Myosin
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Myosins are class of eight molecular motor proteins found in eukaryote tissues. It is one of the key motor systems in cells; it is best known that myosin II plays a major role in both muscle contractions and cytokinesis. Other members of the myosin family have other purposes as well; myosin I and V participate in the transport of membrane vesicles while myosins VI, VII, and XV have functions related to hearing and hair cell stereocilia structure.
Together with actin filaments, myosin provides the mechanism for movement along actin fibers, utilizing energy from ATP. The specific conformational rearrangements throughout the chemo-mechanical transduction process are still not known.
Myosin's structure consists of one or two heavy chains bound to several light chains. Combined, these chains form a protein with a head, neck and tail domain. The size and form of these chains follow the function of the particular myosin
The Muscle is composed of single muscle cells (sometimes known as "muscle fibers"). Within the cells are myofibrils; the basic unit of a the contractile apparatus of a myofibril is the sarcomere, which is composed of three different filament systems, the thin filaments assembled by actin proteins, the thick filament system consisting of myosin as well as the elastic filament system composed of the giant protein titin.