If muscle contracts upon stimulation, calcium ions bind to _, which exposes the binding sites for the myosin cross-bridges to attach to.
Correct answer: C. Troponin
- A. Actin
- B. Myosin
- C. Troponin
- D. Sarcomere
Explanation
Calcium binds to troponin C, causing the conformational shift in tropomyosin that reveals myosin-binding sites on actin. ATP then binds to myosin. OPTIONS A, B & D are incorrect.
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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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