Introduction to the Cytoskeleton: Study with Video Lessons, Practice Problems & Examples

The cytoskeleton is a dynamic network of proteins in the cytoplasm, crucial for maintaining cell shape, structure, movement, and intracellular transport. It consists of three main components: microfilaments, made of actin and the smallest in size; intermediate filaments, composed of various proteins and of intermediate size; and microtubules, the largest, formed from tubulin. Additionally, cilia and flagella, both made of microtubules, facilitate cell movement, with cilia being short and numerous, while flagella are longer and whip-like.

Introduction to the Cytoskeleton

In this video, we're going to begin our introduction to the cytoskeleton, and so the cytoskeleton can be defined as a network of elongated proteins in the cytoplasm of a cell. And so, you can see that the root cyto in cytoskeleton correlates with the root cyto in cytoplasm. Now, the cytoskeleton of a cell actually has multiple diverse functions, and we'll get to talk about some of those diverse functions in our video here very shortly. Now, it is important to note that the cytoskeleton does have some resemblance to our own skeletons. And so, just like our skeletons provide our bodies with the shape and structure, and the skeleton also helps with movement because what would our movement be without our skeletons? Well, the cytoskeleton does something similar for the cells. And so, what you'll notice here is that some of the functions of the cytoskeleton include providing the cell with its cell shape, cell structure as well as providing movement for the cell, and it can also be involved with transportation in terms of transporting molecules within the cell, and it can also be important for biosignaling to help cells communicate with other cells and also for cells to be able to respond to their environments. And so, you can see how the cytoskeleton has many different diverse functions, and some of those functions including the shape, the structure, and the movement can correlate with our own skeleton. So that can make it somewhat easier for you to remember the functions of the cytoskeleton. And so, really there are 3 major components of the cytoskeleton that you should be familiar with, and notice that we have them numbered down below; 1, 2, 3, and so the very first component are going to be the microfilaments. And recall that the root micro is a root that means small, and in fact, this is important because microfilaments, they are going to be the smallest of the cytoskeleton components. So the microfilaments are the smallest in size, and usually, the microfilaments are going to be made of thin rods of repeating actin subunits. And so these, actin protein subunits are smaller components that come together in a repeating fashion in order to make up these microfilaments. And so if we take a look at our image down below of the cytoskeleton, you'll notice that we have a really cool micrograph of a bunch of cells on the left-hand side, and all of these different colors that you see represent the different components of the cytoskeleton. And again, there are 3 main components, and the first that we're talking about are the microfilaments which are shown on the far left here. And so notice that each of these red little circles represents actin proteins, actin subunits that again come together in a repeating fashion in order to make up the microfilaments which are going to be the smallest in size. Next, what we have are the intermediate filaments and the intermediate filaments, as their name implies, they are going to be intermediate in size. That means that they are not going to be the smallest in size and they are not going to be the largest in size. They are going to be in between the two. And also, these intermediate filaments can be made of variable proteins. So there are different proteins that can come together to make these intermediate filaments. And so if we look at our image down below, notice that the intermediate filaments are being shown here in blue. Now last but not least, what we have are the microtubules. Now you'll notice that microtubules also have this root micro, and so it's important to keep in mind that the microtubules are actually not the smallest in this case. Instead, the microtubules are going to be the largest, and so this micro root here can be somewhat misleading. However, what you can think of with the microtubules, you can focus on this tube part, and when you think of tubes like a water slide, you think of really large tubes, and so that can help remind you that the microtubules are actually going to be the largest in their size. And so the microtubules are the largest in size, and they form again these large cylindrical tubes that are made of repeating tubulin proteins. And so the tubulin proteins will come together in a repeating fashion in order to make up the microtubules. And so if we look at our image down below of these microtubules, notice that each of these little green circles that you see represents the tubulin protein subunits that come together in a repeating fashion to make this entire microtubule. And so, the interesting thing about the cytoskeleton is that it is very dynamic, meaning that it changes a lot all the time. These cytoskeleton components, all of them, can be spontaneously broken down and also spontaneously built together, so that they can change and be fitted to the cell's need at any particular time. And so, again, the cytoskeleton is going to function in many different ways, including cell shape, structure, movement, transportation, and biosignaling. And so, this concludes our brief introduction to the cytoskeleton and the 3 components: microfilaments, intermediate filaments, and microtubules, and we'll be able to get some practice applying these concepts moving forward. So I'll see you all in our next video.

What component of the cytoskeletons do motor proteins use to transport vesicles?

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

Cilia & Flagella

In this video, we're going to distinguish between cilia and flagella. The microtubules that we introduced in our last lesson video as one of the major components of the cytoskeleton are actually a major structural component of two cellular structures, cilia and flagella. Both cilia and flagella provide cell movement, which means that the microtubules are very important for cell movement as we introduced in our last lesson video. Below, we're going to distinguish between cilia and flagella.

Cilia consist of multiple short hair-like structures that move like oars and can either move objects in the surroundings relative to the cell, or they can help provide cell movement itself, allowing the cell to move throughout its environment. On the other hand, flagella, instead of being short, are actually much longer, tail-like structures that move like a whip in order to provide cell movement. Flagella are mainly used to provide cell movement and typically are not going to be used to move other objects in the surrounding like what cilia can sometimes be used for.

Below, you can take a look at our image to distinguish cilia and flagella. Over here on the left-hand side, we're showing you a scanning micrograph of cilia. You can see that these structures are the short hair-like structures that we were talking about before that can move like oars in order to either move objects in the surroundings or to move the cell itself. Notice that there are multiple cilia here, and they are shorter hair-like structures.

On the right-hand side, we're showing you a scanning electron micrograph of some sperm cells, and these sperm cells have flagella. You can see that here is the body of the cell and the long tail that comes off of the body of the cell right here are referred to as the flagella. These tails are much longer than the short cilia and move like whips to provide cell movement.

This concludes our introduction to cilia and flagella and how they're both made of microtubules, which means that microtubules are important for cell movement. We'll be able to get some practice applying some of the concepts that we've learned here as we move forward in our course. I'll see you all in our next video.

In human cells, ___________________ are used to move a cell within its environment while ___________________ are used to move objects in the environment relative to the cell.

• A. Cilia, pseudopodia.
• B. Flagella; cilia.
• C. Cilia; flagella.
• D. Microfilaments; microtubules.

Here’s what students ask on this topic:

What are the main components of the cytoskeleton and their functions?

The cytoskeleton consists of three main components: microfilaments, intermediate filaments, and microtubules. Microfilaments, made of actin, are the smallest and provide cell shape, structure, and movement. Intermediate filaments, composed of various proteins, offer mechanical support and help maintain cell integrity. Microtubules, the largest, are formed from tubulin and are crucial for cell movement, intracellular transport, and the formation of cilia and flagella. Together, these components maintain cell shape, enable movement, and facilitate intracellular transport and signaling.

How do microfilaments, intermediate filaments, and microtubules differ in structure and function?

Microfilaments are the smallest cytoskeletal components, made of actin subunits, and are involved in cell shape, structure, and movement. Intermediate filaments are of intermediate size, composed of various proteins, and provide mechanical support and stability to cells. Microtubules are the largest, formed from tubulin subunits, and are essential for cell movement, intracellular transport, and the formation of cilia and flagella. Each component has a unique structure and specific functions that contribute to the overall dynamics and functionality of the cytoskeleton.

What roles do cilia and flagella play in cell movement?

Cilia and flagella are structures made of microtubules that facilitate cell movement. Cilia are short, hair-like structures that move like oars, either moving objects in the cell's surroundings or propelling the cell itself. Flagella are longer, whip-like structures that primarily provide cell movement by whipping back and forth. Both structures are crucial for the motility of certain cells, such as sperm cells (flagella) and cells lining the respiratory tract (cilia).

How do microtubules contribute to intracellular transport?

Microtubules play a critical role in intracellular transport by serving as tracks for the movement of organelles, vesicles, and other cellular components. Motor proteins, such as kinesin and dynein, move along microtubules, carrying cargo to specific locations within the cell. This transport system is essential for distributing materials, maintaining cellular organization, and facilitating communication within the cell.

Why is the cytoskeleton considered dynamic, and what are the implications of this property?

The cytoskeleton is considered dynamic because its components—microfilaments, intermediate filaments, and microtubules—can be rapidly assembled and disassembled in response to the cell's needs. This dynamic nature allows the cytoskeleton to adapt to changes in the cell's environment, support cell movement, and facilitate processes such as cell division and intracellular transport. The ability to remodel quickly is crucial for the cell's ability to respond to stimuli and maintain homeostasis.