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MDCAT Biology QUESTION #4292
Question 1
Why are thick filaments unable to bind with thin filaments in a relaxed muscle fiber?
  • Actin blocks the myosin binding site
  • Tropomyosin blocks the myosin binding site✔️
  • Troponin blocks the myosin binding site
  • Tropomyosin blocks the troponin binding site
Correct Answer Explanation
In a relaxed muscle, tropomyosin covers the myosin-binding sites on actin filaments, preventing cross-bridge formation. Calcium ions ($Ca^{2+}$) are required to move tropomyosin away.