The cytoskeleton is transparent in standard light and electron microscope preparations, and is therefore "invisible. 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 made of tubulin subunits (see diagram on pg. 82 of Purves) and are often used by cells to hold their shape. Microtubules are also the major component of cilia and flagella. Microfilaments are made of actin subunits. These microfilaments are ap