Final answer:
The powerstroke in muscle contraction is caused by the hydrolysis of ATP to ADP and inorganic phosphate, mobilizing the myosin molecules to interact with actin, which leads to muscle contraction. ADP and phosphate dissociate from the myosin head, triggering the power stroke.
Step-by-step explanation:
A powerstroke in muscle contraction is facilitated by the hydrolysis of ATP and the subsequent release of a phosphate group. This process involves the binding and movement of multiple myosin molecules. When ATP is hydrolyzed to ADP and inorganic phosphate (Pi), energy is released. This energy is then used to change the conformation of the myosin head into a "cocked" position, which contains potential energy for muscle contraction.
Following the hydrolysis, ADP and Pi dissociate from the myosin head, initiating the power stroke. The myosin head forms a cross-bridge with actin, allowing for the sliding of actin and myosin filaments past each other, which results in muscle contraction. After the power stroke, a new ATP molecule binds to the myosin head, causing it to release actin and return to a cocked configuration, ready for another cycle of muscle contraction.