How does the presence of calcium ions affect the interaction between actin and myosin?

• A. Calcium ions bind directly to myosin, enhancing its binding to actin.
• B. Calcium ions inhibit ATP hydrolysis, stopping muscle contraction.
• C. Calcium ions bind to troponin, causing tropomyosin to move and expose actin binding sites for myosin.
• D. Calcium ions bind to actin, preventing myosin from attaching.

Answer: (C)