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Actin is a protein in a muscle fiber sarcomere that, with myosin, is responsible for contraction and relaxation. During contraction, actin filaments are pulled toward the center of the sarcomere by the action of the myosin filaments, causing the sarcomere to shorten.

The actin proteins in the sarcomere make up the thin I-band of the myofilament, together with troponin and tropomyosin, which form the core of the thick filament made up the the myosin proteins. Each actin molecule has a myosin binding site which the head of the mysoin filament attaches, which is referred to as a cross-bridge.

Actin is a major component of the cytoskeleton of cells and is present in all eukaryotic cells.

Myofilament diagram of muscle cell showing actin and myosin

This page created 17 Sep 2011 22:14
Last updated 17 Jul 2016 22:23

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