Transcription
Hello everybody, welcome to our first, uh, lecture about proteins, or our first slide on proteins.
Um, so the first thing to understand about proteins is that, based on this little piece of information here, it says proteins are polymers. Now, this word polymer, we've seen it before. Uh, whenever you see the word polymer, you should be thinking of a molecule that is very long. It's like a chain, and it's long because there's, um, one thing that's repeated over and over again, joined up together. Kind of like, um, all the cars on a railroad chain, railroad train. So a long, long molecule, but it's made long because there's lots of things that are repeated over and over again and all hooked up.
Now, this picture down here kind of clearly represents a polymer because it's, you can see the repeated things are these beads. They've got different colors, but they're, and they're all hooked together in a chain. So this is one way that we can show a protein. But we've been seeing proteins before when we were learning about membrane pieces and parts, and they're usually drawn as these blobs, more like this kind of blob thing, or the, the collagen, the long purple wormy things. And what's misleading in, in these kind of diagrams is it looks like this is like solid, right? It's all colored in. It's really not solid.
Um, what I'm going to, and what I'm going to use for the rest of this video, or the rest of these videos on proteins, is, is this is a model to kind of simulate proteins. So I don't, if you can see these, this is just a bunch of pony beads, different colors, all strung together on wire. So I can move them around. And so when you see these purple blobs that look like a solid thing, it's not a solid thing. It's actually a long chain of parts all put together like this. The beads are the parts, and it's all kind of tangled up into a big lump like this. So you know, this looks sort of solid, but really it isn't. Really, it's a chain, and that's what this purple is supposed to be. It looks solid, but it's not. It's a big old squiggly chain of a molecule, all tangled up like this. So that's what we're gonna get into in this whole next series of slides is proteins and their structure.
So proteins are polymers. They're made of this repeating unit, and the thing that repeats in proteins is called an amino acid. So come on, let me go forward. Each, uh, bead on this chain is a single amino acid. So on my model here, each individual bead is representing a single amino acid. So my protein is pretty long, you know, it's got, I mean, maybe 200 of them all hooked together in a long chain. All right.
So what we're going to do next is look at what these amino acids look like. So this is a molecular structure of an amino acid. This is one of the last molecular structures I'm going to have you look at and memorize. So I do need you to be able to memorize and recognize this. Now, amino acids are pretty easy to recognize and learn, and we're going to go through the parts right here.
So, um, every amino acid, let me backtrack. There are actually, um, 20 different amino acids that exist in nature, and those 20 different amino acids are used to build all the proteins that we use in our bodies. So you can think of the amino acids as the letters in our English language alphabet. Um, so in the English language, we have 26 individual different letters, A through Z. But we can take those different letters and we can arrange them in groups, um, different orders, and different lengths of letters, and we can make all the words in the dictionary. So while we only have 26 letters, there's, I don't know, hundreds and thousands of words that we can make with the 26 letters by arranging them in different orders and different lengths. And that's exactly how amino acids work for proteins. There's only 20 of them, 20 different ones, but you can arrange them in all kinds of different orders and all kinds of different lengths. And every time you make a different order, every time you make a different length, you're making a different type of protein.
So on my little model here, you can see I've got different color beads. There is 20 different color beads. They're arranged in different, in this order. So yellow, yellow, if you can see this, yellow, yellow, pink, purple, yellow, white, pink, yellow, yellow, purple. This is one protein. If I had another chain with a different order of colored beads, it would be a different protein. So for example, one might be hemoglobin, and one might be insulin, or one might be keratin, or maybe collagen, or something like that. Right?
So let's look at this amino acid here. Um, so to start with, with an amino acid, you're always going to have a central carbon right here. All right. So that's our central carbon. It's also known, known as the alpha carbon, like alpha, like the most important, the alpha carbon. And so, uh, carbon makes four bonds, four covalent bonds. So here are its four bonds: one, two, three, four. Right. Um, and for an amino acid, it's set, what's going to be on each bond. So, um, one of the things you're going to find on the bond is the, on the carbon, is the amino group, which is where you get the name amino acid from. All right. So one of the bonds is going to go to an amino group, NH2. So you should know your functional groups by now. There is my amino group. On another one of the bonds, we're going to have a carboxyl group. Again, you should recognize the carboxyl group: C double bond O, OH. Right? That's carboxyl. And carboxyl groups are also acidic in nature. So that's where the acid comes from. So this is amino acid. That's how it gets its name. All right.
Um, so we've got two of the bonds dealt with. On one of the other bonds, there's always a hydrogen atom. So there we go, an H. And then on the fourth and final bond, we're going to put something called the R group, also sometimes known as the side chain. So some textbooks call this the side chain, some textbooks call this an R group. All right. Here they're kind of using both because they've got an R and they're calling it a side chain. Um, and the side chain is how you, if you were to look up R in the periodic table, there is no R. So you're like, what is this? What could R be? R is standing here for, um, something different for each amino acid. So there's 20 different things that can go here, 20 different sets of atoms could be joined on here, and that's what makes one amino acid different from the next. That's what creates the 20 different amino acids. All the amino acids have this in common. They're all going to have the amino, the hydrogen, and the carboxyl group. And then there's going to be a side chain. And depending on the amino acid you're looking at, that's going to specify what side chain it is.
So let's go through that one more time. I'm going to draw one out here. I'm going to try and make it neat, but I can't promise anything. So, and if you're going to draw an amino acid, you're always going to have a central carbon. And that central carbon is always going to have four bonds because carbon makes four bonds. Any carbon is going to have four bonds. All right. One of the bonds is going to have the amino group for the, um, I mean, the name amino acid. There's my amino group. One of the bonds is going to have a carboxyl group: C double bond O, OH. Right? That's my carboxyl group. Uh, one of the bonds is gonna have an H, and one of the bonds is gonna have your R group or your side chain.
Now, uh, on purpose, I drew this one, this, in my example, flipped around compared to that one. On this one, the H is at the top and the R is at the bottom. Do you see that? On mine, I put the R at the top and the H to the bottom. It doesn't matter. These are all kind of like, they can all rotate around. It doesn't matter the order you draw them on. If you really wanted to get wild, you could even do that. Go away. You could even do the carboxyl here and the R over here. It doesn't really matter where they're placed, as long as on one bond you've got the amino group, on one bond you've got the carboxyl group, on one bond you've got the R group, and on the other bond you've got the hydrogen. So I mean, you won't often see it drawn out like this in this kind of weird arrangement. Usually, you see it either like this one, or like the first one I drew with the amino group on the left, the carboxyl on the right, and the R and the H at the top or bottom. All right.
So that is a generic amino acid and a basic introduction to proteins.