Out of three polypeptides of troponin one binds to the actin chain, another binds to tropomyosin while third binds:
Correct answer: D. Calcium ions
- A. Myosin
- B. Collagen
- C. Sodium ions
- D. Calcium ions
Explanation
The correct answer is option D. The troponin complex consists of three subunits: one binds to actin, another to tropomyosin, and the third to calcium ions. When calcium ions bind to troponin, it triggers a conformational shift that displaces tropomyosin from the myosin-binding sites on actin, allowing cross-bridge formation and muscle contraction.Option A, Myosin, does not directly bind to troponin; it interacts with actin to produce contraction.Option B, Collagen, is unrelated to the troponin complex and the mechanism of muscle contraction.Option C, Sodium ions, are crucial for initiating action potentials but do not interact with troponin.
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About Muscle Contraction
Muscle contraction is explained by the sliding filament model, in which myosin heads pull actin filaments within sarcomeres using ATP. The topic covers calcium, troponin, tropomyosin, the neuromuscular junction and relaxation, with attention to how filament length stays almost constant while the sarcomere shortens.
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