BIOL 200 Lecture Notes - Andrew Huxley, James Spudich, Hugh Huxley
28 Jul 2012
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Document Summary
Myosin translocates actin filaments across a glass slide. Myosin-ii forms bundles that pull actin filaments inward. Muscles are made of billions of contractile bundles. Sarcomeres are tightly packed arrays of actin filaments and myosin filaments. Contraction is fast: only 50 ms for a type-ii fiber. 5-10 ms latent period between signal from brain and start of contraction. 40-45 ms contraction phase from fully elongated to fully contracted. The crossbridge cycle couples 1 atp hydrolysis to 1 power stroke . Atp hydrolysis puts myosin into a strained conformation. Phosphate release relaxes the strain in the myosin head. New atp binding releases myosin from the actin filament. Failure of myosin to detach in the absence of atp causes rigor mortis. The power stroke is understood at atomic resolution. The neck domain of myosin acts as a lever arm. Muscles face 3 design challenges: prevent continuous contraction, freeze the structure of the sarcomere, activate contraction.
