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And these cyclin-dependent kinases will work together with a protein you might be able to guess the name of, cyclins. Because what else would these kinases depend on? So an important thing to notice is that these cyclin-dependent kinases or CDKs are always present. All the different types are always present in a cell, ... | Cell cycle control Cells MCAT Khan Academy.mp3 |
All the different types are always present in a cell, but their default form or their default function is for them to be inactive. And so they need to be activated by these cyclin proteins. And the point of regulation here is that specific cyclins, so I'll write specific with just spec, so specific cyclins are made at ... | Cell cycle control Cells MCAT Khan Academy.mp3 |
And again, the reason why they're both so important is that when you have a cyclin-dependent kinase, it is only active when they are bound to a specific cyclin. It's at this point again that this guy is active. And the CDK is the business end of this complex. So that's the reason why in G1 you'll see the production of ... | Cell cycle control Cells MCAT Khan Academy.mp3 |
So that's the reason why in G1 you'll see the production of cyclins D and cyclin E. And from there you'll see CDK2 bound to your cyclin E, and at the same time you'll also have your CDK4 bound to your cyclin D. These activated kinases then, specifically the CDK4 cyclin D complex, will phosphorylate a protein called RB.... | Cell cycle control Cells MCAT Khan Academy.mp3 |
The phosphate group renders it inactive. And this is sort of the setup we have as we go further on in our cell cycle. In the S phase we have cyclin A produced. Cyclin A will complex again with CDK2 most directly to activate DNA replication. So it helps to activate DNA replication. And in a similar way we have cyclin B ... | Cell cycle control Cells MCAT Khan Academy.mp3 |
And the letters I'm going to use, these are the shorthands for the various nucleotide bases that make up a sequence of DNA. So let's say that I have some thymine, thymine, cytosine, guanine, cytosine, thymine, adenine, thymine, thymine, and let's throw another thymine in there. So that would be our sequence of DNA. And... | Impact of mutations on translation into amino acids High school biology Khan Academy.mp3 |
And what would be the corresponding sequence of RNA that it would be transcribed into? If you remember this from previous videos, pause this video and try to figure that out. Well, the key thing to appreciate is if we're talking about base pairs in DNA, adenine pairs with thymine, cytosine pairs with guanine. But if we... | Impact of mutations on translation into amino acids High school biology Khan Academy.mp3 |
But if we're talking about pairing into RNA, well then, instead of thymine in the RNA, you would have uracil. So the RNA here is, well, the thymine in the DNA would correspond to an adenine in the RNA. Adenine, guanine, cytosine, guanine, adenine. And now since this is an RNA strand, instead of having a thymine right o... | Impact of mutations on translation into amino acids High school biology Khan Academy.mp3 |
And now since this is an RNA strand, instead of having a thymine right over here, this would be a uracil. Adenine, adenine, adenine. So this process that we just did, this is transcription. Transcription, transcription. Transcription from DNA, DNA to RNA. Now the next step, if we're talking about the whole process of h... | Impact of mutations on translation into amino acids High school biology Khan Academy.mp3 |
Transcription, transcription. Transcription from DNA, DNA to RNA. Now the next step, if we're talking about the whole process of how does this information actually have an effect on the body is we're gonna go from the RNA and translate that into a protein. And the way we do that, we've seen this in previous videos, is ... | Impact of mutations on translation into amino acids High school biology Khan Academy.mp3 |
And the way we do that, we've seen this in previous videos, is every three of these bases, that's a codon, that it codes for a particular amino acid. Now to figure out what amino acid it codes for, we look at an amino acid translation table. And there's different types that you might see. This is the most typical type.... | Impact of mutations on translation into amino acids High school biology Khan Academy.mp3 |
This is the most typical type. So the first base is A, second base is A, third base is G. First base A, second base A, we're in this cell, third base is G. And so that will code for the amino acid lysine. So we could write L-Y-S, short for lysine here. We could have also gotten that from a different type of translation... | Impact of mutations on translation into amino acids High school biology Khan Academy.mp3 |
We could have also gotten that from a different type of translation table. For example, you might see a circular one that looks like that. But we would have gotten the same result. A-A-G, start at the center, A-A-G codes for lysine. Then the next codon, and if you're getting as excited about this as I am, I encourage y... | Impact of mutations on translation into amino acids High school biology Khan Academy.mp3 |
A-A-G, start at the center, A-A-G codes for lysine. Then the next codon, and if you're getting as excited about this as I am, I encourage you to pause this video and try to keep translating this. The next codon is C-G-A, C-G-A, arginine. C-G-A, arginine, arginine. And then the next one is U-A-A, U-A-A. Well here they h... | Impact of mutations on translation into amino acids High school biology Khan Academy.mp3 |
C-G-A, arginine, arginine. And then the next one is U-A-A, U-A-A. Well here they have this little black circular dot. What does that mean? Well that means stop codon. And sometimes they'll just write the word stop there. So this is stop. | Impact of mutations on translation into amino acids High school biology Khan Academy.mp3 |
What does that mean? Well that means stop codon. And sometimes they'll just write the word stop there. So this is stop. There is not an amino acid called stop. This actually signals to, and this is happening in a ribosome, this is signaling for the translation process to stop. This is the end of our amino acid chain, o... | Impact of mutations on translation into amino acids High school biology Khan Academy.mp3 |
So this is stop. There is not an amino acid called stop. This actually signals to, and this is happening in a ribosome, this is signaling for the translation process to stop. This is the end of our amino acid chain, of our polypeptide chain. And so we will stop right over there. But now let's do some interesting things... | Impact of mutations on translation into amino acids High school biology Khan Academy.mp3 |
This is the end of our amino acid chain, of our polypeptide chain. And so we will stop right over there. But now let's do some interesting things. Let's think about situations where there are mutations, where some of these bases, maybe something gets inserted, maybe something gets deleted, maybe something gets swapped ... | Impact of mutations on translation into amino acids High school biology Khan Academy.mp3 |
Let's think about situations where there are mutations, where some of these bases, maybe something gets inserted, maybe something gets deleted, maybe something gets swapped out. And so let's start with what's known as a point mutation. So let's say this C gets swapped out for an A. Well if that happened, then on the RN... | Impact of mutations on translation into amino acids High school biology Khan Academy.mp3 |
Well if that happened, then on the RNA strand, all of a sudden this would be a uracil. And if that is a uracil, this A-A-G would still be there, coding for lysine, but this second codon is now different. What would it now code for? Well C-U-A, C-U-A. It'll now code for leucine instead of arginine. Leucine, L-E-U. This ... | Impact of mutations on translation into amino acids High school biology Khan Academy.mp3 |
Well C-U-A, C-U-A. It'll now code for leucine instead of arginine. Leucine, L-E-U. This is fairly typical for a substitution mutation. It might change a particular amino acid. But sometimes it could be more significant. For example, if this G was swapped out for an A, then this C on the RNA would then be a U, and then ... | Impact of mutations on translation into amino acids High school biology Khan Academy.mp3 |
This is fairly typical for a substitution mutation. It might change a particular amino acid. But sometimes it could be more significant. For example, if this G was swapped out for an A, then this C on the RNA would then be a U, and then what would happen? Well this first codon would still code for lysine, but the secon... | Impact of mutations on translation into amino acids High school biology Khan Academy.mp3 |
For example, if this G was swapped out for an A, then this C on the RNA would then be a U, and then what would happen? Well this first codon would still code for lysine, but the second one would be U-G-A. U-G-A. Now all of a sudden it codes for a stop codon. And so the actual translation process would stop, which could... | Impact of mutations on translation into amino acids High school biology Khan Academy.mp3 |
Now all of a sudden it codes for a stop codon. And so the actual translation process would stop, which could be a very, very big deal if this DNA sequence, if the normal non-mutated polypeptide had to keep going on and on and on. Over here it just happened to have a stop codon next, but you can imagine if they had just... | Impact of mutations on translation into amino acids High school biology Khan Academy.mp3 |
Now another type of mutation that typically has a fairly significant effect is a frame shift mutation. And that's where something gets inserted or deleted and shifts everything. So for example, instead of the A being swapped in for the G, what if the A got inserted here? So then our sequence would look like this. T-T-C... | Impact of mutations on translation into amino acids High school biology Khan Academy.mp3 |
So then our sequence would look like this. T-T-C, and then we have A, and then you have G-C-T, G-C-T-A-T-T-T. So what just happened here, this was our original sequence, but the A got inserted here, it didn't replace the G, and so everything got shifted to the right. Now what are we coding for? Well when we transcribe ... | Impact of mutations on translation into amino acids High school biology Khan Academy.mp3 |
Now what are we coding for? Well when we transcribe to RNA, this will be A-A-G-U-C-G-A-U-A-A. And now this first codon still codes for lysine, we've seen that multiple times. But what about this second codon? The second codon over here, U-C-G, U-C-G, that's serine. U-C-G, that's serine. We got a different amino acid. | Impact of mutations on translation into amino acids High school biology Khan Academy.mp3 |
But what about this second codon? The second codon over here, U-C-G, U-C-G, that's serine. U-C-G, that's serine. We got a different amino acid. And what's interesting is, it's not just that one amino acid is changing, we're gonna see that keeps happening. So now we have A-U-A, A-U-A. Here we have isoleucine, so isoleuc... | Impact of mutations on translation into amino acids High school biology Khan Academy.mp3 |
We got a different amino acid. And what's interesting is, it's not just that one amino acid is changing, we're gonna see that keeps happening. So now we have A-U-A, A-U-A. Here we have isoleucine, so isoleucine right over here, which is different than what we had before, we now don't have a stop codon anymore. We would... | Impact of mutations on translation into amino acids High school biology Khan Academy.mp3 |
Here we have isoleucine, so isoleucine right over here, which is different than what we had before, we now don't have a stop codon anymore. We would keep going on and on. And so you can imagine a frame shift mutation, where you either insert something or you take it out, so that the whole frame gets shifted, can have a... | Impact of mutations on translation into amino acids High school biology Khan Academy.mp3 |
Now lucky for us, even though mutations are always going on, there are many proofreading mechanisms in biological systems to make them less frequent than they otherwise would be. And people are still understanding how these proofreading mechanisms fully happen. Another thing to appreciate is, we often associate a mutat... | Impact of mutations on translation into amino acids High school biology Khan Academy.mp3 |
And oftentimes, it is a bad thing. What used to be a functional protein may no longer be a functional protein, because the amino acids, the coding got stopped short, or there was a frame shift mutation, it's just coding for completely different things. So sometimes it could be very bad, and some diseases actually are c... | Impact of mutations on translation into amino acids High school biology Khan Academy.mp3 |
Oftentimes, the mutation might not be a big deal. Maybe something gets swapped out, maybe only one amino acid changes, and it doesn't really change the ability of the protein to do its job, in which case it doesn't matter. But every now and then, a mutation can actually be a good thing. In fact, we need the mutation in... | Impact of mutations on translation into amino acids High school biology Khan Academy.mp3 |
What is a non-coding RNA? Well, a non-coding RNA, or an NCRNA, as it is abbreviated, is a functional RNA molecule that actually skips this last step, and is not translated into a protein. In other words, they just go directly from transcription into an RNA molecule, and then go off to perform any number of vital functi... | Non-coding RNA (ncRNA) Biomolecules MCAT Khan Academy.mp3 |
And there are many examples of non-coding RNAs, including microRNAs, ribosomal RNA, transfer RNA, the list goes on and on. And as we go through each of these different types and examples of non-coding RNAs, you'll start to see that there's sort of an emerging theme here, and that is that most of these non-coding RNAs p... | Non-coding RNA (ncRNA) Biomolecules MCAT Khan Academy.mp3 |
MicroRNAs, or mRNAs, function in transcriptional and post-transcriptional regulation of gene expression, and they do this by base pairing with complementary sequences within mRNA or messenger RNA molecules. And this usually results in gene silencing through translational repression or target degradation. In essence, th... | Non-coding RNA (ncRNA) Biomolecules MCAT Khan Academy.mp3 |
Now, the next set of non-coding RNAs that we'll be talking about are all involved in translation, the first of which is ribosomal RNA. Now, ribosomes are the cellular machinery used to translate mRNA into proteins, and it is made up of one type of RNA molecule, ribosomal RNA. Transfer RNAs are an adapter molecule that ... | Non-coding RNA (ncRNA) Biomolecules MCAT Khan Academy.mp3 |
And so this is another type of non-coding RNA that you'll see in translation. The third type is called SNO-RNA, which stands for small nucleolar RNA, and it's a class of small RNA molecules that guide covalent modifications of ribosomal RNA, transfer RNA, and small nuclear RNAs, primarily through methylation, which is ... | Non-coding RNA (ncRNA) Biomolecules MCAT Khan Academy.mp3 |
In this video, we're going to talk a little bit about membrane receptors. Membrane receptors are really important because they are the things that actually allow our cells to communicate with the outside world. Without membrane receptors, our cells wouldn't be able to work together and they wouldn't be able to form the... | Membrane Receptors Nervous system physiology NCLEX-RN Khan Academy.mp3 |
A membrane receptor is essentially an integral protein that is embedded in the cell membrane that takes part in communication with the outside environment. For short, I'm just going to say it's an integral protein that communicates with the outside environment. The way membrane receptors work is that in our bodies, the... | Membrane Receptors Nervous system physiology NCLEX-RN Khan Academy.mp3 |
We call these extracellular signaling molecules because they are outsider cells. Let's say this outside area is the extracellular portion. Let's say we have a pink signaling molecule. For the sake of diagramming, I'm going to say it looks like a triangle. In reality, signaling molecules do not look like triangles. Sign... | Membrane Receptors Nervous system physiology NCLEX-RN Khan Academy.mp3 |
For the sake of diagramming, I'm going to say it looks like a triangle. In reality, signaling molecules do not look like triangles. Signaling molecules can be a variety of things. They can be ions or molecules, essentially, that bind to another chemical entity. We also call these ligands. A ligand can be something like... | Membrane Receptors Nervous system physiology NCLEX-RN Khan Academy.mp3 |
They can be ions or molecules, essentially, that bind to another chemical entity. We also call these ligands. A ligand can be something like a neurotransmitter, a hormone, cell recognition molecules. What these can do is these can attach to our membrane receptors and trigger changes inside the cell. I'm going to do the... | Membrane Receptors Nervous system physiology NCLEX-RN Khan Academy.mp3 |
What these can do is these can attach to our membrane receptors and trigger changes inside the cell. I'm going to do the membrane receptors in a nice blue color. Remember we say they're integral proteins. Integral proteins are proteins that go through the entire cell membrane. Let's say here we have our nice integral p... | Membrane Receptors Nervous system physiology NCLEX-RN Khan Academy.mp3 |
Integral proteins are proteins that go through the entire cell membrane. Let's say here we have our nice integral protein. What will happen, essentially, is this ligand will bind to our integral protein. This integral protein, which again appears in our cell membrane, will actually bind to that nice triangle-shaped lig... | Membrane Receptors Nervous system physiology NCLEX-RN Khan Academy.mp3 |
This integral protein, which again appears in our cell membrane, will actually bind to that nice triangle-shaped ligand that we have, like this. Now what we have is our ligand receptor complex. Just a fancy way of saying our ligand and our membrane receptor have bound. Once this happens, this can essentially tell the c... | Membrane Receptors Nervous system physiology NCLEX-RN Khan Academy.mp3 |
Once this happens, this can essentially tell the cell what to do. This can explain things like how hormones function, how our nerve impulses work, why our cells divide, cell death. It also explains why our cell allows certain things into the cell and other things not sometimes. In terms of a bigger real-world applicati... | Membrane Receptors Nervous system physiology NCLEX-RN Khan Academy.mp3 |
In terms of a bigger real-world application, this is really critically important in designing pharmaceutical drugs. In fact, a very big percentage of pharmaceutical drugs actually target our membrane receptors. This is actually why some drugs can target specific cells. Some drugs might only target your liver, while oth... | Membrane Receptors Nervous system physiology NCLEX-RN Khan Academy.mp3 |
Some drugs might only target your liver, while other drugs might target your heart. The reason why is because different cells might actually have different receptors, and these receptors might bind different things. This whole process of binding and telling the cell what to do, we actually have a really special name fo... | Membrane Receptors Nervous system physiology NCLEX-RN Khan Academy.mp3 |
It's called signal transduction. This is a process that we call signal transduction. What happens during signal transduction is an extracellular signal molecule, so this is our ligand, binds to our membrane receptor. These receptor proteins then cause an intracellular response. After binding, there will be what's calle... | Membrane Receptors Nervous system physiology NCLEX-RN Khan Academy.mp3 |
These receptor proteins then cause an intracellular response. After binding, there will be what's called an intracellular response. This receptor will bind to the protein, and this will cause the protein to actually change conformation, which then activates intracellular signaling proteins, so proteins on the intracell... | Membrane Receptors Nervous system physiology NCLEX-RN Khan Academy.mp3 |
This activates a cascade of protein signals that will alter the behavior of our cell. Sounds really complicated. Essentially, the way this works is we have an original signal, our ligand. This can be, again, a hormone, a neurotransmitter, something like that. This original signal is passed along. It'll bind to our prot... | Membrane Receptors Nervous system physiology NCLEX-RN Khan Academy.mp3 |
This can be, again, a hormone, a neurotransmitter, something like that. This original signal is passed along. It'll bind to our protein, and that protein will tell other proteins inside the cell about what's going on. This signal is propagated throughout the cell, causing the cell to perform a specific function. You'll... | Membrane Receptors Nervous system physiology NCLEX-RN Khan Academy.mp3 |
This signal is propagated throughout the cell, causing the cell to perform a specific function. You'll notice that in the diagram, we actually drew a really specific shape for our ligand. We chose a triangle. I chose a triangle because it's a little easier to draw, but this triangle actually fits right into the protein... | Membrane Receptors Nervous system physiology NCLEX-RN Khan Academy.mp3 |
I chose a triangle because it's a little easier to draw, but this triangle actually fits right into the protein that I was drawing, which has an empty triangle space. This is actually really important. Each specific receptor, so the thing that's missing a triangle, can only bind to a few types and often only one specif... | Membrane Receptors Nervous system physiology NCLEX-RN Khan Academy.mp3 |
It can only bind that specific triangle-pinked ligand. Membrane receptors allow our body and cells to transfer information, and it can be very, very specific about it. This is important because when our body releases a hormone, it's kind of floating around in our entire bloodstream. How does our pancreas know that the ... | Membrane Receptors Nervous system physiology NCLEX-RN Khan Academy.mp3 |
How does our pancreas know that the hormone's intended for it? How would our heart cells not react to it? This is why. The membrane receptors have a very specific preference for certain specific types of ligands. This is what we call our lock and key model. If we imagine our ligand as the key and our receptor protein a... | Membrane Receptors Nervous system physiology NCLEX-RN Khan Academy.mp3 |
The membrane receptors have a very specific preference for certain specific types of ligands. This is what we call our lock and key model. If we imagine our ligand as the key and our receptor protein as a lock, our receptor protein as a lock needs a very specific type of key in order to open it. Just like how our keych... | Membrane Receptors Nervous system physiology NCLEX-RN Khan Academy.mp3 |
Just like how our keychain, we might have a key to our mailbox and a key to our front door, maybe a key to our desk. Each of these keys does something different and opens a different lock. That's kind of how our cells work. I just want to make a note that this is a slightly outdated model. Our updated model is actually... | Membrane Receptors Nervous system physiology NCLEX-RN Khan Academy.mp3 |
I just want to make a note that this is a slightly outdated model. Our updated model is actually what we call induced fit. These two concepts are very similar, but instead of saying that the ligands and the membrane receptors have very, very specific shape, induced fit brings a little more flexibility. It says the liga... | Membrane Receptors Nervous system physiology NCLEX-RN Khan Academy.mp3 |
It says the ligands and the membrane receptors can sometimes change conformations, kind of like how dough can be a little squishy so that they can fit each other. Overall, there are still a ton of new membrane receptors that are being discovered. As far as we know, we can group membrane receptors into three large group... | Membrane Receptors Nervous system physiology NCLEX-RN Khan Academy.mp3 |
The first group we call ligand-gated ion channels. The second group we call G-protein coupled receptors. Lastly, our third group we call enzyme-linked receptors. In summary, essentially we have really important membrane receptors in our cell membrane. These are integral proteins that allow our cells to communicate with... | Membrane Receptors Nervous system physiology NCLEX-RN Khan Academy.mp3 |
In summary, essentially we have really important membrane receptors in our cell membrane. These are integral proteins that allow our cells to communicate with the outside environment. The process in which these integral proteins work, these membrane receptors work, is that we have a ligand, which can be an ion or a mol... | Membrane Receptors Nervous system physiology NCLEX-RN Khan Academy.mp3 |
It can bind to our integral protein, causing a process that we call signal transduction. Signal transduction essentially means that our original signal, our ligand, is propagated throughout the cell as different proteins are activated, causing our intracellular response. Ligands and membrane receptors have a very speci... | Membrane Receptors Nervous system physiology NCLEX-RN 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.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.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.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.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.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.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.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.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.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.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.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.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.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.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.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.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.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.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.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.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.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.mp3 |
This oxygen is that oxygen right there. 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. that hydrogen is there, but then that could get nabbed up by another passing water molecule to becom... | Molecular structure of DNA Macromolecules Biology Khan Academy.mp3 |
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 you know, 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... | Molecular structure of DNA Macromolecules Biology Khan Academy.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.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.mp3 |
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 we compare these two mol... | Molecular structure of DNA Macromolecules Biology Khan Academy.mp3 |
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 just has, this guy has an OH and an H. This guy implicitly has just two hydrogens over here. So he's missing an oxygen. So this is de... | Molecular structure of DNA Macromolecules Biology Khan Academy.mp3 |
So deoxyribose, 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 deoxyribose, I guess... | Molecular structure of DNA Macromolecules Biology Khan Academy.mp3 |
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 deoxyribo comes from. And then the last piece of it, ... | Molecular structure of DNA Macromolecules Biology Khan Academy.mp3 |
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, nitrogenous, nitrogenous bases. And you can see we have different types of nitrogenous bases. This is a nitrogenous base. This is, this ri... | Molecular structure of DNA Macromolecules Biology Khan Academy.mp3 |
So nitrogenous, nitrogenous, nitrogenous bases. And you can see we have different types of nitrogenous bases. This is a nitrogenous base. This is, 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. | Molecular structure of DNA Macromolecules Biology Khan Academy.mp3 |
This is, 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.mp3 |
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, you have two rings, we call them purines. as a general classif... | Molecular structure of DNA Macromolecules Biology Khan Academy.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, 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 jus... | Molecular structure of DNA Macromolecules Biology Khan Academy.mp3 |
as a general classification term. 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... | Molecular structure of DNA Macromolecules Biology Khan Academy.mp3 |
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