Hi. In this video, we're going to be talking about kinesins and dyneins. So, we all know that cells have to transport things throughout the cell because that's how they function and interact with different organelles and different cells. And so, we're going to talk about transport, specifically how they do this and which proteins actually do it. This actually doesn't even have to be cellular; there are just, like, 2 kinds of movement that we're going to talk about. So the first is Brownian movement, and these are random thermal motions. So the best way I can imagine this is if you have a glass of water, and you just sprinkle a little pepper in there, and you actually just watch that pepper really closely. Even if you're not holding the water, even if it's just sitting on a table, like, not no one's moving it, there's not an earthquake, you know, this water is still, you're going to see that pepper still move. And, it's going to move very slowly, but it's still going to move. And, so, that moves, not because anything is pushing it, but because there are just random thermal motions that cause it to float around, essentially. But, that's not the movement we're going to talk about. The movement that we're focusing on is saltatory movement. So this is a jerky stepwise movement, but this movement has a purpose. These things are going somewhere, and they got have something to do. They're not just like pepper, like, randomly floating in a glass of water. There's there a function for this. And usually, they move in one single direction.
So this type of movement in the cell is run by motor proteins. Direction. So they only go in one direction. So the two classes of these are kinesins and dyneins. So kinesins move molecules towards the plus end of the microtubule, which is going to be away from the cell body, so away from the cell nucleus out towards the plasma membrane. There are multiple kinds, 14 families of these, but kinesin 1 is the one we are going to focus on. As an example, it's the most prominent, and it's the one you need to know about. Then, there's dyneins. These move molecules the opposite way towards the minus end, so this is going to be directing towards the cell body.
And dyneins interact with these special proteins called dynactin proteins, and they keep dynein attached and help dynein move cargo molecules over long distances. So the cell is kind of big in relation to a single protein, and so those are kind of very far distances if you're traveling from the nucleus to the plasma membrane. So sometimes they need extra proteins to help them along, help carry, help, you know, keep them motivated to keep going, and so dynactin proteins are that. Now, there are multiple classes of motor proteins, and each one has a different speed. Each one goes to different places and has different functions, carries different things. So, there are kind of these large families. But I think it's interesting that they all have different speeds. So, it is just kind of like, I don't know, different cars, have different speeds and different motor proteins have different speeds as well.
So, here you have examples of what they look. They have this funny shape here, which we'll actually get into in a second. But you can see dyneins are moving towards the minus end, whereas kinesins are moving towards the plus end. So this is going to be towards the cell body, and this is going to be away from the cell body. So, if we were to draw a cell here, the nucleus would be this direction, whereas the plasma membrane would be up here. That's what that would look like.
So, motor proteins, like I just said, they have a specific structure. So, you have these, so they're dimers first of all, so it means there are 2 subunits. And they have 2 heads and a single tail, so they look like this. And so, the 2 heads bind to the microtubules in one orientation, meaning either the plus or the minus end, and they are responsible for hydrolyzing the ATP to ADP as they move along the microtubules. The tail on the other side acts, that's what binds to the cargo and carries it throughout the cell. And, so, the heads go through these repeated cycles of ATP hydrolysis to continually bind and step forward, bind and step forward, bind and step forward and release. So, they just kind of step forward.
And I'll show you an image of that in a second. And so, it's called processive movement when this movement is occurring for really long distances, but it's not falling off, and so motor proteins are like that. Motor proteins can carry things throughout the entire cell without falling off, so they're given a special process of movement term. So here's Kinesin. So here's the microtubule. Let me back out of the way and see everything. Here's the microtubule. You can see the different subunits, alpha and beta tubulin. And, here you have the kinesin with its two heads and its tail. And, you can see that it kind of just like wobbles down, you know. So, here it's bound to ADP. This is, going to be bound to ATP. And, it switches between ATP and ADP, in order to project the kinesin forward, down the microtubule. So, that's how kinesins, dyneins, and motor proteins work. So now let's move on.
