It is usually left out of drawings of the cell, but it is an important, complex, and dynamic cell component. The cytoskeleton maintains the cell's shape, anchors organelles in place, and moves parts of the cell in processes of growth and motility. There are many types of protein filaments that make up the cytoskeleton, but two of the most studied aspects are the microtubule and actin cytoskeletons.
Microtubules are also the major component of cilia and flagella.
Microfilaments are made of actin subunits. These microfilaments are approximately a third of the diameter of a microtubule, and are often used by cells to change their shapes as well as hold structures. There are a great number of proteins associated with the cytoskeleton, controlling its structure by directing bundling and alignment of filaments, as well as by moving the filaments around. Cytoskeletal components are also critical for the process of cell division. A brief overview of this process is shown in the next diagram.