electrons of other elements are configured, or maybe other atoms of that same element. We can start to predict how an atom of one element can react with another atom of that same element, or an atom of one element, how it could react, or how it could bond, or not bond, or be attracted to, or repel another atom of another element. So for example, and we'll learn a lot more about this in the future, is it is possible for another atom someplace to swipe away an electron from a carbon, just because for whatever reason, and we'll talk about certain elements, certain neutral atoms of certain elements have a larger affinity for electrons than others."}, {"video_title": "Elements and atoms   Atoms, compounds, and ions   Chemistry   Khan Academy.mp3", "Sentence": "And that actually forms a lot of our understanding of chemistry. It's based on how many electrons an atom has, or a certain element has, and how those electrons are configured, and how the electrons of other elements are configured, or maybe other atoms of that same element. We can start to predict how an atom of one element can react with another atom of that same element, or an atom of one element, how it could react, or how it could bond, or not bond, or be attracted to, or repel another atom of another element. So for example, and we'll learn a lot more about this in the future, is it is possible for another atom someplace to swipe away an electron from a carbon, just because for whatever reason, and we'll talk about certain elements, certain neutral atoms of certain elements have a larger affinity for electrons than others. So one, maybe one of those, swipes an electron away from a carbon, and then this carbon will be having less electrons than protons. So then it would have five electrons and six protons, and then it would have a net positive charge. So in this carbon-12, the first version I did, I had six protons, six electrons, the charge is canceled out."}, {"video_title": "Elements and atoms   Atoms, compounds, and ions   Chemistry   Khan Academy.mp3", "Sentence": "So for example, and we'll learn a lot more about this in the future, is it is possible for another atom someplace to swipe away an electron from a carbon, just because for whatever reason, and we'll talk about certain elements, certain neutral atoms of certain elements have a larger affinity for electrons than others. So one, maybe one of those, swipes an electron away from a carbon, and then this carbon will be having less electrons than protons. So then it would have five electrons and six protons, and then it would have a net positive charge. So in this carbon-12, the first version I did, I had six protons, six electrons, the charge is canceled out. If I lose an electron, then I only have five of these, and then I would have a net positive charge. And we're going to talk a lot more about all of this throughout the chemistry playlist, but hopefully you have an appreciation that this is already starting to get really cool. Once we can already get to this really fundamental building block called the atom, and what's even neater is that this fundamental building block is built of even more fundamental building blocks, and these things can all be swapped around to change the properties of an atom, or to even go from an atom of one element to an atom of another element."}, {"video_title": "Capillary action and why we see a meniscus   Chemistry   Khan Academy.mp3", "Sentence": "But it's actually not the case, and I encourage you to try it. You might have even observed this before. The surface of the water will not be flat. The surface of the water will actually be higher near the glass than it is when it's away from the glass. It forms a shape that looks something like that. And so the first thing we might ask is, well, what do we call this thing? And this right over here is called a meniscus."}, {"video_title": "Capillary action and why we see a meniscus   Chemistry   Khan Academy.mp3", "Sentence": "The surface of the water will actually be higher near the glass than it is when it's away from the glass. It forms a shape that looks something like that. And so the first thing we might ask is, well, what do we call this thing? And this right over here is called a meniscus. Meniscus. And in particular, this meniscus, because the fluid is higher near the container than it is when you're away from the container, we would call this a concave meniscus. And you might say, well, if this is a concave meniscus, are there any situations where we might have a convex meniscus?"}, {"video_title": "Capillary action and why we see a meniscus   Chemistry   Khan Academy.mp3", "Sentence": "And this right over here is called a meniscus. Meniscus. And in particular, this meniscus, because the fluid is higher near the container than it is when you're away from the container, we would call this a concave meniscus. And you might say, well, if this is a concave meniscus, are there any situations where we might have a convex meniscus? Well, sure, you can have a convex meniscus. If you were to take that same glass beaker, instead of filling it with water, if you filled it with, say, mercury, if you filled it with mercury, you would get a meniscus that looks like this, where there's a bulge near the center when you're further away from the container than when you're at the container. And so let me actually, let me just label this."}, {"video_title": "Capillary action and why we see a meniscus   Chemistry   Khan Academy.mp3", "Sentence": "And you might say, well, if this is a concave meniscus, are there any situations where we might have a convex meniscus? Well, sure, you can have a convex meniscus. If you were to take that same glass beaker, instead of filling it with water, if you filled it with, say, mercury, if you filled it with mercury, you would get a meniscus that looks like this, where there's a bulge near the center when you're further away from the container than when you're at the container. And so let me actually, let me just label this. This is a convex meniscus. But it's one thing to just observe this and to name them, to say, hey, this is a meniscus, this is a concave meniscus. But a more interesting question is, why does it actually happen?"}, {"video_title": "Capillary action and why we see a meniscus   Chemistry   Khan Academy.mp3", "Sentence": "And so let me actually, let me just label this. This is a convex meniscus. But it's one thing to just observe this and to name them, to say, hey, this is a meniscus, this is a concave meniscus. But a more interesting question is, why does it actually happen? And so you might imagine this concave meniscus is because the fluid is more attracted to the container than it is to itself. And you might be saying, wait, wait, hold on, hold on a second here. We've been talking about how water has this polarity, it has partial negative end, each water molecule has a partially negative and has partially positive ends at the hydrogens."}, {"video_title": "Capillary action and why we see a meniscus   Chemistry   Khan Academy.mp3", "Sentence": "But a more interesting question is, why does it actually happen? And so you might imagine this concave meniscus is because the fluid is more attracted to the container than it is to itself. And you might be saying, wait, wait, hold on, hold on a second here. We've been talking about how water has this polarity, it has partial negative end, each water molecule has a partially negative and has partially positive ends at the hydrogens. So let me write this down, partial positive charges at the hydrogens, and that causes this hydrogen bonding to form and water, and that's what kind of gives water all of these special properties. You're telling me that it's more attracted to the glass than it is to itself? And I would say, yes, I am telling you that."}, {"video_title": "Capillary action and why we see a meniscus   Chemistry   Khan Academy.mp3", "Sentence": "We've been talking about how water has this polarity, it has partial negative end, each water molecule has a partially negative and has partially positive ends at the hydrogens. So let me write this down, partial positive charges at the hydrogens, and that causes this hydrogen bonding to form and water, and that's what kind of gives water all of these special properties. You're telling me that it's more attracted to the glass than it is to itself? And I would say, yes, I am telling you that. And you could imagine why it is going to be more attracted to the glass than itself, because glass actually has, the molecules in glass actually are quite polar. And glass, typically made up of silicon, a silicon oxide lattice, for every one silicon atom, you have two oxygen atoms, you see that right over there, for every one silicon, you have two oxygen atoms. And it turns out that the electronegativity difference between oxygen and silicon is even higher than the electronegativity difference between oxygen and hydrogen."}, {"video_title": "Capillary action and why we see a meniscus   Chemistry   Khan Academy.mp3", "Sentence": "And I would say, yes, I am telling you that. And you could imagine why it is going to be more attracted to the glass than itself, because glass actually has, the molecules in glass actually are quite polar. And glass, typically made up of silicon, a silicon oxide lattice, for every one silicon atom, you have two oxygen atoms, you see that right over there, for every one silicon, you have two oxygen atoms. And it turns out that the electronegativity difference between oxygen and silicon is even higher than the electronegativity difference between oxygen and hydrogen. Silicon is even less electronegative than hydrogen. So the oxygens are really able to hog silicon's electrons, especially the ones that are involved in the bonding. So you have partial charges, partial positive charges form at the silicon, and then you still have partial negative charges form around the oxygens."}, {"video_title": "Capillary action and why we see a meniscus   Chemistry   Khan Academy.mp3", "Sentence": "And it turns out that the electronegativity difference between oxygen and silicon is even higher than the electronegativity difference between oxygen and hydrogen. Silicon is even less electronegative than hydrogen. So the oxygens are really able to hog silicon's electrons, especially the ones that are involved in the bonding. So you have partial charges, partial positive charges form at the silicon, and then you still have partial negative charges form around the oxygens. Form around the oxygens. So these are partial negative and partial positive at the silicon. And so you can imagine what's going to happen at the interface, and let me make this clear what's going on."}, {"video_title": "Capillary action and why we see a meniscus   Chemistry   Khan Academy.mp3", "Sentence": "So you have partial charges, partial positive charges form at the silicon, and then you still have partial negative charges form around the oxygens. Form around the oxygens. So these are partial negative and partial positive at the silicon. And so you can imagine what's going to happen at the interface, and let me make this clear what's going on. This, what I am circling right now, that is the water. This right over here, that's the water molecules. And what we see over here, what we see over here, these are the glass molecules."}, {"video_title": "Capillary action and why we see a meniscus   Chemistry   Khan Academy.mp3", "Sentence": "And so you can imagine what's going to happen at the interface, and let me make this clear what's going on. This, what I am circling right now, that is the water. This right over here, that's the water molecules. And what we see over here, what we see over here, these are the glass molecules. So this is the glass right over here. And sure, the water is attracted to itself because of the hydrogen bonds, but it has some kinetic energy. Remember, these things are jostling around, they're bouncing around, we're in a liquid state."}, {"video_title": "Capillary action and why we see a meniscus   Chemistry   Khan Academy.mp3", "Sentence": "And what we see over here, what we see over here, these are the glass molecules. So this is the glass right over here. And sure, the water is attracted to itself because of the hydrogen bonds, but it has some kinetic energy. Remember, these things are jostling around, they're bouncing around, we're in a liquid state. And so you can imagine all of a sudden, maybe this, let me see, maybe this character, this water molecule right over here, maybe a moment ago it was right over here, but it popped up here, just got knocked by another molecule, had enough kinetic energy to jump up here, but once it came up, came in contact with the glass surface right over here, the glass molecules, it stuck to them. Because it's partially positive end, it's partially positive end at the hydrogen, with the, let me do that in that green color. The partially positive end at the hydrogens would be attracted to the partially negative ends of the oxygens in the glass."}, {"video_title": "Capillary action and why we see a meniscus   Chemistry   Khan Academy.mp3", "Sentence": "Remember, these things are jostling around, they're bouncing around, we're in a liquid state. And so you can imagine all of a sudden, maybe this, let me see, maybe this character, this water molecule right over here, maybe a moment ago it was right over here, but it popped up here, just got knocked by another molecule, had enough kinetic energy to jump up here, but once it came up, came in contact with the glass surface right over here, the glass molecules, it stuck to them. Because it's partially positive end, it's partially positive end at the hydrogen, with the, let me do that in that green color. The partially positive end at the hydrogens would be attracted to the partially negative ends of the oxygens in the glass. And so it'll stick to it. This is actually a stronger partial charge than what you would actually see in the water because there's a bigger electronegativity difference between the silicon and the oxygen in the glass than the oxygen and the hydrogen in the water. So these things just keep bumping around, maybe there's another water molecule that just gets knocked in the right way, all of a sudden for a very brief moment it gets knocked up here, and then it's going to stick to the glass."}, {"video_title": "Capillary action and why we see a meniscus   Chemistry   Khan Academy.mp3", "Sentence": "The partially positive end at the hydrogens would be attracted to the partially negative ends of the oxygens in the glass. And so it'll stick to it. This is actually a stronger partial charge than what you would actually see in the water because there's a bigger electronegativity difference between the silicon and the oxygen in the glass than the oxygen and the hydrogen in the water. So these things just keep bumping around, maybe there's another water molecule that just gets knocked in the right way, all of a sudden for a very brief moment it gets knocked up here, and then it's going to stick to the glass. And this phenomenon of something sticking to its container, we would call that adhesion. So what you see going on here, that is called adhesion. Adhesion, and adhesion is the reason why you also see the water a little bit higher there."}, {"video_title": "Capillary action and why we see a meniscus   Chemistry   Khan Academy.mp3", "Sentence": "So these things just keep bumping around, maybe there's another water molecule that just gets knocked in the right way, all of a sudden for a very brief moment it gets knocked up here, and then it's going to stick to the glass. And this phenomenon of something sticking to its container, we would call that adhesion. So what you see going on here, that is called adhesion. Adhesion, and adhesion is the reason why you also see the water a little bit higher there. And when you talk about something sticking to itself, we call that cohesion, and that's what the hydrogen bonds are doing inside the water. So this right over here, that over there, that is cohesion. So that's why we have things, why we observe a meniscus like this, but there's also, there's even more fascinating properties of adhesion."}, {"video_title": "Capillary action and why we see a meniscus   Chemistry   Khan Academy.mp3", "Sentence": "Adhesion, and adhesion is the reason why you also see the water a little bit higher there. And when you talk about something sticking to itself, we call that cohesion, and that's what the hydrogen bonds are doing inside the water. So this right over here, that over there, that is cohesion. So that's why we have things, why we observe a meniscus like this, but there's also, there's even more fascinating properties of adhesion. If I were to take a container of water, if I were to take a container of water, and just to be clear what's going on here with the mercury, the mercury is more attracted to itself than it is to the glass container, so it bulges right over there. But let's go back to water. So let's say this is a big tub of water."}, {"video_title": "Capillary action and why we see a meniscus   Chemistry   Khan Academy.mp3", "Sentence": "So that's why we have things, why we observe a meniscus like this, but there's also, there's even more fascinating properties of adhesion. If I were to take a container of water, if I were to take a container of water, and just to be clear what's going on here with the mercury, the mercury is more attracted to itself than it is to the glass container, so it bulges right over there. But let's go back to water. So let's say this is a big tub of water. I fill it, so I fill the water right over here. Now let's say I take a glass tube, and the material matters. It has to be a polar material."}, {"video_title": "Capillary action and why we see a meniscus   Chemistry   Khan Academy.mp3", "Sentence": "So let's say this is a big tub of water. I fill it, so I fill the water right over here. Now let's say I take a glass tube, and the material matters. It has to be a polar material. That's why you'll see the meniscus in glass, but you might not see it, or you won't see it if you're dealing with a plastic tube, because the plastic does not have that polarity. But let's say you were to take a glass tube, a thin glass tube this time, so much thinner than even a beaker. So you take a thin glass tube, and you stick it in the water, you will observe something very cool, and I encourage you to do this if you can get your hands on a thin glass tube."}, {"video_title": "Capillary action and why we see a meniscus   Chemistry   Khan Academy.mp3", "Sentence": "It has to be a polar material. That's why you'll see the meniscus in glass, but you might not see it, or you won't see it if you're dealing with a plastic tube, because the plastic does not have that polarity. But let's say you were to take a glass tube, a thin glass tube this time, so much thinner than even a beaker. So you take a thin glass tube, and you stick it in the water, you will observe something very cool, and I encourage you to do this if you can get your hands on a thin glass tube. You will notice that the water is actually going to defy gravity and start climbing up this thin glass tube. And so that's interesting. Why is that happening?"}, {"video_title": "Capillary action and why we see a meniscus   Chemistry   Khan Academy.mp3", "Sentence": "So you take a thin glass tube, and you stick it in the water, you will observe something very cool, and I encourage you to do this if you can get your hands on a thin glass tube. You will notice that the water is actually going to defy gravity and start climbing up this thin glass tube. And so that's interesting. Why is that happening? Well, this phenomenon, which we call capillary action, capillary action, the word capillary, it'll refer to anything from a very, very narrow tube, and we also have capillaries in our circulation system. Capillaries are our thinnest blood vessels, or they're very, very, very, very thin, and there's actually capillary action inside of our capillaries. But what we're seeing here, this is called capillary action."}, {"video_title": "Capillary action and why we see a meniscus   Chemistry   Khan Academy.mp3", "Sentence": "Why is that happening? Well, this phenomenon, which we call capillary action, capillary action, the word capillary, it'll refer to anything from a very, very narrow tube, and we also have capillaries in our circulation system. Capillaries are our thinnest blood vessels, or they're very, very, very, very thin, and there's actually capillary action inside of our capillaries. But what we're seeing here, this is called capillary action. And it's really just this adhesion occurring more intensely, because more of the water molecules are able to come in touch with the polar glass lattice. And so you can imagine we have glass here. If you also had glass over here, and actually it would be very hard to find something that's that thin, that's on the order of only a few molecules, but I'm not drawing things at scale."}, {"video_title": "Capillary action and why we see a meniscus   Chemistry   Khan Academy.mp3", "Sentence": "But what we're seeing here, this is called capillary action. And it's really just this adhesion occurring more intensely, because more of the water molecules are able to come in touch with the polar glass lattice. And so you can imagine we have glass here. If you also had glass over here, and actually it would be very hard to find something that's that thin, that's on the order of only a few molecules, but I'm not drawing things at scale. You can imagine now, okay, maybe another water molecule could jump up here and stick to the glass there, and then one just gets bumped the right way, jumps up and jumps there. And if we didn't have a polar container, if we didn't have a hydrophilic container, well then the thing might just jump back down. But because it went up there, it kind of just stuck to it, and then it's vibrating there, and then maybe another water molecule gets attracted to it because of its hydrogen bonds, and then it gets bumped the right way, and then it gets bumped with the higher part of the container but then it sticks there."}, {"video_title": "Capillary action and why we see a meniscus   Chemistry   Khan Academy.mp3", "Sentence": "If you also had glass over here, and actually it would be very hard to find something that's that thin, that's on the order of only a few molecules, but I'm not drawing things at scale. You can imagine now, okay, maybe another water molecule could jump up here and stick to the glass there, and then one just gets bumped the right way, jumps up and jumps there. And if we didn't have a polar container, if we didn't have a hydrophilic container, well then the thing might just jump back down. But because it went up there, it kind of just stuck to it, and then it's vibrating there, and then maybe another water molecule gets attracted to it because of its hydrogen bonds, and then it gets bumped the right way, and then it gets bumped with the higher part of the container but then it sticks there. And so it starts climbing the container. And that's what capillary action is. And it's not just some neat parlor trick."}, {"video_title": "Capillary action and why we see a meniscus   Chemistry   Khan Academy.mp3", "Sentence": "But because it went up there, it kind of just stuck to it, and then it's vibrating there, and then maybe another water molecule gets attracted to it because of its hydrogen bonds, and then it gets bumped the right way, and then it gets bumped with the higher part of the container but then it sticks there. And so it starts climbing the container. And that's what capillary action is. And it's not just some neat parlor trick. We actually probably use capillary action in our everyday lives all the time, but beyond the fact that it's actually happening in your capillaries in your body that allows you to live. But if you spill something on your counter, so let's say that's a spill right over there. You spill some, maybe you spill some water or you spill some milk."}, {"video_title": "Capillary action and why we see a meniscus   Chemistry   Khan Academy.mp3", "Sentence": "And it's not just some neat parlor trick. We actually probably use capillary action in our everyday lives all the time, but beyond the fact that it's actually happening in your capillaries in your body that allows you to live. But if you spill something on your counter, so let's say that's a spill right over there. You spill some, maybe you spill some water or you spill some milk. And if you take a paper towel, if you take a paper towel, in fact, if you took a paper towel like this, if you held it vertically, you will see the water start to be absorbed into the paper towel. This kind of absorption action that you see, that actually is capillary action. It's the water going into the small little gaps of the paper towel, that's because it is attracted to the actual paper towel."}, {"video_title": "DNA Spells Evolution.mp3", "Sentence": "That's the answer to all the big questions he had. How does variation emerge and how could that be transmitted? Let's return to our brown bears stranded in the Arctic to consider the impact of genetics on our understanding of evolution. Each bear is made up of cells. And if we take a brown bear cell and tunnel into its nucleus, we find DNA, the molecule with the genetic instructions for building, in this case, a brown bear, written in a four-letter code. Now, the thing about DNA, it's not perfect. When it's copied, mistakes get made."}, {"video_title": "DNA Spells Evolution.mp3", "Sentence": "Each bear is made up of cells. And if we take a brown bear cell and tunnel into its nucleus, we find DNA, the molecule with the genetic instructions for building, in this case, a brown bear, written in a four-letter code. Now, the thing about DNA, it's not perfect. When it's copied, mistakes get made. Mutations, in other words, that sometimes affect an organism's traits and that sometimes can be passed from parent to offspring. So the variation at the heart of evolution, it's genetic variation. Slight differences in DNA that, for example, could make some bears a bit lighter in color, a bit more insulated against the cold, and a bit more capable of digesting fattier foods like seals."}, {"video_title": "DNA Spells Evolution.mp3", "Sentence": "When it's copied, mistakes get made. Mutations, in other words, that sometimes affect an organism's traits and that sometimes can be passed from parent to offspring. So the variation at the heart of evolution, it's genetic variation. Slight differences in DNA that, for example, could make some bears a bit lighter in color, a bit more insulated against the cold, and a bit more capable of digesting fattier foods like seals. Evolution is essentially any change in the genetic composition of a population. Mutations are random, so they're not always helpful. But the bears with mutations that gave them some advantage for Arctic living survived and reproduced more often than bears without them."}, {"video_title": "DNA Spells Evolution.mp3", "Sentence": "Slight differences in DNA that, for example, could make some bears a bit lighter in color, a bit more insulated against the cold, and a bit more capable of digesting fattier foods like seals. Evolution is essentially any change in the genetic composition of a population. Mutations are random, so they're not always helpful. But the bears with mutations that gave them some advantage for Arctic living survived and reproduced more often than bears without them. They passed the genes responsible for those adaptations onto their cubs. Over generations, more bears inherited and elaborated on these and other changes in the DNA. The eventual result?"}, {"video_title": "DNA Spells Evolution.mp3", "Sentence": "But the bears with mutations that gave them some advantage for Arctic living survived and reproduced more often than bears without them. They passed the genes responsible for those adaptations onto their cubs. Over generations, more bears inherited and elaborated on these and other changes in the DNA. The eventual result? A polar bear. And when we tunnel into its cells, we find polar bear DNA. Think of DNA as the raw material that, across billions of years, evolution has molded and built into countless forms of life."}, {"video_title": "Sodium potassium pump   Membranes and transport   Biology   Khan Academy.mp3", "Sentence": "And as the name implies, it pumps sodium and potassium, but it does it in different directions. So this little depiction right over here, this is my drawing, my rendition of the sodium-potassium pump. It's a transmembrane, excuse me, protein complex right over here. And in this resting state, it is open to the inside of the cell, and it has an affinity for sodium ions. And so the sodium ions, you see three sodium ions depicted here in blue, they're going to bind to the pump. And once they bind to it, then it's going to be, it's going to want to be phosphorylated by an ATP. And we see that right over here."}, {"video_title": "Sodium potassium pump   Membranes and transport   Biology   Khan Academy.mp3", "Sentence": "And in this resting state, it is open to the inside of the cell, and it has an affinity for sodium ions. And so the sodium ions, you see three sodium ions depicted here in blue, they're going to bind to the pump. And once they bind to it, then it's going to be, it's going to want to be phosphorylated by an ATP. And we see that right over here. This is ATP, adenosine triphosphate. And when it gets phosphorylated, it's a release of energy, and it allows the conformation of the actual protein to change. So the new conformation of the protein, it's now going to open up to the outside, close off to the inside, and now it's no longer going to have an affinity for sodium ions, but an affinity for potassium ions."}, {"video_title": "Sodium potassium pump   Membranes and transport   Biology   Khan Academy.mp3", "Sentence": "And we see that right over here. This is ATP, adenosine triphosphate. And when it gets phosphorylated, it's a release of energy, and it allows the conformation of the actual protein to change. So the new conformation of the protein, it's now going to open up to the outside, close off to the inside, and now it's no longer going to have an affinity for sodium ions, but an affinity for potassium ions. And this is fascinating, that release of energy, change of conformation, that these proteins really are these molecular machines, these fascinating molecular machines. But once that happens, this change of conformation, the sodium ions are going to be released outside of the cell, and then you're going to have potassium ions that are going to bind from the outside. And then once that happens, the change in conformation, it's going to get dephosphorylated, and then you're going to go back to your original conformation, your original conformation right over here, where you no longer have an affinity for potassium ions."}, {"video_title": "Sodium potassium pump   Membranes and transport   Biology   Khan Academy.mp3", "Sentence": "So the new conformation of the protein, it's now going to open up to the outside, close off to the inside, and now it's no longer going to have an affinity for sodium ions, but an affinity for potassium ions. And this is fascinating, that release of energy, change of conformation, that these proteins really are these molecular machines, these fascinating molecular machines. But once that happens, this change of conformation, the sodium ions are going to be released outside of the cell, and then you're going to have potassium ions that are going to bind from the outside. And then once that happens, the change in conformation, it's going to get dephosphorylated, and then you're going to go back to your original conformation, your original conformation right over here, where you no longer have an affinity for potassium ions. They're going to be released, and then you're going to be back in the original phase. So this is fascinating. By using ATP, by using energy, this is active transport."}, {"video_title": "Sodium potassium pump   Membranes and transport   Biology   Khan Academy.mp3", "Sentence": "And then once that happens, the change in conformation, it's going to get dephosphorylated, and then you're going to go back to your original conformation, your original conformation right over here, where you no longer have an affinity for potassium ions. They're going to be released, and then you're going to be back in the original phase. So this is fascinating. By using ATP, by using energy, this is active transport. It takes energy to do this. Let me write this down. This is active transport that we are talking about right over here."}, {"video_title": "Sodium potassium pump   Membranes and transport   Biology   Khan Academy.mp3", "Sentence": "By using ATP, by using energy, this is active transport. It takes energy to do this. Let me write this down. This is active transport that we are talking about right over here. We're able to pump, using an ATP, we're able to pump three sodium ions out, three sodium ions out. So let me write that down. Three sodium ions out, and in the process, we pump two potassium ions in."}, {"video_title": "Sodium potassium pump   Membranes and transport   Biology   Khan Academy.mp3", "Sentence": "This is active transport that we are talking about right over here. We're able to pump, using an ATP, we're able to pump three sodium ions out, three sodium ions out. So let me write that down. Three sodium ions out, and in the process, we pump two potassium ions in. So we pump two potassium ions in. Now you might say, okay, the outside, since these both have positive charge, but I have three sodium going out, two potassium going in, that must make the outside more positive than the inside, and that actually is true. But that by itself isn't fully responsible."}, {"video_title": "Sodium potassium pump   Membranes and transport   Biology   Khan Academy.mp3", "Sentence": "Three sodium ions out, and in the process, we pump two potassium ions in. So we pump two potassium ions in. Now you might say, okay, the outside, since these both have positive charge, but I have three sodium going out, two potassium going in, that must make the outside more positive than the inside, and that actually is true. But that by itself isn't fully responsible. It's actually only partially responsible for the electric potential difference between the inside of the membrane and the outside of the membrane. What really sets that up is that you actually have channel proteins that allow potassium ions to move down, to diffuse down their concentration gradient. So let's think about what happens."}, {"video_title": "Sodium potassium pump   Membranes and transport   Biology   Khan Academy.mp3", "Sentence": "But that by itself isn't fully responsible. It's actually only partially responsible for the electric potential difference between the inside of the membrane and the outside of the membrane. What really sets that up is that you actually have channel proteins that allow potassium ions to move down, to diffuse down their concentration gradient. So let's think about what happens. Before I even talk about these channel proteins right over here, because of the sodium-potassium pump, what is sodium's concentration gradient? Well, it has a higher concentration on the outside, has a higher concentration on the outside, and it has a lower concentration on the inside. This is sodium's concentration gradient."}, {"video_title": "Sodium potassium pump   Membranes and transport   Biology   Khan Academy.mp3", "Sentence": "So let's think about what happens. Before I even talk about these channel proteins right over here, because of the sodium-potassium pump, what is sodium's concentration gradient? Well, it has a higher concentration on the outside, has a higher concentration on the outside, and it has a lower concentration on the inside. This is sodium's concentration gradient. What is potassium's concentration gradient? Well, potassium is getting pumped in from the outside into the cell. So potassium has the opposite concentration gradient."}, {"video_title": "Sodium potassium pump   Membranes and transport   Biology   Khan Academy.mp3", "Sentence": "This is sodium's concentration gradient. What is potassium's concentration gradient? Well, potassium is getting pumped in from the outside into the cell. So potassium has the opposite concentration gradient. It has a high concentration inside, and it has a low concentration outside. Now, if we let potassium go through, we've talked in previous videos about ions just not being that permeable, just the general membrane, if it's not facilitated in some way, isn't that permeable to things like ions, like sodium and potassium ions. But if you have channel proteins right over here that let the potassium get out, what's going to happen?"}, {"video_title": "Sodium potassium pump   Membranes and transport   Biology   Khan Academy.mp3", "Sentence": "So potassium has the opposite concentration gradient. It has a high concentration inside, and it has a low concentration outside. Now, if we let potassium go through, we've talked in previous videos about ions just not being that permeable, just the general membrane, if it's not facilitated in some way, isn't that permeable to things like ions, like sodium and potassium ions. But if you have channel proteins right over here that let the potassium get out, what's going to happen? Well, you might have one of two answers. You might say, well, look, hey, you know, things diffuse down their concentration gradient. You have a higher probability, since you have more potassium here than up here, higher probability of them going in the right direction on this side and moving from this side to that side than you have them going from that side to that side."}, {"video_title": "Sodium potassium pump   Membranes and transport   Biology   Khan Academy.mp3", "Sentence": "But if you have channel proteins right over here that let the potassium get out, what's going to happen? Well, you might have one of two answers. You might say, well, look, hey, you know, things diffuse down their concentration gradient. You have a higher probability, since you have more potassium here than up here, higher probability of them going in the right direction on this side and moving from this side to that side than you have them going from that side to that side. And so you would have a net outflow of potassium. And some of you might say, well, okay, that makes sense if you only care about the concentration gradient, but what happens if we look at the charge? Because we're saying that the inside of the cell is going to be less positive, less positive, and the outside of the cell is going to be more positive because it has more, we have the net ion change, so it's going to be more, more positive out here."}, {"video_title": "Sodium potassium pump   Membranes and transport   Biology   Khan Academy.mp3", "Sentence": "You have a higher probability, since you have more potassium here than up here, higher probability of them going in the right direction on this side and moving from this side to that side than you have them going from that side to that side. And so you would have a net outflow of potassium. And some of you might say, well, okay, that makes sense if you only care about the concentration gradient, but what happens if we look at the charge? Because we're saying that the inside of the cell is going to be less positive, less positive, and the outside of the cell is going to be more positive because it has more, we have the net ion change, so it's going to be more, more positive out here. So positive ions, they don't like, you want to move away from charges that are the same as you. You want to move towards, you want to move to the places that are more negative. So you'd say, well, these potassium ions are positively charged."}, {"video_title": "Sodium potassium pump   Membranes and transport   Biology   Khan Academy.mp3", "Sentence": "Because we're saying that the inside of the cell is going to be less positive, less positive, and the outside of the cell is going to be more positive because it has more, we have the net ion change, so it's going to be more, more positive out here. So positive ions, they don't like, you want to move away from charges that are the same as you. You want to move towards, you want to move to the places that are more negative. So you'd say, well, these potassium ions are positively charged. Why would they want to go from a less positive place to a more positive place? And if you are saying either one of these things, talking about the concentration gradient or talking about the electric potential difference, you are actually going to be right in both cases. These are going to be balancing forces."}, {"video_title": "Sodium potassium pump   Membranes and transport   Biology   Khan Academy.mp3", "Sentence": "So you'd say, well, these potassium ions are positively charged. Why would they want to go from a less positive place to a more positive place? And if you are saying either one of these things, talking about the concentration gradient or talking about the electric potential difference, you are actually going to be right in both cases. These are going to be balancing forces. The concentration gradient is going to allow some of these potassium ions to pour out, but the concentrations of potassium ions aren't going to fully equalize because of the electric potential difference, because, hey, it's more positive out here, it's less positive here. When they're moving out, they're going against what their charge wants to do. They're going with the concentration gradient, but at some point, that is going to balance out."}, {"video_title": "Sodium potassium pump   Membranes and transport   Biology   Khan Academy.mp3", "Sentence": "These are going to be balancing forces. The concentration gradient is going to allow some of these potassium ions to pour out, but the concentrations of potassium ions aren't going to fully equalize because of the electric potential difference, because, hey, it's more positive out here, it's less positive here. When they're moving out, they're going against what their charge wants to do. They're going with the concentration gradient, but at some point, that is going to balance out. And by going through this process, by pumping sodium out with a larger ratio than what you're pumping potassium in, and then you further allowing more positive charge to go out, you're establishing what's called the resting membrane potential for a cell. And this is super important for all cells, but especially neuron cells, or neural cells, or neurons. And those are going to spend 2 3rds of their energy just to establish or to keep the resting membrane potential."}, {"video_title": "Sodium potassium pump   Membranes and transport   Biology   Khan Academy.mp3", "Sentence": "They're going with the concentration gradient, but at some point, that is going to balance out. And by going through this process, by pumping sodium out with a larger ratio than what you're pumping potassium in, and then you further allowing more positive charge to go out, you're establishing what's called the resting membrane potential for a cell. And this is super important for all cells, but especially neuron cells, or neural cells, or neurons. And those are going to spend 2 3rds of their energy just to establish or to keep the resting membrane potential. As we'll see in the videos on neurons, that's because they keep leveraging that potential to send signals down the neuron. But the resting membrane potential, it's less positive here and more positive there. If you measure this relative to, let me make that a little bit neater, relative to this right over here, this difference is, depending on what estimates you look at, approximately negative 70 millivolts."}, {"video_title": "Sodium potassium pump   Membranes and transport   Biology   Khan Academy.mp3", "Sentence": "And those are going to spend 2 3rds of their energy just to establish or to keep the resting membrane potential. As we'll see in the videos on neurons, that's because they keep leveraging that potential to send signals down the neuron. But the resting membrane potential, it's less positive here and more positive there. If you measure this relative to, let me make that a little bit neater, relative to this right over here, this difference is, depending on what estimates you look at, approximately negative 70 millivolts. I've seen estimates of negative 60, negative 80, negative 70 millivolts. And this is key for neurons, but it's key for all cells. Now, the sodium potassium pump isn't just about establishing the resting membrane potential."}, {"video_title": "Sodium potassium pump   Membranes and transport   Biology   Khan Academy.mp3", "Sentence": "If you measure this relative to, let me make that a little bit neater, relative to this right over here, this difference is, depending on what estimates you look at, approximately negative 70 millivolts. I've seen estimates of negative 60, negative 80, negative 70 millivolts. And this is key for neurons, but it's key for all cells. Now, the sodium potassium pump isn't just about establishing the resting membrane potential. Having this higher sodium concentration on the outside can also be used later on for other forms of active transport. When they move down their gradient, you can do things like co-transport glucose molecules. So, biological systems are far more complicated than I often give credit for in these videos, but I want to give you a full appreciation for this."}, {"video_title": "How does climate change affect biodiversity.mp3", "Sentence": "First, I want to emphasize that virtually everything we do locally has global consequences. When we talk about something like a greenhouse gas or a pollutant, that's something we produce locally from our car or from other things that make up so many of our day-to-day human activities. But in the grand scale of things, even these local activities and impacts can have global effects. Greenhouse gases aren't just carbon dioxide. They also include water vapor, methane, ozone, and nitrous oxide. But for this tutorial, we want to focus on the major effects of carbon dioxide, which chemists refer to as CO2. Increases in the amount of carbon dioxide in the atmosphere mostly come through the burning of fossil fuels."}, {"video_title": "How does climate change affect biodiversity.mp3", "Sentence": "Greenhouse gases aren't just carbon dioxide. They also include water vapor, methane, ozone, and nitrous oxide. But for this tutorial, we want to focus on the major effects of carbon dioxide, which chemists refer to as CO2. Increases in the amount of carbon dioxide in the atmosphere mostly come through the burning of fossil fuels. Fossil fuels contain huge amounts of carbon, and when they're burned, they not only release heat energy, but they also release carbon dioxide. Although it's the energy, the heat, that we want, carbon dioxide is a side product of the burning. That's why atmospheric CO2 is increasing."}, {"video_title": "How does climate change affect biodiversity.mp3", "Sentence": "Increases in the amount of carbon dioxide in the atmosphere mostly come through the burning of fossil fuels. Fossil fuels contain huge amounts of carbon, and when they're burned, they not only release heat energy, but they also release carbon dioxide. Although it's the energy, the heat, that we want, carbon dioxide is a side product of the burning. That's why atmospheric CO2 is increasing. Why are so many people concerned about that in terms of global change? The answer means we need to say a few words about the greenhouse effect and how that actually works. Light rays from the sun arrive in our atmosphere as shorter wavelength radiation."}, {"video_title": "How does climate change affect biodiversity.mp3", "Sentence": "That's why atmospheric CO2 is increasing. Why are so many people concerned about that in terms of global change? The answer means we need to say a few words about the greenhouse effect and how that actually works. Light rays from the sun arrive in our atmosphere as shorter wavelength radiation. This light energy hits the surface of the earth. Some of it is reflected back in the form of slightly longer wavelength radiation, but it's this longer wavelength radiation that falls into what is known as the infrared area of the spectrum. Infrared is the same as heat, basically."}, {"video_title": "How does climate change affect biodiversity.mp3", "Sentence": "Light rays from the sun arrive in our atmosphere as shorter wavelength radiation. This light energy hits the surface of the earth. Some of it is reflected back in the form of slightly longer wavelength radiation, but it's this longer wavelength radiation that falls into what is known as the infrared area of the spectrum. Infrared is the same as heat, basically. So when light hits the surface of the earth, it's changed into heat energy. That heat energy is, to a certain extent, absorbed, and some of it's reflected back up into space. But greenhouse gases actually have a kind of snacking preference for longer wave radiation like infrared energy."}, {"video_title": "How does climate change affect biodiversity.mp3", "Sentence": "Infrared is the same as heat, basically. So when light hits the surface of the earth, it's changed into heat energy. That heat energy is, to a certain extent, absorbed, and some of it's reflected back up into space. But greenhouse gases actually have a kind of snacking preference for longer wave radiation like infrared energy. This keeps the heat energy close to the earth's surface instead of allowing it to go out into space. The more greenhouse gas you have, the more the heat builds up. It's no coincidence that this is called the greenhouse effect."}, {"video_title": "How does climate change affect biodiversity.mp3", "Sentence": "But greenhouse gases actually have a kind of snacking preference for longer wave radiation like infrared energy. This keeps the heat energy close to the earth's surface instead of allowing it to go out into space. The more greenhouse gas you have, the more the heat builds up. It's no coincidence that this is called the greenhouse effect. It works almost exactly like a gardener's greenhouse. A greenhouse is made of panes of glass and all that nice sunlight goes through the glass. It strikes the plants, the soil, the stuff inside the greenhouse."}, {"video_title": "How does climate change affect biodiversity.mp3", "Sentence": "It's no coincidence that this is called the greenhouse effect. It works almost exactly like a gardener's greenhouse. A greenhouse is made of panes of glass and all that nice sunlight goes through the glass. It strikes the plants, the soil, the stuff inside the greenhouse. But much of it becomes infrared light, or heat, held within your greenhouse and bouncing around through the air inside to make things nice and warm. To a certain extent, like our little plants in the greenhouse, earth's organisms benefit from the greenhouse effect. Life on earth would probably be quite different, or perhaps not exist at all, if we didn't have some greenhouse effect."}, {"video_title": "How does climate change affect biodiversity.mp3", "Sentence": "It strikes the plants, the soil, the stuff inside the greenhouse. But much of it becomes infrared light, or heat, held within your greenhouse and bouncing around through the air inside to make things nice and warm. To a certain extent, like our little plants in the greenhouse, earth's organisms benefit from the greenhouse effect. Life on earth would probably be quite different, or perhaps not exist at all, if we didn't have some greenhouse effect. The problem is that now we've increased the rate at which greenhouse gases are being introduced to the atmosphere, and therefore the rate at which warming occurs. Even gardeners have to regulate the flow of light into a greenhouse to keep it from overheating and cooking their veggies before they even get picked off the plant. So there's your problem."}, {"video_title": "How does climate change affect biodiversity.mp3", "Sentence": "Life on earth would probably be quite different, or perhaps not exist at all, if we didn't have some greenhouse effect. The problem is that now we've increased the rate at which greenhouse gases are being introduced to the atmosphere, and therefore the rate at which warming occurs. Even gardeners have to regulate the flow of light into a greenhouse to keep it from overheating and cooking their veggies before they even get picked off the plant. So there's your problem. Rate. It's not so much that CO2 buildup is happening, it's happened before in the history of the earth. Scientists even see cycles to these things."}, {"video_title": "How does climate change affect biodiversity.mp3", "Sentence": "So there's your problem. Rate. It's not so much that CO2 buildup is happening, it's happened before in the history of the earth. Scientists even see cycles to these things. But it's the current rate at which CO2 content is changing that's the running theme behind all of the problems that we're seeing today. Life just can't keep up. Here's a graph that demonstrates CO2 content in our atmosphere over time."}, {"video_title": "How does climate change affect biodiversity.mp3", "Sentence": "Scientists even see cycles to these things. But it's the current rate at which CO2 content is changing that's the running theme behind all of the problems that we're seeing today. Life just can't keep up. Here's a graph that demonstrates CO2 content in our atmosphere over time. What I like about this particular one is we go from about 400,000 years ago to the present. We've got these 100,000 year intervals and a series of interesting drops and peaks and drops and peaks. And then coming to the present, it kind of goes off the charts so much that we've got to magnify that part of the graph to see it better."}, {"video_title": "How does climate change affect biodiversity.mp3", "Sentence": "Here's a graph that demonstrates CO2 content in our atmosphere over time. What I like about this particular one is we go from about 400,000 years ago to the present. We've got these 100,000 year intervals and a series of interesting drops and peaks and drops and peaks. And then coming to the present, it kind of goes off the charts so much that we've got to magnify that part of the graph to see it better. In here, in the industrial age, we're experiencing this greatly enhanced period of carbon dioxide production through the activities of humans. There are agencies out there that are very concerned with this problem. One of them is the Intergovernmental Panel on Climate Change, or IPCC."}, {"video_title": "How does climate change affect biodiversity.mp3", "Sentence": "And then coming to the present, it kind of goes off the charts so much that we've got to magnify that part of the graph to see it better. In here, in the industrial age, we're experiencing this greatly enhanced period of carbon dioxide production through the activities of humans. There are agencies out there that are very concerned with this problem. One of them is the Intergovernmental Panel on Climate Change, or IPCC. According to the most conservative IPCC estimates, the global temperature on earth, and this is an average temperature over the whole planet, by the way, is going to rise 1.1 to 2.9 degrees Celsius during this century. That's 2 to 5.2 degrees Fahrenheit. Modeling or estimating what will happen is tricky, which is why we have these suggested ranges instead of precise single figures."}, {"video_title": "How does climate change affect biodiversity.mp3", "Sentence": "One of them is the Intergovernmental Panel on Climate Change, or IPCC. According to the most conservative IPCC estimates, the global temperature on earth, and this is an average temperature over the whole planet, by the way, is going to rise 1.1 to 2.9 degrees Celsius during this century. That's 2 to 5.2 degrees Fahrenheit. Modeling or estimating what will happen is tricky, which is why we have these suggested ranges instead of precise single figures. But what we can say is that in the worst-case scenario models, we're talking 2.4 to over 6 degrees Celsius, and that's a whopping 4.3 to 11.5 degrees Fahrenheit. Imagine the repercussions. If I think about going to my thermostat and just suddenly overnight dialing it up 10 degrees, not only are my electric and gas bills going to go through the roof, but it gets beyond cozy when it's over 80 degrees in my house."}, {"video_title": "How does climate change affect biodiversity.mp3", "Sentence": "Modeling or estimating what will happen is tricky, which is why we have these suggested ranges instead of precise single figures. But what we can say is that in the worst-case scenario models, we're talking 2.4 to over 6 degrees Celsius, and that's a whopping 4.3 to 11.5 degrees Fahrenheit. Imagine the repercussions. If I think about going to my thermostat and just suddenly overnight dialing it up 10 degrees, not only are my electric and gas bills going to go through the roof, but it gets beyond cozy when it's over 80 degrees in my house. It's not really my optimum temperature. For one thing, the ice in my drink is going to melt a heck of a lot faster, which is equally unfortunately one of the major problems for the earth as well. We're talking, of course, about global sea level rise."}, {"video_title": "How does climate change affect biodiversity.mp3", "Sentence": "If I think about going to my thermostat and just suddenly overnight dialing it up 10 degrees, not only are my electric and gas bills going to go through the roof, but it gets beyond cozy when it's over 80 degrees in my house. It's not really my optimum temperature. For one thing, the ice in my drink is going to melt a heck of a lot faster, which is equally unfortunately one of the major problems for the earth as well. We're talking, of course, about global sea level rise. It's really the continental ice masses that should be giving us the greatest cause for concern. It's fairly simple. Melting of ice on places like Greenland and high mountains, for example, will result in more water going into the ocean."}, {"video_title": "How does climate change affect biodiversity.mp3", "Sentence": "We're talking, of course, about global sea level rise. It's really the continental ice masses that should be giving us the greatest cause for concern. It's fairly simple. Melting of ice on places like Greenland and high mountains, for example, will result in more water going into the ocean. The frozen elephant in the room is Antarctica, because almost all of the ice there is on the continent, which means that when it melts, it will add enormously to the amount of water in the ocean. Even partial melting of Greenland and Antarctica together could result in 4 to 6 meters, or about 13 to 20 feet, more water in the ocean worldwide. But it could take several hundred years for that."}, {"video_title": "How does climate change affect biodiversity.mp3", "Sentence": "Melting of ice on places like Greenland and high mountains, for example, will result in more water going into the ocean. The frozen elephant in the room is Antarctica, because almost all of the ice there is on the continent, which means that when it melts, it will add enormously to the amount of water in the ocean. Even partial melting of Greenland and Antarctica together could result in 4 to 6 meters, or about 13 to 20 feet, more water in the ocean worldwide. But it could take several hundred years for that. People are looking at this very, very carefully, because if you think about 20 feet, that's enough that entire countries like the Maldives, which exist largely as low-lying atolls in the Indian Ocean, would disappear underwater. Almost any low-lying area, the Netherlands, aka Holland, for example, or New Orleans, would face serious additional flooding threats. And then you add to that things like hurricane and typhoon storm surges, and it's an enormous problem."}, {"video_title": "How does climate change affect biodiversity.mp3", "Sentence": "But it could take several hundred years for that. People are looking at this very, very carefully, because if you think about 20 feet, that's enough that entire countries like the Maldives, which exist largely as low-lying atolls in the Indian Ocean, would disappear underwater. Almost any low-lying area, the Netherlands, aka Holland, for example, or New Orleans, would face serious additional flooding threats. And then you add to that things like hurricane and typhoon storm surges, and it's an enormous problem. What does this mean for biodiversity, though? Well, in the first place, you're going to lose these low-lying places, and therefore their habitats and the species living in them. Some of these habitats are home to rare and endangered species."}, {"video_title": "How does climate change affect biodiversity.mp3", "Sentence": "And then you add to that things like hurricane and typhoon storm surges, and it's an enormous problem. What does this mean for biodiversity, though? Well, in the first place, you're going to lose these low-lying places, and therefore their habitats and the species living in them. Some of these habitats are home to rare and endangered species. Apart from the actual change in sea level, what really is a major problem for biodiversity is the warming itself. Again, remember that every species has its own optimal habitat and tolerance ranges, and that includes all the things that go along with living in the right temperature regime. The IPCC estimates that a 4\u00b0C increase, just over 7\u00b0F, is going to result in major extinction due to the inability of organisms to adapt to the changes."}, {"video_title": "How does climate change affect biodiversity.mp3", "Sentence": "Some of these habitats are home to rare and endangered species. Apart from the actual change in sea level, what really is a major problem for biodiversity is the warming itself. Again, remember that every species has its own optimal habitat and tolerance ranges, and that includes all the things that go along with living in the right temperature regime. The IPCC estimates that a 4\u00b0C increase, just over 7\u00b0F, is going to result in major extinction due to the inability of organisms to adapt to the changes. It's this rate thing again. Organisms can't move to cooler areas fast enough or adapt fast enough. Sure, some migratory animals can change their patterns of migration a bit, but what about the organisms that can't change?"}, {"video_title": "How does climate change affect biodiversity.mp3", "Sentence": "The IPCC estimates that a 4\u00b0C increase, just over 7\u00b0F, is going to result in major extinction due to the inability of organisms to adapt to the changes. It's this rate thing again. Organisms can't move to cooler areas fast enough or adapt fast enough. Sure, some migratory animals can change their patterns of migration a bit, but what about the organisms that can't change? What about the ones that can't move? Entire forests come to mind. Think of mountain ranges."}, {"video_title": "How does climate change affect biodiversity.mp3", "Sentence": "Sure, some migratory animals can change their patterns of migration a bit, but what about the organisms that can't change? What about the ones that can't move? Entire forests come to mind. Think of mountain ranges. Forests will move further up the mountainsides, completely altering or displacing entire ecosystems as they go. And we've got really interesting examples from some of our own investigators here at the Academy, people like Dave Kavanagh, who studies endemic beetles specialized to live in the icy areas high on mountains. These colder places are disappearing."}, {"video_title": "How does climate change affect biodiversity.mp3", "Sentence": "Think of mountain ranges. Forests will move further up the mountainsides, completely altering or displacing entire ecosystems as they go. And we've got really interesting examples from some of our own investigators here at the Academy, people like Dave Kavanagh, who studies endemic beetles specialized to live in the icy areas high on mountains. These colder places are disappearing. The beetles are moving to higher and higher elevations, but pretty soon they're going to run out of mountain. Even marine ecosystems are not immune. A 2\u00b0C increase in the ocean, about 3.5\u00b0F, doesn't sound like that much, but it's a lot because we're talking about a huge amount of extra heat over the entire huge size of the ocean."}, {"video_title": "How does climate change affect biodiversity.mp3", "Sentence": "These colder places are disappearing. The beetles are moving to higher and higher elevations, but pretty soon they're going to run out of mountain. Even marine ecosystems are not immune. A 2\u00b0C increase in the ocean, about 3.5\u00b0F, doesn't sound like that much, but it's a lot because we're talking about a huge amount of extra heat over the entire huge size of the ocean. And we've been talking about an average number. Some places are going to be warmer than that. Some are going to be cooler, but an overall 2\u00b0C increase is enough to result in major coral reef die-offs."}, {"video_title": "How does climate change affect biodiversity.mp3", "Sentence": "A 2\u00b0C increase in the ocean, about 3.5\u00b0F, doesn't sound like that much, but it's a lot because we're talking about a huge amount of extra heat over the entire huge size of the ocean. And we've been talking about an average number. Some places are going to be warmer than that. Some are going to be cooler, but an overall 2\u00b0C increase is enough to result in major coral reef die-offs. Reefs just can't respond to these rapid temperature changes fast enough, nor move to other places, even assuming that other suitable habitat was available. Those are some of the effects of global warming, but we also need to talk about the chemistry of adding CO2 to the world's ecosystem. There's some early evidence that shows all the regions of the world are going to be affected one way or another just by this simple addition of CO2, even if you don't talk about the global warming consequences."}, {"video_title": "How does climate change affect biodiversity.mp3", "Sentence": "Some are going to be cooler, but an overall 2\u00b0C increase is enough to result in major coral reef die-offs. Reefs just can't respond to these rapid temperature changes fast enough, nor move to other places, even assuming that other suitable habitat was available. Those are some of the effects of global warming, but we also need to talk about the chemistry of adding CO2 to the world's ecosystem. There's some early evidence that shows all the regions of the world are going to be affected one way or another just by this simple addition of CO2, even if you don't talk about the global warming consequences. Studies indicate that plant life tends to react to an increase in CO2 by building more of themselves through that amazing process of photosynthesis. The amount of carbon dioxide that plants use and turn into organic molecules for their own use is what we're talking about in fancy terminology like sequestration and carbon fixation. It's just plants saying, Oh, hey, there's more carbon dioxide."}, {"video_title": "How does climate change affect biodiversity.mp3", "Sentence": "There's some early evidence that shows all the regions of the world are going to be affected one way or another just by this simple addition of CO2, even if you don't talk about the global warming consequences. Studies indicate that plant life tends to react to an increase in CO2 by building more of themselves through that amazing process of photosynthesis. The amount of carbon dioxide that plants use and turn into organic molecules for their own use is what we're talking about in fancy terminology like sequestration and carbon fixation. It's just plants saying, Oh, hey, there's more carbon dioxide. I can make more of myself. That sounds on the face of it like a good thing. How bad could more plants actually be?"}, {"video_title": "How does climate change affect biodiversity.mp3", "Sentence": "It's just plants saying, Oh, hey, there's more carbon dioxide. I can make more of myself. That sounds on the face of it like a good thing. How bad could more plants actually be? In fact, sequestration and fixation are likely reasons that we haven't already had truly runaway global warming. But there's a limit. There's an upper level to how much plants can collect, use, or sequester carbon and thereby reduce surrounding carbon dioxide levels."}, {"video_title": "How does climate change affect biodiversity.mp3", "Sentence": "How bad could more plants actually be? In fact, sequestration and fixation are likely reasons that we haven't already had truly runaway global warming. But there's a limit. There's an upper level to how much plants can collect, use, or sequester carbon and thereby reduce surrounding carbon dioxide levels. That's because CO2 is not usually the chemical that runs out first as plants build more of themselves. It's kind of like saying, Well, you know, I could put lots and lots of oil in my car and it seems to be running fine without remembering to add some gas every now and then. You're going to run out of gas and your car eventually stops, even though you have lots of oil."}, {"video_title": "How does climate change affect biodiversity.mp3", "Sentence": "There's an upper level to how much plants can collect, use, or sequester carbon and thereby reduce surrounding carbon dioxide levels. That's because CO2 is not usually the chemical that runs out first as plants build more of themselves. It's kind of like saying, Well, you know, I could put lots and lots of oil in my car and it seems to be running fine without remembering to add some gas every now and then. You're going to run out of gas and your car eventually stops, even though you have lots of oil. Biodiversity in that sense could actually decrease as the carbon dioxide levels increase because you've got unequal abilities among plant species to sequester or absorb all this new carbon dioxide. As that happens, biodiversity or species richness can drop because plants more sensitive to the limitations of other necessary chemicals will die. Forests, marine phytoplankton, and their surrounding ecosystems become less functional as species die off and therefore less effective in sequestering carbon dioxide, causing a kind of feedback loop in which global climate change actually gets worse and worse as the unused CO2 builds up."}, {"video_title": "Extranuclear inheritance 1   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "Normally when we think about DNA, we think about the nucleus of a cell. And that's because a cell's DNA is contained in its nucleus. But there are actually a few exceptions to this general rule. So there are certain organelles that actually have their own DNA. And two very famous examples of this is the, well are the mitochondria and chloroplasts. So mitochondria and chloroplasts have their own DNA, which I'm just going to scribble in here in blue. And not only do they have their own DNA, but they can actually replicate their DNA and replicate themselves independently of the nucleus of the cell in which they are."}, {"video_title": "Extranuclear inheritance 1   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "So there are certain organelles that actually have their own DNA. And two very famous examples of this is the, well are the mitochondria and chloroplasts. So mitochondria and chloroplasts have their own DNA, which I'm just going to scribble in here in blue. And not only do they have their own DNA, but they can actually replicate their DNA and replicate themselves independently of the nucleus of the cell in which they are. So let's just talk briefly about mitochondria. So mitochondria are these organelles found in eukaryotic cells. And they're sometimes referred to as the powerhouse of a cell because they break down glucose to make this high energy molecule called ATP."}, {"video_title": "Extranuclear inheritance 1   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "And not only do they have their own DNA, but they can actually replicate their DNA and replicate themselves independently of the nucleus of the cell in which they are. So let's just talk briefly about mitochondria. So mitochondria are these organelles found in eukaryotic cells. And they're sometimes referred to as the powerhouse of a cell because they break down glucose to make this high energy molecule called ATP. And then the cell takes this ATP and uses it for all sorts of cellular processes. And the mitochondrial DNA, written like that, mtDNA, has about 37 genes in it. And these genes, most of them have to do with the cellular respiration that's going on in the mitochondria."}, {"video_title": "Extranuclear inheritance 1   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "And they're sometimes referred to as the powerhouse of a cell because they break down glucose to make this high energy molecule called ATP. And then the cell takes this ATP and uses it for all sorts of cellular processes. And the mitochondrial DNA, written like that, mtDNA, has about 37 genes in it. And these genes, most of them have to do with the cellular respiration that's going on in the mitochondria. Let's talk a bit about chloroplasts. So chloroplasts are these organelles that are found in plant cells. They're also found in algae cells."}, {"video_title": "Extranuclear inheritance 1   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "And these genes, most of them have to do with the cellular respiration that's going on in the mitochondria. Let's talk a bit about chloroplasts. So chloroplasts are these organelles that are found in plant cells. They're also found in algae cells. And chloroplasts are the site of photosynthesis. If we wanted to be more specific, so you have these stacks called granum. Well, in singular it's granum, plural it's grana."}, {"video_title": "Extranuclear inheritance 1   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "They're also found in algae cells. And chloroplasts are the site of photosynthesis. If we wanted to be more specific, so you have these stacks called granum. Well, in singular it's granum, plural it's grana. And those granum are made up of these, that's an M over there. And those granum are made up of these little circles called thylakoids. And photosynthesis happens within these thylakoids."}, {"video_title": "Extranuclear inheritance 1   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "Well, in singular it's granum, plural it's grana. And those granum are made up of these, that's an M over there. And those granum are made up of these little circles called thylakoids. And photosynthesis happens within these thylakoids. So during photosynthesis, sunlight is harnessed, of course, with a bunch of other steps to make glucose. So this is where the concept of making its own food comes from. It's actually making glucose, it's making its own food."}, {"video_title": "Extranuclear inheritance 1   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "And photosynthesis happens within these thylakoids. So during photosynthesis, sunlight is harnessed, of course, with a bunch of other steps to make glucose. So this is where the concept of making its own food comes from. It's actually making glucose, it's making its own food. And then that glucose goes to the mitochondria of that cell and gets broken down, make ATP, and then the cell uses that ATP for whatever it needs to do. The DNA in chloroplasts, sometimes written cpDNA, has about 100 genes. And these genes also, most of them have to do with proteins or things that are involved in photosynthesis."}, {"video_title": "Extranuclear inheritance 1   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "It's actually making glucose, it's making its own food. And then that glucose goes to the mitochondria of that cell and gets broken down, make ATP, and then the cell uses that ATP for whatever it needs to do. The DNA in chloroplasts, sometimes written cpDNA, has about 100 genes. And these genes also, most of them have to do with proteins or things that are involved in photosynthesis. And the reason that this is interesting is, well, let's take a look at how sexual production normally takes place. We have an egg cell, and the nucleus of this egg cell has only half the amount of DNA that a normal cell in that organism would have, so we call that N. And then we have a sperm cell. Remember, the sperm cell is really much, much smaller than an egg cell, so this is in no way drawn to scale."}, {"video_title": "Extranuclear inheritance 1   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "And these genes also, most of them have to do with proteins or things that are involved in photosynthesis. And the reason that this is interesting is, well, let's take a look at how sexual production normally takes place. We have an egg cell, and the nucleus of this egg cell has only half the amount of DNA that a normal cell in that organism would have, so we call that N. And then we have a sperm cell. Remember, the sperm cell is really much, much smaller than an egg cell, so this is in no way drawn to scale. And the sperm cell also has in its nucleus only half the amount of DNA that cells in this organism normally have, so that's also N. But then they fuse to make a zygote. And this zygote is 2N. It has the normal amount of DNA that a cell in this organism would have."}, {"video_title": "Extranuclear inheritance 1   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "Remember, the sperm cell is really much, much smaller than an egg cell, so this is in no way drawn to scale. And the sperm cell also has in its nucleus only half the amount of DNA that cells in this organism normally have, so that's also N. But then they fuse to make a zygote. And this zygote is 2N. It has the normal amount of DNA that a cell in this organism would have. Half of it comes from the egg cell, and half of it comes from the sperm cell. And then this zygote is going to divide into two cells, and then those two cells, of course, divide further. And this goes on and on until they are enough cells to put together an organism."}, {"video_title": "Extranuclear inheritance 1   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "It has the normal amount of DNA that a cell in this organism would have. Half of it comes from the egg cell, and half of it comes from the sperm cell. And then this zygote is going to divide into two cells, and then those two cells, of course, divide further. And this goes on and on until they are enough cells to put together an organism. But this egg cell, well, it's a fully developed cell, and it not only has genetic information, but it has organelles in the cytoplasm. So it has these mitochondria in its cytoplasm, and those mitochondria have DNA in it, which I'm just going to scribble some blue inside. And the zygote also has those mitochondria, because remember, the zygote is, well, practically an egg cell, but with the only difference being that its nucleus has the additional DNA of the sperm cell."}, {"video_title": "Extranuclear inheritance 1   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "And this goes on and on until they are enough cells to put together an organism. But this egg cell, well, it's a fully developed cell, and it not only has genetic information, but it has organelles in the cytoplasm. So it has these mitochondria in its cytoplasm, and those mitochondria have DNA in it, which I'm just going to scribble some blue inside. And the zygote also has those mitochondria, because remember, the zygote is, well, practically an egg cell, but with the only difference being that its nucleus has the additional DNA of the sperm cell. And remember, the sperm cell does not donate anything to the egg cell except for half of the DNA in the nucleus. It does not give the zygote anything else. So you have a zygote with those mitochondria, and of course they have their DNA in it."}, {"video_title": "Extranuclear inheritance 1   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "And the zygote also has those mitochondria, because remember, the zygote is, well, practically an egg cell, but with the only difference being that its nucleus has the additional DNA of the sperm cell. And remember, the sperm cell does not donate anything to the egg cell except for half of the DNA in the nucleus. It does not give the zygote anything else. So you have a zygote with those mitochondria, and of course they have their DNA in it. And then this zygote replicates itself, so it replicates the nucleus, but it also replicates the mitochondria in the cytoplasm. And these cells will, I'm going to skip out the nucleus, I'm just drawing the mitochondria, so you have these mitochondria, but these mitochondria came only from the egg cell. None of those mitochondria came from the sperm cell."}, {"video_title": "Extranuclear inheritance 1   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "So you have a zygote with those mitochondria, and of course they have their DNA in it. And then this zygote replicates itself, so it replicates the nucleus, but it also replicates the mitochondria in the cytoplasm. And these cells will, I'm going to skip out the nucleus, I'm just drawing the mitochondria, so you have these mitochondria, but these mitochondria came only from the egg cell. None of those mitochondria came from the sperm cell. And so this brings us to the concept of maternal inheritance. And maternal inheritance, well, it's basically like, exactly the way it sounds, it's inheritance that happens only from the maternal line, or only from the egg cell. So right here, we're showing that the mitochondria that this organism will eventually have originates from the mitochondria that came only from the egg cell and not from the sperm cell."}, {"video_title": "Extranuclear inheritance 1   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "None of those mitochondria came from the sperm cell. And so this brings us to the concept of maternal inheritance. And maternal inheritance, well, it's basically like, exactly the way it sounds, it's inheritance that happens only from the maternal line, or only from the egg cell. So right here, we're showing that the mitochondria that this organism will eventually have originates from the mitochondria that came only from the egg cell and not from the sperm cell. And therefore, it exhibits maternal inheritance. So both mitochondria and chloroplasts exhibit maternal inheritance because they are in the egg cell that eventually becomes the organism. And maternal inheritance, it's interesting to note, is contrary to Mendelian genetics."}, {"video_title": "Extranuclear inheritance 1   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "So right here, we're showing that the mitochondria that this organism will eventually have originates from the mitochondria that came only from the egg cell and not from the sperm cell. And therefore, it exhibits maternal inheritance. So both mitochondria and chloroplasts exhibit maternal inheritance because they are in the egg cell that eventually becomes the organism. And maternal inheritance, it's interesting to note, is contrary to Mendelian genetics. So maternal inheritance is contrary to Mendelian genetics because Mendelian genetics assumes that half of the DNA comes from the egg cell, half from the sperm cell. It does not take into account any sort of genetic information that comes from only one of the gametes, for example, just from the egg cell. And in fact, everything we just described here can be referred to as extra-nuclear inheritance."}, {"video_title": "Extranuclear inheritance 1   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "And maternal inheritance, it's interesting to note, is contrary to Mendelian genetics. So maternal inheritance is contrary to Mendelian genetics because Mendelian genetics assumes that half of the DNA comes from the egg cell, half from the sperm cell. It does not take into account any sort of genetic information that comes from only one of the gametes, for example, just from the egg cell. And in fact, everything we just described here can be referred to as extra-nuclear inheritance. So extra-nuclear inheritance would refer to any genes that are passed on from structures that are not in the nucleus. So extra-nuclear meaning outside of the nucleus. So mitochondria and chloroplasts are outside of the nucleus, so when they are inherited, we refer to it as extra-nuclear inheritance."}, {"video_title": "Cell size   Structure of a cell   Biology   Khan Academy.mp3", "Sentence": "And I have some pictures of cells here. This picture right over here, this picture of Pseudomonas bacteria, each of these pill-shaped things, this is a bacterial cell. And just to get a sense of scale, the width of this pill is around one micrometer. So this is approximately one micrometer, which is the same thing as one millionth of a meter, or you could think of it as one thousandth of a millimeter, whatever helps you conceptualize this better. And then the length here, this is about five micrometers. This is approximately five micrometers. Now over here, I have some pictures of cells that you would find in the human body."}, {"video_title": "Cell size   Structure of a cell   Biology   Khan Academy.mp3", "Sentence": "So this is approximately one micrometer, which is the same thing as one millionth of a meter, or you could think of it as one thousandth of a millimeter, whatever helps you conceptualize this better. And then the length here, this is about five micrometers. This is approximately five micrometers. Now over here, I have some pictures of cells that you would find in the human body. These are red blood cells. These have a diameter of about seven micrometers. You see a similar scale for these white blood cells or some other things in here."}, {"video_title": "Cell size   Structure of a cell   Biology   Khan Academy.mp3", "Sentence": "Now over here, I have some pictures of cells that you would find in the human body. These are red blood cells. These have a diameter of about seven micrometers. You see a similar scale for these white blood cells or some other things in here. Over here, we see a human sperm cell about to penetrate a human egg cell. And human egg cells are some of the largest cells you'd find, especially if we're talking about spherical cells. And this cell here, this is going to have a diameter on the order of 100 micrometers."}, {"video_title": "Cell size   Structure of a cell   Biology   Khan Academy.mp3", "Sentence": "You see a similar scale for these white blood cells or some other things in here. Over here, we see a human sperm cell about to penetrate a human egg cell. And human egg cells are some of the largest cells you'd find, especially if we're talking about spherical cells. And this cell here, this is going to have a diameter on the order of 100 micrometers. So the first question we would, and it's kind of neat that all of these pictures are almost on the same scale, so you can almost compare them. But the first question we ask is, well, how small can a cell get? Well, if you think about it, a cell is a living thing."}, {"video_title": "Cell size   Structure of a cell   Biology   Khan Academy.mp3", "Sentence": "And this cell here, this is going to have a diameter on the order of 100 micrometers. So the first question we would, and it's kind of neat that all of these pictures are almost on the same scale, so you can almost compare them. But the first question we ask is, well, how small can a cell get? Well, if you think about it, a cell is a living thing. It's actually quite complex. It has to have information, it has DNA, it has to be able to replicate itself. It has all of this metabolic machinery."}, {"video_title": "Cell size   Structure of a cell   Biology   Khan Academy.mp3", "Sentence": "Well, if you think about it, a cell is a living thing. It's actually quite complex. It has to have information, it has DNA, it has to be able to replicate itself. It has all of this metabolic machinery. So I just did some reading, and the smallest cells observed, and I think this might be the smallest cells period, although there might be future ones that are discovered that are even smaller, are actually on the order of about a few hundred nanometers. Remember, a thousand nanometers would be the width of this pill. So a few hundred nanometers, like maybe something like that, would be maybe 300 nanometers."}, {"video_title": "Cell size   Structure of a cell   Biology   Khan Academy.mp3", "Sentence": "It has all of this metabolic machinery. So I just did some reading, and the smallest cells observed, and I think this might be the smallest cells period, although there might be future ones that are discovered that are even smaller, are actually on the order of about a few hundred nanometers. Remember, a thousand nanometers would be the width of this pill. So a few hundred nanometers, like maybe something like that, would be maybe 300 nanometers. These were the smallest cells discovered so far. They were bacterial cells. They were discovered at the University of California, Berkeley."}, {"video_title": "Cell size   Structure of a cell   Biology   Khan Academy.mp3", "Sentence": "So a few hundred nanometers, like maybe something like that, would be maybe 300 nanometers. These were the smallest cells discovered so far. They were bacterial cells. They were discovered at the University of California, Berkeley. And we think that this is pretty close to the lower bound, because you've got to remember, we have to store all of this genetic information and all of this cellular machinery. So that stuff's complex, and you can only get so small. But what about the upper bound of cells?"}, {"video_title": "Cell size   Structure of a cell   Biology   Khan Academy.mp3", "Sentence": "They were discovered at the University of California, Berkeley. And we think that this is pretty close to the lower bound, because you've got to remember, we have to store all of this genetic information and all of this cellular machinery. So that stuff's complex, and you can only get so small. But what about the upper bound of cells? Well, one of the things that tends to be the limiting factor, and there's other things as well, but it's the ability for, it's the ratio of volume to surface area. And why does volume, why does that, why does the ratio of volume to surface area matter? Well, because the surface is what interfaces the cell with its surroundings."}, {"video_title": "Cell size   Structure of a cell   Biology   Khan Academy.mp3", "Sentence": "But what about the upper bound of cells? Well, one of the things that tends to be the limiting factor, and there's other things as well, but it's the ability for, it's the ratio of volume to surface area. And why does volume, why does that, why does the ratio of volume to surface area matter? Well, because the surface is what interfaces the cell with its surroundings. It has to take in nutrients and take out the waste. So each unit of surface area, it has to process the inputs and the outputs for a certain volume of cells, or for a certain volume of the cell. And as we'll see as the cell grows, the volume and surface area don't grow together."}, {"video_title": "Cell size   Structure of a cell   Biology   Khan Academy.mp3", "Sentence": "Well, because the surface is what interfaces the cell with its surroundings. It has to take in nutrients and take out the waste. So each unit of surface area, it has to process the inputs and the outputs for a certain volume of cells, or for a certain volume of the cell. And as we'll see as the cell grows, the volume and surface area don't grow together. The volume increases faster than the surface area does. So as you grow, each unit of surface area has to handle the processing with the environment for more and more volume. At some point, it just can't handle it."}, {"video_title": "Cell size   Structure of a cell   Biology   Khan Academy.mp3", "Sentence": "And as we'll see as the cell grows, the volume and surface area don't grow together. The volume increases faster than the surface area does. So as you grow, each unit of surface area has to handle the processing with the environment for more and more volume. At some point, it just can't handle it. It can't take in nutrients and get rid of waste fast enough. And to make that a little bit more tangible, let's think about it mathematically. So the volume, the volume of a sphere, let's say this is a sphere here, so let me make it look a little bit more three-dimensional."}, {"video_title": "Cell size   Structure of a cell   Biology   Khan Academy.mp3", "Sentence": "At some point, it just can't handle it. It can't take in nutrients and get rid of waste fast enough. And to make that a little bit more tangible, let's think about it mathematically. So the volume, the volume of a sphere, let's say this is a sphere here, so let me make it look a little bit more three-dimensional. If it has radius r, its volume is going to be 4 3rds pi r cubed. Now its surface area is going to be, its surface area is going to be 4 pi r squared. Now let's calculate the ratio of volume to surface area, because that's what we really care about, the ratio of volume to surface area is, I want to do surface area in yellow, to surface area is equal to, it's equal to 4 3rds pi r cubed over 4 pi r squared."}, {"video_title": "Cell size   Structure of a cell   Biology   Khan Academy.mp3", "Sentence": "So the volume, the volume of a sphere, let's say this is a sphere here, so let me make it look a little bit more three-dimensional. If it has radius r, its volume is going to be 4 3rds pi r cubed. Now its surface area is going to be, its surface area is going to be 4 pi r squared. Now let's calculate the ratio of volume to surface area, because that's what we really care about, the ratio of volume to surface area is, I want to do surface area in yellow, to surface area is equal to, it's equal to 4 3rds pi r cubed over 4 pi r squared. Now luckily, this simplifies quite nicely. 4 divided by 4 is 1, pi divided by pi is 1, r to the 3rd divided by r squared is just going to be r. So this all simplified very nicely to r over 3. And if we wanted to care about units, it would be cubic units of volume, or it would be cubic units divided by square units, whichever unit we're looking at."}, {"video_title": "Cell size   Structure of a cell   Biology   Khan Academy.mp3", "Sentence": "Now let's calculate the ratio of volume to surface area, because that's what we really care about, the ratio of volume to surface area is, I want to do surface area in yellow, to surface area is equal to, it's equal to 4 3rds pi r cubed over 4 pi r squared. Now luckily, this simplifies quite nicely. 4 divided by 4 is 1, pi divided by pi is 1, r to the 3rd divided by r squared is just going to be r. So this all simplified very nicely to r over 3. And if we wanted to care about units, it would be cubic units of volume, or it would be cubic units divided by square units, whichever unit we're looking at. So this is going to be r over 3. So let's use this to think about what happens as a cell gets much larger. So for simplicity, let's focus on this white blood cell here, and just to make the math easy, let's assume that it has a radius, let's assume it has a radius of 3 micrometers."}, {"video_title": "Cell size   Structure of a cell   Biology   Khan Academy.mp3", "Sentence": "And if we wanted to care about units, it would be cubic units of volume, or it would be cubic units divided by square units, whichever unit we're looking at. So this is going to be r over 3. So let's use this to think about what happens as a cell gets much larger. So for simplicity, let's focus on this white blood cell here, and just to make the math easy, let's assume that it has a radius, let's assume it has a radius of 3 micrometers. I'm going to do this in a color you can see. 3 micrometers. So in that case, for this cell, its volume to surface area is going to be 3, we could just say 3 micrometers divided by 3, but I'll put 3, we could say 3 micrometers divided by 3, which of course is just going to be 1 micrometer."}, {"video_title": "Cell size   Structure of a cell   Biology   Khan Academy.mp3", "Sentence": "So for simplicity, let's focus on this white blood cell here, and just to make the math easy, let's assume that it has a radius, let's assume it has a radius of 3 micrometers. I'm going to do this in a color you can see. 3 micrometers. So in that case, for this cell, its volume to surface area is going to be 3, we could just say 3 micrometers divided by 3, but I'll put 3, we could say 3 micrometers divided by 3, which of course is just going to be 1 micrometer. But having a unit of 1 micrometer for volume to surface area doesn't really make a lot of sense. An equivalent unit would say 1 cubic micrometer per square micrometer, because we're doing volume to surface area. Now obviously if you let the units cancel, you did the dimensional analysis, you'd be just left with this micrometer."}, {"video_title": "Cell size   Structure of a cell   Biology   Khan Academy.mp3", "Sentence": "So in that case, for this cell, its volume to surface area is going to be 3, we could just say 3 micrometers divided by 3, but I'll put 3, we could say 3 micrometers divided by 3, which of course is just going to be 1 micrometer. But having a unit of 1 micrometer for volume to surface area doesn't really make a lot of sense. An equivalent unit would say 1 cubic micrometer per square micrometer, because we're doing volume to surface area. Now obviously if you let the units cancel, you did the dimensional analysis, you'd be just left with this micrometer. But this helps us conceptualize it a little bit more, because it says that each square micrometer needs to handle 1 cubic micrometer of cellular volume. So each square micrometer, so square micrometer for this guy over here is going to be around that size, it's going to handle the processing on average for 1 cubic micrometer of volume. Alright, that seems reasonable, and that's a reasonable size for a cell."}, {"video_title": "Cell size   Structure of a cell   Biology   Khan Academy.mp3", "Sentence": "Now obviously if you let the units cancel, you did the dimensional analysis, you'd be just left with this micrometer. But this helps us conceptualize it a little bit more, because it says that each square micrometer needs to handle 1 cubic micrometer of cellular volume. So each square micrometer, so square micrometer for this guy over here is going to be around that size, it's going to handle the processing on average for 1 cubic micrometer of volume. Alright, that seems reasonable, and that's a reasonable size for a cell. But what if we were to increase things by a factor of 1,000? Or increase the radius by a factor of 1,000? And I'm obviously not drawing this to scale, but let's say we find some new organism or we theorize some organism that's cellular radius, instead of it being three micrometers, so this was three micrometers, it's 3,000."}, {"video_title": "Cell size   Structure of a cell   Biology   Khan Academy.mp3", "Sentence": "Alright, that seems reasonable, and that's a reasonable size for a cell. But what if we were to increase things by a factor of 1,000? Or increase the radius by a factor of 1,000? And I'm obviously not drawing this to scale, but let's say we find some new organism or we theorize some organism that's cellular radius, instead of it being three micrometers, so this was three micrometers, it's 3,000. 3,000 millionths of a meter. And just to be clear, this isn't ginormous by our scales, this would be three millimeters. This would be three millimeters, it would be visible by the human eye, the kind of threshold of what the human eye can see is about a tenth of a millimeter, which is 100 micrometers."}, {"video_title": "Cell size   Structure of a cell   Biology   Khan Academy.mp3", "Sentence": "And I'm obviously not drawing this to scale, but let's say we find some new organism or we theorize some organism that's cellular radius, instead of it being three micrometers, so this was three micrometers, it's 3,000. 3,000 millionths of a meter. And just to be clear, this isn't ginormous by our scales, this would be three millimeters. This would be three millimeters, it would be visible by the human eye, the kind of threshold of what the human eye can see is about a tenth of a millimeter, which is 100 micrometers. This is approximately, or this is one tenth of a millimeter. So in the right conditions, you could just barely see a human egg cell. But this right over here, this would be still small by our scales, but let's just think about what happens to the volume to surface area."}, {"video_title": "Cell size   Structure of a cell   Biology   Khan Academy.mp3", "Sentence": "This would be three millimeters, it would be visible by the human eye, the kind of threshold of what the human eye can see is about a tenth of a millimeter, which is 100 micrometers. This is approximately, or this is one tenth of a millimeter. So in the right conditions, you could just barely see a human egg cell. But this right over here, this would be still small by our scales, but let's just think about what happens to the volume to surface area. Volume to surface area, 3,000 micrometers divided by three, 3,000 micrometers divided by three, we'd be left with, this is 1,000 micrometers, or even better, we could write this as 1,000 cubic micrometers per square micrometer. So now each square micrometer, in this case it had to handle a cubic micrometer of volume, but now it has to handle 1,000, 1,000 cubic micrometers of volume. So it has to handle much more volume."}, {"video_title": "Cell size   Structure of a cell   Biology   Khan Academy.mp3", "Sentence": "But this right over here, this would be still small by our scales, but let's just think about what happens to the volume to surface area. Volume to surface area, 3,000 micrometers divided by three, 3,000 micrometers divided by three, we'd be left with, this is 1,000 micrometers, or even better, we could write this as 1,000 cubic micrometers per square micrometer. So now each square micrometer, in this case it had to handle a cubic micrometer of volume, but now it has to handle 1,000, 1,000 cubic micrometers of volume. So it has to handle much more volume. And that's gonna break down. It's not gonna be able to exchange the gases, exchange the nutrients, exchange the waste fast enough for this cell to function. So this is a very important ratio, volume to surface area for cells."}, {"video_title": "Cell size   Structure of a cell   Biology   Khan Academy.mp3", "Sentence": "So it has to handle much more volume. And that's gonna break down. It's not gonna be able to exchange the gases, exchange the nutrients, exchange the waste fast enough for this cell to function. So this is a very important ratio, volume to surface area for cells. And it actually ends up, well, I'll just talk about cells in general. It actually tends to be an interesting thing as a lot of things grow, volume to surface area or mass, or, well, there's a lot of other ratios that are interesting, but this is one of them. Now the other factor that will play in is also as the cell gets larger, the machinery has to just traverse more distances."}, {"video_title": "Cell size   Structure of a cell   Biology   Khan Academy.mp3", "Sentence": "So this is a very important ratio, volume to surface area for cells. And it actually ends up, well, I'll just talk about cells in general. It actually tends to be an interesting thing as a lot of things grow, volume to surface area or mass, or, well, there's a lot of other ratios that are interesting, but this is one of them. Now the other factor that will play in is also as the cell gets larger, the machinery has to just traverse more distances. You have to transport things over longer distances, which also can become cumbersome. But the volume to surface area is a really interesting one to think about why we don't tend to see very, very, very large, especially spherical cells. And the reason why I emphasize spherical cells is because you do see cells that are longer than even this scale, like nerve cells."}, {"video_title": "Cell size   Structure of a cell   Biology   Khan Academy.mp3", "Sentence": "Now the other factor that will play in is also as the cell gets larger, the machinery has to just traverse more distances. You have to transport things over longer distances, which also can become cumbersome. But the volume to surface area is a really interesting one to think about why we don't tend to see very, very, very large, especially spherical cells. And the reason why I emphasize spherical cells is because you do see cells that are longer than even this scale, like nerve cells. And they get by with that. They have other adaptations, but one of them is to just be really skinny and long. So this is one way that they can maximize their surface area."}, {"video_title": "Cell size   Structure of a cell   Biology   Khan Academy.mp3", "Sentence": "And the reason why I emphasize spherical cells is because you do see cells that are longer than even this scale, like nerve cells. And they get by with that. They have other adaptations, but one of them is to just be really skinny and long. So this is one way that they can maximize their surface area. So like that, this is a nerve cell. Other ways that you'll see cells that maximize their surface area is that they have a lot of things that kind of stick out to maximize. So cells are clearly not all spherical."}, {"video_title": "Cell size   Structure of a cell   Biology   Khan Academy.mp3", "Sentence": "So this is one way that they can maximize their surface area. So like that, this is a nerve cell. Other ways that you'll see cells that maximize their surface area is that they have a lot of things that kind of stick out to maximize. So cells are clearly not all spherical. So they could have other things that maximize their surface area like that. So there's a bunch of adaptations, but in general, modeling them as a sphere isn't a crazy thing to do. And this is why we don't tend to see cells much larger than a human egg cell."}, {"video_title": "Phenotype plasticity   Heredity   AP Biology   Khan Academy.mp3", "Sentence": "You can see his name on his patch right over there. And then this is Scott Kelly. And the reason why we want to look at these two astronauts in particular is to think about genotype and phenotype that we have been introduced to in other videos. So just as a bit of a review, when people talk about genotype, they're talking about the actual genetic information encoded in an organism's genes. So if you go inside a cell, we have chromosomes, and then on those chromosomes, each chromosome's a long stretch of DNA, and then sections of that long stretch of DNA will code for various things, often, usually, various proteins. But there's a difference between what is actually, what information is in one's genes versus what actually gets expressed. The observable characteristics, that is phenotype."}, {"video_title": "Phenotype plasticity   Heredity   AP Biology   Khan Academy.mp3", "Sentence": "So just as a bit of a review, when people talk about genotype, they're talking about the actual genetic information encoded in an organism's genes. So if you go inside a cell, we have chromosomes, and then on those chromosomes, each chromosome's a long stretch of DNA, and then sections of that long stretch of DNA will code for various things, often, usually, various proteins. But there's a difference between what is actually, what information is in one's genes versus what actually gets expressed. The observable characteristics, that is phenotype. And two people with the same genotype, they might have a very similar phenotype, but they won't necessarily have an identical phenotype because above and beyond the genes affecting phenotype, you also have the environment affecting someone's phenotype. So as you can see here, Mark and Scott Kelly, they're identical twins. They have the same genotype."}, {"video_title": "Phenotype plasticity   Heredity   AP Biology   Khan Academy.mp3", "Sentence": "The observable characteristics, that is phenotype. And two people with the same genotype, they might have a very similar phenotype, but they won't necessarily have an identical phenotype because above and beyond the genes affecting phenotype, you also have the environment affecting someone's phenotype. So as you can see here, Mark and Scott Kelly, they're identical twins. They have the same genotype. But if you just look at their facial characteristics, you can see that you could tell the difference between the two. And it's not just the fact that Mark has a mustache and that Scott doesn't. We could draw in a mustache."}, {"video_title": "Phenotype plasticity   Heredity   AP Biology   Khan Academy.mp3", "Sentence": "They have the same genotype. But if you just look at their facial characteristics, you can see that you could tell the difference between the two. And it's not just the fact that Mark has a mustache and that Scott doesn't. We could draw in a mustache. You would still see that they look different. And that's because their bodies developed in different ways based on the environment that they happen to be in. And this idea that the same genotype could result in variations of phenotype, this is known as phenotype plasticity."}, {"video_title": "Phenotype plasticity   Heredity   AP Biology   Khan Academy.mp3", "Sentence": "We could draw in a mustache. You would still see that they look different. And that's because their bodies developed in different ways based on the environment that they happen to be in. And this idea that the same genotype could result in variations of phenotype, this is known as phenotype plasticity. Phenotype. Phenotype plasticity. And maybe in one of the most extreme experiments ever conducted on phenotype plasticity, Nassau was intrigued to see, well, what would happen to the gene expression if Scott Kelly spent an extensive period of time in space while his twin brother didn't?"}, {"video_title": "Phenotype plasticity   Heredity   AP Biology   Khan Academy.mp3", "Sentence": "And this idea that the same genotype could result in variations of phenotype, this is known as phenotype plasticity. Phenotype. Phenotype plasticity. And maybe in one of the most extreme experiments ever conducted on phenotype plasticity, Nassau was intrigued to see, well, what would happen to the gene expression if Scott Kelly spent an extensive period of time in space while his twin brother didn't? So they looked at how their bodies expressed certain characteristics before Scott spent an extended period of time in space. And then after he spent that time in space, they studied his body. And they saw that there was differences in the mitochondria, differences in which genes were expressed."}, {"video_title": "Phenotype plasticity   Heredity   AP Biology   Khan Academy.mp3", "Sentence": "And maybe in one of the most extreme experiments ever conducted on phenotype plasticity, Nassau was intrigued to see, well, what would happen to the gene expression if Scott Kelly spent an extensive period of time in space while his twin brother didn't? So they looked at how their bodies expressed certain characteristics before Scott spent an extended period of time in space. And then after he spent that time in space, they studied his body. And they saw that there was differences in the mitochondria, differences in which genes were expressed. In fact, there was a 7% difference in the gene expression after the extended time in space for Scott. So that's the example of that space environment changing Scott's phenotype. And the NASA scientists theorized that it was a low oxygen environment."}, {"video_title": "DNA and chromatin regulation   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "So the regulation of gene expression can be modulated at virtually any step in the process, from the initiation of transcription all the way to post-translational modification of a protein, and every step in between. And it's the ability to regulate all these different steps that helps the cell to have the versatility and the adaptability of an efficient ninja, so that it expends energy to express the appropriate proteins only when needed. Or you can think of the cell as a lazy couch potato that wants to expend the least amount of energy as possible. So starting at the beginning of gene expression, let's talk about gene regulation as it pertains to DNA and chromatin regulation. Let's talk about the structure of DNA. DNA is packed into chromosomes in the form of chromatin, also known as supercoiled DNA. And so chromatin is made up of DNA, histone proteins, and non-histone proteins."}, {"video_title": "DNA and chromatin regulation   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "So starting at the beginning of gene expression, let's talk about gene regulation as it pertains to DNA and chromatin regulation. Let's talk about the structure of DNA. DNA is packed into chromosomes in the form of chromatin, also known as supercoiled DNA. And so chromatin is made up of DNA, histone proteins, and non-histone proteins. And there are repeating units in chromatin called nucleosomes, which are made up of 146 base pairs of double-helical DNA that is wrapped around a core of eight histones. And there are four different types of histones within this structure of eight that you should be aware of. And they're named H2A, H2B, H3, and H4."}, {"video_title": "DNA and chromatin regulation   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "And so chromatin is made up of DNA, histone proteins, and non-histone proteins. And there are repeating units in chromatin called nucleosomes, which are made up of 146 base pairs of double-helical DNA that is wrapped around a core of eight histones. And there are four different types of histones within this structure of eight that you should be aware of. And they're named H2A, H2B, H3, and H4. That's just the nomenclature they've been given. Now, acetylation occurs at the amino terminal tails of these histone proteins by an enzyme called histone acetyltransferase, which I'll just abbreviate as HAT. And this is a reversible modification."}, {"video_title": "DNA and chromatin regulation   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "And they're named H2A, H2B, H3, and H4. That's just the nomenclature they've been given. Now, acetylation occurs at the amino terminal tails of these histone proteins by an enzyme called histone acetyltransferase, which I'll just abbreviate as HAT. And this is a reversible modification. So the acetylation of histones is sort of kept in balance by another enzyme that removes these acetyl groups, which is called histone deacetylase, or HDAC, HDAC. The acetylation of histones leads to uncoiling of this chromatin structure. And this allows it to be accessed by transcriptional machinery for the expression of genes."}, {"video_title": "DNA and chromatin regulation   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "And this is a reversible modification. So the acetylation of histones is sort of kept in balance by another enzyme that removes these acetyl groups, which is called histone deacetylase, or HDAC, HDAC. The acetylation of histones leads to uncoiling of this chromatin structure. And this allows it to be accessed by transcriptional machinery for the expression of genes. On the flip side of this, histone deacetylation leads to a condensed or closed structure of the chromatin, and less transcription of those genes. When these modifications that regulate gene expression are inheritable, they are referred to as epigenetic regulation. So when it comes to gene expression in DNA, you can basically think of DNA as coming in two flavors."}, {"video_title": "DNA and chromatin regulation   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "And this allows it to be accessed by transcriptional machinery for the expression of genes. On the flip side of this, histone deacetylation leads to a condensed or closed structure of the chromatin, and less transcription of those genes. When these modifications that regulate gene expression are inheritable, they are referred to as epigenetic regulation. So when it comes to gene expression in DNA, you can basically think of DNA as coming in two flavors. Densely packed and transcriptionally inactive DNA, which is called heterochromatin, and then less dense transcriptionally active DNA, which is euchromatin. And I like to think of heterochromatin as being densely packed and hibernating, like heterochromatin and hibernating both begin with H, kind of like a bunch of densely packed bears that are closed off in their cave for the winter. Whereas euchromatin is waiting there with open arms, welcoming the transcriptional machinery to transcribe away."}, {"video_title": "DNA and chromatin regulation   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "So when it comes to gene expression in DNA, you can basically think of DNA as coming in two flavors. Densely packed and transcriptionally inactive DNA, which is called heterochromatin, and then less dense transcriptionally active DNA, which is euchromatin. And I like to think of heterochromatin as being densely packed and hibernating, like heterochromatin and hibernating both begin with H, kind of like a bunch of densely packed bears that are closed off in their cave for the winter. Whereas euchromatin is waiting there with open arms, welcoming the transcriptional machinery to transcribe away. Now often, you will see that histone deacetylation is combined with another type of DNA regulatory mechanism, and that is DNA methylation. And this occurs in a process called gene silencing. And this is a more permanent method of sort of down-regulating the transcription of genes."}, {"video_title": "DNA and chromatin regulation   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "Whereas euchromatin is waiting there with open arms, welcoming the transcriptional machinery to transcribe away. Now often, you will see that histone deacetylation is combined with another type of DNA regulatory mechanism, and that is DNA methylation. And this occurs in a process called gene silencing. And this is a more permanent method of sort of down-regulating the transcription of genes. And DNA methylation involves the addition of a methyl group, which is a carbon with three hydrogens, to the cytosine DNA nucleotides by an enzyme appropriately called methyl transferase. And this typically occurs in cytosine-rich sequences called CpG islands. Don't forget that cytosine pairs with G, guanine, so that's why there are Cg islands that you'll find."}, {"video_title": "DNA and chromatin regulation   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "And this is a more permanent method of sort of down-regulating the transcription of genes. And DNA methylation involves the addition of a methyl group, which is a carbon with three hydrogens, to the cytosine DNA nucleotides by an enzyme appropriately called methyl transferase. And this typically occurs in cytosine-rich sequences called CpG islands. Don't forget that cytosine pairs with G, guanine, so that's why there are Cg islands that you'll find. DNA methylation stably alters the expression of genes. And so it occurs as cells divide and differentiate from embryonic stem cells into specific tissues. And so this is essential for normal development and is associated with other processes such as genomic imprinting and X chromosome inactivation, topics for another discussion."}, {"video_title": "DNA and chromatin regulation   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "Don't forget that cytosine pairs with G, guanine, so that's why there are Cg islands that you'll find. DNA methylation stably alters the expression of genes. And so it occurs as cells divide and differentiate from embryonic stem cells into specific tissues. And so this is essential for normal development and is associated with other processes such as genomic imprinting and X chromosome inactivation, topics for another discussion. And abnormal DNA methylation has been implicated in carcinogenesis, or the development of cancer. So you can see how the normal functioning of DNA methylation is a critical regulatory mechanism for our cells. Now, DNA methylation may affect the transcription of genes in two ways."}, {"video_title": "DNA and chromatin regulation   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "And so this is essential for normal development and is associated with other processes such as genomic imprinting and X chromosome inactivation, topics for another discussion. And abnormal DNA methylation has been implicated in carcinogenesis, or the development of cancer. So you can see how the normal functioning of DNA methylation is a critical regulatory mechanism for our cells. Now, DNA methylation may affect the transcription of genes in two ways. First, the methylation of DNA itself may physically impede the binding of transcriptional proteins to the gene. And second, and likely more important, methylated DNA may be bound by proteins known as methyl CpG binding domain proteins, or MBDs for short. Now, MBD proteins can then recruit additional proteins to the locus or particular location in a chromosome, certain genes, such as histone deacetylases and other chromatin remodeling proteins."}, {"video_title": "Extranuclear inheritance 1   Biomolecules   MCAT   Khan Academy (2).mp3", "Sentence": "And that's because a cell's DNA is contained in its nucleus. But there are actually a few exceptions to this general rule. So there are certain organelles that actually have their own DNA. And two very famous examples of this is the, well are the mitochondria and chloroplasts. So mitochondria and chloroplasts have their own DNA, which I'm just going to scribble in here in blue. And not only do they have their own DNA, but they can actually replicate their DNA and replicate themselves independently of the nucleus of the cell in which they are. So let's just talk briefly about mitochondria."}, {"video_title": "Extranuclear inheritance 1   Biomolecules   MCAT   Khan Academy (2).mp3", "Sentence": "And two very famous examples of this is the, well are the mitochondria and chloroplasts. So mitochondria and chloroplasts have their own DNA, which I'm just going to scribble in here in blue. And not only do they have their own DNA, but they can actually replicate their DNA and replicate themselves independently of the nucleus of the cell in which they are. So let's just talk briefly about mitochondria. So mitochondria are these organelles found in eukaryotic cells. And they're sometimes referred to as the powerhouse of a cell because they break down glucose to make this high energy molecule called ATP. And then the cell takes this ATP and uses it for all sorts of cellular processes."}, {"video_title": "Extranuclear inheritance 1   Biomolecules   MCAT   Khan Academy (2).mp3", "Sentence": "So let's just talk briefly about mitochondria. So mitochondria are these organelles found in eukaryotic cells. And they're sometimes referred to as the powerhouse of a cell because they break down glucose to make this high energy molecule called ATP. And then the cell takes this ATP and uses it for all sorts of cellular processes. And the mitochondrial DNA, written like that, mtDNA, has about 37 genes in it. And these genes, most of them have to do with the cellular respiration that's going on in the mitochondria. Let's talk a bit about chloroplasts."}, {"video_title": "Extranuclear inheritance 1   Biomolecules   MCAT   Khan Academy (2).mp3", "Sentence": "And then the cell takes this ATP and uses it for all sorts of cellular processes. And the mitochondrial DNA, written like that, mtDNA, has about 37 genes in it. And these genes, most of them have to do with the cellular respiration that's going on in the mitochondria. Let's talk a bit about chloroplasts. So chloroplasts are these organelles that are found in plant cells. They're also found in algae cells. And chloroplasts are the site of photosynthesis."}, {"video_title": "Extranuclear inheritance 1   Biomolecules   MCAT   Khan Academy (2).mp3", "Sentence": "Let's talk a bit about chloroplasts. So chloroplasts are these organelles that are found in plant cells. They're also found in algae cells. And chloroplasts are the site of photosynthesis. If we wanted to be more specific, so you have these stacks called granum. Well, in singular it's granum, plural it's grana. And those granum are made up of these, that's an M over there."}, {"video_title": "Extranuclear inheritance 1   Biomolecules   MCAT   Khan Academy (2).mp3", "Sentence": "And chloroplasts are the site of photosynthesis. If we wanted to be more specific, so you have these stacks called granum. Well, in singular it's granum, plural it's grana. And those granum are made up of these, that's an M over there. And those granum are made up of these little circles called thylakoids. And photosynthesis happens within these thylakoids. So during photosynthesis, sunlight is harnessed, of course, with a bunch of other steps to make glucose."}, {"video_title": "Extranuclear inheritance 1   Biomolecules   MCAT   Khan Academy (2).mp3", "Sentence": "And those granum are made up of these, that's an M over there. And those granum are made up of these little circles called thylakoids. And photosynthesis happens within these thylakoids. So during photosynthesis, sunlight is harnessed, of course, with a bunch of other steps to make glucose. So this is where the concept of making its own food comes from. It's actually making glucose, it's making its own food. And then that glucose goes to the mitochondria of that cell and gets broken down, make ATP, and then the cell uses that ATP for whatever it needs to do."}, {"video_title": "Extranuclear inheritance 1   Biomolecules   MCAT   Khan Academy (2).mp3", "Sentence": "So during photosynthesis, sunlight is harnessed, of course, with a bunch of other steps to make glucose. So this is where the concept of making its own food comes from. It's actually making glucose, it's making its own food. And then that glucose goes to the mitochondria of that cell and gets broken down, make ATP, and then the cell uses that ATP for whatever it needs to do. The DNA in chloroplasts, sometimes written cpDNA, has about 100 genes. And these genes also, most of them have to do with proteins or things that are involved in photosynthesis. And the reason that this is interesting is, well, let's take a look at how sexual production normally takes place."}, {"video_title": "Extranuclear inheritance 1   Biomolecules   MCAT   Khan Academy (2).mp3", "Sentence": "And then that glucose goes to the mitochondria of that cell and gets broken down, make ATP, and then the cell uses that ATP for whatever it needs to do. The DNA in chloroplasts, sometimes written cpDNA, has about 100 genes. And these genes also, most of them have to do with proteins or things that are involved in photosynthesis. And the reason that this is interesting is, well, let's take a look at how sexual production normally takes place. We have an egg cell, and the nucleus of this egg cell has only half the amount of DNA that a normal cell in that organism would have, so we call that N. And then we have a sperm cell. Remember, the sperm cell is really much, much smaller than an egg cell, so this is in no way drawn to scale. And the sperm cell also has in its nucleus only half the amount of DNA that cells in this organism normally have, so that's also N. But then they fuse to make a zygote."}, {"video_title": "Extranuclear inheritance 1   Biomolecules   MCAT   Khan Academy (2).mp3", "Sentence": "And the reason that this is interesting is, well, let's take a look at how sexual production normally takes place. We have an egg cell, and the nucleus of this egg cell has only half the amount of DNA that a normal cell in that organism would have, so we call that N. And then we have a sperm cell. Remember, the sperm cell is really much, much smaller than an egg cell, so this is in no way drawn to scale. And the sperm cell also has in its nucleus only half the amount of DNA that cells in this organism normally have, so that's also N. But then they fuse to make a zygote. And this zygote is 2N. It has the normal amount of DNA that a cell in this organism would have. Half of it comes from the egg cell, and half of it comes from the sperm cell."}, {"video_title": "Extranuclear inheritance 1   Biomolecules   MCAT   Khan Academy (2).mp3", "Sentence": "And the sperm cell also has in its nucleus only half the amount of DNA that cells in this organism normally have, so that's also N. But then they fuse to make a zygote. And this zygote is 2N. It has the normal amount of DNA that a cell in this organism would have. Half of it comes from the egg cell, and half of it comes from the sperm cell. And then this zygote is going to divide into two cells, and then those two cells, of course, divide further. And this goes on and on until they are enough cells to put together an organism. But this egg cell, well, it's a fully developed cell, and it not only has genetic information, but it has organelles in the cytoplasm."}, {"video_title": "Extranuclear inheritance 1   Biomolecules   MCAT   Khan Academy (2).mp3", "Sentence": "Half of it comes from the egg cell, and half of it comes from the sperm cell. And then this zygote is going to divide into two cells, and then those two cells, of course, divide further. And this goes on and on until they are enough cells to put together an organism. But this egg cell, well, it's a fully developed cell, and it not only has genetic information, but it has organelles in the cytoplasm. So it has these mitochondria in its cytoplasm, and those mitochondria have DNA in it, which I'm just going to scribble some blue inside. And the zygote also has those mitochondria, because remember, the zygote is, well, practically an egg cell, but with the only difference being that its nucleus has the additional DNA of the sperm cell. And remember, the sperm cell does not donate anything to the egg cell except for half of the DNA in the nucleus."}, {"video_title": "Extranuclear inheritance 1   Biomolecules   MCAT   Khan Academy (2).mp3", "Sentence": "But this egg cell, well, it's a fully developed cell, and it not only has genetic information, but it has organelles in the cytoplasm. So it has these mitochondria in its cytoplasm, and those mitochondria have DNA in it, which I'm just going to scribble some blue inside. And the zygote also has those mitochondria, because remember, the zygote is, well, practically an egg cell, but with the only difference being that its nucleus has the additional DNA of the sperm cell. And remember, the sperm cell does not donate anything to the egg cell except for half of the DNA in the nucleus. It does not give the zygote anything else. So you have a zygote with those mitochondria, and of course they have their DNA in it. And then this zygote replicates itself, so it replicates the nucleus, but it also replicates the mitochondria in the cytoplasm."}, {"video_title": "Extranuclear inheritance 1   Biomolecules   MCAT   Khan Academy (2).mp3", "Sentence": "And remember, the sperm cell does not donate anything to the egg cell except for half of the DNA in the nucleus. It does not give the zygote anything else. So you have a zygote with those mitochondria, and of course they have their DNA in it. And then this zygote replicates itself, so it replicates the nucleus, but it also replicates the mitochondria in the cytoplasm. And these cells will, I'm going to skip out the nucleus, I'm just drawing the mitochondria, so you have these mitochondria, but these mitochondria came only from the egg cell. None of those mitochondria came from the sperm cell. And so this brings us to the concept of maternal inheritance."}, {"video_title": "Extranuclear inheritance 1   Biomolecules   MCAT   Khan Academy (2).mp3", "Sentence": "And then this zygote replicates itself, so it replicates the nucleus, but it also replicates the mitochondria in the cytoplasm. And these cells will, I'm going to skip out the nucleus, I'm just drawing the mitochondria, so you have these mitochondria, but these mitochondria came only from the egg cell. None of those mitochondria came from the sperm cell. And so this brings us to the concept of maternal inheritance. And maternal inheritance, well, it's basically like, exactly the way it sounds, it's inheritance that happens only from the maternal line, or only from the egg cell. So right here, we're showing that the mitochondria that this organism will eventually have originates from the mitochondria that came only from the egg cell and not from the sperm cell. And therefore, it exhibits maternal inheritance."}, {"video_title": "Extranuclear inheritance 1   Biomolecules   MCAT   Khan Academy (2).mp3", "Sentence": "And so this brings us to the concept of maternal inheritance. And maternal inheritance, well, it's basically like, exactly the way it sounds, it's inheritance that happens only from the maternal line, or only from the egg cell. So right here, we're showing that the mitochondria that this organism will eventually have originates from the mitochondria that came only from the egg cell and not from the sperm cell. And therefore, it exhibits maternal inheritance. So both mitochondria and chloroplasts exhibit maternal inheritance because they are in the egg cell that eventually becomes the organism. And maternal inheritance, it's interesting to note, is contrary to Mendelian genetics. So maternal inheritance is contrary to Mendelian genetics because Mendelian genetics assumes that half of the DNA comes from the egg cell, half from the sperm cell."}, {"video_title": "Extranuclear inheritance 1   Biomolecules   MCAT   Khan Academy (2).mp3", "Sentence": "And therefore, it exhibits maternal inheritance. So both mitochondria and chloroplasts exhibit maternal inheritance because they are in the egg cell that eventually becomes the organism. And maternal inheritance, it's interesting to note, is contrary to Mendelian genetics. So maternal inheritance is contrary to Mendelian genetics because Mendelian genetics assumes that half of the DNA comes from the egg cell, half from the sperm cell. It does not take into account any sort of genetic information that comes from only one of the gametes, for example, just from the egg cell. And in fact, everything we just described here can be referred to as extra-nuclear inheritance. So extra-nuclear inheritance would refer to any genes that are passed on from structures that are not in the nucleus."}, {"video_title": "Extranuclear inheritance 1   Biomolecules   MCAT   Khan Academy (2).mp3", "Sentence": "So maternal inheritance is contrary to Mendelian genetics because Mendelian genetics assumes that half of the DNA comes from the egg cell, half from the sperm cell. It does not take into account any sort of genetic information that comes from only one of the gametes, for example, just from the egg cell. And in fact, everything we just described here can be referred to as extra-nuclear inheritance. So extra-nuclear inheritance would refer to any genes that are passed on from structures that are not in the nucleus. So extra-nuclear meaning outside of the nucleus. So mitochondria and chloroplasts are outside of the nucleus, so when they are inherited, we refer to it as extra-nuclear inheritance. So now that we've introduced extra-nuclear inheritance, let's actually take a look at one of the early experiments that helped to discover extra-nuclear inheritance."}, {"video_title": "Exploring Ecosystems Tropical Rainforest Diversity   California Academy of Sciences (2).mp3", "Sentence": "At the California Academy of Sciences, our mission is to explore, explain, and sustain tropical rainforests. Scientists, like Michelle Troutwine, are experts in these efforts, conducting research to help us better understand the structure and diversity of rainforest ecosystems. Entering a tropical rainforest, we find vertical layers of life, each with its own unique structure and composition. The forest floor receives very little sunlight. It is a hot, humid place where animals like leafcutter ants spend their time foraging for food. Just above the floor is a thick layer of shrubs, small trees, and flowering plants. Here in the rainforest understory, you find amphibians, like the poison dart frog, whose toxic skin protects it from predators."}, {"video_title": "Exploring Ecosystems Tropical Rainforest Diversity   California Academy of Sciences (2).mp3", "Sentence": "The forest floor receives very little sunlight. It is a hot, humid place where animals like leafcutter ants spend their time foraging for food. Just above the floor is a thick layer of shrubs, small trees, and flowering plants. Here in the rainforest understory, you find amphibians, like the poison dart frog, whose toxic skin protects it from predators. Rising higher, we find a bright, connected layer of tree branches and leaves. The canopy contains a wide variety of species, including squirrel monkeys, who travel and feed in large social groups. Breaking through, we enter the emergent layer, an open space containing only the highest treetop."}, {"video_title": "Exploring Ecosystems Tropical Rainforest Diversity   California Academy of Sciences (2).mp3", "Sentence": "Here in the rainforest understory, you find amphibians, like the poison dart frog, whose toxic skin protects it from predators. Rising higher, we find a bright, connected layer of tree branches and leaves. The canopy contains a wide variety of species, including squirrel monkeys, who travel and feed in large social groups. Breaking through, we enter the emergent layer, an open space containing only the highest treetop. Here, we find camouflaged insects called katydids, who feed on young, tender leaves. Now imagine you are a biologist researching arthropod diversity in the Peruvian rainforest. You and your team sample each forest layer, recording the number of species found and at what height."}, {"video_title": "Exploring Ecosystems Tropical Rainforest Diversity   California Academy of Sciences (2).mp3", "Sentence": "Breaking through, we enter the emergent layer, an open space containing only the highest treetop. Here, we find camouflaged insects called katydids, who feed on young, tender leaves. Now imagine you are a biologist researching arthropod diversity in the Peruvian rainforest. You and your team sample each forest layer, recording the number of species found and at what height. Looking over your field notes now, what trends do you see? How do the layers differ in species richness? Take a moment to pause the video and examine the graph."}, {"video_title": "Exploring Ecosystems Tropical Rainforest Diversity   California Academy of Sciences (2).mp3", "Sentence": "You and your team sample each forest layer, recording the number of species found and at what height. Looking over your field notes now, what trends do you see? How do the layers differ in species richness? Take a moment to pause the video and examine the graph. The canopy is believed to house over 70% of species found in the rainforest, making it the most species-rich of the four layers. To measure species diversity, researchers like Michelle must take into account both species richness, the number of different species, and species evenness, the abundance of each species. Imagine you survey three different rainforest communities and identify the following species at the following abundances."}, {"video_title": "Exploring Ecosystems Tropical Rainforest Diversity   California Academy of Sciences (2).mp3", "Sentence": "Take a moment to pause the video and examine the graph. The canopy is believed to house over 70% of species found in the rainforest, making it the most species-rich of the four layers. To measure species diversity, researchers like Michelle must take into account both species richness, the number of different species, and species evenness, the abundance of each species. Imagine you survey three different rainforest communities and identify the following species at the following abundances. Looking at your field notes now, which community appears to be most diverse? While each has the same number of species, community B has greater evenness, a more balanced number of individuals from each species. We recognize community B as being more diverse because of its high species richness and its high species evenness."}, {"video_title": "Exploring Ecosystems Tropical Rainforest Diversity   California Academy of Sciences (2).mp3", "Sentence": "Imagine you survey three different rainforest communities and identify the following species at the following abundances. Looking at your field notes now, which community appears to be most diverse? While each has the same number of species, community B has greater evenness, a more balanced number of individuals from each species. We recognize community B as being more diverse because of its high species richness and its high species evenness. Why is this important? More diverse ecological communities tend to be more stable and resilient to change. This means a more diverse tropical rainforest is better able to respond to disturbances like deforestation and climate change."}, {"video_title": "Exploring Ecosystems Tropical Rainforest Diversity   California Academy of Sciences (2).mp3", "Sentence": "We recognize community B as being more diverse because of its high species richness and its high species evenness. Why is this important? More diverse ecological communities tend to be more stable and resilient to change. This means a more diverse tropical rainforest is better able to respond to disturbances like deforestation and climate change. Even with these findings, there are still many unanswered questions about tropical rainforests and the species that inhabit them. Such as, why are tropical rainforests so diverse? Why does the canopy have high species richness?"}, {"video_title": "Phases of meiosis I   Cells   MCAT   Khan Academy.mp3", "Sentence": "And to be more precise, meiosis I, and to be even more precise in that, prophase I. But we spent a good bit of time on prophase I because some interesting things happened. Some things happened just like prophase and mitosis, where the nuclear envelope disappears or starts to disappear. You have the chromosomes go into their dense form that has kind of this classic shape that you could see from a microscope. But what was unique or what was interesting about meiosis I and prophase I in particular is that you have this chromosomal crossover that it's a pretty typical thing to happen in meiosis I. And it happens or tends to happen in a fairly clean way, where homologous sections of these homologous pairs crossover. So these sections of the chromosome tend to code for the same genes."}, {"video_title": "Phases of meiosis I   Cells   MCAT   Khan Academy.mp3", "Sentence": "You have the chromosomes go into their dense form that has kind of this classic shape that you could see from a microscope. But what was unique or what was interesting about meiosis I and prophase I in particular is that you have this chromosomal crossover that it's a pretty typical thing to happen in meiosis I. And it happens or tends to happen in a fairly clean way, where homologous sections of these homologous pairs crossover. So these sections of the chromosome tend to code for the same genes. They're just different variants of those same genes. They might have different alleles. And once again, this just adds more variation as we get into sexual reproduction."}, {"video_title": "Phases of meiosis I   Cells   MCAT   Khan Academy.mp3", "Sentence": "So these sections of the chromosome tend to code for the same genes. They're just different variants of those same genes. They might have different alleles. And once again, this just adds more variation as we get into sexual reproduction. So it's kind of a neat thing that happens here. But now let's continue with meiosis, and in particular meiosis I. And you could guess what the next phase is going to be called."}, {"video_title": "Phases of meiosis I   Cells   MCAT   Khan Academy.mp3", "Sentence": "And once again, this just adds more variation as we get into sexual reproduction. So it's kind of a neat thing that happens here. But now let's continue with meiosis, and in particular meiosis I. And you could guess what the next phase is going to be called. It is metaphase I. Metaphase. Metaphase I. And it has some similarities with metaphase and mitosis."}, {"video_title": "Phases of meiosis I   Cells   MCAT   Khan Academy.mp3", "Sentence": "And you could guess what the next phase is going to be called. It is metaphase I. Metaphase. Metaphase I. And it has some similarities with metaphase and mitosis. So in metaphase I, so let me draw my cell. So this is the cellular membrane right over there. I have my centrosomes, which are now going to play more significant roles."}, {"video_title": "Phases of meiosis I   Cells   MCAT   Khan Academy.mp3", "Sentence": "And it has some similarities with metaphase and mitosis. So in metaphase I, so let me draw my cell. So this is the cellular membrane right over there. I have my centrosomes, which are now going to play more significant roles. The nuclear membrane is now gone. And just like in metaphase and mitosis, my chromosomes are going to line up along, here I'll draw it kind of this up-down axis. So let's do that."}, {"video_title": "Phases of meiosis I   Cells   MCAT   Khan Academy.mp3", "Sentence": "I have my centrosomes, which are now going to play more significant roles. The nuclear membrane is now gone. And just like in metaphase and mitosis, my chromosomes are going to line up along, here I'll draw it kind of this up-down axis. So let's do that. So you have this one right over here. This is one chromosome, two sister chromatids, and we had the chromosomal crossover, so it has a little bit of pink here. I'm going to have to take a little bit of time to switch colors a little bit more frequently."}, {"video_title": "Phases of meiosis I   Cells   MCAT   Khan Academy.mp3", "Sentence": "So let's do that. So you have this one right over here. This is one chromosome, two sister chromatids, and we had the chromosomal crossover, so it has a little bit of pink here. I'm going to have to take a little bit of time to switch colors a little bit more frequently. And then you have the one, at least most of which you got from your mother. But there's been a little bit of chromosomal crossover over here as well. So let me draw that."}, {"video_title": "Phases of meiosis I   Cells   MCAT   Khan Academy.mp3", "Sentence": "I'm going to have to take a little bit of time to switch colors a little bit more frequently. And then you have the one, at least most of which you got from your mother. But there's been a little bit of chromosomal crossover over here as well. So let me draw that. And then you have this one, and just for the sake of, so you have this one, this chromosome from your father. It has replicated, so it's now two sister chromatids. And this one from your mother."}, {"video_title": "Phases of meiosis I   Cells   MCAT   Khan Academy.mp3", "Sentence": "So let me draw that. And then you have this one, and just for the sake of, so you have this one, this chromosome from your father. It has replicated, so it's now two sister chromatids. And this one from your mother. And I'm not going to show the chromosomal crossover here. Maybe it didn't happen over here. No homologous recombination over here."}, {"video_title": "Phases of meiosis I   Cells   MCAT   Khan Academy.mp3", "Sentence": "And this one from your mother. And I'm not going to show the chromosomal crossover here. Maybe it didn't happen over here. No homologous recombination over here. So these are, I guess, shorter. Now let me draw the centromeres. The centromeres I've started doing in this blue color."}, {"video_title": "Phases of meiosis I   Cells   MCAT   Khan Academy.mp3", "Sentence": "No homologous recombination over here. So these are, I guess, shorter. Now let me draw the centromeres. The centromeres I've started doing in this blue color. So the centromeres. And then the centrosomes, you have these microtubules that start, they can push the centrosomes away from each other. But they also attach at the kinetochores to the chromosomes."}, {"video_title": "Phases of meiosis I   Cells   MCAT   Khan Academy.mp3", "Sentence": "The centromeres I've started doing in this blue color. So the centromeres. And then the centrosomes, you have these microtubules that start, they can push the centrosomes away from each other. But they also attach at the kinetochores to the chromosomes. Just like that. So, and these are, you know, the microtubules, you'll see people just talk about, oh, these connect and they're able to move things around. But I find this incredible."}, {"video_title": "Phases of meiosis I   Cells   MCAT   Khan Academy.mp3", "Sentence": "But they also attach at the kinetochores to the chromosomes. Just like that. So, and these are, you know, the microtubules, you'll see people just talk about, oh, these connect and they're able to move things around. But I find this incredible. That you just have a bunch of proteins through just kind of chemical and thermodynamic processes are able to do really interesting things like move chromosomes to different parts of the cell so that we eventually can get these gametes that can participate in sexual reproduction. This is an amazing thing. And, you know, it's kind of, it's developed over billions of years of evolution."}, {"video_title": "Phases of meiosis I   Cells   MCAT   Khan Academy.mp3", "Sentence": "But I find this incredible. That you just have a bunch of proteins through just kind of chemical and thermodynamic processes are able to do really interesting things like move chromosomes to different parts of the cell so that we eventually can get these gametes that can participate in sexual reproduction. This is an amazing thing. And, you know, it's kind of, it's developed over billions of years of evolution. But it's just mind-boggling to think about the complexity. And not all of this is completely understood exactly how all of this works. I mean, you have these kind of motor proteins that help move the chromosomes along these microtubules can elongate and shorten in interesting ways."}, {"video_title": "Phases of meiosis I   Cells   MCAT   Khan Academy.mp3", "Sentence": "And, you know, it's kind of, it's developed over billions of years of evolution. But it's just mind-boggling to think about the complexity. And not all of this is completely understood exactly how all of this works. I mean, you have these kind of motor proteins that help move the chromosomes along these microtubules can elongate and shorten in interesting ways. So it's a really fascinating process. But anyway, this is what's happening in metaphase one. Now you can probably guess what happens after that."}, {"video_title": "Phases of meiosis I   Cells   MCAT   Khan Academy.mp3", "Sentence": "I mean, you have these kind of motor proteins that help move the chromosomes along these microtubules can elongate and shorten in interesting ways. So it's a really fascinating process. But anyway, this is what's happening in metaphase one. Now you can probably guess what happens after that. We then move to anaphase one. So let me, we now go to anaphase one. I'll write that over here."}, {"video_title": "Phases of meiosis I   Cells   MCAT   Khan Academy.mp3", "Sentence": "Now you can probably guess what happens after that. We then move to anaphase one. So let me, we now go to anaphase one. I'll write that over here. Anaphase, anaphase one. And just like in anaphase and mitosis, over here, the chromosomes start getting pulled apart. Except for one significant difference."}, {"video_title": "Phases of meiosis I   Cells   MCAT   Khan Academy.mp3", "Sentence": "I'll write that over here. Anaphase, anaphase one. And just like in anaphase and mitosis, over here, the chromosomes start getting pulled apart. Except for one significant difference. And this is actually a very significant difference. In mitosis, in mitosis, the sister chromatids get pulled apart. The sister chromatids get pulled apart to become two daughter chromosomes."}, {"video_title": "Phases of meiosis I   Cells   MCAT   Khan Academy.mp3", "Sentence": "Except for one significant difference. And this is actually a very significant difference. In mitosis, in mitosis, the sister chromatids get pulled apart. The sister chromatids get pulled apart to become two daughter chromosomes. That does not happen in anaphase one. In anaphase one, the sister chromatids stay together. It's the homologous pairs that get pulled apart."}, {"video_title": "Phases of meiosis I   Cells   MCAT   Khan Academy.mp3", "Sentence": "The sister chromatids get pulled apart to become two daughter chromosomes. That does not happen in anaphase one. In anaphase one, the sister chromatids stay together. It's the homologous pairs that get pulled apart. So let me draw that. So this homologous pair up here gets pulled apart. The two sister chromatids do not get pulled apart here."}, {"video_title": "Phases of meiosis I   Cells   MCAT   Khan Academy.mp3", "Sentence": "It's the homologous pairs that get pulled apart. So let me draw that. So this homologous pair up here gets pulled apart. The two sister chromatids do not get pulled apart here. So you have this one is getting pulled onto this side. So this one's getting pulled onto this side. It has a little bit from the original, so a little bit of that right over there."}, {"video_title": "Phases of meiosis I   Cells   MCAT   Khan Academy.mp3", "Sentence": "The two sister chromatids do not get pulled apart here. So you have this one is getting pulled onto this side. So this one's getting pulled onto this side. It has a little bit from the original, so a little bit of that right over there. And then you have this one getting pulled on this side. So draw it the best I can. The colors, alright, so it looks like that."}, {"video_title": "Phases of meiosis I   Cells   MCAT   Khan Academy.mp3", "Sentence": "It has a little bit from the original, so a little bit of that right over there. And then you have this one getting pulled on this side. So draw it the best I can. The colors, alright, so it looks like that. Oh, it's nice to have, it's kind of easy to keep track of because these switch colors like that. And then you have this one getting pulled on this side. This one getting pulled on this side."}, {"video_title": "Phases of meiosis I   Cells   MCAT   Khan Academy.mp3", "Sentence": "The colors, alright, so it looks like that. Oh, it's nice to have, it's kind of easy to keep track of because these switch colors like that. And then you have this one getting pulled on this side. This one getting pulled on this side. And finally, finally, this one getting pulled onto that side. And let me draw the centrosomes. So that's my, whoops, centrosome."}, {"video_title": "Phases of meiosis I   Cells   MCAT   Khan Academy.mp3", "Sentence": "This one getting pulled on this side. And finally, finally, this one getting pulled onto that side. And let me draw the centrosomes. So that's my, whoops, centrosome. And once again, it's pulling. It's, or I guess you could say the chromosomes being moved. And these things are pushing each other apart."}, {"video_title": "Phases of meiosis I   Cells   MCAT   Khan Academy.mp3", "Sentence": "So that's my, whoops, centrosome. And once again, it's pulling. It's, or I guess you could say the chromosomes being moved. And these things are pushing each other apart. The two centrosomes might be pushing apart to get to the opposite ends of the actual cell. But they're bringing, there's all sorts of interesting mechanisms that are bringing along these microtubules, bringing the chromosomes. Once again, splitting the homologous pairs."}, {"video_title": "Phases of meiosis I   Cells   MCAT   Khan Academy.mp3", "Sentence": "And these things are pushing each other apart. The two centrosomes might be pushing apart to get to the opposite ends of the actual cell. But they're bringing, there's all sorts of interesting mechanisms that are bringing along these microtubules, bringing the chromosomes. Once again, splitting the homologous pairs. And how they split is random. You know, this pink one could have been on the right side. This orange one could have been on the left side."}, {"video_title": "Phases of meiosis I   Cells   MCAT   Khan Academy.mp3", "Sentence": "Once again, splitting the homologous pairs. And how they split is random. You know, this pink one could have been on the right side. This orange one could have been on the left side. Or vice versa. Once again, this adds more kind of variation amongst the gametes. So even all of the resulting gametes that get produced, they all will have different genetic information."}, {"video_title": "Phases of meiosis I   Cells   MCAT   Khan Academy.mp3", "Sentence": "This orange one could have been on the left side. Or vice versa. Once again, this adds more kind of variation amongst the gametes. So even all of the resulting gametes that get produced, they all will have different genetic information. So this is anaphase one. You're pulling these apart. And then you can imagine what happens in telophase one."}, {"video_title": "Phases of meiosis I   Cells   MCAT   Khan Academy.mp3", "Sentence": "So even all of the resulting gametes that get produced, they all will have different genetic information. So this is anaphase one. You're pulling these apart. And then you can imagine what happens in telophase one. So telophase one. Telophase. Telophase one."}, {"video_title": "Phases of meiosis I   Cells   MCAT   Khan Academy.mp3", "Sentence": "And then you can imagine what happens in telophase one. So telophase one. Telophase. Telophase one. Telophase one. And this is fairly analogous to what happens in mitosis in telophase. So now you have your cytokinesis is beginning."}, {"video_title": "Phases of meiosis I   Cells   MCAT   Khan Academy.mp3", "Sentence": "Telophase one. Telophase one. And this is fairly analogous to what happens in mitosis in telophase. So now you have your cytokinesis is beginning. So, and actually it might even begin earlier. In mitosis it happens as early as anaphase. At least the cytokinesis is starting."}, {"video_title": "Phases of meiosis I   Cells   MCAT   Khan Academy.mp3", "Sentence": "So now you have your cytokinesis is beginning. So, and actually it might even begin earlier. In mitosis it happens as early as anaphase. At least the cytokinesis is starting. But you're starting to see that. These two things, the homologous pairs are fully split apart and they're at opposite ends. And actually they could begin to, they can begin to unravel into their chromatin state."}, {"video_title": "Phases of meiosis I   Cells   MCAT   Khan Academy.mp3", "Sentence": "At least the cytokinesis is starting. But you're starting to see that. These two things, the homologous pairs are fully split apart and they're at opposite ends. And actually they could begin to, they can begin to unravel into their chromatin state. So this one began to unravel into its chromatin, into its chromatin state. It has a little bit of the magenta. Whoops, it has a little bit of the magenta right over here."}, {"video_title": "Phases of meiosis I   Cells   MCAT   Khan Academy.mp3", "Sentence": "And actually they could begin to, they can begin to unravel into their chromatin state. So this one began to unravel into its chromatin, into its chromatin state. It has a little bit of the magenta. Whoops, it has a little bit of the magenta right over here. This is unraveling as well. This is unraveling like that. Once again into its chromatin state."}, {"video_title": "Phases of meiosis I   Cells   MCAT   Khan Academy.mp3", "Sentence": "Whoops, it has a little bit of the magenta right over here. This is unraveling as well. This is unraveling like that. Once again into its chromatin state. The cellular, and let me do the other ones as well. So this is, this one right over here beginning to unravel. This one over here beginning to unravel."}, {"video_title": "Phases of meiosis I   Cells   MCAT   Khan Academy.mp3", "Sentence": "Once again into its chromatin state. The cellular, and let me do the other ones as well. So this is, this one right over here beginning to unravel. This one over here beginning to unravel. It's got a little bit of orange on it. It's got a little bit of orange on it. The nuclear membrane begins to form again."}, {"video_title": "Phases of meiosis I   Cells   MCAT   Khan Academy.mp3", "Sentence": "This one over here beginning to unravel. It's got a little bit of orange on it. It's got a little bit of orange on it. The nuclear membrane begins to form again. The nuclear membrane begins to form again. In some ways it's reversing what happened in prophase one where the nuclear membrane disappeared and the chromosomes condensed. And let me draw, let me draw, this is centrosomes which are outside of the nuclear membrane just like that."}, {"video_title": "Phases of meiosis I   Cells   MCAT   Khan Academy.mp3", "Sentence": "The nuclear membrane begins to form again. The nuclear membrane begins to form again. In some ways it's reversing what happened in prophase one where the nuclear membrane disappeared and the chromosomes condensed. And let me draw, let me draw, this is centrosomes which are outside of the nuclear membrane just like that. And the microtubules are also dissolving. The microtubules are also dissolving. And you have your cytokinesis."}, {"video_title": "Phases of meiosis I   Cells   MCAT   Khan Academy.mp3", "Sentence": "And let me draw, let me draw, this is centrosomes which are outside of the nuclear membrane just like that. And the microtubules are also dissolving. The microtubules are also dissolving. And you have your cytokinesis. So your cytokinesis, so these separate, these separate into two cells. So once again when we did the overview of meiosis we said look, the first phase of meiosis you go from a diploid, a diploid germ cell to two haploid cells. And these aren't quite our end product yet."}, {"video_title": "Phases of meiosis I   Cells   MCAT   Khan Academy.mp3", "Sentence": "And you have your cytokinesis. So your cytokinesis, so these separate, these separate into two cells. So once again when we did the overview of meiosis we said look, the first phase of meiosis you go from a diploid, a diploid germ cell to two haploid cells. And these aren't quite our end product yet. This right over here, what we have just gone through, what we have just gone through, all of this combined that we have just gone through, this is meiosis one. And in the next video we're gonna go through meiosis two. Whoops, I didn't mean to do that."}, {"video_title": "Phases of meiosis I   Cells   MCAT   Khan Academy.mp3", "Sentence": "And these aren't quite our end product yet. This right over here, what we have just gone through, what we have just gone through, all of this combined that we have just gone through, this is meiosis one. And in the next video we're gonna go through meiosis two. Whoops, I didn't mean to do that. This is, so let's see. All of this is meiosis one. Let me write that in a different color and bold."}, {"video_title": "Phases of meiosis I   Cells   MCAT   Khan Academy.mp3", "Sentence": "Whoops, I didn't mean to do that. This is, so let's see. All of this is meiosis one. Let me write that in a different color and bold. So this is all meiosis, meiosis one here. And you can see each of these cells now have a haploid number. They now have the haploid, haploid number of two chromosomes each."}, {"video_title": "Phases of meiosis I   Cells   MCAT   Khan Academy.mp3", "Sentence": "Let me write that in a different color and bold. So this is all meiosis, meiosis one here. And you can see each of these cells now have a haploid number. They now have the haploid, haploid number of two chromosomes each. Now each of those two chromosomes do have two sister chromatids. And as we'll see meiosis two, which is very similar to mitosis, is going to split up the sister chromatids from each of these chromosomes, which gives us two daughter chromosomes. So we're gonna see that over here."}, {"video_title": "Phases of meiosis I   Cells   MCAT   Khan Academy.mp3", "Sentence": "They now have the haploid, haploid number of two chromosomes each. Now each of those two chromosomes do have two sister chromatids. And as we'll see meiosis two, which is very similar to mitosis, is going to split up the sister chromatids from each of these chromosomes, which gives us two daughter chromosomes. So we're gonna see that over here. So your haploid number here is two. You have two chromosomes here and you have two chromosomes there. And we'll explore meiosis two in the next video."}, {"video_title": "Plant cell walls   Structure of a cell   Biology   Khan Academy.mp3", "Sentence": "And so the next question is, well, what gives them that shape? What allows them to form that kind of cubic rectangular prism shape? And the answer is, it's the cell wall. So that's the cell wall. So let's make sure we can orient ourselves properly in this picture. So clearly, if I didn't have this cutout, all I would be seeing is the outside. All I would be seeing is the cell wall, but we've cut it out, and we can see the different layers."}, {"video_title": "Plant cell walls   Structure of a cell   Biology   Khan Academy.mp3", "Sentence": "So that's the cell wall. So let's make sure we can orient ourselves properly in this picture. So clearly, if I didn't have this cutout, all I would be seeing is the outside. All I would be seeing is the cell wall, but we've cut it out, and we can see the different layers. We have the cell wall on the outside. Right below that, we have the cellular membrane, or the plasma membrane. So that's the cell, cellular membrane, cellular membrane, right under that."}, {"video_title": "Plant cell walls   Structure of a cell   Biology   Khan Academy.mp3", "Sentence": "All I would be seeing is the cell wall, but we've cut it out, and we can see the different layers. We have the cell wall on the outside. Right below that, we have the cellular membrane, or the plasma membrane. So that's the cell, cellular membrane, cellular membrane, right under that. And then under that, the cellular membrane is containing the cytoplasm, and inside of the cytoplasm, we have all sorts of things. This big thing that is taking up a lot of the volume inside of this plant cell, that's a vacuole, which we have described in other videos. Vacuole."}, {"video_title": "Plant cell walls   Structure of a cell   Biology   Khan Academy.mp3", "Sentence": "So that's the cell, cellular membrane, cellular membrane, right under that. And then under that, the cellular membrane is containing the cytoplasm, and inside of the cytoplasm, we have all sorts of things. This big thing that is taking up a lot of the volume inside of this plant cell, that's a vacuole, which we have described in other videos. Vacuole. And it's a combination of this internal pressure, things like the vacuole, and just frankly, the pressure from all of the fluid inside the cell pushing outwards, plus the cell wall kind of holding it all in. That's what gives plants their structure. That's why a plant is able to grow and be upright."}, {"video_title": "Plant cell walls   Structure of a cell   Biology   Khan Academy.mp3", "Sentence": "Vacuole. And it's a combination of this internal pressure, things like the vacuole, and just frankly, the pressure from all of the fluid inside the cell pushing outwards, plus the cell wall kind of holding it all in. That's what gives plants their structure. That's why a plant is able to grow and be upright. So that's my drawing of a plant. I actually have a plant in my room that I'm looking at right now, and it's able to grow and be upright. And so you have the cell wall, you have the cellular membrane, you have the other organelles, I have some chloroplasts here, key for photosynthesis, have our good friend's mitochondria, we have our nuclear membrane, I should say this yellow thing is the inner nuclear membrane, has the DNA inside, then you have the endoplasmic reticulum kind of containing that, the rough ER containing the, or having the ribosomes on the membrane, the smooth ER not having the ribosomes, Golgi apparatus, so that's a little bit of a review, but our focus here is on the cell wall."}, {"video_title": "Plant cell walls   Structure of a cell   Biology   Khan Academy.mp3", "Sentence": "That's why a plant is able to grow and be upright. So that's my drawing of a plant. I actually have a plant in my room that I'm looking at right now, and it's able to grow and be upright. And so you have the cell wall, you have the cellular membrane, you have the other organelles, I have some chloroplasts here, key for photosynthesis, have our good friend's mitochondria, we have our nuclear membrane, I should say this yellow thing is the inner nuclear membrane, has the DNA inside, then you have the endoplasmic reticulum kind of containing that, the rough ER containing the, or having the ribosomes on the membrane, the smooth ER not having the ribosomes, Golgi apparatus, so that's a little bit of a review, but our focus here is on the cell wall. So let's go back to that. So if we zoom in on this, if we zoom in on the cell wall right over here, we can look at this diagram. And over here, it might be a little bit surprising to you, because when I've always imagined a wall, a cell wall, I imagined something like a brick wall, something that's impenetrable."}, {"video_title": "Plant cell walls   Structure of a cell   Biology   Khan Academy.mp3", "Sentence": "And so you have the cell wall, you have the cellular membrane, you have the other organelles, I have some chloroplasts here, key for photosynthesis, have our good friend's mitochondria, we have our nuclear membrane, I should say this yellow thing is the inner nuclear membrane, has the DNA inside, then you have the endoplasmic reticulum kind of containing that, the rough ER containing the, or having the ribosomes on the membrane, the smooth ER not having the ribosomes, Golgi apparatus, so that's a little bit of a review, but our focus here is on the cell wall. So let's go back to that. So if we zoom in on this, if we zoom in on the cell wall right over here, we can look at this diagram. And over here, it might be a little bit surprising to you, because when I've always imagined a wall, a cell wall, I imagined something like a brick wall, something that's impenetrable. But this drawing shows us something different. And just to be clear what's going on here, so this is our cellular membrane. Sorry, I wrote cellular membrane."}, {"video_title": "Plant cell walls   Structure of a cell   Biology   Khan Academy.mp3", "Sentence": "And over here, it might be a little bit surprising to you, because when I've always imagined a wall, a cell wall, I imagined something like a brick wall, something that's impenetrable. But this drawing shows us something different. And just to be clear what's going on here, so this is our cellular membrane. Sorry, I wrote cellular membrane. So right over here, I have my lipid bilayer. And then right on top of that, I have the cell wall. But you see, it isn't just a thick, like a brick wall, something that's impenetrable."}, {"video_title": "Plant cell walls   Structure of a cell   Biology   Khan Academy.mp3", "Sentence": "Sorry, I wrote cellular membrane. So right over here, I have my lipid bilayer. And then right on top of that, I have the cell wall. But you see, it isn't just a thick, like a brick wall, something that's impenetrable. You see, you have all of these polysaccharide fibers running across it. So you have things like cellulose, which we saw is a polymer of glucose arranged in a certain way. Hemicellulose, which has different types of monomers associated with it."}, {"video_title": "Plant cell walls   Structure of a cell   Biology   Khan Academy.mp3", "Sentence": "But you see, it isn't just a thick, like a brick wall, something that's impenetrable. You see, you have all of these polysaccharide fibers running across it. So you have things like cellulose, which we saw is a polymer of glucose arranged in a certain way. Hemicellulose, which has different types of monomers associated with it. We have pectin, which is another polysaccharide. And all of these things, you've actually probably eaten, if not today, probably in the last week. When we talk about fiber in your diet, you're talking about things like the cellulose and the pectin, things that your body can't digest."}, {"video_title": "Plant cell walls   Structure of a cell   Biology   Khan Academy.mp3", "Sentence": "Hemicellulose, which has different types of monomers associated with it. We have pectin, which is another polysaccharide. And all of these things, you've actually probably eaten, if not today, probably in the last week. When we talk about fiber in your diet, you're talking about things like the cellulose and the pectin, things that your body can't digest. But when you eat a plant, you're getting it because you're eating their cell walls. And it does cool things, like slows the absorption of glucose in your intestines. It absorbs water, so I guess you could say things pass a little bit easier."}, {"video_title": "Plant cell walls   Structure of a cell   Biology   Khan Academy.mp3", "Sentence": "When we talk about fiber in your diet, you're talking about things like the cellulose and the pectin, things that your body can't digest. But when you eat a plant, you're getting it because you're eating their cell walls. And it does cool things, like slows the absorption of glucose in your intestines. It absorbs water, so I guess you could say things pass a little bit easier. But just to see, the key thing here is this isn't a wall. This actually allows, or it is a wall. It's officially the cell wall."}, {"video_title": "Plant cell walls   Structure of a cell   Biology   Khan Academy.mp3", "Sentence": "It absorbs water, so I guess you could say things pass a little bit easier. But just to see, the key thing here is this isn't a wall. This actually allows, or it is a wall. It's officially the cell wall. But it's not a thick, it's not an impenetrable wall like you might associate the wall of the room that you're in. You can see that it has space for small molecules to flow. And it's really more like a mesh or like a fabric."}, {"video_title": "Plant cell walls   Structure of a cell   Biology   Khan Academy.mp3", "Sentence": "It's officially the cell wall. But it's not a thick, it's not an impenetrable wall like you might associate the wall of the room that you're in. You can see that it has space for small molecules to flow. And it's really more like a mesh or like a fabric. And so the cellular membrane actually has access to the fluid and to the molecules that are between the cells. And so just to be clear what we're looking at, this layer right here, that's the cellular membrane. That's the lipid bilayer."}, {"video_title": "Plant cell walls   Structure of a cell   Biology   Khan Academy.mp3", "Sentence": "And it's really more like a mesh or like a fabric. And so the cellular membrane actually has access to the fluid and to the molecules that are between the cells. And so just to be clear what we're looking at, this layer right here, that's the cellular membrane. That's the lipid bilayer. This right over here, this is the cell wall. I'll do that in a different color. That is the cell wall."}, {"video_title": "Plant cell walls   Structure of a cell   Biology   Khan Academy.mp3", "Sentence": "That's the lipid bilayer. This right over here, this is the cell wall. I'll do that in a different color. That is the cell wall. And then right above the cell wall, that's the space between the cells, which we call the middle lamella. So the space between the cells we call the middle lamella. So this also is, this right over here is also the middle lamella."}, {"video_title": "Plant cell walls   Structure of a cell   Biology   Khan Academy.mp3", "Sentence": "That is the cell wall. And then right above the cell wall, that's the space between the cells, which we call the middle lamella. So the space between the cells we call the middle lamella. So this also is, this right over here is also the middle lamella. So all of that is interesting, but you might say, okay, well, how hard is a cell? I get that it's a mesh, but clearly the cells are able, or the plants are able to stand upright. Is that because the cell wall provides all of that rigidity?"}, {"video_title": "Plant cell walls   Structure of a cell   Biology   Khan Academy.mp3", "Sentence": "So this also is, this right over here is also the middle lamella. So all of that is interesting, but you might say, okay, well, how hard is a cell? I get that it's a mesh, but clearly the cells are able, or the plants are able to stand upright. Is that because the cell wall provides all of that rigidity? And the answer is kind of. The cell wall is like this mesh. It helps these cells have their shape."}, {"video_title": "Plant cell walls   Structure of a cell   Biology   Khan Academy.mp3", "Sentence": "Is that because the cell wall provides all of that rigidity? And the answer is kind of. The cell wall is like this mesh. It helps these cells have their shape. But if you stop watering a plant, you're going to see it kind of wilt over. And that's because part of its ability to stand up is from the internal pressure of the cells, but also part of its shape is the actual cell wall. Now, some of you might say, well, I've seen plants that are much, much more rigid than this plant you've just drawn."}, {"video_title": "Plant cell walls   Structure of a cell   Biology   Khan Academy.mp3", "Sentence": "It helps these cells have their shape. But if you stop watering a plant, you're going to see it kind of wilt over. And that's because part of its ability to stand up is from the internal pressure of the cells, but also part of its shape is the actual cell wall. Now, some of you might say, well, I've seen plants that are much, much more rigid than this plant you've just drawn. What about things like trees? What about wood? Wood seems very rigid, in fact, so rigid that we can build actual walls out of wood."}, {"video_title": "Plant cell walls   Structure of a cell   Biology   Khan Academy.mp3", "Sentence": "Now, some of you might say, well, I've seen plants that are much, much more rigid than this plant you've just drawn. What about things like trees? What about wood? Wood seems very rigid, in fact, so rigid that we can build actual walls out of wood. And the answer there is these more mature plants, actually, once the cell has stopped growing and you have your cell wall, more layers of cellulose and other molecules can be built to form what's called a secondary cell wall. So this could be viewed as a primary cell wall, and then a thicker secondary cell wall could be built, which gives a much, much, much more rigidity. And so when you look at wood, what gives wood its structure, even if you were to take out all of the water, even if you were to dehydrate the wood, it's still going to have its rigidity because the cellulose layers and the other molecules, they're so thick that it's able to have its rigid form."}, {"video_title": "Plant cell walls   Structure of a cell   Biology   Khan Academy.mp3", "Sentence": "Wood seems very rigid, in fact, so rigid that we can build actual walls out of wood. And the answer there is these more mature plants, actually, once the cell has stopped growing and you have your cell wall, more layers of cellulose and other molecules can be built to form what's called a secondary cell wall. So this could be viewed as a primary cell wall, and then a thicker secondary cell wall could be built, which gives a much, much, much more rigidity. And so when you look at wood, what gives wood its structure, even if you were to take out all of the water, even if you were to dehydrate the wood, it's still going to have its rigidity because the cellulose layers and the other molecules, they're so thick that it's able to have its rigid form. Now, the last thing I want to talk about, we've already seen that the cellular membrane has access to the molecules floating around between cells, but there's actually also direct tunnels between adjacent plant cells. And those direct tunnels I've drawn here on this outside of the cell wall is these little yellow circles. These are plasmodesmata."}, {"video_title": "Plant cell walls   Structure of a cell   Biology   Khan Academy.mp3", "Sentence": "And so when you look at wood, what gives wood its structure, even if you were to take out all of the water, even if you were to dehydrate the wood, it's still going to have its rigidity because the cellulose layers and the other molecules, they're so thick that it's able to have its rigid form. Now, the last thing I want to talk about, we've already seen that the cellular membrane has access to the molecules floating around between cells, but there's actually also direct tunnels between adjacent plant cells. And those direct tunnels I've drawn here on this outside of the cell wall is these little yellow circles. These are plasmodesmata. Plasmo, these are plasmodesmata. And to get a better understanding of what they're like, imagine this is one cell, so I'll write here cell one, and let's say this is cell two, cell two right over here, and I have a cross section. You see the plasmodesmata are these tunnels that form between not just the membrane and the cell wall, and the plasmodesmata, it forms between the two cells."}, {"video_title": "Plant cell walls   Structure of a cell   Biology   Khan Academy.mp3", "Sentence": "These are plasmodesmata. Plasmo, these are plasmodesmata. And to get a better understanding of what they're like, imagine this is one cell, so I'll write here cell one, and let's say this is cell two, cell two right over here, and I have a cross section. You see the plasmodesmata are these tunnels that form between not just the membrane and the cell wall, and the plasmodesmata, it forms between the two cells. And so you can actually have a flow of cytosol and small molecules directly, directly between these two cells. And if you want to get a little bit more involved in the structure, you have this kind of smooth endoplasmic reticulum pipe going through it. But I want to make it very clear, because a lot of times when you study biology, it's all explained, it seems all neat and clean in a textbook, but people are still studying exactly why do we have these things?"}, {"video_title": "Plant cell walls   Structure of a cell   Biology   Khan Academy.mp3", "Sentence": "You see the plasmodesmata are these tunnels that form between not just the membrane and the cell wall, and the plasmodesmata, it forms between the two cells. And so you can actually have a flow of cytosol and small molecules directly, directly between these two cells. And if you want to get a little bit more involved in the structure, you have this kind of smooth endoplasmic reticulum pipe going through it. But I want to make it very clear, because a lot of times when you study biology, it's all explained, it seems all neat and clean in a textbook, but people are still studying exactly why do we have these things? Why are they necessary? What gets transported across these things, and how are they able to transport it, under what conditions are they? So all of these areas, when you were to kind of dig one layer deeper than frankly I'm talking about, you're getting into an area of active research."}, {"video_title": "DNA   Biomolecules   MCAT   Khan Academy (4).mp3", "Sentence": "For example, someone might have told you, hey, you walk kind of like your dad, or your smile is kind of like your mom, or your eyes are like one of your uncles or your grandparents. And so there's always been this notion of inherited traits. But it wasn't until the 1800s that that started to be studied in a more scientific way with Gregor Mendel, the father of genetics. But even then, even Mendel, who was starting to understand the mechanisms of, or he was trying to understand how inheritance happens, and he even could start to breed certain types of things, even he didn't know exactly what was the molecular basis for inheritance. And the answer to that question wasn't figured out until fairly recent times, until the mid-20th century, not until the structure of DNA was established by Watson and Crick. And their work was based on the work of many others, especially folks like Rosalind Franklin, who essentially provided the bulk of the data for Watson and Crick's work, Maurice Wilkins, and many, many, many other folks. But it was really the structure of DNA that made people say, hey, that looks like the molecule that's storing the information."}, {"video_title": "DNA   Biomolecules   MCAT   Khan Academy (4).mp3", "Sentence": "But even then, even Mendel, who was starting to understand the mechanisms of, or he was trying to understand how inheritance happens, and he even could start to breed certain types of things, even he didn't know exactly what was the molecular basis for inheritance. And the answer to that question wasn't figured out until fairly recent times, until the mid-20th century, not until the structure of DNA was established by Watson and Crick. And their work was based on the work of many others, especially folks like Rosalind Franklin, who essentially provided the bulk of the data for Watson and Crick's work, Maurice Wilkins, and many, many, many other folks. But it was really the structure of DNA that made people say, hey, that looks like the molecule that's storing the information. And just to be clear, DNA wasn't discovered in 1953. DNA was discovered in the mid-1800s. It was this kind of, this molecule that was inside of nuclei, of cells, and for some time, people said, oh, maybe this could be a molecular basis of inheritance."}, {"video_title": "DNA   Biomolecules   MCAT   Khan Academy (4).mp3", "Sentence": "But it was really the structure of DNA that made people say, hey, that looks like the molecule that's storing the information. And just to be clear, DNA wasn't discovered in 1953. DNA was discovered in the mid-1800s. It was this kind of, this molecule that was inside of nuclei, of cells, and for some time, people said, oh, maybe this could be a molecular basis of inheritance. You know, you could imagine what you would need to be a molecular basis of inheritance. It would have to be a molecule or a series of molecules that could contain information, that could be replicated, that could be expressed in some way. But it wasn't until 1953, when this double helix structure of DNA was established that people said, hey, this looks like our molecule."}, {"video_title": "DNA   Biomolecules   MCAT   Khan Academy (4).mp3", "Sentence": "It was this kind of, this molecule that was inside of nuclei, of cells, and for some time, people said, oh, maybe this could be a molecular basis of inheritance. You know, you could imagine what you would need to be a molecular basis of inheritance. It would have to be a molecule or a series of molecules that could contain information, that could be replicated, that could be expressed in some way. But it wasn't until 1953, when this double helix structure of DNA was established that people said, hey, this looks like our molecule. So first, let's just talk about the structure here, and then actually we'll talk about where this name, DNA, deoxyribonucleic acid, comes from. And then we'll talk a little bit about why the structure lends itself well to something that stores information, that can replicate its information, and that could express its information. We might go in-depth on the expression of information in future videos."}, {"video_title": "DNA   Biomolecules   MCAT   Khan Academy (4).mp3", "Sentence": "But it wasn't until 1953, when this double helix structure of DNA was established that people said, hey, this looks like our molecule. So first, let's just talk about the structure here, and then actually we'll talk about where this name, DNA, deoxyribonucleic acid, comes from. And then we'll talk a little bit about why the structure lends itself well to something that stores information, that can replicate its information, and that could express its information. We might go in-depth on the expression of information in future videos. So this structure right over here, and this is a visual depiction of a DNA molecule, you can view this as kind of a twisted ladder. It has these two, I guess you could say, sides of the ladder that are twisted. That is one side right over there, and then it is another side."}, {"video_title": "DNA   Biomolecules   MCAT   Khan Academy (4).mp3", "Sentence": "We might go in-depth on the expression of information in future videos. So this structure right over here, and this is a visual depiction of a DNA molecule, you can view this as kind of a twisted ladder. It has these two, I guess you could say, sides of the ladder that are twisted. That is one side right over there, and then it is another side. There is another side right over here. And in between those two sides, or connecting those two sides of that twisted ladder, you have these rungs. And these rungs are actually where the information, the genetic information is, I guess you could say, stored in some way."}, {"video_title": "DNA   Biomolecules   MCAT   Khan Academy (4).mp3", "Sentence": "That is one side right over there, and then it is another side. There is another side right over here. And in between those two sides, or connecting those two sides of that twisted ladder, you have these rungs. And these rungs are actually where the information, the genetic information is, I guess you could say, stored in some way. Because these rungs, it's a sequence of different bases. And when I say bases, you might say, wait, this says acid, why are you saying bases right over here? Well, the word deoxyribonucleic acid comes from the fact that this backbone is made up of a combination of sugar and phosphate."}, {"video_title": "DNA   Biomolecules   MCAT   Khan Academy (4).mp3", "Sentence": "And these rungs are actually where the information, the genetic information is, I guess you could say, stored in some way. Because these rungs, it's a sequence of different bases. And when I say bases, you might say, wait, this says acid, why are you saying bases right over here? Well, the word deoxyribonucleic acid comes from the fact that this backbone is made up of a combination of sugar and phosphate. And the sugar that makes up the backbone is deoxyribose, so that's essentially the D in DNA. And then the phosphate group is acidic, and that's where you get the acid part of it. And nucleic is, hey, this was found in nuclei of cells."}, {"video_title": "DNA   Biomolecules   MCAT   Khan Academy (4).mp3", "Sentence": "Well, the word deoxyribonucleic acid comes from the fact that this backbone is made up of a combination of sugar and phosphate. And the sugar that makes up the backbone is deoxyribose, so that's essentially the D in DNA. And then the phosphate group is acidic, and that's where you get the acid part of it. And nucleic is, hey, this was found in nuclei of cells. It is nucleic acid, deoxyribonucleic acid. But it's not, it also, it is actually mildly acidic all in total, but for every acid, it actually also has a base. And that base, those bases form the rung of the ladders."}, {"video_title": "DNA   Biomolecules   MCAT   Khan Academy (4).mp3", "Sentence": "And nucleic is, hey, this was found in nuclei of cells. It is nucleic acid, deoxyribonucleic acid. But it's not, it also, it is actually mildly acidic all in total, but for every acid, it actually also has a base. And that base, those bases form the rung of the ladders. And actually, each rung is a pair of bases. And as I said, that's where the information is actually stored. Well, what am I talking about?"}, {"video_title": "DNA   Biomolecules   MCAT   Khan Academy (4).mp3", "Sentence": "And that base, those bases form the rung of the ladders. And actually, each rung is a pair of bases. And as I said, that's where the information is actually stored. Well, what am I talking about? Well, let me talk about the four different bases that make up the rungs of a DNA molecule. So you have adenine. And so, for example, this part right over here, this section of that rung might be adenine."}, {"video_title": "DNA   Biomolecules   MCAT   Khan Academy (4).mp3", "Sentence": "Well, what am I talking about? Well, let me talk about the four different bases that make up the rungs of a DNA molecule. So you have adenine. And so, for example, this part right over here, this section of that rung might be adenine. Maybe this right over here is adenine. This right over here. Remember, each of these rungs are made up by, it's a pair of bases."}, {"video_title": "DNA   Biomolecules   MCAT   Khan Academy (4).mp3", "Sentence": "And so, for example, this part right over here, this section of that rung might be adenine. Maybe this right over here is adenine. This right over here. Remember, each of these rungs are made up by, it's a pair of bases. And that might be adenine. Maybe this is adenine. And I could stop there."}, {"video_title": "DNA   Biomolecules   MCAT   Khan Academy (4).mp3", "Sentence": "Remember, each of these rungs are made up by, it's a pair of bases. And that might be adenine. Maybe this is adenine. And I could stop there. I'll do a little more adenine. Maybe that's adenine right over there. And adenine always pairs with the base thymine."}, {"video_title": "DNA   Biomolecules   MCAT   Khan Academy (4).mp3", "Sentence": "And I could stop there. I'll do a little more adenine. Maybe that's adenine right over there. And adenine always pairs with the base thymine. So let me write that down. So adenine pairs with thymine. Thymine."}, {"video_title": "DNA   Biomolecules   MCAT   Khan Academy (4).mp3", "Sentence": "And adenine always pairs with the base thymine. So let me write that down. So adenine pairs with thymine. Thymine. So if that's an adenine there, then this is going to be a thymine. If this is an adenine, then this is going to be a thymine. Or if I drew the thymine first, well, I'll say, okay, it's going to pair with the adenine."}, {"video_title": "DNA   Biomolecules   MCAT   Khan Academy (4).mp3", "Sentence": "Thymine. So if that's an adenine there, then this is going to be a thymine. If this is an adenine, then this is going to be a thymine. Or if I drew the thymine first, well, I'll say, okay, it's going to pair with the adenine. So this is going to be a thymine right over here. This is going to be a thymine. If I were to draw this, this would be a thymine right over here."}, {"video_title": "DNA   Biomolecules   MCAT   Khan Academy (4).mp3", "Sentence": "Or if I drew the thymine first, well, I'll say, okay, it's going to pair with the adenine. So this is going to be a thymine right over here. This is going to be a thymine. If I were to draw this, this would be a thymine right over here. Now, the other two bases, you have cytosine, which pairs with guanine, or guanine that pairs with cytosine. So guanine. And we're not going to go into the molecular structure of these bases just yet, although these are good names to know because they show up a lot and they really form kind of the code, your genetic code."}, {"video_title": "DNA   Biomolecules   MCAT   Khan Academy (4).mp3", "Sentence": "If I were to draw this, this would be a thymine right over here. Now, the other two bases, you have cytosine, which pairs with guanine, or guanine that pairs with cytosine. So guanine. And we're not going to go into the molecular structure of these bases just yet, although these are good names to know because they show up a lot and they really form kind of the code, your genetic code. So guanine pairs with cytosine. Guanine and cytosine. Cytosine."}, {"video_title": "DNA   Biomolecules   MCAT   Khan Academy (4).mp3", "Sentence": "And we're not going to go into the molecular structure of these bases just yet, although these are good names to know because they show up a lot and they really form kind of the code, your genetic code. So guanine pairs with cytosine. Guanine and cytosine. Cytosine. So actually, if this is, let's say there's some cytosine there, let's say cytosine right over here, maybe this is cytosine, maybe this is cytosine, maybe this is cytosine, this is cytosine, and maybe this is cytosine, then it always pairs with the guanine. If we're talking about, so let's see, this is guanine then, then this will be guanine, this is guanine, this is guanine, I actually didn't draw stuff here, but this is guanine, I didn't say what these could be, but these would be made of pairs of, they could be adenine-thymine pairs, and it could be adenine on either side or the thymine on either side, and they could be made of guanine-cytosine pairs, where the guanine or the cytosine is on either side. Actually, just to make it a little bit more complete, let me just color in the rungs here as best as I can."}, {"video_title": "DNA   Biomolecules   MCAT   Khan Academy (4).mp3", "Sentence": "Cytosine. So actually, if this is, let's say there's some cytosine there, let's say cytosine right over here, maybe this is cytosine, maybe this is cytosine, maybe this is cytosine, this is cytosine, and maybe this is cytosine, then it always pairs with the guanine. If we're talking about, so let's see, this is guanine then, then this will be guanine, this is guanine, this is guanine, I actually didn't draw stuff here, but this is guanine, I didn't say what these could be, but these would be made of pairs of, they could be adenine-thymine pairs, and it could be adenine on either side or the thymine on either side, and they could be made of guanine-cytosine pairs, where the guanine or the cytosine is on either side. Actually, just to make it a little bit more complete, let me just color in the rungs here as best as I can. So those are guanine, so they're gonna pair with cytosine, pair with cytosine, pair with cytosine. And when it's drawn this way, you might start to see how this is essentially a code, the order of which the bases are, I guess the order in which we have these, or the sequence of these bases essentially encode the information that make you you, and you could debate, well, how much of it is nature versus nurture, and when people say nature, you know, it's literally genetic, and that's an ongoing debate, but it does code for things like your hair color, when you see that your smile is similar to your parents. It is because that information, to a large degree, is encoded genetically."}, {"video_title": "DNA   Biomolecules   MCAT   Khan Academy (4).mp3", "Sentence": "Actually, just to make it a little bit more complete, let me just color in the rungs here as best as I can. So those are guanine, so they're gonna pair with cytosine, pair with cytosine, pair with cytosine. And when it's drawn this way, you might start to see how this is essentially a code, the order of which the bases are, I guess the order in which we have these, or the sequence of these bases essentially encode the information that make you you, and you could debate, well, how much of it is nature versus nurture, and when people say nature, you know, it's literally genetic, and that's an ongoing debate, but it does code for things like your hair color, when you see that your smile is similar to your parents. It is because that information, to a large degree, is encoded genetically. It affects a lot of what makes you you, and actually not even just within a species, but also across species. Humans have more genetic material in common with other humans than they do with, say, a plant, but all living creatures as we know them have genetic information. This is the basis by which they are passing down their actual traits."}, {"video_title": "DNA   Biomolecules   MCAT   Khan Academy (4).mp3", "Sentence": "It is because that information, to a large degree, is encoded genetically. It affects a lot of what makes you you, and actually not even just within a species, but also across species. Humans have more genetic material in common with other humans than they do with, say, a plant, but all living creatures as we know them have genetic information. This is the basis by which they are passing down their actual traits. Now, you might be saying, well, how much genetic information does a human being have? And the number will either disappoint you or you might find it mind-boggling. The human genome, and every species has a different number of base pairs, to a large degree correlated with how complex they are, although not always, but the human genome has six million, sorry, not six million, six billion."}, {"video_title": "DNA   Biomolecules   MCAT   Khan Academy (4).mp3", "Sentence": "This is the basis by which they are passing down their actual traits. Now, you might be saying, well, how much genetic information does a human being have? And the number will either disappoint you or you might find it mind-boggling. The human genome, and every species has a different number of base pairs, to a large degree correlated with how complex they are, although not always, but the human genome has six million, sorry, not six million, six billion. Six million would be disappointing. Even billion might be disappointing. Six billion base pairs."}, {"video_title": "DNA   Biomolecules   MCAT   Khan Academy (4).mp3", "Sentence": "The human genome, and every species has a different number of base pairs, to a large degree correlated with how complex they are, although not always, but the human genome has six million, sorry, not six million, six billion. Six million would be disappointing. Even billion might be disappointing. Six billion base pairs. Six billion base pairs. And when you have your full complement of chromosomes, and this is in most of the cells in your body, outside of your sex cells, the sperm or the egg cells, this is going to be spread over 46 chromosomes. 46 chromosomes, or I guess you could say 23 pair of chromosomes."}, {"video_title": "DNA   Biomolecules   MCAT   Khan Academy (4).mp3", "Sentence": "Six billion base pairs. Six billion base pairs. And when you have your full complement of chromosomes, and this is in most of the cells in your body, outside of your sex cells, the sperm or the egg cells, this is going to be spread over 46 chromosomes. 46 chromosomes, or I guess you could say 23 pair of chromosomes. So if you divide six billion by 46, you get a little over, on average, 100 million, I think it's 100 and something million base pairs per chromosome. And some chromosomes are longer, actually some of the longest are over 200 million, and some might be shorter. That's just on average."}, {"video_title": "DNA   Biomolecules   MCAT   Khan Academy (4).mp3", "Sentence": "46 chromosomes, or I guess you could say 23 pair of chromosomes. So if you divide six billion by 46, you get a little over, on average, 100 million, I think it's 100 and something million base pairs per chromosome. And some chromosomes are longer, actually some of the longest are over 200 million, and some might be shorter. That's just on average. Now, this number might, to some of you, might be exciting. You're like, oh, I thought I was a simple creature. I didn't know I was this complex."}, {"video_title": "DNA   Biomolecules   MCAT   Khan Academy (4).mp3", "Sentence": "That's just on average. Now, this number might, to some of you, might be exciting. You're like, oh, I thought I was a simple creature. I didn't know I was this complex. Six billion, that's a lot of base pairs. That feels like a lot of information. For others of you, it might not feel so great."}, {"video_title": "DNA   Biomolecules   MCAT   Khan Academy (4).mp3", "Sentence": "I didn't know I was this complex. Six billion, that's a lot of base pairs. That feels like a lot of information. For others of you, it might not feel so great. You might say, hey, wait, I could store this much information on a modern thumb drive or on a hard disk. I thought I was more unique than that. And of course, we all are special and unique, but you might say, oh, six billion base pairs, I thought I was infinitely complex and whatever else, and there's some arguments for that along some other directions."}, {"video_title": "DNA   Biomolecules   MCAT   Khan Academy (4).mp3", "Sentence": "For others of you, it might not feel so great. You might say, hey, wait, I could store this much information on a modern thumb drive or on a hard disk. I thought I was more unique than that. And of course, we all are special and unique, but you might say, oh, six billion base pairs, I thought I was infinitely complex and whatever else, and there's some arguments for that along some other directions. But this is the approximate length, I guess you could say, the approximate size of the actual human genome. And when we talk about chromosomes, and we'll talk about chromosomes in much more depth, imagine taking this zoomed in thing that you have right over here, and over here, I don't know how many we have, like one, two, three, four, five, six, seven, eight, nine, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19. We have about 20 base pairs depicted here."}, {"video_title": "DNA   Biomolecules   MCAT   Khan Academy (4).mp3", "Sentence": "And of course, we all are special and unique, but you might say, oh, six billion base pairs, I thought I was infinitely complex and whatever else, and there's some arguments for that along some other directions. But this is the approximate length, I guess you could say, the approximate size of the actual human genome. And when we talk about chromosomes, and we'll talk about chromosomes in much more depth, imagine taking this zoomed in thing that you have right over here, and over here, I don't know how many we have, like one, two, three, four, five, six, seven, eight, nine, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19. We have about 20 base pairs depicted here. Imagine if you had about 200 million of these base pairs, and then you were to take this thing and you were to kind of coil it up into that thing is a chromosome. Is a chromosome. And you're saying, wait, I have that much information in most of the cells of my body?"}, {"video_title": "DNA   Biomolecules   MCAT   Khan Academy (4).mp3", "Sentence": "We have about 20 base pairs depicted here. Imagine if you had about 200 million of these base pairs, and then you were to take this thing and you were to kind of coil it up into that thing is a chromosome. Is a chromosome. And you're saying, wait, I have that much information in most of the cells of my body? This thing must be incredibly compact. And if you said that, I would say, yes, you are correct. This, the radius, the radius of the DNA molecule is on the order of one nanometer."}, {"video_title": "DNA   Biomolecules   MCAT   Khan Academy (4).mp3", "Sentence": "And you're saying, wait, I have that much information in most of the cells of my body? This thing must be incredibly compact. And if you said that, I would say, yes, you are correct. This, the radius, the radius of the DNA molecule is on the order of one nanometer. One nanometer, which is a billionth of a meter. So you can start to assess kind of the scale of this thing. This is a very dense way to actually store information."}, {"video_title": "DNA   Biomolecules   MCAT   Khan Academy (4).mp3", "Sentence": "This, the radius, the radius of the DNA molecule is on the order of one nanometer. One nanometer, which is a billionth of a meter. So you can start to assess kind of the scale of this thing. This is a very dense way to actually store information. But just to have an appreciation of, and you might have seen it when I was coloring in, on why the structure lends itself to being able to replicate the information or even to be able to translate or express the information, let's think about if you were to take this ladder and you were to just kind of split all the base pairs. So you just have one half of them. So you essentially have half of the ladder."}, {"video_title": "DNA   Biomolecules   MCAT   Khan Academy (4).mp3", "Sentence": "This is a very dense way to actually store information. But just to have an appreciation of, and you might have seen it when I was coloring in, on why the structure lends itself to being able to replicate the information or even to be able to translate or express the information, let's think about if you were to take this ladder and you were to just kind of split all the base pairs. So you just have one half of them. So you essentially have half of the ladder. And so if you only have half of the ladder, you're able to construct the other half of the ladder. Let's take an example. Let's say, and I'll just use the first letter to abbreviate for each of these bases."}, {"video_title": "DNA   Biomolecules   MCAT   Khan Academy (4).mp3", "Sentence": "So you essentially have half of the ladder. And so if you only have half of the ladder, you're able to construct the other half of the ladder. Let's take an example. Let's say, and I'll just use the first letter to abbreviate for each of these bases. So let's say you have some, so let's say this is one of the, this is the sugar phosphate backbone right over here. So this could be one of the sides. And let's say there's some adenine, actually, let me do them in the right color."}, {"video_title": "DNA   Biomolecules   MCAT   Khan Academy (4).mp3", "Sentence": "Let's say, and I'll just use the first letter to abbreviate for each of these bases. So let's say you have some, so let's say this is one of the, this is the sugar phosphate backbone right over here. So this could be one of the sides. And let's say there's some adenine, actually, let me do them in the right color. So you've got some adenine, adenine, maybe some adenine right over here. Maybe there's an adenine there. Maybe you have some thymine, thymine, maybe thymine right over here."}, {"video_title": "DNA   Biomolecules   MCAT   Khan Academy (4).mp3", "Sentence": "And let's say there's some adenine, actually, let me do them in the right color. So you've got some adenine, adenine, maybe some adenine right over here. Maybe there's an adenine there. Maybe you have some thymine, thymine, maybe thymine right over here. Then you have some, you have some guanine, guanine, guanine. And then let's say you have some cytosine and you have some cytosine. So with just half of this ladder, I guess you could say, you're able to construct the other half."}, {"video_title": "DNA   Biomolecules   MCAT   Khan Academy (4).mp3", "Sentence": "Maybe you have some thymine, thymine, maybe thymine right over here. Then you have some, you have some guanine, guanine, guanine. And then let's say you have some cytosine and you have some cytosine. So with just half of this ladder, I guess you could say, you're able to construct the other half. And that's actually how DNA replicates. This ladder splits and then each of those two halves of that ladder are able to construct versions of the other half, or versions of the other half are able to be constructed on top of that half. So how does that happen?"}, {"video_title": "DNA   Biomolecules   MCAT   Khan Academy (4).mp3", "Sentence": "So with just half of this ladder, I guess you could say, you're able to construct the other half. And that's actually how DNA replicates. This ladder splits and then each of those two halves of that ladder are able to construct versions of the other half, or versions of the other half are able to be constructed on top of that half. So how does that happen? Well, it's based on how these bases pair. Adenine always pairs with thymine if we're talking about DNA. So if you have an A there, you're gonna have a T on this end, T on this end."}, {"video_title": "DNA   Biomolecules   MCAT   Khan Academy (4).mp3", "Sentence": "So how does that happen? Well, it's based on how these bases pair. Adenine always pairs with thymine if we're talking about DNA. So if you have an A there, you're gonna have a T on this end, T on this end. T's right all over here, T right over there. If you have a T on that end, you're gonna have an A right over there, A, A. If you have a G, a guanine on this side, you're gonna have a cytosine on the other side."}, {"video_title": "DNA   Biomolecules   MCAT   Khan Academy (4).mp3", "Sentence": "So if you have an A there, you're gonna have a T on this end, T on this end. T's right all over here, T right over there. If you have a T on that end, you're gonna have an A right over there, A, A. If you have a G, a guanine on this side, you're gonna have a cytosine on the other side. Cytosine, cytosine, cytosine. And if you have a cytosine, you're gonna have a guanine on the other side. And so hopefully that gives you an appreciation of how DNA can replicate itself."}, {"video_title": "DNA   Biomolecules   MCAT   Khan Academy (4).mp3", "Sentence": "If you have a G, a guanine on this side, you're gonna have a cytosine on the other side. Cytosine, cytosine, cytosine. And if you have a cytosine, you're gonna have a guanine on the other side. And so hopefully that gives you an appreciation of how DNA can replicate itself. And as we'll see also, how this information can be translated to other forms of either related molecules, but eventually to proteins. And just to kind of round out this video, to get a real visual sense of what the DNA molecule looks like, or I guess a different visual depiction from this, I found this animated, that animated GIF that, you know, if you haven't fully digested what a double helix looks like, this is it. And you see here, you see your sugar phosphate bases here."}, {"video_title": "DNA   Biomolecules   MCAT   Khan Academy (4).mp3", "Sentence": "And so hopefully that gives you an appreciation of how DNA can replicate itself. And as we'll see also, how this information can be translated to other forms of either related molecules, but eventually to proteins. And just to kind of round out this video, to get a real visual sense of what the DNA molecule looks like, or I guess a different visual depiction from this, I found this animated, that animated GIF that, you know, if you haven't fully digested what a double helix looks like, this is it. And you see here, you see your sugar phosphate bases here. You see kind of the sugars and phosphate, the sugars and the phosphates alternating along this backbone. And then the rungs of the latter are these base pairs. So this is one of the bases, that's the corresponding, I guess you could say partner."}, {"video_title": "Dehydration synthesis or a condensation reaction   Biology   Khan Academy.mp3", "Sentence": "In the previous video, we talked about the importance of glucose as a simple sugar. We talked about its molecular structure. What I want to do in this video is study how glucose can be, how we can use it as a building block for more complex sugars and more complex carbohydrates. So this right over here, I've copy and pasted two glucose molecules. We can number their carbons. This is one, two, three, four, five, six. One, two, three, four, five, six."}, {"video_title": "Dehydration synthesis or a condensation reaction   Biology   Khan Academy.mp3", "Sentence": "So this right over here, I've copy and pasted two glucose molecules. We can number their carbons. This is one, two, three, four, five, six. One, two, three, four, five, six. We have them in their cyclic form. And what we're going to do is explore what would happen if this oxygen right over here, I'll highlight it in this magenta color, were to use one of its lone pairs, one of its lone pairs to do what's in organic chemistry referred to as a nucleophilic attack on the number one carbon on the left-hand glucose molecule. And the reason why that could happen is this number one carbon right over here, it's attached to two oxygens."}, {"video_title": "Dehydration synthesis or a condensation reaction   Biology   Khan Academy.mp3", "Sentence": "One, two, three, four, five, six. We have them in their cyclic form. And what we're going to do is explore what would happen if this oxygen right over here, I'll highlight it in this magenta color, were to use one of its lone pairs, one of its lone pairs to do what's in organic chemistry referred to as a nucleophilic attack on the number one carbon on the left-hand glucose molecule. And the reason why that could happen is this number one carbon right over here, it's attached to two oxygens. Oxygens are very electronegative. They like to hog electrons when they're in a covalent bond. So that's going to give this carbon a partially positive charge."}, {"video_title": "Dehydration synthesis or a condensation reaction   Biology   Khan Academy.mp3", "Sentence": "And the reason why that could happen is this number one carbon right over here, it's attached to two oxygens. Oxygens are very electronegative. They like to hog electrons when they're in a covalent bond. So that's going to give this carbon a partially positive charge. And this oxygen is very electronegative. It's going to hog the electrons from this hydrogen and the number four carbon on the right-hand glucose molecule. So it's going to have a partially negative charge."}, {"video_title": "Dehydration synthesis or a condensation reaction   Biology   Khan Academy.mp3", "Sentence": "So that's going to give this carbon a partially positive charge. And this oxygen is very electronegative. It's going to hog the electrons from this hydrogen and the number four carbon on the right-hand glucose molecule. So it's going to have a partially negative charge. And so it is going to be nucleophilic. It's going to be attracted to, I guess you could say, the carbon nucleus, to the partially positive charge right over here. And so as it does that, it's going to use a lone pair to form a bond."}, {"video_title": "Dehydration synthesis or a condensation reaction   Biology   Khan Academy.mp3", "Sentence": "So it's going to have a partially negative charge. And so it is going to be nucleophilic. It's going to be attracted to, I guess you could say, the carbon nucleus, to the partially positive charge right over here. And so as it does that, it's going to use a lone pair to form a bond. It's going to share it with the carbon. And then the carbon can let go of another bond. So it could let go of both of these electrons in that bond."}, {"video_title": "Dehydration synthesis or a condensation reaction   Biology   Khan Academy.mp3", "Sentence": "And so as it does that, it's going to use a lone pair to form a bond. It's going to share it with the carbon. And then the carbon can let go of another bond. So it could let go of both of these electrons in that bond. Now, you could say, maybe that just goes back to the oxygen and it forms a hydroxide anion. Or we could imagine, well, maybe it'll be used. Maybe it forms a hydroxide anion first."}, {"video_title": "Dehydration synthesis or a condensation reaction   Biology   Khan Academy.mp3", "Sentence": "So it could let go of both of these electrons in that bond. Now, you could say, maybe that just goes back to the oxygen and it forms a hydroxide anion. Or we could imagine, well, maybe it'll be used. Maybe it forms a hydroxide anion first. Or maybe that bond immediately goes and picks up a hydrogen ion out of the solution, from a hydronium ion sitting someplace. So this can be used to form a bond with this hydrogen ion. Which is really, this is just a proton here."}, {"video_title": "Dehydration synthesis or a condensation reaction   Biology   Khan Academy.mp3", "Sentence": "Maybe it forms a hydroxide anion first. Or maybe that bond immediately goes and picks up a hydrogen ion out of the solution, from a hydronium ion sitting someplace. So this can be used to form a bond with this hydrogen ion. Which is really, this is just a proton here. You take an electron away from hydrogen, it's just going to be a proton. Well, what's that going to do? Well, that's going to link these two glucose molecules."}, {"video_title": "Dehydration synthesis or a condensation reaction   Biology   Khan Academy.mp3", "Sentence": "Which is really, this is just a proton here. You take an electron away from hydrogen, it's just going to be a proton. Well, what's that going to do? Well, that's going to link these two glucose molecules. And it's going to link it just like this. And it's important to keep track of our molecules here. So this oxygen is now going to be this oxygen."}, {"video_title": "Dehydration synthesis or a condensation reaction   Biology   Khan Academy.mp3", "Sentence": "Well, that's going to link these two glucose molecules. And it's going to link it just like this. And it's important to keep track of our molecules here. So this oxygen is now going to be this oxygen. It is now going to be that oxygen. This bond between the number four carbon on the right-hand side of that oxygen is this bond right over here. This, when we took this electron pair to form, this bond with the number one carbon, that is, let me do it in that magenta color, that is this bond right over here."}, {"video_title": "Dehydration synthesis or a condensation reaction   Biology   Khan Academy.mp3", "Sentence": "So this oxygen is now going to be this oxygen. It is now going to be that oxygen. This bond between the number four carbon on the right-hand side of that oxygen is this bond right over here. This, when we took this electron pair to form, this bond with the number one carbon, that is, let me do it in that magenta color, that is this bond right over here. The oxygen, this oxygen, is now this oxygen right over here. And this electron pair is now formed a bond with this hydrogen. So we could say, well, that could be, let me do that in blue."}, {"video_title": "Dehydration synthesis or a condensation reaction   Biology   Khan Academy.mp3", "Sentence": "This, when we took this electron pair to form, this bond with the number one carbon, that is, let me do it in that magenta color, that is this bond right over here. The oxygen, this oxygen, is now this oxygen right over here. And this electron pair is now formed a bond with this hydrogen. So we could say, well, that could be, let me do that in blue. That could be this bond right over here. Now, the one difference is, based on how I've drawn it, this oxygen, sorry, this oxygen, the way I've drawn it, it's attached to the number one carbon here, the number four carbon here. We have that over, we've already done that over here."}, {"video_title": "Dehydration synthesis or a condensation reaction   Biology   Khan Academy.mp3", "Sentence": "So we could say, well, that could be, let me do that in blue. That could be this bond right over here. Now, the one difference is, based on how I've drawn it, this oxygen, sorry, this oxygen, the way I've drawn it, it's attached to the number one carbon here, the number four carbon here. We have that over, we've already done that over here. Number one carbon on the left molecule, number four carbon on the right molecule. But we also have it bonded, we also have it bonded to a hydrogen. So just the way I've done it right now, it's still bonded to a hydrogen."}, {"video_title": "Dehydration synthesis or a condensation reaction   Biology   Khan Academy.mp3", "Sentence": "We have that over, we've already done that over here. Number one carbon on the left molecule, number four carbon on the right molecule. But we also have it bonded, we also have it bonded to a hydrogen. So just the way I've done it right now, it's still bonded to a hydrogen. It's going to have a net positive, it's going to have a net positive charge. Over here, it was neutral, it was neutral right over here, but then it's now sharing its electrons. It's now sharing both of those electrons in a covalent bond."}, {"video_title": "Dehydration synthesis or a condensation reaction   Biology   Khan Academy.mp3", "Sentence": "So just the way I've done it right now, it's still bonded to a hydrogen. It's going to have a net positive, it's going to have a net positive charge. Over here, it was neutral, it was neutral right over here, but then it's now sharing its electrons. It's now sharing both of those electrons in a covalent bond. And so you can think of it as giving, it's giving it away, it's giving away an electron to this carbon, so it's going to have a net positive charge. But then to get back to neutral, you could imagine, well, maybe, maybe some type of a water molecule could grab that ion. So this, maybe this one right over here, this one right over here, could grab that hydrogen, and then these electrons, both of them, and it would just grab the hydrogen nucleus, the proton, and so these two electrons could go back to this oxygen, and then become, this oxygen would become neutral."}, {"video_title": "Dehydration synthesis or a condensation reaction   Biology   Khan Academy.mp3", "Sentence": "It's now sharing both of those electrons in a covalent bond. And so you can think of it as giving, it's giving it away, it's giving away an electron to this carbon, so it's going to have a net positive charge. But then to get back to neutral, you could imagine, well, maybe, maybe some type of a water molecule could grab that ion. So this, maybe this one right over here, this one right over here, could grab that hydrogen, and then these electrons, both of them, and it would just grab the hydrogen nucleus, the proton, and so these two electrons could go back to this oxygen, and then become, this oxygen would become neutral. And so what we would be left with, what we would be left with, actually, let me just erase this, is that this hydrogen, this hydrogen would now be attached, would now be attached to this oxygen, and we would have a hydronium, hydronium ion. And this is reasonable, we essentially had some hydronium, we had a hydrogen proton out here before, and we still do, now it's attached to a water. So we haven't, you know, we've taken a proton, and we've given back a proton, so we haven't, you know, net-net, kind of added charge, or taken charge away, taken charge away from the system."}, {"video_title": "Dehydration synthesis or a condensation reaction   Biology   Khan Academy.mp3", "Sentence": "So this, maybe this one right over here, this one right over here, could grab that hydrogen, and then these electrons, both of them, and it would just grab the hydrogen nucleus, the proton, and so these two electrons could go back to this oxygen, and then become, this oxygen would become neutral. And so what we would be left with, what we would be left with, actually, let me just erase this, is that this hydrogen, this hydrogen would now be attached, would now be attached to this oxygen, and we would have a hydronium, hydronium ion. And this is reasonable, we essentially had some hydronium, we had a hydrogen proton out here before, and we still do, now it's attached to a water. So we haven't, you know, we've taken a proton, and we've given back a proton, so we haven't, you know, net-net, kind of added charge, or taken charge away, taken charge away from the system. But the important thing that we just saw is, as these two things, as these two things essentially attached, we lost, we lost a water molecule, or I guess net-net, this system lost a water molecule. It took up a charge to do it, to build that water molecule, but the thing that really kind of escaped from both of these two molecules is, is this, is this, is this right over here. This H is this H. This oxygen is this oxygen."}, {"video_title": "Dehydration synthesis or a condensation reaction   Biology   Khan Academy.mp3", "Sentence": "So we haven't, you know, we've taken a proton, and we've given back a proton, so we haven't, you know, net-net, kind of added charge, or taken charge away, taken charge away from the system. But the important thing that we just saw is, as these two things, as these two things essentially attached, we lost, we lost a water molecule, or I guess net-net, this system lost a water molecule. It took up a charge to do it, to build that water molecule, but the thing that really kind of escaped from both of these two molecules is, is this, is this, is this right over here. This H is this H. This oxygen is this oxygen. And this hydrogen is this hydrogen right over here. And so this type of a reaction, in which we're synthesizing a more complex molecule, a longer chain of, a longer chain of glucose, of glucose molecules, this is called a dehydration synthesis. So what we just did, this right over here is called a dehydration, dehydration synthesis."}, {"video_title": "Dehydration synthesis or a condensation reaction   Biology   Khan Academy.mp3", "Sentence": "This H is this H. This oxygen is this oxygen. And this hydrogen is this hydrogen right over here. And so this type of a reaction, in which we're synthesizing a more complex molecule, a longer chain of, a longer chain of glucose, of glucose molecules, this is called a dehydration synthesis. So what we just did, this right over here is called a dehydration, dehydration synthesis. Why are we calling it a dehydration synthesis? Well, we've just taken a water out. If you imagine losing water, we talk about, that's, you're getting dehydrated."}, {"video_title": "Dehydration synthesis or a condensation reaction   Biology   Khan Academy.mp3", "Sentence": "So what we just did, this right over here is called a dehydration, dehydration synthesis. Why are we calling it a dehydration synthesis? Well, we've just taken a water out. If you imagine losing water, we talk about, that's, you're getting dehydrated. So this, and why synthesis? Well, we put two things together. We synthesized a larger molecule."}, {"video_title": "Dehydration synthesis or a condensation reaction   Biology   Khan Academy.mp3", "Sentence": "If you imagine losing water, we talk about, that's, you're getting dehydrated. So this, and why synthesis? Well, we put two things together. We synthesized a larger molecule. Sometimes this would be, this would be called a condensation reaction. Condensation reaction. And by doing this, these two glucose molecules are able to form a disaccharide now."}, {"video_title": "Dehydration synthesis or a condensation reaction   Biology   Khan Academy.mp3", "Sentence": "We synthesized a larger molecule. Sometimes this would be, this would be called a condensation reaction. Condensation reaction. And by doing this, these two glucose molecules are able to form a disaccharide now. So each individually, each individually, they were monosaccharides. So this one on the right, that's a monosaccharide. What does monosaccharide mean?"}, {"video_title": "Dehydration synthesis or a condensation reaction   Biology   Khan Academy.mp3", "Sentence": "And by doing this, these two glucose molecules are able to form a disaccharide now. So each individually, each individually, they were monosaccharides. So this one on the right, that's a monosaccharide. What does monosaccharide mean? Well, it means, mono means single or one, and saccharide comes from the Greek word for sugar. The Greek word for sugar is, I'm gonna mispronounce it, is saccharone. When people talk about something being saccharine, they're saying something that's very, very sweet."}, {"video_title": "Dehydration synthesis or a condensation reaction   Biology   Khan Academy.mp3", "Sentence": "What does monosaccharide mean? Well, it means, mono means single or one, and saccharide comes from the Greek word for sugar. The Greek word for sugar is, I'm gonna mispronounce it, is saccharone. When people talk about something being saccharine, they're saying something that's very, very sweet. The Greek word for sugar is saccharine. So saccharide means it's a sugar, it's a single sugar. So that, the meaning there is sugar."}, {"video_title": "Dehydration synthesis or a condensation reaction   Biology   Khan Academy.mp3", "Sentence": "When people talk about something being saccharine, they're saying something that's very, very sweet. The Greek word for sugar is saccharine. So saccharide means it's a sugar, it's a single sugar. So that, the meaning there is sugar. And the general term saccharide refers to not just these simple sugars, monosaccharides, but it could mean two of these things put together, and there's other simple sugars, fructose and others, or it could mean a huge number of these put together. You could have polysaccharides. And that whole class, saccharides, these we also associate with carbohydrates."}, {"video_title": "Dehydration synthesis or a condensation reaction   Biology   Khan Academy.mp3", "Sentence": "So that, the meaning there is sugar. And the general term saccharide refers to not just these simple sugars, monosaccharides, but it could mean two of these things put together, and there's other simple sugars, fructose and others, or it could mean a huge number of these put together. You could have polysaccharides. And that whole class, saccharides, these we also associate with carbohydrates. Now this, now we went from two monosaccharides to right over here, this is a disaccharide. This is a disaccharide. We have two monosaccharides were involved."}, {"video_title": "Dehydration synthesis or a condensation reaction   Biology   Khan Academy.mp3", "Sentence": "And that whole class, saccharides, these we also associate with carbohydrates. Now this, now we went from two monosaccharides to right over here, this is a disaccharide. This is a disaccharide. We have two monosaccharides were involved. This is a disaccharide, and this particular disaccharide is maltose or malt sugar. Maltose. So the whole point of this video is to see how you can start with these simple sugars, these monosaccharides, and form disaccharides."}, {"video_title": "Dehydration synthesis or a condensation reaction   Biology   Khan Academy.mp3", "Sentence": "We have two monosaccharides were involved. This is a disaccharide, and this particular disaccharide is maltose or malt sugar. Maltose. So the whole point of this video is to see how you can start with these simple sugars, these monosaccharides, and form disaccharides. In fact, you could keep going. You could keep having dehydration synthesis, condensation reactions, to keep adding more and more monosaccharides to build longer and longer chains. So if you were to keep doing that, if you were to keep building chains of these things, now you're getting into the world of polysaccharides."}, {"video_title": "Dehydration synthesis or a condensation reaction   Biology   Khan Academy.mp3", "Sentence": "So the whole point of this video is to see how you can start with these simple sugars, these monosaccharides, and form disaccharides. In fact, you could keep going. You could keep having dehydration synthesis, condensation reactions, to keep adding more and more monosaccharides to build longer and longer chains. So if you were to keep doing that, if you were to keep building chains of these things, now you're getting into the world of polysaccharides. Polysaccharides. Or many simple sugars, many monosaccharides, many monosaccharides put together. And this is the case for sugar, but this is something that you'll see often in chemistry, where you have a single unit."}, {"video_title": "Dehydration synthesis or a condensation reaction   Biology   Khan Academy.mp3", "Sentence": "So if you were to keep doing that, if you were to keep building chains of these things, now you're getting into the world of polysaccharides. Polysaccharides. Or many simple sugars, many monosaccharides, many monosaccharides put together. And this is the case for sugar, but this is something that you'll see often in chemistry, where you have a single unit. Here it's a single sugar, but if we talk it in more general terms, we would call it a monomer. And then if we have a bunch of these monomers put together, we would call it a polymer. Now, polysaccharides are super important, and you have probably eaten some polysaccharides today, and you probably have some polys, in fact, I'm sure you have some polysaccharides stored in your cells right now."}, {"video_title": "Dehydration synthesis or a condensation reaction   Biology   Khan Academy.mp3", "Sentence": "And this is the case for sugar, but this is something that you'll see often in chemistry, where you have a single unit. Here it's a single sugar, but if we talk it in more general terms, we would call it a monomer. And then if we have a bunch of these monomers put together, we would call it a polymer. Now, polysaccharides are super important, and you have probably eaten some polysaccharides today, and you probably have some polys, in fact, I'm sure you have some polysaccharides stored in your cells right now. If you put a bunch of glucose molecules, if we were to keep this process going, and we were to have a bunch of glucose molecules together, when you find it in plants, it'll often be in the form of a starch. So a polysaccharide that you'll find in a plant is a starch, a bunch of glucoses put together. In your own cells, to have a immediate energy store, a bunch of glucoses put together is glycogen."}, {"video_title": "Semi conservative replication   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "Let's take a piece of DNA and let's just unwind it into its two strands and just help us remember that DNA is really a very, very long molecule. I'm going to put arrows here on our two strands of DNA. And the question I want to ask you is, if we were to replicate this DNA, what would the end result look like? So I'm kind of skipping over the entire process of how the DNA is replicated and focusing just on the product. And so we have three choices. The first is conservative replication. And in conservative replication, we have our old pair of DNA and then we synthesize a completely new pair of DNA."}, {"video_title": "Semi conservative replication   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "So I'm kind of skipping over the entire process of how the DNA is replicated and focusing just on the product. And so we have three choices. The first is conservative replication. And in conservative replication, we have our old pair of DNA and then we synthesize a completely new pair of DNA. So you can see the old pair that looks just the same as what we had before in yellow, and then we have a completely new pair, which is represented in blue. Our next choice is dispersive replication. And in dispersive replication, we're going to end up with two pairs of DNA."}, {"video_title": "Semi conservative replication   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "And in conservative replication, we have our old pair of DNA and then we synthesize a completely new pair of DNA. So you can see the old pair that looks just the same as what we had before in yellow, and then we have a completely new pair, which is represented in blue. Our next choice is dispersive replication. And in dispersive replication, we're going to end up with two pairs of DNA. And in each one of those pairs, we have some old DNA and new DNA dispersed within that double-stranded DNA. So you can see there's yellow and blue mixed up together. And it wouldn't necessarily have to be in the ratio that I drew it in."}, {"video_title": "Semi conservative replication   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "And in dispersive replication, we're going to end up with two pairs of DNA. And in each one of those pairs, we have some old DNA and new DNA dispersed within that double-stranded DNA. So you can see there's yellow and blue mixed up together. And it wouldn't necessarily have to be in the ratio that I drew it in. I drew it in this kind of neat ratio where the yellow and blues are the same size, but perhaps the yellows would be a little bit bigger and maybe some of the blue parts smaller, or vice versa. And the third option we have is semi-conservative replication. And in semi-conservative replication, each pair has one old strand that you see in yellow, of course, and one new strand that's in blue."}, {"video_title": "Semi conservative replication   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "And it wouldn't necessarily have to be in the ratio that I drew it in. I drew it in this kind of neat ratio where the yellow and blues are the same size, but perhaps the yellows would be a little bit bigger and maybe some of the blue parts smaller, or vice versa. And the third option we have is semi-conservative replication. And in semi-conservative replication, each pair has one old strand that you see in yellow, of course, and one new strand that's in blue. And this question was answered by two scientists, one by the name of Mezelson and one by the name of Stahl. And they conducted a famous experiment, which was named after them. So the Mezelson-Stahl experiment."}, {"video_title": "Surface area to volume ratio of cells   Cell structure and function   AP Biology   Khan Academy.mp3", "Sentence": "So let's say that this is a cell. So we know that all sorts of activity is going on inside of this cell here, and we will study that in a lot more depth as we go further in our study of biology. But it's important to realize that this cell and the activity in that cell is not operating in isolation. That in order to live, that cell needs resources from the outside world. So resources need to make their way through that outer membrane of the cell so it can be used inside that cellular machinery. And as that cell does what it does, it's also going to generate waste products, and that needs to be released somehow across that membrane. So you also have waste."}, {"video_title": "Surface area to volume ratio of cells   Cell structure and function   AP Biology   Khan Academy.mp3", "Sentence": "That in order to live, that cell needs resources from the outside world. So resources need to make their way through that outer membrane of the cell so it can be used inside that cellular machinery. And as that cell does what it does, it's also going to generate waste products, and that needs to be released somehow across that membrane. So you also have waste. And you also have energy that is going to be transferred either from the inside of the cell to the outside or from the outside to the inside. A lot of times, we imagine that all of the activity inside of the cell is generating thermal energy that has to be dissipated somehow, and that is usually the case, not always. And so you have thermal energy that has to be dissipated."}, {"video_title": "Surface area to volume ratio of cells   Cell structure and function   AP Biology   Khan Academy.mp3", "Sentence": "So you also have waste. And you also have energy that is going to be transferred either from the inside of the cell to the outside or from the outside to the inside. A lot of times, we imagine that all of the activity inside of the cell is generating thermal energy that has to be dissipated somehow, and that is usually the case, not always. And so you have thermal energy that has to be dissipated. Now, you might see something interesting, or maybe you haven't seen it just yet, is that you have all of this activity operating in the volume of the cell, but then all of this exchange, all of the resources coming in, the waste coming out, the thermal energy going in either direction, it has to be somehow diffused across this surface, across this two-dimensional surface. So this raises an interesting question. As our volume increases, what happens to the ratio of our surface to our volume?"}, {"video_title": "Surface area to volume ratio of cells   Cell structure and function   AP Biology   Khan Academy.mp3", "Sentence": "And so you have thermal energy that has to be dissipated. Now, you might see something interesting, or maybe you haven't seen it just yet, is that you have all of this activity operating in the volume of the cell, but then all of this exchange, all of the resources coming in, the waste coming out, the thermal energy going in either direction, it has to be somehow diffused across this surface, across this two-dimensional surface. So this raises an interesting question. As our volume increases, what happens to the ratio of our surface to our volume? Because you could imagine maybe at some point, the volume gets large enough that you don't have enough surface area to do these three things well. And so let's think about this ratio. Let's think about the ratio of our surface area to volume."}, {"video_title": "Surface area to volume ratio of cells   Cell structure and function   AP Biology   Khan Academy.mp3", "Sentence": "As our volume increases, what happens to the ratio of our surface to our volume? Because you could imagine maybe at some point, the volume gets large enough that you don't have enough surface area to do these three things well. And so let's think about this ratio. Let's think about the ratio of our surface area to volume. And I'm gonna get a little bit mathy here. You don't have to know the math for the context of a biology course, but you need to know what the conclusion is that the math is going to give us. So if this is a sphere of radius r, the surface area of this sphere is going to be four pi r squared, and the volume of this sphere is going to be 4 3rds pi r cubed."}, {"video_title": "Surface area to volume ratio of cells   Cell structure and function   AP Biology   Khan Academy.mp3", "Sentence": "Let's think about the ratio of our surface area to volume. And I'm gonna get a little bit mathy here. You don't have to know the math for the context of a biology course, but you need to know what the conclusion is that the math is going to give us. So if this is a sphere of radius r, the surface area of this sphere is going to be four pi r squared, and the volume of this sphere is going to be 4 3rds pi r cubed. So this pi would cancel with that pi. If we divide the numerator and the denominator by r squared, we get a one there, and then we just get an r right over here. If we divide both of these by four, you get a one there, and this is just going to be a 1 3rd."}, {"video_title": "Surface area to volume ratio of cells   Cell structure and function   AP Biology   Khan Academy.mp3", "Sentence": "So if this is a sphere of radius r, the surface area of this sphere is going to be four pi r squared, and the volume of this sphere is going to be 4 3rds pi r cubed. So this pi would cancel with that pi. If we divide the numerator and the denominator by r squared, we get a one there, and then we just get an r right over here. If we divide both of these by four, you get a one there, and this is just going to be a 1 3rd. And so we are going to be left with one over 1 3rd r, or we could just write this as this is equal to three over r. And so we see at least for a spherical cell like this, as r increases, as our cell gets larger and larger, the ratio between our surface area to volume decreases. So let me write that. As r goes up, then the ratio between our surface area to volume, surface area to volume, is going to go down."}, {"video_title": "Surface area to volume ratio of cells   Cell structure and function   AP Biology   Khan Academy.mp3", "Sentence": "If we divide both of these by four, you get a one there, and this is just going to be a 1 3rd. And so we are going to be left with one over 1 3rd r, or we could just write this as this is equal to three over r. And so we see at least for a spherical cell like this, as r increases, as our cell gets larger and larger, the ratio between our surface area to volume decreases. So let me write that. As r goes up, then the ratio between our surface area to volume, surface area to volume, is going to go down. The bigger your denominator, the lower the value is going to be. And so what that tells us is is that as the volume of our cell increases, as our cell gets bigger and bigger and bigger, we have less surface area per unit of volume. And so it's going to make that exchange of the resources, the waste, and that energy harder and harder and harder."}, {"video_title": "Surface area to volume ratio of cells   Cell structure and function   AP Biology   Khan Academy.mp3", "Sentence": "As r goes up, then the ratio between our surface area to volume, surface area to volume, is going to go down. The bigger your denominator, the lower the value is going to be. And so what that tells us is is that as the volume of our cell increases, as our cell gets bigger and bigger and bigger, we have less surface area per unit of volume. And so it's going to make that exchange of the resources, the waste, and that energy harder and harder and harder. And we would get a similar result if instead of doing a spherical cell, let's say we did a cuboidal cell. So let's do it like this, a cuboidal cell. You might see this in some plants, something that's roughly cuboidal or rectangular in some way, or a rectangular prism, I should say."}, {"video_title": "Surface area to volume ratio of cells   Cell structure and function   AP Biology   Khan Academy.mp3", "Sentence": "And so it's going to make that exchange of the resources, the waste, and that energy harder and harder and harder. And we would get a similar result if instead of doing a spherical cell, let's say we did a cuboidal cell. So let's do it like this, a cuboidal cell. You might see this in some plants, something that's roughly cuboidal or rectangular in some way, or a rectangular prism, I should say. But let's say it's x by x by x. We could do the same exercise. Our ratio of surface area to volume is going to be what?"}, {"video_title": "Surface area to volume ratio of cells   Cell structure and function   AP Biology   Khan Academy.mp3", "Sentence": "You might see this in some plants, something that's roughly cuboidal or rectangular in some way, or a rectangular prism, I should say. But let's say it's x by x by x. We could do the same exercise. Our ratio of surface area to volume is going to be what? Well, our surface area, you have six faces that each have an area of x squared. So our surface area is going to be six x squared. And then our volume is going to be x times x times x over x to the third."}, {"video_title": "Surface area to volume ratio of cells   Cell structure and function   AP Biology   Khan Academy.mp3", "Sentence": "Our ratio of surface area to volume is going to be what? Well, our surface area, you have six faces that each have an area of x squared. So our surface area is going to be six x squared. And then our volume is going to be x times x times x over x to the third. And so this is going to be, divide the numerator and denominator by x squared, you get six over x. So once again, you see that as x increases, our ratio of surface area to volume decreases. As our denominator increases, well, then that whole expression is going to decrease."}, {"video_title": "Surface area to volume ratio of cells   Cell structure and function   AP Biology   Khan Academy.mp3", "Sentence": "And then our volume is going to be x times x times x over x to the third. And so this is going to be, divide the numerator and denominator by x squared, you get six over x. So once again, you see that as x increases, our ratio of surface area to volume decreases. As our denominator increases, well, then that whole expression is going to decrease. So given this phenomena, it makes it hard for larger and larger cells to exist because for all the activity happening in the volume, they don't have enough surface area to do all of this exchange. Now, there are things we see in biological systems that help cells get further than what we see here. If you imagine the two-dimensional cross-section of this cell, one way to increase the surface area to volume is for the membrane to look more like this."}, {"video_title": "Surface area to volume ratio of cells   Cell structure and function   AP Biology   Khan Academy.mp3", "Sentence": "As our denominator increases, well, then that whole expression is going to decrease. So given this phenomena, it makes it hard for larger and larger cells to exist because for all the activity happening in the volume, they don't have enough surface area to do all of this exchange. Now, there are things we see in biological systems that help cells get further than what we see here. If you imagine the two-dimensional cross-section of this cell, one way to increase the surface area to volume is for the membrane to look more like this. The more folds you have, the higher surface area to volume that you are going to have. And you indeed see this in a lot of biology. Anytime you want a high surface area to volume, you tend to see things like these folds in the membranes of the cells."}, {"video_title": "Second Law of Thermodynamics and entropy   Biology   Khan Academy.mp3", "Sentence": "And just to get us in the right frame of mind, I have this image here from the Hubble telescope of the night sky, and each of these dots, these are not stars, these are galaxies. That's a galaxy, that's a galaxy there, that's a galaxy. And so hopefully this gets you in a little bit more of a cosmological scale. But let's think about what this is actually telling us. The entropy of the universe only increases. So entropy, we can define that as the disorder of a system, and we're really talking about the number of states that a system could take on. And then we're saying the universe, but we could also say the entropy of a closed system only increases, a system that is fully contained, that's not interacting with its surroundings, because the universe is the ultimate closed system."}, {"video_title": "Second Law of Thermodynamics and entropy   Biology   Khan Academy.mp3", "Sentence": "But let's think about what this is actually telling us. The entropy of the universe only increases. So entropy, we can define that as the disorder of a system, and we're really talking about the number of states that a system could take on. And then we're saying the universe, but we could also say the entropy of a closed system only increases, a system that is fully contained, that's not interacting with its surroundings, because the universe is the ultimate closed system. There's nothing for it, outside of it, to interact with thermodynamically. And I'll do a quick review of open and closed systems, just so we make sure we understand that. So if I had a campfire, so I have some logs, and I had the flame going right over here, so that's the campfire."}, {"video_title": "Second Law of Thermodynamics and entropy   Biology   Khan Academy.mp3", "Sentence": "And then we're saying the universe, but we could also say the entropy of a closed system only increases, a system that is fully contained, that's not interacting with its surroundings, because the universe is the ultimate closed system. There's nothing for it, outside of it, to interact with thermodynamically. And I'll do a quick review of open and closed systems, just so we make sure we understand that. So if I had a campfire, so I have some logs, and I had the flame going right over here, so that's the campfire. If I were to just look at the logs and the fire, that's going to be an open system, because it's clearly interacting thermodynamically with its surroundings. It's releasing heat, it's warming up the air molecules around it, it's releasing light out into the universe. There could be interactions from the rest of the universe into the system, so it isn't isolated from the rest of everything else."}, {"video_title": "Second Law of Thermodynamics and entropy   Biology   Khan Academy.mp3", "Sentence": "So if I had a campfire, so I have some logs, and I had the flame going right over here, so that's the campfire. If I were to just look at the logs and the fire, that's going to be an open system, because it's clearly interacting thermodynamically with its surroundings. It's releasing heat, it's warming up the air molecules around it, it's releasing light out into the universe. There could be interactions from the rest of the universe into the system, so it isn't isolated from the rest of everything else. But a closed system, it is isolated. And it's very hard to create a true closed system in our everyday life, but we can approximate it, and the one that you've probably experienced in the not-too-distant past is an ice cooler. An ice cooler, we're at least attempting to thermodynamically isolate the inside of the cooler from the outside, from the rest of the universe."}, {"video_title": "Second Law of Thermodynamics and entropy   Biology   Khan Academy.mp3", "Sentence": "There could be interactions from the rest of the universe into the system, so it isn't isolated from the rest of everything else. But a closed system, it is isolated. And it's very hard to create a true closed system in our everyday life, but we can approximate it, and the one that you've probably experienced in the not-too-distant past is an ice cooler. An ice cooler, we're at least attempting to thermodynamically isolate the inside of the cooler from the outside, from the rest of the universe. And the way we do it is we have some type of an insulating material, maybe some styrofoam, and we could put, and we'd use it to maybe store ice. But it's not a perfect closed system, because eventually the heat from the rest of the universe will warm up the walls of the cooler, and eventually that heat will warm up, will be transferred to the ice, and it will warm it up, and it will melt it. So it's not a perfect closed system, but it's a good approximation, because we're at least attempting to isolate it thermodynamically from the rest of the universe."}, {"video_title": "Second Law of Thermodynamics and entropy   Biology   Khan Academy.mp3", "Sentence": "An ice cooler, we're at least attempting to thermodynamically isolate the inside of the cooler from the outside, from the rest of the universe. And the way we do it is we have some type of an insulating material, maybe some styrofoam, and we could put, and we'd use it to maybe store ice. But it's not a perfect closed system, because eventually the heat from the rest of the universe will warm up the walls of the cooler, and eventually that heat will warm up, will be transferred to the ice, and it will warm it up, and it will melt it. So it's not a perfect closed system, but it's a good approximation, because we're at least attempting to isolate it thermodynamically from the rest of the universe. And I can even make a little cover of this just so that we really wanted to isolate it. And in research labs, you'll see things that are much better approximations of closed systems, but even those, at some level, are they're going to interact with the rest of the universe. The ultimate closed system, so this is a closed system, is really the universe."}, {"video_title": "Second Law of Thermodynamics and entropy   Biology   Khan Academy.mp3", "Sentence": "So it's not a perfect closed system, but it's a good approximation, because we're at least attempting to isolate it thermodynamically from the rest of the universe. And I can even make a little cover of this just so that we really wanted to isolate it. And in research labs, you'll see things that are much better approximations of closed systems, but even those, at some level, are they're going to interact with the rest of the universe. The ultimate closed system, so this is a closed system, is really the universe. Nothing to interact with outside of it thermodynamically. So let's think a little bit about this definition. The entropy of the universe only increases."}, {"video_title": "Second Law of Thermodynamics and entropy   Biology   Khan Academy.mp3", "Sentence": "The ultimate closed system, so this is a closed system, is really the universe. Nothing to interact with outside of it thermodynamically. So let's think a little bit about this definition. The entropy of the universe only increases. Why does this make intuitive sense? Well, the best example I can think of is just straight up diffusion. So if I were to have, let's say I have a container, so I have a container, and I'll make it a closed container."}, {"video_title": "Second Law of Thermodynamics and entropy   Biology   Khan Academy.mp3", "Sentence": "The entropy of the universe only increases. Why does this make intuitive sense? Well, the best example I can think of is just straight up diffusion. So if I were to have, let's say I have a container, so I have a container, and I'll make it a closed container. We'll say this is some kind of theoretical ideal closed system here. Now let's say I had some ideal gas. So I had some ideal gas molecules right over here."}, {"video_title": "Second Law of Thermodynamics and entropy   Biology   Khan Academy.mp3", "Sentence": "So if I were to have, let's say I have a container, so I have a container, and I'll make it a closed container. We'll say this is some kind of theoretical ideal closed system here. Now let's say I had some ideal gas. So I had some ideal gas molecules right over here. They have some average temperature, but that means they all each have their own individual kinetic energy. They're all bouncing around in different ways. What's going to happen over time?"}, {"video_title": "Second Law of Thermodynamics and entropy   Biology   Khan Academy.mp3", "Sentence": "So I had some ideal gas molecules right over here. They have some average temperature, but that means they all each have their own individual kinetic energy. They're all bouncing around in different ways. What's going to happen over time? Well, over time, the ones on the left here, they're going to bounce off this wall, and then they're eventually going to go in this direction. So over time, you're going to have a situation where the system is going to look something more like this. So the system is going to look more like this."}, {"video_title": "Second Law of Thermodynamics and entropy   Biology   Khan Academy.mp3", "Sentence": "What's going to happen over time? Well, over time, the ones on the left here, they're going to bounce off this wall, and then they're eventually going to go in this direction. So over time, you're going to have a situation where the system is going to look something more like this. So the system is going to look more like this. Let's see, this is six particles. These six particles are going to diffuse throughout the container. So they're going to diffuse throughout the container."}, {"video_title": "Second Law of Thermodynamics and entropy   Biology   Khan Academy.mp3", "Sentence": "So the system is going to look more like this. Let's see, this is six particles. These six particles are going to diffuse throughout the container. So they're going to diffuse throughout the container. They're going to take up more of the space of the container. Now what just happened in that process? Well, when you knew that the particles were confined to this little section of the container, there were fewer possible states."}, {"video_title": "Second Law of Thermodynamics and entropy   Biology   Khan Academy.mp3", "Sentence": "So they're going to diffuse throughout the container. They're going to take up more of the space of the container. Now what just happened in that process? Well, when you knew that the particles were confined to this little section of the container, there were fewer possible states. You had lower entropy than when you are here. When you know that it's filled up the container, there's more possible locations, more possible orientations for it. And so you're going to have more states."}, {"video_title": "Second Law of Thermodynamics and entropy   Biology   Khan Academy.mp3", "Sentence": "Well, when you knew that the particles were confined to this little section of the container, there were fewer possible states. You had lower entropy than when you are here. When you know that it's filled up the container, there's more possible locations, more possible orientations for it. And so you're going to have more states. You have higher entropy. Higher, higher, higher entropy. And in general, these processes where you have the entropy increasing, we call these irreversible processes."}, {"video_title": "Second Law of Thermodynamics and entropy   Biology   Khan Academy.mp3", "Sentence": "And so you're going to have more states. You have higher entropy. Higher, higher, higher entropy. And in general, these processes where you have the entropy increasing, we call these irreversible processes. Irreversible, irreversible processes. And why is it irreversible? Well, there's some probability that these molecules might just gather back into this corner of it, but it's very, very low probability."}, {"video_title": "Second Law of Thermodynamics and entropy   Biology   Khan Academy.mp3", "Sentence": "And in general, these processes where you have the entropy increasing, we call these irreversible processes. Irreversible, irreversible processes. And why is it irreversible? Well, there's some probability that these molecules might just gather back into this corner of it, but it's very, very low probability. And this is when we're dealing with six molecules, but in real systems, we'd be dealing with a much larger than six molecules. We'll be dealing with millions of millions of millions of millions of molecules. We'll deal with things with between 20 and 30 zeros of molecules."}, {"video_title": "Second Law of Thermodynamics and entropy   Biology   Khan Academy.mp3", "Sentence": "Well, there's some probability that these molecules might just gather back into this corner of it, but it's very, very low probability. And this is when we're dealing with six molecules, but in real systems, we'd be dealing with a much larger than six molecules. We'll be dealing with millions of millions of millions of millions of molecules. We'll deal with things with between 20 and 30 zeros of molecules. And there, it's very unlikely that they just all bump together in the right way to start taking a smaller volume when they could actually fill the container. And so that's why you don't see smoke just naturally turn into some type of shaped particle or take up less space as opposed to filling its container. So this is irreversible because you went from a fewer number of potential states in the smaller volume to a higher number of potential states."}, {"video_title": "Second Law of Thermodynamics and entropy   Biology   Khan Academy.mp3", "Sentence": "We'll deal with things with between 20 and 30 zeros of molecules. And there, it's very unlikely that they just all bump together in the right way to start taking a smaller volume when they could actually fill the container. And so that's why you don't see smoke just naturally turn into some type of shaped particle or take up less space as opposed to filling its container. So this is irreversible because you went from a fewer number of potential states in the smaller volume to a higher number of potential states. And the universe is constantly doing this. That's why the entropy of the universe is only increasing. Now, there's some processes that it feels like the entropy isn't increasing that much."}, {"video_title": "Second Law of Thermodynamics and entropy   Biology   Khan Academy.mp3", "Sentence": "So this is irreversible because you went from a fewer number of potential states in the smaller volume to a higher number of potential states. And the universe is constantly doing this. That's why the entropy of the universe is only increasing. Now, there's some processes that it feels like the entropy isn't increasing that much. So if you were to take one billiard ball right over here and you were to roll it into another billiard ball right over here and transfer the momentum to that one, it feels like that could go the other way around. Like that other billiard ball could hit this one and go backwards. And at a macro level, it feels like this is a reversible process and people will tend to call this reversible."}, {"video_title": "Second Law of Thermodynamics and entropy   Biology   Khan Academy.mp3", "Sentence": "Now, there's some processes that it feels like the entropy isn't increasing that much. So if you were to take one billiard ball right over here and you were to roll it into another billiard ball right over here and transfer the momentum to that one, it feels like that could go the other way around. Like that other billiard ball could hit this one and go backwards. And at a macro level, it feels like this is a reversible process and people will tend to call this reversible. But if you really were to go on a microscopic level, and it looks like the entropy isn't increasing that much, but if you were looking at it on a microscopic level, and just to be clear, the entropy, you know, when this ball is moving and this is stationary, going to a state where this is moving and this is stationary, it doesn't look like the entropy is increasing that much. And so that's why they tend to call this reversible because you tend to observe things where maybe this one, it could go backwards. This could hit this one and then this one could go, you can kind of run the film in rewind."}, {"video_title": "Second Law of Thermodynamics and entropy   Biology   Khan Academy.mp3", "Sentence": "And at a macro level, it feels like this is a reversible process and people will tend to call this reversible. But if you really were to go on a microscopic level, and it looks like the entropy isn't increasing that much, but if you were looking at it on a microscopic level, and just to be clear, the entropy, you know, when this ball is moving and this is stationary, going to a state where this is moving and this is stationary, it doesn't look like the entropy is increasing that much. And so that's why they tend to call this reversible because you tend to observe things where maybe this one, it could go backwards. This could hit this one and then this one could go, you can kind of run the film in rewind. But even there, if you were to look at a microscopic level, you would see that some heat is being generated and that some molecules in the ball are getting excited as they collide and as they have friction with the air and as they roll on the ground over here. And you're never going to get those molecules to go back into the state that they were before, that you actually do have the entropy increasing in the system. So even when in our everyday lives, people talk in thermodynamics, people talk about reversible processes, they're only approximately reversible in that the entropy's only increasing a little bit."}, {"video_title": "Second Law of Thermodynamics and entropy   Biology   Khan Academy.mp3", "Sentence": "This could hit this one and then this one could go, you can kind of run the film in rewind. But even there, if you were to look at a microscopic level, you would see that some heat is being generated and that some molecules in the ball are getting excited as they collide and as they have friction with the air and as they roll on the ground over here. And you're never going to get those molecules to go back into the state that they were before, that you actually do have the entropy increasing in the system. So even when in our everyday lives, people talk in thermodynamics, people talk about reversible processes, they're only approximately reversible in that the entropy's only increasing a little bit. It's not like there's zero increase in entropy. Irreversible reactions, these are the ones, diffusion is a very obvious one, where it's very clear that you have an increase in entropy and it feels like it's a very, very low probability, almost zero probability, of this thing ever going back to where it was. And you won't observe it, because when you're talking about that many molecules, something with 20 or 30 zeros of molecules, the odds of all of them just doing the right thing, you could wait around a very long time and never actually observe that happening."}, {"video_title": "Second Law of Thermodynamics and entropy   Biology   Khan Academy.mp3", "Sentence": "So even when in our everyday lives, people talk in thermodynamics, people talk about reversible processes, they're only approximately reversible in that the entropy's only increasing a little bit. It's not like there's zero increase in entropy. Irreversible reactions, these are the ones, diffusion is a very obvious one, where it's very clear that you have an increase in entropy and it feels like it's a very, very low probability, almost zero probability, of this thing ever going back to where it was. And you won't observe it, because when you're talking about that many molecules, something with 20 or 30 zeros of molecules, the odds of all of them just doing the right thing, you could wait around a very long time and never actually observe that happening. And so hopefully this makes sense, that the disorder in this way, the number of states only increases as you have more and more interactions. And a lot of that is coming from heat. Everything you're doing right now, when I'm making this video, my body is generating heat."}, {"video_title": "Second Law of Thermodynamics and entropy   Biology   Khan Academy.mp3", "Sentence": "And you won't observe it, because when you're talking about that many molecules, something with 20 or 30 zeros of molecules, the odds of all of them just doing the right thing, you could wait around a very long time and never actually observe that happening. And so hopefully this makes sense, that the disorder in this way, the number of states only increases as you have more and more interactions. And a lot of that is coming from heat. Everything you're doing right now, when I'm making this video, my body is generating heat. That heat is dissipating into the universe. That is adding to the number of states that the universe can actually take on. As I move my hands, my little digital pencil that I'm using, it's causing friction."}, {"video_title": "Second Law of Thermodynamics and entropy   Biology   Khan Academy.mp3", "Sentence": "Everything you're doing right now, when I'm making this video, my body is generating heat. That heat is dissipating into the universe. That is adding to the number of states that the universe can actually take on. As I move my hands, my little digital pencil that I'm using, it's causing friction. That's releasing heat into the universe. My computer is running, releasing heat into the universe. You watching this, releasing heat into the universe."}, {"video_title": "Cellular evidence of common ancestry   Natural selection   AP Biology   Khan Academy.mp3", "Sentence": "Perhaps the most mind-blowing idea in all of biology is the concept that all living things we know of, based on current evidence that we have, all originated from a common ancestor. So it doesn't matter whether we're talking about a simple bacterial cell, which actually in reality isn't so simple after all, a tree made up of trillions and trillions of cells, a hairy primate made up of trillions and trillions cells, or seemingly well-dressed agriculture kittens, which are also made of trillions and trillions of cells, that they all share a common ancestor. You might have seen things like these evolutionary trees. This is an example right over here. This is saying the same thing, that everything that we see in the world today, all living things, regardless of what domain they're in, and we would be a subset of animals right over here. There's so many animal species that they all share a common ancestor several billions of years ago. But you should be skeptical."}, {"video_title": "Cellular evidence of common ancestry   Natural selection   AP Biology   Khan Academy.mp3", "Sentence": "This is an example right over here. This is saying the same thing, that everything that we see in the world today, all living things, regardless of what domain they're in, and we would be a subset of animals right over here. There's so many animal species that they all share a common ancestor several billions of years ago. But you should be skeptical. We are scientists here. How do we believe this? What is the evidence for that?"}, {"video_title": "Cellular evidence of common ancestry   Natural selection   AP Biology   Khan Academy.mp3", "Sentence": "But you should be skeptical. We are scientists here. How do we believe this? What is the evidence for that? And one piece of evidence is by looking at the cellular level and look at commonalities amongst different groups and realize that it would be unlikely for them to develop independently of each other. For example, all life forms that we know of have DNA. They all have RNA."}, {"video_title": "Cellular evidence of common ancestry   Natural selection   AP Biology   Khan Academy.mp3", "Sentence": "What is the evidence for that? And one piece of evidence is by looking at the cellular level and look at commonalities amongst different groups and realize that it would be unlikely for them to develop independently of each other. For example, all life forms that we know of have DNA. They all have RNA. And it isn't just how they encode information. It's also processes, biochemical processes, that occur in the cells. They all have some form of glycolysis."}, {"video_title": "Cellular evidence of common ancestry   Natural selection   AP Biology   Khan Academy.mp3", "Sentence": "They all have RNA. And it isn't just how they encode information. It's also processes, biochemical processes, that occur in the cells. They all have some form of glycolysis. But this seems, and these aren't the only things that we've observed are common to all life forms. They're all based on cells as the basic units, which are bound by a membrane. And so in theory, these things, I guess, could have developed independently of each other without having a common ancestor."}, {"video_title": "Cellular evidence of common ancestry   Natural selection   AP Biology   Khan Academy.mp3", "Sentence": "They all have some form of glycolysis. But this seems, and these aren't the only things that we've observed are common to all life forms. They're all based on cells as the basic units, which are bound by a membrane. And so in theory, these things, I guess, could have developed independently of each other without having a common ancestor. But having a common ancestor is the best explanation of why we see these different processes. Some of these are quite complex or these different structures throughout life as we know it. And so you're saying, all right, I can maybe buy that, that there's this common ancestor right over here."}, {"video_title": "Cellular evidence of common ancestry   Natural selection   AP Biology   Khan Academy.mp3", "Sentence": "And so in theory, these things, I guess, could have developed independently of each other without having a common ancestor. But having a common ancestor is the best explanation of why we see these different processes. Some of these are quite complex or these different structures throughout life as we know it. And so you're saying, all right, I can maybe buy that, that there's this common ancestor right over here. But how do we construct this tree? How do we know when things branched off? Because some of these branches off of these trees, once again, these would have occurred hundreds of millions or billions of years ago, and none of us were around to observe that happening."}, {"video_title": "Cellular evidence of common ancestry   Natural selection   AP Biology   Khan Academy.mp3", "Sentence": "And so you're saying, all right, I can maybe buy that, that there's this common ancestor right over here. But how do we construct this tree? How do we know when things branched off? Because some of these branches off of these trees, once again, these would have occurred hundreds of millions or billions of years ago, and none of us were around to observe that happening. And once again, that goes to more structural evidence. So for example, amongst what we now classify as eukaryotes, so everything in this brown color, this branch of the tree right over here, we see that all of them have membrane-bound organelles. Membrane-bound organelles."}, {"video_title": "Cellular evidence of common ancestry   Natural selection   AP Biology   Khan Academy.mp3", "Sentence": "Because some of these branches off of these trees, once again, these would have occurred hundreds of millions or billions of years ago, and none of us were around to observe that happening. And once again, that goes to more structural evidence. So for example, amongst what we now classify as eukaryotes, so everything in this brown color, this branch of the tree right over here, we see that all of them have membrane-bound organelles. Membrane-bound organelles. These are things like a nucleus or mitochondria that we study in many other videos. They all have linear chromosomes. So in other groups in this tree of life, in this evolutionary tree, you might have circular chromosomes, but common to all eukaryotes are the linear chromosomes."}, {"video_title": "Cellular evidence of common ancestry   Natural selection   AP Biology   Khan Academy.mp3", "Sentence": "Membrane-bound organelles. These are things like a nucleus or mitochondria that we study in many other videos. They all have linear chromosomes. So in other groups in this tree of life, in this evolutionary tree, you might have circular chromosomes, but common to all eukaryotes are the linear chromosomes. And they all have chromosomes that contain introns. Introns are sequences of DNA that don't code for genes that will then code into proteins. And we're still exploring what the point of introns are, but the reason why all of these have been classified together is that they have these similarities."}, {"video_title": "Cellular evidence of common ancestry   Natural selection   AP Biology   Khan Academy.mp3", "Sentence": "So in other groups in this tree of life, in this evolutionary tree, you might have circular chromosomes, but common to all eukaryotes are the linear chromosomes. And they all have chromosomes that contain introns. Introns are sequences of DNA that don't code for genes that will then code into proteins. And we're still exploring what the point of introns are, but the reason why all of these have been classified together is that they have these similarities. And so we believe that they would have formed their own branch. And based on how similar things are, that's where we theorize when things might have branched off. And now that we have more sophisticated tools of sequencing DNA and RNA, we can look at how different those sequences are to construct more and more precise trees like this."}, {"video_title": "Natural Selection and the Owl Butterfly (2).mp3", "Sentence": "But then once everything became soot-filled, all of a sudden, the dark moths were less likely to be caught by predators. And so all of the white moths were less likely to be able to reproduce successfully. So the black moth trait, or that variant, dominated. And then if you came a little bit later and you saw all the moths have turned black, it's like, oh, these moths are geniuses. They appear to have somehow engineered their way to stay camouflaged. And the point I was making there is that, look, that wasn't engineered or an explicit move on the part of the moths or the DNA. That that was just a natural byproduct of them having some variation, and some of that variation was selected for."}, {"video_title": "Natural Selection and the Owl Butterfly (2).mp3", "Sentence": "And then if you came a little bit later and you saw all the moths have turned black, it's like, oh, these moths are geniuses. They appear to have somehow engineered their way to stay camouflaged. And the point I was making there is that, look, that wasn't engineered or an explicit move on the part of the moths or the DNA. That that was just a natural byproduct of them having some variation, and some of that variation was selected for. So with that example, that was pretty simple, black or white. But what about more complicated things? So for example, here I have a couple of pictures of what's commonly called the owl butterfly."}, {"video_title": "Natural Selection and the Owl Butterfly (2).mp3", "Sentence": "That that was just a natural byproduct of them having some variation, and some of that variation was selected for. So with that example, that was pretty simple, black or white. But what about more complicated things? So for example, here I have a couple of pictures of what's commonly called the owl butterfly. And what's amazing here, and it's pretty obvious if I probably don't have to point out to you, is that its wing looks like half of an owl's eye. I mean, I can almost draw a beak here and draw another wing there, and you can imagine an owl staring at us. And here, too, I can imagine a beak here, and you would think an owl in there, too."}, {"video_title": "Natural Selection and the Owl Butterfly (2).mp3", "Sentence": "So for example, here I have a couple of pictures of what's commonly called the owl butterfly. And what's amazing here, and it's pretty obvious if I probably don't have to point out to you, is that its wing looks like half of an owl's eye. I mean, I can almost draw a beak here and draw another wing there, and you can imagine an owl staring at us. And here, too, I can imagine a beak here, and you would think an owl in there, too. And so the question is, how does something this good show up randomly? I mean, you could imagine, OK, little spots or black and white or gray, but how does something that looks so much like an eye generate randomly? Now, the answer is, well, there's a couple of answers."}, {"video_title": "Natural Selection and the Owl Butterfly (2).mp3", "Sentence": "And here, too, I can imagine a beak here, and you would think an owl in there, too. And so the question is, how does something this good show up randomly? I mean, you could imagine, OK, little spots or black and white or gray, but how does something that looks so much like an eye generate randomly? Now, the answer is, well, there's a couple of answers. One is, why does this eye exist, or this eye-like pattern, or this owl-like eyes pattern? And there, the jury's still out on that. I read a little bit about it on Wikipedia, and these are all of these images I got from Wikipedia."}, {"video_title": "Natural Selection and the Owl Butterfly (2).mp3", "Sentence": "Now, the answer is, well, there's a couple of answers. One is, why does this eye exist, or this eye-like pattern, or this owl-like eyes pattern? And there, the jury's still out on that. I read a little bit about it on Wikipedia, and these are all of these images I got from Wikipedia. And Wikipedia, they said, look, there's two competing theories here. One theory is that this, even though to us humans, the way we see things, it looks like an owl's eye, that this is actually a decoy. That this is, you know, when some predator is about to chase these, wants to eat one of these things, they kind of go for the thing that looks most substantive."}, {"video_title": "Natural Selection and the Owl Butterfly (2).mp3", "Sentence": "I read a little bit about it on Wikipedia, and these are all of these images I got from Wikipedia. And Wikipedia, they said, look, there's two competing theories here. One theory is that this, even though to us humans, the way we see things, it looks like an owl's eye, that this is actually a decoy. That this is, you know, when some predator is about to chase these, wants to eat one of these things, they kind of go for the thing that looks most substantive. So instead of going for the butterfly's body, which doesn't look that substantive, they go for the big black thing. They say, oh, that looks like it's protein-rich, and it'll be a good meal. So they try to snap and bite at that, and if they bite at that, sure, the guy's wings are going to be clipped a little bit, and it's going to suck, but the animal itself, the actual butterfly, would survive, and maybe it can repair its wings."}, {"video_title": "Natural Selection and the Owl Butterfly (2).mp3", "Sentence": "That this is, you know, when some predator is about to chase these, wants to eat one of these things, they kind of go for the thing that looks most substantive. So instead of going for the butterfly's body, which doesn't look that substantive, they go for the big black thing. They say, oh, that looks like it's protein-rich, and it'll be a good meal. So they try to snap and bite at that, and if they bite at that, sure, the guy's wings are going to be clipped a little bit, and it's going to suck, but the animal itself, the actual butterfly, would survive, and maybe it can repair its wings. I don't know the actual biology of the owl butterfly. That's one theory, and then the argument against that goes, well, no, if that was the case, then you'd want the black spot even further back along its, you know, you'd want the spot way far away from the body. You'd want it back here instead of right here, because there's still a chance if something chomps at this little black spot that it'll still get the abdomen of the butterfly."}, {"video_title": "Natural Selection and the Owl Butterfly (2).mp3", "Sentence": "So they try to snap and bite at that, and if they bite at that, sure, the guy's wings are going to be clipped a little bit, and it's going to suck, but the animal itself, the actual butterfly, would survive, and maybe it can repair its wings. I don't know the actual biology of the owl butterfly. That's one theory, and then the argument against that goes, well, no, if that was the case, then you'd want the black spot even further back along its, you know, you'd want the spot way far away from the body. You'd want it back here instead of right here, because there's still a chance if something chomps at this little black spot that it'll still get the abdomen of the butterfly. Now, the other theory as to why this exists, and you know, who knows, maybe it's a little bit of both. Maybe both of these are true. Maybe this offers two advantages."}, {"video_title": "Natural Selection and the Owl Butterfly (2).mp3", "Sentence": "You'd want it back here instead of right here, because there's still a chance if something chomps at this little black spot that it'll still get the abdomen of the butterfly. Now, the other theory as to why this exists, and you know, who knows, maybe it's a little bit of both. Maybe both of these are true. Maybe this offers two advantages. The other theory, and this is kind of the one that jumps out at us when we see this, hey, this looks like an owl, maybe this is to scare away the things that are likely to eat this dude. So maybe if, and it does turn out in my reading, that they are lizards that like to eat these type of butterflies. And those lizards probably don't like to be around birds or owls, because those owls eat them."}, {"video_title": "Natural Selection and the Owl Butterfly (2).mp3", "Sentence": "Maybe this offers two advantages. The other theory, and this is kind of the one that jumps out at us when we see this, hey, this looks like an owl, maybe this is to scare away the things that are likely to eat this dude. So maybe if, and it does turn out in my reading, that they are lizards that like to eat these type of butterflies. And those lizards probably don't like to be around birds or owls, because those owls eat them. So that might be deterrent. And then the other example they said is, look, they tend to be eaten by this lizard right here. This is what Wikipedia told me."}, {"video_title": "Natural Selection and the Owl Butterfly (2).mp3", "Sentence": "And those lizards probably don't like to be around birds or owls, because those owls eat them. So that might be deterrent. And then the other example they said is, look, they tend to be eaten by this lizard right here. This is what Wikipedia told me. And that this lizard tends to be eaten by this frog right there, and that the eyes of this butterfly are not too dissimilar to the eyes of this frog. And you know, we can debate whether or not that's the case. And if this was the predator we're trying to mimic, you could make an argument that maybe we would have had more green on our wing."}, {"video_title": "Natural Selection and the Owl Butterfly (2).mp3", "Sentence": "This is what Wikipedia told me. And that this lizard tends to be eaten by this frog right there, and that the eyes of this butterfly are not too dissimilar to the eyes of this frog. And you know, we can debate whether or not that's the case. And if this was the predator we're trying to mimic, you could make an argument that maybe we would have had more green on our wing. But that's not the point of this video. But it's a fun discussion to have as to what is useful about this eye. But let's have the question, how did that eye come about?"}, {"video_title": "Natural Selection and the Owl Butterfly (2).mp3", "Sentence": "And if this was the predator we're trying to mimic, you could make an argument that maybe we would have had more green on our wing. But that's not the point of this video. But it's a fun discussion to have as to what is useful about this eye. But let's have the question, how did that eye come about? And when I say that eye, I mean the pattern on that wing. What set of events allowed this to happen? Because when I described evolution, and we know that everything in our biological kingdom is just a set of proteins and then stuff that maybe the protein can't."}, {"video_title": "Natural Selection and the Owl Butterfly (2).mp3", "Sentence": "But let's have the question, how did that eye come about? And when I say that eye, I mean the pattern on that wing. What set of events allowed this to happen? Because when I described evolution, and we know that everything in our biological kingdom is just a set of proteins and then stuff that maybe the protein can't. But mainly protein. And that protein's all coded for by DNA. I'm going to do future videos on DNA."}, {"video_title": "Natural Selection and the Owl Butterfly (2).mp3", "Sentence": "Because when I described evolution, and we know that everything in our biological kingdom is just a set of proteins and then stuff that maybe the protein can't. But mainly protein. And that protein's all coded for by DNA. I'm going to do future videos on DNA. But DNA is just a sequence of base pairs. It's a sequence of these molecules. And we represent the adenine and guanine and then cytosine and thymine."}, {"video_title": "Natural Selection and the Owl Butterfly (2).mp3", "Sentence": "I'm going to do future videos on DNA. But DNA is just a sequence of base pairs. It's a sequence of these molecules. And we represent the adenine and guanine and then cytosine and thymine. And maybe you have a couple of adenines in a row and some guanine and thymine. And I'll do a lot more on this in the future. But the idea is, look, it's just coded for by this sequence of these molecules."}, {"video_title": "Natural Selection and the Owl Butterfly (2).mp3", "Sentence": "And we represent the adenine and guanine and then cytosine and thymine. And maybe you have a couple of adenines in a row and some guanine and thymine. And I'll do a lot more on this in the future. But the idea is, look, it's just coded for by this sequence of these molecules. How do you get a sequence? How do you go from a butterfly that has no eye to all of a sudden an eye that goes there? Obviously, just one change that happens from a random mutation, maybe that G turns into an A, or maybe this C and this T get deleted."}, {"video_title": "Natural Selection and the Owl Butterfly (2).mp3", "Sentence": "But the idea is, look, it's just coded for by this sequence of these molecules. How do you get a sequence? How do you go from a butterfly that has no eye to all of a sudden an eye that goes there? Obviously, just one change that happens from a random mutation, maybe that G turns into an A, or maybe this C and this T get deleted. So everything. That alone isn't going to develop this beautiful of a pattern or this useful of a pattern. So how do the random changes explain something that's this intricate?"}, {"video_title": "Natural Selection and the Owl Butterfly (2).mp3", "Sentence": "Obviously, just one change that happens from a random mutation, maybe that G turns into an A, or maybe this C and this T get deleted. So everything. That alone isn't going to develop this beautiful of a pattern or this useful of a pattern. So how do the random changes explain something that's this intricate? And this is my explanation. And obviously, I wasn't sitting there watching over the thousands or millions of years as these owl butterflies emerged. So this is just my theory of how natural selection does explain this type of phenomenon."}, {"video_title": "Natural Selection and the Owl Butterfly (2).mp3", "Sentence": "So how do the random changes explain something that's this intricate? And this is my explanation. And obviously, I wasn't sitting there watching over the thousands or millions of years as these owl butterflies emerged. So this is just my theory of how natural selection does explain this type of phenomenon. You have a world where you have, in some environment, you have butterflies. And their wings look like, let's say you have some butterflies that are generally like this. That's their wing."}, {"video_title": "Natural Selection and the Owl Butterfly (2).mp3", "Sentence": "So this is just my theory of how natural selection does explain this type of phenomenon. You have a world where you have, in some environment, you have butterflies. And their wings look like, let's say you have some butterflies that are generally like this. That's their wing. And it's a very bad drawing, but I think you get the idea. And there's just some general patterns. We've seen it before."}, {"video_title": "Natural Selection and the Owl Butterfly (2).mp3", "Sentence": "That's their wing. And it's a very bad drawing, but I think you get the idea. And there's just some general patterns. We've seen it before. There's variation. And the variation does show up from these little random changes in DNA. And I think we can all believe that, that most of these changes are kind of benign."}, {"video_title": "Natural Selection and the Owl Butterfly (2).mp3", "Sentence": "We've seen it before. There's variation. And the variation does show up from these little random changes in DNA. And I think we can all believe that, that most of these changes are kind of benign. Maybe they just set up differently where a little pattern will show up or a little speck of pigment will show up with a slightly different color. And we even see amongst these owl butterflies, there is variation. This dude's wing is different than that guy's wing, with the commonality that they do have these eye-looking shapes."}, {"video_title": "Natural Selection and the Owl Butterfly (2).mp3", "Sentence": "And I think we can all believe that, that most of these changes are kind of benign. Maybe they just set up differently where a little pattern will show up or a little speck of pigment will show up with a slightly different color. And we even see amongst these owl butterflies, there is variation. This dude's wing is different than that guy's wing, with the commonality that they do have these eye-looking shapes. And there's not just one. There's actually multiple. This guy has this other thing up here that looks interesting."}, {"video_title": "Natural Selection and the Owl Butterfly (2).mp3", "Sentence": "This dude's wing is different than that guy's wing, with the commonality that they do have these eye-looking shapes. And there's not just one. There's actually multiple. This guy has this other thing up here that looks interesting. And they have multiple things, but the one really noticeable feature is this eye-looking thing. So how do we go from this to an eye-looking thing? So the idea is you have some variation."}, {"video_title": "Natural Selection and the Owl Butterfly (2).mp3", "Sentence": "This guy has this other thing up here that looks interesting. And they have multiple things, but the one really noticeable feature is this eye-looking thing. So how do we go from this to an eye-looking thing? So the idea is you have some variation. One guy might look like that. Another guy or gal might, just randomly, their dot might be something like that. Another gal or guy, these wings are really badly drawn, but you get the idea."}, {"video_title": "Natural Selection and the Owl Butterfly (2).mp3", "Sentence": "So the idea is you have some variation. One guy might look like that. Another guy or gal might, just randomly, their dot might be something like that. Another gal or guy, these wings are really badly drawn, but you get the idea. This is the butterfly's antenna right there. That's its body. Another person's patterns, or butterfly's patterns, might look like this."}, {"video_title": "Natural Selection and the Owl Butterfly (2).mp3", "Sentence": "Another gal or guy, these wings are really badly drawn, but you get the idea. This is the butterfly's antenna right there. That's its body. Another person's patterns, or butterfly's patterns, might look like this. And so they're just random. But when they go into a certain environment, for whatever reason, maybe one of its predators, maybe that theory that these are supposed to look like eyes is true. And so actually, maybe this guy just has a random pattern here."}, {"video_title": "Natural Selection and the Owl Butterfly (2).mp3", "Sentence": "Another person's patterns, or butterfly's patterns, might look like this. And so they're just random. But when they go into a certain environment, for whatever reason, maybe one of its predators, maybe that theory that these are supposed to look like eyes is true. And so actually, maybe this guy just has a random pattern here. And so this guy, and I'm not saying that it's definitely better, they're both going to be found and killed by predators. But it's all probabilistic. Maybe this guy has a 1% less chance of getting a predator."}, {"video_title": "Natural Selection and the Owl Butterfly (2).mp3", "Sentence": "And so actually, maybe this guy just has a random pattern here. And so this guy, and I'm not saying that it's definitely better, they're both going to be found and killed by predators. But it's all probabilistic. Maybe this guy has a 1% less chance of getting a predator. Because when a predator just looks at them out of the corner of that eye, that little, really hazy region kind of looks like an eye. And a predator would be better off just not messing with it. And they'd rather go after the dude that looks like this."}, {"video_title": "Natural Selection and the Owl Butterfly (2).mp3", "Sentence": "Maybe this guy has a 1% less chance of getting a predator. Because when a predator just looks at them out of the corner of that eye, that little, really hazy region kind of looks like an eye. And a predator would be better off just not messing with it. And they'd rather go after the dude that looks like this. So it's just a slight probability. Now you might say, OK, what's 1% going to do? But when you compound that 1% over thousands and thousands of generations, all of a sudden, this trait might dominate."}, {"video_title": "Natural Selection and the Owl Butterfly (2).mp3", "Sentence": "And they'd rather go after the dude that looks like this. So it's just a slight probability. Now you might say, OK, what's 1% going to do? But when you compound that 1% over thousands and thousands of generations, all of a sudden, this trait might dominate. And because he's just going to be killed that less frequently. 1% less frequently. Now maybe this guy has a similar trait, but his spot is closer to the abdomen."}, {"video_title": "Natural Selection and the Owl Butterfly (2).mp3", "Sentence": "But when you compound that 1% over thousands and thousands of generations, all of a sudden, this trait might dominate. And because he's just going to be killed that less frequently. 1% less frequently. Now maybe this guy has a similar trait, but his spot is closer to the abdomen. And here it's a trade-off. Because maybe some predators get scared away by this concentration of pigment. And once again, I'm not saying that we're here yet."}, {"video_title": "Natural Selection and the Owl Butterfly (2).mp3", "Sentence": "Now maybe this guy has a similar trait, but his spot is closer to the abdomen. And here it's a trade-off. Because maybe some predators get scared away by this concentration of pigment. And once again, I'm not saying that we're here yet. We're not at this kind of very advanced, sophisticated pattern yet. We're at this random concentration of pigment that just shows up. So we see that people who have this concentration of pigment further away from their abdomen, they do well."}, {"video_title": "Natural Selection and the Owl Butterfly (2).mp3", "Sentence": "And once again, I'm not saying that we're here yet. We're not at this kind of very advanced, sophisticated pattern yet. We're at this random concentration of pigment that just shows up. So we see that people who have this concentration of pigment further away from their abdomen, they do well. But when it's too close, maybe some predators think that that's actually an insect and they want to eat it. So that's actually a bad trait. So what happens is this guy dominates."}, {"video_title": "Natural Selection and the Owl Butterfly (2).mp3", "Sentence": "So we see that people who have this concentration of pigment further away from their abdomen, they do well. But when it's too close, maybe some predators think that that's actually an insect and they want to eat it. So that's actually a bad trait. So what happens is this guy dominates. And so within this population, you start having a lot of variation, because he's more likely to pass on these traits. And I want to make that point very clear. This isn't what happens over the course of an animal's lifetime."}, {"video_title": "Natural Selection and the Owl Butterfly (2).mp3", "Sentence": "So what happens is this guy dominates. And so within this population, you start having a lot of variation, because he's more likely to pass on these traits. And I want to make that point very clear. This isn't what happens over the course of an animal's lifetime. It's not like if somehow I experience something, or at least our current theory, if I experience something, that I can somehow pass on that knowledge to my child. What it says is if my DNA just happens to have just some variation that happens to be more useful or more likely for me to survive to reproduction and for my children to survive, then that will start to dominate in the population. So then the population, you're going to have variations within that."}, {"video_title": "Natural Selection and the Owl Butterfly (2).mp3", "Sentence": "This isn't what happens over the course of an animal's lifetime. It's not like if somehow I experience something, or at least our current theory, if I experience something, that I can somehow pass on that knowledge to my child. What it says is if my DNA just happens to have just some variation that happens to be more useful or more likely for me to survive to reproduction and for my children to survive, then that will start to dominate in the population. So then the population, you're going to have variations within that. Maybe some guys, it's going to get a little bit look like that, maybe another one's going to look a little bit like that. Maybe there's some spots there. You can kind of view it as the variation is, quote unquote, exploring."}, {"video_title": "Natural Selection and the Owl Butterfly (2).mp3", "Sentence": "So then the population, you're going to have variations within that. Maybe some guys, it's going to get a little bit look like that, maybe another one's going to look a little bit like that. Maybe there's some spots there. You can kind of view it as the variation is, quote unquote, exploring. But I want to be very clear not to use any active verbs here, because this is all being done really as almost a common sense process, where everything changes. The changes that are most suited are the ones that are going to survive more frequently. And then the next generation is going to have more of that, and then you'll have variation within that change."}, {"video_title": "Natural Selection and the Owl Butterfly (2).mp3", "Sentence": "You can kind of view it as the variation is, quote unquote, exploring. But I want to be very clear not to use any active verbs here, because this is all being done really as almost a common sense process, where everything changes. The changes that are most suited are the ones that are going to survive more frequently. And then the next generation is going to have more of that, and then you'll have variation within that change. And then this one might be like that. And maybe this is the one. These were good compared to that, but now when you're competing amongst themselves, this one is able to reproduce 1% more than this guy or this guy."}, {"video_title": "Natural Selection and the Owl Butterfly (2).mp3", "Sentence": "And then the next generation is going to have more of that, and then you'll have variation within that change. And then this one might be like that. And maybe this is the one. These were good compared to that, but now when you're competing amongst themselves, this one is able to reproduce 1% more than this guy or this guy. So this guy becomes, and maybe it's some combination of all the above, and they mix and match. It's a hugely complex system. But then this guy represents most of the population."}, {"video_title": "Natural Selection and the Owl Butterfly (2).mp3", "Sentence": "These were good compared to that, but now when you're competing amongst themselves, this one is able to reproduce 1% more than this guy or this guy. So this guy becomes, and maybe it's some combination of all the above, and they mix and match. It's a hugely complex system. But then this guy represents most of the population. And when I say this guy, I'm saying this guy's genetic information, at least as which pertains to his wings. And then you get variation amongst that. Maybe some of it, they have a little small dot, and there's some dots around it."}, {"video_title": "Natural Selection and the Owl Butterfly (2).mp3", "Sentence": "But then this guy represents most of the population. And when I say this guy, I'm saying this guy's genetic information, at least as which pertains to his wings. And then you get variation amongst that. Maybe some of it, they have a little small dot, and there's some dots around it. Maybe it's like this. Maybe one of them digresses and goes back here, but then he has trouble competing, so he gets knocked out again. And then some other people have it back here."}, {"video_title": "Natural Selection and the Owl Butterfly (2).mp3", "Sentence": "Maybe some of it, they have a little small dot, and there's some dots around it. Maybe it's like this. Maybe one of them digresses and goes back here, but then he has trouble competing, so he gets knocked out again. And then some other people have it back here. I think you get the point. That this isn't happening overnight. These changes can be fairly incremental, but we're doing it over thousands of generations."}, {"video_title": "Natural Selection and the Owl Butterfly (2).mp3", "Sentence": "And then some other people have it back here. I think you get the point. That this isn't happening overnight. These changes can be fairly incremental, but we're doing it over thousands of generations. So when you're talking about thousands of generations, or even millions of generations, even a 1% advantage can be significant. And when you accumulate those variations over a large period of time, you can get to fairly intricate patterns like this. So I just wanted to explain that, because this is often used as, hey, sure, I can believe the butterfly moth, or I can even maybe believe the examples of the antibiotics and the bacteria or the flu."}, {"video_title": "Natural Selection and the Owl Butterfly (2).mp3", "Sentence": "These changes can be fairly incremental, but we're doing it over thousands of generations. So when you're talking about thousands of generations, or even millions of generations, even a 1% advantage can be significant. And when you accumulate those variations over a large period of time, you can get to fairly intricate patterns like this. So I just wanted to explain that, because this is often used as, hey, sure, I can believe the butterfly moth, or I can even maybe believe the examples of the antibiotics and the bacteria or the flu. I mean, because those are kind of real-time examples. But how does something this intricate show up? And I actually want to make a point here."}, {"video_title": "Natural Selection and the Owl Butterfly (2).mp3", "Sentence": "So I just wanted to explain that, because this is often used as, hey, sure, I can believe the butterfly moth, or I can even maybe believe the examples of the antibiotics and the bacteria or the flu. I mean, because those are kind of real-time examples. But how does something this intricate show up? And I actually want to make a point here. We think this is more intricate because we can relate to it in our everyday lives. But if you actually look at a structure of a bacteria and how it operates, or what a virus does to infiltrate an immune system or a cell, that's actually on a lot more levels, a lot more intricate than a design. In fact, the whole reason why I'm using this as an example is because this is a fairly simple example, as opposed to kind of explaining the metabolism of a certain type of bacteria and how that might change and how it might become immune to penicillin or whatever else."}, {"video_title": "Natural Selection and the Owl Butterfly (2).mp3", "Sentence": "And I actually want to make a point here. We think this is more intricate because we can relate to it in our everyday lives. But if you actually look at a structure of a bacteria and how it operates, or what a virus does to infiltrate an immune system or a cell, that's actually on a lot more levels, a lot more intricate than a design. In fact, the whole reason why I'm using this as an example is because this is a fairly simple example, as opposed to kind of explaining the metabolism of a certain type of bacteria and how that might change and how it might become immune to penicillin or whatever else. But I want to make this very clear that these very intricate things, they don't happen overnight. It's not like one butterfly was completely, one uniform hot pink color, and then all of a sudden they have a child whose wings looked just like this. No, it happens over large periods of time."}, {"video_title": "Natural Selection and the Owl Butterfly (2).mp3", "Sentence": "In fact, the whole reason why I'm using this as an example is because this is a fairly simple example, as opposed to kind of explaining the metabolism of a certain type of bacteria and how that might change and how it might become immune to penicillin or whatever else. But I want to make this very clear that these very intricate things, they don't happen overnight. It's not like one butterfly was completely, one uniform hot pink color, and then all of a sudden they have a child whose wings looked just like this. No, it happens over large periods of time. Although there might be some little weird hormonal change that does this, but I'm not going to go there. But that is possible. But I just want to make this point because I think the more examples we see, the more it'll kind of hit home that this is a passive process."}, {"video_title": "Natural Selection and the Owl Butterfly (2).mp3", "Sentence": "No, it happens over large periods of time. Although there might be some little weird hormonal change that does this, but I'm not going to go there. But that is possible. But I just want to make this point because I think the more examples we see, the more it'll kind of hit home that this is a passive process. We're not talking about these things happening overnight. And it's actually really interesting to kind of look at our world around us and look at ecosystems as they are today, and try to think really hard about how something came to be, what it's useful for, why it might have been selected for. For example, are things, are traits that occur after reproduction selected for?"}, {"video_title": "Natural Selection and the Owl Butterfly (2).mp3", "Sentence": "But I just want to make this point because I think the more examples we see, the more it'll kind of hit home that this is a passive process. We're not talking about these things happening overnight. And it's actually really interesting to kind of look at our world around us and look at ecosystems as they are today, and try to think really hard about how something came to be, what it's useful for, why it might have been selected for. For example, are things, are traits that occur after reproduction selected for? Well, probably not, unless they affect the reproduction of the next cycle. For example, you might say, oh, well, the trait to be nurturing after reproductive years, that's after reproductive years. No, but it helps your offspring reproduce."}, {"video_title": "Natural Selection and the Owl Butterfly (2).mp3", "Sentence": "For example, are things, are traits that occur after reproduction selected for? Well, probably not, unless they affect the reproduction of the next cycle. For example, you might say, oh, well, the trait to be nurturing after reproductive years, that's after reproductive years. No, but it helps your offspring reproduce. But we already see a lot of diseases, especially once we get beyond our reproductive and our child-rearing years. So once we get into our 50s and 60s, the incidences of diseases increases exponentially from when we're younger, and that's because they're no longer being selected for, because it no longer affects our ability to reproduce, because we've already reproduced, we've already raised our children so that they could reproduce. So anything that happens at that point is now not being selected for."}, {"video_title": "Biodiversity ecosystems and ecological networks.mp3", "Sentence": "If we think about our biodiversity tutorials as an archipelago, then today we visit this island to discover why biodiversity is so important. In terms of biodiversity, we mean a lot of different things. In this case, we're going to talk about something that's known as species richness, because that's something that we can measure. Because counting up the number of species, going out and finding out how many species there are in a given environment is something that we can actually do. There are different species of plants, there are many different species of animals, many different species of microbes, and many different species of fungi. And they all interact in their environment to create what we would call an ecosystem. Eco is an interesting word."}, {"video_title": "Biodiversity ecosystems and ecological networks.mp3", "Sentence": "Because counting up the number of species, going out and finding out how many species there are in a given environment is something that we can actually do. There are different species of plants, there are many different species of animals, many different species of microbes, and many different species of fungi. And they all interact in their environment to create what we would call an ecosystem. Eco is an interesting word. It's an ancient word that means house. So it's a system of what goes on in your house, that is, where we all live. All of these different organisms are interacting."}, {"video_title": "Biodiversity ecosystems and ecological networks.mp3", "Sentence": "Eco is an interesting word. It's an ancient word that means house. So it's a system of what goes on in your house, that is, where we all live. All of these different organisms are interacting. They're behaving together. They're interacting with one another. Some of them eat each other."}, {"video_title": "Biodiversity ecosystems and ecological networks.mp3", "Sentence": "All of these different organisms are interacting. They're behaving together. They're interacting with one another. Some of them eat each other. Some of them eat what others decompose into. And they, plus the physical environment or the house, form the ecosystem. Why would the number of species, in other words, species richness, be crucial to the way an ecosystem functions?"}, {"video_title": "Biodiversity ecosystems and ecological networks.mp3", "Sentence": "Some of them eat each other. Some of them eat what others decompose into. And they, plus the physical environment or the house, form the ecosystem. Why would the number of species, in other words, species richness, be crucial to the way an ecosystem functions? What is it about the number of species that makes the ecosystem work better and contribute to the resiliency or the stability of the ecosystem? Scientists are really beginning to study this, and the emerging field is referred to as BEF, biodiversity ecosystem function. We can think of any ecosystem as species that network one to another."}, {"video_title": "Biodiversity ecosystems and ecological networks.mp3", "Sentence": "Why would the number of species, in other words, species richness, be crucial to the way an ecosystem functions? What is it about the number of species that makes the ecosystem work better and contribute to the resiliency or the stability of the ecosystem? Scientists are really beginning to study this, and the emerging field is referred to as BEF, biodiversity ecosystem function. We can think of any ecosystem as species that network one to another. They have interactions with each other. They can be a lot of different interactions. They can live on top of one another, like certain birds nesting in trees."}, {"video_title": "Biodiversity ecosystems and ecological networks.mp3", "Sentence": "We can think of any ecosystem as species that network one to another. They have interactions with each other. They can be a lot of different interactions. They can live on top of one another, like certain birds nesting in trees. Or even more crucially, these things might eat one another. This is a diagram, a network diagram, of, believe it or not, a relatively simple ecosystem in which the organisms are interacting one with the other. We can draw lines between the species to indicate those interactions."}, {"video_title": "Biodiversity ecosystems and ecological networks.mp3", "Sentence": "They can live on top of one another, like certain birds nesting in trees. Or even more crucially, these things might eat one another. This is a diagram, a network diagram, of, believe it or not, a relatively simple ecosystem in which the organisms are interacting one with the other. We can draw lines between the species to indicate those interactions. And we can make the lines directional to show that material or matter and energy are moving from one species to another. When one organism takes a bite of another, it not only gets a mouthful of matter or food, but that food contains energy. So these arrows show the direction that energy is flowing from one species to another."}, {"video_title": "Biodiversity ecosystems and ecological networks.mp3", "Sentence": "We can draw lines between the species to indicate those interactions. And we can make the lines directional to show that material or matter and energy are moving from one species to another. When one organism takes a bite of another, it not only gets a mouthful of matter or food, but that food contains energy. So these arrows show the direction that energy is flowing from one species to another. The most important thing about these webs is that the strength of these interactions can vary. That is, the interdependence of the organisms in the web can vary. And here's something that might be counterintuitive."}, {"video_title": "Biodiversity ecosystems and ecological networks.mp3", "Sentence": "So these arrows show the direction that energy is flowing from one species to another. The most important thing about these webs is that the strength of these interactions can vary. That is, the interdependence of the organisms in the web can vary. And here's something that might be counterintuitive. These interactions become less important the more species you have within a network. You can think of it as the interactions being spread among more players. But what happens when there are fewer players?"}, {"video_title": "Biodiversity ecosystems and ecological networks.mp3", "Sentence": "And here's something that might be counterintuitive. These interactions become less important the more species you have within a network. You can think of it as the interactions being spread among more players. But what happens when there are fewer players? Let's say we've got a really super simple set of interactions where this owl is eating that mouse, but can also eat this squirrel. This gives the owl options. If we remove one of these, take that guy right out of there, then we only have two species that are interacting with each other."}, {"video_title": "Biodiversity ecosystems and ecological networks.mp3", "Sentence": "But what happens when there are fewer players? Let's say we've got a really super simple set of interactions where this owl is eating that mouse, but can also eat this squirrel. This gives the owl options. If we remove one of these, take that guy right out of there, then we only have two species that are interacting with each other. And it's really easy to disturb this system. This guy will just eat all of these guys and boom, you can cause total ecological collapse. So the higher the biodiversity or species richness in a system or in a network, the stronger it is, the more stable it will be because of all the additional options open to the organisms in it."}, {"video_title": "Biodiversity ecosystems and ecological networks.mp3", "Sentence": "If we remove one of these, take that guy right out of there, then we only have two species that are interacting with each other. And it's really easy to disturb this system. This guy will just eat all of these guys and boom, you can cause total ecological collapse. So the higher the biodiversity or species richness in a system or in a network, the stronger it is, the more stable it will be because of all the additional options open to the organisms in it. Think of that old saying about putting all your eggs in one basket. Not all interactions within a given ecosystem or network are exactly the same strength because some species have stronger interactions with each other than they do with some other species. For example, let's imagine that somewhere in here you've got one of these guys."}, {"video_title": "Biodiversity ecosystems and ecological networks.mp3", "Sentence": "So the higher the biodiversity or species richness in a system or in a network, the stronger it is, the more stable it will be because of all the additional options open to the organisms in it. Think of that old saying about putting all your eggs in one basket. Not all interactions within a given ecosystem or network are exactly the same strength because some species have stronger interactions with each other than they do with some other species. For example, let's imagine that somewhere in here you've got one of these guys. And he's eating plankton, the microscopic organisms living in the water. And they're going in. These guys are the producer end of things, the ones who can photosynthesize and make chemical energy from sunlight."}, {"video_title": "Biodiversity ecosystems and ecological networks.mp3", "Sentence": "For example, let's imagine that somewhere in here you've got one of these guys. And he's eating plankton, the microscopic organisms living in the water. And they're going in. These guys are the producer end of things, the ones who can photosynthesize and make chemical energy from sunlight. And remember, food equals energy. So what we're talking about is a lot of energy flowing from the producers to the consumer, represented by Mr. Whale over here. That's what these lines represent."}, {"video_title": "Biodiversity ecosystems and ecological networks.mp3", "Sentence": "These guys are the producer end of things, the ones who can photosynthesize and make chemical energy from sunlight. And remember, food equals energy. So what we're talking about is a lot of energy flowing from the producers to the consumer, represented by Mr. Whale over here. That's what these lines represent. They represent the flow of energy through the ecosystem. Eventually, the whale succumbs to life and dies. And poor Mr. Whale ends up on the sea floor."}, {"video_title": "Biodiversity ecosystems and ecological networks.mp3", "Sentence": "That's what these lines represent. They represent the flow of energy through the ecosystem. Eventually, the whale succumbs to life and dies. And poor Mr. Whale ends up on the sea floor. Are things over at that point? Definitely not because at that point, he's going to give up stuff that ends up as part of the producer's food web. It's shown, actually we're starting to get some really great new evidence, that these events where whales fall onto the sea bottom start an ecosystem of their own in ways."}, {"video_title": "Biodiversity ecosystems and ecological networks.mp3", "Sentence": "And poor Mr. Whale ends up on the sea floor. Are things over at that point? Definitely not because at that point, he's going to give up stuff that ends up as part of the producer's food web. It's shown, actually we're starting to get some really great new evidence, that these events where whales fall onto the sea bottom start an ecosystem of their own in ways. This is known as a whale fall. Don't get under one. It's always best not to be under one."}, {"video_title": "Biodiversity ecosystems and ecological networks.mp3", "Sentence": "It's shown, actually we're starting to get some really great new evidence, that these events where whales fall onto the sea bottom start an ecosystem of their own in ways. This is known as a whale fall. Don't get under one. It's always best not to be under one. But when the whale does hit the bottom, all kinds of interesting stuff happens. Lots of organisms come and feed on the whale. There's a succession of organisms, that is, organismal communities that change over time as the condition of the whale itself changes, that turn this whale from a fleshy organism to bones, and eventually even the bones are eaten."}, {"video_title": "Biodiversity ecosystems and ecological networks.mp3", "Sentence": "It's always best not to be under one. But when the whale does hit the bottom, all kinds of interesting stuff happens. Lots of organisms come and feed on the whale. There's a succession of organisms, that is, organismal communities that change over time as the condition of the whale itself changes, that turn this whale from a fleshy organism to bones, and eventually even the bones are eaten. So this huge influx of energy that the whale's been accumulating from these producers, the plankton, that it's been feeding on, is returned to the environment, cycled back through the ecosystem. You might imagine that that complex set of events that I just diagrammed here are part of this little bit of web. It turns out that where you get concentrated clusters of things happening in these webs, it's usually because energy is being run through the larger organisms in the system."}, {"video_title": "Biodiversity ecosystems and ecological networks.mp3", "Sentence": "There's a succession of organisms, that is, organismal communities that change over time as the condition of the whale itself changes, that turn this whale from a fleshy organism to bones, and eventually even the bones are eaten. So this huge influx of energy that the whale's been accumulating from these producers, the plankton, that it's been feeding on, is returned to the environment, cycled back through the ecosystem. You might imagine that that complex set of events that I just diagrammed here are part of this little bit of web. It turns out that where you get concentrated clusters of things happening in these webs, it's usually because energy is being run through the larger organisms in the system. And when you disturb a bit of that, where you've got large amounts of energy flowing through the system, you can get a real drop in ecosystem function. If you take the whales out of the equation, by overhunting them, you get this drop in ecosystem function because there's this removal of an entire major energy flow system from this network. Think of it a little bit like this tremendous thing that we have now, this internet."}, {"video_title": "Biodiversity ecosystems and ecological networks.mp3", "Sentence": "It turns out that where you get concentrated clusters of things happening in these webs, it's usually because energy is being run through the larger organisms in the system. And when you disturb a bit of that, where you've got large amounts of energy flowing through the system, you can get a real drop in ecosystem function. If you take the whales out of the equation, by overhunting them, you get this drop in ecosystem function because there's this removal of an entire major energy flow system from this network. Think of it a little bit like this tremendous thing that we have now, this internet. If you draw a diagram of the interactions amongst all of the servers and all of the things that push messages through the internet, there are places where that network's going to show a lot of stuff going on, a major hub in the internet. A lot of messages are flowing through. Like Google's servers, for example."}, {"video_title": "Biodiversity ecosystems and ecological networks.mp3", "Sentence": "Think of it a little bit like this tremendous thing that we have now, this internet. If you draw a diagram of the interactions amongst all of the servers and all of the things that push messages through the internet, there are places where that network's going to show a lot of stuff going on, a major hub in the internet. A lot of messages are flowing through. Like Google's servers, for example. Google is going to be at the center of one of these big clusters of a lot of messages going through. Other servers may not be so important. Those servers are going to be places like my desktop where I'm just messaging my kid to tell him to come home for dinner."}, {"video_title": "Biodiversity ecosystems and ecological networks.mp3", "Sentence": "Like Google's servers, for example. Google is going to be at the center of one of these big clusters of a lot of messages going through. Other servers may not be so important. Those servers are going to be places like my desktop where I'm just messaging my kid to tell him to come home for dinner. If you take my server out of the system, it's not going to disturb the entire web. But you can see what happens if you suddenly take Google out of the system. You're going to greatly perturb that particular ecosystem."}, {"video_title": "Biodiversity ecosystems and ecological networks.mp3", "Sentence": "Those servers are going to be places like my desktop where I'm just messaging my kid to tell him to come home for dinner. If you take my server out of the system, it's not going to disturb the entire web. But you can see what happens if you suddenly take Google out of the system. You're going to greatly perturb that particular ecosystem. So these webs of interaction throughout an ecosystem are really, really important. If the system is bigger with more species and more interactions, you're going to reduce the chance that a perturbation or a disturbance is going to have a really negative impact because you're just reducing the chance that you're going to take out something that's really crucial. The other thing about this is that all of these things are doing something different."}, {"video_title": "Biodiversity ecosystems and ecological networks.mp3", "Sentence": "You're going to greatly perturb that particular ecosystem. So these webs of interaction throughout an ecosystem are really, really important. If the system is bigger with more species and more interactions, you're going to reduce the chance that a perturbation or a disturbance is going to have a really negative impact because you're just reducing the chance that you're going to take out something that's really crucial. The other thing about this is that all of these things are doing something different. They're all doing different things in the ecosystem. So if you imagine one of my favorite things, I love planes. Here's a complicated plane with four engines, lots of moving parts, piston engines roaring away."}, {"video_title": "Biodiversity ecosystems and ecological networks.mp3", "Sentence": "The other thing about this is that all of these things are doing something different. They're all doing different things in the ecosystem. So if you imagine one of my favorite things, I love planes. Here's a complicated plane with four engines, lots of moving parts, piston engines roaring away. You've got a rudder here. You've got ailerons. Imagine this aircraft flying along."}, {"video_title": "Biodiversity ecosystems and ecological networks.mp3", "Sentence": "Here's a complicated plane with four engines, lots of moving parts, piston engines roaring away. You've got a rudder here. You've got ailerons. Imagine this aircraft flying along. If you take out, say, the curtains that are in the window, you're probably not going to bring the plane down. But if you do something like remove a couple of the crucial bolts at the base of the wing here where it connects to the fuselage, then the wing's going to fall off and we're going to have a problem because before you know it, the airplane's going to crash. Same thing with the ecosystem."}, {"video_title": "Biodiversity ecosystems and ecological networks.mp3", "Sentence": "Imagine this aircraft flying along. If you take out, say, the curtains that are in the window, you're probably not going to bring the plane down. But if you do something like remove a couple of the crucial bolts at the base of the wing here where it connects to the fuselage, then the wing's going to fall off and we're going to have a problem because before you know it, the airplane's going to crash. Same thing with the ecosystem. Everything's doing something different. Some things will matter more than others if you remove them. The more bolts, the better."}, {"video_title": "New localities lead to new biodiversity (2).mp3", "Sentence": "These barriers can lead to divergences resulting in speciation through the restriction of gene flow. However, what we'd like to focus on here is that there's another way to really accentuate the effects of restricted gene flow, and that's something called dispersal. This is basically the way that species of plants, animals, and other organisms expand their ranges, their distributions on Earth, through movements of individuals that increase the sizes of the ranges of populations and therefore the ranges of the species themselves. Dispersal can also lead to speciation. Species like plants that have a rooted-to-the-ground or sedentary habit, like I sometimes have when there's a hockey game on, even plants have dispersal stages in the form of seeds that can be distributed in air or in water or even in and on other organisms. Bird migration is an obvious dispersal mechanism. Bird movements can easily result in the establishment of new populations of a species where they didn't exist before."}, {"video_title": "New localities lead to new biodiversity (2).mp3", "Sentence": "Dispersal can also lead to speciation. Species like plants that have a rooted-to-the-ground or sedentary habit, like I sometimes have when there's a hockey game on, even plants have dispersal stages in the form of seeds that can be distributed in air or in water or even in and on other organisms. Bird migration is an obvious dispersal mechanism. Bird movements can easily result in the establishment of new populations of a species where they didn't exist before. But did you know that spiders can also disperse through something called ballooning? Young spiders especially can release fine silk threads that are caught by the wind, carrying the spider aloft and to new territories. There are many other examples of dispersal."}, {"video_title": "New localities lead to new biodiversity (2).mp3", "Sentence": "Bird movements can easily result in the establishment of new populations of a species where they didn't exist before. But did you know that spiders can also disperse through something called ballooning? Young spiders especially can release fine silk threads that are caught by the wind, carrying the spider aloft and to new territories. There are many other examples of dispersal. The spores of fungi that blow in the wind and get up my nose and give me allergies, or a sneeze full of bacteria or viruses. Even that's a dispersal technique that has evolved among microbes that increases their ranges during cold and flu season. Things like corals, sea urchins, and snails also disperse."}, {"video_title": "New localities lead to new biodiversity (2).mp3", "Sentence": "There are many other examples of dispersal. The spores of fungi that blow in the wind and get up my nose and give me allergies, or a sneeze full of bacteria or viruses. Even that's a dispersal technique that has evolved among microbes that increases their ranges during cold and flu season. Things like corals, sea urchins, and snails also disperse. Mostly they do this during the earliest stages of their lives, drifting through the water as little larvae. These larvae can be carried significant distances and when they eventually settle down on the substrate and metamorphose or change from the juvenile dispersing stage into a small version of the more sedentary adult, they establish new populations and expand the species ranges. Organisms or pieces and mats of vegetation that wash into the ocean from land can harbor terrestrial organisms that go along for the ride and are taken out to sea."}, {"video_title": "New localities lead to new biodiversity (2).mp3", "Sentence": "Things like corals, sea urchins, and snails also disperse. Mostly they do this during the earliest stages of their lives, drifting through the water as little larvae. These larvae can be carried significant distances and when they eventually settle down on the substrate and metamorphose or change from the juvenile dispersing stage into a small version of the more sedentary adult, they establish new populations and expand the species ranges. Organisms or pieces and mats of vegetation that wash into the ocean from land can harbor terrestrial organisms that go along for the ride and are taken out to sea. They may drift to new places to live and if they land and are successful, this can result in the establishment of a new population. All these events in nature make it worth asking, what happens at the end of these Olympian journeys, these organismal odysseys? If the conditions are right and the organisms can continue to survive, a new population can be established in a new place."}, {"video_title": "New localities lead to new biodiversity (2).mp3", "Sentence": "Organisms or pieces and mats of vegetation that wash into the ocean from land can harbor terrestrial organisms that go along for the ride and are taken out to sea. They may drift to new places to live and if they land and are successful, this can result in the establishment of a new population. All these events in nature make it worth asking, what happens at the end of these Olympian journeys, these organismal odysseys? If the conditions are right and the organisms can continue to survive, a new population can be established in a new place. The ability to survive and reproduce in this new place is key. In the case of sexual species, individuals need to be carrying viable young when they arrive or find a member of the opposite sex with which to produce new generations. If you think of a coconut, which can travel hundreds of miles floating in the ocean, washing up on a bare lava shore, it's going to have a much harder time of it than if it washes up on a sandy beach."}, {"video_title": "New localities lead to new biodiversity (2).mp3", "Sentence": "If the conditions are right and the organisms can continue to survive, a new population can be established in a new place. The ability to survive and reproduce in this new place is key. In the case of sexual species, individuals need to be carrying viable young when they arrive or find a member of the opposite sex with which to produce new generations. If you think of a coconut, which can travel hundreds of miles floating in the ocean, washing up on a bare lava shore, it's going to have a much harder time of it than if it washes up on a sandy beach. In other words, the conditions have to be right for the establishment of a new population. In general, the greater the distance between a new population and the original population, the more likely the gene flow will be restricted between the two populations and the more likely the two populations will diverge from each other. And this takes us to the idea of isolation."}, {"video_title": "New localities lead to new biodiversity (2).mp3", "Sentence": "If you think of a coconut, which can travel hundreds of miles floating in the ocean, washing up on a bare lava shore, it's going to have a much harder time of it than if it washes up on a sandy beach. In other words, the conditions have to be right for the establishment of a new population. In general, the greater the distance between a new population and the original population, the more likely the gene flow will be restricted between the two populations and the more likely the two populations will diverge from each other. And this takes us to the idea of isolation. Isolation can be very obvious on islands, but it's interesting to remember that not all islands have to be in the middle of a body of water. You can have isolation among oases in a desert, for example. You can have isolation on the tops of mountains or in the valleys between the mountains."}, {"video_title": "New localities lead to new biodiversity (2).mp3", "Sentence": "And this takes us to the idea of isolation. Isolation can be very obvious on islands, but it's interesting to remember that not all islands have to be in the middle of a body of water. You can have isolation among oases in a desert, for example. You can have isolation on the tops of mountains or in the valleys between the mountains. Or you can have isolation in a fragment of rainforest that's surrounded by extensively clear-cut land. And these habitat islands can exhibit the same principles of isolation and restriction of gene flow that influence speciation. Amazing patterns of speciation can emerge in all of these systems because there are some pretty basic rules that emerge logically from thinking about islands, dispersal, and isolation, leading to an entire field of study known as island biogeography."}, {"video_title": "New localities lead to new biodiversity (2).mp3", "Sentence": "You can have isolation on the tops of mountains or in the valleys between the mountains. Or you can have isolation in a fragment of rainforest that's surrounded by extensively clear-cut land. And these habitat islands can exhibit the same principles of isolation and restriction of gene flow that influence speciation. Amazing patterns of speciation can emerge in all of these systems because there are some pretty basic rules that emerge logically from thinking about islands, dispersal, and isolation, leading to an entire field of study known as island biogeography. One of these rules is that islands can be harder or easier to get to depending on how far away they are. This is known as the distance factor. Second, the longer the island has been in existence, the more likely it is that organisms have already arrived there and the longer they have had to diverge from their parent population."}, {"video_title": "New localities lead to new biodiversity (2).mp3", "Sentence": "Amazing patterns of speciation can emerge in all of these systems because there are some pretty basic rules that emerge logically from thinking about islands, dispersal, and isolation, leading to an entire field of study known as island biogeography. One of these rules is that islands can be harder or easier to get to depending on how far away they are. This is known as the distance factor. Second, the longer the island has been in existence, the more likely it is that organisms have already arrived there and the longer they have had to diverge from their parent population. That's the time factor. A third concept is that the smaller the island, the less likely it is for a species to get there in the first place. That would be called the area factor."}, {"video_title": "New localities lead to new biodiversity (2).mp3", "Sentence": "Second, the longer the island has been in existence, the more likely it is that organisms have already arrived there and the longer they have had to diverge from their parent population. That's the time factor. A third concept is that the smaller the island, the less likely it is for a species to get there in the first place. That would be called the area factor. Fourthly, diverse environmental conditions on an island can enhance the island's biodiversity because there's a greater chance that the right climate, the right ecological resources will be present. And we can refer to this as the habitat factor. A fifth logical rule concerns the location of the island with respect to things like currents and winds that allow new energy in the form of nutrients to flow into the system, supporting ecosystem functions or increasing or decreasing the likelihood of new colonizers arriving."}, {"video_title": "New localities lead to new biodiversity (2).mp3", "Sentence": "That would be called the area factor. Fourthly, diverse environmental conditions on an island can enhance the island's biodiversity because there's a greater chance that the right climate, the right ecological resources will be present. And we can refer to this as the habitat factor. A fifth logical rule concerns the location of the island with respect to things like currents and winds that allow new energy in the form of nutrients to flow into the system, supporting ecosystem functions or increasing or decreasing the likelihood of new colonizers arriving. And I would call that the flow factor. A sixth factor is just chance and random events that also play a big role. I'm not sure there's a name for that one, so I'm calling it the serendipity factor."}, {"video_title": "New localities lead to new biodiversity (2).mp3", "Sentence": "A fifth logical rule concerns the location of the island with respect to things like currents and winds that allow new energy in the form of nutrients to flow into the system, supporting ecosystem functions or increasing or decreasing the likelihood of new colonizers arriving. And I would call that the flow factor. A sixth factor is just chance and random events that also play a big role. I'm not sure there's a name for that one, so I'm calling it the serendipity factor. An example of that might be a freak storm that carries organisms with it. You might think of other factors or tweaks to these basic rules. For example, if you throw in the fact that organisms differ greatly in their ability to disperse, you have a rich and complicated overlay of things influencing the biodiversity on any particular island and why that biodiversity can be so different from one island to the next."}, {"video_title": "New localities lead to new biodiversity (2).mp3", "Sentence": "I'm not sure there's a name for that one, so I'm calling it the serendipity factor. An example of that might be a freak storm that carries organisms with it. You might think of other factors or tweaks to these basic rules. For example, if you throw in the fact that organisms differ greatly in their ability to disperse, you have a rich and complicated overlay of things influencing the biodiversity on any particular island and why that biodiversity can be so different from one island to the next. Here's a simplified graph that illustrates a couple of these factors. You've got basically two sets of curves. One set refers to how close or far an island might be to the mainland and how that affects the rate of colonization."}, {"video_title": "New localities lead to new biodiversity (2).mp3", "Sentence": "For example, if you throw in the fact that organisms differ greatly in their ability to disperse, you have a rich and complicated overlay of things influencing the biodiversity on any particular island and why that biodiversity can be so different from one island to the next. Here's a simplified graph that illustrates a couple of these factors. You've got basically two sets of curves. One set refers to how close or far an island might be to the mainland and how that affects the rate of colonization. And the other set refers to whether the islands are large or small and how that's related to the rate or probability of extinction. The horizontal axis represents increasing species richness. So you have a couple of interesting and important intersection points that mark the lower richness of a small distant island compared to that of a large nearby island."}, {"video_title": "New localities lead to new biodiversity (2).mp3", "Sentence": "One set refers to how close or far an island might be to the mainland and how that affects the rate of colonization. And the other set refers to whether the islands are large or small and how that's related to the rate or probability of extinction. The horizontal axis represents increasing species richness. So you have a couple of interesting and important intersection points that mark the lower richness of a small distant island compared to that of a large nearby island. This graph incorporates a couple of other things. One is the balancing of colonization and extinction. The more crowded the island becomes, the more likely it is that extinctions will happen."}, {"video_title": "New localities lead to new biodiversity (2).mp3", "Sentence": "So you have a couple of interesting and important intersection points that mark the lower richness of a small distant island compared to that of a large nearby island. This graph incorporates a couple of other things. One is the balancing of colonization and extinction. The more crowded the island becomes, the more likely it is that extinctions will happen. It also summarizes the idea that large islands close to the mainland's source of new populations, places like, say, Madagascar, will have lots and lots of species. But remember that on a big island like Madagascar, we have the habitat factor too. Populations can disperse on the island itself, find new habitats, encounter new barriers, and all kinds of new species can arise."}, {"video_title": "New localities lead to new biodiversity (2).mp3", "Sentence": "The more crowded the island becomes, the more likely it is that extinctions will happen. It also summarizes the idea that large islands close to the mainland's source of new populations, places like, say, Madagascar, will have lots and lots of species. But remember that on a big island like Madagascar, we have the habitat factor too. Populations can disperse on the island itself, find new habitats, encounter new barriers, and all kinds of new species can arise. And if you look at what's going on in Madagascar, that's definitely true. Madagascar has lots of endemics, species that arose there and nowhere else. Also, the geologic evidence is strong that Madagascar broke free from Africa in the past, carrying with it subsets of species that existed on Africa and then continued to diverge and evolve on Madagascar."}, {"video_title": "New localities lead to new biodiversity (2).mp3", "Sentence": "Populations can disperse on the island itself, find new habitats, encounter new barriers, and all kinds of new species can arise. And if you look at what's going on in Madagascar, that's definitely true. Madagascar has lots of endemics, species that arose there and nowhere else. Also, the geologic evidence is strong that Madagascar broke free from Africa in the past, carrying with it subsets of species that existed on Africa and then continued to diverge and evolve on Madagascar. In contrast, consider the Galapagos. This archipelago of islands is relatively far from any mainland and sprung up there through volcanism. These remote islands had almost no life on them when they first appeared."}, {"video_title": "New localities lead to new biodiversity (2).mp3", "Sentence": "Also, the geologic evidence is strong that Madagascar broke free from Africa in the past, carrying with it subsets of species that existed on Africa and then continued to diverge and evolve on Madagascar. In contrast, consider the Galapagos. This archipelago of islands is relatively far from any mainland and sprung up there through volcanism. These remote islands had almost no life on them when they first appeared. There were fewer species arriving there, but because of the multitude of islands within the archipelago, there is subsequent speciation of populations that make it to one island and then island hop from there. Lots of island groups illustrate these ideas. Hawaii and the Philippines, for example, in any of those island groupings, you can see all of these overlapping factors at work."}, {"video_title": "New localities lead to new biodiversity (2).mp3", "Sentence": "These remote islands had almost no life on them when they first appeared. There were fewer species arriving there, but because of the multitude of islands within the archipelago, there is subsequent speciation of populations that make it to one island and then island hop from there. Lots of island groups illustrate these ideas. Hawaii and the Philippines, for example, in any of those island groupings, you can see all of these overlapping factors at work. It's a grand and beautiful view, I think, of how islands can foster the formation of new species. But the graph can also tell you something about why so many island species are in such trouble. The island biogeography curves summarize that as well because we've got this word in there, extinction."}, {"video_title": "New localities lead to new biodiversity (2).mp3", "Sentence": "Hawaii and the Philippines, for example, in any of those island groupings, you can see all of these overlapping factors at work. It's a grand and beautiful view, I think, of how islands can foster the formation of new species. But the graph can also tell you something about why so many island species are in such trouble. The island biogeography curves summarize that as well because we've got this word in there, extinction. Many island populations are vulnerable to extinction. I've been talking about all of this with no humans involved, but if you put humans in the equation, drop them into that island ecosystem, who's to say what the dimensions of the effects will be down the road? How do the curves get changed by human activity?"}, {"video_title": "New localities lead to new biodiversity (2).mp3", "Sentence": "The island biogeography curves summarize that as well because we've got this word in there, extinction. Many island populations are vulnerable to extinction. I've been talking about all of this with no humans involved, but if you put humans in the equation, drop them into that island ecosystem, who's to say what the dimensions of the effects will be down the road? How do the curves get changed by human activity? What happens to the extinction curves? How steep will they be? How big are the effects that humans have on these systems of endemic species?"}, {"video_title": "Phases of meiosis II   Cells   MCAT   Khan Academy.mp3", "Sentence": "In the last video, we had completed meiosis one, and now we're ready to go into meiosis two. And you might be wondering, well, hey, you know, after mitosis, we went back into our interphase. Is there kind of a rest period between our two phases of meiosis? And the answer is sometimes. There can be a rest period where you have an interphase two, and that will depend on the type of cell and the species and all of that, but it is possible. So I'll actually put that over here. So we could have an interphase two."}, {"video_title": "Phases of meiosis II   Cells   MCAT   Khan Academy.mp3", "Sentence": "And the answer is sometimes. There can be a rest period where you have an interphase two, and that will depend on the type of cell and the species and all of that, but it is possible. So I'll actually put that over here. So we could have an interphase two. So interphase two, which you could kind of view as a rest period, but then we get into meiosis two, which will allow us to complete all of meiosis. So you could imagine meiosis two starts with prophase two. And in prophase two, now I'm dealing with two cells here."}, {"video_title": "Phases of meiosis II   Cells   MCAT   Khan Academy.mp3", "Sentence": "So we could have an interphase two. So interphase two, which you could kind of view as a rest period, but then we get into meiosis two, which will allow us to complete all of meiosis. So you could imagine meiosis two starts with prophase two. And in prophase two, now I'm dealing with two cells here. So in prophase two, and I'm gonna do it for both of the cells that I have after I finished meiosis one. So in prophase two, so let me, that's one of the cells. I'm not gonna have space to draw it properly."}, {"video_title": "Phases of meiosis II   Cells   MCAT   Khan Academy.mp3", "Sentence": "And in prophase two, now I'm dealing with two cells here. So in prophase two, and I'm gonna do it for both of the cells that I have after I finished meiosis one. So in prophase two, so let me, that's one of the cells. I'm not gonna have space to draw it properly. So let me draw it. So let me draw this one first. So this is one of the cells right over here, and then this is the other cell right over here."}, {"video_title": "Phases of meiosis II   Cells   MCAT   Khan Academy.mp3", "Sentence": "I'm not gonna have space to draw it properly. So let me draw it. So let me draw this one first. So this is one of the cells right over here, and then this is the other cell right over here. In prophase two, just like in prophase one, and just like in prophase in mitosis, and let me write the phases here. This is prophase two we're talking about. Prophase two, your nuclear envelope dissolves again."}, {"video_title": "Phases of meiosis II   Cells   MCAT   Khan Academy.mp3", "Sentence": "So this is one of the cells right over here, and then this is the other cell right over here. In prophase two, just like in prophase one, and just like in prophase in mitosis, and let me write the phases here. This is prophase two we're talking about. Prophase two, your nuclear envelope dissolves again. So let me show a dissolving nuclear envelope. So your nuclear envelope dissolves again. And your chromosomes, once again, condense, I guess you could say into their denser form."}, {"video_title": "Phases of meiosis II   Cells   MCAT   Khan Academy.mp3", "Sentence": "Prophase two, your nuclear envelope dissolves again. So let me show a dissolving nuclear envelope. So your nuclear envelope dissolves again. And your chromosomes, once again, condense, I guess you could say into their denser form. So it's gonna look like this, this, and this on this side. It has a little bit of the magenta that was from the chromosomal crossover back in prophase one. And then you have this character right over here that is shorter."}, {"video_title": "Phases of meiosis II   Cells   MCAT   Khan Academy.mp3", "Sentence": "And your chromosomes, once again, condense, I guess you could say into their denser form. So it's gonna look like this, this, and this on this side. It has a little bit of the magenta that was from the chromosomal crossover back in prophase one. And then you have this character right over here that is shorter. You have this chromosome right over here, and it had a little orange section from the chromosomal crossover, just like this. And then you have the shorter orange chromosome just like that, so they have condensed. And you've actually, each of these cells now will have duplicate centrosomes."}, {"video_title": "Phases of meiosis II   Cells   MCAT   Khan Academy.mp3", "Sentence": "And then you have this character right over here that is shorter. You have this chromosome right over here, and it had a little orange section from the chromosomal crossover, just like this. And then you have the shorter orange chromosome just like that, so they have condensed. And you've actually, each of these cells now will have duplicate centrosomes. So the centrosomes have replicated, and they will start to migrate to opposite ends of the cell. So once again, very strong analogy, especially to, frankly, prophase from mitosis. So now let's keep going."}, {"video_title": "Phases of meiosis II   Cells   MCAT   Khan Academy.mp3", "Sentence": "And you've actually, each of these cells now will have duplicate centrosomes. So the centrosomes have replicated, and they will start to migrate to opposite ends of the cell. So once again, very strong analogy, especially to, frankly, prophase from mitosis. So now let's keep going. We're now ready to go to metaphase two. Metaphase two. Metaphase, metaphase two."}, {"video_title": "Phases of meiosis II   Cells   MCAT   Khan Academy.mp3", "Sentence": "So now let's keep going. We're now ready to go to metaphase two. Metaphase two. Metaphase, metaphase two. And let me draw my two cells. So this is one of them, and this is the other. Let me draw an arrow here so you can see that we are entering into another phase."}, {"video_title": "Phases of meiosis II   Cells   MCAT   Khan Academy.mp3", "Sentence": "Metaphase, metaphase two. And let me draw my two cells. So this is one of them, and this is the other. Let me draw an arrow here so you can see that we are entering into another phase. So we are entering into another phase, metaphase two. And you can just imagine, it's very similar to what happens in metaphase and mitosis. And actually, all of meiosis two is very similar to what happens in mitosis."}, {"video_title": "Phases of meiosis II   Cells   MCAT   Khan Academy.mp3", "Sentence": "Let me draw an arrow here so you can see that we are entering into another phase. So we are entering into another phase, metaphase two. And you can just imagine, it's very similar to what happens in metaphase and mitosis. And actually, all of meiosis two is very similar to what happens in mitosis. So in metaphase two, our centrosomes have migrated to the poles. So our centrosomes have migrated to the poles. I'm gonna do it twice, because I'm now dealing with two different cells."}, {"video_title": "Phases of meiosis II   Cells   MCAT   Khan Academy.mp3", "Sentence": "And actually, all of meiosis two is very similar to what happens in mitosis. So in metaphase two, our centrosomes have migrated to the poles. So our centrosomes have migrated to the poles. I'm gonna do it twice, because I'm now dealing with two different cells. My nuclear membrane is now, it's now disappeared. And I have my now dense chromosomes lining up along the equator here. So this magenta one, it'll line up right over here."}, {"video_title": "Phases of meiosis II   Cells   MCAT   Khan Academy.mp3", "Sentence": "I'm gonna do it twice, because I'm now dealing with two different cells. My nuclear membrane is now, it's now disappeared. And I have my now dense chromosomes lining up along the equator here. So this magenta one, it'll line up right over here. So it might look like that. And actually, let me draw all the magenta ones now, since I have my magenta color selected. So this is the longer one and this one."}, {"video_title": "Phases of meiosis II   Cells   MCAT   Khan Academy.mp3", "Sentence": "So this magenta one, it'll line up right over here. So it might look like that. And actually, let me draw all the magenta ones now, since I have my magenta color selected. So this is the longer one and this one. This had a little bit of orange in it. Let me, has a little bit of the orange here. And then I had the shorter orange chromosome."}, {"video_title": "Phases of meiosis II   Cells   MCAT   Khan Academy.mp3", "Sentence": "So this is the longer one and this one. This had a little bit of orange in it. Let me, has a little bit of the orange here. And then I had the shorter orange chromosome. Shorter orange chromosome. And on this cell, I had the longer, the larger orange chromosome. So it had a little bit of pink on it."}, {"video_title": "Phases of meiosis II   Cells   MCAT   Khan Academy.mp3", "Sentence": "And then I had the shorter orange chromosome. Shorter orange chromosome. And on this cell, I had the longer, the larger orange chromosome. So it had a little bit of pink on it. And of course, you have your microtubules that are, I've been doing that in blue, so let me continue doing it in blue. That are pushing the centrosomes apart, but are also attaching to the chromosomes at the kinetochores. At the kinetochores."}, {"video_title": "Phases of meiosis II   Cells   MCAT   Khan Academy.mp3", "Sentence": "So it had a little bit of pink on it. And of course, you have your microtubules that are, I've been doing that in blue, so let me continue doing it in blue. That are pushing the centrosomes apart, but are also attaching to the chromosomes at the kinetochores. At the kinetochores. So there you go, and remember this right over here where the two sister chromatids attach, those are our centromeres. So let me just draw it all out like this. So it might go, might be something like that."}, {"video_title": "Phases of meiosis II   Cells   MCAT   Khan Academy.mp3", "Sentence": "At the kinetochores. So there you go, and remember this right over here where the two sister chromatids attach, those are our centromeres. So let me just draw it all out like this. So it might go, might be something like that. And now we're ready for anaphase two. And you can imagine what's about to happen. Things are about to pull apart."}, {"video_title": "Phases of meiosis II   Cells   MCAT   Khan Academy.mp3", "Sentence": "So it might go, might be something like that. And now we're ready for anaphase two. And you can imagine what's about to happen. Things are about to pull apart. And once again, this is analogous to what happens in anaphase in mitosis. So let me, so anaphase two. Anaphase, anaphase two."}, {"video_title": "Phases of meiosis II   Cells   MCAT   Khan Academy.mp3", "Sentence": "Things are about to pull apart. And once again, this is analogous to what happens in anaphase in mitosis. So let me, so anaphase two. Anaphase, anaphase two. I'm gonna draw my cells again. This is taking me twice as long because I have to do it for twice as many cells. So that's one cell there."}, {"video_title": "Phases of meiosis II   Cells   MCAT   Khan Academy.mp3", "Sentence": "Anaphase, anaphase two. I'm gonna draw my cells again. This is taking me twice as long because I have to do it for twice as many cells. So that's one cell there. This is another cell here. This is, I got a centrosome here, centrosome here, centrosome here, centrosome here. And then the key here, and this is why it's like mitosis and not like anaphase in meiosis one, is instead of, or like in mitosis, we're now going to split the sister chromatids so they now become two daughter chromosomes."}, {"video_title": "Phases of meiosis II   Cells   MCAT   Khan Academy.mp3", "Sentence": "So that's one cell there. This is another cell here. This is, I got a centrosome here, centrosome here, centrosome here, centrosome here. And then the key here, and this is why it's like mitosis and not like anaphase in meiosis one, is instead of, or like in mitosis, we're now going to split the sister chromatids so they now become two daughter chromosomes. When they're connected, they're just, together they're viewed as sister chromatids that make up one chromosome. But now they get, now they're getting pulled apart. So this one might get pulled in this direction, and then this one might get pulled in this direction."}, {"video_title": "Phases of meiosis II   Cells   MCAT   Khan Academy.mp3", "Sentence": "And then the key here, and this is why it's like mitosis and not like anaphase in meiosis one, is instead of, or like in mitosis, we're now going to split the sister chromatids so they now become two daughter chromosomes. When they're connected, they're just, together they're viewed as sister chromatids that make up one chromosome. But now they get, now they're getting pulled apart. So this one might get pulled in this direction, and then this one might get pulled in this direction. It has a little bit of, has a little bit of the magenta right over here, and then one of the sister chromatids, which would now be a daughter chromosome, going in upwards, and one of them going downwards. And let me draw all the micro, all the microtubules here, all the microtubules that are doing, that are super involved in all of this work of getting things to the right sides of the cells. And this is gonna happen in this cell as well."}, {"video_title": "Phases of meiosis II   Cells   MCAT   Khan Academy.mp3", "Sentence": "So this one might get pulled in this direction, and then this one might get pulled in this direction. It has a little bit of, has a little bit of the magenta right over here, and then one of the sister chromatids, which would now be a daughter chromosome, going in upwards, and one of them going downwards. And let me draw all the micro, all the microtubules here, all the microtubules that are doing, that are super involved in all of this work of getting things to the right sides of the cells. And this is gonna happen in this cell as well. So in this cell, so this one might be going down here, and this one is moving up here. And this one had a little chunk of orange on it. So let me draw that, little chunk of orange."}, {"video_title": "Phases of meiosis II   Cells   MCAT   Khan Academy.mp3", "Sentence": "And this is gonna happen in this cell as well. So in this cell, so this one might be going down here, and this one is moving up here. And this one had a little chunk of orange on it. So let me draw that, little chunk of orange. And then once again, one of the formerly sister chromatids, now daughter chromosomes going up there, and now going down over here, over here. And let me draw all of the microtubules, microtubules that are really, well, I've said it multiple times, super involved in actual the movement going on. They're elongating, there's these motor proteins that are moving the chromosomes along."}, {"video_title": "Phases of meiosis II   Cells   MCAT   Khan Academy.mp3", "Sentence": "So let me draw that, little chunk of orange. And then once again, one of the formerly sister chromatids, now daughter chromosomes going up there, and now going down over here, over here. And let me draw all of the microtubules, microtubules that are really, well, I've said it multiple times, super involved in actual the movement going on. They're elongating, there's these motor proteins that are moving the chromosomes along. Once again, they're connected at the kinetochores right over here, connected at the kinetochores right over there. And now we're almost done. We're ready to move into telophase two."}, {"video_title": "Phases of meiosis II   Cells   MCAT   Khan Academy.mp3", "Sentence": "They're elongating, there's these motor proteins that are moving the chromosomes along. Once again, they're connected at the kinetochores right over here, connected at the kinetochores right over there. And now we're almost done. We're ready to move into telophase two. So we're now going to go into telophase two. Telophase, telophase two, where my two cells are now becoming four cells. So telophase two, I'm gonna show the cytokinesis starting to happen."}, {"video_title": "Phases of meiosis II   Cells   MCAT   Khan Academy.mp3", "Sentence": "We're ready to move into telophase two. So we're now going to go into telophase two. Telophase, telophase two, where my two cells are now becoming four cells. So telophase two, I'm gonna show the cytokinesis starting to happen. So telophase two, so turning into four cells, starting to show the cytokinesis happening. On, in this cell up here, I have this character and has a little bit of magenta right over here. That's this right over there, and then you have the shorter magenta one."}, {"video_title": "Phases of meiosis II   Cells   MCAT   Khan Academy.mp3", "Sentence": "So telophase two, I'm gonna show the cytokinesis starting to happen. So telophase two, so turning into four cells, starting to show the cytokinesis happening. On, in this cell up here, I have this character and has a little bit of magenta right over here. That's this right over there, and then you have the shorter magenta one. And actually they are starting to, they're starting to unravel into their chromatin form, so maybe I'll draw that a little bit. And then this one right over here is starting to unravel into its chromatin form. And so is that one."}, {"video_title": "Phases of meiosis II   Cells   MCAT   Khan Academy.mp3", "Sentence": "That's this right over there, and then you have the shorter magenta one. And actually they are starting to, they're starting to unravel into their chromatin form, so maybe I'll draw that a little bit. And then this one right over here is starting to unravel into its chromatin form. And so is that one. Whoops, I'm gonna do that in that magenta color. Starting to unravel into its chromatin form. I'm gonna do it over here."}, {"video_title": "Phases of meiosis II   Cells   MCAT   Khan Academy.mp3", "Sentence": "And so is that one. Whoops, I'm gonna do that in that magenta color. Starting to unravel into its chromatin form. I'm gonna do it over here. This one is starting to unravel, and so is this one. So, and so is, and so is, I'm having trouble changing colors. And so is that one."}, {"video_title": "Phases of meiosis II   Cells   MCAT   Khan Academy.mp3", "Sentence": "I'm gonna do it over here. This one is starting to unravel, and so is this one. So, and so is, and so is, I'm having trouble changing colors. And so is that one. And then up here, this one's starting to unravel, this one over here, and this longer, mostly magenta one is also starting to unravel. Also starting to unravel. You start having your nuclear envelope form again."}, {"video_title": "Phases of meiosis II   Cells   MCAT   Khan Academy.mp3", "Sentence": "And so is that one. And then up here, this one's starting to unravel, this one over here, and this longer, mostly magenta one is also starting to unravel. Also starting to unravel. You start having your nuclear envelope form again. So your nuclear envelope is forming again. Nuclear envelope is forming. Your microtubules are dissolving."}, {"video_title": "Phases of meiosis II   Cells   MCAT   Khan Academy.mp3", "Sentence": "You start having your nuclear envelope form again. So your nuclear envelope is forming again. Nuclear envelope is forming. Your microtubules are dissolving. Let me draw the centrosomes. They're outside of the nuclear envelope. Outside of the nuclear envelope."}, {"video_title": "Phases of meiosis II   Cells   MCAT   Khan Academy.mp3", "Sentence": "Your microtubules are dissolving. Let me draw the centrosomes. They're outside of the nuclear envelope. Outside of the nuclear envelope. And of course, you are finally dividing the cells. Your cytokinesis happens. So now you have your four cells that each have a haploid number."}, {"video_title": "Phases of meiosis II   Cells   MCAT   Khan Academy.mp3", "Sentence": "Outside of the nuclear envelope. And of course, you are finally dividing the cells. Your cytokinesis happens. So now you have your four cells that each have a haploid number. They each have two chromosomes. Remember, your diploid number was four. The germ cell had four chromosomes."}, {"video_title": "Phases of meiosis II   Cells   MCAT   Khan Academy.mp3", "Sentence": "So now you have your four cells that each have a haploid number. They each have two chromosomes. Remember, your diploid number was four. The germ cell had four chromosomes. Two pairs of homologous chromosomes. Now, each of your resulting gametes, these are now gametes now. These are gametes."}, {"video_title": "Phases of meiosis II   Cells   MCAT   Khan Academy.mp3", "Sentence": "The germ cell had four chromosomes. Two pairs of homologous chromosomes. Now, each of your resulting gametes, these are now gametes now. These are gametes. They have a haploid number. But we started with a haploid number at the beginning of meiosis two. So that's why meiosis two is often compared to mitosis."}, {"video_title": "Phases of meiosis II   Cells   MCAT   Khan Academy.mp3", "Sentence": "These are gametes. They have a haploid number. But we started with a haploid number at the beginning of meiosis two. So that's why meiosis two is often compared to mitosis. So let me make this clear. This right over here is meiosis two because it preserves the number of chromosomes, just like mitosis. So this is meiosis two right over here."}, {"video_title": "Phases of meiosis II   Cells   MCAT   Khan Academy.mp3", "Sentence": "So that's why meiosis two is often compared to mitosis. So let me make this clear. This right over here is meiosis two because it preserves the number of chromosomes, just like mitosis. So this is meiosis two right over here. Meiosis two. We started with a haploid number and we finished with a haploid number just like this. And now these gametes are ready for some fertilization."}, {"video_title": "Phases of meiosis II   Cells   MCAT   Khan Academy.mp3", "Sentence": "So this is meiosis two right over here. Meiosis two. We started with a haploid number and we finished with a haploid number just like this. And now these gametes are ready for some fertilization. And it's important to realize now, now these each have two chromosomes and these are not homologous chromosomes. These are coding for different genes. But then they will, each of these, have the potential to fuse with, if this is, say, a sperm cell, then this could fuse with an egg and then together they can create a diploid number of chromosomes."}, {"video_title": "Phases of meiosis II   Cells   MCAT   Khan Academy.mp3", "Sentence": "And now these gametes are ready for some fertilization. And it's important to realize now, now these each have two chromosomes and these are not homologous chromosomes. These are coding for different genes. But then they will, each of these, have the potential to fuse with, if this is, say, a sperm cell, then this could fuse with an egg and then together they can create a diploid number of chromosomes. It could have the full complement of homologous pairs. But that's what these are for. These are for sexual reproduction."}, {"video_title": "Translation (mRNA to protein)   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "So that might be one gene right over there. This might be another gene. That might be a gene right over there. And each of those genes can code for specific polypeptides or specific proteins. And the key question is, is how do you go from the information encoded in these genes, encoded as sequences of DNA, how do you go from that? How do you go from the gene, which is encoded in DNA, how do you go from that to protein, which is made up of polypeptides, which are made up of amino acids? And this is often called the central dogma of biology, but we already saw in the video of transcription that the first step is to go from the gene to messenger RNA, that the RNA, the messenger RNA, you can view it as a transcript, we have rewritten the information now as RNA."}, {"video_title": "Translation (mRNA to protein)   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "And each of those genes can code for specific polypeptides or specific proteins. And the key question is, is how do you go from the information encoded in these genes, encoded as sequences of DNA, how do you go from that? How do you go from the gene, which is encoded in DNA, how do you go from that to protein, which is made up of polypeptides, which are made up of amino acids? And this is often called the central dogma of biology, but we already saw in the video of transcription that the first step is to go from the gene to messenger RNA, that the RNA, the messenger RNA, you can view it as a transcript, we have rewritten the information now as RNA. And then the next step, which we're going to dive into in this video, is going from that messenger RNA to protein, and this process is called translation, because we're literally translating that information into a polypeptide sequence. And you can see a little bit visually here, and this is all review, we covered a lot of this in the video on transcription, and the overview video on transcription and translation is if you look at a eukaryotic cell and the bacteria in a prokaryotic cell, it's analogous, you just don't have the nuclear membrane, and you're not going to do the processing step that I'm going to talk about in a little bit, and we went in detail on the video on transcription. But you start with the DNA, you have your RNA polymerase as the main actor that's able to transcribe the RNA from that."}, {"video_title": "Translation (mRNA to protein)   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "And this is often called the central dogma of biology, but we already saw in the video of transcription that the first step is to go from the gene to messenger RNA, that the RNA, the messenger RNA, you can view it as a transcript, we have rewritten the information now as RNA. And then the next step, which we're going to dive into in this video, is going from that messenger RNA to protein, and this process is called translation, because we're literally translating that information into a polypeptide sequence. And you can see a little bit visually here, and this is all review, we covered a lot of this in the video on transcription, and the overview video on transcription and translation is if you look at a eukaryotic cell and the bacteria in a prokaryotic cell, it's analogous, you just don't have the nuclear membrane, and you're not going to do the processing step that I'm going to talk about in a little bit, and we went in detail on the video on transcription. But you start with the DNA, you have your RNA polymerase as the main actor that's able to transcribe the RNA from that. If we're talking about a eukaryotic cell, what you end up with, we wouldn't call mRNA, we would call that pre-mRNA, pre-mRNA, which then needs to be processed. The introns need to be taken out, we add a cap and a tail here, and if we're talking about a eukaryotic cell we'll then formally call that mRNA. And then it can travel, and this is where we get into the translation step, it can travel to a ribosome, which is where it will be translated into a polypeptide sequence."}, {"video_title": "Translation (mRNA to protein)   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "But you start with the DNA, you have your RNA polymerase as the main actor that's able to transcribe the RNA from that. If we're talking about a eukaryotic cell, what you end up with, we wouldn't call mRNA, we would call that pre-mRNA, pre-mRNA, which then needs to be processed. The introns need to be taken out, we add a cap and a tail here, and if we're talking about a eukaryotic cell we'll then formally call that mRNA. And then it can travel, and this is where we get into the translation step, it can travel to a ribosome, which is where it will be translated into a polypeptide sequence. And you see the analogous thing happening here in this bacterial, or this prokaryotic cell right over here, except you don't see the nuclear membrane, because this is prokaryotic, and you don't see that processing step, so you could just consider this straight, this is mRNA right over there. So the questions are, well how does this thing happen and what even is a ribosome? So let's zoom in a little bit on a ribosome right over here, and there's a couple of interesting actors."}, {"video_title": "Translation (mRNA to protein)   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "And then it can travel, and this is where we get into the translation step, it can travel to a ribosome, which is where it will be translated into a polypeptide sequence. And you see the analogous thing happening here in this bacterial, or this prokaryotic cell right over here, except you don't see the nuclear membrane, because this is prokaryotic, and you don't see that processing step, so you could just consider this straight, this is mRNA right over there. So the questions are, well how does this thing happen and what even is a ribosome? So let's zoom in a little bit on a ribosome right over here, and there's a couple of interesting actors. One, as you can imagine, is the ribosome itself, and it is made up of proteins plus ribosomal RNA. So in the video on transcription we're already familiar with messenger RNA, and we often view RNA like DNA as primarily encoding information, it's acting as a transcript for a gene, but it doesn't have to only encode information. It can also, so this is proteins plus, that's not a T there, this is a plus, it can also provide a functional structural role, which it does in ribosomal RNA."}, {"video_title": "Translation (mRNA to protein)   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "So let's zoom in a little bit on a ribosome right over here, and there's a couple of interesting actors. One, as you can imagine, is the ribosome itself, and it is made up of proteins plus ribosomal RNA. So in the video on transcription we're already familiar with messenger RNA, and we often view RNA like DNA as primarily encoding information, it's acting as a transcript for a gene, but it doesn't have to only encode information. It can also, so this is proteins plus, that's not a T there, this is a plus, it can also provide a functional structural role, which it does in ribosomal RNA. And this big, this looks like an oversized hamburger bun or something right over here, this is super oversimplification of what a ribosome looks like, and I encourage you to do a web search for image searches for ribosomes, and then you can get a more appreciation of how beautiful these structures are and how intricate they actually are. So this is the site, and you can broadly think of the ribosome as having this, this is the top bun and the bottom bun, and it's going to travel along the mRNA from the five prime end to the three prime end, reading it and taking that information and turning it into a sequence of amino acids. So how does that actually happen?"}, {"video_title": "Translation (mRNA to protein)   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "It can also, so this is proteins plus, that's not a T there, this is a plus, it can also provide a functional structural role, which it does in ribosomal RNA. And this big, this looks like an oversized hamburger bun or something right over here, this is super oversimplification of what a ribosome looks like, and I encourage you to do a web search for image searches for ribosomes, and then you can get a more appreciation of how beautiful these structures are and how intricate they actually are. So this is the site, and you can broadly think of the ribosome as having this, this is the top bun and the bottom bun, and it's going to travel along the mRNA from the five prime end to the three prime end, reading it and taking that information and turning it into a sequence of amino acids. So how does that actually happen? Well, each of these three, every three nucleotides, every three nucleotides there, you recall that a codon. So that's a codon, this is, let me do this in a color that is visible on both white and black. So this next three nucleotides is a codon, this is a codon, this is a codon."}, {"video_title": "Translation (mRNA to protein)   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "So how does that actually happen? Well, each of these three, every three nucleotides, every three nucleotides there, you recall that a codon. So that's a codon, this is, let me do this in a color that is visible on both white and black. So this next three nucleotides is a codon, this is a codon, this is a codon. And what's actually, the information is actually encoded in the nitrogenous bases. So this first codon right over here, we see it's AUG, so the nitrogenous bases are adenine, uracil, and guanine. And this has, this codon, it codes for the amino acid, the amino acid methionine, but this is also, this is a good one to know, AUG, let me write it over here."}, {"video_title": "Translation (mRNA to protein)   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "So this next three nucleotides is a codon, this is a codon, this is a codon. And what's actually, the information is actually encoded in the nitrogenous bases. So this first codon right over here, we see it's AUG, so the nitrogenous bases are adenine, uracil, and guanine. And this has, this codon, it codes for the amino acid, the amino acid methionine, but this is also, this is a good one to know, AUG, let me write it over here. AUG, AUG is known as the start codon, start codon. This is where the ribosome will initially attach to start translating that messenger RNA. And so we've, the way that this drawing is, that we are just starting to translate this messenger RNA."}, {"video_title": "Translation (mRNA to protein)   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "And this has, this codon, it codes for the amino acid, the amino acid methionine, but this is also, this is a good one to know, AUG, let me write it over here. AUG, AUG is known as the start codon, start codon. This is where the ribosome will initially attach to start translating that messenger RNA. And so we've, the way that this drawing is, that we are just starting to translate this messenger RNA. So how does that actually happen? How do we get from these three-letter sequences to specific amino acids? Well, let's think about it."}, {"video_title": "Translation (mRNA to protein)   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "And so we've, the way that this drawing is, that we are just starting to translate this messenger RNA. So how does that actually happen? How do we get from these three-letter sequences to specific amino acids? Well, let's think about it. How many possible three-letter sequences are there? Well, there are four possible nitrogenous bases there. So there's four possible, so if you have a codon, and it has three places, there's four possible things that could be in the first place, there's four possible things that could be in the second place, and there's four possible things that could be in the third place."}, {"video_title": "Translation (mRNA to protein)   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "Well, let's think about it. How many possible three-letter sequences are there? Well, there are four possible nitrogenous bases there. So there's four possible, so if you have a codon, and it has three places, there's four possible things that could be in the first place, there's four possible things that could be in the second place, and there's four possible things that could be in the third place. So there are 64, 64 possible permutations. Four times four times four, permutations. So you could think of it, there's 64 different codons, different ways of arranging the A, the U, and the G. And that's good because there are many amino acids."}, {"video_title": "Translation (mRNA to protein)   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "So there's four possible, so if you have a codon, and it has three places, there's four possible things that could be in the first place, there's four possible things that could be in the second place, and there's four possible things that could be in the third place. So there are 64, 64 possible permutations. Four times four times four, permutations. So you could think of it, there's 64 different codons, different ways of arranging the A, the U, and the G. And that's good because there are many amino acids. And this is actually overkill because there's actually 22 standard amino acids, 22 standard amino acids, and 21 that are typically found in eukaryotic cells. So we have more than enough, more than enough permutations to cover the different amino acids. And it's not hard to find tables that will actually show us what the different sequences, what they actually code for."}, {"video_title": "Translation (mRNA to protein)   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "So you could think of it, there's 64 different codons, different ways of arranging the A, the U, and the G. And that's good because there are many amino acids. And this is actually overkill because there's actually 22 standard amino acids, 22 standard amino acids, and 21 that are typically found in eukaryotic cells. So we have more than enough, more than enough permutations to cover the different amino acids. And it's not hard to find tables that will actually show us what the different sequences, what they actually code for. So you can see here, you can take the first letter, the second letter, and then the third letter, figure, look at the different sequences, and you can say, okay, look at that. A, U, G, adenine, uracil, guanine, that codes for methionine right over here. You could, and you could do that with any of them."}, {"video_title": "Translation (mRNA to protein)   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "And it's not hard to find tables that will actually show us what the different sequences, what they actually code for. So you can see here, you can take the first letter, the second letter, and then the third letter, figure, look at the different sequences, and you can say, okay, look at that. A, U, G, adenine, uracil, guanine, that codes for methionine right over here. You could, and you could do that with any of them. You could say cytosine, uracil, uracil, that codes for leucine. And you can see that it's not just one amino acid per codon, that here you have four codons, all code for, all code for leucine. And so it turns out that 61 of the codons, let me write this down, so 61 of the codons of the possible 64 code for amino acids, amino, amino acids, and three play a role that essentially tells the ribosome to stop."}, {"video_title": "Translation (mRNA to protein)   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "You could, and you could do that with any of them. You could say cytosine, uracil, uracil, that codes for leucine. And you can see that it's not just one amino acid per codon, that here you have four codons, all code for, all code for leucine. And so it turns out that 61 of the codons, let me write this down, so 61 of the codons of the possible 64 code for amino acids, amino, amino acids, and three play a role that essentially tells the ribosome to stop. Three codons, three codons are stop codons, and you can see them right over here. UAA, UAG, UGA, that's how the ribosome knows to stop translating. So AUG, that's a start codon, and it codes for methionine, so that lets you know that, well, these polypeptide chains are going to start with methionine, and then these characters tell it where to stop."}, {"video_title": "Translation (mRNA to protein)   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "And so it turns out that 61 of the codons, let me write this down, so 61 of the codons of the possible 64 code for amino acids, amino, amino acids, and three play a role that essentially tells the ribosome to stop. Three codons, three codons are stop codons, and you can see them right over here. UAA, UAG, UGA, that's how the ribosome knows to stop translating. So AUG, that's a start codon, and it codes for methionine, so that lets you know that, well, these polypeptide chains are going to start with methionine, and then these characters tell it where to stop. But how do, how does the amino acid actually get, how do they all get tied up together to form this polypeptide, and how do they get matched up, how do they actually get matched up with the appropriate codon? And that's where we have another RNA-based actor, and this is tRNA. So tRNA, the T stands for transfer, transfer RNA."}, {"video_title": "Translation (mRNA to protein)   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "So AUG, that's a start codon, and it codes for methionine, so that lets you know that, well, these polypeptide chains are going to start with methionine, and then these characters tell it where to stop. But how do, how does the amino acid actually get, how do they all get tied up together to form this polypeptide, and how do they get matched up, how do they actually get matched up with the appropriate codon? And that's where we have another RNA-based actor, and this is tRNA. So tRNA, the T stands for transfer, transfer RNA. There's a bunch of different tRNAs that each can bind to specific amino acids, and on parts of those tRNA, they have what are called anticodons that pair with the appropriate codon. So this tRNA, and that's not what it looks like, I'll show you in a second what it looks like, that's a tRNA molecule, tRNA. At one end of the molecule, it's binding to the appropriate amino acid, methionine, right over here, and then at the other end of the molecule, although it's in the middle of the tRNA actual chain, you have your anticodon, and your anticodon matches up to the appropriate codon."}, {"video_title": "Translation (mRNA to protein)   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "So tRNA, the T stands for transfer, transfer RNA. There's a bunch of different tRNAs that each can bind to specific amino acids, and on parts of those tRNA, they have what are called anticodons that pair with the appropriate codon. So this tRNA, and that's not what it looks like, I'll show you in a second what it looks like, that's a tRNA molecule, tRNA. At one end of the molecule, it's binding to the appropriate amino acid, methionine, right over here, and then at the other end of the molecule, although it's in the middle of the tRNA actual chain, you have your anticodon, and your anticodon matches up to the appropriate codon. And so this is how, they bump into each other the right way, and the ribosome's going to facilitate it, that the AUG is going to be associated with the methionine. And if we look at what tRNA actually looks like, and this is still just a visualization, so this is a strand of tRNA, you get a sense of, okay, it's a sequence of RNA right over here. This is its, I guess you could say, you could think of it as its two-dimensional structure, but then it wraps around itself to form this fairly complex molecule."}, {"video_title": "Translation (mRNA to protein)   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "At one end of the molecule, it's binding to the appropriate amino acid, methionine, right over here, and then at the other end of the molecule, although it's in the middle of the tRNA actual chain, you have your anticodon, and your anticodon matches up to the appropriate codon. And so this is how, they bump into each other the right way, and the ribosome's going to facilitate it, that the AUG is going to be associated with the methionine. And if we look at what tRNA actually looks like, and this is still just a visualization, so this is a strand of tRNA, you get a sense of, okay, it's a sequence of RNA right over here. This is its, I guess you could say, you could think of it as its two-dimensional structure, but then it wraps around itself to form this fairly complex molecule. And the anticodon, which is right here, it's kind of in the middle of the sequence, it forms the basis for this end of the molecule. That's the part that's going to pair with the codon on the mRNA. And then at the other end of the molecule, at the other end of the molecule is where you actually bind to the appropriate amino acid."}, {"video_title": "Translation (mRNA to protein)   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "This is its, I guess you could say, you could think of it as its two-dimensional structure, but then it wraps around itself to form this fairly complex molecule. And the anticodon, which is right here, it's kind of in the middle of the sequence, it forms the basis for this end of the molecule. That's the part that's going to pair with the codon on the mRNA. And then at the other end of the molecule, at the other end of the molecule is where you actually bind to the appropriate amino acid. So I know what you're thinking. All right, I see that the ribosome, it knows where to start. It starts at the start codon."}, {"video_title": "Translation (mRNA to protein)   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "And then at the other end of the molecule, at the other end of the molecule is where you actually bind to the appropriate amino acid. So I know what you're thinking. All right, I see that the ribosome, it knows where to start. It starts at the start codon. I see how the appropriate tRNA can bring the appropriate amino acid, but how does the chain actually form? And you can view this in three steps, and associated with those three steps are three sites on the ribosome. And the three sites, we call this the A site."}, {"video_title": "Translation (mRNA to protein)   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "It starts at the start codon. I see how the appropriate tRNA can bring the appropriate amino acid, but how does the chain actually form? And you can view this in three steps, and associated with those three steps are three sites on the ribosome. And the three sites, we call this the A site. A, I don't know if you're gonna be able to see it if I write it in black. A, or yellow, all right, let me write it in blue. So that is the A site."}, {"video_title": "Translation (mRNA to protein)   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "And the three sites, we call this the A site. A, I don't know if you're gonna be able to see it if I write it in black. A, or yellow, all right, let me write it in blue. So that is the A site. This is the P site. And this is the E site. And I'll talk in a second why we call them A, P, and E. So the A site is where the appropriate tRNA initially bounds, the tRNA that's bound to an amino acid."}, {"video_title": "Translation (mRNA to protein)   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "So that is the A site. This is the P site. And this is the E site. And I'll talk in a second why we call them A, P, and E. So the A site is where the appropriate tRNA initially bounds, the tRNA that's bound to an amino acid. And so you can see we're starting the translation process. The next thing that's going to happen is another tRNA, the one that matches, that has an anticodon that matches the UAU, that's going to bond over here on the A site. And it's bringing the appropriate amino acid with it."}, {"video_title": "Translation (mRNA to protein)   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "And I'll talk in a second why we call them A, P, and E. So the A site is where the appropriate tRNA initially bounds, the tRNA that's bound to an amino acid. And so you can see we're starting the translation process. The next thing that's going to happen is another tRNA, the one that matches, that has an anticodon that matches the UAU, that's going to bond over here on the A site. And it's bringing the appropriate amino acid with it. It's bringing the tyrosine with it. So why is that called the A site? Well, A stands for aminoacyl, or an easy way to remember it, it's the tRNA, it's the place where the tRNA that's bound to an amino acid, just one amino acid, is going to bind on the ribosome."}, {"video_title": "Translation (mRNA to protein)   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "And it's bringing the appropriate amino acid with it. It's bringing the tyrosine with it. So why is that called the A site? Well, A stands for aminoacyl, or an easy way to remember it, it's the tRNA, it's the place where the tRNA that's bound to an amino acid, just one amino acid, is going to bind on the ribosome. And so once that happens, once this character comes here, let me draw that. Once this character comes right over here, this is going to be AUA, and it's bound to the tyrosine, well then you can have a peptide bond form between the two amino acids, and the ribosome, and the ribosome itself, can move to the right. So this tRNA will then be in the E site, this tRNA will then be in the P site, and then the A site will be open for another amino acid carrying tRNA."}, {"video_title": "Translation (mRNA to protein)   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "Well, A stands for aminoacyl, or an easy way to remember it, it's the tRNA, it's the place where the tRNA that's bound to an amino acid, just one amino acid, is going to bind on the ribosome. And so once that happens, once this character comes here, let me draw that. Once this character comes right over here, this is going to be AUA, and it's bound to the tyrosine, well then you can have a peptide bond form between the two amino acids, and the ribosome, and the ribosome itself, can move to the right. So this tRNA will then be in the E site, this tRNA will then be in the P site, and then the A site will be open for another amino acid carrying tRNA. So what does P and E, what do the P and E site stand for? Well, you can see a little bit more clearly right over here. So the P site is where you have the polypeptide chain actually forming."}, {"video_title": "Translation (mRNA to protein)   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "So this tRNA will then be in the E site, this tRNA will then be in the P site, and then the A site will be open for another amino acid carrying tRNA. So what does P and E, what do the P and E site stand for? Well, you can see a little bit more clearly right over here. So the P site is where you have the polypeptide chain actually forming. And so the P site is often, well, one way to remember it is, is that's where you have the polypeptide chain, and now you have a new A site, where you can bring in a new amino acid, and then the ribosome is going to shift, is once this is bound, the ribosome, the peptide bond forms, and then the ribosome can shift to the right. When the ribosome shifts to the right, we're gonna be in this position, where the thing that was here, that was in the A site, now the polypeptide is attached to it, it is going to now be in the P site, and the thing that was in the P site is now going to be in the E site. It is now ready to exit, and that's why it's called the E site, because that's the site from which you exit."}, {"video_title": "Translation (mRNA to protein)   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "So the P site is where you have the polypeptide chain actually forming. And so the P site is often, well, one way to remember it is, is that's where you have the polypeptide chain, and now you have a new A site, where you can bring in a new amino acid, and then the ribosome is going to shift, is once this is bound, the ribosome, the peptide bond forms, and then the ribosome can shift to the right. When the ribosome shifts to the right, we're gonna be in this position, where the thing that was here, that was in the A site, now the polypeptide is attached to it, it is going to now be in the P site, and the thing that was in the P site is now going to be in the E site. It is now ready to exit, and that's why it's called the E site, because that's the site from which you exit. And so this is going to keep happening until we get to one of the stop codons. And when you get to one of the stop codons, then the appropriate polypeptide is going to be released, and we will have created this thing that could either be a protein or part of a protein. So this is very exciting, because this is happening in your cells as we speak."}, {"video_title": "Importance of water for life   Chemistry of life   AP Biology   Khan Academy.mp3", "Sentence": "When we look out into the cosmos for alien life, many folks look for signs of water on moons or planets. And that's because life as we know it is dependent on water. And to understand that, we just have to take a closer look at some of the properties of water. So what you see here are some molecules of water. This might be a review for you. Every water molecule has one oxygen atom. And it is bonded to two hydrogens."}, {"video_title": "Importance of water for life   Chemistry of life   AP Biology   Khan Academy.mp3", "Sentence": "So what you see here are some molecules of water. This might be a review for you. Every water molecule has one oxygen atom. And it is bonded to two hydrogens. So that is a hydrogen. And that is a hydrogen as well. And the nature of that bond, it is a covalent bond, which means that the oxygen shares electrons with each of the hydrogen atoms."}, {"video_title": "Importance of water for life   Chemistry of life   AP Biology   Khan Academy.mp3", "Sentence": "And it is bonded to two hydrogens. So that is a hydrogen. And that is a hydrogen as well. And the nature of that bond, it is a covalent bond, which means that the oxygen shares electrons with each of the hydrogen atoms. But oxygen is more electronegative. And that's just a fancy way of saying that even though those electrons are shared, they're going to be spending more time around the oxygen than around the hydrogens. One way to think about it is oxygen likes to hog electrons more than hydrogen does."}, {"video_title": "Importance of water for life   Chemistry of life   AP Biology   Khan Academy.mp3", "Sentence": "And the nature of that bond, it is a covalent bond, which means that the oxygen shares electrons with each of the hydrogen atoms. But oxygen is more electronegative. And that's just a fancy way of saying that even though those electrons are shared, they're going to be spending more time around the oxygen than around the hydrogens. One way to think about it is oxygen likes to hog electrons more than hydrogen does. And since the electrons will spend more time around the oxygen than around the hydrogen, and because it's a bent molecule with the hydrogens on one side of the molecule, what happens is the side where the oxygen is, where the electrons spend more time, that gets a partially negative charge. So this is the lowercase Greek letter delta. That just means partially negative charge."}, {"video_title": "Importance of water for life   Chemistry of life   AP Biology   Khan Academy.mp3", "Sentence": "One way to think about it is oxygen likes to hog electrons more than hydrogen does. And since the electrons will spend more time around the oxygen than around the hydrogen, and because it's a bent molecule with the hydrogens on one side of the molecule, what happens is the side where the oxygen is, where the electrons spend more time, that gets a partially negative charge. So this is the lowercase Greek letter delta. That just means partially negative charge. And then the sides where the hydrogens are, those acquire a partial positive charge. And so what you see here is that a water molecule is not charged in aggregate, but either side has a partial charge. So it is a polar molecule."}, {"video_title": "Importance of water for life   Chemistry of life   AP Biology   Khan Academy.mp3", "Sentence": "That just means partially negative charge. And then the sides where the hydrogens are, those acquire a partial positive charge. And so what you see here is that a water molecule is not charged in aggregate, but either side has a partial charge. So it is a polar molecule. And so you can imagine when you put a bunch of water molecules together, what might happen? Well, the partially positive side of one water molecule, where the hydrogens are, would be attracted to the partially negative side of another water molecule. And so they would be attracted."}, {"video_title": "Importance of water for life   Chemistry of life   AP Biology   Khan Academy.mp3", "Sentence": "So it is a polar molecule. And so you can imagine when you put a bunch of water molecules together, what might happen? Well, the partially positive side of one water molecule, where the hydrogens are, would be attracted to the partially negative side of another water molecule. And so they would be attracted. And this is known as a hydrogen-hydrogen-hydrogen bond. And I could keep drawing that. This is going to be partially positive here."}, {"video_title": "Importance of water for life   Chemistry of life   AP Biology   Khan Academy.mp3", "Sentence": "And so they would be attracted. And this is known as a hydrogen-hydrogen-hydrogen bond. And I could keep drawing that. This is going to be partially positive here. This is going to be partially negative. They will attract. This oxygen end is going to be attracted to that hydrogen end."}, {"video_title": "Importance of water for life   Chemistry of life   AP Biology   Khan Academy.mp3", "Sentence": "This is going to be partially positive here. This is going to be partially negative. They will attract. This oxygen end is going to be attracted to that hydrogen end. This oxygen end is going to be attracted to that hydrogen end as well. And so it's this hydrogen bonding that gives water a lot of the properties that make it special, as far as we know, for harboring life or for even allowing life to be possible. Life, as we understand it, needs a fluid environment."}, {"video_title": "Importance of water for life   Chemistry of life   AP Biology   Khan Academy.mp3", "Sentence": "This oxygen end is going to be attracted to that hydrogen end. This oxygen end is going to be attracted to that hydrogen end as well. And so it's this hydrogen bonding that gives water a lot of the properties that make it special, as far as we know, for harboring life or for even allowing life to be possible. Life, as we understand it, needs a fluid environment. Things move around and bump into each other. And it's these hydrogen bonds, when the temperature and conditions are appropriate, that allow water to be in that liquid form, where they're strong enough so that the water stays together, but they're weak enough so that they allow the water molecules to flow past each other. And not only does it provide a good fluid environment, it's a very good solvent."}, {"video_title": "Importance of water for life   Chemistry of life   AP Biology   Khan Academy.mp3", "Sentence": "Life, as we understand it, needs a fluid environment. Things move around and bump into each other. And it's these hydrogen bonds, when the temperature and conditions are appropriate, that allow water to be in that liquid form, where they're strong enough so that the water stays together, but they're weak enough so that they allow the water molecules to flow past each other. And not only does it provide a good fluid environment, it's a very good solvent. Water is often known as the universal solvent. But it's worth putting a disclaimer here. Even though people say it is a universal solvent, that does not mean that it dissolves everything."}, {"video_title": "Importance of water for life   Chemistry of life   AP Biology   Khan Academy.mp3", "Sentence": "And not only does it provide a good fluid environment, it's a very good solvent. Water is often known as the universal solvent. But it's worth putting a disclaimer here. Even though people say it is a universal solvent, that does not mean that it dissolves everything. Water does dissolve more things in its liquid state than anything else we know about. But there are many molecules that it cannot dissolve well. The things that it does dissolve well are polar molecules or things that have a charge."}, {"video_title": "Importance of water for life   Chemistry of life   AP Biology   Khan Academy.mp3", "Sentence": "Even though people say it is a universal solvent, that does not mean that it dissolves everything. Water does dissolve more things in its liquid state than anything else we know about. But there are many molecules that it cannot dissolve well. The things that it does dissolve well are polar molecules or things that have a charge. For example, when sodium chloride dissolves in water, a sodium ion is positive. So that is positively charged. And so you could imagine it might be attracted to the side of the water molecules where the oxygen is, but it dissolves well."}, {"video_title": "Importance of water for life   Chemistry of life   AP Biology   Khan Academy.mp3", "Sentence": "The things that it does dissolve well are polar molecules or things that have a charge. For example, when sodium chloride dissolves in water, a sodium ion is positive. So that is positively charged. And so you could imagine it might be attracted to the side of the water molecules where the oxygen is, but it dissolves well. But things that don't have charge don't tend to dissolve well in water. But even the property that there are certain things that it does not dissolve is also good for life. Later on in biology, we're going to study phospholipid bilayers, where you have these molecules where one end is hydrophilic, which means it's attracted to water molecules, and then the other ends are hydrophobic, which means they're not attracted to water molecules."}, {"video_title": "Importance of water for life   Chemistry of life   AP Biology   Khan Academy.mp3", "Sentence": "And so you could imagine it might be attracted to the side of the water molecules where the oxygen is, but it dissolves well. But things that don't have charge don't tend to dissolve well in water. But even the property that there are certain things that it does not dissolve is also good for life. Later on in biology, we're going to study phospholipid bilayers, where you have these molecules where one end is hydrophilic, which means it's attracted to water molecules, and then the other ends are hydrophobic, which means they're not attracted to water molecules. And many evolutionary biologists believe that this property of having one side that's hydrophilic and one side that's hydrophobic would have allowed these molecules to start collecting into membranes, eventually forming these spherical membranes, which could be the containers for early cellular life. Now, another property of water which makes it very suitable for life is its high heat capacity. Sometimes you'll hear people say it has a high specific heat."}, {"video_title": "Importance of water for life   Chemistry of life   AP Biology   Khan Academy.mp3", "Sentence": "Later on in biology, we're going to study phospholipid bilayers, where you have these molecules where one end is hydrophilic, which means it's attracted to water molecules, and then the other ends are hydrophobic, which means they're not attracted to water molecules. And many evolutionary biologists believe that this property of having one side that's hydrophilic and one side that's hydrophobic would have allowed these molecules to start collecting into membranes, eventually forming these spherical membranes, which could be the containers for early cellular life. Now, another property of water which makes it very suitable for life is its high heat capacity. Sometimes you'll hear people say it has a high specific heat. And a specific heat is the amount of energy needed to raise one gram of water by one degree Celsius. And you might say, why does that matter for life? Well, many life forms can only operate within a certain range of temperatures."}, {"video_title": "Importance of water for life   Chemistry of life   AP Biology   Khan Academy.mp3", "Sentence": "Sometimes you'll hear people say it has a high specific heat. And a specific heat is the amount of energy needed to raise one gram of water by one degree Celsius. And you might say, why does that matter for life? Well, many life forms can only operate within a certain range of temperatures. And so if it was really easy to raise the temperature of water really high or very low temperatures very fast, well, that would make it much harder for life to operate within water or even life to be made up of water. A related idea to this is that water also has a high heat of vaporization. We talk more about this in detail in other videos."}, {"video_title": "Importance of water for life   Chemistry of life   AP Biology   Khan Academy.mp3", "Sentence": "Well, many life forms can only operate within a certain range of temperatures. And so if it was really easy to raise the temperature of water really high or very low temperatures very fast, well, that would make it much harder for life to operate within water or even life to be made up of water. A related idea to this is that water also has a high heat of vaporization. We talk more about this in detail in other videos. But this is talking about how much energy does it take for water to go from its liquid form to its gas form. And this is proven valuable in many life forms for a form of cooling, where the vaporization of water, evaporative cooling, can take heat away from an organism so that it doesn't overheat. Other properties that are important about water include cohesion and adhesion."}, {"video_title": "Importance of water for life   Chemistry of life   AP Biology   Khan Academy.mp3", "Sentence": "We talk more about this in detail in other videos. But this is talking about how much energy does it take for water to go from its liquid form to its gas form. And this is proven valuable in many life forms for a form of cooling, where the vaporization of water, evaporative cooling, can take heat away from an organism so that it doesn't overheat. Other properties that are important about water include cohesion and adhesion. Cohesion is the property of water molecules that it is attracted to other water molecules. And you saw it here with the hydrogen bonds. But when you look at a macro scale, you'll see things like water droplets form."}, {"video_title": "Importance of water for life   Chemistry of life   AP Biology   Khan Academy.mp3", "Sentence": "Other properties that are important about water include cohesion and adhesion. Cohesion is the property of water molecules that it is attracted to other water molecules. And you saw it here with the hydrogen bonds. But when you look at a macro scale, you'll see things like water droplets form. You've all seen water droplets or dew droplets. These droplets can form if not for the cohesion of water. And even one drop can be an environment in which thousands of microorganisms can live."}, {"video_title": "Importance of water for life   Chemistry of life   AP Biology   Khan Academy.mp3", "Sentence": "But when you look at a macro scale, you'll see things like water droplets form. You've all seen water droplets or dew droplets. These droplets can form if not for the cohesion of water. And even one drop can be an environment in which thousands of microorganisms can live. Adhesion is the property of water where it can adhere to other things. You might have seen this in a glass test tube, where it looks like the water is kind of crawling up the top of the sides. And that's because some of the polarity of the glass molecules of the test tube."}, {"video_title": "Importance of water for life   Chemistry of life   AP Biology   Khan Academy.mp3", "Sentence": "And even one drop can be an environment in which thousands of microorganisms can live. Adhesion is the property of water where it can adhere to other things. You might have seen this in a glass test tube, where it looks like the water is kind of crawling up the top of the sides. And that's because some of the polarity of the glass molecules of the test tube. But this property, along with the cohesion, is what allows water to transport nutrients, say, from the roots of a tree all the way to the top of a tree. These properties are also in action in our own blood vessels, when you get to the really small blood vessels, the capillaries. And that is called capillaries because you have capillary action of water, which is due to its cohesion and its adhesion."}, {"video_title": "Importance of water for life   Chemistry of life   AP Biology   Khan Academy.mp3", "Sentence": "And that's because some of the polarity of the glass molecules of the test tube. But this property, along with the cohesion, is what allows water to transport nutrients, say, from the roots of a tree all the way to the top of a tree. These properties are also in action in our own blood vessels, when you get to the really small blood vessels, the capillaries. And that is called capillaries because you have capillary action of water, which is due to its cohesion and its adhesion. A last property of water, and this is not an exhaustive list, is that it is less dense as a solid. So another way to think about it is ice, which is solid water, is less dense than liquid water. Now, you might be thinking, why does that matter for life?"}, {"video_title": "Importance of water for life   Chemistry of life   AP Biology   Khan Academy.mp3", "Sentence": "And that is called capillaries because you have capillary action of water, which is due to its cohesion and its adhesion. A last property of water, and this is not an exhaustive list, is that it is less dense as a solid. So another way to think about it is ice, which is solid water, is less dense than liquid water. Now, you might be thinking, why does that matter for life? Well, imagine the environments where we think life first arose. If you imagine some type of a pond, and this is the cross-section of it, if ice was more dense than liquid water, and for many substances that is the case, the solid form tends to be more dense, then what would happen? If it's cold up here in the air, say in the winter, then this part would freeze."}, {"video_title": "Importance of water for life   Chemistry of life   AP Biology   Khan Academy.mp3", "Sentence": "Now, you might be thinking, why does that matter for life? Well, imagine the environments where we think life first arose. If you imagine some type of a pond, and this is the cross-section of it, if ice was more dense than liquid water, and for many substances that is the case, the solid form tends to be more dense, then what would happen? If it's cold up here in the air, say in the winter, then this part would freeze. But then as it got more dense, it would sink to the bottom right over there. Then the next surface water would freeze and sink to the bottom. And then over time, the entire lake or the entire pond would freeze over."}, {"video_title": "Importance of water for life   Chemistry of life   AP Biology   Khan Academy.mp3", "Sentence": "If it's cold up here in the air, say in the winter, then this part would freeze. But then as it got more dense, it would sink to the bottom right over there. Then the next surface water would freeze and sink to the bottom. And then over time, the entire lake or the entire pond would freeze over. And life would not be able to live in that pond because when water freezes, it breaks membrane-bound structures as we know it. And so that would not be suitable for life. But because ice is less dense than water, what typically happens is just that top layer freezes, and then it'll freeze down as things get colder and colder."}, {"video_title": "Importance of water for life   Chemistry of life   AP Biology   Khan Academy.mp3", "Sentence": "And then over time, the entire lake or the entire pond would freeze over. And life would not be able to live in that pond because when water freezes, it breaks membrane-bound structures as we know it. And so that would not be suitable for life. But because ice is less dense than water, what typically happens is just that top layer freezes, and then it'll freeze down as things get colder and colder. But you have an entire environment where life can continue to thrive even when the air is much colder than what is suitable for life. And because of water's high specific heat, that temperature variation in that water is going to be much less than the temperature variation outside of the water, either in the air or on the land. So this is just an introduction, but hopefully it makes you appreciate water a little more."}, {"video_title": "Importance of water for life   Chemistry of life   AP Biology   Khan Academy.mp3", "Sentence": "But because ice is less dense than water, what typically happens is just that top layer freezes, and then it'll freeze down as things get colder and colder. But you have an entire environment where life can continue to thrive even when the air is much colder than what is suitable for life. And because of water's high specific heat, that temperature variation in that water is going to be much less than the temperature variation outside of the water, either in the air or on the land. So this is just an introduction, but hopefully it makes you appreciate water a little more. And remember, and I've said this in other videos, we are mostly water. One way to think about it is that each of us is made up of trillions of cells which are primarily made up of water and exist in a water-based environment. They coordinate with each other and eventually have emergent complexity that thinks that it is a sentient being like each of us."}, {"video_title": "Fertilization terminology gametes, zygotes, haploid, diploid   MCAT   Khan Academy.mp3", "Sentence": "So that's a sperm cell, and this is an egg cell, or we could call this an ovum, an ovum. And even this scene depicted right over here, this is the end of an epic competition, because this sperm cell is one of two to 300 million that is vying for this ovum. So there's two to 300 million of these characters, and they're all vying for this ovum. And the one that you see that's about to fuse for it, this is the winner of this incredibly, this is, remember, two to 300, 200 million to 300 million sperm are trying to get here. So this is a major victory, and to some degree, we should all feel pretty good about ourselves, because we are all the byproduct of that one in 200 to 300 million sperm cells that won this race getting to our mother's ovum. So the sperm cell came from our father, the egg cell, this is all happening, this is all happening inside of our mothers, the egg cell is from our mother. Now, once this happens, let's talk a little bit about the terminology."}, {"video_title": "Fertilization terminology gametes, zygotes, haploid, diploid   MCAT   Khan Academy.mp3", "Sentence": "And the one that you see that's about to fuse for it, this is the winner of this incredibly, this is, remember, two to 300, 200 million to 300 million sperm are trying to get here. So this is a major victory, and to some degree, we should all feel pretty good about ourselves, because we are all the byproduct of that one in 200 to 300 million sperm cells that won this race getting to our mother's ovum. So the sperm cell came from our father, the egg cell, this is all happening, this is all happening inside of our mothers, the egg cell is from our mother. Now, once this happens, let's talk a little bit about the terminology. So once these two fuse, we call this, or the process of them fusing, we call that fertilization. Fertilize, fertilization. And it produces a cell that then differentiates into all of the cells of our body."}, {"video_title": "Fertilization terminology gametes, zygotes, haploid, diploid   MCAT   Khan Academy.mp3", "Sentence": "Now, once this happens, let's talk a little bit about the terminology. So once these two fuse, we call this, or the process of them fusing, we call that fertilization. Fertilize, fertilization. And it produces a cell that then differentiates into all of the cells of our body. So you can imagine this is an important process. So let's make sure that we understand the different terminology, the different words for the different things that are acting in this process. So each of these sex cells, I guess we could say, the sperm cell and the ovum, these are each called gametes."}, {"video_title": "Fertilization terminology gametes, zygotes, haploid, diploid   MCAT   Khan Academy.mp3", "Sentence": "And it produces a cell that then differentiates into all of the cells of our body. So you can imagine this is an important process. So let's make sure that we understand the different terminology, the different words for the different things that are acting in this process. So each of these sex cells, I guess we could say, the sperm cell and the ovum, these are each called gametes. So this right over here is a gamete, is a gamete, and the ovum is a gamete, the egg cell is also a gamete. And as we'll see, each gamete has half the number of chromosomes as your body cells, or most of your, or the somatic cells in your body, so outside of your sex cells that might be in your ovaries or your testes, depending on whether you're male or female, these have half the number. So let's dig a little bit deeper into what I mean there."}, {"video_title": "Fertilization terminology gametes, zygotes, haploid, diploid   MCAT   Khan Academy.mp3", "Sentence": "So each of these sex cells, I guess we could say, the sperm cell and the ovum, these are each called gametes. So this right over here is a gamete, is a gamete, and the ovum is a gamete, the egg cell is also a gamete. And as we'll see, each gamete has half the number of chromosomes as your body cells, or most of your, or the somatic cells in your body, so outside of your sex cells that might be in your ovaries or your testes, depending on whether you're male or female, these have half the number. So let's dig a little bit deeper into what I mean there. So I'm gonna, so let's just do a blowup of this sperm, of the sperm cell right over here. So blowup of the sperm cell. And I'm not gonna draw it to scale."}, {"video_title": "Fertilization terminology gametes, zygotes, haploid, diploid   MCAT   Khan Academy.mp3", "Sentence": "So let's dig a little bit deeper into what I mean there. So I'm gonna, so let's just do a blowup of this sperm, of the sperm cell right over here. So blowup of the sperm cell. And I'm not gonna draw it to scale. You see the sperm cell is much smaller than the egg cell, but just to give a sense, so let me draw the nucleus of this sperm cell, so just like that. If we're talking about a human being, and I'm assuming you're a human being, so that might be of interest to you, this will have 23 chromosomes from your father. So let's do them, one, two, three, four, five, six, seven, eight, nine, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22."}, {"video_title": "Fertilization terminology gametes, zygotes, haploid, diploid   MCAT   Khan Academy.mp3", "Sentence": "And I'm not gonna draw it to scale. You see the sperm cell is much smaller than the egg cell, but just to give a sense, so let me draw the nucleus of this sperm cell, so just like that. If we're talking about a human being, and I'm assuming you're a human being, so that might be of interest to you, this will have 23 chromosomes from your father. So let's do them, one, two, three, four, five, six, seven, eight, nine, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22. And for the 23rd one, that's going to be your sex-determining chromosome. So if your father contributes an X, you are going to be female. If your father contributes a Y, you are going to be male."}, {"video_title": "Fertilization terminology gametes, zygotes, haploid, diploid   MCAT   Khan Academy.mp3", "Sentence": "So let's do them, one, two, three, four, five, six, seven, eight, nine, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22. And for the 23rd one, that's going to be your sex-determining chromosome. So if your father contributes an X, you are going to be female. If your father contributes a Y, you are going to be male. So this is, these are the chromosomes in the male gamete, or I guess I say the gamete that your father's contributing, the sperm. So this is a gamete right over here. And that's going to fuse with the egg, the ovum that your mother is contributing."}, {"video_title": "Fertilization terminology gametes, zygotes, haploid, diploid   MCAT   Khan Academy.mp3", "Sentence": "If your father contributes a Y, you are going to be male. So this is, these are the chromosomes in the male gamete, or I guess I say the gamete that your father's contributing, the sperm. So this is a gamete right over here. And that's going to fuse with the egg, the ovum that your mother is contributing. And once again, I'm not drawing that to scale. So this is the egg, and let me draw its nucleus. So that's its nucleus."}, {"video_title": "Fertilization terminology gametes, zygotes, haploid, diploid   MCAT   Khan Academy.mp3", "Sentence": "And that's going to fuse with the egg, the ovum that your mother is contributing. And once again, I'm not drawing that to scale. So this is the egg, and let me draw its nucleus. So that's its nucleus. Once again, none of this is drawn to scale. And your mother is also going to contribute 23 chromosomes. So one, two, three, four, five, six, seven, eight, nine, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22."}, {"video_title": "Fertilization terminology gametes, zygotes, haploid, diploid   MCAT   Khan Academy.mp3", "Sentence": "So that's its nucleus. Once again, none of this is drawn to scale. And your mother is also going to contribute 23 chromosomes. So one, two, three, four, five, six, seven, eight, nine, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22. And then she will contribute an X chromosome for the sex-determining. So your sex-determining chromosomes are going to be XY. You're going to be male."}, {"video_title": "Fertilization terminology gametes, zygotes, haploid, diploid   MCAT   Khan Academy.mp3", "Sentence": "So one, two, three, four, five, six, seven, eight, nine, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22. And then she will contribute an X chromosome for the sex-determining. So your sex-determining chromosomes are going to be XY. You're going to be male. If this was XX, you're going to be female. So this is also a gamete here. So a gamete is the general term for either a sperm or an egg."}, {"video_title": "Fertilization terminology gametes, zygotes, haploid, diploid   MCAT   Khan Academy.mp3", "Sentence": "You're going to be male. If this was XX, you're going to be female. So this is also a gamete here. So a gamete is the general term for either a sperm or an egg. Now once these two things are fused, so once they are fused, what do we have? Once they're fused, then we're going to have a, you could say a fertilized egg, but we're going to call that a zygote. So let me draw that."}, {"video_title": "Fertilization terminology gametes, zygotes, haploid, diploid   MCAT   Khan Academy.mp3", "Sentence": "So a gamete is the general term for either a sperm or an egg. Now once these two things are fused, so once they are fused, what do we have? Once they're fused, then we're going to have a, you could say a fertilized egg, but we're going to call that a zygote. So let me draw that. I'll do this in a new color. I'm running out of space, and I want this all to fit on the same piece, all on the same screen. So I'll draw it not quite at scale."}, {"video_title": "Fertilization terminology gametes, zygotes, haploid, diploid   MCAT   Khan Academy.mp3", "Sentence": "So let me draw that. I'll do this in a new color. I'm running out of space, and I want this all to fit on the same piece, all on the same screen. So I'll draw it not quite at scale. And so let me draw the nucleus of the zygote. I'm going to make the nucleus fairly large so that we can focus on the chromosomes in it. Once again, none of this is drawn to scale."}, {"video_title": "Fertilization terminology gametes, zygotes, haploid, diploid   MCAT   Khan Academy.mp3", "Sentence": "So I'll draw it not quite at scale. And so let me draw the nucleus of the zygote. I'm going to make the nucleus fairly large so that we can focus on the chromosomes in it. Once again, none of this is drawn to scale. So you're going to have the 23 chromosomes from your father. So let me do that. One, two, three, four, five, six, seven, eight, nine, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, and 23."}, {"video_title": "Fertilization terminology gametes, zygotes, haploid, diploid   MCAT   Khan Academy.mp3", "Sentence": "Once again, none of this is drawn to scale. So you're going to have the 23 chromosomes from your father. So let me do that. One, two, three, four, five, six, seven, eight, nine, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, and 23. And then the 23 chromosomes from your mother. One, two, three, four, five, six, seven, eight, nine, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, and 23. So you got that X chromosome from your mother."}, {"video_title": "Fertilization terminology gametes, zygotes, haploid, diploid   MCAT   Khan Academy.mp3", "Sentence": "One, two, three, four, five, six, seven, eight, nine, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, and 23. And then the 23 chromosomes from your mother. One, two, three, four, five, six, seven, eight, nine, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, and 23. So you got that X chromosome from your mother. And as you might have noticed, I've drawn them in pairs. So you now have a total, let me make it clear. You have 23 chromosomes here."}, {"video_title": "Fertilization terminology gametes, zygotes, haploid, diploid   MCAT   Khan Academy.mp3", "Sentence": "So you got that X chromosome from your mother. And as you might have noticed, I've drawn them in pairs. So you now have a total, let me make it clear. You have 23 chromosomes here. 23 chromosomes, chromosomes in the sperm. You have 23 chromosomes, 23 chromosomes in the egg. And now you have 46 chromosomes in the fertilized egg."}, {"video_title": "Fertilization terminology gametes, zygotes, haploid, diploid   MCAT   Khan Academy.mp3", "Sentence": "You have 23 chromosomes here. 23 chromosomes, chromosomes in the sperm. You have 23 chromosomes, 23 chromosomes in the egg. And now you have 46 chromosomes in the fertilized egg. 46 chromosomes. And now that we have a full contingent of chromosomes, and then this cell can now keep replicating, keep splitting and differentiating into all of what makes you you, we call this right over here, we call this a zygote. Zygote."}, {"video_title": "Fertilization terminology gametes, zygotes, haploid, diploid   MCAT   Khan Academy.mp3", "Sentence": "And now you have 46 chromosomes in the fertilized egg. 46 chromosomes. And now that we have a full contingent of chromosomes, and then this cell can now keep replicating, keep splitting and differentiating into all of what makes you you, we call this right over here, we call this a zygote. Zygote. So one way to think about it, the gametes are the sex cells that have half the number of chromosomes. And the zygote is the cell that's now ready to differentiate into an actual organism that has double the number, that has a full contingency of chromosomes, that has 46 chromosomes. And you see I made them in pairs."}, {"video_title": "Fertilization terminology gametes, zygotes, haploid, diploid   MCAT   Khan Academy.mp3", "Sentence": "Zygote. So one way to think about it, the gametes are the sex cells that have half the number of chromosomes. And the zygote is the cell that's now ready to differentiate into an actual organism that has double the number, that has a full contingency of chromosomes, that has 46 chromosomes. And you see I made them in pairs. And these pairs, we call these homologous pairs. And in each of these pairs, this is a pair of homologous chromosomes. Pair of homologous chromosomes."}, {"video_title": "Fertilization terminology gametes, zygotes, haploid, diploid   MCAT   Khan Academy.mp3", "Sentence": "And you see I made them in pairs. And these pairs, we call these homologous pairs. And in each of these pairs, this is a pair of homologous chromosomes. Pair of homologous chromosomes. So what does that mean? Well, that means that in general, these two chromosomes, you've got one from your father, one from your mother, they code for the same things. They code for the same proteins."}, {"video_title": "Fertilization terminology gametes, zygotes, haploid, diploid   MCAT   Khan Academy.mp3", "Sentence": "Pair of homologous chromosomes. So what does that mean? Well, that means that in general, these two chromosomes, you've got one from your father, one from your mother, they code for the same things. They code for the same proteins. But there are different variants of how they code for those proteins, those traits that you have. So gross oversimplification is, let's say that there was a gene, let's say that there is a gene on that one from your father that helps code for hair color. Well, there would be a similar, there would be another variant of that gene on the chromosome from your mother that helps code for hair color as well."}, {"video_title": "Fertilization terminology gametes, zygotes, haploid, diploid   MCAT   Khan Academy.mp3", "Sentence": "They code for the same proteins. But there are different variants of how they code for those proteins, those traits that you have. So gross oversimplification is, let's say that there was a gene, let's say that there is a gene on that one from your father that helps code for hair color. Well, there would be a similar, there would be another variant of that gene on the chromosome from your mother that helps code for hair color as well. So these are homologous chromosomes. These two chromosomes code in general for the same things. And so the zygote now has, you could say it has 46 chromosomes, or you could say it has 23 pairs of homologous chromosomes."}, {"video_title": "Fertilization terminology gametes, zygotes, haploid, diploid   MCAT   Khan Academy.mp3", "Sentence": "Well, there would be a similar, there would be another variant of that gene on the chromosome from your mother that helps code for hair color as well. So these are homologous chromosomes. These two chromosomes code in general for the same things. And so the zygote now has, you could say it has 46 chromosomes, or you could say it has 23 pairs of homologous chromosomes. And this is, once again, this is the case for human beings. If we're talking about some other species, instead of 23 pairs of homologous chromosomes, or 46 chromosomes in total, you might be talking about 10 pairs of homologous chromosomes with 20 chromosomes in general. Now, to help, biologists, to help clarify when they're talking about the number of chromosomes for a given species, they introduce two words, haploid and diploid."}, {"video_title": "Fertilization terminology gametes, zygotes, haploid, diploid   MCAT   Khan Academy.mp3", "Sentence": "And so the zygote now has, you could say it has 46 chromosomes, or you could say it has 23 pairs of homologous chromosomes. And this is, once again, this is the case for human beings. If we're talking about some other species, instead of 23 pairs of homologous chromosomes, or 46 chromosomes in total, you might be talking about 10 pairs of homologous chromosomes with 20 chromosomes in general. Now, to help, biologists, to help clarify when they're talking about the number of chromosomes for a given species, they introduce two words, haploid and diploid. And haploid, haploid is referring to when you have half the full contingency of chromosomes. So for human beings, the haploid number is 23. So this is the haploid, haploid number, haploid number, haploid number, it is 23."}, {"video_title": "Fertilization terminology gametes, zygotes, haploid, diploid   MCAT   Khan Academy.mp3", "Sentence": "Now, to help, biologists, to help clarify when they're talking about the number of chromosomes for a given species, they introduce two words, haploid and diploid. And haploid, haploid is referring to when you have half the full contingency of chromosomes. So for human beings, the haploid number is 23. So this is the haploid, haploid number, haploid number, haploid number, it is 23. For another species, it would be something else. And haploid is based on the prefix hapl, or that's the prefix for single. So you have kind of a single member, I guess you could think of it, of each of the pairs."}, {"video_title": "Fertilization terminology gametes, zygotes, haploid, diploid   MCAT   Khan Academy.mp3", "Sentence": "So this is the haploid, haploid number, haploid number, haploid number, it is 23. For another species, it would be something else. And haploid is based on the prefix hapl, or that's the prefix for single. So you have kind of a single member, I guess you could think of it, of each of the pairs. And now, you have both of each pair, you have both chromosomes in each pair, or you have the full contingency. And this 46 chromosomes, this is called the diploid number. The diploid number for humans, diploid."}, {"video_title": "Fertilization terminology gametes, zygotes, haploid, diploid   MCAT   Khan Academy.mp3", "Sentence": "So you have kind of a single member, I guess you could think of it, of each of the pairs. And now, you have both of each pair, you have both chromosomes in each pair, or you have the full contingency. And this 46 chromosomes, this is called the diploid number. The diploid number for humans, diploid. The diploid number right over here. And when people talk in general, and we will speak in general when we start talking about mitosis and meiosis, for a given species, they will refer to the haploid number, they will refer to the haploid number as N, N chromosomes, and they'll refer to the diploid number as just twice that, as 2N chromosomes. So hopefully this gets you familiar with some of the vocabulary around fertilization and haploid and diploid and zygotes and gametes, and also makes you feel a little bit better about yourself that just to exist, you, at least, I guess, half of your chromosomes had to win an incredibly competitive race."}, {"video_title": "Introduction to the cell   Cells   High school biology   Khan Academy.mp3", "Sentence": "Some would argue that maybe viruses are even a more basic unit of life, but the organisms that we consider living like ourselves are made up of cells, and all living organisms that we for sure consider living are made up of at least one cell. So most basic unit of life. For example, me, this thing that's making a video right now, I'm made up of tens of trillions of these cells. Now a common misconception is, well these things must be small, and they indeed are very, very, very small. Some cells are on the order of one micrometer long, and a micrometer is one millionth of a meter, or you could say one thousandth of a millimeter. And so when you think of something that small, sometimes there's an assumption that it must be simple. But you could not be more wrong if you assume that a cell is simple."}, {"video_title": "Introduction to the cell   Cells   High school biology   Khan Academy.mp3", "Sentence": "Now a common misconception is, well these things must be small, and they indeed are very, very, very small. Some cells are on the order of one micrometer long, and a micrometer is one millionth of a meter, or you could say one thousandth of a millimeter. And so when you think of something that small, sometimes there's an assumption that it must be simple. But you could not be more wrong if you assume that a cell is simple. This right over here is a picture of a budding yeast cell. You can see that it's budding off right over here. But this just begins to show you some of the complexity of the cell itself, or of any cell."}, {"video_title": "Introduction to the cell   Cells   High school biology   Khan Academy.mp3", "Sentence": "But you could not be more wrong if you assume that a cell is simple. This right over here is a picture of a budding yeast cell. You can see that it's budding off right over here. But this just begins to show you some of the complexity of the cell itself, or of any cell. And in other videos, we're gonna talk about different types of cells, different types of structures you'll see in some cells versus others. This right over here is a eukaryotic cell, which we will talk more about in other videos. Now all cells have a membrane that separate it from the outside world."}, {"video_title": "Introduction to the cell   Cells   High school biology   Khan Academy.mp3", "Sentence": "But this just begins to show you some of the complexity of the cell itself, or of any cell. And in other videos, we're gonna talk about different types of cells, different types of structures you'll see in some cells versus others. This right over here is a eukaryotic cell, which we will talk more about in other videos. Now all cells have a membrane that separate it from the outside world. You see the membrane right over here. This is just a cross-section. You could imagine a three-dimensional version of this."}, {"video_title": "Introduction to the cell   Cells   High school biology   Khan Academy.mp3", "Sentence": "Now all cells have a membrane that separate it from the outside world. You see the membrane right over here. This is just a cross-section. You could imagine a three-dimensional version of this. So this is the cell, cell membrane, kind of defines the cell in some way. And in general, the things inside the cell membrane is considered the cytoplasm. Cytoplasm."}, {"video_title": "Introduction to the cell   Cells   High school biology   Khan Academy.mp3", "Sentence": "You could imagine a three-dimensional version of this. So this is the cell, cell membrane, kind of defines the cell in some way. And in general, the things inside the cell membrane is considered the cytoplasm. Cytoplasm. Sometimes you will hear the term cytosol. A cytoplasm includes not just the fluid, but also all the stuff in the fluid, while the cytosol is referring to the fluid alone. And then depending on the complexity of a cell, so this is right here, this yeast cell, this is a eukaryotic cell, which we will cover in more depth in other videos."}, {"video_title": "Introduction to the cell   Cells   High school biology   Khan Academy.mp3", "Sentence": "Cytoplasm. Sometimes you will hear the term cytosol. A cytoplasm includes not just the fluid, but also all the stuff in the fluid, while the cytosol is referring to the fluid alone. And then depending on the complexity of a cell, so this is right here, this yeast cell, this is a eukaryotic cell, which we will cover in more depth in other videos. But one of the features of a eukaryotic cell is that you will have a membrane-bound nucleus. Now you see it in this diagram right over here. This is not a common feature to all cells, but the only reason why I'm mentioning it in this video is officially the cytoplasm does not include the stuff inside the nucleus."}, {"video_title": "Introduction to the cell   Cells   High school biology   Khan Academy.mp3", "Sentence": "And then depending on the complexity of a cell, so this is right here, this yeast cell, this is a eukaryotic cell, which we will cover in more depth in other videos. But one of the features of a eukaryotic cell is that you will have a membrane-bound nucleus. Now you see it in this diagram right over here. This is not a common feature to all cells, but the only reason why I'm mentioning it in this video is officially the cytoplasm does not include the stuff inside the nucleus. In a eukaryotic cell, that is called the nucleoplasm, but we'll talk more about that in other videos. Now another feature that is common to all cells is the notion of a ribosome. And this picture is full of ribosomes."}, {"video_title": "Introduction to the cell   Cells   High school biology   Khan Academy.mp3", "Sentence": "This is not a common feature to all cells, but the only reason why I'm mentioning it in this video is officially the cytoplasm does not include the stuff inside the nucleus. In a eukaryotic cell, that is called the nucleoplasm, but we'll talk more about that in other videos. Now another feature that is common to all cells is the notion of a ribosome. And this picture is full of ribosomes. All these little dots right here, these little red dots, let me change my pen color, all these little red dots here, these are ribosomes. And you might assume, wow, these are so small compared to this already small thing, this cell. Surely they are simple, but they're actually fairly complex RNA and protein structures that their main function is producing protein."}, {"video_title": "Introduction to the cell   Cells   High school biology   Khan Academy.mp3", "Sentence": "And this picture is full of ribosomes. All these little dots right here, these little red dots, let me change my pen color, all these little red dots here, these are ribosomes. And you might assume, wow, these are so small compared to this already small thing, this cell. Surely they are simple, but they're actually fairly complex RNA and protein structures that their main function is producing protein. Producing protein. You could view these as almost the protein factories of living organisms. They can take genetic information in the form of RNA and produce proteins out of them."}, {"video_title": "Introduction to the cell   Cells   High school biology   Khan Academy.mp3", "Sentence": "Surely they are simple, but they're actually fairly complex RNA and protein structures that their main function is producing protein. Producing protein. You could view these as almost the protein factories of living organisms. They can take genetic information in the form of RNA and produce proteins out of them. And you can see, this cell is full of ribosomes, and we're gonna talk about different types of ribosomes in a future video. Now another thing that is typical in most cells is genetic information. And typically, that genetic information is stored as DNA."}, {"video_title": "Introduction to the cell   Cells   High school biology   Khan Academy.mp3", "Sentence": "They can take genetic information in the form of RNA and produce proteins out of them. And you can see, this cell is full of ribosomes, and we're gonna talk about different types of ribosomes in a future video. Now another thing that is typical in most cells is genetic information. And typically, that genetic information is stored as DNA. Now I say in most cells because it turns out that even in our own bodies, mature red blood cells don't have any DNA anymore, and there's other cells that do the same thing. But in general, in order for a cell to function and replicate, it needs some genetic information, and that is stored in DNA. That's true in both prokaryotic cells and eukaryotic cells."}, {"video_title": "Introduction to the cell   Cells   High school biology   Khan Academy.mp3", "Sentence": "And typically, that genetic information is stored as DNA. Now I say in most cells because it turns out that even in our own bodies, mature red blood cells don't have any DNA anymore, and there's other cells that do the same thing. But in general, in order for a cell to function and replicate, it needs some genetic information, and that is stored in DNA. That's true in both prokaryotic cells and eukaryotic cells. Prokaryotes are ones that don't have a well-defined nucleus and membrane-bound, what we call organelles, which are these substructures in cells, which we will talk more about in other videos. In a prokaryotic cell, the DNA is just floating around in the cytoplasm, while in a eukaryotic cell, the DNA, for the most part, is inside of your nucleus. And it is part of the nucleoplasm."}, {"video_title": "Introduction to the cell   Cells   High school biology   Khan Academy.mp3", "Sentence": "That's true in both prokaryotic cells and eukaryotic cells. Prokaryotes are ones that don't have a well-defined nucleus and membrane-bound, what we call organelles, which are these substructures in cells, which we will talk more about in other videos. In a prokaryotic cell, the DNA is just floating around in the cytoplasm, while in a eukaryotic cell, the DNA, for the most part, is inside of your nucleus. And it is part of the nucleoplasm. So I'll leave you there for now. The last thing I want you to appreciate is just the scale. As I mentioned, cells are small."}, {"video_title": "Introduction to the cell   Cells   High school biology   Khan Academy.mp3", "Sentence": "And it is part of the nucleoplasm. So I'll leave you there for now. The last thing I want you to appreciate is just the scale. As I mentioned, cells are small. This picture of a yeast cell right over here, this is a micrometer on this scale. It would be about, would be about that. That would be one micrometer."}, {"video_title": "Introduction to the cell   Cells   High school biology   Khan Academy.mp3", "Sentence": "As I mentioned, cells are small. This picture of a yeast cell right over here, this is a micrometer on this scale. It would be about, would be about that. That would be one micrometer. And to put that in context, the width of a human hair, and it actually depends on your hair, whether it's soft or whether it's more like my hair, and it kind of sticks up and you have thicker hair, but if this is a human hair right over here, this is a width of a human hair, this thing, its width is anywhere from 20 to 180 micrometers. My thick hair is probably closer to the 180 micrometers. So one way to think about it, you could probably take 20 or so of these yeast cells, end to end, and these yeast cells, these aren't even the small cells by any stretch of the imagination, and put them end to end, 20 or 30 of these, across one human hair."}, {"video_title": "Introduction to the cell   Cells   High school biology   Khan Academy.mp3", "Sentence": "That would be one micrometer. And to put that in context, the width of a human hair, and it actually depends on your hair, whether it's soft or whether it's more like my hair, and it kind of sticks up and you have thicker hair, but if this is a human hair right over here, this is a width of a human hair, this thing, its width is anywhere from 20 to 180 micrometers. My thick hair is probably closer to the 180 micrometers. So one way to think about it, you could probably take 20 or so of these yeast cells, end to end, and these yeast cells, these aren't even the small cells by any stretch of the imagination, and put them end to end, 20 or 30 of these, across one human hair. And that's what's mind-blowing, because even at that scale, you have this complexity. And even this picture doesn't do proper justice to the complexity. There's all sorts of structures inside of this that you can't even see that help transport things and move things around and give the structure of the cell."}, {"video_title": "Leading and lagging strands in DNA replication   MCAT   Khan Academy.mp3", "Sentence": "Let's talk a little bit in more depth about how DNA actually copies itself, how it actually replicates. And we're gonna talk about the actual actors in the process. Now, as I talk about it, I'm gonna talk a lot about the three prime and the five prime ends of a DNA molecule. And if that is completely unfamiliar to you, I encourage you to watch the video on the anti-parallel structure of DNA. And I'll give a little bit of a quick review here just in case you saw it, but it was a little while ago. This is a zoom in of DNA. It's actually the zoom in from that video."}, {"video_title": "Leading and lagging strands in DNA replication   MCAT   Khan Academy.mp3", "Sentence": "And if that is completely unfamiliar to you, I encourage you to watch the video on the anti-parallel structure of DNA. And I'll give a little bit of a quick review here just in case you saw it, but it was a little while ago. This is a zoom in of DNA. It's actually the zoom in from that video. And when we talk about the five prime and three prime ends, we're referring to what's happening on the riboses that form part of this phosphate sugar backbone. So we have ribose right over here, five carbon sugar, and we can number the carbons. This is the one prime carbon, that's the two prime carbon, that's the three prime carbon, that's the four prime carbon, and that's the five prime carbon."}, {"video_title": "Leading and lagging strands in DNA replication   MCAT   Khan Academy.mp3", "Sentence": "It's actually the zoom in from that video. And when we talk about the five prime and three prime ends, we're referring to what's happening on the riboses that form part of this phosphate sugar backbone. So we have ribose right over here, five carbon sugar, and we can number the carbons. This is the one prime carbon, that's the two prime carbon, that's the three prime carbon, that's the four prime carbon, and that's the five prime carbon. So this side of the ladder, you could say, it is going in the, it is going, let me draw a little line here, this is going in the three prime to five prime direction. So this end is three prime, and then this end is five prime. It's going three prime to five prime."}, {"video_title": "Leading and lagging strands in DNA replication   MCAT   Khan Academy.mp3", "Sentence": "This is the one prime carbon, that's the two prime carbon, that's the three prime carbon, that's the four prime carbon, and that's the five prime carbon. So this side of the ladder, you could say, it is going in the, it is going, let me draw a little line here, this is going in the three prime to five prime direction. So this end is three prime, and then this end is five prime. It's going three prime to five prime. Notice, this phosphate connects to the three prime, then we go to the five prime, connects to a phosphate, this connects to a three prime, then it connects, then we go to the five prime, connects to a phosphate. Now on this end, as we said, it's anti-parallel. It's parallel, but it's oriented the other way."}, {"video_title": "Leading and lagging strands in DNA replication   MCAT   Khan Academy.mp3", "Sentence": "It's going three prime to five prime. Notice, this phosphate connects to the three prime, then we go to the five prime, connects to a phosphate, this connects to a three prime, then it connects, then we go to the five prime, connects to a phosphate. Now on this end, as we said, it's anti-parallel. It's parallel, but it's oriented the other way. So this is the three prime, this is the five prime, this is the three prime, this is the five prime. And so this is just what we're talking about when we talk about the anti-parallel structure. These two backbones, these two strands are parallel to each other, but they're oriented in opposite directions."}, {"video_title": "Leading and lagging strands in DNA replication   MCAT   Khan Academy.mp3", "Sentence": "It's parallel, but it's oriented the other way. So this is the three prime, this is the five prime, this is the three prime, this is the five prime. And so this is just what we're talking about when we talk about the anti-parallel structure. These two backbones, these two strands are parallel to each other, but they're oriented in opposite directions. So this is the three prime end, and this is the five prime end. And this is going to be really important for understanding replication, because the DNA polymerase, the things that's adding more and more nucleotides to grow a DNA strand, it can only add nucleotides on the three prime end. So if we were talking about this right over here, we would only be able to add, we would only be able to add going that way."}, {"video_title": "Leading and lagging strands in DNA replication   MCAT   Khan Academy.mp3", "Sentence": "These two backbones, these two strands are parallel to each other, but they're oriented in opposite directions. So this is the three prime end, and this is the five prime end. And this is going to be really important for understanding replication, because the DNA polymerase, the things that's adding more and more nucleotides to grow a DNA strand, it can only add nucleotides on the three prime end. So if we were talking about this right over here, we would only be able to add, we would only be able to add going that way. We wouldn't be able to add going, we wouldn't be able to add going that way. So one way to think about it is you can only add nucleotides on the three prime end, or you can only extend, you can only extend DNA going from five prime to three prime. If you're only adding on the three prime end, then you're going from the five prime to the three prime direction."}, {"video_title": "Leading and lagging strands in DNA replication   MCAT   Khan Academy.mp3", "Sentence": "So if we were talking about this right over here, we would only be able to add, we would only be able to add going that way. We wouldn't be able to add going, we wouldn't be able to add going that way. So one way to think about it is you can only add nucleotides on the three prime end, or you can only extend, you can only extend DNA going from five prime to three prime. If you're only adding on the three prime end, then you're going from the five prime to the three prime direction. You can't go from the three prime to the five prime direction. You can't continue to add on the five prime side using polymerase. So what am I talking about with polymerase?"}, {"video_title": "Leading and lagging strands in DNA replication   MCAT   Khan Academy.mp3", "Sentence": "If you're only adding on the three prime end, then you're going from the five prime to the three prime direction. You can't go from the three prime to the five prime direction. You can't continue to add on the five prime side using polymerase. So what am I talking about with polymerase? Well, let's look at this diagram right over here that really gives us an overview of all of the different actors. So here is just our DNA strand, and you can imagine it's just somewhat natural in its natural unreplicated form. And you can see we've labeled here the three prime and the five prime ends."}, {"video_title": "Leading and lagging strands in DNA replication   MCAT   Khan Academy.mp3", "Sentence": "So what am I talking about with polymerase? Well, let's look at this diagram right over here that really gives us an overview of all of the different actors. So here is just our DNA strand, and you can imagine it's just somewhat natural in its natural unreplicated form. And you can see we've labeled here the three prime and the five prime ends. And you could follow one of these backbones. This three prime, if you follow it all the way over here, it goes, this is the corresponding five prime end. So this and this are the same strand."}, {"video_title": "Leading and lagging strands in DNA replication   MCAT   Khan Academy.mp3", "Sentence": "And you can see we've labeled here the three prime and the five prime ends. And you could follow one of these backbones. This three prime, if you follow it all the way over here, it goes, this is the corresponding five prime end. So this and this are the same strand. And this one, if you follow it along, if you go all the way over here, is the same strand. So this is the three prime end of it, and then this is the five prime end of it. Now the first thing, and we've talked about this in previous videos where we gave an overview of replication, is the general idea is that the two sides of our helix, the two DNA, the double helix, needs to get split, and then we can build another, we can build another side of the ladder on each of those two split ends."}, {"video_title": "Leading and lagging strands in DNA replication   MCAT   Khan Academy.mp3", "Sentence": "So this and this are the same strand. And this one, if you follow it along, if you go all the way over here, is the same strand. So this is the three prime end of it, and then this is the five prime end of it. Now the first thing, and we've talked about this in previous videos where we gave an overview of replication, is the general idea is that the two sides of our helix, the two DNA, the double helix, needs to get split, and then we can build another, we can build another side of the ladder on each of those two split ends. You could really view this as, if this is a zipper, you unzip it, and then you put new zippers on either end. But there's a lot of, in reality, it is far more complex than just saying, oh, let's open a zipper and put new zippers on it. It involves a whole bunch of enzymes and all sorts of things, and even in this diagram, we're not showing all of the different actors, but we're showing you the primary actors, at least the ones that you'll hear discussed when people talk about DNA replication."}, {"video_title": "Leading and lagging strands in DNA replication   MCAT   Khan Academy.mp3", "Sentence": "Now the first thing, and we've talked about this in previous videos where we gave an overview of replication, is the general idea is that the two sides of our helix, the two DNA, the double helix, needs to get split, and then we can build another, we can build another side of the ladder on each of those two split ends. You could really view this as, if this is a zipper, you unzip it, and then you put new zippers on either end. But there's a lot of, in reality, it is far more complex than just saying, oh, let's open a zipper and put new zippers on it. It involves a whole bunch of enzymes and all sorts of things, and even in this diagram, we're not showing all of the different actors, but we're showing you the primary actors, at least the ones that you'll hear discussed when people talk about DNA replication. So the first thing that needs to happen, right over here, it's all tightly wound. So let me write that. It is tightly, tightly wound."}, {"video_title": "Leading and lagging strands in DNA replication   MCAT   Khan Academy.mp3", "Sentence": "It involves a whole bunch of enzymes and all sorts of things, and even in this diagram, we're not showing all of the different actors, but we're showing you the primary actors, at least the ones that you'll hear discussed when people talk about DNA replication. So the first thing that needs to happen, right over here, it's all tightly wound. So let me write that. It is tightly, tightly wound. And it actually turns out, the more that we unwind it on one side, the more tightly wound it gets on this side. So in order for us to unzip the zipper, we need to have an enzyme that helps us unwind this tightly wound helix. And that enzyme is the topoisomerase."}, {"video_title": "Leading and lagging strands in DNA replication   MCAT   Khan Academy.mp3", "Sentence": "It is tightly, tightly wound. And it actually turns out, the more that we unwind it on one side, the more tightly wound it gets on this side. So in order for us to unzip the zipper, we need to have an enzyme that helps us unwind this tightly wound helix. And that enzyme is the topoisomerase. And the way that it actually works is it breaks up parts of the backbones temporarily so that it can unwind, and then they get back together. But the general high-level idea is it unwinds it, so then the helicase enzyme, and the helicase really doesn't look like this little triangle that's cutting things. These things are actually far more fascinating if you were to actually see the molecular structure of helicase."}, {"video_title": "Leading and lagging strands in DNA replication   MCAT   Khan Academy.mp3", "Sentence": "And that enzyme is the topoisomerase. And the way that it actually works is it breaks up parts of the backbones temporarily so that it can unwind, and then they get back together. But the general high-level idea is it unwinds it, so then the helicase enzyme, and the helicase really doesn't look like this little triangle that's cutting things. These things are actually far more fascinating if you were to actually see the molecular structure of helicase. But what helicase is doing is it's breaking those hydrogen bonds between our nitrogenous bases. In this case, this is an adenine here, this is a thymine. It would break that hydrogen bond between these two."}, {"video_title": "Leading and lagging strands in DNA replication   MCAT   Khan Academy.mp3", "Sentence": "These things are actually far more fascinating if you were to actually see the molecular structure of helicase. But what helicase is doing is it's breaking those hydrogen bonds between our nitrogenous bases. In this case, this is an adenine here, this is a thymine. It would break that hydrogen bond between these two. So first, you unwind it. Then the topoisomerase unwinds it. Then the helicase breaks them up."}, {"video_title": "Leading and lagging strands in DNA replication   MCAT   Khan Academy.mp3", "Sentence": "It would break that hydrogen bond between these two. So first, you unwind it. Then the topoisomerase unwinds it. Then the helicase breaks them up. And then we actually think about these two strands differently, because as I mentioned, you can only add nucleotides going from the five prime to the three prime direction. So this strand on the bottom right over here, which we will call our leading strand, this one actually has it pretty straightforward. Remember, this is the five prime end right over here, so it can add going in that direction."}, {"video_title": "Leading and lagging strands in DNA replication   MCAT   Khan Academy.mp3", "Sentence": "Then the helicase breaks them up. And then we actually think about these two strands differently, because as I mentioned, you can only add nucleotides going from the five prime to the three prime direction. So this strand on the bottom right over here, which we will call our leading strand, this one actually has it pretty straightforward. Remember, this is the five prime end right over here, so it can add going in that direction. It can add going in that direction right over here. This is the five prime to three prime. So what needs to happen here is to start the process, you need an RNA primer."}, {"video_title": "Leading and lagging strands in DNA replication   MCAT   Khan Academy.mp3", "Sentence": "Remember, this is the five prime end right over here, so it can add going in that direction. It can add going in that direction right over here. This is the five prime to three prime. So what needs to happen here is to start the process, you need an RNA primer. And the character that puts an RNA primer, that is DNA primase. We'll talk a little bit more about these characters up here on the lagging strand. But they'll add an RNA, let me do this in a color you can see."}, {"video_title": "Leading and lagging strands in DNA replication   MCAT   Khan Academy.mp3", "Sentence": "So what needs to happen here is to start the process, you need an RNA primer. And the character that puts an RNA primer, that is DNA primase. We'll talk a little bit more about these characters up here on the lagging strand. But they'll add an RNA, let me do this in a color you can see. An RNA primer will be added here. And then once there's a primer, then DNA polymerase can just start adding nucleotides. It can start adding nucleotides at the three prime end."}, {"video_title": "Leading and lagging strands in DNA replication   MCAT   Khan Academy.mp3", "Sentence": "But they'll add an RNA, let me do this in a color you can see. An RNA primer will be added here. And then once there's a primer, then DNA polymerase can just start adding nucleotides. It can start adding nucleotides at the three prime end. And the reason why the leading strand, it has it pretty easy, is this DNA polymerase right over here, this polymerase. And once again, they aren't these perfect rectangles as on this diagram, they're actually much more fascinating than that. You see DNA polymerase up there, you also see one over here, polymerase."}, {"video_title": "Leading and lagging strands in DNA replication   MCAT   Khan Academy.mp3", "Sentence": "It can start adding nucleotides at the three prime end. And the reason why the leading strand, it has it pretty easy, is this DNA polymerase right over here, this polymerase. And once again, they aren't these perfect rectangles as on this diagram, they're actually much more fascinating than that. You see DNA polymerase up there, you also see one over here, polymerase. This polymerase can just, you can kind of think of it as following the open zipper, and then just keep adding, keep adding nucleotides at the three prime end. And so this one seems pretty straightforward. Now, you might say, well, wouldn't it be easy if we could just add nucleotides at a five prime end?"}, {"video_title": "Leading and lagging strands in DNA replication   MCAT   Khan Academy.mp3", "Sentence": "You see DNA polymerase up there, you also see one over here, polymerase. This polymerase can just, you can kind of think of it as following the open zipper, and then just keep adding, keep adding nucleotides at the three prime end. And so this one seems pretty straightforward. Now, you might say, well, wouldn't it be easy if we could just add nucleotides at a five prime end? Because then we could say, look, this is going from three prime to five prime. Well, maybe that polymerase or different polymerase could just keep adding nucleotides like that, and then everything would be easy. Well, it turns out that that is not the case."}, {"video_title": "Leading and lagging strands in DNA replication   MCAT   Khan Academy.mp3", "Sentence": "Now, you might say, well, wouldn't it be easy if we could just add nucleotides at a five prime end? Because then we could say, look, this is going from three prime to five prime. Well, maybe that polymerase or different polymerase could just keep adding nucleotides like that, and then everything would be easy. Well, it turns out that that is not the case. You cannot add nucleotides at the five prime end. And let me be clear, this three prime right over here, I'm talking about this strand. This strand over here, let me do this in another color, this strand right over here, this is the three prime end, this is the five prime end."}, {"video_title": "Leading and lagging strands in DNA replication   MCAT   Khan Academy.mp3", "Sentence": "Well, it turns out that that is not the case. You cannot add nucleotides at the five prime end. And let me be clear, this three prime right over here, I'm talking about this strand. This strand over here, let me do this in another color, this strand right over here, this is the three prime end, this is the five prime end. And so you can't just keep adding nucleotides just like that. And so how does biology handle this? Well, it handles this by adding primers right, as this opening happens, it'll add primers."}, {"video_title": "Leading and lagging strands in DNA replication   MCAT   Khan Academy.mp3", "Sentence": "This strand over here, let me do this in another color, this strand right over here, this is the three prime end, this is the five prime end. And so you can't just keep adding nucleotides just like that. And so how does biology handle this? Well, it handles this by adding primers right, as this opening happens, it'll add primers. And this diagram shows a primer is just one nucleotide, but a primer is typically several nucleotides, roughly 10 nucleotides. So it'll add roughly 10 RNA nucleotides right over here, and that's done by the DNA primase. So the DNA primase is going along, the lagging is going along this side, this, I could say the top strand, and it's adding the RNA primer, which won't be just one nucleotide, it tends to be several of them."}, {"video_title": "Leading and lagging strands in DNA replication   MCAT   Khan Academy.mp3", "Sentence": "Well, it handles this by adding primers right, as this opening happens, it'll add primers. And this diagram shows a primer is just one nucleotide, but a primer is typically several nucleotides, roughly 10 nucleotides. So it'll add roughly 10 RNA nucleotides right over here, and that's done by the DNA primase. So the DNA primase is going along, the lagging is going along this side, this, I could say the top strand, and it's adding the RNA primer, which won't be just one nucleotide, it tends to be several of them. And then once you have that RNA primer, then the polymerase can add in the five prime to three prime direction. It can add on the three prime end. So then it can just start adding DNA like that."}, {"video_title": "Leading and lagging strands in DNA replication   MCAT   Khan Academy.mp3", "Sentence": "So the DNA primase is going along, the lagging is going along this side, this, I could say the top strand, and it's adding the RNA primer, which won't be just one nucleotide, it tends to be several of them. And then once you have that RNA primer, then the polymerase can add in the five prime to three prime direction. It can add on the three prime end. So then it can just start adding DNA like that. And so you can imagine this process, it kind of, you add a, the primase puts some primer here, and then you start building from the five prime to the three prime direction. You start building just like that, and then you skip a little bit, and then that happens again. So you end up with all these fragments of DNA, and those fragments are called Okazaki fragments."}, {"video_title": "Leading and lagging strands in DNA replication   MCAT   Khan Academy.mp3", "Sentence": "So then it can just start adding DNA like that. And so you can imagine this process, it kind of, you add a, the primase puts some primer here, and then you start building from the five prime to the three prime direction. You start building just like that, and then you skip a little bit, and then that happens again. So you end up with all these fragments of DNA, and those fragments are called Okazaki fragments. So the Okazaki fragments. And so what you have happening here on the lagging strand, you can think of it as, why is it called the lagging strand? Well, you have to do it in this kind of, it feels like a suboptimal way, where you have to keep creating these Okazaki fragments as you follow this opening."}, {"video_title": "Leading and lagging strands in DNA replication   MCAT   Khan Academy.mp3", "Sentence": "So you end up with all these fragments of DNA, and those fragments are called Okazaki fragments. So the Okazaki fragments. And so what you have happening here on the lagging strand, you can think of it as, why is it called the lagging strand? Well, you have to do it in this kind of, it feels like a suboptimal way, where you have to keep creating these Okazaki fragments as you follow this opening. And so it lags, it's going to be a slower process. But then all of these strands can be put together using the DNA ligase. The DNA ligase."}, {"video_title": "Leading and lagging strands in DNA replication   MCAT   Khan Academy.mp3", "Sentence": "Well, you have to do it in this kind of, it feels like a suboptimal way, where you have to keep creating these Okazaki fragments as you follow this opening. And so it lags, it's going to be a slower process. But then all of these strands can be put together using the DNA ligase. The DNA ligase. Not only will the strands be put together, but then you also have the RNA being actually replaced with DNA, and then when all is said and done, you are going to have a strand of DNA being replicated, or being created right up here. And so when it's all done, you're going to have two double strands. One up here on the lagging strand, and one down here on the leading strand."}, {"video_title": "Cellular communication   Cells   MCAT   Khan Academy.mp3", "Sentence": "So here you are sitting in your classroom, and you desperately want to tell your friend here something. So you write a little note, and you pass it to them from your hand directly to their hand. So they see the note, but no one else sees it. It's just for them. But let's say you want to tell your friend across the room something. I don't know about you, but when I was in elementary school, I used to write notes on pieces of paper, fold it up into a paper airplane, and I had pretty good aim back then, so I'd throw my paper airplane over to my friend across some distance, and they'd get my message. And again, they'd be the only one who got the message."}, {"video_title": "Cellular communication   Cells   MCAT   Khan Academy.mp3", "Sentence": "It's just for them. But let's say you want to tell your friend across the room something. I don't know about you, but when I was in elementary school, I used to write notes on pieces of paper, fold it up into a paper airplane, and I had pretty good aim back then, so I'd throw my paper airplane over to my friend across some distance, and they'd get my message. And again, they'd be the only one who got the message. No one else got my little paper airplane message. And if I wanted to tell a few friends something, I might call a little huddle and actually say a few things just to this group of friends here. So my voice would cross this small distance between us."}, {"video_title": "Cellular communication   Cells   MCAT   Khan Academy.mp3", "Sentence": "And again, they'd be the only one who got the message. No one else got my little paper airplane message. And if I wanted to tell a few friends something, I might call a little huddle and actually say a few things just to this group of friends here. So my voice would cross this small distance between us. Now let's kick things up a notch. I was kind of a rebel in elementary school, and sometimes I'd go to the secretary's desk and take over the intercom to say funny things to my friends, maybe to tell them to meet me at the flagpole or on the playground at recess or something. And so this intercom message that I'd send out, that would go to everyone."}, {"video_title": "Cellular communication   Cells   MCAT   Khan Academy.mp3", "Sentence": "So my voice would cross this small distance between us. Now let's kick things up a notch. I was kind of a rebel in elementary school, and sometimes I'd go to the secretary's desk and take over the intercom to say funny things to my friends, maybe to tell them to meet me at the flagpole or on the playground at recess or something. And so this intercom message that I'd send out, that would go to everyone. It would be broadcasted to the whole school. And so those who wanted to come meet me would do that, and those who wouldn't, wouldn't. And we can think of cells as little people that do really similar things because you might not always think about it, but it's really, really important that cells are able to talk to each other."}, {"video_title": "Cellular communication   Cells   MCAT   Khan Academy.mp3", "Sentence": "And so this intercom message that I'd send out, that would go to everyone. It would be broadcasted to the whole school. And so those who wanted to come meet me would do that, and those who wouldn't, wouldn't. And we can think of cells as little people that do really similar things because you might not always think about it, but it's really, really important that cells are able to talk to each other. And evolutionarily, cells being able to communicate with each other are a major reason why we're as complex as we are as human beings. And I'll give you examples of when cells might talk to each other as we go along here. So how do cells pass notes to each other?"}, {"video_title": "Cellular communication   Cells   MCAT   Khan Academy.mp3", "Sentence": "And we can think of cells as little people that do really similar things because you might not always think about it, but it's really, really important that cells are able to talk to each other. And evolutionarily, cells being able to communicate with each other are a major reason why we're as complex as we are as human beings. And I'll give you examples of when cells might talk to each other as we go along here. So how do cells pass notes to each other? How do they directly communicate with each other? Well, one way is by actual direct contact. So cells have lots of proteins stuck into their plasma membranes here that serve a lot of functions."}, {"video_title": "Cellular communication   Cells   MCAT   Khan Academy.mp3", "Sentence": "So how do cells pass notes to each other? How do they directly communicate with each other? Well, one way is by actual direct contact. So cells have lots of proteins stuck into their plasma membranes here that serve a lot of functions. And the most important one is for communication. So let's look at a macrophage here. This is a type of white blood cell that's a part of your immune system."}, {"video_title": "Cellular communication   Cells   MCAT   Khan Academy.mp3", "Sentence": "So cells have lots of proteins stuck into their plasma membranes here that serve a lot of functions. And the most important one is for communication. So let's look at a macrophage here. This is a type of white blood cell that's a part of your immune system. So when these macrophages see a foreign invader, maybe a little bacteria or a virus, they can ingest it. They can ingest it, then they break it down, and then they display a little piece of it, which is now called an antigen, on their surface. So they show it off on their surface with one of these cell surface proteins here."}, {"video_title": "Cellular communication   Cells   MCAT   Khan Academy.mp3", "Sentence": "This is a type of white blood cell that's a part of your immune system. So when these macrophages see a foreign invader, maybe a little bacteria or a virus, they can ingest it. They can ingest it, then they break it down, and then they display a little piece of it, which is now called an antigen, on their surface. So they show it off on their surface with one of these cell surface proteins here. And this one in particular is called an MHC2 protein. So now this little antigen here has become the note that they want to pass on. This antigen is the message."}, {"video_title": "Cellular communication   Cells   MCAT   Khan Academy.mp3", "Sentence": "So they show it off on their surface with one of these cell surface proteins here. And this one in particular is called an MHC2 protein. So now this little antigen here has become the note that they want to pass on. This antigen is the message. And so another white blood cell, maybe a helper T cell might come along and then grab hold of this antigen here with one of its cell membrane proteins, in this case a T cell receptor. So just by doing this, the macrophage here managed to pass a message onto the helper T cell here. And now, based on which antigen this is, the T cell can decide whether to start a full-blown immune response."}, {"video_title": "Cellular communication   Cells   MCAT   Khan Academy.mp3", "Sentence": "This antigen is the message. And so another white blood cell, maybe a helper T cell might come along and then grab hold of this antigen here with one of its cell membrane proteins, in this case a T cell receptor. So just by doing this, the macrophage here managed to pass a message onto the helper T cell here. And now, based on which antigen this is, the T cell can decide whether to start a full-blown immune response. Maybe it'll go off and ring more alarm bells by activating other antibody cells, which are called B cells. Or not, maybe they'll just do nothing. It just depends on what type of note this is."}, {"video_title": "Cellular communication   Cells   MCAT   Khan Academy.mp3", "Sentence": "And now, based on which antigen this is, the T cell can decide whether to start a full-blown immune response. Maybe it'll go off and ring more alarm bells by activating other antibody cells, which are called B cells. Or not, maybe they'll just do nothing. It just depends on what type of note this is. So when cells directly touch to communicate, sort of unsurprisingly, this is called direct cell-cell communication, or just direct binding. Now, what about our other methods of communication? Cells can also communicate over short distances."}, {"video_title": "Cellular communication   Cells   MCAT   Khan Academy.mp3", "Sentence": "It just depends on what type of note this is. So when cells directly touch to communicate, sort of unsurprisingly, this is called direct cell-cell communication, or just direct binding. Now, what about our other methods of communication? Cells can also communicate over short distances. This is our paper airplane here. So for example, let's look at two neurons. So they're in close approximation, but one end of a neuron doesn't quite touch the start of the next neuron here."}, {"video_title": "Cellular communication   Cells   MCAT   Khan Academy.mp3", "Sentence": "Cells can also communicate over short distances. This is our paper airplane here. So for example, let's look at two neurons. So they're in close approximation, but one end of a neuron doesn't quite touch the start of the next neuron here. There's a little gap there called the synaptic cleft. So what neurons do is they release little signals called neurotransmitters to communicate with each other. So neurotransmitters get released from the end of this neuron, and they'll diffuse across this little distance here until they bind onto one of the dendrites of this next neuron."}, {"video_title": "Cellular communication   Cells   MCAT   Khan Academy.mp3", "Sentence": "So they're in close approximation, but one end of a neuron doesn't quite touch the start of the next neuron here. There's a little gap there called the synaptic cleft. So what neurons do is they release little signals called neurotransmitters to communicate with each other. So neurotransmitters get released from the end of this neuron, and they'll diffuse across this little distance here until they bind onto one of the dendrites of this next neuron. And that effectively passes the message on from this neuron to this next neuron. The paper airplane is thrown from here to here, and this is called neural communication. And over here, just like calling a huddle, one cell can talk to a small group of cells locally as well."}, {"video_title": "Cellular communication   Cells   MCAT   Khan Academy.mp3", "Sentence": "So neurotransmitters get released from the end of this neuron, and they'll diffuse across this little distance here until they bind onto one of the dendrites of this next neuron. And that effectively passes the message on from this neuron to this next neuron. The paper airplane is thrown from here to here, and this is called neural communication. And over here, just like calling a huddle, one cell can talk to a small group of cells locally as well. So for example, just underneath our skin, let's say the skin inside our nose, we have these immune cells called mast cells, and they're really important in mediating allergic reactions. That's why I purposely picked the nose here. So let's say you're allergic to certain pollens, and one day in the spring you found yourself walking through the park."}, {"video_title": "Cellular communication   Cells   MCAT   Khan Academy.mp3", "Sentence": "And over here, just like calling a huddle, one cell can talk to a small group of cells locally as well. So for example, just underneath our skin, let's say the skin inside our nose, we have these immune cells called mast cells, and they're really important in mediating allergic reactions. That's why I purposely picked the nose here. So let's say you're allergic to certain pollens, and one day in the spring you found yourself walking through the park. Inevitably, you'd breathe in some pollen, and then the pollen would go on to attach to these antibodies stuck to our mast cells. And what happens as a response to this is that the mast cells release little chemical signals called histamine. So histamine acts as our short-range message."}, {"video_title": "Cellular communication   Cells   MCAT   Khan Academy.mp3", "Sentence": "So let's say you're allergic to certain pollens, and one day in the spring you found yourself walking through the park. Inevitably, you'd breathe in some pollen, and then the pollen would go on to attach to these antibodies stuck to our mast cells. And what happens as a response to this is that the mast cells release little chemical signals called histamine. So histamine acts as our short-range message. It travels around to cells in the area to let them know that an allergen has been found, and lets them know to start preparing for an allergic reaction to take place. And this type of communication is called paracrine signaling, paracrine meaning nearby. Finally, the intercom takeover."}, {"video_title": "Cellular communication   Cells   MCAT   Khan Academy.mp3", "Sentence": "So histamine acts as our short-range message. It travels around to cells in the area to let them know that an allergen has been found, and lets them know to start preparing for an allergic reaction to take place. And this type of communication is called paracrine signaling, paracrine meaning nearby. Finally, the intercom takeover. How do our cells talk to huge groups of cells at once? Well, they do that by endocrine signaling. So for example, cells in our pituitary gland in our brain make a lot of the important hormones in our bodies."}, {"video_title": "Cellular communication   Cells   MCAT   Khan Academy.mp3", "Sentence": "Finally, the intercom takeover. How do our cells talk to huge groups of cells at once? Well, they do that by endocrine signaling. So for example, cells in our pituitary gland in our brain make a lot of the important hormones in our bodies. So let's say that they're making growth hormone, GH, to send around to all the cells in the body. Sending this hormone is their form of communication here. So they'll create the growth hormone inside their cell bodies, and they'll release them into the bloodstream."}, {"video_title": "Cellular communication   Cells   MCAT   Khan Academy.mp3", "Sentence": "So for example, cells in our pituitary gland in our brain make a lot of the important hormones in our bodies. So let's say that they're making growth hormone, GH, to send around to all the cells in the body. Sending this hormone is their form of communication here. So they'll create the growth hormone inside their cell bodies, and they'll release them into the bloodstream. And now our growth hormone can travel through the bloodstream and get to literally any place in the body. So every cell of your body has the opportunity to get this growth hormone message. It doesn't mean that every cell will necessarily respond to the message."}, {"video_title": "Homeostasis.mp3", "Sentence": "How do you maintain a steady body temperature when you're exposed to ice packs or hot water bottles? Healthy body temperature is 37 degrees Celsius or 98.6 degrees Fahrenheit. I need to keep a steady temperature near 98.6 degrees Fahrenheit or else crucial molecules in my body will change shape and stop working and I'll die. Homeostasis is a scientific term for my body's ability to maintain its proper equilibrium temperature. But what if I'm exposed to steaming hot water or freezing cold ice? How does my body maintain its equilibrium temperature then? Let's see."}, {"video_title": "Homeostasis.mp3", "Sentence": "Homeostasis is a scientific term for my body's ability to maintain its proper equilibrium temperature. But what if I'm exposed to steaming hot water or freezing cold ice? How does my body maintain its equilibrium temperature then? Let's see. I'll cover myself with ice packs and see how my body reacts. Five cold minutes later, let me check my body temperature. Sure enough, it's still near normal body temperature, homeostasis in action."}, {"video_title": "Homeostasis.mp3", "Sentence": "Let's see. I'll cover myself with ice packs and see how my body reacts. Five cold minutes later, let me check my body temperature. Sure enough, it's still near normal body temperature, homeostasis in action. Within a degree or so of 98.6 is still considered normal and despite how cold I feel, I haven't actually gotten any colder. How did my body do this? It made me feel cold and want to warm myself up by shivering, little muscle movements that generate heat."}, {"video_title": "Homeostasis.mp3", "Sentence": "Sure enough, it's still near normal body temperature, homeostasis in action. Within a degree or so of 98.6 is still considered normal and despite how cold I feel, I haven't actually gotten any colder. How did my body do this? It made me feel cold and want to warm myself up by shivering, little muscle movements that generate heat. See how pale my arm looks? After noticing the cold, my body directed my blood to my core and less to my skin and extremities. My arm quickly loses heat to the cold environment, but the temperature stays constant in my core, which is thicker, so it loses less heat to the environment."}, {"video_title": "Homeostasis.mp3", "Sentence": "It made me feel cold and want to warm myself up by shivering, little muscle movements that generate heat. See how pale my arm looks? After noticing the cold, my body directed my blood to my core and less to my skin and extremities. My arm quickly loses heat to the cold environment, but the temperature stays constant in my core, which is thicker, so it loses less heat to the environment. I also get goosebumps where my hair stands on end, creating an insulating layer like the jacket my body wishes I were wearing. So my body uses a lot of tools to keep my temperature up. When my body senses that it's cold, homeostasis mechanisms make me shiver, draw blood away from my skin, and give me goosebumps."}, {"video_title": "Homeostasis.mp3", "Sentence": "My arm quickly loses heat to the cold environment, but the temperature stays constant in my core, which is thicker, so it loses less heat to the environment. I also get goosebumps where my hair stands on end, creating an insulating layer like the jacket my body wishes I were wearing. So my body uses a lot of tools to keep my temperature up. When my body senses that it's cold, homeostasis mechanisms make me shiver, draw blood away from my skin, and give me goosebumps. These make me warmer, so my core temperature isn't changed. My body uses some of the opposite tools to cool down. It directs blood to the surface to cool down, making me a bit pink."}, {"video_title": "Homeostasis.mp3", "Sentence": "When my body senses that it's cold, homeostasis mechanisms make me shiver, draw blood away from my skin, and give me goosebumps. These make me warmer, so my core temperature isn't changed. My body uses some of the opposite tools to cool down. It directs blood to the surface to cool down, making me a bit pink. It needs to resort to more extreme measures if I want to be active in the heat, because moving my muscles uses energy and lets off heat, sort of like shivering to keep warm in the cold, but in this case, my body needs to counteract the warmth that the movement causes. My body makes me feel exhausted, urging me to stop running in place, but that's not enough if I'm excited to be running for some reason. It also makes me sweat."}, {"video_title": "Homeostasis.mp3", "Sentence": "It directs blood to the surface to cool down, making me a bit pink. It needs to resort to more extreme measures if I want to be active in the heat, because moving my muscles uses energy and lets off heat, sort of like shivering to keep warm in the cold, but in this case, my body needs to counteract the warmth that the movement causes. My body makes me feel exhausted, urging me to stop running in place, but that's not enough if I'm excited to be running for some reason. It also makes me sweat. In order to get the energy to evaporate into the air, sweat pulls heat from my body, and this helps me cool down. Not all animals have as effective sweat glands as people do, so people can endure longer periods of intense activity than many other animals. When I got warm, homeostasis mechanisms let my blood move near the surface of my skin and made me sweat, so I got cooler."}, {"video_title": "Homeostasis.mp3", "Sentence": "It also makes me sweat. In order to get the energy to evaporate into the air, sweat pulls heat from my body, and this helps me cool down. Not all animals have as effective sweat glands as people do, so people can endure longer periods of intense activity than many other animals. When I got warm, homeostasis mechanisms let my blood move near the surface of my skin and made me sweat, so I got cooler. There are other forms of homeostasis to regulate things besides temperature. For example, when your blood pressure drops suddenly, which can happen if you stand up suddenly, your blood vessel is constricted, which brings your blood pressure up to normal. Also, if your blood sugar rises, which can happen after eating, your pancreas releases insulin to lower your blood sugar back to normal."}, {"video_title": "Population growth rate based on birth and death rates   Ecology   AP Biology   Khan Academy.mp3", "Sentence": "When you take an AP biology exam, it is likely that it will include a formula sheet that will include formulas like this on it. And it can be a little bit intimidating at first because we're not used to seeing formulas like this that involve, in fact, this is formerly calculus notation in a biology class. But what we'll see in this video is that this formula is actually just trying to express something that's fairly intuitive and something that you actually don't even need calculus or even much algebra, but then we'll connect it to this to see that it all makes sense. So putting this aside, let me just ask you a simple question. Let's say we're studying a population and we see that the birth rate, the birth rate of this population is equal to 60, let's say we're studying a population of bunnies, 60 bunnies, bunnies per year. And let's say we know that the death rate of bunnies, death rate is equal to 15 bunnies, bunnies per year. Now without even paying attention to this formula sheet up there, what do you think, given this data, is the population, population growth rate for this population of bunnies?"}, {"video_title": "Population growth rate based on birth and death rates   Ecology   AP Biology   Khan Academy.mp3", "Sentence": "So putting this aside, let me just ask you a simple question. Let's say we're studying a population and we see that the birth rate, the birth rate of this population is equal to 60, let's say we're studying a population of bunnies, 60 bunnies, bunnies per year. And let's say we know that the death rate of bunnies, death rate is equal to 15 bunnies, bunnies per year. Now without even paying attention to this formula sheet up there, what do you think, given this data, is the population, population growth rate for this population of bunnies? Pause this video and see if you can answer that. Well, your population growth rate, if you think about just even say a given year, in that year, you'll grow your population by 60 bunnies per year. So you will grow by 60 bunnies per year, but then you would shrink by the 15 that died."}, {"video_title": "Population growth rate based on birth and death rates   Ecology   AP Biology   Khan Academy.mp3", "Sentence": "Now without even paying attention to this formula sheet up there, what do you think, given this data, is the population, population growth rate for this population of bunnies? Pause this video and see if you can answer that. Well, your population growth rate, if you think about just even say a given year, in that year, you'll grow your population by 60 bunnies per year. So you will grow by 60 bunnies per year, but then you would shrink by the 15 that died. So it would shrink by 15 bunnies, bunnies per year. And so in that year, you would net out 45 bunnies. And that's a rate, because you're saying per year."}, {"video_title": "Population growth rate based on birth and death rates   Ecology   AP Biology   Khan Academy.mp3", "Sentence": "So you will grow by 60 bunnies per year, but then you would shrink by the 15 that died. So it would shrink by 15 bunnies, bunnies per year. And so in that year, you would net out 45 bunnies. And that's a rate, because you're saying per year. So you would grow by 45 bunnies, bunnies in that year. And that would be your population growth rate. Now the thing that we just did very intuitively, you don't need advanced math to think through what we just did."}, {"video_title": "Population growth rate based on birth and death rates   Ecology   AP Biology   Khan Academy.mp3", "Sentence": "And that's a rate, because you're saying per year. So you would grow by 45 bunnies, bunnies in that year. And that would be your population growth rate. Now the thing that we just did very intuitively, you don't need advanced math to think through what we just did. That's exactly what this formula is saying. This notation, where you say D something DT, this is the rate at which this something is changing with respect to time. So this is just a fancy way of saying, what is the rate at which our population is changing with respect to time?"}, {"video_title": "Population growth rate based on birth and death rates   Ecology   AP Biology   Khan Academy.mp3", "Sentence": "Now the thing that we just did very intuitively, you don't need advanced math to think through what we just did. That's exactly what this formula is saying. This notation, where you say D something DT, this is the rate at which this something is changing with respect to time. So this is just a fancy way of saying, what is the rate at which our population is changing with respect to time? There's other ways that you could have written that. If you didn't wanna use calculus notation, you could have written change in population for a given change in time. The Greek letter delta often denotes change in."}, {"video_title": "Population growth rate based on birth and death rates   Ecology   AP Biology   Khan Academy.mp3", "Sentence": "So this is just a fancy way of saying, what is the rate at which our population is changing with respect to time? There's other ways that you could have written that. If you didn't wanna use calculus notation, you could have written change in population for a given change in time. The Greek letter delta often denotes change in. And what this formula says is exactly what we did. It would be the difference between the birth rate, which is the letter B in this formula, the birth rate right over here, and the death rate. The death rate is the letter D in this formula."}, {"video_title": "Population growth rate based on birth and death rates   Ecology   AP Biology   Khan Academy.mp3", "Sentence": "The Greek letter delta often denotes change in. And what this formula says is exactly what we did. It would be the difference between the birth rate, which is the letter B in this formula, the birth rate right over here, and the death rate. The death rate is the letter D in this formula. You have it right over here. And that's exactly what we did over there. So it's all very intuitive."}, {"video_title": "Population growth rate based on birth and death rates   Ecology   AP Biology   Khan Academy.mp3", "Sentence": "The death rate is the letter D in this formula. You have it right over here. And that's exactly what we did over there. So it's all very intuitive. Now, if I were in charge of the formula sheet, I might have expressed it a little bit different. Maybe I would have used notation like this. Maybe I would have written in plain English."}, {"video_title": "Enzyme reaction velocity and pH   Cellular energetics   AP Biology   Khan Academy.mp3", "Sentence": "In this video, we're gonna talk about enzymes, and in particular, we're gonna talk about the effect of pH on enzymes, how acidic or basic the environment is, how that affects enzyme activity. So just as a bit of a review, enzymes are molecules that help catalyze various reactions, and they are all throughout biological systems. Most enzymes are proteins, large proteins oftentimes, made up of chains of amino acids, and so I could draw a chain of amino acid where each of these circles represents an amino acid, and the primary structure is just a sequence of the amino acids, but there's also a secondary structure on how this amino acid backbone interacts with itself, and a lot of that is based on hydrogen bonding. So that amino acid and that amino acid, maybe it forms some type of hydrogen bond, and just as a review, a hydrogen bond is an interaction between hydrogen and a more electronegative atom. So for example, we've seen this in water. Let me draw a couple of water molecules right over here, and this is all review. In water, you have these covalent bonds between the oxygen and the hydrogen, so arguably, they're sharing the electrons, but because oxygen is more electronegative, it likes to hog the electrons more, the electrons spend more time around the oxygens, so the oxygen end of a water molecule gets a partially negative charge, and then the hydrogen ends of a water molecule get a partially positive, partially positive charge."}, {"video_title": "Enzyme reaction velocity and pH   Cellular energetics   AP Biology   Khan Academy.mp3", "Sentence": "So that amino acid and that amino acid, maybe it forms some type of hydrogen bond, and just as a review, a hydrogen bond is an interaction between hydrogen and a more electronegative atom. So for example, we've seen this in water. Let me draw a couple of water molecules right over here, and this is all review. In water, you have these covalent bonds between the oxygen and the hydrogen, so arguably, they're sharing the electrons, but because oxygen is more electronegative, it likes to hog the electrons more, the electrons spend more time around the oxygens, so the oxygen end of a water molecule gets a partially negative charge, and then the hydrogen ends of a water molecule get a partially positive, partially positive charge. This is the Greek lowercase delta for partially, partial charge is what it's typically used for, and so the partially negative ends would be attracted to the partially positive ends of another molecule, and that's what hydrogen bonds are. It's not always between hydrogen and oxygen. In fact, oftentimes, it's between hydrogen and nitrogen, which is another electronegative atom, and these hydrogen bonds, not only do they help define the secondary structure of the proteins, which helps define the shape of the protein, they can also interact with the substrate of the protein, the things that the protein's trying to catalyze reactions on."}, {"video_title": "Enzyme reaction velocity and pH   Cellular energetics   AP Biology   Khan Academy.mp3", "Sentence": "In water, you have these covalent bonds between the oxygen and the hydrogen, so arguably, they're sharing the electrons, but because oxygen is more electronegative, it likes to hog the electrons more, the electrons spend more time around the oxygens, so the oxygen end of a water molecule gets a partially negative charge, and then the hydrogen ends of a water molecule get a partially positive, partially positive charge. This is the Greek lowercase delta for partially, partial charge is what it's typically used for, and so the partially negative ends would be attracted to the partially positive ends of another molecule, and that's what hydrogen bonds are. It's not always between hydrogen and oxygen. In fact, oftentimes, it's between hydrogen and nitrogen, which is another electronegative atom, and these hydrogen bonds, not only do they help define the secondary structure of the proteins, which helps define the shape of the protein, they can also interact with the substrate of the protein, the things that the protein's trying to catalyze reactions on. So for example, if that's the substrate, and I'm just doing it as a big red circle, parts of it might form hydrogen bonds with the enzyme itself, and if you wanna see a more complex picture of that, this is a detailed schematic of a substrate interacting with an enzyme, where what you see circled in yellow, that is the substrate here, and you see these dotted lines, those are the hydrogen bonds, so you can see a hydrogen bond between a hydrogen and a nitrogen, a hydrogen bond between an oxygen and a hydrogen, and so the yellow part is a substrate, and all the stuff that's wrapping around it, that is the enzyme itself. So with that out of the way, how does pH play into it? Well, we just have to remind ourselves what pH is."}, {"video_title": "Enzyme reaction velocity and pH   Cellular energetics   AP Biology   Khan Academy.mp3", "Sentence": "In fact, oftentimes, it's between hydrogen and nitrogen, which is another electronegative atom, and these hydrogen bonds, not only do they help define the secondary structure of the proteins, which helps define the shape of the protein, they can also interact with the substrate of the protein, the things that the protein's trying to catalyze reactions on. So for example, if that's the substrate, and I'm just doing it as a big red circle, parts of it might form hydrogen bonds with the enzyme itself, and if you wanna see a more complex picture of that, this is a detailed schematic of a substrate interacting with an enzyme, where what you see circled in yellow, that is the substrate here, and you see these dotted lines, those are the hydrogen bonds, so you can see a hydrogen bond between a hydrogen and a nitrogen, a hydrogen bond between an oxygen and a hydrogen, and so the yellow part is a substrate, and all the stuff that's wrapping around it, that is the enzyme itself. So with that out of the way, how does pH play into it? Well, we just have to remind ourselves what pH is. pH, which is often viewed as the power of hydrogen, that's where the P comes from, is the negative log, or at least the way it's introduced in many introductory chemistry class, the negative log of the hydrogen ion concentration, and a hydrogen ion is essentially a proton. Well, how would this affect an enzyme's shape and its ability to interact with the substrate, the thing that it's trying to act on? Well, if you have a bunch of, depending on how many hydrogen ions you have floating around, and oftentimes it'll be in the form of hydronium, which is a water molecule where the oxygen is bonded to one extra hydrogen proton, well, it might mess with these hydrogen bonds, where some of these hydrogen protons usurp the bond with the negative end of one of these molecules, or repel some of the positive ends of some of these molecules in a certain way, and so you can imagine that different enzymes might have a different level of activity at different levels of pH, and that actually is the case."}, {"video_title": "Enzyme reaction velocity and pH   Cellular energetics   AP Biology   Khan Academy.mp3", "Sentence": "Well, we just have to remind ourselves what pH is. pH, which is often viewed as the power of hydrogen, that's where the P comes from, is the negative log, or at least the way it's introduced in many introductory chemistry class, the negative log of the hydrogen ion concentration, and a hydrogen ion is essentially a proton. Well, how would this affect an enzyme's shape and its ability to interact with the substrate, the thing that it's trying to act on? Well, if you have a bunch of, depending on how many hydrogen ions you have floating around, and oftentimes it'll be in the form of hydronium, which is a water molecule where the oxygen is bonded to one extra hydrogen proton, well, it might mess with these hydrogen bonds, where some of these hydrogen protons usurp the bond with the negative end of one of these molecules, or repel some of the positive ends of some of these molecules in a certain way, and so you can imagine that different enzymes might have a different level of activity at different levels of pH, and that actually is the case. In fact, you'll often see a diagram that looks like this. So in the vertical axis, you will often see reaction, reaction velocity, where reaction velocity goes higher as we go higher in the vertical direction, and in this axis right over here, you might see our level of pH. And remember, pH, because you have this negative out front, a high hydrogen ion concentration, because of this negative, that will give you a low pH, and that is associated with acidic environments, and a low hydrogen ion concentration, that's associated with a high pH, once again because of this negative out front, and that's associated with a more basic situation, and if your pH is around seven, then that would be a neutral situation."}, {"video_title": "Enzyme reaction velocity and pH   Cellular energetics   AP Biology   Khan Academy.mp3", "Sentence": "Well, if you have a bunch of, depending on how many hydrogen ions you have floating around, and oftentimes it'll be in the form of hydronium, which is a water molecule where the oxygen is bonded to one extra hydrogen proton, well, it might mess with these hydrogen bonds, where some of these hydrogen protons usurp the bond with the negative end of one of these molecules, or repel some of the positive ends of some of these molecules in a certain way, and so you can imagine that different enzymes might have a different level of activity at different levels of pH, and that actually is the case. In fact, you'll often see a diagram that looks like this. So in the vertical axis, you will often see reaction, reaction velocity, where reaction velocity goes higher as we go higher in the vertical direction, and in this axis right over here, you might see our level of pH. And remember, pH, because you have this negative out front, a high hydrogen ion concentration, because of this negative, that will give you a low pH, and that is associated with acidic environments, and a low hydrogen ion concentration, that's associated with a high pH, once again because of this negative out front, and that's associated with a more basic situation, and if your pH is around seven, then that would be a neutral situation. But different enzymes, activities peak at different pHs. So for example, you might have an enzyme like this whose activity peaks at a pH of, let's say this is right over here, a pH of four, which is relatively acidic, and you would typically see this type of an enzyme in say a place like the stomach, which is a very acidic environment, and then you might see other enzymes that actually don't do too well in an acidic environment, but do quite well in a more neutral environment. So for example, this peak might be at say a pH of seven, and then you might have other enzymes that do better in a basic environment."}, {"video_title": "Enzyme reaction velocity and pH   Cellular energetics   AP Biology   Khan Academy.mp3", "Sentence": "And remember, pH, because you have this negative out front, a high hydrogen ion concentration, because of this negative, that will give you a low pH, and that is associated with acidic environments, and a low hydrogen ion concentration, that's associated with a high pH, once again because of this negative out front, and that's associated with a more basic situation, and if your pH is around seven, then that would be a neutral situation. But different enzymes, activities peak at different pHs. So for example, you might have an enzyme like this whose activity peaks at a pH of, let's say this is right over here, a pH of four, which is relatively acidic, and you would typically see this type of an enzyme in say a place like the stomach, which is a very acidic environment, and then you might see other enzymes that actually don't do too well in an acidic environment, but do quite well in a more neutral environment. So for example, this peak might be at say a pH of seven, and then you might have other enzymes that do better in a basic environment. And we actually do see this in the human body. For example, lipase, which is an enzyme that breaks down fat. When it's found in the stomach, that particular version of lipase, it actually has optimum activity closer to this at a pH of roughly four or five, while lipase that is secreted from the pancreas, which acts in the small intestines, which is a more neutral environment or even slightly basic, its optimal activity is at a pH of eight."}, {"video_title": "Enzyme reaction velocity and pH   Cellular energetics   AP Biology   Khan Academy.mp3", "Sentence": "So for example, this peak might be at say a pH of seven, and then you might have other enzymes that do better in a basic environment. And we actually do see this in the human body. For example, lipase, which is an enzyme that breaks down fat. When it's found in the stomach, that particular version of lipase, it actually has optimum activity closer to this at a pH of roughly four or five, while lipase that is secreted from the pancreas, which acts in the small intestines, which is a more neutral environment or even slightly basic, its optimal activity is at a pH of eight. So I will leave you there. Big picture is is that a lot of an enzyme's shape or its ability to interact with the substrate is based on hydrogen bonds. And so you can imagine hydrogen bonds could be influenced by hydrogen ion concentration."}, {"video_title": "Per capita population growth and exponential growth   Ecology   AP Biology   Khan Academy.mp3", "Sentence": "We related that to some of the seemingly complex formulas that you might see on an AP Biology formula sheet. Now we're going to extend that conversation to discuss some of the other formulas you might see, but to realize that they really are just intuition using a little bit of fancy math notation. So just as a little bit of review, we looked at an example where in a population, the birth rate is 60 bunnies per year. We're talking about bunnies here. It's a population of bunnies. And the death rate is 15 bunnies per year. Well, what's the population growth rate?"}, {"video_title": "Per capita population growth and exponential growth   Ecology   AP Biology   Khan Academy.mp3", "Sentence": "We're talking about bunnies here. It's a population of bunnies. And the death rate is 15 bunnies per year. Well, what's the population growth rate? Well, in a given year, you would expect 60 bunnies to be born, so that would add to the population, and you would expect 15 bunnies to die, so that would take away from the population for a net increase of 49 bunnies per year. And to put that in the language of your AP Biology formula sheet, the notation they use for population growth rate, they use a fancy notation. So actually, let me just write it over here."}, {"video_title": "Per capita population growth and exponential growth   Ecology   AP Biology   Khan Academy.mp3", "Sentence": "Well, what's the population growth rate? Well, in a given year, you would expect 60 bunnies to be born, so that would add to the population, and you would expect 15 bunnies to die, so that would take away from the population for a net increase of 49 bunnies per year. And to put that in the language of your AP Biology formula sheet, the notation they use for population growth rate, they use a fancy notation. So actually, let me just write it over here. They say n is equal to your population. n is equal to population, and then your population growth rate, they use calculus notation, so our change in population per change in time. This is really talking about something in calculus, so it's instantaneous change, but we don't have to get too bogged down with that just yet."}, {"video_title": "Per capita population growth and exponential growth   Ecology   AP Biology   Khan Academy.mp3", "Sentence": "So actually, let me just write it over here. They say n is equal to your population. n is equal to population, and then your population growth rate, they use calculus notation, so our change in population per change in time. This is really talking about something in calculus, so it's instantaneous change, but we don't have to get too bogged down with that just yet. But your population growth rate, which you could use this notation for, is equal to your birth rate, 60 bunnies per year, and the notation they use for birth rate is just b. They don't use the same rate notation for that. I probably would have, but that's fine."}, {"video_title": "Per capita population growth and exponential growth   Ecology   AP Biology   Khan Academy.mp3", "Sentence": "This is really talking about something in calculus, so it's instantaneous change, but we don't have to get too bogged down with that just yet. But your population growth rate, which you could use this notation for, is equal to your birth rate, 60 bunnies per year, and the notation they use for birth rate is just b. They don't use the same rate notation for that. I probably would have, but that's fine. I'm just trying to make you familiar with what you might see. And then minus the death rate, minus d. So this right over here is something that you would see on that formula sheet, but it makes fairly intuitive sense. Now the next idea we're going to think about is something known as a per capita growth rate of population."}, {"video_title": "Per capita population growth and exponential growth   Ecology   AP Biology   Khan Academy.mp3", "Sentence": "I probably would have, but that's fine. I'm just trying to make you familiar with what you might see. And then minus the death rate, minus d. So this right over here is something that you would see on that formula sheet, but it makes fairly intuitive sense. Now the next idea we're going to think about is something known as a per capita growth rate of population. Let me write it out in words first. So here we're going to think about a per capita growth rate, or population growth rate. Per capita population growth rate."}, {"video_title": "Per capita population growth and exponential growth   Ecology   AP Biology   Khan Academy.mp3", "Sentence": "Now the next idea we're going to think about is something known as a per capita growth rate of population. Let me write it out in words first. So here we're going to think about a per capita growth rate, or population growth rate. Per capita population growth rate. Now per capita means you could view it as on average per individual. What is the average growth rate per individual? What is that going to be?"}, {"video_title": "Per capita population growth and exponential growth   Ecology   AP Biology   Khan Academy.mp3", "Sentence": "Per capita population growth rate. Now per capita means you could view it as on average per individual. What is the average growth rate per individual? What is that going to be? Pause this video and try to think about it. Well, one way you could think about it, it's the total population growth rate divided by the population, divided by the number of people there are. So it's going to be our population growth rate, growth rate, divided by, divided by our population."}, {"video_title": "Per capita population growth and exponential growth   Ecology   AP Biology   Khan Academy.mp3", "Sentence": "What is that going to be? Pause this video and try to think about it. Well, one way you could think about it, it's the total population growth rate divided by the population, divided by the number of people there are. So it's going to be our population growth rate, growth rate, divided by, divided by our population. Population. Now let's say that we have a population of 300 bunnies. Actually, let's make the math a little bit simpler."}, {"video_title": "Per capita population growth and exponential growth   Ecology   AP Biology   Khan Academy.mp3", "Sentence": "So it's going to be our population growth rate, growth rate, divided by, divided by our population. Population. Now let's say that we have a population of 300 bunnies. Actually, let's make the math a little bit simpler. Let's say we have a population of 450 bunnies. So what is going to be our per capita population growth rate? Pause this video and try to figure that out."}, {"video_title": "Per capita population growth and exponential growth   Ecology   AP Biology   Khan Academy.mp3", "Sentence": "Actually, let's make the math a little bit simpler. Let's say we have a population of 450 bunnies. So what is going to be our per capita population growth rate? Pause this video and try to figure that out. Well, if we have a population of 450 bunnies, 450 bunnies, our population growth rate per the number of people we, or number of bunnies, I should say, is going to be equal to, our population growth rate is 45 bunnies, bunnies per year. And that's going to be for every 450 bunnies. 450 bunnies, which will get us to, 45 divided by 450 is 0.1."}, {"video_title": "Per capita population growth and exponential growth   Ecology   AP Biology   Khan Academy.mp3", "Sentence": "Pause this video and try to figure that out. Well, if we have a population of 450 bunnies, 450 bunnies, our population growth rate per the number of people we, or number of bunnies, I should say, is going to be equal to, our population growth rate is 45 bunnies, bunnies per year. And that's going to be for every 450 bunnies. 450 bunnies, which will get us to, 45 divided by 450 is 0.1. And then the units, bunnies cancel with bunnies, so it's 0.1 per year. Now why is per capita population growth rate interesting? Well, it tells us just how likely, and in most populations, you need at least a male and a female in order to reproduce, but there are some organisms that can just split and reproduce asexually."}, {"video_title": "Per capita population growth and exponential growth   Ecology   AP Biology   Khan Academy.mp3", "Sentence": "450 bunnies, which will get us to, 45 divided by 450 is 0.1. And then the units, bunnies cancel with bunnies, so it's 0.1 per year. Now why is per capita population growth rate interesting? Well, it tells us just how likely, and in most populations, you need at least a male and a female in order to reproduce, but there are some organisms that can just split and reproduce asexually. But it tells us on average, per individual organism, how much are they going to grow per year. So it gives you a sense of that. Now connecting it to the notation that you might see on an AP Biology formula sheet, it would look like this."}, {"video_title": "Per capita population growth and exponential growth   Ecology   AP Biology   Khan Academy.mp3", "Sentence": "Well, it tells us just how likely, and in most populations, you need at least a male and a female in order to reproduce, but there are some organisms that can just split and reproduce asexually. But it tells us on average, per individual organism, how much are they going to grow per year. So it gives you a sense of that. Now connecting it to the notation that you might see on an AP Biology formula sheet, it would look like this. The per capita population growth rate is usually denoted by the lowercase letter r, and then they would say that that is going to be equal to our population growth rate, which we've already seen that notation, the rate of change of our population with respect to time, dn dt, divided by our population, divided by our population. Now we can algebraically manipulate this a little bit to get another expression. We could multiply both sides times our uppercase N times our population, and we're going to get dn dt is equal to N times r, or r times N. Let me rewrite it."}, {"video_title": "Per capita population growth and exponential growth   Ecology   AP Biology   Khan Academy.mp3", "Sentence": "Now connecting it to the notation that you might see on an AP Biology formula sheet, it would look like this. The per capita population growth rate is usually denoted by the lowercase letter r, and then they would say that that is going to be equal to our population growth rate, which we've already seen that notation, the rate of change of our population with respect to time, dn dt, divided by our population, divided by our population. Now we can algebraically manipulate this a little bit to get another expression. We could multiply both sides times our uppercase N times our population, and we're going to get dn dt is equal to N times r, or r times N. Let me rewrite it. We could rewrite this as dn dt is equal to our per capita population growth rate times our population. Now this, once again, makes sense. If you say, okay, this is how many people, how many individuals I have, and if in a given year, they grow by this much on average, well, if you multiply the two, you'll know how much the whole population has grown."}, {"video_title": "Per capita population growth and exponential growth   Ecology   AP Biology   Khan Academy.mp3", "Sentence": "We could multiply both sides times our uppercase N times our population, and we're going to get dn dt is equal to N times r, or r times N. Let me rewrite it. We could rewrite this as dn dt is equal to our per capita population growth rate times our population. Now this, once again, makes sense. If you say, okay, this is how many people, how many individuals I have, and if in a given year, they grow by this much on average, well, if you multiply the two, you'll know how much the whole population has grown. So if we didn't know these numbers, and someone said, hey, well, actually, we could think about this. Let's think about now a population of 1,000 bunnies. So if N was equal to 1,000, and let's say they're the same type of bunnies that have the same probability of reproducing and the same likelihood, so we know that r is equal to 0.1 per year."}, {"video_title": "Per capita population growth and exponential growth   Ecology   AP Biology   Khan Academy.mp3", "Sentence": "If you say, okay, this is how many people, how many individuals I have, and if in a given year, they grow by this much on average, well, if you multiply the two, you'll know how much the whole population has grown. So if we didn't know these numbers, and someone said, hey, well, actually, we could think about this. Let's think about now a population of 1,000 bunnies. So if N was equal to 1,000, and let's say they're the same type of bunnies that have the same probability of reproducing and the same likelihood, so we know that r is equal to 0.1 per year. For this population of bunnies, what is going to be our population growth rate? Pause this video and try to figure that out. Well, in this situation, dn dt is going to be our per capita population growth rate, so it's going to be 0.1 per year times our population times 1,000 bunnies."}, {"video_title": "Per capita population growth and exponential growth   Ecology   AP Biology   Khan Academy.mp3", "Sentence": "So if N was equal to 1,000, and let's say they're the same type of bunnies that have the same probability of reproducing and the same likelihood, so we know that r is equal to 0.1 per year. For this population of bunnies, what is going to be our population growth rate? Pause this video and try to figure that out. Well, in this situation, dn dt is going to be our per capita population growth rate, so it's going to be 0.1 per year times our population times 1,000 bunnies. Bunnies, I'll keep my units here. Bunnies. And so this is going to be equal to 1,000 times 110th is 100."}, {"video_title": "Per capita population growth and exponential growth   Ecology   AP Biology   Khan Academy.mp3", "Sentence": "Well, in this situation, dn dt is going to be our per capita population growth rate, so it's going to be 0.1 per year times our population times 1,000 bunnies. Bunnies, I'll keep my units here. Bunnies. And so this is going to be equal to 1,000 times 110th is 100. We're in that color. So 100 bunnies per year. So hopefully you're getting an appreciation for why these types of formulas, which are fairly straightforward, they're using just a fancy notation, are useful."}, {"video_title": "Per capita population growth and exponential growth   Ecology   AP Biology   Khan Academy.mp3", "Sentence": "And so this is going to be equal to 1,000 times 110th is 100. We're in that color. So 100 bunnies per year. So hopefully you're getting an appreciation for why these types of formulas, which are fairly straightforward, they're using just a fancy notation, are useful. Now, this is also an interesting thing to look at because even though that this is in fancy calculus notation and they're saying that our rate of change of population is equal to r times our population, this is actually a differential equation, if you were to think about what this population, the type of population this would describe, this would actually be a population that's growing exponentially. So this is often known as an exponential growth equation. Let me write that down."}, {"video_title": "Per capita population growth and exponential growth   Ecology   AP Biology   Khan Academy.mp3", "Sentence": "So hopefully you're getting an appreciation for why these types of formulas, which are fairly straightforward, they're using just a fancy notation, are useful. Now, this is also an interesting thing to look at because even though that this is in fancy calculus notation and they're saying that our rate of change of population is equal to r times our population, this is actually a differential equation, if you were to think about what this population, the type of population this would describe, this would actually be a population that's growing exponentially. So this is often known as an exponential growth equation. Let me write that down. Exponential, exponential growth. And in other, in your math classes, in your calculus classes, or even in your pre-calculus classes, you will study exponential growth. In a biology class, you're really just thinking about how to manipulate this a little bit, but just to give you a little sense of what's going on with exponential growth, if you have a population of bunnies with this type of exponential growth, what is happening here, this is time, and this is your population, so you're going to have some starting population here, and it's just going to grow exponentially."}, {"video_title": "Per capita population growth and exponential growth   Ecology   AP Biology   Khan Academy.mp3", "Sentence": "Let me write that down. Exponential, exponential growth. And in other, in your math classes, in your calculus classes, or even in your pre-calculus classes, you will study exponential growth. In a biology class, you're really just thinking about how to manipulate this a little bit, but just to give you a little sense of what's going on with exponential growth, if you have a population of bunnies with this type of exponential growth, what is happening here, this is time, and this is your population, so you're going to have some starting population here, and it's just going to grow exponentially. And the higher the r is, the steeper this exponential growth curve is going to be. But this describes how populations can grow if they are not constrained by the environment in any way. They have just as much land, as much water, and as much food as they need."}, {"video_title": "Per capita population growth and exponential growth   Ecology   AP Biology   Khan Academy.mp3", "Sentence": "In a biology class, you're really just thinking about how to manipulate this a little bit, but just to give you a little sense of what's going on with exponential growth, if you have a population of bunnies with this type of exponential growth, what is happening here, this is time, and this is your population, so you're going to have some starting population here, and it's just going to grow exponentially. And the higher the r is, the steeper this exponential growth curve is going to be. But this describes how populations can grow if they are not constrained by the environment in any way. They have just as much land, as much water, and as much food as they need. Eventually, the bunnies will fill the surface of the Earth and the universe. Now, obviously, we know that that is not a realistic situation, that any ecosystem has some natural carrying capacity. There's only so much food, there's only so much land."}, {"video_title": "Per capita population growth and exponential growth   Ecology   AP Biology   Khan Academy.mp3", "Sentence": "They have just as much land, as much water, and as much food as they need. Eventually, the bunnies will fill the surface of the Earth and the universe. Now, obviously, we know that that is not a realistic situation, that any ecosystem has some natural carrying capacity. There's only so much food, there's only so much land. At some point, there's just going to be bunnies falling from trees, and it's going to be much easier for predators to get them, and all these other things. And we will discuss that in the next video. How do we adapt the exponential growth equation right over here to factor in a little bit more of a real-world situation, where at some population, you're going to be hitting up against the carrying capacity of the environment?"}, {"video_title": "Mutagens and carcinogens   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "Now nucleotides from DNA are transcribed to their complementary forms on RNA, which are then read as codons, or groups of three, to code for specific amino acids in a larger protein. Now, if you mutate one of the nucleotides on DNA, like turn this thymine base into an adenine base, then that will affect the RNA sequence, and ultimately the protein that follows. So, we say that mutations are mistakes in a cell's DNA that ultimately lead to abnormal protein production. So what is a mutagen? Well, a mutagen is any chemical substance or physical event that can cause genetic mutations. Chemical substances, like certain poisons, could be mutagens, or physical events, like UV light or different kinds of radiation, could also be mutagenic. And we classify mutagens into two different categories."}, {"video_title": "Mutagens and carcinogens   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "So what is a mutagen? Well, a mutagen is any chemical substance or physical event that can cause genetic mutations. Chemical substances, like certain poisons, could be mutagens, or physical events, like UV light or different kinds of radiation, could also be mutagenic. And we classify mutagens into two different categories. So let's say we have a person over here. A mutagen could be classified as endogenous, if it comes from inside this person's body, and it's some mutagen that's already found in the organism. But an exogenous mutation is one that comes from outside the affected organism, something that's from the external environment."}, {"video_title": "Mutagens and carcinogens   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "And we classify mutagens into two different categories. So let's say we have a person over here. A mutagen could be classified as endogenous, if it comes from inside this person's body, and it's some mutagen that's already found in the organism. But an exogenous mutation is one that comes from outside the affected organism, something that's from the external environment. So what are some examples of some endogenous mutagens? Well, the most significant endogenous mutagens are what we call reactive oxygen species, or ROS. And ROS are naturally occurring metabolites in the human body that are produced by mitochondria during oxidative phosphorylation."}, {"video_title": "Mutagens and carcinogens   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "But an exogenous mutation is one that comes from outside the affected organism, something that's from the external environment. So what are some examples of some endogenous mutagens? Well, the most significant endogenous mutagens are what we call reactive oxygen species, or ROS. And ROS are naturally occurring metabolites in the human body that are produced by mitochondria during oxidative phosphorylation. So if we have this guy here, who's about to chow down on a big meal, you can expect that during the metabolism of the meal, his mitochondria will produce a bunch of ROS, like O2 dot minus, which we call superoxide, which is an oxygen molecule with one extra electron, as well as some hydrogen peroxide, which is another ROS that your body can produce. Now reactive oxygen species, as you may be able to tell by their name, contain oxygen, like both of these examples do. But they're also highly reactive with different cell components, including DNA."}, {"video_title": "Mutagens and carcinogens   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "And ROS are naturally occurring metabolites in the human body that are produced by mitochondria during oxidative phosphorylation. So if we have this guy here, who's about to chow down on a big meal, you can expect that during the metabolism of the meal, his mitochondria will produce a bunch of ROS, like O2 dot minus, which we call superoxide, which is an oxygen molecule with one extra electron, as well as some hydrogen peroxide, which is another ROS that your body can produce. Now reactive oxygen species, as you may be able to tell by their name, contain oxygen, like both of these examples do. But they're also highly reactive with different cell components, including DNA. And by reacting with DNA, they can actually cause significant damage to a cell's genetic code. One example of this type of damage is the double-strand break. And ROS can actually break a DNA's double helix into two smaller pieces."}, {"video_title": "Mutagens and carcinogens   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "But they're also highly reactive with different cell components, including DNA. And by reacting with DNA, they can actually cause significant damage to a cell's genetic code. One example of this type of damage is the double-strand break. And ROS can actually break a DNA's double helix into two smaller pieces. And you can see why this type of a reaction could cause a mutation, since it quite significantly changes the structure of the cell's DNA. The next type of DNA damage that ROS can cause is base modification. And that's when the nucleic acid bases are changed or swapped around."}, {"video_title": "Mutagens and carcinogens   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "And ROS can actually break a DNA's double helix into two smaller pieces. And you can see why this type of a reaction could cause a mutation, since it quite significantly changes the structure of the cell's DNA. The next type of DNA damage that ROS can cause is base modification. And that's when the nucleic acid bases are changed or swapped around. And that can pretty readily cause point mutations, or maybe even other kinds. Now you may be wondering, why would a cell ever make something that could damage itself? Well, it turns out that ROS actually have a couple of beneficial effects on a cell."}, {"video_title": "Mutagens and carcinogens   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "And that's when the nucleic acid bases are changed or swapped around. And that can pretty readily cause point mutations, or maybe even other kinds. Now you may be wondering, why would a cell ever make something that could damage itself? Well, it turns out that ROS actually have a couple of beneficial effects on a cell. And cells actually have a couple of ways to make sure that they don't cause damage. But sometimes, ROS levels get really high, and cells can't deal with them anymore. We call this oxidative stress."}, {"video_title": "Mutagens and carcinogens   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "Well, it turns out that ROS actually have a couple of beneficial effects on a cell. And cells actually have a couple of ways to make sure that they don't cause damage. But sometimes, ROS levels get really high, and cells can't deal with them anymore. We call this oxidative stress. And antioxidants are something that your doctor might have told you they're good for you. And it turns out that part of what antioxidants do is help make sure that ROS don't damage your DNA. Now let's look at a couple examples of exogenous mutagens."}, {"video_title": "Mutagens and carcinogens   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "We call this oxidative stress. And antioxidants are something that your doctor might have told you they're good for you. And it turns out that part of what antioxidants do is help make sure that ROS don't damage your DNA. Now let's look at a couple examples of exogenous mutagens. And there are many different types of exogenous mutagens, but we're really only going to talk about two. Now intercalators are one example. And one of them is called ethidium bromide, which you may be familiar with if you've ever done a PCR experiment before."}, {"video_title": "Mutagens and carcinogens   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "Now let's look at a couple examples of exogenous mutagens. And there are many different types of exogenous mutagens, but we're really only going to talk about two. Now intercalators are one example. And one of them is called ethidium bromide, which you may be familiar with if you've ever done a PCR experiment before. And what ethidium bromide will do is it'll jump into a DNA double helix and stick itself between the two strands. And when these intercalators intercalate into DNA, they can deform the structure of the DNA and cause some serious problems. Base analogs, like 5-bromouracil, which we also call 5-BU, pretend to be a certain base, but then act differently than that base normally would."}, {"video_title": "Mutagens and carcinogens   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "And one of them is called ethidium bromide, which you may be familiar with if you've ever done a PCR experiment before. And what ethidium bromide will do is it'll jump into a DNA double helix and stick itself between the two strands. And when these intercalators intercalate into DNA, they can deform the structure of the DNA and cause some serious problems. Base analogs, like 5-bromouracil, which we also call 5-BU, pretend to be a certain base, but then act differently than that base normally would. So in the case of 5-BU, it's an analog of uracil and looks a lot like it, but once it's incorporated into DNA, it can shift between two different forms. And in its keto form, it will pair best with adidine. While it's in enol form, it will pair best with guanine."}, {"video_title": "Mutagens and carcinogens   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "Base analogs, like 5-bromouracil, which we also call 5-BU, pretend to be a certain base, but then act differently than that base normally would. So in the case of 5-BU, it's an analog of uracil and looks a lot like it, but once it's incorporated into DNA, it can shift between two different forms. And in its keto form, it will pair best with adidine. While it's in enol form, it will pair best with guanine. Now if you're familiar with organic chemistry, you might know that 5-BU can convert between its keto and enol form through something called a tautomerization reaction. And overall, you can see how this base analog might be able to induce mutations in a DNA structure. Now, the last thing we're going to talk about is what a carcinogen is."}, {"video_title": "Mutagens and carcinogens   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "While it's in enol form, it will pair best with guanine. Now if you're familiar with organic chemistry, you might know that 5-BU can convert between its keto and enol form through something called a tautomerization reaction. And overall, you can see how this base analog might be able to induce mutations in a DNA structure. Now, the last thing we're going to talk about is what a carcinogen is. Now carcinogens can be mutagens, but not all of them are. But in general, you can say that a carcinogen is something that can lead to cancer, which if you remember is when cells in an organism divide uncontrollably and can form big masses of cells called tumours. Now some carcinogens will work by making mutations in DNA that lead to cancer, but sometimes they might carry out their effect simply by increasing the rate at which a bunch of cells divide without actually affecting their DNA."}, {"video_title": "Mutagens and carcinogens   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "Now, the last thing we're going to talk about is what a carcinogen is. Now carcinogens can be mutagens, but not all of them are. But in general, you can say that a carcinogen is something that can lead to cancer, which if you remember is when cells in an organism divide uncontrollably and can form big masses of cells called tumours. Now some carcinogens will work by making mutations in DNA that lead to cancer, but sometimes they might carry out their effect simply by increasing the rate at which a bunch of cells divide without actually affecting their DNA. And some examples of carcinogens are tobacco, which come from cigarettes, asbestos, which used to be used as home insulation, and even UV radiation. So what did we learn? Well first we learned that mutagens are chemical or physical substances or events that can increase the probability of genetic mutations occurring."}, {"video_title": "Molecular variation   Cellular energetics   AP Biology   Khan Academy.mp3", "Sentence": "You're probably familiar with the idea that you have a variation of genetic makeups in a population, but even within an organism, you have variation in the types of molecules that an organism can produce and when they produce them. So for example, we know that we all have DNA, all organisms, living organisms that we know about, they have DNA, I'll just do this as a quick drawing of DNA. We know that we have genes in our DNA that code eventually, they go from DNA to messenger RNA and then they go to the ribosomes to be translated into proteins. And these proteins are a major way of expressing what is encoded in our DNA. Now it turns out that our DNA will encode for not only multiple proteins, but multiple types of the same protein and it can encode for some of these proteins more under certain circumstances and other proteins more in other circumstances based on environmental factors. Those environmental factors might influence what part of the DNA is being transcribed into mRNA, which then gets translated into proteins at different times. And there's several very interesting examples of this."}, {"video_title": "Molecular variation   Cellular energetics   AP Biology   Khan Academy.mp3", "Sentence": "And these proteins are a major way of expressing what is encoded in our DNA. Now it turns out that our DNA will encode for not only multiple proteins, but multiple types of the same protein and it can encode for some of these proteins more under certain circumstances and other proteins more in other circumstances based on environmental factors. Those environmental factors might influence what part of the DNA is being transcribed into mRNA, which then gets translated into proteins at different times. And there's several very interesting examples of this. It turns out that hemoglobin, which you might recognize as the protein complex that binds to oxygen in our red blood cells, that the type of predominant hemoglobin changes from when we are inside our mother's wombs to when we become independent beings. So this right over here is a picture of a hemoglobin molecule. You see your four heme groups that each bind to oxygen."}, {"video_title": "Molecular variation   Cellular energetics   AP Biology   Khan Academy.mp3", "Sentence": "And there's several very interesting examples of this. It turns out that hemoglobin, which you might recognize as the protein complex that binds to oxygen in our red blood cells, that the type of predominant hemoglobin changes from when we are inside our mother's wombs to when we become independent beings. So this right over here is a picture of a hemoglobin molecule. You see your four heme groups that each bind to oxygen. And when you're a fetus, the primary type of hemoglobin is hemoglobin F. And then once we come out of our mother's wounds, the hemoglobin F stops getting produced and we go to hemoglobin A. Now you might say, well, why do we have this variation in the type of hemoglobin? And the answer is is that those are two different environments."}, {"video_title": "Molecular variation   Cellular energetics   AP Biology   Khan Academy.mp3", "Sentence": "You see your four heme groups that each bind to oxygen. And when you're a fetus, the primary type of hemoglobin is hemoglobin F. And then once we come out of our mother's wounds, the hemoglobin F stops getting produced and we go to hemoglobin A. Now you might say, well, why do we have this variation in the type of hemoglobin? And the answer is is that those are two different environments. When a fetus is in the mother's womb, it's not directly breathing. It's getting its oxygen from the mother's blood. The mother's blood does not mix directly with the baby's blood, but there's a boundary where you have the mother's blood here and I'll say this is the baby's blood right over here."}, {"video_title": "Molecular variation   Cellular energetics   AP Biology   Khan Academy.mp3", "Sentence": "And the answer is is that those are two different environments. When a fetus is in the mother's womb, it's not directly breathing. It's getting its oxygen from the mother's blood. The mother's blood does not mix directly with the baby's blood, but there's a boundary where you have the mother's blood here and I'll say this is the baby's blood right over here. And you have the gas exchange of the oxygen going through that boundary. And then of course the release of the carbon dioxide going the other way. And this environment where the baby's red blood cells have to bind to the oxygen is a relatively low oxygen environment compared to say our lungs because it has oxygenated and deoxygenated blood mixing in that same place and it does not have direct access to say the lungs."}, {"video_title": "Molecular variation   Cellular energetics   AP Biology   Khan Academy.mp3", "Sentence": "The mother's blood does not mix directly with the baby's blood, but there's a boundary where you have the mother's blood here and I'll say this is the baby's blood right over here. And you have the gas exchange of the oxygen going through that boundary. And then of course the release of the carbon dioxide going the other way. And this environment where the baby's red blood cells have to bind to the oxygen is a relatively low oxygen environment compared to say our lungs because it has oxygenated and deoxygenated blood mixing in that same place and it does not have direct access to say the lungs. And so in this low oxygen environment, the hemoglobin molecules have to be really, really, really good at binding to oxygen. And we can see that from this diagram right over here where the horizontal axis is the partial pressure of oxygen and the vertical axis is how saturated with oxygen these different hemoglobin molecules can become. And you can see that the fetal hemoglobin which is depicted by this blue curve, it gets 50% saturated at a lower partial pressure of oxygen than the adult hemoglobin."}, {"video_title": "Molecular variation   Cellular energetics   AP Biology   Khan Academy.mp3", "Sentence": "And this environment where the baby's red blood cells have to bind to the oxygen is a relatively low oxygen environment compared to say our lungs because it has oxygenated and deoxygenated blood mixing in that same place and it does not have direct access to say the lungs. And so in this low oxygen environment, the hemoglobin molecules have to be really, really, really good at binding to oxygen. And we can see that from this diagram right over here where the horizontal axis is the partial pressure of oxygen and the vertical axis is how saturated with oxygen these different hemoglobin molecules can become. And you can see that the fetal hemoglobin which is depicted by this blue curve, it gets 50% saturated at a lower partial pressure of oxygen than the adult hemoglobin. So one way to think about it, it is stickier, it binds with that oxygen, it can pull that oxygen out of the blood far better which makes sense for the environment that the fetus is in. But once it comes out of the mother's womb, it doesn't need that stickiness. And there's some drawbacks to that stickiness as well because it makes it hard for that oxygen to go into as many of the body's tissues."}, {"video_title": "Molecular variation   Cellular energetics   AP Biology   Khan Academy.mp3", "Sentence": "And you can see that the fetal hemoglobin which is depicted by this blue curve, it gets 50% saturated at a lower partial pressure of oxygen than the adult hemoglobin. So one way to think about it, it is stickier, it binds with that oxygen, it can pull that oxygen out of the blood far better which makes sense for the environment that the fetus is in. But once it comes out of the mother's womb, it doesn't need that stickiness. And there's some drawbacks to that stickiness as well because it makes it hard for that oxygen to go into as many of the body's tissues. And so that's why you have this transition from hemoglobin F to hemoglobin A. And it's not just hemoglobin where we see this molecular variation. Plants and other organisms that conduct photosynthesis contain multiple types of chlorophyll."}, {"video_title": "Molecular variation   Cellular energetics   AP Biology   Khan Academy.mp3", "Sentence": "And there's some drawbacks to that stickiness as well because it makes it hard for that oxygen to go into as many of the body's tissues. And so that's why you have this transition from hemoglobin F to hemoglobin A. And it's not just hemoglobin where we see this molecular variation. Plants and other organisms that conduct photosynthesis contain multiple types of chlorophyll. Remember, chlorophyll is a very important molecule in capturing light energy which can then be used to help synthesize carbohydrates in things like plants. And here we see how two different chlorophyll molecules, both that would be found in plants, how well they absorb light of different frequencies. So you can see chlorophyll A is really good at absorbing the violet bordering on blue light, while chlorophyll B is better at the blue-green type of light."}, {"video_title": "Molecular variation   Cellular energetics   AP Biology   Khan Academy.mp3", "Sentence": "Plants and other organisms that conduct photosynthesis contain multiple types of chlorophyll. Remember, chlorophyll is a very important molecule in capturing light energy which can then be used to help synthesize carbohydrates in things like plants. And here we see how two different chlorophyll molecules, both that would be found in plants, how well they absorb light of different frequencies. So you can see chlorophyll A is really good at absorbing the violet bordering on blue light, while chlorophyll B is better at the blue-green type of light. And then you have another peak here where chlorophyll B is better at absorbing an orangish-red, while chlorophyll A is better at absorbing, I guess you could say, a red bordering on infrared wavelength. And the reason why this is valuable is that the light that the plant gets, especially at different times of day, at different times of year, is going to have different wavelengths. And so this just lets the plant capture more energy that it can use in photosynthesis."}, {"video_title": "Molecular variation   Cellular energetics   AP Biology   Khan Academy.mp3", "Sentence": "So you can see chlorophyll A is really good at absorbing the violet bordering on blue light, while chlorophyll B is better at the blue-green type of light. And then you have another peak here where chlorophyll B is better at absorbing an orangish-red, while chlorophyll A is better at absorbing, I guess you could say, a red bordering on infrared wavelength. And the reason why this is valuable is that the light that the plant gets, especially at different times of day, at different times of year, is going to have different wavelengths. And so this just lets the plant capture more energy that it can use in photosynthesis. And these were just two examples of molecular variation. In our cellular membranes, there's multiple types of phospholipids that are forming the phospholipid bilayer. And those multiple types have different levels of how fluid they are at different temperatures."}, {"video_title": "Molecular variation   Cellular energetics   AP Biology   Khan Academy.mp3", "Sentence": "And so this just lets the plant capture more energy that it can use in photosynthesis. And these were just two examples of molecular variation. In our cellular membranes, there's multiple types of phospholipids that are forming the phospholipid bilayer. And those multiple types have different levels of how fluid they are at different temperatures. And there are animal studies that show that the variations change depending on the conditions. For example, a cold-blooded animal might have more of the fluid phospholipids when it is very cold, so that the membranes don't become overly rigid. But I will leave you there."}, {"video_title": "Organism life history and fecundity    Ecology   Khan Academy.mp3", "Sentence": "What we're gonna talk about in this video is what I consider one of the most fascinating subjects in biology, and that's the variation we see from species to species in life histories and life spans and their rate of reproduction. For example, we have three different species here. On the left, we have an African elephant. An African elephant, you might know, can live a long time, especially out in the wild. It can live many decades, even 40, 50, 60 years, and their life history actually parallels human, at least modern human life history in a lot of ways. The first 10 years of their life, they are very dependent on their parents. After that, they kind of enter into a bit of an adolescence, very similar to how humans do, where in theory, they could reproduce, but they don't tend to, and they are still somewhat dependent."}, {"video_title": "Organism life history and fecundity    Ecology   Khan Academy.mp3", "Sentence": "An African elephant, you might know, can live a long time, especially out in the wild. It can live many decades, even 40, 50, 60 years, and their life history actually parallels human, at least modern human life history in a lot of ways. The first 10 years of their life, they are very dependent on their parents. After that, they kind of enter into a bit of an adolescence, very similar to how humans do, where in theory, they could reproduce, but they don't tend to, and they are still somewhat dependent. And then they move into a phase when they do reproduce, and they will reproduce on the order of once every two to four, once every two to four years, a female African elephant will reproduce. Their gestation period, the amount of time that the baby elephant will be in the mother's womb is on the order, it's actually longer than for humans. Humans, you probably know, is nine months."}, {"video_title": "Organism life history and fecundity    Ecology   Khan Academy.mp3", "Sentence": "After that, they kind of enter into a bit of an adolescence, very similar to how humans do, where in theory, they could reproduce, but they don't tend to, and they are still somewhat dependent. And then they move into a phase when they do reproduce, and they will reproduce on the order of once every two to four, once every two to four years, a female African elephant will reproduce. Their gestation period, the amount of time that the baby elephant will be in the mother's womb is on the order, it's actually longer than for humans. Humans, you probably know, is nine months. For an African elephant, it is 22 months. And so because of that, they can reproduce about once every two to four years. Now, another example, and these are actually elephants and rabbits might not look closely related to you, but they are actually still pretty closely related if you think about the entire tree of life."}, {"video_title": "Organism life history and fecundity    Ecology   Khan Academy.mp3", "Sentence": "Humans, you probably know, is nine months. For an African elephant, it is 22 months. And so because of that, they can reproduce about once every two to four years. Now, another example, and these are actually elephants and rabbits might not look closely related to you, but they are actually still pretty closely related if you think about the entire tree of life. They are both mammals, and actually, everything we're considering here are animals. We're gonna consider African elephant, rabbit, and we're gonna consider salmon. But what I'm talking about applies to all life."}, {"video_title": "Organism life history and fecundity    Ecology   Khan Academy.mp3", "Sentence": "Now, another example, and these are actually elephants and rabbits might not look closely related to you, but they are actually still pretty closely related if you think about the entire tree of life. They are both mammals, and actually, everything we're considering here are animals. We're gonna consider African elephant, rabbit, and we're gonna consider salmon. But what I'm talking about applies to all life. It applies to bacteria, it applies to trees. There's a huge variation in their fecundity, the rate at which they reproduce. Let me write that word down."}, {"video_title": "Organism life history and fecundity    Ecology   Khan Academy.mp3", "Sentence": "But what I'm talking about applies to all life. It applies to bacteria, it applies to trees. There's a huge variation in their fecundity, the rate at which they reproduce. Let me write that word down. Fecundity, fecundity, the rate at which they reproduce, and also variation in their actual lifespan, whether you're talking about a tree, or a bacteria, or a fish, or a mammal. But just going from one mammal to another, let's go to a rabbit, and depending on which type of rabbit you're talking about, but a rabbit could, lifespan is in the single-digit years. But unlike an elephant, an elephant, the first 10, 15, 20 years of their life, they aren't in that reproductive phase of their life."}, {"video_title": "Organism life history and fecundity    Ecology   Khan Academy.mp3", "Sentence": "Let me write that word down. Fecundity, fecundity, the rate at which they reproduce, and also variation in their actual lifespan, whether you're talking about a tree, or a bacteria, or a fish, or a mammal. But just going from one mammal to another, let's go to a rabbit, and depending on which type of rabbit you're talking about, but a rabbit could, lifespan is in the single-digit years. But unlike an elephant, an elephant, the first 10, 15, 20 years of their life, they aren't in that reproductive phase of their life. A rabbit enters into that reproductive phase of their life within several months, within four or five months of birth. And once they enter into that reproductive phase, and I'm showing the reproductive phase in magenta here, they can reproduce a lot. They have high fecundity."}, {"video_title": "Organism life history and fecundity    Ecology   Khan Academy.mp3", "Sentence": "But unlike an elephant, an elephant, the first 10, 15, 20 years of their life, they aren't in that reproductive phase of their life. A rabbit enters into that reproductive phase of their life within several months, within four or five months of birth. And once they enter into that reproductive phase, and I'm showing the reproductive phase in magenta here, they can reproduce a lot. They have high fecundity. They have a very high reproductive rate. Every time a female rabbit has a litter, it can have many, many baby rabbits in it. The numbers I found were one to 14, one to 14 rabbits."}, {"video_title": "Organism life history and fecundity    Ecology   Khan Academy.mp3", "Sentence": "They have high fecundity. They have a very high reproductive rate. Every time a female rabbit has a litter, it can have many, many baby rabbits in it. The numbers I found were one to 14, one to 14 rabbits. And not only can they have one to 14 rabbits every time they have a litter, but they can do this on the order of once a month. So every month. So even though the lifespan of that female rabbit, depending on which type of rabbit you're talking about, might be, it might be three, four, five, six years, depending on the type of rabbit you're talking about, you can imagine, if they're producing, let's say 10 rabbits every month per year, they could produce 120 rabbits, or if they could produce 10 rabbits per month, 12 months a year, that's 120 rabbits a year over several years."}, {"video_title": "Organism life history and fecundity    Ecology   Khan Academy.mp3", "Sentence": "The numbers I found were one to 14, one to 14 rabbits. And not only can they have one to 14 rabbits every time they have a litter, but they can do this on the order of once a month. So every month. So even though the lifespan of that female rabbit, depending on which type of rabbit you're talking about, might be, it might be three, four, five, six years, depending on the type of rabbit you're talking about, you can imagine, if they're producing, let's say 10 rabbits every month per year, they could produce 120 rabbits, or if they could produce 10 rabbits per month, 12 months a year, that's 120 rabbits a year over several years. And then you can imagine those rabbits very quickly, the female ones, if we assume roughly half of them are female, that half can very quickly get into that reproductive phase and then start reproducing at a similar rate. So on an individual level, a female rabbit has high fecundity, and then on a population level, that group of rabbits would also have very, very high fecundity. And then we could look at another example."}, {"video_title": "Organism life history and fecundity    Ecology   Khan Academy.mp3", "Sentence": "So even though the lifespan of that female rabbit, depending on which type of rabbit you're talking about, might be, it might be three, four, five, six years, depending on the type of rabbit you're talking about, you can imagine, if they're producing, let's say 10 rabbits every month per year, they could produce 120 rabbits, or if they could produce 10 rabbits per month, 12 months a year, that's 120 rabbits a year over several years. And then you can imagine those rabbits very quickly, the female ones, if we assume roughly half of them are female, that half can very quickly get into that reproductive phase and then start reproducing at a similar rate. So on an individual level, a female rabbit has high fecundity, and then on a population level, that group of rabbits would also have very, very high fecundity. And then we could look at another example. And this is the example of salmon, and there's many types of salmon. But the general way that salmon, the general life cycle that salmon go through is they are born, and they are usually born up some stream and usually some water that is, where there isn't a strong current, and then once the baby salmon are born, and they could be born in groups of hundreds or thousands, they make their way down that river, down that stream, into the ocean, and then they have many years of a growth phase in the ocean where they get larger and larger. They're not reproducing then, and then when they are ready to reproduce, they fight their way back up the same stream that they were born in, or the same river that they were born in, they fight their way back up to it, and they reproduce, and this is both the males and the females, the males fertilize, the females produce the eggs, the males fertilize the eggs, and then they die."}, {"video_title": "Organism life history and fecundity    Ecology   Khan Academy.mp3", "Sentence": "And then we could look at another example. And this is the example of salmon, and there's many types of salmon. But the general way that salmon, the general life cycle that salmon go through is they are born, and they are usually born up some stream and usually some water that is, where there isn't a strong current, and then once the baby salmon are born, and they could be born in groups of hundreds or thousands, they make their way down that river, down that stream, into the ocean, and then they have many years of a growth phase in the ocean where they get larger and larger. They're not reproducing then, and then when they are ready to reproduce, they fight their way back up the same stream that they were born in, or the same river that they were born in, they fight their way back up to it, and they reproduce, and this is both the males and the females, the males fertilize, the females produce the eggs, the males fertilize the eggs, and then they die. So they have one reproductive event, so you have one reproductive event, and then death, and then they kill, they just die, and people are still understanding why exactly does this happen. So one reproductive event, reproductive event, and then they die, and there's actually a technical term for species that do this, the salmon isn't the only one, where they have that one, they go out with, you can kind of view it as a big bang, where they have that one reproductive event where they might have hundreds or even thousands of eggs, but then they die, this is called semelparity. Let me write this down."}, {"video_title": "Organism life history and fecundity    Ecology   Khan Academy.mp3", "Sentence": "They're not reproducing then, and then when they are ready to reproduce, they fight their way back up the same stream that they were born in, or the same river that they were born in, they fight their way back up to it, and they reproduce, and this is both the males and the females, the males fertilize, the females produce the eggs, the males fertilize the eggs, and then they die. So they have one reproductive event, so you have one reproductive event, and then death, and then they kill, they just die, and people are still understanding why exactly does this happen. So one reproductive event, reproductive event, and then they die, and there's actually a technical term for species that do this, the salmon isn't the only one, where they have that one, they go out with, you can kind of view it as a big bang, where they have that one reproductive event where they might have hundreds or even thousands of eggs, but then they die, this is called semelparity. Let me write this down. So this is called semelparity. Semel comes from the Latin for once, parity comes from the Latin for to beget, so to beget once, you're reproducing once, and then in the case of salmon, you are dying. And you might say, okay, if that's semelparity, what would we call an elephant or rabbits, rabbits for sure, and elephants as well, they can have multiple reproductive events."}, {"video_title": "Organism life history and fecundity    Ecology   Khan Academy.mp3", "Sentence": "Let me write this down. So this is called semelparity. Semel comes from the Latin for once, parity comes from the Latin for to beget, so to beget once, you're reproducing once, and then in the case of salmon, you are dying. And you might say, okay, if that's semelparity, what would we call an elephant or rabbits, rabbits for sure, and elephants as well, they can have multiple reproductive events. Well, there, that is called iteroparity. Itero, iteroparity, you might have heard the word iterate, that means to repeat something or to do something over and over again. Itero is the root for, it means repeat, so iteroparity, beget, repeatedly."}, {"video_title": "Organism life history and fecundity    Ecology   Khan Academy.mp3", "Sentence": "And you might say, okay, if that's semelparity, what would we call an elephant or rabbits, rabbits for sure, and elephants as well, they can have multiple reproductive events. Well, there, that is called iteroparity. Itero, iteroparity, you might have heard the word iterate, that means to repeat something or to do something over and over again. Itero is the root for, it means repeat, so iteroparity, beget, repeatedly. And so that's what animals like elephant and for sure, rabbits are actually doing. And what's fascinating about all of this is, and this is a question that I've wondered many, since I first realized when I was young, that wow, why is there so much variation here, is why has nature selected for, or why have these species found niches in which they can operate in which it makes sense, where natural selection has selected for these very different lifespans, these very different reproduction rates, this variation in fecundity, this sometimes iteroparity, sometimes semelparity. And it is a bit of, it's not a mystery."}, {"video_title": "Organism life history and fecundity    Ecology   Khan Academy.mp3", "Sentence": "Itero is the root for, it means repeat, so iteroparity, beget, repeatedly. And so that's what animals like elephant and for sure, rabbits are actually doing. And what's fascinating about all of this is, and this is a question that I've wondered many, since I first realized when I was young, that wow, why is there so much variation here, is why has nature selected for, or why have these species found niches in which they can operate in which it makes sense, where natural selection has selected for these very different lifespans, these very different reproduction rates, this variation in fecundity, this sometimes iteroparity, sometimes semelparity. And it is a bit of, it's not a mystery. People are studying this and they have good hypotheses, but we don't know for sure, especially from species to species. And a framework you could use to think about it is a species, they're trying to optimize survival. And not even of the individual, they're trying to optimize survival of really their genetic information."}, {"video_title": "Organism life history and fecundity    Ecology   Khan Academy.mp3", "Sentence": "And it is a bit of, it's not a mystery. People are studying this and they have good hypotheses, but we don't know for sure, especially from species to species. And a framework you could use to think about it is a species, they're trying to optimize survival. And not even of the individual, they're trying to optimize survival of really their genetic information. That's what, it's not like the species or the genes are actively trying to do it, but natural selection is doing that for them. So let's call this box natural selection. Natural selection."}, {"video_title": "Organism life history and fecundity    Ecology   Khan Academy.mp3", "Sentence": "And not even of the individual, they're trying to optimize survival of really their genetic information. That's what, it's not like the species or the genes are actively trying to do it, but natural selection is doing that for them. So let's call this box natural selection. Natural selection. And so what you have coming out of this is the fittest genes. And when we talk about fittest genes, we're not talking about somehow that some are better than others. We're just saying for that environment, the ones that seem, the genes that produce the traits that are most suitable to survival and most suitable towards reproduction."}, {"video_title": "Organism life history and fecundity    Ecology   Khan Academy.mp3", "Sentence": "Natural selection. And so what you have coming out of this is the fittest genes. And when we talk about fittest genes, we're not talking about somehow that some are better than others. We're just saying for that environment, the ones that seem, the genes that produce the traits that are most suitable to survival and most suitable towards reproduction. And then the inputs that are going into this natural selection box are things like availability of energy, of food, of, well I'll call it free energy. Availability, because it's not just, obviously plants can get that free energy from the sun. Availability."}, {"video_title": "Organism life history and fecundity    Ecology   Khan Academy.mp3", "Sentence": "We're just saying for that environment, the ones that seem, the genes that produce the traits that are most suitable to survival and most suitable towards reproduction. And then the inputs that are going into this natural selection box are things like availability of energy, of food, of, well I'll call it free energy. Availability, because it's not just, obviously plants can get that free energy from the sun. Availability. Availability of energy. We could talk about the predatory environment. Predatory, predatory environment."}, {"video_title": "Organism life history and fecundity    Ecology   Khan Academy.mp3", "Sentence": "Availability. Availability of energy. We could talk about the predatory environment. Predatory, predatory environment. We could talk about disease. Disease. Every moment that an organism is alive, it has to worry about these things."}, {"video_title": "Organism life history and fecundity    Ecology   Khan Academy.mp3", "Sentence": "Predatory, predatory environment. We could talk about disease. Disease. Every moment that an organism is alive, it has to worry about these things. It has to worry about finding food or competing for food. It has to worry about predators. It has to worry about disease."}, {"video_title": "Organism life history and fecundity    Ecology   Khan Academy.mp3", "Sentence": "Every moment that an organism is alive, it has to worry about these things. It has to worry about finding food or competing for food. It has to worry about predators. It has to worry about disease. And once again, the individual organism is not sitting there. It's not necessary that these salmon are like, oh I hope I don't catch a disease. Or they might not even be stressed about the bears that might try to grab them as they go upstream."}, {"video_title": "Organism life history and fecundity    Ecology   Khan Academy.mp3", "Sentence": "It has to worry about disease. And once again, the individual organism is not sitting there. It's not necessary that these salmon are like, oh I hope I don't catch a disease. Or they might not even be stressed about the bears that might try to grab them as they go upstream. But these are the factors that play into how, or what gets selected for, I guess is the best way to phrase it. And in terms of, from a species point of view, the various dials, well these are things like reproduction, like what does a species decide to do given these constraints? And so the various dials are fecundity, actually let me write it this, rate of reproduction, age of reproduction, and these are related, age of reproduction, things like lifespan, and these are all related in some way, lifespan, growth, growth, health."}, {"video_title": "Organism life history and fecundity    Ecology   Khan Academy.mp3", "Sentence": "Or they might not even be stressed about the bears that might try to grab them as they go upstream. But these are the factors that play into how, or what gets selected for, I guess is the best way to phrase it. And in terms of, from a species point of view, the various dials, well these are things like reproduction, like what does a species decide to do given these constraints? And so the various dials are fecundity, actually let me write it this, rate of reproduction, age of reproduction, and these are related, age of reproduction, things like lifespan, and these are all related in some way, lifespan, growth, growth, health. And a species and an organism is making trade-offs all of the time. The salmon goes through that huge phase where it's deciding to apply most of its energy towards growth and survival, and then all of a sudden it kicks into another gear where it actually uses a lot of that energy that was stored up to go upstream and it goes into a reproductive phase, and then it dies. And natural selection has, this has happened, arguably because that somehow helps the salmon's DNA to spread more."}, {"video_title": "Organism life history and fecundity    Ecology   Khan Academy.mp3", "Sentence": "And so the various dials are fecundity, actually let me write it this, rate of reproduction, age of reproduction, and these are related, age of reproduction, things like lifespan, and these are all related in some way, lifespan, growth, growth, health. And a species and an organism is making trade-offs all of the time. The salmon goes through that huge phase where it's deciding to apply most of its energy towards growth and survival, and then all of a sudden it kicks into another gear where it actually uses a lot of that energy that was stored up to go upstream and it goes into a reproductive phase, and then it dies. And natural selection has, this has happened, arguably because that somehow helps the salmon's DNA to spread more. Maybe somehow it adds nutrients to the water, or they put all of that energy to go upstream so that their offspring will have an easier time going downstream. But there's also other trade-offs. You could have things that lay, a salmon might, a female salmon might lay thousands of eggs but very few of those actually make it through the full cycle."}, {"video_title": "Organism life history and fecundity    Ecology   Khan Academy.mp3", "Sentence": "And natural selection has, this has happened, arguably because that somehow helps the salmon's DNA to spread more. Maybe somehow it adds nutrients to the water, or they put all of that energy to go upstream so that their offspring will have an easier time going downstream. But there's also other trade-offs. You could have things that lay, a salmon might, a female salmon might lay thousands of eggs but very few of those actually make it through the full cycle. The estimates I've seen is out of those thousands of eggs that get laid, only about three make it back. This was the example I saw for sockeye salmon. On average, only three of them make it back for the next year."}, {"video_title": "DNA   Biomolecules   MCAT   Khan Academy (2).mp3", "Sentence": "As long as human beings have been around, I could imagine that they've noticed that offspring tend to have traits in common with the parent. For example, someone might have told you, hey, you walk kind of like your dad, or your smile is kind of like your mom, or your eyes are like one of your uncles or your grandparents. And so there's always been this notion of inherited traits. But it wasn't until the 1800s that that started to be studied in a more scientific way with Gregor Mendel, the father of genetics. But even then, even Mendel, who was starting to understand the mechanisms of, or he was trying to understand how inheritance happens, and he even could start to breed certain types of things, even he didn't know exactly what was the molecular basis for inheritance. And the answer to that question wasn't figured out until fairly recent times, until the mid-20th century, not until the structure of DNA was established by Watson and Crick. And their work was based on the work of many others, especially folks like Rosalind Franklin, who essentially provided the bulk of the data for Watson and Crick's work, Maurice Wilkins, and many, many, many other folks."}, {"video_title": "DNA   Biomolecules   MCAT   Khan Academy (2).mp3", "Sentence": "But it wasn't until the 1800s that that started to be studied in a more scientific way with Gregor Mendel, the father of genetics. But even then, even Mendel, who was starting to understand the mechanisms of, or he was trying to understand how inheritance happens, and he even could start to breed certain types of things, even he didn't know exactly what was the molecular basis for inheritance. And the answer to that question wasn't figured out until fairly recent times, until the mid-20th century, not until the structure of DNA was established by Watson and Crick. And their work was based on the work of many others, especially folks like Rosalind Franklin, who essentially provided the bulk of the data for Watson and Crick's work, Maurice Wilkins, and many, many, many other folks. But it was really the structure of DNA that made people say, hey, that looks like the molecule that's storing the information. And just to be clear, DNA wasn't discovered in 1953. DNA was discovered in the mid-1800s."}, {"video_title": "DNA   Biomolecules   MCAT   Khan Academy (2).mp3", "Sentence": "And their work was based on the work of many others, especially folks like Rosalind Franklin, who essentially provided the bulk of the data for Watson and Crick's work, Maurice Wilkins, and many, many, many other folks. But it was really the structure of DNA that made people say, hey, that looks like the molecule that's storing the information. And just to be clear, DNA wasn't discovered in 1953. DNA was discovered in the mid-1800s. It was this kind of, this molecule that was inside of nuclei, of cells, and for some time, people said, oh, maybe this could be a molecular basis of inheritance. You know, you could imagine what you would need to be a molecular basis of inheritance. It would have to be a molecule or a series of molecules that could contain information, that could be replicated, that could be expressed in some way."}, {"video_title": "DNA   Biomolecules   MCAT   Khan Academy (2).mp3", "Sentence": "DNA was discovered in the mid-1800s. It was this kind of, this molecule that was inside of nuclei, of cells, and for some time, people said, oh, maybe this could be a molecular basis of inheritance. You know, you could imagine what you would need to be a molecular basis of inheritance. It would have to be a molecule or a series of molecules that could contain information, that could be replicated, that could be expressed in some way. But it wasn't until 1953, when this double helix structure of DNA was established that people said, hey, this looks like our molecule. So first, let's just talk about the structure here, and then actually we'll talk about where this name, DNA, deoxyribonucleic acid, comes from. And then we'll talk a little bit about why the structure lends itself well to something that stores information, that can replicate its information, and that could express its information."}, {"video_title": "DNA   Biomolecules   MCAT   Khan Academy (2).mp3", "Sentence": "It would have to be a molecule or a series of molecules that could contain information, that could be replicated, that could be expressed in some way. But it wasn't until 1953, when this double helix structure of DNA was established that people said, hey, this looks like our molecule. So first, let's just talk about the structure here, and then actually we'll talk about where this name, DNA, deoxyribonucleic acid, comes from. And then we'll talk a little bit about why the structure lends itself well to something that stores information, that can replicate its information, and that could express its information. We might go in-depth on the expression of information in future videos. So this structure right over here, and this is a visual depiction of a DNA molecule, you can view this as kind of a twisted ladder. It has these two, I guess you could say, sides of the ladder that are twisted."}, {"video_title": "DNA   Biomolecules   MCAT   Khan Academy (2).mp3", "Sentence": "And then we'll talk a little bit about why the structure lends itself well to something that stores information, that can replicate its information, and that could express its information. We might go in-depth on the expression of information in future videos. So this structure right over here, and this is a visual depiction of a DNA molecule, you can view this as kind of a twisted ladder. It has these two, I guess you could say, sides of the ladder that are twisted. That is one side right over there, and then it is another side. There is another side right over here. And in between those two sides, or connecting those two sides of that twisted ladder, you have these rungs."}, {"video_title": "DNA   Biomolecules   MCAT   Khan Academy (2).mp3", "Sentence": "It has these two, I guess you could say, sides of the ladder that are twisted. That is one side right over there, and then it is another side. There is another side right over here. And in between those two sides, or connecting those two sides of that twisted ladder, you have these rungs. And these rungs are actually where the information, the genetic information is, I guess you could say, stored in some way. Because these rungs, it's a sequence of different bases. And when I say bases, you might say, wait, this says acid, why are you saying bases right over here?"}, {"video_title": "DNA   Biomolecules   MCAT   Khan Academy (2).mp3", "Sentence": "And in between those two sides, or connecting those two sides of that twisted ladder, you have these rungs. And these rungs are actually where the information, the genetic information is, I guess you could say, stored in some way. Because these rungs, it's a sequence of different bases. And when I say bases, you might say, wait, this says acid, why are you saying bases right over here? Well, the word deoxyribonucleic acid comes from the fact that this backbone is made up of a combination of sugar and phosphate. And the sugar that makes up the backbone is deoxyribose, so that's essentially the D in DNA. And then the phosphate group is acidic, and that's where you get the acid part of it."}, {"video_title": "DNA   Biomolecules   MCAT   Khan Academy (2).mp3", "Sentence": "And when I say bases, you might say, wait, this says acid, why are you saying bases right over here? Well, the word deoxyribonucleic acid comes from the fact that this backbone is made up of a combination of sugar and phosphate. And the sugar that makes up the backbone is deoxyribose, so that's essentially the D in DNA. And then the phosphate group is acidic, and that's where you get the acid part of it. And nucleic is, hey, this was found in nuclei of cells. It is nucleic acid, deoxyribonucleic acid. But it's not, it also, it is actually mildly acidic all in total, but for every acid, it actually also has a base."}, {"video_title": "DNA   Biomolecules   MCAT   Khan Academy (2).mp3", "Sentence": "And then the phosphate group is acidic, and that's where you get the acid part of it. And nucleic is, hey, this was found in nuclei of cells. It is nucleic acid, deoxyribonucleic acid. But it's not, it also, it is actually mildly acidic all in total, but for every acid, it actually also has a base. And that base, those bases form the rung of the ladders. And actually, each rung is a pair of bases. And as I said, that's where the information is actually stored."}, {"video_title": "DNA   Biomolecules   MCAT   Khan Academy (2).mp3", "Sentence": "But it's not, it also, it is actually mildly acidic all in total, but for every acid, it actually also has a base. And that base, those bases form the rung of the ladders. And actually, each rung is a pair of bases. And as I said, that's where the information is actually stored. Well, what am I talking about? Well, let me talk about the four different bases that make up the rungs of a DNA molecule. So you have adenine."}, {"video_title": "DNA   Biomolecules   MCAT   Khan Academy (2).mp3", "Sentence": "And as I said, that's where the information is actually stored. Well, what am I talking about? Well, let me talk about the four different bases that make up the rungs of a DNA molecule. So you have adenine. And so, for example, this part right over here, this section of that rung might be adenine. Maybe this right over here is adenine. This right over here."}, {"video_title": "DNA   Biomolecules   MCAT   Khan Academy (2).mp3", "Sentence": "So you have adenine. And so, for example, this part right over here, this section of that rung might be adenine. Maybe this right over here is adenine. This right over here. Remember, each of these rungs are made up by, it's a pair of bases. And that might be adenine. Maybe this is adenine."}, {"video_title": "DNA   Biomolecules   MCAT   Khan Academy (2).mp3", "Sentence": "This right over here. Remember, each of these rungs are made up by, it's a pair of bases. And that might be adenine. Maybe this is adenine. And I could stop there. I'll do a little more adenine. Maybe that's adenine right over there."}, {"video_title": "DNA   Biomolecules   MCAT   Khan Academy (2).mp3", "Sentence": "Maybe this is adenine. And I could stop there. I'll do a little more adenine. Maybe that's adenine right over there. And adenine always pairs with the base thymine. So let me write that down. So adenine pairs with thymine."}, {"video_title": "DNA   Biomolecules   MCAT   Khan Academy (2).mp3", "Sentence": "Maybe that's adenine right over there. And adenine always pairs with the base thymine. So let me write that down. So adenine pairs with thymine. Thymine. So if that's an adenine there, then this is going to be a thymine. If this is an adenine, then this is going to be a thymine."}, {"video_title": "DNA   Biomolecules   MCAT   Khan Academy (2).mp3", "Sentence": "So adenine pairs with thymine. Thymine. So if that's an adenine there, then this is going to be a thymine. If this is an adenine, then this is going to be a thymine. Or if I drew the thymine first, well, I'll say, okay, it's going to pair with the adenine. So this is going to be a thymine right over here. This is going to be a thymine."}, {"video_title": "DNA   Biomolecules   MCAT   Khan Academy (2).mp3", "Sentence": "If this is an adenine, then this is going to be a thymine. Or if I drew the thymine first, well, I'll say, okay, it's going to pair with the adenine. So this is going to be a thymine right over here. This is going to be a thymine. If I were to draw this, this would be a thymine right over here. Now, the other two bases, you have cytosine, which pairs with guanine, or guanine that pairs with cytosine. So guanine."}, {"video_title": "DNA   Biomolecules   MCAT   Khan Academy (2).mp3", "Sentence": "This is going to be a thymine. If I were to draw this, this would be a thymine right over here. Now, the other two bases, you have cytosine, which pairs with guanine, or guanine that pairs with cytosine. So guanine. And we're not going to go into the molecular structure of these bases just yet, although these are good names to know because they show up a lot and they really form kind of the code, your genetic code. So guanine pairs with cytosine. Guanine and cytosine."}, {"video_title": "DNA   Biomolecules   MCAT   Khan Academy (2).mp3", "Sentence": "So guanine. And we're not going to go into the molecular structure of these bases just yet, although these are good names to know because they show up a lot and they really form kind of the code, your genetic code. So guanine pairs with cytosine. Guanine and cytosine. Cytosine. So actually, if this is, let's say there's some cytosine there, let's say cytosine right over here, maybe this is cytosine, maybe this is cytosine, maybe this is cytosine, this is cytosine, and maybe this is cytosine, then it always pairs with the guanine. If we're talking about, so let's see, this is guanine then, then this will be guanine, this is guanine, this is guanine, I actually didn't draw stuff here, but this is guanine, I didn't say what these could be, but these would be made of pairs of, they could be adenine-thymine pairs, and it could be adenine on either side or the thymine on either side, and they could be made of guanine-cytosine pairs, where the guanine or the cytosine is on either side."}, {"video_title": "DNA   Biomolecules   MCAT   Khan Academy (2).mp3", "Sentence": "Guanine and cytosine. Cytosine. So actually, if this is, let's say there's some cytosine there, let's say cytosine right over here, maybe this is cytosine, maybe this is cytosine, maybe this is cytosine, this is cytosine, and maybe this is cytosine, then it always pairs with the guanine. If we're talking about, so let's see, this is guanine then, then this will be guanine, this is guanine, this is guanine, I actually didn't draw stuff here, but this is guanine, I didn't say what these could be, but these would be made of pairs of, they could be adenine-thymine pairs, and it could be adenine on either side or the thymine on either side, and they could be made of guanine-cytosine pairs, where the guanine or the cytosine is on either side. Actually, just to make it a little bit more complete, let me just color in the rungs here as best as I can. So those are guanine, so they're gonna pair with cytosine, pair with cytosine, pair with cytosine. And when it's drawn this way, you might start to see how this is essentially a code, the order of which the bases are, I guess the order in which we have these, or the sequence of these bases essentially encode the information that make you you, and you could debate, well, how much of it is nature versus nurture, and when people say nature, you know, it's literally genetic, and that's an ongoing debate, but it does code for things like your hair color, when you see that your smile is similar to your parents."}, {"video_title": "DNA   Biomolecules   MCAT   Khan Academy (2).mp3", "Sentence": "If we're talking about, so let's see, this is guanine then, then this will be guanine, this is guanine, this is guanine, I actually didn't draw stuff here, but this is guanine, I didn't say what these could be, but these would be made of pairs of, they could be adenine-thymine pairs, and it could be adenine on either side or the thymine on either side, and they could be made of guanine-cytosine pairs, where the guanine or the cytosine is on either side. Actually, just to make it a little bit more complete, let me just color in the rungs here as best as I can. So those are guanine, so they're gonna pair with cytosine, pair with cytosine, pair with cytosine. And when it's drawn this way, you might start to see how this is essentially a code, the order of which the bases are, I guess the order in which we have these, or the sequence of these bases essentially encode the information that make you you, and you could debate, well, how much of it is nature versus nurture, and when people say nature, you know, it's literally genetic, and that's an ongoing debate, but it does code for things like your hair color, when you see that your smile is similar to your parents. It is because that information, to a large degree, is encoded genetically. It affects a lot of what makes you you, and actually not even just within a species, but also across species. Humans have more genetic material in common with other humans than they do with, say, a plant, but all living creatures as we know them have genetic information."}, {"video_title": "DNA   Biomolecules   MCAT   Khan Academy (2).mp3", "Sentence": "And when it's drawn this way, you might start to see how this is essentially a code, the order of which the bases are, I guess the order in which we have these, or the sequence of these bases essentially encode the information that make you you, and you could debate, well, how much of it is nature versus nurture, and when people say nature, you know, it's literally genetic, and that's an ongoing debate, but it does code for things like your hair color, when you see that your smile is similar to your parents. It is because that information, to a large degree, is encoded genetically. It affects a lot of what makes you you, and actually not even just within a species, but also across species. Humans have more genetic material in common with other humans than they do with, say, a plant, but all living creatures as we know them have genetic information. This is the basis by which they are passing down their actual traits. Now, you might be saying, well, how much genetic information does a human being have? And the number will either disappoint you or you might find it mind-boggling."}, {"video_title": "DNA   Biomolecules   MCAT   Khan Academy (2).mp3", "Sentence": "Humans have more genetic material in common with other humans than they do with, say, a plant, but all living creatures as we know them have genetic information. This is the basis by which they are passing down their actual traits. Now, you might be saying, well, how much genetic information does a human being have? And the number will either disappoint you or you might find it mind-boggling. The human genome, and every species has a different number of base pairs, to a large degree correlated with how complex they are, although not always, but the human genome has six million, sorry, not six million, six billion. Six million would be disappointing. Even billion might be disappointing."}, {"video_title": "DNA   Biomolecules   MCAT   Khan Academy (2).mp3", "Sentence": "And the number will either disappoint you or you might find it mind-boggling. The human genome, and every species has a different number of base pairs, to a large degree correlated with how complex they are, although not always, but the human genome has six million, sorry, not six million, six billion. Six million would be disappointing. Even billion might be disappointing. Six billion base pairs. Six billion base pairs. And when you have your full complement of chromosomes, and this is in most of the cells in your body, outside of your sex cells, the sperm or the egg cells, this is going to be spread over 46 chromosomes."}, {"video_title": "DNA   Biomolecules   MCAT   Khan Academy (2).mp3", "Sentence": "Even billion might be disappointing. Six billion base pairs. Six billion base pairs. And when you have your full complement of chromosomes, and this is in most of the cells in your body, outside of your sex cells, the sperm or the egg cells, this is going to be spread over 46 chromosomes. 46 chromosomes, or I guess you could say 23 pair of chromosomes. So if you divide six billion by 46, you get a little over, on average, 100 million, I think it's 100 and something million base pairs per chromosome. And some chromosomes are longer, actually some of the longest are over 200 million, and some might be shorter."}, {"video_title": "DNA   Biomolecules   MCAT   Khan Academy (2).mp3", "Sentence": "And when you have your full complement of chromosomes, and this is in most of the cells in your body, outside of your sex cells, the sperm or the egg cells, this is going to be spread over 46 chromosomes. 46 chromosomes, or I guess you could say 23 pair of chromosomes. So if you divide six billion by 46, you get a little over, on average, 100 million, I think it's 100 and something million base pairs per chromosome. And some chromosomes are longer, actually some of the longest are over 200 million, and some might be shorter. That's just on average. Now, this number might, to some of you, might be exciting. You're like, oh, I thought I was a simple creature."}, {"video_title": "DNA   Biomolecules   MCAT   Khan Academy (2).mp3", "Sentence": "And some chromosomes are longer, actually some of the longest are over 200 million, and some might be shorter. That's just on average. Now, this number might, to some of you, might be exciting. You're like, oh, I thought I was a simple creature. I didn't know I was this complex. Six billion, that's a lot of base pairs. That feels like a lot of information."}, {"video_title": "DNA   Biomolecules   MCAT   Khan Academy (2).mp3", "Sentence": "You're like, oh, I thought I was a simple creature. I didn't know I was this complex. Six billion, that's a lot of base pairs. That feels like a lot of information. For others of you, it might not feel so great. You might say, hey, wait, I could store this much information on a modern thumb drive or on a hard disk. I thought I was more unique than that."}, {"video_title": "DNA   Biomolecules   MCAT   Khan Academy (2).mp3", "Sentence": "That feels like a lot of information. For others of you, it might not feel so great. You might say, hey, wait, I could store this much information on a modern thumb drive or on a hard disk. I thought I was more unique than that. And of course, we all are special and unique, but you might say, oh, six billion base pairs, I thought I was infinitely complex and whatever else, and there's some arguments for that along some other directions. But this is the approximate length, I guess you could say, the approximate size of the actual human genome. And when we talk about chromosomes, and we'll talk about chromosomes in much more depth, imagine taking this zoomed in thing that you have right over here, and over here, I don't know how many we have, like one, two, three, four, five, six, seven, eight, nine, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19."}, {"video_title": "DNA   Biomolecules   MCAT   Khan Academy (2).mp3", "Sentence": "I thought I was more unique than that. And of course, we all are special and unique, but you might say, oh, six billion base pairs, I thought I was infinitely complex and whatever else, and there's some arguments for that along some other directions. But this is the approximate length, I guess you could say, the approximate size of the actual human genome. And when we talk about chromosomes, and we'll talk about chromosomes in much more depth, imagine taking this zoomed in thing that you have right over here, and over here, I don't know how many we have, like one, two, three, four, five, six, seven, eight, nine, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19. We have about 20 base pairs depicted here. Imagine if you had about 200 million of these base pairs, and then you were to take this thing and you were to kind of coil it up into that thing is a chromosome. Is a chromosome."}, {"video_title": "DNA   Biomolecules   MCAT   Khan Academy (2).mp3", "Sentence": "And when we talk about chromosomes, and we'll talk about chromosomes in much more depth, imagine taking this zoomed in thing that you have right over here, and over here, I don't know how many we have, like one, two, three, four, five, six, seven, eight, nine, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19. We have about 20 base pairs depicted here. Imagine if you had about 200 million of these base pairs, and then you were to take this thing and you were to kind of coil it up into that thing is a chromosome. Is a chromosome. And you're saying, wait, I have that much information in most of the cells of my body? This thing must be incredibly compact. And if you said that, I would say, yes, you are correct."}, {"video_title": "DNA   Biomolecules   MCAT   Khan Academy (2).mp3", "Sentence": "Is a chromosome. And you're saying, wait, I have that much information in most of the cells of my body? This thing must be incredibly compact. And if you said that, I would say, yes, you are correct. This, the radius, the radius of the DNA molecule is on the order of one nanometer. One nanometer, which is a billionth of a meter. So you can start to assess kind of the scale of this thing."}, {"video_title": "DNA   Biomolecules   MCAT   Khan Academy (2).mp3", "Sentence": "And if you said that, I would say, yes, you are correct. This, the radius, the radius of the DNA molecule is on the order of one nanometer. One nanometer, which is a billionth of a meter. So you can start to assess kind of the scale of this thing. This is a very dense way to actually store information. But just to have an appreciation of, and you might have seen it when I was coloring in, on why the structure lends itself to being able to replicate the information or even to be able to translate or express the information, let's think about if you were to take this ladder and you were to just kind of split all the base pairs. So you just have one half of them."}, {"video_title": "DNA   Biomolecules   MCAT   Khan Academy (2).mp3", "Sentence": "So you can start to assess kind of the scale of this thing. This is a very dense way to actually store information. But just to have an appreciation of, and you might have seen it when I was coloring in, on why the structure lends itself to being able to replicate the information or even to be able to translate or express the information, let's think about if you were to take this ladder and you were to just kind of split all the base pairs. So you just have one half of them. So you essentially have half of the ladder. And so if you only have half of the ladder, you're able to construct the other half of the ladder. Let's take an example."}, {"video_title": "DNA   Biomolecules   MCAT   Khan Academy (2).mp3", "Sentence": "So you just have one half of them. So you essentially have half of the ladder. And so if you only have half of the ladder, you're able to construct the other half of the ladder. Let's take an example. Let's say, and I'll just use the first letter to abbreviate for each of these bases. So let's say you have some, so let's say this is one of the, this is the sugar phosphate backbone right over here. So this could be one of the sides."}, {"video_title": "DNA   Biomolecules   MCAT   Khan Academy (2).mp3", "Sentence": "Let's take an example. Let's say, and I'll just use the first letter to abbreviate for each of these bases. So let's say you have some, so let's say this is one of the, this is the sugar phosphate backbone right over here. So this could be one of the sides. And let's say there's some adenine, actually, let me do them in the right color. So you've got some adenine, adenine, maybe some adenine right over here. Maybe there's an adenine there."}, {"video_title": "DNA   Biomolecules   MCAT   Khan Academy (2).mp3", "Sentence": "So this could be one of the sides. And let's say there's some adenine, actually, let me do them in the right color. So you've got some adenine, adenine, maybe some adenine right over here. Maybe there's an adenine there. Maybe you have some thymine, thymine, maybe thymine right over here. Then you have some, you have some guanine, guanine, guanine. And then let's say you have some cytosine and you have some cytosine."}, {"video_title": "DNA   Biomolecules   MCAT   Khan Academy (2).mp3", "Sentence": "Maybe there's an adenine there. Maybe you have some thymine, thymine, maybe thymine right over here. Then you have some, you have some guanine, guanine, guanine. And then let's say you have some cytosine and you have some cytosine. So with just half of this ladder, I guess you could say, you're able to construct the other half. And that's actually how DNA replicates. This ladder splits and then each of those two halves of that ladder are able to construct versions of the other half, or versions of the other half are able to be constructed on top of that half."}, {"video_title": "DNA   Biomolecules   MCAT   Khan Academy (2).mp3", "Sentence": "And then let's say you have some cytosine and you have some cytosine. So with just half of this ladder, I guess you could say, you're able to construct the other half. And that's actually how DNA replicates. This ladder splits and then each of those two halves of that ladder are able to construct versions of the other half, or versions of the other half are able to be constructed on top of that half. So how does that happen? Well, it's based on how these bases pair. Adenine always pairs with thymine if we're talking about DNA."}, {"video_title": "DNA   Biomolecules   MCAT   Khan Academy (2).mp3", "Sentence": "This ladder splits and then each of those two halves of that ladder are able to construct versions of the other half, or versions of the other half are able to be constructed on top of that half. So how does that happen? Well, it's based on how these bases pair. Adenine always pairs with thymine if we're talking about DNA. So if you have an A there, you're gonna have a T on this end, T on this end. T's right all over here, T right over there. If you have a T on that end, you're gonna have an A right over there, A, A."}, {"video_title": "DNA   Biomolecules   MCAT   Khan Academy (2).mp3", "Sentence": "Adenine always pairs with thymine if we're talking about DNA. So if you have an A there, you're gonna have a T on this end, T on this end. T's right all over here, T right over there. If you have a T on that end, you're gonna have an A right over there, A, A. If you have a G, a guanine on this side, you're gonna have a cytosine on the other side. Cytosine, cytosine, cytosine. And if you have a cytosine, you're gonna have a guanine on the other side."}, {"video_title": "DNA   Biomolecules   MCAT   Khan Academy (2).mp3", "Sentence": "If you have a T on that end, you're gonna have an A right over there, A, A. If you have a G, a guanine on this side, you're gonna have a cytosine on the other side. Cytosine, cytosine, cytosine. And if you have a cytosine, you're gonna have a guanine on the other side. And so hopefully that gives you an appreciation of how DNA can replicate itself. And as we'll see also, how this information can be translated to other forms of either related molecules, but eventually to proteins. And just to kind of round out this video, to get a real visual sense of what the DNA molecule looks like, or I guess a different visual depiction from this, I found this animated, that animated GIF that, you know, if you haven't fully digested what a double helix looks like, this is it."}, {"video_title": "DNA   Biomolecules   MCAT   Khan Academy (2).mp3", "Sentence": "And if you have a cytosine, you're gonna have a guanine on the other side. And so hopefully that gives you an appreciation of how DNA can replicate itself. And as we'll see also, how this information can be translated to other forms of either related molecules, but eventually to proteins. And just to kind of round out this video, to get a real visual sense of what the DNA molecule looks like, or I guess a different visual depiction from this, I found this animated, that animated GIF that, you know, if you haven't fully digested what a double helix looks like, this is it. And you see here, you see your sugar phosphate bases here. You see kind of the sugars and phosphate, the sugars and the phosphates alternating along this backbone. And then the rungs of the latter are these base pairs."}, {"video_title": "DNA   Biomolecules   MCAT   Khan Academy (2).mp3", "Sentence": "And just to kind of round out this video, to get a real visual sense of what the DNA molecule looks like, or I guess a different visual depiction from this, I found this animated, that animated GIF that, you know, if you haven't fully digested what a double helix looks like, this is it. And you see here, you see your sugar phosphate bases here. You see kind of the sugars and phosphate, the sugars and the phosphates alternating along this backbone. And then the rungs of the latter are these base pairs. So this is one of the bases, that's the corresponding, I guess you could say partner. And you could see that along all the way up and down this molecule. Very exciting."}, {"video_title": "Impact of changes to trophic pyramids   Ecology   AP Biology   Khan Academy.mp3", "Sentence": "So one way to think about this, it tells us who is eating whom and who is producing energy and then who is able to leverage that energy. So at the base of a trophic pyramid, you have your primary producers. Primary producers. These are often known as autotrophs because they're able to take energy from the sun, so sun's energy, and nutrients that are available to them, and store some of that energy as biomass. And biomass is just a fancy word for the actual substance of the organism that is inherently storing energy. When someone tells you that that piece of food has a certain number of calories, that's because there's energy stored in it, calories are a unit of energy. And so let's just say if you were to take a square meter, if you were to average on a per square meter basis, these primary producers in this environment, let's say they're able to store 20,000 kilocalories per square meter per year."}, {"video_title": "Impact of changes to trophic pyramids   Ecology   AP Biology   Khan Academy.mp3", "Sentence": "These are often known as autotrophs because they're able to take energy from the sun, so sun's energy, and nutrients that are available to them, and store some of that energy as biomass. And biomass is just a fancy word for the actual substance of the organism that is inherently storing energy. When someone tells you that that piece of food has a certain number of calories, that's because there's energy stored in it, calories are a unit of energy. And so let's just say if you were to take a square meter, if you were to average on a per square meter basis, these primary producers in this environment, let's say they're able to store 20,000 kilocalories per square meter per year. What's interesting about a trophic pyramid, it helps describe, well, okay, that energy stored in biomass, what happens then? Well, then you could go to the next level and you could view these as your primary or first level consumers. So first level, I could call them level one or primary consumers."}, {"video_title": "Impact of changes to trophic pyramids   Ecology   AP Biology   Khan Academy.mp3", "Sentence": "And so let's just say if you were to take a square meter, if you were to average on a per square meter basis, these primary producers in this environment, let's say they're able to store 20,000 kilocalories per square meter per year. What's interesting about a trophic pyramid, it helps describe, well, okay, that energy stored in biomass, what happens then? Well, then you could go to the next level and you could view these as your primary or first level consumers. So first level, I could call them level one or primary consumers. These are the organisms that would eat the primary producers but not all of that energy gets restored as biomass in these organisms. In fact, there is a lot of loss. On average, when we look at ecosystems, it tends to be only about 10% makes it from one level of our trophic pyramid to the next."}, {"video_title": "Impact of changes to trophic pyramids   Ecology   AP Biology   Khan Academy.mp3", "Sentence": "So first level, I could call them level one or primary consumers. These are the organisms that would eat the primary producers but not all of that energy gets restored as biomass in these organisms. In fact, there is a lot of loss. On average, when we look at ecosystems, it tends to be only about 10% makes it from one level of our trophic pyramid to the next. So at this level, on average per square meter, instead of 20,000 kilocalories being stored as biomass per year, you'd only have 10% of that. So it might only be 2,000. 2,000 kilocalories per square meter per year."}, {"video_title": "Impact of changes to trophic pyramids   Ecology   AP Biology   Khan Academy.mp3", "Sentence": "On average, when we look at ecosystems, it tends to be only about 10% makes it from one level of our trophic pyramid to the next. So at this level, on average per square meter, instead of 20,000 kilocalories being stored as biomass per year, you'd only have 10% of that. So it might only be 2,000. 2,000 kilocalories per square meter per year. So notice, you have that drop off. And then if you go to the next level after that, you could view these as the secondary consumers. These are the folks who might eat the primary consumers, the first level consumers."}, {"video_title": "Impact of changes to trophic pyramids   Ecology   AP Biology   Khan Academy.mp3", "Sentence": "2,000 kilocalories per square meter per year. So notice, you have that drop off. And then if you go to the next level after that, you could view these as the secondary consumers. These are the folks who might eat the primary consumers, the first level consumers. You get another 10% drop off. So you, or I should say 90% drop off, only 10% gets transferred. So about 200, 200 kilocalories per square meter per year."}, {"video_title": "Impact of changes to trophic pyramids   Ecology   AP Biology   Khan Academy.mp3", "Sentence": "These are the folks who might eat the primary consumers, the first level consumers. You get another 10% drop off. So you, or I should say 90% drop off, only 10% gets transferred. So about 200, 200 kilocalories per square meter per year. And it keeps happening. The folks who eat those folks, well then you've dropped off at this level right over here. You could call these the third level consumers or sometimes viewed as tertiary consumers."}, {"video_title": "Impact of changes to trophic pyramids   Ecology   AP Biology   Khan Academy.mp3", "Sentence": "So about 200, 200 kilocalories per square meter per year. And it keeps happening. The folks who eat those folks, well then you've dropped off at this level right over here. You could call these the third level consumers or sometimes viewed as tertiary consumers. This would be, this would be about 20 kilocalories per square meter per year. And this doesn't mean that every square meter will have exactly 20 kilocalories of biomass of, let's say in this example, snake. It just means that if you were to look at the biomass of snakes and you were to average them across this ecosystem, the surface area, that you might average about 20 kilocalories per square meter per year."}, {"video_title": "Impact of changes to trophic pyramids   Ecology   AP Biology   Khan Academy.mp3", "Sentence": "You could call these the third level consumers or sometimes viewed as tertiary consumers. This would be, this would be about 20 kilocalories per square meter per year. And this doesn't mean that every square meter will have exactly 20 kilocalories of biomass of, let's say in this example, snake. It just means that if you were to look at the biomass of snakes and you were to average them across this ecosystem, the surface area, that you might average about 20 kilocalories per square meter per year. And then you get to the top of this pyramid. And this you could view as your level four consumer. You could view this as, since they're at the top of the pyramid, this is sometimes known as the apex predator."}, {"video_title": "Impact of changes to trophic pyramids   Ecology   AP Biology   Khan Academy.mp3", "Sentence": "It just means that if you were to look at the biomass of snakes and you were to average them across this ecosystem, the surface area, that you might average about 20 kilocalories per square meter per year. And then you get to the top of this pyramid. And this you could view as your level four consumer. You could view this as, since they're at the top of the pyramid, this is sometimes known as the apex predator. But every stage here, you only are able to transfer 10% of the biomass. So here you have two kilocalories per square meter per year. And what's useful about this, it helps us understand what an ecosystem can support."}, {"video_title": "Impact of changes to trophic pyramids   Ecology   AP Biology   Khan Academy.mp3", "Sentence": "You could view this as, since they're at the top of the pyramid, this is sometimes known as the apex predator. But every stage here, you only are able to transfer 10% of the biomass. So here you have two kilocalories per square meter per year. And what's useful about this, it helps us understand what an ecosystem can support. It can support a lot of biomass of our primary producers, but it can support very little biomass of our apex predators. And that's why if you were to go into the forest, you would see very few apex predators. If you were to look at the apex predators and you were to think about their biomass in terms of kilocalories and spread it over their region where they have to find food, it would be much lower than the average biomass per square meter of say the grass and the trees."}, {"video_title": "Impact of changes to trophic pyramids   Ecology   AP Biology   Khan Academy.mp3", "Sentence": "And what's useful about this, it helps us understand what an ecosystem can support. It can support a lot of biomass of our primary producers, but it can support very little biomass of our apex predators. And that's why if you were to go into the forest, you would see very few apex predators. If you were to look at the apex predators and you were to think about their biomass in terms of kilocalories and spread it over their region where they have to find food, it would be much lower than the average biomass per square meter of say the grass and the trees. Now, an interesting thing is, well, where is a lot of that energy getting lost to? Well, a lot of cases, these organisms are moving around, they have to do things, they have processes in their own body, and those things all generate heat. So even plants, even plants generate heat."}, {"video_title": "Impact of changes to trophic pyramids   Ecology   AP Biology   Khan Academy.mp3", "Sentence": "If you were to look at the apex predators and you were to think about their biomass in terms of kilocalories and spread it over their region where they have to find food, it would be much lower than the average biomass per square meter of say the grass and the trees. Now, an interesting thing is, well, where is a lot of that energy getting lost to? Well, a lot of cases, these organisms are moving around, they have to do things, they have processes in their own body, and those things all generate heat. So even plants, even plants generate heat. So all of these characters are, there's some energy that's being released as heat. Also, when these players die, they're decomposed by other organisms. So all this biomass, it's either just going to die or it's going to get eaten, but even when it gets eaten, all of the energy doesn't get transferred."}, {"video_title": "Impact of changes to trophic pyramids   Ecology   AP Biology   Khan Academy.mp3", "Sentence": "So even plants, even plants generate heat. So all of these characters are, there's some energy that's being released as heat. Also, when these players die, they're decomposed by other organisms. So all this biomass, it's either just going to die or it's going to get eaten, but even when it gets eaten, all of the energy doesn't get transferred. Some of it stays in the undigested material, which we refer to as poop. And so those dead bodies, that dead biomass or this poop that still contains energy is going to be fed on by what we call decomposers. Decomposers."}, {"video_title": "Impact of changes to trophic pyramids   Ecology   AP Biology   Khan Academy.mp3", "Sentence": "So all this biomass, it's either just going to die or it's going to get eaten, but even when it gets eaten, all of the energy doesn't get transferred. Some of it stays in the undigested material, which we refer to as poop. And so those dead bodies, that dead biomass or this poop that still contains energy is going to be fed on by what we call decomposers. Decomposers. And they really break things down into nutrients, which then can be consumed by the primary producers as they utilize the sun's energy and keep the cycle going after that. Now, one interesting thing to think about is what if there are changes to the ecosystem? What if, for example, a nearby volcano erupts and that volcano, let me draw that, it's a fun thing to draw, that volcano erupts and ash goes into the sky and all year it's just really gray, what would you think would happen?"}, {"video_title": "Impact of changes to trophic pyramids   Ecology   AP Biology   Khan Academy.mp3", "Sentence": "Decomposers. And they really break things down into nutrients, which then can be consumed by the primary producers as they utilize the sun's energy and keep the cycle going after that. Now, one interesting thing to think about is what if there are changes to the ecosystem? What if, for example, a nearby volcano erupts and that volcano, let me draw that, it's a fun thing to draw, that volcano erupts and ash goes into the sky and all year it's just really gray, what would you think would happen? Well, the sun's energy that's able to hit the surface of the earth in this area would go down by a good bit. And so if that went down by a good bit, then the primary producers might not be able to store 20,000 kilocalories per square meter per year. It might go down to 2,000 kilocalories per square meter per year, and in which case you dropped a zero off of all of these."}, {"video_title": "Impact of changes to trophic pyramids   Ecology   AP Biology   Khan Academy.mp3", "Sentence": "What if, for example, a nearby volcano erupts and that volcano, let me draw that, it's a fun thing to draw, that volcano erupts and ash goes into the sky and all year it's just really gray, what would you think would happen? Well, the sun's energy that's able to hit the surface of the earth in this area would go down by a good bit. And so if that went down by a good bit, then the primary producers might not be able to store 20,000 kilocalories per square meter per year. It might go down to 2,000 kilocalories per square meter per year, and in which case you dropped a zero off of all of these. So instead of 20,000, it might go to 2,000. Instead of 2,000, this would be 200. Instead of 200, this would be 20."}, {"video_title": "Impact of changes to trophic pyramids   Ecology   AP Biology   Khan Academy.mp3", "Sentence": "It might go down to 2,000 kilocalories per square meter per year, and in which case you dropped a zero off of all of these. So instead of 20,000, it might go to 2,000. Instead of 2,000, this would be 200. Instead of 200, this would be 20. Instead of 20, this would be two. Instead of two, this would 0.2. And so something like the loss of light energy, even though this apex predator doesn't directly photosynthesize, a lot fewer of them are gonna be able to be supported in that ecosystem if you have a lot less energy stored at biomass at the primary production level because there's just less of sun's energy to be able to be stored as biomass."}, {"video_title": "Impact of changes to trophic pyramids   Ecology   AP Biology   Khan Academy.mp3", "Sentence": "Instead of 200, this would be 20. Instead of 20, this would be two. Instead of two, this would 0.2. And so something like the loss of light energy, even though this apex predator doesn't directly photosynthesize, a lot fewer of them are gonna be able to be supported in that ecosystem if you have a lot less energy stored at biomass at the primary production level because there's just less of sun's energy to be able to be stored as biomass. There could be other things that happen in the ecosystem. Let's say that some pesticides get introduced and some of these level one consumers start dying out. Well, then you might have less of the transfer of biomass from the primary producer level to the primary consumer level, which once again might affect these other levels of the trophic pyramid."}, {"video_title": "Impact of changes to trophic pyramids   Ecology   AP Biology   Khan Academy.mp3", "Sentence": "And so something like the loss of light energy, even though this apex predator doesn't directly photosynthesize, a lot fewer of them are gonna be able to be supported in that ecosystem if you have a lot less energy stored at biomass at the primary production level because there's just less of sun's energy to be able to be stored as biomass. There could be other things that happen in the ecosystem. Let's say that some pesticides get introduced and some of these level one consumers start dying out. Well, then you might have less of the transfer of biomass from the primary producer level to the primary consumer level, which once again might affect these other levels of the trophic pyramid. So this is an interesting thing to think about. Ecosystems are these really complex intertwined things, and one impact at one area could have far-reaching consequences throughout the entire ecosystem. It's also interesting to think of ecosystems as energy transfer, energies coming from the sun, and it's being cycled through this ecosystem, through this pyramid."}, {"video_title": "Predator prey cycle   Ecology   Khan Academy.mp3", "Sentence": "What I want to do in this video is think about how different populations that share the same ecosystem can interact with each other and actually provide a feedback loop on each other. And there's many cases of this, but the most cited general example is the case when one population wants to eat another population. And so you have the predator population that likes to eat the prey. So you have a predator and prey interactions. I'm doing the prey in I guess a somewhat bloody color, I guess, because they're going to be eaten. So let's just think about how these populations could interact. Let me draw a little chart here that you're probably familiar with by now where we show how a population can change over time."}, {"video_title": "Predator prey cycle   Ecology   Khan Academy.mp3", "Sentence": "So you have a predator and prey interactions. I'm doing the prey in I guess a somewhat bloody color, I guess, because they're going to be eaten. So let's just think about how these populations could interact. Let me draw a little chart here that you're probably familiar with by now where we show how a population can change over time. So the time, the horizontal axis is time. The vertical axis is population. Population."}, {"video_title": "Predator prey cycle   Ecology   Khan Academy.mp3", "Sentence": "Let me draw a little chart here that you're probably familiar with by now where we show how a population can change over time. So the time, the horizontal axis is time. The vertical axis is population. Population. And so let's just, in our starting point, let's say that our prey is starting out at a relatively high point. Let's say we're right there in time. And let's say for whatever reason, our predator population is relatively low."}, {"video_title": "Predator prey cycle   Ecology   Khan Academy.mp3", "Sentence": "Population. And so let's just, in our starting point, let's say that our prey is starting out at a relatively high point. Let's say we're right there in time. And let's say for whatever reason, our predator population is relatively low. So what do we think is going to happen here? Well, at this point, with a low density of predators, it's going to be much easier for them to find a meal, and it's going to be much easier for the prey to get caught. So since it's easier for the predators to find a meal, you can imagine their population starting to increase."}, {"video_title": "Predator prey cycle   Ecology   Khan Academy.mp3", "Sentence": "And let's say for whatever reason, our predator population is relatively low. So what do we think is going to happen here? Well, at this point, with a low density of predators, it's going to be much easier for them to find a meal, and it's going to be much easier for the prey to get caught. So since it's easier for the predators to find a meal, you can imagine their population starting to increase. But what's going to happen as their population is increasing? Well, it's going to be more likely that the prey is going to get caught. There's going to be more of their hunters around, more of the predators around, so that population is going to start decreasing all the way to a point where if the population of the prey gets low enough, the predators are going to have, they're going to start having trouble finding food again, and so that their population might start to decrease."}, {"video_title": "Predator prey cycle   Ecology   Khan Academy.mp3", "Sentence": "So since it's easier for the predators to find a meal, you can imagine their population starting to increase. But what's going to happen as their population is increasing? Well, it's going to be more likely that the prey is going to get caught. There's going to be more of their hunters around, more of the predators around, so that population is going to start decreasing all the way to a point where if the population of the prey gets low enough, the predators are going to have, they're going to start having trouble finding food again, and so that their population might start to decrease. And as their population decreases, what's going to happen to the prey? Well, then there's going to be less predators around, so they might be able to, their population might start to increase. And so I think you see what's happening."}, {"video_title": "Predator prey cycle   Ecology   Khan Academy.mp3", "Sentence": "There's going to be more of their hunters around, more of the predators around, so that population is going to start decreasing all the way to a point where if the population of the prey gets low enough, the predators are going to have, they're going to start having trouble finding food again, and so that their population might start to decrease. And as their population decreases, what's going to happen to the prey? Well, then there's going to be less predators around, so they might be able to, their population might start to increase. And so I think you see what's happening. The predator and prey, they can kind of form this cyclic interaction with each other. And what I've just drawn, this is often known as the predator-prey cycle. And I just reasoned through that you could imagine a world where you could have the cycle between predator and prey populations, but you can also run computer simulations that will show this."}, {"video_title": "Predator prey cycle   Ecology   Khan Academy.mp3", "Sentence": "And so I think you see what's happening. The predator and prey, they can kind of form this cyclic interaction with each other. And what I've just drawn, this is often known as the predator-prey cycle. And I just reasoned through that you could imagine a world where you could have the cycle between predator and prey populations, but you can also run computer simulations that will show this. And even observational data out in the field also shows this. One of the often cited examples is interactions between the snowshoe hare, which would be the prey in this situation, and the Canadian lynx, which would be the predator, the predator in this situation. And you see a very similar cycle to what I just drew, kind of just reasoning through it."}, {"video_title": "Predator prey cycle   Ecology   Khan Academy.mp3", "Sentence": "And I just reasoned through that you could imagine a world where you could have the cycle between predator and prey populations, but you can also run computer simulations that will show this. And even observational data out in the field also shows this. One of the often cited examples is interactions between the snowshoe hare, which would be the prey in this situation, and the Canadian lynx, which would be the predator, the predator in this situation. And you see a very similar cycle to what I just drew, kind of just reasoning through it. And this right here is actual data. You see the passage of time here, and this is a long passage of time. We're starting in the early 1800s, going all the way to the early mid-1900s, so it's roughly 100 years of data that we're showing."}, {"video_title": "Predator prey cycle   Ecology   Khan Academy.mp3", "Sentence": "And you see a very similar cycle to what I just drew, kind of just reasoning through it. And this right here is actual data. You see the passage of time here, and this is a long passage of time. We're starting in the early 1800s, going all the way to the early mid-1900s, so it's roughly 100 years of data that we're showing. And in the vertical axis, you have thousands of animals, and we're plotting both the population of snowshoe hares and Canadian lynx in a certain area on this chart. And as you see, when the prey population is high, when the prey population, sorry, when the predator population is high, when we have a lot of the Canadian lynx around, that we see a lower, a lower population of the prey, of the hare. But then, as, since you have a low population of the food in this situation, the predator population starts to decrease."}, {"video_title": "Predator prey cycle   Ecology   Khan Academy.mp3", "Sentence": "We're starting in the early 1800s, going all the way to the early mid-1900s, so it's roughly 100 years of data that we're showing. And in the vertical axis, you have thousands of animals, and we're plotting both the population of snowshoe hares and Canadian lynx in a certain area on this chart. And as you see, when the prey population is high, when the prey population, sorry, when the predator population is high, when we have a lot of the Canadian lynx around, that we see a lower, a lower population of the prey, of the hare. But then, as, since you have a low population of the food in this situation, the predator population starts to decrease. So let me draw an arrow here. The predator population starts to decrease, and, let me do that same blue color. So the predator population decreases, and as that predator population decreases, well, then the prey population increases, because there's less folks around to hunt them."}, {"video_title": "Predator prey cycle   Ecology   Khan Academy.mp3", "Sentence": "But then, as, since you have a low population of the food in this situation, the predator population starts to decrease. So let me draw an arrow here. The predator population starts to decrease, and, let me do that same blue color. So the predator population decreases, and as that predator population decreases, well, then the prey population increases, because there's less folks around to hunt them. So the prey population increases. And you see that the other way around. When the prey population is really, is, well, maybe we'll show it right over here."}, {"video_title": "Predator prey cycle   Ecology   Khan Academy.mp3", "Sentence": "So the predator population decreases, and as that predator population decreases, well, then the prey population increases, because there's less folks around to hunt them. So the prey population increases. And you see that the other way around. When the prey population is really, is, well, maybe we'll show it right over here. And this is real data, so it's not always super clean. But when the prey population is really, really high, and the predator population is relatively low, well, then the predators say, hey, it's really easy for us to find meals right now. That was kind of that starting point, in that, in when I just was reasoning through it."}, {"video_title": "Predator prey cycle   Ecology   Khan Academy.mp3", "Sentence": "When the prey population is really, is, well, maybe we'll show it right over here. And this is real data, so it's not always super clean. But when the prey population is really, really high, and the predator population is relatively low, well, then the predators say, hey, it's really easy for us to find meals right now. That was kind of that starting point, in that, in when I just was reasoning through it. And so their population starts, so, oops, what did I do? There, there, let me make sure. So their population starts to increase, and as the predator population increases, well, the prey population, the prey population is going to decrease."}, {"video_title": "Differences in translation between prokaryotes and eukaryotes   MCAT   Khan Academy.mp3", "Sentence": "And I want to focus mainly on the mRNA just before it's ready to be translated. So let's start with our prokaryotic mRNA and let's look at our five prime side first. So we have this yellow part right here and that's the non-coding region. And it's called the non-coding region because the ribosome is not actually going to read that part. So that particular sequence of amino acids is not that important. And then after the non-coding region we have the Shine-Dalgarno sequence. And the Shine-Dalgarno sequence is the site that the ribosome's going to recognize and bind to."}, {"video_title": "Differences in translation between prokaryotes and eukaryotes   MCAT   Khan Academy.mp3", "Sentence": "And it's called the non-coding region because the ribosome is not actually going to read that part. So that particular sequence of amino acids is not that important. And then after the non-coding region we have the Shine-Dalgarno sequence. And the Shine-Dalgarno sequence is the site that the ribosome's going to recognize and bind to. So let's just do a ribosome right over here. This is where the prokaryotic ribosome is going to bind. And then after the Shine-Dalgarno sequence we have another non-coding region, just going to abbreviate it NCR."}, {"video_title": "Differences in translation between prokaryotes and eukaryotes   MCAT   Khan Academy.mp3", "Sentence": "And the Shine-Dalgarno sequence is the site that the ribosome's going to recognize and bind to. So let's just do a ribosome right over here. This is where the prokaryotic ribosome is going to bind. And then after the Shine-Dalgarno sequence we have another non-coding region, just going to abbreviate it NCR. And then we have our start codon, which is typically AUG. So that tells us to start. And so the ribosome's going to start translating."}, {"video_title": "Differences in translation between prokaryotes and eukaryotes   MCAT   Khan Academy.mp3", "Sentence": "And then after the Shine-Dalgarno sequence we have another non-coding region, just going to abbreviate it NCR. And then we have our start codon, which is typically AUG. So that tells us to start. And so the ribosome's going to start translating. It's going to read this entire section, put together the corresponding polypeptide chain until it hits the stop codon, which tells it to stop translating. And then we have another non-coding region. Let's look at our eukaryotic mRNA."}, {"video_title": "Differences in translation between prokaryotes and eukaryotes   MCAT   Khan Academy.mp3", "Sentence": "And so the ribosome's going to start translating. It's going to read this entire section, put together the corresponding polypeptide chain until it hits the stop codon, which tells it to stop translating. And then we have another non-coding region. Let's look at our eukaryotic mRNA. And so it's pretty similar, but you can see there are some differences. So we'll start with our 5' side first. So you see this red nucleotide right over here."}, {"video_title": "Differences in translation between prokaryotes and eukaryotes   MCAT   Khan Academy.mp3", "Sentence": "Let's look at our eukaryotic mRNA. And so it's pretty similar, but you can see there are some differences. So we'll start with our 5' side first. So you see this red nucleotide right over here. That's the 5' cap. And the 5' cap is simply a guanine nucleotide, so I'm going to draw a G inside, guanine. And it's going to have a methyl group somewhere on the molecule."}, {"video_title": "Differences in translation between prokaryotes and eukaryotes   MCAT   Khan Academy.mp3", "Sentence": "So you see this red nucleotide right over here. That's the 5' cap. And the 5' cap is simply a guanine nucleotide, so I'm going to draw a G inside, guanine. And it's going to have a methyl group somewhere on the molecule. So I'm going to draw a methyl group. And the bond between this guanine and the nucleotide right near it is a bond that's different than the bond you'd typically find between two nucleotides. And so that's really all the 5' cap is."}, {"video_title": "Differences in translation between prokaryotes and eukaryotes   MCAT   Khan Academy.mp3", "Sentence": "And it's going to have a methyl group somewhere on the molecule. So I'm going to draw a methyl group. And the bond between this guanine and the nucleotide right near it is a bond that's different than the bond you'd typically find between two nucleotides. And so that's really all the 5' cap is. And the 5' cap is actually the ribosomal binding site in eukaryotes. So that means that in eukaryotes the ribosome is going to recognize this particular part and bind to it. So after the 5' cap, we have this other non-coding region, which the ribosome's not going to translate."}, {"video_title": "Differences in translation between prokaryotes and eukaryotes   MCAT   Khan Academy.mp3", "Sentence": "And so that's really all the 5' cap is. And the 5' cap is actually the ribosomal binding site in eukaryotes. So that means that in eukaryotes the ribosome is going to recognize this particular part and bind to it. So after the 5' cap, we have this other non-coding region, which the ribosome's not going to translate. And then the ribosome's going to hit the start codon again, AUG. Tells it to start, and it's going to start translating. So it's going to translate this entire section until it hits the stop codon. And then we have another non-coding region."}, {"video_title": "Differences in translation between prokaryotes and eukaryotes   MCAT   Khan Academy.mp3", "Sentence": "So after the 5' cap, we have this other non-coding region, which the ribosome's not going to translate. And then the ribosome's going to hit the start codon again, AUG. Tells it to start, and it's going to start translating. So it's going to translate this entire section until it hits the stop codon. And then we have another non-coding region. And then we hit something that looks different than what we've seen in the prokaryotic mRNAs, this section with blue nucleotides. And that's called the poly-A tail. And the poly-A tail is a bunch of nucleotides that are all As, or adenines."}, {"video_title": "Differences in translation between prokaryotes and eukaryotes   MCAT   Khan Academy.mp3", "Sentence": "And then we have another non-coding region. And then we hit something that looks different than what we've seen in the prokaryotic mRNAs, this section with blue nucleotides. And that's called the poly-A tail. And the poly-A tail is a bunch of nucleotides that are all As, or adenines. So I'm going to draw As inside all of these nucleotides. And the poly-A tail is actually pretty long. So it's typically anywhere between 100 and 250 nucleotides long."}, {"video_title": "Differences in translation between prokaryotes and eukaryotes   MCAT   Khan Academy.mp3", "Sentence": "And the poly-A tail is a bunch of nucleotides that are all As, or adenines. So I'm going to draw As inside all of these nucleotides. And the poly-A tail is actually pretty long. So it's typically anywhere between 100 and 250 nucleotides long. So that's pretty long. So I didn't exactly draw it to scale. And the purpose of both the 5' cap and the poly-A tail is to prevent this mRNA from being degraded by enzymes."}, {"video_title": "Differences in translation between prokaryotes and eukaryotes   MCAT   Khan Academy.mp3", "Sentence": "So it's typically anywhere between 100 and 250 nucleotides long. So that's pretty long. So I didn't exactly draw it to scale. And the purpose of both the 5' cap and the poly-A tail is to prevent this mRNA from being degraded by enzymes. So it acts as this kind of signal that does not allow enzymes to break it down or degrade it. And so you might be wondering, well, what about prokaryotic mRNA? How come they don't have anything similar to prevent it from being degraded?"}, {"video_title": "Differences in translation between prokaryotes and eukaryotes   MCAT   Khan Academy.mp3", "Sentence": "And the purpose of both the 5' cap and the poly-A tail is to prevent this mRNA from being degraded by enzymes. So it acts as this kind of signal that does not allow enzymes to break it down or degrade it. And so you might be wondering, well, what about prokaryotic mRNA? How come they don't have anything similar to prevent it from being degraded? And the brief answer to that question is that in prokaryotic cells, transcription, that's an R, and translation, both happen in the same place. So prokaryotic cells don't exactly have a nucleus. They have this, you know, like cytosol, and transcription and translation are happening in the same place."}, {"video_title": "Differences in translation between prokaryotes and eukaryotes   MCAT   Khan Academy.mp3", "Sentence": "How come they don't have anything similar to prevent it from being degraded? And the brief answer to that question is that in prokaryotic cells, transcription, that's an R, and translation, both happen in the same place. So prokaryotic cells don't exactly have a nucleus. They have this, you know, like cytosol, and transcription and translation are happening in the same place. And not only are they happening in the same place, but they can actually be happening at the same time. So you can have a piece of mRNA that's being formed. And while it's being formed, the ribosome will attach to it and begin to translate it."}, {"video_title": "Differences in translation between prokaryotes and eukaryotes   MCAT   Khan Academy.mp3", "Sentence": "They have this, you know, like cytosol, and transcription and translation are happening in the same place. And not only are they happening in the same place, but they can actually be happening at the same time. So you can have a piece of mRNA that's being formed. And while it's being formed, the ribosome will attach to it and begin to translate it. But in eukaryotic cells, things are a little bit different. So transcription happens in the nucleus, and translation happens in the cytoplasm, where there are ribosomes. And so the mRNA, after it's made, has to travel from the nucleus to the cytoplasm to where the ribosomes are."}, {"video_title": "Differences in translation between prokaryotes and eukaryotes   MCAT   Khan Academy.mp3", "Sentence": "And while it's being formed, the ribosome will attach to it and begin to translate it. But in eukaryotic cells, things are a little bit different. So transcription happens in the nucleus, and translation happens in the cytoplasm, where there are ribosomes. And so the mRNA, after it's made, has to travel from the nucleus to the cytoplasm to where the ribosomes are. And so because it's traveling this relatively large distance, it's going to encounter a lot of different things, including enzymes that might break it down. And so it needs this extra protection to prevent it from being damaged in any way. There's one more difference I want to talk about in how translation happens in prokaryotes and eukaryotes, and that is what the first amino acid in the polypeptide chain will be."}, {"video_title": "Differences in translation between prokaryotes and eukaryotes   MCAT   Khan Academy.mp3", "Sentence": "And so the mRNA, after it's made, has to travel from the nucleus to the cytoplasm to where the ribosomes are. And so because it's traveling this relatively large distance, it's going to encounter a lot of different things, including enzymes that might break it down. And so it needs this extra protection to prevent it from being damaged in any way. There's one more difference I want to talk about in how translation happens in prokaryotes and eukaryotes, and that is what the first amino acid in the polypeptide chain will be. So in prokaryotic cells, the first amino acid in the chain is always formal methionine. And formal methionine is simply the amino acid methionine, but with a formal group attached. And in case you don't remember what a formal group looks like, it looks like that."}, {"video_title": "Differences in translation between prokaryotes and eukaryotes   MCAT   Khan Academy.mp3", "Sentence": "There's one more difference I want to talk about in how translation happens in prokaryotes and eukaryotes, and that is what the first amino acid in the polypeptide chain will be. So in prokaryotic cells, the first amino acid in the chain is always formal methionine. And formal methionine is simply the amino acid methionine, but with a formal group attached. And in case you don't remember what a formal group looks like, it looks like that. In eukaryotic cells, the first amino acid in all the polypeptide chains is simply methionine. And it's interesting to note that formal methionine is actually, acts as an alarm system in the human body. So if you had some bacterial cells in your body that were damaged in any way, there would be these formal methionines floating around."}, {"video_title": "Allopatric and sympatric speciation   Biology   Khan Academy.mp3", "Sentence": "Fertile, fertile offspring. So for example, in this picture right over here, you have a bunch of species of both modern elephants and previous, or now non-existent, species that are related to modern elephants. But today, on Earth, you have Asian elephants and you have African elephants, and they are each a species. An Asian elephant can interbreed and produce fertile offspring with another Asian elephant, and an African elephant can interbreed and produce fertile offspring with another African elephant, but they can't do it with each other. An Asian elephant and an African elephant cannot get together and interbreed to produce fertile offspring. We know, people have actually tried this. But the next question, or the most obvious question, and this is one of the central questions of evolution, is, well, how do you get these species?"}, {"video_title": "Allopatric and sympatric speciation   Biology   Khan Academy.mp3", "Sentence": "An Asian elephant can interbreed and produce fertile offspring with another Asian elephant, and an African elephant can interbreed and produce fertile offspring with another African elephant, but they can't do it with each other. An Asian elephant and an African elephant cannot get together and interbreed to produce fertile offspring. We know, people have actually tried this. But the next question, or the most obvious question, and this is one of the central questions of evolution, is, well, how do you get these species? We see drawings like we have on the right. On the left, we have actually some of Darwin's original drawings showing this evolutionarily tree, showing how over and over again, we have this branching from a parent species into two, I guess you could say, different child species. You see this here with the elephants."}, {"video_title": "Allopatric and sympatric speciation   Biology   Khan Academy.mp3", "Sentence": "But the next question, or the most obvious question, and this is one of the central questions of evolution, is, well, how do you get these species? We see drawings like we have on the right. On the left, we have actually some of Darwin's original drawings showing this evolutionarily tree, showing how over and over again, we have this branching from a parent species into two, I guess you could say, different child species. You see this here with the elephants. At some point, the Asian elephant and the African elephant shared a common ancestor. And it was also, based on this diagram, a common ancestor of the mammoth. And you go even further back, it's the common ancestor of this species that I'm not familiar with, the Anancus."}, {"video_title": "Allopatric and sympatric speciation   Biology   Khan Academy.mp3", "Sentence": "You see this here with the elephants. At some point, the Asian elephant and the African elephant shared a common ancestor. And it was also, based on this diagram, a common ancestor of the mammoth. And you go even further back, it's the common ancestor of this species that I'm not familiar with, the Anancus. And you could keep going back, but how does this tree branch, how do you actually get speciation? How does the variation within a population, within a species, get so extreme and in some ways so separate from each other that they can no longer interbreed and produce fertile offspring? Well, there's a couple of ways to think about it."}, {"video_title": "Allopatric and sympatric speciation   Biology   Khan Academy.mp3", "Sentence": "And you go even further back, it's the common ancestor of this species that I'm not familiar with, the Anancus. And you could keep going back, but how does this tree branch, how do you actually get speciation? How does the variation within a population, within a species, get so extreme and in some ways so separate from each other that they can no longer interbreed and produce fertile offspring? Well, there's a couple of ways to think about it. The most obvious way that you could imagine this happens, or maybe the most intuitive way that you could imagine this happening, is through geographic separation. And the technical term for speciation, which is the formation of new species, so speciation, actually, let me just write it this way, the technical term for speciation due to geographic separation is allopatric. Allopatric speciation."}, {"video_title": "Allopatric and sympatric speciation   Biology   Khan Academy.mp3", "Sentence": "Well, there's a couple of ways to think about it. The most obvious way that you could imagine this happens, or maybe the most intuitive way that you could imagine this happening, is through geographic separation. And the technical term for speciation, which is the formation of new species, so speciation, actually, let me just write it this way, the technical term for speciation due to geographic separation is allopatric. Allopatric speciation. So speciation is just the formation of new species. And allo comes from the word other, and patric comes from the root or the word homeland. So it's really talking about other geographies or other homelands or geographic separation."}, {"video_title": "Allopatric and sympatric speciation   Biology   Khan Academy.mp3", "Sentence": "Allopatric speciation. So speciation is just the formation of new species. And allo comes from the word other, and patric comes from the root or the word homeland. So it's really talking about other geographies or other homelands or geographic separation. And one commonly cited example here are the antelope squirrels. So if you were to go to the American Southwest a long time ago, before the Grand Canyon was a canyon, when the Colorado River was just kinda going through and wasn't a major barrier, there was a parent species, an ancestral species, to both of these characters that lived on both sides of the river. And on different times of the year, it was able to get across the river, it's able to, the squirrels on the north and the squirrels on the south were able to interbreed and produce fertile offspring, so they were all one species."}, {"video_title": "Allopatric and sympatric speciation   Biology   Khan Academy.mp3", "Sentence": "So it's really talking about other geographies or other homelands or geographic separation. And one commonly cited example here are the antelope squirrels. So if you were to go to the American Southwest a long time ago, before the Grand Canyon was a canyon, when the Colorado River was just kinda going through and wasn't a major barrier, there was a parent species, an ancestral species, to both of these characters that lived on both sides of the river. And on different times of the year, it was able to get across the river, it's able to, the squirrels on the north and the squirrels on the south were able to interbreed and produce fertile offspring, so they were all one species. But over time, the Colorado River started to erode more and more soil and rock, and so this became what we now consider to be the Grand Canyon. And so over time, this became a very significant geographic barrier. No longer could, before they could travel across, but once it became the Grand Canyon, it became very difficult or impossible for them to travel across."}, {"video_title": "Allopatric and sympatric speciation   Biology   Khan Academy.mp3", "Sentence": "And on different times of the year, it was able to get across the river, it's able to, the squirrels on the north and the squirrels on the south were able to interbreed and produce fertile offspring, so they were all one species. But over time, the Colorado River started to erode more and more soil and rock, and so this became what we now consider to be the Grand Canyon. And so over time, this became a very significant geographic barrier. No longer could, before they could travel across, but once it became the Grand Canyon, it became very difficult or impossible for them to travel across. And so now you have these two different populations, they have the same parent species, but they're now geographically isolated. And since the creation of the, or while we have the creation of the Grand Canyon, since it became very hard or impossible for them to cross, you've now had enough, both genetic drift, also natural selection, these are the evolutionary processes that we've talked about, where the Harris's antelope squirrel, which lives on the south side, and is right over here, it's this picture, and the white-tailed antelope squirrel, which lives on the north side, even though they look quite similar, as you can see from these pictures, they have now diverged enough that they are different species, that they no longer will be able to, they will no longer be able to interbreed and produce fertile offspring. So it's fairly intuitive how allopatric speciation can work, geographic separation, no longer can interbreed, and over time, their genes change through natural selection and genetic drift."}, {"video_title": "Allopatric and sympatric speciation   Biology   Khan Academy.mp3", "Sentence": "No longer could, before they could travel across, but once it became the Grand Canyon, it became very difficult or impossible for them to travel across. And so now you have these two different populations, they have the same parent species, but they're now geographically isolated. And since the creation of the, or while we have the creation of the Grand Canyon, since it became very hard or impossible for them to cross, you've now had enough, both genetic drift, also natural selection, these are the evolutionary processes that we've talked about, where the Harris's antelope squirrel, which lives on the south side, and is right over here, it's this picture, and the white-tailed antelope squirrel, which lives on the north side, even though they look quite similar, as you can see from these pictures, they have now diverged enough that they are different species, that they no longer will be able to, they will no longer be able to interbreed and produce fertile offspring. So it's fairly intuitive how allopatric speciation can work, geographic separation, no longer can interbreed, and over time, their genes change through natural selection and genetic drift. But what about situations where they stay in the same place, where theoretically, they could get together, they could interact, could you still have speciation? And the answer is yes. And that form of speciation, where you are still in the same geography, that is called sympatric speciation."}, {"video_title": "Allopatric and sympatric speciation   Biology   Khan Academy.mp3", "Sentence": "So it's fairly intuitive how allopatric speciation can work, geographic separation, no longer can interbreed, and over time, their genes change through natural selection and genetic drift. But what about situations where they stay in the same place, where theoretically, they could get together, they could interact, could you still have speciation? And the answer is yes. And that form of speciation, where you are still in the same geography, that is called sympatric speciation. Let me write that down. Sympatric speciation. And examples of sympatric speciation are a little bit less obvious, or a little bit less intuitive, but there's an example that people believe is sympatric speciation happening before our eyes."}, {"video_title": "Allopatric and sympatric speciation   Biology   Khan Academy.mp3", "Sentence": "And that form of speciation, where you are still in the same geography, that is called sympatric speciation. Let me write that down. Sympatric speciation. And examples of sympatric speciation are a little bit less obvious, or a little bit less intuitive, but there's an example that people believe is sympatric speciation happening before our eyes. So this species, the technical term, Ragoletis pomamnula, I know I'm mispronouncing it right over here, this is native to North America, and before European settlers brought apples to North America they hung out and they laid their eggs and their maggots were inside of, or they leveraged the hawthorn fruit right over here. So they would go to the hawthorn trees and they would use the hawthorn fruit to lay their eggs and for their young to kind of consume. But once the European settlers came and introduced apples into North America, a certain, I guess you could say a subgroup, of Ragoletis pomamnula started to leverage the apples."}, {"video_title": "Allopatric and sympatric speciation   Biology   Khan Academy.mp3", "Sentence": "And examples of sympatric speciation are a little bit less obvious, or a little bit less intuitive, but there's an example that people believe is sympatric speciation happening before our eyes. So this species, the technical term, Ragoletis pomamnula, I know I'm mispronouncing it right over here, this is native to North America, and before European settlers brought apples to North America they hung out and they laid their eggs and their maggots were inside of, or they leveraged the hawthorn fruit right over here. So they would go to the hawthorn trees and they would use the hawthorn fruit to lay their eggs and for their young to kind of consume. But once the European settlers came and introduced apples into North America, a certain, I guess you could say a subgroup, of Ragoletis pomamnula started to leverage the apples. So started to lay their eggs and their maggots would grow inside of the apples. And they've actually now diverged, not into fully different species now, in theory they can still interbreed and produce fertile offspring, but they don't tend to do it anymore. That it tends to be, even though they're in the same geography and it's not hard to fly from the hawthorn tree to the apple tree, they don't tend to do it."}, {"video_title": "Allopatric and sympatric speciation   Biology   Khan Academy.mp3", "Sentence": "But once the European settlers came and introduced apples into North America, a certain, I guess you could say a subgroup, of Ragoletis pomamnula started to leverage the apples. So started to lay their eggs and their maggots would grow inside of the apples. And they've actually now diverged, not into fully different species now, in theory they can still interbreed and produce fertile offspring, but they don't tend to do it anymore. That it tends to be, even though they're in the same geography and it's not hard to fly from the hawthorn tree to the apple tree, they don't tend to do it. And because of this behavioral divergence that some decided to go to the apples, some decided to stay at the hawthorn, they actually are now developing different traits that are selected for depending on that, I guess you could say initial preference or that initial bias for which fruit they wanna use to lay their eggs in. So for example, the ones that are in the apple tree, they now have, their breeding cycle is more aligned with the growing season for apples. While the ones in the hawthorn tree, their breeding cycle is more aligned with what for the growing cycle for the hawthorn."}, {"video_title": "Allopatric and sympatric speciation   Biology   Khan Academy.mp3", "Sentence": "That it tends to be, even though they're in the same geography and it's not hard to fly from the hawthorn tree to the apple tree, they don't tend to do it. And because of this behavioral divergence that some decided to go to the apples, some decided to stay at the hawthorn, they actually are now developing different traits that are selected for depending on that, I guess you could say initial preference or that initial bias for which fruit they wanna use to lay their eggs in. So for example, the ones that are in the apple tree, they now have, their breeding cycle is more aligned with the growing season for apples. While the ones in the hawthorn tree, their breeding cycle is more aligned with what for the growing cycle for the hawthorn. And so biologists believe that this is an example of sympatric speciation happening before our eyes, that if we were to wait a few hundred more years, possibly a thousand years or more, that this will diverge into two different species that will no longer be able to interbreed and produce fertile offspring. Another example of sympatric speciation, which is a little bit more wild in some ways, it's a little bit more out there, but this would be an example with plants. So as we learn in other Khan Academy videos, organisms like human beings, and in fact many sexually reproducing organisms, they're diploid organisms."}, {"video_title": "Allopatric and sympatric speciation   Biology   Khan Academy.mp3", "Sentence": "While the ones in the hawthorn tree, their breeding cycle is more aligned with what for the growing cycle for the hawthorn. And so biologists believe that this is an example of sympatric speciation happening before our eyes, that if we were to wait a few hundred more years, possibly a thousand years or more, that this will diverge into two different species that will no longer be able to interbreed and produce fertile offspring. Another example of sympatric speciation, which is a little bit more wild in some ways, it's a little bit more out there, but this would be an example with plants. So as we learn in other Khan Academy videos, organisms like human beings, and in fact many sexually reproducing organisms, they're diploid organisms. They have two sets of organisms, they have two sets of chromosomes. For example, human beings have two sets of 23 chromosomes for a total of 46 chromosomes, 23 from your mom, 23 from your dad. And so we are diploid organisms."}, {"video_title": "Allopatric and sympatric speciation   Biology   Khan Academy.mp3", "Sentence": "So as we learn in other Khan Academy videos, organisms like human beings, and in fact many sexually reproducing organisms, they're diploid organisms. They have two sets of organisms, they have two sets of chromosomes. For example, human beings have two sets of 23 chromosomes for a total of 46 chromosomes, 23 from your mom, 23 from your dad. And so we are diploid organisms. And in general, there are errors that occur during reproduction and errors that occur during meiosis that can lead to polyploidy, where an organism can have more than two sets of, or can start, or a potential organism could have more than two sets of chromosomes. In the animal kingdom, that doesn't work out too well. Usually that does not produce a viable embryo, a viable zygote."}, {"video_title": "Allopatric and sympatric speciation   Biology   Khan Academy.mp3", "Sentence": "And so we are diploid organisms. And in general, there are errors that occur during reproduction and errors that occur during meiosis that can lead to polyploidy, where an organism can have more than two sets of, or can start, or a potential organism could have more than two sets of chromosomes. In the animal kingdom, that doesn't work out too well. Usually that does not produce a viable embryo, a viable zygote. But in the plant kingdom, this is, it tolerates it a little bit more. So you could have a situation where you have a diploid plant and through meiosis, through an error in meiosis, instead of producing haploid egg and sperms, it produces diploid egg and sperm, which then are able to get together to form a tetraploid plant. So a plant that has four sets of chromosomes instead of two sets of chromosomes."}, {"video_title": "Allopatric and sympatric speciation   Biology   Khan Academy.mp3", "Sentence": "Usually that does not produce a viable embryo, a viable zygote. But in the plant kingdom, this is, it tolerates it a little bit more. So you could have a situation where you have a diploid plant and through meiosis, through an error in meiosis, instead of producing haploid egg and sperms, it produces diploid egg and sperm, which then are able to get together to form a tetraploid plant. So a plant that has four sets of chromosomes instead of two sets of chromosomes. And then once that tetraploid plant exists, it might only be able to reproduce with other tetraploid plants versus the diploid plant. So you have the diploid plants here when meiosis is working properly, and I'll put that in quotes because maybe, arguably, this error is what helps for speciation sometimes, especially in the plant kingdom. It is, it can produce this haploid egg or sperm."}, {"video_title": "Allopatric and sympatric speciation   Biology   Khan Academy.mp3", "Sentence": "So a plant that has four sets of chromosomes instead of two sets of chromosomes. And then once that tetraploid plant exists, it might only be able to reproduce with other tetraploid plants versus the diploid plant. So you have the diploid plants here when meiosis is working properly, and I'll put that in quotes because maybe, arguably, this error is what helps for speciation sometimes, especially in the plant kingdom. It is, it can produce this haploid egg or sperm. The tetroid plant would then, through its meiosis, its ploidy, I guess you could say, halves when it goes to the egg or the sperm, but you're now going to have a non-viable or infertile triploid plant because the separation won't happen properly in meiosis for this thing if it's even viable. So all of a sudden, this tetraploid plant is now, you've had speciation occur. It could be viewed as a new species, and you could think about things like this happening as a potential, and we don't understand all of it, and we don't understand how all of the speciation that we now observe has actually occurred, but you can even imagine as this being a mechanism for why you have an increase in the number of chromosomes in certain species versus others."}, {"video_title": "G Protein Coupled Receptors   Nervous system physiology   NCLEX-RN   Khan Academy.mp3", "Sentence": "G-protein coupled receptors are only found in eukaryotes, and they comprise of the largest known class of membrane receptors. In fact, humans have more than 1,000 known different types of GPCRs, and each one is specific to a particular function. They are a very unique membrane receptor, and they are the target of around 30% to 50% of all modern medicinal drugs. In fact, the ligands that bind range from things like light-sensitive compounds to odors, pheromones, hormones, and even neurotransmitters. GPCRs can regulate the immune system, growth, our sense of smell, taste, visual, behavioral, and our mood, including things like serotonin and dopamine. Even now, many G-proteins and GPCRs still have unknown functions and is a topic heavily researched. In fact, in just 2012, a Nobel Prize in chemistry was awarded for research on GPCRs."}, {"video_title": "G Protein Coupled Receptors   Nervous system physiology   NCLEX-RN   Khan Academy.mp3", "Sentence": "In fact, the ligands that bind range from things like light-sensitive compounds to odors, pheromones, hormones, and even neurotransmitters. GPCRs can regulate the immune system, growth, our sense of smell, taste, visual, behavioral, and our mood, including things like serotonin and dopamine. Even now, many G-proteins and GPCRs still have unknown functions and is a topic heavily researched. In fact, in just 2012, a Nobel Prize in chemistry was awarded for research on GPCRs. To start off, let's talk a little bit about the structure of GPCRs. It's impossible to really have a discussion about how GPCRs work without having an understanding of what they look like. The most important characteristic of GPCRs is that they have seven transmembrane alpha helices."}, {"video_title": "G Protein Coupled Receptors   Nervous system physiology   NCLEX-RN   Khan Academy.mp3", "Sentence": "In fact, in just 2012, a Nobel Prize in chemistry was awarded for research on GPCRs. To start off, let's talk a little bit about the structure of GPCRs. It's impossible to really have a discussion about how GPCRs work without having an understanding of what they look like. The most important characteristic of GPCRs is that they have seven transmembrane alpha helices. If we have this being our cell membrane, and we have this being the extracellular side, and this being the intracellular side, if we have a GPCR, a G-protein coupled receptor, it'll span this membrane seven times. So let's say it starts here, and we go one, two, three, four, five, six, seven. This is one of the most important characteristics of a GPCR."}, {"video_title": "G Protein Coupled Receptors   Nervous system physiology   NCLEX-RN   Khan Academy.mp3", "Sentence": "The most important characteristic of GPCRs is that they have seven transmembrane alpha helices. If we have this being our cell membrane, and we have this being the extracellular side, and this being the intracellular side, if we have a GPCR, a G-protein coupled receptor, it'll span this membrane seven times. So let's say it starts here, and we go one, two, three, four, five, six, seven. This is one of the most important characteristics of a GPCR. They have seven transmembrane alpha helices. Since this is such a unique and interesting structural characteristic, we often also call GPCRs seven transmembrane receptors. So just to quickly label, this is our GPCR here."}, {"video_title": "G Protein Coupled Receptors   Nervous system physiology   NCLEX-RN   Khan Academy.mp3", "Sentence": "This is one of the most important characteristics of a GPCR. They have seven transmembrane alpha helices. Since this is such a unique and interesting structural characteristic, we often also call GPCRs seven transmembrane receptors. So just to quickly label, this is our GPCR here. As the name implies, GPCRs interact with G-proteins. They're coupled with G-proteins. Now, it's important to talk a little bit about the structure of G-proteins also."}, {"video_title": "G Protein Coupled Receptors   Nervous system physiology   NCLEX-RN   Khan Academy.mp3", "Sentence": "So just to quickly label, this is our GPCR here. As the name implies, GPCRs interact with G-proteins. They're coupled with G-proteins. Now, it's important to talk a little bit about the structure of G-proteins also. G-proteins, in general, are specialized proteins which have the ability to bind GTP and GDP. In other words, they are able to bind guanosine triphosphate and guanosine diphosphate. Hence the name G-proteins."}, {"video_title": "G Protein Coupled Receptors   Nervous system physiology   NCLEX-RN   Khan Academy.mp3", "Sentence": "Now, it's important to talk a little bit about the structure of G-proteins also. G-proteins, in general, are specialized proteins which have the ability to bind GTP and GDP. In other words, they are able to bind guanosine triphosphate and guanosine diphosphate. Hence the name G-proteins. Now, some G-proteins are small proteins with a single subunit. However, when we talk about GPCRs, all G-proteins that associate with GPCRs are heterotrimeric, meaning that they have three different subunits, three sections. So I'm going to go ahead and draw this out."}, {"video_title": "G Protein Coupled Receptors   Nervous system physiology   NCLEX-RN   Khan Academy.mp3", "Sentence": "Hence the name G-proteins. Now, some G-proteins are small proteins with a single subunit. However, when we talk about GPCRs, all G-proteins that associate with GPCRs are heterotrimeric, meaning that they have three different subunits, three sections. So I'm going to go ahead and draw this out. The first section we call the alpha subunit. The first subunit or section of this protein we call the alpha subunit. The second we call beta."}, {"video_title": "G Protein Coupled Receptors   Nervous system physiology   NCLEX-RN   Khan Academy.mp3", "Sentence": "So I'm going to go ahead and draw this out. The first section we call the alpha subunit. The first subunit or section of this protein we call the alpha subunit. The second we call beta. And the third we call gamma. So all three of these together, our alpha, beta, and gamma subunits together, is our G-protein. You'll notice that I drew the alpha and gamma subunits with a little tail-looking thing in our cell membrane."}, {"video_title": "G Protein Coupled Receptors   Nervous system physiology   NCLEX-RN   Khan Academy.mp3", "Sentence": "The second we call beta. And the third we call gamma. So all three of these together, our alpha, beta, and gamma subunits together, is our G-protein. You'll notice that I drew the alpha and gamma subunits with a little tail-looking thing in our cell membrane. And the reason why is because these are the two subunits, our alpha and gamma, which are attached to the cell membrane by what we call lipid anchors. Now, the final thing about this picture that I need to draw in is our GDP or GTP. As you remember, the whole point of a G-protein is because it binds GTP or GDP."}, {"video_title": "G Protein Coupled Receptors   Nervous system physiology   NCLEX-RN   Khan Academy.mp3", "Sentence": "You'll notice that I drew the alpha and gamma subunits with a little tail-looking thing in our cell membrane. And the reason why is because these are the two subunits, our alpha and gamma, which are attached to the cell membrane by what we call lipid anchors. Now, the final thing about this picture that I need to draw in is our GDP or GTP. As you remember, the whole point of a G-protein is because it binds GTP or GDP. Right now, this protein is inactive. And so it binds GDP, guanosine diphosphate. This GDP binds to the alpha subunit."}, {"video_title": "G Protein Coupled Receptors   Nervous system physiology   NCLEX-RN   Khan Academy.mp3", "Sentence": "As you remember, the whole point of a G-protein is because it binds GTP or GDP. Right now, this protein is inactive. And so it binds GDP, guanosine diphosphate. This GDP binds to the alpha subunit. When this protein becomes activated, and we'll talk in just a second how that happens, it will actually bind GTP instead. So now that we've drawn out our actual picture of our G-protein, let's talk a little bit about how our signaling pathway actually happens. That's the whole point of membrane receptors is that they respond to signaling molecules and ligands, and they respond to the environment."}, {"video_title": "G Protein Coupled Receptors   Nervous system physiology   NCLEX-RN   Khan Academy.mp3", "Sentence": "This GDP binds to the alpha subunit. When this protein becomes activated, and we'll talk in just a second how that happens, it will actually bind GTP instead. So now that we've drawn out our actual picture of our G-protein, let's talk a little bit about how our signaling pathway actually happens. That's the whole point of membrane receptors is that they respond to signaling molecules and ligands, and they respond to the environment. So as we mentioned before, G-protein coupled receptors interact with a wide variety of molecules on the outer surface of cells. Each receptor binds to usually one or just a few very specific molecules, fitting together like a lock and key. So if we pretend that our signaling molecule is a circle like this, the shape in which it should bind to the GPCR should be complementary."}, {"video_title": "G Protein Coupled Receptors   Nervous system physiology   NCLEX-RN   Khan Academy.mp3", "Sentence": "That's the whole point of membrane receptors is that they respond to signaling molecules and ligands, and they respond to the environment. So as we mentioned before, G-protein coupled receptors interact with a wide variety of molecules on the outer surface of cells. Each receptor binds to usually one or just a few very specific molecules, fitting together like a lock and key. So if we pretend that our signaling molecule is a circle like this, the shape in which it should bind to the GPCR should be complementary. When this green signaling molecule binds to our GPCR, our GPCR will actually undergo what we call a conformational change. Its shape of this GPCR will change, which in turn triggers a complex chain of events, which will ultimately influence different cell functions. So as we mentioned, our first step here is, of course, the ligand."}, {"video_title": "G Protein Coupled Receptors   Nervous system physiology   NCLEX-RN   Khan Academy.mp3", "Sentence": "So if we pretend that our signaling molecule is a circle like this, the shape in which it should bind to the GPCR should be complementary. When this green signaling molecule binds to our GPCR, our GPCR will actually undergo what we call a conformational change. Its shape of this GPCR will change, which in turn triggers a complex chain of events, which will ultimately influence different cell functions. So as we mentioned, our first step here is, of course, the ligand. The signaling molecule has to bind to our GPCR. Once this ligand binds, our GPCR is going to undergo a conformational change. Let's just go ahead and redraw our GPCR."}, {"video_title": "G Protein Coupled Receptors   Nervous system physiology   NCLEX-RN   Khan Academy.mp3", "Sentence": "So as we mentioned, our first step here is, of course, the ligand. The signaling molecule has to bind to our GPCR. Once this ligand binds, our GPCR is going to undergo a conformational change. Let's just go ahead and redraw our GPCR. Again, 1, 2, 3, 4, 5, 6, 7, our 7 alpha helices. Now, it's a little tougher to draw a conformational change, but the protein is actually going to look completely different. So here, because of this binding, we're going to have a conformational change."}, {"video_title": "G Protein Coupled Receptors   Nervous system physiology   NCLEX-RN   Khan Academy.mp3", "Sentence": "Let's just go ahead and redraw our GPCR. Again, 1, 2, 3, 4, 5, 6, 7, our 7 alpha helices. Now, it's a little tougher to draw a conformational change, but the protein is actually going to look completely different. So here, because of this binding, we're going to have a conformational change. The protein conformation of the GPCR will alter. So let's just write out our first two steps real quick. So step one, we have the ligand binds to our GPCR."}, {"video_title": "G Protein Coupled Receptors   Nervous system physiology   NCLEX-RN   Khan Academy.mp3", "Sentence": "So here, because of this binding, we're going to have a conformational change. The protein conformation of the GPCR will alter. So let's just write out our first two steps real quick. So step one, we have the ligand binds to our GPCR. Step two, we said that we undergo a conformational change. So our GPCR undergoes conformational change. What happens next is, because of this conformational change, our alpha subunit, which I'm going to draw in here, is actually going to exchange this GDP for GTP."}, {"video_title": "G Protein Coupled Receptors   Nervous system physiology   NCLEX-RN   Khan Academy.mp3", "Sentence": "So step one, we have the ligand binds to our GPCR. Step two, we said that we undergo a conformational change. So our GPCR undergoes conformational change. What happens next is, because of this conformational change, our alpha subunit, which I'm going to draw in here, is actually going to exchange this GDP for GTP. So just keep track. Step three, our alpha subunit exchanges GDP for GTP. So the molecule is swapped out."}, {"video_title": "G Protein Coupled Receptors   Nervous system physiology   NCLEX-RN   Khan Academy.mp3", "Sentence": "What happens next is, because of this conformational change, our alpha subunit, which I'm going to draw in here, is actually going to exchange this GDP for GTP. So just keep track. Step three, our alpha subunit exchanges GDP for GTP. So the molecule is swapped out. Instead of GDP, we have GTP. Now, because we have GTP bound to this alpha subunit, it'll now cause our alpha subunit to dissociate and move away from our beta and gamma subunit. Now, once this happens, these two different sections, our alpha subunit and our beta gamma dimer, these two together, are actually going to find a protein in the membrane."}, {"video_title": "G Protein Coupled Receptors   Nervous system physiology   NCLEX-RN   Khan Academy.mp3", "Sentence": "So the molecule is swapped out. Instead of GDP, we have GTP. Now, because we have GTP bound to this alpha subunit, it'll now cause our alpha subunit to dissociate and move away from our beta and gamma subunit. Now, once this happens, these two different sections, our alpha subunit and our beta gamma dimer, these two together, are actually going to find a protein in the membrane. It's going to alter and regulate the function of that protein. So we could have another protein, for example, here that the alpha subunit will find and regulate the function. So let's go ahead and write this out."}, {"video_title": "G Protein Coupled Receptors   Nervous system physiology   NCLEX-RN   Khan Academy.mp3", "Sentence": "Now, once this happens, these two different sections, our alpha subunit and our beta gamma dimer, these two together, are actually going to find a protein in the membrane. It's going to alter and regulate the function of that protein. So we could have another protein, for example, here that the alpha subunit will find and regulate the function. So let's go ahead and write this out. Step four, our alpha subunit dissociates and regulates target proteins. Now, during this step, there are a few things I like to note. The first is that both the alpha subunit and the beta gamma dimer can interact with other proteins to relay messages."}, {"video_title": "G Protein Coupled Receptors   Nervous system physiology   NCLEX-RN   Khan Academy.mp3", "Sentence": "So let's go ahead and write this out. Step four, our alpha subunit dissociates and regulates target proteins. Now, during this step, there are a few things I like to note. The first is that both the alpha subunit and the beta gamma dimer can interact with other proteins to relay messages. We're going to focus in on the alpha subunit because it tends to be more common and more however the beta gamma subunits can still regulate functions of other proteins. The target proteins can be enzymes that produce second messengers, which we'll talk a little more about in a second, or ion channels that also let ions be second messengers. Now, as we mentioned, G proteins are incredibly diverse."}, {"video_title": "G Protein Coupled Receptors   Nervous system physiology   NCLEX-RN   Khan Academy.mp3", "Sentence": "The first is that both the alpha subunit and the beta gamma dimer can interact with other proteins to relay messages. We're going to focus in on the alpha subunit because it tends to be more common and more however the beta gamma subunits can still regulate functions of other proteins. The target proteins can be enzymes that produce second messengers, which we'll talk a little more about in a second, or ion channels that also let ions be second messengers. Now, as we mentioned, G proteins are incredibly diverse. Some G proteins can stimulate activity, while others can also inhibit. Now, step five, once this alpha subunit activates a target protein, this target protein can then relay a signal. As long as this ligand is bound to the GPCR, this process where our alpha subunit dissociates, looks for a protein, and regulates that target protein, causing a whole chain of events, can happen repeatedly, as long as this ligand is bound."}, {"video_title": "G Protein Coupled Receptors   Nervous system physiology   NCLEX-RN   Khan Academy.mp3", "Sentence": "Now, as we mentioned, G proteins are incredibly diverse. Some G proteins can stimulate activity, while others can also inhibit. Now, step five, once this alpha subunit activates a target protein, this target protein can then relay a signal. As long as this ligand is bound to the GPCR, this process where our alpha subunit dissociates, looks for a protein, and regulates that target protein, causing a whole chain of events, can happen repeatedly, as long as this ligand is bound. Now, how can we actually make this thing go back to normal? Well, step six is that our GTP is hydrolyzed to GDP. So our GTP loses a phosphate in hydrolysis and becomes GDP."}, {"video_title": "G Protein Coupled Receptors   Nervous system physiology   NCLEX-RN   Khan Academy.mp3", "Sentence": "As long as this ligand is bound to the GPCR, this process where our alpha subunit dissociates, looks for a protein, and regulates that target protein, causing a whole chain of events, can happen repeatedly, as long as this ligand is bound. Now, how can we actually make this thing go back to normal? Well, step six is that our GTP is hydrolyzed to GDP. So our GTP loses a phosphate in hydrolysis and becomes GDP. Once this happens, everything goes back to normal, and the ligand will leave, and everything will go back to looking the way it was, and ready to combine with another ligand in the future. This often happens on its own. Eventually, the GTP will be hydrolyzed and become GDP."}, {"video_title": "G Protein Coupled Receptors   Nervous system physiology   NCLEX-RN   Khan Academy.mp3", "Sentence": "So our GTP loses a phosphate in hydrolysis and becomes GDP. Once this happens, everything goes back to normal, and the ligand will leave, and everything will go back to looking the way it was, and ready to combine with another ligand in the future. This often happens on its own. Eventually, the GTP will be hydrolyzed and become GDP. Though our body actually has a few ways to regulate this, one common way out of a few is the RGS protein, which is regulation of G protein signaling. And this can accelerate this step. Now that we actually know the steps to this, let's talk about an example."}, {"video_title": "G Protein Coupled Receptors   Nervous system physiology   NCLEX-RN   Khan Academy.mp3", "Sentence": "Eventually, the GTP will be hydrolyzed and become GDP. Though our body actually has a few ways to regulate this, one common way out of a few is the RGS protein, which is regulation of G protein signaling. And this can accelerate this step. Now that we actually know the steps to this, let's talk about an example. A very common example of GPCR function in our cell actually involves epinephrine, or adrenaline. This is our fight or flight response. So let's pretend that this green ligand, this green signaling molecule, is epinephrine."}, {"video_title": "G Protein Coupled Receptors   Nervous system physiology   NCLEX-RN   Khan Academy.mp3", "Sentence": "Now that we actually know the steps to this, let's talk about an example. A very common example of GPCR function in our cell actually involves epinephrine, or adrenaline. This is our fight or flight response. So let's pretend that this green ligand, this green signaling molecule, is epinephrine. And let's pretend that our GPCR is our adrenergic receptor. Once this epinephrine binds to our adrenergic receptor, our GPCR in our body that binds epinephrine, this adrenergic receptor will undergo a conformational change. It will swap out this GDP on this alpha subunit for GTP."}, {"video_title": "G Protein Coupled Receptors   Nervous system physiology   NCLEX-RN   Khan Academy.mp3", "Sentence": "So let's pretend that this green ligand, this green signaling molecule, is epinephrine. And let's pretend that our GPCR is our adrenergic receptor. Once this epinephrine binds to our adrenergic receptor, our GPCR in our body that binds epinephrine, this adrenergic receptor will undergo a conformational change. It will swap out this GDP on this alpha subunit for GTP. And this alpha subunit will now seek out this other protein and regulate its function. And it just so happens that the protein that it seeks out is going to be called adenylate cyclase. Now we have our adenylate cyclase being activated, stimulated by our alpha subunit."}, {"video_title": "G Protein Coupled Receptors   Nervous system physiology   NCLEX-RN   Khan Academy.mp3", "Sentence": "It will swap out this GDP on this alpha subunit for GTP. And this alpha subunit will now seek out this other protein and regulate its function. And it just so happens that the protein that it seeks out is going to be called adenylate cyclase. Now we have our adenylate cyclase being activated, stimulated by our alpha subunit. And what the adenylate cyclase will do is it will take ATP, adenosine triphosphate, and it will produce CAMP, cyclic adenosine monophosphate. So it'll take away two phosphates from our triphosphate and it will make it monophosphate. Once this happens, our cyclic AMP here is what we call a second messenger."}, {"video_title": "G Protein Coupled Receptors   Nervous system physiology   NCLEX-RN   Khan Academy.mp3", "Sentence": "Now we have our adenylate cyclase being activated, stimulated by our alpha subunit. And what the adenylate cyclase will do is it will take ATP, adenosine triphosphate, and it will produce CAMP, cyclic adenosine monophosphate. So it'll take away two phosphates from our triphosphate and it will make it monophosphate. Once this happens, our cyclic AMP here is what we call a second messenger. So our signal, our epinephrine, goes through this entire process and the signal is transformed into another signal, this cyclic AMP, which is now inside our cells. And this cyclic AMP will now tell our cell to do other things. For example, is that it'll increase our heart rate."}, {"video_title": "G Protein Coupled Receptors   Nervous system physiology   NCLEX-RN   Khan Academy.mp3", "Sentence": "Once this happens, our cyclic AMP here is what we call a second messenger. So our signal, our epinephrine, goes through this entire process and the signal is transformed into another signal, this cyclic AMP, which is now inside our cells. And this cyclic AMP will now tell our cell to do other things. For example, is that it'll increase our heart rate. It'll also dilate our skeletal muscle blood vessels. Remember, fight or flight. We need to start running or fighting."}, {"video_title": "G Protein Coupled Receptors   Nervous system physiology   NCLEX-RN   Khan Academy.mp3", "Sentence": "For example, is that it'll increase our heart rate. It'll also dilate our skeletal muscle blood vessels. Remember, fight or flight. We need to start running or fighting. And so our muscles are going to have their blood vessels dilate. And finally, all of this process is going to require a lot of energy. So we're going to actually break down glycogen to glucose."}, {"video_title": "G Protein Coupled Receptors   Nervous system physiology   NCLEX-RN   Khan Academy.mp3", "Sentence": "We need to start running or fighting. And so our muscles are going to have their blood vessels dilate. And finally, all of this process is going to require a lot of energy. So we're going to actually break down glycogen to glucose. Now remember, this is our biggest group of cell membrane receptors. It's a pretty complicated process. Just go over it again."}, {"video_title": "G Protein Coupled Receptors   Nervous system physiology   NCLEX-RN   Khan Academy.mp3", "Sentence": "So we're going to actually break down glycogen to glucose. Now remember, this is our biggest group of cell membrane receptors. It's a pretty complicated process. Just go over it again. For example, our epinephrine binds to our GPCR. This GPCR then changes its shape and undergoes a conformational change. It switches out the GDP to GTP on the alpha subunit, which causes our alpha subunit to dissociate, which will then regulate another protein."}, {"video_title": "G Protein Coupled Receptors   Nervous system physiology   NCLEX-RN   Khan Academy.mp3", "Sentence": "Just go over it again. For example, our epinephrine binds to our GPCR. This GPCR then changes its shape and undergoes a conformational change. It switches out the GDP to GTP on the alpha subunit, which causes our alpha subunit to dissociate, which will then regulate another protein. And this protein will turn ATP into cyclic AMP, which is our second messenger. And this second messenger will now tell our body to do other things. For example, increase heart rate, dilate blood vessels, break down glycogen into glucose."}, {"video_title": "G Protein Coupled Receptors   Nervous system physiology   NCLEX-RN   Khan Academy.mp3", "Sentence": "It switches out the GDP to GTP on the alpha subunit, which causes our alpha subunit to dissociate, which will then regulate another protein. And this protein will turn ATP into cyclic AMP, which is our second messenger. And this second messenger will now tell our body to do other things. For example, increase heart rate, dilate blood vessels, break down glycogen into glucose. Now other GPCRs in our body, the other 1,000, are going to do other things but undergo a similar process. So in summary, GPCRs are a large, diverse family of cell surface receptors that respond to many different external signals. Binding of our signaling molecule, or ligand, to our GPCR results in G protein activation, which then triggers the production of other second messengers."}, {"video_title": "Molecular structure of RNA   Macromolecules   Biology   Khan Academy.mp3", "Sentence": "In fact, right depicted in front of us, we have two strands of DNA forming a double helix. And we can look at the telltale signs that this is DNA. And in particular, we can look at the five-carbon sugar on its backbone. We see, and let's actually number the carbons. This is one prime, two prime, three prime, four prime, five prime. We can see on the two-prime carbon, we don't have an oxygen attached to it. We don't have a hydroxyl group attached to it."}, {"video_title": "Molecular structure of RNA   Macromolecules   Biology   Khan Academy.mp3", "Sentence": "We see, and let's actually number the carbons. This is one prime, two prime, three prime, four prime, five prime. We can see on the two-prime carbon, we don't have an oxygen attached to it. We don't have a hydroxyl group attached to it. And because of that, we know that this is not ribose. This is deoxyribose. This right over here is deoxyribose."}, {"video_title": "Molecular structure of RNA   Macromolecules   Biology   Khan Academy.mp3", "Sentence": "We don't have a hydroxyl group attached to it. And because of that, we know that this is not ribose. This is deoxyribose. This right over here is deoxyribose. And these two are also deoxyribose. So that tells us that we have two strands of DNA, deoxyribonucleic acid. So let me write this down."}, {"video_title": "Molecular structure of RNA   Macromolecules   Biology   Khan Academy.mp3", "Sentence": "This right over here is deoxyribose. And these two are also deoxyribose. So that tells us that we have two strands of DNA, deoxyribonucleic acid. So let me write this down. This part of the chain, this is derived from a deoxyribose being attached to phosphate groups in a nitrogenous base. So deoxyribose. So what would we have to do if we wanted, instead of viewing this as two strands of DNA in a double helix formation, well, how would we have to rearrange, how would we have to edit the left-hand strand if instead we wanted to imagine that the left-hand strand is, say, messenger RNA being generated during transcription with a single strand of DNA here on the right?"}, {"video_title": "Molecular structure of RNA   Macromolecules   Biology   Khan Academy.mp3", "Sentence": "So let me write this down. This part of the chain, this is derived from a deoxyribose being attached to phosphate groups in a nitrogenous base. So deoxyribose. So what would we have to do if we wanted, instead of viewing this as two strands of DNA in a double helix formation, well, how would we have to rearrange, how would we have to edit the left-hand strand if instead we wanted to imagine that the left-hand strand is, say, messenger RNA being generated during transcription with a single strand of DNA here on the right? Well, to turn this into RNA, or to make it look like RNA, on the two prime carbon, well, we wanna turn the deoxyribose into just ribose, so we would wanna add a hydroxyl group right over here. So add a hydroxyl group over there. Actually, let me do that."}, {"video_title": "Molecular structure of RNA   Macromolecules   Biology   Khan Academy.mp3", "Sentence": "So what would we have to do if we wanted, instead of viewing this as two strands of DNA in a double helix formation, well, how would we have to rearrange, how would we have to edit the left-hand strand if instead we wanted to imagine that the left-hand strand is, say, messenger RNA being generated during transcription with a single strand of DNA here on the right? Well, to turn this into RNA, or to make it look like RNA, on the two prime carbon, well, we wanna turn the deoxyribose into just ribose, so we would wanna add a hydroxyl group right over here. So add a hydroxyl group over there. Actually, let me do that. Do the hydrogens in white. So add one hydroxyl group there. And I wanna do it on all the sugars on the left strand's backbone."}, {"video_title": "Molecular structure of RNA   Macromolecules   Biology   Khan Academy.mp3", "Sentence": "Actually, let me do that. Do the hydrogens in white. So add one hydroxyl group there. And I wanna do it on all the sugars on the left strand's backbone. If I want this to be a single strand of RNA, and RNA tends to be single-stranded. So oxygen and then a hydrogen. And so this hydroxyl, adding this hydroxyl group, instead of just having another hydrogen, just a hydrogen by itself over there, this tells us that this sugar is no longer deoxyribose."}, {"video_title": "Molecular structure of RNA   Macromolecules   Biology   Khan Academy.mp3", "Sentence": "And I wanna do it on all the sugars on the left strand's backbone. If I want this to be a single strand of RNA, and RNA tends to be single-stranded. So oxygen and then a hydrogen. And so this hydroxyl, adding this hydroxyl group, instead of just having another hydrogen, just a hydrogen by itself over there, this tells us that this sugar is no longer deoxyribose. This is ribose. So now we have ribose. We now have ribose in our backbone, which is a telltale sign that, well, at least now we have the backbone of RNA, ribonucleic acid, versus DNA, deoxyribonucleic acid."}, {"video_title": "Molecular structure of RNA   Macromolecules   Biology   Khan Academy.mp3", "Sentence": "And so this hydroxyl, adding this hydroxyl group, instead of just having another hydrogen, just a hydrogen by itself over there, this tells us that this sugar is no longer deoxyribose. This is ribose. So now we have ribose. We now have ribose in our backbone, which is a telltale sign that, well, at least now we have the backbone of RNA, ribonucleic acid, versus DNA, deoxyribonucleic acid. Now you might think we're done, but we're not quite done, because the nitrogenous bases on RNA are slightly different than the nitrogenous bases on DNA. On DNA, your nitrogenous bases are adenine, guanine, are adenine, guanine, and adenine and guanine are the two-ringed nitrogenous bases right over here. This is adenine, this is guanine."}, {"video_title": "Molecular structure of RNA   Macromolecules   Biology   Khan Academy.mp3", "Sentence": "We now have ribose in our backbone, which is a telltale sign that, well, at least now we have the backbone of RNA, ribonucleic acid, versus DNA, deoxyribonucleic acid. Now you might think we're done, but we're not quite done, because the nitrogenous bases on RNA are slightly different than the nitrogenous bases on DNA. On DNA, your nitrogenous bases are adenine, guanine, are adenine, guanine, and adenine and guanine are the two-ringed nitrogenous bases right over here. This is adenine, this is guanine. And you also have cytosine. Cytosine, I'm gonna do these all in different colors. Cytosine and thymine."}, {"video_title": "Molecular structure of RNA   Macromolecules   Biology   Khan Academy.mp3", "Sentence": "This is adenine, this is guanine. And you also have cytosine. Cytosine, I'm gonna do these all in different colors. Cytosine and thymine. I'm getting to the punchline too fast. And this right over here is cytosine, and this is thymine. And cytosine and thymine are single-ringed nitrogenous bases."}, {"video_title": "Molecular structure of RNA   Macromolecules   Biology   Khan Academy.mp3", "Sentence": "Cytosine and thymine. I'm getting to the punchline too fast. And this right over here is cytosine, and this is thymine. And cytosine and thymine are single-ringed nitrogenous bases. We call them pyrimidines, adenine and guanine. We call them purines. This is a little bit of a review."}, {"video_title": "Molecular structure of RNA   Macromolecules   Biology   Khan Academy.mp3", "Sentence": "And cytosine and thymine are single-ringed nitrogenous bases. We call them pyrimidines, adenine and guanine. We call them purines. This is a little bit of a review. In RNA, you still have adenine, you still have guanine, you still have cytosine, but instead of thymine, you have a very close relative of thymine, and that is uracil. So the way that this is drawn right now, this nitrogenous base, remember when we started this video, it was double-stranded DNA, this nitrogenous base right over here is thymine, and it bonds, it forms hydrogen bonds with adenine right over here. If I want to turn it into uracil, I just have to get rid of this methyl group right over here."}, {"video_title": "Molecular structure of RNA   Macromolecules   Biology   Khan Academy.mp3", "Sentence": "This is a little bit of a review. In RNA, you still have adenine, you still have guanine, you still have cytosine, but instead of thymine, you have a very close relative of thymine, and that is uracil. So the way that this is drawn right now, this nitrogenous base, remember when we started this video, it was double-stranded DNA, this nitrogenous base right over here is thymine, and it bonds, it forms hydrogen bonds with adenine right over here. If I want to turn it into uracil, I just have to get rid of this methyl group right over here. So if I just do this, if I just do this, and if I were to replace it with a hydrogen that is just implicitly bonded there, well now I'm dealing with uracil. So now I'm dealing with uracil. So you see that uracil and thymine are very close molecules, or they're very similar nitrogenous bases, and that's why they can play a very similar role."}, {"video_title": "Molecular structure of RNA   Macromolecules   Biology   Khan Academy.mp3", "Sentence": "If I want to turn it into uracil, I just have to get rid of this methyl group right over here. So if I just do this, if I just do this, and if I were to replace it with a hydrogen that is just implicitly bonded there, well now I'm dealing with uracil. So now I'm dealing with uracil. So you see that uracil and thymine are very close molecules, or they're very similar nitrogenous bases, and that's why they can play a very similar role. And it's still the case. And so what uracil pairs with, it pairs still with adenine, the same thing that thymine pairs with, and everything else is of course still the same. Now an interesting question, an interesting question is why uracil?"}, {"video_title": "Molecular structure of RNA   Macromolecules   Biology   Khan Academy.mp3", "Sentence": "So you see that uracil and thymine are very close molecules, or they're very similar nitrogenous bases, and that's why they can play a very similar role. And it's still the case. And so what uracil pairs with, it pairs still with adenine, the same thing that thymine pairs with, and everything else is of course still the same. Now an interesting question, an interesting question is why uracil? Why not thymine? Or you could say why thymine? Why not uracil?"}, {"video_title": "Molecular structure of RNA   Macromolecules   Biology   Khan Academy.mp3", "Sentence": "Now an interesting question, an interesting question is why uracil? Why not thymine? Or you could say why thymine? Why not uracil? And based on what I've read, it actually turns out that uracil is a little bit more error prone. It might be able to bond with other things when you're coding. It's a little bit less stable than thymine."}, {"video_title": "Molecular structure of RNA   Macromolecules   Biology   Khan Academy.mp3", "Sentence": "Why not uracil? And based on what I've read, it actually turns out that uracil is a little bit more error prone. It might be able to bond with other things when you're coding. It's a little bit less stable than thymine. And so uracil, uracil, uracil makes the RNA molecule, or actually makes the machinery of information transfer, it makes it less stable. It's a less stable, I guess, way to transfer information. And based on what I've read, in evolutionary history, RNA molecules, most people believe, predate DNA molecules."}, {"video_title": "Molecular structure of RNA   Macromolecules   Biology   Khan Academy.mp3", "Sentence": "It's a little bit less stable than thymine. And so uracil, uracil, uracil makes the RNA molecule, or actually makes the machinery of information transfer, it makes it less stable. It's a less stable, I guess, way to transfer information. And based on what I've read, in evolutionary history, RNA molecules, most people believe, predate DNA molecules. And then when you, so in the early stages you had a lot of change, and so uracil molecules were just fine, and there was a lot of errors and whatever else, but then once you had, I guess, information needed to be a little bit more persistent and a little less error prone, well then thymine helped stabilize, thymine helped stabilize things. There's also the view of, well why is uracil stuck around? Well RNA molecules, they have all of these roles in cells, messenger RNA molecules are taking information from the DNA and getting it transcribed, or getting it translated at the ribosome, but they shouldn't hang out forever."}, {"video_title": "Molecular structure of RNA   Macromolecules   Biology   Khan Academy.mp3", "Sentence": "And based on what I've read, in evolutionary history, RNA molecules, most people believe, predate DNA molecules. And then when you, so in the early stages you had a lot of change, and so uracil molecules were just fine, and there was a lot of errors and whatever else, but then once you had, I guess, information needed to be a little bit more persistent and a little less error prone, well then thymine helped stabilize, thymine helped stabilize things. There's also the view of, well why is uracil stuck around? Well RNA molecules, they have all of these roles in cells, messenger RNA molecules are taking information from the DNA and getting it transcribed, or getting it translated at the ribosome, but they shouldn't hang out forever. You actually want them to be somewhat unstable. So it's an interesting question to think about. Why do we have uracil instead of thymine?"}, {"video_title": "Molecular structure of RNA   Macromolecules   Biology   Khan Academy.mp3", "Sentence": "Well RNA molecules, they have all of these roles in cells, messenger RNA molecules are taking information from the DNA and getting it transcribed, or getting it translated at the ribosome, but they shouldn't hang out forever. You actually want them to be somewhat unstable. So it's an interesting question to think about. Why do we have uracil instead of thymine? Or why do we have thymine instead of uracil? But this is one of the telltale signs of, that we are now dealing with an RNA molecule. So now what we have on the left hand side, now all of this business, actually let me do this in a different color, all of this business, this strand, this strand right over here, we can now, the way it's drawn, we can now consider this an RNA molecule."}, {"video_title": "Molecular structure of RNA   Macromolecules   Biology   Khan Academy.mp3", "Sentence": "Why do we have uracil instead of thymine? Or why do we have thymine instead of uracil? But this is one of the telltale signs of, that we are now dealing with an RNA molecule. So now what we have on the left hand side, now all of this business, actually let me do this in a different color, all of this business, this strand, this strand right over here, we can now, the way it's drawn, we can now consider this an RNA molecule. And if we assume that this is happening during transcription, when a DNA molecule, where a single strand of DNA would want to replicate its information, then this over here would be mRNA, messenger, messenger RNA. And so what's going on here? Well, let's think about it."}, {"video_title": "Molecular structure of RNA   Macromolecules   Biology   Khan Academy.mp3", "Sentence": "So now what we have on the left hand side, now all of this business, actually let me do this in a different color, all of this business, this strand, this strand right over here, we can now, the way it's drawn, we can now consider this an RNA molecule. And if we assume that this is happening during transcription, when a DNA molecule, where a single strand of DNA would want to replicate its information, then this over here would be mRNA, messenger, messenger RNA. And so what's going on here? Well, let's think about it. This one, the way it's, the RNA, the messenger RNA, the way it's oriented, we have, if we go, we have phosphate group, then we go to five prime carbon, four prime, three prime, then phosphate group, then five prime, four prime, three prime, then phosphate group. So this is oriented five prime on top, three prime on the bottom. While this DNA molecule is oriented the other way."}, {"video_title": "Molecular structure of RNA   Macromolecules   Biology   Khan Academy.mp3", "Sentence": "Well, let's think about it. This one, the way it's, the RNA, the messenger RNA, the way it's oriented, we have, if we go, we have phosphate group, then we go to five prime carbon, four prime, three prime, then phosphate group, then five prime, four prime, three prime, then phosphate group. So this is oriented five prime on top, three prime on the bottom. While this DNA molecule is oriented the other way. This is a five prime carbon, this is a three prime carbon. So we have phosphate, three prime, five prime, phosphate. So we have three prime is on top, and five prime is on the bottom."}, {"video_title": "Molecular structure of RNA   Macromolecules   Biology   Khan Academy.mp3", "Sentence": "While this DNA molecule is oriented the other way. This is a five prime carbon, this is a three prime carbon. So we have phosphate, three prime, five prime, phosphate. So we have three prime is on top, and five prime is on the bottom. So if we wanted to think about what's happening, maybe using the symbols for the nitrogenous bases, we could say, all right, we have our mRNA molecule here, and this is its five prime end, and this is its three prime end. And then the first, the top nitrogenous base right over here, this is uracil. This is uracil."}, {"video_title": "Molecular structure of RNA   Macromolecules   Biology   Khan Academy.mp3", "Sentence": "So we have three prime is on top, and five prime is on the bottom. So if we wanted to think about what's happening, maybe using the symbols for the nitrogenous bases, we could say, all right, we have our mRNA molecule here, and this is its five prime end, and this is its three prime end. And then the first, the top nitrogenous base right over here, this is uracil. This is uracil. And then the second one over here, this is, sorry, over here, this is cytosine. So this is cytosine. This is cytosine right over here."}, {"video_title": "Molecular structure of RNA   Macromolecules   Biology   Khan Academy.mp3", "Sentence": "This is uracil. And then the second one over here, this is, sorry, over here, this is cytosine. So this is cytosine. This is cytosine right over here. And this is being transcribed from a DNA molecule, from this DNA molecule on the right-hand side. So this is DNA. And this DNA has an anti-parallel orientation."}, {"video_title": "Molecular structure of RNA   Macromolecules   Biology   Khan Academy.mp3", "Sentence": "This is cytosine right over here. And this is being transcribed from a DNA molecule, from this DNA molecule on the right-hand side. So this is DNA. And this DNA has an anti-parallel orientation. It's parallel, but it's kind of flipped over. The sugars are pointed in a different direction. So this is going from, this is the three prime end, this is the five prime end."}, {"video_title": "Molecular structure of RNA   Macromolecules   Biology   Khan Academy.mp3", "Sentence": "And this DNA has an anti-parallel orientation. It's parallel, but it's kind of flipped over. The sugars are pointed in a different direction. So this is going from, this is the three prime end, this is the five prime end. And we see that the uracil is hydrogen bonded to adenine. Adenine right over here. So adenine, and I'll draw dotted lines to show the hydrogen bonds."}, {"video_title": "Molecular structure of RNA   Macromolecules   Biology   Khan Academy.mp3", "Sentence": "So this is going from, this is the three prime end, this is the five prime end. And we see that the uracil is hydrogen bonded to adenine. Adenine right over here. So adenine, and I'll draw dotted lines to show the hydrogen bonds. And that the cytosine is hydrogen bonded to guanine. To guanine. So this right over here, that is guanine."}, {"video_title": "Molecular structure of RNA   Macromolecules   Biology   Khan Academy.mp3", "Sentence": "So adenine, and I'll draw dotted lines to show the hydrogen bonds. And that the cytosine is hydrogen bonded to guanine. To guanine. So this right over here, that is guanine. And actually I'll do the hydrogen bonds in white. So, you know, they are, actually there's multiple hydrogen bonds going on here. But just to be clear, this is mRNA, and on the right we have DNA."}, {"video_title": "Molecular structure of RNA   Macromolecules   Biology   Khan Academy.mp3", "Sentence": "So this right over here, that is guanine. And actually I'll do the hydrogen bonds in white. So, you know, they are, actually there's multiple hydrogen bonds going on here. But just to be clear, this is mRNA, and on the right we have DNA. And this could be happening during transcription. This could be happening during, I'm having trouble changing colors. This could be happening during transcription."}, {"video_title": "Molecular structure of RNA   Macromolecules   Biology   Khan Academy.mp3", "Sentence": "But just to be clear, this is mRNA, and on the right we have DNA. And this could be happening during transcription. This could be happening during, I'm having trouble changing colors. This could be happening during transcription. Now what are the types of RNAs out there? We've talked about this in other videos. Well you have messenger RNA, which is an important role in taking information from DNA and getting it eventually translated with the help of tRNAs and ribosomes."}, {"video_title": "Molecular structure of RNA   Macromolecules   Biology   Khan Academy.mp3", "Sentence": "This could be happening during transcription. Now what are the types of RNAs out there? We've talked about this in other videos. Well you have messenger RNA, which is an important role in taking information from DNA and getting it eventually translated with the help of tRNAs and ribosomes. And though I've just mentioned another type of RNA, and that's transfer RNA. So transfer RNA, tRNA. tRNA."}, {"video_title": "Molecular structure of RNA   Macromolecules   Biology   Khan Academy.mp3", "Sentence": "Well you have messenger RNA, which is an important role in taking information from DNA and getting it eventually translated with the help of tRNAs and ribosomes. And though I've just mentioned another type of RNA, and that's transfer RNA. So transfer RNA, tRNA. tRNA. And in the video, the overview video on transcription and translation, we talk about how tRNA does this. But it brings amino acids, it has amino acids attached at one end, and then it has anticodons on the other end that essentially pair, that pair with codon fragment or codons on the mRNA, and then that allows it to construct proteins. And this actually is, this right over here is a visualization of a tRNA molecule."}, {"video_title": "Molecular structure of RNA   Macromolecules   Biology   Khan Academy.mp3", "Sentence": "tRNA. And in the video, the overview video on transcription and translation, we talk about how tRNA does this. But it brings amino acids, it has amino acids attached at one end, and then it has anticodons on the other end that essentially pair, that pair with codon fragment or codons on the mRNA, and then that allows it to construct proteins. And this actually is, this right over here is a visualization of a tRNA molecule. So a lot of times when we think about DNA, we think about, okay, mRNA or RNA is an intermediary to be able to eventually translate it into proteins. And that is often the case, but sometimes you also just want the RNA itself. The RNA itself plays a role in the cell beyond just transmitting information."}, {"video_title": "Molecular structure of RNA   Macromolecules   Biology   Khan Academy.mp3", "Sentence": "And this actually is, this right over here is a visualization of a tRNA molecule. So a lot of times when we think about DNA, we think about, okay, mRNA or RNA is an intermediary to be able to eventually translate it into proteins. And that is often the case, but sometimes you also just want the RNA itself. The RNA itself plays a role in the cell beyond just transmitting information. And that's an example here with tRNA. And you can see it's interesting configuration where the amino acid will attach roughly in that area up there. And then you see the anticodon, the anticodon right down here in the bottom right."}, {"video_title": "Molecular structure of RNA   Macromolecules   Biology   Khan Academy.mp3", "Sentence": "The RNA itself plays a role in the cell beyond just transmitting information. And that's an example here with tRNA. And you can see it's interesting configuration where the amino acid will attach roughly in that area up there. And then you see the anticodon, the anticodon right down here in the bottom right. And different tRNA molecules will attach to different amino acids and they'll have different anticodons here. So this is another use for RNA. And then others include ribosomal RNA."}, {"video_title": "Molecular structure of RNA   Macromolecules   Biology   Khan Academy.mp3", "Sentence": "And then you see the anticodon, the anticodon right down here in the bottom right. And different tRNA molecules will attach to different amino acids and they'll have different anticodons here. So this is another use for RNA. And then others include ribosomal RNA. Ribosomal RNA. And they actually play a structural role in ribosomes, which is where translation occurs. And you also have things called microRNA."}, {"video_title": "Molecular structure of RNA   Macromolecules   Biology   Khan Academy.mp3", "Sentence": "And then others include ribosomal RNA. Ribosomal RNA. And they actually play a structural role in ribosomes, which is where translation occurs. And you also have things called microRNA. MicroRNA, which are short chains of RNA, which could be used to regulate the translation of other RNA molecules. So RNA, you know, DNA gets a lot of the attention, but RNA is really, really, really important. And a lot of people believe that RNA came first."}, {"video_title": "Mitosis   Cells   MCAT   Khan Academy.mp3", "Sentence": "And now we're gonna talk about the actual cell division. We're gonna talk about mitosis. And if we wanted to be precise, mitosis is the process by which this one nucleus will turn into two nuclei that each have the original genetic information. Now, as we exit mitosis, we get into cytokinesis, which will then split these two nuclei into, or they'll put each of the nuclei into a separate cell when we split the cytoplasm right over here, when we split, or the cell essentially turns into two cells. But let's see how all of this happens. So the first phase, and I'll leave the end of interphase right over here. We have this big cell."}, {"video_title": "Mitosis   Cells   MCAT   Khan Academy.mp3", "Sentence": "Now, as we exit mitosis, we get into cytokinesis, which will then split these two nuclei into, or they'll put each of the nuclei into a separate cell when we split the cytoplasm right over here, when we split, or the cell essentially turns into two cells. But let's see how all of this happens. So the first phase, and I'll leave the end of interphase right over here. We have this big cell. Our DNA has been replicated. We have two centrosomes right over here. The first phase of mitosis involves a cell, and I might draw it a little bit smaller just so I have enough space here."}, {"video_title": "Mitosis   Cells   MCAT   Khan Academy.mp3", "Sentence": "We have this big cell. Our DNA has been replicated. We have two centrosomes right over here. The first phase of mitosis involves a cell, and I might draw it a little bit smaller just so I have enough space here. So involves, so this is the cell right over here. So we're gonna go to this phase right over here. And a few things start happening."}, {"video_title": "Mitosis   Cells   MCAT   Khan Academy.mp3", "Sentence": "The first phase of mitosis involves a cell, and I might draw it a little bit smaller just so I have enough space here. So involves, so this is the cell right over here. So we're gonna go to this phase right over here. And a few things start happening. One, the DNA, the chromosomes, go from being in their chromatin form where they're all spread out to kind of a more condensed form that you can actually see from a light microscope. So for example, that magenta chromosome, which is now made up of two sister chromatids after replication, we talk about that in the interphase video, it might look something like this in a, it might look something like this if you were to look in a microscope. It's unlikely to be magenta, but it's gonna have kind of that classic chromosome shape that you're used to seeing in textbooks."}, {"video_title": "Mitosis   Cells   MCAT   Khan Academy.mp3", "Sentence": "And a few things start happening. One, the DNA, the chromosomes, go from being in their chromatin form where they're all spread out to kind of a more condensed form that you can actually see from a light microscope. So for example, that magenta chromosome, which is now made up of two sister chromatids after replication, we talk about that in the interphase video, it might look something like this in a, it might look something like this if you were to look in a microscope. It's unlikely to be magenta, but it's gonna have kind of that classic chromosome shape that you're used to seeing in textbooks. And it has the centromere that connects these two sister chromatids. Right now, both of these two sister chromatids combined are considered to be one chromosome, even though before replication, it was still considered, the magenta stuff was still considered to be one chromosome. And we can draw the blue chromosome."}, {"video_title": "Mitosis   Cells   MCAT   Khan Academy.mp3", "Sentence": "It's unlikely to be magenta, but it's gonna have kind of that classic chromosome shape that you're used to seeing in textbooks. And it has the centromere that connects these two sister chromatids. Right now, both of these two sister chromatids combined are considered to be one chromosome, even though before replication, it was still considered, the magenta stuff was still considered to be one chromosome. And we can draw the blue chromosome. Once again, it's now in the condensed form. That's one sister chromatid right over there. That's another sister chromatid."}, {"video_title": "Mitosis   Cells   MCAT   Khan Academy.mp3", "Sentence": "And we can draw the blue chromosome. Once again, it's now in the condensed form. That's one sister chromatid right over there. That's another sister chromatid. They are connected at the centromere. At the centromere. So they're condensing now as we enter into mitosis."}, {"video_title": "Mitosis   Cells   MCAT   Khan Academy.mp3", "Sentence": "That's another sister chromatid. They are connected at the centromere. At the centromere. So they're condensing now as we enter into mitosis. And the nuclear membrane, the nuclear membrane starts to, starts to go away. So the nuclear membrane is starting to go away. And these two centrosomes start to migrate to opposite sides of the cell."}, {"video_title": "Mitosis   Cells   MCAT   Khan Academy.mp3", "Sentence": "So they're condensing now as we enter into mitosis. And the nuclear membrane, the nuclear membrane starts to, starts to go away. So the nuclear membrane is starting to go away. And these two centrosomes start to migrate to opposite sides of the cell. So one of them's going over here, and one of them's maybe going to go over here. So they're migrating, migrating to opposite sides of the cell. And it's pretty incredible."}, {"video_title": "Mitosis   Cells   MCAT   Khan Academy.mp3", "Sentence": "And these two centrosomes start to migrate to opposite sides of the cell. So one of them's going over here, and one of them's maybe going to go over here. So they're migrating, migrating to opposite sides of the cell. And it's pretty incredible. You know, when we, it's easy to say, oh, this happens and then that happens. But remember, this cell doesn't have a brain. This is all happening through chemical and thermodynamic reactions, and the way, you know, just based on certain triggers of where the cell is in its life cycle."}, {"video_title": "Mitosis   Cells   MCAT   Khan Academy.mp3", "Sentence": "And it's pretty incredible. You know, when we, it's easy to say, oh, this happens and then that happens. But remember, this cell doesn't have a brain. This is all happening through chemical and thermodynamic reactions, and the way, you know, just based on certain triggers of where the cell is in its life cycle. It's amazing that this is happening. It's amazing that the structures, and what sometimes we consider to be a simple thing, but this actually incredibly complex thing, is actually, it kind of quote unquote knows what to do, even though it has no intelligence here. And a lot of what I'm talking about, the general overview of the process is well understood, but scientists are still understanding exactly how do the different things happen, when they should happen, and by what mechanism, and what's actually happening sometimes in a molecular or atomic basis."}, {"video_title": "Mitosis   Cells   MCAT   Khan Academy.mp3", "Sentence": "This is all happening through chemical and thermodynamic reactions, and the way, you know, just based on certain triggers of where the cell is in its life cycle. It's amazing that this is happening. It's amazing that the structures, and what sometimes we consider to be a simple thing, but this actually incredibly complex thing, is actually, it kind of quote unquote knows what to do, even though it has no intelligence here. And a lot of what I'm talking about, the general overview of the process is well understood, but scientists are still understanding exactly how do the different things happen, when they should happen, and by what mechanism, and what's actually happening sometimes in a molecular or atomic basis. But anyway, this first phase of mitosis, the nuclear envelope, the nuclear membrane starts to disappear. The centrosomes migrate to the opposite ends of the cell, and our DNA condenses into kind of the condensed form of the chromosomes. We call this prophase."}, {"video_title": "Mitosis   Cells   MCAT   Khan Academy.mp3", "Sentence": "And a lot of what I'm talking about, the general overview of the process is well understood, but scientists are still understanding exactly how do the different things happen, when they should happen, and by what mechanism, and what's actually happening sometimes in a molecular or atomic basis. But anyway, this first phase of mitosis, the nuclear envelope, the nuclear membrane starts to disappear. The centrosomes migrate to the opposite ends of the cell, and our DNA condenses into kind of the condensed form of the chromosomes. We call this prophase. Prophase. Prophase of mitosis. Now in the next phase, in the next phase, let me draw my cell again."}, {"video_title": "Mitosis   Cells   MCAT   Khan Academy.mp3", "Sentence": "We call this prophase. Prophase. Prophase of mitosis. Now in the next phase, in the next phase, let me draw my cell again. I'm doing that same green color. In the next phase, your nuclear membrane is now gone, and the chromosomes start lining up in the middle of the cells. So you have the blue one right over here."}, {"video_title": "Mitosis   Cells   MCAT   Khan Academy.mp3", "Sentence": "Now in the next phase, in the next phase, let me draw my cell again. I'm doing that same green color. In the next phase, your nuclear membrane is now gone, and the chromosomes start lining up in the middle of the cells. So you have the blue one right over here. The blue one, that's one sister chromatid. Here's another sister chromatid. And they are connected at the centromere, not to be confused with a centrosome."}, {"video_title": "Mitosis   Cells   MCAT   Khan Academy.mp3", "Sentence": "So you have the blue one right over here. The blue one, that's one sister chromatid. Here's another sister chromatid. And they are connected at the centromere, not to be confused with a centrosome. And then here's the magenta, one of the magenta sister chromatids, and another one. And once again, it's not magenta in real life, I'm just making it in magenta because it looks nice. That's the centromere right over there."}, {"video_title": "Mitosis   Cells   MCAT   Khan Academy.mp3", "Sentence": "And they are connected at the centromere, not to be confused with a centrosome. And then here's the magenta, one of the magenta sister chromatids, and another one. And once again, it's not magenta in real life, I'm just making it in magenta because it looks nice. That's the centromere right over there. Our centrosomes are at opposite ends of the cell at this point, at opposite ends of the cell. And you might have heard the word, let me label this again, I labeled it in a previous video. That's centrosomes."}, {"video_title": "Mitosis   Cells   MCAT   Khan Academy.mp3", "Sentence": "That's the centromere right over there. Our centrosomes are at opposite ends of the cell at this point, at opposite ends of the cell. And you might have heard the word, let me label this again, I labeled it in a previous video. That's centrosomes. Centrosomes where the two sister chromatids are connected. That's a centromere. Centromere."}, {"video_title": "Mitosis   Cells   MCAT   Khan Academy.mp3", "Sentence": "That's centrosomes. Centrosomes where the two sister chromatids are connected. That's a centromere. Centromere. Now you might have heard the word centriole. Centrioles are actually, they help, they exist inside the centrosomes. They're these two kind of cylindrical looking structures."}, {"video_title": "Mitosis   Cells   MCAT   Khan Academy.mp3", "Sentence": "Centromere. Now you might have heard the word centriole. Centrioles are actually, they help, they exist inside the centrosomes. They're these two kind of cylindrical looking structures. Each of the centrosomes have two centrioles. But for the sake of this video, you could say, well the centrioles are just part of the centrosomes. But I'm just listing you all the words that involve centri-something."}, {"video_title": "Mitosis   Cells   MCAT   Khan Academy.mp3", "Sentence": "They're these two kind of cylindrical looking structures. Each of the centrosomes have two centrioles. But for the sake of this video, you could say, well the centrioles are just part of the centrosomes. But I'm just listing you all the words that involve centri-something. Centrioles right over there. And you have two of them per centrosome. So hopefully that helps clarify some confusion."}, {"video_title": "Mitosis   Cells   MCAT   Khan Academy.mp3", "Sentence": "But I'm just listing you all the words that involve centri-something. Centrioles right over there. And you have two of them per centrosome. So hopefully that helps clarify some confusion. But these things line up. And a lot of what you're about to see, this orchestration, these things moving around in the cell, things lining up and soon things pulling apart, these are all coordinated with actually a fairly sophisticated mechanism of kind of a scaffold of these kind of ropes, these microtubules. And the centrosomes role, until now I've just been kind of drawing them."}, {"video_title": "Mitosis   Cells   MCAT   Khan Academy.mp3", "Sentence": "So hopefully that helps clarify some confusion. But these things line up. And a lot of what you're about to see, this orchestration, these things moving around in the cell, things lining up and soon things pulling apart, these are all coordinated with actually a fairly sophisticated mechanism of kind of a scaffold of these kind of ropes, these microtubules. And the centrosomes role, until now I've just been kind of drawing them. You're like, well what do they do? Well the centrosomes role is these microtubules extend from them to each other and to the centromeres of these chromosomes. And to a large degree, although they're not the only actors here, they help pull and push things in the right way."}, {"video_title": "Mitosis   Cells   MCAT   Khan Academy.mp3", "Sentence": "And the centrosomes role, until now I've just been kind of drawing them. You're like, well what do they do? Well the centrosomes role is these microtubules extend from them to each other and to the centromeres of these chromosomes. And to a large degree, although they're not the only actors here, they help pull and push things in the right way. So these help make sure that the two centrosomes push away from each other. And then as we'll see in the next phase, that they're able to pull one of each of the sister chromatids from each of the pairs towards each of them. So this right over here where you see where the nuclear envelope is now gone, the chromosomes have been lined up just like this and your centrosomes are on opposite sides of your cell, we call this the metaphase."}, {"video_title": "Mitosis   Cells   MCAT   Khan Academy.mp3", "Sentence": "And to a large degree, although they're not the only actors here, they help pull and push things in the right way. So these help make sure that the two centrosomes push away from each other. And then as we'll see in the next phase, that they're able to pull one of each of the sister chromatids from each of the pairs towards each of them. So this right over here where you see where the nuclear envelope is now gone, the chromosomes have been lined up just like this and your centrosomes are on opposite sides of your cell, we call this the metaphase. We call this the metaphase of mitosis. And then you can imagine what's going to happen next. What's going to happen next?"}, {"video_title": "Mitosis   Cells   MCAT   Khan Academy.mp3", "Sentence": "So this right over here where you see where the nuclear envelope is now gone, the chromosomes have been lined up just like this and your centrosomes are on opposite sides of your cell, we call this the metaphase. We call this the metaphase of mitosis. And then you can imagine what's going to happen next. What's going to happen next? What's going to happen next is, and let me, I don't want to draw it too big because I want to be able to fit it all in one page. What's going to happen next is that those microtubules are going to start pulling on each of the sister chromatids. Let me draw that."}, {"video_title": "Mitosis   Cells   MCAT   Khan Academy.mp3", "Sentence": "What's going to happen next? What's going to happen next is, and let me, I don't want to draw it too big because I want to be able to fit it all in one page. What's going to happen next is that those microtubules are going to start pulling on each of the sister chromatids. Let me draw that. So let me draw, so you have this centrosome right over here, you have all these microtubules in your cell. You have this centrosome right over here, all those microtubules, and this one is going to be pulling, is going to be getting one of the blue chromatids to pull towards it or to move towards it. So let me draw that."}, {"video_title": "Mitosis   Cells   MCAT   Khan Academy.mp3", "Sentence": "Let me draw that. So let me draw, so you have this centrosome right over here, you have all these microtubules in your cell. You have this centrosome right over here, all those microtubules, and this one is going to be pulling, is going to be getting one of the blue chromatids to pull towards it or to move towards it. So let me draw that. So this is one blue chromatid right over here. And this one is going to be pulling the other blue chromatid towards it. And same thing for the magenta."}, {"video_title": "Mitosis   Cells   MCAT   Khan Academy.mp3", "Sentence": "So let me draw that. So this is one blue chromatid right over here. And this one is going to be pulling the other blue chromatid towards it. And same thing for the magenta. And same thing for the magenta. So that one's being pulled that way and this one is being pulled that way. And just in case you're concerned about some more of the words, the vocabulary involved, the point at which these microtubules connect to what used to be sister chromatids, but now that they're apart, we now call them chromosomes."}, {"video_title": "Mitosis   Cells   MCAT   Khan Academy.mp3", "Sentence": "And same thing for the magenta. And same thing for the magenta. So that one's being pulled that way and this one is being pulled that way. And just in case you're concerned about some more of the words, the vocabulary involved, the point at which these microtubules connect to what used to be sister chromatids, but now that they're apart, we now call them chromosomes. When they were merged, this was one chromosome and they have two sister chromatids. But now they're apart, we would actually now consider these each an independent chromosome. So now you actually have four chromosomes over here."}, {"video_title": "Mitosis   Cells   MCAT   Khan Academy.mp3", "Sentence": "And just in case you're concerned about some more of the words, the vocabulary involved, the point at which these microtubules connect to what used to be sister chromatids, but now that they're apart, we now call them chromosomes. When they were merged, this was one chromosome and they have two sister chromatids. But now they're apart, we would actually now consider these each an independent chromosome. So now you actually have four chromosomes over here. And this point right over here, we call a kinetochore. Kinetochore, and even exactly how that interface works and exactly how things move is not fully understood. Some of this stuff is understood, but some of this is still an area of research."}, {"video_title": "Mitosis   Cells   MCAT   Khan Academy.mp3", "Sentence": "So now you actually have four chromosomes over here. And this point right over here, we call a kinetochore. Kinetochore, and even exactly how that interface works and exactly how things move is not fully understood. Some of this stuff is understood, but some of this is still an area of research. So something even as basic as cell division, not so basic after all. So this right over here where you can start to see the DNA kind of migrating to their respective sides of the cell, we call this the anaphase. We call this the anaphase."}, {"video_title": "Mitosis   Cells   MCAT   Khan Academy.mp3", "Sentence": "Some of this stuff is understood, but some of this is still an area of research. So something even as basic as cell division, not so basic after all. So this right over here where you can start to see the DNA kind of migrating to their respective sides of the cell, we call this the anaphase. We call this the anaphase. And then that takes us to the last formal phase of mitosis, and that is called telophase. Telophase. And in telophase, let me do my best job to draw it."}, {"video_title": "Mitosis   Cells   MCAT   Khan Academy.mp3", "Sentence": "We call this the anaphase. And then that takes us to the last formal phase of mitosis, and that is called telophase. Telophase. And in telophase, let me do my best job to draw it. And you can already see I've started to draw that the cells, the cellular membrane's starting to pinch in kind of in preparation for cytokinesis, in preparation for the cell splitting into two cells. So I'll do it a little bit more. Cytokinesis is usually described as kind of being a separate process than mitosis, although it is obviously they are, they kind of together help the cell fully turn into two cells."}, {"video_title": "Mitosis   Cells   MCAT   Khan Academy.mp3", "Sentence": "And in telophase, let me do my best job to draw it. And you can already see I've started to draw that the cells, the cellular membrane's starting to pinch in kind of in preparation for cytokinesis, in preparation for the cell splitting into two cells. So I'll do it a little bit more. Cytokinesis is usually described as kind of being a separate process than mitosis, although it is obviously they are, they kind of together help the cell fully turn into two cells. So now in telophase, so you have this, what used to be a sister chromatid, now we could call it a chromosome on its own. And we have this chromosome. And we have, and we have this chromosome right over there, let me actually do it on both sides."}, {"video_title": "Mitosis   Cells   MCAT   Khan Academy.mp3", "Sentence": "Cytokinesis is usually described as kind of being a separate process than mitosis, although it is obviously they are, they kind of together help the cell fully turn into two cells. So now in telophase, so you have this, what used to be a sister chromatid, now we could call it a chromosome on its own. And we have this chromosome. And we have, and we have this chromosome right over there, let me actually do it on both sides. So you have there, and you have, you have this right over here. And actually, let me draw it a little bit different. Because at this phase, you're really starting to unwind what happened at prophase."}, {"video_title": "Mitosis   Cells   MCAT   Khan Academy.mp3", "Sentence": "And we have, and we have this chromosome right over there, let me actually do it on both sides. So you have there, and you have, you have this right over here. And actually, let me draw it a little bit different. Because at this phase, you're really starting to unwind what happened at prophase. So prophase, you have the disappearance of the nuclear membrane, and you have the condensation of the chromosomes into this form here. Telophase, that's unwinding a little bit. So actually let me draw the two centrosomes."}, {"video_title": "Mitosis   Cells   MCAT   Khan Academy.mp3", "Sentence": "Because at this phase, you're really starting to unwind what happened at prophase. So prophase, you have the disappearance of the nuclear membrane, and you have the condensation of the chromosomes into this form here. Telophase, that's unwinding a little bit. So actually let me draw the two centrosomes. So you have one centrosome, do that same color that I had before. So you have one centrosome right here, you have another centrosome right over there. And now the DNA, this blue DNA, this chromosome's now here, but it's starting to get a little, underwound a little bit."}, {"video_title": "Mitosis   Cells   MCAT   Khan Academy.mp3", "Sentence": "So actually let me draw the two centrosomes. So you have one centrosome, do that same color that I had before. So you have one centrosome right here, you have another centrosome right over there. And now the DNA, this blue DNA, this chromosome's now here, but it's starting to get a little, underwound a little bit. Same thing on this side right over here. Magenta chromosome is on here, but once again, it's starting to get a little bit unwound. Same thing over here."}, {"video_title": "Mitosis   Cells   MCAT   Khan Academy.mp3", "Sentence": "And now the DNA, this blue DNA, this chromosome's now here, but it's starting to get a little, underwound a little bit. Same thing on this side right over here. Magenta chromosome is on here, but once again, it's starting to get a little bit unwound. Same thing over here. And you start to have nuclear membranes forming around the DNA. So once again, it's kind of redoing what was undone in prophase. Undone in prophase."}, {"video_title": "Mitosis   Cells   MCAT   Khan Academy.mp3", "Sentence": "Same thing over here. And you start to have nuclear membranes forming around the DNA. So once again, it's kind of redoing what was undone in prophase. Undone in prophase. And so when you're done, you essentially, you're gonna have these nuclear membranes, the DNA is gonna go back to its chromatin form, and then you have cytokinesis. And cytokinesis is the process by which this gets fully pinched together, and you have two separate cells. And some folks will say, oh, it kind of begins in anaphase, and it finishes after telophase, but it's kind of happening near the end of mitosis, in parallel with it."}, {"video_title": "Mitosis   Cells   MCAT   Khan Academy.mp3", "Sentence": "Undone in prophase. And so when you're done, you essentially, you're gonna have these nuclear membranes, the DNA is gonna go back to its chromatin form, and then you have cytokinesis. And cytokinesis is the process by which this gets fully pinched together, and you have two separate cells. And some folks will say, oh, it kind of begins in anaphase, and it finishes after telophase, but it's kind of happening near the end of mitosis, in parallel with it. So this is cytokinesis. Cytokinesis. Cytokinesis right over here."}, {"video_title": "Mitosis   Cells   MCAT   Khan Academy.mp3", "Sentence": "And some folks will say, oh, it kind of begins in anaphase, and it finishes after telophase, but it's kind of happening near the end of mitosis, in parallel with it. So this is cytokinesis. Cytokinesis. Cytokinesis right over here. This essentially is how this larger cell that had two nuclei, how this divides, fully divides into two cells. And at that point, you're back to, you're back to this phase of the cell cycle. Now each of these, now two cells, are going to go through interphase."}, {"video_title": "Mitosis   Cells   MCAT   Khan Academy.mp3", "Sentence": "Cytokinesis right over here. This essentially is how this larger cell that had two nuclei, how this divides, fully divides into two cells. And at that point, you're back to, you're back to this phase of the cell cycle. Now each of these, now two cells, are going to go through interphase. G1, S phase, replicate their DNA. G2 phase, grow some more, and then go through mitosis again. And then these two will turn into four cells."}, {"video_title": "Gene environment interaction   Behavior   MCAT   Khan Academy.mp3", "Sentence": "And to say that the genes and the environment are both important is really true, but really more specifically, they interact. And so I've alluded to this previously with the tea and the hot water example, but I want to get really specific with the language here, because not only do our genes and our environment both affect our behavior, their effect is really dependent on each other. Okay, so say you have two babies in the nursery of a hospital. One we'll say is genetically predisposed to be much more attractive than the other one. So we have this attractive baby, and we have this really hideous baby, and as a result, the beautiful baby over here, it receives more affection and more attention, and it grows up to be generally more sociable and well-adjusted. But suppose even further that at birth, both of these babies share a combination of genes that predisposes depression. As we've learned, the environment activates those genes, so in this case, maybe the genes are activated by environmental stressors."}, {"video_title": "Gene environment interaction   Behavior   MCAT   Khan Academy.mp3", "Sentence": "One we'll say is genetically predisposed to be much more attractive than the other one. So we have this attractive baby, and we have this really hideous baby, and as a result, the beautiful baby over here, it receives more affection and more attention, and it grows up to be generally more sociable and well-adjusted. But suppose even further that at birth, both of these babies share a combination of genes that predisposes depression. As we've learned, the environment activates those genes, so in this case, maybe the genes are activated by environmental stressors. So both babies have these genes, but throughout life, this cute and ultra-lovable baby is surrounded by this great and supportive network, and it has reduced stress, so its genes aren't stimulated to create the combination of neurotransmitters and other proteins that are involved in depression. But over here, this ugly baby is cranking out these proteins like crazy. And maybe that's because this baby is getting made fun of all the time, or maybe it's because it just has less friends."}, {"video_title": "Gene environment interaction   Behavior   MCAT   Khan Academy.mp3", "Sentence": "As we've learned, the environment activates those genes, so in this case, maybe the genes are activated by environmental stressors. So both babies have these genes, but throughout life, this cute and ultra-lovable baby is surrounded by this great and supportive network, and it has reduced stress, so its genes aren't stimulated to create the combination of neurotransmitters and other proteins that are involved in depression. But over here, this ugly baby is cranking out these proteins like crazy. And maybe that's because this baby is getting made fun of all the time, or maybe it's because it just has less friends. So I guess the cute baby's genes are somewhat responsible for setting up the environment, but really also the environment is responsible, at least to some degree, in keeping those depression genes at bay. Similarly, the less fortunate baby over here, his genes play a role in his tough life, and that tough life is activating the genes that are associated with creating the neurotransmitters of depression. So this is kind of a crude example of gene and environment interacting with each other, but a more specific example is the genetic condition PKU, or phenylketonuria."}, {"video_title": "Gene environment interaction   Behavior   MCAT   Khan Academy.mp3", "Sentence": "And maybe that's because this baby is getting made fun of all the time, or maybe it's because it just has less friends. So I guess the cute baby's genes are somewhat responsible for setting up the environment, but really also the environment is responsible, at least to some degree, in keeping those depression genes at bay. Similarly, the less fortunate baby over here, his genes play a role in his tough life, and that tough life is activating the genes that are associated with creating the neurotransmitters of depression. So this is kind of a crude example of gene and environment interacting with each other, but a more specific example is the genetic condition PKU, or phenylketonuria. So P-K-U. And phenylketonuria is a genetic condition in humans that's caused by mutations to a gene that code for a liver enzyme. And that liver enzyme is phenylalanine hydroxylase, so PAH."}, {"video_title": "Gene environment interaction   Behavior   MCAT   Khan Academy.mp3", "Sentence": "So this is kind of a crude example of gene and environment interacting with each other, but a more specific example is the genetic condition PKU, or phenylketonuria. So P-K-U. And phenylketonuria is a genetic condition in humans that's caused by mutations to a gene that code for a liver enzyme. And that liver enzyme is phenylalanine hydroxylase, so PAH. But because the enzyme is missing the amino acid phenylalanine, it doesn't get converted into the amino acid tyrosine during one of the metabolic pathways in our body. And so this causes a buildup of phenylalanine in the body, which can cause problems for brain development and even other problems. So PKU, it affects one in about 15,000 babies in the U.S., but most of these babies grow up without any major problems."}, {"video_title": "Gene environment interaction   Behavior   MCAT   Khan Academy.mp3", "Sentence": "And that liver enzyme is phenylalanine hydroxylase, so PAH. But because the enzyme is missing the amino acid phenylalanine, it doesn't get converted into the amino acid tyrosine during one of the metabolic pathways in our body. And so this causes a buildup of phenylalanine in the body, which can cause problems for brain development and even other problems. So PKU, it affects one in about 15,000 babies in the U.S., but most of these babies grow up without any major problems. And it turns out that during infant screening, these babies are identified and they're placed on a special phenylalanine-free diet. So because they're not taking in all of this phenylalanine, it's resulting in a less problematic buildup of the phenylalanine in the body. So it's really an interaction, again, between our genes and our environment that initiates the body's responses and behavior."}, {"video_title": "Gene environment interaction   Behavior   MCAT   Khan Academy.mp3", "Sentence": "So PKU, it affects one in about 15,000 babies in the U.S., but most of these babies grow up without any major problems. And it turns out that during infant screening, these babies are identified and they're placed on a special phenylalanine-free diet. So because they're not taking in all of this phenylalanine, it's resulting in a less problematic buildup of the phenylalanine in the body. So it's really an interaction, again, between our genes and our environment that initiates the body's responses and behavior. So we see that the environment is dependent on genetic predisposition, but gene expression is also dependent on the environment. And this is the phenomenon that we're referring to as gene-environment interaction. So this idea is going to shift our vocabulary away from phrases like nature versus nurture, and it's going to bring us to a more correct phraseology, nature through nurture."}, {"video_title": "Introduction to Evolution and Natural Selection.mp3", "Sentence": "And whenever we hear this word, I mean, even if we don't hear it in the biological context, we imagine that something is changing. It is evolving. And so when people use the word evolution in our everyday context, they think of this notion of change, that this is going to test my drawing ability. But you see an ape, bunt over. We've all seen this picture at the Natural Museum, and he's walking hunchback like that, and his head's bent down. And I'm doing my best. That's the ape."}, {"video_title": "Introduction to Evolution and Natural Selection.mp3", "Sentence": "But you see an ape, bunt over. We've all seen this picture at the Natural Museum, and he's walking hunchback like that, and his head's bent down. And I'm doing my best. That's the ape. Maybe he's also wearing a hat. And then they show this picture where he slowly, slowly becomes more and more upright. And eventually, he turns into some dude who's just walking on his way to work, also just as happy."}, {"video_title": "Introduction to Evolution and Natural Selection.mp3", "Sentence": "That's the ape. Maybe he's also wearing a hat. And then they show this picture where he slowly, slowly becomes more and more upright. And eventually, he turns into some dude who's just walking on his way to work, also just as happy. And now he's walking completely upright. And it's some kind of implication that walking upright is better than not walking upright, et cetera, et cetera. Oh, he doesn't have a tail anymore."}, {"video_title": "Introduction to Evolution and Natural Selection.mp3", "Sentence": "And eventually, he turns into some dude who's just walking on his way to work, also just as happy. And now he's walking completely upright. And it's some kind of implication that walking upright is better than not walking upright, et cetera, et cetera. Oh, he doesn't have a tail anymore. Let me eliminate that. This guy does have a tail. Let me do it in an appropriate width."}, {"video_title": "Introduction to Evolution and Natural Selection.mp3", "Sentence": "Oh, he doesn't have a tail anymore. Let me eliminate that. This guy does have a tail. Let me do it in an appropriate width. This guy has a tail, so you're going to have to excuse my drawing skills. But we've all seen this. If you've ever gone to a natural history museum, they'll just make more and more upright apes."}, {"video_title": "Introduction to Evolution and Natural Selection.mp3", "Sentence": "Let me do it in an appropriate width. This guy has a tail, so you're going to have to excuse my drawing skills. But we've all seen this. If you've ever gone to a natural history museum, they'll just make more and more upright apes. And eventually, you get to a human being. And it's this idea that the apes somehow changed into a human being. And I've seen this in multiple contexts, even inside of biology classes and even the scientific community."}, {"video_title": "Introduction to Evolution and Natural Selection.mp3", "Sentence": "If you've ever gone to a natural history museum, they'll just make more and more upright apes. And eventually, you get to a human being. And it's this idea that the apes somehow changed into a human being. And I've seen this in multiple contexts, even inside of biology classes and even the scientific community. They'll say, oh, the ape evolved into the human, or the ape evolved into the pre-human, the guy that almost stood upright. The guy that was a little bit hunched back, so he looked a little bit like an ape and a little bit like a human, and so on and so forth. And I want to be very clear here."}, {"video_title": "Introduction to Evolution and Natural Selection.mp3", "Sentence": "And I've seen this in multiple contexts, even inside of biology classes and even the scientific community. They'll say, oh, the ape evolved into the human, or the ape evolved into the pre-human, the guy that almost stood upright. The guy that was a little bit hunched back, so he looked a little bit like an ape and a little bit like a human, and so on and so forth. And I want to be very clear here. Even though this process did happen, that you did have creatures that over time accumulated changes that maybe their ancestors might have looked more like this, and eventually they looked more like this, there was no active process going on called evolution. It's not like the ape said, gee, I would like my kids to look more like this dude, so somehow I'm going to get my DNA to get enough changes to look more like this. And it's not like the DNA knew."}, {"video_title": "Introduction to Evolution and Natural Selection.mp3", "Sentence": "And I want to be very clear here. Even though this process did happen, that you did have creatures that over time accumulated changes that maybe their ancestors might have looked more like this, and eventually they looked more like this, there was no active process going on called evolution. It's not like the ape said, gee, I would like my kids to look more like this dude, so somehow I'm going to get my DNA to get enough changes to look more like this. And it's not like the DNA knew. The DNA didn't say, hey, it is better to be walking than to be kind of hunched back like an ape, and so therefore, I am going to try to somehow spontaneously change into this dude. That's not what evolution is. It's not like some people imagine that maybe there's a tree, and on that tree there's a bunch of good fruit at the top of the tree."}, {"video_title": "Introduction to Evolution and Natural Selection.mp3", "Sentence": "And it's not like the DNA knew. The DNA didn't say, hey, it is better to be walking than to be kind of hunched back like an ape, and so therefore, I am going to try to somehow spontaneously change into this dude. That's not what evolution is. It's not like some people imagine that maybe there's a tree, and on that tree there's a bunch of good fruit at the top of the tree. Maybe they're apples. And then maybe you have some type of cow-like creature, or maybe it's some type of horse-like creature that says, gee, I would like to get to those apples. And that just because they want to get there, maybe the next generation, they keep trying to raise their neck."}, {"video_title": "Introduction to Evolution and Natural Selection.mp3", "Sentence": "It's not like some people imagine that maybe there's a tree, and on that tree there's a bunch of good fruit at the top of the tree. Maybe they're apples. And then maybe you have some type of cow-like creature, or maybe it's some type of horse-like creature that says, gee, I would like to get to those apples. And that just because they want to get there, maybe the next generation, they keep trying to raise their neck. And then after generation after generation, their necks get longer and longer, and eventually they turn into giraffes. That is not what evolution is, and that's not what it implies. Although sometimes the everyday notion of the word seems to make us think that way."}, {"video_title": "Introduction to Evolution and Natural Selection.mp3", "Sentence": "And that just because they want to get there, maybe the next generation, they keep trying to raise their neck. And then after generation after generation, their necks get longer and longer, and eventually they turn into giraffes. That is not what evolution is, and that's not what it implies. Although sometimes the everyday notion of the word seems to make us think that way. What evolution is, and actually this is the word that I prefer to use, it's natural selection. Natural selection, let me write that word down. And literally what it means is that in any population of living organisms, you're going to have some variation."}, {"video_title": "Introduction to Evolution and Natural Selection.mp3", "Sentence": "Although sometimes the everyday notion of the word seems to make us think that way. What evolution is, and actually this is the word that I prefer to use, it's natural selection. Natural selection, let me write that word down. And literally what it means is that in any population of living organisms, you're going to have some variation. And this is an important key word here. Variation just means, look, there's just some change. If you look at the kids in your school, you'll see variation."}, {"video_title": "Introduction to Evolution and Natural Selection.mp3", "Sentence": "And literally what it means is that in any population of living organisms, you're going to have some variation. And this is an important key word here. Variation just means, look, there's just some change. If you look at the kids in your school, you'll see variation. Some people are tall, some people are short, some people have blonde hair, some people have black hair, so on and so forth. There's always variation. And what natural selection is, is this process that sometimes environmental factors will select for certain variations."}, {"video_title": "Introduction to Evolution and Natural Selection.mp3", "Sentence": "If you look at the kids in your school, you'll see variation. Some people are tall, some people are short, some people have blonde hair, some people have black hair, so on and so forth. There's always variation. And what natural selection is, is this process that sometimes environmental factors will select for certain variations. Some variations might not matter at all, but some variations matter a lot. One example that's given in every biology book, but it really is interesting. I believe they're called the peppered moth, and this was pre-industrial revolution England."}, {"video_title": "Introduction to Evolution and Natural Selection.mp3", "Sentence": "And what natural selection is, is this process that sometimes environmental factors will select for certain variations. Some variations might not matter at all, but some variations matter a lot. One example that's given in every biology book, but it really is interesting. I believe they're called the peppered moth, and this was pre-industrial revolution England. Most peppered moths, there was just this variation. Some of them were, I guess we could call them more peppered than others. So some of them might look like this."}, {"video_title": "Introduction to Evolution and Natural Selection.mp3", "Sentence": "I believe they're called the peppered moth, and this was pre-industrial revolution England. Most peppered moths, there was just this variation. Some of them were, I guess we could call them more peppered than others. So some of them might look like this. So it had spots like that. Some of them might have looked more like that. And of course, they had some black spots on them."}, {"video_title": "Introduction to Evolution and Natural Selection.mp3", "Sentence": "So some of them might look like this. So it had spots like that. Some of them might have looked more like that. And of course, they had some black spots on them. And then some of them might have been, you know, just barely have any spots. You just have this natural variation. Like you'd see in any population of animals, you'll see some variation in colors."}, {"video_title": "Introduction to Evolution and Natural Selection.mp3", "Sentence": "And of course, they had some black spots on them. And then some of them might have been, you know, just barely have any spots. You just have this natural variation. Like you'd see in any population of animals, you'll see some variation in colors. Now, they were all happy probably for thousands of years, just this natural variation. It was a non-important trait for these peppered moths. But then all of a sudden, the Industrial Revolution happens in England, and all this soot gets released from all of these factories that are running these steam engines powered by coal."}, {"video_title": "Introduction to Evolution and Natural Selection.mp3", "Sentence": "Like you'd see in any population of animals, you'll see some variation in colors. Now, they were all happy probably for thousands of years, just this natural variation. It was a non-important trait for these peppered moths. But then all of a sudden, the Industrial Revolution happens in England, and all this soot gets released from all of these factories that are running these steam engines powered by coal. And so all of a sudden, a lot of the things that once were gray or white, for example, maybe some tree trunks. Let me draw some tree trunks. Maybe there were some tree trunks that used to look like this."}, {"video_title": "Introduction to Evolution and Natural Selection.mp3", "Sentence": "But then all of a sudden, the Industrial Revolution happens in England, and all this soot gets released from all of these factories that are running these steam engines powered by coal. And so all of a sudden, a lot of the things that once were gray or white, for example, maybe some tree trunks. Let me draw some tree trunks. Maybe there were some tree trunks that used to look like this. Maybe some tree trunks used to look something like this. And a peppered moth would be pretty OK. And maybe there were some tree trunks that were pretty dark. But all of a sudden, the Industrial Revolution happens."}, {"video_title": "Introduction to Evolution and Natural Selection.mp3", "Sentence": "Maybe there were some tree trunks that used to look like this. Maybe some tree trunks used to look something like this. And a peppered moth would be pretty OK. And maybe there were some tree trunks that were pretty dark. But all of a sudden, the Industrial Revolution happens. Everything gets covered with soot from the coal being burned. And then all of a sudden, all the trees look like this. They're just completely pitch black, or they're a lot darker than they were before."}, {"video_title": "Introduction to Evolution and Natural Selection.mp3", "Sentence": "But all of a sudden, the Industrial Revolution happens. Everything gets covered with soot from the coal being burned. And then all of a sudden, all the trees look like this. They're just completely pitch black, or they're a lot darker than they were before. Now, all of a sudden, you've had a major change to these moths' environment. And you have to think, what is going to select for these moths? Well, one thing that might get these moths are birds and the ability of the birds to see the moths."}, {"video_title": "Introduction to Evolution and Natural Selection.mp3", "Sentence": "They're just completely pitch black, or they're a lot darker than they were before. Now, all of a sudden, you've had a major change to these moths' environment. And you have to think, what is going to select for these moths? Well, one thing that might get these moths are birds and the ability of the birds to see the moths. So all of a sudden, if the environment became a lot blacker than it was before, you can guess what's going to happen. The birds are going to see this dude a lot easier than they're going to see this dude. Because this dude on a black background, he's going to be a lot harder to see."}, {"video_title": "Introduction to Evolution and Natural Selection.mp3", "Sentence": "Well, one thing that might get these moths are birds and the ability of the birds to see the moths. So all of a sudden, if the environment became a lot blacker than it was before, you can guess what's going to happen. The birds are going to see this dude a lot easier than they're going to see this dude. Because this dude on a black background, he's going to be a lot harder to see. And it's not like the birds won't catch this guy. They'll catch all of them. But they're going to catch this guy a lot more frequently."}, {"video_title": "Introduction to Evolution and Natural Selection.mp3", "Sentence": "Because this dude on a black background, he's going to be a lot harder to see. And it's not like the birds won't catch this guy. They'll catch all of them. But they're going to catch this guy a lot more frequently. So you can imagine what happens. If the birds start catching these guys before they can reproduce, or maybe while they're reproducing, what's going to happen? This guy, the darker dudes, are going to reproduce a lot more often."}, {"video_title": "Introduction to Evolution and Natural Selection.mp3", "Sentence": "But they're going to catch this guy a lot more frequently. So you can imagine what happens. If the birds start catching these guys before they can reproduce, or maybe while they're reproducing, what's going to happen? This guy, the darker dudes, are going to reproduce a lot more often. And all of a sudden, you're going to have a lot more moths that look like this. You're going to have a lot more of these dudes. So what happened here?"}, {"video_title": "Introduction to Evolution and Natural Selection.mp3", "Sentence": "This guy, the darker dudes, are going to reproduce a lot more often. And all of a sudden, you're going to have a lot more moths that look like this. You're going to have a lot more of these dudes. So what happened here? Was there any design, or was there any active change by any of the moths? I mean, it looks like a really smart thing to do, to become black, right? Your surrounding became black, and you wait a couple of generations of these moths, and now all of a sudden, the moths are black."}, {"video_title": "Introduction to Evolution and Natural Selection.mp3", "Sentence": "So what happened here? Was there any design, or was there any active change by any of the moths? I mean, it looks like a really smart thing to do, to become black, right? Your surrounding became black, and you wait a couple of generations of these moths, and now all of a sudden, the moths are black. And you might say, wow, those moths are geniuses. They all somehow decided to evolve into black moths in order to hide from the birds more easily. But that's not what happened."}, {"video_title": "Introduction to Evolution and Natural Selection.mp3", "Sentence": "Your surrounding became black, and you wait a couple of generations of these moths, and now all of a sudden, the moths are black. And you might say, wow, those moths are geniuses. They all somehow decided to evolve into black moths in order to hide from the birds more easily. But that's not what happened. You had a lot of variation in your peppered moth population. And what happened was that when everything turned darker and darker, these dudes right here, or dudettes, had a lot less success in reproducing. These guys just reproduced more and more and more."}, {"video_title": "Introduction to Evolution and Natural Selection.mp3", "Sentence": "But that's not what happened. You had a lot of variation in your peppered moth population. And what happened was that when everything turned darker and darker, these dudes right here, or dudettes, had a lot less success in reproducing. These guys just reproduced more and more and more. And these guys got eaten up before they were able to do, so maybe while they were reproducing, so that they couldn't produce as many offspring. And then this trait just became dominant. And then the peppered moth just became, you can kind of view it as a black moth."}, {"video_title": "Introduction to Evolution and Natural Selection.mp3", "Sentence": "These guys just reproduced more and more and more. And these guys got eaten up before they were able to do, so maybe while they were reproducing, so that they couldn't produce as many offspring. And then this trait just became dominant. And then the peppered moth just became, you can kind of view it as a black moth. Now you might say, OK, Sal, that's one example. I need more. This is natural selection."}, {"video_title": "Introduction to Evolution and Natural Selection.mp3", "Sentence": "And then the peppered moth just became, you can kind of view it as a black moth. Now you might say, OK, Sal, that's one example. I need more. This is natural selection. It's purported to apply to everything. It purports to explain why we evolved from basic bacteria, or maybe even self-replicating RNA, which I will talk about more in the future. I need more evidence of this."}, {"video_title": "Introduction to Evolution and Natural Selection.mp3", "Sentence": "This is natural selection. It's purported to apply to everything. It purports to explain why we evolved from basic bacteria, or maybe even self-replicating RNA, which I will talk about more in the future. I need more evidence of this. I need to see it in real time. And the best example of this is really the flu. And I'll do other videos in the future on what viruses are and how they replicate."}, {"video_title": "Introduction to Evolution and Natural Selection.mp3", "Sentence": "I need more evidence of this. I need to see it in real time. And the best example of this is really the flu. And I'll do other videos in the future on what viruses are and how they replicate. And viruses are actually fascinating, because it's not even clear that they're alive. They're literally just little buckets of DNA and sometimes RNA, which we'll learn is genetic information. And they're just contained in these viral, these little protein containers that are these neat geometrical shapes."}, {"video_title": "Introduction to Evolution and Natural Selection.mp3", "Sentence": "And I'll do other videos in the future on what viruses are and how they replicate. And viruses are actually fascinating, because it's not even clear that they're alive. They're literally just little buckets of DNA and sometimes RNA, which we'll learn is genetic information. And they're just contained in these viral, these little protein containers that are these neat geometrical shapes. And that's all they are. They really don't have, you know, they're not like regular living organisms that actively move and that actively have metabolisms and all that. What they do is they take that little DNA and they inject it into other things that can process it."}, {"video_title": "Introduction to Evolution and Natural Selection.mp3", "Sentence": "And they're just contained in these viral, these little protein containers that are these neat geometrical shapes. And that's all they are. They really don't have, you know, they're not like regular living organisms that actively move and that actively have metabolisms and all that. What they do is they take that little DNA and they inject it into other things that can process it. And then they use that DNA to produce more viruses. But anyway, we could do a whole series of videos on viruses. But the flu is a virus."}, {"video_title": "Introduction to Evolution and Natural Selection.mp3", "Sentence": "What they do is they take that little DNA and they inject it into other things that can process it. And then they use that DNA to produce more viruses. But anyway, we could do a whole series of videos on viruses. But the flu is a virus. And what happens every year is you have a certain type of virus and they have some variation. And I'll just make the variation by, I don't know, how many dots they have. And they infect, let's say it's a human flu, they infect humans, and slowly our immune systems, which we can make a whole set of videos on as well, start to recognize the virus and are able to attack them before they can do a lot of damage."}, {"video_title": "Introduction to Evolution and Natural Selection.mp3", "Sentence": "But the flu is a virus. And what happens every year is you have a certain type of virus and they have some variation. And I'll just make the variation by, I don't know, how many dots they have. And they infect, let's say it's a human flu, they infect humans, and slowly our immune systems, which we can make a whole set of videos on as well, start to recognize the virus and are able to attack them before they can do a lot of damage. So now you can imagine what happens if, let's say that this is the current flu. Let me do all of them. They all have these little two dots and that's how, and we'll talk in the future what these dots are and how they can be recognized, but let's say that's how our immune system recognize them."}, {"video_title": "Introduction to Evolution and Natural Selection.mp3", "Sentence": "And they infect, let's say it's a human flu, they infect humans, and slowly our immune systems, which we can make a whole set of videos on as well, start to recognize the virus and are able to attack them before they can do a lot of damage. So now you can imagine what happens if, let's say that this is the current flu. Let me do all of them. They all have these little two dots and that's how, and we'll talk in the future what these dots are and how they can be recognized, but let's say that's how our immune system recognize them. They start realizing, oh, any time I get this little green dude with two dots on it, that's not a good thing to have around, so I'm going to attack it in some way and destroy it before he infects my DNA and all the rest. And so you have a very strong natural selection once immune systems learn what this virus is, and we'll talk more about what learning means for an immune system, that they'll start attacking these guys. But flu, you can kind of think of them as being tricky, but they're not really tricky."}, {"video_title": "Introduction to Evolution and Natural Selection.mp3", "Sentence": "They all have these little two dots and that's how, and we'll talk in the future what these dots are and how they can be recognized, but let's say that's how our immune system recognize them. They start realizing, oh, any time I get this little green dude with two dots on it, that's not a good thing to have around, so I'm going to attack it in some way and destroy it before he infects my DNA and all the rest. And so you have a very strong natural selection once immune systems learn what this virus is, and we'll talk more about what learning means for an immune system, that they'll start attacking these guys. But flu, you can kind of think of them as being tricky, but they're not really tricky. They're not sentient objects, but what they do do is they constantly change. So what you have is, in any flu population, you're always having a little bit of change. So maybe the great majority of them have those two dots, but maybe every now and then one of them has one dot, one of them has three dots, and maybe that's just a random mutation."}, {"video_title": "Introduction to Evolution and Natural Selection.mp3", "Sentence": "But flu, you can kind of think of them as being tricky, but they're not really tricky. They're not sentient objects, but what they do do is they constantly change. So what you have is, in any flu population, you're always having a little bit of change. So maybe the great majority of them have those two dots, but maybe every now and then one of them has one dot, one of them has three dots, and maybe that's just a random mutation. This just randomly happened. Maybe one in every million of these viruses have this only one dot instead of two dots. But what's going to happen as soon as, let's say, the human immune system gets used to attacking the virus with the two red dots?"}, {"video_title": "Introduction to Evolution and Natural Selection.mp3", "Sentence": "So maybe the great majority of them have those two dots, but maybe every now and then one of them has one dot, one of them has three dots, and maybe that's just a random mutation. This just randomly happened. Maybe one in every million of these viruses have this only one dot instead of two dots. But what's going to happen as soon as, let's say, the human immune system gets used to attacking the virus with the two red dots? Well, then this guy isn't going to have to compete with the other virus capsules for infecting people. He's going to have people's DNA all to himself. And so he or she or whatever you want to call this virus is then going to be more successful."}, {"video_title": "Introduction to Evolution and Natural Selection.mp3", "Sentence": "But what's going to happen as soon as, let's say, the human immune system gets used to attacking the virus with the two red dots? Well, then this guy isn't going to have to compete with the other virus capsules for infecting people. He's going to have people's DNA all to himself. And so he or she or whatever you want to call this virus is then going to be more successful. So by next year's flu season, when people start sneezing and are able to spread it on doorknobs and whatever else again, this guy is going to be the new flu virus. So when you see this process of every year there's a new flu virus, that is evolution and natural selection in real time. It is happening."}, {"video_title": "Introduction to Evolution and Natural Selection.mp3", "Sentence": "And so he or she or whatever you want to call this virus is then going to be more successful. So by next year's flu season, when people start sneezing and are able to spread it on doorknobs and whatever else again, this guy is going to be the new flu virus. So when you see this process of every year there's a new flu virus, that is evolution and natural selection in real time. It is happening. It isn't this thing that only happens over eons and eons of time, although most of the substantial things that we see in our lives or even ourselves are based on these things that happened over eons and eons of time. But it happens on a yearly basis. Another example is if you think about antibiotics and bacteria."}, {"video_title": "Introduction to Evolution and Natural Selection.mp3", "Sentence": "It is happening. It isn't this thing that only happens over eons and eons of time, although most of the substantial things that we see in our lives or even ourselves are based on these things that happened over eons and eons of time. But it happens on a yearly basis. Another example is if you think about antibiotics and bacteria. Bacteria are these little cells that move around. And we'll talk more about them. They actually are definitely living."}, {"video_title": "Introduction to Evolution and Natural Selection.mp3", "Sentence": "Another example is if you think about antibiotics and bacteria. Bacteria are these little cells that move around. And we'll talk more about them. They actually are definitely living. They have metabolisms and whatever else. And this is just a nice note. When people talk about infections, it could either be a viral infection, which are these things that go and infect your DNA and then use your cell mechanisms to reproduce."}, {"video_title": "Introduction to Evolution and Natural Selection.mp3", "Sentence": "They actually are definitely living. They have metabolisms and whatever else. And this is just a nice note. When people talk about infections, it could either be a viral infection, which are these things that go and infect your DNA and then use your cell mechanisms to reproduce. Or it could be a bacterial infection, which are literally little cells that move around and they release toxins that make you sick and whatever else. So bacteria, these are what antibiotics kill. They attack bacteria."}, {"video_title": "Introduction to Evolution and Natural Selection.mp3", "Sentence": "When people talk about infections, it could either be a viral infection, which are these things that go and infect your DNA and then use your cell mechanisms to reproduce. Or it could be a bacterial infection, which are literally little cells that move around and they release toxins that make you sick and whatever else. So bacteria, these are what antibiotics kill. They attack bacteria. They kill them. Now, you probably, if you know a couple of doctors or whatever, and you say, hey, I'm sick. I think I have a bacterial infection."}, {"video_title": "Introduction to Evolution and Natural Selection.mp3", "Sentence": "They attack bacteria. They kill them. Now, you probably, if you know a couple of doctors or whatever, and you say, hey, I'm sick. I think I have a bacterial infection. Give me some antibiotics. A responsible doctor says, no, I won't give you antibiotics just willy-nilly, because what happens is the more antibiotics you use, you're more likely to create versions and I want to be very careful about the word create, because you're not actively creating them. But let's say, and let me finish my sentence, you're very likely to help select for antibiotic-resistant bacterias."}, {"video_title": "Introduction to Evolution and Natural Selection.mp3", "Sentence": "I think I have a bacterial infection. Give me some antibiotics. A responsible doctor says, no, I won't give you antibiotics just willy-nilly, because what happens is the more antibiotics you use, you're more likely to create versions and I want to be very careful about the word create, because you're not actively creating them. But let's say, and let me finish my sentence, you're very likely to help select for antibiotic-resistant bacterias. Now, how does that work? So let's say that these are all bacteria and you have gazillions of them, right? And every now and then you get one that's slightly different."}, {"video_title": "Introduction to Evolution and Natural Selection.mp3", "Sentence": "But let's say, and let me finish my sentence, you're very likely to help select for antibiotic-resistant bacterias. Now, how does that work? So let's say that these are all bacteria and you have gazillions of them, right? And every now and then you get one that's slightly different. Now, in a population of bacteria, these all will make you equally sick, and this is just some random difference in the bacteria, maybe on its DNA some slight different changes happened, but whatever happened. These all are the kind of bacteria, you don't want to get a lot of them in your system. Your immune system can attack them and fight them off, but if you get a lot of them, they might kill you or make you sick or whatever else."}, {"video_title": "Introduction to Evolution and Natural Selection.mp3", "Sentence": "And every now and then you get one that's slightly different. Now, in a population of bacteria, these all will make you equally sick, and this is just some random difference in the bacteria, maybe on its DNA some slight different changes happened, but whatever happened. These all are the kind of bacteria, you don't want to get a lot of them in your system. Your immune system can attack them and fight them off, but if you get a lot of them, they might kill you or make you sick or whatever else. Now, if everyone just starts using antibiotics when they're not sick or when they don't really need to in a life or death situation, you might have an antibiotic that is really good at killing the green bacteria. But what happens if you all of a sudden kill a lot of the green bacteria? Well, now the blue bacteria have the whole ecosystem that before it was competing with all these green dudes to get all the good stuff inside of your body, but now he's all alone, and now he can replicate willy-nilly."}, {"video_title": "Introduction to Evolution and Natural Selection.mp3", "Sentence": "Your immune system can attack them and fight them off, but if you get a lot of them, they might kill you or make you sick or whatever else. Now, if everyone just starts using antibiotics when they're not sick or when they don't really need to in a life or death situation, you might have an antibiotic that is really good at killing the green bacteria. But what happens if you all of a sudden kill a lot of the green bacteria? Well, now the blue bacteria have the whole ecosystem that before it was competing with all these green dudes to get all the good stuff inside of your body, but now he's all alone, and now he can replicate willy-nilly. So now he's going to replicate willy-nilly. And this is, once again, it wasn't like there was any design, there was any intelligent process here that said, look, some bacteria said, I'm going to be a little bit smarter and design myself to resist this antibiotic threat. No."}, {"video_title": "Introduction to Evolution and Natural Selection.mp3", "Sentence": "Well, now the blue bacteria have the whole ecosystem that before it was competing with all these green dudes to get all the good stuff inside of your body, but now he's all alone, and now he can replicate willy-nilly. So now he's going to replicate willy-nilly. And this is, once again, it wasn't like there was any design, there was any intelligent process here that said, look, some bacteria said, I'm going to be a little bit smarter and design myself to resist this antibiotic threat. No. There's just these random changes that happen, and mutations and viruses and bacteria happen frequently. And there are these random changes that happen. And this might be a one in a billion change."}, {"video_title": "Introduction to Evolution and Natural Selection.mp3", "Sentence": "No. There's just these random changes that happen, and mutations and viruses and bacteria happen frequently. And there are these random changes that happen. And this might be a one in a billion change. But all of a sudden, if you start killing off all of the people that it's competing with, this guy can start replicating really fast and then become the dominant bacteria. And then all of a sudden, that antibiotic that you had developed very carefully to destroy the green dudes is useless. And you have this superbug."}, {"video_title": "Introduction to Evolution and Natural Selection.mp3", "Sentence": "And this might be a one in a billion change. But all of a sudden, if you start killing off all of the people that it's competing with, this guy can start replicating really fast and then become the dominant bacteria. And then all of a sudden, that antibiotic that you had developed very carefully to destroy the green dudes is useless. And you have this superbug. You might have heard the word superbug. That's what a superbug is. It's not like it designed itself somehow."}, {"video_title": "Introduction to Evolution and Natural Selection.mp3", "Sentence": "And you have this superbug. You might have heard the word superbug. That's what a superbug is. It's not like it designed itself somehow. It's just that we got very good at killing its competition, and so we allowed it to take over. And we can't kill it because all of the drugs were just good at killing its competition. That these bacteria just keep mutating and keep mutating."}, {"video_title": "Introduction to Evolution and Natural Selection.mp3", "Sentence": "It's not like it designed itself somehow. It's just that we got very good at killing its competition, and so we allowed it to take over. And we can't kill it because all of the drugs were just good at killing its competition. That these bacteria just keep mutating and keep mutating. And if we use these antibiotics a little bit too heavily, we'll always be selecting for the things that won't be affected by the antibiotics. Well, anyway, I think I've spoken long enough. But this is a fascinating, fascinating topic."}, {"video_title": "Introduction to Evolution and Natural Selection.mp3", "Sentence": "That these bacteria just keep mutating and keep mutating. And if we use these antibiotics a little bit too heavily, we'll always be selecting for the things that won't be affected by the antibiotics. Well, anyway, I think I've spoken long enough. But this is a fascinating, fascinating topic. And I really wanted to make this my very first video or lecture, if you will, on biology. Because if you really went to, you know, biology is the study of life, and we can talk about what life is, whether viruses are living, whatnot. But if you really want to study living systems, you really can't make any assumptions other than natural selection."}, {"video_title": "Introduction to Evolution and Natural Selection.mp3", "Sentence": "But this is a fascinating, fascinating topic. And I really wanted to make this my very first video or lecture, if you will, on biology. Because if you really went to, you know, biology is the study of life, and we can talk about what life is, whether viruses are living, whatnot. But if you really want to study living systems, you really can't make any assumptions other than natural selection. We could go to another planet where the creatures don't have DNA. Or maybe they have some other type of hereditary information stored in their cells. Or they replicate some other way."}, {"video_title": "Introduction to Evolution and Natural Selection.mp3", "Sentence": "But if you really want to study living systems, you really can't make any assumptions other than natural selection. We could go to another planet where the creatures don't have DNA. Or maybe they have some other type of hereditary information stored in their cells. Or they replicate some other way. Or they're not even carbon-based. Maybe they're silicon-based. And if we went to that type of a planet in order to study the biology on that planet, everything else we know about biology, about viruses and DNA, would be useless."}, {"video_title": "Introduction to Evolution and Natural Selection.mp3", "Sentence": "Or they replicate some other way. Or they're not even carbon-based. Maybe they're silicon-based. And if we went to that type of a planet in order to study the biology on that planet, everything else we know about biology, about viruses and DNA, would be useless. But if we do understand this one concept of natural selection, that your environment will select. And there's no active process here. It's just random stuff happened."}, {"video_title": "Introduction to Evolution and Natural Selection.mp3", "Sentence": "And if we went to that type of a planet in order to study the biology on that planet, everything else we know about biology, about viruses and DNA, would be useless. But if we do understand this one concept of natural selection, that your environment will select. And there's no active process here. It's just random stuff happened. And they randomly select for random changes. And over large swaths of time, and these are unimaginably large swaths of time, those changes essentially accumulate and they might accumulate into fairly significant things. We'll talk more about this in another video."}, {"video_title": "Surface area of a box.mp3", "Sentence": "And there's a couple of ways to tackle it. The first way is, well, let's figure out the surface area of the sides that we can see and then think about what the surface area of the sides that we can't see are and how they might relate and then add them all together. So let's do that. So the front of the box is 20 centimeters tall and 10 centimeters wide. It's a rectangle, so to figure out its area, we can just multiply 20 centimeters times 10 centimeters and that's going to give us 200 centimeters. 200 square centimeters, I should say. 200 square centimeters, that's the area of the front."}, {"video_title": "Surface area of a box.mp3", "Sentence": "So the front of the box is 20 centimeters tall and 10 centimeters wide. It's a rectangle, so to figure out its area, we can just multiply 20 centimeters times 10 centimeters and that's going to give us 200 centimeters. 200 square centimeters, I should say. 200 square centimeters, that's the area of the front. Let me write it over here as well, 200. Now, we also know there's another side that has the exact same area as the front of the box and that's the back of the box. So let's write another 200 square centimeters for the back of the box."}, {"video_title": "Surface area of a box.mp3", "Sentence": "200 square centimeters, that's the area of the front. Let me write it over here as well, 200. Now, we also know there's another side that has the exact same area as the front of the box and that's the back of the box. So let's write another 200 square centimeters for the back of the box. Now let's figure out the area of the top of the box. The top of the box is, we see the box is 3 centimeters deep. So this right over here is 3 centimeters."}, {"video_title": "Surface area of a box.mp3", "Sentence": "So let's write another 200 square centimeters for the back of the box. Now let's figure out the area of the top of the box. The top of the box is, we see the box is 3 centimeters deep. So this right over here is 3 centimeters. It's 3 centimeters deep and it's 10 centimeters wide. We see the box is 10 centimeters wide. So the top of the box is going to be 3 centimeters times 10 centimeters, which is 30 square centimeters of area."}, {"video_title": "Surface area of a box.mp3", "Sentence": "So this right over here is 3 centimeters. It's 3 centimeters deep and it's 10 centimeters wide. We see the box is 10 centimeters wide. So the top of the box is going to be 3 centimeters times 10 centimeters, which is 30 square centimeters of area. So that's the top of the box, 30 square centimeters. Well, the bottom of the box is going to have the exact same area. We just can't see it right now, so that's going to be another 30."}, {"video_title": "Surface area of a box.mp3", "Sentence": "So the top of the box is going to be 3 centimeters times 10 centimeters, which is 30 square centimeters of area. So that's the top of the box, 30 square centimeters. Well, the bottom of the box is going to have the exact same area. We just can't see it right now, so that's going to be another 30. And we have two more sides because this box has six sides. We have this side panel that is 20 centimeters tall. We see that the height of the box is 20 centimeters."}, {"video_title": "Surface area of a box.mp3", "Sentence": "We just can't see it right now, so that's going to be another 30. And we have two more sides because this box has six sides. We have this side panel that is 20 centimeters tall. We see that the height of the box is 20 centimeters. And 3 centimeters deep. So 3 times 20, 3 times 20, that's 20 centimeters right there. 3 centimeters times 20 centimeters is going to give us 60 square centimeters."}, {"video_title": "Surface area of a box.mp3", "Sentence": "We see that the height of the box is 20 centimeters. And 3 centimeters deep. So 3 times 20, 3 times 20, that's 20 centimeters right there. 3 centimeters times 20 centimeters is going to give us 60 square centimeters. Now that's this side panel, but there's another side panel that has the exact same area that's on the other side of the box. So 60 centimeters squared or squared centimeters for this side and then another 60 for the corresponding side opposite to it that we can't see. And now we can just add up all of these together."}, {"video_title": "Overview of cell signaling.mp3", "Sentence": "What I want to do in this video is give ourselves a quick overview of the different ways that cells can communicate with each other. And maybe the most basic one is just through direct contact. Direct contact. And this can happen several different ways. One way could be you just have neighboring cells. So this is one cell right over here. And this is the neighboring cell right over here."}, {"video_title": "Overview of cell signaling.mp3", "Sentence": "And this can happen several different ways. One way could be you just have neighboring cells. So this is one cell right over here. And this is the neighboring cell right over here. And they actually might have gaps in their membranes. If these are plant cells, we would call these gaps gap junctions. So you might have the, I just drew two of them."}, {"video_title": "Overview of cell signaling.mp3", "Sentence": "And this is the neighboring cell right over here. And they actually might have gaps in their membranes. If these are plant cells, we would call these gaps gap junctions. So you might have the, I just drew two of them. And this is obviously just kind of a two-dimensional slice. So we're not fully appreciating the three-dimensional structure. But the basic idea is maybe the cell on the left starts producing some molecules, especially some small molecules that are able to go through these gap junctions."}, {"video_title": "Overview of cell signaling.mp3", "Sentence": "So you might have the, I just drew two of them. And this is obviously just kind of a two-dimensional slice. So we're not fully appreciating the three-dimensional structure. But the basic idea is maybe the cell on the left starts producing some molecules, especially some small molecules that are able to go through these gap junctions. And when they're able to go through the gap junctions, maybe they latch on to some proteins in the second cell that start maybe activating them in a certain way or inhibit them in a certain way or trigger some type of reaction. And so then you have a response in the second cell. So this would be a form of communication."}, {"video_title": "Overview of cell signaling.mp3", "Sentence": "But the basic idea is maybe the cell on the left starts producing some molecules, especially some small molecules that are able to go through these gap junctions. And when they're able to go through the gap junctions, maybe they latch on to some proteins in the second cell that start maybe activating them in a certain way or inhibit them in a certain way or trigger some type of reaction. And so then you have a response in the second cell. So this would be a form of communication. Something happened in this first cell to produce these molecules. Those molecules were able to get into the second cell and trigger a response. And as I mentioned, if these are animal cells, we would call these gaps, we'd call them gap junctions."}, {"video_title": "Overview of cell signaling.mp3", "Sentence": "So this would be a form of communication. Something happened in this first cell to produce these molecules. Those molecules were able to get into the second cell and trigger a response. And as I mentioned, if these are animal cells, we would call these gaps, we'd call them gap junctions. So that right over there, that is a gap junction. And we cover this in other videos. And if we're talking about plant cells, we can have very similar things happening, but we wouldn't call them gap junctions."}, {"video_title": "Overview of cell signaling.mp3", "Sentence": "And as I mentioned, if these are animal cells, we would call these gaps, we'd call them gap junctions. So that right over there, that is a gap junction. And we cover this in other videos. And if we're talking about plant cells, we can have very similar things happening, but we wouldn't call them gap junctions. These would be gaps not just through the, not even tunnels through the membrane. It would also be through the cell walls. If we're talking about plants, they would be plasmodesmata."}, {"video_title": "Overview of cell signaling.mp3", "Sentence": "And if we're talking about plant cells, we can have very similar things happening, but we wouldn't call them gap junctions. These would be gaps not just through the, not even tunnels through the membrane. It would also be through the cell walls. If we're talking about plants, they would be plasmodesmata. Plasmodesmata. And we talk about these more in the structure of cell videos. But there's other ways that you could communicate via direct contact."}, {"video_title": "Overview of cell signaling.mp3", "Sentence": "If we're talking about plants, they would be plasmodesmata. Plasmodesmata. And we talk about these more in the structure of cell videos. But there's other ways that you could communicate via direct contact. You could imagine maybe some cells that are floating around in the bloodstream. Maybe this is one cell over here. Maybe this is another cell over here."}, {"video_title": "Overview of cell signaling.mp3", "Sentence": "But there's other ways that you could communicate via direct contact. You could imagine maybe some cells that are floating around in the bloodstream. Maybe this is one cell over here. Maybe this is another cell over here. And they have complementary surface proteins, surface proteins that are able to bind to each other. So maybe this one has a surface protein that looks like this. I'm obviously exaggerating its shape."}, {"video_title": "Overview of cell signaling.mp3", "Sentence": "Maybe this is another cell over here. And they have complementary surface proteins, surface proteins that are able to bind to each other. So maybe this one has a surface protein that looks like this. I'm obviously exaggerating its shape. The protein would look exactly like this inverted triangle. But this one has a surface protein like this, and I'm also exaggerating its size relative to its cell just so we can appreciate how they could maybe lock together. So this one has a surface protein like that."}, {"video_title": "Overview of cell signaling.mp3", "Sentence": "I'm obviously exaggerating its shape. The protein would look exactly like this inverted triangle. But this one has a surface protein like this, and I'm also exaggerating its size relative to its cell just so we can appreciate how they could maybe lock together. So this one has a surface protein like that. And when they bind to each other, it might change the proteins in some way and then trigger a reaction in each of these cells. The communication then continues. If this protein changes a little bit, it might activate something."}, {"video_title": "Overview of cell signaling.mp3", "Sentence": "So this one has a surface protein like that. And when they bind to each other, it might change the proteins in some way and then trigger a reaction in each of these cells. The communication then continues. If this protein changes a little bit, it might activate something. It might activate the release of some molecules, might activate some other proteins, might catalyze some type of reaction. We've seen this in multiple other videos. All sorts of crazy biological reactions could happen inside of cells."}, {"video_title": "Overview of cell signaling.mp3", "Sentence": "If this protein changes a little bit, it might activate something. It might activate the release of some molecules, might activate some other proteins, might catalyze some type of reaction. We've seen this in multiple other videos. All sorts of crazy biological reactions could happen inside of cells. But it might elicit a, it could elicit a response. And actually it could even elicit a response in both cells. Some type of response."}, {"video_title": "Overview of cell signaling.mp3", "Sentence": "All sorts of crazy biological reactions could happen inside of cells. But it might elicit a, it could elicit a response. And actually it could even elicit a response in both cells. Some type of response. They know that they are latched on. They know that they are latched on to someone else. Now direct contact, you could imagine, is not the only way that you could have cell-cell signaling."}, {"video_title": "Overview of cell signaling.mp3", "Sentence": "Some type of response. They know that they are latched on. They know that they are latched on to someone else. Now direct contact, you could imagine, is not the only way that you could have cell-cell signaling. You could actually have cells start to signal over a little bit of a distance by releasing molecules into the extracellular space and eventually even into the bloodstream. So for example, let me draw a cell. A cell right over here."}, {"video_title": "Overview of cell signaling.mp3", "Sentence": "Now direct contact, you could imagine, is not the only way that you could have cell-cell signaling. You could actually have cells start to signal over a little bit of a distance by releasing molecules into the extracellular space and eventually even into the bloodstream. So for example, let me draw a cell. A cell right over here. And maybe it's able to produce some molecules. And these molecules, either, they might be lipid soluble and maybe make their way through the cellular membrane on their own, or maybe they are packed in nice vesicles that allow them to traverse the membrane. So when you get actually, so the membrane of the vesicle merges with the membrane of the cell."}, {"video_title": "Overview of cell signaling.mp3", "Sentence": "A cell right over here. And maybe it's able to produce some molecules. And these molecules, either, they might be lipid soluble and maybe make their way through the cellular membrane on their own, or maybe they are packed in nice vesicles that allow them to traverse the membrane. So when you get actually, so the membrane of the vesicle merges with the membrane of the cell. And then it allows these things to get out. And so you can imagine, if another cell has the right receptors for these, that would signal some type of a response, or it will form some form of communication. So let's say that I have, actually let me draw a couple of cells."}, {"video_title": "Overview of cell signaling.mp3", "Sentence": "So when you get actually, so the membrane of the vesicle merges with the membrane of the cell. And then it allows these things to get out. And so you can imagine, if another cell has the right receptors for these, that would signal some type of a response, or it will form some form of communication. So let's say that I have, actually let me draw a couple of cells. So let's say I have this cell over here. And then I have this cell over here. And let's say that this cell has the right receptor."}, {"video_title": "Overview of cell signaling.mp3", "Sentence": "So let's say that I have, actually let me draw a couple of cells. So let's say I have this cell over here. And then I have this cell over here. And let's say that this cell has the right receptor. Has the right receptor. And this cell doesn't. It could have other receptors."}, {"video_title": "Overview of cell signaling.mp3", "Sentence": "And let's say that this cell has the right receptor. Has the right receptor. And this cell doesn't. It could have other receptors. Maybe it has receptors like that. But it's not the right receptor. And so these molecules that were released by this first cell could bind, not on this character, not on this protein, this surface protein, but it could bind on this character."}, {"video_title": "Overview of cell signaling.mp3", "Sentence": "It could have other receptors. Maybe it has receptors like that. But it's not the right receptor. And so these molecules that were released by this first cell could bind, not on this character, not on this protein, this surface protein, but it could bind on this character. So it could bind on this character. And when it does so, this protein that's on the cellular membrane, it might change its shape, it might do all sorts of things, but that signal can be then taken, somehow it can continue on into the cell, and once again, you might elicit some type of response. And we'll go into more detail in future videos on exactly how that happens, or what these responses actually might be."}, {"video_title": "Overview of cell signaling.mp3", "Sentence": "And so these molecules that were released by this first cell could bind, not on this character, not on this protein, this surface protein, but it could bind on this character. So it could bind on this character. And when it does so, this protein that's on the cellular membrane, it might change its shape, it might do all sorts of things, but that signal can be then taken, somehow it can continue on into the cell, and once again, you might elicit some type of response. And we'll go into more detail in future videos on exactly how that happens, or what these responses actually might be. Now, if this is over a short distance, if this is over, if this is a short distance, short, if this is a short distance, short distance, we would call this paracrine. This would be part of the paracrine system, or we would call this paracrine communication. Let me write that down."}, {"video_title": "Overview of cell signaling.mp3", "Sentence": "And we'll go into more detail in future videos on exactly how that happens, or what these responses actually might be. Now, if this is over a short distance, if this is over, if this is a short distance, short, if this is a short distance, short distance, we would call this paracrine. This would be part of the paracrine system, or we would call this paracrine communication. Let me write that down. Paracrine, paracrine system, or paracrine communication, or paracrine signaling. And we would call these paracrine factors. But if it was happening over long distances, say maybe these molecules, they enter into the bloodstream, so they make their way into the bloodstream right over here."}, {"video_title": "Overview of cell signaling.mp3", "Sentence": "Let me write that down. Paracrine, paracrine system, or paracrine communication, or paracrine signaling. And we would call these paracrine factors. But if it was happening over long distances, say maybe these molecules, they enter into the bloodstream, so they make their way into the bloodstream right over here. So let me depict somehow that this is the bloodstream. So this is the bloodstream, bloodstream, and they're able to make, and they're able to go through the bloodstream over longer distances to other molecules, to other molecules. So maybe this one has the right receptors for those, for those, for those molecules."}, {"video_title": "Overview of cell signaling.mp3", "Sentence": "But if it was happening over long distances, say maybe these molecules, they enter into the bloodstream, so they make their way into the bloodstream right over here. So let me depict somehow that this is the bloodstream. So this is the bloodstream, bloodstream, and they're able to make, and they're able to go through the bloodstream over longer distances to other molecules, to other molecules. So maybe this one has the right receptors for those, for those, for those molecules. Then we call this endocrine system, or this is endocrine signaling. So long distances, long, long distances, we would call this the endocrine system, or endocrine, endocrine signaling, endocrine signaling. And we're talking about the endocrine system and endocrine signaling."}, {"video_title": "Overview of cell signaling.mp3", "Sentence": "So maybe this one has the right receptors for those, for those, for those molecules. Then we call this endocrine system, or this is endocrine signaling. So long distances, long, long distances, we would call this the endocrine system, or endocrine, endocrine signaling, endocrine signaling. And we're talking about the endocrine system and endocrine signaling. These molecules, which could just be, you know, they could be all sorts of different types of molecules. They could be steroids. They could be proteins of some kind."}, {"video_title": "Overview of cell signaling.mp3", "Sentence": "And we're talking about the endocrine system and endocrine signaling. These molecules, which could just be, you know, they could be all sorts of different types of molecules. They could be steroids. They could be proteins of some kind. We call, in this case, we would call them hormones. You've probably heard the word before, and we will do a whole series of videos on hormones. But these molecules actually can even affect the cell that produced them."}, {"video_title": "Overview of cell signaling.mp3", "Sentence": "They could be proteins of some kind. We call, in this case, we would call them hormones. You've probably heard the word before, and we will do a whole series of videos on hormones. But these molecules actually can even affect the cell that produced them. For example, the cell that produced it might have the right receptor, might have the right receptor. And so if it's able to signal, if it's able to trigger a reaction in itself, so if these things are able to trigger a reaction in itself, we would call that an autocrine process. Autocrine."}, {"video_title": "Overview of cell signaling.mp3", "Sentence": "But these molecules actually can even affect the cell that produced them. For example, the cell that produced it might have the right receptor, might have the right receptor. And so if it's able to signal, if it's able to trigger a reaction in itself, so if these things are able to trigger a reaction in itself, we would call that an autocrine process. Autocrine. It is acting on itself. And just so you're familiar with some of the terminology, these proteins on the surface, and this would be the case especially if you have a, if you have non-lipid soluble types of signaling factors or molecules right over here, these proteins, well, actually even if they're on the surface or even if they're within the cell, we would call them receptors. So that right over there, that is a receptor."}, {"video_title": "Overview of cell signaling.mp3", "Sentence": "Autocrine. It is acting on itself. And just so you're familiar with some of the terminology, these proteins on the surface, and this would be the case especially if you have a, if you have non-lipid soluble types of signaling factors or molecules right over here, these proteins, well, actually even if they're on the surface or even if they're within the cell, we would call them receptors. So that right over there, that is a receptor. Receptor. And the molecules themselves, these things that bind onto the receptor, we call them the ligand. Ligand in general is a general term for something that binds onto a receptor."}, {"video_title": "Overview of cell signaling.mp3", "Sentence": "So that right over there, that is a receptor. Receptor. And the molecules themselves, these things that bind onto the receptor, we call them the ligand. Ligand in general is a general term for something that binds onto a receptor. And so at that point where you bind onto a receptor, whether you're talking about the paracrine process or endocrine, endo, actually endo, I left a C out here, endocrine signaling, this process where it kind of starts to, where it latches on, we would call that a signal perception. And then when this protein, you know, somehow changes its shape or starts catalyzing a reaction or inhibiting a reaction, we would call this the signal transduction. Transduction."}, {"video_title": "Overview of cell signaling.mp3", "Sentence": "Ligand in general is a general term for something that binds onto a receptor. And so at that point where you bind onto a receptor, whether you're talking about the paracrine process or endocrine, endo, actually endo, I left a C out here, endocrine signaling, this process where it kind of starts to, where it latches on, we would call that a signal perception. And then when this protein, you know, somehow changes its shape or starts catalyzing a reaction or inhibiting a reaction, we would call this the signal transduction. Transduction. It's bringing the signal into the cell, and then you have your actual, you have your actual cellular response. So hopefully you appreciate that as just a bit of an overview of how cells can signal with each other. In future videos, we'll go into a little bit more detail, especially the endocrine system and our understanding of hormones."}, {"video_title": "Biodiversity and natural selection.mp3", "Sentence": "And we could leave it at that. We could all go home because we're done. But that's not going to make much of a video. What we really want to ask ourselves is, what is that? What is evolution? And how does it result in biodiversity? I like to think of the study of evolution as following two fairly simple pathways."}, {"video_title": "Biodiversity and natural selection.mp3", "Sentence": "What we really want to ask ourselves is, what is that? What is evolution? And how does it result in biodiversity? I like to think of the study of evolution as following two fairly simple pathways. These paths are pattern and process. Both of these are not only fascinating areas of study, but are crucial in expanding our knowledge of how life originated and how it continues to evolve. The pattern pathway studies the shape of evolution itself by looking at relationships, relationships among organisms over time."}, {"video_title": "Biodiversity and natural selection.mp3", "Sentence": "I like to think of the study of evolution as following two fairly simple pathways. These paths are pattern and process. Both of these are not only fascinating areas of study, but are crucial in expanding our knowledge of how life originated and how it continues to evolve. The pattern pathway studies the shape of evolution itself by looking at relationships, relationships among organisms over time. And to do that, you need to create a diagram or structure that links these organisms in time, showing a branching sequence of relationships, much like a family tree or genealogy. These evolutionary trees record not only the relationships among the organisms, but the events that occurred over time that indicate why we think these different organisms are related. Organisms depicted by genealogical trees really are a subject all on their own called phylogenetic systematics."}, {"video_title": "Biodiversity and natural selection.mp3", "Sentence": "The pattern pathway studies the shape of evolution itself by looking at relationships, relationships among organisms over time. And to do that, you need to create a diagram or structure that links these organisms in time, showing a branching sequence of relationships, much like a family tree or genealogy. These evolutionary trees record not only the relationships among the organisms, but the events that occurred over time that indicate why we think these different organisms are related. Organisms depicted by genealogical trees really are a subject all on their own called phylogenetic systematics. But let's set that aside for a moment. The process path is maybe a slightly better way to start. We want to talk about the mechanisms of evolution, how it actually happens."}, {"video_title": "Biodiversity and natural selection.mp3", "Sentence": "Organisms depicted by genealogical trees really are a subject all on their own called phylogenetic systematics. But let's set that aside for a moment. The process path is maybe a slightly better way to start. We want to talk about the mechanisms of evolution, how it actually happens. These are the drivers of the diversity along the multitude of lineages that spring out, branching and branching up the tree, up the limbs of the tree of life. Darwin and even some of his predecessors understood this. They could see that things could change, that the pattern of life, this tree, existed, that evolution happened, and that the relationships among organisms could be traced by looking at features of those organisms and how they changed depending on where they were in the tree."}, {"video_title": "Biodiversity and natural selection.mp3", "Sentence": "We want to talk about the mechanisms of evolution, how it actually happens. These are the drivers of the diversity along the multitude of lineages that spring out, branching and branching up the tree, up the limbs of the tree of life. Darwin and even some of his predecessors understood this. They could see that things could change, that the pattern of life, this tree, existed, that evolution happened, and that the relationships among organisms could be traced by looking at features of those organisms and how they changed depending on where they were in the tree. They could see, for example, that the wings of birds, the front legs of mammals and reptiles, and in fact all the four-limbed animals, indicated that there was some common relationship there. There was a common lineage. But at the same time, you could have change among the branches within those lineages."}, {"video_title": "Biodiversity and natural selection.mp3", "Sentence": "They could see that things could change, that the pattern of life, this tree, existed, that evolution happened, and that the relationships among organisms could be traced by looking at features of those organisms and how they changed depending on where they were in the tree. They could see, for example, that the wings of birds, the front legs of mammals and reptiles, and in fact all the four-limbed animals, indicated that there was some common relationship there. There was a common lineage. But at the same time, you could have change among the branches within those lineages. You could get a change in the front leg to a wing or to a grasping arm. General patterns were evident in everything. But at the time, there wasn't a good understanding of the mechanisms, the processes that could explain how these obviously changing, yet related forms could come about."}, {"video_title": "Biodiversity and natural selection.mp3", "Sentence": "But at the same time, you could have change among the branches within those lineages. You could get a change in the front leg to a wing or to a grasping arm. General patterns were evident in everything. But at the time, there wasn't a good understanding of the mechanisms, the processes that could explain how these obviously changing, yet related forms could come about. Darwin and his contemporaries read a lot of stuff about variation, which was visible all around them. It could all be seen. They realized that not all the individuals in a species or even in a population were exact duplicates of each other."}, {"video_title": "Biodiversity and natural selection.mp3", "Sentence": "But at the time, there wasn't a good understanding of the mechanisms, the processes that could explain how these obviously changing, yet related forms could come about. Darwin and his contemporaries read a lot of stuff about variation, which was visible all around them. It could all be seen. They realized that not all the individuals in a species or even in a population were exact duplicates of each other. This was a surprise to some people, but the evidence was everywhere, even in things as simple as the speed of racehorses. If you didn't have variation in how fast horses could run, the races would be pretty boring. Races actually demonstrate how horses were chosen for variations in speed."}, {"video_title": "Biodiversity and natural selection.mp3", "Sentence": "They realized that not all the individuals in a species or even in a population were exact duplicates of each other. This was a surprise to some people, but the evidence was everywhere, even in things as simple as the speed of racehorses. If you didn't have variation in how fast horses could run, the races would be pretty boring. Races actually demonstrate how horses were chosen for variations in speed. Humans bred fast horses with each other to get even faster horses. And these horses were selected for being the fastest. And that's the key word, selection."}, {"video_title": "Biodiversity and natural selection.mp3", "Sentence": "Races actually demonstrate how horses were chosen for variations in speed. Humans bred fast horses with each other to get even faster horses. And these horses were selected for being the fastest. And that's the key word, selection. Darwin thought, hey, what if nature worked that way? What if nature selected organisms somehow? He noticed that the form and the physiology and the behavior of plants and animals varied within natural populations just as much as they did in domesticated populations of things like horses."}, {"video_title": "Biodiversity and natural selection.mp3", "Sentence": "And that's the key word, selection. Darwin thought, hey, what if nature worked that way? What if nature selected organisms somehow? He noticed that the form and the physiology and the behavior of plants and animals varied within natural populations just as much as they did in domesticated populations of things like horses. Darwin realized that what we're really talking about here are the beginnings of the understanding of the evolutionary mechanism behind evolution, natural selection. Natural selection means that some natural variants, some individuals with different form or physiology or behavior might be better at getting through life than others. Better, that is, at gathering food, staying away from predators, turning sunlight into usable energy, resisting wind, having good root systems."}, {"video_title": "Biodiversity and natural selection.mp3", "Sentence": "He noticed that the form and the physiology and the behavior of plants and animals varied within natural populations just as much as they did in domesticated populations of things like horses. Darwin realized that what we're really talking about here are the beginnings of the understanding of the evolutionary mechanism behind evolution, natural selection. Natural selection means that some natural variants, some individuals with different form or physiology or behavior might be better at getting through life than others. Better, that is, at gathering food, staying away from predators, turning sunlight into usable energy, resisting wind, having good root systems. In other words, fitting the circumstances of the environment and surviving. What Darwin was really saying is that fitness of an individual meant being better able to produce offspring that had traits like the parent, traits that would help the offspring be better suited to the conditions of their environment. This has been referred to as survival of the fittest."}, {"video_title": "Biodiversity and natural selection.mp3", "Sentence": "Better, that is, at gathering food, staying away from predators, turning sunlight into usable energy, resisting wind, having good root systems. In other words, fitting the circumstances of the environment and surviving. What Darwin was really saying is that fitness of an individual meant being better able to produce offspring that had traits like the parent, traits that would help the offspring be better suited to the conditions of their environment. This has been referred to as survival of the fittest. Actually, I prefer the phrase survival of the fitter because fittest implies that there's an endpoint, that there's a goal, but there isn't. It's all relative because there are so many compromises and trade-offs in being well suited to a place as complex as the natural world that organisms can never reach that perfect match in all respects. This process of the environment selecting variants that are better suited to that environment, no matter how complex, is called natural selection."}, {"video_title": "Biodiversity and natural selection.mp3", "Sentence": "This has been referred to as survival of the fittest. Actually, I prefer the phrase survival of the fitter because fittest implies that there's an endpoint, that there's a goal, but there isn't. It's all relative because there are so many compromises and trade-offs in being well suited to a place as complex as the natural world that organisms can never reach that perfect match in all respects. This process of the environment selecting variants that are better suited to that environment, no matter how complex, is called natural selection. And those traits that make the selected variants better able to survive and reproduce and pass on those traits to future generations are known as adaptations. For example, a wild population of redwood trees might have some individuals that attain greater heights than others, and this results in better exposure to sunlight on foggy days, enhancing their ability to make food by photosynthesis when a change in the environment, such as the fog rolling in, challenges the survival of shorter trees. This in turn not only increases their individual chances for survival, but it also makes available more energy to the taller redwoods to produce more seeds that carry this tallness trait into future generations."}, {"video_title": "Biodiversity and natural selection.mp3", "Sentence": "This process of the environment selecting variants that are better suited to that environment, no matter how complex, is called natural selection. And those traits that make the selected variants better able to survive and reproduce and pass on those traits to future generations are known as adaptations. For example, a wild population of redwood trees might have some individuals that attain greater heights than others, and this results in better exposure to sunlight on foggy days, enhancing their ability to make food by photosynthesis when a change in the environment, such as the fog rolling in, challenges the survival of shorter trees. This in turn not only increases their individual chances for survival, but it also makes available more energy to the taller redwoods to produce more seeds that carry this tallness trait into future generations. So you get natural selection for a tallness trait and an adaptation to an environment that can present changes. Of course, as I mentioned, these simplistic examples kind of skim over the fact that there's always a series of trade-offs in nature. We have to consider, for example, that taller trees might have more trouble getting moisture from the roots all the way up to the tips of those highest branches, or that they could be more exposed to storms that could knock them down, or maybe there's some other physiological cause that we might not even have thought of."}, {"video_title": "Biodiversity and natural selection.mp3", "Sentence": "This in turn not only increases their individual chances for survival, but it also makes available more energy to the taller redwoods to produce more seeds that carry this tallness trait into future generations. So you get natural selection for a tallness trait and an adaptation to an environment that can present changes. Of course, as I mentioned, these simplistic examples kind of skim over the fact that there's always a series of trade-offs in nature. We have to consider, for example, that taller trees might have more trouble getting moisture from the roots all the way up to the tips of those highest branches, or that they could be more exposed to storms that could knock them down, or maybe there's some other physiological cause that we might not even have thought of. All these factors are part of a complicated balance that optimizes life to a given environmental situation or set of competing, selective factors. Stuff happens. Life is never simple."}, {"video_title": "Biodiversity and natural selection.mp3", "Sentence": "We have to consider, for example, that taller trees might have more trouble getting moisture from the roots all the way up to the tips of those highest branches, or that they could be more exposed to storms that could knock them down, or maybe there's some other physiological cause that we might not even have thought of. All these factors are part of a complicated balance that optimizes life to a given environmental situation or set of competing, selective factors. Stuff happens. Life is never simple. To me, all these aspects come together to represent the great beauties of life, this constant interplay of processes that results in the complexity of biodiversity, what Darwin called grandeur in this view of life. The flip side of this selection coin is that individuals in a population can also be selected against because they're less well-adapted, sometimes because of susceptibility to diseases or simply by not being good at avoiding being eaten, something that keeps those individuals from being reproductively successful. You might have noticed by now that there's an important element to this story of variation, selection, and adaptation that's missing here."}, {"video_title": "Biodiversity and natural selection.mp3", "Sentence": "Life is never simple. To me, all these aspects come together to represent the great beauties of life, this constant interplay of processes that results in the complexity of biodiversity, what Darwin called grandeur in this view of life. The flip side of this selection coin is that individuals in a population can also be selected against because they're less well-adapted, sometimes because of susceptibility to diseases or simply by not being good at avoiding being eaten, something that keeps those individuals from being reproductively successful. You might have noticed by now that there's an important element to this story of variation, selection, and adaptation that's missing here. Darwin noticed it too, he was a very smart guy and he fully recognized that there had to be some way by which organisms could pass on those selected traits, those adaptations to their offspring. It wouldn't work otherwise. There had to be a way that the offspring of individuals that had been selected for could inherit the traits of their successful parents and ancestors."}, {"video_title": "Biodiversity and natural selection.mp3", "Sentence": "You might have noticed by now that there's an important element to this story of variation, selection, and adaptation that's missing here. Darwin noticed it too, he was a very smart guy and he fully recognized that there had to be some way by which organisms could pass on those selected traits, those adaptations to their offspring. It wouldn't work otherwise. There had to be a way that the offspring of individuals that had been selected for could inherit the traits of their successful parents and ancestors. In Darwin's day, there wasn't a good understanding of a mechanism for that. It was only much later that scientists discovered how information is stored in genetic material and passed on to offspring. Today, our detailed understanding of evolutionary processes is built on the discoveries of both Darwin and geneticists."}, {"video_title": "Biodiversity and natural selection.mp3", "Sentence": "There had to be a way that the offspring of individuals that had been selected for could inherit the traits of their successful parents and ancestors. In Darwin's day, there wasn't a good understanding of a mechanism for that. It was only much later that scientists discovered how information is stored in genetic material and passed on to offspring. Today, our detailed understanding of evolutionary processes is built on the discoveries of both Darwin and geneticists. Stepping back now to put it all together, we can see that for all this to work, several different things have to be going on. You have to have variation in nature among the members of a population. You have to have natural forces that can select for or against the enhanced reproduction of individuals who possess certain variations."}, {"video_title": "Biodiversity and natural selection.mp3", "Sentence": "Today, our detailed understanding of evolutionary processes is built on the discoveries of both Darwin and geneticists. Stepping back now to put it all together, we can see that for all this to work, several different things have to be going on. You have to have variation in nature among the members of a population. You have to have natural forces that can select for or against the enhanced reproduction of individuals who possess certain variations. And you have to have a mechanism by which those selected variations get passed on, inherited by offspring and their future generations. These simple concepts are essentially all you really need for evolution to happen. And from these basic principles, we get all the complicated interweavings and interactions among all the factors that become the underlying drivers of Earth's biodiversity."}, {"video_title": "Chromosomal crossover in Meiosis I.mp3", "Sentence": "As we mentioned already, a germ cell is a cell that it can either go through mitosis to produce other germ cells, or it can undergo meiosis in order to produce gametes. So this is a germ cell right over here. Let me draw the nuclear membrane. So that's the nucleus. Let me draw the nucleus a little bit larger just because that's where we care a lot about the chromosomes in it. And let me draw a centrosome, which will play a role later on. I want to do that in this blue color."}, {"video_title": "Chromosomal crossover in Meiosis I.mp3", "Sentence": "So that's the nucleus. Let me draw the nucleus a little bit larger just because that's where we care a lot about the chromosomes in it. And let me draw a centrosome, which will play a role later on. I want to do that in this blue color. Each centrosome has two centrioles in it. I just want to clarify some of the terminology. And in the mitosis videos, I focused on cells of an organism, I just kind of made it up, that had two chromosomes, that had a diploid number of two, that had one homologous pair, that had one chromosome from each of its parents."}, {"video_title": "Chromosomal crossover in Meiosis I.mp3", "Sentence": "I want to do that in this blue color. Each centrosome has two centrioles in it. I just want to clarify some of the terminology. And in the mitosis videos, I focused on cells of an organism, I just kind of made it up, that had two chromosomes, that had a diploid number of two, that had one homologous pair, that had one chromosome from each of its parents. For this video, I'm going to focus on a species, not human beings that would have 23 pairs or 46 chromosomes. I'm going to focus on a species that's diploid number is four. And so let's say it has two chromosomes from the father."}, {"video_title": "Chromosomal crossover in Meiosis I.mp3", "Sentence": "And in the mitosis videos, I focused on cells of an organism, I just kind of made it up, that had two chromosomes, that had a diploid number of two, that had one homologous pair, that had one chromosome from each of its parents. For this video, I'm going to focus on a species, not human beings that would have 23 pairs or 46 chromosomes. I'm going to focus on a species that's diploid number is four. And so let's say it has two chromosomes from the father. Let me do that. I'll do that in this orange color. I'll do it in the chromatin, or I'll kind of depict the chromatin state."}, {"video_title": "Chromosomal crossover in Meiosis I.mp3", "Sentence": "And so let's say it has two chromosomes from the father. Let me do that. I'll do that in this orange color. I'll do it in the chromatin, or I'll kind of depict the chromatin state. It's kind of unwound, so maybe it has a long one from the father, and it has a short one from the father. And then it has homologous chromosomes from the mother. So it would have the long one from the mother, and it would have the short one, the short one from the mother, just like that."}, {"video_title": "Chromosomal crossover in Meiosis I.mp3", "Sentence": "I'll do it in the chromatin, or I'll kind of depict the chromatin state. It's kind of unwound, so maybe it has a long one from the father, and it has a short one from the father. And then it has homologous chromosomes from the mother. So it would have the long one from the mother, and it would have the short one, the short one from the mother, just like that. And obviously this is a huge simplification, but hopefully this gets the point across. So here it has a diploid number of chromosomes. So this is, let me write this down, this is diploid number is equal to, we have four chromosomes."}, {"video_title": "Chromosomal crossover in Meiosis I.mp3", "Sentence": "So it would have the long one from the mother, and it would have the short one, the short one from the mother, just like that. And obviously this is a huge simplification, but hopefully this gets the point across. So here it has a diploid number of chromosomes. So this is, let me write this down, this is diploid number is equal to, we have four chromosomes. And then this thing, this germ cell, let me write this down, this is a germ cell right over here. It will go through interphase, so let me draw that. So it will go through interphase, in which it grows, and it can replicate its DNA and its centrosome."}, {"video_title": "Chromosomal crossover in Meiosis I.mp3", "Sentence": "So this is, let me write this down, this is diploid number is equal to, we have four chromosomes. And then this thing, this germ cell, let me write this down, this is a germ cell right over here. It will go through interphase, so let me draw that. So it will go through interphase, in which it grows, and it can replicate its DNA and its centrosome. And so let me draw that. So after it goes through interphase, I want to use my space carefully because I have a lot of steps to go through. After it goes through interphase, I am going to have in my nucleus, in my nucleus here, my DNA will have replicated."}, {"video_title": "Chromosomal crossover in Meiosis I.mp3", "Sentence": "So it will go through interphase, in which it grows, and it can replicate its DNA and its centrosome. And so let me draw that. So after it goes through interphase, I want to use my space carefully because I have a lot of steps to go through. After it goes through interphase, I am going to have in my nucleus, in my nucleus here, my DNA will have replicated. So this long chromosome from my father, now all the DNA will have replicated. So it might look something like that. And it's attached at a centromere, all these centro words, at a centromere right here."}, {"video_title": "Chromosomal crossover in Meiosis I.mp3", "Sentence": "After it goes through interphase, I am going to have in my nucleus, in my nucleus here, my DNA will have replicated. So this long chromosome from my father, now all the DNA will have replicated. So it might look something like that. And it's attached at a centromere, all these centro words, at a centromere right here. But I'm still trying to draw it in kind of the chromatin state. It's actually all spread out. It's not bunched up so you can see it very clearly as these Xs in a simple microscope."}, {"video_title": "Chromosomal crossover in Meiosis I.mp3", "Sentence": "And it's attached at a centromere, all these centro words, at a centromere right here. But I'm still trying to draw it in kind of the chromatin state. It's actually all spread out. It's not bunched up so you can see it very clearly as these Xs in a simple microscope. So it's just replicated. And after replicating, it is still one chromosome. It has twice the genetic material, but it is still one chromosome."}, {"video_title": "Chromosomal crossover in Meiosis I.mp3", "Sentence": "It's not bunched up so you can see it very clearly as these Xs in a simple microscope. So it's just replicated. And after replicating, it is still one chromosome. It has twice the genetic material, but it is still one chromosome. That one chromosome is now made up of two sister chromatids. We talk a lot about that in the mitosis video, but it doesn't hurt to reinforce because it can get a little bit confusing. And then you have that shorter chromosome from the father."}, {"video_title": "Chromosomal crossover in Meiosis I.mp3", "Sentence": "It has twice the genetic material, but it is still one chromosome. That one chromosome is now made up of two sister chromatids. We talk a lot about that in the mitosis video, but it doesn't hurt to reinforce because it can get a little bit confusing. And then you have that shorter chromosome from the father. And then that also replicates into two sister chromatids attached at a centromere. So these are still two chromosomes from the father. It has twice the amount of DNA, but it's containing the same information, just duplicate versions of that same information."}, {"video_title": "Chromosomal crossover in Meiosis I.mp3", "Sentence": "And then you have that shorter chromosome from the father. And then that also replicates into two sister chromatids attached at a centromere. So these are still two chromosomes from the father. It has twice the amount of DNA, but it's containing the same information, just duplicate versions of that same information. And the same thing's going to happen from the mother. You had that long chromosome from the mother homologous to this one right over here. It's going to replicate."}, {"video_title": "Chromosomal crossover in Meiosis I.mp3", "Sentence": "It has twice the amount of DNA, but it's containing the same information, just duplicate versions of that same information. And the same thing's going to happen from the mother. You had that long chromosome from the mother homologous to this one right over here. It's going to replicate. So it's now going to be two sister chromatids. And then you have a short strand from the mother that was homologous to this one from your father. And that's also going to replicate."}, {"video_title": "Chromosomal crossover in Meiosis I.mp3", "Sentence": "It's going to replicate. So it's now going to be two sister chromatids. And then you have a short strand from the mother that was homologous to this one from your father. And that's also going to replicate. And so it's like that. And at the end of interphase, it would actually all be spread out. Once again, it won't be bunched up into these clearly discernible Xs."}, {"video_title": "Chromosomal crossover in Meiosis I.mp3", "Sentence": "And that's also going to replicate. And so it's like that. And at the end of interphase, it would actually all be spread out. Once again, it won't be bunched up into these clearly discernible Xs. I drew them a little bit that way, otherwise you would have trouble seeing how it replicated. And we also have replicated our centrosome as we've gone through interphase. Now we are ready."}, {"video_title": "Chromosomal crossover in Meiosis I.mp3", "Sentence": "Once again, it won't be bunched up into these clearly discernible Xs. I drew them a little bit that way, otherwise you would have trouble seeing how it replicated. And we also have replicated our centrosome as we've gone through interphase. Now we are ready. In fact, now we are ready for either mitosis or meiosis. But as I said, the focus of this video is going to be meiosis. So let's do some meiosis."}, {"video_title": "Chromosomal crossover in Meiosis I.mp3", "Sentence": "Now we are ready. In fact, now we are ready for either mitosis or meiosis. But as I said, the focus of this video is going to be meiosis. So let's do some meiosis. So the first several phases we call meiosis I. And the beginning of meiosis I is prophase I. So let's see what happens in prophase I."}, {"video_title": "Chromosomal crossover in Meiosis I.mp3", "Sentence": "So let's do some meiosis. So the first several phases we call meiosis I. And the beginning of meiosis I is prophase I. So let's see what happens in prophase I. So prophase I, so let me draw the cell right over here. So prophase I, a couple of things happen. The nuclear membrane begins to dissolve."}, {"video_title": "Chromosomal crossover in Meiosis I.mp3", "Sentence": "So let's see what happens in prophase I. So prophase I, so let me draw the cell right over here. So prophase I, a couple of things happen. The nuclear membrane begins to dissolve. This is very similar to prophase when we were looking at mitosis. So the nuclear envelope begins to dissolve. These things start to maybe migrate a little bit."}, {"video_title": "Chromosomal crossover in Meiosis I.mp3", "Sentence": "The nuclear membrane begins to dissolve. This is very similar to prophase when we were looking at mitosis. So the nuclear envelope begins to dissolve. These things start to maybe migrate a little bit. So these characters are starting to go at different ends. And the DNA starts to bunch up into kind of its condensed form. So now I can start to draw it as proper."}, {"video_title": "Chromosomal crossover in Meiosis I.mp3", "Sentence": "These things start to maybe migrate a little bit. So these characters are starting to go at different ends. And the DNA starts to bunch up into kind of its condensed form. So now I can start to draw it as proper. So this is the one from the father right over here. And this is the one from the mother. And I'm drawing them overlapping on purpose because something very interesting happens, especially in meiosis."}, {"video_title": "Chromosomal crossover in Meiosis I.mp3", "Sentence": "So now I can start to draw it as proper. So this is the one from the father right over here. And this is the one from the mother. And I'm drawing them overlapping on purpose because something very interesting happens, especially in meiosis. So this is the mother right over here. This is, let me see, I'll do the centromere in blue now. That's a centromere."}, {"video_title": "Chromosomal crossover in Meiosis I.mp3", "Sentence": "And I'm drawing them overlapping on purpose because something very interesting happens, especially in meiosis. So this is the mother right over here. This is, let me see, I'll do the centromere in blue now. That's a centromere. That's the centromere. Now this is the shorter ones from the father. These are the shorter ones from the mother."}, {"video_title": "Chromosomal crossover in Meiosis I.mp3", "Sentence": "That's a centromere. That's the centromere. Now this is the shorter ones from the father. These are the shorter ones from the mother. And actually let me just draw them on opposite sides just to show that they don't have to, the ones from the father aren't always on the left-hand side. So this is the shorter one from the father. They could be all on the left-hand side, but it doesn't necessarily have to be."}, {"video_title": "Chromosomal crossover in Meiosis I.mp3", "Sentence": "These are the shorter ones from the mother. And actually let me just draw them on opposite sides just to show that they don't have to, the ones from the father aren't always on the left-hand side. So this is the shorter one from the father. They could be all on the left-hand side, but it doesn't necessarily have to be. And then this is the shorter one from the mother. And I won't draw these overlapping, although they could have. Shorter one from the mother."}, {"video_title": "Chromosomal crossover in Meiosis I.mp3", "Sentence": "They could be all on the left-hand side, but it doesn't necessarily have to be. And then this is the shorter one from the mother. And I won't draw these overlapping, although they could have. Shorter one from the mother. And once again, each of these, this is a homologous pair. That's a homologous pair over there. Now the DNA has been replicated, so in each of the chromosomes in a homologous pair, you have two sister chromatids."}, {"video_title": "Chromosomal crossover in Meiosis I.mp3", "Sentence": "Shorter one from the mother. And once again, each of these, this is a homologous pair. That's a homologous pair over there. Now the DNA has been replicated, so in each of the chromosomes in a homologous pair, you have two sister chromatids. And so in this entire homologous pair, you have four chromatids. And so this is sometimes called a tetrad. So let me just give ourselves some terminology."}, {"video_title": "Chromosomal crossover in Meiosis I.mp3", "Sentence": "Now the DNA has been replicated, so in each of the chromosomes in a homologous pair, you have two sister chromatids. And so in this entire homologous pair, you have four chromatids. And so this is sometimes called a tetrad. So let me just give ourselves some terminology. So this right over here is called a tetrad, or often called a tetrad. Now the reason why I drew this overlapping is when we are in prophase one, in meiosis one, let me label this, this is prophase one, you can get some genetic recombination, some homologous recombination. Once again, this is a homologous pair, one chromosome from the father, that I've gotten from the father, the species or the cell got from its father cell, and one from the mother."}, {"video_title": "Chromosomal crossover in Meiosis I.mp3", "Sentence": "So let me just give ourselves some terminology. So this right over here is called a tetrad, or often called a tetrad. Now the reason why I drew this overlapping is when we are in prophase one, in meiosis one, let me label this, this is prophase one, you can get some genetic recombination, some homologous recombination. Once again, this is a homologous pair, one chromosome from the father, that I've gotten from the father, the species or the cell got from its father cell, and one from the mother. And they're homologous in that they might contain different base pairs, different actual DNA, but they code for the same genes. So, you know, oversimplification, but in a similar place on each of these, it might code for eye color, or I don't know, personality, and nothing is that simple, or how tall you get, and it's not that simple in DNA, but just to give you an idea of how it is. And the reason why I overlapped them like this is to show how the recombination can occur."}, {"video_title": "Chromosomal crossover in Meiosis I.mp3", "Sentence": "Once again, this is a homologous pair, one chromosome from the father, that I've gotten from the father, the species or the cell got from its father cell, and one from the mother. And they're homologous in that they might contain different base pairs, different actual DNA, but they code for the same genes. So, you know, oversimplification, but in a similar place on each of these, it might code for eye color, or I don't know, personality, and nothing is that simple, or how tall you get, and it's not that simple in DNA, but just to give you an idea of how it is. And the reason why I overlapped them like this is to show how the recombination can occur. So actually, let me zoom in. So this is the one from the father, once again, it's in all in the condensed form. This is one chromosome made up of two sister chromatids right over here, and I drew the centromere, not to be confused with centrosomes, that's where they are, those two sister chromatids are attached."}, {"video_title": "Chromosomal crossover in Meiosis I.mp3", "Sentence": "And the reason why I overlapped them like this is to show how the recombination can occur. So actually, let me zoom in. So this is the one from the father, once again, it's in all in the condensed form. This is one chromosome made up of two sister chromatids right over here, and I drew the centromere, not to be confused with centrosomes, that's where they are, those two sister chromatids are attached. And then I will draw the homologous chromosome from the mother. So the homologous chromosome from the mother, just like that, homologous chromosome from the mother. And the recombination can occur at a point right over here."}, {"video_title": "Chromosomal crossover in Meiosis I.mp3", "Sentence": "This is one chromosome made up of two sister chromatids right over here, and I drew the centromere, not to be confused with centrosomes, that's where they are, those two sister chromatids are attached. And then I will draw the homologous chromosome from the mother. So the homologous chromosome from the mother, just like that, homologous chromosome from the mother. And the recombination can occur at a point right over here. So after you're done the recombination, this side might look something more like this. So let me draw it like this. So they essentially break up and swap those little sections, is one way to think about it."}, {"video_title": "Chromosomal crossover in Meiosis I.mp3", "Sentence": "And the recombination can occur at a point right over here. So after you're done the recombination, this side might look something more like this. So let me draw it like this. So they essentially break up and swap those little sections, is one way to think about it. So this one will now have a little piece from the mother, and it might code for similar genes, but now it contains the mother's genetic information. And then this one over here will now have the piece, and you could say even the homologous piece, from the father. Let me do this to two centromeres."}, {"video_title": "Chromosomal crossover in Meiosis I.mp3", "Sentence": "So they essentially break up and swap those little sections, is one way to think about it. So this one will now have a little piece from the mother, and it might code for similar genes, but now it contains the mother's genetic information. And then this one over here will now have the piece, and you could say even the homologous piece, from the father. Let me do this to two centromeres. And this is really interesting. All the time there could be recombination, and often times it can lead to non-optimal things, nonsense code in DNA, and might lead to a non-functional organism. But this happens fairly common in meiosis."}, {"video_title": "Chromosomal crossover in Meiosis I.mp3", "Sentence": "Let me do this to two centromeres. And this is really interesting. All the time there could be recombination, and often times it can lead to non-optimal things, nonsense code in DNA, and might lead to a non-functional organism. But this happens fairly common in meiosis. And it's a way, once again, to get more variation. We've talked about sexual reproduction before, and sexual reproduction introduces variation into a population. And this, obviously, when different sperms find different eggs, that introduces variation."}, {"video_title": "Chromosomal crossover in Meiosis I.mp3", "Sentence": "But this happens fairly common in meiosis. And it's a way, once again, to get more variation. We've talked about sexual reproduction before, and sexual reproduction introduces variation into a population. And this, obviously, when different sperms find different eggs, that introduces variation. But then even amongst homologous pairs, you can actually have exchange between these chromosomes. And that's interesting, because as we mentioned, each of these chromosomes, they code for a bunch of different genes. And a gene is kind of what can code for a specific or a set of proteins."}, {"video_title": "Chromosomal crossover in Meiosis I.mp3", "Sentence": "And this, obviously, when different sperms find different eggs, that introduces variation. But then even amongst homologous pairs, you can actually have exchange between these chromosomes. And that's interesting, because as we mentioned, each of these chromosomes, they code for a bunch of different genes. And a gene is kind of what can code for a specific or a set of proteins. And so this right over here, let's say, and this is what I'm about to say is going to be a huge oversimplification. Maybe right over here, you coded for eye color, or it was related to, or it helped code for eye color, and you got that from your dad. And here, it helped code for eye color, and you got that from your mom."}, {"video_title": "Chromosomal crossover in Meiosis I.mp3", "Sentence": "And a gene is kind of what can code for a specific or a set of proteins. And so this right over here, let's say, and this is what I'm about to say is going to be a huge oversimplification. Maybe right over here, you coded for eye color, or it was related to, or it helped code for eye color, and you got that from your dad. And here, it helped code for eye color, and you got that from your mom. Your mom might have trended you towards a lighter eye color, and your dad might have trended you towards a darker eye color. But now, the one from your mom is on this chromosome, this gene. And then the one, or they're both the same gene, they're just different alleles."}, {"video_title": "Chromosomal crossover in Meiosis I.mp3", "Sentence": "And here, it helped code for eye color, and you got that from your mom. Your mom might have trended you towards a lighter eye color, and your dad might have trended you towards a darker eye color. But now, the one from your mom is on this chromosome, this gene. And then the one, or they're both the same gene, they're just different alleles. They're coding for different variants of that gene. And then the allele from your dad is over here. And once again, some people get confused with genes and chromosomes and all this."}, {"video_title": "Chromosomal crossover in Meiosis I.mp3", "Sentence": "And then the one, or they're both the same gene, they're just different alleles. They're coding for different variants of that gene. And then the allele from your dad is over here. And once again, some people get confused with genes and chromosomes and all this. Each of these chromosomes contain a bunch of genes. These are very long DNA molecules. These code for a bunch of different genes."}, {"video_title": "Chromosomal crossover in Meiosis I.mp3", "Sentence": "And once again, some people get confused with genes and chromosomes and all this. Each of these chromosomes contain a bunch of genes. These are very long DNA molecules. These code for a bunch of different genes. So a gene will be a little section of here that could code for a particular protein. So that's what happens in prophase one. In prophase one, you have this condensation of your chromosomes, of your homologous pairs."}, {"video_title": "Chromosomal crossover in Meiosis I.mp3", "Sentence": "These code for a bunch of different genes. So a gene will be a little section of here that could code for a particular protein. So that's what happens in prophase one. In prophase one, you have this condensation of your chromosomes, of your homologous pairs. You can have this recombination, and it's really interesting. This recombination doesn't tend to happen at just random points that would kind of break the genetic information. It tends to happen at fairly clean points."}, {"video_title": "Chromosomal crossover in Meiosis I.mp3", "Sentence": "In prophase one, you have this condensation of your chromosomes, of your homologous pairs. You can have this recombination, and it's really interesting. This recombination doesn't tend to happen at just random points that would kind of break the genetic information. It tends to happen at fairly clean points. And the places where this breakup is happening, these are called, the plural, if you just talk about one point, it's a chiasma. Or if you're talking about the plurals, chiasmata. Sounds like it could be a horror movie."}, {"video_title": "Chromosomal crossover in Meiosis I.mp3", "Sentence": "It tends to happen at fairly clean points. And the places where this breakup is happening, these are called, the plural, if you just talk about one point, it's a chiasma. Or if you're talking about the plurals, chiasmata. Sounds like it could be a horror movie. So chiasma. And the fact that they tend to happen fairly cleanly, this is, once again, kind of the beauty of the universe, or at least of biology, is that through billions of years of evolution, these things have kind of optimized for more variation and to happen in fairly clean ways. So I'm gonna leave this video right there."}, {"video_title": "Trp operon.mp3", "Sentence": "Two of the most studied operons are the tryp operon and the lac operon. And what I want to do in this video is focus on the tryp operon, which is essential for the production of tryptophan. Tryp, tryptophan, which you might recognize as an amino acid, often associated with Thanksgiving and turkey dinner. But tryptophan, as all or most amino acids, are essential for creating the polypeptides, the proteins that you use in your body. And so the tryp operon, and here we're gonna be talking about not your body, well, we're gonna be talking about something that's in your body, we're gonna talk about E. coli. It is an operon that is on the E. coli, that is part of the E. coli genome, and just in this diagram, the way it's drawn, it would be sitting, it would be sitting right over here. And just as a reminder, an operon is a combination of a set of genes as well as the regulatory DNA sequences for that set of genes."}, {"video_title": "Trp operon.mp3", "Sentence": "But tryptophan, as all or most amino acids, are essential for creating the polypeptides, the proteins that you use in your body. And so the tryp operon, and here we're gonna be talking about not your body, well, we're gonna be talking about something that's in your body, we're gonna talk about E. coli. It is an operon that is on the E. coli, that is part of the E. coli genome, and just in this diagram, the way it's drawn, it would be sitting, it would be sitting right over here. And just as a reminder, an operon is a combination of a set of genes as well as the regulatory DNA sequences for that set of genes. In particular, you have the promoter, you have the operator right over here. The promoter is where the RNA polymerase binds and would start the transcription process. The operator is where a repressor binds, and this is going to be essential for understanding how the tryp operon works."}, {"video_title": "Trp operon.mp3", "Sentence": "And just as a reminder, an operon is a combination of a set of genes as well as the regulatory DNA sequences for that set of genes. In particular, you have the promoter, you have the operator right over here. The promoter is where the RNA polymerase binds and would start the transcription process. The operator is where a repressor binds, and this is going to be essential for understanding how the tryp operon works. And so what do these genes actually code for? Well, these genes code for enzymes that are used in the construction of tryptophan. And I'm always amazed that enzymes can be used to construct what are essentially molecules that are much smaller than the enzymes themselves."}, {"video_title": "Trp operon.mp3", "Sentence": "The operator is where a repressor binds, and this is going to be essential for understanding how the tryp operon works. And so what do these genes actually code for? Well, these genes code for enzymes that are used in the construction of tryptophan. And I'm always amazed that enzymes can be used to construct what are essentially molecules that are much smaller than the enzymes themselves. In fact, the enzymes involved are made up of amino acids, but then they're used to make particular amino acids. And so tryp E, D, C, B, A, they're all, once they are transcribed into mRNA and then translated into ribosomes, these enzymes are used to create tryptophan for tryptophan biosynthesis. So let's think about how this works."}, {"video_title": "Trp operon.mp3", "Sentence": "And I'm always amazed that enzymes can be used to construct what are essentially molecules that are much smaller than the enzymes themselves. In fact, the enzymes involved are made up of amino acids, but then they're used to make particular amino acids. And so tryp E, D, C, B, A, they're all, once they are transcribed into mRNA and then translated into ribosomes, these enzymes are used to create tryptophan for tryptophan biosynthesis. So let's think about how this works. So if we are in a low tryptophan environment, our E. coli, it needs tryptophan. It needs that amino acid as a building block for its proteins. So in that world, it makes sense that in a low tryptophan environment, the RNA polymerase can just latch on to the promoter and begin the transcription process, transcribe these five genes into mRNA, which then can be translated into those enzymes, and then you will have more tryptophan biosynthesis."}, {"video_title": "Trp operon.mp3", "Sentence": "So let's think about how this works. So if we are in a low tryptophan environment, our E. coli, it needs tryptophan. It needs that amino acid as a building block for its proteins. So in that world, it makes sense that in a low tryptophan environment, the RNA polymerase can just latch on to the promoter and begin the transcription process, transcribe these five genes into mRNA, which then can be translated into those enzymes, and then you will have more tryptophan biosynthesis. That makes sense, that you wanna create tryptophan if you're in an environment that does not have a lot of tryptophan. But what if we did have a lot of tryptophan? Well, if you have a lot of something around, you shouldn't waste energy creating more of it."}, {"video_title": "Trp operon.mp3", "Sentence": "So in that world, it makes sense that in a low tryptophan environment, the RNA polymerase can just latch on to the promoter and begin the transcription process, transcribe these five genes into mRNA, which then can be translated into those enzymes, and then you will have more tryptophan biosynthesis. That makes sense, that you wanna create tryptophan if you're in an environment that does not have a lot of tryptophan. But what if we did have a lot of tryptophan? Well, if you have a lot of something around, you shouldn't waste energy creating more of it. You have to appreciate that all organisms that are around today are the byproducts of billions of years of evolution, and they've learned to be very careful, or the ones that are selected for tend to be the ones that don't waste resources. And so when you have tryptophan around, you probably don't want this transcription to occur. So it would make sense that maybe tryptophan can act as a co-repressor for a repressor molecule, for a repressor enzyme that would attach to the operator and block the RNA polymerase from transcribing, and that's exactly what happens."}, {"video_title": "Trp operon.mp3", "Sentence": "Well, if you have a lot of something around, you shouldn't waste energy creating more of it. You have to appreciate that all organisms that are around today are the byproducts of billions of years of evolution, and they've learned to be very careful, or the ones that are selected for tend to be the ones that don't waste resources. And so when you have tryptophan around, you probably don't want this transcription to occur. So it would make sense that maybe tryptophan can act as a co-repressor for a repressor molecule, for a repressor enzyme that would attach to the operator and block the RNA polymerase from transcribing, and that's exactly what happens. So when you're in a high tryptophan environment, and tryptophan obviously does not look like these little yellow quadrilaterals over there, but that's just for our visualization purposes, and neither does RNA polymerase look like that, or neither does the tryp receptor repressor look like that. In fact, I encourage you to web search this and see how they actually look, they're fascinating. But when you have a lot of tryptophan, the tryptophan can act as a co-repressor."}, {"video_title": "Trp operon.mp3", "Sentence": "So it would make sense that maybe tryptophan can act as a co-repressor for a repressor molecule, for a repressor enzyme that would attach to the operator and block the RNA polymerase from transcribing, and that's exactly what happens. So when you're in a high tryptophan environment, and tryptophan obviously does not look like these little yellow quadrilaterals over there, but that's just for our visualization purposes, and neither does RNA polymerase look like that, or neither does the tryp receptor repressor look like that. In fact, I encourage you to web search this and see how they actually look, they're fascinating. But when you have a lot of tryptophan, the tryptophan can act as a co-repressor. It can bind to the tryp repressor, essentially activate it, so that it'll change its conformation so that it can then attach to the operator in the operon. And once it's attached to the operator, well then the RNA polymerase can no longer move forward with transcription. So as you can see, this is a very valuable feedback loop, or not even necessarily feedback."}, {"video_title": "Trp operon.mp3", "Sentence": "But when you have a lot of tryptophan, the tryptophan can act as a co-repressor. It can bind to the tryp repressor, essentially activate it, so that it'll change its conformation so that it can then attach to the operator in the operon. And once it's attached to the operator, well then the RNA polymerase can no longer move forward with transcription. So as you can see, this is a very valuable feedback loop, or not even necessarily feedback. If you're in an environment with a lot of tryptophan, don't create tryptophan. Or if you just have a lot of tryptophan laying around, don't create more tryptophan. If you don't have tryptophan around, well then the repressor won't be co-repressed, I guess you can say, and then the tryptophan will actually be created."}, {"video_title": "Trp operon.mp3", "Sentence": "So as you can see, this is a very valuable feedback loop, or not even necessarily feedback. If you're in an environment with a lot of tryptophan, don't create tryptophan. Or if you just have a lot of tryptophan laying around, don't create more tryptophan. If you don't have tryptophan around, well then the repressor won't be co-repressed, I guess you can say, and then the tryptophan will actually be created. Now tryptophan's an interesting thing, because the control of transcription isn't the only place where you have some type of a feedback loop, or kind of a conditional situation. You can actually have direct feedback inhibition between the proteins. And so this part isn't related to the transcription."}, {"video_title": "Trp operon.mp3", "Sentence": "If you don't have tryptophan around, well then the repressor won't be co-repressed, I guess you can say, and then the tryptophan will actually be created. Now tryptophan's an interesting thing, because the control of transcription isn't the only place where you have some type of a feedback loop, or kind of a conditional situation. You can actually have direct feedback inhibition between the proteins. And so this part isn't related to the transcription. But if this is a precursor of tryptophan, it's all very abstract in this diagram, and let's say enzyme one turns into precursor two, enzyme two turns into precursor three, and enzyme three turns it into tryptophan, well you actually have direct feedback inhibition where tryptophan can then bind or interact with enzyme one here. Could interact with enzyme one. Let me do it in a color you could see."}, {"video_title": "Trp operon.mp3", "Sentence": "And so this part isn't related to the transcription. But if this is a precursor of tryptophan, it's all very abstract in this diagram, and let's say enzyme one turns into precursor two, enzyme two turns into precursor three, and enzyme three turns it into tryptophan, well you actually have direct feedback inhibition where tryptophan can then bind or interact with enzyme one here. Could interact with enzyme one. Let me do it in a color you could see. Could interact with enzyme one, so that it can no longer act as efficiently taking precursor one to precursor two. So this right over here, this is the classic feedback inhibition. Feedback inhibition."}, {"video_title": "Trp operon.mp3", "Sentence": "Let me do it in a color you could see. Could interact with enzyme one, so that it can no longer act as efficiently taking precursor one to precursor two. So this right over here, this is the classic feedback inhibition. Feedback inhibition. The focus of this video, we're talking about operons and gene regulation, but it's important to realize that the regulation of the creation of tryptophan doesn't only occur at the transcription level. And I'm not gonna go into this video, it's a slightly more advanced topic, but there's also regulation of tryptophan biosynthesis through a process called attenuation, which doesn't affect the start of transcription, but it affects how things get completed, and it will keep tryptophan from being completely, or the entire process from going to completion. But the ones that are most typically talked about are what we just talked about here, where you have your tryptophan acts as a co-repressor of the tryp repressor, and also the feedback inhibition, which once again is not really about gene regulation, but you can see how the product of this process can go back and inhibit one of the first enzymes."}, {"video_title": "Exploring Ecosystems Tropical Rainforest Diversity   California Academy of Sciences.mp3", "Sentence": "At the California Academy of Sciences, our mission is to explore, explain, and sustain tropical rainforests. Scientists, like Michelle Troutwine, are experts in these efforts, conducting research to help us better understand the structure and diversity of rainforest ecosystems. Entering a tropical rainforest, we find vertical layers of life, each with its own unique structure and composition. The forest floor receives very little sunlight. It is a hot, humid place where animals like leafcutter ants spend their time foraging for food. Just above the floor is a thick layer of shrubs, small trees, and flowering plants. Here in the rainforest understory, you find amphibians, like the poison dart frog, whose toxic skin protects it from predators."}, {"video_title": "Exploring Ecosystems Tropical Rainforest Diversity   California Academy of Sciences.mp3", "Sentence": "The forest floor receives very little sunlight. It is a hot, humid place where animals like leafcutter ants spend their time foraging for food. Just above the floor is a thick layer of shrubs, small trees, and flowering plants. Here in the rainforest understory, you find amphibians, like the poison dart frog, whose toxic skin protects it from predators. Rising higher, we find a bright, connected layer of tree branches and leaves. The canopy contains a wide variety of species, including squirrel monkeys, who travel and feed in large social groups. Breaking through, we enter the emergent layer, an open space containing only the highest treetop."}, {"video_title": "Exploring Ecosystems Tropical Rainforest Diversity   California Academy of Sciences.mp3", "Sentence": "Here in the rainforest understory, you find amphibians, like the poison dart frog, whose toxic skin protects it from predators. Rising higher, we find a bright, connected layer of tree branches and leaves. The canopy contains a wide variety of species, including squirrel monkeys, who travel and feed in large social groups. Breaking through, we enter the emergent layer, an open space containing only the highest treetop. Here, we find camouflaged insects called katydids, who feed on young, tender leaves. Now imagine you are a biologist researching arthropod diversity in the Peruvian rainforest. You and your team sample each forest layer, recording the number of species found and at what height."}, {"video_title": "Exploring Ecosystems Tropical Rainforest Diversity   California Academy of Sciences.mp3", "Sentence": "Breaking through, we enter the emergent layer, an open space containing only the highest treetop. Here, we find camouflaged insects called katydids, who feed on young, tender leaves. Now imagine you are a biologist researching arthropod diversity in the Peruvian rainforest. You and your team sample each forest layer, recording the number of species found and at what height. Looking over your field notes now, what trends do you see? How do the layers differ in species richness? Take a moment to pause the video and examine the graph."}, {"video_title": "Exploring Ecosystems Tropical Rainforest Diversity   California Academy of Sciences.mp3", "Sentence": "You and your team sample each forest layer, recording the number of species found and at what height. Looking over your field notes now, what trends do you see? How do the layers differ in species richness? Take a moment to pause the video and examine the graph. The canopy is believed to house over 70% of species found in the rainforest, making it the most species-rich of the four layers. To measure species diversity, researchers like Michelle must take into account both species richness, the number of different species, and species evenness, the abundance of each species. Imagine you survey three different rainforest communities and identify the following species at the following abundances."}, {"video_title": "Exploring Ecosystems Tropical Rainforest Diversity   California Academy of Sciences.mp3", "Sentence": "Take a moment to pause the video and examine the graph. The canopy is believed to house over 70% of species found in the rainforest, making it the most species-rich of the four layers. To measure species diversity, researchers like Michelle must take into account both species richness, the number of different species, and species evenness, the abundance of each species. Imagine you survey three different rainforest communities and identify the following species at the following abundances. Looking at your field notes now, which community appears to be most diverse? While each has the same number of species, community B has greater evenness, a more balanced number of individuals from each species. We recognize community B as being more diverse because of its high species richness and its high species evenness."}, {"video_title": "Exploring Ecosystems Tropical Rainforest Diversity   California Academy of Sciences.mp3", "Sentence": "Imagine you survey three different rainforest communities and identify the following species at the following abundances. Looking at your field notes now, which community appears to be most diverse? While each has the same number of species, community B has greater evenness, a more balanced number of individuals from each species. We recognize community B as being more diverse because of its high species richness and its high species evenness. Why is this important? More diverse ecological communities tend to be more stable and resilient to change. This means a more diverse tropical rainforest is better able to respond to disturbances like deforestation and climate change."}, {"video_title": "Exploring Ecosystems Tropical Rainforest Diversity   California Academy of Sciences.mp3", "Sentence": "We recognize community B as being more diverse because of its high species richness and its high species evenness. Why is this important? More diverse ecological communities tend to be more stable and resilient to change. This means a more diverse tropical rainforest is better able to respond to disturbances like deforestation and climate change. Even with these findings, there are still many unanswered questions about tropical rainforests and the species that inhabit them. Such as, why are tropical rainforests so diverse? Why does the canopy have high species richness?"}, {"video_title": "Earth formation   Life on earth and in the universe   Cosmology & Astronomy   Khan Academy.mp3", "Sentence": "And we're going to start really at the formation of Earth, or the formation of our solar system, or the formation of the sun. And our best sense of what actually happened is that there was a supernova in our vicinity of the galaxy. And this right here is a picture of a supernova remnant, actually the remnant for Kepler's supernova. The supernova in this picture actually happened 400 years ago in 1604. So right at the center, a star essentially exploded and for a few weeks was the brightest object in the night sky. And it was observed by Kepler and other people in 1604. And this is what it looks like now."}, {"video_title": "Earth formation   Life on earth and in the universe   Cosmology & Astronomy   Khan Academy.mp3", "Sentence": "The supernova in this picture actually happened 400 years ago in 1604. So right at the center, a star essentially exploded and for a few weeks was the brightest object in the night sky. And it was observed by Kepler and other people in 1604. And this is what it looks like now. So this is what we see is kind of the shock wave that's been traveling out for the past 400 years. And so now it must be many light years across. It wasn't obviously, matter wasn't traveling at the speed of light, but it must have been traveling pretty, pretty fast, at least relativistic speeds where a reasonable fraction of the speed of light."}, {"video_title": "Earth formation   Life on earth and in the universe   Cosmology & Astronomy   Khan Academy.mp3", "Sentence": "And this is what it looks like now. So this is what we see is kind of the shock wave that's been traveling out for the past 400 years. And so now it must be many light years across. It wasn't obviously, matter wasn't traveling at the speed of light, but it must have been traveling pretty, pretty fast, at least relativistic speeds where a reasonable fraction of the speed of light. So this has traveled a good bit out now. But what you can imagine is when you have the shock wave traveling out from a supernova, let's say you had a cloud of molecules, a cloud of gas, that before the shock wave came by, it just wasn't dense enough. It wasn't dense enough for gravity to take over and for it to accrete essentially into a solar system."}, {"video_title": "Earth formation   Life on earth and in the universe   Cosmology & Astronomy   Khan Academy.mp3", "Sentence": "It wasn't obviously, matter wasn't traveling at the speed of light, but it must have been traveling pretty, pretty fast, at least relativistic speeds where a reasonable fraction of the speed of light. So this has traveled a good bit out now. But what you can imagine is when you have the shock wave traveling out from a supernova, let's say you had a cloud of molecules, a cloud of gas, that before the shock wave came by, it just wasn't dense enough. It wasn't dense enough for gravity to take over and for it to accrete essentially into a solar system. But when the shock wave passes by, it compresses all of this gas and all of this material and all of these molecules. So it now does have that critical density to form, to accrete into a star and a solar system. And so we think that's what's happening."}, {"video_title": "Earth formation   Life on earth and in the universe   Cosmology & Astronomy   Khan Academy.mp3", "Sentence": "It wasn't dense enough for gravity to take over and for it to accrete essentially into a solar system. But when the shock wave passes by, it compresses all of this gas and all of this material and all of these molecules. So it now does have that critical density to form, to accrete into a star and a solar system. And so we think that's what's happening. The reason why we feel pretty strongly that it must have been caused by a supernova is that the only way that the really heavy elements can form or the only way that we know that they can form is in kind of the heat of a supernova. And our uranium, the uranium that seems to be in our solar system on Earth, seems to have formed roughly at the time of the formation of Earth, at about 4 and 1 half billion years ago. And we'll talk in a little bit more depth in future videos on exactly how people figure that out."}, {"video_title": "Earth formation   Life on earth and in the universe   Cosmology & Astronomy   Khan Academy.mp3", "Sentence": "And so we think that's what's happening. The reason why we feel pretty strongly that it must have been caused by a supernova is that the only way that the really heavy elements can form or the only way that we know that they can form is in kind of the heat of a supernova. And our uranium, the uranium that seems to be in our solar system on Earth, seems to have formed roughly at the time of the formation of Earth, at about 4 and 1 half billion years ago. And we'll talk in a little bit more depth in future videos on exactly how people figure that out. But since the uranium seems about the same age as our solar system, it must have been formed at around the same time. And so it must have been formed by a supernova. And it must be coming from a supernova."}, {"video_title": "Earth formation   Life on earth and in the universe   Cosmology & Astronomy   Khan Academy.mp3", "Sentence": "And we'll talk in a little bit more depth in future videos on exactly how people figure that out. But since the uranium seems about the same age as our solar system, it must have been formed at around the same time. And so it must have been formed by a supernova. And it must be coming from a supernova. So a supernova shock wave must have passed through our part of the universe. And that's a good reason for gas to get compressed and begin to accrete. So you fast forward a few million years ago that gas would have accreted into something like this."}, {"video_title": "Earth formation   Life on earth and in the universe   Cosmology & Astronomy   Khan Academy.mp3", "Sentence": "And it must be coming from a supernova. So a supernova shock wave must have passed through our part of the universe. And that's a good reason for gas to get compressed and begin to accrete. So you fast forward a few million years ago that gas would have accreted into something like this. It would have reached the critical temperature, critical density, and pressure at the center for ignition to occur, for fusion to start to happen, for hydrogen to start fusing into helium. This right here is our early sun. Around the sun, you have all of the gases and particles and molecules that had enough angular velocity to not fall into the sun, to go into orbit around the sun."}, {"video_title": "Earth formation   Life on earth and in the universe   Cosmology & Astronomy   Khan Academy.mp3", "Sentence": "So you fast forward a few million years ago that gas would have accreted into something like this. It would have reached the critical temperature, critical density, and pressure at the center for ignition to occur, for fusion to start to happen, for hydrogen to start fusing into helium. This right here is our early sun. Around the sun, you have all of the gases and particles and molecules that had enough angular velocity to not fall into the sun, to go into orbit around the sun. They were actually supported by a little bit of pressure, too. Because you can kind of view this as kind of a big cloud of gas. So they're always bumping into each other."}, {"video_title": "Earth formation   Life on earth and in the universe   Cosmology & Astronomy   Khan Academy.mp3", "Sentence": "Around the sun, you have all of the gases and particles and molecules that had enough angular velocity to not fall into the sun, to go into orbit around the sun. They were actually supported by a little bit of pressure, too. Because you can kind of view this as kind of a big cloud of gas. So they're always bumping into each other. But for the most part, it was their angular velocity. And over the next tens of millions of years, they'll slowly bump into each other and clump into each other. Even small particles have gravity."}, {"video_title": "Earth formation   Life on earth and in the universe   Cosmology & Astronomy   Khan Academy.mp3", "Sentence": "So they're always bumping into each other. But for the most part, it was their angular velocity. And over the next tens of millions of years, they'll slowly bump into each other and clump into each other. Even small particles have gravity. And they're going to slowly become rocks and asteroids and eventually what we'd call planetesimals, which are really kind of view them as seeds of planets or early planets. And then those would have a reasonable amount of gravity. And other things would be attracted to them and slowly clump up to them."}, {"video_title": "Earth formation   Life on earth and in the universe   Cosmology & Astronomy   Khan Academy.mp3", "Sentence": "Even small particles have gravity. And they're going to slowly become rocks and asteroids and eventually what we'd call planetesimals, which are really kind of view them as seeds of planets or early planets. And then those would have a reasonable amount of gravity. And other things would be attracted to them and slowly clump up to them. But this wasn't like a simple process. You could imagine you might have one planetesimal form. And maybe there's another planetesimal form."}, {"video_title": "Earth formation   Life on earth and in the universe   Cosmology & Astronomy   Khan Academy.mp3", "Sentence": "And other things would be attracted to them and slowly clump up to them. But this wasn't like a simple process. You could imagine you might have one planetesimal form. And maybe there's another planetesimal form. And instead of having a nice, gentle, those two guys accreting into each other, they might have huge relative velocities and ram into each other and then just shatter. So this wasn't just a nice, gentle process of constant accretion. It would actually have been a very violent process."}, {"video_title": "Earth formation   Life on earth and in the universe   Cosmology & Astronomy   Khan Academy.mp3", "Sentence": "And maybe there's another planetesimal form. And instead of having a nice, gentle, those two guys accreting into each other, they might have huge relative velocities and ram into each other and then just shatter. So this wasn't just a nice, gentle process of constant accretion. It would actually have been a very violent process. It actually happened early in Earth's history. And we actually think this is why the moon formed. So at some point, you fast forward a little bit from this."}, {"video_title": "Earth formation   Life on earth and in the universe   Cosmology & Astronomy   Khan Academy.mp3", "Sentence": "It would actually have been a very violent process. It actually happened early in Earth's history. And we actually think this is why the moon formed. So at some point, you fast forward a little bit from this. Earth would have formed, or I should say the mass that eventually becomes our modern Earth would have been forming. Let me draw it over here. So let's say that that is our modern Earth."}, {"video_title": "Earth formation   Life on earth and in the universe   Cosmology & Astronomy   Khan Academy.mp3", "Sentence": "So at some point, you fast forward a little bit from this. Earth would have formed, or I should say the mass that eventually becomes our modern Earth would have been forming. Let me draw it over here. So let's say that that is our modern Earth. And what we think happened is that another protoplanet, or it was actually a planet because it was roughly the size of Mars, ran into what is eventually going to become our Earth. And this is actually a picture of it. This is an artist's depiction of that collision, where this planet right here is the size of Mars."}, {"video_title": "Earth formation   Life on earth and in the universe   Cosmology & Astronomy   Khan Academy.mp3", "Sentence": "So let's say that that is our modern Earth. And what we think happened is that another protoplanet, or it was actually a planet because it was roughly the size of Mars, ran into what is eventually going to become our Earth. And this is actually a picture of it. This is an artist's depiction of that collision, where this planet right here is the size of Mars. And it ran into what eventually would become Earth. And this we call Theia. This is Theia."}, {"video_title": "Earth formation   Life on earth and in the universe   Cosmology & Astronomy   Khan Academy.mp3", "Sentence": "This is an artist's depiction of that collision, where this planet right here is the size of Mars. And it ran into what eventually would become Earth. And this we call Theia. This is Theia. And what we believe happened, and if you go onto the internet, you'll see some simulations that talk about this, is that we think it was a glancing blow, that it wasn't a direct hit that would have just kind of shattered each of them and turned them into one big molten ball. We think it was a glancing blow, something like this. So if this was essentially Earth, obviously Earth got changed dramatically once Theia ran into it."}, {"video_title": "Earth formation   Life on earth and in the universe   Cosmology & Astronomy   Khan Academy.mp3", "Sentence": "This is Theia. And what we believe happened, and if you go onto the internet, you'll see some simulations that talk about this, is that we think it was a glancing blow, that it wasn't a direct hit that would have just kind of shattered each of them and turned them into one big molten ball. We think it was a glancing blow, something like this. So if this was essentially Earth, obviously Earth got changed dramatically once Theia ran into it. But Theia is right over here. And we think it was a glancing blow, where it came and it hit Earth at kind of an angle. And then obviously the combined energies from that interaction would have made both of them molten."}, {"video_title": "Earth formation   Life on earth and in the universe   Cosmology & Astronomy   Khan Academy.mp3", "Sentence": "So if this was essentially Earth, obviously Earth got changed dramatically once Theia ran into it. But Theia is right over here. And we think it was a glancing blow, where it came and it hit Earth at kind of an angle. And then obviously the combined energies from that interaction would have made both of them molten. And frankly, they probably already were molten, because you had a bunch of smaller collisions and accretion events and little things hitting the surface of probably both of them during this entire period. But this would have had a glancing blow on Earth and essentially splashed a bunch of molten material out into orbit. So it would have just come in, had a glancing blow on Earth, and then splashed a bunch of molten material."}, {"video_title": "Earth formation   Life on earth and in the universe   Cosmology & Astronomy   Khan Academy.mp3", "Sentence": "And then obviously the combined energies from that interaction would have made both of them molten. And frankly, they probably already were molten, because you had a bunch of smaller collisions and accretion events and little things hitting the surface of probably both of them during this entire period. But this would have had a glancing blow on Earth and essentially splashed a bunch of molten material out into orbit. So it would have just come in, had a glancing blow on Earth, and then splashed a bunch of molten material. Some of it would have been captured by Earth. So this is the before, and then the after. You could imagine Earth is kind of this molten, super hot ball."}, {"video_title": "Earth formation   Life on earth and in the universe   Cosmology & Astronomy   Khan Academy.mp3", "Sentence": "So it would have just come in, had a glancing blow on Earth, and then splashed a bunch of molten material. Some of it would have been captured by Earth. So this is the before, and then the after. You could imagine Earth is kind of this molten, super hot ball. And some of it just gets splashed into orbit from the collision. And let me see if I can draw Theia here. So Theia has collided."}, {"video_title": "Earth formation   Life on earth and in the universe   Cosmology & Astronomy   Khan Academy.mp3", "Sentence": "You could imagine Earth is kind of this molten, super hot ball. And some of it just gets splashed into orbit from the collision. And let me see if I can draw Theia here. So Theia has collided. And it's also molten now, because huge energies. And it splashes some of it into orbit. And if we fast forward a little bit, this stuff that got splashed into orbit, it's going in that direction."}, {"video_title": "Earth formation   Life on earth and in the universe   Cosmology & Astronomy   Khan Academy.mp3", "Sentence": "So Theia has collided. And it's also molten now, because huge energies. And it splashes some of it into orbit. And if we fast forward a little bit, this stuff that got splashed into orbit, it's going in that direction. That becomes our moon. And then the rest of this material eventually kind of condenses back into a spherical shape and is what we now call our Earth. So that's how we actually think right now that the moon actually formed."}, {"video_title": "Earth formation   Life on earth and in the universe   Cosmology & Astronomy   Khan Academy.mp3", "Sentence": "And if we fast forward a little bit, this stuff that got splashed into orbit, it's going in that direction. That becomes our moon. And then the rest of this material eventually kind of condenses back into a spherical shape and is what we now call our Earth. So that's how we actually think right now that the moon actually formed. And even after this happened, the Earth still had a lot more, I guess, violence to experience. So just to get a sense of where we are in the history of Earth, we're going to refer to this time clock a lot over the next few videos. This time clock starts right here at the formation of our solar system 4.6 billion years ago, probably coinciding with some type of supernova."}, {"video_title": "Earth formation   Life on earth and in the universe   Cosmology & Astronomy   Khan Academy.mp3", "Sentence": "So that's how we actually think right now that the moon actually formed. And even after this happened, the Earth still had a lot more, I guess, violence to experience. So just to get a sense of where we are in the history of Earth, we're going to refer to this time clock a lot over the next few videos. This time clock starts right here at the formation of our solar system 4.6 billion years ago, probably coinciding with some type of supernova. And as we go clockwise on this diagram, we're moving forward in time. And we're going to go all the way forward to the present period. And just so you understand some of the terminology, GA means billions of years ago, G for giga."}, {"video_title": "Earth formation   Life on earth and in the universe   Cosmology & Astronomy   Khan Academy.mp3", "Sentence": "This time clock starts right here at the formation of our solar system 4.6 billion years ago, probably coinciding with some type of supernova. And as we go clockwise on this diagram, we're moving forward in time. And we're going to go all the way forward to the present period. And just so you understand some of the terminology, GA means billions of years ago, G for giga. MA means millions of years ago, M for mega. So where we are right now, the moon has formed. We're in what we call the Hadean period."}, {"video_title": "Earth formation   Life on earth and in the universe   Cosmology & Astronomy   Khan Academy.mp3", "Sentence": "And just so you understand some of the terminology, GA means billions of years ago, G for giga. MA means millions of years ago, M for mega. So where we are right now, the moon has formed. We're in what we call the Hadean period. Or actually, I shouldn't say period. It's the Hadean eon of Earth. Period is actually another time period."}, {"video_title": "Earth formation   Life on earth and in the universe   Cosmology & Astronomy   Khan Academy.mp3", "Sentence": "We're in what we call the Hadean period. Or actually, I shouldn't say period. It's the Hadean eon of Earth. Period is actually another time period. So let me make this very clear. It's the Hadean. We are in the Hadean eon."}, {"video_title": "Earth formation   Life on earth and in the universe   Cosmology & Astronomy   Khan Academy.mp3", "Sentence": "Period is actually another time period. So let me make this very clear. It's the Hadean. We are in the Hadean eon. And an eon is kind of the largest period of time that we talk about, especially relative to Earth. And it's roughly 500 million to a billion years is an eon. And what makes the Hadean eon distinctive, well, from a geological point of view, what makes it distinctive is it's really we don't have any rocks from the Hadean period."}, {"video_title": "Earth formation   Life on earth and in the universe   Cosmology & Astronomy   Khan Academy.mp3", "Sentence": "We are in the Hadean eon. And an eon is kind of the largest period of time that we talk about, especially relative to Earth. And it's roughly 500 million to a billion years is an eon. And what makes the Hadean eon distinctive, well, from a geological point of view, what makes it distinctive is it's really we don't have any rocks from the Hadean period. We don't have any kind of macroscopic scale rocks from the Hadean period. And that's because at that time, we believe, the Earth was just this molten ball of kind of magma and lava. And it was molten because it was the product of all of these accretion events and all of these collisions and all this kinetic energy turning into heat."}, {"video_title": "Earth formation   Life on earth and in the universe   Cosmology & Astronomy   Khan Academy.mp3", "Sentence": "And what makes the Hadean eon distinctive, well, from a geological point of view, what makes it distinctive is it's really we don't have any rocks from the Hadean period. We don't have any kind of macroscopic scale rocks from the Hadean period. And that's because at that time, we believe, the Earth was just this molten ball of kind of magma and lava. And it was molten because it was the product of all of these accretion events and all of these collisions and all this kinetic energy turning into heat. So if you were to look at the surface of the Earth, if you were to be on the surface of the Earth during the Hadean eon, which you probably wouldn't want to be because you might get hit by a falling meteorite or probably burned by some magma or whatever, it would look like this. And you wouldn't be able to breathe anyway. This is what the surface of the Earth would look like."}, {"video_title": "Earth formation   Life on earth and in the universe   Cosmology & Astronomy   Khan Academy.mp3", "Sentence": "And it was molten because it was the product of all of these accretion events and all of these collisions and all this kinetic energy turning into heat. So if you were to look at the surface of the Earth, if you were to be on the surface of the Earth during the Hadean eon, which you probably wouldn't want to be because you might get hit by a falling meteorite or probably burned by some magma or whatever, it would look like this. And you wouldn't be able to breathe anyway. This is what the surface of the Earth would look like. It would look like a big magma pool. And that's why we don't have any rocks from there. Because the rocks were just constantly being recycled, being dissolved, and churned inside of this giant molten ball."}, {"video_title": "Earth formation   Life on earth and in the universe   Cosmology & Astronomy   Khan Academy.mp3", "Sentence": "This is what the surface of the Earth would look like. It would look like a big magma pool. And that's why we don't have any rocks from there. Because the rocks were just constantly being recycled, being dissolved, and churned inside of this giant molten ball. And frankly, the Earth still is a giant molten ball. It's just we live on the super thin, cooled crust of that molten ball. If you go right below that crust, and we'll talk a little bit more about that in future videos, you will get magma."}, {"video_title": "Earth formation   Life on earth and in the universe   Cosmology & Astronomy   Khan Academy.mp3", "Sentence": "Because the rocks were just constantly being recycled, being dissolved, and churned inside of this giant molten ball. And frankly, the Earth still is a giant molten ball. It's just we live on the super thin, cooled crust of that molten ball. If you go right below that crust, and we'll talk a little bit more about that in future videos, you will get magma. And if you go dig deeper, you'll have liquid iron. So I mean, it still is a molten ball. And this whole period is just a violent, not only was Earth itself volcanic, molten ball, it began to harden as you get to the late Hadean eon."}, {"video_title": "Earth formation   Life on earth and in the universe   Cosmology & Astronomy   Khan Academy.mp3", "Sentence": "If you go right below that crust, and we'll talk a little bit more about that in future videos, you will get magma. And if you go dig deeper, you'll have liquid iron. So I mean, it still is a molten ball. And this whole period is just a violent, not only was Earth itself volcanic, molten ball, it began to harden as you get to the late Hadean eon. But we also had stuff falling from the sky and constantly colliding with Earth and really just continuing to add to the heat of this molten ball. Anyway, I'll leave you there. And as you can imagine, at this point, as far as we can tell, there was no life on Earth."}, {"video_title": "Earth formation   Life on earth and in the universe   Cosmology & Astronomy   Khan Academy.mp3", "Sentence": "And this whole period is just a violent, not only was Earth itself volcanic, molten ball, it began to harden as you get to the late Hadean eon. But we also had stuff falling from the sky and constantly colliding with Earth and really just continuing to add to the heat of this molten ball. Anyway, I'll leave you there. And as you can imagine, at this point, as far as we can tell, there was no life on Earth. Some people believe that maybe some life could have formed in the late Hadean eon. But for the most part, this is completely inhospitable for any life forming. So I'll leave you there."}, {"video_title": "Competitive inhibition   Energy and enzymes   Biology   Khan Academy.mp3", "Sentence": "So let's say this right over here, this is our enzyme, and we have our substrate, and it goes and it binds to the active site, to the active site of the enzyme. So let's say it binds right over there. So that site on the enzyme, we call the active site, where the substrate binds, and then the enzyme catalyzes a reaction. Maybe it breaks up the substrate into two smaller molecules. And so after the reaction, after the reaction, we, the enzyme, whoops, after the reaction, the enzyme is unchanged, but a reaction has been catalyzed. We now have, we now have the substrate being broken up, in this case at least, into two smaller molecules. Maybe I'll draw them, that's one of them, and this is the other one right over here."}, {"video_title": "Competitive inhibition   Energy and enzymes   Biology   Khan Academy.mp3", "Sentence": "Maybe it breaks up the substrate into two smaller molecules. And so after the reaction, after the reaction, we, the enzyme, whoops, after the reaction, the enzyme is unchanged, but a reaction has been catalyzed. We now have, we now have the substrate being broken up, in this case at least, into two smaller molecules. Maybe I'll draw them, that's one of them, and this is the other one right over here. So they just came, they just came from the active site. Once the reaction is catalyzed, they don't have the affinity to the active site anymore, and they break off. So this enzyme has just catalyzed this reaction."}, {"video_title": "Competitive inhibition   Energy and enzymes   Biology   Khan Academy.mp3", "Sentence": "Maybe I'll draw them, that's one of them, and this is the other one right over here. So they just came, they just came from the active site. Once the reaction is catalyzed, they don't have the affinity to the active site anymore, and they break off. So this enzyme has just catalyzed this reaction. What I wanna talk about in this video is how this might be inhibited, and specifically how it might be inhibited competitively. So we're gonna talk about competitive inhibition. So competitive, let me write it over here, competitive, competitive inhibition, inhibition."}, {"video_title": "Competitive inhibition   Energy and enzymes   Biology   Khan Academy.mp3", "Sentence": "So this enzyme has just catalyzed this reaction. What I wanna talk about in this video is how this might be inhibited, and specifically how it might be inhibited competitively. So we're gonna talk about competitive inhibition. So competitive, let me write it over here, competitive, competitive inhibition, inhibition. So the classic case of competitive inhibition, if there's some molecule that competes for the substrate at the active site, as we'll see, this isn't the only form of competitive inhibition, but this is the one that you will most typically see in a textbook. So let's do, so that's our enzyme again, and so that's our enzyme, and we've already seen that this is an, this right over here where I'm circling, that is the active site, active, active site, and if the molecule, the intended substrate, I guess you could say, gets to it, we're gonna have this first scenario up here. But in classic competitive inhibition, or at least the version I'm just gonna show you right now, you could have another molecule, you could have another molecule that, let's say it looks something like this, that can compete for the active site, and if it gets to the active site first, so if it gets there first, so let me show what's going to happen."}, {"video_title": "Competitive inhibition   Energy and enzymes   Biology   Khan Academy.mp3", "Sentence": "So competitive, let me write it over here, competitive, competitive inhibition, inhibition. So the classic case of competitive inhibition, if there's some molecule that competes for the substrate at the active site, as we'll see, this isn't the only form of competitive inhibition, but this is the one that you will most typically see in a textbook. So let's do, so that's our enzyme again, and so that's our enzyme, and we've already seen that this is an, this right over here where I'm circling, that is the active site, active, active site, and if the molecule, the intended substrate, I guess you could say, gets to it, we're gonna have this first scenario up here. But in classic competitive inhibition, or at least the version I'm just gonna show you right now, you could have another molecule, you could have another molecule that, let's say it looks something like this, that can compete for the active site, and if it gets to the active site first, so if it gets there first, so let me show what's going to happen. So then we have our enzyme, we have the other molecule, not the intended substrate, binds to the active site first. Well now the intended substrate, the one for which the enzyme catalyzed a reaction, isn't able to bind, and the reaction isn't going to happen. And you can see very clearly that they are competing for the enzyme, and in this case, they're competing for the active site."}, {"video_title": "Competitive inhibition   Energy and enzymes   Biology   Khan Academy.mp3", "Sentence": "But in classic competitive inhibition, or at least the version I'm just gonna show you right now, you could have another molecule, you could have another molecule that, let's say it looks something like this, that can compete for the active site, and if it gets to the active site first, so if it gets there first, so let me show what's going to happen. So then we have our enzyme, we have the other molecule, not the intended substrate, binds to the active site first. Well now the intended substrate, the one for which the enzyme catalyzed a reaction, isn't able to bind, and the reaction isn't going to happen. And you can see very clearly that they are competing for the enzyme, and in this case, they're competing for the active site. Now this isn't the only form of competitive inhibition. Another form of competitive inhibition is allosteric competitive inhibition. Let me write this down."}, {"video_title": "Competitive inhibition   Energy and enzymes   Biology   Khan Academy.mp3", "Sentence": "And you can see very clearly that they are competing for the enzyme, and in this case, they're competing for the active site. Now this isn't the only form of competitive inhibition. Another form of competitive inhibition is allosteric competitive inhibition. Let me write this down. So you have allosteric, competitive, competitive inhibition. Now I'm having trouble writing. Inhibition."}, {"video_title": "Competitive inhibition   Energy and enzymes   Biology   Khan Academy.mp3", "Sentence": "Let me write this down. So you have allosteric, competitive, competitive inhibition. Now I'm having trouble writing. Inhibition. And an allosteric site is a site other than the active site. But in competitive, in allosteric competitive inhibition, or competitive allosteric inhibition, however you want to say it, you have a scenario where the competitor, the competitor doesn't bind to the active site, but binds to a site that is not the active site, an allosteric site, we could say. So in that one, the competitor maybe might bind here."}, {"video_title": "Competitive inhibition   Energy and enzymes   Biology   Khan Academy.mp3", "Sentence": "Inhibition. And an allosteric site is a site other than the active site. But in competitive, in allosteric competitive inhibition, or competitive allosteric inhibition, however you want to say it, you have a scenario where the competitor, the competitor doesn't bind to the active site, but binds to a site that is not the active site, an allosteric site, we could say. So in that one, the competitor maybe might bind here. So that's clearly not the active site. So maybe the competitor looks something like that. It didn't bind to the active site, but by binding there, the active site is no longer, can no longer bind to the intended substrate."}, {"video_title": "Competitive inhibition   Energy and enzymes   Biology   Khan Academy.mp3", "Sentence": "So in that one, the competitor maybe might bind here. So that's clearly not the active site. So maybe the competitor looks something like that. It didn't bind to the active site, but by binding there, the active site is no longer, can no longer bind to the intended substrate. So you have the same effect. You have the same effect right over here where this thing isn't going to bind. But if this thing binds first, let me draw that scenario."}, {"video_title": "Competitive inhibition   Energy and enzymes   Biology   Khan Academy.mp3", "Sentence": "It didn't bind to the active site, but by binding there, the active site is no longer, can no longer bind to the intended substrate. So you have the same effect. You have the same effect right over here where this thing isn't going to bind. But if this thing binds first, let me draw that scenario. So if the intended substrate binds first, then the competitor can't bind. So in this scenario, if the substrate is able to get to the active site, well then, the competitor can't bind. So once again, they're competing."}, {"video_title": "Competitive inhibition   Energy and enzymes   Biology   Khan Academy.mp3", "Sentence": "But if this thing binds first, let me draw that scenario. So if the intended substrate binds first, then the competitor can't bind. So in this scenario, if the substrate is able to get to the active site, well then, the competitor can't bind. So once again, they're competing. So I'll draw the competitor up here. So then the competitor, whoever gets to it first gets the enzyme. So in this situation, the competitor's not going to bind."}, {"video_title": "Competitive inhibition   Energy and enzymes   Biology   Khan Academy.mp3", "Sentence": "So once again, they're competing. So I'll draw the competitor up here. So then the competitor, whoever gets to it first gets the enzyme. So in this situation, the competitor's not going to bind. So that's true of whether you're talking about competitive inhibition where they're competing for the active site. If the competitor gets there first, the intended substrate isn't going to get there and the reaction isn't going to be catalyzed. Or if the intended substrate gets first, then the competitor's not going to be able to get there."}, {"video_title": "Competitive inhibition   Energy and enzymes   Biology   Khan Academy.mp3", "Sentence": "So in this situation, the competitor's not going to bind. So that's true of whether you're talking about competitive inhibition where they're competing for the active site. If the competitor gets there first, the intended substrate isn't going to get there and the reaction isn't going to be catalyzed. Or if the intended substrate gets first, then the competitor's not going to be able to get there. In fact, it could have been this situation where because the substrate got there first, the competitor, the competitor isn't going to be able to bind to the active site. When we're talking about allosteric competitive inhibition, we're still competing for the enzyme. Only one's going to get it."}, {"video_title": "Competitive inhibition   Energy and enzymes   Biology   Khan Academy.mp3", "Sentence": "Or if the intended substrate gets first, then the competitor's not going to be able to get there. In fact, it could have been this situation where because the substrate got there first, the competitor, the competitor isn't going to be able to bind to the active site. When we're talking about allosteric competitive inhibition, we're still competing for the enzyme. Only one's going to get it. If one gets to the enzyme first, then the other one's not going to be able to get there. They are competing for the enzyme, but the competitor, the non-substrate, is just acting at an allosteric site. By binding to an allosteric site, it changes the conformation of the enzyme so that the active site no longer binds to the substrate."}, {"video_title": "Competitive inhibition   Energy and enzymes   Biology   Khan Academy.mp3", "Sentence": "Only one's going to get it. If one gets to the enzyme first, then the other one's not going to be able to get there. They are competing for the enzyme, but the competitor, the non-substrate, is just acting at an allosteric site. By binding to an allosteric site, it changes the conformation of the enzyme so that the active site no longer binds to the substrate. And I want to really emphasize this point because when I first learned this, I said, oh, and it's often sometimes confused and even some things you'll read on the internet, that they'll say that this allosteric type of inhibition, they'll call this non-competitive because you're not competing for the active site, but that is actually not the case. In non-competitive inhibition, and I'm going to do the whole next video on non-competitive inhibition, in non-competitive inhibition, the inhibitor, the inhibitor right over here, can bind regardless of whether the substrate has bound or not, but when the inhibitor does bind, it prevents the reaction from moving forward. It changes the conformation of the protein so it no longer catalyzes the reaction."}, {"video_title": "Competitive inhibition   Energy and enzymes   Biology   Khan Academy.mp3", "Sentence": "By binding to an allosteric site, it changes the conformation of the enzyme so that the active site no longer binds to the substrate. And I want to really emphasize this point because when I first learned this, I said, oh, and it's often sometimes confused and even some things you'll read on the internet, that they'll say that this allosteric type of inhibition, they'll call this non-competitive because you're not competing for the active site, but that is actually not the case. In non-competitive inhibition, and I'm going to do the whole next video on non-competitive inhibition, in non-competitive inhibition, the inhibitor, the inhibitor right over here, can bind regardless of whether the substrate has bound or not, but when the inhibitor does bind, it prevents the reaction from moving forward. It changes the conformation of the protein so it no longer catalyzes the reaction. So non-competitive, they both can bind, but if the inhibitor is there, the reaction isn't going to proceed. In competitive inhibition, whether we're talking about allosteric or non-allosteric competitive inhibition, only one of the substrate or the inhibitor is going to be able to bind. They're competing for the enzyme."}, {"video_title": "Evidence for evolution    Biology   Khan Academy.mp3", "Sentence": "This is by Theodosia Dobzhansky, who's a famous biologist, he's passed away now. And what he's saying is absolutely true, and this is why it's so important to appreciate the evidence for evolution and natural selection, and to understand them, because before the theory of evolution, biology was just about observation and classification without having a cohesive narrative for how all of this came about. And since Darwin had come up with this theory in the mid-19th century, we've had far more tools to back it up beyond just the observations we had up until that point. We have our tools around dating in the fossil record, which gives us much more evidence. We have our tools of microbiology and genetics, which gives us even stronger evidence. So a lot of times people say, oh, it's theory of evolution, is it just a theory? Well, it's about as strong as theories get."}, {"video_title": "Evidence for evolution    Biology   Khan Academy.mp3", "Sentence": "We have our tools around dating in the fossil record, which gives us much more evidence. We have our tools of microbiology and genetics, which gives us even stronger evidence. So a lot of times people say, oh, it's theory of evolution, is it just a theory? Well, it's about as strong as theories get. And without it, as Theodosia Dobzhansky said, biology as we know it, and all of the progress we've made in biology, frankly, wouldn't make any sense and probably would not have happened. Now, I'm going to broadly go into three types of evidence in this video for evolution and natural selection. The first is structural."}, {"video_title": "Evidence for evolution    Biology   Khan Academy.mp3", "Sentence": "Well, it's about as strong as theories get. And without it, as Theodosia Dobzhansky said, biology as we know it, and all of the progress we've made in biology, frankly, wouldn't make any sense and probably would not have happened. Now, I'm going to broadly go into three types of evidence in this video for evolution and natural selection. The first is structural. And these are the types of things that folks like Darwin would have observed, that people have been observing in biology for a long time, but evolution and natural selection starts to make a lot more sense of it. And here we're talking about the macro structure, things that we can, for the most part, observe with our eyes or with a very simple microscope. The next level is what we've learned, really over the last 100 or so years, at the micro level, in microbiology."}, {"video_title": "Evidence for evolution    Biology   Khan Academy.mp3", "Sentence": "The first is structural. And these are the types of things that folks like Darwin would have observed, that people have been observing in biology for a long time, but evolution and natural selection starts to make a lot more sense of it. And here we're talking about the macro structure, things that we can, for the most part, observe with our eyes or with a very simple microscope. The next level is what we've learned, really over the last 100 or so years, at the micro level, in microbiology. Microbiology, and especially in genetics. So this has really firmed up the theory of evolution. And then the last dimension we'll look at is direct observation."}, {"video_title": "Evidence for evolution    Biology   Khan Academy.mp3", "Sentence": "The next level is what we've learned, really over the last 100 or so years, at the micro level, in microbiology. Microbiology, and especially in genetics. So this has really firmed up the theory of evolution. And then the last dimension we'll look at is direct observation. Direct observation. And this is really where it goes beyond a theory. We are seeing it happen."}, {"video_title": "Evidence for evolution    Biology   Khan Academy.mp3", "Sentence": "And then the last dimension we'll look at is direct observation. Direct observation. And this is really where it goes beyond a theory. We are seeing it happen. A lot of times people say, oh, it's a theory, it happened, the theory says it happened over tens of millions of years, but no one was around to really observe, even if we see a lot of evidence, no one knows if it for sure happened. But if you're directly observing things, well, you know it's for sure happening. And as we'll see, evolution does not only occur over timescales of millions or tens of millions of years, it actually can occur, and we see it occurring all the time on scales well within a human observational capacity, within just a matter of months or years."}, {"video_title": "Evidence for evolution    Biology   Khan Academy.mp3", "Sentence": "We are seeing it happen. A lot of times people say, oh, it's a theory, it happened, the theory says it happened over tens of millions of years, but no one was around to really observe, even if we see a lot of evidence, no one knows if it for sure happened. But if you're directly observing things, well, you know it's for sure happening. And as we'll see, evolution does not only occur over timescales of millions or tens of millions of years, it actually can occur, and we see it occurring all the time on scales well within a human observational capacity, within just a matter of months or years. So let's go through each of these. So first let's talk about structural. And this is a very high-level overview."}, {"video_title": "Evidence for evolution    Biology   Khan Academy.mp3", "Sentence": "And as we'll see, evolution does not only occur over timescales of millions or tens of millions of years, it actually can occur, and we see it occurring all the time on scales well within a human observational capacity, within just a matter of months or years. So let's go through each of these. So first let's talk about structural. And this is a very high-level overview. I encourage you to do more research on it. You will find loads and loads and loads of any type of this evidence. So the first thing I wanna talk about is homologous structures, homologous structures that you see throughout the biological world."}, {"video_title": "Evidence for evolution    Biology   Khan Academy.mp3", "Sentence": "And this is a very high-level overview. I encourage you to do more research on it. You will find loads and loads and loads of any type of this evidence. So the first thing I wanna talk about is homologous structures, homologous structures that you see throughout the biological world. Homologous, homologous structures. And the word homologous means things that have similar structures, similar position, similar ancestry, but not necessarily the exact same function. And here you see examples of a, well, as a human we would consider a forearm."}, {"video_title": "Evidence for evolution    Biology   Khan Academy.mp3", "Sentence": "So the first thing I wanna talk about is homologous structures, homologous structures that you see throughout the biological world. Homologous, homologous structures. And the word homologous means things that have similar structures, similar position, similar ancestry, but not necessarily the exact same function. And here you see examples of a, well, as a human we would consider a forearm. You see the human forearm and wrist. And then you see the homologous structures in dogs and birds and whales. And even though this part of those animals have very different functions, a human does not walk on its hands for the most part."}, {"video_title": "Evidence for evolution    Biology   Khan Academy.mp3", "Sentence": "And here you see examples of a, well, as a human we would consider a forearm. You see the human forearm and wrist. And then you see the homologous structures in dogs and birds and whales. And even though this part of those animals have very different functions, a human does not walk on its hands for the most part. A dog does walk on its front legs. A bird isn't walking at all. It's using them to flap its wings."}, {"video_title": "Evidence for evolution    Biology   Khan Academy.mp3", "Sentence": "And even though this part of those animals have very different functions, a human does not walk on its hands for the most part. A dog does walk on its front legs. A bird isn't walking at all. It's using them to flap its wings. And a whale, this is making up its actual fins. It's using them to propel or to control their movement inside of the water. And even though they have these very, very different functions, and at first when you look at a human and a bird and a whale, on the outside they might look reasonably different."}, {"video_title": "Evidence for evolution    Biology   Khan Academy.mp3", "Sentence": "It's using them to flap its wings. And a whale, this is making up its actual fins. It's using them to propel or to control their movement inside of the water. And even though they have these very, very different functions, and at first when you look at a human and a bird and a whale, on the outside they might look reasonably different. When you look at these bone structures, they are eerily similar, especially with the color-coded, especially color-coded the way it is. So these are, this is a very strong hint that maybe humans, dogs, birds, and whales share a common ancestor more recently in the past than say other animals or organisms, I should say, that don't have, whose structures aren't as homologous as these are right over here. And if you were independently trying to create structures for what each of these different species are doing, it's not obvious that you would have such homologous structures actually be involved."}, {"video_title": "Evidence for evolution    Biology   Khan Academy.mp3", "Sentence": "And even though they have these very, very different functions, and at first when you look at a human and a bird and a whale, on the outside they might look reasonably different. When you look at these bone structures, they are eerily similar, especially with the color-coded, especially color-coded the way it is. So these are, this is a very strong hint that maybe humans, dogs, birds, and whales share a common ancestor more recently in the past than say other animals or organisms, I should say, that don't have, whose structures aren't as homologous as these are right over here. And if you were independently trying to create structures for what each of these different species are doing, it's not obvious that you would have such homologous structures actually be involved. Now these are all species that exist today. These are all species that exist on the planet at the same time. But we also see structural evidence by going into the fossil record."}, {"video_title": "Evidence for evolution    Biology   Khan Academy.mp3", "Sentence": "And if you were independently trying to create structures for what each of these different species are doing, it's not obvious that you would have such homologous structures actually be involved. Now these are all species that exist today. These are all species that exist on the planet at the same time. But we also see structural evidence by going into the fossil record. In the last few hundred years, or really in the last hundred years is where we've gotten really good at it, we've gotten good at looking at different layers of different layers of rock strata and being able to date them and saying, okay, that layer was laid down X million years ago. That layer was laid down a little bit more recent. This one was even more recent."}, {"video_title": "Evidence for evolution    Biology   Khan Academy.mp3", "Sentence": "But we also see structural evidence by going into the fossil record. In the last few hundred years, or really in the last hundred years is where we've gotten really good at it, we've gotten good at looking at different layers of different layers of rock strata and being able to date them and saying, okay, that layer was laid down X million years ago. That layer was laid down a little bit more recent. This one was even more recent. And then looking at fossils within that to say, okay, 20 million years ago, there were species around that looked like that. And then 10 million years ago, there were species that looked like that. And one example is if you look at horse-like animals."}, {"video_title": "Evidence for evolution    Biology   Khan Academy.mp3", "Sentence": "This one was even more recent. And then looking at fossils within that to say, okay, 20 million years ago, there were species around that looked like that. And then 10 million years ago, there were species that looked like that. And one example is if you look at horse-like animals. So this is right over here. We're talking about horses, zebras, donkeys, mules, things like that. The modern ones, well, this is their bone structure."}, {"video_title": "Evidence for evolution    Biology   Khan Academy.mp3", "Sentence": "And one example is if you look at horse-like animals. So this is right over here. We're talking about horses, zebras, donkeys, mules, things like that. The modern ones, well, this is their bone structure. But if you look at the fossil record from 12 to five million years ago, you see fossils that look like this. And they're very close. So you see, it's very believable that you see you could have evolution from this to that."}, {"video_title": "Evidence for evolution    Biology   Khan Academy.mp3", "Sentence": "The modern ones, well, this is their bone structure. But if you look at the fossil record from 12 to five million years ago, you see fossils that look like this. And they're very close. So you see, it's very believable that you see you could have evolution from this to that. But then you go further back, and once again, it seems like a very gradual process. And once again, this is happening over, these are from 12 to five million years ago, these are from 16 to 12 million years ago, these are from over 34 million years ago. And so you can see how this is happening at a very, very gradual pace."}, {"video_title": "Evidence for evolution    Biology   Khan Academy.mp3", "Sentence": "So you see, it's very believable that you see you could have evolution from this to that. But then you go further back, and once again, it seems like a very gradual process. And once again, this is happening over, these are from 12 to five million years ago, these are from 16 to 12 million years ago, these are from over 34 million years ago. And so you can see how this is happening at a very, very gradual pace. And the mechanism, and we go into some depth in other videos in Khan Academy, you have variation species, you have the environment selecting for it. The environment might change, or different things happen, so you have different forms of selection, different types of combinations sprout up, they're more suitable for their environment, they start to reproduce better, they become the dominant species, or they take over certain parts of a niche or an ecosystem. And so you have this change, this heritable change of traits over time."}, {"video_title": "Evidence for evolution    Biology   Khan Academy.mp3", "Sentence": "And so you can see how this is happening at a very, very gradual pace. And the mechanism, and we go into some depth in other videos in Khan Academy, you have variation species, you have the environment selecting for it. The environment might change, or different things happen, so you have different forms of selection, different types of combinations sprout up, they're more suitable for their environment, they start to reproduce better, they become the dominant species, or they take over certain parts of a niche or an ecosystem. And so you have this change, this heritable change of traits over time. And so when you look at the fossil record, it makes a lot of sense that, okay, this is strong evidence for evolution, that the animals that we see today weren't just put on, just created all of a sudden, and haven't changed since then, that there's a constant change, and we can see it directly through the fossil record. Now, the next point of evidence, I will put a bit of a caveat, because the gentleman who first created this, his name was Haeckel, he was a controversial figure, he had some spurious theories, and even this diagram that he created, it seems like he fudged a little bit of the drawings in order to make a stronger argument, but even with modern observations, these drawings are pretty close to being correct. And it's very, very compelling, it shows the embryonic development of a whole series of species, from a fish on the left, to a reptile, to birds, to mammals, and another mammal, to non-human mammals, and of course, to humans."}, {"video_title": "Evidence for evolution    Biology   Khan Academy.mp3", "Sentence": "And so you have this change, this heritable change of traits over time. And so when you look at the fossil record, it makes a lot of sense that, okay, this is strong evidence for evolution, that the animals that we see today weren't just put on, just created all of a sudden, and haven't changed since then, that there's a constant change, and we can see it directly through the fossil record. Now, the next point of evidence, I will put a bit of a caveat, because the gentleman who first created this, his name was Haeckel, he was a controversial figure, he had some spurious theories, and even this diagram that he created, it seems like he fudged a little bit of the drawings in order to make a stronger argument, but even with modern observations, these drawings are pretty close to being correct. And it's very, very compelling, it shows the embryonic development of a whole series of species, from a fish on the left, to a reptile, to birds, to mammals, and another mammal, to non-human mammals, and of course, to humans. And you can see at the early stages, they look eerily similar. In fact, you see proto-gill slits in all of these animals, which later differentiate into things that are more suitable for what that animal actually becomes. And Haeckel, he's the guy who coined ontogeny recapitulates phylogeny, which is a very fancy way of saying that your embryonic development is telling the story of the evolutionary past, which isn't true, but you'll even hear people quote that today."}, {"video_title": "Evidence for evolution    Biology   Khan Academy.mp3", "Sentence": "And it's very, very compelling, it shows the embryonic development of a whole series of species, from a fish on the left, to a reptile, to birds, to mammals, and another mammal, to non-human mammals, and of course, to humans. And you can see at the early stages, they look eerily similar. In fact, you see proto-gill slits in all of these animals, which later differentiate into things that are more suitable for what that animal actually becomes. And Haeckel, he's the guy who coined ontogeny recapitulates phylogeny, which is a very fancy way of saying that your embryonic development is telling the story of the evolutionary past, which isn't true, but you'll even hear people quote that today. But his drawings and his observations, this is compelling evidence for life-sharing a common ancestry, coming from similar origins that got more and more different over time through the process of natural selection. So everything I've talked about so far has been kind of macro-structure, things we can observe. The next thing I'm gonna talk about is you can think about it as micro-structures or processes, and this is microbiology."}, {"video_title": "Evidence for evolution    Biology   Khan Academy.mp3", "Sentence": "And Haeckel, he's the guy who coined ontogeny recapitulates phylogeny, which is a very fancy way of saying that your embryonic development is telling the story of the evolutionary past, which isn't true, but you'll even hear people quote that today. But his drawings and his observations, this is compelling evidence for life-sharing a common ancestry, coming from similar origins that got more and more different over time through the process of natural selection. So everything I've talked about so far has been kind of macro-structure, things we can observe. The next thing I'm gonna talk about is you can think about it as micro-structures or processes, and this is microbiology. Micro-biology. And biolo-biology. Microbiology."}, {"video_title": "Evidence for evolution    Biology   Khan Academy.mp3", "Sentence": "The next thing I'm gonna talk about is you can think about it as micro-structures or processes, and this is microbiology. Micro-biology. And biolo-biology. Microbiology. And the more we understand about microbiology, the more compelling case of evolution. Because when we look at even, you know, one, all life forms that we know, they involve DNA. How the DNA gets replicated and translated and transcribed is very similar from one life form to another."}, {"video_title": "Evidence for evolution    Biology   Khan Academy.mp3", "Sentence": "Microbiology. And the more we understand about microbiology, the more compelling case of evolution. Because when we look at even, you know, one, all life forms that we know, they involve DNA. How the DNA gets replicated and translated and transcribed is very similar from one life form to another. The idea of DNA going to, DNA coding for proteins, proteins that are made up of amino acids is something that we see throughout biology. Amino acids, which once again, hints at a common ancestry. And not only are those molecular, and many of the very proteins, are very, very similar, more similar than if you looked at the macro level or even at the structural level between different species."}, {"video_title": "Evidence for evolution    Biology   Khan Academy.mp3", "Sentence": "How the DNA gets replicated and translated and transcribed is very similar from one life form to another. The idea of DNA going to, DNA coding for proteins, proteins that are made up of amino acids is something that we see throughout biology. Amino acids, which once again, hints at a common ancestry. And not only are those molecular, and many of the very proteins, are very, very similar, more similar than if you looked at the macro level or even at the structural level between different species. And not just do they share these common micro-structures and processes, but the actual information stored in things like DNA also are very, very strong evidence for evolution. So this is a picture, I got this from, I got this from the site, I should give proper credit, 23andme.com. But this, and you'll see other data like this that's very similar to this, which is how much genetic similarity do we have between different species?"}, {"video_title": "Evidence for evolution    Biology   Khan Academy.mp3", "Sentence": "And not only are those molecular, and many of the very proteins, are very, very similar, more similar than if you looked at the macro level or even at the structural level between different species. And not just do they share these common micro-structures and processes, but the actual information stored in things like DNA also are very, very strong evidence for evolution. So this is a picture, I got this from, I got this from the site, I should give proper credit, 23andme.com. But this, and you'll see other data like this that's very similar to this, which is how much genetic similarity do we have between different species? And these numbers tell us how much genetic similarity at a high level do we have with chimpanzees, mice, fruit flies, yeast, and plants. And the fact that we have 26% of our genes in common with yeast is mind-blowing. Because at a macro level, it doesn't seem like there's a lot in common with yeast."}, {"video_title": "Evidence for evolution    Biology   Khan Academy.mp3", "Sentence": "But this, and you'll see other data like this that's very similar to this, which is how much genetic similarity do we have between different species? And these numbers tell us how much genetic similarity at a high level do we have with chimpanzees, mice, fruit flies, yeast, and plants. And the fact that we have 26% of our genes in common with yeast is mind-blowing. Because at a macro level, it doesn't seem like there's a lot in common with yeast. But when you get at a microbiological level, there's a good bit that's in common with yeast. And chimpanzees, we do relate to them. Their facial expressions often feel eerily human, their behaviors often feel eerily human, but their genes show just how close to human beings they actually are."}, {"video_title": "Evidence for evolution    Biology   Khan Academy.mp3", "Sentence": "Because at a macro level, it doesn't seem like there's a lot in common with yeast. But when you get at a microbiological level, there's a good bit that's in common with yeast. And chimpanzees, we do relate to them. Their facial expressions often feel eerily human, their behaviors often feel eerily human, but their genes show just how close to human beings they actually are. And this actually shows that even, you know, mice are way closer, if you looked at the entire tree of life, based on genetic evidence, things like mice and even fruit flies are awfully close to human beings, especially if you were to compare it to bacteria or plants. But once again, you share all of these common processes, and the fact that we can now measure how far things are away allows us to create a very accurate tree of life, especially thinking about how far in the past we had evolutionary common ancestors. Now the last thing that I promised I would talk about is direct evidence."}, {"video_title": "Evidence for evolution    Biology   Khan Academy.mp3", "Sentence": "Their facial expressions often feel eerily human, their behaviors often feel eerily human, but their genes show just how close to human beings they actually are. And this actually shows that even, you know, mice are way closer, if you looked at the entire tree of life, based on genetic evidence, things like mice and even fruit flies are awfully close to human beings, especially if you were to compare it to bacteria or plants. But once again, you share all of these common processes, and the fact that we can now measure how far things are away allows us to create a very accurate tree of life, especially thinking about how far in the past we had evolutionary common ancestors. Now the last thing that I promised I would talk about is direct evidence. Direct evidence of evolution. And I talk about this in the first evolution video. But the direct evidence we see all the time with things like bacteria, where you have bacteria, let's say growing around, and we have antibiotics that we use in our body to kill bacteria."}, {"video_title": "Evidence for evolution    Biology   Khan Academy.mp3", "Sentence": "Now the last thing that I promised I would talk about is direct evidence. Direct evidence of evolution. And I talk about this in the first evolution video. But the direct evidence we see all the time with things like bacteria, where you have bacteria, let's say growing around, and we have antibiotics that we use in our body to kill bacteria. But the reason why many physicians and scientists will tell you don't overuse antibiotics is because the more you use it, it causes a very strong natural selection process for bacteria that are going to be resistant to that antibiotic. So if you keep using an antibiotic and the bacteria keep changing, there's more and more variation, well, you're gonna kill a lot of the bacteria, but if even one of them is resistant to that antibiotic that you use, well then all of its competition is gonna get killed, and so that drug-resistant superbug, it's often called, is going to be able to go nuts, and that antibiotic isn't going to be able to do anything. And if you look at science today, if you look at medicine today, this is kind of an arms race."}, {"video_title": "Evidence for evolution    Biology   Khan Academy.mp3", "Sentence": "But the direct evidence we see all the time with things like bacteria, where you have bacteria, let's say growing around, and we have antibiotics that we use in our body to kill bacteria. But the reason why many physicians and scientists will tell you don't overuse antibiotics is because the more you use it, it causes a very strong natural selection process for bacteria that are going to be resistant to that antibiotic. So if you keep using an antibiotic and the bacteria keep changing, there's more and more variation, well, you're gonna kill a lot of the bacteria, but if even one of them is resistant to that antibiotic that you use, well then all of its competition is gonna get killed, and so that drug-resistant superbug, it's often called, is going to be able to go nuts, and that antibiotic isn't going to be able to do anything. And if you look at science today, if you look at medicine today, this is kind of an arms race. You have this constant need to create new antibiotics because more and more bacteria are becoming drug-resistant. They're becoming what's often called superbugs, where they are resistant to the existing antibiotics. And this is evolution and natural selection happening on a human scale."}, {"video_title": "Operons and gene regulation in bacteria.mp3", "Sentence": "So we're gonna talk a little bit about DNA regulation. And this is the general idea that if you look at an organism's genome, that not all of the genes are being transcribed and translated at the same time. It could actually depend on the type of cell that DNA is inside of, or it could depend on the environment for that organism. So for example, if you look at, say, a multicellular organism, this, maybe this is, and these are oversimplifications right over here, maybe this is some type of immune cell, immune cell. And let's say that this over here is a muscle cell. And they're not necessarily, or not likely to be these perfect circles, but this is just for the idea. And they're going to have the exact same DNA."}, {"video_title": "Operons and gene regulation in bacteria.mp3", "Sentence": "So for example, if you look at, say, a multicellular organism, this, maybe this is, and these are oversimplifications right over here, maybe this is some type of immune cell, immune cell. And let's say that this over here is a muscle cell. And they're not necessarily, or not likely to be these perfect circles, but this is just for the idea. And they're going to have the exact same DNA. So the DNA in both of these is the same. So DNA is the same inside, and these are going to be, these are eukaryotes, so I'll draw the nuclear membrane there, same DNA. But they have very different roles inside of this organism."}, {"video_title": "Operons and gene regulation in bacteria.mp3", "Sentence": "And they're going to have the exact same DNA. So the DNA in both of these is the same. So DNA is the same inside, and these are going to be, these are eukaryotes, so I'll draw the nuclear membrane there, same DNA. But they have very different roles inside of this organism. So it doesn't make sense, in fact, in order for them to even have different structures, they're gonna have to produce different proteins. They're gonna have different enzyme proteins inside of their cytoplasm. And so DNA regulation, one way to think about it is, well, if they have the exact same genome, how do they regulate which of those genes are being transcribed and then translated, and which ones aren't?"}, {"video_title": "Operons and gene regulation in bacteria.mp3", "Sentence": "But they have very different roles inside of this organism. So it doesn't make sense, in fact, in order for them to even have different structures, they're gonna have to produce different proteins. They're gonna have different enzyme proteins inside of their cytoplasm. And so DNA regulation, one way to think about it is, well, if they have the exact same genome, how do they regulate which of those genes are being transcribed and then translated, and which ones aren't? And even if you think about a unicellular organism, right here we have a bacteria. And so it's just one cell, but even it will not want to transcribe and translate all of its genes at the same time. For example, this over here, so this is the bacterial chromosome."}, {"video_title": "Operons and gene regulation in bacteria.mp3", "Sentence": "And so DNA regulation, one way to think about it is, well, if they have the exact same genome, how do they regulate which of those genes are being transcribed and then translated, and which ones aren't? And even if you think about a unicellular organism, right here we have a bacteria. And so it's just one cell, but even it will not want to transcribe and translate all of its genes at the same time. For example, this over here, so this is the bacterial chromosome. This right over here might be a gene involved in the digestion of a certain type of food, if that food is present. This type of, and actually it could even be several genes that are involved in that type of food, and we will actually go into a little bit more detail about when you have several genes that are related and they tend to be transcribed all at once or not transcribed all at once. So maybe that's related to digesting or consuming some type of food."}, {"video_title": "Operons and gene regulation in bacteria.mp3", "Sentence": "For example, this over here, so this is the bacterial chromosome. This right over here might be a gene involved in the digestion of a certain type of food, if that food is present. This type of, and actually it could even be several genes that are involved in that type of food, and we will actually go into a little bit more detail about when you have several genes that are related and they tend to be transcribed all at once or not transcribed all at once. So maybe that's related to digesting or consuming some type of food. Maybe you have some genes over here that are related to some type of stress mechanism. Maybe it needs to go into hibernation sometime. And so if it's not under stress, it does not have to express these genes."}, {"video_title": "Operons and gene regulation in bacteria.mp3", "Sentence": "So maybe that's related to digesting or consuming some type of food. Maybe you have some genes over here that are related to some type of stress mechanism. Maybe it needs to go into hibernation sometime. And so if it's not under stress, it does not have to express these genes. But if it is under stress, it does have to express these. Likewise, if that thing that it needs to digest is around, it needs to transcribe these. If it's not around, it does not need to transcribe it."}, {"video_title": "Operons and gene regulation in bacteria.mp3", "Sentence": "And so if it's not under stress, it does not have to express these genes. But if it is under stress, it does have to express these. Likewise, if that thing that it needs to digest is around, it needs to transcribe these. If it's not around, it does not need to transcribe it. So that's how DNA regulation works, whether you're talking about a eukaryote or a prokaryotic organism. And so what we're gonna do in this video is focus a little bit more, or a lot more, on the prokaryote side, especially we're gonna talk about this bacterium. When we talked about transcription in general in several videos ago and in several videos, we talked about the idea of a promoter, that you have a gene that is a sequence of DNA that's part of the broader chromosome, and we said, okay, that RNA polymerase needs to attach someplace."}, {"video_title": "Operons and gene regulation in bacteria.mp3", "Sentence": "If it's not around, it does not need to transcribe it. So that's how DNA regulation works, whether you're talking about a eukaryote or a prokaryotic organism. And so what we're gonna do in this video is focus a little bit more, or a lot more, on the prokaryote side, especially we're gonna talk about this bacterium. When we talked about transcription in general in several videos ago and in several videos, we talked about the idea of a promoter, that you have a gene that is a sequence of DNA that's part of the broader chromosome, and we said, okay, that RNA polymerase needs to attach someplace. So that RNA polymerase needs to attach someplace. And we called that place that the RNA polymerase attaches, we call that the promoter, and then the polymerase will transcribe the gene. And when we first talked about the idea of a promoter, we said, and this is generally true in eukaryotes, that each promoter is associated with a gene, or each gene has a promoter."}, {"video_title": "Operons and gene regulation in bacteria.mp3", "Sentence": "When we talked about transcription in general in several videos ago and in several videos, we talked about the idea of a promoter, that you have a gene that is a sequence of DNA that's part of the broader chromosome, and we said, okay, that RNA polymerase needs to attach someplace. So that RNA polymerase needs to attach someplace. And we called that place that the RNA polymerase attaches, we call that the promoter, and then the polymerase will transcribe the gene. And when we first talked about the idea of a promoter, we said, and this is generally true in eukaryotes, that each promoter is associated with a gene, or each gene has a promoter. But when we're talking about prokaryotes, and in this case we're talking about this bacterium, it's actually typical to have multiple genes grouped together that have one promoter. So this promoter here, and a promoter is actually called a regulatory DNA sequence. Let me write this down."}, {"video_title": "Operons and gene regulation in bacteria.mp3", "Sentence": "And when we first talked about the idea of a promoter, we said, and this is generally true in eukaryotes, that each promoter is associated with a gene, or each gene has a promoter. But when we're talking about prokaryotes, and in this case we're talking about this bacterium, it's actually typical to have multiple genes grouped together that have one promoter. So this promoter here, and a promoter is actually called a regulatory DNA sequence. Let me write this down. So the promoter, so that's this part right over here, that's the sequence, that is a regulatory, regulatory DNA sequence. Well, that's what the RNA polymerase, which I drew as this big blob, it's a protein here, this big blob, will attach to, and then it will begin to transcribe all of these genes as a bundle. And when you have a promoter associated with multiple genes, that combination of the promoter and the genes, and once again, when I'm talking about the promoters and the genes, I'm talking about sequences of DNA, that combination is called an operon."}, {"video_title": "Operons and gene regulation in bacteria.mp3", "Sentence": "Let me write this down. So the promoter, so that's this part right over here, that's the sequence, that is a regulatory, regulatory DNA sequence. Well, that's what the RNA polymerase, which I drew as this big blob, it's a protein here, this big blob, will attach to, and then it will begin to transcribe all of these genes as a bundle. And when you have a promoter associated with multiple genes, that combination of the promoter and the genes, and once again, when I'm talking about the promoters and the genes, I'm talking about sequences of DNA, that combination is called an operon. This is called an operon. It's a combination of that regulatory DNA sequence, which says, hey, RNA polymerase, bind here so you can start transcribing, and the genes that it essentially promotes the transcription of. And then of course, that transcription process takes that genetic information in DNA, transcribes it into messenger RNA, which can then go with the ribosomes, and we have the whole translation process, this should all be review, to produce the actual proteins that have functions within or even potentially outside of the cell."}, {"video_title": "Operons and gene regulation in bacteria.mp3", "Sentence": "And when you have a promoter associated with multiple genes, that combination of the promoter and the genes, and once again, when I'm talking about the promoters and the genes, I'm talking about sequences of DNA, that combination is called an operon. This is called an operon. It's a combination of that regulatory DNA sequence, which says, hey, RNA polymerase, bind here so you can start transcribing, and the genes that it essentially promotes the transcription of. And then of course, that transcription process takes that genetic information in DNA, transcribes it into messenger RNA, which can then go with the ribosomes, and we have the whole translation process, this should all be review, to produce the actual proteins that have functions within or even potentially outside of the cell. And so we're gonna dig a little bit deeper in is what can enhance this process, make this happen more frequently, or things that might inhibit this process in some way. So as I mentioned before, this is just what I had just drawn we have our big RNA polymerase blob, and this is an oversimplification for what it looks like, attaching to the regulatory DNA sequence, which we call the promoter, and then it will do the transcription, which will produce mRNA, which encodes the information in those genes. But what if we're in an environment where we don't want to transcribe this particular operon, this particular series, or maybe I should say this particular series of genes?"}, {"video_title": "Operons and gene regulation in bacteria.mp3", "Sentence": "And then of course, that transcription process takes that genetic information in DNA, transcribes it into messenger RNA, which can then go with the ribosomes, and we have the whole translation process, this should all be review, to produce the actual proteins that have functions within or even potentially outside of the cell. And so we're gonna dig a little bit deeper in is what can enhance this process, make this happen more frequently, or things that might inhibit this process in some way. So as I mentioned before, this is just what I had just drawn we have our big RNA polymerase blob, and this is an oversimplification for what it looks like, attaching to the regulatory DNA sequence, which we call the promoter, and then it will do the transcription, which will produce mRNA, which encodes the information in those genes. But what if we're in an environment where we don't want to transcribe this particular operon, this particular series, or maybe I should say this particular series of genes? Well then, we might, something in our environment might allow repressors to take action. So what are we talking about a repressor? Well a repressor, a repressor, right over here, you see it attaching to a sequence of DNA after the promoter and so it blocks, it blocks the RNA polymerase from being able to do the transcription."}, {"video_title": "Operons and gene regulation in bacteria.mp3", "Sentence": "But what if we're in an environment where we don't want to transcribe this particular operon, this particular series, or maybe I should say this particular series of genes? Well then, we might, something in our environment might allow repressors to take action. So what are we talking about a repressor? Well a repressor, a repressor, right over here, you see it attaching to a sequence of DNA after the promoter and so it blocks, it blocks the RNA polymerase from being able to do the transcription. And so this right over here, this is a protein that is called the repressor, it's literally repressing the transcription. And the regulatory DNA sequence where it attaches, that is called the operator. So once again, promoter was a regulatory sequence where the RNA polymerase can attach, and then the operator is a regulatory sequence where a repressor can attach and keep that RNA polymerase from actually being able to perform the actual transcription and so this keeps the gene from keeping, continuing to transcribe and then translate these actual genes."}, {"video_title": "Operons and gene regulation in bacteria.mp3", "Sentence": "Well a repressor, a repressor, right over here, you see it attaching to a sequence of DNA after the promoter and so it blocks, it blocks the RNA polymerase from being able to do the transcription. And so this right over here, this is a protein that is called the repressor, it's literally repressing the transcription. And the regulatory DNA sequence where it attaches, that is called the operator. So once again, promoter was a regulatory sequence where the RNA polymerase can attach, and then the operator is a regulatory sequence where a repressor can attach and keep that RNA polymerase from actually being able to perform the actual transcription and so this keeps the gene from keeping, continuing to transcribe and then translate these actual genes. And you might even have extra mechanisms, and you can even think of them as feedback mechanisms or ways to understand the environment, where the repressor, I should say, this protein can only do its job, can only, so let's say that's its repressor, where it can only do its job if it has other molecules that attach to it. So maybe this one can only do its job if it has another molecule attached to it, and in that case, these smaller molecules, these are called co-repressors. Co, co-repressor."}, {"video_title": "Operons and gene regulation in bacteria.mp3", "Sentence": "So once again, promoter was a regulatory sequence where the RNA polymerase can attach, and then the operator is a regulatory sequence where a repressor can attach and keep that RNA polymerase from actually being able to perform the actual transcription and so this keeps the gene from keeping, continuing to transcribe and then translate these actual genes. And you might even have extra mechanisms, and you can even think of them as feedback mechanisms or ways to understand the environment, where the repressor, I should say, this protein can only do its job, can only, so let's say that's its repressor, where it can only do its job if it has other molecules that attach to it. So maybe this one can only do its job if it has another molecule attached to it, and in that case, these smaller molecules, these are called co-repressors. Co, co-repressor. Repressor. And we'll go into more detail when we talk about things like the trypophoron, of how tryptophan, an amino acid, can actually act as a co-repressor. Now over here, we have the other way around, where we want even more transcription."}, {"video_title": "Operons and gene regulation in bacteria.mp3", "Sentence": "Co, co-repressor. Repressor. And we'll go into more detail when we talk about things like the trypophoron, of how tryptophan, an amino acid, can actually act as a co-repressor. Now over here, we have the other way around, where we want even more transcription. In that case, we would have something called, we would have an activator. And this, let me shade it in, this DNA right over here, this would be the regulatory sequence where the activator binds. And so this would be positive feedback."}, {"video_title": "Operons and gene regulation in bacteria.mp3", "Sentence": "Now over here, we have the other way around, where we want even more transcription. In that case, we would have something called, we would have an activator. And this, let me shade it in, this DNA right over here, this would be the regulatory sequence where the activator binds. And so this would be positive feedback. When you have more activators, you're gonna get more transcription, while this would be, and actually, I shouldn't even call it feedback, because that implies that somehow these products produce the activator, or these products produce the repressor, but that's not necessarily the case. It could be, you could imagine that case, but it's not necessarily the case. I should just say that this is repressing, and this is activating."}, {"video_title": "Operons and gene regulation in bacteria.mp3", "Sentence": "And so this would be positive feedback. When you have more activators, you're gonna get more transcription, while this would be, and actually, I shouldn't even call it feedback, because that implies that somehow these products produce the activator, or these products produce the repressor, but that's not necessarily the case. It could be, you could imagine that case, but it's not necessarily the case. I should just say that this is repressing, and this is activating. It's going to make more of the transcription actually happen. And just as we could have co-repressors, small molecules that you could think of as activating the repressor, you can also have small molecules that can turn the activator on. And these small molecules that turn the activator on, these are called inducers."}, {"video_title": "Operons and gene regulation in bacteria.mp3", "Sentence": "I should just say that this is repressing, and this is activating. It's going to make more of the transcription actually happen. And just as we could have co-repressors, small molecules that you could think of as activating the repressor, you can also have small molecules that can turn the activator on. And these small molecules that turn the activator on, these are called inducers. So this right over here, these are inducers. So this protein right here couldn't activate that operon, but now that you have these inducers, and we'll study that a little bit more when we think about the lac operon, this could be a small sugar of some kind, well, then it can turn on the activation. So this right over here is called an inducer."}, {"video_title": "Operons and gene regulation in bacteria.mp3", "Sentence": "And these small molecules that turn the activator on, these are called inducers. So this right over here, these are inducers. So this protein right here couldn't activate that operon, but now that you have these inducers, and we'll study that a little bit more when we think about the lac operon, this could be a small sugar of some kind, well, then it can turn on the activation. So this right over here is called an inducer. So that's just a high-level overview of DNA regulation. As you can imagine, this can get very, very interesting and complex, where you have your repressors and co-repressors and activators and inducers that might be dependent on the environment that the cell is in, what's going on in its broader ecosystem. There's all sorts of feedback and feed-forward loops that might be going on."}, {"video_title": "Gel electrophoresis   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "How long are those fragments? How many base pairs long are they? Well, you might say, well, why don't I just take them out and count them, except for the fact that they're incredibly small and incredibly hard to handle. Even a fairly large fragment of DNA, let's say we're talking about something that's on the order of 5,000 base pairs, well, that's going to be approximately one to two micrometers long if you were to completely stretch it out, and we can't even start to think about how thin the actual diameter is. But lengthwise, the long way, it's only going to be one to two micrometers, which is super duper small. This is one to two thousandths of a millimeter. So that's not going to help us to somehow try to manipulate it physically with our hands or with kind of rough tools."}, {"video_title": "Gel electrophoresis   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "Even a fairly large fragment of DNA, let's say we're talking about something that's on the order of 5,000 base pairs, well, that's going to be approximately one to two micrometers long if you were to completely stretch it out, and we can't even start to think about how thin the actual diameter is. But lengthwise, the long way, it's only going to be one to two micrometers, which is super duper small. This is one to two thousandths of a millimeter. So that's not going to help us to somehow try to manipulate it physically with our hands or with kind of rough tools. So how do we do that? And we could have other vials there. How do we see how long the DNA strands that are sitting in those vials actually are?"}, {"video_title": "Gel electrophoresis   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "So that's not going to help us to somehow try to manipulate it physically with our hands or with kind of rough tools. So how do we do that? And we could have other vials there. How do we see how long the DNA strands that are sitting in those vials actually are? And the technique we're going to use, gel electrophoresis, it actually could be used for DNA strands, it could be used for RNA, it could also be used for proteins, any of these macromolecules, to see how long are those fragments. And so let me write this down. Gel electrophoresis."}, {"video_title": "Gel electrophoresis   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "How do we see how long the DNA strands that are sitting in those vials actually are? And the technique we're going to use, gel electrophoresis, it actually could be used for DNA strands, it could be used for RNA, it could also be used for proteins, any of these macromolecules, to see how long are those fragments. And so let me write this down. Gel electrophoresis. Electrophoresis. And it's called gel electrophoresis because it involves a gel, it involves electric charge, and phoresis is just referring to the fact that we are going to cause the DNA fragments to migrate through a gel because of the charge. So phoresis is referring to the migration or the movement of the actual DNA."}, {"video_title": "Gel electrophoresis   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "Gel electrophoresis. Electrophoresis. And it's called gel electrophoresis because it involves a gel, it involves electric charge, and phoresis is just referring to the fact that we are going to cause the DNA fragments to migrate through a gel because of the charge. So phoresis is referring to the migration or the movement of the actual DNA. So how do we do this? Well, here is our setup right over here. We have our gel that's inside of a, that's embedded in a buffer solution."}, {"video_title": "Gel electrophoresis   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "So phoresis is referring to the migration or the movement of the actual DNA. So how do we do this? Well, here is our setup right over here. We have our gel that's inside of a, that's embedded in a buffer solution. So this gel, the most typical one is agarose gel, that's a polysaccharide that we get from seaweed, and it's literally a gel. It's a gelatinous material. And what we're going to do is, we're going to put, we're going to take samples, so we might take a little sample from this one right over here, and we'll put it in this well right over here, and you can view these wells as little divots in the gel."}, {"video_title": "Gel electrophoresis   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "We have our gel that's inside of a, that's embedded in a buffer solution. So this gel, the most typical one is agarose gel, that's a polysaccharide that we get from seaweed, and it's literally a gel. It's a gelatinous material. And what we're going to do is, we're going to put, we're going to take samples, so we might take a little sample from this one right over here, and we'll put it in this well right over here, and you can view these wells as little divots in the gel. You could take a little sample from here and put it into this well, and then you could put a sample from here, and you could put it in that well. And it's going to be bathed inside this buffer. So you can see the buffer I drew this fluid, and that's really just water with some salts in it, and the buffer is going to keep the pH from going too far out of bounds as we place a charge across this entire thing, because if the pH gets too far in the basic or acidic side, it might actually affect the DNA or affect the charge on the DNA."}, {"video_title": "Gel electrophoresis   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "And what we're going to do is, we're going to put, we're going to take samples, so we might take a little sample from this one right over here, and we'll put it in this well right over here, and you can view these wells as little divots in the gel. You could take a little sample from here and put it into this well, and then you could put a sample from here, and you could put it in that well. And it's going to be bathed inside this buffer. So you can see the buffer I drew this fluid, and that's really just water with some salts in it, and the buffer is going to keep the pH from going too far out of bounds as we place a charge across this entire thing, because if the pH gets too far in the basic or acidic side, it might actually affect the DNA or affect the charge on the DNA. And what we're going to do is, we're going to put a charge across this whole setup, where the side where the wells are, where we're going to place the DNA, that's going to be where we're going to put the negative electrode. So that's our negative electrode there. And the other end is going to be our positive electrode."}, {"video_title": "Gel electrophoresis   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "So you can see the buffer I drew this fluid, and that's really just water with some salts in it, and the buffer is going to keep the pH from going too far out of bounds as we place a charge across this entire thing, because if the pH gets too far in the basic or acidic side, it might actually affect the DNA or affect the charge on the DNA. And what we're going to do is, we're going to put a charge across this whole setup, where the side where the wells are, where we're going to place the DNA, that's going to be where we're going to put the negative electrode. So that's our negative electrode there. And the other end is going to be our positive electrode. And we're going to use the fact that DNA has a negative charge at the typical pHs, or at the pHs that we are going to be dealing with. And we could go back into previous videos, and we can see it right over here. You see these negative charges on our phosphate backbone."}, {"video_title": "Gel electrophoresis   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "And the other end is going to be our positive electrode. And we're going to use the fact that DNA has a negative charge at the typical pHs, or at the pHs that we are going to be dealing with. And we could go back into previous videos, and we can see it right over here. You see these negative charges on our phosphate backbone. And so what is going to happen? What is going to happen once we connect both of these to a power source, and then this side is negative and this side is positive? Well, the DNA is going to want to migrate."}, {"video_title": "Gel electrophoresis   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "You see these negative charges on our phosphate backbone. And so what is going to happen? What is going to happen once we connect both of these to a power source, and then this side is negative and this side is positive? Well, the DNA is going to want to migrate. Now, let's think about what will happen. Will shorter things migrate further, or will longer things migrate further? Well, you might say, well, longer things are going to have more negative charge, so maybe they go farther away."}, {"video_title": "Gel electrophoresis   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "Well, the DNA is going to want to migrate. Now, let's think about what will happen. Will shorter things migrate further, or will longer things migrate further? Well, you might say, well, longer things are going to have more negative charge, so maybe they go farther away. But then you also have to remember that they're also moving more mass. So their charge per mass is going to be the same, regardless of length. And so what determines how far something gets, how much it migrates over a certain amount of time, is how small it is."}, {"video_title": "Gel electrophoresis   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "Well, you might say, well, longer things are going to have more negative charge, so maybe they go farther away. But then you also have to remember that they're also moving more mass. So their charge per mass is going to be the same, regardless of length. And so what determines how far something gets, how much it migrates over a certain amount of time, is how small it is. Remember, we have this agarose gel. And people are still studying the exact mechanism of how this DNA, or these macromolecules, actually migrate through the polysaccharide. But if you imagine this polysaccharide as kind of this mesh, this net, this sieve, well, smaller things are going to be able to go through the gaps easier than the larger things."}, {"video_title": "Gel electrophoresis   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "And so what determines how far something gets, how much it migrates over a certain amount of time, is how small it is. Remember, we have this agarose gel. And people are still studying the exact mechanism of how this DNA, or these macromolecules, actually migrate through the polysaccharide. But if you imagine this polysaccharide as kind of this mesh, this net, this sieve, well, smaller things are going to be able to go through the gaps easier than the larger things. And so if you let some time pass, if you let some time pass, some of the DNA, let's say this DNA gets around there, let's say, and I'm just color, you actually wouldn't see these colors. Let's say this DNA gets around that far, so it doesn't get as far. Let's say that this DNA doesn't migrate."}, {"video_title": "Gel electrophoresis   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "But if you imagine this polysaccharide as kind of this mesh, this net, this sieve, well, smaller things are going to be able to go through the gaps easier than the larger things. And so if you let some time pass, if you let some time pass, some of the DNA, let's say this DNA gets around there, let's say, and I'm just color, you actually wouldn't see these colors. Let's say this DNA gets around that far, so it doesn't get as far. Let's say that this DNA doesn't migrate. Let's say it has some that migrates that far, and let's say it has some that migrates that far. And so if you just saw this, you wait some amount of time, and you were to come back, and you were to see this migration, you were to see this migration occur, and the longer you wait, the further these things are gonna get. In fact, if you wait too long, they're gonna fall off all the way over the other edge."}, {"video_title": "Gel electrophoresis   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "Let's say that this DNA doesn't migrate. Let's say it has some that migrates that far, and let's say it has some that migrates that far. And so if you just saw this, you wait some amount of time, and you were to come back, and you were to see this migration, you were to see this migration occur, and the longer you wait, the further these things are gonna get. In fact, if you wait too long, they're gonna fall off all the way over the other edge. Is, if you just saw this, you'd say, okay, well, this strand right over here, these must be smaller DNA molecules. They must be shorter. These must be a little bit longer, and these must be even longer than that."}, {"video_title": "Gel electrophoresis   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "In fact, if you wait too long, they're gonna fall off all the way over the other edge. Is, if you just saw this, you'd say, okay, well, this strand right over here, these must be smaller DNA molecules. They must be shorter. These must be a little bit longer, and these must be even longer than that. And this grouping right over here is going to be the longest of all, so this was a mixture of some longer strands, and still longer ones, but not quite as long. And for example, maybe there are some really short strands. Maybe there are some really short strands in that, what I'm drawing as, what I'm drawing as, that orange group right over here."}, {"video_title": "Gel electrophoresis   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "These must be a little bit longer, and these must be even longer than that. And this grouping right over here is going to be the longest of all, so this was a mixture of some longer strands, and still longer ones, but not quite as long. And for example, maybe there are some really short strands. Maybe there are some really short strands in that, what I'm drawing as, what I'm drawing as, that orange group right over here. So what I just did right over here, this could tell you the relative length of these strands, but how would you actually measure them? Well, that's where you can go find standardized solutions, which we call a DNA ladder. So let's say you go get the DNA ladder."}, {"video_title": "Gel electrophoresis   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "Maybe there are some really short strands in that, what I'm drawing as, what I'm drawing as, that orange group right over here. So what I just did right over here, this could tell you the relative length of these strands, but how would you actually measure them? Well, that's where you can go find standardized solutions, which we call a DNA ladder. So let's say you go get the DNA ladder. I'm gonna draw it in pink. So you literally could buy this. You could even buy it online."}, {"video_title": "Gel electrophoresis   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "So let's say you go get the DNA ladder. I'm gonna draw it in pink. So you literally could buy this. You could even buy it online. And the standard solution, let's say it separates like this. So it separates like that, goes there. Let's say some of it goes like there, and some of it goes like there."}, {"video_title": "Gel electrophoresis   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "You could even buy it online. And the standard solution, let's say it separates like this. So it separates like that, goes there. Let's say some of it goes like there, and some of it goes like there. Well, you would be able to know from the labeling, or whichever one you choose to buy, that this grouping here, this is all of the DNA that is 5,000 base pairs, let's say. Let's say this right over here is 1,500 base pairs. And let's say this over here is, let's say this over here is 500 base pairs long."}, {"video_title": "Gel electrophoresis   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "Let's say some of it goes like there, and some of it goes like there. Well, you would be able to know from the labeling, or whichever one you choose to buy, that this grouping here, this is all of the DNA that is 5,000 base pairs, let's say. Let's say this right over here is 1,500 base pairs. And let's say this over here is, let's say this over here is 500 base pairs long. And so now you can use this DNA ladder, these standardized ones, to gauge how long, how many base pairs these are. So you say, okay, this blue one here, this is a bunch of DNA that's a little bit longer than 500 base pairs, but it's shorter than 1,500 base pairs. You can see this green one here."}, {"video_title": "Gel electrophoresis   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "And let's say this over here is, let's say this over here is 500 base pairs long. And so now you can use this DNA ladder, these standardized ones, to gauge how long, how many base pairs these are. So you say, okay, this blue one here, this is a bunch of DNA that's a little bit longer than 500 base pairs, but it's shorter than 1,500 base pairs. You can see this green one here. Well, it's a little bit longer than 1,500 base pairs. It didn't migrate quite as far as this big bundle of 1,500 base pairs that it did. And so then you can get a better approximation."}, {"video_title": "Gel electrophoresis   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "You can see this green one here. Well, it's a little bit longer than 1,500 base pairs. It didn't migrate quite as far as this big bundle of 1,500 base pairs that it did. And so then you can get a better approximation. And you can choose your ladder based on what you think you are going to find there, what you're actually going to look for. Now, the other thing to appreciate is, when you see the DNA having migrated this far, you might say, okay, is this one DNA strand? Is that one DNA strand that I'm looking at?"}, {"video_title": "Gel electrophoresis   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "And so then you can get a better approximation. And you can choose your ladder based on what you think you are going to find there, what you're actually going to look for. Now, the other thing to appreciate is, when you see the DNA having migrated this far, you might say, okay, is this one DNA strand? Is that one DNA strand that I'm looking at? And just going back to the measurements, no. That is many, many, many, many DNAs that you're looking at. And they're not all stretched out like that."}, {"video_title": "Gel electrophoresis   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "Is that one DNA strand that I'm looking at? And just going back to the measurements, no. That is many, many, many, many DNAs that you're looking at. And they're not all stretched out like that. Remember, even something that is 5,000 base pairs long is only going to be one to two micrometers if you stretch it out. So you wouldn't even be able to see it. It's a thousandth of a millimeter."}, {"video_title": "Gel electrophoresis   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "And they're not all stretched out like that. Remember, even something that is 5,000 base pairs long is only going to be one to two micrometers if you stretch it out. So you wouldn't even be able to see it. It's a thousandth of a millimeter. You wouldn't even be able to see it. So this is many, many, many molecules of DNA is migrating that far. And they would have to be that small to be able to migrate through that polysaccharide gel."}, {"video_title": "Gel electrophoresis   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "It's a thousandth of a millimeter. You wouldn't even be able to see it. So this is many, many, many molecules of DNA is migrating that far. And they would have to be that small to be able to migrate through that polysaccharide gel. Now, the last thing you're probably saying is, okay, wait, but how am I even seeing it over here? How do I actually see this DNA, especially if they're these super, super small molecules? And the answer is you put some type of marker on the DNA that will make them visible, some type of dye or something that might become fluorescent."}, {"video_title": "Gel electrophoresis   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "And they would have to be that small to be able to migrate through that polysaccharide gel. Now, the last thing you're probably saying is, okay, wait, but how am I even seeing it over here? How do I actually see this DNA, especially if they're these super, super small molecules? And the answer is you put some type of marker on the DNA that will make them visible, some type of dye or something that might become fluorescent. And one of the typical things that people often use is ethidium bromide. And ethidium bromide is called an intercalating agent. And it's a molecule, you can see the ethidium right over here."}, {"video_title": "Gel electrophoresis   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "And the answer is you put some type of marker on the DNA that will make them visible, some type of dye or something that might become fluorescent. And one of the typical things that people often use is ethidium bromide. And ethidium bromide is called an intercalating agent. And it's a molecule, you can see the ethidium right over here. These are two DNA, two backbones of DNA. You can see the base pairs bonding here. And then this right over here, that is ethidium that has fit itself."}, {"video_title": "Gel electrophoresis   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "And it's a molecule, you can see the ethidium right over here. These are two DNA, two backbones of DNA. You can see the base pairs bonding here. And then this right over here, that is ethidium that has fit itself. That's why we call it intercalating. It has fit itself in between the rungs of the ladder. And when it does so inside of DNA, it actually becomes fluorescent when you apply UV light to it."}, {"video_title": "Gel electrophoresis   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "And then this right over here, that is ethidium that has fit itself. That's why we call it intercalating. It has fit itself in between the rungs of the ladder. And when it does so inside of DNA, it actually becomes fluorescent when you apply UV light to it. So if you put this ethidium bromide into all of your DNA right over here, and then as it migrates, and then if you were to turn on the UV light, it would become fluorescent. And you would actually see these things. And so if you wanted to see what it actually would look like in real life, well, this is what it would look like if you were to look at it straight on."}, {"video_title": "Gel electrophoresis   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "And when it does so inside of DNA, it actually becomes fluorescent when you apply UV light to it. So if you put this ethidium bromide into all of your DNA right over here, and then as it migrates, and then if you were to turn on the UV light, it would become fluorescent. And you would actually see these things. And so if you wanted to see what it actually would look like in real life, well, this is what it would look like if you were to look at it straight on. Where this would have been a well, let me make it a little bit easier to read. So right over here would have been the well where you would put the DNA ladder. And it would come up with standardized measurements."}, {"video_title": "Gel electrophoresis   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "And so if you wanted to see what it actually would look like in real life, well, this is what it would look like if you were to look at it straight on. Where this would have been a well, let me make it a little bit easier to read. So right over here would have been the well where you would put the DNA ladder. And it would come up with standardized measurements. Maybe that's our 5,000 base pairs. This right over here is our 1,500 base pairs. And this right over here is our 500 base pairs."}, {"video_title": "Gel electrophoresis   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "And it would come up with standardized measurements. Maybe that's our 5,000 base pairs. This right over here is our 1,500 base pairs. And this right over here is our 500 base pairs. And then let's say you had some solution of some other DNA. And you wait a little while, and you see, look, it migrated not quite as far as the 500 base pairs. So it must be a little bit, this must be a bundle of things a little bit longer than 500 base pairs, but for sure, a lot shorter than 1,500 base pairs."}, {"video_title": "Gel electrophoresis   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "And this right over here is our 500 base pairs. And then let's say you had some solution of some other DNA. And you wait a little while, and you see, look, it migrated not quite as far as the 500 base pairs. So it must be a little bit, this must be a bundle of things a little bit longer than 500 base pairs, but for sure, a lot shorter than 1,500 base pairs. And once again, it doesn't have to have just one fragment length. You could have had another group that was maybe right at 1,500 base pairs. And you've probably seen this."}, {"video_title": "Gel electrophoresis   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "So it must be a little bit, this must be a bundle of things a little bit longer than 500 base pairs, but for sure, a lot shorter than 1,500 base pairs. And once again, it doesn't have to have just one fragment length. You could have had another group that was maybe right at 1,500 base pairs. And you've probably seen this. Whenever you see people talking about genetic analysis and things like this, you're often seeing people looking at one of these readouts from gel electrophoresis. So now you know what's actually going on here. This isn't a strand of DNA."}, {"video_title": "Gel electrophoresis   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "And you've probably seen this. Whenever you see people talking about genetic analysis and things like this, you're often seeing people looking at one of these readouts from gel electrophoresis. So now you know what's actually going on here. This isn't a strand of DNA. This is a bunch of DNA that has been tagged with some type of a dye or the ethidium bromide or something like that. And it's a bunch of those molecules, and they've migrated based on the charge. They're trying to get away from that negative charge to the positive charge."}, {"video_title": "Osmosis   Membranes and transport   Biology   Khan Academy.mp3", "Sentence": "Now what do I mean by a semi-permeable membrane? That means they allow some things to go through and not other things. And let's say this semi-permeable membrane, it does allow water molecules to pass. And in a few seconds we'll talk about what it does not allow to pass, which makes it semi-permeable. But let's just think about what would happen if we just had water molecules on either side. Well, we've already talked about it in the videos on diffusion. The water molecules, since we have an equal concentration on either side, the probability that one of these water molecules goes this way in a certain amount of time is equal to the probability that a water molecule goes from right to left in the same amount of time."}, {"video_title": "Osmosis   Membranes and transport   Biology   Khan Academy.mp3", "Sentence": "And in a few seconds we'll talk about what it does not allow to pass, which makes it semi-permeable. But let's just think about what would happen if we just had water molecules on either side. Well, we've already talked about it in the videos on diffusion. The water molecules, since we have an equal concentration on either side, the probability that one of these water molecules goes this way in a certain amount of time is equal to the probability that a water molecule goes from right to left in the same amount of time. And that's because we have equal concentrations. And these things are all bouncing around in all different ways. They all have, they all are, they all have different velocities."}, {"video_title": "Osmosis   Membranes and transport   Biology   Khan Academy.mp3", "Sentence": "The water molecules, since we have an equal concentration on either side, the probability that one of these water molecules goes this way in a certain amount of time is equal to the probability that a water molecule goes from right to left in the same amount of time. And that's because we have equal concentrations. And these things are all bouncing around in all different ways. They all have, they all are, they all have different velocities. They have different speeds and in different directions. And we just have to think about it probabilistically. The probability of going from left to right through one of these gaps is going to be equal to the probability of going right to left in any given period of time."}, {"video_title": "Osmosis   Membranes and transport   Biology   Khan Academy.mp3", "Sentence": "They all have, they all are, they all have different velocities. They have different speeds and in different directions. And we just have to think about it probabilistically. The probability of going from left to right through one of these gaps is going to be equal to the probability of going right to left in any given period of time. But now let's make this interesting. Let's treat our water as a solvent and let's put some solute in it. So let's dissolve some solute."}, {"video_title": "Osmosis   Membranes and transport   Biology   Khan Academy.mp3", "Sentence": "The probability of going from left to right through one of these gaps is going to be equal to the probability of going right to left in any given period of time. But now let's make this interesting. Let's treat our water as a solvent and let's put some solute in it. So let's dissolve some solute. So let's throw some solute particles here. And I'm gonna make it, make them bigger so you can see they would physically have trouble passing through these gaps. There's other ways where you could have semipermeable membranes that use charge to allow certain things to pass through and not others."}, {"video_title": "Osmosis   Membranes and transport   Biology   Khan Academy.mp3", "Sentence": "So let's dissolve some solute. So let's throw some solute particles here. And I'm gonna make it, make them bigger so you can see they would physically have trouble passing through these gaps. There's other ways where you could have semipermeable membranes that use charge to allow certain things to pass through and not others. But it's easier to visualize the size. And thinking about the membrane as only allowing certain things of certain size to pass through. So let's throw some solute there."}, {"video_title": "Osmosis   Membranes and transport   Biology   Khan Academy.mp3", "Sentence": "There's other ways where you could have semipermeable membranes that use charge to allow certain things to pass through and not others. But it's easier to visualize the size. And thinking about the membrane as only allowing certain things of certain size to pass through. So let's throw some solute there. And actually I'll throw a little bit of solute here too. I'll do one or two particles right over here. But I'm gonna do many more."}, {"video_title": "Osmosis   Membranes and transport   Biology   Khan Academy.mp3", "Sentence": "So let's throw some solute there. And actually I'll throw a little bit of solute here too. I'll do one or two particles right over here. But I'm gonna do many more. I'm gonna do many more over there on the right hand side. So we have a higher concentration of solute on the right hand side. And this is a semipermeable membrane."}, {"video_title": "Osmosis   Membranes and transport   Biology   Khan Academy.mp3", "Sentence": "But I'm gonna do many more. I'm gonna do many more over there on the right hand side. So we have a higher concentration of solute on the right hand side. And this is a semipermeable membrane. And you can see even from the size where I drew these gaps, these big particles aren't going to be able to go through the membrane. They aren't going to be able to diffuse. If they were allowed to diffuse, then they would just go down their concentration gradient."}, {"video_title": "Osmosis   Membranes and transport   Biology   Khan Academy.mp3", "Sentence": "And this is a semipermeable membrane. And you can see even from the size where I drew these gaps, these big particles aren't going to be able to go through the membrane. They aren't going to be able to diffuse. If they were allowed to diffuse, then they would just go down their concentration gradient. And in any given moment of time, you would have a higher chance of one of these big particles moving from the right to the left than from the left to the right. Because you just have more on the right hand side. But this is a semipermeable membrane."}, {"video_title": "Osmosis   Membranes and transport   Biology   Khan Academy.mp3", "Sentence": "If they were allowed to diffuse, then they would just go down their concentration gradient. And in any given moment of time, you would have a higher chance of one of these big particles moving from the right to the left than from the left to the right. Because you just have more on the right hand side. But this is a semipermeable membrane. And these things aren't just going to be allowed to naturally diffuse. Now all of these big particles, they all have their own unique velocities. So they all have their unique velocities."}, {"video_title": "Osmosis   Membranes and transport   Biology   Khan Academy.mp3", "Sentence": "But this is a semipermeable membrane. And these things aren't just going to be allowed to naturally diffuse. Now all of these big particles, they all have their own unique velocities. So they all have their unique velocities. What do we think is going to happen? Well let's just think about the problem. We know that the big particles can't diffuse from one side to another."}, {"video_title": "Osmosis   Membranes and transport   Biology   Khan Academy.mp3", "Sentence": "So they all have their unique velocities. What do we think is going to happen? Well let's just think about the problem. We know that the big particles can't diffuse from one side to another. But what's going to happen to the water molecules? Well the water molecules on the left hand side, they're not gonna be stopped. If they're bouncing in the right way, they can bounce from the left to the right, or they can move from the left to the right through one of these gaps."}, {"video_title": "Osmosis   Membranes and transport   Biology   Khan Academy.mp3", "Sentence": "We know that the big particles can't diffuse from one side to another. But what's going to happen to the water molecules? Well the water molecules on the left hand side, they're not gonna be stopped. If they're bouncing in the right way, they can bounce from the left to the right, or they can move from the left to the right through one of these gaps. But what about the ones on the right side? Well if they're the just right conditions, if they're the just right conditions, maybe this character could move through this. So you're definitely going to have water molecules going back and forth."}, {"video_title": "Osmosis   Membranes and transport   Biology   Khan Academy.mp3", "Sentence": "If they're bouncing in the right way, they can bounce from the left to the right, or they can move from the left to the right through one of these gaps. But what about the ones on the right side? Well if they're the just right conditions, if they're the just right conditions, maybe this character could move through this. So you're definitely going to have water molecules going back and forth. But I'd argue that the ones on the right hand side, there's a lower probability of water molecules from the right hand side moving to the left as from the left hand side moving to the right. And why is that? Well there's all this interference at play from these big molecules that aren't able to diffuse."}, {"video_title": "Osmosis   Membranes and transport   Biology   Khan Academy.mp3", "Sentence": "So you're definitely going to have water molecules going back and forth. But I'd argue that the ones on the right hand side, there's a lower probability of water molecules from the right hand side moving to the left as from the left hand side moving to the right. And why is that? Well there's all this interference at play from these big molecules that aren't able to diffuse. These are gonna be bouncing around. Sometimes they're going to be even, sometimes you could imagine them even blocking, they're going to be blocking the approach to these openings. If this membrane wasn't here, they wouldn't block the approach, they would just keep on going."}, {"video_title": "Osmosis   Membranes and transport   Biology   Khan Academy.mp3", "Sentence": "Well there's all this interference at play from these big molecules that aren't able to diffuse. These are gonna be bouncing around. Sometimes they're going to be even, sometimes you could imagine them even blocking, they're going to be blocking the approach to these openings. If this membrane wasn't here, they wouldn't block the approach, they would just keep on going. But since that membrane is there, they might block it or they might ricochet off. And while they ricochet off, they might push on some water molecules. They might push on some water molecules going in this direction right over there."}, {"video_title": "Osmosis   Membranes and transport   Biology   Khan Academy.mp3", "Sentence": "If this membrane wasn't here, they wouldn't block the approach, they would just keep on going. But since that membrane is there, they might block it or they might ricochet off. And while they ricochet off, they might push on some water molecules. They might push on some water molecules going in this direction right over there. And so an argument can be made that these water molecules, some of them will still make it from right to left, but you have a lower probability of going from right to left as you have from going to left to right. And so because of this, you would have a net inflow of water from this area where you have a low solute concentration. Remember the solute is the thing that's dissolved in the water."}, {"video_title": "Osmosis   Membranes and transport   Biology   Khan Academy.mp3", "Sentence": "They might push on some water molecules going in this direction right over there. And so an argument can be made that these water molecules, some of them will still make it from right to left, but you have a lower probability of going from right to left as you have from going to left to right. And so because of this, you would have a net inflow of water from this area where you have a low solute concentration. Remember the solute is the thing that's dissolved in the water. And in general, we always consider the solvent to be whatever there's more of. In this case, it's water, and water is probably the most typical solvent. And the solute is whatever there's less of."}, {"video_title": "Osmosis   Membranes and transport   Biology   Khan Academy.mp3", "Sentence": "Remember the solute is the thing that's dissolved in the water. And in general, we always consider the solvent to be whatever there's more of. In this case, it's water, and water is probably the most typical solvent. And the solute is whatever there's less of. So the solute is dissolved in the solvent. And so we have a net migration of the water molecules from this solution that has a low solute concentration to one that has a higher solute concentration. And this phenomenon we call osmosis."}, {"video_title": "Osmosis   Membranes and transport   Biology   Khan Academy.mp3", "Sentence": "And the solute is whatever there's less of. So the solute is dissolved in the solvent. And so we have a net migration of the water molecules from this solution that has a low solute concentration to one that has a higher solute concentration. And this phenomenon we call osmosis. We call this osmosis. And there's other arguments for osmosis. And it's something that we've observed many, many, many times."}, {"video_title": "Osmosis   Membranes and transport   Biology   Khan Academy.mp3", "Sentence": "And this phenomenon we call osmosis. We call this osmosis. And there's other arguments for osmosis. And it's something that we've observed many, many, many times. If you put something that's used to fresh water and it has skin or it has membranes that allows water to pass through it, put it in salt water. You know, kind of the famous things like slugs will not do well in the presence of salt because the water inside the slug will do exactly what is happening in this diagram. Now, this mechanism that I just talked about, that the molecules that cannot pass through the membrane, blocking the water molecules from going right to left, ricocheting off and maybe causing the ones that are on the right side to maybe move in this direction when they bounce into them, that's one explanation."}, {"video_title": "Osmosis   Membranes and transport   Biology   Khan Academy.mp3", "Sentence": "And it's something that we've observed many, many, many times. If you put something that's used to fresh water and it has skin or it has membranes that allows water to pass through it, put it in salt water. You know, kind of the famous things like slugs will not do well in the presence of salt because the water inside the slug will do exactly what is happening in this diagram. Now, this mechanism that I just talked about, that the molecules that cannot pass through the membrane, blocking the water molecules from going right to left, ricocheting off and maybe causing the ones that are on the right side to maybe move in this direction when they bounce into them, that's one explanation. Another possibility is many times the solute that's being dissolved in water has some charge associated with it. So when we think of, say, regular table salt, you have sodium ions. Regular table salt is sodium chloride."}, {"video_title": "Osmosis   Membranes and transport   Biology   Khan Academy.mp3", "Sentence": "Now, this mechanism that I just talked about, that the molecules that cannot pass through the membrane, blocking the water molecules from going right to left, ricocheting off and maybe causing the ones that are on the right side to maybe move in this direction when they bounce into them, that's one explanation. Another possibility is many times the solute that's being dissolved in water has some charge associated with it. So when we think of, say, regular table salt, you have sodium ions. Regular table salt is sodium chloride. But when you put it in the water, you have sodium ions and you have chloride ions. And you have chloride ions. These are negative, so the chlorides are negative, the sodium ions are positive."}, {"video_title": "Osmosis   Membranes and transport   Biology   Khan Academy.mp3", "Sentence": "Regular table salt is sodium chloride. But when you put it in the water, you have sodium ions and you have chloride ions. And you have chloride ions. These are negative, so the chlorides are negative, the sodium ions are positive. And above and beyond doing some of the mechanical blockage that I just talked about, there's also the idea that possibly that because they are ionic, they have charge, and water has partial charges, they also might stick to more of the water. So the waters that stick to them aren't going to be available to move through the membrane. And so what do I mean by the water's going to stick to them?"}, {"video_title": "Osmosis   Membranes and transport   Biology   Khan Academy.mp3", "Sentence": "These are negative, so the chlorides are negative, the sodium ions are positive. And above and beyond doing some of the mechanical blockage that I just talked about, there's also the idea that possibly that because they are ionic, they have charge, and water has partial charges, they also might stick to more of the water. So the waters that stick to them aren't going to be available to move through the membrane. And so what do I mean by the water's going to stick to them? Well, when we think about a water molecule, it's an oxygen, and on the oxygen end you have a partially negative charge, and then you have two hydrogens. Two, excuse me, I'll write it this way. You have two hydrogens right over here."}, {"video_title": "Osmosis   Membranes and transport   Biology   Khan Academy.mp3", "Sentence": "And so what do I mean by the water's going to stick to them? Well, when we think about a water molecule, it's an oxygen, and on the oxygen end you have a partially negative charge, and then you have two hydrogens. Two, excuse me, I'll write it this way. You have two hydrogens right over here. There's a partially positive charge. And so they're going to be, this oxygen end, away from the hydrogens, is going to be attracted to the sodium molecule, and so it's gonna be less, so if the sodium molecule can't make it through, this guy's gonna wanna stick to the sodium molecule. And so you can kind of imagine all of these water molecules sticking to the sodium molecule, which would make it less likely that these would pass from right to left than the ones that are passing from left to right."}, {"video_title": "Osmosis   Membranes and transport   Biology   Khan Academy.mp3", "Sentence": "You have two hydrogens right over here. There's a partially positive charge. And so they're going to be, this oxygen end, away from the hydrogens, is going to be attracted to the sodium molecule, and so it's gonna be less, so if the sodium molecule can't make it through, this guy's gonna wanna stick to the sodium molecule. And so you can kind of imagine all of these water molecules sticking to the sodium molecule, which would make it less likely that these would pass from right to left than the ones that are passing from left to right. Similarly, if you have a negatively charged ion like this, well, then you could orient the water the other way, where the partially positive charged hydrogen ends are going to be attracted to the chloride ion right over here. And since the chloride ion might not be able to get through, well, then these molecules that are stuck to it are going to be less likely to flow through. These molecules are gonna be more attracted to the chloride or more attracted to the sodium ions than they would be to other water molecules that only have partial charges."}, {"video_title": "Osmosis   Membranes and transport   Biology   Khan Academy.mp3", "Sentence": "And so you can kind of imagine all of these water molecules sticking to the sodium molecule, which would make it less likely that these would pass from right to left than the ones that are passing from left to right. Similarly, if you have a negatively charged ion like this, well, then you could orient the water the other way, where the partially positive charged hydrogen ends are going to be attracted to the chloride ion right over here. And since the chloride ion might not be able to get through, well, then these molecules that are stuck to it are going to be less likely to flow through. These molecules are gonna be more attracted to the chloride or more attracted to the sodium ions than they would be to other water molecules that only have partial charges. These have full charges. So if these can't get through, well, then maybe it's a lower probability that these are going to get through as well. But the combined effects of all of these, and I'd love for any of y'all to point me to a nice simulation, or maybe we'll create one on the Khan Academy Computer Science Program, to show this, is that you're going to have a higher probability of the water molecules over here going from left to right than the water molecules over here going right to left from mechanical blockage, and or these big molecules ricocheting off and pushing them in the wrong direction, or because they're just stuck to the big molecules because the big molecules are charged."}, {"video_title": "Electrochemical gradients and secondary active transport   Khan Academy.mp3", "Sentence": "And it does that by pumping, actively pumping, three sodium ions out for every two potassium ions it pumps in, and that by itself, that ratio of three to two by itself doesn't establish the full resting membrane potential, but then the potassium ions are allowed to start diffusing down their concentration gradient from the inside back to the outside. And of course, there's a balancing force there, or a balancing factor there, and that's the charge. Because if the outside is more positive than the inside, a positively charged ion, which the potassium ions are, well, they're not gonna wanna go up here so much because of their charge. It's more positive here than it is over here. They'd actually wanna go back. But their concentration gradient, they're gonna be bumping into the bottom of this channel more than the top, and so you're going to have a balance. They're going to start diffusing through, but you're not going to have equal concentrations because the charge is going to keep them back here."}, {"video_title": "Electrochemical gradients and secondary active transport   Khan Academy.mp3", "Sentence": "It's more positive here than it is over here. They'd actually wanna go back. But their concentration gradient, they're gonna be bumping into the bottom of this channel more than the top, and so you're going to have a balance. They're going to start diffusing through, but you're not going to have equal concentrations because the charge is going to keep them back here. But what about the sodium ions? The sodium ions are getting more and more concentrated up here, and up here is getting more and more positive. If the sodium ions were left to their own devices, if there was no membrane over here, they would naturally, if we just looked at the concentration gradient, they would naturally want to diffuse down."}, {"video_title": "Electrochemical gradients and secondary active transport   Khan Academy.mp3", "Sentence": "They're going to start diffusing through, but you're not going to have equal concentrations because the charge is going to keep them back here. But what about the sodium ions? The sodium ions are getting more and more concentrated up here, and up here is getting more and more positive. If the sodium ions were left to their own devices, if there was no membrane over here, they would naturally, if we just looked at the concentration gradient, they would naturally want to diffuse down. We have a high concentration over here. We have a low concentration over there. So if there was no membrane, then they would just naturally diffuse from high to low, that's their concentration gradient."}, {"video_title": "Electrochemical gradients and secondary active transport   Khan Academy.mp3", "Sentence": "If the sodium ions were left to their own devices, if there was no membrane over here, they would naturally, if we just looked at the concentration gradient, they would naturally want to diffuse down. We have a high concentration over here. We have a low concentration over there. So if there was no membrane, then they would just naturally diffuse from high to low, that's their concentration gradient. And also if there was no membrane, we've already talked about it being much more positive on this side than it is on this side. Or you could say we have a positive potential difference between here and here. So the positively charged ions, like the sodiums up here, would want to go down because of their charge."}, {"video_title": "Electrochemical gradients and secondary active transport   Khan Academy.mp3", "Sentence": "So if there was no membrane, then they would just naturally diffuse from high to low, that's their concentration gradient. And also if there was no membrane, we've already talked about it being much more positive on this side than it is on this side. Or you could say we have a positive potential difference between here and here. So the positively charged ions, like the sodiums up here, would want to go down because of their charge. And so there's two reasons why they would want to go from this side of the membrane to that side of the membrane, their concentration gradient and their charge, the electric potential. There's this potential energy of them wanting to get away from all the positive charges. And so that combined motivation for the sodium ions to go in that direction, we call that the electrochemical gradient."}, {"video_title": "Electrochemical gradients and secondary active transport   Khan Academy.mp3", "Sentence": "So the positively charged ions, like the sodiums up here, would want to go down because of their charge. And so there's two reasons why they would want to go from this side of the membrane to that side of the membrane, their concentration gradient and their charge, the electric potential. There's this potential energy of them wanting to get away from all the positive charges. And so that combined motivation for the sodium ions to go in that direction, we call that the electrochemical gradient. Electrochemical gradient. And I already said it once, but I'll say it again. It's a combination of the electric gradient and the chemical gradient."}, {"video_title": "Electrochemical gradients and secondary active transport   Khan Academy.mp3", "Sentence": "And so that combined motivation for the sodium ions to go in that direction, we call that the electrochemical gradient. Electrochemical gradient. And I already said it once, but I'll say it again. It's a combination of the electric gradient and the chemical gradient. The chemical gradient, you have higher concentration here, lower here, you would want to diffuse down. More things are gonna bump on this side than on this side, so you're gonna have a net flow down if you didn't have this membrane here. And then when you think about the electric potential, more positive on this side than this side, so positive ions would want to go down."}, {"video_title": "Electrochemical gradients and secondary active transport   Khan Academy.mp3", "Sentence": "It's a combination of the electric gradient and the chemical gradient. The chemical gradient, you have higher concentration here, lower here, you would want to diffuse down. More things are gonna bump on this side than on this side, so you're gonna have a net flow down if you didn't have this membrane here. And then when you think about the electric potential, more positive on this side than this side, so positive ions would want to go down. And so you could view this gradient as a source of potential energy. And cells, in fact, use this gradient. In fact, the sodium electrochemical gradient as a source of energy."}, {"video_title": "Electrochemical gradients and secondary active transport   Khan Academy.mp3", "Sentence": "And then when you think about the electric potential, more positive on this side than this side, so positive ions would want to go down. And so you could view this gradient as a source of potential energy. And cells, in fact, use this gradient. In fact, the sodium electrochemical gradient as a source of energy. And so let's say that this protein right over here, this is what we're going to call a symporter. This is a symporter. And what it does is it uses the electrochemical gradient of one ion, in this case, sodium."}, {"video_title": "Electrochemical gradients and secondary active transport   Khan Academy.mp3", "Sentence": "In fact, the sodium electrochemical gradient as a source of energy. And so let's say that this protein right over here, this is what we're going to call a symporter. This is a symporter. And what it does is it uses the electrochemical gradient of one ion, in this case, sodium. So it uses the fact that sodium really wants to go through the membrane. And it uses that energy. Imagine like water falling down a waterfall and it can turn a turbine or it can turn a water mill type of thing."}, {"video_title": "Electrochemical gradients and secondary active transport   Khan Academy.mp3", "Sentence": "And what it does is it uses the electrochemical gradient of one ion, in this case, sodium. So it uses the fact that sodium really wants to go through the membrane. And it uses that energy. Imagine like water falling down a waterfall and it can turn a turbine or it can turn a water mill type of thing. And so it uses that energy of the sodium flowing down its electrochemical gradient. It wants to go in this direction for two reasons, concentration and electric potential. So, or I guess you could say it's electrostatic charge."}, {"video_title": "Electrochemical gradients and secondary active transport   Khan Academy.mp3", "Sentence": "Imagine like water falling down a waterfall and it can turn a turbine or it can turn a water mill type of thing. And so it uses that energy of the sodium flowing down its electrochemical gradient. It wants to go in this direction for two reasons, concentration and electric potential. So, or I guess you could say it's electrostatic charge. And then it uses that energy to transport other things. And the most famous symporter with sodium is glucose. It's going to use that."}, {"video_title": "Electrochemical gradients and secondary active transport   Khan Academy.mp3", "Sentence": "So, or I guess you could say it's electrostatic charge. And then it uses that energy to transport other things. And the most famous symporter with sodium is glucose. It's going to use that. The sodium and the glucose are going to go together. And the glucose is being transported against its concentration gradient. And so if you're going to transport something against its concentration gradient, you're going to have to use active transport."}, {"video_title": "Electrochemical gradients and secondary active transport   Khan Academy.mp3", "Sentence": "It's going to use that. The sodium and the glucose are going to go together. And the glucose is being transported against its concentration gradient. And so if you're going to transport something against its concentration gradient, you're going to have to use active transport. So this concentration gradient, so let me be clear on glucose's concentration gradient. It looks like this. You have high concentration over here and you have low right over here."}, {"video_title": "Electrochemical gradients and secondary active transport   Khan Academy.mp3", "Sentence": "And so if you're going to transport something against its concentration gradient, you're going to have to use active transport. So this concentration gradient, so let me be clear on glucose's concentration gradient. It looks like this. You have high concentration over here and you have low right over here. The cell might not want to waste all this glucose. It wants to get as much glucose into the cell or across the membrane as possible. And so it's going to have to do some active transport to go against its concentration gradient, to go in this direction."}, {"video_title": "Electrochemical gradients and secondary active transport   Khan Academy.mp3", "Sentence": "You have high concentration over here and you have low right over here. The cell might not want to waste all this glucose. It wants to get as much glucose into the cell or across the membrane as possible. And so it's going to have to do some active transport to go against its concentration gradient, to go in this direction. And over here, the source of energy to go against the concentration gradient is the stored potential energy from the electrochemical gradient of the sodium. And so this type of active transport where you're using the energy that was stored up through another form of active transport, the sodium-potassium pump, we call this secondary active transport. So what's going over here, this sodium-glucose symporter, this is secondary active transport."}, {"video_title": "Reaction coupling to create glucose 6 phosphate   Biology   Khan Academy.mp3", "Sentence": "It's super valuable in biological systems to be able to take a glucose molecule and to phosphorylate it. So let's start with a glucose molecule and phosphorylate it. And the reason why is once you have this phosphate group, let me make sure I put that charge right over there, once you have this phosphate group, or once you have this negative charge on this glucose 6-phosphate, it becomes much harder for it to leave the cell. The cell wants to hog as many glucose molecules as it can. When the glucose isn't charged, it's able to pass through the cellular membrane, but then once it becomes phosphorylated, it's going to stay in the cell. And glucose 6-phosphate right over here, this is a very important input to a whole series of processes inside of cells. Now unfortunately, this reaction of taking glucose and phosphorylating it, it requires energy."}, {"video_title": "Reaction coupling to create glucose 6 phosphate   Biology   Khan Academy.mp3", "Sentence": "The cell wants to hog as many glucose molecules as it can. When the glucose isn't charged, it's able to pass through the cellular membrane, but then once it becomes phosphorylated, it's going to stay in the cell. And glucose 6-phosphate right over here, this is a very important input to a whole series of processes inside of cells. Now unfortunately, this reaction of taking glucose and phosphorylating it, it requires energy. It's endergonic. It's not going to happen spontaneously. It has a positive delta G. It is endergonic."}, {"video_title": "Reaction coupling to create glucose 6 phosphate   Biology   Khan Academy.mp3", "Sentence": "Now unfortunately, this reaction of taking glucose and phosphorylating it, it requires energy. It's endergonic. It's not going to happen spontaneously. It has a positive delta G. It is endergonic. And so you can imagine what we're going to need to make it happen. We're going to have to use the energy currency of the cell, our good friend ATP. And the way that we're going to make this reaction happen is we're going to couple what's essentially, you could view it as a hydrolysis of ATP, although we won't have exactly a water molecule in the mechanism, but what's functionally the hydrolysis of ATP into ADP and a phosphate group, which is very energetically favorable."}, {"video_title": "Reaction coupling to create glucose 6 phosphate   Biology   Khan Academy.mp3", "Sentence": "It has a positive delta G. It is endergonic. And so you can imagine what we're going to need to make it happen. We're going to have to use the energy currency of the cell, our good friend ATP. And the way that we're going to make this reaction happen is we're going to couple what's essentially, you could view it as a hydrolysis of ATP, although we won't have exactly a water molecule in the mechanism, but what's functionally the hydrolysis of ATP into ADP and a phosphate group, which is very energetically favorable. It is exergonic. It would happen spontaneously under the right conditions. It won't just always happen inside of an aqueous solution."}, {"video_title": "Reaction coupling to create glucose 6 phosphate   Biology   Khan Academy.mp3", "Sentence": "And the way that we're going to make this reaction happen is we're going to couple what's essentially, you could view it as a hydrolysis of ATP, although we won't have exactly a water molecule in the mechanism, but what's functionally the hydrolysis of ATP into ADP and a phosphate group, which is very energetically favorable. It is exergonic. It would happen spontaneously under the right conditions. It won't just always happen inside of an aqueous solution. It needs a little bit of activation energy or an enzyme to lower the activation energy, but the net reaction, it is exergonic. So what we can do is we can couple these two reactions. And so when we couple the two reactions, we have ATP plus glucose reacting, and we use an enzyme, the general term for it is hexokinase, to facilitate this reaction, to lower the activation energy."}, {"video_title": "Reaction coupling to create glucose 6 phosphate   Biology   Khan Academy.mp3", "Sentence": "It won't just always happen inside of an aqueous solution. It needs a little bit of activation energy or an enzyme to lower the activation energy, but the net reaction, it is exergonic. So what we can do is we can couple these two reactions. And so when we couple the two reactions, we have ATP plus glucose reacting, and we use an enzyme, the general term for it is hexokinase, to facilitate this reaction, to lower the activation energy. It's going to yield glucose 6-phosphate and ADP. Now what's the delta G for this reaction going to be? Well, it's a coupled reaction."}, {"video_title": "Reaction coupling to create glucose 6 phosphate   Biology   Khan Academy.mp3", "Sentence": "And so when we couple the two reactions, we have ATP plus glucose reacting, and we use an enzyme, the general term for it is hexokinase, to facilitate this reaction, to lower the activation energy. It's going to yield glucose 6-phosphate and ADP. Now what's the delta G for this reaction going to be? Well, it's a coupled reaction. You can view it as a combination of these two reactions. And so roughly speaking, you can say, well, let's just add the delta G's. So if you add the delta G's here, you're going to get, if you add this negative delta G, this exergonic and this positive delta G, you're going to get negative 30.5 plus 13.8."}, {"video_title": "Reaction coupling to create glucose 6 phosphate   Biology   Khan Academy.mp3", "Sentence": "Well, it's a coupled reaction. You can view it as a combination of these two reactions. And so roughly speaking, you can say, well, let's just add the delta G's. So if you add the delta G's here, you're going to get, if you add this negative delta G, this exergonic and this positive delta G, you're going to get negative 30.5 plus 13.8. That's going to be negative 16.7 kilojoules per mole. And so this coupled reaction is going to be exergonic, not quite as exergonic as a hydrolysis, because now you're going to be using some of that energy, but this can happen spontaneously, especially if you can lower the activation energy enough for it to happen. And so let's now look at the mechanism of how it happens."}, {"video_title": "Reaction coupling to create glucose 6 phosphate   Biology   Khan Academy.mp3", "Sentence": "So if you add the delta G's here, you're going to get, if you add this negative delta G, this exergonic and this positive delta G, you're going to get negative 30.5 plus 13.8. That's going to be negative 16.7 kilojoules per mole. And so this coupled reaction is going to be exergonic, not quite as exergonic as a hydrolysis, because now you're going to be using some of that energy, but this can happen spontaneously, especially if you can lower the activation energy enough for it to happen. And so let's now look at the mechanism of how it happens. Now without an enzyme, the way that this reaction needs to occur is that you have an electron pair right over here on this hydroxyl group, that it needs to do what's called a nucleophilic attack on this phosphorus right over here. But without an enzyme, it's going to be very hard for it to do it. It's going to have a high activation energy because it's going to be impaired by all of this negative charge from these oxygens right over here."}, {"video_title": "Reaction coupling to create glucose 6 phosphate   Biology   Khan Academy.mp3", "Sentence": "And so let's now look at the mechanism of how it happens. Now without an enzyme, the way that this reaction needs to occur is that you have an electron pair right over here on this hydroxyl group, that it needs to do what's called a nucleophilic attack on this phosphorus right over here. But without an enzyme, it's going to be very hard for it to do it. It's going to have a high activation energy because it's going to be impaired by all of this negative charge from these oxygens right over here. You can imagine, electrons don't like going through a lot of negative charge. They're repulsed by negative charge. So we're going to need an enzyme to help facilitate this reaction, to help lower the energy to actually start, and essentially get these electrons out of the way."}, {"video_title": "Reaction coupling to create glucose 6 phosphate   Biology   Khan Academy.mp3", "Sentence": "It's going to have a high activation energy because it's going to be impaired by all of this negative charge from these oxygens right over here. You can imagine, electrons don't like going through a lot of negative charge. They're repulsed by negative charge. So we're going to need an enzyme to help facilitate this reaction, to help lower the energy to actually start, and essentially get these electrons out of the way. And the enzyme, or the general term for the enzymes that do this, is called hexokinase. And hexokinase, let me write this down, and the way it does is it provides ions to, one way to think about it is to keep these electrons over here busy. And in particular, it has a magnesium ion right over here, and this is bound to the rest of the hexokinase."}, {"video_title": "Reaction coupling to create glucose 6 phosphate   Biology   Khan Academy.mp3", "Sentence": "So we're going to need an enzyme to help facilitate this reaction, to help lower the energy to actually start, and essentially get these electrons out of the way. And the enzyme, or the general term for the enzymes that do this, is called hexokinase. And hexokinase, let me write this down, and the way it does is it provides ions to, one way to think about it is to keep these electrons over here busy. And in particular, it has a magnesium ion right over here, and this is bound to the rest of the hexokinase. Remember, this is all happening in three dimensions, so the hexokinase is kind of wrapping around it. So these can keep these electrons busy. There's other ions on the hexokinase that can keep these electrons busy."}, {"video_title": "Reaction coupling to create glucose 6 phosphate   Biology   Khan Academy.mp3", "Sentence": "And in particular, it has a magnesium ion right over here, and this is bound to the rest of the hexokinase. Remember, this is all happening in three dimensions, so the hexokinase is kind of wrapping around it. So these can keep these electrons busy. There's other ions on the hexokinase that can keep these electrons busy. Other positive ions keep these electrons busy. And so these electrons can sneak in and do the nucleophilic attack. And remember, when we talk about enzymes, these are these protein, let me do it in the same color that I wrote the hexokinase in."}, {"video_title": "Reaction coupling to create glucose 6 phosphate   Biology   Khan Academy.mp3", "Sentence": "There's other ions on the hexokinase that can keep these electrons busy. Other positive ions keep these electrons busy. And so these electrons can sneak in and do the nucleophilic attack. And remember, when we talk about enzymes, these are these protein, let me do it in the same color that I wrote the hexokinase in. These are these complex protein structures right over here, just like this. And so you might have the magnesium ion, let me do that in that purple color, just right over there, and then maybe the glucose molecule gets bound right over here, and then maybe you have your ATP gets bound right over here. And I'm obviously, I'm just kind of giving you an example."}, {"video_title": "Reaction coupling to create glucose 6 phosphate   Biology   Khan Academy.mp3", "Sentence": "And remember, when we talk about enzymes, these are these protein, let me do it in the same color that I wrote the hexokinase in. These are these complex protein structures right over here, just like this. And so you might have the magnesium ion, let me do that in that purple color, just right over there, and then maybe the glucose molecule gets bound right over here, and then maybe you have your ATP gets bound right over here. And I'm obviously, I'm just kind of giving you an example. This isn't exactly what's happening. But by essentially wrapping it with this positive charge, it's able to pull the electrons away to help facilitate this nucleophilic attack that needs to happen for the reaction to proceed. And so this bond right over here between this oxygen and this phosphorus, that is going to be this bond right over here."}, {"video_title": "Reaction coupling to create glucose 6 phosphate   Biology   Khan Academy.mp3", "Sentence": "And I'm obviously, I'm just kind of giving you an example. This isn't exactly what's happening. But by essentially wrapping it with this positive charge, it's able to pull the electrons away to help facilitate this nucleophilic attack that needs to happen for the reaction to proceed. And so this bond right over here between this oxygen and this phosphorus, that is going to be this bond right over here. And as this happens, then these two electrons can be taken by this character. And so this oxygen is this oxygen right over here and now has a negative charge. And so what we've just resulted with is glucose 6-phosphate and ADP."}, {"video_title": "Reaction coupling to create glucose 6 phosphate   Biology   Khan Academy.mp3", "Sentence": "And so this bond right over here between this oxygen and this phosphorus, that is going to be this bond right over here. And as this happens, then these two electrons can be taken by this character. And so this oxygen is this oxygen right over here and now has a negative charge. And so what we've just resulted with is glucose 6-phosphate and ADP. And it's energetically favorable. It's exergonic. It's going to happen, assuming that you have the enzyme there to help distract these electrons, lowering the activation energy."}, {"video_title": "Reaction coupling to create glucose 6 phosphate   Biology   Khan Academy.mp3", "Sentence": "And so what we've just resulted with is glucose 6-phosphate and ADP. And it's energetically favorable. It's exergonic. It's going to happen, assuming that you have the enzyme there to help distract these electrons, lowering the activation energy. And I know what you're thinking. We had this hydrogen right over here, so this hydrogen should be right over here still. And then another water molecule could come and nab the hydrogen proton, and so you're left once again with just the glucose 6-phosphate."}, {"video_title": "Reaction coupling to create glucose 6 phosphate   Biology   Khan Academy.mp3", "Sentence": "It's going to happen, assuming that you have the enzyme there to help distract these electrons, lowering the activation energy. And I know what you're thinking. We had this hydrogen right over here, so this hydrogen should be right over here still. And then another water molecule could come and nab the hydrogen proton, and so you're left once again with just the glucose 6-phosphate. So this hopefully gives you a sense of how reaction coupling occurs and also a sense of how ATP is actually useful. When I first learned about ATP, I'm like, okay, fine. It really wants to let go of this phosphate group."}, {"video_title": "Reaction coupling to create glucose 6 phosphate   Biology   Khan Academy.mp3", "Sentence": "And then another water molecule could come and nab the hydrogen proton, and so you're left once again with just the glucose 6-phosphate. So this hopefully gives you a sense of how reaction coupling occurs and also a sense of how ATP is actually useful. When I first learned about ATP, I'm like, okay, fine. It really wants to let go of this phosphate group. It's energetically favorable. But how is that actually used to drive things, to actually do things in the system that might not be energetically favorable? And hopefully this gives you a sense of how it's done and also the importance of an enzyme in facilitating it."}, {"video_title": "Activation and inhibition of signal transduction pathways   AP Biology   Khan Academy.mp3", "Sentence": "And so what's happening here is if you were in the unfortunate situation, this is not something that you would wish on anyone, if they were to have the cholera bacteria in their gut, so let's say that this is the cholera bacteria, that cholera bacteria in your intestines will release what we can call the cholera toxin. And here it's depicted in very abstract fashion by a circle on top of a triangle. That's not what it actually looks like. It's a protein complex with various protein subunits. It's just drawn this way so that we can think about this triangle part interacting with this receptor on the epithelial cell. And so what happens is this cholera toxin, it will interact with this ganglioside receptor. And you don't have to know the details here, really just the idea of what's going on."}, {"video_title": "Activation and inhibition of signal transduction pathways   AP Biology   Khan Academy.mp3", "Sentence": "It's a protein complex with various protein subunits. It's just drawn this way so that we can think about this triangle part interacting with this receptor on the epithelial cell. And so what happens is this cholera toxin, it will interact with this ganglioside receptor. And you don't have to know the details here, really just the idea of what's going on. And then once it does that, when you see these arrows on these transduction pathways, you could view it as that is going to activate the next step or sometimes you might say might promote the next step or make it more likely to happen. But what then happens is once this thing has interacted, the A part of the subunit goes in, interacts with the G protein. You don't have to know all the details here, but G proteins are something that you'll see in a lot of signal transduction pathways."}, {"video_title": "Activation and inhibition of signal transduction pathways   AP Biology   Khan Academy.mp3", "Sentence": "And you don't have to know the details here, really just the idea of what's going on. And then once it does that, when you see these arrows on these transduction pathways, you could view it as that is going to activate the next step or sometimes you might say might promote the next step or make it more likely to happen. But what then happens is once this thing has interacted, the A part of the subunit goes in, interacts with the G protein. You don't have to know all the details here, but G proteins are something that you'll see in a lot of signal transduction pathways. There's not just one G protein. There's a whole family of proteins called G proteins. And you can view them as molecular switches."}, {"video_title": "Activation and inhibition of signal transduction pathways   AP Biology   Khan Academy.mp3", "Sentence": "You don't have to know all the details here, but G proteins are something that you'll see in a lot of signal transduction pathways. There's not just one G protein. There's a whole family of proteins called G proteins. And you can view them as molecular switches. They can get turned on and off based on how they're interacting with other molecules, their conformation, their shape changes. And so that might activate or deactivate them. But you can follow these arrows and you can see what eventually happens."}, {"video_title": "Activation and inhibition of signal transduction pathways   AP Biology   Khan Academy.mp3", "Sentence": "And you can view them as molecular switches. They can get turned on and off based on how they're interacting with other molecules, their conformation, their shape changes. And so that might activate or deactivate them. But you can follow these arrows and you can see what eventually happens. And you don't have to know every detail here. Eventually it leads to adenylate cyclase, then cyclic AMP, then the protein kinase gets involved. But the end result from this pathway is that you have these ions being released from this epithelial cell."}, {"video_title": "Activation and inhibition of signal transduction pathways   AP Biology   Khan Academy.mp3", "Sentence": "But you can follow these arrows and you can see what eventually happens. And you don't have to know every detail here. Eventually it leads to adenylate cyclase, then cyclic AMP, then the protein kinase gets involved. But the end result from this pathway is that you have these ions being released from this epithelial cell. And with that, that causes the water to leave the cell. And that's what causes diarrhea. So the toxin gets your gut cells, gets your intestinal cells to start releasing water."}, {"video_title": "Activation and inhibition of signal transduction pathways   AP Biology   Khan Academy.mp3", "Sentence": "But the end result from this pathway is that you have these ions being released from this epithelial cell. And with that, that causes the water to leave the cell. And that's what causes diarrhea. So the toxin gets your gut cells, gets your intestinal cells to start releasing water. So then you're going to have very, very, very bad diarrhea. So that's the big picture. But now we can think about what might happen in certain situations."}, {"video_title": "Activation and inhibition of signal transduction pathways   AP Biology   Khan Academy.mp3", "Sentence": "So the toxin gets your gut cells, gets your intestinal cells to start releasing water. So then you're going to have very, very, very bad diarrhea. So that's the big picture. But now we can think about what might happen in certain situations. So if I were to ask you, let's say this epithelial cell somehow had a mutation so its ganglioside receptor does not interact well with the B subunit here, with the cholera toxin. What would happen then? Pause this video and try to think about that."}, {"video_title": "Activation and inhibition of signal transduction pathways   AP Biology   Khan Academy.mp3", "Sentence": "But now we can think about what might happen in certain situations. So if I were to ask you, let's say this epithelial cell somehow had a mutation so its ganglioside receptor does not interact well with the B subunit here, with the cholera toxin. What would happen then? Pause this video and try to think about that. All right, so for whatever reason, this epithelial cell had a ganglioside receptor that was a little bit different and it couldn't interact as efficiently with the cholera toxin. Well, in that situation, this activation would not be happening, or at least would not be happening as efficiently. And so someone with that type of a ganglioside receptor, there might be some other negative side effects, but they actually would not get as bad diarrhea from the cholera toxin because this whole signal transduction pathway would not be happening or would not be happening as strong."}, {"video_title": "Activation and inhibition of signal transduction pathways   AP Biology   Khan Academy.mp3", "Sentence": "Pause this video and try to think about that. All right, so for whatever reason, this epithelial cell had a ganglioside receptor that was a little bit different and it couldn't interact as efficiently with the cholera toxin. Well, in that situation, this activation would not be happening, or at least would not be happening as efficiently. And so someone with that type of a ganglioside receptor, there might be some other negative side effects, but they actually would not get as bad diarrhea from the cholera toxin because this whole signal transduction pathway would not be happening or would not be happening as strong. Now, on the other hand, it turns out that there's molecules that can disrupt this signal transduction pathway. So what we have right over here, this is an opioid receptor. And if it gets activated, then it will activate another G protein."}, {"video_title": "Activation and inhibition of signal transduction pathways   AP Biology   Khan Academy.mp3", "Sentence": "And so someone with that type of a ganglioside receptor, there might be some other negative side effects, but they actually would not get as bad diarrhea from the cholera toxin because this whole signal transduction pathway would not be happening or would not be happening as strong. Now, on the other hand, it turns out that there's molecules that can disrupt this signal transduction pathway. So what we have right over here, this is an opioid receptor. And if it gets activated, then it will activate another G protein. This one is different than the one here, but it's part of that same family. And when you see this type of thing, when you see a line with this flathead instead of an arrow, that means it's inhibiting that process. So for example, this opioid receptor is receptive to a molecule known as enkephalin."}, {"video_title": "Activation and inhibition of signal transduction pathways   AP Biology   Khan Academy.mp3", "Sentence": "And if it gets activated, then it will activate another G protein. This one is different than the one here, but it's part of that same family. And when you see this type of thing, when you see a line with this flathead instead of an arrow, that means it's inhibiting that process. So for example, this opioid receptor is receptive to a molecule known as enkephalin. Once again, you don't have to know that. What you should know is that, okay, you have this molecule outside of the cell that can interact with the opioid receptor, which will then activate a G protein. And what's interesting is that this G protein is actually an inhibitor of this step right over here."}, {"video_title": "Activation and inhibition of signal transduction pathways   AP Biology   Khan Academy.mp3", "Sentence": "So for example, this opioid receptor is receptive to a molecule known as enkephalin. Once again, you don't have to know that. What you should know is that, okay, you have this molecule outside of the cell that can interact with the opioid receptor, which will then activate a G protein. And what's interesting is that this G protein is actually an inhibitor of this step right over here. And so if you have cholera and the cholera toxins in your gut, but you also expose those epithelial cells to enkephalin, well, that might make the diarrhea a little bit less bad because if this gets disrupted, or at least if it gets inhibited, then the rest of this pathway will not happen or it will not happen quite as strong. So that leads to another question. If there was some mutation in the opioid receptor here, so it wasn't as good at binding to enkephalin, what would be the end result?"}, {"video_title": "Activation and inhibition of signal transduction pathways   AP Biology   Khan Academy.mp3", "Sentence": "And what's interesting is that this G protein is actually an inhibitor of this step right over here. And so if you have cholera and the cholera toxins in your gut, but you also expose those epithelial cells to enkephalin, well, that might make the diarrhea a little bit less bad because if this gets disrupted, or at least if it gets inhibited, then the rest of this pathway will not happen or it will not happen quite as strong. So that leads to another question. If there was some mutation in the opioid receptor here, so it wasn't as good at binding to enkephalin, what would be the end result? So if your opioid receptor is somehow not as receptive to enkephalin, well, then enkephalin will not be as effective at being able to stop this signal transduction pathway because the enkephalin will not be able to bind with that opioid receptor, and so this inhibition will not occur, and so you would just have the regular transduction pathway from the cholera toxin occurring, which results in diarrhea. So I'll leave you there. The big thing to appreciate is when you see these pathways, arrows you can view as activation or they're leading to the next step, and these lines with these flat heads, this is about inhibition."}, {"video_title": "Activation and inhibition of signal transduction pathways   AP Biology   Khan Academy.mp3", "Sentence": "If there was some mutation in the opioid receptor here, so it wasn't as good at binding to enkephalin, what would be the end result? So if your opioid receptor is somehow not as receptive to enkephalin, well, then enkephalin will not be as effective at being able to stop this signal transduction pathway because the enkephalin will not be able to bind with that opioid receptor, and so this inhibition will not occur, and so you would just have the regular transduction pathway from the cholera toxin occurring, which results in diarrhea. So I'll leave you there. The big thing to appreciate is when you see these pathways, arrows you can view as activation or they're leading to the next step, and these lines with these flat heads, this is about inhibition. And it's pretty typical to see questions, and especially if you're a scientist, you might construct these pathways, but you'll also get questions on, hey, if there's a mutation on something that is activating part of the pathway, what will happen? And then the pathway won't happen as much or maybe at all. And if there's a mutation in something that inhibits the pathway, what would happen?"}, {"video_title": "Organelles in eukaryotic cells   Cells   High school biology   Khan Academy (3).mp3", "Sentence": "And the first place to start is just to remind ourselves what it means for a cell to be eukaryotic. It means that inside the cell, there are membrane-bound organelles. Now what does that mean? Well, you could view it as sub-compartments within the cell, membrane-bound organelles. And in this video in particular, we're going to highlight some of these membrane-bound organelles that make the cells eukaryotic. So let's just start with some of the ingredients that we know is true of all cells. So you'll have your cellular membrane here, a little bit big so that we have a lot of space to draw things in."}, {"video_title": "Organelles in eukaryotic cells   Cells   High school biology   Khan Academy (3).mp3", "Sentence": "Well, you could view it as sub-compartments within the cell, membrane-bound organelles. And in this video in particular, we're going to highlight some of these membrane-bound organelles that make the cells eukaryotic. So let's just start with some of the ingredients that we know is true of all cells. So you'll have your cellular membrane here, a little bit big so that we have a lot of space to draw things in. So this is our cellular membrane. I'll do a nice shading so you appreciate that it'll actually be three-dimensional. We see so many slices of cells that sometimes we forget that they are more spherical or that they have three-dimensional shape to them."}, {"video_title": "Organelles in eukaryotic cells   Cells   High school biology   Khan Academy (3).mp3", "Sentence": "So you'll have your cellular membrane here, a little bit big so that we have a lot of space to draw things in. So this is our cellular membrane. I'll do a nice shading so you appreciate that it'll actually be three-dimensional. We see so many slices of cells that sometimes we forget that they are more spherical or that they have three-dimensional shape to them. They're not all spherical. They can have different shapes. Now all cells, and there are some exceptions that we've talked about in previous videos, I should say most cells will have some genetic information in them in the form of DNA."}, {"video_title": "Organelles in eukaryotic cells   Cells   High school biology   Khan Academy (3).mp3", "Sentence": "We see so many slices of cells that sometimes we forget that they are more spherical or that they have three-dimensional shape to them. They're not all spherical. They can have different shapes. Now all cells, and there are some exceptions that we've talked about in previous videos, I should say most cells will have some genetic information in them in the form of DNA. So that is our DNA right over there. Now one of the key characteristics of a eukaryotic cell is that that genetic information is going to be inside a membrane-bound organelle. And that membrane-bound organelle or the membrane that binds or that surrounds the DNA here, that is the nuclear membrane."}, {"video_title": "Organelles in eukaryotic cells   Cells   High school biology   Khan Academy (3).mp3", "Sentence": "Now all cells, and there are some exceptions that we've talked about in previous videos, I should say most cells will have some genetic information in them in the form of DNA. So that is our DNA right over there. Now one of the key characteristics of a eukaryotic cell is that that genetic information is going to be inside a membrane-bound organelle. And that membrane-bound organelle or the membrane that binds or that surrounds the DNA here, that is the nuclear membrane. So let me draw the nuclear membrane right over here. And I'll put some shading in to appreciate that that also is going to be in three dimensions around the DNA. And so that is the first membrane-bound organelle that we're going to discuss, the nucleus."}, {"video_title": "Organelles in eukaryotic cells   Cells   High school biology   Khan Academy (3).mp3", "Sentence": "And that membrane-bound organelle or the membrane that binds or that surrounds the DNA here, that is the nuclear membrane. So let me draw the nuclear membrane right over here. And I'll put some shading in to appreciate that that also is going to be in three dimensions around the DNA. And so that is the first membrane-bound organelle that we're going to discuss, the nucleus. Now the nucleus, it turns out, is connected to another membrane-bound organelle. And we're gonna study this in future videos. What right here, I'm drawing holes or pores in the nuclear membrane."}, {"video_title": "Organelles in eukaryotic cells   Cells   High school biology   Khan Academy (3).mp3", "Sentence": "And so that is the first membrane-bound organelle that we're going to discuss, the nucleus. Now the nucleus, it turns out, is connected to another membrane-bound organelle. And we're gonna study this in future videos. What right here, I'm drawing holes or pores in the nuclear membrane. And those pores connect to something, it's a very fancy word, called the endoplasmic reticulum. And the endoplasmic reticulum is essentially these layers of these membranes. So I'm gonna do my best job at trying to draw an endoplasmic reticulum."}, {"video_title": "Organelles in eukaryotic cells   Cells   High school biology   Khan Academy (3).mp3", "Sentence": "What right here, I'm drawing holes or pores in the nuclear membrane. And those pores connect to something, it's a very fancy word, called the endoplasmic reticulum. And the endoplasmic reticulum is essentially these layers of these membranes. So I'm gonna do my best job at trying to draw an endoplasmic reticulum. Imagine extending from these pores, going into a space that has these, really these layered membranes that have a lot of surface area. And I'm not gonna go all the way around this nucleus, but in many cells, it will go around all the way around the nucleus. And this right over here, and this is just a rough diagram, that is our endoplasmic, endoplasmic, not splasmic, endoplasmic, endoplasmic reticulum, which I've mentioned in previous videos would be an excellent name for a band."}, {"video_title": "Organelles in eukaryotic cells   Cells   High school biology   Khan Academy (3).mp3", "Sentence": "So I'm gonna do my best job at trying to draw an endoplasmic reticulum. Imagine extending from these pores, going into a space that has these, really these layered membranes that have a lot of surface area. And I'm not gonna go all the way around this nucleus, but in many cells, it will go around all the way around the nucleus. And this right over here, and this is just a rough diagram, that is our endoplasmic, endoplasmic, not splasmic, endoplasmic, endoplasmic reticulum, which I've mentioned in previous videos would be an excellent name for a band. And what goes on in the endoplasmic reticulum is when you are in the process of taking that genetic information from DNA, and as we talk about in other videos, it gets transcribed into mRNA, so that mRNA is now containing that information. That mRNA will make its way out of that nuclear membrane through one of these pores, and then make its way to a ribosome that is attached to the membrane of the endoplasmic reticulum. And so that's a ribosome there."}, {"video_title": "Organelles in eukaryotic cells   Cells   High school biology   Khan Academy (3).mp3", "Sentence": "And this right over here, and this is just a rough diagram, that is our endoplasmic, endoplasmic, not splasmic, endoplasmic, endoplasmic reticulum, which I've mentioned in previous videos would be an excellent name for a band. And what goes on in the endoplasmic reticulum is when you are in the process of taking that genetic information from DNA, and as we talk about in other videos, it gets transcribed into mRNA, so that mRNA is now containing that information. That mRNA will make its way out of that nuclear membrane through one of these pores, and then make its way to a ribosome that is attached to the membrane of the endoplasmic reticulum. And so that's a ribosome there. I'm gonna do a bunch of ribosomes. And so, as we've talked about in previous videos, the ribosomes are really where you take that genetic information from that mRNA, and then you translate it into a protein. So the ribosomes are the protein synthesis, so let me label that."}, {"video_title": "Organelles in eukaryotic cells   Cells   High school biology   Khan Academy (3).mp3", "Sentence": "And so that's a ribosome there. I'm gonna do a bunch of ribosomes. And so, as we've talked about in previous videos, the ribosomes are really where you take that genetic information from that mRNA, and then you translate it into a protein. So the ribosomes are the protein synthesis, so let me label that. So this right over here is a ribosome. And some ribosomes might be attached to the endoplasmic reticulum. Some of them might just be floating out here in the cytoplasm, so that would be a free ribosome."}, {"video_title": "Organelles in eukaryotic cells   Cells   High school biology   Khan Academy (3).mp3", "Sentence": "So the ribosomes are the protein synthesis, so let me label that. So this right over here is a ribosome. And some ribosomes might be attached to the endoplasmic reticulum. Some of them might just be floating out here in the cytoplasm, so that would be a free ribosome. Free ribosome. And even from the point of view of the endoplasmic reticulum, the parts of the endoplasmic reticulum where you have ribosomes attached, this is known as rough endoplasmic reticulum. It's the ribosomes that are making them rough."}, {"video_title": "Organelles in eukaryotic cells   Cells   High school biology   Khan Academy (3).mp3", "Sentence": "Some of them might just be floating out here in the cytoplasm, so that would be a free ribosome. Free ribosome. And even from the point of view of the endoplasmic reticulum, the parts of the endoplasmic reticulum where you have ribosomes attached, this is known as rough endoplasmic reticulum. It's the ribosomes that are making them rough. It looks that way in a microscope. So I'll say rough ER for endoplasmic reticulum for short. And then you also have parts of the endoplasmic reticulum where you do not have ribosomes attached, and because that looks smooth through our microscope, it has been called, you can imagine, smooth endoplasmic reticulum."}, {"video_title": "Organelles in eukaryotic cells   Cells   High school biology   Khan Academy (3).mp3", "Sentence": "It's the ribosomes that are making them rough. It looks that way in a microscope. So I'll say rough ER for endoplasmic reticulum for short. And then you also have parts of the endoplasmic reticulum where you do not have ribosomes attached, and because that looks smooth through our microscope, it has been called, you can imagine, smooth endoplasmic reticulum. There are things known as Golgi bodies. Once again, another fascinating name. Gotta love these names in biology."}, {"video_title": "Organelles in eukaryotic cells   Cells   High school biology   Khan Academy (3).mp3", "Sentence": "And then you also have parts of the endoplasmic reticulum where you do not have ribosomes attached, and because that looks smooth through our microscope, it has been called, you can imagine, smooth endoplasmic reticulum. There are things known as Golgi bodies. Once again, another fascinating name. Gotta love these names in biology. That look kind of like an endoplasmic reticulum, but detached from the nuclear membrane. So let's say it's something like that. That's my best drawing there."}, {"video_title": "Organelles in eukaryotic cells   Cells   High school biology   Khan Academy (3).mp3", "Sentence": "Gotta love these names in biology. That look kind of like an endoplasmic reticulum, but detached from the nuclear membrane. So let's say it's something like that. That's my best drawing there. That's a Golgi body. And these are really good at packaging molecules, even proteins that might have just been produced, and packaging them so that they can be used outside of the cell, for example. So, and we'll go into detail in other videos where a protein might go to the Golgi body, get a little envelope around it, get some little processing going on, and then make its way outside of a cell."}, {"video_title": "Organelles in eukaryotic cells   Cells   High school biology   Khan Academy (3).mp3", "Sentence": "That's my best drawing there. That's a Golgi body. And these are really good at packaging molecules, even proteins that might have just been produced, and packaging them so that they can be used outside of the cell, for example. So, and we'll go into detail in other videos where a protein might go to the Golgi body, get a little envelope around it, get some little processing going on, and then make its way outside of a cell. Now, another, and this is maybe one of the most famous membrane-bound organelles outside of the nucleus, is what's known as the powerhouse of the cell, and that is the mitochondria. And so I'll do this mitochondria in magenta because that's a nice, powerful color. So mitochondria, and I love mitochondria because it's fascinating how they even came to be."}, {"video_title": "Organelles in eukaryotic cells   Cells   High school biology   Khan Academy (3).mp3", "Sentence": "So, and we'll go into detail in other videos where a protein might go to the Golgi body, get a little envelope around it, get some little processing going on, and then make its way outside of a cell. Now, another, and this is maybe one of the most famous membrane-bound organelles outside of the nucleus, is what's known as the powerhouse of the cell, and that is the mitochondria. And so I'll do this mitochondria in magenta because that's a nice, powerful color. So mitochondria, and I love mitochondria because it's fascinating how they even came to be. Mitochondria actually have their own DNA, and all of your mitochondrial DNA comes from your mother, and so that's actually very interesting for tracing maternal lineage. But mitochondria, this is where your, I'm gonna say, let's see what we can see inside of this. This is where your ATP is produced."}, {"video_title": "Organelles in eukaryotic cells   Cells   High school biology   Khan Academy (3).mp3", "Sentence": "So mitochondria, and I love mitochondria because it's fascinating how they even came to be. Mitochondria actually have their own DNA, and all of your mitochondrial DNA comes from your mother, and so that's actually very interesting for tracing maternal lineage. But mitochondria, this is where your, I'm gonna say, let's see what we can see inside of this. This is where your ATP is produced. This is your mitochondria. It's really the powerhouse of the cell. What's interesting about mitochondria is evolutionary biologists believe that the ancestors of mitochondria, because mitochondria have their own DNA, they might have been independent organisms, independent cells, and at some point in our evolutionary past, they started living in symbiosis inside of what would be the ancestors of our cells, and then over time, they became so codependent that they started to replicate together, and mitochondria, in fact, became part of these eukaryotic cells."}, {"video_title": "Organelles in eukaryotic cells   Cells   High school biology   Khan Academy (3).mp3", "Sentence": "This is where your ATP is produced. This is your mitochondria. It's really the powerhouse of the cell. What's interesting about mitochondria is evolutionary biologists believe that the ancestors of mitochondria, because mitochondria have their own DNA, they might have been independent organisms, independent cells, and at some point in our evolutionary past, they started living in symbiosis inside of what would be the ancestors of our cells, and then over time, they became so codependent that they started to replicate together, and mitochondria, in fact, became part of these eukaryotic cells. Now, if this eukaryotic cell was a plant cell or maybe an algae cell, you would have something called chloroplasts there. We don't have them, because we don't have photosynthesis, but this is a chloroplast, and if you could see inside, you could see the little thylakoid stacks right over here. You could see the little thylakoids if you could see inside, and so this right over here is a chloroplast, chloroplast, and this would be plants and algae."}, {"video_title": "Organelles in eukaryotic cells   Cells   High school biology   Khan Academy (3).mp3", "Sentence": "What's interesting about mitochondria is evolutionary biologists believe that the ancestors of mitochondria, because mitochondria have their own DNA, they might have been independent organisms, independent cells, and at some point in our evolutionary past, they started living in symbiosis inside of what would be the ancestors of our cells, and then over time, they became so codependent that they started to replicate together, and mitochondria, in fact, became part of these eukaryotic cells. Now, if this eukaryotic cell was a plant cell or maybe an algae cell, you would have something called chloroplasts there. We don't have them, because we don't have photosynthesis, but this is a chloroplast, and if you could see inside, you could see the little thylakoid stacks right over here. You could see the little thylakoids if you could see inside, and so this right over here is a chloroplast, chloroplast, and this would be plants and algae. Animals do not have these, and these are where you have your photosynthesis take place, photosynthesis. Now, there's also some other membrane-bound organelles that are maybe less famous than the mitochondria or the chloroplast or, for sure, the nucleus, and that might be something like a vacuole, and in plants, vacuoles tend to be very big. I could draw it, you know, this is three-dimensional, so I'll draw it on top of some of what I've drawn before, so if a vacuole right over here, this is a, and a plant can be a fairly significant compartment inside."}, {"video_title": "Organelles in eukaryotic cells   Cells   High school biology   Khan Academy (3).mp3", "Sentence": "You could see the little thylakoids if you could see inside, and so this right over here is a chloroplast, chloroplast, and this would be plants and algae. Animals do not have these, and these are where you have your photosynthesis take place, photosynthesis. Now, there's also some other membrane-bound organelles that are maybe less famous than the mitochondria or the chloroplast or, for sure, the nucleus, and that might be something like a vacuole, and in plants, vacuoles tend to be very big. I could draw it, you know, this is three-dimensional, so I'll draw it on top of some of what I've drawn before, so if a vacuole right over here, this is a, and a plant can be a fairly significant compartment inside. In fact, it can even give structure to the plant itself because it is so big, and it contains water and enzymes. It's viewed as a kind of a storage compartment, but it can also contain enzymes that help digest things, that help break things down so that they can be used in some way, so that is a vacuole, and they don't just exist in plants. They can also exist in animal cells, but in plant cells, they tend to be, they can be very, very, very visible."}, {"video_title": "Organelles in eukaryotic cells   Cells   High school biology   Khan Academy (3).mp3", "Sentence": "I could draw it, you know, this is three-dimensional, so I'll draw it on top of some of what I've drawn before, so if a vacuole right over here, this is a, and a plant can be a fairly significant compartment inside. In fact, it can even give structure to the plant itself because it is so big, and it contains water and enzymes. It's viewed as a kind of a storage compartment, but it can also contain enzymes that help digest things, that help break things down so that they can be used in some way, so that is a vacuole, and they don't just exist in plants. They can also exist in animal cells, but in plant cells, they tend to be, they can be very, very, very visible. Now, something that is somewhat related to some of the function that a vacuole plays that are most associated with animal cells, but now there's evidence that they also exist in plant cells, is the idea of a lysosome, so a lysosome right over here, that also is a compartment, and it's going to contain a whole series of enzymes in it that is useful for lysing, you could say, that is useful for breaking down either waste products as the cell lives, or even foreign substances that might not be helpful for the cells, so it's gonna contain a bunch of enzymes, and it helps break down things. Now, I'll leave you there. These aren't all of the structures in eukaryotic cells, but these are enough of the structures so that you can appreciate that there are a lot of membrane-bound organelles in eukaryotic cells, and to be clear, even if I were to show all of the membrane-bound structures, that's not all the complexity of a cell."}, {"video_title": "Organelles in eukaryotic cells   Cells   High school biology   Khan Academy (3).mp3", "Sentence": "They can also exist in animal cells, but in plant cells, they tend to be, they can be very, very, very visible. Now, something that is somewhat related to some of the function that a vacuole plays that are most associated with animal cells, but now there's evidence that they also exist in plant cells, is the idea of a lysosome, so a lysosome right over here, that also is a compartment, and it's going to contain a whole series of enzymes in it that is useful for lysing, you could say, that is useful for breaking down either waste products as the cell lives, or even foreign substances that might not be helpful for the cells, so it's gonna contain a bunch of enzymes, and it helps break down things. Now, I'll leave you there. These aren't all of the structures in eukaryotic cells, but these are enough of the structures so that you can appreciate that there are a lot of membrane-bound organelles in eukaryotic cells, and to be clear, even if I were to show all of the membrane-bound structures, that's not all the complexity of a cell. The big thing to appreciate is the cells are incredibly complex. There's all sorts of structures in here that help transport things, that move things around. If you could shrink yourself down and look inside of a cell, it would look more complex than the most complex cities."}, {"video_title": "Organelles in eukaryotic cells   Cells   High school biology   Khan Academy (3).mp3", "Sentence": "These aren't all of the structures in eukaryotic cells, but these are enough of the structures so that you can appreciate that there are a lot of membrane-bound organelles in eukaryotic cells, and to be clear, even if I were to show all of the membrane-bound structures, that's not all the complexity of a cell. The big thing to appreciate is the cells are incredibly complex. There's all sorts of structures in here that help transport things, that move things around. If you could shrink yourself down and look inside of a cell, it would look more complex than the most complex cities. There's all sorts of activities, things being moved around, shuttled around. The cell itself is replicating and copying things, and so this is just the beginning. We're just starting to scratch the surface at the complexity of the most basic unit of life."}, {"video_title": "Boveri-Sutton Chromosome Theory.mp3", "Sentence": "Like a lot of times in science, the big discoveries, the ones that really change people's thinking, aren't really taken that seriously at first. And actually Mendel's work, a lot of people either didn't take it seriously or kind of ignored it in 1866. And it wasn't until the early 1900s that people rediscovered his work and realized, wait, wait, there's something very, very powerful here and we might be able to connect it to things that we're actually observing inside of cells. But let's just remind ourselves about Mendel's work. So for most of human history, we've recognized probably that, okay, it looks like animals, or not just animals, any type of living creature seems to pass on traits to their offspring. I could look at you and I'd say, oh, you know, your hair is kind of like your dad's and your eyes are kind of like your mom's. Maybe your nose looks like something in between."}, {"video_title": "Boveri-Sutton Chromosome Theory.mp3", "Sentence": "But let's just remind ourselves about Mendel's work. So for most of human history, we've recognized probably that, okay, it looks like animals, or not just animals, any type of living creature seems to pass on traits to their offspring. I could look at you and I'd say, oh, you know, your hair is kind of like your dad's and your eyes are kind of like your mom's. Maybe your nose looks like something in between. You walk a little bit like your uncle. So we've always recognized that we pass on traits to our offspring, but we didn't really have a rigorous way of thinking about it. And we definitely didn't have any way to make predictions that were testable based on those traits."}, {"video_title": "Boveri-Sutton Chromosome Theory.mp3", "Sentence": "Maybe your nose looks like something in between. You walk a little bit like your uncle. So we've always recognized that we pass on traits to our offspring, but we didn't really have a rigorous way of thinking about it. And we definitely didn't have any way to make predictions that were testable based on those traits. And that's what Mendel gave us. He said, well, look, I'm observing, and he did this with pea plants, I observe these heritable factors. And there might be heritable factors on, let's say, height."}, {"video_title": "Boveri-Sutton Chromosome Theory.mp3", "Sentence": "And we definitely didn't have any way to make predictions that were testable based on those traits. And that's what Mendel gave us. He said, well, look, I'm observing, and he did this with pea plants, I observe these heritable factors. And there might be heritable factors on, let's say, height. If we're talking about plants, it would be the height of a plant. There might be heritable factors on, let's say, flower color. So, flower, flower color."}, {"video_title": "Boveri-Sutton Chromosome Theory.mp3", "Sentence": "And there might be heritable factors on, let's say, height. If we're talking about plants, it would be the height of a plant. There might be heritable factors on, let's say, flower color. So, flower, flower color. And he recognized that there were different versions of those factors. And so a given plant might have one of the tall versions, so they might have a tall version for the height factor, and they might have a short version. Or they might have two talls, or they might have two shorts."}, {"video_title": "Boveri-Sutton Chromosome Theory.mp3", "Sentence": "So, flower, flower color. And he recognized that there were different versions of those factors. And so a given plant might have one of the tall versions, so they might have a tall version for the height factor, and they might have a short version. Or they might have two talls, or they might have two shorts. Or they might have a red factor, and they have a pink factor. Or they could have two reds, two reds, it would look like that. Or two pinks would look like that."}, {"video_title": "Boveri-Sutton Chromosome Theory.mp3", "Sentence": "Or they might have two talls, or they might have two shorts. Or they might have a red factor, and they have a pink factor. Or they could have two reds, two reds, it would look like that. Or two pinks would look like that. But the important realization was that there was these versions of the factor. And today, we call these factors, we say, hey, there's a gene for height, if there is one. Or that there is a gene for flower colors, and those variations of the genes, today, we call these alleles."}, {"video_title": "Boveri-Sutton Chromosome Theory.mp3", "Sentence": "Or two pinks would look like that. But the important realization was that there was these versions of the factor. And today, we call these factors, we say, hey, there's a gene for height, if there is one. Or that there is a gene for flower colors, and those variations of the genes, today, we call these alleles. So we'd say, hey, you have the variation, you have one copy of the tall allele and one copy of the short. Let me just write it this way, let me just say these are all, these are all alleles right here. So you have one tall allele, one short allele."}, {"video_title": "Boveri-Sutton Chromosome Theory.mp3", "Sentence": "Or that there is a gene for flower colors, and those variations of the genes, today, we call these alleles. So we'd say, hey, you have the variation, you have one copy of the tall allele and one copy of the short. Let me just write it this way, let me just say these are all, these are all alleles right here. So you have one tall allele, one short allele. And what Mendel did is he realized, well look, these things are, he didn't know how, but these things are the things that get passed on from a parent to their offspring. And he started to describe about how they got passed on. He observed that even if you have two of these, that they tend to segregate when you go to the next generation."}, {"video_title": "Boveri-Sutton Chromosome Theory.mp3", "Sentence": "So you have one tall allele, one short allele. And what Mendel did is he realized, well look, these things are, he didn't know how, but these things are the things that get passed on from a parent to their offspring. And he started to describe about how they got passed on. He observed that even if you have two of these, that they tend to segregate when you go to the next generation. And what do we mean by segregation? Or I guess we could say the law of segregation. The law of segregation."}, {"video_title": "Boveri-Sutton Chromosome Theory.mp3", "Sentence": "He observed that even if you have two of these, that they tend to segregate when you go to the next generation. And what do we mean by segregation? Or I guess we could say the law of segregation. The law of segregation. Well that means if this was, if I'm a pea plant and these are the versions that I have, to my offspring, I might pass on an A, a capital A, the tall one, or I could pass on the lowercase a. I might pass on the tall, or I might pass on the red version of the flower color factor, or I might pass on, or I might pass on the pink one. And he also realized that whether or not I pass on the capital A or the lowercase a, it's independent of whether I pass on the capital B or the lowercase b. So they independently assort."}, {"video_title": "Boveri-Sutton Chromosome Theory.mp3", "Sentence": "The law of segregation. Well that means if this was, if I'm a pea plant and these are the versions that I have, to my offspring, I might pass on an A, a capital A, the tall one, or I could pass on the lowercase a. I might pass on the tall, or I might pass on the red version of the flower color factor, or I might pass on, or I might pass on the pink one. And he also realized that whether or not I pass on the capital A or the lowercase a, it's independent of whether I pass on the capital B or the lowercase b. So they independently assort. How this one assorts is independent of how this one assorts. So independent assortment. Independent."}, {"video_title": "Boveri-Sutton Chromosome Theory.mp3", "Sentence": "So they independently assort. How this one assorts is independent of how this one assorts. So independent assortment. Independent. Independent assortment. Independent assortment. Law."}, {"video_title": "Boveri-Sutton Chromosome Theory.mp3", "Sentence": "Independent. Independent assortment. Independent assortment. Law. Law of independent assortment. And he also observed that some of these versions dominate the other one. So if an offspring has a tall version and a short one, if the tall one is dominant, the observed trait will still look tall."}, {"video_title": "Boveri-Sutton Chromosome Theory.mp3", "Sentence": "Law. Law of independent assortment. And he also observed that some of these versions dominate the other one. So if an offspring has a tall version and a short one, if the tall one is dominant, the observed trait will still look tall. And that the only way they look short is if they have two versions of the short one. And so that one he described as his law of dominance. And if all of this is completely new to you, I encourage you to watch the videos on Mendelian genetics on Khan Academy."}, {"video_title": "Boveri-Sutton Chromosome Theory.mp3", "Sentence": "So if an offspring has a tall version and a short one, if the tall one is dominant, the observed trait will still look tall. And that the only way they look short is if they have two versions of the short one. And so that one he described as his law of dominance. And if all of this is completely new to you, I encourage you to watch the videos on Mendelian genetics on Khan Academy. But this is just gonna appreciate a little bit of a historical appreciation. But as big of a deal as Mendel's work was, it's also important to realize what he didn't know. He had no idea of how this was actually happening at a molecular level or at a cellular level."}, {"video_title": "Boveri-Sutton Chromosome Theory.mp3", "Sentence": "And if all of this is completely new to you, I encourage you to watch the videos on Mendelian genetics on Khan Academy. But this is just gonna appreciate a little bit of a historical appreciation. But as big of a deal as Mendel's work was, it's also important to realize what he didn't know. He had no idea of how this was actually happening at a molecular level or at a cellular level. And it wasn't until the early 1900s that people started to have fairly robust theories of how this happens. And so in 1902 and 1903, so 1902, 1903, these two gentlemen independently start coming up with the chromosome theory of inheritance. And it's called the Boveri-Sutton chromosome theory of inheritance, because right around the same time, they both started to realize that maybe chromosomes were the actual molecular mechanism, the cellular mechanism by which these factors segregate and independently assort."}, {"video_title": "Boveri-Sutton Chromosome Theory.mp3", "Sentence": "He had no idea of how this was actually happening at a molecular level or at a cellular level. And it wasn't until the early 1900s that people started to have fairly robust theories of how this happens. And so in 1902 and 1903, so 1902, 1903, these two gentlemen independently start coming up with the chromosome theory of inheritance. And it's called the Boveri-Sutton chromosome theory of inheritance, because right around the same time, they both started to realize that maybe chromosomes were the actual molecular mechanism, the cellular mechanism by which these factors segregate and independently assort. And so this is, let me write this down, this is the Boveri-Sutton, and sometimes called the Sutton-Boveri, Boveri-Sutton chromosome theory. Chromosome theory. And even though they're starting to say maybe chromosomes have something to do with it, they still don't know exactly what is inside the chromosomes that are allowing somehow this information to be encoded."}, {"video_title": "Boveri-Sutton Chromosome Theory.mp3", "Sentence": "And it's called the Boveri-Sutton chromosome theory of inheritance, because right around the same time, they both started to realize that maybe chromosomes were the actual molecular mechanism, the cellular mechanism by which these factors segregate and independently assort. And so this is, let me write this down, this is the Boveri-Sutton, and sometimes called the Sutton-Boveri, Boveri-Sutton chromosome theory. Chromosome theory. And even though they're starting to say maybe chromosomes have something to do with it, they still don't know exactly what is inside the chromosomes that are allowing somehow this information to be encoded. And we'll get to that, and we will get to that in a little bit. But let me just underline this, Boveri-Sutton chromosome theory. And so what was their key insight?"}, {"video_title": "Boveri-Sutton Chromosome Theory.mp3", "Sentence": "And even though they're starting to say maybe chromosomes have something to do with it, they still don't know exactly what is inside the chromosomes that are allowing somehow this information to be encoded. And we'll get to that, and we will get to that in a little bit. But let me just underline this, Boveri-Sutton chromosome theory. And so what was their key insight? Well, they started to look inside of cells. Meiosis was observed actually after Mendel published his laws of inheritance. And then chromosomes, or how chromosomes behave in meiosis were discovered after that."}, {"video_title": "Boveri-Sutton Chromosome Theory.mp3", "Sentence": "And so what was their key insight? Well, they started to look inside of cells. Meiosis was observed actually after Mendel published his laws of inheritance. And then chromosomes, or how chromosomes behave in meiosis were discovered after that. And then these guys, they independently studied different organisms. Walter Sutton, he studied grasshoppers. Theodore Boveri, he studied sea urchins."}, {"video_title": "Boveri-Sutton Chromosome Theory.mp3", "Sentence": "And then chromosomes, or how chromosomes behave in meiosis were discovered after that. And then these guys, they independently studied different organisms. Walter Sutton, he studied grasshoppers. Theodore Boveri, he studied sea urchins. But they looked at meiosis, and they looked at the reproduction and the fertilization during these processes, and they saw that the chromosomes seemed to do things that were very similar to these laws of segregation, laws of independent assortment, laws of dominance. And actually, the law of dominance we'll talk more about in future videos. But he saw that, let's say that you had an organism here, and in this particular organism, I just did it for simplification, it has two pairs of homologous chromosomes."}, {"video_title": "Boveri-Sutton Chromosome Theory.mp3", "Sentence": "Theodore Boveri, he studied sea urchins. But they looked at meiosis, and they looked at the reproduction and the fertilization during these processes, and they saw that the chromosomes seemed to do things that were very similar to these laws of segregation, laws of independent assortment, laws of dominance. And actually, the law of dominance we'll talk more about in future videos. But he saw that, let's say that you had an organism here, and in this particular organism, I just did it for simplification, it has two pairs of homologous chromosomes. So what does homologous chromosomes mean? Well, these two are different chromosomes, but they seem to be very similar. It seems like they're kind of the same length, same size, same shape."}, {"video_title": "Boveri-Sutton Chromosome Theory.mp3", "Sentence": "But he saw that, let's say that you had an organism here, and in this particular organism, I just did it for simplification, it has two pairs of homologous chromosomes. So what does homologous chromosomes mean? Well, these two are different chromosomes, but they seem to be very similar. It seems like they're kind of the same length, same size, same shape. So that's one pair of homologous chromosomes. That's another pair of homologous chromosomes. So notice, homologous chromosomes, two things that are kind of looking the same, but maybe they're a little bit different, we're not sure."}, {"video_title": "Boveri-Sutton Chromosome Theory.mp3", "Sentence": "It seems like they're kind of the same length, same size, same shape. So that's one pair of homologous chromosomes. That's another pair of homologous chromosomes. So notice, homologous chromosomes, two things that are kind of looking the same, but maybe they're a little bit different, we're not sure. Well, maybe this is what fits what's going on right over here with these factors. Maybe, just maybe, maybe one of these chromosomes somehow has on it someplace what encodes for the capital A, and maybe the other chromosome in a similar part of the chromosome, in a similar part of the chromosome, has what encodes, in a similar part of the chromosome, has what encodes for a lowercase a. Now this is starting to make sense because they would be homologous chromosomes, similar, the chromosomes look like they code for the same thing, for the same factors, for the same genes, but there might be some variation between these chromosomes."}, {"video_title": "Boveri-Sutton Chromosome Theory.mp3", "Sentence": "So notice, homologous chromosomes, two things that are kind of looking the same, but maybe they're a little bit different, we're not sure. Well, maybe this is what fits what's going on right over here with these factors. Maybe, just maybe, maybe one of these chromosomes somehow has on it someplace what encodes for the capital A, and maybe the other chromosome in a similar part of the chromosome, in a similar part of the chromosome, has what encodes, in a similar part of the chromosome, has what encodes for a lowercase a. Now this is starting to make sense because they would be homologous chromosomes, similar, the chromosomes look like they code for the same thing, for the same factors, for the same genes, but there might be some variation between these chromosomes. And these guys weren't, you know, they weren't able to somehow sequence the chromosomes, so they didn't know, they didn't even know that the DNA was what was important in the chromosomes. But they said, well, it looks like these two things, as we look through the process of meiosis, it seems like they segregate from each other. For example, this capital A one, it'll replicate, so you have capital A, but then, and then this is the lowercase a one right over here, you might have some crossover, and we'll talk about that when you, you can review meiosis if that looks unfamiliar."}, {"video_title": "Boveri-Sutton Chromosome Theory.mp3", "Sentence": "Now this is starting to make sense because they would be homologous chromosomes, similar, the chromosomes look like they code for the same thing, for the same factors, for the same genes, but there might be some variation between these chromosomes. And these guys weren't, you know, they weren't able to somehow sequence the chromosomes, so they didn't know, they didn't even know that the DNA was what was important in the chromosomes. But they said, well, it looks like these two things, as we look through the process of meiosis, it seems like they segregate from each other. For example, this capital A one, it'll replicate, so you have capital A, but then, and then this is the lowercase a one right over here, you might have some crossover, and we'll talk about that when you, you can review meiosis if that looks unfamiliar. But then they segregate. You could have your capital A ones right over here, and then these sister chromatids split apart, so capital A, capital A, and then you have lowercase a, these lowercase a ones, they segregate. And they independently sort from the other chromosomes."}, {"video_title": "Boveri-Sutton Chromosome Theory.mp3", "Sentence": "For example, this capital A one, it'll replicate, so you have capital A, but then, and then this is the lowercase a one right over here, you might have some crossover, and we'll talk about that when you, you can review meiosis if that looks unfamiliar. But then they segregate. You could have your capital A ones right over here, and then these sister chromatids split apart, so capital A, capital A, and then you have lowercase a, these lowercase a ones, they segregate. And they independently sort from the other chromosomes. So this one right over here might be the capital B, this might be the lowercase b. And whether or not this gets a, whether or not this gets a capital B or a lowercase b is independent of whether it got a capital A or a lowercase a. So it seems like these chromosomes independently sort."}, {"video_title": "Boveri-Sutton Chromosome Theory.mp3", "Sentence": "And they independently sort from the other chromosomes. So this one right over here might be the capital B, this might be the lowercase b. And whether or not this gets a, whether or not this gets a capital B or a lowercase b is independent of whether it got a capital A or a lowercase a. So it seems like these chromosomes independently sort. And so they came up with this chromosomal theory that it looks like maybe chromosomes are what contain these heritable factors that Mendel was talking about, because it seems like chromosomes behave very similar to those heritable factors. Maybe chromosomes code for multiple of these heritable factors that segregate and independently sort. And as we know now, they were right."}, {"video_title": "Boveri-Sutton Chromosome Theory.mp3", "Sentence": "So it seems like these chromosomes independently sort. And so they came up with this chromosomal theory that it looks like maybe chromosomes are what contain these heritable factors that Mendel was talking about, because it seems like chromosomes behave very similar to those heritable factors. Maybe chromosomes code for multiple of these heritable factors that segregate and independently sort. And as we know now, they were right. So this was a very, very big deal. But it's important to realize that they weren't sure. They established the theory, they were able to make some observations with the grasshoppers and the sea urchins, and they saw the patterns between what Mendel was describing and the way chromosomes behave during meiosis."}, {"video_title": "Boveri-Sutton Chromosome Theory.mp3", "Sentence": "And as we know now, they were right. So this was a very, very big deal. But it's important to realize that they weren't sure. They established the theory, they were able to make some observations with the grasshoppers and the sea urchins, and they saw the patterns between what Mendel was describing and the way chromosomes behave during meiosis. And then they know that each of these products of meiosis, each of these gametes, will then go and form with other gametes to form the next orgasms. So you say, oh, look, parents will contribute either a capital A or a lowercase a, either a capital B or a lowercase b. So it says this is very similar to what Mendel was describing."}, {"video_title": "Boveri-Sutton Chromosome Theory.mp3", "Sentence": "They established the theory, they were able to make some observations with the grasshoppers and the sea urchins, and they saw the patterns between what Mendel was describing and the way chromosomes behave during meiosis. And then they know that each of these products of meiosis, each of these gametes, will then go and form with other gametes to form the next orgasms. So you say, oh, look, parents will contribute either a capital A or a lowercase a, either a capital B or a lowercase b. So it says this is very similar to what Mendel was describing. So they laid the groundwork for the theory, but they still weren't sure. They didn't definitively prove it. And it will take a few more, another decade or so, until it's definitively proven."}, {"video_title": "An introduction to genetic mutations   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "Today I'm going to give you a quick introduction into genetic mutations. But first, let's go over the central dogma of molecular biology, which is just the idea that genetic information in a cell is stored in the form of DNA. And this DNA is used to generate complementary RNA through a process called transcription. That RNA is then used to synthesize a corresponding protein through the process of translation. So looking at a quick example, our short DNA strand here will be used to generate an RNA strand. Remember that A pairs with U, or T, and C pairs with G. Next, our RNA will be used to generate protein through translation. And remember that during this process, RNA nucleotides are read in groups of three, called codons, in order to generate corresponding amino acids."}, {"video_title": "An introduction to genetic mutations   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "That RNA is then used to synthesize a corresponding protein through the process of translation. So looking at a quick example, our short DNA strand here will be used to generate an RNA strand. Remember that A pairs with U, or T, and C pairs with G. Next, our RNA will be used to generate protein through translation. And remember that during this process, RNA nucleotides are read in groups of three, called codons, in order to generate corresponding amino acids. Now, just very generally, we say that mutations have the effect of making this synthesized protein not turn out quite right. So I'm going to give a quick shout-out to sickle cell disease, which is an example of a disease that's caused by a genetic mutation. So you may remember that there is a protein in red blood cells called hemoglobin, which we can also call Hb."}, {"video_title": "An introduction to genetic mutations   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "And remember that during this process, RNA nucleotides are read in groups of three, called codons, in order to generate corresponding amino acids. Now, just very generally, we say that mutations have the effect of making this synthesized protein not turn out quite right. So I'm going to give a quick shout-out to sickle cell disease, which is an example of a disease that's caused by a genetic mutation. So you may remember that there is a protein in red blood cells called hemoglobin, which we can also call Hb. And hemoglobin is a protein that coordinates to iron ions in order to hold onto oxygen molecules and transport them throughout the body. Now, the mutation that causes sickle cell disease results in a mutated form of hemoglobin, called HbS, being formed, where the S is for the word sickle. And the difference between normal hemoglobin and HbS is that one glutamate amino acid residue is being replaced with a valine amino acid residue."}, {"video_title": "An introduction to genetic mutations   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "So you may remember that there is a protein in red blood cells called hemoglobin, which we can also call Hb. And hemoglobin is a protein that coordinates to iron ions in order to hold onto oxygen molecules and transport them throughout the body. Now, the mutation that causes sickle cell disease results in a mutated form of hemoglobin, called HbS, being formed, where the S is for the word sickle. And the difference between normal hemoglobin and HbS is that one glutamate amino acid residue is being replaced with a valine amino acid residue. And this small change results in all of these mutated HbS proteins aggregating together in a red blood cell, which makes it very difficult for that red blood cell to transport oxygen effectively. Now, just a side point, remember that red blood cells are initially generated from hematopoietic stem cells through a process called hematopoiesis. So where are mutations found, and how did they come up in the first place?"}, {"video_title": "An introduction to genetic mutations   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "And the difference between normal hemoglobin and HbS is that one glutamate amino acid residue is being replaced with a valine amino acid residue. And this small change results in all of these mutated HbS proteins aggregating together in a red blood cell, which makes it very difficult for that red blood cell to transport oxygen effectively. Now, just a side point, remember that red blood cells are initially generated from hematopoietic stem cells through a process called hematopoiesis. So where are mutations found, and how did they come up in the first place? Well, let's look at a couple of different possible mistakes that could lead to an incorrectly produced protein. So first, we'll see what happens if a cell makes a mistake during translation. And we'll stick with our example of sickle cell disease from before."}, {"video_title": "An introduction to genetic mutations   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "So where are mutations found, and how did they come up in the first place? Well, let's look at a couple of different possible mistakes that could lead to an incorrectly produced protein. So first, we'll see what happens if a cell makes a mistake during translation. And we'll stick with our example of sickle cell disease from before. So let's say that we have this sample piece of DNA with three nucleotides from the gene coding for hemoglobin. This DNA is transcribed to form the complementary RNA sequence GAG. Now, that GAG would normally correspond to a glutamate residue during translation."}, {"video_title": "An introduction to genetic mutations   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "And we'll stick with our example of sickle cell disease from before. So let's say that we have this sample piece of DNA with three nucleotides from the gene coding for hemoglobin. This DNA is transcribed to form the complementary RNA sequence GAG. Now, that GAG would normally correspond to a glutamate residue during translation. But a mistake during translation might lead to a valine residue being translated instead to produce the mutated hemoglobin associated with sickle cell disease. But notice that if a mutation happens during translation, the cell will only produce one mutated hemoglobin, or HBS, for each overall mistake. And since cells are making tons and tons of hemoglobin, just one mutated protein might not have that big of an effect on the cell."}, {"video_title": "An introduction to genetic mutations   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "Now, that GAG would normally correspond to a glutamate residue during translation. But a mistake during translation might lead to a valine residue being translated instead to produce the mutated hemoglobin associated with sickle cell disease. But notice that if a mutation happens during translation, the cell will only produce one mutated hemoglobin, or HBS, for each overall mistake. And since cells are making tons and tons of hemoglobin, just one mutated protein might not have that big of an effect on the cell. So we can say that mistakes during translation probably don't cause mutations like the one associated with sickle cell disease. So next, we'll look at mistakes during transcription. Again, we have our CTC piece of DNA, which would normally make GHG on RNA."}, {"video_title": "An introduction to genetic mutations   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "And since cells are making tons and tons of hemoglobin, just one mutated protein might not have that big of an effect on the cell. So we can say that mistakes during translation probably don't cause mutations like the one associated with sickle cell disease. So next, we'll look at mistakes during transcription. Again, we have our CTC piece of DNA, which would normally make GHG on RNA. But maybe a mistake occurs which leads to the transcription of a GUG instead, which would then code for the valine associated with mutated hemoglobin. Now, if this mistake occurred, the cell would only make a few mutated hemoglobins for each mistake, since an individual strand of messenger RNA will only be translated a couple of times before being degraded. So we can say that mistakes during transcription probably don't cause mutations like the one associated with sickle cell disease."}, {"video_title": "An introduction to genetic mutations   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "Again, we have our CTC piece of DNA, which would normally make GHG on RNA. But maybe a mistake occurs which leads to the transcription of a GUG instead, which would then code for the valine associated with mutated hemoglobin. Now, if this mistake occurred, the cell would only make a few mutated hemoglobins for each mistake, since an individual strand of messenger RNA will only be translated a couple of times before being degraded. So we can say that mistakes during transcription probably don't cause mutations like the one associated with sickle cell disease. Finally, we'll look at mistakes in the DNA strand. If our CTC and DNA is mistakenly turned into a CAC, then our corresponding RNA from transcription will be changed. And ultimately, a valine would be produced instead of a glutamic acid."}, {"video_title": "An introduction to genetic mutations   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "So we can say that mistakes during transcription probably don't cause mutations like the one associated with sickle cell disease. Finally, we'll look at mistakes in the DNA strand. If our CTC and DNA is mistakenly turned into a CAC, then our corresponding RNA from transcription will be changed. And ultimately, a valine would be produced instead of a glutamic acid. Now, since a cell's DNA stores all of its genetic information, that mistake would lead to all future hemoglobins produced from that gene being mutated. So overall, we can say that mutations will usually result from mistakes in a cell's DNA and not from the RNA or the protein. So where do these types of mutations come from?"}, {"video_title": "An introduction to genetic mutations   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "And ultimately, a valine would be produced instead of a glutamic acid. Now, since a cell's DNA stores all of its genetic information, that mistake would lead to all future hemoglobins produced from that gene being mutated. So overall, we can say that mutations will usually result from mistakes in a cell's DNA and not from the RNA or the protein. So where do these types of mutations come from? Well, there are two ways a person can get a genetic mutation. The first is that they inherit it from their parents. Remember that DNA is passed down from parents to offspring."}, {"video_title": "An introduction to genetic mutations   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "So where do these types of mutations come from? Well, there are two ways a person can get a genetic mutation. The first is that they inherit it from their parents. Remember that DNA is passed down from parents to offspring. So if we have a mutated father here, then there's a good chance that at least one of his kids will inherit that mutated gene the same way that the child might inherit any amount of that parent's DNA. The other possibility is that the mutation will come on spontaneously, which is where a person suddenly gets a mutation in their DNA without their parents having had the same mutation. And spontaneous mutations can come from many different sources, with just a few examples being from DNA replication errors, environmental factors like certain poisons."}, {"video_title": "An introduction to genetic mutations   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "Remember that DNA is passed down from parents to offspring. So if we have a mutated father here, then there's a good chance that at least one of his kids will inherit that mutated gene the same way that the child might inherit any amount of that parent's DNA. The other possibility is that the mutation will come on spontaneously, which is where a person suddenly gets a mutation in their DNA without their parents having had the same mutation. And spontaneous mutations can come from many different sources, with just a few examples being from DNA replication errors, environmental factors like certain poisons. Or it's also possible that genetic mutations can come on entirely randomly. So what did we learn? Well, first we learned that mutations originate at the DNA level and not at the RNA or protein level."}, {"video_title": "An introduction to genetic mutations   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "And spontaneous mutations can come from many different sources, with just a few examples being from DNA replication errors, environmental factors like certain poisons. Or it's also possible that genetic mutations can come on entirely randomly. So what did we learn? Well, first we learned that mutations originate at the DNA level and not at the RNA or protein level. But the effects of a mutation, like the example we gave with sickle cell disease, are found with problems with the proteins that are ultimately expressed by the mutated DNA. Now, like every rule, there are a couple of exceptions to this one. But we can say that the effects of a mutation are usually found at the protein level."}, {"video_title": "Beginnings of life   Life on earth and in the universe   Cosmology & Astronomy   Khan Academy.mp3", "Sentence": "It was named for Hades, or the ancient Greek underworld. Hades is also the name of the god that ran the Greek underworld, Zeus's oldest brother. And it was an appropriate name, although the idea of the ancient Greek notion of the underworld isn't exactly the more modern notion of hell. But it was a hellish environment. You had all this lava flowing around. You had things impacting the Earth from space. And as far as we can tell right now, it was completely inhospitable to life."}, {"video_title": "Beginnings of life   Life on earth and in the universe   Cosmology & Astronomy   Khan Academy.mp3", "Sentence": "But it was a hellish environment. You had all this lava flowing around. You had things impacting the Earth from space. And as far as we can tell right now, it was completely inhospitable to life. And to make matters worse, even though the Earth started to cool down a little bit, maybe the crust became a little bit more solid. Maybe the collisions started to happen less and less as we started to go a few hundred million years fast forward after Thea rammed into the early Earth and formed the moon. There was something called the late heavy bombardment."}, {"video_title": "Beginnings of life   Life on earth and in the universe   Cosmology & Astronomy   Khan Academy.mp3", "Sentence": "And as far as we can tell right now, it was completely inhospitable to life. And to make matters worse, even though the Earth started to cool down a little bit, maybe the crust became a little bit more solid. Maybe the collisions started to happen less and less as we started to go a few hundred million years fast forward after Thea rammed into the early Earth and formed the moon. There was something called the late heavy bombardment. And right now the consensus is that whatever we are descended from would have had to come about after the late heavy bombardment. Because this was a time where so many things from outer space were hitting Earth that it was so violent that it might have killed off any kind of primitive, self-replicating organisms or molecules that might have existed before it. And I won't go into the physics of the late heavy bombardment, but we believe that it happened because Uranus and Neptune, so this is the sun right here."}, {"video_title": "Beginnings of life   Life on earth and in the universe   Cosmology & Astronomy   Khan Academy.mp3", "Sentence": "There was something called the late heavy bombardment. And right now the consensus is that whatever we are descended from would have had to come about after the late heavy bombardment. Because this was a time where so many things from outer space were hitting Earth that it was so violent that it might have killed off any kind of primitive, self-replicating organisms or molecules that might have existed before it. And I won't go into the physics of the late heavy bombardment, but we believe that it happened because Uranus and Neptune, so this is the sun right here. That is the sun. This is the asteroid belt that's outside the orbits of the inner rocky planets. That Uranus and Neptune, their orbits moved outward."}, {"video_title": "Beginnings of life   Life on earth and in the universe   Cosmology & Astronomy   Khan Academy.mp3", "Sentence": "And I won't go into the physics of the late heavy bombardment, but we believe that it happened because Uranus and Neptune, so this is the sun right here. That is the sun. This is the asteroid belt that's outside the orbits of the inner rocky planets. That Uranus and Neptune, their orbits moved outward. And I'm not going to go into the physics, but what that caused is gravitationally it caused a lot of the asteroids in the asteroid belt to move inward and start impacting the inner planets. And of course, Earth was one of the inner planets. And I should make the sun like orange or something, not blue."}, {"video_title": "Beginnings of life   Life on earth and in the universe   Cosmology & Astronomy   Khan Academy.mp3", "Sentence": "That Uranus and Neptune, their orbits moved outward. And I'm not going to go into the physics, but what that caused is gravitationally it caused a lot of the asteroids in the asteroid belt to move inward and start impacting the inner planets. And of course, Earth was one of the inner planets. And I should make the sun like orange or something, not blue. I don't want you to think that's Earth. And it also impacted the moon. And it's more obvious on the moon because the moon does not have an atmosphere to kind of smooth over the impact."}, {"video_title": "Beginnings of life   Life on earth and in the universe   Cosmology & Astronomy   Khan Academy.mp3", "Sentence": "And I should make the sun like orange or something, not blue. I don't want you to think that's Earth. And it also impacted the moon. And it's more obvious on the moon because the moon does not have an atmosphere to kind of smooth over the impact. So the consensus is that only after the late heavy bombardment was Earth kind of ready for life. And we believe that the first life formed 3.8 to 4 billion years ago. Remember, G for giga, 4 billion years ago."}, {"video_title": "Beginnings of life   Life on earth and in the universe   Cosmology & Astronomy   Khan Academy.mp3", "Sentence": "And it's more obvious on the moon because the moon does not have an atmosphere to kind of smooth over the impact. So the consensus is that only after the late heavy bombardment was Earth kind of ready for life. And we believe that the first life formed 3.8 to 4 billion years ago. Remember, G for giga, 4 billion years ago. And when we talk about life at this period, we're not talking about squirrels or panda bears. We're talking about extremely simple life forms. We're talking about prokaryotes."}, {"video_title": "Beginnings of life   Life on earth and in the universe   Cosmology & Astronomy   Khan Academy.mp3", "Sentence": "Remember, G for giga, 4 billion years ago. And when we talk about life at this period, we're not talking about squirrels or panda bears. We're talking about extremely simple life forms. We're talking about prokaryotes. And let me give you a little primer on that right now, although we go into much more detail in the biology playlist, we're talking about prokaryotes. And I'll compare them to eukaryotes. Prokaryotes are, for the most part, unicellular organisms that have no nucleuses."}, {"video_title": "Beginnings of life   Life on earth and in the universe   Cosmology & Astronomy   Khan Academy.mp3", "Sentence": "We're talking about prokaryotes. And let me give you a little primer on that right now, although we go into much more detail in the biology playlist, we're talking about prokaryotes. And I'll compare them to eukaryotes. Prokaryotes are, for the most part, unicellular organisms that have no nucleuses. They also don't have any other membrane-bound, what we'd call organelles, or these little parts of the cells that perform specific functions like mitochondria. So their DNA is just kind of floating around. So let me draw this character's DNA."}, {"video_title": "Beginnings of life   Life on earth and in the universe   Cosmology & Astronomy   Khan Academy.mp3", "Sentence": "Prokaryotes are, for the most part, unicellular organisms that have no nucleuses. They also don't have any other membrane-bound, what we'd call organelles, or these little parts of the cells that perform specific functions like mitochondria. So their DNA is just kind of floating around. So let me draw this character's DNA. So it's just floating around, just like that. And prokaryote literally means before kernel or before a nucleus. Eukaryotes do have a nucleus where all of their DNA is."}, {"video_title": "Beginnings of life   Life on earth and in the universe   Cosmology & Astronomy   Khan Academy.mp3", "Sentence": "So let me draw this character's DNA. So it's just floating around, just like that. And prokaryote literally means before kernel or before a nucleus. Eukaryotes do have a nucleus where all of their DNA is. So this is the nuclear membrane, and then all of its DNA is floating inside of the nucleus. And then it also has other membrane-bound organelles. Mitochondria is kind of the most famous of them."}, {"video_title": "Beginnings of life   Life on earth and in the universe   Cosmology & Astronomy   Khan Academy.mp3", "Sentence": "Eukaryotes do have a nucleus where all of their DNA is. So this is the nuclear membrane, and then all of its DNA is floating inside of the nucleus. And then it also has other membrane-bound organelles. Mitochondria is kind of the most famous of them. So it also has things like mitochondria. We'll learn more about that in future videos. Mitochondria, we believe, is essentially one prokaryote crawling inside of another prokaryote and kind of starting to become a symbiotic organism with each other."}, {"video_title": "Beginnings of life   Life on earth and in the universe   Cosmology & Astronomy   Khan Academy.mp3", "Sentence": "Mitochondria is kind of the most famous of them. So it also has things like mitochondria. We'll learn more about that in future videos. Mitochondria, we believe, is essentially one prokaryote crawling inside of another prokaryote and kind of starting to become a symbiotic organism with each other. But I won't go into that right now. But when we talk about life at this period, we're talking about prokaryotes. And we still have prokaryotes on the planet."}, {"video_title": "Beginnings of life   Life on earth and in the universe   Cosmology & Astronomy   Khan Academy.mp3", "Sentence": "Mitochondria, we believe, is essentially one prokaryote crawling inside of another prokaryote and kind of starting to become a symbiotic organism with each other. But I won't go into that right now. But when we talk about life at this period, we're talking about prokaryotes. And we still have prokaryotes on the planet. Bacteria and archaea are examples of prokaryotes. And just to give you a little bit of a tidbit right here, this kind of shows our current understanding of where we think things branched off from. So at this point of the tree is some common ancestor to prokaryotes and eukaryotes."}, {"video_title": "Beginnings of life   Life on earth and in the universe   Cosmology & Astronomy   Khan Academy.mp3", "Sentence": "And we still have prokaryotes on the planet. Bacteria and archaea are examples of prokaryotes. And just to give you a little bit of a tidbit right here, this kind of shows our current understanding of where we think things branched off from. So at this point of the tree is some common ancestor to prokaryotes and eukaryotes. So these are the prokaryotes right over here, the bacteria and the archaea. And here is the eukaryotes. And this first living thing, or this first set of living things, we think might have just been some type of self-replicating molecules."}, {"video_title": "Beginnings of life   Life on earth and in the universe   Cosmology & Astronomy   Khan Academy.mp3", "Sentence": "So at this point of the tree is some common ancestor to prokaryotes and eukaryotes. So these are the prokaryotes right over here, the bacteria and the archaea. And here is the eukaryotes. And this first living thing, or this first set of living things, we think might have just been some type of self-replicating molecules. And slowly some membrane might have come around and became a little bit more organized. DNA, RNA, maybe RNA was that original self-replicating molecule, became the method of kind of transmitting information from one generation to the next. So it's really still an open question of exactly what that first life is, or even how do you define that first life."}, {"video_title": "Beginnings of life   Life on earth and in the universe   Cosmology & Astronomy   Khan Academy.mp3", "Sentence": "And this first living thing, or this first set of living things, we think might have just been some type of self-replicating molecules. And slowly some membrane might have come around and became a little bit more organized. DNA, RNA, maybe RNA was that original self-replicating molecule, became the method of kind of transmitting information from one generation to the next. So it's really still an open question of exactly what that first life is, or even how do you define that first life. But based on studying the genetic makeup of current organisms, this is how we think the tree of life came about. So we have one common ancestor, then they broke apart, and then the archaea and eukaryotes have a common ancestor that's different from the bacteria. And we'll talk more about that in the future."}, {"video_title": "Beginnings of life   Life on earth and in the universe   Cosmology & Astronomy   Khan Academy.mp3", "Sentence": "So it's really still an open question of exactly what that first life is, or even how do you define that first life. But based on studying the genetic makeup of current organisms, this is how we think the tree of life came about. So we have one common ancestor, then they broke apart, and then the archaea and eukaryotes have a common ancestor that's different from the bacteria. And we'll talk more about that in the future. And this right here, just so you can visualize it, this is an example of bacteria. This is E. coli or Escherichia coli. It's just an example of bacteria."}, {"video_title": "Beginnings of life   Life on earth and in the universe   Cosmology & Astronomy   Khan Academy.mp3", "Sentence": "And we'll talk more about that in the future. And this right here, just so you can visualize it, this is an example of bacteria. This is E. coli or Escherichia coli. It's just an example of bacteria. It comes in a bunch of shapes and forms. But it's a prokaryotic life form. And the earliest life forms we also think were anaerobes."}, {"video_title": "Beginnings of life   Life on earth and in the universe   Cosmology & Astronomy   Khan Academy.mp3", "Sentence": "It's just an example of bacteria. It comes in a bunch of shapes and forms. But it's a prokaryotic life form. And the earliest life forms we also think were anaerobes. These are things that did not need, one, that they did not need oxygen, and they, for the most part, found oxygen poisonous. And the earliest life forms also probably did not perform photosynthesis. They might have gotten their energy from other sources, chemically, from this kind of extremely volatile environment that they were in at that time."}, {"video_title": "Beginnings of life   Life on earth and in the universe   Cosmology & Astronomy   Khan Academy.mp3", "Sentence": "And the earliest life forms we also think were anaerobes. These are things that did not need, one, that they did not need oxygen, and they, for the most part, found oxygen poisonous. And the earliest life forms also probably did not perform photosynthesis. They might have gotten their energy from other sources, chemically, from this kind of extremely volatile environment that they were in at that time. So if we fast forward a little bit, and this is actually a major event in the history of Earth. And these are huge timescales we're talking about. I mean, remember, I'm kind of just nonchalantly saying, oh, 4.6 billion years ago to 3.8 billion years ago, that's just 800 million years."}, {"video_title": "Beginnings of life   Life on earth and in the universe   Cosmology & Astronomy   Khan Academy.mp3", "Sentence": "They might have gotten their energy from other sources, chemically, from this kind of extremely volatile environment that they were in at that time. So if we fast forward a little bit, and this is actually a major event in the history of Earth. And these are huge timescales we're talking about. I mean, remember, I'm kind of just nonchalantly saying, oh, 4.6 billion years ago to 3.8 billion years ago, that's just 800 million years. Remember, and I'll talk about this, grass has only existed for 50 million years. This is 800 million years. Humans and chimpanzees only diverged 5 million years ago."}, {"video_title": "Beginnings of life   Life on earth and in the universe   Cosmology & Astronomy   Khan Academy.mp3", "Sentence": "I mean, remember, I'm kind of just nonchalantly saying, oh, 4.6 billion years ago to 3.8 billion years ago, that's just 800 million years. Remember, and I'll talk about this, grass has only existed for 50 million years. This is 800 million years. Humans and chimpanzees only diverged 5 million years ago. This is 800 million years we're talking about. From ancient Greece to now, we're only talking about 2,500 years. You multiply that times 1,000."}, {"video_title": "Beginnings of life   Life on earth and in the universe   Cosmology & Astronomy   Khan Academy.mp3", "Sentence": "Humans and chimpanzees only diverged 5 million years ago. This is 800 million years we're talking about. From ancient Greece to now, we're only talking about 2,500 years. You multiply that times 1,000. You multiply that times 1,000, you get 2.5 million years. And this is 800 million years we're talking about. So these are extremely huge periods of time."}, {"video_title": "Beginnings of life   Life on earth and in the universe   Cosmology & Astronomy   Khan Academy.mp3", "Sentence": "You multiply that times 1,000. You multiply that times 1,000, you get 2.5 million years. And this is 800 million years we're talking about. So these are extremely huge periods of time. And that's why we call them eons. Eons are 500 million to a billion years. Now, the dividing line between the Hadean Eon and the Archean Eon, and it's kind of a fuzzy dividing line, but most people place it about 3.8 billion years ago, is kind of the earliest rocks that we can observe."}, {"video_title": "Beginnings of life   Life on earth and in the universe   Cosmology & Astronomy   Khan Academy.mp3", "Sentence": "So these are extremely huge periods of time. And that's why we call them eons. Eons are 500 million to a billion years. Now, the dividing line between the Hadean Eon and the Archean Eon, and it's kind of a fuzzy dividing line, but most people place it about 3.8 billion years ago, is kind of the earliest rocks that we can observe. And so we have rocks that are roughly 3.8 billion years ago, so we kind of put that as the beginning of the Archean Eon. And so there's two things there. One, rocks have survived from the beginning of the Archean Eon, and also that's roughly when we think that the first life existed."}, {"video_title": "Beginnings of life   Life on earth and in the universe   Cosmology & Astronomy   Khan Academy.mp3", "Sentence": "Now, the dividing line between the Hadean Eon and the Archean Eon, and it's kind of a fuzzy dividing line, but most people place it about 3.8 billion years ago, is kind of the earliest rocks that we can observe. And so we have rocks that are roughly 3.8 billion years ago, so we kind of put that as the beginning of the Archean Eon. And so there's two things there. One, rocks have survived from the beginning of the Archean Eon, and also that's roughly when we think that the first life existed. And so we're now in the Archean Eon. And you might say, oh, maybe Earth is a more pleasant place now. But it would not be."}, {"video_title": "Beginnings of life   Life on earth and in the universe   Cosmology & Astronomy   Khan Academy.mp3", "Sentence": "One, rocks have survived from the beginning of the Archean Eon, and also that's roughly when we think that the first life existed. And so we're now in the Archean Eon. And you might say, oh, maybe Earth is a more pleasant place now. But it would not be. It still has no to little oxygen in the environment. If you were to go to Earth at that time, it might have looked something like this. It would have been a reddish sky."}, {"video_title": "Beginnings of life   Life on earth and in the universe   Cosmology & Astronomy   Khan Academy.mp3", "Sentence": "But it would not be. It still has no to little oxygen in the environment. If you were to go to Earth at that time, it might have looked something like this. It would have been a reddish sky. You would have had nitrogen and methane and carbon dioxide in the atmosphere. There would have been nothing for you to breathe. There still would have been a lot of volcanic activity."}, {"video_title": "Beginnings of life   Life on earth and in the universe   Cosmology & Astronomy   Khan Academy.mp3", "Sentence": "It would have been a reddish sky. You would have had nitrogen and methane and carbon dioxide in the atmosphere. There would have been nothing for you to breathe. There still would have been a lot of volcanic activity. This right here, these are pictures of stromatolites. And these are formed from bacteria that are bringing in sediment particles, and over time, these things get built up. But the most significant event in the Archean period, at least in my humble opinion, was what we believe started to happen about 3.5 billion years ago."}, {"video_title": "Beginnings of life   Life on earth and in the universe   Cosmology & Astronomy   Khan Academy.mp3", "Sentence": "There still would have been a lot of volcanic activity. This right here, these are pictures of stromatolites. And these are formed from bacteria that are bringing in sediment particles, and over time, these things get built up. But the most significant event in the Archean period, at least in my humble opinion, was what we believe started to happen about 3.5 billion years ago. And this is prokaryotes, or especially bacteria, evolving to actually utilize energy from the sun to actually do photosynthesis. And the real fascinating byproduct of that, other than the fact that they can now use energy directly from the sun, is that it started to produce oxygen. So it starts to produce oxygen."}, {"video_title": "Beginnings of life   Life on earth and in the universe   Cosmology & Astronomy   Khan Academy.mp3", "Sentence": "But the most significant event in the Archean period, at least in my humble opinion, was what we believe started to happen about 3.5 billion years ago. And this is prokaryotes, or especially bacteria, evolving to actually utilize energy from the sun to actually do photosynthesis. And the real fascinating byproduct of that, other than the fact that they can now use energy directly from the sun, is that it started to produce oxygen. So it starts to produce oxygen. And at first, this oxygen, even though it was being produced by the cyanobacteria, by this blue-green bacteria, it really didn't accumulate in the atmosphere, because you had all of this iron that was dissolved in the oceans. And let me be clear, all of the life that we're going to be talking about for really the next several billion years, it all occurred in the ocean. We had no ozone layer now."}, {"video_title": "Beginnings of life   Life on earth and in the universe   Cosmology & Astronomy   Khan Academy.mp3", "Sentence": "So it starts to produce oxygen. And at first, this oxygen, even though it was being produced by the cyanobacteria, by this blue-green bacteria, it really didn't accumulate in the atmosphere, because you had all of this iron that was dissolved in the oceans. And let me be clear, all of the life that we're going to be talking about for really the next several billion years, it all occurred in the ocean. We had no ozone layer now. The land was being irradiated. The land was just a completely inhospitable environment for life. So all of this was occurring in the ocean."}, {"video_title": "Beginnings of life   Life on earth and in the universe   Cosmology & Astronomy   Khan Academy.mp3", "Sentence": "We had no ozone layer now. The land was being irradiated. The land was just a completely inhospitable environment for life. So all of this was occurring in the ocean. And so the first oxygen that actually got produced, it actually, instead of just being released into the atmosphere, it ended up bonding with the iron that was dissolved in the ocean at that time. So it actually didn't have a chance to accumulate in the atmosphere. And when we fast forward past the Archean period, we're going to see that once a lot of that iron was oxidized, and the oxygen really did start to get released in the atmosphere, it actually had, it's funny to say, a cataclysmic effect or a catastrophic effect on the other anaerobic life on the planet at the time."}, {"video_title": "Beginnings of life   Life on earth and in the universe   Cosmology & Astronomy   Khan Academy.mp3", "Sentence": "So all of this was occurring in the ocean. And so the first oxygen that actually got produced, it actually, instead of just being released into the atmosphere, it ended up bonding with the iron that was dissolved in the ocean at that time. So it actually didn't have a chance to accumulate in the atmosphere. And when we fast forward past the Archean period, we're going to see that once a lot of that iron was oxidized, and the oxygen really did start to get released in the atmosphere, it actually had, it's funny to say, a cataclysmic effect or a catastrophic effect on the other anaerobic life on the planet at the time. And it's funny to say that, because it was a catastrophe for them, but it was kind of a necessary thing that had to happen for us to happen. So for us, it was a blessing that this cyanobacteria started to pump out a lot of oxygen and eventually oxidized all of the iron and eventually released a lot of oxygen in the atmosphere and killed off all of this anaerobic bacteria so that eventually we could, us oxygen-breathing organisms could come about. But that's not going to happen for a while."}, {"video_title": "Simpson's index of diversity   Ecology   AP Biology   Khan Academy.mp3", "Sentence": "So in this table here, we have two different communities, community one and community two, and each of them contained three different species, and we see the populations of those three different species, and we also see that the total number of individuals in each community is the same. They both have a total of 1,000 individuals. Now my question to you, just intuitively, based on the data in this table, which community would you say is more diverse and why? Community one or community two? All right, now let's think about this together. So as we already talked about, they have the same number of individuals, and you might be thinking that the number of species could be related to the diversity, and you'd be right. The number of species does contribute to the diversity, but we're dealing with a situation where both communities have the same number of species."}, {"video_title": "Simpson's index of diversity   Ecology   AP Biology   Khan Academy.mp3", "Sentence": "Community one or community two? All right, now let's think about this together. So as we already talked about, they have the same number of individuals, and you might be thinking that the number of species could be related to the diversity, and you'd be right. The number of species does contribute to the diversity, but we're dealing with a situation where both communities have the same number of species. They each have three species. But when we look at the data, it's clear that community two is mostly species A, and you have very small groups of species B and species C, while community one is more evenly spread. So just intuitively, it feels like community one is maybe more diverse."}, {"video_title": "Simpson's index of diversity   Ecology   AP Biology   Khan Academy.mp3", "Sentence": "The number of species does contribute to the diversity, but we're dealing with a situation where both communities have the same number of species. They each have three species. But when we look at the data, it's clear that community two is mostly species A, and you have very small groups of species B and species C, while community one is more evenly spread. So just intuitively, it feels like community one is maybe more diverse. But this was just on my intuition or our intuition, and the numbers are pretty clear here. It's evenly distributed amongst the species here, and here it's very heavily weighted on species A. But it might not always be this clear, so it'd be useful to have some type of quantitative way to measure the diversity of a population."}, {"video_title": "Simpson's index of diversity   Ecology   AP Biology   Khan Academy.mp3", "Sentence": "So just intuitively, it feels like community one is maybe more diverse. But this was just on my intuition or our intuition, and the numbers are pretty clear here. It's evenly distributed amongst the species here, and here it's very heavily weighted on species A. But it might not always be this clear, so it'd be useful to have some type of quantitative way to measure the diversity of a population. And lucky for us, there is a quantitative way to do that called Simpson's, I'll write it down, Simpson's diversity index. And the way you calculate it, it's equal to one minus the sum of, for each species, you take the number of that species divided by the community size squared. So for each of the species, you do this calculation, square it, and then you add it up for each of those species."}, {"video_title": "Simpson's index of diversity   Ecology   AP Biology   Khan Academy.mp3", "Sentence": "But it might not always be this clear, so it'd be useful to have some type of quantitative way to measure the diversity of a population. And lucky for us, there is a quantitative way to do that called Simpson's, I'll write it down, Simpson's diversity index. And the way you calculate it, it's equal to one minus the sum of, for each species, you take the number of that species divided by the community size squared. So for each of the species, you do this calculation, square it, and then you add it up for each of those species. So let's figure out Simpson's diversity index for both community one and community two. And I encourage you, you could pause the video and try to work on it on your own before I work through it with you. So let's start with community one."}, {"video_title": "Simpson's index of diversity   Ecology   AP Biology   Khan Academy.mp3", "Sentence": "So for each of the species, you do this calculation, square it, and then you add it up for each of those species. So let's figure out Simpson's diversity index for both community one and community two. And I encourage you, you could pause the video and try to work on it on your own before I work through it with you. So let's start with community one. So I'll say diversity index for community one, I'll just put that in parentheses, is going to be equal to one minus, so we have 325 over 1,000 squared. Remember, we're gonna sum on each of these species, plus 305, 305 over 1,000 squared, plus 370 over 1,000 squared. And I need to close my parentheses."}, {"video_title": "Simpson's index of diversity   Ecology   AP Biology   Khan Academy.mp3", "Sentence": "So let's start with community one. So I'll say diversity index for community one, I'll just put that in parentheses, is going to be equal to one minus, so we have 325 over 1,000 squared. Remember, we're gonna sum on each of these species, plus 305, 305 over 1,000 squared, plus 370 over 1,000 squared. And I need to close my parentheses. And I can simplify this a little bit. This is going to be equal to one minus, so all of these 1,000 squareds, 1,000 squared is a million, so it's gonna be everything over one million, one million, and then we're going to have 325 squared plus 305 squared plus 370 squared. And that is going to give us 325 squared plus 305 squared plus 370 squared is equal to that, that's the numerator here, now I'm gonna divide that by a million, divided by one, one, two, three, one, two, three, that is a million, it equals this, and then I'm gonna subtract that from one."}, {"video_title": "Simpson's index of diversity   Ecology   AP Biology   Khan Academy.mp3", "Sentence": "And I need to close my parentheses. And I can simplify this a little bit. This is going to be equal to one minus, so all of these 1,000 squareds, 1,000 squared is a million, so it's gonna be everything over one million, one million, and then we're going to have 325 squared plus 305 squared plus 370 squared. And that is going to give us 325 squared plus 305 squared plus 370 squared is equal to that, that's the numerator here, now I'm gonna divide that by a million, divided by one, one, two, three, one, two, three, that is a million, it equals this, and then I'm gonna subtract that from one. So I'm just gonna put a negative sign here and say plus one is equal to 0.664. So this is going to be approximately equal to 0.664. Now let's do the same thing for community two."}, {"video_title": "Simpson's index of diversity   Ecology   AP Biology   Khan Academy.mp3", "Sentence": "And that is going to give us 325 squared plus 305 squared plus 370 squared is equal to that, that's the numerator here, now I'm gonna divide that by a million, divided by one, one, two, three, one, two, three, that is a million, it equals this, and then I'm gonna subtract that from one. So I'm just gonna put a negative sign here and say plus one is equal to 0.664. So this is going to be approximately equal to 0.664. Now let's do the same thing for community two. So if I write it over here, the diversity index for community two is going to be equal to one minus, I'll put a big parentheses here, and we're going to have 925 over 1,000 squared plus 40 over 1,000 squared plus 35 over 1,000 squared. And if we simplify in a similar way, that's going to be equal to one minus all these 1,000 squareds, that's just a million, and that's a common denominator. And so you're gonna have 925 squared plus 40 squared plus 35 squared, and then this is going to be approximately equal to 925 squared plus 40 squared plus 35 squared plus 35 squared is equal to this, divided by a million, so divided by one, one, two, three, one, two, three, yep, six zeros, is equal to that, and then you subtract that from one and you get, which is approximately equal to 0.142."}, {"video_title": "First Law of Thermodynamics introduction   Biology   Khan Academy.mp3", "Sentence": "Let's now explore the first law of thermodynamics. And before we're even talking about the first law of thermodynamics, some of you might be saying, well, what are thermodynamics? And you could tell from the roots of this word, you have thermo, related to thermal, it's dealing with temperature, and the dynamics, the properties of temperature. How do they move? How does temperature behave? And that's pretty much what thermodynamics is. It's about, it's the study of heat and temperature and how it relates to energy and work and how different forms of energy can be transferred from one form to another."}, {"video_title": "First Law of Thermodynamics introduction   Biology   Khan Academy.mp3", "Sentence": "How do they move? How does temperature behave? And that's pretty much what thermodynamics is. It's about, it's the study of heat and temperature and how it relates to energy and work and how different forms of energy can be transferred from one form to another. And that's actually at the heart of the first law of thermodynamics, which we touched on on the introduction to energy video. And the first law of thermodynamics tells us that energy, energy, this is an important one I'm gonna write down, energy cannot be created or destroyed. Cannot be created, created or destroyed, or destroyed."}, {"video_title": "First Law of Thermodynamics introduction   Biology   Khan Academy.mp3", "Sentence": "It's about, it's the study of heat and temperature and how it relates to energy and work and how different forms of energy can be transferred from one form to another. And that's actually at the heart of the first law of thermodynamics, which we touched on on the introduction to energy video. And the first law of thermodynamics tells us that energy, energy, this is an important one I'm gonna write down, energy cannot be created or destroyed. Cannot be created, created or destroyed, or destroyed. It can only be converted from one form to another. It can, it can only, only be converted, only be converted, I'm having trouble writing today, converted from one form, from one form to another. Or you could transfer it, but you're not going to, you're not going to create or destroy it."}, {"video_title": "First Law of Thermodynamics introduction   Biology   Khan Academy.mp3", "Sentence": "Cannot be created, created or destroyed, or destroyed. It can only be converted from one form to another. It can, it can only, only be converted, only be converted, I'm having trouble writing today, converted from one form, from one form to another. Or you could transfer it, but you're not going to, you're not going to create or destroy it. And the whole thing that I, the rest of this video, I just wanna really have you internalize that. And I wanna look at a bunch of examples and think about, well, what is the energy that we're observing or that we're seeing in a system? And then thinking about where is that energy coming from?"}, {"video_title": "First Law of Thermodynamics introduction   Biology   Khan Academy.mp3", "Sentence": "Or you could transfer it, but you're not going to, you're not going to create or destroy it. And the whole thing that I, the rest of this video, I just wanna really have you internalize that. And I wanna look at a bunch of examples and think about, well, what is the energy that we're observing or that we're seeing in a system? And then thinking about where is that energy coming from? That to appreciate that it's not just coming out of nowhere and that it's not just disappearing, it's not getting destroyed either. And so let's start with this example of a light bulb. And I encourage you to pause this video, think about the forms of energy that we can see here, and then think about where is that energy coming from and where is it going?"}, {"video_title": "First Law of Thermodynamics introduction   Biology   Khan Academy.mp3", "Sentence": "And then thinking about where is that energy coming from? That to appreciate that it's not just coming out of nowhere and that it's not just disappearing, it's not getting destroyed either. And so let's start with this example of a light bulb. And I encourage you to pause this video, think about the forms of energy that we can see here, and then think about where is that energy coming from and where is it going? Well, the most obvious form of energy that you see here, and this is the whole point of a light bulb, is you see the radiant energy. You see the electromagnetic waves, the light being emitted from it. And that light, so this is radiant energy, radiant energy, and that radiant energy, that radiant energy is due to the heat in the filament right over here, as the electrons go through it, it generates heat."}, {"video_title": "First Law of Thermodynamics introduction   Biology   Khan Academy.mp3", "Sentence": "And I encourage you to pause this video, think about the forms of energy that we can see here, and then think about where is that energy coming from and where is it going? Well, the most obvious form of energy that you see here, and this is the whole point of a light bulb, is you see the radiant energy. You see the electromagnetic waves, the light being emitted from it. And that light, so this is radiant energy, radiant energy, and that radiant energy, that radiant energy is due to the heat in the filament right over here, as the electrons go through it, it generates heat. So you have thermal energy. So you have thermal energy as well. Thermal, thermal energy."}, {"video_title": "First Law of Thermodynamics introduction   Biology   Khan Academy.mp3", "Sentence": "And that light, so this is radiant energy, radiant energy, and that radiant energy, that radiant energy is due to the heat in the filament right over here, as the electrons go through it, it generates heat. So you have thermal energy. So you have thermal energy as well. Thermal, thermal energy. But where does this radiant and thermal energy come from? Once again, the first law of thermodynamics tells us it's not just being created out of thin air, it must be converted or being transferred from someplace. Well, I just gave you a hint."}, {"video_title": "First Law of Thermodynamics introduction   Biology   Khan Academy.mp3", "Sentence": "Thermal, thermal energy. But where does this radiant and thermal energy come from? Once again, the first law of thermodynamics tells us it's not just being created out of thin air, it must be converted or being transferred from someplace. Well, I just gave you a hint. This thermal energy is due to the electrons moving through the filament. They're moving through the filament, which has some resistance, and that generates heat. So the electrons are moving through this, and as they move through that resistor, they generate heat."}, {"video_title": "First Law of Thermodynamics introduction   Biology   Khan Academy.mp3", "Sentence": "Well, I just gave you a hint. This thermal energy is due to the electrons moving through the filament. They're moving through the filament, which has some resistance, and that generates heat. So the electrons are moving through this, and as they move through that resistor, they generate heat. So you actually have the kinetic energy of the electrons. I'll just write KE for short, kinetic energy of the actual electrons. Well, where is that kinetic energy coming from?"}, {"video_title": "First Law of Thermodynamics introduction   Biology   Khan Academy.mp3", "Sentence": "So the electrons are moving through this, and as they move through that resistor, they generate heat. So you actually have the kinetic energy of the electrons. I'll just write KE for short, kinetic energy of the actual electrons. Well, where is that kinetic energy coming from? Well, that's coming from the potential energy. Maybe this thing is plugged into a socket of some kind. So let me draw an electric socket right over here."}, {"video_title": "First Law of Thermodynamics introduction   Biology   Khan Academy.mp3", "Sentence": "Well, where is that kinetic energy coming from? Well, that's coming from the potential energy. Maybe this thing is plugged into a socket of some kind. So let me draw an electric socket right over here. And the electric socket, I'll draw the electric socket, if this is the electric socket in your home, there is a electrostatic potential between these two terminals. And so when you make a connection, the electrons are able to move. And we'll get into the details of AC and DC current in the future, but there's an electrostatic potential from this point to this point, if we assume that's the direction that the electrons are going in."}, {"video_title": "First Law of Thermodynamics introduction   Biology   Khan Academy.mp3", "Sentence": "So let me draw an electric socket right over here. And the electric socket, I'll draw the electric socket, if this is the electric socket in your home, there is a electrostatic potential between these two terminals. And so when you make a connection, the electrons are able to move. And we'll get into the details of AC and DC current in the future, but there's an electrostatic potential from this point to this point, if we assume that's the direction that the electrons are going in. And so it's that potential energy being converted to this kinetic energy of the electrons, which is really in the form of a current. And then that gets converted into thermal energy and radiant energy. Now what happens after, let's say you unplug the light, the light goes dark, what happened to all of that energy?"}, {"video_title": "First Law of Thermodynamics introduction   Biology   Khan Academy.mp3", "Sentence": "And we'll get into the details of AC and DC current in the future, but there's an electrostatic potential from this point to this point, if we assume that's the direction that the electrons are going in. And so it's that potential energy being converted to this kinetic energy of the electrons, which is really in the form of a current. And then that gets converted into thermal energy and radiant energy. Now what happens after, let's say you unplug the light, the light goes dark, what happened to all of that energy? Is it still there? Well, yeah, that thermal energy is going to continue to dissipate through the system. And this right over here would be an open system."}, {"video_title": "First Law of Thermodynamics introduction   Biology   Khan Academy.mp3", "Sentence": "Now what happens after, let's say you unplug the light, the light goes dark, what happened to all of that energy? Is it still there? Well, yeah, that thermal energy is going to continue to dissipate through the system. And this right over here would be an open system. It's going to, the air inside the light bulb, you can't fully see the light bulb right here, but it looks something like this. That's going to heat up, but then it's going to heat up the glass surrounding the light bulb, and that's going to heat up the surrounding air. So the thermal energy is going to be transferred, and that radiant energy is going to move outward, and it could be used, it could be converted into other forms of energy, most likely thermal energy."}, {"video_title": "First Law of Thermodynamics introduction   Biology   Khan Academy.mp3", "Sentence": "And this right over here would be an open system. It's going to, the air inside the light bulb, you can't fully see the light bulb right here, but it looks something like this. That's going to heat up, but then it's going to heat up the glass surrounding the light bulb, and that's going to heat up the surrounding air. So the thermal energy is going to be transferred, and that radiant energy is going to move outward, and it could be used, it could be converted into other forms of energy, most likely thermal energy. It is also probably going to heat up other things. Well, what about a pool table? When I hit a, if I hit a pool, a billiard ball or a pool ball right over here, well, where's that energy going?"}, {"video_title": "First Law of Thermodynamics introduction   Biology   Khan Academy.mp3", "Sentence": "So the thermal energy is going to be transferred, and that radiant energy is going to move outward, and it could be used, it could be converted into other forms of energy, most likely thermal energy. It is also probably going to heat up other things. Well, what about a pool table? When I hit a, if I hit a pool, a billiard ball or a pool ball right over here, well, where's that energy going? Well, some of that energy might be going to go hit the next ball, which might go to hit the next ball, but as we all know, if we've ever played pool, at some point, they're going to stop. So what happened to all of that energy? Well, while they were rolling, while they were rolling, there was some air resistance."}, {"video_title": "First Law of Thermodynamics introduction   Biology   Khan Academy.mp3", "Sentence": "When I hit a, if I hit a pool, a billiard ball or a pool ball right over here, well, where's that energy going? Well, some of that energy might be going to go hit the next ball, which might go to hit the next ball, but as we all know, if we've ever played pool, at some point, they're going to stop. So what happened to all of that energy? Well, while they were rolling, while they were rolling, there was some air resistance. There was some air resistance, so they're bumping against the air molecules, and it's really friction due to air, and that energy is essentially going to be converted to heat. And one trend that you're going to see very frequently is as systems progress, a lot more of the energy tends to turn into heat rather than doing useful work. And so you're going to have, as the billiard balls move, there's the air, and so that's going to be converted, some of that kinetic energy is going to be turned into heat energy."}, {"video_title": "First Law of Thermodynamics introduction   Biology   Khan Academy.mp3", "Sentence": "Well, while they were rolling, while they were rolling, there was some air resistance. There was some air resistance, so they're bumping against the air molecules, and it's really friction due to air, and that energy is essentially going to be converted to heat. And one trend that you're going to see very frequently is as systems progress, a lot more of the energy tends to turn into heat rather than doing useful work. And so you're going to have, as the billiard balls move, there's the air, and so that's going to be converted, some of that kinetic energy is going to be turned into heat energy. You're also going to have friction with the actual felt on the table, and that friction, you're going to have molecules rubbing up against each other. That's also going to be converted into heat, and so because that kinetic energy gets sapped off, gets keeping sapped away from the friction, which is essentially converting the kinetic energy into heat energy, eventually you won't have any more kinetic energy. Now what about this weightlifter here?"}, {"video_title": "First Law of Thermodynamics introduction   Biology   Khan Academy.mp3", "Sentence": "And so you're going to have, as the billiard balls move, there's the air, and so that's going to be converted, some of that kinetic energy is going to be turned into heat energy. You're also going to have friction with the actual felt on the table, and that friction, you're going to have molecules rubbing up against each other. That's also going to be converted into heat, and so because that kinetic energy gets sapped off, gets keeping sapped away from the friction, which is essentially converting the kinetic energy into heat energy, eventually you won't have any more kinetic energy. Now what about this weightlifter here? He's using the chemical energy in the ATP in his muscles that converts into kinetic energy that moves his muscles, that moves this weight, but once he's in this position, what happened to all of that energy? Well, a lot of that energy is now being stored in potential, it's the potential energy. He's got this big weight, he's got that big weight above his head, and if he were to just let go, that thing would fall."}, {"video_title": "First Law of Thermodynamics introduction   Biology   Khan Academy.mp3", "Sentence": "Now what about this weightlifter here? He's using the chemical energy in the ATP in his muscles that converts into kinetic energy that moves his muscles, that moves this weight, but once he's in this position, what happened to all of that energy? Well, a lot of that energy is now being stored in potential, it's the potential energy. He's got this big weight, he's got that big weight above his head, and if he were to just let go, that thing would fall. I wouldn't recommend he do that, but that thing would fall quite fast, and so now it's all, or a lot of it, has been stored up in potential energy, but he would have also generated heat. His muscles would have generated heat, even the act of moving it through the air, there's gonna be some heat in the air, some friction with it, and so I want you to appreciate that this energy is not coming out of nowhere. It is being converted from one form or another, being transferred from one part of the system to another."}, {"video_title": "First Law of Thermodynamics introduction   Biology   Khan Academy.mp3", "Sentence": "He's got this big weight, he's got that big weight above his head, and if he were to just let go, that thing would fall. I wouldn't recommend he do that, but that thing would fall quite fast, and so now it's all, or a lot of it, has been stored up in potential energy, but he would have also generated heat. His muscles would have generated heat, even the act of moving it through the air, there's gonna be some heat in the air, some friction with it, and so I want you to appreciate that this energy is not coming out of nowhere. It is being converted from one form or another, being transferred from one part of the system to another. Now we can look at these examples over here. Same thing with a runner. What happens after, you can buy the fact that okay, his chemical energy is allowing his muscles to move, and that's turning into his whole kinetic energy for his entire body."}, {"video_title": "First Law of Thermodynamics introduction   Biology   Khan Academy.mp3", "Sentence": "It is being converted from one form or another, being transferred from one part of the system to another. Now we can look at these examples over here. Same thing with a runner. What happens after, you can buy the fact that okay, his chemical energy is allowing his muscles to move, and that's turning into his whole kinetic energy for his entire body. His body is moving, but at some point he stops. Where did all that energy go? Well, some of it will be heat in his body that's being dissipated into the broader system, into the air, and also when he was running, there was this contact with the ground."}, {"video_title": "First Law of Thermodynamics introduction   Biology   Khan Academy.mp3", "Sentence": "What happens after, you can buy the fact that okay, his chemical energy is allowing his muscles to move, and that's turning into his whole kinetic energy for his entire body. His body is moving, but at some point he stops. Where did all that energy go? Well, some of it will be heat in his body that's being dissipated into the broader system, into the air, and also when he was running, there was this contact with the ground. That's gonna make the molecules in the ground vibrate a little bit. Some of it will be transferred as sound, so the air particles moving through the air, and a lot of it will be heat, and we're gonna see that over and over and over again. The diver up here, you have mostly potential energy."}, {"video_title": "First Law of Thermodynamics introduction   Biology   Khan Academy.mp3", "Sentence": "Well, some of it will be heat in his body that's being dissipated into the broader system, into the air, and also when he was running, there was this contact with the ground. That's gonna make the molecules in the ground vibrate a little bit. Some of it will be transferred as sound, so the air particles moving through the air, and a lot of it will be heat, and we're gonna see that over and over and over again. The diver up here, you have mostly potential energy. Then it converts to kinetic energy as he's get almost in the water, but what happens once he falls into the water? Well, then that energy is going to be transferred as you're gonna have these waves of water move away, and it will also increase friction. So, well, actually you would have had friction as he fell down, so that would have generated some heat, and there would have been also some heat with the friction with the water."}, {"video_title": "First Law of Thermodynamics introduction   Biology   Khan Academy.mp3", "Sentence": "The diver up here, you have mostly potential energy. Then it converts to kinetic energy as he's get almost in the water, but what happens once he falls into the water? Well, then that energy is going to be transferred as you're gonna have these waves of water move away, and it will also increase friction. So, well, actually you would have had friction as he fell down, so that would have generated some heat, and there would have been also some heat with the friction with the water. You normally don't think of friction with the water, but there is some friction with the actual water, and there's also these waves, you have higher kinetic energy of the actual water being transferred outward from where he actually dropped in. And I could keep going on and on. You have the chemical potential energy of the fuel here."}, {"video_title": "First Law of Thermodynamics introduction   Biology   Khan Academy.mp3", "Sentence": "So, well, actually you would have had friction as he fell down, so that would have generated some heat, and there would have been also some heat with the friction with the water. You normally don't think of friction with the water, but there is some friction with the actual water, and there's also these waves, you have higher kinetic energy of the actual water being transferred outward from where he actually dropped in. And I could keep going on and on. You have the chemical potential energy of the fuel here. You have combustion occurring, and then that gets converted into the thermal energy and the radiant energy of what we associate with fire, and that doesn't disappear. It just keeps the radiating outwards. The radiant energy just keeps radiating outward."}, {"video_title": "First Law of Thermodynamics introduction   Biology   Khan Academy.mp3", "Sentence": "You have the chemical potential energy of the fuel here. You have combustion occurring, and then that gets converted into the thermal energy and the radiant energy of what we associate with fire, and that doesn't disappear. It just keeps the radiating outwards. The radiant energy just keeps radiating outward. Maybe it might heat up something, and the thermal energy will just keep radiating outward, or I should say the thermal energy will just dissipate outward and heat up the things around it. Same thing with our lightning example. You start with the electrostatic, you started with this electrostatic potential where the bottom of the clouds were more negative, and then the ground is positive as well, and at some point, that potential energy turns into kinetic energy as the electrons transfer through the air, and then that gets converted into, or to a good bit, it's gonna be converted to heat and radiant energy."}, {"video_title": "Reproductive isolation   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "Have you ever wondered how we classify different organisms into different species? Well, before we look at that, let's go over the difference between asexual reproduction and sexual reproduction. In asexual reproduction, one organism, like a single bacterium, will divide into two daughter cells that are both genetically identical to the original cell. In sexual reproduction, two members of the same species will reproduce together in order to form genetically unique offspring. Now in general, we say that organisms that reproduce asexually usually have low genetic diversity, whereas sexually reproducing species have high genetic diversity. So what is a species? Now this can be a very difficult question to answer."}, {"video_title": "Reproductive isolation   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "In sexual reproduction, two members of the same species will reproduce together in order to form genetically unique offspring. Now in general, we say that organisms that reproduce asexually usually have low genetic diversity, whereas sexually reproducing species have high genetic diversity. So what is a species? Now this can be a very difficult question to answer. For sexually reproducing organisms, we can say that two organisms, like this cat and this human, are members of different species if they are unable to have offspring together. However, for asexually reproducing organisms, like bacteria, protists, and archaea, it's a little more confusing. These species don't mate with other organisms, so we have a difficult time classifying them into different categories."}, {"video_title": "Reproductive isolation   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "Now this can be a very difficult question to answer. For sexually reproducing organisms, we can say that two organisms, like this cat and this human, are members of different species if they are unable to have offspring together. However, for asexually reproducing organisms, like bacteria, protists, and archaea, it's a little more confusing. These species don't mate with other organisms, so we have a difficult time classifying them into different categories. And we call this the species problem. But in this video, we're going to spend time just looking at those sexually reproducing organisms. And these are separated into different species by different forms of what we call reproductive isolation."}, {"video_title": "Reproductive isolation   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "These species don't mate with other organisms, so we have a difficult time classifying them into different categories. And we call this the species problem. But in this video, we're going to spend time just looking at those sexually reproducing organisms. And these are separated into different species by different forms of what we call reproductive isolation. And this is the idea that there are many forces that stop two different organisms from having offspring together. And we can divide these forces into two separate categories, prezygotic forms and postzygotic forms. Prezygotic isolation refers to all the different forces that prevent two organisms from having offspring together that occur prior to the formation of a zygote."}, {"video_title": "Reproductive isolation   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "And these are separated into different species by different forms of what we call reproductive isolation. And this is the idea that there are many forces that stop two different organisms from having offspring together. And we can divide these forces into two separate categories, prezygotic forms and postzygotic forms. Prezygotic isolation refers to all the different forces that prevent two organisms from having offspring together that occur prior to the formation of a zygote. And remember that a zygote is a single cell that is made up of the genetic material of both organisms that are reproduced together. Postzygotic forms of isolation we'll get into a little bit later. So the first type of prezygotic isolation is temporal slash habitat isolation."}, {"video_title": "Reproductive isolation   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "Prezygotic isolation refers to all the different forces that prevent two organisms from having offspring together that occur prior to the formation of a zygote. And remember that a zygote is a single cell that is made up of the genetic material of both organisms that are reproduced together. Postzygotic forms of isolation we'll get into a little bit later. So the first type of prezygotic isolation is temporal slash habitat isolation. And temporal isolation refers to the fact that not all organisms mate at the same time. Some mate at night, while others mate during the day. Some mate in spring, while others mate in winter."}, {"video_title": "Reproductive isolation   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "So the first type of prezygotic isolation is temporal slash habitat isolation. And temporal isolation refers to the fact that not all organisms mate at the same time. Some mate at night, while others mate during the day. Some mate in spring, while others mate in winter. If two organisms do not find mates at the same time, then they are temporally isolated. Habitat isolation refers to the place where the organisms mate. Some may prefer mating in the forest, while others prefer mating in the mountains."}, {"video_title": "Reproductive isolation   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "Some mate in spring, while others mate in winter. If two organisms do not find mates at the same time, then they are temporally isolated. Habitat isolation refers to the place where the organisms mate. Some may prefer mating in the forest, while others prefer mating in the mountains. And if two organisms don't find mates in the same place, then they are also isolated. If time and place aren't a problem, then the next barrier is behavioral isolation, which refers to mate selection and how organisms go about attracting a mate. So not all organisms will attract a mate the same way."}, {"video_title": "Reproductive isolation   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "Some may prefer mating in the forest, while others prefer mating in the mountains. And if two organisms don't find mates in the same place, then they are also isolated. If time and place aren't a problem, then the next barrier is behavioral isolation, which refers to mate selection and how organisms go about attracting a mate. So not all organisms will attract a mate the same way. Perhaps one animal, like a bird, will attract a mate by singing a song, whereas this bunny rabbit may do a little dance to attract a mate. So we have behavioral isolation, and now we have mechanical isolation, which deals with the physical inability of two organisms to mate, even if they wanted to. Now a great example of this is a huge animal, like an elephant, being unable to mate with a tiny mouse."}, {"video_title": "Reproductive isolation   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "So not all organisms will attract a mate the same way. Perhaps one animal, like a bird, will attract a mate by singing a song, whereas this bunny rabbit may do a little dance to attract a mate. So we have behavioral isolation, and now we have mechanical isolation, which deals with the physical inability of two organisms to mate, even if they wanted to. Now a great example of this is a huge animal, like an elephant, being unable to mate with a tiny mouse. If two organisms do mate successfully, they may still encounter gametic isolation, which is when fertilization between the two gametes to form a zygote is impossible. Now once the zygote has been formed, you can move on and look at post-zygotic forms of reproductive isolation. And the first form is zygote mortality."}, {"video_title": "Reproductive isolation   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "Now a great example of this is a huge animal, like an elephant, being unable to mate with a tiny mouse. If two organisms do mate successfully, they may still encounter gametic isolation, which is when fertilization between the two gametes to form a zygote is impossible. Now once the zygote has been formed, you can move on and look at post-zygotic forms of reproductive isolation. And the first form is zygote mortality. And this occurs when, even if the two gametes from the two organisms can fuse successfully and form a zygote, that zygote would have a high mortality rate and be unable to develop into a mature offspring. Next we have hybrid inviability, which occurs when a zygote is able to grow into a mature offspring, but that offspring will have a high mortality rate and won't be able to grow into a mature adult. Finally we have the last form of reproductive isolation, which is hybrid sterility."}, {"video_title": "Reproductive isolation   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "And the first form is zygote mortality. And this occurs when, even if the two gametes from the two organisms can fuse successfully and form a zygote, that zygote would have a high mortality rate and be unable to develop into a mature offspring. Next we have hybrid inviability, which occurs when a zygote is able to grow into a mature offspring, but that offspring will have a high mortality rate and won't be able to grow into a mature adult. Finally we have the last form of reproductive isolation, which is hybrid sterility. And this is when the offspring can grow into a mature adult, but that mature adult is not able to mate and have offspring of its own. So if two sexually reproducing organisms are not isolated by any of these barriers, then we can generally say that they are members of the same species. So what did we learn?"}, {"video_title": "Reproductive isolation   Biomolecules   MCAT   Khan Academy.mp3", "Sentence": "Finally we have the last form of reproductive isolation, which is hybrid sterility. And this is when the offspring can grow into a mature adult, but that mature adult is not able to mate and have offspring of its own. So if two sexually reproducing organisms are not isolated by any of these barriers, then we can generally say that they are members of the same species. So what did we learn? Well first we learned about the species problem, and how classifying different organisms into different species can be quite difficult. And we have a pretty good definition for sexually reproducing organisms, but not really for asexually reproducing organisms. And next we learned about reproductive isolation, and how we can say that two sexually reproducing organisms are reproductively isolated if they are unable to freely produce fertile offspring together."}, {"video_title": "Mutation as a source of variation   Gene expression and regulation   AP Biology   Khan Academy.mp3", "Sentence": "For certain traits, your environment might make certain of them better for reproduction, better for survival, evading predators, better for finding food. And let's say these circles, for whatever reason, they're an environment where maybe being blue makes it a little bit easier to evade predators and a little bit easier to reproduce and find food. Well then, in the next generation, in the next generation, because the blue's more likely to be able to get to reproduction, because they weren't eaten, you're likely to have more blues. So let me draw a few more blues, and maybe a little bit less of the other ones, because they're also competing for resources amongst each other, at least in this model that I'm doing. And so over time, if this blue phenotype, remember, phenotype is the expressed trait that's actually observable versus the genotype, which is the underlying genetics, which is sometimes observable and sometimes not. But as you can see, if in this environment, blue seems to carry some advantage, even if it's a slight probabilistic advantage, over many generations, blue will start to dominate. And so you start to see that evolution of this population to being more blue as a species."}, {"video_title": "Mutation as a source of variation   Gene expression and regulation   AP Biology   Khan Academy.mp3", "Sentence": "So let me draw a few more blues, and maybe a little bit less of the other ones, because they're also competing for resources amongst each other, at least in this model that I'm doing. And so over time, if this blue phenotype, remember, phenotype is the expressed trait that's actually observable versus the genotype, which is the underlying genetics, which is sometimes observable and sometimes not. But as you can see, if in this environment, blue seems to carry some advantage, even if it's a slight probabilistic advantage, over many generations, blue will start to dominate. And so you start to see that evolution of this population to being more blue as a species. So you have these blue circles. So one way to think about it is you have variation in a species is really what natural selection is based off of certain variants might be more favorable than others. So that is what's really necessary for natural selection to fuel evolution, to fuel evolution."}, {"video_title": "Mutation as a source of variation   Gene expression and regulation   AP Biology   Khan Academy.mp3", "Sentence": "And so you start to see that evolution of this population to being more blue as a species. So you have these blue circles. So one way to think about it is you have variation in a species is really what natural selection is based off of certain variants might be more favorable than others. So that is what's really necessary for natural selection to fuel evolution, to fuel evolution. Now, a key question is, where does this variation in a population come from? And to think about that, we just have to remind ourselves where our phenotypes come from. How do these expressed traits get expressed?"}, {"video_title": "Mutation as a source of variation   Gene expression and regulation   AP Biology   Khan Academy.mp3", "Sentence": "So that is what's really necessary for natural selection to fuel evolution, to fuel evolution. Now, a key question is, where does this variation in a population come from? And to think about that, we just have to remind ourselves where our phenotypes come from. How do these expressed traits get expressed? Well, in all the living organisms we're aware of, we have DNA. As human beings, we have 23 pair of chromosomes, and each chromosome you could view as just a very, very, very, very long strand of DNA, and sections of that DNA code for various traits. And each of those sections that code for, say, a certain protein or a part of an enzyme, we call those things genes."}, {"video_title": "Mutation as a source of variation   Gene expression and regulation   AP Biology   Khan Academy.mp3", "Sentence": "How do these expressed traits get expressed? Well, in all the living organisms we're aware of, we have DNA. As human beings, we have 23 pair of chromosomes, and each chromosome you could view as just a very, very, very, very long strand of DNA, and sections of that DNA code for various traits. And each of those sections that code for, say, a certain protein or a part of an enzyme, we call those things genes. We call those things genes. So we have multiple chromosomes. We have 20, as human beings, different species have different number, but as human beings, we have 23 pair of chromosomes."}, {"video_title": "Mutation as a source of variation   Gene expression and regulation   AP Biology   Khan Academy.mp3", "Sentence": "And each of those sections that code for, say, a certain protein or a part of an enzyme, we call those things genes. We call those things genes. So we have multiple chromosomes. We have 20, as human beings, different species have different number, but as human beings, we have 23 pair of chromosomes. Each chromosome you view as a long strand of DNA. Parts of that DNA code for specific genes. And then if you were to zoom in, if you were to zoom in on those genes, you would see these nucleotide sequences."}, {"video_title": "Mutation as a source of variation   Gene expression and regulation   AP Biology   Khan Academy.mp3", "Sentence": "We have 20, as human beings, different species have different number, but as human beings, we have 23 pair of chromosomes. Each chromosome you view as a long strand of DNA. Parts of that DNA code for specific genes. And then if you were to zoom in, if you were to zoom in on those genes, you would see these nucleotide sequences. This is all a review. We've seen this in other videos, where you see your adenine, your guanine, your cytosine, your thymine, in order that carries the information that will eventually be coded into mRNA, which then gets coded into protein. Now, there's two primary sources of variation."}, {"video_title": "Mutation as a source of variation   Gene expression and regulation   AP Biology   Khan Academy.mp3", "Sentence": "And then if you were to zoom in, if you were to zoom in on those genes, you would see these nucleotide sequences. This is all a review. We've seen this in other videos, where you see your adenine, your guanine, your cytosine, your thymine, in order that carries the information that will eventually be coded into mRNA, which then gets coded into protein. Now, there's two primary sources of variation. One source of variation is sexual reproduction. Sexual reproduction. Now, not all organisms reproduce sexually, but many of the ones that we know, including human beings, do."}, {"video_title": "Mutation as a source of variation   Gene expression and regulation   AP Biology   Khan Academy.mp3", "Sentence": "Now, there's two primary sources of variation. One source of variation is sexual reproduction. Sexual reproduction. Now, not all organisms reproduce sexually, but many of the ones that we know, including human beings, do. We're a male member of the species and a female member of the species. Each contribute a random half of their chromosomes to the next organism. So one way to think about sexual reproduction is it keeps shuffling the different versions of the genes that you have in the population into different combinations of those versions of genes."}, {"video_title": "Mutation as a source of variation   Gene expression and regulation   AP Biology   Khan Academy.mp3", "Sentence": "Now, not all organisms reproduce sexually, but many of the ones that we know, including human beings, do. We're a male member of the species and a female member of the species. Each contribute a random half of their chromosomes to the next organism. So one way to think about sexual reproduction is it keeps shuffling the different versions of the genes that you have in the population into different combinations of those versions of genes. And so that generates variation. But sexual reproduction by itself will not create new versions of genes, which we call alleles, or new genes entirely. And so the primary way that that happens is through mutations."}, {"video_title": "Mutation as a source of variation   Gene expression and regulation   AP Biology   Khan Academy.mp3", "Sentence": "So one way to think about sexual reproduction is it keeps shuffling the different versions of the genes that you have in the population into different combinations of those versions of genes. And so that generates variation. But sexual reproduction by itself will not create new versions of genes, which we call alleles, or new genes entirely. And so the primary way that that happens is through mutations. And you might have guessed that we were going to talk about that, because I had this title up here. So another source of variation, and you could almost view this as a more fundamental one, because this would happen even in organisms that aren't reproducing sexually, is that over time, there could be just random mistakes. There could be edits to these genes."}, {"video_title": "Mutation as a source of variation   Gene expression and regulation   AP Biology   Khan Academy.mp3", "Sentence": "And so the primary way that that happens is through mutations. And you might have guessed that we were going to talk about that, because I had this title up here. So another source of variation, and you could almost view this as a more fundamental one, because this would happen even in organisms that aren't reproducing sexually, is that over time, there could be just random mistakes. There could be edits to these genes. And it could be a random, maybe this G gets turned into a C randomly. Or maybe this T and A gets cut out during the DNA replication process. These mutations, which are all about genotype, and let me make this very clear."}, {"video_title": "Mutation as a source of variation   Gene expression and regulation   AP Biology   Khan Academy.mp3", "Sentence": "There could be edits to these genes. And it could be a random, maybe this G gets turned into a C randomly. Or maybe this T and A gets cut out during the DNA replication process. These mutations, which are all about genotype, and let me make this very clear. So when we're looking at this sequence, we're thinking about genotype. Differences in genotype are not always obvious from expressed traits. So sometimes they do change phenotype, or they're observable in phenotype."}, {"video_title": "Mutation as a source of variation   Gene expression and regulation   AP Biology   Khan Academy.mp3", "Sentence": "These mutations, which are all about genotype, and let me make this very clear. So when we're looking at this sequence, we're thinking about genotype. Differences in genotype are not always obvious from expressed traits. So sometimes they do change phenotype, or they're observable in phenotype. Sometimes they're not. But when they are observable in phenotype, as I just mentioned, many times it could be a negative change in phenotype, where it makes it less viable for that organism, or it's harder for them to survive and reproduce. But every now and then, it could result in a variation in phenotype that is maybe neutral, or even confers some type of advantage."}, {"video_title": "Mutation as a source of variation   Gene expression and regulation   AP Biology   Khan Academy.mp3", "Sentence": "So sometimes they do change phenotype, or they're observable in phenotype. Sometimes they're not. But when they are observable in phenotype, as I just mentioned, many times it could be a negative change in phenotype, where it makes it less viable for that organism, or it's harder for them to survive and reproduce. But every now and then, it could result in a variation in phenotype that is maybe neutral, or even confers some type of advantage. So it might have been a random mutation that somehow turned one of these white circles into a blue circle. And there might have been another mutation that turned a white circle into a square, and that just wasn't even viable as an organism. But the blue circles happen to be, in the environment they're in, happen to be a favorable variation."}, {"video_title": "Water potential example   Cell structure and function   AP Biology   Khan Academy.mp3", "Sentence": "Each cube was then placed in one of six open beakers, each containing a different sucrose solution. The cubes remained in the beakers for 24 hours at a constant temperature of 23 degrees Celsius. After 24 hours, the cubes were removed from the beakers, blotted, and re-weighed. The percent change in mass due to a net gain or loss of water was calculated for each cube, and the results are shown in the graph to the right. So this graph right over here. A straight line is drawn on the graph to help estimate results from other sucrose concentrations not tested. Using the straight line on the graph, calculate the water potential in bars of the potato core cubes at 23 degrees Celsius, give your answer to one decimal place."}, {"video_title": "Water potential example   Cell structure and function   AP Biology   Khan Academy.mp3", "Sentence": "The percent change in mass due to a net gain or loss of water was calculated for each cube, and the results are shown in the graph to the right. So this graph right over here. A straight line is drawn on the graph to help estimate results from other sucrose concentrations not tested. Using the straight line on the graph, calculate the water potential in bars of the potato core cubes at 23 degrees Celsius, give your answer to one decimal place. So pause this video and see if you can work that out. All right, so first let's make sure we're understanding what's going on here. So there was a potato."}, {"video_title": "Water potential example   Cell structure and function   AP Biology   Khan Academy.mp3", "Sentence": "Using the straight line on the graph, calculate the water potential in bars of the potato core cubes at 23 degrees Celsius, give your answer to one decimal place. So pause this video and see if you can work that out. All right, so first let's make sure we're understanding what's going on here. So there was a potato. We took six cubes from that potato, and we stuck those six cubes into six different sucrose molarity solutions. And so this data point right over here, this was a situation where we took one of the cubes, so this was a sucrose solution. This was a solution actually that contained no sucrose, and so when we put the cube in that solution, we saw a net gain of mass."}, {"video_title": "Water potential example   Cell structure and function   AP Biology   Khan Academy.mp3", "Sentence": "So there was a potato. We took six cubes from that potato, and we stuck those six cubes into six different sucrose molarity solutions. And so this data point right over here, this was a situation where we took one of the cubes, so this was a sucrose solution. This was a solution actually that contained no sucrose, and so when we put the cube in that solution, we saw a net gain of mass. It looks like it's about 22% gain in mass. And so that would have happened because water would have flowed into the cube. Now the other extreme right over here, this is a solution that has a lot of sucrose in it, a very high sucrose concentration."}, {"video_title": "Water potential example   Cell structure and function   AP Biology   Khan Academy.mp3", "Sentence": "This was a solution actually that contained no sucrose, and so when we put the cube in that solution, we saw a net gain of mass. It looks like it's about 22% gain in mass. And so that would have happened because water would have flowed into the cube. Now the other extreme right over here, this is a solution that has a lot of sucrose in it, a very high sucrose concentration. And when we put a cube in there, we see that the mass of that cube went down by 25%. And that would have been because of a net outflow of water from that cube. So how do we figure out the water potential of the core cubes at 23 degrees Celsius?"}, {"video_title": "Water potential example   Cell structure and function   AP Biology   Khan Academy.mp3", "Sentence": "Now the other extreme right over here, this is a solution that has a lot of sucrose in it, a very high sucrose concentration. And when we put a cube in there, we see that the mass of that cube went down by 25%. And that would have been because of a net outflow of water from that cube. So how do we figure out the water potential of the core cubes at 23 degrees Celsius? Well, we could think about a situation where there's some sucrose concentration where if the cube and the sucrose solution have the same water potential, then you're not going to have any net inflow or outflow. And so where do we see that on the graph? Well what we'd want to do, we have that line where they're trying to fit the data points, and so where would we expect to see 0% change in mass?"}, {"video_title": "Water potential example   Cell structure and function   AP Biology   Khan Academy.mp3", "Sentence": "So how do we figure out the water potential of the core cubes at 23 degrees Celsius? Well, we could think about a situation where there's some sucrose concentration where if the cube and the sucrose solution have the same water potential, then you're not going to have any net inflow or outflow. And so where do we see that on the graph? Well what we'd want to do, we have that line where they're trying to fit the data points, and so where would we expect to see 0% change in mass? So we would go right over here to 0% change in mass. We would go to the line right over there. And then we see that this line would say that there's a 0% change in mass."}, {"video_title": "Water potential example   Cell structure and function   AP Biology   Khan Academy.mp3", "Sentence": "Well what we'd want to do, we have that line where they're trying to fit the data points, and so where would we expect to see 0% change in mass? So we would go right over here to 0% change in mass. We would go to the line right over there. And then we see that this line would say that there's a 0% change in mass. See if this is.4 right over here, this is.5 right over here. So this is about a 0.44 molar sucrose solution. 0.44 molar solution."}, {"video_title": "Water potential example   Cell structure and function   AP Biology   Khan Academy.mp3", "Sentence": "And then we see that this line would say that there's a 0% change in mass. See if this is.4 right over here, this is.5 right over here. So this is about a 0.44 molar sucrose solution. 0.44 molar solution. So if we can figure out the water potential of this 0.44 molar sucrose solution, well that's also going to be the water potential of the potato cubes. Well how do we do that? Well we've seen the equations before where we introduced ourselves to the idea of water potential, that water potential, using the Greek letter psi, is going to be equal to the solute potential plus the pressure potential."}, {"video_title": "Water potential example   Cell structure and function   AP Biology   Khan Academy.mp3", "Sentence": "0.44 molar solution. So if we can figure out the water potential of this 0.44 molar sucrose solution, well that's also going to be the water potential of the potato cubes. Well how do we do that? Well we've seen the equations before where we introduced ourselves to the idea of water potential, that water potential, using the Greek letter psi, is going to be equal to the solute potential plus the pressure potential. Now we're dealing with all open containers, we don't have anything that's some piston or something that's pressing down on these containers. And so because of that, the pressure potential is going to be equal to 0. And so we just have to figure out the solute potential."}, {"video_title": "Water potential example   Cell structure and function   AP Biology   Khan Academy.mp3", "Sentence": "Well we've seen the equations before where we introduced ourselves to the idea of water potential, that water potential, using the Greek letter psi, is going to be equal to the solute potential plus the pressure potential. Now we're dealing with all open containers, we don't have anything that's some piston or something that's pressing down on these containers. And so because of that, the pressure potential is going to be equal to 0. And so we just have to figure out the solute potential. So the solute potential, we have introduced ourselves to this formula in previous videos, it's negative i times c times r times t. This i right over here, this is our ionization constant. This is, since we're dealing with sucrose solution, it says okay, if I took sucrose and put it into water, every one of those sucrose molecules, does it stay one molecule or does it disassociate? Well sucrose just disassociates, it doesn't disassociate at all, it just stays one molecule, so this would be one."}, {"video_title": "Water potential example   Cell structure and function   AP Biology   Khan Academy.mp3", "Sentence": "And so we just have to figure out the solute potential. So the solute potential, we have introduced ourselves to this formula in previous videos, it's negative i times c times r times t. This i right over here, this is our ionization constant. This is, since we're dealing with sucrose solution, it says okay, if I took sucrose and put it into water, every one of those sucrose molecules, does it stay one molecule or does it disassociate? Well sucrose just disassociates, it doesn't disassociate at all, it just stays one molecule, so this would be one. If we're dealing with say sodium chloride, each sodium chloride molecule would disassociate into a sodium ion and a chloride ion, and so then this would be two. But this was one for sucrose. C is the molarity of our solution, and so we estimated that to be 0.44."}, {"video_title": "Water potential example   Cell structure and function   AP Biology   Khan Academy.mp3", "Sentence": "Well sucrose just disassociates, it doesn't disassociate at all, it just stays one molecule, so this would be one. If we're dealing with say sodium chloride, each sodium chloride molecule would disassociate into a sodium ion and a chloride ion, and so then this would be two. But this was one for sucrose. C is the molarity of our solution, and so we estimated that to be 0.44. So let me write this down. Our solute water potential is going to be equal to negative one times 0.44, and that's going to be moles, I'll write down all the units, moles per liter, times, it's sometimes called the pressure constant in this context, but this is also the universal gas constant. If you were doing something like the AP exam, they would give you what this is."}, {"video_title": "Water potential example   Cell structure and function   AP Biology   Khan Academy.mp3", "Sentence": "C is the molarity of our solution, and so we estimated that to be 0.44. So let me write this down. Our solute water potential is going to be equal to negative one times 0.44, and that's going to be moles, I'll write down all the units, moles per liter, times, it's sometimes called the pressure constant in this context, but this is also the universal gas constant. If you were doing something like the AP exam, they would give you what this is. So this is 0.0831 liters times bars, all of that over mole Kelvin. If you're used to seeing other values of this, it's probably because they're dealing with other units right over here, but this is the universal gas constant. And then we have to multiply that times the temperature that we're dealing with in Kelvin."}, {"video_title": "Water potential example   Cell structure and function   AP Biology   Khan Academy.mp3", "Sentence": "If you were doing something like the AP exam, they would give you what this is. So this is 0.0831 liters times bars, all of that over mole Kelvin. If you're used to seeing other values of this, it's probably because they're dealing with other units right over here, but this is the universal gas constant. And then we have to multiply that times the temperature that we're dealing with in Kelvin. Now it's 23 degrees Celsius. To convert to Kelvin, we just add to 273. So 273 plus 23 is going to be 296 Kelvin."}, {"video_title": "Water potential example   Cell structure and function   AP Biology   Khan Academy.mp3", "Sentence": "And then we have to multiply that times the temperature that we're dealing with in Kelvin. Now it's 23 degrees Celsius. To convert to Kelvin, we just add to 273. So 273 plus 23 is going to be 296 Kelvin. And so this is going to be equal to, we have a negative here, and we can look at the units. We have the liter canceling out with liters, moles canceling out with moles, Kelvin canceling out with Kelvin. So we're going to get something in bars, which makes sense."}, {"video_title": "Water potential example   Cell structure and function   AP Biology   Khan Academy.mp3", "Sentence": "So 273 plus 23 is going to be 296 Kelvin. And so this is going to be equal to, we have a negative here, and we can look at the units. We have the liter canceling out with liters, moles canceling out with moles, Kelvin canceling out with Kelvin. So we're going to get something in bars, which makes sense. That is the unit for our water potential. And then we get the calculator out. So we have 0.44 times 0.0831 times 296."}, {"video_title": "Water potential example   Cell structure and function   AP Biology   Khan Academy.mp3", "Sentence": "So we're going to get something in bars, which makes sense. That is the unit for our water potential. And then we get the calculator out. So we have 0.44 times 0.0831 times 296. 296 is equal to, and they want us to round our answer to one decimal place, so approximately 10.8. And we already had that negative out front. So negative 10.8 bars."}, {"video_title": "Water potential example   Cell structure and function   AP Biology   Khan Academy.mp3", "Sentence": "So we have 0.44 times 0.0831 times 296. 296 is equal to, and they want us to round our answer to one decimal place, so approximately 10.8. And we already had that negative out front. So negative 10.8 bars. And we're done. So, to join us today, you'll see the information out front of my blog, so click to log in school. Don't forget to sign up."}, {"video_title": "Intro to the endocrine system   Health & Medicine   Khan Academy.mp3", "Sentence": "Hi, Sal. And so what are we going to talk about? Well the topic for today is endocrinology, which is the study of hormones. And the word hormone is derived from the Greek word which means arouse the activity. And what hormones do is they're chemical messengers that are made at one part of the body and typically go to another part of the body to, as suggested, arouse the activity and give function to another organ. So they're essentially kind of signaling, a way to communicate between one part of the body and the other. Exactly."}, {"video_title": "Intro to the endocrine system   Health & Medicine   Khan Academy.mp3", "Sentence": "And the word hormone is derived from the Greek word which means arouse the activity. And what hormones do is they're chemical messengers that are made at one part of the body and typically go to another part of the body to, as suggested, arouse the activity and give function to another organ. So they're essentially kind of signaling, a way to communicate between one part of the body and the other. Exactly. They're very sophisticated communicators. I think that's a perfect term. And I think the other way to think of it is our body communicates in some ways directly."}, {"video_title": "Intro to the endocrine system   Health & Medicine   Khan Academy.mp3", "Sentence": "Exactly. They're very sophisticated communicators. I think that's a perfect term. And I think the other way to think of it is our body communicates in some ways directly. For instance, nerves innervate muscle. And when you want to contract your muscle, you give a signal from your brain. It goes down the nerve and it directly attaches to the muscle and causes it to contract."}, {"video_title": "Intro to the endocrine system   Health & Medicine   Khan Academy.mp3", "Sentence": "And I think the other way to think of it is our body communicates in some ways directly. For instance, nerves innervate muscle. And when you want to contract your muscle, you give a signal from your brain. It goes down the nerve and it directly attaches to the muscle and causes it to contract. Whereas hormones are more like the Wi-Fi of the human body. They're wireless. They are made at one place."}, {"video_title": "Intro to the endocrine system   Health & Medicine   Khan Academy.mp3", "Sentence": "It goes down the nerve and it directly attaches to the muscle and causes it to contract. Whereas hormones are more like the Wi-Fi of the human body. They're wireless. They are made at one place. They go into the bloodstream, which is like the airwaves, if you will. And then they work on another part of the body at a distance without directly connecting to that part of the body mechanically. And are hormones, are they a specific type of protein or a specific type of chemical?"}, {"video_title": "Intro to the endocrine system   Health & Medicine   Khan Academy.mp3", "Sentence": "They are made at one place. They go into the bloodstream, which is like the airwaves, if you will. And then they work on another part of the body at a distance without directly connecting to that part of the body mechanically. And are hormones, are they a specific type of protein or a specific type of chemical? Are there really anything that does what you just described? It's pretty much anything, but they fall into two major categories. They're small molecules that typically derive from amino acids."}, {"video_title": "Intro to the endocrine system   Health & Medicine   Khan Academy.mp3", "Sentence": "And are hormones, are they a specific type of protein or a specific type of chemical? Are there really anything that does what you just described? It's pretty much anything, but they fall into two major categories. They're small molecules that typically derive from amino acids. And those molecules are just, oh, 300 to 500 at most Daltons, which are molecular mass units up to large proteins that can be hundreds and hundreds of amino acids in size. I see. So anything."}, {"video_title": "Intro to the endocrine system   Health & Medicine   Khan Academy.mp3", "Sentence": "They're small molecules that typically derive from amino acids. And those molecules are just, oh, 300 to 500 at most Daltons, which are molecular mass units up to large proteins that can be hundreds and hundreds of amino acids in size. I see. So anything. Anything that just really has this signaling function. That's right. Would be considered a hormone."}, {"video_title": "Intro to the endocrine system   Health & Medicine   Khan Academy.mp3", "Sentence": "So anything. Anything that just really has this signaling function. That's right. Would be considered a hormone. Right. And the other thing is we talk about hormones in three sort of subcategories. We call some of them endocrine hormones, where they really get into the bloodstream and work at a far distance."}, {"video_title": "Intro to the endocrine system   Health & Medicine   Khan Academy.mp3", "Sentence": "Would be considered a hormone. Right. And the other thing is we talk about hormones in three sort of subcategories. We call some of them endocrine hormones, where they really get into the bloodstream and work at a far distance. And we'll give some examples with your diagram right there in just a minute. But there are others that are called paracrine hormones. And paracrine hormones are more regionally active."}, {"video_title": "Intro to the endocrine system   Health & Medicine   Khan Academy.mp3", "Sentence": "We call some of them endocrine hormones, where they really get into the bloodstream and work at a far distance. And we'll give some examples with your diagram right there in just a minute. But there are others that are called paracrine hormones. And paracrine hormones are more regionally active. So they might be made, let's say, in one part of the body and work within a small distance of that site of synthesis. And then the third category, which is less common, would be autocrine hormones. And the autocrine hormones are actually made directly at one cell and work on that same cell or in the cell right next door at a very, very small distance."}, {"video_title": "Intro to the endocrine system   Health & Medicine   Khan Academy.mp3", "Sentence": "And paracrine hormones are more regionally active. So they might be made, let's say, in one part of the body and work within a small distance of that site of synthesis. And then the third category, which is less common, would be autocrine hormones. And the autocrine hormones are actually made directly at one cell and work on that same cell or in the cell right next door at a very, very small distance. I see. Are these things, you know, when you work, so the endocrine hormones, I think I have a mental model for it. They're kind of released and far away in the body someplace."}, {"video_title": "Intro to the endocrine system   Health & Medicine   Khan Academy.mp3", "Sentence": "And the autocrine hormones are actually made directly at one cell and work on that same cell or in the cell right next door at a very, very small distance. I see. Are these things, you know, when you work, so the endocrine hormones, I think I have a mental model for it. They're kind of released and far away in the body someplace. If they're picked up by the right receptor, they'll have the right function. The paracrine hormones, is their effect small because they only are able to travel a small distance or is it something else? Typically, the paracrine hormones do get into the bloodstream, but the concentration of the receptor, the receiving end, as you suggested, is right close by."}, {"video_title": "Intro to the endocrine system   Health & Medicine   Khan Academy.mp3", "Sentence": "They're kind of released and far away in the body someplace. If they're picked up by the right receptor, they'll have the right function. The paracrine hormones, is their effect small because they only are able to travel a small distance or is it something else? Typically, the paracrine hormones do get into the bloodstream, but the concentration of the receptor, the receiving end, as you suggested, is right close by. So what tends to make a paracrine hormone work regionally is that the high concentration of the receptors are very close to the site of synthesis. I see. I see."}, {"video_title": "Intro to the endocrine system   Health & Medicine   Khan Academy.mp3", "Sentence": "Typically, the paracrine hormones do get into the bloodstream, but the concentration of the receptor, the receiving end, as you suggested, is right close by. So what tends to make a paracrine hormone work regionally is that the high concentration of the receptors are very close to the site of synthesis. I see. I see. And the same with autocrine is often they're made and there's a very high concentration of the receiving end right at that cell, right next to that cell. And this might be a silly question, but, you know, it's called endocrinology. Are there paracrinologists?"}, {"video_title": "Intro to the endocrine system   Health & Medicine   Khan Academy.mp3", "Sentence": "I see. And the same with autocrine is often they're made and there's a very high concentration of the receiving end right at that cell, right next to that cell. And this might be a silly question, but, you know, it's called endocrinology. Are there paracrinologists? Well, it's a good point. I don't think so. I think we just, perhaps because the paracrine function of hormones was discovered later, we still carry this all under the umbrella of endocrinology."}, {"video_title": "Intro to the endocrine system   Health & Medicine   Khan Academy.mp3", "Sentence": "Are there paracrinologists? Well, it's a good point. I don't think so. I think we just, perhaps because the paracrine function of hormones was discovered later, we still carry this all under the umbrella of endocrinology. Right. So all of hormones is endocrinology, even though endocrine hormones are the ones that act at far distances. That's right."}, {"video_title": "Intro to the endocrine system   Health & Medicine   Khan Academy.mp3", "Sentence": "I think we just, perhaps because the paracrine function of hormones was discovered later, we still carry this all under the umbrella of endocrinology. Right. So all of hormones is endocrinology, even though endocrine hormones are the ones that act at far distances. That's right. I think that's a good way to summarize it. Now, I like the diagram that you created here because it illustrates some of the major endocrine organs, the ones we'll be focusing on in later lectures. So the first one that you showed very nicely in the head, at the base of the brain is that orange structure, and that would be the pituitary gland."}, {"video_title": "Intro to the endocrine system   Health & Medicine   Khan Academy.mp3", "Sentence": "That's right. I think that's a good way to summarize it. Now, I like the diagram that you created here because it illustrates some of the major endocrine organs, the ones we'll be focusing on in later lectures. So the first one that you showed very nicely in the head, at the base of the brain is that orange structure, and that would be the pituitary gland. That's right. And the pituitary gland is called the master gland because from the pituitary we make hormones that work on yet other organs. So I'll give you an example, one of the hormones that's made by the pituitary is called thyroid stimulating hormone or TSH."}, {"video_title": "Intro to the endocrine system   Health & Medicine   Khan Academy.mp3", "Sentence": "So the first one that you showed very nicely in the head, at the base of the brain is that orange structure, and that would be the pituitary gland. That's right. And the pituitary gland is called the master gland because from the pituitary we make hormones that work on yet other organs. So I'll give you an example, one of the hormones that's made by the pituitary is called thyroid stimulating hormone or TSH. And after it leaves the pituitary, it goes into the circulation and it acts on the thyroid gland where there are high receptors for TSH on the surface of the thyroid cells. And it stimulates the thyroid gland to make thyroid hormone, typically thyroxine T4 or triiodothyronine T3. Those would be the two main circulating thyroid hormones."}, {"video_title": "Intro to the endocrine system   Health & Medicine   Khan Academy.mp3", "Sentence": "So I'll give you an example, one of the hormones that's made by the pituitary is called thyroid stimulating hormone or TSH. And after it leaves the pituitary, it goes into the circulation and it acts on the thyroid gland where there are high receptors for TSH on the surface of the thyroid cells. And it stimulates the thyroid gland to make thyroid hormone, typically thyroxine T4 or triiodothyronine T3. Those would be the two main circulating thyroid hormones. And what do those do? Those regulate metabolism, they regulate appetite, they regulate thermogenesis, they regulate muscle function, they have widespread activities on other parts of the body. But it kind of upregulates or downregulates the entire body and the metabolism."}, {"video_title": "Intro to the endocrine system   Health & Medicine   Khan Academy.mp3", "Sentence": "Those would be the two main circulating thyroid hormones. And what do those do? Those regulate metabolism, they regulate appetite, they regulate thermogenesis, they regulate muscle function, they have widespread activities on other parts of the body. But it kind of upregulates or downregulates the entire body and the metabolism. That's right. So someone with hyperthyroidism would have very high metabolism. You may know the classic picture of someone with a high heart rate, rapid metabolism, weight loss, that would be someone with excess amounts of thyroid hormone."}, {"video_title": "Intro to the endocrine system   Health & Medicine   Khan Academy.mp3", "Sentence": "But it kind of upregulates or downregulates the entire body and the metabolism. That's right. So someone with hyperthyroidism would have very high metabolism. You may know the classic picture of someone with a high heart rate, rapid metabolism, weight loss, that would be someone with excess amounts of thyroid hormone. And then you see pretty much the inverse picture when someone has a deficiency of thyroid hormone and someone with hypothyroidism. So it's critical to maintain just the right amount of almost all of these hormones and the thyroid hormones are good examples of that. But the ultimate regulation is from that pituitary gland."}, {"video_title": "Intro to the endocrine system   Health & Medicine   Khan Academy.mp3", "Sentence": "You may know the classic picture of someone with a high heart rate, rapid metabolism, weight loss, that would be someone with excess amounts of thyroid hormone. And then you see pretty much the inverse picture when someone has a deficiency of thyroid hormone and someone with hypothyroidism. So it's critical to maintain just the right amount of almost all of these hormones and the thyroid hormones are good examples of that. But the ultimate regulation is from that pituitary gland. This is kind of the master one. It sends a signal there and then that kind of does the\u2026 That's right. And we'll talk later about feedback loops because how does the pituitary know when to stop making TSH?"}, {"video_title": "Intro to the endocrine system   Health & Medicine   Khan Academy.mp3", "Sentence": "But the ultimate regulation is from that pituitary gland. This is kind of the master one. It sends a signal there and then that kind of does the\u2026 That's right. And we'll talk later about feedback loops because how does the pituitary know when to stop making TSH? And basically, like a thermostat, it can sense the levels of thyroid hormone and when those levels are just at the right level and not too high, it will decrease the amount of TSH it makes. If the levels are too low, it will increase TSH to try to stimulate the thyroid gland to make yet more thyroid hormone. Very cool."}, {"video_title": "Intro to the endocrine system   Health & Medicine   Khan Academy.mp3", "Sentence": "And we'll talk later about feedback loops because how does the pituitary know when to stop making TSH? And basically, like a thermostat, it can sense the levels of thyroid hormone and when those levels are just at the right level and not too high, it will decrease the amount of TSH it makes. If the levels are too low, it will increase TSH to try to stimulate the thyroid gland to make yet more thyroid hormone. Very cool. And what else do we have here? Okay. So the other hormones, some of the major ones, the pituitary, in addition to making the thyroid stimulating hormones, it makes a hormone called ACTH, adrenal corticotrophic hormone, which acts on the adrenal cortex."}, {"video_title": "Intro to the endocrine system   Health & Medicine   Khan Academy.mp3", "Sentence": "Very cool. And what else do we have here? Okay. So the other hormones, some of the major ones, the pituitary, in addition to making the thyroid stimulating hormones, it makes a hormone called ACTH, adrenal corticotrophic hormone, which acts on the adrenal cortex. And the adrenal is that gland exactly that sits on top of the kidney and the outer layers of the adrenal gland are the adrenal cortex and those are stimulated by ACTH. And they're not related to the kidney. They just sit on top there."}, {"video_title": "Intro to the endocrine system   Health & Medicine   Khan Academy.mp3", "Sentence": "So the other hormones, some of the major ones, the pituitary, in addition to making the thyroid stimulating hormones, it makes a hormone called ACTH, adrenal corticotrophic hormone, which acts on the adrenal cortex. And the adrenal is that gland exactly that sits on top of the kidney and the outer layers of the adrenal gland are the adrenal cortex and those are stimulated by ACTH. And they're not related to the kidney. They just sit on top there. They're structurally there. Right. They're related only in that sense that the blood supply is rich like the kidney's blood supply and they happen to sit above the kidney."}, {"video_title": "Intro to the endocrine system   Health & Medicine   Khan Academy.mp3", "Sentence": "They just sit on top there. They're structurally there. Right. They're related only in that sense that the blood supply is rich like the kidney's blood supply and they happen to sit above the kidney. And they're called adrenal because they're adjacent to the kidney, which is the renal part. Oh, that should have been obvious. I never realized that."}, {"video_title": "Intro to the endocrine system   Health & Medicine   Khan Academy.mp3", "Sentence": "They're related only in that sense that the blood supply is rich like the kidney's blood supply and they happen to sit above the kidney. And they're called adrenal because they're adjacent to the kidney, which is the renal part. Oh, that should have been obvious. I never realized that. And they filter blood or do any of the key functions that the kidney subserves. I see. And what's their role?"}, {"video_title": "Intro to the endocrine system   Health & Medicine   Khan Academy.mp3", "Sentence": "I never realized that. And they filter blood or do any of the key functions that the kidney subserves. I see. And what's their role? So the adrenal glands make the adrenal hormones like cortisol, which regulates glucose metabolism and is important to maintaining blood pressure and well-being. And then it makes mineralocorticoids like aldosterone, which is important for regulating salt and water balance. You also have adrenal androgens, which are somewhat important and those three hormones are the main hormones made by the adrenal cortex."}, {"video_title": "Intro to the endocrine system   Health & Medicine   Khan Academy.mp3", "Sentence": "And what's their role? So the adrenal glands make the adrenal hormones like cortisol, which regulates glucose metabolism and is important to maintaining blood pressure and well-being. And then it makes mineralocorticoids like aldosterone, which is important for regulating salt and water balance. You also have adrenal androgens, which are somewhat important and those three hormones are the main hormones made by the adrenal cortex. I see. The ACTH primarily regulates the cortisol and the adrenal androgens. And there's another system that regulates the mineralocorticoids that we'll talk about later."}, {"video_title": "Intro to the endocrine system   Health & Medicine   Khan Academy.mp3", "Sentence": "You also have adrenal androgens, which are somewhat important and those three hormones are the main hormones made by the adrenal cortex. I see. The ACTH primarily regulates the cortisol and the adrenal androgens. And there's another system that regulates the mineralocorticoids that we'll talk about later. Okay. And we have a few more organs here. Yeah."}, {"video_title": "Intro to the endocrine system   Health & Medicine   Khan Academy.mp3", "Sentence": "And there's another system that regulates the mineralocorticoids that we'll talk about later. Okay. And we have a few more organs here. Yeah. So also out of the pituitary, we make luteinizing hormone and follicle stimulating hormone. Those would be abbreviated LH and FSH. LH and FSH."}, {"video_title": "Intro to the endocrine system   Health & Medicine   Khan Academy.mp3", "Sentence": "Yeah. So also out of the pituitary, we make luteinizing hormone and follicle stimulating hormone. Those would be abbreviated LH and FSH. LH and FSH. And those act on the gonads. So in the male, it'll act on the testis and the female, it'll act on the ovaries to stimulate the development of sperm in the male and oocytes or eggs in the female and also the production of gonadal steroids, primarily testosterone in the male and estradiol in the female. Right, right."}, {"video_title": "Intro to the endocrine system   Health & Medicine   Khan Academy.mp3", "Sentence": "LH and FSH. And those act on the gonads. So in the male, it'll act on the testis and the female, it'll act on the ovaries to stimulate the development of sperm in the male and oocytes or eggs in the female and also the production of gonadal steroids, primarily testosterone in the male and estradiol in the female. Right, right. And are we missing anything? Well, there are two other hormones that also derive from the anterior pituitary and those would be growth hormone that's critical for optimal growth of long bones. Pituitary really does do a lot."}, {"video_title": "Intro to the endocrine system   Health & Medicine   Khan Academy.mp3", "Sentence": "Right, right. And are we missing anything? Well, there are two other hormones that also derive from the anterior pituitary and those would be growth hormone that's critical for optimal growth of long bones. Pituitary really does do a lot. It does. Yeah. And so that would target..."}, {"video_title": "Intro to the endocrine system   Health & Medicine   Khan Academy.mp3", "Sentence": "Pituitary really does do a lot. It does. Yeah. And so that would target... So the space here would drive human growth hormone? Yeah, human growth hormone. And that would act on long bones, for instance."}, {"video_title": "Intro to the endocrine system   Health & Medicine   Khan Academy.mp3", "Sentence": "And so that would target... So the space here would drive human growth hormone? Yeah, human growth hormone. And that would act on long bones, for instance. And then we would have prolactin, which is important in women for lactation, being able to breastfeed after delivering a child. And insulin is... Insulin is key, but it doesn't come from the pituitary. So now we're going to work our way down a little bit."}, {"video_title": "Intro to the endocrine system   Health & Medicine   Khan Academy.mp3", "Sentence": "And that would act on long bones, for instance. And then we would have prolactin, which is important in women for lactation, being able to breastfeed after delivering a child. And insulin is... Insulin is key, but it doesn't come from the pituitary. So now we're going to work our way down a little bit. We talked about the thyroid gland making thyroid hormone. And then when you get to the pancreas, which is that yellow structure right in the middle, inside the pancreas, there are small islands called the islets of Langerhans. And the islets within the pancreas make endocrine hormones like insulin and glucagon."}, {"video_title": "Intro to the endocrine system   Health & Medicine   Khan Academy.mp3", "Sentence": "So now we're going to work our way down a little bit. We talked about the thyroid gland making thyroid hormone. And then when you get to the pancreas, which is that yellow structure right in the middle, inside the pancreas, there are small islands called the islets of Langerhans. And the islets within the pancreas make endocrine hormones like insulin and glucagon. But insulin is vital. Without insulin, you have diabetes. And without insulin, you don't transport glucose into muscle and remove glucose from the bloodstream normally."}, {"video_title": "Intro to the endocrine system   Health & Medicine   Khan Academy.mp3", "Sentence": "And the islets within the pancreas make endocrine hormones like insulin and glucagon. But insulin is vital. Without insulin, you have diabetes. And without insulin, you don't transport glucose into muscle and remove glucose from the bloodstream normally. Right. And the absence of insulin can produce all of the symptoms of diabetes that we'll talk about later. Right."}, {"video_title": "Intro to the endocrine system   Health & Medicine   Khan Academy.mp3", "Sentence": "And without insulin, you don't transport glucose into muscle and remove glucose from the bloodstream normally. Right. And the absence of insulin can produce all of the symptoms of diabetes that we'll talk about later. Right. And it seems just structurally, you have the pancreas right here, you have the adrenal glands right there, that they're all near those kind of that interchange on the... Because they're also important to get to where they need to get to. That's a good observation. They all have a lot of venous drainage from them so that when they make their hormone, it gets into the bloodstream rather quickly because they are vital structures."}, {"video_title": "Intro to the endocrine system   Health & Medicine   Khan Academy.mp3", "Sentence": "Right. And it seems just structurally, you have the pancreas right here, you have the adrenal glands right there, that they're all near those kind of that interchange on the... Because they're also important to get to where they need to get to. That's a good observation. They all have a lot of venous drainage from them so that when they make their hormone, it gets into the bloodstream rather quickly because they are vital structures. Very cool. So I think we could leave it there and then in the next video, you have some pictures I think would be pretty interesting. Okay."}, {"video_title": "Intro to the endocrine system   Health & Medicine   Khan Academy.mp3", "Sentence": "They all have a lot of venous drainage from them so that when they make their hormone, it gets into the bloodstream rather quickly because they are vital structures. Very cool. So I think we could leave it there and then in the next video, you have some pictures I think would be pretty interesting. Okay. Yeah. In the next video, we'll talk about sort of how you have to have the right amount of the hormone or else things go awry. Very cool."}, {"video_title": "Prokaryotic and eukaryotic cells   Biology   Khan Academy.mp3", "Sentence": "When we want to categorize life as we know it at a very high level, we can categorize it as either eukaryotic, eukaryotic, or as a eukaryote, eukaryote, or as a prokaryote, pro, prokaryote. And the largest distinction between a eukaryote and a prokaryote are membrane-bound structures that eukaryotes have that prokaryotes, prokaryotes don't have. And the most noticeable of which is a membrane-bound nucleus. So in a eukaryote, the genetic information is going to be inside a membrane-bound nucleus. So this right over here, this is the nucleus. This is the nucleus, and you have your genetic information inside it. You have your DNA."}, {"video_title": "Prokaryotic and eukaryotic cells   Biology   Khan Academy.mp3", "Sentence": "So in a eukaryote, the genetic information is going to be inside a membrane-bound nucleus. So this right over here, this is the nucleus. This is the nucleus, and you have your genetic information inside it. You have your DNA. Here, for a prokaryotic cell, you're going to have your DNA, and it might be bundled up into a section of the cell. We would call that a nucleoid. But it's not membrane-bound."}, {"video_title": "Prokaryotic and eukaryotic cells   Biology   Khan Academy.mp3", "Sentence": "You have your DNA. Here, for a prokaryotic cell, you're going to have your DNA, and it might be bundled up into a section of the cell. We would call that a nucleoid. But it's not membrane-bound. So let me write this down. No membrane, membrane, membrane, let me write a little, membrane-bound, membrane-bound nucleus. But that's not just, that's not the only distinction between eukaryotes and prokaryotes, although it's the one that's most noted."}, {"video_title": "Prokaryotic and eukaryotic cells   Biology   Khan Academy.mp3", "Sentence": "But it's not membrane-bound. So let me write this down. No membrane, membrane, membrane, let me write a little, membrane-bound, membrane-bound nucleus. But that's not just, that's not the only distinction between eukaryotes and prokaryotes, although it's the one that's most noted. In fact, the word eukaryote, the karyote part, comes from the Greek for nut or kernel. So let me make this clear. So this is referring to a nut, a nut, or a kernel, or a kernel, while prokaryote means before the nut or kernel."}, {"video_title": "Prokaryotic and eukaryotic cells   Biology   Khan Academy.mp3", "Sentence": "But that's not just, that's not the only distinction between eukaryotes and prokaryotes, although it's the one that's most noted. In fact, the word eukaryote, the karyote part, comes from the Greek for nut or kernel. So let me make this clear. So this is referring to a nut, a nut, or a kernel, or a kernel, while prokaryote means before the nut or kernel. So we don't see, and I guess you could think of the nut or the kernel as the membrane-bound structure, especially the membrane-bound nucleus over here. But that's not all. Eukaryotes will also have other membrane-bound structures that you will not see in prokaryotes."}, {"video_title": "Prokaryotic and eukaryotic cells   Biology   Khan Academy.mp3", "Sentence": "So this is referring to a nut, a nut, or a kernel, or a kernel, while prokaryote means before the nut or kernel. So we don't see, and I guess you could think of the nut or the kernel as the membrane-bound structure, especially the membrane-bound nucleus over here. But that's not all. Eukaryotes will also have other membrane-bound structures that you will not see in prokaryotes. For example, you will tend to see mitochondria, mitochondria in a eukaryotic cell, both plant and animal cells, but you won't see it in a prokaryotic cell. And there's other types of membrane-bound structures. You could see things like Golgi apparatus."}, {"video_title": "Prokaryotic and eukaryotic cells   Biology   Khan Academy.mp3", "Sentence": "Eukaryotes will also have other membrane-bound structures that you will not see in prokaryotes. For example, you will tend to see mitochondria, mitochondria in a eukaryotic cell, both plant and animal cells, but you won't see it in a prokaryotic cell. And there's other types of membrane-bound structures. You could see things like Golgi apparatus. And this over here is a micrograph of a eukaryotic cell. And you see the Golgi apparatus right over here, which helps package proteins. You see a micrograph of mitochondria."}, {"video_title": "Prokaryotic and eukaryotic cells   Biology   Khan Academy.mp3", "Sentence": "You could see things like Golgi apparatus. And this over here is a micrograph of a eukaryotic cell. And you see the Golgi apparatus right over here, which helps package proteins. You see a micrograph of mitochondria. This is a micrograph of the nucleus. So this right over here is the nuclear membrane. And then you see all the genetic information."}, {"video_title": "Prokaryotic and eukaryotic cells   Biology   Khan Academy.mp3", "Sentence": "You see a micrograph of mitochondria. This is a micrograph of the nucleus. So this right over here is the nuclear membrane. And then you see all the genetic information. It's all spread out. It's in chromatin form right over here. But you see it's especially densely packed right over here."}, {"video_title": "Prokaryotic and eukaryotic cells   Biology   Khan Academy.mp3", "Sentence": "And then you see all the genetic information. It's all spread out. It's in chromatin form right over here. But you see it's especially densely packed right over here. And we've also depicted it in this right over there. So this is all the DNA in chromatin form, but this part that looks extra dense or dark in this micrograph right over there, we call that the nucleolus. We call that the nucleolus."}, {"video_title": "Prokaryotic and eukaryotic cells   Biology   Khan Academy.mp3", "Sentence": "But you see it's especially densely packed right over here. And we've also depicted it in this right over there. So this is all the DNA in chromatin form, but this part that looks extra dense or dark in this micrograph right over there, we call that the nucleolus. We call that the nucleolus. And we now know that this is where ribosomal RNA is being produced. And ribosomal RNA, that forms part of the structure of ribosomes, which are essential in the translation, or I guess you could say the construction of proteins based on the information in mRNA. And we can go into a lot more depth in that in other videos."}, {"video_title": "Prokaryotic and eukaryotic cells   Biology   Khan Academy.mp3", "Sentence": "We call that the nucleolus. And we now know that this is where ribosomal RNA is being produced. And ribosomal RNA, that forms part of the structure of ribosomes, which are essential in the translation, or I guess you could say the construction of proteins based on the information in mRNA. And we can go into a lot more depth in that in other videos. So these are ribosomes right over here, and they're made up of ribosomal RNA, and they're also made up of proteins. And so this nucleolus over there, that's where that's happening, that denser part of the nucleus. So the key distinction, eukaryotic cell, you have a membrane-bound nucleus."}, {"video_title": "Prokaryotic and eukaryotic cells   Biology   Khan Academy.mp3", "Sentence": "And we can go into a lot more depth in that in other videos. So these are ribosomes right over here, and they're made up of ribosomal RNA, and they're also made up of proteins. And so this nucleolus over there, that's where that's happening, that denser part of the nucleus. So the key distinction, eukaryotic cell, you have a membrane-bound nucleus. You have other membrane-bound structures like mitochondria. In fact, there's some theories that mitochondria first evolved as prokaryotic organisms that eventually lived in symbiosis inside of eukaryotic, inside of a larger eukaryotic cell. And then the other distinction is that in eukaryotes, the DNA tends to be in multiple strands."}, {"video_title": "Prokaryotic and eukaryotic cells   Biology   Khan Academy.mp3", "Sentence": "So the key distinction, eukaryotic cell, you have a membrane-bound nucleus. You have other membrane-bound structures like mitochondria. In fact, there's some theories that mitochondria first evolved as prokaryotic organisms that eventually lived in symbiosis inside of eukaryotic, inside of a larger eukaryotic cell. And then the other distinction is that in eukaryotes, the DNA tends to be in multiple strands. So the DNA, if you were to kind of straighten it out, it would be in multiple strands. While in a prokaryote, the DNA tends to be circular. It can be all flipped around and whatever else, but at the end of the day, it would be circular DNA."}, {"video_title": "Prokaryotic and eukaryotic cells   Biology   Khan Academy.mp3", "Sentence": "And then the other distinction is that in eukaryotes, the DNA tends to be in multiple strands. So the DNA, if you were to kind of straighten it out, it would be in multiple strands. While in a prokaryote, the DNA tends to be circular. It can be all flipped around and whatever else, but at the end of the day, it would be circular DNA. So those are the three core distinctions, nuclear membrane, other membrane-bound organelles like mitochondria and the Golgi apparatus. And then you also have multiple single strands of DNA versus circular DNA. Other things is that eukaryotes tend to be larger, while prokaryotes tend to be smaller and they tend to be simpler."}, {"video_title": "Prokaryotic and eukaryotic cells   Biology   Khan Academy.mp3", "Sentence": "It can be all flipped around and whatever else, but at the end of the day, it would be circular DNA. So those are the three core distinctions, nuclear membrane, other membrane-bound organelles like mitochondria and the Golgi apparatus. And then you also have multiple single strands of DNA versus circular DNA. Other things is that eukaryotes tend to be larger, while prokaryotes tend to be smaller and they tend to be simpler. So now that we know the key distinctions, what are examples of eukaryotes? Well, eukaryotes include most of what we interact with on a daily basis, or we think we're interacting with on a daily basis. This includes all multicellular organisms."}, {"video_title": "Prokaryotic and eukaryotic cells   Biology   Khan Academy.mp3", "Sentence": "Other things is that eukaryotes tend to be larger, while prokaryotes tend to be smaller and they tend to be simpler. So now that we know the key distinctions, what are examples of eukaryotes? Well, eukaryotes include most of what we interact with on a daily basis, or we think we're interacting with on a daily basis. This includes all multicellular organisms. So multicellular, multicellular organisms. So I'm thinking animals, plants, fungi. It includes protists."}, {"video_title": "Prokaryotic and eukaryotic cells   Biology   Khan Academy.mp3", "Sentence": "This includes all multicellular organisms. So multicellular, multicellular organisms. So I'm thinking animals, plants, fungi. It includes protists. This is a paramecium right over here. This is eukaryotic. It's going to have a membrane-bound nucleus and other organelles."}, {"video_title": "Prokaryotic and eukaryotic cells   Biology   Khan Academy.mp3", "Sentence": "It includes protists. This is a paramecium right over here. This is eukaryotic. It's going to have a membrane-bound nucleus and other organelles. This right over here, these are onion root tip cells. So these are plant cells, and you can actually see it's been stained. You can actually see the membrane-bound nucleus here, and this is actually a cool picture because you can see the cells at different stages of mitosis, which is interesting."}, {"video_title": "Prokaryotic and eukaryotic cells   Biology   Khan Academy.mp3", "Sentence": "It's going to have a membrane-bound nucleus and other organelles. This right over here, these are onion root tip cells. So these are plant cells, and you can actually see it's been stained. You can actually see the membrane-bound nucleus here, and this is actually a cool picture because you can see the cells at different stages of mitosis, which is interesting. Animal cells, the things that make you you. You are eukaryotic. So what is prokaryotic?"}, {"video_title": "Prokaryotic and eukaryotic cells   Biology   Khan Academy.mp3", "Sentence": "You can actually see the membrane-bound nucleus here, and this is actually a cool picture because you can see the cells at different stages of mitosis, which is interesting. Animal cells, the things that make you you. You are eukaryotic. So what is prokaryotic? Well, bacteria is probably the most common example of that. Bacteria right over here. These are prokaryotes, and the thing that's talked about a lot less is archaea."}, {"video_title": "Prokaryotic and eukaryotic cells   Biology   Khan Academy.mp3", "Sentence": "So what is prokaryotic? Well, bacteria is probably the most common example of that. Bacteria right over here. These are prokaryotes, and the thing that's talked about a lot less is archaea. And archaea, people initially thought that these were a form of bacteria that just lived in very extreme conditions, but now they know that it's a completely different domain of life. Archaea. Archaea."}, {"video_title": "Prokaryotic and eukaryotic cells   Biology   Khan Academy.mp3", "Sentence": "These are prokaryotes, and the thing that's talked about a lot less is archaea. And archaea, people initially thought that these were a form of bacteria that just lived in very extreme conditions, but now they know that it's a completely different domain of life. Archaea. Archaea. And so when we think about the domains of life, people, the current thought is that you have bacteria here, bacteria here, you have archaea, you have archaea, archaea, and then you have, and then you have eukaryotes. I'll do it there. And then you have eukaryotes."}, {"video_title": "Prokaryotic and eukaryotic cells   Biology   Khan Academy.mp3", "Sentence": "Archaea. And so when we think about the domains of life, people, the current thought is that you have bacteria here, bacteria here, you have archaea, you have archaea, archaea, and then you have, and then you have eukaryotes. I'll do it there. And then you have eukaryotes. Eukaryotes. And these are things that have all of the traits that we've talked about, and so these include plants and animals and fungi and unicellular eukaryotes, protists and things like that. And so if we, once again, just high level, we would consider these prokaryotes, and these, of course, are the eukaryotes."}, {"video_title": "Prokaryotic and eukaryotic cells   Biology   Khan Academy.mp3", "Sentence": "And then you have eukaryotes. Eukaryotes. And these are things that have all of the traits that we've talked about, and so these include plants and animals and fungi and unicellular eukaryotes, protists and things like that. And so if we, once again, just high level, we would consider these prokaryotes, and these, of course, are the eukaryotes. So hopefully that gives you a good overview of things."}, {"video_title": "Prokaryotic and eukaryotic cells   Biology   Khan Academy.mp3", "Sentence": "And so if we, once again, just high level, we would consider these prokaryotes, and these, of course, are the eukaryotes. So hopefully that gives you a good overview of things."}]