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And those lizards probably don't like to be around birds or owls, because those owls eat them. So that might be deterrent. And then the other example they said is, look, they tend to be eaten by this lizard right here. This is what Wikipedia told me. And that this lizard tends to be eaten by this frog right there, and ... | Natural Selection and the Owl Butterfly.mp3 |
This is what Wikipedia told me. And that this lizard tends to be eaten by this frog right there, and that the eyes of this butterfly are not too dissimilar to the eyes of this frog. And you know, we can debate whether or not that's the case. And if this was the predator we're trying to mimic, you could make an argument... | Natural Selection and the Owl Butterfly.mp3 |
And if this was the predator we're trying to mimic, you could make an argument that maybe we would have had more green on our wing. But that's not the point of this video. But it's a fun discussion to have as to what is useful about this eye. But let's have the question, how did that eye come about? And when I say that... | Natural Selection and the Owl Butterfly.mp3 |
But let's have the question, how did that eye come about? And when I say that eye, I mean the pattern on that wing. What set of events allowed this to happen? Because when I described evolution, and we know that everything in our biological kingdom is just a set of proteins and then stuff that maybe the protein can't. ... | Natural Selection and the Owl Butterfly.mp3 |
Because when I described evolution, and we know that everything in our biological kingdom is just a set of proteins and then stuff that maybe the protein can't. But mainly protein. And that protein's all coded for by DNA. I'm going to do future videos on DNA. But DNA is just a sequence of base pairs. It's a sequence of... | Natural Selection and the Owl Butterfly.mp3 |
I'm going to do future videos on DNA. But DNA is just a sequence of base pairs. It's a sequence of these molecules. And we represent the adenine and guanine and then cytosine and thymine. And maybe you have a couple of adenines in a row and some guanine and thymine. And I'll do a lot more on this in the future. But the... | Natural Selection and the Owl Butterfly.mp3 |
And we represent the adenine and guanine and then cytosine and thymine. And maybe you have a couple of adenines in a row and some guanine and thymine. And I'll do a lot more on this in the future. But the idea is, look, it's just coded for by this sequence of these molecules. How do you get a sequence? How do you go fr... | Natural Selection and the Owl Butterfly.mp3 |
But the idea is, look, it's just coded for by this sequence of these molecules. How do you get a sequence? How do you go from a butterfly that has no eye to all of a sudden an eye that goes there? Obviously, just one change that happens from a random mutation, maybe that G turns into an A, or maybe this C and this T ge... | Natural Selection and the Owl Butterfly.mp3 |
Obviously, just one change that happens from a random mutation, maybe that G turns into an A, or maybe this C and this T get deleted. So everything. That alone isn't going to develop this beautiful of a pattern or this useful of a pattern. So how do the random changes explain something that's this intricate? And this i... | Natural Selection and the Owl Butterfly.mp3 |
So how do the random changes explain something that's this intricate? And this is my explanation. And obviously, I wasn't sitting there watching over the thousands or millions of years as these owl butterflies emerged. So this is just my theory of how natural selection does explain this type of phenomenon. You have a w... | Natural Selection and the Owl Butterfly.mp3 |
So this is just my theory of how natural selection does explain this type of phenomenon. You have a world where you have, in some environment, you have butterflies. And their wings look like, let's say you have some butterflies that are generally like this. That's their wing. And it's a very bad drawing, but I think yo... | Natural Selection and the Owl Butterfly.mp3 |
That's their wing. And it's a very bad drawing, but I think you get the idea. And there's just some general patterns. We've seen it before. There's variation. And the variation does show up from these little random changes in DNA. And I think we can all believe that, that most of these changes are kind of benign. | Natural Selection and the Owl Butterfly.mp3 |
We've seen it before. There's variation. And the variation does show up from these little random changes in DNA. And I think we can all believe that, that most of these changes are kind of benign. Maybe they just set up differently where a little pattern will show up or a little speck of pigment will show up with a sli... | Natural Selection and the Owl Butterfly.mp3 |
And I think we can all believe that, that most of these changes are kind of benign. Maybe they just set up differently where a little pattern will show up or a little speck of pigment will show up with a slightly different color. And we even see amongst these owl butterflies, there is variation. This dude's wing is dif... | Natural Selection and the Owl Butterfly.mp3 |
This dude's wing is different than that guy's wing, with the commonality that they do have these eye-looking shapes. And there's not just one. There's actually multiple. This guy has this other thing up here that looks interesting. And they have multiple things, but the one really noticeable feature is this eye-looking... | Natural Selection and the Owl Butterfly.mp3 |
This guy has this other thing up here that looks interesting. And they have multiple things, but the one really noticeable feature is this eye-looking thing. So how do we go from this to an eye-looking thing? So the idea is you have some variation. One guy might look like that. Another guy or gal might, just randomly, ... | Natural Selection and the Owl Butterfly.mp3 |
So the idea is you have some variation. One guy might look like that. Another guy or gal might, just randomly, their dot might be something like that. Another gal or guy, these wings are really badly drawn, but you get the idea. This is the butterfly's antenna right there. That's its body. Another person's patterns, or... | Natural Selection and the Owl Butterfly.mp3 |
Another gal or guy, these wings are really badly drawn, but you get the idea. This is the butterfly's antenna right there. That's its body. Another person's patterns, or butterfly's patterns, might look like this. And so they're just random. But when they go into a certain environment, for whatever reason, maybe one of... | Natural Selection and the Owl Butterfly.mp3 |
Another person's patterns, or butterfly's patterns, might look like this. And so they're just random. But when they go into a certain environment, for whatever reason, maybe one of its predators, maybe that theory that these are supposed to look like eyes is true. And so actually, maybe this guy just has a random patte... | Natural Selection and the Owl Butterfly.mp3 |
And so actually, maybe this guy just has a random pattern here. And so this guy, and I'm not saying that it's definitely better, they're both going to be found and killed by predators. But it's all probabilistic. Maybe this guy has a 1% less chance of getting a predator. Because when a predator just looks at them out o... | Natural Selection and the Owl Butterfly.mp3 |
Maybe this guy has a 1% less chance of getting a predator. Because when a predator just looks at them out of the corner of that eye, that little, really hazy region kind of looks like an eye. And a predator would be better off just not messing with it. And they'd rather go after the dude that looks like this. So it's j... | Natural Selection and the Owl Butterfly.mp3 |
And they'd rather go after the dude that looks like this. So it's just a slight probability. Now you might say, OK, what's 1% going to do? But when you compound that 1% over thousands and thousands of generations, all of a sudden, this trait might dominate. And because he's just going to be killed that less frequently.... | Natural Selection and the Owl Butterfly.mp3 |
But when you compound that 1% over thousands and thousands of generations, all of a sudden, this trait might dominate. And because he's just going to be killed that less frequently. 1% less frequently. Now maybe this guy has a similar trait, but his spot is closer to the abdomen. And here it's a trade-off. Because mayb... | Natural Selection and the Owl Butterfly.mp3 |
Now maybe this guy has a similar trait, but his spot is closer to the abdomen. And here it's a trade-off. Because maybe some predators get scared away by this concentration of pigment. And once again, I'm not saying that we're here yet. We're not at this kind of very advanced, sophisticated pattern yet. We're at this r... | Natural Selection and the Owl Butterfly.mp3 |
And once again, I'm not saying that we're here yet. We're not at this kind of very advanced, sophisticated pattern yet. We're at this random concentration of pigment that just shows up. So we see that people who have this concentration of pigment further away from their abdomen, they do well. But when it's too close, m... | Natural Selection and the Owl Butterfly.mp3 |
So we see that people who have this concentration of pigment further away from their abdomen, they do well. But when it's too close, maybe some predators think that that's actually an insect and they want to eat it. So that's actually a bad trait. So what happens is this guy dominates. And so within this population, yo... | Natural Selection and the Owl Butterfly.mp3 |
So what happens is this guy dominates. And so within this population, you start having a lot of variation, because he's more likely to pass on these traits. And I want to make that point very clear. This isn't what happens over the course of an animal's lifetime. It's not like if somehow I experience something, or at l... | Natural Selection and the Owl Butterfly.mp3 |
This isn't what happens over the course of an animal's lifetime. It's not like if somehow I experience something, or at least our current theory, if I experience something, that I can somehow pass on that knowledge to my child. What it says is if my DNA just happens to have just some variation that happens to be more u... | Natural Selection and the Owl Butterfly.mp3 |
So then the population, you're going to have variations within that. Maybe some guys, it's going to get a little bit look like that, maybe another one's going to look a little bit like that. Maybe there's some spots there. You can kind of view it as the variation is, quote unquote, exploring. But I want to be very clea... | Natural Selection and the Owl Butterfly.mp3 |
You can kind of view it as the variation is, quote unquote, exploring. But I want to be very clear not to use any active verbs here, because this is all being done really as almost a common sense process, where everything changes. The changes that are most suited are the ones that are going to survive more frequently. ... | Natural Selection and the Owl Butterfly.mp3 |
And then the next generation is going to have more of that, and then you'll have variation within that change. And then this one might be like that. And maybe this is the one. These were good compared to that, but now when you're competing amongst themselves, this one is able to reproduce 1% more than this guy or this ... | Natural Selection and the Owl Butterfly.mp3 |
These were good compared to that, but now when you're competing amongst themselves, this one is able to reproduce 1% more than this guy or this guy. So this guy becomes, and maybe it's some combination of all the above, and they mix and match. It's a hugely complex system. But then this guy represents most of the popul... | Natural Selection and the Owl Butterfly.mp3 |
But then this guy represents most of the population. And when I say this guy, I'm saying this guy's genetic information, at least as which pertains to his wings. And then you get variation amongst that. Maybe some of it, they have a little small dot, and there's some dots around it. Maybe it's like this. Maybe one of t... | Natural Selection and the Owl Butterfly.mp3 |
Maybe some of it, they have a little small dot, and there's some dots around it. Maybe it's like this. Maybe one of them digresses and goes back here, but then he has trouble competing, so he gets knocked out again. And then some other people have it back here. I think you get the point. That this isn't happening overn... | Natural Selection and the Owl Butterfly.mp3 |
And then some other people have it back here. I think you get the point. That this isn't happening overnight. These changes can be fairly incremental, but we're doing it over thousands of generations. So when you're talking about thousands of generations, or even millions of generations, even a 1% advantage can be sign... | Natural Selection and the Owl Butterfly.mp3 |
These changes can be fairly incremental, but we're doing it over thousands of generations. So when you're talking about thousands of generations, or even millions of generations, even a 1% advantage can be significant. And when you accumulate those variations over a large period of time, you can get to fairly intricate... | Natural Selection and the Owl Butterfly.mp3 |
So I just wanted to explain that, because this is often used as, hey, sure, I can believe the butterfly moth, or I can even maybe believe the examples of the antibiotics and the bacteria or the flu. I mean, because those are kind of real-time examples. But how does something this intricate show up? And I actually want ... | Natural Selection and the Owl Butterfly.mp3 |
And I actually want to make a point here. We think this is more intricate because we can relate to it in our everyday lives. But if you actually look at a structure of a bacteria and how it operates, or what a virus does to infiltrate an immune system or a cell, that's actually on a lot more levels, a lot more intricat... | Natural Selection and the Owl Butterfly.mp3 |
In fact, the whole reason why I'm using this as an example is because this is a fairly simple example, as opposed to kind of explaining the metabolism of a certain type of bacteria and how that might change and how it might become immune to penicillin or whatever else. But I want to make this very clear that these very... | Natural Selection and the Owl Butterfly.mp3 |
No, it happens over large periods of time. Although there might be some little weird hormonal change that does this, but I'm not going to go there. But that is possible. But I just want to make this point because I think the more examples we see, the more it'll kind of hit home that this is a passive process. We're not... | Natural Selection and the Owl Butterfly.mp3 |
But I just want to make this point because I think the more examples we see, the more it'll kind of hit home that this is a passive process. We're not talking about these things happening overnight. And it's actually really interesting to kind of look at our world around us and look at ecosystems as they are today, and... | Natural Selection and the Owl Butterfly.mp3 |
For example, are things, are traits that occur after reproduction selected for? Well, probably not, unless they affect the reproduction of the next cycle. For example, you might say, oh, well, the trait to be nurturing after reproductive years, that's after reproductive years. No, but it helps your offspring reproduce.... | Natural Selection and the Owl Butterfly.mp3 |
Before we go in depth on meiosis, I want to do a very high level overview comparing mitosis to meiosis. So in mitosis, and this is all a review if you've watched the mitosis video. In mitosis, we start with a cell, we start with a cell that has a diploid number of chromosomes. I'll just write 2N to show it has the dipl... | Comparing mitosis and meiosis Cells MCAT Khan Academy.mp3 |
I'll just write 2N to show it has the diploid number. For human beings, this would be 46 chromosomes. 46 for humans. You get 23 chromosomes from your mother, 23 chromosomes from your father, or you could say you have 23 homologous pairs, which leads to 46 chromosomes. Now after the process of mitosis happens, and you h... | Comparing mitosis and meiosis Cells MCAT Khan Academy.mp3 |
You get 23 chromosomes from your mother, 23 chromosomes from your father, or you could say you have 23 homologous pairs, which leads to 46 chromosomes. Now after the process of mitosis happens, and you have your cytokinesis and all the rest, you end up with two cells that each have the same genetic information as the o... | Comparing mitosis and meiosis Cells MCAT Khan Academy.mp3 |
So 2N and 2N. And now each of these cells are just like this cell was. It can go through interphase again, and it grows, and it can replicate its DNA and its centrosomes, and grow some more, and then each of these can go through mitosis again. And this is actually how most of the cells in your body grow. This is how yo... | Comparing mitosis and meiosis Cells MCAT Khan Academy.mp3 |
And this is actually how most of the cells in your body grow. This is how you turn from a single cell organism into you, or for the most part, into you. So that is mitosis. And one way to think about it, it's a cycle. After each of these things go through mitosis, they can then go through the entire cell cycle again. A... | Comparing mitosis and meiosis Cells MCAT Khan Academy.mp3 |
And one way to think about it, it's a cycle. After each of these things go through mitosis, they can then go through the entire cell cycle again. And let me write this a little bit neater. Mitosis. That S was a little bit hard to read. Now what happens in meiosis? What happens in meiosis? | Comparing mitosis and meiosis Cells MCAT Khan Academy.mp3 |
Mitosis. That S was a little bit hard to read. Now what happens in meiosis? What happens in meiosis? I'll do that over here. In meiosis, something slightly different happens. And it happens in two phases. | Comparing mitosis and meiosis Cells MCAT Khan Academy.mp3 |
What happens in meiosis? I'll do that over here. In meiosis, something slightly different happens. And it happens in two phases. So you will start with a cell that has a diploid number of chromosomes. So you will start with a cell that has a diploid number of chromosomes. And in its interphase, it also replicates its D... | Comparing mitosis and meiosis Cells MCAT Khan Academy.mp3 |
And it happens in two phases. So you will start with a cell that has a diploid number of chromosomes. So you will start with a cell that has a diploid number of chromosomes. And in its interphase, it also replicates its DNA. And then it goes through something called meiosis I. And in meiosis I, what you end up with is ... | Comparing mitosis and meiosis Cells MCAT Khan Academy.mp3 |
And in its interphase, it also replicates its DNA. And then it goes through something called meiosis I. And in meiosis I, what you end up with is two cells that now have a haploid number of chromosomes. So you end up with two cells. You now have two cells that each have a haploid number of chromosomes. So you have N, a... | Comparing mitosis and meiosis Cells MCAT Khan Academy.mp3 |
So you end up with two cells. You now have two cells that each have a haploid number of chromosomes. So you have N, and you have N. So if we're talking about human beings, you have 46 chromosomes here, and now you have 23 chromosomes in this nucleus, and now you have 23 in this nucleus, but you're still not done. Then ... | Comparing mitosis and meiosis Cells MCAT Khan Academy.mp3 |
Then each of these will then go through a phase, which I'll talk about in a second, which is very similar to mitosis, which will duplicate this entire cell into two. So actually, let me do it like this. So now, this one, you're going to have four. You're going to have four cells that each have the haploid number of chr... | Comparing mitosis and meiosis Cells MCAT Khan Academy.mp3 |
You're going to have four cells that each have the haploid number of chromosomes. And they all don't necessarily have the same genetic information anymore. Because as we go through this first phase, right over here of meiosis, and this first phase where you go from diploid to haploid, right over here, this is called me... | Comparing mitosis and meiosis Cells MCAT Khan Academy.mp3 |
So this one might get some of the homologous, some of the ones that you originally got from your father, and some of the ones that you originally got from your mother. Some of the ones that you originally got from your father, some of the ones that you originally got from your mother. They split randomly, but each homo... | Comparing mitosis and meiosis Cells MCAT Khan Academy.mp3 |
And then in this phase, meiosis two, so this phase right over here is called meiosis two, it's very similar to mitosis, except you're now dealing with cells that start off with the haploid number. And it's important to realize meiosis is not a cycle. These cells that you have over here, these are gametes. These are sex... | Comparing mitosis and meiosis Cells MCAT Khan Academy.mp3 |
These are sex cells. These are gametes. These can now be used in fertilization. If we're talking about, if you're male, this is happening in your testes, and these are going to be sperm cells. If you are female, this is happening in your ovaries, and these are going to be egg cells. If you are a tree, this could be pol... | Comparing mitosis and meiosis Cells MCAT Khan Academy.mp3 |
If we're talking about, if you're male, this is happening in your testes, and these are going to be sperm cells. If you are female, this is happening in your ovaries, and these are going to be egg cells. If you are a tree, this could be pollen, or it could be an ovule. So these are, but these are used for fertilization... | Comparing mitosis and meiosis Cells MCAT Khan Academy.mp3 |
So these are, but these are used for fertilization. These will fuse together in sexual reproduction to get to a fertilized egg, which then can undergo mitosis to create an entirely new organism. So not a cycle here, although I guess once, these will find sex cells from another organism and fuse with them, and then thos... | Comparing mitosis and meiosis Cells MCAT Khan Academy.mp3 |
But it's not the case with mitosis, where this could just keep on going and going and going. This cell is just like this cell, while these sex cells are different than this one right over here. Now, where does this happen in the body? And we've talked about this in previous videos. These are the bulk of, these are your... | Comparing mitosis and meiosis Cells MCAT Khan Academy.mp3 |
And we've talked about this in previous videos. These are the bulk of, these are your somatic cells right over here. These are the ones that make up the bulk of your body, somatic cells. And where is this happening? Well, this is happening in germ cells. As we mentioned, if you're male, it's in your testes, and if you'... | Comparing mitosis and meiosis Cells MCAT Khan Academy.mp3 |
The answer actually lies in the expression of that DNA, which genes are actively transcribed and which ones aren't. And there are several ways in which gene regulation occurs at the level of transcription, and so we're going to be talking about the main ones here. Now, let's draw out a hypothetical gene here, and assoc... | Regulation of transcription Biomolecules MCAT Khan Academy.mp3 |
And this sequence is called the promoter, and there's another sequence in between the promoter and the gene called the operator. The operator is the sequence of DNA to which a transcription factor protein can bind, and the promoter is the sequence of DNA to which the RNA polymerase binds to start transcription. Now, fi... | Regulation of transcription Biomolecules MCAT Khan Academy.mp3 |
General transcription factors plus RNA polymerase and another protein complex called the mediator multiple protein complex constitute the basic transcriptional apparatus, which positions RNA polymerase right at the start of a protein coding sequence or a gene and then releases the polymerase to transcribe the messenger... | Regulation of transcription Biomolecules MCAT Khan Academy.mp3 |
An example of an activator is the catabolite activator protein, or CAP, and this protein activates transcription of the lac operon in E. coli. In the case of the lac operon in E. coli, cyclic adenosine monophosphate, or C-AMP, is produced during glucose starvation. This C-AMP actually binds to the catabolite activator ... | Regulation of transcription Biomolecules MCAT Khan Academy.mp3 |
And then this activator, the CAP, then makes a direct protein-to-protein interaction with RNA polymerase that recruits the RNA polymerase to the promoter. Now, enhancers are sites on the DNA that are bound to by activators in order to loop the DNA in a certain way that brings a specific promoter to the initiation compl... | Regulation of transcription Biomolecules MCAT Khan Academy.mp3 |
And while enhancers are usually what are called cis-acting, cis meaning the same or acting on the same chromosome, an enhancer doesn't necessarily need to be particularly close to the gene that it acts on, and sometimes it's not even located on the same chromosome. Enhancers don't act on the promoter region itself, but... | Regulation of transcription Biomolecules MCAT Khan Academy.mp3 |
So here I've drawn a little schematic of what it might look like to have the enhancer actually change the structure of the DNA so that the DNA is now looping around. Here you still have your promoter sequence, the operator sequence, the gene sequence, and the enhancer sequence. And having the DNA looped in such a way s... | Regulation of transcription Biomolecules MCAT Khan Academy.mp3 |
Now let's talk about repressors. Repressors are proteins that bind to the operator, impeding RNA polymerase's progress along the strand and thus impeding the expression of the gene. Now if an inducer, which is a molecule that initiates gene expression, is present, then it can actually interact with the repressor protei... | Regulation of transcription Biomolecules MCAT Khan Academy.mp3 |
And then this frees up RNA polymerase to then transcribe the gene further down on the DNA strand. One example of a repressor protein is the repressor protein associated again with the lac operon operator, which prevents the transcription of genes used in lactose metabolism unless lactose, which is the inducer molecule,... | Regulation of transcription Biomolecules MCAT Khan Academy.mp3 |
And this mechanism is very similar to that of the enhancer sequences that I just talked about. And similarly, silencers can be located several bases upstream or downstream from the actual promoter of the gene. And when a repressor protein binds to the silencer region of the DNA, RNA polymerase is prevented from binding... | Regulation of transcription Biomolecules MCAT Khan Academy.mp3 |
Now a few notes about the differences between prokaryotes and eukaryotes when it comes to transcriptional regulation. In prokaryotes, the regulation of transcription is really needed for the cell to be able to quickly adapt to the ever-changing outer environment that it is sitting in. The presence, the quantity, the ty... | Regulation of transcription Biomolecules MCAT Khan Academy.mp3 |
The photo is referring to that it's going to use light somehow, and what's it going to do with that light energy? Well, it's going to synthesize something, and in particular, what it's going to synthesize, as we'll see, is sugar. So we are going to go from energy and light, let me just write light, light energy, and we... | Breaking down photosynthesis stages.mp3 |
Very broadly speaking, obviously this is a very, very high-level overview, but light energy isn't the only input here. We're also going to need some water, and as we go into future videos, we'll see what that water is used for. It's actually a source of electrons to do this, to make use of that light energy, frankly. A... | Breaking down photosynthesis stages.mp3 |
And we're also going to need, we're also going to need some carbon dioxide. Really, as a source of carbons, because there's a lot of carbon in those sugars, we're essentially going to fix the carbon. We're going to take it from this carbon dioxide gas and we're going to incorporate it into organic molecules and eventua... | Breaking down photosynthesis stages.mp3 |
And sugar isn't the only output. Another byproduct of this process is molecular oxygen. Once you strip the, you strip a couple of electrons from the water and the hydrogen ions are stripped away from it as well, all you're left with is oxygen. And you do that twice, then you have O2 and you have molecular oxygen. And t... | Breaking down photosynthesis stages.mp3 |
And you do that twice, then you have O2 and you have molecular oxygen. And this is a byproduct of photosynthesis, but you can imagine this is very important to life on Earth as we know it, in particular for us. We would have trouble breathing if this was not a byproduct of photosynthesis. Now what I'm going to do now i... | Breaking down photosynthesis stages.mp3 |
Now what I'm going to do now is break this out into two stages. And these two stages, we can call the light-dependent reactions, light-dependent, dependent reactions. And then the second stage, I will call the Calvin cycle. Calvin, Calvin cycle. And as the name implies, the light-dependent reactions are dependent on li... | Breaking down photosynthesis stages.mp3 |
Calvin, Calvin cycle. And as the name implies, the light-dependent reactions are dependent on light. So what's happening here is we're gonna take light energy, light energy, plus we're gonna take the water as a source of electrons, and we're going to use these two things, we're gonna use these two things to produce, to... | Breaking down photosynthesis stages.mp3 |
So we're gonna produce ATP, which is a store of energy. And we're also going to reduce NADP plus into NADPH, which has energy as a strong reducing agent. So this is what is happening, broadly speaking, in the light reactions. And then in the Calvin cycle, what we're gonna do is we're gonna take these products of the li... | Breaking down photosynthesis stages.mp3 |
And then in the Calvin cycle, what we're gonna do is we're gonna take these products of the light-dependent reactions. So we're gonna take our ATP and our NADPH, and we can use their energy in conjunction with some carbon dioxide, with some carbon dioxide, in order to produce, in order to produce sugar, in order to pro... | Breaking down photosynthesis stages.mp3 |
Oh, of course, I'm missing one of the byproducts of the light-dependent reactions, a very important one. I'm missing the molecular, the molecular oxygen. So once again, this is what makes up photosynthesis, but you can break it up into these two segments. Light-dependent reaction is using the energy from photons and li... | Breaking down photosynthesis stages.mp3 |
Let's say we're dealing with two oxygen atoms. So let me draw one oxygen here. A neutral oxygen has eight electrons total, but six of them are in its outer shell. So it has one, two, three, four, five, six valence electrons. And the way that I arranged them is I paired them up last. So you have these two valence electr... | Covalent bonds Molecular and ionic compound structure and properties AP Chemistry Khan Academy.mp3 |
So it has one, two, three, four, five, six valence electrons. And the way that I arranged them is I paired them up last. So you have these two valence electrons that are not paired with another electron. And now let me draw another oxygen, and I'm going to do it with a different color so that we can keep track of the e... | Covalent bonds Molecular and ionic compound structure and properties AP Chemistry Khan Academy.mp3 |
And now let me draw another oxygen, and I'm going to do it with a different color so that we can keep track of the electrons. So another oxygen right over there also has six valence electrons. One, two, three, four, five, six valence electrons. Now this oxygen on the left, in order to become more stable, it would love ... | Covalent bonds Molecular and ionic compound structure and properties AP Chemistry Khan Academy.mp3 |
Now this oxygen on the left, in order to become more stable, it would love to somehow gain or maybe share two more electrons. And of course this oxygen on the right, it's still oxygen. It also would love to gain or share two more valence electrons so how could it do it? Well what if the oxygen on the left shared this e... | Covalent bonds Molecular and ionic compound structure and properties AP Chemistry Khan Academy.mp3 |
Well what if the oxygen on the left shared this electron and this electron with the oxygen on the right, and the oxygen on the right shared this electron and this electron with the oxygen on the left? Well if they did that, you would have something that looks like this. You have your oxygen on the left, you have the ox... | Covalent bonds Molecular and ionic compound structure and properties AP Chemistry Khan Academy.mp3 |
This shows that there are two electrons that are being shared by these two oxygens and let's say that these two electrons are also being shared. You would do that with a line like this and then we could draw the remainder of the valence electrons. This oxygen on the left had, outside of the electrons that are being sha... | Covalent bonds Molecular and ionic compound structure and properties AP Chemistry Khan Academy.mp3 |
One, two, three, four. Now what's interesting here is these shared electrons, these are going to cause these oxygens to stick together. If they don't stick together, these electrons aren't going to be shared. So what we have formed here is known as a covalent bond. Covalent bond. And what's interesting is it allows bot... | Covalent bonds Molecular and ionic compound structure and properties AP Chemistry Khan Academy.mp3 |
So what we have formed here is known as a covalent bond. Covalent bond. And what's interesting is it allows both of these oxygens in some ways to be more stable. From the left oxygen's point of view, it had six valence electrons, but now it's able to share two more. Remember, each of these bonds, each of these lines re... | Covalent bonds Molecular and ionic compound structure and properties AP Chemistry Khan Academy.mp3 |
From the left oxygen's point of view, it had six valence electrons, but now it's able to share two more. Remember, each of these bonds, each of these lines represent two electrons. So this oxygen could say, hey, I get to have one, two, three, four, six, eight electrons that I'm dealing with, and the same thing is going... | Covalent bonds Molecular and ionic compound structure and properties AP Chemistry Khan Academy.mp3 |
Now there are some covalent bonds that are between not so equals. So for example, if we're talking about water, and if we're talking about how oxygen bonds with hydrogen. So if we have oxygen right over here, once again I can draw it six valence electrons. One, two, three, four, five, and let me just draw the sixth one... | Covalent bonds Molecular and ionic compound structure and properties AP Chemistry Khan Academy.mp3 |
One, two, three, four, five, and let me just draw the sixth one right over there. And if I have hydrogen, hydrogen has one valence electron. So let's say that's a hydrogen right over there with one valence electron, maybe another hydrogen right over there with one valence electron. Oxygen and hydrogen form covalent bon... | Covalent bonds Molecular and ionic compound structure and properties AP Chemistry Khan Academy.mp3 |
Oxygen and hydrogen form covalent bonds. In fact, that is how water is formed. And so what would that look like? Well, it would look like this. You have oxygen right over here. You have these two pairs of electrons that I keep drawing. And then this electron right over here could be shared with the hydrogen, and that h... | Covalent bonds Molecular and ionic compound structure and properties AP Chemistry Khan Academy.mp3 |
Well, it would look like this. You have oxygen right over here. You have these two pairs of electrons that I keep drawing. And then this electron right over here could be shared with the hydrogen, and that hydrogen's electron could be shared with the oxygen. So that forms a covalent bond with this hydrogen. And then th... | Covalent bonds Molecular and ionic compound structure and properties AP Chemistry Khan Academy.mp3 |
And then this electron right over here could be shared with the hydrogen, and that hydrogen's electron could be shared with the oxygen. So that forms a covalent bond with this hydrogen. And then this electron from the oxygen can be shared with the hydrogen, and that electron from the hydrogen can be shared with the oxy... | Covalent bonds Molecular and ionic compound structure and properties AP Chemistry Khan Academy.mp3 |
And so that would form a covalent bond with that other hydrogen. And now here, once again, oxygen can kind of pretend like it has eight valence electrons, two, four, six, eight. And the hydrogens can kind of pretend that it has two valence electrons. But the one difference here is that oxygen is a lot more electronegat... | Covalent bonds Molecular and ionic compound structure and properties AP Chemistry Khan Academy.mp3 |
But the one difference here is that oxygen is a lot more electronegative than hydrogen. It's to the right of hydrogen. It's in this top right corner outside of, other than the noble gases, that really like to hog electrons. So what do you think is going to happen here? Well, the electrons in each of these covalent bond... | Covalent bonds Molecular and ionic compound structure and properties AP Chemistry Khan Academy.mp3 |
So what do you think is going to happen here? Well, the electrons in each of these covalent bonds are going to hang out around the oxygen more often than around the hydrogen. So if the electrons spend more time around the oxygen, you're going to have, in general, more negative charge around the oxygen. And so you're go... | Covalent bonds Molecular and ionic compound structure and properties AP Chemistry Khan Academy.mp3 |
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