[Answer] What is actin?

Answer: Thin filament protein. Twisted into a double helix and appears like a double-stranded chain of pearls. Contains the myosin-binding site.
What is actin?

Actin is a family of globular multi-functional proteins that form microfilaments. It is found in essentially all eukaryotic cells where it may be present at a concentration of over 100 μM; its mass is roughly 42-kDa with a diameter of 4 to 7 nm.

An actin protein is the monomeric subunit of two types of filaments in cells: microfilaments one of the three major components of the cytoskeleton and thin filaments part of the contractile apparatus in muscle cells. It can be present as either a free monomer called G-actin (globular) or as part of a linear polymer microfilament called F-actin (filamentous) bo…

An actin protein is the monomeric subunit of two types of filaments in cells: microfilaments one of the three major components of the cytoskeleton and thin filaments part of the contractile apparatus in muscle cells. It can be present as either a free monomer called G-actin (globular) or as part of a linear polymer microfilament called F-actin (filamentous) both of which are essential for such important cellular functions as the mobility and contraction of cells during cell division . Actin participates in many important cellular processes including muscle contraction cell motility cell division and cytokinesis vesicle and organelle movement cell signaling and the establishment and maintenance of cell junctions and cell shape. Many of these processes are mediated by extensive and intimate interactions of actin with cellular membranes . In vertebrates three main groups of actin isoforms alpha beta and gamma have been identified. The alpha actins found in muscle tissues are a major constituent of the contractile apparatus. The beta and gamma actins coexist in most cell types as components of the cytoskeleton and as mediators of internal cell motility . It is believed that the diverse range of structu…

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