Transcription
All right, so in this slide, we are looking at, uh, the something we call the phospholipid bilayer. This is something that was introduced at the very end of the previous unit. And so, the phospholipid molecule, first of all, we learned about them. Uh, here's a, here's a diagram of one of them. There's a whole bunch of them all lined up here. They have, in this diagram, you see they have a purple head and they have two zig-zaggy tails. And if you remember from the end of unit one, phospholipid molecules have, um, a head portion that is charged, and so it likes water. It's hydrophilic. And the tails are uncharged or nonpolar, and so they do not like water.
And when you dump these molecules in water, and that's what this kind of colors, this is supposed to be water here and water here, um, they will arrange themselves in this kind of sandwich formation, um, so that they, uh, push the water to the outside and down here. And then you've got this greasy, high hydrophobic core. Let me fix my pen here, it's kind of thin. Um, this is a hydrophobic core and hydrophilic heads on either side.
All right, so this phospholipid bilayer structure is, um, what basically makes up the membranes that wrap around every living cell. Every cell is surrounded by a membrane. And on this slide, you can see, um, one, two, three, four, five different pictures of, um, phospholipid bilayers. The first one right here in the middle, uh, a very cartoony-looking one, purple and yellow. And then over here, we see the molecule shown in different ways. So let me change color so you can see my pen. Um, so here you can see the heads at the top and at the bottom, and then the tails are these gray pieces. Again, you see the same thing over here.
Now, the bottom diagrams, I really like these diagrams because it's showing all this green stuff. Like, what is this green stuff supposed to represent? I'm going to give you a few minutes to think about this. So, what's all this stuff here and all this stuff here? What do those green things represent? So, in these diagrams, that green mass is representing all the bajillions and gazillions of water molecules that are in a living organism. And you can see how they're just, they're so crowded together here on the outside, and they're so crowded together here on the inside. But separating the outside from the inside is this hydro, hydrophobic core of the phospholipid bilayer. So it represents the boundary between out and in.
Now, obviously, from this diagram, there's no way to tell which side is the out and which side is the in. I just labeled them arbitrarily. But you can see how the water molecules are kind of helping to keep this bilayer in place. If you got rid of all this water, if all this green stuff wasn't here, then there'd be no reason for the molecules, the their phospholipid phospholipid molecules to arrange themselves in this bilayer. They wouldn't have to get their tails away from the water because there'd be no water there to get away from. And so the presence of water in our bodies actually helps to maintain the structure of our membranes because it holds this bilayer sandwich kind of structure in place.
Uh, so I have another diagram right here. I'm just going to skip to, uh, which is a bit more complicated. Um, but again, you can see the phospholipid bite, bilayer. The yellow are the heads and the green are the tails. So lots of them all clustered together. And then in this diagram, look at all this water up here. Oh my gosh, you can just get an idea about how crowded it is molecularly inside of your body. I mean, there's molecules everywhere. I love this picture just because of the visual it gives you of the water crowding on either side of the, um, of the membrane. You can see something purple hidden in here, and we're going to get to what that is in a couple of, um, slides' time, but hold, hold your thought on that.
Now, I'm going to go back to this slide and, um, this cute little guy here who is, um, wiggling around. Um, so in all of the diagrams, you know, around the outside here, uh, it's very static, right? The the phospholipids are all lined up. And even here, this one for sure, they look like little soldiers all lined up one by one in a row. That's really not what it's like in inside of a in a cell membrane. Um, if you remember from before, we learned about how temperature is really a measurement of how fast molecules are wibbling around and moving. And your body is quite warm. Your body is at 37 degrees Celsius, which is 98.6 Fahrenheit. And so that's pretty warm, which means all the molecules inside your body are moving. They're jiggling around, and that includes the phospholipids that make up the bilayer.
Um, so, uh, he just stopped. I don't know what I clicked to make him stop. Let's see if we can get him dancing again. Hold on. Oh, okay. My, um, PowerPoint keeps freezing up today. So we're just going to go with it from here. Um, so all these phospholipid bimolecules are jiggling around side by side, uh, in this bilayer. So they're constantly moving. It is not this rigid, uh, soldiers all lined up making a a hard barrier. It's very, very dynamic, and the phospholipid molecules can wiggle away from each other and wiggle back together, and their little chinks open up when they dance. When we are dancing next, it's like if you imagine a very crowded dance floor full of people trying to dance. They're all shoulder to shoulder, and they're doing their best to dance in a club or something. Um, every now and then they'll bump into each other. Every now and then they'll dance apart, and a little gap will appear, and that kind of happens all the time in the three-dimensional structure of the membrane.