Actin filaments, also known as microfilaments or F-actin, are one of three major components of the cytoskeleton. Actin filaments are polymers of globular actin subunits, G-actin, organized as a two-stranded helical structure of about 7 nm in diameter. Actin filaments are polar, with one fast-growing barbed end and one slow-growing pointed end, the dynamics of which are important to the organization and function of actin filaments. Actin filaments play major roles in mechanical support and cell shape, as well as in cell motility and contractility. They can be organized in long and straight bundles, as well as in three dimensional networks of filaments, with close connections to the plasma membrane. Actin filaments also connect cells to the extracellular matrix, through focal adhesions. During cytokinesis, actin filaments and the motor protein myosin form the contractile ring at the cell cortex, which upon constriction gives rise to a cleavage furrow and eventually divides the cell into two daughter cells. Actin filaments also serve as avenues for intracellular transport of vesicles and organelles, and provide a scaffold for cellular processes such as signal transduction.
Actin filaments are often concentrated in close proximity to the plasma membrane, in the region known as the cell cortex, often extending from sites of cell adhesion or membrane protrusion. Actin filaments can be found as long and rather straight bundles of filaments or as branched networks of thinner filaments.
Read more about the proteome of actin filaments.