Sentence stringlengths 158 2.09k | video_title stringlengths 11 104 |
|---|---|
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 o... | Endomembrane system Structure of a cell Biology Khan Academy.mp3 |
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 co... | Endomembrane system Structure of a cell Biology Khan Academy.mp3 |
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 assoc... | Endomembrane system Structure of a cell Biology Khan Academy.mp3 |
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 ... | Endomembrane system Structure of a cell Biology Khan Academy.mp3 |
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 t... | Endomembrane system Structure of a cell Biology Khan Academy.mp3 |
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... | Endomembrane system Structure of a cell Biology Khan Academy.mp3 |
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 h... | Endomembrane system Structure of a cell Biology Khan Academy.mp3 |
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 th... | Endomembrane system Structure of a cell Biology Khan Academy.mp3 |
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... | Endomembrane system Structure of a cell Biology Khan Academy.mp3 |
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 lyso... | Endomembrane system Structure of a cell Biology Khan Academy.mp3 |
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. W... | Endosymbiosis theory Cell structure and function AP Biology Khan Academy.mp3 |
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 mi... | Endosymbiosis theory Cell structure and function AP Biology Khan Academy.mp3 |
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. An... | Endosymbiosis theory Cell structure and function AP Biology Khan Academy.mp3 |
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, independ... | Endosymbiosis theory Cell structure and function AP Biology Khan Academy.mp3 |
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... | Endosymbiosis theory Cell structure and function AP Biology Khan Academy.mp3 |
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... | Endosymbiosis theory Cell structure and function AP Biology Khan Academy.mp3 |
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 e... | Endosymbiosis theory Cell structure and function AP Biology Khan Academy.mp3 |
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 wh... | Scale of cells Structure of a cell Biology Khan Academy.mp3 |
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 ove... | Scale of cells Structure of a cell Biology Khan Academy.mp3 |
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 visuali... | Scale of cells Structure of a cell Biology Khan Academy.mp3 |
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 milli... | Scale of cells Structure of a cell Biology Khan Academy.mp3 |
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... | Scale of cells Structure of a cell Biology Khan Academy.mp3 |
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 bi... | Scale of cells Structure of a cell Biology Khan Academy.mp3 |
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... | Scale of cells Structure of a cell Biology Khan Academy.mp3 |
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... | Scale of cells Structure of a cell Biology Khan Academy.mp3 |
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 of cells Structure of a cell Biology Khan Academy.mp3 |
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 ... | Scale of cells Structure of a cell Biology Khan Academy.mp3 |
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 th... | Scale of cells Structure of a cell Biology Khan Academy.mp3 |
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 ... | Scale of cells Structure of a cell Biology Khan Academy.mp3 |
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 act... | Scale of cells Structure of a cell Biology Khan Academy.mp3 |
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 h... | Scale of cells Structure of a cell Biology Khan Academy.mp3 |
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... | Scale of cells Structure of a cell Biology Khan Academy.mp3 |
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 mete... | Scale of cells Structure of a cell Biology Khan Academy.mp3 |
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 mete... | Scale of cells Structure of a cell Biology Khan Academy.mp3 |
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 con... | Scale of cells Structure of a cell Biology Khan Academy.mp3 |
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 ... | Scale of cells Structure of a cell Biology Khan Academy.mp3 |
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 wh... | Scale of cells Structure of a cell Biology Khan Academy.mp3 |
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 w... | Scale of cells Structure of a cell Biology Khan Academy.mp3 |
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... | Scale of cells Structure of a cell Biology Khan Academy.mp3 |
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 re... | Pedigree for determining probability of exhibiting sex linked recessive trait Khan Academy (2).mp3 |
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 figu... | Pedigree for determining probability of exhibiting sex linked recessive trait Khan Academy (2).mp3 |
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... | Pedigree for determining probability of exhibiting sex linked recessive trait Khan Academy (2).mp3 |
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... | Pedigree for determining probability of exhibiting sex linked recessive trait Khan Academy (2).mp3 |
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... | Pedigree for determining probability of exhibiting sex linked recessive trait Khan Academy (2).mp3 |
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... | Pedigree for determining probability of exhibiting sex linked recessive trait Khan Academy (2).mp3 |
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 mus... | Pedigree for determining probability of exhibiting sex linked recessive trait Khan Academy (2).mp3 |
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 ... | Pedigree for determining probability of exhibiting sex linked recessive trait Khan Academy (2).mp3 |
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 t... | Pedigree for determining probability of exhibiting sex linked recessive trait Khan Academy (2).mp3 |
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 reces... | Pedigree for determining probability of exhibiting sex linked recessive trait Khan Academy (2).mp3 |
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 all... | Pedigree for determining probability of exhibiting sex linked recessive trait Khan Academy (2).mp3 |
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 fr... | Pedigree for determining probability of exhibiting sex linked recessive trait Khan Academy (2).mp3 |
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 ... | Pedigree for determining probability of exhibiting sex linked recessive trait Khan Academy (2).mp3 |
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 al... | Pedigree for determining probability of exhibiting sex linked recessive trait Khan Academy (2).mp3 |
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 o... | Pedigree for determining probability of exhibiting sex linked recessive trait Khan Academy (2).mp3 |
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... | Pedigree for determining probability of exhibiting sex linked recessive trait Khan Academy (2).mp3 |
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 ca... | Pedigree for determining probability of exhibiting sex linked recessive trait Khan Academy (2).mp3 |
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 f... | Pedigree for determining probability of exhibiting sex linked recessive trait Khan Academy (2).mp3 |
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 ... | Pedigree for determining probability of exhibiting sex linked recessive trait Khan Academy (2).mp3 |
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 chro... | Pedigree for determining probability of exhibiting sex linked recessive trait Khan Academy (2).mp3 |
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. B... | Genetic drift, bottleneck effect and founder effect Biology Khan Academy.mp3 |
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 i... | Genetic drift, bottleneck effect and founder effect Biology Khan Academy.mp3 |
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'r... | Genetic drift, bottleneck effect and founder effect Biology Khan Academy.mp3 |
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 cha... | Genetic drift, bottleneck effect and founder effect Biology Khan Academy.mp3 |
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 t... | Genetic drift, bottleneck effect and founder effect Biology Khan Academy.mp3 |
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... | Genetic drift, bottleneck effect and founder effect Biology Khan Academy.mp3 |
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 t... | Genetic drift, bottleneck effect and founder effect Biology Khan Academy.mp3 |
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.... | Genetic drift, bottleneck effect and founder effect Biology Khan Academy.mp3 |
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 ... | Genetic drift, bottleneck effect and founder effect Biology Khan Academy.mp3 |
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 lik... | Genetic drift, bottleneck effect and founder effect Biology Khan Academy.mp3 |
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 ... | Genetic drift, bottleneck effect and founder effect Biology Khan Academy.mp3 |
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 ho... | Genetic drift, bottleneck effect and founder effect Biology Khan Academy.mp3 |
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 re... | Genetic drift, bottleneck effect and founder effect Biology Khan Academy.mp3 |
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 l... | Genetic drift, bottleneck effect and founder effect Biology Khan Academy.mp3 |
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 ... | Genetic drift, bottleneck effect and founder effect Biology Khan Academy.mp3 |
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 ver... | Genetic drift, bottleneck effect and founder effect Biology Khan Academy.mp3 |
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 peo... | Genetic drift, bottleneck effect and founder effect Biology Khan Academy.mp3 |
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... | Genetic drift, bottleneck effect and founder effect Biology Khan Academy.mp3 |
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... | Genetic drift, bottleneck effect and founder effect Biology Khan Academy.mp3 |
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... | Genetic drift, bottleneck effect and founder effect Biology Khan Academy.mp3 |
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 bottlenec... | Genetic drift, bottleneck effect and founder effect Biology Khan Academy.mp3 |
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 ten... | Genetic drift, bottleneck effect and founder effect Biology Khan Academy.mp3 |
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 vi... | Genetic drift, bottleneck effect and founder effect Biology Khan Academy.mp3 |
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 putt... | Genetic drift, bottleneck effect and founder effect Biology Khan Academy.mp3 |
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, ... | Genetic drift, bottleneck effect and founder effect Biology Khan Academy.mp3 |
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 becomi... | Genetic drift, bottleneck effect and founder effect Biology Khan Academy.mp3 |
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 co... | Genetic drift, bottleneck effect and founder effect Biology Khan Academy.mp3 |
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 the... | Genetic drift, bottleneck effect and founder effect Biology Khan Academy.mp3 |
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.... | Genetic drift, bottleneck effect and founder effect Biology Khan Academy.mp3 |
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 po... | Genetic drift, bottleneck effect and founder effect Biology Khan Academy.mp3 |
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 g... | Genetic drift, bottleneck effect and founder effect Biology Khan Academy.mp3 |
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 ... | Conceptual overview of light dependent reactions.mp3 |
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... | Conceptual overview of light dependent reactions.mp3 |
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 se... | Conceptual overview of light dependent reactions.mp3 |
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... | Conceptual overview of light dependent reactions.mp3 |
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... | Conceptual overview of light dependent reactions.mp3 |
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 h... | Conceptual overview of light dependent reactions.mp3 |
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 i... | Conceptual overview of light dependent reactions.mp3 |
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 wave... | Conceptual overview of light dependent reactions.mp3 |
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 st... | Conceptual overview of light dependent reactions.mp3 |
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 electr... | Conceptual overview of light dependent reactions.mp3 |
Subsets and Splits
No community queries yet
The top public SQL queries from the community will appear here once available.