When calcium binds to troponin, what happens to tropomyosin?

• A. It binds and covers the actin binding site
• B. It is removed from the actin binding site
• C. It creates a crossbridge structure
• D. It triggers ATP hydrolysis and myosin movement

Answer: (B)

Verified step by step guidance

1. Understand the role of calcium in muscle contraction: Calcium ions play a crucial role in the regulation of muscle contraction by binding to troponin, a regulatory protein associated with the actin filaments in muscle cells.
2. Identify the function of troponin: Troponin is a complex of three proteins (troponin C, I, and T) that regulate the interaction between actin and myosin, the proteins responsible for muscle contraction.
3. Recognize the effect of calcium binding to troponin: When calcium ions bind to troponin C, it causes a conformational change in the troponin complex.
4. Determine the impact on tropomyosin: The conformational change in troponin moves tropomyosin away from the actin binding sites, exposing them for myosin binding.
5. Conclude the process: With the actin binding sites exposed, myosin heads can attach to actin, forming crossbridges, which is a critical step in muscle contraction.