ross-bridges form between binding sites on actin myofilaments and __________.Multiple Choicetroponintropomyosincalcium ionsmyosin heads

Answering the Multiple Choice Question

In the context of muscle contraction, the correct answer involves understanding the role of various proteins associated with actin filaments.

1. Understanding the Components:

   • Actin Myofilaments: The thin filaments in muscle fibers that interact with thick filaments during contraction.
   • Troponin: A protein that regulates muscle contraction by controlling the interaction between actin and myosin.
   • Tropomyosin: A protein that blocks the binding sites on actin for myosin heads when muscles are relaxed.
   • Calcium Ions: Ions that bind to troponin, leading to the conformational change that removes tropomyosin and allows myosin heads to bind to actin.
   • Myosin Heads: The part of the thick filament that binds to actin during muscle contraction.

2. Analysis:

   • Ross-bridges, or cross-bridges, specifically refer to the interactions that occur between the myosin heads (thick filaments) and the binding sites on actin (thin filaments) during muscle contraction.
   • The formation of these cross-bridges is a crucial step in the sliding filament theory of muscle contraction.

Final Answer

The correct answer is myosin heads. Cross-bridges form between binding sites on actin myofilaments and myosin heads during muscle contraction.