Final answer:
Thick filaments in muscle cells are composed of myosin, while thin filaments are primarily composed of actin. Tropomyosin and troponin are other components of thin filaments. Thick filaments allow for muscle contraction, while thin filaments regulate the process by blocking the binding sites of actin and myosin.
Step-by-step explanation:
Thick filaments in muscle cells are composed of the protein myosin. The tail of a myosin molecule connects with other myosin molecules to form the central region of a thick filament near the M line, while the heads align on either side of the thick filament where the thin filaments overlap.
On the other hand, thin filaments are primarily composed of the protein actin. They also contain two other components, tropomyosin and troponin. Actin has binding sites for myosin attachment, while tropomyosin strands block these binding sites to prevent actin-myosin interactions when the muscles are at rest.
Troponin consists of three subunits, with one binding to tropomyosin, one binding to actin, and one binding to calcium ions.