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So, today we're going to talk about the overall effects of a genetic mutation, and how mutations impact the affected organism as a whole. But first, I want to review the central dogma of molecular biology, and how genetic information in a cell is stored in the form of DNA, which is then transcribed to form RNA, which is then translated to form protein. Now nucleotides from DNA are transcribed to their complementary forms on RNA, which are then read as codons, or groups of three, to code for specific amino acids in a larger protein. Now if you mutate one of the nucleotides on DNA, like turning a thymine base into an adenine base, then that will affect the RNA sequence, and ultimately the protein that follows. So we say that mutations are generally mistakes in a cell's DNA that lead to abnormal protein production. So are mutations good, or are they bad? And what kind of effect do they have on the affected organism? | The effects of mutations Biomolecules MCAT Khan Academy.mp3 |
Now if you mutate one of the nucleotides on DNA, like turning a thymine base into an adenine base, then that will affect the RNA sequence, and ultimately the protein that follows. So we say that mutations are generally mistakes in a cell's DNA that lead to abnormal protein production. So are mutations good, or are they bad? And what kind of effect do they have on the affected organism? Well there isn't really a good answer to this question at all, and there are many, many different types of mutations out there that can result in big structural changes, like the little pictures I've drawn out here, or may result in little subtle changes that might go completely unnoticed. It's very difficult to call a mutation good or bad though, since it really depends on a huge number of things, including the environment that the organism lives in. So let's look at an example of a good mutation. | The effects of mutations Biomolecules MCAT Khan Academy.mp3 |
And what kind of effect do they have on the affected organism? Well there isn't really a good answer to this question at all, and there are many, many different types of mutations out there that can result in big structural changes, like the little pictures I've drawn out here, or may result in little subtle changes that might go completely unnoticed. It's very difficult to call a mutation good or bad though, since it really depends on a huge number of things, including the environment that the organism lives in. So let's look at an example of a good mutation. So the bacteria Streptococcus pneumoniae is the bacteria that you typically see associated with pneumonia, and one of the more popular treatments for pneumonia is giving the infected person an antibiotic like penicillin, which would help kill all of the bacteria and get rid of the disease. But sometimes you can find some mutated Streptococcus bacteria that will have a special trait that makes them resistant to penicillin, and now penicillin won't kill them as easily as it'll kill the bacteria without the mutation. Now we call this a good mutation because the bacteria are living in a human host, where they're likely to encounter this deadly penicillin, and being resistant to antibiotics like penicillin would then be beneficial to the bacteria. | The effects of mutations Biomolecules MCAT Khan Academy.mp3 |
So let's look at an example of a good mutation. So the bacteria Streptococcus pneumoniae is the bacteria that you typically see associated with pneumonia, and one of the more popular treatments for pneumonia is giving the infected person an antibiotic like penicillin, which would help kill all of the bacteria and get rid of the disease. But sometimes you can find some mutated Streptococcus bacteria that will have a special trait that makes them resistant to penicillin, and now penicillin won't kill them as easily as it'll kill the bacteria without the mutation. Now we call this a good mutation because the bacteria are living in a human host, where they're likely to encounter this deadly penicillin, and being resistant to antibiotics like penicillin would then be beneficial to the bacteria. And just to clarify, I'm calling this a good mutation for the bacteria, not really for the human infected, since it'll be harder for them to get rid of the bacteria that are resistant to certain antibiotics. So now let's look at an example of a bad mutation. So the disease cystic fibrosis is usually caused by a mutation in the CFTR gene. | The effects of mutations Biomolecules MCAT Khan Academy.mp3 |
Now we call this a good mutation because the bacteria are living in a human host, where they're likely to encounter this deadly penicillin, and being resistant to antibiotics like penicillin would then be beneficial to the bacteria. And just to clarify, I'm calling this a good mutation for the bacteria, not really for the human infected, since it'll be harder for them to get rid of the bacteria that are resistant to certain antibiotics. So now let's look at an example of a bad mutation. So the disease cystic fibrosis is usually caused by a mutation in the CFTR gene. Now I'm not really going to go into detail about how this mutation actually hurts you, but I'll leave you with the idea that what it does is it makes the mucus that you'd find in a person's lungs really, really thick, which makes it really hard for people affected with the disease to breathe. So in general, we can say that the mutation causing cystic fibrosis would be a quote-unquote bad mutation. But mutations aren't strictly good or strictly bad. | The effects of mutations Biomolecules MCAT Khan Academy.mp3 |
So the disease cystic fibrosis is usually caused by a mutation in the CFTR gene. Now I'm not really going to go into detail about how this mutation actually hurts you, but I'll leave you with the idea that what it does is it makes the mucus that you'd find in a person's lungs really, really thick, which makes it really hard for people affected with the disease to breathe. So in general, we can say that the mutation causing cystic fibrosis would be a quote-unquote bad mutation. But mutations aren't strictly good or strictly bad. In fact, there are some mutations that can cause some favorable and some disadvantageous effects. Sickle cell disease results from a mutation in a protein called hemoglobin that you'd find in red blood cells. And this mutation turns hemoglobin into a much less functional form, which we'll call HBS. | The effects of mutations Biomolecules MCAT Khan Academy.mp3 |
But mutations aren't strictly good or strictly bad. In fact, there are some mutations that can cause some favorable and some disadvantageous effects. Sickle cell disease results from a mutation in a protein called hemoglobin that you'd find in red blood cells. And this mutation turns hemoglobin into a much less functional form, which we'll call HBS. And it's much less efficient at moving oxygen around the human body. But another effect of sickle cell disease is that it makes the diseased person less susceptible to malaria. Now malaria is a parasite that grows and multiplies in red blood cells and can have a lot of nasty effects on the host organism. | The effects of mutations Biomolecules MCAT Khan Academy.mp3 |
And this mutation turns hemoglobin into a much less functional form, which we'll call HBS. And it's much less efficient at moving oxygen around the human body. But another effect of sickle cell disease is that it makes the diseased person less susceptible to malaria. Now malaria is a parasite that grows and multiplies in red blood cells and can have a lot of nasty effects on the host organism. And the malaria parasite can't really grow as well in red blood cells that are affected with sickle cell disease. So in this case, the mutation associated with this disease has one bad effect, which is that the HBS isn't as good as carrying oxygen around the body, but also a good effect in that it makes it less likely that the diseased person will be affected by malaria, since they can't grow as well in the human's red blood cells. So what did we learn? | The effects of mutations Biomolecules MCAT Khan Academy.mp3 |
Now malaria is a parasite that grows and multiplies in red blood cells and can have a lot of nasty effects on the host organism. And the malaria parasite can't really grow as well in red blood cells that are affected with sickle cell disease. So in this case, the mutation associated with this disease has one bad effect, which is that the HBS isn't as good as carrying oxygen around the body, but also a good effect in that it makes it less likely that the diseased person will be affected by malaria, since they can't grow as well in the human's red blood cells. So what did we learn? Well, first we learned that the effects of the mutation will usually, but not always, appear at the protein level. There are some exceptions to this rule. And second, we learned that genetic mutations can have advantageous, deleterious, or neutral effects depending on the type of mutation, the environment that the affected organism lives in, as well as a multitude of other factors. | The effects of mutations Biomolecules MCAT Khan Academy.mp3 |
If P is the frequency of the blue allele, Q is the frequency of the brown allele, well, and if they're the only two versions, well, if you add the frequency of P of the blue plus the frequency of the brown, they're gonna add up to 100%, or one. And if you square both sides of this, you would get this expression right over here, and we talk about that this is the probability, or you could say the frequency of being a homozygous, homozygous for the blue. This is the probability of having two alleles for the brown. And then right here in the middle, this is the probability of being a heterozygote. And why is that? Well, because you could get a blue from your mom and a brown from your dad, or a blue from your dad and a brown from your mom. So there's two ways to get that PQ combination. | Discussions of conditions for Hardy Weinberg Biology Khan Academy.mp3 |
And then right here in the middle, this is the probability of being a heterozygote. And why is that? Well, because you could get a blue from your mom and a brown from your dad, or a blue from your dad and a brown from your mom. So there's two ways to get that PQ combination. Now the key idea here is Hardy-Weinberg assumes a stable allele frequency. So let me write that really big. Because all of these other conditions that you might see are really like, well, what are all the different ways that you could somehow not have stable allele frequency? | Discussions of conditions for Hardy Weinberg Biology Khan Academy.mp3 |
So there's two ways to get that PQ combination. Now the key idea here is Hardy-Weinberg assumes a stable allele frequency. So let me write that really big. Because all of these other conditions that you might see are really like, well, what are all the different ways that you could somehow not have stable allele frequency? So let me write this down. Stable allele frequency. Stable allele frequency. | Discussions of conditions for Hardy Weinberg Biology Khan Academy.mp3 |
Because all of these other conditions that you might see are really like, well, what are all the different ways that you could somehow not have stable allele frequency? So let me write this down. Stable allele frequency. Stable allele frequency. So a lot of times, there's a temptation to memorize a bunch of stuff. You might wanna do that, but the more important thing is to get the underlying idea. And the underlying idea is, well, will something somehow cause the allele frequency to be unstable? | Discussions of conditions for Hardy Weinberg Biology Khan Academy.mp3 |
Stable allele frequency. So a lot of times, there's a temptation to memorize a bunch of stuff. You might wanna do that, but the more important thing is to get the underlying idea. And the underlying idea is, well, will something somehow cause the allele frequency to be unstable? And actually, another way to say stable allele frequency is no evolution. No evolution. Evolution is a change in the heritable traits in a population, and that will include a change in allele frequency. | Discussions of conditions for Hardy Weinberg Biology Khan Academy.mp3 |
And the underlying idea is, well, will something somehow cause the allele frequency to be unstable? And actually, another way to say stable allele frequency is no evolution. No evolution. Evolution is a change in the heritable traits in a population, and that will include a change in allele frequency. And if you think about the two ways that you could have a population evolving, well, you can have selection. So we're gonna assume no selection. Actually, there's more than two ways. | Discussions of conditions for Hardy Weinberg Biology Khan Academy.mp3 |
Evolution is a change in the heritable traits in a population, and that will include a change in allele frequency. And if you think about the two ways that you could have a population evolving, well, you can have selection. So we're gonna assume no selection. Actually, there's more than two ways. You could have genetic engineering and all sorts of things. So we're gonna assume, but the mainstream ways, I guess you could say, we can assume no selection. We can assume no genetic drift. | Discussions of conditions for Hardy Weinberg Biology Khan Academy.mp3 |
Actually, there's more than two ways. You could have genetic engineering and all sorts of things. So we're gonna assume, but the mainstream ways, I guess you could say, we can assume no selection. We can assume no genetic drift. Remember, selection is certain traits that make that organism more fit for that environment. Well, those traits are going to be more likely to be passed on. Genetic drift is random chance changes in the allele frequency. | Discussions of conditions for Hardy Weinberg Biology Khan Academy.mp3 |
We can assume no genetic drift. Remember, selection is certain traits that make that organism more fit for that environment. Well, those traits are going to be more likely to be passed on. Genetic drift is random chance changes in the allele frequency. It could be due to small populations. It could be due to members of the population migrating or some type of bottleneck effect, some natural disaster that really gets you to that small population. So that's the big picture. | Discussions of conditions for Hardy Weinberg Biology Khan Academy.mp3 |
Genetic drift is random chance changes in the allele frequency. It could be due to small populations. It could be due to members of the population migrating or some type of bottleneck effect, some natural disaster that really gets you to that small population. So that's the big picture. But given that big picture, I wanna dive deep into some of the assumptions that you might see in your biology class, just so you feel comfortable with them and you see that we're talking about the same thing. So the ones that I mentioned in that introductory video are no selection, and that's consistent with no evolution. I also talk about no net mutation, also consistent with no evolution. | Discussions of conditions for Hardy Weinberg Biology Khan Academy.mp3 |
So that's the big picture. But given that big picture, I wanna dive deep into some of the assumptions that you might see in your biology class, just so you feel comfortable with them and you see that we're talking about the same thing. So the ones that I mentioned in that introductory video are no selection, and that's consistent with no evolution. I also talk about no net mutation, also consistent with no evolution. Once again, we don't wanna change the allele frequency. If there was net mutation, maybe some of those blue versions of the gene get a mutation, and they're now maybe a different version, or they're definitely not blue anymore, so the allele frequency would change. The reason why we care about large population is mainly for genetic drift. | Discussions of conditions for Hardy Weinberg Biology Khan Academy.mp3 |
I also talk about no net mutation, also consistent with no evolution. Once again, we don't wanna change the allele frequency. If there was net mutation, maybe some of those blue versions of the gene get a mutation, and they're now maybe a different version, or they're definitely not blue anymore, so the allele frequency would change. The reason why we care about large population is mainly for genetic drift. If you have a very small population, just due to random chance, it's more likely that the allele frequencies can change appreciably. Now, other conditions that you will often see are things like random mating, that whether an orgasm has the blue or the brown version of the gene, that that doesn't make them any more or less desirable to a member of the opposite sex. And if you think about it, you might say, well, isn't that a form of selection? | Discussions of conditions for Hardy Weinberg Biology Khan Academy.mp3 |
The reason why we care about large population is mainly for genetic drift. If you have a very small population, just due to random chance, it's more likely that the allele frequencies can change appreciably. Now, other conditions that you will often see are things like random mating, that whether an orgasm has the blue or the brown version of the gene, that that doesn't make them any more or less desirable to a member of the opposite sex. And if you think about it, you might say, well, isn't that a form of selection? And you'd say, well, yes, it kind of is, but this is sometimes broken out as another way. Now, also, no migration, that you don't have, the population isn't growing by other organisms entering it or isn't shrinking by other organisms leaving, or there's not a mixing of population between two populations, and once again, it's all because we care about stable allele frequencies. Now, if we wanna go even further than that, and sometimes you will hear these types of things mentioned, although I just mentioned the five mainstream things, which all boil down to stable allele frequency, no evolution, no selection, no genetic drift, but sometimes we are assuming that we are dealing with diploid organisms, that you're getting one set of chromosomes from your mom, one set of chromosomes from your dad, or one version of an allele from your mom, one version of an allele from your dad, and you might say, well, how can you be other than diploid? | Discussions of conditions for Hardy Weinberg Biology Khan Academy.mp3 |
And if you think about it, you might say, well, isn't that a form of selection? And you'd say, well, yes, it kind of is, but this is sometimes broken out as another way. Now, also, no migration, that you don't have, the population isn't growing by other organisms entering it or isn't shrinking by other organisms leaving, or there's not a mixing of population between two populations, and once again, it's all because we care about stable allele frequencies. Now, if we wanna go even further than that, and sometimes you will hear these types of things mentioned, although I just mentioned the five mainstream things, which all boil down to stable allele frequency, no evolution, no selection, no genetic drift, but sometimes we are assuming that we are dealing with diploid organisms, that you're getting one set of chromosomes from your mom, one set of chromosomes from your dad, or one version of an allele from your mom, one version of an allele from your dad, and you might say, well, how can you be other than diploid? Well, you could be, there are tetraploid populations, especially this can happen in plants, or we could get two sets of chromosomes from your mom, two sets of chromosomes from your dad. We are assuming sexual reproduction, that we're not dealing with cloning, and or just budding, where you're just a copy of another organism from generation to generation. We're assuming that whether you are blue or brown, whether you have those versions, that that's not correlated with what sex you are. | Discussions of conditions for Hardy Weinberg Biology Khan Academy.mp3 |
Now, if we wanna go even further than that, and sometimes you will hear these types of things mentioned, although I just mentioned the five mainstream things, which all boil down to stable allele frequency, no evolution, no selection, no genetic drift, but sometimes we are assuming that we are dealing with diploid organisms, that you're getting one set of chromosomes from your mom, one set of chromosomes from your dad, or one version of an allele from your mom, one version of an allele from your dad, and you might say, well, how can you be other than diploid? Well, you could be, there are tetraploid populations, especially this can happen in plants, or we could get two sets of chromosomes from your mom, two sets of chromosomes from your dad. We are assuming sexual reproduction, that we're not dealing with cloning, and or just budding, where you're just a copy of another organism from generation to generation. We're assuming that whether you are blue or brown, whether you have those versions, that that's not correlated with what sex you are. So allele frequency, allele frequency, same in all sexes, in all sexes, and we're assuming sexual reproduction. Once again, we're assuming one where there's only two sexes. So you could, if you were to think about, if you were to let your imagination go wild, you could imagine a lot of other constraints to put here, or other ways that the, where you could no longer have, apply the Hardy-Weinberg, where this is, we have two alleles, we're assuming sexual reproduction, diploid, you're getting a mom from your mom, from your dad, and just here are all the conditions that help us ensure that we have a stable allele frequency. | Discussions of conditions for Hardy Weinberg Biology Khan Academy.mp3 |
We're assuming that whether you are blue or brown, whether you have those versions, that that's not correlated with what sex you are. So allele frequency, allele frequency, same in all sexes, in all sexes, and we're assuming sexual reproduction. Once again, we're assuming one where there's only two sexes. So you could, if you were to think about, if you were to let your imagination go wild, you could imagine a lot of other constraints to put here, or other ways that the, where you could no longer have, apply the Hardy-Weinberg, where this is, we have two alleles, we're assuming sexual reproduction, diploid, you're getting a mom from your mom, from your dad, and just here are all the conditions that help us ensure that we have a stable allele frequency. Now the one thing you're saying, okay, I can, you know, diploid, sexual reproduction, okay, but isn't, isn't, you know, isn't there always a chance for a little bit of genetic drift? Isn't there, you know, just the history of the world, is that we have this evolution? And the answer is yes. | Discussions of conditions for Hardy Weinberg Biology Khan Academy.mp3 |
So what are some applications of DNA technology? Applications, DNA technology. Alright, well let's first look at medicine. So what are some applications of DNA technology in medicine? Well, one of the really big, the two big things where recombinant DNA technology was first used was to create insulin and human growth hormone. So before the advent of recombinant DNA technology, insulin and growth hormone were really, really hard to manufacture. You basically had to isolate it from another human and purify it and then give it to patients. | Applications of DNA technologies Biomolecules MCAT Khan Academy.mp3 |
So what are some applications of DNA technology in medicine? Well, one of the really big, the two big things where recombinant DNA technology was first used was to create insulin and human growth hormone. So before the advent of recombinant DNA technology, insulin and growth hormone were really, really hard to manufacture. You basically had to isolate it from another human and purify it and then give it to patients. But with recombinant DNA technology, you can basically just grow these proteins in E. coli. You can grow them and culture them in E. coli bacteria. So this really has changed the way that medicine is practiced and it's really helped a whole bunch of people. | Applications of DNA technologies Biomolecules MCAT Khan Academy.mp3 |
You basically had to isolate it from another human and purify it and then give it to patients. But with recombinant DNA technology, you can basically just grow these proteins in E. coli. You can grow them and culture them in E. coli bacteria. So this really has changed the way that medicine is practiced and it's really helped a whole bunch of people. So vaccines is another application of DNA technology. A while ago, vaccines were made by first denaturing the disease and then after the disease has been weakened, they would inject it into a human and they would hope that their immune system would be able to put up a fight against the weakened virus. And that way in the future, if they were infected with that virus, they would at least have some kind of immune response towards the virus. | Applications of DNA technologies Biomolecules MCAT Khan Academy.mp3 |
So this really has changed the way that medicine is practiced and it's really helped a whole bunch of people. So vaccines is another application of DNA technology. A while ago, vaccines were made by first denaturing the disease and then after the disease has been weakened, they would inject it into a human and they would hope that their immune system would be able to put up a fight against the weakened virus. And that way in the future, if they were infected with that virus, they would at least have some kind of immune response towards the virus. The problem with this was that the patient would sometimes get the disease because you're injecting a weak virus, but sometimes it wasn't weak enough. So with DNA technology, they can actually recreate the outer shell of the virus and inject that. So it's a lot more cost effective and it doesn't have the risk of actually causing the disease in the host. | Applications of DNA technologies Biomolecules MCAT Khan Academy.mp3 |
And that way in the future, if they were infected with that virus, they would at least have some kind of immune response towards the virus. The problem with this was that the patient would sometimes get the disease because you're injecting a weak virus, but sometimes it wasn't weak enough. So with DNA technology, they can actually recreate the outer shell of the virus and inject that. So it's a lot more cost effective and it doesn't have the risk of actually causing the disease in the host. So this is much safer and it is cheaper and it produces a better immune response. And so some vaccines that we actually use recombinant DNA technology to create include the Hep B virus and the herpes virus and malaria. So these are some applications of DNA technology in medicine. | Applications of DNA technologies Biomolecules MCAT Khan Academy.mp3 |
So it's a lot more cost effective and it doesn't have the risk of actually causing the disease in the host. So this is much safer and it is cheaper and it produces a better immune response. And so some vaccines that we actually use recombinant DNA technology to create include the Hep B virus and the herpes virus and malaria. So these are some applications of DNA technology in medicine. Another cool application of DNA technology is in solving crimes. So solving crimes, so in forensics. So there are parts of the genome known as non-coding regions of the genome. | Applications of DNA technologies Biomolecules MCAT Khan Academy.mp3 |
So these are some applications of DNA technology in medicine. Another cool application of DNA technology is in solving crimes. So solving crimes, so in forensics. So there are parts of the genome known as non-coding regions of the genome. And these regions can actually help forensic scientists identify specific individuals. So they can look at things like short tandem repeats, STRs. And these are basically short sequences of DNA, like two to six base pairs long. | Applications of DNA technologies Biomolecules MCAT Khan Academy.mp3 |
So there are parts of the genome known as non-coding regions of the genome. And these regions can actually help forensic scientists identify specific individuals. So they can look at things like short tandem repeats, STRs. And these are basically short sequences of DNA, like two to six base pairs long. And they're normally found in really high amounts. They're just these short repeats that are found in really high amounts and to varying degrees between different individuals. So they actually sequence these short tandem repeats. | Applications of DNA technologies Biomolecules MCAT Khan Academy.mp3 |
And these are basically short sequences of DNA, like two to six base pairs long. And they're normally found in really high amounts. They're just these short repeats that are found in really high amounts and to varying degrees between different individuals. So they actually sequence these short tandem repeats. They could identify specific individuals given a DNA sample. They can also look at mitochondrial DNA. So mitochondrial DNA is inherited from your mother and it's found in really high amounts within an individual cell. | Applications of DNA technologies Biomolecules MCAT Khan Academy.mp3 |
So they actually sequence these short tandem repeats. They could identify specific individuals given a DNA sample. They can also look at mitochondrial DNA. So mitochondrial DNA is inherited from your mother and it's found in really high amounts within an individual cell. So even if there's very little sample available, forensic scientists can analyze mitochondrial DNA in order to identify a potential suspect. Another technology that is used in forensic science is Y chromosome typing. So that's basically YSTR. | Applications of DNA technologies Biomolecules MCAT Khan Academy.mp3 |
So mitochondrial DNA is inherited from your mother and it's found in really high amounts within an individual cell. So even if there's very little sample available, forensic scientists can analyze mitochondrial DNA in order to identify a potential suspect. Another technology that is used in forensic science is Y chromosome typing. So that's basically YSTR. And this is looking at short tandem repeats found on the Y chromosome. And so DNA technology has helped scientists pick out individuals that have committed various crimes based on DNA samples that people that they were able to find. So agriculture is another field that has greatly benefited from recombinant DNA technology. | Applications of DNA technologies Biomolecules MCAT Khan Academy.mp3 |
So that's basically YSTR. And this is looking at short tandem repeats found on the Y chromosome. And so DNA technology has helped scientists pick out individuals that have committed various crimes based on DNA samples that people that they were able to find. So agriculture is another field that has greatly benefited from recombinant DNA technology. So, for example, scientists can now create plants that are crops that are resistant to insects and that are resistant to herbicides and can also delay ripening of the crop so that you can transport the crop from the farm to the store. So by doing this, you're basically able to create more crops to feed a growing population of individuals. And it also helps with the economy because then you've got farmers that are growing all their crops. | Applications of DNA technologies Biomolecules MCAT Khan Academy.mp3 |
We have other videos where we talk about how small molecules or ions might be able to go through a cell's membrane in different ways, whether actively or passively, maybe facilitated in some way. What we want to talk about in this video is how we can do this for larger things. So we're going to focus on here is bulk, bulk transport, transport. So this first example, you could imagine this, this cell with this mauve or purple colored membrane is engulfing this big green thing, which is maybe a bacteria or something. And so you see that the membrane, let me make it very clear, this is inside, this is inside the cell, this is outside, outside the cell. And you can see the cellular membrane starts to wrap around this, I guess we can think of this as a bacteria. Then it fully wraps around, and then that membrane that was wrapping around the bacteria pinches off, and now the bacteria is inside of the cell, and it's wrapped by this membrane. | Endocytosis, phagocytosis, and pinocytosis Biology Khan Academy.mp3 |
So this first example, you could imagine this, this cell with this mauve or purple colored membrane is engulfing this big green thing, which is maybe a bacteria or something. And so you see that the membrane, let me make it very clear, this is inside, this is inside the cell, this is outside, outside the cell. And you can see the cellular membrane starts to wrap around this, I guess we can think of this as a bacteria. Then it fully wraps around, and then that membrane that was wrapping around the bacteria pinches off, and now the bacteria is inside of the cell, and it's wrapped by this membrane. And this process, where you're engulfing these large things, we call this phagocytosis. So this is phago, phagocytosis. And the prefix, I guess you could say phago, comes from the Greek for to eat. | Endocytosis, phagocytosis, and pinocytosis Biology Khan Academy.mp3 |
Then it fully wraps around, and then that membrane that was wrapping around the bacteria pinches off, and now the bacteria is inside of the cell, and it's wrapped by this membrane. And this process, where you're engulfing these large things, we call this phagocytosis. So this is phago, phagocytosis. And the prefix, I guess you could say phago, comes from the Greek for to eat. So this is literally about cell eating. And in many cases, this thing that is now in here, you could view this as the cell's food, this compartment that is holding this, in this case, bacteria, is going to transport it maybe to a lysosome so it can be processed and digested in some way. We would call this big compartment, this membrane-bound compartment, we would call this a food vacuole. | Endocytosis, phagocytosis, and pinocytosis Biology Khan Academy.mp3 |
And the prefix, I guess you could say phago, comes from the Greek for to eat. So this is literally about cell eating. And in many cases, this thing that is now in here, you could view this as the cell's food, this compartment that is holding this, in this case, bacteria, is going to transport it maybe to a lysosome so it can be processed and digested in some way. We would call this big compartment, this membrane-bound compartment, we would call this a food vacuole. Food, food vacuole. Now, this scenario down here is similar but different. Over here I have the cell, which is, I see part of its membrane, and it's in magenta right over here. | Endocytosis, phagocytosis, and pinocytosis Biology Khan Academy.mp3 |
We would call this big compartment, this membrane-bound compartment, we would call this a food vacuole. Food, food vacuole. Now, this scenario down here is similar but different. Over here I have the cell, which is, I see part of its membrane, and it's in magenta right over here. We can see the phospholipid bilayer. That's why I drew two lines for the membrane. And instead of engulfing a large particle or bacteria, it's just engulfing some fluid. | Endocytosis, phagocytosis, and pinocytosis Biology Khan Academy.mp3 |
Over here I have the cell, which is, I see part of its membrane, and it's in magenta right over here. We can see the phospholipid bilayer. That's why I drew two lines for the membrane. And instead of engulfing a large particle or bacteria, it's just engulfing some fluid. It's engulfing some fluid. So you see it's starting to wrap around this section of fluid, wraps even more around this section of fluid, and then the membrane that was around it completely pinches off and goes into the cell. And I'm drawing all of these things in two dimensions, but this would actually be happening in three dimensions. | Endocytosis, phagocytosis, and pinocytosis Biology Khan Academy.mp3 |
And instead of engulfing a large particle or bacteria, it's just engulfing some fluid. It's engulfing some fluid. So you see it's starting to wrap around this section of fluid, wraps even more around this section of fluid, and then the membrane that was around it completely pinches off and goes into the cell. And I'm drawing all of these things in two dimensions, but this would actually be happening in three dimensions. So this wouldn't just be a circle, this right over here would be a sphere. And this thing that has been pinched off and is now inside the cell, we call this a vesicle, which is just a general term for these membrane-bound compartments inside of cells. And this process where the cell has essentially drunk a bunch of fluid and the stuff that happens to be in the fluid, we call this pinocytosis. | Endocytosis, phagocytosis, and pinocytosis Biology Khan Academy.mp3 |
And I'm drawing all of these things in two dimensions, but this would actually be happening in three dimensions. So this wouldn't just be a circle, this right over here would be a sphere. And this thing that has been pinched off and is now inside the cell, we call this a vesicle, which is just a general term for these membrane-bound compartments inside of cells. And this process where the cell has essentially drunk a bunch of fluid and the stuff that happens to be in the fluid, we call this pinocytosis. Pinocytosis. Pinocytosis. And pino comes from the Greek word to drink. | Endocytosis, phagocytosis, and pinocytosis Biology Khan Academy.mp3 |
And this process where the cell has essentially drunk a bunch of fluid and the stuff that happens to be in the fluid, we call this pinocytosis. Pinocytosis. Pinocytosis. And pino comes from the Greek word to drink. And I'm always fascinated by word roots, and I'm not a linguistic expert here, but it's neat because even in languages I'm familiar with, like Hindi and Urdu, the word pina means to drink. So it's a, and maybe it's even related to the word pani, which is in those words, in those languages. I know all of these have a shared linguistic root, so it's always fascinating to see these, to see these linguistic connections. | Endocytosis, phagocytosis, and pinocytosis Biology Khan Academy.mp3 |
And pino comes from the Greek word to drink. And I'm always fascinated by word roots, and I'm not a linguistic expert here, but it's neat because even in languages I'm familiar with, like Hindi and Urdu, the word pina means to drink. So it's a, and maybe it's even related to the word pani, which is in those words, in those languages. I know all of these have a shared linguistic root, so it's always fascinating to see these, to see these linguistic connections. So this is pinocytosis, where the cell is drinking, so to speak, but it's also getting the other stuff that's in that fluid. This is phagocytosis, the cell is eating. And those, these are both special cases of, I guess the more general term of engulfing in this way, which is called endocytosis. | Endocytosis, phagocytosis, and pinocytosis Biology Khan Academy.mp3 |
I know all of these have a shared linguistic root, so it's always fascinating to see these, to see these linguistic connections. So this is pinocytosis, where the cell is drinking, so to speak, but it's also getting the other stuff that's in that fluid. This is phagocytosis, the cell is eating. And those, these are both special cases of, I guess the more general term of engulfing in this way, which is called endocytosis. Endo, endocytosis. So phagocytosis is a form of endocytosis, and pinocytosis is a form of endocytosis. Now the next question you might say is, okay, I can get that this happens, this can be observed under a microscope, but how does it happen? | Endocytosis, phagocytosis, and pinocytosis Biology Khan Academy.mp3 |
And those, these are both special cases of, I guess the more general term of engulfing in this way, which is called endocytosis. Endo, endocytosis. So phagocytosis is a form of endocytosis, and pinocytosis is a form of endocytosis. Now the next question you might say is, okay, I can get that this happens, this can be observed under a microscope, but how does it happen? How does the cell wrap around and pinch around? And like I say in a lot of videos, people think that we understand some of it, but this is not fully, fully understood. There's views that, well, the cytoskeleton must be involved in some way. | Endocytosis, phagocytosis, and pinocytosis Biology Khan Academy.mp3 |
Now the next question you might say is, okay, I can get that this happens, this can be observed under a microscope, but how does it happen? How does the cell wrap around and pinch around? And like I say in a lot of videos, people think that we understand some of it, but this is not fully, fully understood. There's views that, well, the cytoskeleton must be involved in some way. It has to create space here for this thing to be able to pinch off and move in that direction. It maybe will help, actually, the cell's membrane wrap around in some way, but these are all areas of active research. How does this endocytosis actually occur? | Endocytosis, phagocytosis, and pinocytosis Biology Khan Academy.mp3 |
In fact, right depicted in front of us, we have two strands of DNA forming a double helix. And we can look at the telltale signs that this is DNA. And in particular, we can look at the five-carbon sugar on its backbone. We see, and let's actually number the carbons. This is one prime, two prime, three prime, four prime, five prime. We can see on the two-prime carbon, we don't have an oxygen attached to it. We don't have a hydroxyl group attached to it. | Molecular structure of RNA Macromolecules Biology Khan Academy (3).mp3 |
We see, and let's actually number the carbons. This is one prime, two prime, three prime, four prime, five prime. We can see on the two-prime carbon, we don't have an oxygen attached to it. We don't have a hydroxyl group attached to it. And because of that, we know that this is not ribose. This is deoxyribose. This right over here is deoxyribose. | Molecular structure of RNA Macromolecules Biology Khan Academy (3).mp3 |
We don't have a hydroxyl group attached to it. And because of that, we know that this is not ribose. This is deoxyribose. This right over here is deoxyribose. And these two are also deoxyribose. So that tells us that we have two strands of DNA, deoxyribonucleic acid. So let me write this down. | Molecular structure of RNA Macromolecules Biology Khan Academy (3).mp3 |
This right over here is deoxyribose. And these two are also deoxyribose. So that tells us that we have two strands of DNA, deoxyribonucleic acid. So let me write this down. This part of the chain, this is derived from a deoxyribose being attached to phosphate groups in a nitrogenous base. So deoxyribose. So what would we have to do if we wanted, instead of viewing this as two strands of DNA in a double helix formation, well, how would we have to rearrange, how would we have to edit the left-hand strand if instead we wanted to imagine that the left-hand strand is, say, messenger RNA being generated during transcription with a single strand of DNA here on the right? | Molecular structure of RNA Macromolecules Biology Khan Academy (3).mp3 |
So let me write this down. This part of the chain, this is derived from a deoxyribose being attached to phosphate groups in a nitrogenous base. So deoxyribose. So what would we have to do if we wanted, instead of viewing this as two strands of DNA in a double helix formation, well, how would we have to rearrange, how would we have to edit the left-hand strand if instead we wanted to imagine that the left-hand strand is, say, messenger RNA being generated during transcription with a single strand of DNA here on the right? Well, to turn this into RNA, or to make it look like RNA, on the two prime carbon, well, we wanna turn the deoxyribose into just ribose, so we would wanna add a hydroxyl group right over here. So add a hydroxyl group over there. Actually, let me do that. | Molecular structure of RNA Macromolecules Biology Khan Academy (3).mp3 |
So what would we have to do if we wanted, instead of viewing this as two strands of DNA in a double helix formation, well, how would we have to rearrange, how would we have to edit the left-hand strand if instead we wanted to imagine that the left-hand strand is, say, messenger RNA being generated during transcription with a single strand of DNA here on the right? Well, to turn this into RNA, or to make it look like RNA, on the two prime carbon, well, we wanna turn the deoxyribose into just ribose, so we would wanna add a hydroxyl group right over here. So add a hydroxyl group over there. Actually, let me do that. Do the hydrogens in white. So add one hydroxyl group there. And I wanna do it on all the sugars on the left strand's backbone. | Molecular structure of RNA Macromolecules Biology Khan Academy (3).mp3 |
Actually, let me do that. Do the hydrogens in white. So add one hydroxyl group there. And I wanna do it on all the sugars on the left strand's backbone. If I want this to be a single strand of RNA, and RNA tends to be single-stranded. So oxygen and then a hydrogen. And so this hydroxyl, adding this hydroxyl group, instead of just having another hydrogen, just a hydrogen by itself over there, this tells us that this sugar is no longer deoxyribose. | Molecular structure of RNA Macromolecules Biology Khan Academy (3).mp3 |
And I wanna do it on all the sugars on the left strand's backbone. If I want this to be a single strand of RNA, and RNA tends to be single-stranded. So oxygen and then a hydrogen. And so this hydroxyl, adding this hydroxyl group, instead of just having another hydrogen, just a hydrogen by itself over there, this tells us that this sugar is no longer deoxyribose. This is ribose. So now we have ribose. We now have ribose in our backbone, which is a telltale sign that, well, at least now we have the backbone of RNA, ribonucleic acid, versus DNA, deoxyribonucleic acid. | Molecular structure of RNA Macromolecules Biology Khan Academy (3).mp3 |
And so this hydroxyl, adding this hydroxyl group, instead of just having another hydrogen, just a hydrogen by itself over there, this tells us that this sugar is no longer deoxyribose. This is ribose. So now we have ribose. We now have ribose in our backbone, which is a telltale sign that, well, at least now we have the backbone of RNA, ribonucleic acid, versus DNA, deoxyribonucleic acid. Now you might think we're done, but we're not quite done, because the nitrogenous bases on RNA are slightly different than the nitrogenous bases on DNA. On DNA, your nitrogenous bases are adenine, guanine, are adenine, guanine, and adenine and guanine are the two-ringed nitrogenous bases right over here. This is adenine, this is guanine. | Molecular structure of RNA Macromolecules Biology Khan Academy (3).mp3 |
We now have ribose in our backbone, which is a telltale sign that, well, at least now we have the backbone of RNA, ribonucleic acid, versus DNA, deoxyribonucleic acid. Now you might think we're done, but we're not quite done, because the nitrogenous bases on RNA are slightly different than the nitrogenous bases on DNA. On DNA, your nitrogenous bases are adenine, guanine, are adenine, guanine, and adenine and guanine are the two-ringed nitrogenous bases right over here. This is adenine, this is guanine. And you also have cytosine. Cytosine, I'm gonna do these all in different colors. Cytosine and thymine. | Molecular structure of RNA Macromolecules Biology Khan Academy (3).mp3 |
This is adenine, this is guanine. And you also have cytosine. Cytosine, I'm gonna do these all in different colors. Cytosine and thymine. I'm getting to the punchline too fast. And this right over here is cytosine, and this is thymine. And cytosine and thymine are single-ringed nitrogenous bases. | Molecular structure of RNA Macromolecules Biology Khan Academy (3).mp3 |
Cytosine and thymine. I'm getting to the punchline too fast. And this right over here is cytosine, and this is thymine. And cytosine and thymine are single-ringed nitrogenous bases. We call them pyrimidines, adenine and guanine. We call them purines. This is a little bit of a review. | Molecular structure of RNA Macromolecules Biology Khan Academy (3).mp3 |
And cytosine and thymine are single-ringed nitrogenous bases. We call them pyrimidines, adenine and guanine. We call them purines. This is a little bit of a review. In RNA, you still have adenine, you still have guanine, you still have cytosine, but instead of thymine, you have a very close relative of thymine, and that is uracil. So the way that this is drawn right now, this nitrogenous base, remember when we started this video, it was double-stranded DNA, this nitrogenous base right over here is thymine, and it bonds, it forms hydrogen bonds with adenine right over here. If I want to turn it into uracil, I just have to get rid of this methyl group right over here. | Molecular structure of RNA Macromolecules Biology Khan Academy (3).mp3 |
This is a little bit of a review. In RNA, you still have adenine, you still have guanine, you still have cytosine, but instead of thymine, you have a very close relative of thymine, and that is uracil. So the way that this is drawn right now, this nitrogenous base, remember when we started this video, it was double-stranded DNA, this nitrogenous base right over here is thymine, and it bonds, it forms hydrogen bonds with adenine right over here. If I want to turn it into uracil, I just have to get rid of this methyl group right over here. So if I just do this, if I just do this, and if I were to replace it with a hydrogen that is just implicitly bonded there, well now I'm dealing with uracil. So now I'm dealing with uracil. So you see that uracil and thymine are very close molecules, or they're very similar nitrogenous bases, and that's why they can play a very similar role. | Molecular structure of RNA Macromolecules Biology Khan Academy (3).mp3 |
If I want to turn it into uracil, I just have to get rid of this methyl group right over here. So if I just do this, if I just do this, and if I were to replace it with a hydrogen that is just implicitly bonded there, well now I'm dealing with uracil. So now I'm dealing with uracil. So you see that uracil and thymine are very close molecules, or they're very similar nitrogenous bases, and that's why they can play a very similar role. And it's still the case. And so what uracil pairs with, it pairs still with adenine, the same thing that thymine pairs with, and everything else is of course still the same. Now an interesting question, an interesting question is why uracil? | Molecular structure of RNA Macromolecules Biology Khan Academy (3).mp3 |
So you see that uracil and thymine are very close molecules, or they're very similar nitrogenous bases, and that's why they can play a very similar role. And it's still the case. And so what uracil pairs with, it pairs still with adenine, the same thing that thymine pairs with, and everything else is of course still the same. Now an interesting question, an interesting question is why uracil? Why not thymine? Or you could say why thymine? Why not uracil? | Molecular structure of RNA Macromolecules Biology Khan Academy (3).mp3 |
Now an interesting question, an interesting question is why uracil? Why not thymine? Or you could say why thymine? Why not uracil? And based on what I've read, it actually turns out that uracil is a little bit more error prone. It might be able to bond with other things when you're coding. It's a little bit less stable than thymine. | Molecular structure of RNA Macromolecules Biology Khan Academy (3).mp3 |
Why not uracil? And based on what I've read, it actually turns out that uracil is a little bit more error prone. It might be able to bond with other things when you're coding. It's a little bit less stable than thymine. And so uracil, uracil, uracil makes the RNA molecule, or actually makes the machinery of information transfer, it makes it less stable. It's a less stable, I guess, way to transfer information. And based on what I've read, in evolutionary history, RNA molecules, most people believe, predate DNA molecules. | Molecular structure of RNA Macromolecules Biology Khan Academy (3).mp3 |
It's a little bit less stable than thymine. And so uracil, uracil, uracil makes the RNA molecule, or actually makes the machinery of information transfer, it makes it less stable. It's a less stable, I guess, way to transfer information. And based on what I've read, in evolutionary history, RNA molecules, most people believe, predate DNA molecules. And then when you, so in the early stages you had a lot of change, and so uracil molecules were just fine, and there was a lot of errors and whatever else, but then once you had, I guess, information needed to be a little bit more persistent and a little less error prone, well then thymine helped stabilize, thymine helped stabilize things. There's also the view of, well why is uracil stuck around? Well RNA molecules, they have all of these roles in cells, messenger RNA molecules are taking information from the DNA and getting it transcribed, or getting it translated at the ribosome, but they shouldn't hang out forever. | Molecular structure of RNA Macromolecules Biology Khan Academy (3).mp3 |
And based on what I've read, in evolutionary history, RNA molecules, most people believe, predate DNA molecules. And then when you, so in the early stages you had a lot of change, and so uracil molecules were just fine, and there was a lot of errors and whatever else, but then once you had, I guess, information needed to be a little bit more persistent and a little less error prone, well then thymine helped stabilize, thymine helped stabilize things. There's also the view of, well why is uracil stuck around? Well RNA molecules, they have all of these roles in cells, messenger RNA molecules are taking information from the DNA and getting it transcribed, or getting it translated at the ribosome, but they shouldn't hang out forever. You actually want them to be somewhat unstable. So it's an interesting question to think about. Why do we have uracil instead of thymine? | Molecular structure of RNA Macromolecules Biology Khan Academy (3).mp3 |
Well RNA molecules, they have all of these roles in cells, messenger RNA molecules are taking information from the DNA and getting it transcribed, or getting it translated at the ribosome, but they shouldn't hang out forever. You actually want them to be somewhat unstable. So it's an interesting question to think about. Why do we have uracil instead of thymine? Or why do we have thymine instead of uracil? But this is one of the telltale signs of, that we are now dealing with an RNA molecule. So now what we have on the left hand side, now all of this business, actually let me do this in a different color, all of this business, this strand, this strand right over here, we can now, the way it's drawn, we can now consider this an RNA molecule. | Molecular structure of RNA Macromolecules Biology Khan Academy (3).mp3 |
Why do we have uracil instead of thymine? Or why do we have thymine instead of uracil? But this is one of the telltale signs of, that we are now dealing with an RNA molecule. So now what we have on the left hand side, now all of this business, actually let me do this in a different color, all of this business, this strand, this strand right over here, we can now, the way it's drawn, we can now consider this an RNA molecule. And if we assume that this is happening during transcription, when a DNA molecule, where a single strand of DNA would want to replicate its information, then this over here would be mRNA, messenger, messenger RNA. And so what's going on here? Well, let's think about it. | Molecular structure of RNA Macromolecules Biology Khan Academy (3).mp3 |
So now what we have on the left hand side, now all of this business, actually let me do this in a different color, all of this business, this strand, this strand right over here, we can now, the way it's drawn, we can now consider this an RNA molecule. And if we assume that this is happening during transcription, when a DNA molecule, where a single strand of DNA would want to replicate its information, then this over here would be mRNA, messenger, messenger RNA. And so what's going on here? Well, let's think about it. This one, the way it's, the RNA, the messenger RNA, the way it's oriented, we have, if we go, we have phosphate group, then we go to five prime carbon, four prime, three prime, then phosphate group, then five prime, four prime, three prime, then phosphate group. So this is oriented five prime on top, three prime on the bottom. While this DNA molecule is oriented the other way. | Molecular structure of RNA Macromolecules Biology Khan Academy (3).mp3 |
Well, let's think about it. This one, the way it's, the RNA, the messenger RNA, the way it's oriented, we have, if we go, we have phosphate group, then we go to five prime carbon, four prime, three prime, then phosphate group, then five prime, four prime, three prime, then phosphate group. So this is oriented five prime on top, three prime on the bottom. While this DNA molecule is oriented the other way. This is a five prime carbon, this is a three prime carbon. So we have phosphate, three prime, five prime, phosphate. So we have three prime is on top, and five prime is on the bottom. | Molecular structure of RNA Macromolecules Biology Khan Academy (3).mp3 |
While this DNA molecule is oriented the other way. This is a five prime carbon, this is a three prime carbon. So we have phosphate, three prime, five prime, phosphate. So we have three prime is on top, and five prime is on the bottom. So if we wanted to think about what's happening, maybe using the symbols for the nitrogenous bases, we could say, all right, we have our mRNA molecule here, and this is its five prime end, and this is its three prime end. And then the first, the top nitrogenous base right over here, this is uracil. This is uracil. | Molecular structure of RNA Macromolecules Biology Khan Academy (3).mp3 |
So we have three prime is on top, and five prime is on the bottom. So if we wanted to think about what's happening, maybe using the symbols for the nitrogenous bases, we could say, all right, we have our mRNA molecule here, and this is its five prime end, and this is its three prime end. And then the first, the top nitrogenous base right over here, this is uracil. This is uracil. And then the second one over here, this is, sorry, over here, this is cytosine. So this is cytosine. This is cytosine right over here. | Molecular structure of RNA Macromolecules Biology Khan Academy (3).mp3 |
This is uracil. And then the second one over here, this is, sorry, over here, this is cytosine. So this is cytosine. This is cytosine right over here. And this is being transcribed from a DNA molecule, from this DNA molecule on the right-hand side. So this is DNA. And this DNA has an anti-parallel orientation. | Molecular structure of RNA Macromolecules Biology Khan Academy (3).mp3 |
This is cytosine right over here. And this is being transcribed from a DNA molecule, from this DNA molecule on the right-hand side. So this is DNA. And this DNA has an anti-parallel orientation. It's parallel, but it's kind of flipped over. The sugars are pointed in a different direction. So this is going from, this is the three prime end, this is the five prime end. | Molecular structure of RNA Macromolecules Biology Khan Academy (3).mp3 |
And this DNA has an anti-parallel orientation. It's parallel, but it's kind of flipped over. The sugars are pointed in a different direction. So this is going from, this is the three prime end, this is the five prime end. And we see that the uracil is hydrogen bonded to adenine. Adenine right over here. So adenine, and I'll draw dotted lines to show the hydrogen bonds. | Molecular structure of RNA Macromolecules Biology Khan Academy (3).mp3 |
So this is going from, this is the three prime end, this is the five prime end. And we see that the uracil is hydrogen bonded to adenine. Adenine right over here. So adenine, and I'll draw dotted lines to show the hydrogen bonds. And that the cytosine is hydrogen bonded to guanine. To guanine. So this right over here, that is guanine. | Molecular structure of RNA Macromolecules Biology Khan Academy (3).mp3 |
So adenine, and I'll draw dotted lines to show the hydrogen bonds. And that the cytosine is hydrogen bonded to guanine. To guanine. So this right over here, that is guanine. And actually I'll do the hydrogen bonds in white. So, you know, they are, actually there's multiple hydrogen bonds going on here. But just to be clear, this is mRNA, and on the right we have DNA. | Molecular structure of RNA Macromolecules Biology Khan Academy (3).mp3 |
So this right over here, that is guanine. And actually I'll do the hydrogen bonds in white. So, you know, they are, actually there's multiple hydrogen bonds going on here. But just to be clear, this is mRNA, and on the right we have DNA. And this could be happening during transcription. This could be happening during, I'm having trouble changing colors. This could be happening during transcription. | Molecular structure of RNA Macromolecules Biology Khan Academy (3).mp3 |
But just to be clear, this is mRNA, and on the right we have DNA. And this could be happening during transcription. This could be happening during, I'm having trouble changing colors. This could be happening during transcription. Now what are the types of RNAs out there? We've talked about this in other videos. Well you have messenger RNA, which is an important role in taking information from DNA and getting it eventually translated with the help of tRNAs and ribosomes. | Molecular structure of RNA Macromolecules Biology Khan Academy (3).mp3 |
This could be happening during transcription. Now what are the types of RNAs out there? We've talked about this in other videos. Well you have messenger RNA, which is an important role in taking information from DNA and getting it eventually translated with the help of tRNAs and ribosomes. And though I've just mentioned another type of RNA, and that's transfer RNA. So transfer RNA, tRNA. tRNA. | Molecular structure of RNA Macromolecules Biology Khan Academy (3).mp3 |
Well you have messenger RNA, which is an important role in taking information from DNA and getting it eventually translated with the help of tRNAs and ribosomes. And though I've just mentioned another type of RNA, and that's transfer RNA. So transfer RNA, tRNA. tRNA. And in the video, the overview video on transcription and translation, we talk about how tRNA does this. But it brings amino acids, it has amino acids attached at one end, and then it has anticodons on the other end that essentially pair, that pair with codon fragment or codons on the mRNA, and then that allows it to construct proteins. And this actually is, this right over here is a visualization of a tRNA molecule. | Molecular structure of RNA Macromolecules Biology Khan Academy (3).mp3 |
tRNA. And in the video, the overview video on transcription and translation, we talk about how tRNA does this. But it brings amino acids, it has amino acids attached at one end, and then it has anticodons on the other end that essentially pair, that pair with codon fragment or codons on the mRNA, and then that allows it to construct proteins. And this actually is, this right over here is a visualization of a tRNA molecule. So a lot of times when we think about DNA, we think about, okay, mRNA or RNA is an intermediary to be able to eventually translate it into proteins. And that is often the case, but sometimes you also just want the RNA itself. The RNA itself plays a role in the cell beyond just transmitting information. | Molecular structure of RNA Macromolecules Biology Khan Academy (3).mp3 |
And this actually is, this right over here is a visualization of a tRNA molecule. So a lot of times when we think about DNA, we think about, okay, mRNA or RNA is an intermediary to be able to eventually translate it into proteins. And that is often the case, but sometimes you also just want the RNA itself. The RNA itself plays a role in the cell beyond just transmitting information. And that's an example here with tRNA. And you can see it's interesting configuration where the amino acid will attach roughly in that area up there. And then you see the anticodon, the anticodon right down here in the bottom right. | Molecular structure of RNA Macromolecules Biology Khan Academy (3).mp3 |
The RNA itself plays a role in the cell beyond just transmitting information. And that's an example here with tRNA. And you can see it's interesting configuration where the amino acid will attach roughly in that area up there. And then you see the anticodon, the anticodon right down here in the bottom right. And different tRNA molecules will attach to different amino acids and they'll have different anticodons here. So this is another use for RNA. And then others include ribosomal RNA. | Molecular structure of RNA Macromolecules Biology Khan Academy (3).mp3 |
And then you see the anticodon, the anticodon right down here in the bottom right. And different tRNA molecules will attach to different amino acids and they'll have different anticodons here. So this is another use for RNA. And then others include ribosomal RNA. Ribosomal RNA. And they actually play a structural role in ribosomes, which is where translation occurs. And you also have things called microRNA. | Molecular structure of RNA Macromolecules Biology Khan Academy (3).mp3 |
And then others include ribosomal RNA. Ribosomal RNA. And they actually play a structural role in ribosomes, which is where translation occurs. And you also have things called microRNA. MicroRNA, which are short chains of RNA, which could be used to regulate the translation of other RNA molecules. So RNA, you know, DNA gets a lot of the attention, but RNA is really, really, really important. And a lot of people believe that RNA came first. | Molecular structure of RNA Macromolecules Biology Khan Academy (3).mp3 |
And usually it's a piece of DNA that codes for something we care about. It is a gene that will express itself as a protein that we think is useful in some way. Now you might have also heard the term cloning in terms of the Clone Wars and Star Wars or Dolly the sheep, and that is a related idea. If you're cloning an animal or an organism, like a sheep, well then you are creating an animal that has the exact genetic material as the original animal. But when we talk about cloning and DNA cloning, we're talking about something a little bit simpler. Although as we'll see, it's still quite fascinating. It's identical copies of a piece of DNA. | DNA cloning and recombinant DNA Biomolecules MCAT Khan Academy.mp3 |
If you're cloning an animal or an organism, like a sheep, well then you are creating an animal that has the exact genetic material as the original animal. But when we talk about cloning and DNA cloning, we're talking about something a little bit simpler. Although as we'll see, it's still quite fascinating. It's identical copies of a piece of DNA. So how do we do that? Well let's say that this is a strand of DNA right over here, and I'm just drawing it as a line, but this is a double-stranded, and I'll just write it down, this is double-stranded. I don't want to have to take the trouble of keep drawing the multiple strands. | DNA cloning and recombinant DNA Biomolecules MCAT Khan Academy.mp3 |
It's identical copies of a piece of DNA. So how do we do that? Well let's say that this is a strand of DNA right over here, and I'm just drawing it as a line, but this is a double-stranded, and I'll just write it down, this is double-stranded. I don't want to have to take the trouble of keep drawing the multiple strands. Actually let me just draw, let me just try to draw the two strands just so we remind ourselves. So there we go, this is the double-stranded DNA, and let's say that this part of this DNA has a gene that we want to clone. We want to make copies of this right over here. | DNA cloning and recombinant DNA Biomolecules MCAT Khan Academy.mp3 |
I don't want to have to take the trouble of keep drawing the multiple strands. Actually let me just draw, let me just try to draw the two strands just so we remind ourselves. So there we go, this is the double-stranded DNA, and let's say that this part of this DNA has a gene that we want to clone. We want to make copies of this right over here. So gene to clone, gene to clone. Well the first thing we want to do is we want to cut this gene out somehow. And the way we do that is using restriction enzymes. | DNA cloning and recombinant DNA Biomolecules MCAT Khan Academy.mp3 |
We want to make copies of this right over here. So gene to clone, gene to clone. Well the first thing we want to do is we want to cut this gene out somehow. And the way we do that is using restriction enzymes. And there's a bunch of different restriction enzymes, and I personally find it fascinating that we as a civilization have gotten to the point that we can find and identify these enzymes, and we know at what points of DNA that they can cut, they recognize specific sequences, and then we can figure out, well which restriction enzyme should we use to cut out different pieces of DNA? But we have gotten to that point as a civilization. So we use restriction enzymes. | DNA cloning and recombinant DNA Biomolecules MCAT Khan Academy.mp3 |
And the way we do that is using restriction enzymes. And there's a bunch of different restriction enzymes, and I personally find it fascinating that we as a civilization have gotten to the point that we can find and identify these enzymes, and we know at what points of DNA that they can cut, they recognize specific sequences, and then we can figure out, well which restriction enzyme should we use to cut out different pieces of DNA? But we have gotten to that point as a civilization. So we use restriction enzymes. We might use one restriction enzyme, let me use a different color here, that latches on right over here and identifies the genetic sequence right over here and cuts right in the right place. So that might be a restriction enzyme right over there. And then you might use another restriction enzyme that identifies with the sequence at the other side that we want to cut. | DNA cloning and recombinant DNA Biomolecules MCAT Khan Academy.mp3 |
So we use restriction enzymes. We might use one restriction enzyme, let me use a different color here, that latches on right over here and identifies the genetic sequence right over here and cuts right in the right place. So that might be a restriction enzyme right over there. And then you might use another restriction enzyme that identifies with the sequence at the other side that we want to cut. So let me label these. These, those things right over there, those are restriction enzymes. Restriction enzymes. | DNA cloning and recombinant DNA Biomolecules MCAT Khan Academy.mp3 |
And then you might use another restriction enzyme that identifies with the sequence at the other side that we want to cut. So let me label these. These, those things right over there, those are restriction enzymes. Restriction enzymes. And so now you would have, after you apply the restriction enzymes, you will have just that gene. You might have a little bit left over on either side. But essentially you have cut out the gene. | DNA cloning and recombinant DNA Biomolecules MCAT Khan Academy.mp3 |
Restriction enzymes. And so now you would have, after you apply the restriction enzymes, you will have just that gene. You might have a little bit left over on either side. But essentially you have cut out the gene. You have used the restriction enzymes to cut out your gene. And then what you want to do is you want to paste it into what we will call a plasmid. And a plasmid is a piece of genetic material that sits outside of chromosomes but that can reproduce along, or that could, I guess we could say, can replicate along with the machinery of the, or the genetic machinery of the organism. | DNA cloning and recombinant DNA Biomolecules MCAT Khan Academy.mp3 |
But essentially you have cut out the gene. You have used the restriction enzymes to cut out your gene. And then what you want to do is you want to paste it into what we will call a plasmid. And a plasmid is a piece of genetic material that sits outside of chromosomes but that can reproduce along, or that could, I guess we could say, can replicate along with the machinery of the, or the genetic machinery of the organism. Or it could even express itself just like the genes of the organism that are in the chromosomes express themselves. So then, so this is where we cut, let me write this, we cut, we cut out the gene. And then we want to paste it, then we want to paste it into a plasmid. | DNA cloning and recombinant DNA Biomolecules MCAT Khan Academy.mp3 |
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