What causes cross-bridge detachment?

What causes cross-bridge detachment?

• A. ATP attaches to the myosin head and the cross-bridge detaches
• B. Calcium binds to troponin
• C. Myosin head pivots during the stroke
• D. Tropomyosin shifts to block actin

Answer: (A)

Cross-bridge detachment occurs when a molecule of ATP binds to the myosin head, causing the myosin to release from the actin filament. This binding lowers the affinity of myosin for actin, letting the head disengage so the cycle can reset. After detachment, ATP is hydrolyzed, re-energizing and repositioning the myosin head so it can form a new cross-bridge when actin sites are exposed again by calcium altering the troponin-tropomyosin complex. Calcium binding to troponin exposes the myosin-binding sites on actin and initiates contraction, while the power stroke is the actual pulling action of the cross-bridge. Tropomyosin shifting to block actin would prevent attachment in the first place.

Cross-bridge detachment occurs when a molecule of ATP binds to the myosin head, causing the myosin to release from the actin filament. This binding lowers the affinity of myosin for actin, letting the head disengage so the cycle can reset. After detachment, ATP is hydrolyzed, re-energizing and repositioning the myosin head so it can form a new cross-bridge when actin sites are exposed again by calcium altering the troponin-tropomyosin complex. Calcium binding to troponin exposes the myosin-binding sites on actin and initiates contraction, while the power stroke is the actual pulling action of the cross-bridge. Tropomyosin shifting to block actin would prevent attachment in the first place.