 Okay, welcome back everybody. Before we move on to a new topic, this is a summary slide. Again, just trying to pound this information into your heads. Amino acid molecules are connected to each other to make protein molecules. That's all we've been talking about so far. Amino acid molecules that are connected in this way are sometimes called polypeptides, usually called protein molecules. The new topic here is essentially biology. What do protein molecules do? Well, they do anything and everything in the cell. If you can think of a job that your cells need to do, there is probably a protein molecule that is devoted to helping out or doing that job. Just some examples. Your cell is basically like a room or a house. There have to be beams that hold the ceiling up and hold the roof up and things like that in your house. Well, there are protein molecules that help keep the cell to be a certain shape. In other words, there are protein molecules that help prevent the cell from collapsing on itself. That's one job that a protein molecule might do. There are other jobs that speed up chemical reactions. Molecules in living cells that speed up chemical reactions have a special name. They are called enzymes. We will talk about that in a later video here. Some examples of enzymes. There are enzymes that carry other... So there are protein molecules that carry other molecules around in the cell. That might be the job of a protein molecule that pick up another molecule and take it somewhere. There are protein molecules that are involved in copying your genes. Whenever your cells divide and each new cell needs a copy of your genetic material, there are protein molecules whose job is to help make those copies. That's another job. There are protein molecules that help make your muscles move. Obviously, that's a job. There are protein molecules that carry oxygen from your lungs to other parts of your body. You may have heard of this particular protein molecule. It is a molecule. It is a protein molecule called hemoglobin. Hemoglobin is a special protein molecule whose job is to pick up oxygen from your lungs and carry it to other parts of your body that need the oxygen. That's just another job that a protein molecule might do. And there are many others. The punchline of this slide is that there are many different types of protein molecules and each type has its own special job. Just to talk about human proteins in more detail, the estimate is that there are about 25,000 different types of protein molecules that humans can make. So every one of your cells is basically capable of making about 25,000 different types of protein molecules. Each type has a specific job that it is supposed to do. Now for any one particular cell, if you have a cell on your skin, it's probably not going to make all 25,000 different types. It's probably going to make a small number of that 25,000 that helps a skin cell do whatever skin cells do. And if you have a heart muscle cell, it's going to make a different collection of protein molecules that to help it, to help the heart muscle do whatever heart muscles do. Again, each type of protein molecule has a different job. The thing that makes protein molecules different from each other is the order and the type of amino acids that you connect to each other. For example, if I connect a proline amino acid to an alanine amino acid to a glycine amino acid, that is a very tiny protein molecule. Probably doesn't really have a job. I just made it up, but maybe if I connect these amino acids in this particular order, then that protein molecule might do one specific job. If I connect different amino acids in a different order, I might make a protein molecule that does a different job. The type of amino acids and the order that you connect them in has a special name. It's called the sequence of amino acids in your protein molecule. So if I had these particular amino acid molecules connected to each other in this order, and I said what's the sequence of the amino acids in my molecule, you would say, oh, it's proline connected to alanine connected to glycine. Usually you'd put a little M there and a little C there from a previous video. So that's what sequence of amino acids means. It means the kind of amino acids and the order that you connected them in. The only thing that's really different about those amino acids is the side chains, right? All the other parts of the amino acid molecules are identical. It's basically the order that you connect the side chains to each other in that makes different protein molecules have different jobs. Now, on this particular slide, I'm just going to try to show you an example of one specific type of protein molecule doing its job. This weird picture here, this is a frog embryo. Each of these things that I'm circling here, these are cells inside of the frog embryo. So this is very early on for the embryo. If this got enough food and the cells divided enough, this would eventually turn into, I guess, a tadpole, then that turns into a frog. But right now it's just basically a blob of cells and just to orient you some more, right? This is one cell, that's another cell, another cell, et cetera, et cetera. These yellow things, these yellow stuff, is the DNA inside of each of the cells. So this is little froggy DNA, this is froggy DNA, et cetera, et cetera. The blue things that you see, this blue stuff here in the cell, those are one type of protein molecules, many, many copies of the same type of protein molecule. The job of this particular protein molecule is that when this cell divides, this blue protein molecule is going to yank one of the copies of the cell's DNA to the new cell. So if there's going to be a new cell that forms over here, these blue molecules have to pull one copy of this yellow stuff, one copy of the DNA over into the new cell. And these blue molecules over here, they have to pull on one copy of the DNA and yank it into the new cell as well. And basically, that's the job of these blue protein molecules. They have one specific job, it's to pull the DNA into the new cell, so that every new cell gets the correct amount and the correct type of DNA that all the cells need. And I'm just going to show you a video of that. This is a time-lapse video of the frog embryo cells dividing, and you can see that you'll be able to see the DNA getting yanked into the new cells. It's probably good to focus on this one over here. You can see that they got pulled, that yellow stuff got pulled in opposite directions. I think it'll repeat. Here it is repeating, so this cell is going to divide, and then that yellow stuff gets pulled in opposite directions because the blue molecules are pulling it. The blue stuff that you're looking at in those cells, that's just one type of protein molecule. There are thousands of others running around in each of those cells that are doing other jobs. You just can't see them because whoever made this video found a special way of highlighting just one protein molecule. Like I said, there are many other types of protein molecules in those cells that you just can't see that are doing other jobs. And this is the last slide in this particular video. There are other videos coming, but this is the last slide for this video. This is just kind of a silly mind game, but here are two words you may have heard of these before. Usually students have heard the word rabies before. That's a disease that you can get from certain animals. That's not the greatest disease for people to get. Serbia is certainly not rabies. It is a country in Eastern Europe. But the point I'm trying to make with these two words is that they are made of the same letters, but they mean different things because the letters are arranged in different ways. With English, we have 26 letters in our alphabet. But we can make hundreds of thousands of different words with just 26 letters, and each word means something slightly different usually. But the only thing different about the words is the way that we arrange the letters. If I arrange the letters this way, I'm talking about a country in Eastern Europe. If I take the same letters and I arrange them in a different way, I'm talking about some disease. The point that I'm trying to make here is that you should think of the amino acids. How many do we have universally? We have 20 of them. You should think of the 20 amino acids as kind of like letters, like letters in our alphabet, and the way that you connect the amino acids to each other gives you different protein molecules in the same way that we connect letters and we get different words that mean different things. Different protein molecules have different jobs. What do I mean by different molecule? How are they different? They're different in the way the order that the amino acids are connected to each other in. For example, I'm using the three-letter abbreviation here. If I take valine and connect it to leucine, connect it to serine, proline, alanine, and keep going, I will make hemoglobin, which its job is to carry oxygen from your lungs to other parts of your body. But I only get hemoglobin if I connect these amino acids in that particular way. Hemoglobin keeps going on. That's what the dot dot dot means there, but this is the beginning of it. If I connect different amino acids in a different order, if I connect lysine to lysine to glutamic acid to glutamic acid, etc., I make a protein molecule called myosin which helps your muscles contract. And on and on and on. If you connect the amino acids in a different way like this, you make a protein molecule that helps to copy your DNA. I'll stop with the examples there. The point I'm trying to make here is that each different type of protein molecule has a different amino acid sequence. And again, sequence just means the order that the amino acids are connected in. And different sequences give you different behaviors for the protein molecules, give you different jobs. The fancy way that chemists and biologists say this, they love saying this, is they say amino acid sequence dictates function. That is just a fancy pants way of saying the order that you connect the amino acid molecules to each other in controls what job the protein molecule does. That's all it's saying. But you might hear that. You might hear that in A and P for all I know. And that's the end of this video. More stuff coming up.