Understanding the Cell's Cytoskeleton

The next topic we're going to discuss in relation to the structure of the cell is the cytoskeleton. Now the cytoskeleton is a network of protein fibers that permeate all of the cell and it basically functions to give the cell structure as well as motility. So in a way we can imagine that the cytoskeleton is like the bone structure of our body. It gives the cell its structure, it gives the cell its shape. It also gives the cell the ability to resist different types of forces and pressures. But the cytoskeleton is more than that. Not only is it a scaffolding system, it's also a highway system. It gives the cell the ability to move things within that cell. And it gives the cell the ability to organize the organelles and structures found within that cell. So the cytoskeleton is a very important structure. Now, there are three different types of fibers that are found within the cytoskeleton. We have microfilaments, we have intermediate filaments, and also microtubules. And let's begin by discussing the microfilaments. The microfilaments are the thinnest of the three types of protein fibers, and their diameter ranges from 6 to 7 nanometers. Now, they are basically composed entirely of one type of linear protein known as actin. And one common example of the use of microfilaments is in the contraction of cells, and specifically in the contraction of muscle cells, one type of cell found in our bodies. So basically, during muscle contraction, what happens is there is an interaction taking place between the actin found in our microfilament as well as a different type of protein known as myosin. So myosin basically grabs the actin, it pulls on it, so it walks on it, and this creates our contraction of the muscle cell. Now microfilaments contain a negative end as well as a positive end. So let's suppose this is the negative end and this is our positive end. and the actin essentially grows beginning from our positive end and the negative end is attached to some type of structure within the cell now as our actin grows from the positive end of our microfilament eventually it pushes against some type of structure within the cell for example the cell membrane and this gives the cell the ability to resist tensile forces so microfilaments give the cell tensile strength. So we see that not only are they responsible for our contraction of cells, such as the muscle cells, they also stabilize the shape and structure of our cell and they give our cell tensile strength. Now let's move on to the second type of fiber known as the intermediate filament and these are known as intermediates because they're slightly greater in diameter than the smallest type the microfilament so our diameter of intermediate filaments is about 10 nanometers so these fibers are actually composed of several types of different proteins and are slightly thicker than the micro the microfilaments that we discussed in this section here Now, just like the microfilaments, these intermediate filaments also give the cell tensile strength. They increase the stability of the cell and give the cell its shape as well as its structure. Now, one important difference between microfilaments and intermediate filaments is intermediate filaments are also found in the nucleus of our cell. So intermediate filaments compose the nuclear lamina, which is basically the fiber skeleton system found within our nucleus. So that's one major difference between microfilaments and our intermediate filaments. But both types of filaments give the cell structure. They give the cell the shape and increase the tensile strength of our cell. So basically, if we try to pull on the cell, what keeps the cell from being split? are these types of fibers, the microfilaments and our intermediate filaments. Now let's move on to the thickest type of filament fiber known as the microtubules. So microtubules are the largest of the three and are rigid hollow tubes made of a protein known as tubulin. And there are two versions of tubulin. We have alpha as well as beta tubulin. And together, the alpha and the beta tubulin proteins, which are globular proteins, they basically create a helical structure that winds as shown. So we have this winding in a helical-like fashion, and we create a hollow center. So this structure here is the microtubule. So notice that the actin, and the intermediate filament. So the microfilaments and intermediate filaments do not contain a hollow center, but the microtubules do contain a hollow center, and that's exactly why they're called tubules, because they create this hollow-like tube. Now, just like our microfilaments, our microtubules, which are 23 nanometers in diameter, so notice they are larger than the microfilaments or the intermediate filaments, the microtubules have a positive end as well as the negative end. And the positive end is the end from where our microtubule grows. The negative end inside an animal cell is usually found within a region given by MTOC, where MTOC stands for the microtubule organizing center. And within our eukaryotic animal cells, this is known as our centrosome. So it's the centrosome region that contains our centrioles. So essentially our microtubules are made within our centrosome. Now if the centrosome is responsible for cell division that implies that the microtubules are also involved in cell division and that's exactly right. One function of our microtubule is to basically separate our chromosomes during cell division. So the microtubules are responsible for creating the mitotic spindle that is formed during cell division. Now another function of microtubule is to basically transport things within the cell. So we can imagine the microtubule is to be the highway system within our cell. So we can move things from one location to a different location within the cell as a result of these network of highways, our microtubules. Now, another important function of microtubules is the formation of specialized structures that help the cell move. And these structures include our flagella as well as cilia. Now, the flagella inside eukaryotes is made of this tubulin. But inside prokaryotes, Our flagella is not made from tubulin, so it's not made from microtubules. It's made from a different type of protein known as flagellin. And we're going to discuss the difference between the flagellins, cyprokaryotes, and eukaryotes in a different lecture. So don't worry about that just yet. So now that we discussed the three different types of fibers that are found within the cytoskeleton of the eukaryotic cell, let's basically summarize our findings. Let's discuss what each type is and what each type does. So let's begin with the microfilament. The microfilament is composed of a single protein known as actin. The protein is linear, and so we form this linear type of structure, and it's the thinnest type of structure. It's about six to seven nanometers in length. Now, the function of our microfilament is in muscle contraction, in phagocytosis, in tensile strength, and cytoplasmic streaming. So cytoplasmic streaming basically refers... to the amoeboid-like movement of our cell. Phagocytosis refers to our invagination and engulfing of extracellular materials using the cell membrane. And tensile strain basically means our cell is able to resist tensile forces and tensile pressures. Now, let's move on to our intermediate filament. The intermediate filament has intermediate thickness it's about 10 nanometers and several different types of proteins are found within our intermediate filament now the special thing about intermediate filaments is that not only are they found within a cytoplasm they're also found within the nuclear plasma thin our nucleus and they're also found outside our cell so the function of intermediate filament is to give our cell tensile strength and increase the stability of our cell structure. The intermediate filaments, because they're found outside our cell, are also involved in creating structures between different cells, so binding cells together. And finally, the microtubule, the thickest and the largest and the strongest, type of fiber found in our skeleton. It has a thickness of about 23 nanometers, and it's composed of one type of protein, tubulin, that comes in two forms. We have alpha and beta tubulin. So basically, the alpha and beta globular tubulin proteins create a helical structure that is hollow at the center, and that's why we call it a tubule. Now, the function of microtubules is to... increase the compressive strength. So we see that microfilaments and intermediate filaments give our cell the ability to resist pulling, but our microtubules give the cell the ability to resist compression. So it gives, increases the cells compressive strength. It also is involved in forming the mitotic spindle and it's involved in forming cilia. flagella, as well as involved in intracellular movements, basically moving things within our cell. And these are the three different types of protein fibers found within the cytoskeleton of our eukaryotic cell.

It gives the cell its structure, it gives the cell its shape. It also gives the cell the ability to resist different types of forces and pressures. But the cytoskeleton is more than that. Not only is it a scaffolding system, it's also a highway system.

It gives the cell the ability to move things within that cell. And it gives the cell the ability to organize the organelles and structures found within that cell. So the cytoskeleton is a very important structure. Now, there are three different types of fibers that are found within the cytoskeleton. We have microfilaments, we have intermediate filaments, and also microtubules.

And let's begin by discussing the microfilaments. The microfilaments are the thinnest of the three types of protein fibers, and their diameter ranges from 6 to 7 nanometers. Now, they are basically composed entirely of one type of linear protein known as actin.

And one common example of the use of microfilaments is in the contraction of cells, and specifically in the contraction of muscle cells, one type of cell found in our bodies. So basically, during muscle contraction, what happens is there is an interaction taking place between the actin found in our microfilament as well as a different type of protein known as myosin. So myosin basically grabs the actin, it pulls on it, so it walks on it, and this creates our contraction of the muscle cell. Now microfilaments contain a negative end as well as a positive end. So let's suppose this is the negative end and this is our positive end.

and the actin essentially grows beginning from our positive end and the negative end is attached to some type of structure within the cell now as our actin grows from the positive end of our microfilament eventually it pushes against some type of structure within the cell for example the cell membrane and this gives the cell the ability to resist tensile forces so microfilaments give the cell tensile strength. So we see that not only are they responsible for our contraction of cells, such as the muscle cells, they also stabilize the shape and structure of our cell and they give our cell tensile strength. Now let's move on to the second type of fiber known as the intermediate filament and these are known as intermediates because they're slightly greater in diameter than the smallest type the microfilament so our diameter of intermediate filaments is about 10 nanometers so these fibers are actually composed of several types of different proteins and are slightly thicker than the micro the microfilaments that we discussed in this section here Now, just like the microfilaments, these intermediate filaments also give the cell tensile strength.

They increase the stability of the cell and give the cell its shape as well as its structure. Now, one important difference between microfilaments and intermediate filaments is intermediate filaments are also found in the nucleus of our cell. So intermediate filaments compose the nuclear lamina, which is basically the fiber skeleton system found within our nucleus.

So that's one major difference between microfilaments and our intermediate filaments. But both types of filaments give the cell structure. They give the cell the shape and increase the tensile strength of our cell.

So basically, if we try to pull on the cell, what keeps the cell from being split? are these types of fibers, the microfilaments and our intermediate filaments. Now let's move on to the thickest type of filament fiber known as the microtubules.

So microtubules are the largest of the three and are rigid hollow tubes made of a protein known as tubulin. And there are two versions of tubulin. We have alpha as well as beta tubulin. And together, the alpha and the beta tubulin proteins, which are globular proteins, they basically create a helical structure that winds as shown. So we have this winding in a helical-like fashion, and we create a hollow center.

So this structure here is the microtubule. So notice that the actin, and the intermediate filament. So the microfilaments and intermediate filaments do not contain a hollow center, but the microtubules do contain a hollow center, and that's exactly why they're called tubules, because they create this hollow-like tube.

Now, just like our microfilaments, our microtubules, which are 23 nanometers in diameter, so notice they are larger than the microfilaments or the intermediate filaments, the microtubules have a positive end as well as the negative end. And the positive end is the end from where our microtubule grows. The negative end inside an animal cell is usually found within a region given by MTOC, where MTOC stands for the microtubule organizing center. And within our eukaryotic animal cells, this is known as our centrosome.

So it's the centrosome region that contains our centrioles. So essentially our microtubules are made within our centrosome. Now if the centrosome is responsible for cell division that implies that the microtubules are also involved in cell division and that's exactly right. One function of our microtubule is to basically separate our chromosomes during cell division. So the microtubules are responsible for creating the mitotic spindle that is formed during cell division.

Now another function of microtubule is to basically transport things within the cell. So we can imagine the microtubule is to be the highway system within our cell. So we can move things from one location to a different location within the cell as a result of these network of highways, our microtubules. Now, another important function of microtubules is the formation of specialized structures that help the cell move.

And these structures include our flagella as well as cilia. Now, the flagella inside eukaryotes is made of this tubulin. But inside prokaryotes, Our flagella is not made from tubulin, so it's not made from microtubules.

It's made from a different type of protein known as flagellin. And we're going to discuss the difference between the flagellins, cyprokaryotes, and eukaryotes in a different lecture. So don't worry about that just yet. So now that we discussed the three different types of fibers that are found within the cytoskeleton of the eukaryotic cell, let's basically summarize our findings.

Let's discuss what each type is and what each type does. So let's begin with the microfilament. The microfilament is composed of a single protein known as actin.

The protein is linear, and so we form this linear type of structure, and it's the thinnest type of structure. It's about six to seven nanometers in length. Now, the function of our microfilament is in muscle contraction, in phagocytosis, in tensile strength, and cytoplasmic streaming. So cytoplasmic streaming basically refers... to the amoeboid-like movement of our cell.

Phagocytosis refers to our invagination and engulfing of extracellular materials using the cell membrane. And tensile strain basically means our cell is able to resist tensile forces and tensile pressures. Now, let's move on to our intermediate filament. The intermediate filament has intermediate thickness it's about 10 nanometers and several different types of proteins are found within our intermediate filament now the special thing about intermediate filaments is that not only are they found within a cytoplasm they're also found within the nuclear plasma thin our nucleus and they're also found outside our cell so the function of intermediate filament is to give our cell tensile strength and increase the stability of our cell structure. The intermediate filaments, because they're found outside our cell, are also involved in creating structures between different cells, so binding cells together.

And finally, the microtubule, the thickest and the largest and the strongest, type of fiber found in our skeleton. It has a thickness of about 23 nanometers, and it's composed of one type of protein, tubulin, that comes in two forms. We have alpha and beta tubulin. So basically, the alpha and beta globular tubulin proteins create a helical structure that is hollow at the center, and that's why we call it a tubule. Now, the function of microtubules is to...

increase the compressive strength. So we see that microfilaments and intermediate filaments give our cell the ability to resist pulling, but our microtubules give the cell the ability to resist compression. So it gives, increases the cells compressive strength.

It also is involved in forming the mitotic spindle and it's involved in forming cilia. flagella, as well as involved in intracellular movements, basically moving things within our cell. And these are the three different types of protein fibers found within the cytoskeleton of our eukaryotic cell.

Transcript for:Understanding the Cell's Cytoskeleton

Transcript for:
Understanding the Cell's Cytoskeleton