Final answer:
Cross-bridges are comprised of an elongated dimeric protein called myosin, which forms a link with actin filaments during muscle contraction. The cross-bridge cycling process is crucial for muscle contraction and is powered by ATP hydrolysis.
Step-by-step explanation:
The elongated dimeric protein that comprises cross-bridges in muscle contraction is called myosin. Cross-bridge cycling involves the interaction between the myosin heads and the thin actin filaments, a key process in muscle contraction.
During this cycle, myosin heads extend from the thick filaments and bind to actin to form a cross-bridge. This occurs when both adenosine diphosphate (ADP) and inorganic phosphate (Pi) are attached to myosin. The release of Pi after the binding enhances the attachment, leading to the power stroke. This power stroke pulls the actin filament toward the M-line of the sarcomere, resulting in muscle contraction.
Regulatory proteins such as troponin and tropomyosin control the binding of myosin to actin, while ATP provides the energy required for the cross-bridge formation and subsequent filament sliding. The sliding filament model of muscle contraction explains how the thick and thin filaments slide past each other to shorten the muscle during contraction.