Microfilaments and intermediate filaments

- [Voiceover] Microfilaments are found in the cytoplasm and they are composed of a protein known as actin, and many molecules of actin will join together to form an actin polymer. And then the actin polymers will twist around each other to form an actin filament. Microfilaments are mainly involved in the gross movement of the cell. And microfilaments are dynamic, and what we mean by that is that they can lengthen and shorten very frequently, and in that sense, they're similar to microtubules. So, they become longer in a process known as actin polymerization, and they become shorter in a process known as actin depolymerization. And it's the polymerization and depolymerization that helps to move the cell. So, one example of where microfilaments help with the gross movement of the cell is during cell division. So the cell at some point is going to be pinched in that way and then eventually it'll separate into two separate cells, and the microfilaments help the cell make that kind of pinched shape, and then move to create two separate cells. Another example of where microfilaments help with the movement of a cell is in an amoeba. So let's say here is our amoeba cell, and we're gonna say that it's trying to capture this piece of food right over here. So in order for it to do that, it has to extend its pseudopods in that direction, and move it around that food molecule. And what helps those pseudopods move? The microfilaments. Let's move on to intermediate filaments. So, intermediate filaments, in contrast to microtubules and microfilaments, are made up of many different types of proteins that are strung together into polymers. These polymers twist together to make the intermediate filaments. And intermediate filaments are different than microtubules and microfilaments in that they're pretty much permanent. So, once they're made by the cell, they kind of stay put, as opposed to microtubules... I'm just gonna abbreviate like that... and microfilaments that we explained are dynamic. They constantly change depending on the needs of the cell. So, what do intermediate filaments do? Well, they provide structural support for the cell. Or another way to say this is they resist mechanical stress. And in the picture it almost looks like the intermediate filaments are this supporting wire, and if you recall in our introduction to cytoskeleton, we mentioned that the intermediate filaments can be compared to the springs inside of a mattress. So, if you were to sit down on a mattress, you might squish it a little bit, but once you stand up, the mattress will revert to its original shape, thanks to the springs inside. So the intermediate filaments, in blue in this picture, act in the same way.