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But I'll leave you to think about it because maybe that combination might be passed on or it may not be passed on because of this recombination. But we'll talk more about that in the future. But I wanted to introduce this idea of sexual reproduction to you because this really is the main source of variation within a po... | Variation in a Species.mp3 |
And it's kind of a philosophical idea because we almost take the idea of having males and females for granted because it's this universal idea. But I did a little reading on it. It turns out that this actually only emerged about 1.4 billion years ago. That this is almost a useful trait because once you introduce this l... | Variation in a Species.mp3 |
That this is almost a useful trait because once you introduce this level of variation, the natural selection can start. You can kind of say that when you have this more powerful form of variation than just pure mutations, and maybe you might have some primitive form of crossover before. But now that you have this sexua... | Variation in a Species.mp3 |
So they started to essentially outnumber the ones that couldn't. So it became a kind of a very universal trait. But you could have imagined a world, and there are science fiction books written about this, where you have three genders, where you have gender one, two, three. You could have 10 genders. And it just happens... | Variation in a Species.mp3 |
It might tell, it might activate some genes, it might change the metabolism of the cell in some ways, and this signal that goes from the receptor into the cell to make the cell behave in some way, we call that signal transduction. We call it transduction. Signal transduction. And in a previous video, I was kind of hand... | Example of signal transduction pathway.mp3 |
And in a previous video, I was kind of hand-wavy about it, and you might have been saying, well, how does a signal actually go into the cell? How does it actually move through the cell, and how does it actually make things happen? And what I want to do in this video is, I'm not going to go into all of the details, but ... | Example of signal transduction pathway.mp3 |
And hopefully it'll also give you appreciation for how complex biological systems, including you and me, and even each of our individual cells, actually are. So this pathway that we're seeing up here, and you can see that there's a bunch of pathways that all kind of work together and overlap in terms of the enzymes and... | Example of signal transduction pathway.mp3 |
And if you're wondering, what does MAP kinase stand for, and oftentimes people will just say MAPK or M-A-P-K, it stands for mitogen, M for mitogen, mitogen-activated protein kinases. And you might be saying, well, what does mitogen, what does mitogen mean? Well, mitogen refers to things that cause cells to mitose, to a... | Example of signal transduction pathway.mp3 |
Now, what is, so mitogen-activated, so this pathway's going to be activated by a mitogen, mitogen-activated protein kinase. Well, a protein kinase, a kinase, and we've seen kinases multiple times, they're involved in many, many, many biological mechanisms. These are general term for enzymes that help take a higher ener... | Example of signal transduction pathway.mp3 |
And as they transfer them to different molecules, it's able to leverage that energy to actually facilitate some type of a mechanism. Now, as I said, I'm not gonna go into all of the details here, this is actually quite complex, but I wanna make a little bit sense of it. And we're actually gonna talk about a few protein... | Example of signal transduction pathway.mp3 |
So what you have right over here, I'll start with this molecule right over here, this is the ligand, this is the ligand, it's going to be released by some other part of the biological system from some other cell. And this EGF, this stands for epidermal growth factor. And the 1986 Nobel Prize in Medicine was actually gi... | Example of signal transduction pathway.mp3 |
Now this is going to be the ligand, this is essentially what's, you know, when this attaches or when this binds to a receptor, that's going to cause the signal to be transduced, you're gonna have the transduction going into the cell. And so you can imagine, it's going to bind to this membrane receptor, and so EGFR lite... | Example of signal transduction pathway.mp3 |
And it's part of this protein complex, and once this binds, it's able to help activate, it's able to help activate RAS right over here. And RAS, and once again, you know, all of these names, they have these interesting histories associated with them. This stands for rat sarcoma. Rat sarcoma, and sarcomas are cancers in... | Example of signal transduction pathway.mp3 |
Rat sarcoma, and sarcomas are cancers in certain tissues in the body. And it was first discovered associated with certain cancers, that rats that had certain sarcomas, that they were able to see that there were mutations in the genes that produced the RAS protein. And because of those mutations, the RAS protein, that t... | Example of signal transduction pathway.mp3 |
And because they were in their activated mode, this mechanism was kind of overactive, and any of the stop signals weren't actually happening. And so you can imagine a mechanism right over here that is about cell differentiation. That if this mechanism proceeds, it's eventually going to tell the DNA, some portions of th... | Example of signal transduction pathway.mp3 |
And that's exactly what happens in cancer. So this pathway is actually a very important pathway in cancer, and you see, you know, right over here, you actually see the MAP kinase. It's often called, or was originally called ERK, which is extracellular signal regulated kinase. But this is an incredibly important pathway... | Example of signal transduction pathway.mp3 |
Have you ever wondered how we sequence DNA? Well, let's just take a quick look at DNA sequencing. So, we're going to break down DNA sequencing into three different steps. So the first step is you take the sample of DNA that you're interested in sequencing, and you basically use PCR to amplify the sample. So, by using P... | DNA sequencing Biomolecules MCAT Khan Academy.mp3 |
So the first step is you take the sample of DNA that you're interested in sequencing, and you basically use PCR to amplify the sample. So, by using PCR in order to amplify the sample, you're able to generate lots and lots of DNA fragments. So, the next thing that you do is normally in PCR you have to add nucleotides. Y... | DNA sequencing Biomolecules MCAT Khan Academy.mp3 |
You have to give the growing strand the substrate from which it can grow. So normally you add in regular deoxynucleotides, and those look something like this. You've got an OH group here, you've got an H group here, you have a base, and then you've got a carbon group, and oxygen, hydrogen. So this is what a normal nucl... | DNA sequencing Biomolecules MCAT Khan Academy.mp3 |
So this is what a normal nucleotide looks like. But, interspersed in the PCR, what you also want to add is you want to add in something known as a dideoxynucleotide. So a dideoxynucleotide looks something like this. It's basically exactly the same thing, but it only has a hydrogen here. So this oxygen is removed. And w... | DNA sequencing Biomolecules MCAT Khan Academy.mp3 |
It's basically exactly the same thing, but it only has a hydrogen here. So this oxygen is removed. And what that basically does is if this dideoxynucleotide, we can abbreviate DDNTP, if this incorporates into the growing strand, since there's no oxygen group here, the strand can no longer elongate. So you basically hav... | DNA sequencing Biomolecules MCAT Khan Academy.mp3 |
So you basically have termination of strand elongation as soon as this DDNTP incorporates. So what you can do is you can actually fluorescently label the different dideoxynucleotides. So for example, we've got, so for example, we have four different options. So we can label all the G's blue, we can label all the A's re... | DNA sequencing Biomolecules MCAT Khan Academy.mp3 |
So we can label all the G's blue, we can label all the A's red, all the T's green, and all the C's orange. And so basically what you have is you have these dideoxynucleotides with different fluorescent labels getting incorporated into the growing strand. And since PCR is able to amplify, create millions and millions of... | DNA sequencing Biomolecules MCAT Khan Academy.mp3 |
So let's just kind of look at an example. So let's imagine that we've got nucleotide being incorporated here, a regular nucleotide, and then another one incorporated here, and then another one, and then just randomly all of a sudden we have a dideoxynucleotide being incorporated here. And this would stop elongation of ... | DNA sequencing Biomolecules MCAT Khan Academy.mp3 |
So you'd have a DNA strand that's just four nucleotides long. And after another round of PCR, what we might have is we might have one, two, three, four, five, six, it's just growing, it's growing, it's growing, and then all of a sudden, whoa, what happened? You've got a dideoxynucleotide being incorporated. And so basi... | DNA sequencing Biomolecules MCAT Khan Academy.mp3 |
And so basically you just do this, and after you've got millions of samples, you'll eventually be able to have something that looks like this. You'll have maybe just one regular nucleotide, and you've got a dideoxynucleotide incorporated. Or you might have maybe, let's say, two of them. So you'll have two, and then you... | DNA sequencing Biomolecules MCAT Khan Academy.mp3 |
So you'll have two, and then you've got a, let's use this color, so you've got a dideoxynucleotide. So what you can basically do is you can see that you have strands, and they're elongating, and different strands are terminated at different points by a dideoxynucleotide. And so basically, the next step is you use gel e... | DNA sequencing Biomolecules MCAT Khan Academy.mp3 |
For example, someone might have told you, hey, you walk kind of like your dad, or your smile is kind of like your mom, or your eyes are like one of your uncles or your grandparents. And so there's always been this notion of inherited traits. But it wasn't until the 1800s that that started to be studied in a more scient... | DNA Biomolecules MCAT Khan Academy (3).mp3 |
But even then, even Mendel, who was starting to understand the mechanisms of, or he was trying to understand how inheritance happens, and he even could start to breed certain types of things, even he didn't know exactly what was the molecular basis for inheritance. And the answer to that question wasn't figured out unt... | DNA Biomolecules MCAT Khan Academy (3).mp3 |
But it was really the structure of DNA that made people say, hey, that looks like the molecule that's storing the information. And just to be clear, DNA wasn't discovered in 1953. DNA was discovered in the mid-1800s. It was this kind of, this molecule that was inside of nuclei, of cells, and for some time, people said,... | DNA Biomolecules MCAT Khan Academy (3).mp3 |
It was this kind of, this molecule that was inside of nuclei, of cells, and for some time, people said, oh, maybe this could be a molecular basis of inheritance. You know, you could imagine what you would need to be a molecular basis of inheritance. It would have to be a molecule or a series of molecules that could con... | DNA Biomolecules MCAT Khan Academy (3).mp3 |
But it wasn't until 1953, when this double helix structure of DNA was established that people said, hey, this looks like our molecule. So first, let's just talk about the structure here, and then actually we'll talk about where this name, DNA, deoxyribonucleic acid, comes from. And then we'll talk a little bit about wh... | DNA Biomolecules MCAT Khan Academy (3).mp3 |
We might go in-depth on the expression of information in future videos. So this structure right over here, and this is a visual depiction of a DNA molecule, you can view this as kind of a twisted ladder. It has these two, I guess you could say, sides of the ladder that are twisted. That is one side right over there, an... | DNA Biomolecules MCAT Khan Academy (3).mp3 |
That is one side right over there, and then it is another side. There is another side right over here. And in between those two sides, or connecting those two sides of that twisted ladder, you have these rungs. And these rungs are actually where the information, the genetic information is, I guess you could say, stored... | DNA Biomolecules MCAT Khan Academy (3).mp3 |
And these rungs are actually where the information, the genetic information is, I guess you could say, stored in some way. Because these rungs, it's a sequence of different bases. And when I say bases, you might say, wait, this says acid, why are you saying bases right over here? Well, the word deoxyribonucleic acid co... | DNA Biomolecules MCAT Khan Academy (3).mp3 |
Well, the word deoxyribonucleic acid comes from the fact that this backbone is made up of a combination of sugar and phosphate. And the sugar that makes up the backbone is deoxyribose, so that's essentially the D in DNA. And then the phosphate group is acidic, and that's where you get the acid part of it. And nucleic i... | DNA Biomolecules MCAT Khan Academy (3).mp3 |
And nucleic is, hey, this was found in nuclei of cells. It is nucleic acid, deoxyribonucleic acid. But it's not, it also, it is actually mildly acidic all in total, but for every acid, it actually also has a base. And that base, those bases form the rung of the ladders. And actually, each rung is a pair of bases. And a... | DNA Biomolecules MCAT Khan Academy (3).mp3 |
And that base, those bases form the rung of the ladders. And actually, each rung is a pair of bases. And as I said, that's where the information is actually stored. Well, what am I talking about? Well, let me talk about the four different bases that make up the rungs of a DNA molecule. So you have adenine. And so, for ... | DNA Biomolecules MCAT Khan Academy (3).mp3 |
Well, what am I talking about? Well, let me talk about the four different bases that make up the rungs of a DNA molecule. So you have adenine. And so, for example, this part right over here, this section of that rung might be adenine. Maybe this right over here is adenine. This right over here. Remember, each of these ... | DNA Biomolecules MCAT Khan Academy (3).mp3 |
And so, for example, this part right over here, this section of that rung might be adenine. Maybe this right over here is adenine. This right over here. Remember, each of these rungs are made up by, it's a pair of bases. And that might be adenine. Maybe this is adenine. And I could stop there. | DNA Biomolecules MCAT Khan Academy (3).mp3 |
Remember, each of these rungs are made up by, it's a pair of bases. And that might be adenine. Maybe this is adenine. And I could stop there. I'll do a little more adenine. Maybe that's adenine right over there. And adenine always pairs with the base thymine. | DNA Biomolecules MCAT Khan Academy (3).mp3 |
And I could stop there. I'll do a little more adenine. Maybe that's adenine right over there. And adenine always pairs with the base thymine. So let me write that down. So adenine pairs with thymine. Thymine. | DNA Biomolecules MCAT Khan Academy (3).mp3 |
And adenine always pairs with the base thymine. So let me write that down. So adenine pairs with thymine. Thymine. So if that's an adenine there, then this is going to be a thymine. If this is an adenine, then this is going to be a thymine. Or if I drew the thymine first, well, I'll say, okay, it's going to pair with t... | DNA Biomolecules MCAT Khan Academy (3).mp3 |
Thymine. So if that's an adenine there, then this is going to be a thymine. If this is an adenine, then this is going to be a thymine. Or if I drew the thymine first, well, I'll say, okay, it's going to pair with the adenine. So this is going to be a thymine right over here. This is going to be a thymine. If I were to ... | DNA Biomolecules MCAT Khan Academy (3).mp3 |
Or if I drew the thymine first, well, I'll say, okay, it's going to pair with the adenine. So this is going to be a thymine right over here. This is going to be a thymine. If I were to draw this, this would be a thymine right over here. Now, the other two bases, you have cytosine, which pairs with guanine, or guanine t... | DNA Biomolecules MCAT Khan Academy (3).mp3 |
If I were to draw this, this would be a thymine right over here. Now, the other two bases, you have cytosine, which pairs with guanine, or guanine that pairs with cytosine. So guanine. And we're not going to go into the molecular structure of these bases just yet, although these are good names to know because they show... | DNA Biomolecules MCAT Khan Academy (3).mp3 |
And we're not going to go into the molecular structure of these bases just yet, although these are good names to know because they show up a lot and they really form kind of the code, your genetic code. So guanine pairs with cytosine. Guanine and cytosine. Cytosine. So actually, if this is, let's say there's some cytos... | DNA Biomolecules MCAT Khan Academy (3).mp3 |
Cytosine. So actually, if this is, let's say there's some cytosine there, let's say cytosine right over here, maybe this is cytosine, maybe this is cytosine, maybe this is cytosine, this is cytosine, and maybe this is cytosine, then it always pairs with the guanine. If we're talking about, so let's see, this is guanine... | DNA Biomolecules MCAT Khan Academy (3).mp3 |
Actually, just to make it a little bit more complete, let me just color in the rungs here as best as I can. So those are guanine, so they're gonna pair with cytosine, pair with cytosine, pair with cytosine. And when it's drawn this way, you might start to see how this is essentially a code, the order of which the bases... | DNA Biomolecules MCAT Khan Academy (3).mp3 |
It is because that information, to a large degree, is encoded genetically. It affects a lot of what makes you you, and actually not even just within a species, but also across species. Humans have more genetic material in common with other humans than they do with, say, a plant, but all living creatures as we know them... | DNA Biomolecules MCAT Khan Academy (3).mp3 |
This is the basis by which they are passing down their actual traits. Now, you might be saying, well, how much genetic information does a human being have? And the number will either disappoint you or you might find it mind-boggling. The human genome, and every species has a different number of base pairs, to a large d... | DNA Biomolecules MCAT Khan Academy (3).mp3 |
The human genome, and every species has a different number of base pairs, to a large degree correlated with how complex they are, although not always, but the human genome has six million, sorry, not six million, six billion. Six million would be disappointing. Even billion might be disappointing. Six billion base pair... | DNA Biomolecules MCAT Khan Academy (3).mp3 |
Six billion base pairs. Six billion base pairs. And when you have your full complement of chromosomes, and this is in most of the cells in your body, outside of your sex cells, the sperm or the egg cells, this is going to be spread over 46 chromosomes. 46 chromosomes, or I guess you could say 23 pair of chromosomes. So... | DNA Biomolecules MCAT Khan Academy (3).mp3 |
46 chromosomes, or I guess you could say 23 pair of chromosomes. So if you divide six billion by 46, you get a little over, on average, 100 million, I think it's 100 and something million base pairs per chromosome. And some chromosomes are longer, actually some of the longest are over 200 million, and some might be sho... | DNA Biomolecules MCAT Khan Academy (3).mp3 |
That's just on average. Now, this number might, to some of you, might be exciting. You're like, oh, I thought I was a simple creature. I didn't know I was this complex. Six billion, that's a lot of base pairs. That feels like a lot of information. For others of you, it might not feel so great. | DNA Biomolecules MCAT Khan Academy (3).mp3 |
I didn't know I was this complex. Six billion, that's a lot of base pairs. That feels like a lot of information. For others of you, it might not feel so great. You might say, hey, wait, I could store this much information on a modern thumb drive or on a hard disk. I thought I was more unique than that. And of course, w... | DNA Biomolecules MCAT Khan Academy (3).mp3 |
For others of you, it might not feel so great. You might say, hey, wait, I could store this much information on a modern thumb drive or on a hard disk. I thought I was more unique than that. And of course, we all are special and unique, but you might say, oh, six billion base pairs, I thought I was infinitely complex a... | DNA Biomolecules MCAT Khan Academy (3).mp3 |
And of course, we all are special and unique, but you might say, oh, six billion base pairs, I thought I was infinitely complex and whatever else, and there's some arguments for that along some other directions. But this is the approximate length, I guess you could say, the approximate size of the actual human genome. ... | DNA Biomolecules MCAT Khan Academy (3).mp3 |
We have about 20 base pairs depicted here. Imagine if you had about 200 million of these base pairs, and then you were to take this thing and you were to kind of coil it up into that thing is a chromosome. Is a chromosome. And you're saying, wait, I have that much information in most of the cells of my body? This thing... | DNA Biomolecules MCAT Khan Academy (3).mp3 |
And you're saying, wait, I have that much information in most of the cells of my body? This thing must be incredibly compact. And if you said that, I would say, yes, you are correct. This, the radius, the radius of the DNA molecule is on the order of one nanometer. One nanometer, which is a billionth of a meter. So you... | DNA Biomolecules MCAT Khan Academy (3).mp3 |
This, the radius, the radius of the DNA molecule is on the order of one nanometer. One nanometer, which is a billionth of a meter. So you can start to assess kind of the scale of this thing. This is a very dense way to actually store information. But just to have an appreciation of, and you might have seen it when I wa... | DNA Biomolecules MCAT Khan Academy (3).mp3 |
This is a very dense way to actually store information. But just to have an appreciation of, and you might have seen it when I was coloring in, on why the structure lends itself to being able to replicate the information or even to be able to translate or express the information, let's think about if you were to take t... | DNA Biomolecules MCAT Khan Academy (3).mp3 |
So you essentially have half of the ladder. And so if you only have half of the ladder, you're able to construct the other half of the ladder. Let's take an example. Let's say, and I'll just use the first letter to abbreviate for each of these bases. So let's say you have some, so let's say this is one of the, this is ... | DNA Biomolecules MCAT Khan Academy (3).mp3 |
Let's say, and I'll just use the first letter to abbreviate for each of these bases. So let's say you have some, so let's say this is one of the, this is the sugar phosphate backbone right over here. So this could be one of the sides. And let's say there's some adenine, actually, let me do them in the right color. So y... | DNA Biomolecules MCAT Khan Academy (3).mp3 |
And let's say there's some adenine, actually, let me do them in the right color. So you've got some adenine, adenine, maybe some adenine right over here. Maybe there's an adenine there. Maybe you have some thymine, thymine, maybe thymine right over here. Then you have some, you have some guanine, guanine, guanine. And ... | DNA Biomolecules MCAT Khan Academy (3).mp3 |
Maybe you have some thymine, thymine, maybe thymine right over here. Then you have some, you have some guanine, guanine, guanine. And then let's say you have some cytosine and you have some cytosine. So with just half of this ladder, I guess you could say, you're able to construct the other half. And that's actually ho... | DNA Biomolecules MCAT Khan Academy (3).mp3 |
So with just half of this ladder, I guess you could say, you're able to construct the other half. And that's actually how DNA replicates. This ladder splits and then each of those two halves of that ladder are able to construct versions of the other half, or versions of the other half are able to be constructed on top ... | DNA Biomolecules MCAT Khan Academy (3).mp3 |
So how does that happen? Well, it's based on how these bases pair. Adenine always pairs with thymine if we're talking about DNA. So if you have an A there, you're gonna have a T on this end, T on this end. T's right all over here, T right over there. If you have a T on that end, you're gonna have an A right over there,... | DNA Biomolecules MCAT Khan Academy (3).mp3 |
So if you have an A there, you're gonna have a T on this end, T on this end. T's right all over here, T right over there. If you have a T on that end, you're gonna have an A right over there, A, A. If you have a G, a guanine on this side, you're gonna have a cytosine on the other side. Cytosine, cytosine, cytosine. And... | DNA Biomolecules MCAT Khan Academy (3).mp3 |
If you have a G, a guanine on this side, you're gonna have a cytosine on the other side. Cytosine, cytosine, cytosine. And if you have a cytosine, you're gonna have a guanine on the other side. And so hopefully that gives you an appreciation of how DNA can replicate itself. And as we'll see also, how this information c... | DNA Biomolecules MCAT Khan Academy (3).mp3 |
And so hopefully that gives you an appreciation of how DNA can replicate itself. And as we'll see also, how this information can be translated to other forms of either related molecules, but eventually to proteins. And just to kind of round out this video, to get a real visual sense of what the DNA molecule looks like,... | DNA Biomolecules MCAT Khan Academy (3).mp3 |
I don't think it's any secret to anyone that water is essential to life. Most of the biological, or actually frankly, all of the significant biological processes in your body are dependent on water, and are probably occurring inside of water. When you think of the cells in your body, and the cytoplasm inside of your ce... | Hydrogen bonding in water Water, acids, and bases Biology Khan Academy.mp3 |
In fact, me, who is talking to you right now, I am 60 to 70% water. You can think of me as kind of this big bag of water that I'm making a video right now. It's not just human beings that need water. Life as we know it is dependent on water. That's why when we have the search for signs of life on other planets, we're a... | Hydrogen bonding in water Water, acids, and bases Biology Khan Academy.mp3 |
Life as we know it is dependent on water. That's why when we have the search for signs of life on other planets, we're always looking for signs of water. Maybe life can occur in other types of substances, but water is essential to life as we know it. To understand why water is so special, let's start to understand the ... | Hydrogen bonding in water Water, acids, and bases Biology Khan Academy.mp3 |
To understand why water is so special, let's start to understand the structure of water, and how it interacts with itself. Water, as you probably already know, is made up of one oxygen atom, and two hydrogen atoms. And two hydrogen atoms. That's why we call it H2O. H2O. They are bonded with covalent bonds. Covalent bon... | Hydrogen bonding in water Water, acids, and bases Biology Khan Academy.mp3 |
That's why we call it H2O. H2O. They are bonded with covalent bonds. Covalent bonds, each of these bonds, this is a pair of electrons, that both of these atoms get to pretend like they have. You have these two pairs. You might be saying, why did I draw the two hydrogens on this end? Why didn't I draw them on opposite s... | Hydrogen bonding in water Water, acids, and bases Biology Khan Academy.mp3 |
Covalent bonds, each of these bonds, this is a pair of electrons, that both of these atoms get to pretend like they have. You have these two pairs. You might be saying, why did I draw the two hydrogens on this end? Why didn't I draw them on opposite sides of the oxygen? That's because oxygen also has two lone electron ... | Hydrogen bonding in water Water, acids, and bases Biology Khan Academy.mp3 |
Why didn't I draw them on opposite sides of the oxygen? That's because oxygen also has two lone electron pairs. Two lone electron pairs. And these things are always repelling each other. The electrons are repelling from each other. And so, in reality, if we were looking at it three dimensions, the oxygen molecule is ki... | Hydrogen bonding in water Water, acids, and bases Biology Khan Academy.mp3 |
And these things are always repelling each other. The electrons are repelling from each other. And so, in reality, if we were looking at it three dimensions, the oxygen molecule is kind of a tetrahedral shape. I could try to, let me try to draw it a little bit. So if this is the oxygen right over here, then you would h... | Hydrogen bonding in water Water, acids, and bases Biology Khan Academy.mp3 |
I could try to, let me try to draw it a little bit. So if this is the oxygen right over here, then you would have, you could have maybe one lone pair of electrons. I'll draw just a little green circle there. Another lone pair of electrons back here. Then you have the covalent bond. You have the covalent bond to one hyd... | Hydrogen bonding in water Water, acids, and bases Biology Khan Academy.mp3 |
Another lone pair of electrons back here. Then you have the covalent bond. You have the covalent bond to one hydrogen atom. One hydrogen atom right over there. And then you have the covalent bond, then you have the covalent bond to the other hydrogen atom. And so you see it forms this tetrahedral shape. It's pretty clo... | Hydrogen bonding in water Water, acids, and bases Biology Khan Academy.mp3 |
One hydrogen atom right over there. And then you have the covalent bond, then you have the covalent bond to the other hydrogen atom. And so you see it forms this tetrahedral shape. It's pretty close to a tetrahedron. Just like this. But the key is that the hydrogens are on one end of the molecule. This is, we're gonna ... | Hydrogen bonding in water Water, acids, and bases Biology Khan Academy.mp3 |
It's pretty close to a tetrahedron. Just like this. But the key is that the hydrogens are on one end of the molecule. This is, we're gonna see, very, very important to the unique properties or to what gives water its special properties. Now one thing to realize is, you know, it's very, in chemistry, we draw these elect... | Hydrogen bonding in water Water, acids, and bases Biology Khan Academy.mp3 |
This is, we're gonna see, very, very important to the unique properties or to what gives water its special properties. Now one thing to realize is, you know, it's very, in chemistry, we draw these electrons very neatly, these dots up here. We draw these covalent bonds very neatly. But that's not the way that it actuall... | Hydrogen bonding in water Water, acids, and bases Biology Khan Academy.mp3 |
But that's not the way that it actually works. Electrons are jumping around constantly. They're buzzing around. It's actually much more of a, even when you think about electrons, it's more of a probability of where you might find them. And so instead of thinking of these electrons as definitely here or definitely in th... | Hydrogen bonding in water Water, acids, and bases Biology Khan Academy.mp3 |
It's actually much more of a, even when you think about electrons, it's more of a probability of where you might find them. And so instead of thinking of these electrons as definitely here or definitely in these bonds, they're actually more of in this cloud around the different atoms. They're in this cloud that kind of... | Hydrogen bonding in water Water, acids, and bases Biology Khan Academy.mp3 |
And what's interesting about water is oxygen is extremely electronegative. So oxygen, that's oxygen, that's oxygen. It is extremely electronegative. It's one of the more electronegative elements we know of. It's definitely way more electronegative than hydrogen. And you might be saying, well Sal, what does it mean to b... | Hydrogen bonding in water Water, acids, and bases Biology Khan Academy.mp3 |
It's one of the more electronegative elements we know of. It's definitely way more electronegative than hydrogen. And you might be saying, well Sal, what does it mean to be electronegative? Well, electronegative is just a fancy way of saying that it hogs electrons. Hogs electrons. It likes to keep electrons for itself.... | Hydrogen bonding in water Water, acids, and bases Biology Khan Academy.mp3 |
Well, electronegative is just a fancy way of saying that it hogs electrons. Hogs electrons. It likes to keep electrons for itself. Hogs electrons. So that's what's going on. Oxygen likes to keep the electrons more around itself than the partners that it's bonding with. So even in these covalent bonds, you say, hey, we'... | Hydrogen bonding in water Water, acids, and bases Biology Khan Academy.mp3 |
Hogs electrons. So that's what's going on. Oxygen likes to keep the electrons more around itself than the partners that it's bonding with. So even in these covalent bonds, you say, hey, we're supposed to be sharing these electrons. Oxygen says, well, I still want them to spend a little bit more time with me. And so the... | Hydrogen bonding in water Water, acids, and bases Biology Khan Academy.mp3 |
So even in these covalent bonds, you say, hey, we're supposed to be sharing these electrons. Oxygen says, well, I still want them to spend a little bit more time with me. And so they actually do spend more time on the side without the hydrogens than they do around the hydrogens. And you could imagine what this is going... | Hydrogen bonding in water Water, acids, and bases Biology Khan Academy.mp3 |
And you could imagine what this is going to do. This is going to form a partial negative charge at the, I guess you could say the non-hydrogen end, the end that has, well I guess this top end, the way I've drawn it right over here. And this Greek letter delta, this is to signify a partial charge. And it's a partial neg... | Hydrogen bonding in water Water, acids, and bases Biology Khan Academy.mp3 |
And it's a partial negative charge. Because electrons are negative. And then over here, since you have a slight deficiency of electrons, because they're spending so much time around the oxygen, it forms a partial positive charge, partial positive charge right over there. So right when you just look at one, one water mo... | Hydrogen bonding in water Water, acids, and bases Biology Khan Academy.mp3 |
So right when you just look at one, one water molecule, that doesn't seem so interesting. But it becomes really interesting when you look at many water molecules interacting together. So let me draw another water molecule right over here. So it's oxygen. You have two hydrogens. And then you have the bonds between them.... | Hydrogen bonding in water Water, acids, and bases Biology Khan Academy.mp3 |
So it's oxygen. You have two hydrogens. And then you have the bonds between them. You have a partially negative charge there, partially positive charge on that end. And so you can imagine the partial, the side that has a partially negative charge is going to be attracted to the side that has a partially positive charge... | Hydrogen bonding in water Water, acids, and bases Biology Khan Academy.mp3 |
You have a partially negative charge there, partially positive charge on that end. And so you can imagine the partial, the side that has a partially negative charge is going to be attracted to the side that has a partially positive charge. And that attraction, that between these two, this is called a hydrogen bond. So ... | Hydrogen bonding in water Water, acids, and bases Biology Khan Academy.mp3 |
So that right over there is called a hydrogen bond. And this is key to the behavior of water. And we're going to see that in future videos. All the different ways that hydrogen bonds give water its unique characteristics. Hydrogen bonds are weaker than covalent bonds, but they're strong enough to give water that kind o... | Hydrogen bonding in water Water, acids, and bases Biology Khan Academy.mp3 |
All the different ways that hydrogen bonds give water its unique characteristics. Hydrogen bonds are weaker than covalent bonds, but they're strong enough to give water that kind of nice fluid nature when we're thinking about kind of normal, where you'd say normal temperatures and pressures. This nice fluid nature. It ... | Hydrogen bonding in water Water, acids, and bases Biology Khan Academy.mp3 |
It allows these things to be attracted to each other, to have some cohesion, but also to break and reform and flow past each other. So you can imagine another hydrogen bond with another water molecule, another water molecule right over here. So put my hydrogens over there. Put my hydrogens here. Bonds, partial negative... | Hydrogen bonding in water Water, acids, and bases Biology Khan Academy.mp3 |
In the video on competitive inhibition, we saw that competitive inhibition is all about a substrate or potential substrate, an inhibitor competing for the enzyme. And whoever gets there first gets the enzyme. If the inhibitor gets there first, then the substrate isn't able to bind, and of course, no reaction is catalyz... | Noncompetitive inhibition Energy and enzymes Biology Khan Academy.mp3 |
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