Hi. In this video, we're going to be talking about intermediate filaments. So, intermediate filaments, they're cellular components that work to provide the cell with great strength, specifically tensile strength. This just makes the cell really strong and durable. And so, because they make the cell durable, they also have to be the most durable cytoskeletal filaments. They allow the cell to withstand mechanical stress, like pulling, pushing, or twisting. Those types of movements are what intermediate filaments excel at, and that's what they do. They allow the cell to withstand those movements without having the cell completely collapse or break apart.
The reason they have this movement is that intermediate filaments actually form these long strands that are wrapped together, kind of like a rope. A rope can very easily handle being pulled by people, and it doesn't rip in half. It can be pushed together, or it can be twisted, and it doesn't break the rope. Intermediate filaments are exactly the same; they can be pulled, pushed, twisted, but it's not going to break them, and because of them, it's not going to break the cell.
Intermediate filaments work because they're anchored to the plasma membrane, and the nucleus. They are anchored to various portions of the cell, and it's kind of like a rope attaching the nucleus to the plasma membrane. These attachments allow them to float, push, pull against each other, but because they have these intermediate filament "ropes," they don't break apart. Intermediate filaments are formed by individual subunits that link together to form one filament, which makes sense. Then, two filaments form dimers by binding a specific domain called the alpha-helical domain on each of the subunits. So, the subunits are the small things that link together, and each one of them has an alpha-helical domain, and so when they form these filaments they have a bunch of alpha helical domains which allow the filaments to form dimers.
Two sets of dimers come in and arrange themselves in opposite directions, called antiparallel, and they form a tetramer. So, first, you start out with these small subunits to form one filament, then there are two filaments that form dimers, and then two dimers work together to form these tetramers. Importantly, it is important to note here, and you probably don't know why, but I'm going to tell you why in later videos, that they are unique because both ends are the same. I'll show you a picture of what that exactly means, but this is very unique to the cytoskeleton. Usually, everything else has ends that are not the same. So, the fact that intermediate filament ends are the same is a unique feature.
Intermediate filaments are super important. If they're mutated or something's wrong with them, they cause severe diseases like ALS. If you remember the ice bucket challenge, that's ALS. Progerias, a type of advanced aging. They have TLC shows about it. But, yeah. That is intermediate filaments. So this what they look like: So here you have a monomer, and this is made up of a bunch of subunits. So, we'll just say the subunits are here. They're much smaller than that in real life, but it doesn't really matter. So, you have this monomer. Two of those strands form a dimer that are wrapped around each other, and then two dimers form a tetramer. And what you'll see here is that the ends of all of these are exactly the same, which I said was important. So, now there are four classes of intermediate filaments.
The first, let me back out so you can actually see this. The first is keratin, and this is going to be in things like epithelial cells, so that's skin cells. You have the special class of vimentin or vimentin-related. And, these are going to be found at the nucleus into the cell periphery. You have neurofilaments, which are exactly where you think they are, they are going to be in the neuron. And then you have nuclear lamins, and they support the nucleus. So, those are your four classes. Important to know those four classes of intermediate filaments, just because we're not going to go over really anything else to do with intermediate filaments. So, it's a small amount to know about intermediate filaments, so you should probably know it. So, well, let's move on.
