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2. Muscle contraction involves the pulling of actin filaments by myosin II heads of a bipolar filament in sarcomeres. Would
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Ans 2) Myosin-II cant relax muscles. CapZ protein bind (+ end) of actin to Z-disc. Nebulin length is equal to the actin filament.Titin extends from Z-disc to M-line . Tropomodulin caps the (- end of actin). During muscle contration by (ATP and Ca2+ ions),Myosin head moves towards positive end of actin and thus actin comes to the centre of sarcomere and this will reduce the Z-disc length or muscle will contract.

For muscle relaxation, Ca2+ ions should be released from the Actin-Tropomyosin-Troponin complex so that the Myosin binding site will get masked and muscle contration will occur. (Binding of Ca2+ ions expose the Myosin binding site which will result in muscle contraction (since actin can bind to myosin now as the myosin binding site is exposed).

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