Lecture21-2009W - 4 movement of thin filament...

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Muscles and Animal Movement Skeletal muscle Types of muscles (1) Striated a. Skeletal b. Cardiac (2) Smooth Muscle fibers barb2right Myofibrils barb2right Sarcomere barb2right Myofilaments barb2right Actin & Myosin checkbld Z disc checkbld H zone checkbld M line checkbld I band checkbld A band Myofilament Structure: thin & thick filaments (a) Actin head2right polymerization of G-actin barb2right two-stranded helix of F-actin head2right tropomyosin + troponin complex barb2right controlling muscle contraction (b) Myosin head2right heavy chains cross bridges head2right light chains
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Muscle requires ATP to contact Myosin = ATPase molecular motor Cf) rigor mortis Myosin has two binding sites 1. Myosin+actin (rigor) 2. Myosin-ATP 3. ATP hydrolyzed by myosin 4. Actomyosin 5. Power stroke 6. ADP unbound 2 3 4 5 1 6 Contraction of sarcomeres ( Sliding-filament theory) Each myosin head provides a cross-bridge that interacts with an actin filament. Regulation of contractions 1. Ca 2+ binding 2. Myosin-binding site exposed
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Unformatted text preview: 4. movement of thin filament Excitation-contraction Coupling c Role of Calcium: cross-bridge attachment enhanced Cross-bridge cycle: Ca 2+ & ATP Ca 2+-sensitive dye (e.g. furaptra) Exp. 1 Exp. 2 Transverse tubule (T tubule): b Important role in E-C coupling & regulation of [Ca 2+ ]in The Triad Sarcoplasmic reticulum (SR) Ca 2+ storage Receptor molecules in triads (1) Dihydropyridine R (L-type Ca 2+ Ch.) (2) Ryanodine R Summary of Excitation-contraction Coupling 1. AP in motor neuron b ACh release 2. Ligand-gated channels open 3. AP in muscle b depolarizing T-tubules 4. conformational DHPR b RyR opens 5. Ca 2+ release b TN-C 6. Cross bridges b power stroke 7. muscle contraction 2 1 3 4 5 6 7 DHPR = dihydropyridine receptor RyR = ryanodine R...
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