This is the higher level content from B2.2 on organelles and compartmentalization. If you want to learn about the steps and process of aerobic cell respiration and what's going on in the mitochondria, that is definitely covered more in depth in a different topic. But here in this video, we're going to talk specifically about the features of the mitochondria, the form, to help it perform its job, which is function. So I'm going to start out by drawing a mitochondria, and a mitochondria has two membranes. It has an outer membrane and then an inner membrane, and the inner membrane is highly folded, okay, into this more like squiggly type shape, and those folds in the inner membrane are something called cristae.
Okay, now on the inside of the membrane, or that inner membrane is an area called the matrix. And in between this inner membrane and outer membrane, we have something called the intermembrane space. Now, not the inner membrane space, inter means between.
So this is literally the space between the two membranes. Okay, so I've tried to color code this a bit to make it a tad easier to see. I've left this intermembrane space white, just so you're aware. So these are the adaptations.
That's the form. This is the structure. How do each of these contribute to the function of the mitochondria?
So the outer membrane is going to give us separation from the rest of the cell, whereas this intermembrane... embedded in this inner membrane are all the proteins that I need for the electron transport chain and for chemiosmosis, which if you haven't studied that yet, it's okay. Those are just the processes that help create ATP.
So those proteins are super important, right? So I want to have them, but I also want to have a lot of them. So these cristae, the folds in the inner membrane, make more surface area, which means more electron transport chains and ATP-producing proteins, which is good. Now, inside here in this matrix, we have a couple of important processes.
They're called the link reaction and the Krebs cycle. And if you haven't already studied them, that's okay. Right now, we're really focused on form and function. So the form is that it's a membrane that is enclosing a space. and its function is to really concentrate enzymes.
So making sure that we have a high concentration of these enzymes right where we need it. And lastly, this intermembrane space, I mean, it's just a space, how important can it be? So important.
It's small, and so that's going to allow a high concentration of hydrogen ions or protons to rapidly be established. Again, if you haven't studied this yet, it's okay, but protons are going to get pumped from the matrix into this intermembrane space. And we need a high concentration to develop really rapidly in this intermembrane space. If this intermembrane space were big, it would take us a lot of time and a lot of protons to get a high concentration. But because it's slow, that happens relatively quickly.
So again, Now that we're talking about the chloroplast, we should be thinking about photosynthesis, but the actual process of photosynthesis is covered in another topic. This is about form and function. Now the chloroplast, just like the mitochondria, has a double membrane.
It has an outer membrane and an inner membrane. Yet in the chloroplast, that inner membrane is not highly folded. So that's a little bit different. They're actually like really close together. And so together they make up what we call the chloroplast envelope.
Now a chloroplast has to be able to absorb light if it's going to do photosynthesis. And it uses a pigment called chlorophyll to absorb that light. And chlorophyll is found in the membranes of these little disc-like features called thylakoids.
Inside of a chloroplast, you're going to see multiple stacks of thylakoids. We refer to an entire stack as a granum. If you see multiple stacks you can refer to them as grana with an A that just refers to multiple stacks. And then we have a fluid filled space that kind of surrounds all of these grana and that fluid is something called the stroma. So we'll label that down here.
So I've just color-coded these to keep our eye on some important features, and now let's talk about how they function during photosynthesis. So this envelope again is to separate the chloroplast from the rest of the cell, provide some of that compartmentalization. The role of these thylakoids, and I'm just giving you a broad overview, is to kind of store that chlorophyll which is going to absorb the light, and then inside those silicoids, there's a small fluid-filled space.
And you're going to learn a lot about this in C1.3. But we're going to find that that is a good spot for ATP production. So again, it's really little, just like that intermembrane space. And ATP production is really kind of nice and efficient in there because it's a small space in which you can accumulate a proton gradient, a high concentration.
And much like the matrix of the mitochondria, the stroma is going to be a great enclosed space, kind of like inside that chloroplast, to contain all of the enzymes necessary for the Calvin cycle. Again, it's okay if you don't know what happens in the Calvin cycle just yet, but we need to focus on the form and the function, the structures, and how they help accomplish these jobs. So let's now take a look at this membrane surrounding the nucleus.
It is a double membrane, and we're also going to find that it has rather large pores. Now, these pores are created by integral proteins. Those are proteins that are going to span both sides of that membrane.
And what that does is it kind of creates this very large hole in the membrane, this very large pore. And that's important because there are some large molecules that need to be able to move in and out of that nucleus. For example, mRNA is synthesized in the nucleus during transcription, if you've already studied that.
That mRNA needs to be able to travel out of the nucleus and to a ribosome that is in the cytoplasm. So it needs to be able to get out of that nucleus and needs a rather large pore. You may have also noticed in some of the micrographs of cells that there's a dark spot in the nucleus.
That's something called the nucleolus, and that is the site of ribosome production. So ribosomes are actually produced here in the nucleus, but they need to move out into the cytoplasm or to the rough ER. So they need to be able to get out of that nucleus.
Again, that's a great feature of these larger pores. The double membrane, again, not only does it form a larger pore, but it's also easier to break down. This type of structure is going to be much easier to dissolve and then reform, which is exactly what needs to happen during mitosis. So there are some definite structural advantages here.
Again, form and function, the form being the double membrane, function being able to have large pores and able to be broken down and rebuilt easily. Now, one of the organelles that is not surrounded by a membrane is the ribosome. And in eukaryotes, we will find ribosomes in two spots, free-floating in the cytoplasm and attached to the rough endoplasmic reticulum.
Now, it's protein synthesis that we want to associate with ribosomes. That's what's happening there, and you can find out more about that in a different topic. In terms of structure and function, though, for ribosomes, we really want to take a look at where they're located. because where those ribosomes are located tells us a lot about what it is supposed to do.
Ribosomes that are free-floating in the cytoplasm are going to be producing proteins that are needed within the cell. So these guys are producing proteins that are needed somewhere here in the rest of the cell. Ribosomes attached to the rough ER are going to be producing proteins for secretion.
Okay. So these are proteins that are going to be exported from the cell. So let's say this is a pancreas cell. These ribosomes might produce insulin and that insulin is going to be secreted or exported out of the cell and be sent elsewhere. So again, both of them are producing proteins, but just proteins for uses in different places.
Now when I think about drawing the Golgi apparatus, to me it kind of like looks like a wi-fi symbol a little bit. So it's this network of flattened sacks and there's always going to be associated with the Golgi these little vesicles and that's because the Golgi's function so highly depends on vesicle and vesicular transport. So what's going to happen is that the Golgi is going to receive a vesicle from the endoplasmic reticulum, and that vesicle is going to fuse with the Golgi and release its contents into the Golgi.
So let's say this is a protein. The Golgi is then going to process that protein, and processing can mean a lot of different things. It could mean adding on some kind of a group like a carbohydrate, creating quaternary structure by sticking multiple polypeptides together.
or any number of things. Once it's done processing, it is then going to repackage that protein into another vesicle, and then it can be exported out of the cell via exocytosis. And we'll wrap up this video by just talking about other ways that vesicles can be important to cells. So vesicles are going to be formed during endocytosis, and that's covered more in depth in another topic.
So exocytosis is going to be the opposite of that, right? Having a vesicle fuse with the membrane and release contents into the outside. It's not just getting things into or out of the cell that vesicles are important for.
They're also important for transporting things within a cell, like between the rough ER and the Golgi, or with cell growth. In order for a cell to grow, vesicles might pinch off from the endoplasmic reticulum and then fuse with the membrane, becoming part of the membrane, resulting in a bigger membrane, resulting in growth. So these are all the various ways in which the different forms or structures within a cell can help it perform its function.