Transcription
Foreign, what's up Ninja nerds? In this video today, we're going to be talking about the structure and function of the mitochondria. Before we get started, if you guys like this video, makes sense, helps you, benefits you, please support us. Well, wait, can you do that? Hit that like button, comment down in the comment section, please subscribe. Also, if you want some great notes and illustrations, I really, really suggest you guys check them out. They're really good. We have a great engineering team who compiles them, so check them out. Go down in the description box below. It'll take you to our website where you guys can check those out.
All right, mitochondria. It's always referred to as the Powerhouse of the cell, right? We're going to dig a little bit deeper, okay? So when we talk about the mitochondria, let's first go through the structural components of it, and then what we'll do is we'll dig into the function of it step by step, kind of not just sticking with the only factors that it produces ATP. There are a lot of things that this son of a gun can do.
All right, so the mitochondria, first thing is, it's really kind of, I'm not even kidding, this is the way that they hold in the textbook, a sausage-shaped, uh, kind of like organelle inside of the cell. And when we look at it and actually zoom in on the structure, there's a couple of different components that we have to know. The first one is that you have this kind of like membrane, and it's double-layered. It has like an outer membrane out here. So this is called your outer membrane. And again, it's made up of a, like a phospholipid layer, bilayer, actually. Outer membrane. Big thing that I kind of want you to take away from the outer membrane is the outer membrane is a very permeable membrane, okay? So it's a very, very permeable membrane, highly, highly permeable. So it's got these big pouring molecules that allow for things to move in and out of the mitochondria. One big thing that you may see on your exam.
All right, so here's the outer membrane. Then if you look, here's the other component of it right here. You see how we have the outer membrane, which is this kind of maroon line, and then here we have another maroon line that's called the inner membrane. This is called the inner membrane. Again, another phospholipid bilayer, which is pretty cool. Big thing to take away from this one, though, is it is not very permeable. Has a lot of selective proteins, transporters that are present on it that really are very closely regulated and determine what moves in and out of the mitochondria. So this one is less permeable. Really, kind of a big just term that I want you guys to take away from these two.
Now, there's a space and that exists right between these two. So here was the outer, here was the inner. There's a little space between these two, and this little space here is called the intermembrane space. Really, really cool thing about this one, and we'll talk about it later, is that it is really, really highly concentrated with proton ions, which is really, really helpful with your electron transport chain. So we'll get into that a little bit later.
All right, so we got outer membrane, inner membrane, intermembrane space, which is kind of just a little bit of fluid, rich in protons, okay? We come into the inner part here. So one more thing. You see how they have the inner membrane? If we were to follow this thing along, look how it kind of continues, continues, and then you get like these like little invaginations that are coming off of the inner membrane. That's a really, really important thing. So what I want to add on here is with the inner membrane. So with the inner membrane, so with the inner membrane, we're going to rewrite it. There is a specific type. So this kind of invagination is actually called the cristae. So it's a continuation of the inner membrane but invaginates into the center. It's all these things. Here's a crista, here's a crista, here's a crista, crista, crista, crista. Okay, the whole purpose of these puppies is to increase the surface area for a lot of specific types of metabolic reactions that we'll talk about a little bit later.
Okay, so we got outer membrane, inner membrane, intermembrane space. The inner membrane, there's a special type of them which invaginates into the actual center of the mitochondria called the cristae, which increases the surface area for a lot of metabolic reactions. The last part is all of this kind of white space here, which is basically the mitochondrial matrix. So really, all of this in here is called your mitochondrial matrix, and it has a bunch of different fluid and solutes in it. But two particular things that are really pertinent to the matrix, um, the major, the mitochondrial matrix is what's called mitochondrial DNA, which is represented right here. See these little guys right there? That's your mitochondrial DNA. It's really cool because this is actually maternal DNA. So it's maternal DNA. And then the next part here is not only is there maternal DNA, which obviously has some types of genes to encode to make particular RNA to make proteins, but we need certain things that are helpful in making proteins. So mitochondrial DNA can make RNA, but we need ribosomes to be able to translate that RNA and make proteins. And some of these proteins, the mitochondria can make on its own to help with its own functions. So that's a really, really cool thing, and we'll get into that a little bit later. But this is the big, big thing that I want you to understand.
So again, to recap it, this is outer membrane, this is inner membrane. A special invagination of the inner membrane into the center is called the cristae. Which one's highly permeable? Outer. Which one's less permeable? Inner. What's the space between the outer and the inner membrane? The intermembrane space. What is it rich in? Proton ions. And then what is all of this fluid here that is in the center of the mitochondria? The mitochondrial matrix, rich in mitochondrial DNA and ribosomes.
The mitochondrion is an organelle that is the powerhouse for both animal and plant cells. During a process called cellular respiration, the mitochondria make ATP molecules that provide the energy for all of the cell's activities. Cells that need more energy have more mitochondria.
Let's now dig into the function of the mitochondria. Specifically, what I want to talk about is the membranes. So we'll get into the matrix, that's next. But what I want to talk about first is let's talk a little bit about the outer and the inner membrane and what are some of the functions that this puppy does. So let's come down here. The first thing that I want to discuss here is it plays a huge role in protein transport. The membranes. So what we're doing is we're zooming in. This is a cell, sorry. So this is a cell here. This here is the nucleus. So this is our nucleus. Here is a ribosome. These are free ribosomes. And then I'm just zooming in on the mitochondria. So I'm going to represent this as the outer membrane, the intermembrane space, and the inner membrane. And then what would this be? This would be the matrix. So I'm just zooming in onto the part of the mitochondria.
Now, the mitochondria has DNA, right? It has DNA. Here's like some of that mitochondrial DNA, and it can make RNA, which can be helpful to make some proteins. But it doesn't make all the proteins that it needs to be able to function. And so sometimes we have to take some of the proteins from the nucleus. So the nucleus will help us to make RNA. RNA will then make proteins. And these proteins have to get sent into the mitochondria. And that's really, really important. So for example, here, here's our DNA. It's going to make mRNA. mRNA. That mRNA will then come out via the nuclear pores. When it comes out via the nuclear pores, here's my mRNA. It'll then combine with ribosomes. And from this, from the ribosomes, we'll then synthesize what? Proteins. But here's the big thing. These proteins are unfolded. Oh, there we go. It's unfolded. Therefore, it's not super active. It's not the active form, okay?
So the mitochondria has special transporters that really are special in moving these unfolded proteins that it needs to be able to perform reactions inside of this, the mitochondria. It needs to transport it across. So what happens is this protein here will get chaperoned and then will bind onto this like little receptor here. And there is this outer membrane translocase. We literally call them TOMs, translocase of the outer membrane. And what happens is once this unfolded protein binds to the receptor, what it'll do is it'll open up this TOM and move this unfolded protein into the intermembrane space. And the intermembrane space, a little chaperone protein will bind to it and bring it to this next point. So it'll bring it to this next receptor on the inner membrane. When it binds here, it activates this particular, stimulated this receptor, stimulated this receptor. When it stimulates this receptor, it opens up this next channel on the inner membrane. This is called TIM. I'm not even kidding. So translocase of the inner membrane. And when that binds onto the receptor, it opens up and pushes the unfolded protein into the mitochondrial matrix.
In the mitochondrial matrix, we need maybe this protein to perform specific things. Maybe it's an enzyme that plays a role in a lot of metabolic reactions. And I need him. And so what happens is you have specific types of proteases or other enzymes that will then work on this protein and properly fold him together and activate him and make him into a specific special enzyme. And now this is an active, folded enzyme, and it's ready for it to perform its functions inside of the mitochondria. And there's so many different proteins that you need. And so it's a really, really important point because the mitochondrial DNA, right? The mitochondrial DNA, it only makes like 15% of the proteins. So really, when it goes to make proteins, these proteins that it makes is only 15% of what's needed. So that means I need a lot of proteins from the nucleus to help me to perform a lot of the functions. So that's one of the cool things. The mitochondria accepts proteins in their unfolded form, brings them into them, and then activates them by folding them properly, and then uses those for their metabolic reactions. Pretty cool, right?
All right, that's one of the functions of the membrane. Let's go on to another one, which is it plays a role in like miscellaneous transport. And then we'll talk about the big mac daddy function of the mitochondria that the membrane plays a role in, and that is the electron transport chain.
All right, my friend. So now, next one is, it also plays a role. So with protein transport is a big one, but it plays a role in like small miscellaneous things. And this may seem like very, like straightforward, and I, I kind of thought that was common sense. It is, but it's just a quick reminder of things that also, a lot of things move across the mitochondrial membrane, right? And what are those things? Well, I want you to understand, and we're going to get into them a little bit, but metabolic reactions, they're very, very heavily involved in the, the mitochondria. And so in order for some of these metabolic reactions to occur, I have to move things like carbohydrates, right? Across the actual, what? Across the mitochondrial membrane. These have to move in and out because you'll talk later that we do a lot of different things like glycolysis has to occur inside of the mitochondrial matrix, or gluconeogenesis has to occur inside of the mitochondrial matrix, right? We have to move things like fatty acids. So we move things like fatty acids in here as well because they play a role in something that we'll talk about later called beta oxidation, right? We have to move things like amino acids in here, right? Because they may play a role in something called the urea cycle. And so there's a lot of different things that are actually moving across this cell membrane. And that's a really, really important point that there's a lot of ions that are moving across, ions and small macromolecules that are moving across the mitochondrial membrane. Very, very key. And again, I think one of the big things to understand here is if they were to ask you a question regarding the transport of things across the mitochondrial membrane, which of the membranes is very permeable? Outer. And which one is very little permeability? Inner membrane. So a big thing to take away.
Okay, now we come on to the next component here. The next component that I want you guys to understand that is very critical to the function of the mitochondria, and oftentimes what it's referred to with that big buzzword term is the Powerhouse of the cell, produces ATP. ATP is power, energy, right? So this electron transport chain is huge, and it's found primarily on the inner membrane. So you don't really see this involved in the outer membrane, primarily inner membrane. And we're not going to go into crazy detail of all the different processes that are occurring on the electron transport chain. We're going to talk about that in the biochemistry or metabolism playlist. If you guys want to go watch that, we have a playlist where we go through the electron transportation in depth, and we do an overview of it. But the basic concept here is that you have these protein molecules, and they make up these different complexes, like complex one, complex two, complex three, complex four, and a very special molecule called ATP synthase. And what happens with these is that they take things, you know, you have your Krebs cycle, and so from your Krebs cycle, you take a molecule called pyruvate, right? Pyruvate gets converted into acetyl-CoA, and then acetyl-CoA goes through this special thing called the Krebs cycle. So this is called your Krebs cycle. And from the Krebs cycle, which occurs in the mitochondria, we form these high-energy electron transporters called FADH2 and NADHs. And they're carrying with them a lot of electrons in the form of like, they have them in a hydrogen, what's called a hydride ion. And what they do is they take and they transport these electrons onto these proteins, and they drop the electrons off in them. And then these guys pass these electrons down the chain from areas of high energy to areas of low energy. And what that does is, with each time that that happens, it pumps all these protons out into the intermembrane space, pumps all these protons out into the intermembrane space. And you guys remember what I told you was very, very rich in the intermembrane space? I said it for a reason, it's protons. And then these protons, what they do is they move from areas of, in this situation, they move down this ATP synthase. And they move down pretty powerfully. And what it does is, is it moves down this ATP synthase, it creates this energy that the protein can harvest. And when it harvests all that energy, what it allows it to do is, is naturally, something is bound to this, and it's called ADP and an inorganic phosphate. They're kind of stuck to this, this ATP synthase. But as the protons run down this gradient, as electrons are being passed down, it creates this energy that fuses these puppies together. And then what it does is it releases it in the form of ATP. And this process where we make ATP via the electron transport chain is a very specific type, and we call this type of ATP production oxidative phosphorylation. Phosphorylation. So a really, really key component here that's happening in this particular inner membrane.
One side effect, though, that comes from these reactions is that all these electrons that are getting passed along the membrane, sometimes some of these electrons that are really, really rich out here, they can actually combine with things like oxygen, and they can combine with other molecules, and they can make things like hydrogen peroxide or they can make superoxide free radicals. So they basically can increase the formation of things called reactive oxygen species, which is that unfortunate side reaction from the electron transport chain. That's something that can happen as a side reaction of the electron transport chain.
So again, three functions to take away from the inner and outer membrane. Outer membrane highly permeable. Inner membrane less permeable. They allow for miscellaneous things to travel in and out of the mitochondria, specifically for metabolic reactions, things like carbohydrates, things like amino acids, things like fatty acids, and we'll talk about those reactions in a second. They also allow for unfolded proteins that are made by the nucleus, by ribosomes in the cytoplasm, to be transported into the mitochondria so that they can use them for their functions. They don't make all the proteins that they need. They really only make like 15% of the proteins and enzymes that they need. So they need a lot of proteins from, from the actual nucleus, and the last thing is they have the electron transport chain, specifically on the inner membrane. And what does it do? It takes high-energy electrons from NADHs, FADH2s, which are generated from metabolic reactions, passes it on to those things. They pass the electrons down this chain and pump protons into the intermembrane space, and then allows for it to flow back down into the mitochondrial matrix, harvesting energy to make ATP via oxidative phosphorylation. Then an unfortunate side reaction that can occur from the electron transport chain is you can make reactive oxygen species, unfortunately.
All right, my friends, let's now go into a little bit more detail of what are these reactions that occur in the mitochondrial matrix. We've like clipped off a few of these, like, okay, there's, you know, the Krebs cycle, there's gluconeogenesis. I already said those terms, there's the urea cycle, there's fatty acid oxidation. Some of these things that I've said, we're going to kind of quickly go over them and talk about how they're involved, particularly in the mitochondrial matrix, so that if you're asked which of the following reactions occur in the mitochondrial matrix, and you'll see this when we get into biochemistry, you can pick out which one it is likely that's going to be occurring there. All right, and then we'll briefly talk, finishing about mitochondrial DNA and we'll talk about ribosomes. Let's get over there and talk about that.
All right guys, so now we're going to talk about the next component here, which is the functions involved in the mitochondrial matrix. So we went over the inner membrane and outer membrane, how they're particularly involved in things like protein transport, miscellaneous transport of things like nutrients, as well as some ions. And on top of that, we went over the electron on transport chain, a really, really big function for ATP production via oxidative phosphorylation. Well, the matrix, really, what's cool about this is that we already kind of gave a little leeway or kind of like introduced this slightly, that there's a lot of metabolic reactions that can occur in the mitochondria. So really, what I'm looking at inside of this red membrane here, can pretend that this is the combination of the inner, outer membrane, and the intermembrane space. This is just the entire mitochondrial membrane here, and then in this is going to be your mitochondrial matrix, and that here is going to be your cytoplasm inside of the cell. So this is all cell, but we're just zooming in on the mitochondria, particularly the matrix inside there, and then the cytoplasm all out here. Okay?
So what's cool is, you know, whenever you take something like glucose, so you bring glucose into the cell, right? So let's say that you bring glucose into the cell, what we know is that once glucose gets into the cell, it eventually gets converted into something called pyruvate via glycolysis. And then that pyruvate will get brought into the actual mitochondria. When pyruvate is brought into the mitochondria, it then undergoes a conversion into a specific molecule called acetyl-CoA. And then acetyl-CoA will go through these series of like steps, which I don't want to talk about every single substrate, we'll do that later in biochemistry. But this process where it goes through this cycle is called the Krebs cycle. And so what you're seeing is two particular reactions that are occurring here so far. One is you're seeing the conversion of pyruvate into acetyl-CoA. And the second thing you're seeing is the Krebs cycle. And we already briefly talked that coming off of the Krebs cycle is those high-energy molecules that carry electrons called NADH and FADH2. And these go to the electron transport chain where they pass off those electrons, pump protons into the intermembrane space, and they help to generate something called ATP via oxidative phosphorylation.
Well, what's another reaction that can occur here? There's another cool one. You know, whenever we take something like fatty acids, so fatty acids, these are just long chains, like sometimes these suckers can be like 16 carbons long. We can bring these into the mitochondrial matrix across the membrane. So that's another example of transport across that. And then they can go through these series of metabolic reactions where they get broken down into acetyl-CoA. And then you can use them to make energy. This step here is called beta oxidation. This is another one of the reactions that takes place inside of the mitochondria matrix. So so far, we have the conversion of pyruvate into acetyl-CoA, the Krebs cycle, and then beta oxidation of fatty acids.
What else can occur here? There's another really cool one. You know, when you take something like amino acids, amino acids can get brought into the mitochondria as well. And what happens is amino acids eventually, they can get metabolized into something called ammonia, right? So they can actually get metabolized. And when they get metabolized, they give way to products in the Krebs cycle. We're not going to mention which ones. But when it does do that, it can give off something called ammonia. And ammonia is really, really toxic, really nasty son of a gun that you don't want to have to deal with. So what happens is ammonia will go through these like series of reactions here, and it's called the urea cycle. And what happens is it liberates this molecule called urea, which is less toxic in comparison to the ammonia, and it's easier to be excreted. But this cycle here, this cycle that occurs kind of in the, what specifically in the mitochondrion, even a little bit, if you notice over here, even a little bit of the cytoplasm. What's this called? This is called the urea cycle. So this is called the urea cycle. That's another metabolic reaction that takes place where? In the mitochondrial matrix.
Another one, another reaction that's really cool is I can take something like amino acids, I can take something like odd-chain fatty acids, and I can convert them into specific substrates. But then what I can do, which I'm going to represent here with a, let's do it with a pink arrow, is I can convert them back into pyruvate and then back into glucose. You know what this is called when you take something like an amino acid and not-chain fatty acids and make glucose from it? It's called gluconeogenesis. So that's another reaction, which I'm going to represent kind of going in this with the pink arrow. So I'll represent it right here as the fifth reaction. This is called gluconeogenesis. Okay, so that's another one. And then there's one more reaction from the Krebs cycle. You can take some of these intermediates and make something called heme. And some of these molecules of heme are actually synthesized in two places. They can actually be synthesized in both the mitochondrial matrix and they can be synthesized in the cytoplasm. So both of these. So we can make something called heme. There's another reaction. So what's that one? That's the sixth one.
So what I'm trying to tell you here is there are so many metabolic reactions that take place within the mitochondrial matrix. What are some of them? If we were to again recap them, we call these reactions. First one is pyruvate to acetyl-CoA. That's one particular reaction. The second one that is also really important here is the Krebs cycle. That's another particular reaction. Krebs cycle. The third type of reaction here that also occurs is going to be, and I actually made it a two, but that should be a three. I apologize. This is beta oxidation. So this is breaking down fatty acids. So the third one should be beta oxidation of fatty acids. So we'll put beta oxidation. There's actually another one here. So we go three, we go four. This is the urea cycle. So this is the urea cycle. But another big thing that I want to add on here is that urea cycle can occur in two places, as you're noticing by this reaction. It can occur in the mitochondria, but it can also occur where? In the cytoplasm. Another particular reaction besides this one, as we go to five, is this involved in what's called gluconeogenesis. This is called gluconeogenesis. And what is gluconeogenesis? It's taking something like amino acids or taking something like odd-chain fatty acids and converting them back into glucose. But did you notice that this one also takes place in the mitochondria, and it also takes place in the cytoplasm? Another particular reaction is taking something like Krebs cycle intermediates and making heme, and it's involved in two particular places where it's involved in the mitochondria and in the cytoplasm. So that's another particular reaction, which is heme synthesis. Heme synthesis. And again, we can find this in two particular places, both the mitochondria and the cytoplasm. Usually, to remember these combo, I remember HUG: Heme synthesis, Urea cycle, and Gluconeogenesis as a little mnemonic. There is technically one last one if you really wanted to remember. I could take acetyl-CoA and I could shunt them into making something called ketones, and that would be the last particular reaction that could occur inside of the mitochondrial matrix would be something called ketogenesis. Ketogenesis. So you can see there is a lot of metabolic reactions that take place inside of the mitochondria. A massive amount. It's insane. I don't expect you to remember every single one of these steps here. The big thing I want you to understand is that the mitochondria is involved in a ton of metabolic reactions that if you try and remember this now, it'll be helpful whenever we get into biochemistry, and you'll see a lot of these reactions take place over and over and over again that we'll go over.
All right, so this is the big thing I want you to take away from this aspect of the mitochondrial matrix. Let's come down and talk about a couple more things with the mitochondria. So so far, we got protein transport, miscellaneous transport, electron transport chain, we got a lot of metabolic reactions, seven of them, with three of them, HUG, Heme synthesis, urea cycle, and gluconeogenesis, occurring in both the mitochondria and cytoplasm. The last thing is that this son of a gun can be involved in apoptosis. It's actually pretty crazy. I'm not going to go too crazy with this. We'll talk about a more detailed cell pathology. But whenever there's some type of process where a cell is infected or is cancerous or it needs to die, unfortunately, it has to die. There's special molecules present called cytochrome C, and it's located inside of the mitochondrial matrix. Now, naturally, we don't want these things to be leaking out. So there's proteins called like Bcl-2 that really help to prevent this from occurring. But what happens is in apoptosis, you decrease the number of these, and so now we can't control these cytochrome molecules from leaking out. And the cytochrome C molecules, which is supposed to be kept in the mitochondrial matrix, leaks out. And these are nasty molecules because what they do is these cytochrome C molecules, they activate these enzymes called caspases. And these are basically proteases, and they just start ripping through a bunch of different cells. And so they start just damaging cell membrane, damaging organelles, and eventually cause the cell to undergo its death process. Okay, so it'll lead to a lot of signaling processes that will trigger its programmed cell death. That's what apoptosis is. It's programmed cell death.
Okay, my friends, let's move on to the last particular function here for mitochondria, and that's pertaining to the DNA and the ribosomes. What do they really do? It's not too hard to understand. It's that here's our mitochondrial DNA. With this, I could do two things with it. One is I can make more of it. What's that called? DNA replication. This could be important if I want to take maybe and replicate my actual mitochondria. So if I want to take this mitochondria and maybe undergo what's called a fission process and make two of these puppies here, let's say that I wanted to make two of these mitochondria, I would want them both to contain an equal amount of mitochondrial DNA. You know what's super interesting, believe it or not? So fission is a process where bacteria, prokaryotic cells, undergo division. There's a theory, um, back in the day called, well, it's still there, it's called the endosymbiotic theory. The mitochondria, back in the day, used to just be a bacterial cell, a prokaryote, and it would have its own DNA. And then what happened is it got engulfed by a eukaryotic cell. And then when it got engulfed inside of the eukaryotic cell, it then became something called a mitochondria. And so it kind of started down-regulating a lot of its genes and proteins and stuff like that. And the nucleus of a eukaryotic cell became the new factory of DNA and it has its cytoplasm to make many of the proteins that are needed. And the mitochondria just primarily kind of got downgraded to producing ATP and having some metabolic reactions occur in it. So that's something called the endosymbiotic theory. But that's a really cool concept that basically the mitochondria used to be something called prokaryotic cells, and they just got engulfed by eukaryotic cells and they got downgraded to becoming a mitochondria, which is kind of interesting. But that's one thing is we can kind of replicate them to make more of these types of mitochondria via process called fission.
The other concept here is that we can take this mitochondrial DNA and undergo transcription. And we undergo transcription, this makes something called RNA. And these RNA molecules combine with the ribosomes located in the mitochondria. And here's another important point. These ribosomes are called 70S ribosomes. You know what they are in the, the cytoplasm of eukaryotic cells, which we'll talk about soon? They're 80S. That's another question they could potentially ask you, so watch out for that. But from this mitochondrial DNA can replicate to undergo division of the mitochondria, or it can make RNA. And that's really important because you need the DNA to make RNA, you need the RNA to be translated, and the translation process will then synthesize particular types of proteins. And these proteins that it makes generally accounts for about 15% of the proteins that are needed for the mitochondria to be able to perform its functions. So that means it needs a decent chunk, about 85% of the proteins to come from the nuclear DNA, nuclear RNA, then to get translated by the cytosolic ribosomes, and they get transported across the mitochondrial membrane so that it has those functions. That's a really cool concept.
And my friends, that finishes off our discussion on the mitochondria, their structure, their function. I hope it made sense. I hope that you guys take, again, the step-by-step process. We go through the inner, outer membrane, we went through the intermembrane space, talked about their involvement in protein transport, the electron transport chain, and the miscellaneous transport. And then we dug into the matrix a little bit. And then we talked a little bit about how the mitochondrial DNA are involved in replicating itself for the actual mitochondria to divide, or making proteins via transcription, translating those by ribosomes in them, 70S ribosomes, to make proteins for it to function. We also talked about all the metabolic reactions that are plentiful and occurring inside of the mitochondria matrix. I hope it made sense. And as always, the engineers, until next time. [Music] Thank you.