Transcription
All right, ninja nerds, in this video today, we are going to be talking about the structure and function of the cell. Also, if you guys haven't already, go watch our video where we talk about how I study and prepare for videos. Within that, I kind of gave you guys a sneak peek of how I pretty much went through, studied this topic, developed notes, diagrams, and then drew it all on the board. Now, we're going to go through it.
Before we get into this video, though, please continue to support us by hitting that like button, commenting down in the comment section, and please subscribe. All right, ninja nerds, let's get into it.
All right, an engineer. So we're going to take a tour through this cell, talking about what all the structures of the cell are and then what they do. So the first thing we got to talk about is the brain of the cell, the pretty much the center of the cell where everything that a cell is kind of really begins in and all centers around, and that is the nucleus. This is the big mama, the nucleus.
Now, what we have to talk about with the nucleus is a couple of different components of the nucleus. What are the different components of the nucleus? Well, the first part of the nucleus is, as you can see, you see this kind of like blue membrane that's double-layered here. So you have an outer layer and then you have an inner layer on this side, right? So this is our inner layer. These two components make up what's called the nuclear envelope. So you have an outer layer and then you have an inner layer. I know that sounds pretty obvious, but there's a different, there's different functions for the outer and the inner layers.
So the outer layer, let's actually first say the nuclear envelope. You have two layers: the outer layer and the inner layer. What is the purpose of these layers? So the first thing that you need to remember is that the outer layer is where you have lots of ribosomes. So ribosomes are actually going to be kind of found outside on that outer layer. The reason why is, in the actual nucleus, you make, you take DNA and convert it into a structure called mRNA. And mRNA has to move out via the nuclear pores and bind onto ribosomes on these outer membranes, which then get moved to the rough ER. We'll talk about that a little bit later, but that's the big thing I want you to remember about the outer membrane.
The inner membrane has a very, very important protein structure that binds to the, the DNA and histone proteins and controls a lot of cell division. It's this green protein here. That green protein that lines the inner membrane is called lamins. And lamins are very, very important structures that control the structure of the nuclear envelope. They're also important for cell division and interacting a lot with the chromatin. There's actually a disorder whenever there's a mutation in these lamins, it causes progeria. So it's important that we kind of know these two components of the nuclear envelope.
The next thing is, in the nuclear envelope, you see these red proteins that are dispersed throughout it. Those red proteins that are dispersed throughout it, these are called nuclear pores. So what are these called? Nuclear pores. And the whole purpose is, it's honestly pretty straightforward, right? If we want to move things in, ions, or proteins, or nucleotides, or different things in and out of the nucleus, that's the function of the nuclear pores. And there is, things we'll talk about this a little bit later in a more specific video where we go more in detail on the nucleus, but there's special types of transporters that are associated with those nuclear pores. We'll talk about those in other videos. But again, another important thing that's a part of the nuclear envelope, if you will, that actually kind of, uh, kind of separates different portions where there's little pores, is called these nuclear pores. And again, the whole purpose of this is to allow for transport. And what kind of transport? Transport between the cytoplasm to the nucleus, or nucleus to the cytoplasm. That's all it is. Pretty straightforward.
The next one is this red diced-up structure here called the nucleolus. The nucleolus is very, very important. And the reason why is, this is the site of a particular type of RNA synthesis. You know, there is a particular type of RNA, what we call rRNA. So we're going to denote this as rRNA synthesis. This occurs in what structure? This occurs within the nucleolus.
Now, the reason why that's important is, when you take rRNA, you synthesize it within the nucleolus and you combine this with proteins. So then combine with other types of small proteins, guess what you make? You make ribosomes. So really, what we can say is, is that the nucleolus, which is a component in the nucleus, is important for making ribosomes, which is made up of rRNA and small proteins.
The last part of the nucleus is all of these blue structures. You see all these blue structures that are kind of dispersed throughout? I kind of made circles around them. This is called chromatin. This is called chromatin. And chromatin is very, very important because this is what really makes up who we are as kind of humans. And it's very important for us to know the different components of chromatin. So within the nucleus, you have this structure called chromatin.
So what in the heck is chromatin? Chromatin is made up of two primary things: DNA and proteins. But the main protein is histone proteins. Histones. These two things make up our actual genetic material. And this chromatin can actually come in two forms, two important forms. One is called euchromatin. And euchromatin is the loose chromatin. And it's the one that's going to be more for expression of the DNA, to transcribe the DNA and make different types of mRNA, or undergo replication. So euchromatin should be more in the center of the actual nucleus.
And the next one here is going to be hetero, the heterochromatin. And the heterochromatin is going to be the tight chromatin. This is going to be the chromatin that you're actually going to see closer towards the inner membrane of that nuclear envelope. So we're understanding this, right? So we know the different structures and the different components here of the nucleus.
The last thing that I want us to understand here is, what in the heck does the nucleus do? We're going to go into way more detail in this in future videos. But what you need to remember is that chromatin, which is made up of DNA, we can take DNA and do a bunch of things with it. What can we do with it? We can take DNA and we can make more DNA. What is this called? DNA replication. I can take DNA and make RNA, and that is called transcription. And then also, you need to know that there's different types of RNA. What are the different types of RNA? There is tRNA, there is mRNA, and rRNA. So it's important for us to understand these kind of things that are happening with inside the nucleus, which is what you have DNA replication and transcription, and particularly making of RNA molecules. And these are the RNA molecules. And again, we'll go over these in more detail in future videos. But this tells us what the function of the nucleus is and what the components of it are. Let's move on to the next organelles.
Okay, so the next thing that you guys need to know here is this next filamentous membranous structure that is located within the cell. This beautiful organelle is called the rough endoplasmic reticulum. So it's called the rough endoplasmic reticulum. We're going to put ER. So the rough ER, that's commonly how we refer to it as, right? So the rough endoplasmic reticulum, or the rough ER.
Now, the rough ER, if you notice, it's this filamentous kind of network here. But there's another structure here called the smooth endoplasmic reticulum. So you have the rough endoplasmic reticulum and then you have the smooth, the smooth endoplasmic reticulum. The smooth endoplasmic reticulum and rough endoplasmic reticulum differ in what way? This is very simple. You see these little red dots that are located on the rough endoplasmic reticulum? It's called ribosomes. So within the rough ER, this contains ribosomes on that outer kind of membrane structure. On the smooth ER, there is no ribosomes. That's really it. There's nothing much more that you have to know about kind of the structure of the rough ER and the structure of the smooth ER. You know that it's an organelle. And the big difference between these structure-wise is rough ER has ribosomes, smooth ER does not have ribosomes.
So now, the next thing has to come down to what are the differences in function here? That's really where it kind of lays in, right? So the first thing we have to do is, before we move into what it does, we have to kind of pick up a quick point here from the nucleus and move to the rough ER. So you know, we said within the nucleus, you have DNA, and from DNA, you can undergo transcription. What is that called whenever you go from DNA to RNA? Whenever I go from DNA and I make a molecule called mRNA, and that mRNA then binds with a ribosome, here's our ribosome, a little like red dot there. That ribosome will then do what? It'll undergo the process of translation, taking the RNA and making proteins. Well, what happens is that ribosome, it's going to start synthesizing and making proteins from the mRNA. So now I'm going to have this protein that gets pushed in here from the ribosome. Now, that's important because the rough ER is obviously going to be a site of protein synthesis. Then that's one thing we can say. It could be a site of protein synthesis because that's where the ribosomes are kind of sitting on. So that's one function of the rough ER.
So one function of the rough ER, we can say, is it's a site of protein synthesis. Site of protein synthesis. And we're going to talk a little bit because there's different types of proteins that we make: proteins that can be within the cytosol, proteins that can be within different organelles, proteins that we can secrete, proteins that we can put into the membrane. Generally, the proteins that the rough ER is making is going to be proteins that will become lysosomes, so proteins that will be incorporated into our lysosomes, proteins that will go and get incorporated into the different organelles like the membranes of organelles or the cell membrane, or proteins that will be excreted. So that is really the big thing that I want you to remember about the rough ER: site of protein synthesis, but particularly for these types of proteins.
The next thing is, what else does it do with the proteins? We know what synthesizes them, but you know what else? Proteins have to fold a particular way for it to be particularly functional. So it also helps with the folding process. So it plays around what's called protein folding. That's very important. So plays around protein folding. And the next thing is, not only does it help with folding the protein in a particular way, it also has little enzymes located kind of in this actual endoplasmic reticulum that can add on little residues, little sugar residues onto this protein, making it active. What is this called? It's called glycosylation. So it can perform what's called glycosylation. Like cosylation. And there's a particular type. We'll go into this more in more detail. But for the most part, it is called N-type glycosylation. And all that means is, if I were to take a protein here, I took it, the mRNA, took it to the ribosome, ribosome bound to the rough ER, it made the protein, push the protein in the filamentous network of the rough ER, it started folding, and then once we have that protein here that's folded properly, I'm going to just add on a little sugar residue. So this is going to be a little sugar residue, and this is going to be my protein. And this is important because this is the way that we activate these proteins. So that is the function of the rough endoplasmic reticulum.
Now, the next thing, one last thing for this, is remember I told you that the site of protein synthesis for these particular things. So in order for, after the rough ER has kind of gone through this process of synthesizing it, folding it, and then glycosylating it, it then has to package it. So then what happens is, it'll package off. So what happens? Let's say here's the protein. The protein will actually bud into this little portion of the actual rough endoplasmic reticulum. And when it does that, that'll actually bud off, and then I have a vesicle. And within that vesicle is going to be my protein. What protein? Will become a lysosomal protein, and membrane protein, or excreted protein. But in order for that to happen, I have to move this towards the next organelle, which will be the Golgi apparatus. We'll get to that one in a second. But here's going to be that protein that was coming from the rough endoplasmic reticulum and moving towards the Golgi. So now we know all the functions of the rough ER.
Now we've got to go over the functions of the smooth ER. The smooth endoplasmic reticulum. This is a very interesting structure. So there's a lot of different types of enzymes located within this smooth endoplasmic reticulum, particularly enzymes that are associated with lipid synthesis. That's the big thing I want you to take away from this. So it's primarily associated with what? Lipid synthesis. There's going to be a bunch of different enzymes located within these organelles, within this organelle. And what kind of lipids are we synthesizing? Fatty acids. Fatty acids are a big one. Phospholipids are a big one. What else? You know, there's another really important cholesterol molecule with cholesterol. So I kind of give it away. So cholesterol. And cholesterol is important because this can become hormones, steroid hormones, testosterone, progesterone, estrogen, all that good stuff. So this is the big thing I want you to remember: is this is the site of lipid synthesis. So we take precursor molecules that we get from the cell. Let's say here's a precursor molecule. That precursor molecule for the fatty acids, phospholipids, cholesterol, it will get taken up into this smooth endoplasmic reticulum. The enzymes in it will start using these precursors to pop out little cholesterol or lipid molecules. So now, from this, we're going to have the smooth ER take the precursor molecules, perform the lipid synthesis process with the enzymes, and then bud off a particular vesicle, which is going to contain what? Fatty acids, phospholipids, and cholesterol. And then guess where we could send this? We could all send it again to the Golgi, or maybe even send it to the cell membrane. And then from the cell membrane, we may release out cholesterol, maybe release out fatty acids. Pretty cool, right?
There's another set of enzymes that are important here. The next set of enzymes is called CYP450. You're like, what the heck is that? CYP450 enzymes are very, very important for detoxification. So you know whenever your liver, your liver has a very high concentration of these enzymes because that's our detox center, right? So if you go to your liver, there is lots of this enzyme. And the reason why is, any drugs, any toxins, any alcohol, you know, alcohol, ethanol, EtOH, any of these things have to go to the liver. And what your liver does is, is it undergoes a process called biotransformation or xenobiotic metabolism, and it breaks down these substances. And it's because of these enzymes located within the smooth endoplasmic reticulum. So it undergoes what's called biotransformation. Ba-boom. That is important.
The next thing here, this is an interesting one. You know, within our cells, we have glycogen, right? You know, glycogen, it's basically a a big polymer of glucose. And whenever our body needs energy, that glycogen can get broken down into glucose. But there's a particular step whenever you're breaking down glycogen into glucose, there's an intermediate between this called glucose-6-phosphate. Well, in order for glucose-6-phosphate to get converted into glucose, guess what it needs? There's a particular enzyme on the smooth endoplasmic reticulum. And that enzyme will need to take the glucose in, give a little transporter that'll take the glucose-6-phosphate in, and then a particular enzyme that'll rip off that phosphate on the sixth carbon of glucose and make off glucose-6-phosphate and make glucose. So the important thing to remember here is that this actual smooth endoplasmic reticulum is also important for glucose-6-phosphate metabolism. So it's also important for glucose-6-phosphate metabolism. Baboom. Roasted.
Last one, last function. You know, this is a smooth endoplasmic reticulum. It's in, in a lot of different organs. But you know, organs that contain lots and lots and lots of calcium, like in our muscles, there's kind of an analogous structure there called the sarcoplasmic reticulum. These can store lots of calcium. And you know, there's little pumps that are located on the smooth endoplasmic reticulum. And whenever we need calcium, whether it be for different types of transport processes or for muscle contraction, guess what? We can pump that calcium out into the cytosol and utilize it for all these different types of chemical processes. So what is the last function here for the smooth endoplasmic reticulum? It also stores calcium. Ba-boom.
All right, we've covered the functions of the rough ER and the smooth ER. Let's now move on to the Golgi apparatus.
All right, ninja nurses. So what have we established up to this point? So we know that we've understood the function of the rough endoplasmic reticulum. We understand the function of the smooth endoplasmic reticulum. And again, to kind of go off of that, that smooth ER again, what did we say it could also make? The different phospholipids and cholesterol and different types of fatty acids. And that also from the smooth ER can get sent to the Golgi. Now, the vesicles that are coming from these two areas, primarily the rough endoplasmic reticulum, we're going to focus on from this point. But again, realize that everything from the smooth ER as well.
All right, so what is the name of this next organelle that we have to talk about? This is a very, very important structure called the Golgi apparatus. Right? So we're going to call the Golgi. Now, the Golgi apparatus is a very important kind of like packaging organelle, if you will. So it takes these vesicles coming from the rough ER, from the smooth ER, and when it takes it into the Golgi, there's an anatomical term here on this side of the Golgi where these vesicles from the rough ER and smooth ER are going to. This part of the Golgi here is called the cis Golgi. Okay? Or they call the cis face of the Golgi. But we're going to call it cis Golgi. Then what happens is, through these systematic steps, these proteins and different types of fatty molecules that get taken to the Golgi will go through the Golgi. And as it goes through the Golgi, it'll actually bud off, right? So then you're going to bud off some type of molecule in the Golgi, whether that be a protein, whether that be lipids, cholesterol, whatever. It buds off and then leaves the Golgi. This side where the vesicles are coming out of the Golgi and going towards lysosomes or cell membranes or whatever, this is called the trans Golgi, or the trans of the Golgi. So that's an important kind of anatomical term or structure component of the actual Golgi that you need to know.
The next thing here is, we have to kind of primarily focus on the function. So primary function is, it's receiving vesicles containing proteins and different types of sugar molecules, maybe attached to it, as well as different lipids from the rough ER and smooth ER. That's the first function. So first function that you need to know here, so it's receiving vesicles from the rough ER and the smooth ER. That's the first thing. We know it's receiving the vesicles containing proteins or fatty molecules.
Now, let's focus on those proteins because that's where it's more important. The proteins that are getting taken into the Golgi, it might have to modify. We saw that it was folded and modified a little bit in the rough ER, but the Golgi might have to modify it even a little bit more. And how does it do that? So this modification step is very important. And it's again through a couple of different reactions. Remember, we have what's called glycosylation reactions that we talked about with the rough ER. The Golgi can do the same thing. It can do what's called a glycosylation. But this glycosylation reactions where it adds on sugar residues, there's two types: one is the N-type and one is O-type. What's really important to remember is that the Golgi is the only one that can do O-type glycosylations. In other words, I'm adding a sugar residue onto the oxygen component of a protein. That's all it really means. N-type, you're adding a sugar residue to the nitrogen component of the protein. Nothing special.
The other really important step here is, it also has to phosphorylate specific types of proteins. And that is very important. There's a disease called I-cell disease, and it's actually related to this phosphorylation reaction. So that's why we need to know it. So it modifies proteins and some lipid molecules through these glycosylation and phosphorylation reactions.
The next thing is, is it packages these molecules, right? And then after it packages these molecules into their own little vesicles. Remember how we said that these molecules will go through the Golgi, undergo these modifications, get stuck into like a little vesicle, bud off, and then pop off here? It's going to pop off, right? So now I got my vesicle containing my proteins and my lipids and all these things that have been modified even more. Now what happens is, these molecules, we already talked about where they're going to go. They're going to go and become lysosomal proteins, they're going to go and become membrane proteins, or they're going to go and be excreted out of the cell. That is the destination and the function of the Golgi apparatus. So now we understand that.
Now that we've done that, we have to talk about another little structure here, which is our cell membrane. It's another component of the cell.
All right, so the next really, really important component of the cell is the cell membrane. So what we're going to do is, we're going to kind of zoom in on a different part here of the cell, right, which is our cell membrane. And there's different components of the cell membrane. So if you look here, you see like these little red dots with like little, you know, fingers hanging out. This is a part of what's called our phospholipid bilayer. So when we talk about the cell membrane, there's a bunch of different structures that are involved within the cell membrane, and they obviously carry out a very important function.
So what are the different components of the cell membrane? The first component here is these little red little thingies. What are these little red thingies? These are called, this is a part of your phospholipid bilayer. So you have two components of it. If we kind of zoom out on this little guy, you have these two components. This head component of this phospholipid bilayer is actually the phospholipid. And what you need to know about this is that this is polar. What does that mean? Polar means it's water-soluble. So it's the hydrophilic portion. It can interact with water because it has lots of negative charges on it. The other component here is the little tail. This tail, these are fatty acids. And fatty acids are really saturated with hydrogen. And so because of that, they are very non-polar, hydrophobic, don't like to interact with water because they have no real negative or slight changes in charge. That's the important thing here. So we have this on both sides. On the inner cell surface, you would have this phospholipid kind of portion pointing inwards. On the outer side, you would have it pointing outwards. And then you have the tails pointing in towards one another.
The next thing is, you see this little green structure which is kind of lodged between these phospholipids. This green structure here is called cholesterol. Now, you're like, like what the heck? Why is cholesterol coming? Oh, and they even add on here, where could that cholesterol come from? The smooth ER. We packaged it, sent it to the Golgi, and then incorporated it into the membrane. We're putting things together, ninja nerds. But the cholesterol is also incorporated in there. And the cholesterol is important because it controls like fluidity. Okay? So it controls fluidity.
All right, so again, to recap this whole idea of cholesterol with fluidity, again, it's just important to remember that the amount of cholesterol, if you wanted to think about like this, the amount of cholesterol in the cell membrane, the more of it you have, the less space there's going to be between the phospholipids. So there's less fluidity. So more cholesterol, less fluidity. And the less cholesterol you have here, the more space there's going to be between the phospholipids. And so there's going to be more fluidity. So less cholesterol, more fluidity. So that's an important concept with that.
The next component of the cell membrane. So we have the cholesterol, we have the phospholipid bilayer. The next big component here is the proteins. So the next one that you're going to have here is these little proteins. And these proteins here, my pink marker here, these proteins, there's different types of proteins. There's what's called integral proteins and peripheral proteins. And what is really, really important for these proteins is that they have various different functions. They can act as transporters, they can act as little enzymes, they can act as linker proteins between other cells. So they have a lot of different components, a lot of different functions to them. But again, there is integral proteins and peripheral proteins.
The big thing I want you to take away from this of the cell membrane is that it basically acts as a barrier. I mean, I know that sounds super obvious, but it is a barrier. It's a selectively permeable barrier. And only allows for particular types of diffusion that we'll get into later. But there is what's called simple diffusion, right? There's what's called facilitated diffusion. And then there's different types of what's called vesicular transport. And all of these types of processes are involving the cell membrane. So in other words, moving things from outside the cell to inside the cell, we have particular types of processes that we'll have to go into more detail about. But again, big thing I want you to take away from the cell membrane is these different components and how it acts as a barrier for particular types of transport processes.
All right, let's move on to the lysosomes.
All right, so the next structure here is going to be our lysosomes, our beautiful little lysosomes. Now, these are very, very cool kind of organelles. Now, what lysosomes are important is, they're like these little spherical organelles and they contain very interesting little enzymes inside of them. And these enzymes are called hydrolytic enzymes. And really, the simplest way of describing these hydrolytic enzymes is, you have different types: you have proteases, which means that they break down proteins; you have nucleases, which means that they break down nucleic acids; you have lipases, which means they break down lipids; and you have glucosidases, which means they break down carbohydrates. So all of these hydrolytic enzymes are located within these little organelles.
So why is that important? Any macromolecules that you bring into the cell, whether that be from a white blood cell undergoing what's called phagocytosis, whether that be you actually undergoing an endocytosis process from, uh, it's called clathrin-coated mediated endocytosis, that whole process when you're bringing something in, you're bringing in particle matter. And these lysosomes are responsible for using these enzymes to break down macromolecules such as proteins, nucleic acids, lipids, and carbohydrates. That's all they do. So that's important thing to remember from these hydrolytic enzymes is they're going to be responsible for doing what? These all break down macromolecules. They break down macromolecules, their respective macromolecules, as we already said. Okay, that's one thing that I really want you to remember.
The second thing, you know, when organelles are getting worn down, maybe our mitochondria, it's just, it's had a rough day, maybe the cytoskeleton's starting to get all jacked up, maybe our ribosomes have just, they've pooped out and they're done. When these organelles have reached the end of their kind of, let's say, functional capacity, we don't want to keep them anymore. We want to recycle them. We want to break out with the old, in with the new. So what happens is, these lysosomes, you'll actually take and package, let's say that the ribosomes are done, they're tired, they're pooped out. I'm going to form a little vesicle around these ribosomes. And then what I'm going to do is, I'm going to send it to the lysosome. And what did I say that the ribosomes are made up of? Proteins and RNA. So what do you think which enzymes are going to start breaking down this ribosome if you bring it to this lysosome? The proteases and the nucleases. And it'll start breaking down the actual organelle. What is that called? Autophagy. So another important thing that you have to remember is that this is one thing: breaking down macromolecules. The second thing is it undergoes autophagy of organelles. Ba-boom.
Last thing, let's say that a cell has actually been severely damaged. You've really damaged this cell. The point of the cell is at living and surviving anymore is that it's, it's not going to happen. You know what I'm going to do? I'm going to just have these lysosomes bust open. And I'm going to have all of these enzymes, proteases, nucleases, lipases, glucosidases. Guess what they're going to do? They're going to break down all the macromolecule components of the cell. What is that called? That's called autolysis. So that's the next thing to remember is autolysis of damaged cells. Okay, so cells that even if they are damaged and you want to repair them, there's no point of even repairing them at that point. It's time to just start all over. These things will just bust open and release their enzymes and start breaking down the cell. This is the functions of the lysosomes. They're little angry little buggers, aren't they?
All right, next one. Pretty cool ones. These are actually kind of one of my favorite organelles, and these are called peroxisomes. So peroxisomes, these are also spherical kind of like little organelles. And they contain a lot of different enzymes. But by far, one of the most interesting enzymes that they contain is, there's two of them: one is called catalase, and the other one is called oxidase. They have other enzymes, okay? They have like other like metabolic enzymes. We're going to title them as that because it can be kind of confusing if you get into more detail than that. But these are the big enzymes. So the first one I want you to remember is the catalases, oxidases, and then other metabolic enzymes. Why am I kind of telling you all of these things? Well, the catalase and the oxidase is important for free radicals. You know, whenever a cell normally obtains oxygen, that oxygen can get sometimes converted into what's called a superoxide anion. Then that superoxide anion can get converted into hydrogen peroxide. And then that hydrogen peroxide can get converted into what's called a hydroxyl radical. These things right here, from here to here, all of these molecules are free radicals. Very dangerous little suckers. Can bind onto proteins and nucleic acids and cell membrane and just jack the cell up. We don't want these things to accumulate. The particular one that loves to accumulate though in these peroxisomes because of what's called fatty acid metabolism is hydrogen peroxide. It really likes to accumulate in there. So what happens is, these peroxisomes have lots of this catalase enzyme. And what they do is, they take this hydrogen peroxide and use that catalase enzyme to convert this into water and oxygen, which is not, that's not that dangerous, right? That's what we want. So that's one of the beautiful things. Be thankful for these suckers. These little peroxisomes, they're not, they're constantly breaking down this hydrogen peroxide, which is a potential free radical, and making water and oxygen. That's one thing.
You know, it's important for fatty acid metabolism. So they contain little enzymes here, particularly catalysts. You know, catalase not only is important for these free radicals, but it also can break down fatty acids. The first step in fatty acid metabolism. So it plays around what's called fatty acid oxidation. Without going into too much detail, there's actually two types: alpha and beta. And really, all this is, is there's diff, what's that called? Branch chain alpha breaks down what's called branch chain fatty acids. And then beta breaks down, it's called very long chain fatty acids. But either way, you're breaking down these fatty acids into what's called acetyl-CoA molecules. Then not only can it break down fatty acids, but it can actually break down the fatty acids into acetyl-CoA, and then we can use those acetyl-CoA molecules to make lipids. So we can actually make, it can make lipids. And there's a very particular type of lipid and cholesterol. And you know, cholesterol is important because this is also important for making different types of hormones, steroid hormones, and bile acids. But this is the one I want to focus on for a second. The lipid that it makes is very important within the white matter of the brain called plasmalogen. And this plasmalogen is a very particular type of lipid that is important for the white matter. So it's an important component of the myelin within the white matter. So you can have an idea that if there's an issue with the peroxisomes and they can't actually synthesize plasmalogen, what happens to the white matter? There may be a decrease in white matter production, and that may lead to some injuries to the actual nervous system.
The last thing I want you to remember is that there's also a teensy bit of alcohol metabolism. So it also can break down ethanol. There's a tiny little enzyme, that catalase enzyme again coming into play, not only with the fatty acids, but also with the ethanol metabolism. It can also break down ethanol. So these are some of the functions of the peroxisomes. Very, very important type of little organelle.
Now that we've covered that one, let's go into the mitochondria.
All right, ninja. So the next organelle that we're going to talk about here is our mitochondria. Now, the mitochondria is a very cool enzyme, I'm sorry, a very cool organelle. And this thing is commonly just broken down into like the simplest way of explaining it. Everybody always knows this: it's the powerhouse of the cell. It's the, the site of ATP synthesis. Yes, that is true. But we're going to explain about how it actually does that ATP synthesis. But before we do that, again, let's kind of highlight some of the components of this mitochondria.
If you look at the mitochondria, it has an outer membrane. So this is the outer membrane. And it's important to remember that the outer membrane is a smooth membrane. And also, it has a very high permeability. There's a lot of transport proteins on the outer membrane. If you look here, you have this little folded membrane here on the inside. That is called the inner membrane. And usually on most cells, we call this inner membrane the folding, cristae. We call it the cristae of the inner membrane. Now, this inner membrane has less permeability. It's less permeable to the transport of different types of molecules going in and out of it. Okay? So that's the basics. Inside of the mitochondria, you have this structure in here called the mitochondrial matrix. And this is where a lot of the metabolic reactions are occurring. And it's also where the mitochondrial DNA is found.
All right, so we have an idea of the structure of the mitochondria. The next thing is the function. So it's obviously the site of ATP synthesis. But if we were to just take it just a little step further, when we make ATP, we make it in two primary ways: one is called oxidative phosphorylation, the other one is called substrate-level phosphorylation. The mitochondria has little proteins on its inner membrane that are very important and then a component of what's called the electron transport chain. So ATP synthesis on the mitochondria, in the mitochondria, occurs via the electron transport chain. And this type of ATP synthesis is called oxidative phosphorylation. Okay? And that's carried out by this electron transport chain.
The other thing that's important with the mitochondria is that there's a lot of metabolic reactions that occur here. A lot of metabolic reactions. What are some of these metabolic reactions that occur within the mitochondria? Well, some of them, as we know, the Krebs cycle. That's an easy one, right? So the Krebs cycle occurs here, where you have a lot of different intermediates that are involved whenever acetyl-CoA gets converted into the entire complete structure, right? Where you have the acetyl-CoA and then the isocitrate, citrate, alpha-ketoglutarate, all that stuff there. That's a part of this metabolic reaction.
The other one is, you have heme synthesis. So you're making the heme component of different types of, uh, chrome, different types of pigment molecules that are part of the electron transport chain, as well as synthesis of heme for hemoglobin or myoglobin. The other one is the urea cycle occurs here. So the urea cycle is another big one, where you're taking different types of molecules like ammonia and turning it into urea. The other one is called gluconeogenesis, where you're taking things like amino acids and glycerol and odd-chain fatty acids and converting it into glucose, a new glucose molecule. And the last thing that can occur here is what's called ketogenesis, where you're making ketone bodies from acetyl-CoA. So these are some of the metabolic pathways that occur within the mitochondria.
One other thing to remember is, I already told you about this, but in the mitochondria, it has its own little DNA. So we'll put this up here. This is called mitochondrial DNA. And this actually comes from the mother. Okay? So this is actually going to be DNA that comes from the mother. And this DNA can actually make tiny little proteins that can be involved in some of these metabolic reactions on its own.
All right, so the next structure here is going to be our ribosomes. This is the next organelle. Now, ribosomes, we have already kind of alluded to these already. So we're going to have a pretty quick run through these. But obviously, we know that these ribosomes, let's kind of talk a little bit about their structure. There's two components of the ribosome. So you have this large ribosomal subunit. So this is the large subunit. And usually, they always like to say this in eukaryotic cells, this is your 60S ribosome. S means Svedberg unit. But again, large subunit. And then the other one is called your small ribosomal subunit. And in eukaryotic cells, this is a 40S or 40 Svedberg unit of the ribosome. Again, kind of a very non-essential thing to remember. But again, big thing to remember is that there's two units: a small subunit and a large subunit.
The next thing that we have to remember, ribosomes are made up of what two things? We already talked about this: rRNA and proteins. So that's the next thing.
The next thing is that ribosomes can be found in two places. We already know one: it could be found on the rough endoplasmic reticulum. Whenever ribosomes are bound to the rough endoplasmic reticulum, we call these, I know it's super obvious, but it's called membrane-bound ribosomes. Okay? So membrane-bound ribosomes. But if these are just kind of in the cytosol freely circulating, then they are called cytosolic ribosomes or free ribosomes.
The reason why we should understand the difference between these two is that if you guys remember the ribosomes that were on the actual rough endoplasmic reticulum, what happened? What do ribosomes do? I guess that's the big question to ask. Let's actually write that down first. What do ribosomes do? They take mRNA and another structure called tRNA and make proteins. So they're basically a site of protein synthesis, right? And we also give this a particular name called translation. So whenever you're taking things like mRNA and making proteins, well, what happens is, if you have ribosomes that are bound to the rough ER, what are those proteins going to become? Remember what we said? Those will become proteins that'll be a part of lysosomes. Those would be proteins that'll become a part of the membrane, like integral or peripheral proteins, or they'll be proteins that we're going to excrete out of the cell.
Cytosolic ribosomes, those are just going to be making little enzymes, different types of proteins inside the cell that will not leave the cell. So that is important. So these are going to be making cytosolic proteins. And I know that sounds obviously kind of pretty, pretty straightforward, but again, it's something worth mentioning. These are making cytosolic proteins, like different types of enzymes that are involved in a lot of your metabolic pathways that occur in the cytosol. Okay? So that's important. So that gives us the importance of ribosomes, what they, uh, what their structure is, and what they do.
Now, let's finish off with the cytoskeleton.
All right, ninja. So now we got to talk about the cytoskeleton. Now, obviously, when we talk about the cytoskeleton, the cytoskeleton, we're only showing in this kind of one point here. But if you really were to show the way the cytoskeleton looks, it would, it would make this board look disastrous because there would just be lines and fibers all over the entire cell. And that's an important thing to remember that even though we're showing this in kind of like a static zoomed-in view of these cytoskeletal elements, remember they are scattered all around the cell. That's an important thing to remember.
Okay, when we talk about the cytoskeleton, there are three different structures of the cytoskeleton. The first one that I want us to talk about is called your microfilaments. Your microfilaments. And sometimes, to be honest with you, we just refer to this as actin. Okay? And I know you guys have heard of actin if you guys have watched our videos before, you've heard this term actin. It's one of the proteins that are commonly used in muscle contraction, right? So that's an important thing to remember. But when you look at actin, there's these little monomers of actin, and they all come together and make this long polymer of actin, and you get multiple strands of it.
Big thing I want you to remember with this actin structure. First thing, when we talk about function, you know, when you have a muscle cell, there's another protein that actin binds with to cause contraction and relaxation. What is that protein? Myosin. So whenever you have actin and myosin, particularly in a contractile type of cell, what can this do? This can lead to muscle contraction and relaxation. So this is going to be a protein that can be involved in muscle contraction. That is a very important thing to remember. So one thing I want you to remember with the microfilaments are actin is that if it's associated with myosin, it can be involved in contraction.
The second thing, you know, in a cell, if we were to have like a, for example, there's a process called cytokinesis. When a cell is undergoing mitosis, you, if you imagine here, let's say that here I had to a cell that was going to become two cells. So here we had one cell that's becoming two cells, right? Around the central portion here, you form this little constriction ring, right? This little constriction ring around this point here. These actin filaments form that constriction ring and eventually squeeze it to the point where, guess what happens? You bud off from one cell to daughter cells. So it's important for the cytokinesis part of mitosis. So cytokinesis of mitosis. So it forms a little constriction ring around that which helps to split the cells apart.
The other thing it's important for, you know, white blood cells. If you take a white blood cell, let's imagine here I have a white blood cell and I want to move a white blood cell from the blood, I mean, from the blood and have it leave and go out into the tissues. Well, here's a vessel, and you know, the vessel's lined with what's called endothelial cells, right? Well, what happens is that this actual white blood cell wants to be able to squeeze through those actual capillaries. What is that called? Diapedesis. In order for it to do that, it needs to be able to change the shape of the cell. What do we say cytoskeletal elements do? They help to control cell shape, structure, all that good stuff. So what happens is, the actins polymerize in such a way that it allows for this cell to kind of create a particular shape. So all the actin molecules will come at this point and create like this little shape where the white blood cell can squeeze out of the cell. So what is that called? Diapedesis. Diapedesis of white blood cells.
And let's take this one more step. Let's say you have a white blood cell, okay? And here's a little pathogen out here. Here's a little pathogen. And I want to take this pathogen in. In order for me to do that, I need to create these little like things called pseudopods. And what happens is, I create these like little arms or little extensions that come out here to surround that pathogen. The actin molecules need to come in and help to create these little arms that'll basically wrap around the pathogen and bring it in. What is that called? Phagocytosis. So it's also involved in phagocytosis of white blood cells. Babushka. We did it.
All right, next one. The next one is the intermediate filaments. The intermediate filaments. The intermediate filaments are a very interesting.
type of structure and one of the things that we need to know about these intermediate filaments is that they are primarily very tough high tensile not very much movement they don't give they don't have a lot of give to them.
so why that is important is let's say that we take here a cell here is a another cell okay we have two cells and then you know around the cell there's a lot of protein network out here. what is this called all this protein network that sits outside of the cell this is called your extracellular matrix. it's made up of collagen and elastin and a bunch of different types of proteins we know that right.
well what happens is we take this protein here let's actually draw it in another color here let's use this blue here this protein here let's say here we have one end of it it can connect to from the cell can connect the cell to the extracellular matrix that's one thing it can do. so it can help to hold the cell and anchor it to the extracellular matrix.
the other thing here is maybe i have another protein here another protein here in these cells these can connect cell to cell. so they help to anchor and hold the cells to each other.
and then let's add another thing in here you know these little organelles remember i told you that if you imagine the cytoskeleton they're all over this cell imagine here i draw an organelle a mitochondria or you know the nucleus whatever here's our nucleus right these cytoskeletal elements are also going to be bound to these organelles. so it helps to anchor the actual cell to the extracellular mantra matrix anchor cell to cell and anchor the organelles inside of the cell so they're not just kind of like [ __ ] floating around everywhere right.
so that is the function of the intermediate filaments. so three functions is an anchor if you will and it anchors what things. one is cell to cell. two is cell to the extracellular matrix and three is sell to different organelles. we done did it okay.
so the last component here the last part is this microtubules. these are very very cool cytoskeletal elements okay and what i really want you to remember about microtubules okay is they're made up of two different types of protein units. so i drew these in different colors a pink protein maybe that represents what's called alpha tubulin and pretty straightforward right and then with my blue marker here another little dot here is called beta tubulin. these things come together and form these little filaments and then like 13 filaments come together and eventually form this entire microtubular structure.
why this is important is very very interesting. so microtubules one of the really big function here is that it provides what's called intra cellular transport okay. now it's a it seems odd but on these microtubules you have these little proteins imagine here you have like a little protein here okay and these proteins there's two different types of them there's what's called dynein and another one which is called kinesin and these are called motor proteins and what these motor proteins can do is they can bind on to organelles they can bind on to different vesicles which maybe have proteins or lipids or things that you're moving towards the cell membrane are bringing in to the cell these are transporting them throughout the cell to different places that they need to go to that is very important. so again it's acting as the the railway right or the railroad system by which you're transporting different substances by having to use these motor proteins. big thing to take away from this this isn't there's no free lunch on this this requires atp to drive this process this is an atp dependent process for this intracellular motor protein transport.
the second thing that's important for is cell division. you know whenever a cell is going through the mitosis phase there is this phase where you have the chromosomes like this right and they're all lined up okay and metaphase well at that point here the centromere there's little proteins on the side called the kinetochore. what happens is these microtubules they click in to that kinetochore and what happens is as they start to break down they depolymerize it separates these chromosomes into the two separate sister chromatids. so again big thing microtubules connect to the kinetochore where the centromere is the center part of the chromosome and separate them into sister chromatids. so that's the other important thing is cell division particularly separating separates the chromatids okay.
the third thing here is it is important for cellular extensions. cell extensions and what i mean by these extensions is there's two big structures they form the base of these structures and you form what's called the cilia which is a very important structure and you form what's called flagella. these are structures that again you have motor proteins like dyneins and things like that that are incorporated into this these uh cellular extensions but what happens is these cilia and flagella they create a beating like motion or twisting like motion and what that helps for is that if you have these motor proteins which are constantly utilizing atp to beat and create this movement here cilia is good in our respiratory tract because it helps to clear out mucus. it's also in the fallopian tubes you know when you have to move the o or the oocyte or the ovum in this case if it's fertilized you have to move it towards the uterus we need those things and microtubules make up the base of that cilia flagella. in order for the sperm to be able to move towards the oocyte or the in this case the secondary oocyte it needs to have that type of motion and again microtubules make up the base of the flagella and utilize these dynein proteins to create that whipping motion. so now we have an idea what these microtubules do.
hi ninja so in this video we covered the structure and function of the cell. it was a long one but i hope it made sense and i truly hope that you guys enjoyed it and i hope you guys learned a lot. if you guys follow through this entire process of how i study prepare draw and then go through the lecture i hope that you guys were able to come up with a similar process and i hope it helped. all right nigerians as always we thank you love you and until next time.
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