Which protein forms the thick filaments in muscle fibers?

Myosin is the protein that forms the thick filaments in muscle fibers. It plays a crucial role in muscle contraction by interacting with actin, the protein that makes up the thin filaments. During contraction, myosin heads bind to actin filaments, pulling them closer together and thereby shortening the muscle. This process is part of the sliding filament theory, which explains how muscles contract.

Myosin filaments are composed of many myosin molecules that have long tails and globular heads. The heads are capable of binding to actin and have ATPase activity, which provides the energy required for muscle contraction. In contrast, actin is the primary component of thin filaments, tropomyosin is a regulatory protein that covers binding sites on actin when muscles are relaxed, and troponin is a complex of proteins that also plays a regulatory role in muscle contraction by responding to calcium ions. Understanding the specific roles of these proteins helps clarify how muscle fibers function during contraction and relaxation.