Muscle and Bone - Muscle structure and function; Bone...

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Muscle structure and function; Bone Structure: fiber – myofibril – contractile element - fiber: one “giant cell” - many nuclei per cell Myofibril - is the contractile structure - Thin filaments = Actin - Thick filaments = Myosin Contraction: Sarcomere: functional unit of striated muscle - Sarcomere contracts - filaments do not change length; degree of overlap changes; sarcomere is shorter Detail: - Cross bridges = “myosin head groups” - Myosin head group attaches to actin Sliding filament model: - Actin and myosin are bound - ATP binds to myosin and causes a dissociation (i.e. actin and myosin become unbound) - ATP hydrolyzed to ADP + P (note that P still attached!) - Myosin re-attaches … with ADP and P - P is released. When this happens, energy is released - this stimulates the power stroke (conformation change ) The role of Calcium: Actin has two associated proteins: Tropomyosin and Troponin Steps: - Myosin binding site on Actin is blocked by tropomyosin - calcium binds to Troponin - conformational change of Troponin pushes tropomyosin away
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Muscle and Bone - Muscle structure and function; Bone...

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