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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. | Antiparallel structure of DNA strands Biology Khan Academy.mp3 |
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. | Antiparallel structure of DNA strands Biology Khan Academy.mp3 |
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 othe... | Antiparallel structure of DNA strands Biology Khan Academy.mp3 |
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... | Antiparallel structure of DNA strands Biology Khan Academy.mp3 |
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 ... | Antiparallel structure of DNA strands Biology Khan Academy.mp3 |
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... | Antiparallel structure of DNA strands Biology Khan Academy.mp3 |
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 tha... | Antiparallel structure of DNA strands Biology Khan Academy.mp3 |
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... | Antiparallel structure of DNA strands Biology Khan Academy.mp3 |
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... | Antiparallel structure of DNA strands Biology Khan Academy.mp3 |
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 numb... | Antiparallel structure of DNA strands Biology Khan Academy.mp3 |
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 pr... | Antiparallel structure of DNA strands Biology Khan Academy.mp3 |
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. | Antiparallel structure of DNA strands Biology Khan Academy.mp3 |
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 ... | Antiparallel structure of DNA strands Biology Khan Academy.mp3 |
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. | Antiparallel structure of DNA strands Biology Khan Academy.mp3 |
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 conne... | Antiparallel structure of DNA strands Biology Khan Academy.mp3 |
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 phosp... | Antiparallel structure of DNA strands Biology Khan Academy.mp3 |
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 car... | Antiparallel structure of DNA strands Biology Khan Academy.mp3 |
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 pho... | Antiparallel structure of DNA strands Biology Khan Academy.mp3 |
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... | Antiparallel structure of DNA strands Biology Khan Academy.mp3 |
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 ... | Antiparallel structure of DNA strands Biology Khan Academy.mp3 |
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 pri... | Antiparallel structure of DNA strands Biology Khan Academy.mp3 |
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... | Antiparallel structure of DNA strands Biology Khan Academy.mp3 |
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... | Antiparallel structure of DNA strands Biology Khan Academy.mp3 |
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... | Antiparallel structure of DNA strands Biology Khan Academy.mp3 |
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 the... | Antiparallel structure of DNA strands Biology Khan Academy.mp3 |
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... | Antiparallel structure of DNA strands Biology Khan Academy.mp3 |
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.... | Antiparallel structure of DNA strands Biology Khan Academy.mp3 |
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 com... | Interactions between populations Ecology Khan Academy.mp3 |
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,... | Interactions between populations Ecology Khan Academy.mp3 |
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 ... | Interactions between populations Ecology Khan Academy.mp3 |
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... | Interactions between populations Ecology Khan Academy.mp3 |
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 ... | Interactions between populations Ecology Khan Academy.mp3 |
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 bushba... | Interactions between populations Ecology Khan Academy.mp3 |
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... | Interactions between populations Ecology Khan Academy.mp3 |
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 ... | Interactions between populations Ecology Khan Academy.mp3 |
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. | Interactions between populations Ecology Khan Academy.mp3 |
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 ... | Interactions between populations Ecology Khan Academy.mp3 |
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 hav... | Interactions between populations Ecology Khan Academy.mp3 |
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, ... | Interactions between populations Ecology Khan Academy.mp3 |
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 real... | Interactions between populations Ecology Khan Academy.mp3 |
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 bene... | Interactions between populations Ecology Khan Academy.mp3 |
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? | Interactions between populations Ecology Khan Academy.mp3 |
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. | Interactions between populations Ecology Khan Academy.mp3 |
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 yo... | Interactions between populations Ecology Khan Academy.mp3 |
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 fro... | Interactions between populations Ecology Khan Academy.mp3 |
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. | Interactions between populations Ecology Khan Academy.mp3 |
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. | Interactions between populations Ecology Khan Academy.mp3 |
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. | Interactions between populations Ecology Khan Academy.mp3 |
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 w... | Interactions between populations Ecology Khan Academy.mp3 |
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... | Interactions between populations Ecology Khan Academy.mp3 |
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 a... | Interactions between populations Ecology Khan Academy.mp3 |
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 wher... | Interactions between populations Ecology Khan Academy.mp3 |
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 exa... | Interactions between populations Ecology Khan Academy.mp3 |
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 providi... | Interactions between populations Ecology Khan Academy.mp3 |
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 of... | Interactions between populations Ecology Khan Academy.mp3 |
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 ... | Interactions between populations Ecology Khan Academy.mp3 |
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 ac... | Interactions between populations Ecology Khan Academy.mp3 |
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. I... | Interactions between populations Ecology Khan Academy.mp3 |
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 interacti... | Interactions between populations Ecology Khan Academy.mp3 |
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. The... | How Did All Dinosaurs Except Birds Go Extinct.mp3 |
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 after... | How Did All Dinosaurs Except Birds Go Extinct.mp3 |
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 ... | How Did All Dinosaurs Except Birds Go Extinct.mp3 |
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... | How Did All Dinosaurs Except Birds Go Extinct.mp3 |
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... | Loss of cell cycle control in cancer Cells MCAT Khan Academy.mp3 |
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 wi... | Loss of cell cycle control in cancer Cells MCAT Khan Academy.mp3 |
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 ... | Loss of cell cycle control in cancer Cells MCAT Khan Academy.mp3 |
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 tumo... | Loss of cell cycle control in cancer Cells MCAT Khan Academy.mp3 |
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... | Loss of cell cycle control in cancer Cells MCAT Khan Academy.mp3 |
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 ... | Loss of cell cycle control in cancer Cells MCAT Khan Academy.mp3 |
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 cell cycle control in cancer Cells MCAT Khan Academy.mp3 |
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 suppr... | Loss of cell cycle control in cancer Cells MCAT Khan Academy.mp3 |
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 f... | Loss of cell cycle control in cancer Cells MCAT Khan Academy.mp3 |
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 bigge... | Origins of life Biology Khan Academy.mp3 |
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, billi... | Origins of life Biology Khan Academy.mp3 |
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 form... | Origins of life Biology Khan Academy.mp3 |
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... | Origins of life Biology Khan Academy.mp3 |
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 wit... | Origins of life Biology Khan Academy.mp3 |
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... | Origins of life Biology Khan Academy.mp3 |
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 typ... | Origins of life Biology Khan Academy.mp3 |
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 typ... | Origins of life Biology Khan Academy.mp3 |
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 ... | Origins of life Biology Khan Academy.mp3 |
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 ... | Origins of life Biology Khan Academy.mp3 |
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 phosph... | Origins of life Biology Khan Academy.mp3 |
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 slightl... | Origins of life Biology Khan Academy.mp3 |
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 simp... | Origins of life Biology Khan Academy.mp3 |
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 ... | Origins of life Biology Khan Academy.mp3 |
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... | Origins of life Biology Khan Academy.mp3 |
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 oth... | Origins of life Biology Khan Academy.mp3 |
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 ... | Origins of life Biology Khan Academy.mp3 |
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 ... | Origins of life Biology Khan Academy.mp3 |
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 molecu... | Origins of life Biology Khan Academy.mp3 |
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 hav... | Origins of life Biology Khan Academy.mp3 |
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,... | Origins of life Biology Khan Academy.mp3 |
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... | Origins of life Biology Khan Academy.mp3 |
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 hy... | Origins of life Biology Khan Academy.mp3 |
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 ... | Origins of life Biology Khan Academy.mp3 |
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 a... | Origins of life Biology Khan Academy.mp3 |
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 ... | Origins of life Biology Khan Academy.mp3 |
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 a... | Origins of life Biology Khan Academy.mp3 |
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 an... | Animal communication Individuals and Society MCAT Khan Academy.mp3 |
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