Lecture 13 – Muscle Physiology I

Cross bridge formation is initiated when ca enters

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bound to myosin.) Cross-bridge formation is initiated when Ca enters the  cytoplasm and binds to troponin and removes the blocking o the myosin binding  sites by tropomyosin 2. Movement of the cross bridge. Producing tension in the thin filament already in a high energy configuration, bound under tension actin binding changes the configuration of the myosin head and it causes the ADP and  P to be released from the myosin
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OVERVIEW: the binding of energized myosin to actin triggers the release of the strained  conformation which producesthe movment of the bound cross-bridge (the power stroke)  and the release of ADP and P  This slides the actin molecule along the chain 3. Detachment of the cross bridge from the thin filament Binding of a new ATP molecule betqeen actin and myosin changes the configuration of  the myosin head just enough to release the actin filament from the myosin olecule Actin and myosin then dissociate and myosin is bound to ATP 4. ATP Hydrolysis following the dissociation of actin and myosin the ATP bound to myosin is hydrolyzed to  ADP and P, reforming the energized state of myosin and returning the cross-bridge to  the pre-power stroke configuration TROP mechanism Tropomyosin is a threadlike molecule that lies end to end along grooves in the actin  bead spirals In that position cross bridges cannot be formed because it covers the active site Three subunits of troponin One bionds to acin One to tropomyosin One binds to calcium When calcium is present, the configuration of the tropomyosin molecule is changed and  the binding sites are revealed Cross bridging can then happen
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