What is Cytoskeleton:
The cytoskeleton is a network of filaments that shapes the cell, supports its plasma membrane, organizes its internal structures, and is involved in cell transport, mobility, and division.
The cytoskeleton is the internal structure that supports stress and compression forces while maintaining the shape of the cell. In this sense, the cytoskeleton is literally the skeleton of the cell and is located throughout the cell in the cytoplasm.
Among its functions is to fix the plasma membrane, the cell nucleus and all the other structures of the cell in their place. Furthermore, it provides the tracks for the transport of protein vesicles or organelles within the cell and is an essential component for the formation of specialized structures in eukaryotic cells such as flagella, cilia, and centrosomes.
In prokaryotic cells, which do not have a defined cell nucleus, they also have a cytoskeleton that maintains the shape of the cell and helps its cell division, but its composition is different and was only discovered in 1990. 3 elements have been identified called: FtsZ, MreB and crescentin.
Three elements are identified in the structure of the cytoskeleton of eukaryotic cells: microfilaments, intermediate filaments and microtubules.
Microfilaments are the thinnest fibers of the 3 types that make up the cytoskeleton. They are also known as actin filaments, since they are made up of monomers of actin proteins joined together in a way that looks like a double helix.
They are characterized by having directionality. This means that each end of the microfilament is different.
The function of the microfilament is the ratio of rails for the movement of motor proteins called myosin, which, in turn, also form filaments.
Microfilaments can be found in the division of animal cells, such as muscle cells, which, coordinated with other filament structures, help muscles to contract.
Intermediate filaments are composed of many interwoven fibrous protein chains. They are more permanent than microfilaments or microtubules and depending on the cell in which it is found, keratin being the most common.
The function of the intermediate filaments is to support cell tension while maintaining the shape of the cell. Furthermore, they organize internal structures by anchoring the nucleus and organelles in place.
Microtubules are made of tubulin proteins that form a hollow tube. Each tubulin is made up of 2 subunits: alpha-tubulin and beta-tubulin.
Their structure, like that of microfilaments, is dynamic, that is, they can grow and disassemble quickly and also have directionality, each end being different.
Microtubules have several functions:
- First, it provides structural support to the cell by helping it resist compressive forces.
- Second, they create rails for motor proteins (kinesins and dyneins) to carry vesicles and other elements.
- Third, they are the key components for the formation of flagella, cilia, and centrosomes, specialized structures in eukaryotic cells.
Flagella are structures that help movement as we can see, for example, in sperm. On the other hand, the cilia, being shorter and more numerous than the flagella, also help mobility, for example, in respiratory cells, displacing dust from the nostrils.
The structure of both flagella and cilia form a cylinder of 9 pairs of microtubules with another pair in its center plus a basal body that would assemble these 2 structures. The basal body is considered a modified centriole, the centriole being composed of 9 microtubule triplets.