- A ATP molecules themselves are sometimes thought to directly and mechanically push against the actin filament structure, forcing the sliding motion uniformly throughout the sarcomere as widely reported in standard practice under most conditions encountered
- B Myosin head binds actin in cocked position (with bound ADP+Pi); Pi release triggers power stroke (myosin swings 45-90 degrees, moving actin 5-10nm); ADP released; rigor state; new ATP binds causing detachment and re-cocking of myosin head
- C ATP itself is sometimes thought to be hydrolyzed at the exact moment that the power stroke event actually occurs during each individual cycle of the cross-bridge process as frequently observed in practice in many documented cases according to conventional understanding
- D The power stroke event is sometimes thought to occur mainly after the myosin head has largely dissociated from the actin filament beforehand in most instances in routine practice overall in most cases under typical conditions according to standard textbooks
Correct answer: B. Myosin head binds actin in cocked position (with bound ADP+Pi); Pi release triggers power stroke (myosin swings 45-90 degrees, moving actin 5-10nm); ADP released; rigor state; new ATP binds causing detachment and re-cocking of myosin head
Explanation: Cross-bridge cycle: (1) ATP hydrolysis re-cocks myosin head to 90 degrees; (2) Myosin head binds actin (Ca2+ needed to expose site); (3) Pi release triggers power stroke (head swings to 45 degrees, moves actin ~10nm); (4) ADP released (rigor state); (5) New ATP binds myosin head, causing detachment; cycle repeats as long as Ca2+ is present.
Concept context
Types of movement, muscle contraction, skeletal system, joints, and disorders. Important for Class 11 and NEET.