 There's another structure that we're going to, or another protein transporter that enables facilitated diffusion. And I'm sorry about this, but it's called a transporter. I wish I would have used a different word. All of these things are kind of protein transporters. The difference between a transporter, a true transporter, and I don't know how we want to describe this, we're going to distinguish between transporters versus channels. Even though you could argue that channels are kind of like protein transporters, but transporters are active, so watch and be amazed. First of all, here's my cell membrane, and those are my two layers of cell membrane. A transporter is like that little thing that I just started to draw. It looks like, I'm sorry about my picture, it looks like a little, oh, you know, they all look different. So I shouldn't say what it actually looks like, because that's the windy version. That's how I visualize them. Like a little transporter is a protein, and a molecule like, let's say, my good buddy, glucose. There's a little sticky spot in the transporter where glucose can fit. So glucose, transporter is open. Transporters engage in facilitated diffusion. So what has to be true? If I want to take that glucose molecule and move it into the cell, what has to be true? We have to have a high concentration of glucose outside and a low concentration of glucose inside. Do you agree with that? Only if that is true will my facilitated diffusion transporter work. The interesting thing is that transporters can work both ways. They can move glucose into the cell in these circumstances, or if the circumstances change, they can move glucose out of the cell. Along comes your glucose molecule. There's lots of it out here. It attaches to a binding site in my transporter, and this is where an acceptance of, it's a protein with protein structure and the act of glucose binding to the binding site causes the protein to change shape. That's it. Why? How? Doggy dogs go on out and you study organic chemistry and I'm sure I guarantee someone somewhere has a phenomenal explanation that includes a great deal of math and math, but they know why. I don't know why, but that's cool. The fact is it happens. And when the shape change happens, the binding of glucose causes the shape to change. And now the shape changed. So what happens to my binding site? It changes shape and glucose doesn't stick anymore, so glucose falls off. Wow, that is so cool. Once glucose falls off, the shape changes again. What? And then my little binding site is available again. When the binding site is available, we can have something bind and then the shape changes and it dumps it out. We can have transport simply because of that, simply because of those shape changes. This specific transporter that I'm talking about is going to change shape. I didn't draw it all out, but that would be really cool in your notes to draw a picture of the whole thing happening. It's going to dump the glucose inside the cell and it will dump the glucose in the area of low concentration. All right. Oh yeah, what I was going to tell you is that this thing, this transporter is called a glutt transporter. And we will see it again. There are a few transporters that we're naming. We're naming them because we're going to see them and name them when we talk about how cells function in various body systems. The glutt we will see often. Glucose transporter seems like kind of an important one, don't you think? All right, sometimes we need to pump things not down a concentration gradient. Sometimes we need to pump against a concentration or we need to transport against a concentration gradient and that's where we have a different strategy.