[0:07]All right, ninjas. 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 your supports by hitting that like button, commenting down in the comment section, and please subscribe. All right, ninjas, let's get into it. All right, ninjas. So, we're going to take a tour through the cell talking about what all the structures of the cell are and then what they do. So, the first thing that 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 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 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, it's double layered here. So, you have an outer layer, and then you have a 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 on to ribosomes on these outer membranes, which then get moved to the Ruffy R. 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 this 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. And the whole purpose is it's honestly pretty straightforward, right?
[3:07]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 in the nucleus, but there's special types of transporters that are associated with those nuclear pores. And 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 R RNA, what we call R RNA. So, we're going to denote this as R RNA synthesis. This occurs in what structure? This occurs within the nucleolus. Now, the reason why that's important is when you take R RNA, 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 R RNA 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 um, 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 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 constructures 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 a 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 you also, you need to know that there's different types of RNA. What are the different types of RNA? There is T RNA, there is M RNA and R RNA. So, it's important for us to understand this kind of things that are happening within 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 or the Ruffy R. 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 endoplasmic reticulum. The smooth endoplasmic reticulum and rough endoplasmic reticulum differ in what way? This is very simple.
[8:16]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? Because 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.
[9:25]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, is that it's a site of protein synthesis. And we're going to talk a little bit because there's different types of proteins that we make.
[10:17]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'll become lysosomes. So, proteins that'll be incorporated into our lysosomes, proteins that'll go and get incorporated into the different organelles, like the membranes of organelles, or the cell membrane, or proteins that'll 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 it 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 a role in what's called protein folding. That's very important. 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. 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, pushed 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 is kind of gone through these 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 that 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, a membrane protein or a 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 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 uh associated with lipid synthesis. That's 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 organ 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, cholesterol, so I kind of gave 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. So, let's say here's a precursor molecule. That precursor molecule for the fatty acids, phospholipids, cholesterol, it'll 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 molecule, 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 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. We may 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 downs these substances. And it's because of these enzymes located within the smooth endoplasmic reticulum. So, it undergoes what's called biotransformation. Baboom, that is important.
[16:16]The next thing here, and 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 uh energy, that glycogen can be 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, you have 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, well 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 in organs that contain lots and lots and lots of calcium, like in our muscles. There's kind of a a analogous structure there called the uh 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. Baboom. 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, ninjas. 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 smooth ER, again, what did we say? It could also make the different phospholipids and cholesterol and different types of uh fatty acids, and that also from the smooth endoplasmic reticulum 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 it the Golgi. Now, the Golgi apparatus is a very important kind of like packaging uh 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 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 it the Cis face of the Golgi, but we're going to call it Cis Golgi. Then what happens is, through these systematic steps, these uh proteins and different types of uh 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 face of the Golgi.
[20:09]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 uh sugar molecules may be 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.
[20:49]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 different reactions. Remember we had 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 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 glycosylation. 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 that 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 in some lipid molecules through these glycosylation and phosphorylation reactions. The next thing is, is that 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. We're going to pop off here. Right? So, now I got my vesicle containing my proteins and my lipids, 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 the like little, you know, fingers hanging out. These are called, 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. 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, we're going to 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 nonpolar, 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 here is you see this little green structure, which is kind of lodged between these uh phospholipid. This green structure here is called cholesterol. And you're like, what the heck? Why is cholesterol coming? Oh, and they even add on here. Where could that cholesterol have come from? The smooth ER. We packed it, sent it to the Golgi and incorporate it into the membrane. We're putting things together, ninjas. 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 it 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 and 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, from 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 uh later, but there is what's called simple diffusion. Right? There's what's called facilitated diffusion. And then there's different types of uh what's called vesicular transport.
[27:04]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 will 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. Okay. All right, ninjas. So, the next structure here is going to be our lysosomes, our beautiful little lysosomes. 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.
