The cytoskeleton is the network of structural proteins and fibers that form the framework (or skeleton) which gives all cells their shape and stability. In both prokaryotes and eukaryotes, the proteins that make up the cytoskeleton are similar. However, their configurations are considerably different. A feature of eukaryotic cytoskeletons is dynamic structure, which essentially means that they are made of whatever type of proteins are able to the cell. This does not mean that prokaryotic cytoskeletons have no such flexibility; it just means that eukaryotic cytoskeletons will be more dynamic than those of prokaryotes. Another feature that is more prominent in eukaryotes is the cytoskeleton’s ability to work with the extra cellular matrix, and therefore with other cells of the same type to accomplish functions on a more macro scale – i.e., forming living tissue. While the cell membrane is not considered part of the cytoskeleton, they both work very closely together to give the cell its structure, especially during cell reproduction. In addition to the main function of giving a cell its form, the cytoskeleton plays an important part in DNA/chromosomal segregation during cell division and in the actual division & replication (reproduction) of the cell.
Prokaryotic cytoskeletons may be less developed than those of eukaryotes, but theirs is still a composition of structural and functional proteins. In the prokaryotic cytoskeleton, FtsZ is one type of structural protein that plays an important part during cell division. It is the first protein to be activated, and it triggers the development of the cell wall by other proteins. MreB is another cytoskeleton protein that guides the biosynthesis of the cell wall, and it has a role in cell maintenance as well. ParM is a protein that aids in DNA segregation during mitosis. Prokaryotes also have crescentin, which helps the cell maintain its form. The proteins of the primitive prokaryotic cytoskeleton are considered homologues to those found in eukaryotes, meaning they share evolutionary ancestry to the more advanced structural proteins of the eukaryotic cytoskeleton.
In eukaryotes, the cytoskeleton is composed of three main types of fibers: microfilaments, microtubules, and intermediate filaments, which are themselves composed of structural and functional proteins. Microfilaments are made up of actin, microtubules of tubulin, and intermediate filaments are made of various other proteins depending upon the cell type, including vimentin, glial fibrillary acidic proteins, neurofilament proteins, keratins, and nuclear lamins. Apart from stability, microfilaments help generate force, and therefore movement within the cell. This movement is often in the form of contractions, most prominent and essential in muscle cells. Intermediate filaments are the elastic structures that provide the cell with flexibility while still maintaining its form; they therefore resist deformation from pressure and tension. As they are the main structural filaments, they anchor all organelles and compartmentalize the cell, and they even work with the cell membrane or cell wall to enable cell to cell collaboration, which is at the heart of living tissue formation. Microtubules play a key role in intracellular transport and synthesis of the plant cell wall. They also support and maintain extensions of certain cells known as cilia, pseudopodia, and the flagella. During mitosis, they form the mitotic spindle. Other supporting proteins, such as septins, serve as localized attachment sites for other proteins and prevent the diffusion (leaking) of substances from one cell compartment to the other. Additionally, spectrin lines the internal side of the cell membrane, giving it structural support and maintaining it.
The cytoskeleton is the construct in all living organisms that gives a cell its shape and holds its parts together. It is a network of fibers that are made up of proteins that both give the cell its form and provide functions that give structural support. While it is more developed in eukaryotes, in all living cells, the cytoskeleton is dynamic – always open to modifications, reconfigurations, assembly/disassembly as necessary. It also has an important role in cell membrane maintenance and cell-cell collaboration. Apart from these, the cytoskeleton’s proteins work together to facilitate DNA segregation during cell mitosis and make the cell replication/division process possible, among the most important functions of the cytoskeleton.