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How does ATP provide energy to reset myosin heads during the contraction cycle?
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muscle
The structure of striated, or skeletal, muscle. Striated muscle tissue, such as the tissue of the human biceps muscle, consists of long fine fibers, each of which is in effect a bundle of finer myofibrils. Within each myofibril are filaments of the proteins myosin and actin; these filaments slide past one another as the muscle contracts and expands. On each myofibril, regularly occurring dark bands, called Z lines, can be seen where actin and myosin filaments overlap. The region between two Z lines is called a sarcomere; sarcomeres can be considered the primary structural and functional unit of muscle tissue.
In the muscle contraction cycle, ATP plays a critical role in resetting the myosin head to prepare it for subsequent contractions. The process functions as follows:1
- Detachment: The binding of a new ATP molecule to the myosin head causes it to detach from the actin filament.1
- Hydrolysis and Repositioning: Once detached, the myosin head acts as an ATPase enzyme, hydrolyzing the ATP. The energy released from this breakdown is used to reposition—or "cock"—the myosin head into its high-energy state, readying it for another cycle of binding and sliding along the actin filament.213
This cycle of ATP-dependent binding, hydrolysis, and release allows myosin to function as a molecular motor, converting chemical energy into the mechanical work required for muscle contraction.2