 I meant to show you this picture in the last one. So this is a nice color. Sometimes it's handy, like my little drawings and my little analogies, who will ever forget this? But sometimes it's handy to actually have the more professional visual. And here you can see my primary structure is just my little amino acids. Fold those puppies on each other and then you're going to have secondary structure. Take those secondary structures and fold the holy live and tar out of those guys and you're going to have tertiary structure and then stick a couple of them together and you're going to have quaternary structure. That's actually a Wikipedia image, which means it's totally, never mind, I'm not going to say anything about that on YouTube. Okay, so here we are with your structure, you're good. Now let's look at the three groups of proteins that we're going to build using these different structures. Are you ready? I've already hinted away at one of them. Enzymes. Enzymes are protein machines and they actually catalyze. That's the word catalyze chemical reactions. RXN is windy language for reaction. I think that's a legal abbreviation, too. So enzymes catalyze chemical reactions. So a protein has a shape. A molecule comes in and binds to that protein and a chemical reaction takes place because it bound to the enzyme. Enzymes often are required for chemical reactions to take place in living systems and that's because, like, if you think about it, how unbelievable is it that we can be a walking and working chemical reaction? If you've taken chemistry or you've done rigs by a one, then I've probably blown up the gummy bear for you. One time I blew up a gummy bear and I started a fire. I shouldn't say that on YouTube either. Never mind, I didn't. And I knew exactly where the fire extinguisher was. Anyway, why was I talking about that? Because there's lots of energy in chemical reactions and really the chemical reactions that are life, like we have to control those things or else we'll, like, blow stuff up. Let's not do that. Enzymes help make the chemical reactions happen. Chemical reactions that otherwise would take a really long time to happen on their own. We make them happen fast. How does it do it? The enzyme changes shape. When it changes shape, it causes the chemical reaction to take place. That's not all. We're going to be looking at enzymes. Enzymes are going to help us understand how a whole bunch of the chemistry happens. Here's another one, man. Receptors. Ralph, who is my hero in the land of physiology? Ralph has a shirt somewhere that says, receptors, because really if you're, like, taking a test and you are not positive with the answer is, the answer might very well be receptors because receptors are why a whole lot of things happen in your body. Let's draw a picture of receptor. Guess what it's made out of? Protein. It's protein molecule that's usually found in the cell membrane. I don't know why I colored that puppy in. And there's all sorts of them found in the cell membrane, and they all have different shapes, and they all have different functions. Look at all those different shapes that I'm making. Just for the fun of it. Can you see it? That's my Pac-Man receptor. So each of these receptors, like, will, they're embedded in the cell membrane. So they're different than enzymes, but sometimes the difference is a little bit, really? But they connect to a certain shaped molecule. And that molecule, sometimes it's a hormone, sometimes it's a neurotransmitter, sometimes it's a drug. That molecule, that chemical, will come in and bind to the receptor and when it connects to the receptor, it causes a change in the shape of the receptor, and that actually can stimulate something, some kind of chemical reaction, chemical cascade that causes something to happen. Do something. Seriously, like, that's really how it works. So then here comes a different molecule that binds with this one. Look at that molecule, totally different, it causes a different something to happen. And it's busy, oh! It's so cool, because we're going to get to see, like, ooh, what does this molecule cause to happen? What is this, like, what is that chemical cascade that's happening? We get to figure those things out. It's really exciting. The receptor is usually a protein. And, okay, so what if you're a cell that is lacking that receptor? You can think about, like, that cell isn't going to be doing anything. That cell is not going to be affected by this, whatever that molecule is, whether it's a hormone or a neurotransmitter or a drug. That cell will not be affected because it's lacking the proper receptor. Receptors are an important molecule that we will be talking about a lot in this class. Are we finished? We've got one more, transporters, another transporters. You can, there's probably gray in all of these, which I think is kind of interesting, but a transporter is also found in a cell membrane, and it's a protein that somehow allows stuff in and out of the cell. It allows molecules. A receptor binds to a molecule and then causes something to happen. A transporter will actually bring molecules in. I often make my transporters look something like this, and then you can imagine that there's this little transporter sitting in your cell membrane, and when the molecule that it's going to move comes in there, it can actually change its shape because it's a protein. And then the shape changed, and the molecule is now inside the cell. Totally makes sense, right? Once the molecule falls off inside the cell, change the shape back again. Transporters get stuff back and forth. These are three fantastically important types of molecules that we will be dealing with in physio. So the next thing we're going to look at are chemical reactions in general. You can imagine, I mean, these things we're dealing with chemical molecules, so chemical reactions take place. So let's take a look at the kinds of chemical reactions that can happen.