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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 righ... | Phases of meiosis II Cells MCAT Khan Academy.mp3 |
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 ... | Phases of meiosis II Cells MCAT Khan Academy.mp3 |
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. | Phases of meiosis II Cells MCAT Khan Academy.mp3 |
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. | Phases of meiosis II Cells MCAT Khan Academy.mp3 |
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 li... | Phases of meiosis II Cells MCAT Khan Academy.mp3 |
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 th... | Phases of meiosis II Cells MCAT Khan Academy.mp3 |
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 on... | Phases of meiosis II Cells MCAT Khan Academy.mp3 |
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 dr... | Phases of meiosis II Cells MCAT Khan Academy.mp3 |
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 u... | Phases of meiosis II Cells MCAT Khan Academy.mp3 |
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 th... | Phases of meiosis II Cells MCAT Khan Academy.mp3 |
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. Telop... | Phases of meiosis II Cells MCAT Khan Academy.mp3 |
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... | Phases of meiosis II Cells MCAT Khan Academy.mp3 |
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 mage... | Phases of meiosis II Cells MCAT Khan Academy.mp3 |
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... | Phases of meiosis II Cells MCAT Khan Academy.mp3 |
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. | Phases of meiosis II Cells MCAT Khan Academy.mp3 |
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 unrave... | Phases of meiosis II Cells MCAT Khan Academy.mp3 |
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 microtubule... | Phases of meiosis II Cells MCAT Khan Academy.mp3 |
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. | Phases of meiosis II Cells MCAT Khan Academy.mp3 |
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. | Phases of meiosis II Cells MCAT Khan Academy.mp3 |
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. | Phases of meiosis II Cells MCAT Khan Academy.mp3 |
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. | Phases of meiosis II Cells MCAT Khan Academy.mp3 |
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. | Phases of meiosis II Cells MCAT Khan Academy.mp3 |
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 meiosi... | Phases of meiosis II Cells MCAT Khan Academy.mp3 |
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 ... | Phases of meiosis II Cells MCAT Khan Academy.mp3 |
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 c... | Phases of meiosis II Cells MCAT Khan Academy.mp3 |
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 coul... | Phases of meiosis II Cells MCAT Khan Academy.mp3 |
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 g... | Translation (mRNA to protein) Biomolecules MCAT Khan Academy.mp3 |
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... | Translation (mRNA to protein) Biomolecules MCAT Khan Academy.mp3 |
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 t... | Translation (mRNA to protein) Biomolecules MCAT Khan Academy.mp3 |
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... | Translation (mRNA to protein) Biomolecules MCAT Khan Academy.mp3 |
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... | Translation (mRNA to protein) Biomolecules MCAT Khan Academy.mp3 |
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 primar... | Translation (mRNA to protein) Biomolecules MCAT Khan Academy.mp3 |
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 enco... | Translation (mRNA to protein) Biomolecules MCAT Khan Academy.mp3 |
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 wh... | Translation (mRNA to protein) Biomolecules MCAT Khan Academy.mp3 |
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 amin... | Translation (mRNA to protein) Biomolecules MCAT Khan Academy.mp3 |
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 w... | Translation (mRNA to protein) Biomolecules MCAT Khan Academy.mp3 |
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 ... | Translation (mRNA to protein) Biomolecules MCAT Khan Academy.mp3 |
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 t... | Translation (mRNA to protein) Biomolecules MCAT Khan Academy.mp3 |
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 tim... | Translation (mRNA to protein) Biomolecules MCAT Khan Academy.mp3 |
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... | Translation (mRNA to protein) Biomolecules MCAT Khan Academy.mp3 |
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,... | Translation (mRNA to protein) Biomolecules MCAT Khan Academy.mp3 |
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 ... | Translation (mRNA to protein) Biomolecules MCAT Khan Academy.mp3 |
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 h... | Translation (mRNA to protein) Biomolecules MCAT Khan Academy.mp3 |
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 ... | Translation (mRNA to protein) Biomolecules MCAT Khan Academy.mp3 |
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... | Translation (mRNA to protein) Biomolecules MCAT Khan Academy.mp3 |
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 o... | Translation (mRNA to protein) Biomolecules MCAT Khan Academy.mp3 |
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 go... | Translation (mRNA to protein) Biomolecules MCAT Khan Academy.mp3 |
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 ... | Translation (mRNA to protein) Biomolecules MCAT Khan Academy.mp3 |
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 go... | Translation (mRNA to protein) Biomolecules MCAT Khan Academy.mp3 |
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 ... | Translation (mRNA to protein) Biomolecules MCAT Khan Academy.mp3 |
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 happe... | Translation (mRNA to protein) Biomolecules MCAT Khan Academy.mp3 |
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... | Translation (mRNA to protein) Biomolecules MCAT Khan Academy.mp3 |
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 ... | Translation (mRNA to protein) Biomolecules MCAT Khan Academy.mp3 |
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 g... | Translation (mRNA to protein) Biomolecules MCAT Khan Academy.mp3 |
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 cha... | Translation (mRNA to protein) Biomolecules MCAT Khan Academy.mp3 |
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... | Translation (mRNA to protein) Biomolecules MCAT Khan Academy.mp3 |
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 migh... | Importance of water for life Chemistry of life AP Biology Khan Academy.mp3 |
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... | Importance of water for life Chemistry of life AP Biology Khan Academy.mp3 |
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 ele... | Importance of water for life Chemistry of life AP Biology Khan Academy.mp3 |
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 th... | Importance of water for life Chemistry of life AP Biology Khan Academy.mp3 |
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 ... | Importance of water for life Chemistry of life AP Biology Khan Academy.mp3 |
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 w... | Importance of water for life Chemistry of life AP Biology Khan Academy.mp3 |
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 i... | Importance of water for life Chemistry of life AP Biology Khan Academy.mp3 |
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. | Importance of water for life Chemistry of life AP Biology Khan Academy.mp3 |
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 ma... | Importance of water for life Chemistry of life AP Biology Khan Academy.mp3 |
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 ... | Importance of water for life Chemistry of life AP Biology Khan Academy.mp3 |
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... | Importance of water for life Chemistry of life AP Biology Khan Academy.mp3 |
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... | Importance of water for life Chemistry of life AP Biology Khan Academy.mp3 |
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 hav... | Importance of water for life Chemistry of life AP Biology Khan Academy.mp3 |
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 w... | Importance of water for life Chemistry of life AP Biology Khan Academy.mp3 |
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, ... | Importance of water for life Chemistry of life AP Biology Khan Academy.mp3 |
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 p... | Importance of water for life Chemistry of life AP Biology Khan Academy.mp3 |
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... | Importance of water for life Chemistry of life AP Biology Khan Academy.mp3 |
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 ... | Importance of water for life Chemistry of life AP Biology Khan Academy.mp3 |
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 ... | Importance of water for life Chemistry of life AP Biology Khan Academy.mp3 |
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 dro... | Importance of water for life Chemistry of life AP Biology Khan Academy.mp3 |
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 ... | Importance of water for life Chemistry of life AP Biology Khan Academy.mp3 |
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 ... | Importance of water for life Chemistry of life AP Biology Khan Academy.mp3 |
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 real... | Importance of water for life Chemistry of life AP Biology Khan Academy.mp3 |
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... | Importance of water for life Chemistry of life AP Biology Khan Academy.mp3 |
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, th... | Importance of water for life Chemistry of life AP Biology Khan Academy.mp3 |
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 a... | Importance of water for life Chemistry of life AP Biology Khan Academy.mp3 |
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 th... | Importance of water for life Chemistry of life AP Biology Khan Academy.mp3 |
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 s... | Importance of water for life Chemistry of life AP Biology Khan Academy.mp3 |
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 ... | Fertilization terminology gametes, zygotes, haploid, diploid MCAT Khan Academy.mp3 |
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 on... | Fertilization terminology gametes, zygotes, haploid, diploid MCAT Khan Academy.mp3 |
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 pro... | Fertilization terminology gametes, zygotes, haploid, diploid MCAT Khan Academy.mp3 |
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 ... | Fertilization terminology gametes, zygotes, haploid, diploid MCAT Khan Academy.mp3 |
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, o... | Fertilization terminology gametes, zygotes, haploid, diploid MCAT Khan Academy.mp3 |
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 nucle... | Fertilization terminology gametes, zygotes, haploid, diploid MCAT Khan Academy.mp3 |
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 ch... | Fertilization terminology gametes, zygotes, haploid, diploid MCAT Khan Academy.mp3 |
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. ... | Fertilization terminology gametes, zygotes, haploid, diploid MCAT Khan Academy.mp3 |
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 agai... | Fertilization terminology gametes, zygotes, haploid, diploid MCAT Khan Academy.mp3 |
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, th... | Fertilization terminology gametes, zygotes, haploid, diploid MCAT Khan Academy.mp3 |
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-de... | Fertilization terminology gametes, zygotes, haploid, diploid MCAT Khan Academy.mp3 |
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... | Fertilization terminology gametes, zygotes, haploid, diploid MCAT Khan Academy.mp3 |
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, b... | Fertilization terminology gametes, zygotes, haploid, diploid MCAT Khan Academy.mp3 |
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... | Fertilization terminology gametes, zygotes, haploid, diploid MCAT Khan Academy.mp3 |
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. On... | Fertilization terminology gametes, zygotes, haploid, diploid MCAT Khan Academy.mp3 |
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, f... | Fertilization terminology gametes, zygotes, haploid, diploid MCAT Khan Academy.mp3 |
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