Which protein forms the thick filaments in skeletal muscle?

• A. Myosin
• B. Actin
• C. Tropomyosin
• D. Titin

Answer: (A)

Thick filaments in skeletal muscle are formed by myosin molecules. Myosin has long tails that aggregate to create the central shaft of the filament, while the heads protrude outward to form cross-bridges with the actin-containing thin filaments during contraction. The interaction between myosin heads and actin is what generates force when calcium ions allow the binding sites on actin to be exposed. Actin forms the thin filaments, tropomyosin and troponin regulate access to those binding sites, and titin provides elasticity and helps position the thick filaments but does not form them. So the protein that makes the thick filaments is myosin.