The cytoskeleton is found within the cytoplasm of a cell and is fundamental to the functioning and structure of a cell. In fact, current research has found that a cytoskeleton is necessary for all cells, both eukaryotic and prokaryotic.
The cytoskeleton is comprised of three polymers: microtubules, microfilaments and intermediate filaments, along with some accessory proteins. Microfilaments are the smallest in size, followed by intermediate filaments and then microtubules. Furthermore, microfilaments are made up of actin, intermediate filaments are composed of various subunits and microtubules are built of tubulin polymers.
One critical feature of the cytoskeleton is that it has the ability to undergo assembly and disassembly. This need to change cell shape or orientation is triggered by extracellular signals. These two processes, assembly and disassembly, take place simultaneously and become equal at a certain critical concentration.
In terms of cell structure, the cytoskeleton is important for maintaining cell shape, for monitoring the internal organization of membrane networks and for keeping the overall robustness of a cell. Additionally, the cytoskeleton is crucial for functions carried out by a cell. These functions include cell movement through the use of flagella and cilia for example, movement at the organismal level such as through the use of muscles, signal transduction and intracellular traffic such as vesicle transport.
Furthermore, the components of the cytoskeleton contact the cell membrane through focal contacts and cadherins. Cadherins are required for connecting different cells to each other and focal contacts link the cell to the surface.
Understanding the function and overall importance of the cytoskeleton is vital to comprehending the subject of cell biology. Although more detailed and specific information pertaining to this topic becomes rather complicated, this discussion provides a good introduction on how to define the cytoskeleton.