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When cytoplasmic Ca²⁺ levels are low, What blocks the myosin-binding site on actin?

1) Tropomyosin
2) Troponin
3) Myosin
4) Actin

User AndyD
by
7.9k points

1 Answer

5 votes

Final answer:

Tropomyosin blocks the myosin-binding site on actin when Ca²⁺ levels are low; it moves away when calcium binds to troponin, permitting muscle contraction.

Step-by-step explanation:

When cytoplasmic Ca²⁺ levels are low, the myosin-binding site on actin is blocked by tropomyosin. Tropomyosin is a protein that winds around the actin filament chains, covering the myosin-binding sites to prevent interaction with myosin. It is part of the troponin-tropomyosin complex, which is regulated by calcium ions, Ca²⁺. When calcium binds to troponin within the complex, tropomyosin moves away from the myosin-binding sites on actin, allowing for muscle contraction to occur.

User Straff
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