Answer:
Power stroke (myosin head bends) coupled with the release of ADP and phosphate
Explanation:
Muscle contraction results from myosin heads adhering to actin and attracting it inwards. It uses ATP. Myosin adhers to actin at a binding site of its globular actin protein and adheres at another binding site for ATP (hydrolyzed ATP to ADP, Pi and energy)
ATP binding prompts myosin to detach from actin, ATP is changed to ADP and inorganic phosphate, Pi by ATPase. The energy formed at this process orientates myosin head to a “cocked” direction.
The myosin head goes in the direction of the M line, holding the actin with it in the process causing the filaments to orientate nearly 10 nm in the direction of the M line--- power stroke (force is produced), the sarcomere reduces in length and the muscle contracts.
Note: The power stroke is seen when ADP and phosphate disattaches itself from the myosin head.
At the terminal point of the power stroke, the myosin head as low-energy, followed by ADP release.
The attached image shows the cross-bridge muscle contraction cycle, which is activated by Ca2+ sticking to the actin active site. And how actin moves in relation to myosin.
