In this lesson you will discover what the cytoskeleton is, what it’s composed of and the various things the cytoskeleton does for the cell. You will also discover a little bit about the importance of the cytoskeleton.
What is a Cytoskeleton?
Have you ever seen the scene in Harry Potter when the bone in Harry’s arm is made to disappear? Without a bone, his arm starts bending and flapping around like rubber.
That’s because, without a skeleton, there’s nothing to keep our shape intact.Cells also need to have something to keep their shape intact, a cytoskeleton. In fact the word cyto means ‘cell,’ so the cytoskeleton is the cell’s skeleton. Put another way, the cytoskeleton is the framework of the cell.
It is highly organized and also flexible. It doesn’t appear the same as our skeleton, but some parts of it can act like our bones, and some parts can act like our muscles.
The cytoskeleton functions rather like our skeleton. It provides structural support so the cell can keep its shape, move around, and be protected from outside forces.
The effect of outside forces on the cell is called mechanical stress.What is mechanical stress? Imagine two people tugging on your arms in two different directions. The two people tugging on your arms create mechanical stress.
You don’t split in half because your muscles and skeleton prevent the force from doing so. Likewise, the cell can resist changes in shape because of its cytoskeleton.The cytoskeleton has other functions as well.
It gives support to the cell membrane, helps evenly split up chromosomes during cell division, and aids in recovery from any outside injury. It’s also involved in organelle trafficking, which is the movement of cell components, like mitochondria, from one part of the cell to another.Just as there is strength in numbers, the components of the cytoskeleton are not found single stranded but are composed of multiple strands of three main components. In addition to the three main components, there are accessory proteins that aid in cytoskeletal assembly, disassembly, stability, and cellular transport.
Cytoskeleton Structure: Microtubules
There are 206 bones in the human body. The cytoskeleton doesn’t have bones per se, but it does have three main components: microtubules, intermediate filaments, and microfilaments.
Just as your bones are different sizes, the three main components of the cytoskeleton are also different sizes. The biggest are the microtubules. Microtubules resemble what their name implies. They look like small (micro), round, hollow tubes (tubules) and have a diameter of about 24 nanometers.Microtubules are made up of a protein called tubulin.
Interestingly, microtubules’ lucky number seems to be 13. Thirteen tubulin connect to form the tube. Microtubules are very dynamic structures. This means they can easily change. They are constantly growing or shrinking, kind of like a rope raveling and unraveling at one end. Microtubules are involved in the transport of cellular materials and divvying chromosomes during cell division.
Cytoskeleton Structure: Intermediate Filaments
The middle or intermediate-sized components of the cytoskeleton are the intermediate filaments (IF). What is a filament? It’s something that looks like a thin thread. IFs actually resemble thin threads. They are middle-sized, around ten nanometers in diameter, and are the meshwork that supports the cell rather like a net.Interestingly, there are many different kinds of IF proteins, and not all cells have the same type of IF protein. In fact, some cells contain no IF whatsoever.
One type of IF protein is called keratin. You may not have heard of it, but you will know what it forms. Keratin is what helps compose your fingernails and hair, and it aids in holding your skin together. IFs help protect the cell from mechanical stress.
That is, they allow the cell to be stretched or parts of it to bend without being broken apart. They also act as a net to hold genetic material, like DNA, in the nucleus.
Cytoskeleton Structure: Microfilaments
The tiniest main component of the cytoskeleton is the microfilament. Microfilaments are three to six nanometers in diameter and are composed of the protein actin. For this reason they are often referred to as actin filaments. The actin filaments are twisted together like two pieces of thread.
Microfilaments can be found just beneath the cell’s membrane, and some strands are anchored to the cell’s membrane. They are also dynamic structures. One end grows while the other end shrinks, a process called treadmilling. Microfilaments help determine the cell’s shape and aid in cellular movement. They also form the pseudopodia cells used to crawl along surfaces — kind of like little blobs of cell feet. In addition, they are part of the contractile proteins found in muscle cells.
Improper assembly of the cytoskeleton can have bad consequences for an organism.
ALS (amyotrophic lateral sclerosis), also known as Lou Gehrig’s disease, for example, is associated with the abnormal assembly of IF. Alteration in the protein keratin can lead to blistering diseases.Many fungi and other small organisms secrete cytoskeletal toxins to protect themselves. The toxin taxol, for example, stabilizes microtubules and prevents their ease of disassemble. This makes it difficult for the cell to properly divide. Such toxins are used in studying the roles of cytoskeletal structures and have even been employed in cancer treatment.
Let’s review.The cytoskeleton is the cell’s skeleton. It has many functions, such as supporting cell shape, allowing cellular movement and organelle trafficking, aiding in proper cell division, protecting against mechanical stress, and aiding in recovery after injury. Improper assembly or disassembly of the cytoskeleton can lead to various disease states, including ALS. There are three main components of the cytoskeleton: microtubules, intermediate filaments (IF) and microfilaments, along with many other proteins that support those components.
Microtubules, the largest component, are made of tubulin and function in organelle transport and cellular division. IF, the middle-sized component, can be composed of many different types of protein, one of which is keratin that makes up hair and fingernails. IF protects the cell from bending and stretching and forms a net around DNA.
Microfilaments, also called actin filaments, are the smallest component. They are found just beneath the cellular membrane and aid in cellular movement.
|*Largest component *Made of tubulin *Involved in transporting organelles and splitting up the chromosomes during cell division||*Midsize component *Made of different proteins * Protect the cell from mechanical stress *Form a net around the nucleus to hold in the genetic material||*Smallest component *Composed of actin * Help determine the cell’s shape *Aid in cell movement|
When you are finished, you should be able to:
- Explain what the cytoskeleton of a cell is and its purpose
- Name and describe the three components of the cytoskeleton