The cytoskeleton is not a membrane bound organelle, but instead consists of a meshwork of various filaments that extends from the cell membrane and provides the cell with organization, stability, shape and, in some cases, movement. Three main types of filaments make up the cytoskeleton, and each is composed of highly ordered protein subunits:
- Microtubules : These structures are made up of tubulin subunits, arranged in parallel rows that form hollow tubes. Microtubules are critical in vesicle and organelle movement and in cell division.
- Microfilaments : These structures differ in their subunits, but always contain the proteins actin and myosin. They are involved in cell movement.
- Intermediate filaments: These cytoskeletal components differ in their proteins make up, depending on the type of filament, and most are cell specific. All intermediate filaments form structural meshworks in the cytoplasm or in the nuclear envelope. Researchers can usually determine the type of cell they are working with by identifying which types of intermediate filaments are present.