Answer
The Power Stroke
ATP is the source of energy for prolonged muscular activity. In order to initiate contraction, myosin must bid to ATP. Myosin ATPase then hydrolyses ATP ( ADP+Pi) and energy is released; this energy activates the myosin bending the head in a position for hooking. Next the activated myosin head binds to an exposed site on an actin filament and forms a cross-bridge. When the myosin head binds to the actin filament, the former releases the bound ADP and Pi, species. It (the myosin head) then flexes and pulls the actin filament with it in the power stroke. The myosin head remains bound to the actin filament until it picks up a new ATP molecule.
Work Step by Step
The Recovery Stroke.
After contraction, an ATP molecule binds to a myosin head in the cross-bridge complex. This destabilizes the cross-bridge. Next, myosin ATPase hydrolyzes ATP. This reactivates the myosin head and it bends once again into a position that enables it to bind to a new actin filament. This is the recovery stroke.
ATP provides the energy for both power and recovery strokes.
