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And phylum we are, humans and all mammals, we are in the phylum chordates. And chordates, we're actually in the subphylum, which I didn't write here, vertebrates, which means we have a vertebra, we have a spinal column with a spinal cord in it. Chordates are a little bit more general. Chordates is a phylum where kind o... | Taxonomy and the Tree of Life.mp3 |
Chordates is a phylum where kind of the arrangement of where the mouth is, where the digestive organs, where the anus is, where the spinal column is, where the brains, where the eyes, where the mouth, they're kind of all in the same place. And if you think about it, everything I've listed here kind of has the same gene... | Taxonomy and the Tree of Life.mp3 |
And so this is a general way, and I'm not being very rigorous here, is how you describe a chordate. And to show a chordate that is not a mammal, you would just have to think of fish or sharks. So this right over here, this right over here, let me make sure, let me, this right over here is a non-mammal chordate. This is... | Taxonomy and the Tree of Life.mp3 |
This is a great white shark over here. Now let's go even broader, and as you'll see, now we're getting to things that are very, very not, very, very not human-like. So you go one step broader, now we're in Animalia, we're the kingdom of animals, and this is the broadest definition that, or the broadest category that Ca... | Taxonomy and the Tree of Life.mp3 |
Well, actually, he did go into trees as well. But when you think of the kingdom of animals, when you think of things that aren't chordates, you start going into things like insects, and you start going into things like jellyfish. If you go even broader, now we're talking about the domain. You go to eukarya, so these ar... | Taxonomy and the Tree of Life.mp3 |
You go to eukarya, so these are all organisms that have cells, and inside those cells they have complex structures. So if you're eukarya, you have cells with complex structures. If you're a prokarya, which you don't have complex structures inside your cell. But other eukarya that are not animals include things like pla... | Taxonomy and the Tree of Life.mp3 |
But other eukarya that are not animals include things like plants. And obviously I'm giving no justice to this whole branch of the tree of life. It could be just as rich or richer than everything I've drawn over here. This is just a small fraction of the entire tree of life. But let's go even broader than that. So if y... | Taxonomy and the Tree of Life.mp3 |
This is just a small fraction of the entire tree of life. But let's go even broader than that. So if you go even broader than that, and you say, well, what's a kind of life form that isn't eukarya, that wouldn't have these more complex cell structures, these mitochondria in the cells, the cell nucleuses, then you just ... | Taxonomy and the Tree of Life.mp3 |
And if you wanna go even broader, there's things like viruses that you can even debate whether they really even are life, because they are dependent on other life forms for their actual reproduction, but they do have genetic material like everything else. And that, to me, is kind of a mind-blowing idea. As different as... | Taxonomy and the Tree of Life.mp3 |
In this video, we're going to explore a little bit about the cell membrane. So just as a little refresher, let's say this is a picture of our cell with a little tiny nucleus in the middle. Our cell membrane is what's on the outside of our cell. So our cell membrane is what protects our cell from a really harsh outside ... | Cell membrane overview and fluid mosaic model Cells MCAT Khan Academy.mp3 |
So our cell membrane is what protects our cell from a really harsh outside environment. If it weren't for the cell membrane, we wouldn't be alive today because there would be nothing to protect us from the outside world. So we're going to talk about the main three things that make up the cell membrane. The first, phosp... | Cell membrane overview and fluid mosaic model Cells MCAT Khan Academy.mp3 |
The first, phospholipids, the second, cholesterol, and the third, proteins. So the first one we're going to talk about, and this makes up the majority of what's in our cell membrane, are phospholipids. And just for the sake of time, I've pre-drawn a picture of the cell membrane here. And you'll notice that all of these... | Cell membrane overview and fluid mosaic model Cells MCAT Khan Academy.mp3 |
And you'll notice that all of these individual pieces are phospholipids. And a phospholipid looks like this. It has that polar head group, that polar phosphate group, and it has two fatty acid tails. And so this is the way that we normally represent what a phospholipid looks like. And in the cell membrane, you can see ... | Cell membrane overview and fluid mosaic model Cells MCAT Khan Academy.mp3 |
And so this is the way that we normally represent what a phospholipid looks like. And in the cell membrane, you can see that these phospholipids are packed pretty closely, pretty tightly together all throughout the entire membrane. And we're looking at this membrane, this is kind of like a cross-section. You can imagin... | Cell membrane overview and fluid mosaic model Cells MCAT Khan Academy.mp3 |
You can imagine that we cut the membrane in half. So what we have here is actually what we call our phospholipid bilayer. And sometimes it's also called the lipid bilayer. The second thing that we can find in our membrane is cholesterol. Now, we often hear cholesterol in foods and cholesterol in our blood, and we think... | Cell membrane overview and fluid mosaic model Cells MCAT Khan Academy.mp3 |
The second thing that we can find in our membrane is cholesterol. Now, we often hear cholesterol in foods and cholesterol in our blood, and we think it's a bad thing. But in this case, cholesterol is actually very important for our cell membrane. And cholesterol looks like this. And again, just for the sake of time, I'... | Cell membrane overview and fluid mosaic model Cells MCAT Khan Academy.mp3 |
And cholesterol looks like this. And again, just for the sake of time, I've pre-drawn what cholesterol looks like. And you'll notice that cholesterol has a lot of rings, and this gives cholesterol a pretty stable structure. And what cholesterol does is cholesterol kind of inserts itself between phospholipids, kind of l... | Cell membrane overview and fluid mosaic model Cells MCAT Khan Academy.mp3 |
And what cholesterol does is cholesterol kind of inserts itself between phospholipids, kind of like that. And the way I think about it is cholesterol is kind of like a buffer. It maintains the fluidity of our cell membranes. So as temperatures become lower, cholesterol will help increase the fluidity. And as temperatur... | Cell membrane overview and fluid mosaic model Cells MCAT Khan Academy.mp3 |
So as temperatures become lower, cholesterol will help increase the fluidity. And as temperatures become higher, cholesterol will help reduce the fluidity of the cell membrane. So cholesterol keeps our cell membrane in kind of a happy middle ground of fluidity. And the third thing that makes up our cell membrane are pr... | Cell membrane overview and fluid mosaic model Cells MCAT Khan Academy.mp3 |
And the third thing that makes up our cell membrane are proteins. And proteins are actually a big one. And depending on the cell, some cells will actually have a significant amount of protein in the membrane. And so proteins can take two major forms. The first is you can have a protein that crosses the entire membrane.... | Cell membrane overview and fluid mosaic model Cells MCAT Khan Academy.mp3 |
And so proteins can take two major forms. The first is you can have a protein that crosses the entire membrane. We call this an integral protein. We also can call this a transmembrane protein. And this can occur throughout different areas of the cell, like that. And some proteins actually kind of sit on top of the memb... | Cell membrane overview and fluid mosaic model Cells MCAT Khan Academy.mp3 |
We also can call this a transmembrane protein. And this can occur throughout different areas of the cell, like that. And some proteins actually kind of sit on top of the membrane, like this. Or they might sit on another protein, like that. And these are what we call peripheral proteins. There are some very rare protein... | Cell membrane overview and fluid mosaic model Cells MCAT Khan Academy.mp3 |
Or they might sit on another protein, like that. And these are what we call peripheral proteins. There are some very rare proteins that actually can go halfway through the membrane. And even rarer, there are occasionally a few proteins that actually can be found inside the cell membrane, like this, between the two phos... | Cell membrane overview and fluid mosaic model Cells MCAT Khan Academy.mp3 |
And even rarer, there are occasionally a few proteins that actually can be found inside the cell membrane, like this, between the two phospholipids, inside our bilayer. Now, proteins are a very big player in the function of cell membranes. They actually carry out nearly all of the membrane processes that we can think o... | Cell membrane overview and fluid mosaic model Cells MCAT Khan Academy.mp3 |
And the two biggest things that proteins do is, the first, they can actually act as receptors. So the proteins can actually tell the cell what's going on in the outside world. They act as communication. And the second thing that proteins can do, which generally occur in transmembrane proteins, is that proteins can actu... | Cell membrane overview and fluid mosaic model Cells MCAT Khan Academy.mp3 |
And the second thing that proteins can do, which generally occur in transmembrane proteins, is that proteins can actually help transport molecules in and out of the cell. So now that we know the function of proteins, why do you think proteins that are lipid-bound or bound within our lipid bilayer, like this one here, i... | Cell membrane overview and fluid mosaic model Cells MCAT Khan Academy.mp3 |
And lastly, there's one very important type of molecule that actually binds to our lipids or our proteins. And these are carbohydrates. And we call these glyco for short. So they would be glycoproteins, or they might be glycolipids. And what these do is they play a big role in communication. So for example, it allows a... | Cell membrane overview and fluid mosaic model Cells MCAT Khan Academy.mp3 |
So they would be glycoproteins, or they might be glycolipids. And what these do is they play a big role in communication. So for example, it allows a cell to recognize another cell in our body. If they play a role in communication in cells recognizing other cells, where do you think these sugars would go? Well, these s... | Cell membrane overview and fluid mosaic model Cells MCAT Khan Academy.mp3 |
If they play a role in communication in cells recognizing other cells, where do you think these sugars would go? Well, these sugars would mainly occur on the outside of our membrane. So they would kind of stick out on proteins. These would be glycoproteins. And they can be on peripheral or integral proteins. Or they mi... | Cell membrane overview and fluid mosaic model Cells MCAT Khan Academy.mp3 |
These would be glycoproteins. And they can be on peripheral or integral proteins. Or they might stick out on lipids, like this. And these would be glycolipids. Now this is a little confusing to look at. What we've just drawn is a cross-section of our cell membrane. But what if we were looking at the cell membrane from ... | Cell membrane overview and fluid mosaic model Cells MCAT Khan Academy.mp3 |
And these would be glycolipids. Now this is a little confusing to look at. What we've just drawn is a cross-section of our cell membrane. But what if we were looking at the cell membrane from the outside, kind of like a top view? What would that look like? Well, again, for the sake of time, I've pre-drawn our phospholi... | Cell membrane overview and fluid mosaic model Cells MCAT Khan Academy.mp3 |
But what if we were looking at the cell membrane from the outside, kind of like a top view? What would that look like? Well, again, for the sake of time, I've pre-drawn our phospholipids. So if we were looking at the cell membrane from the outside, looking onto the top of the cell membrane, all we would see are these h... | Cell membrane overview and fluid mosaic model Cells MCAT Khan Academy.mp3 |
So if we were looking at the cell membrane from the outside, looking onto the top of the cell membrane, all we would see are these head groups of our phospholipids. We might see some cholesterol in between our cell membranes, like this. And we might see some larger proteins that are on top of our cell membrane, like th... | Cell membrane overview and fluid mosaic model Cells MCAT Khan Academy.mp3 |
And lastly, we might actually see some glycoproteins and glycolipids on the outside. And these would attach themselves to our proteins and our phospholipids, like that. So from the top, this is what our cell membrane would look like. And you know something really special about this? This kind of looks like a piece of a... | Cell membrane overview and fluid mosaic model Cells MCAT Khan Academy.mp3 |
And you know something really special about this? This kind of looks like a piece of art. So if we think back to elementary school, where we had the project where we would put a lot of beans or different macaroni together to create a piece of art, this kind of reminds me of that. So this is actually what we call a mosa... | Cell membrane overview and fluid mosaic model Cells MCAT Khan Academy.mp3 |
So this is actually what we call a mosaic. So scientists kind of thought the same thing. And so scientists actually named this model of the cell the fluid mosaic model. And so the mosaic portion of our cell can be described here. Again, you can see that there are a lot of different pieces, different colorful, different... | Cell membrane overview and fluid mosaic model Cells MCAT Khan Academy.mp3 |
And so the mosaic portion of our cell can be described here. Again, you can see that there are a lot of different pieces, different colorful, different types of pieces, put together to create this beautiful cell membrane. But why did we call it fluid? Well, the reason we call the cell membrane fluid is because these pi... | Cell membrane overview and fluid mosaic model Cells MCAT Khan Academy.mp3 |
Well, the reason we call the cell membrane fluid is because these pieces in our cell membrane can actually move around. They're not set in stone. So the proteins and phospholipids in our cell membrane can move around, like that. This is why we call it fluid. What would that look like if we look at the cell membrane fro... | Cell membrane overview and fluid mosaic model Cells MCAT Khan Academy.mp3 |
This is why we call it fluid. What would that look like if we look at the cell membrane from the top? Well, the movement is actually not two-dimensional, like just up and down or just left and right. It can actually go in a lot of different directions. So our proteins can move all around the cell membrane, and so can o... | Cell membrane overview and fluid mosaic model Cells MCAT Khan Academy.mp3 |
It can actually go in a lot of different directions. So our proteins can move all around the cell membrane, and so can our phospholipids. So again, this is what we call the fluid mosaic model. And just as a little bit of a fun fact, this was only really discovered in 1972. So it was only 40 years ago that we really fig... | Cell membrane overview and fluid mosaic model Cells MCAT Khan Academy.mp3 |
And just as a little bit of a fun fact, this was only really discovered in 1972. So it was only 40 years ago that we really figured out that our cell membrane was actually the fluid mosaic model. So in summary, our cell membrane is made up of three major things. The first are phospholipids. These make up the most of th... | Cell membrane overview and fluid mosaic model Cells MCAT Khan Academy.mp3 |
What we have here is just a small sample of the types of molecules that you will see in a biological system. At the top left right over here, you have an example of an amino acid. Amino acids are the building blocks of proteins. And if we were to take a look at what an amino acid is made up of, in this dark gray color,... | Elemental building blocks of biological molecules Chemistry of life AP Biology Khan Academy.mp3 |
And if we were to take a look at what an amino acid is made up of, in this dark gray color, those are carbon atoms. In the white, you see hydrogen atoms. In the red, you see oxygen atoms. And this blue right over here, that is a nitrogen atom. And as you can see, a lot of these elements keep showing up in these various... | Elemental building blocks of biological molecules Chemistry of life AP Biology Khan Academy.mp3 |
And this blue right over here, that is a nitrogen atom. And as you can see, a lot of these elements keep showing up in these various molecules, especially carbon and hydrogen. But also, you see a lot of oxygen and nitrogen. And as we're about to see, phosphorus also pops up a lot. Now, this isn't a comprehensive list. ... | Elemental building blocks of biological molecules Chemistry of life AP Biology Khan Academy.mp3 |
And as we're about to see, phosphorus also pops up a lot. Now, this isn't a comprehensive list. You'll also see other elements. But these tend to show up fairly frequently. For example, this is a model of ATP, adenosine triphosphate. As we study biology, you'll see that it's often viewed as the currency of energy, the ... | Elemental building blocks of biological molecules Chemistry of life AP Biology Khan Academy.mp3 |
But these tend to show up fairly frequently. For example, this is a model of ATP, adenosine triphosphate. As we study biology, you'll see that it's often viewed as the currency of energy, the molecular currency of energy in biological systems. And once again, we see a lot of carbons in the dark gray. We see the hydroge... | Elemental building blocks of biological molecules Chemistry of life AP Biology Khan Academy.mp3 |
And once again, we see a lot of carbons in the dark gray. We see the hydrogens in this off-white color, or the light gray, I guess you could say. You see your oxygens again. Here, the nitrogen is in this light blue color. And then you see the phosphoruses right over there in that yellow color, phosphorous. This is a mo... | Elemental building blocks of biological molecules Chemistry of life AP Biology Khan Academy.mp3 |
Here, the nitrogen is in this light blue color. And then you see the phosphoruses right over there in that yellow color, phosphorous. This is a model of a triglyceride, often known as a fat molecule. Fat molecules are used for energy storage. And once again, you see many carbons in the dark gray. And then you see these... | Elemental building blocks of biological molecules Chemistry of life AP Biology Khan Academy.mp3 |
Fat molecules are used for energy storage. And once again, you see many carbons in the dark gray. And then you see these hydrogens and then a few oxygens. This is a model of DNA, a small segment of DNA. And this is a much more complex molecule than the other ones we've seen. In fact, this could extend far beyond our sc... | Elemental building blocks of biological molecules Chemistry of life AP Biology Khan Academy.mp3 |
This is a model of DNA, a small segment of DNA. And this is a much more complex molecule than the other ones we've seen. In fact, this could extend far beyond our screen in either direction. But once again, you see these same familiar elements. You see the carbon in the dark gray, the hydrogen in that white color. You ... | Elemental building blocks of biological molecules Chemistry of life AP Biology Khan Academy.mp3 |
But once again, you see these same familiar elements. You see the carbon in the dark gray, the hydrogen in that white color. You see the oxygens in the red, the nitrogens in the blue, and the phosphorous in the yellow. So the big takeaway here is that biological molecules tend to be made up of the same set of elemental... | Elemental building blocks of biological molecules Chemistry of life AP Biology Khan Academy.mp3 |
So the big takeaway here is that biological molecules tend to be made up of the same set of elemental building blocks. And in fact, it isn't just at the elemental level. It can even be at the molecular level. For example, in ATP, you have what's known as a nitrogenous base right over here. You have a five-carbon sugar ... | Elemental building blocks of biological molecules Chemistry of life AP Biology Khan Academy.mp3 |
For example, in ATP, you have what's known as a nitrogenous base right over here. You have a five-carbon sugar right over here. And you have three phosphate groups, or a triphosphate group. In DNA, you have something very similar. The nitrogenous bases are hard to see. They're kind of the rungs of the ladder here. You ... | Elemental building blocks of biological molecules Chemistry of life AP Biology Khan Academy.mp3 |
In DNA, you have something very similar. The nitrogenous bases are hard to see. They're kind of the rungs of the ladder here. You have your five-carbon sugars, also hard to see. And then you have these phosphates as well. In fact, the backbone of DNA is made up of these five-carbon sugars and these phosphates. Now, why... | Elemental building blocks of biological molecules Chemistry of life AP Biology Khan Academy.mp3 |
You have your five-carbon sugars, also hard to see. And then you have these phosphates as well. In fact, the backbone of DNA is made up of these five-carbon sugars and these phosphates. Now, why do these elements keep showing up? Well, these are elements that you will see a lot in Earth. For example, nitrogen makes up ... | Elemental building blocks of biological molecules Chemistry of life AP Biology Khan Academy.mp3 |
Now, why do these elements keep showing up? Well, these are elements that you will see a lot in Earth. For example, nitrogen makes up most of our atmosphere. We have a lot of water on the surface of our planet, which is made up of oxygen and hydrogen. Carbon actually makes up a surprisingly small percentage of our atmo... | Elemental building blocks of biological molecules Chemistry of life AP Biology Khan Academy.mp3 |
We have a lot of water on the surface of our planet, which is made up of oxygen and hydrogen. Carbon actually makes up a surprisingly small percentage of our atmosphere, about 0.04% of our atmosphere. But photosynthetic organisms, like plants, are good at fixing carbon and storing energy in carbon bonds. And when we ea... | Elemental building blocks of biological molecules Chemistry of life AP Biology Khan Academy.mp3 |
And when we eat those, those become part of our bodies. And just to get an appreciation of what we are made up of in terms of elements, we can look at this chart right over here, where we see that we are primarily made up of oxygen, percentage in body. And that's because we're primarily made up of water, and water is p... | Elemental building blocks of biological molecules Chemistry of life AP Biology Khan Academy.mp3 |
It also has hydrogen. Now, second to oxygen is carbon. And then you see nitrogen, phosphorus. We, of course, have a lot of calcium. Calcium, of course, used in bones, but it's also used for things like muscle contractions. And I could keep on going down this list, and you will see these other elements in your study of ... | Elemental building blocks of biological molecules Chemistry of life AP Biology Khan Academy.mp3 |
But what I want to do in this video is dig a little bit deeper, actually get into the molecular structure of DNA. And just as a starting point, let's just remind ourselves what DNA stands for. I'm gonna write the different parts of the word in different colors. So it stands for deoxyribonucleic, ribonucleic, ribonuclei... | Molecular structure of DNA Macromolecules Biology Khan Academy (3).mp3 |
So it stands for deoxyribonucleic, ribonucleic, ribonucleic acid, ribonucleic acid. So I'm just gonna put this on the side. And now let's actually look at the molecular structure and how it relates to this actual name, deoxyribonucleic acid. So DNA is just a general term for nucleic acid. And the term nucleic comes fro... | Molecular structure of DNA Macromolecules Biology Khan Academy (3).mp3 |
So DNA is just a general term for nucleic acid. And the term nucleic comes from the fact that it's found in the nucleus, it's found in the nucleus of eukaryotes. So that's where the nucleic comes from. And we'll talk about in a second why it's called an acid, but I'll wait on that. And now each DNA molecule is made up ... | Molecular structure of DNA Macromolecules Biology Khan Academy (3).mp3 |
And we'll talk about in a second why it's called an acid, but I'll wait on that. And now each DNA molecule is made up of a chain of what we call nucleotides. So what we call nucleotides. So it's made up of nucleotides. So what does a nucleotide look like? Well, what I have right over here is I have two strands, I've zo... | Molecular structure of DNA Macromolecules Biology Khan Academy (3).mp3 |
So it's made up of nucleotides. So what does a nucleotide look like? Well, what I have right over here is I have two strands, I've zoomed in two strands of DNA. So you could view this side right over here as one of the, I guess you could say the backbones of one side of the ladder. This is the other side of the ladder.... | Molecular structure of DNA Macromolecules Biology Khan Academy (3).mp3 |
So you could view this side right over here as one of the, I guess you could say the backbones of one side of the ladder. This is the other side of the ladder. And then each of these bridges, and I will talk about what molecules these are, these are kind of the rungs of the ladder. And a nucleotide, let me separate off... | Molecular structure of DNA Macromolecules Biology Khan Academy (3).mp3 |
And a nucleotide, let me separate off a nucleotide. So a nucleotide would, so what I am coordinating off, what I am coordinating off right over here could be considered a nucleotide. So that's one nucleotide, and then it's connected to another. It's connected to another nucleotide, another nucleotide right over here. A... | Molecular structure of DNA Macromolecules Biology Khan Academy (3).mp3 |
It's connected to another nucleotide, another nucleotide right over here. And on the right-hand side, we have a nucleotide, we have a nucleotide right over there, and then, actually, I wanna do it, let me do it slightly different. We have a nucleotide right over here on the right side, and then right below that, we hav... | Molecular structure of DNA Macromolecules Biology Khan Academy (3).mp3 |
So depicted here, we essentially have four nucleotides. These two are on this left side of the ladder, these two are on the right side of the ladder. Now let's think about the different pieces of that nucleotide. So the one thing that might jump out at you is we have these phosphate groups. So this is a phosphate group... | Molecular structure of DNA Macromolecules Biology Khan Academy (3).mp3 |
So the one thing that might jump out at you is we have these phosphate groups. So this is a phosphate group right over here, this is a phosphate group right over here. Each of these nucleotides have a phosphate group. So this is a phosphate group over here, and this is a phosphate group over here. Now the phosphate gro... | Molecular structure of DNA Macromolecules Biology Khan Academy (3).mp3 |
So this is a phosphate group over here, and this is a phosphate group over here. Now the phosphate groups are actually what make DNA, or actually what make nucleic acid an acid. And you might say, wait, wait, the way you've drawn it, Sal, you have a negative charge. Something with a negative charge would attract proton... | Molecular structure of DNA Macromolecules Biology Khan Academy (3).mp3 |
Something with a negative charge would attract protons, it would sop up protons. How can you call this an acid? This actually looks more basic. And the reason why DNA is typically drawn with these negative charges here is that it's so acidic, and if you put it into a neutral solution, it's actually going to lose its hy... | Molecular structure of DNA Macromolecules Biology Khan Academy (3).mp3 |
And the reason why DNA is typically drawn with these negative charges here is that it's so acidic, and if you put it into a neutral solution, it's actually going to lose its hydrogens. Actually the DNA, if we actually want to be formal about it, the DNA molecules would actually have its phosphates protonated like this,... | Molecular structure of DNA Macromolecules Biology Khan Academy (3).mp3 |
Whoops, just on this phosphate group over here. So if you get rid of the negative charge, and if this was bounded, this is bonded to a hydrogen, this so badly wants to grab these electrons. So this oxygen can grab these electrons, and then this hydrogen will just be grabbed by another water molecule or something, or so... | Molecular structure of DNA Macromolecules Biology Khan Academy (3).mp3 |
That's why we call it an acid. So if it wasn't in a solution, it would have the hydrogens, but it would be very acidic. As soon as you put it into a neutral solution, it's going to lose those hydrogens. So the phosphate groups are what make it an acid, but it's confusing sometimes, because usually when you see it depic... | Molecular structure of DNA Macromolecules Biology Khan Academy (3).mp3 |
So the phosphate groups are what make it an acid, but it's confusing sometimes, because usually when you see it depicted, you see it with these negative charges, and that's because it has already lost its hydrogen protons. You're actually depicting the conjugate base here, but that's where it gets its acidic name from,... | Molecular structure of DNA Macromolecules Biology Khan Academy (3).mp3 |
Now the next thing you might notice, the next thing you might notice is, the next thing you might notice is this group right over here. It is a cycle, it is a ring, and it looks an awful lot like a sugar, and that's because it is a sugar. So this sugar is based on, it's a five-carbon sugar. What I have depicted here, t... | Molecular structure of DNA Macromolecules Biology Khan Academy (3).mp3 |
What I have depicted here, this sugar, this is ribose. So this sugar right over here is ribose. This is when it's just as a straight chain, and like many sugars, it can take a cyclical form. Actually, it can take many different cyclical forms, but the one that's most typically described is when you have the, let me sho... | Molecular structure of DNA Macromolecules Biology Khan Academy (3).mp3 |
Actually, it can take many different cyclical forms, but the one that's most typically described is when you have the, let me show you a number of the carbons, because carbon numbering is important when we talk about DNA. If we start at the carbonyl group right over here, we call that the one carbon, or the one prime c... | Molecular structure of DNA Macromolecules Biology Khan Academy (3).mp3 |
That's the five prime carbon. And so you form the cyclical form of ribose, is if you have the oxygen, you have the oxygen right over here on the four prime carbon, it uses one of its lone pairs, it uses one of its lone pairs to form a bond, to form a bond with, with the one prime, with the one prime carbon. And I drew ... | Molecular structure of DNA Macromolecules Biology Khan Academy (3).mp3 |
And then when it forms that bond, the carbon can let go of one of these double bonds, and then that can, then the oxygen, the oxygen can use that, the oxygen can use those electrons to go grab a hydrogen proton from someplace, so to nab onto a hydrogen proton. So when it does that, you're in this form. And this form, j... | Molecular structure of DNA Macromolecules Biology Khan Academy (3).mp3 |
And where we see this bond, this is a one prime carbon, it was part of a carbonyl, now it lets go of one of those double bonds so that this oxygen can form a bond with a hydrogen proton, so it let go of a double bond there so that this could form a bond with a hydrogen proton. So this hydrogen proton is that hydrogen p... | Molecular structure of DNA Macromolecules Biology Khan Academy (3).mp3 |
Notice, this oxygen is bound to the four prime carbon, and now it's also bound to the one prime carbon. And it was also attached to a hydrogen, It was also attached to a hydrogen, so that hydrogen is there. But then that could get nabbed up by another passing water molecule to become hydronium, so it can get lost. And ... | Molecular structure of DNA Macromolecules Biology Khan Academy (3).mp3 |
And net-net, it grabs up a hydrogen proton right over here, and so it can lose a hydrogen proton right there. So it's not adding or losing net-net. And so you form this cyclical form. And the cyclical form right over here is very close to what we see in a DNA molecule. It's actually exactly what we would see in an RNA ... | Molecular structure of DNA Macromolecules Biology Khan Academy (3).mp3 |
And the cyclical form right over here is very close to what we see in a DNA molecule. It's actually exactly what we would see in an RNA molecule, in ribonucleic acid. And so what do we think we're talking about when we say deoxyribonucleic acid? Well, you could start with, you have a ribose here, but if we got rid of o... | Molecular structure of DNA Macromolecules Biology Khan Academy (3).mp3 |
Well, you could start with, you have a ribose here, but if we got rid of one of the oxygen groups, and in particular, one of, well, actually, if we just got rid of one of the oxygens, we replace a hydroxyl with just a hydrogen, well, then you're gonna have deoxyribose. And you see that over here. This five-member ring,... | Molecular structure of DNA Macromolecules Biology Khan Academy (3).mp3 |
It looks just like this. The hydrogens are implicit to the carbons. We've seen this multiple times. The carbons are at where these lines intersect, or I guess at the edges, or maybe, and also where these lines end right over there. But you see, this does not have an, this molecule, if we compare these two molecules, if... | Molecular structure of DNA Macromolecules Biology Khan Academy (3).mp3 |
The carbons are at where these lines intersect, or I guess at the edges, or maybe, and also where these lines end right over there. But you see, this does not have an, this molecule, if we compare these two molecules, if we compare these two molecules over here, we see that this guy has an OH, and this guy implicitly j... | Molecular structure of DNA Macromolecules Biology Khan Academy (3).mp3 |
So this is deoxyribose. So deoxyribose doesn't have this oxygen. It does not have the oxygen on the two prime carbon. So this, if you get rid of that, this is deoxyribose. So let me circle that. So what we're, this thing right over here, this thing right over here, that is deoxyribose. Deoxy, or it's based on deoxyribo... | Molecular structure of DNA Macromolecules Biology Khan Academy (3).mp3 |
So this, if you get rid of that, this is deoxyribose. So let me circle that. So what we're, this thing right over here, this thing right over here, that is deoxyribose. Deoxy, or it's based on deoxyribose, I guess before it bonded to these other constituents, you could consider this deoxyribose. And so that's where the... | Molecular structure of DNA Macromolecules Biology Khan Academy (3).mp3 |
Deoxy, or it's based on deoxyribose, I guess before it bonded to these other constituents, you could consider this deoxyribose. And so that's where the deoxyribo comes from. And then the last piece of it, the last piece of it is this chunk right over here. And these we call nitrogenous bases. So nitrogenous, nitrogenou... | Molecular structure of DNA Macromolecules Biology Khan Academy (3).mp3 |
And these we call nitrogenous bases. So nitrogenous, nitrogenous, nitrogenous bases. And you can see we have different types of nitrogenous bases. This is a nitrogenous base. This right over here is a different nitrogenous base. This right over here is another different nitrogenous base. Notice this one only has one ri... | Molecular structure of DNA Macromolecules Biology Khan Academy (3).mp3 |
This is a nitrogenous base. This right over here is a different nitrogenous base. This right over here is another different nitrogenous base. Notice this one only has one ring, this one has one ring. This one has two rings. This one over here has two rings. And we have different names for these nitrogenous bases. | Molecular structure of DNA Macromolecules Biology Khan Academy (3).mp3 |
Notice this one only has one ring, this one has one ring. This one has two rings. This one over here has two rings. And we have different names for these nitrogenous bases. The ones with two rings, the general categorization, we call them purines. So nitrogenous bases, if you have two rings, if you have two rings, we c... | Molecular structure of DNA Macromolecules Biology Khan Academy (3).mp3 |
And we have different names for these nitrogenous bases. The ones with two rings, the general categorization, we call them purines. So nitrogenous bases, if you have two rings, if you have two rings, we call them purines, as a general classification term. Let me make sure, purines. And if you have one ring, maybe I'll ... | Molecular structure of DNA Macromolecules Biology Khan Academy (3).mp3 |
Let me make sure, purines. And if you have one ring, maybe I'll just write it this way, one ring, one ring, we call these pyrimidines. Pyrimidines. Pyrimidines. We call these pyrimidines. And these particular, these two on the right, these two purines, this one up here, this is adenine. And we talk about how they pair ... | Molecular structure of DNA Macromolecules Biology Khan Academy (3).mp3 |
Pyrimidines. We call these pyrimidines. And these particular, these two on the right, these two purines, this one up here, this is adenine. And we talk about how they pair in the overview video on DNA. But this one right over here is adenine, this nitrogenous base. This one over here is guanine. That is guanine. | Molecular structure of DNA Macromolecules Biology Khan Academy (3).mp3 |
And we talk about how they pair in the overview video on DNA. But this one right over here is adenine, this nitrogenous base. This one over here is guanine. That is guanine. And then, over here, this single ring nitrogenous base, which makes it a pyrimidine, this is thymine. This right over here is thymine. This is thy... | Molecular structure of DNA Macromolecules Biology Khan Academy (3).mp3 |
That is guanine. And then, over here, this single ring nitrogenous base, which makes it a pyrimidine, this is thymine. This right over here is thymine. This is thymine. And then last but not least, if we're talking about DNA, when we go into RNA, we're also gonna talk about uracil. But when we talk about DNA, this one ... | Molecular structure of DNA Macromolecules Biology Khan Academy (3).mp3 |
This is thymine. And then last but not least, if we're talking about DNA, when we go into RNA, we're also gonna talk about uracil. But when we talk about DNA, this one over here is cytosine. Cytosine. And you can see the way it's structured, that thymine is attracted to adenine, it bonds with adenine, and cytosine bond... | Molecular structure of DNA Macromolecules Biology Khan Academy (3).mp3 |
Cytosine. And you can see the way it's structured, that thymine is attracted to adenine, it bonds with adenine, and cytosine bonds with guanine. So how are they bonding? Well, the way that these nitrogenous bases form the rungs of the ladder, how they're drawn to each other, this is our good old friend hydrogen bonds. ... | Molecular structure of DNA Macromolecules Biology Khan Academy (3).mp3 |
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