Assembly of Cytoskeletal Components

Actin and tubulin are two important cellular components that are involved in cell shape and movement. Actin is present in all mammalian cells and is involved in cellular transport and phagocytosis (eating of extracellular materials), provides rigidity to cell membranes, and when bonded to tropomyosin and troponin, forms the thin filaments of muscle. Thbulin is the subunit from which microtubules are self-assembled. Microtubules are most commonly known for their role in cell division. The mechanisms of self-assembly of these macromolecules have been well studied and are important models of biological assembly processes. Below we examine each of these processes. 

Actin exists in two states within the cytoplasm of the cell in the monomeric form (G-actin) and in the self-assembled or fibrous form (F-actin). G-actin has been shown to exist as an oblate ellipsoid by electron microscopy whereas F-actin exists as a double-helical structure. G- and F-actin exist in cells in equilibrium with actin-binding proteins. These proteins are involved in the polymerization and depolymerization of F-actin. 

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