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Unformatted text preview: al unit of skeletal muscle Found b/t two Z lines (connects thin filaments of two adjoining sarcomeres). Myosin- component of thick filament Protein molecule consisting of two identical subunits shaped somewhat like a golf club. • • • Tail ends are interwined around each other Globular heads project out at one end. Tails oriented toward center of filament and globular heads protrude outward at regular intervals. • • Heads form cross bridges b/t thick and thin filaments Cross bridge has two important sites critical to contractile process • • • • • • • • An actin-binding site. A myosin ATPase (ATP splitting) site Actin Primary structural component of thin filaments Spherical in shape Thin filaments also has other proteins Tropomyosin and troponin Each actin molecule has special binding site for attachment with myosin cross bridges. • • • • Binding results in contraction of muscle fiber. Actin and myosin Actin and myosin are often called contractile proteins. Neither actually contractes. Actin and myosin are not unique to muscle cells, but are more abundant andmore highly organized in muscle cells. • • • • • Tropomyosin and Troponin Often called regulatory proteins Tropomyosin Thread like molecules that lie end to end alongside groove of actin spiral. In this position, covers actin sites blocking interaction that leads to muscle contraction. • • Troponin Made of three polypeptide units • • • • One binds to tropomyosin’ One bind to actin One can bind w/ Ca Troponin- when not bound to Ca, troponin stabilizes tropomyosin in blocking position over actin’s cross-bridge binding sites. • • • • • • • When Ca binds to troponin, tropomyosin moves away from blocking position. With tropomyosin out of the way, actin and myosin bind, interact at cross-bridges Muscle contractions results. Sliding Filament Mechanism Increase in Ca starts filament sliding Decrease in Ca turns off sliding process Thin filaments on each side of sacromere slide inward over stationary thick filaments toward cen...
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This note was uploaded on 09/23/2010 for the course NPB 8746546 taught by Professor Goldberg during the Spring '10 term at UC Davis.
- Spring '10