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BIOL 273 (91)


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University of Waterloo
BIOL 273
Norman Scott

2bFunctio n(MuscleContra ctio n) Musclecontraction - muscle contraction occurs when filaments slide tgt (pg. 405) - degree of overlap b/t thick and thin filaments increases - band width and zones changes: distance from z-disk to z-disk becomes smaller, closer tgt when contraction occurs. Each sarcomere gets shorter > each myofibril in muscle cell gets shorter as well > entire muscle shortens - increase in internal tension (i.e. the force that tends to pull the ends of the muscle toward each other) The overall muscle length MAY decrease (depending on the size of its load). Increase in internal tension when contraction occurs, but not necessarily the decrease in length of the overall muscle - what causes filaments to slide tgt ? - the myosin heads attach to spots of the thin filament and pull the thin filament forward repeatedly - requires energy = ATP (myosin use ATP to force the sliding tgt of the filaments) - myosin: a motor protein (kinesin in nervous system) - the contraction cycle: printed **** - During a contractile cycle, each myosin head group binds temporarily to an ATP molecule, and to the actin molecules of the adjacent filament. The swiveling of the myosin head groups while attached to thin filaments, forces the thin filaments to slide past the thick filaments - cycle goes on until there's nothing to prevent it - the collection of myosin head groups of a single filament pull on all of the nearby thin filaments - every thick filament is causing sliding of the six thin filaments that are surrounding it - every thin filament is being pulled by each of those three thick filaments adjacent to it - the pull is asynchronous, so that sliding is a smooth motion: dragon boat paddlers stroke at the same time so the boat accelerates and glides (NOT the way muscle operates
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