Final answer:
Actin is a protein that forms part of the cytoskeleton's microfilaments involved in maintaining cell shape, cell movement, and muscle contractions.
Step-by-step explanation:
Actin is a protein that plays a crucial role in various cellular functions, including maintaining cell shape, enabling cell movement, and facilitating muscle contraction. As a key component of the cytoskeleton, actin filaments, also known as microfilaments, comprise two intertwined strands of actin. These filaments are essential for the cytoskeletal structure, determining cell rigidity and shape, and are heavily involved in cellular activities such as locomotion and adhesion.
Actin is powered by ATP to assemble into its filamentous form, which acts as a track for the movement of motor proteins like myosin. In muscle cells, thin filaments of actin are interacted with by thick filaments of myosin to facilitate muscle contraction. Microfilaments, with a diameter of about 7 nm, are the thinnest of the three cytoskeletal filaments. They are integral in functions that include but are not limited to keeping cellular shape, forming extensions for cellular movement, and participating in cell-to-cell or cell-to-matrix junctions.