The power stroke in muscle contraction b. the cross-bridge formation between myosin and actin. Therefore , b. the cross-bridge formation between myosin and actin is correct .
During muscle contraction, the thin filaments (actin) and thick filaments (myosin) interact in a highly coordinated manner.
The power stroke is a pivotal event within the cross-bridge cycle. Here's a detailed explanation:
When a muscle is stimulated, calcium ions are released from the sarcoplasmic reticulum (option a).
These calcium ions bind to troponin, leading to a conformational change in tropomyosin, exposing the myosin-binding sites on actin.
Myosin, an ATPase enzyme, hydrolyzes ATP into ADP and inorganic phosphate (option d), resulting in the energized myosin head.
The energized myosin head then forms a cross-bridge by binding to the exposed myosin-binding site on actin.
This is the power stroke (option b). During the power stroke, the myosin head pivots, pulling the thin filament (actin) toward the center of the sarcomere.
This action shortens the sarcomere and causes muscle contraction.
Following the power stroke, ATP binds to the myosin head, leading to its detachment from actin (option c).
This detachment allows the myosin head to reset and form another cross-bridge in the presence of calcium ions, restarting the cycle.
The power stroke corresponds to the force-generating step in muscle contraction, involving the physical movement of myosin along actin filaments, ultimately leading to muscle shortening and force generation.