Have you ever had a burrito? Stuffed to the max with delicious fillings, spicy salsa, rice, beans, the works, all rolled up neatly in a tortilla. Now, add some melted cheese to the mix. And all of the glorious fillings stick together with the most delicious glue, keeping your fillings intact. Mmm, I could actually go for a burrito right now. Sorry. Back to the video (even though I should probably have lunch soon). Think of the cell like the burrito itself, and the cytoskeleton like the melted cheesy goodness that holds all of the toppings in place. The melted cheese — uhh, I mean, sorry, the cytoskeleton — holds everything in place inside the cell, giving it some structure. The cytoskeleton is a really important part of the cell with some incredible functions. Now, nothing really compares to the joy a burrito can bring, but we can try. Let’s learn about the cytoskeleton. Before we get into the function of the cytoskeleton, let’s talk about what’s in a name. Cytoskeleton literally translates to “cell skeleton,” and what does a skeleton do? It gives your body structure, and (with the help of some other organs and tissues, of course) helps you move about. The cytoskeleton has essentially the same job, as it gives your cells structure and allows for mobility. The cytoskeleton also helps keep the organelles in their proper places, acting as the backbone (literally and figuratively) for the cell. Now, while we’re comparing the cytoskeleton to our human skeleton, we might as well draw one more parallel. You know how a human skeleton is composed of a ton of different bones, but functions as one big piece of our body? The same kind of thing applies to the cytoskeleton; it may function as one big system, but it can be broken down into three separate parts. The cytoskeleton is actually a network of three constantly assembling and disassembling protein filaments — we’re talking microtubules, intermediate filaments, and microfilaments — that have different sizes, functions, and structures. Much like the organelles that the cytoskeleton helps keep in order, we’re all about organization here as well. We’re going to talk about the filaments from largest to smallest. So microtubules, you’re up first. Microtubules are the biggest of the filaments making up the cytoskeleton, but by “big” I mean they’re only about 25 nanometers in diameter (so still super tiny). Microtubules are made up of a protein called tubulin, which is quite fitting since “tube” is in the name! Microtubules have two different subunits — an alpha-tubulin and a beta-tubulin. The alpha- and beta- tubulin monomers look sort of like raisins; irregular, and circular proteins. Pairs of these raisin proteins join together at their sides and ends to form a dimer, and then multiple dimers bind together in an alternating pattern: alpha, beta, alpha, beta, alpha, beta. This chain is called a protofilament, and when 13 of them are made, they form a tube...called a microtubule! Microtubules constantly change, coming together, and breaking apart, but just because they’re not permanently tubular, doesn’t mean they don’t have an important job. Microtubules help the cell keep its shape, resisting against external compression and other forces working against the cell. They also help transport different motor proteins, called kinesins and dyneins, as well as form the spindle that helps chromosomes split in cell division. These filaments also are integral parts of other specialized cell structures including flagella and cilia. Flagella and cilia, both important for cellular and material movement, contain dyneins — you know the motor protein we just talked about? — Yeah, dyneins travel along the microtubules in these structures, and generate a force that makes flagella and cilia move. Cilia, for example, help keep your lungs free from dirt by preventing materials from entering, and flagella are important in bacteria, because it helps them move from point A to point B! Now that we know about the biggest filament, let’s move on to the intermediate-sized filament, very aptly named intermediate filaments. Intermediate filaments are, well, intermediate - not the biggest, and not the smallest — with a diameter of about 10 nm. Despite being the middle-sized filament, they’re actually the primary filament in the cytoskeleton. Intermediate filaments (which we can also call them IFs) are made of multiple different (but related) proteins with similar structural features, and are also the most stable component in the cytoskeleton. Because of their durability, IFs make up more durable parts of the body like your hair. The constituent proteins that make up Intermediate Filaments dictate how they’re classified, and overall there are five different IF protein classes. The first two classes of IFs are keratins which are expressed in epithelial cells. The third class of IFs are desmin and vimentin. Vimentin is a major player in providing cell support and regulation, and desmin is a big component of muscle cells. The fourth class of IFs are neurofilaments, which are present in motor neurons and help shape cells. The fifth and final class of IFs is lamins, which help with protein binding and again, provide stability. Intermediate filaments are a more permanent aspect of the cytoskeleton, helping maintain the cell's structural integrity, and keeping the nucleus and organelles where they belong in the cell. They really are the glue that holds everything together (like your skin, for example) — we’d probably be a lot less strong without them! And the last type of filament that makes up the cytoskeleton is the microfilament. And as the name suggests, it’s the smallest of all the filaments, measuring at about 7 nanometers in diameter. Microfilaments are also known as actin filaments, because — you guessed it — they’re made of a protein called actin. Microfilaments may look like long strands of protein, but they’re actually composed of multiple globular actin monomers that arrange themselves in something sort of like a double helix, you know, like the twisted structure that DNA has. Microfilaments as a structure are important, but actin has a lot to do with this too. Actin is run by adenosine triphosphate, or ATP, the molecule that carries energy around the cells. ATP encourages actin to assemble into its microfilament form which, in turn, helps other proteins like myosin move along the cell. Much like the other filaments in the cytoskeleton, they help maintain the shape of the cell and assist in the contracting of muscle cells. White blood cells also know where to go to fight infection because of microfilaments; well, they do a great job of supporting our bodies’ front-line workers! At this point, we should understand two things. One, the cytoskeleton gives structure to the cell, and is composed of multiple different filaments. Two, these filaments — microtubules, intermediate filaments, and microfilaments — each have different functions and structures. Now, let’s look at how they all fit together. This is a picture of a cell, and the spaghetti-looking things you can see hanging out around the cell are the different types of filaments. As you can see, they do exist separately but work together. By connecting themselves to themselves, the plasma, and the other organelles, the filaments help keep structure within the cell. Although many of the cytoskeleton components are constantly assembling, disassembling, and reassembling, they still provide strength to the cell that it wouldn’t otherwise have. The cytoskeleton, the melted cheese glue of the cell burrito, is an incredibly important feature of the cell that shows the power of team work and flexibility — literally and figuratively. Without all three filaments working together (and separately) in perfect harmony, we couldn’t have the structured, mobile cells that we know and love. We’d have a stationary, blob-like cell, and who wants that, really? Thanks for sticking around to learn more about the cytoskeleton. Click on the next video to continue learning more about the human body. Like the video if you want to see more of these on my channel. 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