Transcription
Down below here, uh, in the inside of the cell, so I want to make sure we label this so everyone knows what we're looking at. This is the inside of the cell. Um, this is our phospholipid bilayer, the the barrier, and then this is the outside environment. Now, I'm going to go through two things in this presentation: these, um, orangey strandy things, and then these giant purple worms. All right, so we'll start with the orangey strandy spaghetti looking stuff down here, and this is the cyto, yeah, cytoskeleton. Okay, so the word cyto means to do with the cell, and the skeleton is a skeleton, so this is the skeleton of the cell. Now, this is not a bony skeleton. You're, you know, this is tiny. We're inside of a single cell, and so these are protein molecules, these long, uh, ropey looking things. Um, they should probably be purple, but anyway, uh, to follow along with what we, the color coding here, but anyway, the cytoskeleton is made up of these long, rigid protein fibers. Proteins can be in all kinds of shapes and sizes, and so one thing proteins can do is make long strandy things, and they can be sort of quite rigid, but with a bit of flexible effects to them. And so I want you to think about the cytoskeleton inside as kind of like the tent poles inside of a tent. So if you were to imagine, um, a tent when you take it out of the bag, uh, it's just like a flat piece of fabric, and it doesn't have any shape or structure until you put the tent poles inside, and the tempos kind of poke it out in different directions and build it into whatever shape the tent's going to be, right? Kind of the same thing with a cell. A cell is just a membrane baggy with water inside. So if you just had it on your hand, it would just flop flat like a baggy, Ziploc baggie full of water. So to give this cell its shape, its three-dimensional shape, you have to start kind of poking it out and holding it into these shapes, and that's what the cytoskeleton fibers are there for. They can be built in all kinds of different shapes, so you can have a long, flat cell, you can have a cubic cell, you can have a long, skinny cell. Um, they, cells can take all kinds of different shapes, and that's kind of controlled by how the cytoskeleton fibers align and push out the membrane and keep its shape. But that's the cytoskeleton on the, um, inside. Let me just write that again. Sorry.
All right, on the outside, though, we have something different. This is called, this is long, the extra, which means outside of cellular, so outside the cell matrix, the extracellular matrix, which is a ham, which is a handful, a mouthful. So we like to call it the ECM for short. So the ECM, this is a collection of giant, long, wormy proteins, right, which is what these are, and then these kind of more fine fibers that are made of combinations of polysaccharides, that's why they're green, long chains of sugars, and also some proteiny parts stuck onto them. So this is like, this is like a combination of, um, like another kind of glycoprotein, sugars and protein all fiber together. Now, what are these for? Well, I'm going to write one on here. This purple worm is representing a specific protein called collagen, which you've probably heard of. Now, what the extracellular matrix does is it kind of glues the cells together, um, from the outside. So if you imagine all these Ziploc baggies all piled together, what's going to hold them together? All right, so you have multiple things going on here. The fibery stuff, the feathery fibery stuff, this is kind of like, like a gluey matrix that kind of just goops it all together. The collagen fibers, though, are more kind of more interesting, and they're more like giant bungee cords. All right, so if you think of a bungee cord, it's stretchy, and it has hooks on two, on both ends, and you hook it on one thing, you stretch it, and you hook it on the other thing, and it cinches the two things together, right? And that's kind of what you can imagine collagen doing here. Here, look, it's hooked into the membrane, so it's anchored in here, and then this fiber is going to stretch all the way across to the neighboring cell over here, where it's gonna, can't see it on my diagram, where it's gonna hook in to the neighboring cell, and it's gonna sort of cinch these two cells together so they kind of are close together. And so these giant collagen bungee fibers and this more feathery, um, glycoprotein on the outside kind of just cinch and glue all the cells together to make them more stick. So that's how your liver doesn't disintegrate, or if you buy a steak, which is basically a bunch of cells all glued together, it doesn't fall apart. It's held together by all the collagen fibers that glue the cells together.
Now, collagen is interesting. Um, it's, it over time in our body, we, um, make less of it and it gets destroyed, and, uh, so our cells become sort of less and less elasticy, and you can see that in your skin, right? Um, so, you know, a young kid, if you kind of pinch the, the skin on their hand, it springs right back, it's really bouncy. Now, as you get older, it gets maybe less bouncy. When you're kind of middle-aged like me, you know, I can pinch it up and it will stay, it will go down slowly, but it's not quite as bouncy as it used to be. And if you have an old relative, you can ask them very nicely if you can test their collagen, you can see on their hands, it probably won't bounce back very quick at all. And that's also what's happening on your face as you age and get wrinkles. Um, the collagen is, is gradually over time, um, degrading, and it's going to lose its sponginess, and so eventually your skin will start to not be so springy, and that's what causes wrinkles. And there's really no way to avoid it. It's kind of one of those things. Um, but I guess it is interesting to understand why it happens. And later on in this unit, we'll talk a little bit about, um, collagen, um, creams and that kind of stuff, and why they're probably not a great thing, probably just a waste of money. Anyhow, we'll get to that later. But, um, this, this was the call, the extracellular matrix and the cytoskeleton part of this diagram.