Overview of the Cytoskeleton - Video Tutorials & Practice Problems

Cytoskeleton Overview

Hi. In this video, we're going to be talking about an overview of the cytoskeleton. So what is the cytoskeleton? Well, the cytoskeleton is kind of like a country's roadways. Right? So in a country, people need to travel around to different cities, or they need to transport goods, and that's exactly what the cytoskeleton does for the cell. And so the cytoskeleton is this intricate network of roadways essentially that go throughout the entire cytoskeleton, but instead of being made of concrete, these roadways are made up of different types of protein filaments. And these protein filaments are very organized, just like our roads. I mean, we can look at a map, and we can get anywhere we want to, just by using our road systems. The same thing is in the cell. It's very organized. But unlike the roadways, the cytoskeleton is dynamic, and so what this means is that it is constantly moving and responding to the environment. So our roadways, whenever we make a road or a highway, that pretty much stays there. Right? Like, sometimes they tear down a road or two, but it's not that every single day that road is moving and changing places. The cytoskeleton is much more like sort of those moving staircases in Harry Potter. They're constantly moving, readjusting their direction. They can be taken apart, put back together in just a matter of seconds. And so, they're constantly moving and constantly responding to their environment. So, they're very organized, but their organization is constantly moving. I guess that's much more like the Harry Potter stairways. And so, there are 3 main components of the cytoskeleton. We have these are called, intermediate filaments, microtubules, and actin filaments. Sometimes actin filaments are called microfilaments. But essentially, let's start with intermediate filaments here. And the purpose of this is to provide tensile strength to the nucleus. So, this kind of acts like a protective cage around the DNA because it's around the cell and the nucleus. So it kind of protects the nucleus, and it provides tensile strength, meaning that if something gets pressed together, that tensile strength is going to hold its shape. It's going to just kind of protect that DNA in the roadways. This is or those staircases, depending on which analogy you like. Microtubules are the roadways of the cell. They provide this internal framework, so they kind of provide these like bridges and things throughout the cell. They keep the cell shape, they allow things to be transported across from them. They also play a major role in mitosis, so in cell division. They are responsible for moving that DNA around, helping the cell, move its shape around, depending on what's going on in mitosis at the time. And then they also perform or they make up different unique structures called cilia and flagella, which we're going to talk about a lot in its own topic. But, cilia and flagella are pretty much they allow for cell movement or the cell to move things outside of the environment. And so these microtubules, these are super, super, super important because they're not only acting as roadways, they provide support, they really assist in cell division, and they create distinct organelles that are really important for cell movement for certain types of cells. And then we have actin filaments, which are also called microfilaments. Either thing is the exact same thing, whether you call it actin or microfilament, but these really line the plasma membrane and they help the cell maintain its shape. And so if the cell shape needs to change, for instance, if a cell is moving throughout the body, that cell shape needs to change a lot, then the actin filaments are in charge of that. So here's a microscope slide of the cytoskeleton being labeled. So we can see actin is in red and you can see that's really close to the external part of the cell because it's lining that plasma membrane. And here we have microtubules which are labeled in green, and you can see those are this really intense network that's traveling throughout the entire cell. It's acting as it's providing a roadway essentially for the entire cell. And you can see it goes everywhere, all the way out to the plasma membrane around the nucleus. It can be really highly isolated in some regions, but essentially it travels throughout the whole cell. So how are these cytoskeleton components created? So even though there are 3 different filaments, and we're going to talk about each one of those individually and what the differences are, the actual formation of those filaments and some of their structures are very similar, even though if some of the intricate details are different. So all of these filaments are created, so the actin filaments, the intermediate filaments, and the microtubules are created, through the joining of small subunits. And we call these subunits monomers, and we'll go through each monomer for each different filament is called something different, and we'll talk about that later. But essentially these monomers are joined together through non-covalent bonds. So remember, we want these non-covalent bonds because we said that the cytoskeleton is dynamic, so it's constantly being created and broken down. So the only way that can happen is if we do weaker bonds, which are those non-covalent bonds. And so there are a couple of structures that you need to know. The first is going to be protofilament, and this is what happens when these monomers are joined together. So we have this monomer here, and we join it to this one here, and we join it to this one here, and eventually, you're going to get these long things we call protofilaments. So it's the long string of subunits that we've joined end to end, just like here. So we have this end connecting to this end, connecting to this end, and so on and so forth, and these things can be hundreds of thousands of monomers long. And then when we have multiple protofilaments, often what happens in these, and we'll talk about each individual case individually, but often what happens if we get multiple protofilaments, they end up twisting around each other kind of like a rope, where they form like this helical lattice, which kind of just like if you had two strings and you twisted them, then that's kind of what that would end up looking like. And that's very common in the cytoskeletal components. And then the last term that you really need to know, and this one's super, super important, and that is called nucleation. And essentially, this is how these things get started. So remember, we're starting with these one, these just individual monomers, but eventually, two monomers have to come together. And this process here of the first two monomers coming together actually is really difficult. It's not that easy. Once two monomers are together, it's super easy to add more on. But just like getting those first two together is really difficult, and so this process here is called nucleation. It's the initiation process. So the first time these subunits are assembled together, and it's a special process that isn't actually that easy. So here's an example of nucleation of actin. So we have these actin monomers, they're right now they're called G actin and we'll explain that term later. But, these are actin monomers, it requires some type of energy, like I said it's not easy to go through nucleation, you're going to have some kind of energy, in this case, it's ATP. So ATP gets added to all of these G actins, and then it forms, the nucleation step, forms the first couple of monomers together, and then once these monomers have formed, then the rest of it can be formed super easy. They just start attaching on really easy once the first few have gotten together. So, that is just the overview of the cytoskeleton, the components, the intermediate filaments, microtubules, and actin. We'll go over each one individually, and then just some introductory terms on how these filaments are formed in the cell. So with that, let's move on.

Which of the following is not a component of the cytoskeleton?

• A. Intermediate filaments
• B. Actin filaments
• C. Nucleation
• D. Microtubules

What is the name of the initiation process that beings to assemble the subunits of the cytoskeleton?

• A. Cytoskeleton Initiation
• B. Support Initiation
• C. Nucleation
• D. Protofilament formation