2.9. Cytoskeleton

The cytoskeleton is an intricate network of filamentous proteins that runs throughout the cytosol., and provides an endoskeletal framework for a cell much the same way that bones provide a scaffolding for human bodies. In addition to its structural role, the cytoskeleton also functions as a road network for molecular motors - proteins that move organelles, vesicles, and even other proteins throughout the cell. Microtubules are hollow cytoskeletal tubes that consist of many protein subunits, called tubulin, stacked in a long, narrow coil that is 24 nanometers in diameter. These structures are continuously polymerizing  and degrading, and are hence constantly elongating and shrinking. They provide support to the cell, direct vesicle-bearing molecular motors to the plasma membrane, and are key during cell division. Microfilaments, which are smaller than microtubules (5–7 nanometers in diameter), are also important cytoskeletal elements. The filaments consist of actin proteins stacked in a long column and act as highways for the molecular motor myosin to move along. The coördinated actions of actin and myosin serve in organelle movement and vesicle transport.