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Role of phagocytes in innate or nonspecific immunity NCLEX-RN Khan Academy.mp3
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The whole point of the immune system is to keep out shady things from your body, or if they get in, to kill them. So those shady things would include shady proteins that can do damage to your body, viruses, bacteria, even eukaryotic parasites, and then even fungi. So all sorts of things that if they were to enter your body, they would cause some form of disease. These are collectively called pathogens. So the whole point of the immune system is, on a first line of defense, keep these things out. And then if they were to get into your body, to kill and eliminate them from our system so that we don't get sick and so that we don't die. So I already just mentioned that there's kind of two lines of defense, and even with those, there's kind of subclassifications.
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Role of phagocytes in innate or nonspecific immunity NCLEX-RN Khan Academy.mp3
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These are collectively called pathogens. So the whole point of the immune system is, on a first line of defense, keep these things out. And then if they were to get into your body, to kill and eliminate them from our system so that we don't get sick and so that we don't die. So I already just mentioned that there's kind of two lines of defense, and even with those, there's kind of subclassifications. The first line of defense, I'll just call that the first line, which is essentially just to keep things out. And there's some obvious ones. There's our skin.
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Role of phagocytes in innate or nonspecific immunity NCLEX-RN Khan Academy.mp3
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So I already just mentioned that there's kind of two lines of defense, and even with those, there's kind of subclassifications. The first line of defense, I'll just call that the first line, which is essentially just to keep things out. And there's some obvious ones. There's our skin. Our skin keeps pathogens out, and actually even the oils on our skin are a little bit more acidic, and it's hard for some types of bacteria to thrive in that type of an environment. You have your mucus membranes, and in the mucus there's some chemicals that maybe make it a little bit more difficult for bacteria to survive. And then you even have acidic environments, like your stomach acid.
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Role of phagocytes in innate or nonspecific immunity NCLEX-RN Khan Academy.mp3
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There's our skin. Our skin keeps pathogens out, and actually even the oils on our skin are a little bit more acidic, and it's hard for some types of bacteria to thrive in that type of an environment. You have your mucus membranes, and in the mucus there's some chemicals that maybe make it a little bit more difficult for bacteria to survive. And then you even have acidic environments, like your stomach acid. I'll keep that in the same color. You might not view your stomach as the outside of you, but it fundamentally is. Your whole digestive tract, which I'll make videos on in the near future, is really on the outside of you.
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Role of phagocytes in innate or nonspecific immunity NCLEX-RN Khan Academy.mp3
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And then you even have acidic environments, like your stomach acid. I'll keep that in the same color. You might not view your stomach as the outside of you, but it fundamentally is. Your whole digestive tract, which I'll make videos on in the near future, is really on the outside of you. You can simply model most vertebrate bodies as kind of a donut. And our digestive tract is kind of the inside of the donut. So stomach acid is on the outside of our real bodies, and you can imagine that's a hard environment for a lot of these pathogens to survive in.
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Role of phagocytes in innate or nonspecific immunity NCLEX-RN Khan Academy.mp3
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Your whole digestive tract, which I'll make videos on in the near future, is really on the outside of you. You can simply model most vertebrate bodies as kind of a donut. And our digestive tract is kind of the inside of the donut. So stomach acid is on the outside of our real bodies, and you can imagine that's a hard environment for a lot of these pathogens to survive in. So that's the first line of defense, but we know that that's not good enough. That sometimes these things can get into our bodies, and there we have to start thinking about the second line of defense. What do we do once things are actually in our body?
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Role of phagocytes in innate or nonspecific immunity NCLEX-RN Khan Academy.mp3
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So stomach acid is on the outside of our real bodies, and you can imagine that's a hard environment for a lot of these pathogens to survive in. So that's the first line of defense, but we know that that's not good enough. That sometimes these things can get into our bodies, and there we have to start thinking about the second line of defense. What do we do once things are actually in our body? Second, let me switch colors. So then you have your second line of defense. And here, in both the first and second line, I'm talking about nonspecific immunity.
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Role of phagocytes in innate or nonspecific immunity NCLEX-RN Khan Academy.mp3
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What do we do once things are actually in our body? Second, let me switch colors. So then you have your second line of defense. And here, in both the first and second line, I'm talking about nonspecific immunity. And this is going to make a lot of sense when we start talking about specific immunity. So both of these are nonspecific. And when I say nonspecific, or you can also call them innate, it means that they just generally respond to things that appear bad.
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Role of phagocytes in innate or nonspecific immunity NCLEX-RN Khan Academy.mp3
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And here, in both the first and second line, I'm talking about nonspecific immunity. And this is going to make a lot of sense when we start talking about specific immunity. So both of these are nonspecific. And when I say nonspecific, or you can also call them innate, it means that they just generally respond to things that appear bad. They don't remember the bad things that came before. They don't respond to a particular type of virus or a particular. Well, they do respond to every type of virus or every type of bacteria, but they don't say, oh, this is virus type ABC or this is bacteria type ABC.
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Role of phagocytes in innate or nonspecific immunity NCLEX-RN Khan Academy.mp3
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And when I say nonspecific, or you can also call them innate, it means that they just generally respond to things that appear bad. They don't remember the bad things that came before. They don't respond to a particular type of virus or a particular. Well, they do respond to every type of virus or every type of bacteria, but they don't say, oh, this is virus type ABC or this is bacteria type ABC. They just say, this is a virus. Let me get rid of it or let me not let it in. This is a bacteria.
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Role of phagocytes in innate or nonspecific immunity NCLEX-RN Khan Academy.mp3
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Well, they do respond to every type of virus or every type of bacteria, but they don't say, oh, this is virus type ABC or this is bacteria type ABC. They just say, this is a virus. Let me get rid of it or let me not let it in. This is a bacteria. Let me get rid of it or let me not let it in. It doesn't know what type of bacteria it's dealing with. So this is all the nonspecific or innate immune system.
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Role of phagocytes in innate or nonspecific immunity NCLEX-RN Khan Academy.mp3
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This is a bacteria. Let me get rid of it or let me not let it in. It doesn't know what type of bacteria it's dealing with. So this is all the nonspecific or innate immune system. And we'll go into a lot of detail onto the specific immune system, because you can imagine it becomes very complicated or interesting when you start thinking about your body somehow remembering a virus that it's seen before and being able to respond better to that virus or that bacteria or that protein the second time it sees it. So we're dealing with nonspecific in this case. And the second line of your nonspecific immunity, there are two things.
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Role of phagocytes in innate or nonspecific immunity NCLEX-RN Khan Academy.mp3
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So this is all the nonspecific or innate immune system. And we'll go into a lot of detail onto the specific immune system, because you can imagine it becomes very complicated or interesting when you start thinking about your body somehow remembering a virus that it's seen before and being able to respond better to that virus or that bacteria or that protein the second time it sees it. So we're dealing with nonspecific in this case. And the second line of your nonspecific immunity, there are two things. One is an inflammatory response. And I'm going to do a whole video on this. But in general, we've all experienced inflammatory responses when you see blood flowing to a certain part of an area and you see there's pus.
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Role of phagocytes in innate or nonspecific immunity NCLEX-RN Khan Academy.mp3
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And the second line of your nonspecific immunity, there are two things. One is an inflammatory response. And I'm going to do a whole video on this. But in general, we've all experienced inflammatory responses when you see blood flowing to a certain part of an area and you see there's pus. And I'm going to go into a lot more detail on what an inflammatory response actually is. And what it really is doing is bringing blood and bringing cells that can fight whatever type of infection you have. It's bringing them to the site where maybe you got a cut or maybe where a lot of the bacteria or whatever the pathogen is.
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Role of phagocytes in innate or nonspecific immunity NCLEX-RN Khan Academy.mp3
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But in general, we've all experienced inflammatory responses when you see blood flowing to a certain part of an area and you see there's pus. And I'm going to go into a lot more detail on what an inflammatory response actually is. And what it really is doing is bringing blood and bringing cells that can fight whatever type of infection you have. It's bringing them to the site where maybe you got a cut or maybe where a lot of the bacteria or whatever the pathogen is. So inflammatory response is all about bringing fluid and fighters to the fight. So bringing stuff to the fight. Let me write that.
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Role of phagocytes in innate or nonspecific immunity NCLEX-RN Khan Academy.mp3
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It's bringing them to the site where maybe you got a cut or maybe where a lot of the bacteria or whatever the pathogen is. So inflammatory response is all about bringing fluid and fighters to the fight. So bringing stuff to the fight. Let me write that. And I'm going to do a whole video on that. Bringing stuff to the fight. You can almost imagine.
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Role of phagocytes in innate or nonspecific immunity NCLEX-RN Khan Academy.mp3
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Let me write that. And I'm going to do a whole video on that. Bringing stuff to the fight. You can almost imagine. Bringing weapons to the fight. But the byproduct is that part of your tissue or that part of your body gets inflamed. A lot of fluid there.
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Role of phagocytes in innate or nonspecific immunity NCLEX-RN Khan Academy.mp3
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You can almost imagine. Bringing weapons to the fight. But the byproduct is that part of your tissue or that part of your body gets inflamed. A lot of fluid there. A lot of byproducts of the battle that goes on there. And we'll do a whole video on that. And then the other second line of defense, and it's actually part of the inflammatory response, are phagocytosis or phagocytes.
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Role of phagocytes in innate or nonspecific immunity NCLEX-RN Khan Academy.mp3
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A lot of fluid there. A lot of byproducts of the battle that goes on there. And we'll do a whole video on that. And then the other second line of defense, and it's actually part of the inflammatory response, are phagocytosis or phagocytes. And really what I want to do over the rest of this video is talk in a little bit more detail about phagocytes. Because once we understand what phagocytes do, that's a pretty good building block for going into the specific immune system, and actually it'll help lead into the discussion on the inflammatory response as well. Because phagocytes are really part of the inflammatory response.
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Role of phagocytes in innate or nonspecific immunity NCLEX-RN Khan Academy.mp3
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And then the other second line of defense, and it's actually part of the inflammatory response, are phagocytosis or phagocytes. And really what I want to do over the rest of this video is talk in a little bit more detail about phagocytes. Because once we understand what phagocytes do, that's a pretty good building block for going into the specific immune system, and actually it'll help lead into the discussion on the inflammatory response as well. Because phagocytes are really part of the inflammatory response. So phagocytes are just a class of cell that can eat up pathogens. They can eat up other things really, but when we talk about the immune system, we're talking about pathogens. So let's say that this is a phagocyte right here.
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Role of phagocytes in innate or nonspecific immunity NCLEX-RN Khan Academy.mp3
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Because phagocytes are really part of the inflammatory response. So phagocytes are just a class of cell that can eat up pathogens. They can eat up other things really, but when we talk about the immune system, we're talking about pathogens. So let's say that this is a phagocyte right here. This is a phagocyte right there. It has some kind of a nucleus, whatever. I don't have to focus on the inside of the phagocyte.
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Role of phagocytes in innate or nonspecific immunity NCLEX-RN Khan Academy.mp3
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So let's say that this is a phagocyte right here. This is a phagocyte right there. It has some kind of a nucleus, whatever. I don't have to focus on the inside of the phagocyte. It's a traditional eukaryotic cell. But what I want to do is see what happens when a phagocyte encounters a foreign particle or a foreign bacteria. So let me say this is a foreign bacteria right here.
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Role of phagocytes in innate or nonspecific immunity NCLEX-RN Khan Academy.mp3
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I don't have to focus on the inside of the phagocyte. It's a traditional eukaryotic cell. But what I want to do is see what happens when a phagocyte encounters a foreign particle or a foreign bacteria. So let me say this is a foreign bacteria right here. So the phagocyte, we've already said, is nonspecific. What it does is it has receptors that respond to just things that it knows are bad. You could imagine these are super sensors.
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Role of phagocytes in innate or nonspecific immunity NCLEX-RN Khan Academy.mp3
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So let me say this is a foreign bacteria right here. So the phagocyte, we've already said, is nonspecific. What it does is it has receptors that respond to just things that it knows are bad. You could imagine these are super sensors. So maybe these are super sensors right here. Maybe these are super sensors for bacteria, and the bacteria have proteins on their surface that maybe look something like that. Obviously, they don't look exactly like that.
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Role of phagocytes in innate or nonspecific immunity NCLEX-RN Khan Academy.mp3
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You could imagine these are super sensors. So maybe these are super sensors right here. Maybe these are super sensors for bacteria, and the bacteria have proteins on their surface that maybe look something like that. Obviously, they don't look exactly like that. I'm just drawing them as kind of a Y and a triangle so you can see that they fit. But once these two guys connect, so let me draw the situation where they have connected. So this is the bacteria.
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Role of phagocytes in innate or nonspecific immunity NCLEX-RN Khan Academy.mp3
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Obviously, they don't look exactly like that. I'm just drawing them as kind of a Y and a triangle so you can see that they fit. But once these two guys connect, so let me draw the situation where they have connected. So this is the bacteria. This is the pathogen. And it's really the same idea with a virus or any other type of thing, and we'll actually see in future videos that these guys can actually be tagged by other molecules, which makes these phagocytes want to attack them even more. Well, let's say once they're bonded, so that's the bacteria, the invading pathogen, and now it is bonded.
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Role of phagocytes in innate or nonspecific immunity NCLEX-RN Khan Academy.mp3
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So this is the bacteria. This is the pathogen. And it's really the same idea with a virus or any other type of thing, and we'll actually see in future videos that these guys can actually be tagged by other molecules, which makes these phagocytes want to attack them even more. Well, let's say once they're bonded, so that's the bacteria, the invading pathogen, and now it is bonded. It has triggered the receptor on this phagocyte. This phagocyte will start to engulf. It'll wrap around this pathogen.
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Role of phagocytes in innate or nonspecific immunity NCLEX-RN Khan Academy.mp3
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Well, let's say once they're bonded, so that's the bacteria, the invading pathogen, and now it is bonded. It has triggered the receptor on this phagocyte. This phagocyte will start to engulf. It'll wrap around this pathogen. So it'll start wrapping around the pathogen like that. And these two ends are eventually going to meet, and I can still draw the nucleus in a different color so we know it's not really related to the phagocytosis. So maybe that's the nucleus and there's other organelles sitting in here.
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Role of phagocytes in innate or nonspecific immunity NCLEX-RN Khan Academy.mp3
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It'll wrap around this pathogen. So it'll start wrapping around the pathogen like that. And these two ends are eventually going to meet, and I can still draw the nucleus in a different color so we know it's not really related to the phagocytosis. So maybe that's the nucleus and there's other organelles sitting in here. But then once these two meet, what's it going to look like? Then all of a sudden, that bacteria is going to be completely engulfed by the phagocyte. All of a sudden, that bacteria is going to be completely engulfed, it's going to be inside of the cell.
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Role of phagocytes in innate or nonspecific immunity NCLEX-RN Khan Academy.mp3
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So maybe that's the nucleus and there's other organelles sitting in here. But then once these two meet, what's it going to look like? Then all of a sudden, that bacteria is going to be completely engulfed by the phagocyte. All of a sudden, that bacteria is going to be completely engulfed, it's going to be inside of the cell. So now the cell, once these two ends meet and these membranes merge, then this guy is going to be in his own little membrane bubble, or you can almost imagine it's in its own little vesicle. So this is the pathogen, the bacteria in this case, but the phagocytosis, the process is completely identical in terms of how it engulfs things, if it was a virus or some type of other foreign protein or any type of really foreign molecule. And actually, sometimes it doesn't even occur to foreign stuff.
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Role of phagocytes in innate or nonspecific immunity NCLEX-RN Khan Academy.mp3
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All of a sudden, that bacteria is going to be completely engulfed, it's going to be inside of the cell. So now the cell, once these two ends meet and these membranes merge, then this guy is going to be in his own little membrane bubble, or you can almost imagine it's in its own little vesicle. So this is the pathogen, the bacteria in this case, but the phagocytosis, the process is completely identical in terms of how it engulfs things, if it was a virus or some type of other foreign protein or any type of really foreign molecule. And actually, sometimes it doesn't even occur to foreign stuff. It can occur to stuff that is dying molecules that are not foreign, that just need to be cleared out. But we'll just focus on the immune system, on foreign things right now. So it was merged.
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Role of phagocytes in innate or nonspecific immunity NCLEX-RN Khan Academy.mp3
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And actually, sometimes it doesn't even occur to foreign stuff. It can occur to stuff that is dying molecules that are not foreign, that just need to be cleared out. But we'll just focus on the immune system, on foreign things right now. So it was merged. So then this membrane right here will completely merge and go around this guy like this. And of course, you had your receptors and who knows if they're still there. By the time, let's just draw them there so you see that that part is that part.
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Role of phagocytes in innate or nonspecific immunity NCLEX-RN Khan Academy.mp3
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So it was merged. So then this membrane right here will completely merge and go around this guy like this. And of course, you had your receptors and who knows if they're still there. By the time, let's just draw them there so you see that that part is that part. But once it's fully engulfed, this thing is called a phagosome, which is really just a vesicle that contains that foreign particle that you want to get rid of. And then other fluid or vesicles that contain things that can eat up this phagosome. So let's say that here, this is some vesicle that contains things, lysozymes, and it contains really reactive species of oxygen.
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Role of phagocytes in innate or nonspecific immunity NCLEX-RN Khan Academy.mp3
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By the time, let's just draw them there so you see that that part is that part. But once it's fully engulfed, this thing is called a phagosome, which is really just a vesicle that contains that foreign particle that you want to get rid of. And then other fluid or vesicles that contain things that can eat up this phagosome. So let's say that here, this is some vesicle that contains things, lysozymes, and it contains really reactive species of oxygen. So let's say that it contains a bunch of stuff here. And if this comes in contact with really almost any biological compound, it's going to do some damage. But once the pathogen is completely merged inside the cell, this little package will merge over here and it will dump its contents into this phagosome, into this vesicle containing the pathogen, and then break it up.
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Role of phagocytes in innate or nonspecific immunity NCLEX-RN Khan Academy.mp3
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So let's say that here, this is some vesicle that contains things, lysozymes, and it contains really reactive species of oxygen. So let's say that it contains a bunch of stuff here. And if this comes in contact with really almost any biological compound, it's going to do some damage. But once the pathogen is completely merged inside the cell, this little package will merge over here and it will dump its contents into this phagosome, into this vesicle containing the pathogen, and then break it up. It's essentially digesting it. So obviously, the first role is it just got it out of the way and it killed it. And then the second role, and I'm just going to give a little tidbit right here, and we're going to do it in a lot more detail in future videos.
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Role of phagocytes in innate or nonspecific immunity NCLEX-RN Khan Academy.mp3
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But once the pathogen is completely merged inside the cell, this little package will merge over here and it will dump its contents into this phagosome, into this vesicle containing the pathogen, and then break it up. It's essentially digesting it. So obviously, the first role is it just got it out of the way and it killed it. And then the second role, and I'm just going to give a little tidbit right here, and we're going to do it in a lot more detail in future videos. It breaks it up, so let me draw the whole thing now. I want to keep my colors consistent. It'll break it up.
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Role of phagocytes in innate or nonspecific immunity NCLEX-RN Khan Academy.mp3
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And then the second role, and I'm just going to give a little tidbit right here, and we're going to do it in a lot more detail in future videos. It breaks it up, so let me draw the whole thing now. I want to keep my colors consistent. It'll break it up. So now the thing is all broken up. This is the membrane inside. So that thing is broken up into constituent proteins and other molecules.
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Role of phagocytes in innate or nonspecific immunity NCLEX-RN Khan Academy.mp3
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It'll break it up. So now the thing is all broken up. This is the membrane inside. So that thing is broken up into constituent proteins and other molecules. And then what the phagocyte does, it'll actually take some subset of these molecules, some subset of the proteins, it'll break them down. Proteins are just sequences of amino acids. So normally when people say proteins, they're talking about long sequences of amino acids.
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Role of phagocytes in innate or nonspecific immunity NCLEX-RN Khan Academy.mp3
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So that thing is broken up into constituent proteins and other molecules. And then what the phagocyte does, it'll actually take some subset of these molecules, some subset of the proteins, it'll break them down. Proteins are just sequences of amino acids. So normally when people say proteins, they're talking about long sequences of amino acids. When people talk about short sequences of amino acids or a protein that's broken up a lot, they refer to it as a peptide chain. A peptide chain is a shorter chain of amino acids. So this guy will take some special peptide chains, some special pieces from the thing it just killed, attach them to some other proteins.
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Role of phagocytes in innate or nonspecific immunity NCLEX-RN Khan Academy.mp3
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So normally when people say proteins, they're talking about long sequences of amino acids. When people talk about short sequences of amino acids or a protein that's broken up a lot, they refer to it as a peptide chain. A peptide chain is a shorter chain of amino acids. So this guy will take some special peptide chains, some special pieces from the thing it just killed, attach them to some other proteins. So it'll take maybe a little piece of this bacteria right now. Attach it to other protein. Let me just do that in pink.
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Role of phagocytes in innate or nonspecific immunity NCLEX-RN Khan Academy.mp3
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So this guy will take some special peptide chains, some special pieces from the thing it just killed, attach them to some other proteins. So it'll take maybe a little piece of this bacteria right now. Attach it to other protein. Let me just do that in pink. It'll attach it to this other protein, which is called a major histocompatibility complex. And if we're talking about phagocytes, this will be a major histocompatibility complex type 2. And that's a mouthful of words.
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Role of phagocytes in innate or nonspecific immunity NCLEX-RN Khan Academy.mp3
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Let me just do that in pink. It'll attach it to this other protein, which is called a major histocompatibility complex. And if we're talking about phagocytes, this will be a major histocompatibility complex type 2. And that's a mouthful of words. So let me, so this is a, and this is, it sounds very a strange word, but we're going to see this a lot. So this is major histocompatibility complex. So they abbreviate it MHC.
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Role of phagocytes in innate or nonspecific immunity NCLEX-RN Khan Academy.mp3
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And that's a mouthful of words. So let me, so this is a, and this is, it sounds very a strange word, but we're going to see this a lot. So this is major histocompatibility complex. So they abbreviate it MHC. This is a protein, and it bonds with this peptide that was kind of chunked off or digested off of this invading pathogen, and then this phagocyte will then present it onto its membrane. So this combination, the complex of the MHC, and in this case it's going to be an MHC 2 protein. We're going to talk, so MHC type 2, and we're going to talk about type 1 in the future.
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Role of phagocytes in innate or nonspecific immunity NCLEX-RN Khan Academy.mp3
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So they abbreviate it MHC. This is a protein, and it bonds with this peptide that was kind of chunked off or digested off of this invading pathogen, and then this phagocyte will then present it onto its membrane. So this combination, the complex of the MHC, and in this case it's going to be an MHC 2 protein. We're going to talk, so MHC type 2, and we're going to talk about type 1 in the future. It's going to take this complex and then present it on its surface. And then it's going to present the combination of the MHC type 2 and the little peptide chain that came from the thing and present it on its surface. And the reason why I'm going through all of this pain of explaining this process, you're like, hey, we already got rid of the thing and killed it.
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Role of phagocytes in innate or nonspecific immunity NCLEX-RN Khan Academy.mp3
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We're going to talk, so MHC type 2, and we're going to talk about type 1 in the future. It's going to take this complex and then present it on its surface. And then it's going to present the combination of the MHC type 2 and the little peptide chain that came from the thing and present it on its surface. And the reason why I'm going through all of this pain of explaining this process, you're like, hey, we already got rid of the thing and killed it. Why is Sal worried about what we do with the peptides? This is crucial to our immune system because we'll see other specific parts of our immune system. Remember, so far everything is nonspecific.
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Role of phagocytes in innate or nonspecific immunity NCLEX-RN Khan Academy.mp3
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And the reason why I'm going through all of this pain of explaining this process, you're like, hey, we already got rid of the thing and killed it. Why is Sal worried about what we do with the peptides? This is crucial to our immune system because we'll see other specific parts of our immune system. Remember, so far everything is nonspecific. This guy just said, oh, this is an invader. It doesn't know the type of an invader. It just says, hey, let me bond to this thing and kill it.
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Role of phagocytes in innate or nonspecific immunity NCLEX-RN Khan Academy.mp3
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Remember, so far everything is nonspecific. This guy just said, oh, this is an invader. It doesn't know the type of an invader. It just says, hey, let me bond to this thing and kill it. It's one of these things that I know are foreign to my body. So it kills it, but now it can leave it on its surface. And now the specific parts, the parts that actually have memory and attack specific things, can say, gee, Mr. Phagocyte, look, you've killed something.
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Role of phagocytes in innate or nonspecific immunity NCLEX-RN Khan Academy.mp3
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It just says, hey, let me bond to this thing and kill it. It's one of these things that I know are foreign to my body. So it kills it, but now it can leave it on its surface. And now the specific parts, the parts that actually have memory and attack specific things, can say, gee, Mr. Phagocyte, look, you've killed something. Let me see if I have some specific reactions that can be triggered by this thing that you're presenting. So many phagocytes are also called antigen-presenting cells. And I'm going to go into more detail on what exactly an antigen is.
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Role of phagocytes in innate or nonspecific immunity NCLEX-RN Khan Academy.mp3
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And now the specific parts, the parts that actually have memory and attack specific things, can say, gee, Mr. Phagocyte, look, you've killed something. Let me see if I have some specific reactions that can be triggered by this thing that you're presenting. So many phagocytes are also called antigen-presenting cells. And I'm going to go into more detail on what exactly an antigen is. I called this thing a pathogen. An antigen is essentially, you can view it as a protein or a peptide chain that will trigger, or that can be dealt with within the immune system. I'll be a little bit more, the specific immune system.
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Role of phagocytes in innate or nonspecific immunity NCLEX-RN Khan Academy.mp3
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And I'm going to go into more detail on what exactly an antigen is. I called this thing a pathogen. An antigen is essentially, you can view it as a protein or a peptide chain that will trigger, or that can be dealt with within the immune system. I'll be a little bit more, the specific immune system. And I'm going to be a little bit more nuanced about it when I talk, I'll make a whole video on antigens and antibodies. But right now you can just view it as a peptide chain right there. An antigen is just a protein or a part of a protein.
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Role of phagocytes in innate or nonspecific immunity NCLEX-RN Khan Academy.mp3
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I'll be a little bit more, the specific immune system. And I'm going to be a little bit more nuanced about it when I talk, I'll make a whole video on antigens and antibodies. But right now you can just view it as a peptide chain right there. An antigen is just a protein or a part of a protein. So this is presenting an antigen on its surface that can later be used by other parts. Now, the one thing that, there are many, many types of phagocytes. And just to give you, just so when you see different words you don't get confused by the different types of phagocytes, I'll do a little review of those right now.
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Role of phagocytes in innate or nonspecific immunity NCLEX-RN Khan Academy.mp3
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An antigen is just a protein or a part of a protein. So this is presenting an antigen on its surface that can later be used by other parts. Now, the one thing that, there are many, many types of phagocytes. And just to give you, just so when you see different words you don't get confused by the different types of phagocytes, I'll do a little review of those right now. You have neutrophils. These are actually the most common of the phagocytes. And these are kind of the fast and numerous responders.
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Role of phagocytes in innate or nonspecific immunity NCLEX-RN Khan Academy.mp3
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And just to give you, just so when you see different words you don't get confused by the different types of phagocytes, I'll do a little review of those right now. You have neutrophils. These are actually the most common of the phagocytes. And these are kind of the fast and numerous responders. So these get to a location of infection very fast. So fast and abundant. And phagocytes don't necessarily just have to kill in this way.
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Role of phagocytes in innate or nonspecific immunity NCLEX-RN Khan Academy.mp3
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And these are kind of the fast and numerous responders. So these get to a location of infection very fast. So fast and abundant. And phagocytes don't necessarily just have to kill in this way. I mean, they're called phagocytes because they engulf this way, but we'll in future videos talk about other ways that they can release chemicals or even DNA nets to ensnare pathogens. But neutrophils are fast and abundant. And then you have macrophages, which are kind of, on some level, they're the most versatile and do the heavy lifting, but they're also phagocytes.
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Role of phagocytes in innate or nonspecific immunity NCLEX-RN Khan Academy.mp3
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And phagocytes don't necessarily just have to kill in this way. I mean, they're called phagocytes because they engulf this way, but we'll in future videos talk about other ways that they can release chemicals or even DNA nets to ensnare pathogens. But neutrophils are fast and abundant. And then you have macrophages, which are kind of, on some level, they're the most versatile and do the heavy lifting, but they're also phagocytes. And then you have dendritic cells. And when you first see the word dendritic cell, you think, hey, does this somehow relate to dendrites of the nervous system, and no, they have nothing to do with the nervous system, nothing nervous system about them. The reason why they're called dendritic cells is because they look like they have dendrites.
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Role of phagocytes in innate or nonspecific immunity NCLEX-RN Khan Academy.mp3
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And then you have macrophages, which are kind of, on some level, they're the most versatile and do the heavy lifting, but they're also phagocytes. And then you have dendritic cells. And when you first see the word dendritic cell, you think, hey, does this somehow relate to dendrites of the nervous system, and no, they have nothing to do with the nervous system, nothing nervous system about them. The reason why they're called dendritic cells is because they look like they have dendrites. They'll look like they have these little things coming off of them, just like that. And if you kind of just view it as a division, so they look like neurons on some level, but they don't participate in the nervous system at all. And these tend to be the best activators of the specific immune system that we'll talk about in future videos.
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Molecular structure of DNA Macromolecules Biology Khan Academy.mp3
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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, 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.
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Molecular structure of DNA Macromolecules Biology Khan Academy.mp3
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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 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.
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Molecular structure of DNA Macromolecules Biology Khan Academy.mp3
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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 of a chain of what we call nucleotides. So what we call nucleotides. So it's made up of nucleotides.
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Molecular structure of DNA Macromolecules Biology Khan Academy.mp3
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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 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.
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Molecular structure of DNA Macromolecules Biology Khan Academy.mp3
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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. 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 a nucleotide.
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Molecular structure of DNA Macromolecules Biology Khan Academy.mp3
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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 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.
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Molecular structure of DNA Macromolecules Biology Khan Academy.mp3
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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. 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 have another, we have another nucleotide, we have another nucleotide. So depicted here, we essentially have four nucleotides.
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Molecular structure of DNA Macromolecules Biology Khan Academy.mp3
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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 have another, we have another nucleotide, we have another nucleotide. 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.
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Molecular structure of DNA Macromolecules Biology Khan Academy.mp3
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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 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.
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Molecular structure of DNA Macromolecules Biology Khan Academy.mp3
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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 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 protons, it would sop up protons.
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Molecular structure of DNA Macromolecules Biology Khan Academy.mp3
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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 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 hydrogens.
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Molecular structure of DNA Macromolecules Biology Khan Academy.mp3
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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 hydrogens. Actually the DNA, if we actually want to be formal about it, the DNA molecules would actually have its phosphates protonated like this, but it so badly wants to lose these hydrogen protons, so it typically would be, let me draw it like this. Let me get rid of the negative charge just on this one. Whoops, just on this phosphate group over here.
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Molecular structure of DNA Macromolecules Biology Khan Academy.mp3
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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, but it so badly wants to lose these hydrogen protons, so it typically would be, let me draw it like this. Let me get rid of the negative charge just on this one. 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 the proton will be let go. That's why we call it an acid.
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Molecular structure of DNA Macromolecules Biology Khan Academy.mp3
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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 the proton will be let go. 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 depicted, you see it with these negative charges, and that's because it has already lost its hydrogen protons.
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Molecular structure of DNA Macromolecules Biology Khan Academy.mp3
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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 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, because it starts protonated, or I guess in its acid form it's protonated, but it readily loses it, and so that's where it gets the name acid from. So each of these nucleotides, they have a phosphate group. 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.
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Molecular structure of DNA Macromolecules Biology Khan Academy.mp3
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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, because it starts protonated, or I guess in its acid form it's protonated, but it readily loses it, and so that's where it gets the name acid from. So each of these nucleotides, they have a phosphate group. 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, this sugar, this is ribose.
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Molecular structure of DNA Macromolecules Biology Khan Academy.mp3
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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, 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 show you a number of the carbons, because carbon numbering is important when we talk about DNA.
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Molecular structure of DNA Macromolecules Biology Khan Academy.mp3
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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 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 carbon. One prime, two prime, three prime, four prime, and five prime. That's the five prime carbon.
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Molecular structure of DNA Macromolecules Biology Khan Academy.mp3
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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 carbon. One prime, two prime, three prime, four prime, and five prime. 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 it that way, because it kind of does bend, the whole molecule's going to have to bend that way to form this structure. 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.
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Molecular structure of DNA Macromolecules Biology Khan Academy.mp3
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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 it that way, because it kind of does bend, the whole molecule's going to have to bend that way to form this structure. 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, just to be clear of what we're talking about, this is the one prime carbon, one prime, two prime, three prime, four prime, and five, five prime carbon. 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.
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Molecular structure of DNA Macromolecules Biology Khan Academy.mp3
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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, just to be clear of what we're talking about, this is the one prime carbon, one prime, two prime, three prime, four prime, and five, five prime carbon. 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 proton right over there. And this green bond that gets formed between the four prime carbon, or between the oxygen that's attached to the four prime carbon and the one prime carbon, that's this bond right over here. This oxygen is that oxygen right there.
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Molecular structure of DNA Macromolecules Biology Khan Academy.mp3
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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 proton right over there. And this green bond that gets formed between the four prime carbon, or between the oxygen that's attached to the four prime carbon and the one prime carbon, that's this bond right over here. 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, so that hydrogen is there. But then that could get nabbed up by another passing water molecule to become hydronium, so it can get lost.
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Molecular structure of DNA Macromolecules Biology Khan Academy.mp3
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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, so that hydrogen is there. But then that could get nabbed up by another passing water molecule to become hydronium, so it can get lost. And net-net, it grabs up a hydrogen proton right over here, and so it can lose a hydrogen proton right there. So it's not adding or losing net-net. And so you form this cyclical form.
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Molecular structure of DNA Macromolecules Biology Khan Academy.mp3
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But then that could get nabbed up by another passing water molecule to become hydronium, so it can get lost. And net-net, it grabs up a hydrogen proton right over here, and so it can lose a hydrogen proton right there. So it's not adding or losing net-net. And so you form this cyclical form. And the cyclical form right over here is very close to what we see in a DNA molecule. It's actually exactly what we would see in an RNA molecule, in ribonucleic acid. And so what do we think we're talking about when we say deoxyribonucleic acid?
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Molecular structure of DNA Macromolecules Biology Khan Academy.mp3
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And so you form this cyclical form. And the cyclical form right over here is very close to what we see in a DNA molecule. It's actually exactly what we would see in an RNA 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 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, you have four carbons right over here.
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Molecular structure of DNA Macromolecules Biology Khan Academy.mp3
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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 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, you have four carbons right over here. It looks just like this. The hydrogens are implicit to the carbons. We've seen this multiple times.
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Molecular structure of DNA Macromolecules Biology Khan Academy.mp3
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This five-member ring, you have four carbons right over here. It looks just like this. The hydrogens are implicit to the carbons. We've seen this multiple times. The carbons are at where these lines intersect, or I guess at the edges, or maybe, and also where these lines end right over there. But you see, this does not have an, this molecule, if we compare these two molecules, if 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.
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Molecular structure of DNA Macromolecules Biology Khan Academy.mp3
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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 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 deoxyribose. So deoxyribose doesn't have this oxygen. It does not have the oxygen on the two prime carbon.
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Molecular structure of DNA Macromolecules Biology Khan Academy.mp3
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So he's missing an oxygen. So this is deoxyribose. So deoxyribose doesn't have this oxygen. It does not have the oxygen on the two prime carbon. So this, if you get rid of that, this is deoxyribose. So let me circle that. So what we're, this thing right over here, this thing right over here, that is deoxyribose.
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Molecular structure of DNA Macromolecules Biology Khan Academy.mp3
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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 before it bonded to these other constituents, you could consider this deoxyribose. And so that's where the deoxyribo comes from. And then the last piece of it, the last piece of it is this chunk right over here.
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Molecular structure of DNA Macromolecules Biology Khan Academy.mp3
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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, 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.
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Molecular structure of DNA Macromolecules Biology Khan Academy.mp3
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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 right over here is a different nitrogenous base. This right over here is another different nitrogenous base.
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Molecular structure of DNA Macromolecules Biology Khan Academy.mp3
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And you can see we have different types of nitrogenous bases. This is a nitrogenous base. This right over here is a different nitrogenous base. This right over here is another different nitrogenous base. Notice this one only has one ring, this one has one ring. This one has two rings. This one over here has two rings.
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Molecular structure of DNA Macromolecules Biology Khan Academy.mp3
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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. The ones with two rings, the general categorization, we call them purines. So nitrogenous bases, if you have two rings, if you have two rings, we call them purines as a general classification term.
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Molecular structure of DNA Macromolecules Biology Khan Academy.mp3
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This one over here has two rings. And we have different names for these nitrogenous bases. The ones with two rings, the general categorization, we call them purines. So nitrogenous bases, if you have two rings, if you have two rings, we call them purines as a general classification term. Let me make sure, purines. And if you have one ring, and maybe I'll just write it this way, one ring, one ring, we call these pyrimidines. Pyrimidines.
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Molecular structure of DNA Macromolecules Biology Khan Academy.mp3
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So nitrogenous bases, if you have two rings, if you have two rings, we call them purines as a general classification term. Let me make sure, purines. And if you have one ring, and 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.
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Molecular structure of DNA Macromolecules Biology Khan Academy.mp3
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Pyrimidines. Pyrimidines. We call these pyrimidines. And these particular, these two on the right, these two purines, this one up here, this is adenine. And we talk about how they pair in the overview video on DNA. But this one right over here is adenine, this nitrogenous base. This one over here is guanine.
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Molecular structure of DNA Macromolecules Biology Khan Academy.mp3
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And these particular, these two on the right, these two purines, this one up here, this is adenine. And we talk about how they pair in the overview video on DNA. But this one right over here is adenine, this nitrogenous base. This one over here is guanine. That is guanine. And then, over here, over here, this single ring, this single ring nitrogenous base, which makes it a pyrimidine, this is thymine. This right over here is thymine.
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Molecular structure of DNA Macromolecules Biology Khan Academy.mp3
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This one over here is guanine. That is guanine. And then, over here, over here, this single ring, this single ring nitrogenous base, which makes it a pyrimidine, this is thymine. This right over here is thymine. This is thymine. And then last but not least, if we're talking about DNA, when we go into RNA, we're also gonna talk about uracil. But when we talk about DNA, this one over here is cytosine.
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Molecular structure of DNA Macromolecules Biology Khan Academy.mp3
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This right over here is thymine. This is thymine. And then last but not least, if we're talking about DNA, when we go into RNA, we're also gonna talk about uracil. But when we talk about DNA, this one over here is cytosine. Cy, cytosine. And you can see the way it's structured, that thymine is attracted to adenine, it bonds with adenine, and cytosine bonds with guanine. So how are they bonding?
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Molecular structure of DNA Macromolecules Biology Khan Academy.mp3
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But when we talk about DNA, this one over here is cytosine. Cy, cytosine. And you can see the way it's structured, that thymine is attracted to adenine, it bonds with adenine, and cytosine bonds with guanine. So how are they bonding? Well, the way that these nitrogenous bases form the rungs of the ladder, how they're drawn to each other, this is our good old friend hydrogen bonds. And this all comes out of the fact that nitrogen is quite electronegative, so when nitrogen is bound to a hydrogen, you're going to have a partially negative charge at the nitrogen, let me do this in green. You're gonna have a partial negative charge at the nitrogen and a partially positive charge at the hydrogen.
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Molecular structure of DNA Macromolecules Biology Khan Academy.mp3
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So how are they bonding? Well, the way that these nitrogenous bases form the rungs of the ladder, how they're drawn to each other, this is our good old friend hydrogen bonds. And this all comes out of the fact that nitrogen is quite electronegative, so when nitrogen is bound to a hydrogen, you're going to have a partially negative charge at the nitrogen, let me do this in green. You're gonna have a partial negative charge at the nitrogen and a partially positive charge at the hydrogen. And then oxygen, we've always talked about as being electronegative, so it has a partial negative charge. So the partial negative charge of this oxygen is going to be attracted to the partial positive charge of this hydrogen, and so you're going to have, you're going to have a hydrogen bond. And that same thing is going to happen between this hydrogen, which is going, its electrons are being hogged by this nitrogen, and this nitrogen, which itself hogs electrons, so that forms a hydrogen bond.
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Molecular structure of DNA Macromolecules Biology Khan Academy.mp3
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You're gonna have a partial negative charge at the nitrogen and a partially positive charge at the hydrogen. And then oxygen, we've always talked about as being electronegative, so it has a partial negative charge. So the partial negative charge of this oxygen is going to be attracted to the partial positive charge of this hydrogen, and so you're going to have, you're going to have a hydrogen bond. And that same thing is going to happen between this hydrogen, which is going, its electrons are being hogged by this nitrogen, and this nitrogen, which itself hogs electrons, so that forms a hydrogen bond. And then down here, you have a hydrogen that has a partially positive charge, because its electrons are being hogged, and then you have this oxygen with a partially negative charge, they're going to be attracted to each other, that's a hydrogen bond. Same thing between this nitrogen and that hydrogen, and same thing between this oxygen and that hydrogen. And that's why cytosine and guanine pair up, and that's why thymine and adenine pair up, and we talk about that as well in the overview video of DNA.
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Genetic variation, gene flow, and new species.mp3
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What is the raw material upon which the selective forces in nature are acting? Although he had some ideas about it, what Darwin didn't know was that variation stems from differences in the genetic information contained in each cell of every organism. It's a bit like an alphabet made of only four letters, letters that can be arranged into words of almost any length. The genes can be viewed as words made of these letters. The sequences of nucleotides spell out codes that give orders to the cellular machinery to make the cell work. In fact, the genes help to make cells themselves, ultimately providing the coded information that builds the entire organism. The sequences of nucleotides are arranged in long molecules that have a long name.
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