Transcription
We mentioned in a previous video how um phospholipid molecules are incredibly common in your body because they make up your cell membranes. So I wanted to spend a little bit of time thinking about how that happens.
So if you were to imagine that I had a spoonful of phospholipids, uh, and I was to dump it in a beaker of water, as soon as those phospholipid molecules go into the water, they're going to start interacting in a very specific way with the water molecules. So here is the first thing that they might do. This is called a micelle. Now, this is cut through. In real life, it would be like a sphere, like a ball. And these molecules, these phospholipid molecules, you can see each one. Look, remember the phospholipid molecules have a head that likes water and two tails that dislike water. So head, tail, head, tail, right? So there's many of them here. And again, this is two-dimensional because it's cut through, but really it would be a big ball sphere. And in this example, the blue represents the water. And so we can see how there's water all around here on the outside, and it's touching the heads of the molecules. And that's okay because the heads of the molecules have charges. The water is attracted. They're attracted to the water. There's interactions. This is all happy. The tails, on the other hand, of these molecules have no charges. They hate water. Water hates them. They want to stay away from each other. So the greasy tails are sticking together and pushing out the water. And so you can see how this is arranged with all the tails pointing to the interior of this bubble, and there's no water here. Water is missing, and all the water is around the outside. So this is one thing that these these phospholipids can do. They can create this thing called a micelle.
All right, so that's number one. But here's another option that these phospholipids can do. Um, they can arrange themselves in this kind of a formation. And this is called a phospholipid bilayer. By means to, layer means layer. So we have two layers of phospholipids. Here's the top layer, here's the bottom layer. And they have arranged themselves in such a way that the water is touching their heads along this side, and the water's touching their heads on this side. And then the tails that hate the water are hanging out with each other, and the water is excluded. So this is like a greasy area with tails and no water is here. All right. Um, so this allows the the water molecules and the phospholipid molecules to co-exist and to interact in a way that everyone is sort of stable and happy. That the hydrophilic heads get to touch the water, and the hydrophobic tails get to stay away from the water.
Now I want you to kind of imagine if I was to take this this phospholipid bilayer down here and extend it around in a ring. I'm going to run out of some space, but I'm going to try here and draw. It'll take me a bit, but imagine if I made this longer with more phospholipids, so like lots and lots of phospholipids. Now I'm going to draw them. I'm going to skip some. I'm going to draw them all the way around here. You can see that, right? Yes. All the way around here. I draw the tails if I can. So all these circles represent the heads. All these tails represent the the hydrophobic tails. Getting better at using this pen. It's still not super tidy, but we'll see. So that's the the top part of the bilayer. And then I'll do the bottom part. We'll extend this all the way around too. I'm going to skip some again because I don't have all day to draw little phospholipids. And I'm going to draw these tails going this way. All right. Art was never my strong soup, as you can probably tell, but you can kind of get the idea, right? That that this top layer of phospholipids is extended all the way around, and this bottom layer is extended all the way down. Let me fill that gap in there. There's one pair like that. All right. There obviously wouldn't be gaps in between. It would be all filled in, but I've taken that phospholipid bilayer and I made it much longer and I've wrapped it around them itself and joined it up at the bottom. What I've done here is I have got water outside here, and I've now got water trapped on the inside here. Do you see this? And then in between the water on the outside and the water on the inside, there is this barrier of um hydrophobic, oops, phobic tails. Goes all the way around. Hydrophobic. This whole area through here is the hydrophobic tail area, and it separates the outside from the inside. All right. Gosh, what a mess. Anyway, I hope you followed that because what I created there was um, basically a cell. This phospholipid bilayer that's wrapped around here on itself, that's created a puddle on the inside and separated it from the water on the outside. That's the beginnings of a cell.
All your cells in your body have this phospholipid bilayer membrane wrapped around them, which separates the stuff on the inside, all the water on the inside, from the water on the outside. Really, it separates living on the inside to the non-living on the outside. So that that membrane, that barrier, is the difference between life and death in a way. And it only forms this barrier because of the way the phospholipid molecules are structured, where the heads want to touch the water and the tails want to stay away from the water, which encourages them to make this kind of sandwich bilayer thing so that the molecules are comfortable touching what they want to touch. All right. So that was a little intro to where we're going to go in unit two, um, and why knowing about how all these molecules is super important to understanding how cells and the other parts of biology actually function.