What is Cytoskeleton?

The cytoskeleton in cell biology is a system of fibrillar structures that diffuses the cytoplasm. As such, it can be defined as the part of the cytoplasm which provides a cell with the internal supporting framework.


In addition to providing structural support, it is also involved in various types of movement (where it supports specific cellular structures such as the flagellum) as well as cellular matter movement.


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Cytoskeleton Definition

The cytoskeleton is a network of filaments and tubules that stretches throughout a cell, through the cytoplasm, which is all the substance within a cell except the nucleus itself. It is found in all cells, although the proteins it is made of vary from organism to organism. The cytoskeleton supports the cell, shapes the organelles, organizes and teters them, and plays a role in molecule transport, cell division and cell signaling.


Cytoskeleton Structure and Function

Eukaryotic cells are complex nucleus cells with organs. There are eukaryotic cells in plants , animals , fungi and protists. Prokaryotic cells are less complex, with no true nuclei or organelles other than ribosomes, and they are found in the bacteria and archaea of the single - celled organism.


A cell's cytoskeleton ensures stability, energy, and motility. This provides a cellular scaffolding that arranges the cellular organization into. The figure represents a part of the cytoskeleton of a cell. Note the cytoskeleton is extremely extensive. Notice that the cytoskeleton seems to have many ribosomes attached to it. Polysome refers to two ribosomes, or more. The ribosomes attached to the cytoskeleton are often referred to as' free' ribosomes to differentiate them from those ribosomes attached to the membranes of the nuclear or ER.


Cytoskeleton Structure

Three Types of Cytoskeleton Components:

  • Microfilaments

  • Microtubules

  • Intermediate fibers

Microfilaments

Microfilaments are cytoskeleton filament structures, which consist of actin monomers (f-actin). Here, globular g - actin monomers are polymerized to form filaments of actin polymers (f-actin), commonly known as g - actin. Ultimately, each filament strand (microfilament) is composed of two helically coiled f - actin coils.


It has also been shown that microfilament strands have positive and negative endings that contribute to the regulation of the filaments at both ends. Studies have also found, regarding the development of microfilaments, that new monomers appear to be introduced at a faster rate compared to the negative end at the positive end. There is also an ATP limit at this positive end, which helps to balance it during rapid growth.


Microfilaments are the thinnest / narrowest structures measuring between 3 and 5 nm in diameter compared to the other components of the cytoskeleton. Since they are composed of actin, however, microfilaments are quickly gathered and contribute to the proper functions of the cell.


Microfilaments are normally located at the periphery of the cell, where they run from the plasma membrane to the microvilli (e.g. they can be discovered in the pericanalicular zone where they form the pericanalicular web / meshwork). They are present here in bundles that together form an intracellular three - dimensional meshwork.


Microfilaments are highly diverse and versatile although they are the thinnest components of the cytoskeleton.


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Microtubules

Microtubules are the largest of the three cytoskeleton components, with a diameter ranging from 15 to 20 nm. Microtubules, unlike microfilaments, consist of a single type of globular protein known as tubulin (a protein made up of kd polypeptides and alpha and beta tubulin).


In favorable conditions, tubulin heterodimers join within the cell to form linear protofilaments. Such filaments assemble in turn to form the microtubules (hollow tube-like straws).


Like microfilaments, the cells often arrange microtubules into bundles. However, with some microtubules going through growth cycles and shortening of their population, they have also been shown to be very unstable.


Heterodimer subunits are separated from specific ends of the tubes during shrinkage processes but inserted during the growth phase. This complex instability has been attributed to the high variance in internal organization and size of the microtubule.


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Each microtubule consists of roughly 13 linear protofilaments arranged around a hollow core.


In a cell, microtubules emerge in a hub-spoke fashion from the center of the cell. They radiate from here all through the cytoplasm where they perform a number of functions.


Intermediate Fibers/Intermediate Filaments (IF)

Unlike the other elements of the cytoskeletons, intermediate filaments comprise a large family of polypeptides. For this reason, different types of cells contain a wide variety of intermediate filaments.


Studies have shown that there are more than 50 different types of intermediate filaments classified into six major groups which include:

Type 1 and II – In most epithelial cells, it consists of about 15 different proteins.

Type III - This group of proteins includes such as vimentin and desmin.

Type IV - This group includes proteins such as α-internexin and neurofilament proteins found in nerve cells.

Type V - Lamins are an example of the proteins found in that group.

Type VI - Found in neurons, just like nestin.


Keratin is among the most important proteins involved in forming intermediate filaments. This is the commonly found fibrous protein in the skin and hairs.


Central rod domains of two polypeptide chains are first wrapped around each other during assembly to form a coiled (dimer) structure. The resulting dimers then come together to form tetramers which assemble to form protofilaments at their ends (end to end). In the end, the protofilaments are assembled to form the intermediate filaments.

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In terms of size, intermediate filaments range from 8 to 10 nm in diameter-So the word "intermediate filaments." They are likewise more robust compared to the other two and therefore more enduring.


Although they do not undergo dynamic instability, as is the case with microtubules, proteins are often modified by phosphorylation from intermediate filaments. This plays a significant role in assembling them within the cell.


Intermediate filaments in various types of cells stretch from the nucleus surface to the cell membrane. Such filaments also communicate with the other components of the cytoskeleton through the elaborate network that they form in the cytoplasm, which contributes to their functions.


Cytoskeleton Function

There are several functions to the cytoskeleton. Second, it gives form to the cell. This is particularly important in cells that do not have cell walls, such as animal cells, that do not get their shape from a thick layer outside. It can give movement to the cell, too. Microfilaments and microtubules can disassemble, reassemble and contract, allowing cells to crawl and migrate, and microtubules can help build structures such as cilia and flagella that facilitate cell movement.


The cytoskeleton organizes the cell and holds the organelles of the cell in place, but it also helps to move the organelles throughout the cell. For example, microfilaments pull the vesicle containing the engulfed particles into the cell during endocytosis when a cell involves a molecule. Similarly, during cell division, the cytoskeleton helps move chromosomes.


The foundation of a house is one reference to the cytoskeleton. Like the frame of a house, the cytoskeleton is the cell's "core," which holds structures in place, provides support and gives the cell a definite shape.


Cytoskeleton Diagram

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FAQs (Frequently Asked Questions)

Q1: What is the Cytoskeleton and its Function?

A: A cell's cytoskeleton comprises microtubules, actin filaments, and the intermediate filaments. These structures give form to the cell and help organize the parts of the cell. They also provide a basis for movement and division of cells.

Q2: What are the 3 Types of Cytoskeleton?

A: Microfilaments, microtubules, and intermediate filaments are the principal types of fibers forming the cytoskeleton. Microfilaments are fine, 3 - 6 nm in diameter, thread-like protein fibres. These are predominantly composed of a contractile protein called actin, the most abundant cellular protein.

Q3: Is Cytoskeleton an Organelle?

A: Most eukaryotic cells contain a complex protein fiber network , called the cytoskeleton. It forms a framework for the movement of organs around the cytoplasm-most of the organs are connected to the cytoskeleton. The network comprises microfilament proteins, intermediate filaments and microtubules.

Q4: How Does a Cytoskeleton Look Like?

A: IF's (intermediate filament) actually look like thin threads. They are of medium size, around ten nanometers in diameter, and are the meshwork which supports the cell as if it were a net. Ironically, IF proteins are of many different types and not all cells have the same type of IF protein.