Which filament is known as the thick filament that comprises the myofibril?

The thick filament that comprises the myofibril is known as myosin. This protein is crucial for muscle contraction, functioning as a motor protein that interacts with the thin filaments (actin) during the contraction process. Myosin filaments are characterized by their size and structure, which includes long tail regions and globular heads that extend outward. The heads of the myosin molecules bind to actin, forming cross-bridges, and through a series of chemical reactions involving ATP, they generate the force required for muscle contraction.

Understanding myosin's role provides insight into the mechanics of muscle movement and how muscle fibers are structured and work during contraction and relaxation. The other proteins mentioned, such as actin, tropomyosin, and troponin, play important roles as well, but they are not the thick filaments; rather, they assist in regulating the interaction between thick and thin filaments during the contraction cycle.