Hi. In this video, we're going to be talking about microtubules and cell division. So, microtubules are extremely important for cell division because they are really responsible for reorganizing the cell during the division process. There are many types of microtubules, so I'm going to go over some you need to know. The first type is kinetochore microtubules, and these are going to attach to condensed chromosomes at specific locations called centromeres. Then you have chromosomal microtubules, which attach to a different place than the kinetochore ones, and they attach to chromosomal ends. So these are going to be at the centromeres, which are in the center, and these are going to be at the end. And they attach to the special protein. You don't necessarily need to know it, but I have it here in case you want to know. You may read about polar microtubules. These don't attach to chromosomes but can actually stabilize other microtubules that are attaching to the chromosomes. And then, you have astral microtubules which extend out from centrosomes, to the cell periphery.
So let's see what this looks like. Here, we have our chromosomes, which kind of look like x's here. We have our polar microtubules which remember aren't attached but help stabilize. We have our astral microtubules and we have our kinetochore microtubules which are attaching here.
Now there are two features that are very common during, that are actually required for cell division. These are the mitotic spindle and the contractile ring. And both of these are formed by microtubules. And we'll go over these a lot more when we actually get into cell division, but I just want to introduce them here because we are talking about different types of cytoskeleton elements. The mitotic spindle is responsible for separating or segregating the chromosomes that are replicated into the different cells that have divided. It takes around an hour for the cellular microtubules to be disassembled from wherever they are and to be reorganized to form the mitotic spindle when the cell is like, hey, I'm ready to divide. So whenever the cell decides it's ready to divide, it's got to create the mitotic spindle and that takes about an hour. So it is kind of this complex process, right? Then you have the contractile ring, which is actually responsible for the very end of cell division, and this is the last thing that separates the two daughter cells during cell division.
So I'm going to show you a picture of the mitotic spindle that's created by the microtubules. You can see it here in green. So, these are the mitotic spindles, and this is in one cell. So here's the cell, and you can see you have a spindle here, a spindle here, and all these microtubules are coming down to attach to these chromosomes, which are labeled here in blue. And so, microtubules, other than these two structures, are important for each step of mitosis. So here are all the steps of mitosis. We'll go over them in a different chapter, but just in case, you just want a refresher, you have interphase, prophase, metaphase, anaphase. And in each one of these, the microtubules do something different. So here, the microtubules, they're long, stretched out. In prophase, they begin to move to the opposite side of the cell. They form these mitotic spindles. Then, they organize the middle or organize the chromosomes to the middle. And then finally, in anaphase, those chromatids have to be separated out. And so, microtubules are responsible for all of those movements. So really important, they pretty much drive cell division. And so, how do they do this? They do it through a variety of pathways, but motor proteins are really important in this process.
So here we have the different steps of DNA replication. Like I said, we'll go through these, but you can see that microtubules, which are these long, spider leg-looking things, are super important. They attach the chromosomes, they separate them into two cells, and then they go back and reform whatever they were doing before division happened. So that's how microtubules are important.
So now let's turn the page.
