Which protein is the principal contractile component found in thick filaments?

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

Answer: (A)

Thick filaments are built mainly from myosin, the motor protein. Each myosin molecule has a long tail that helps assemble the thick filament and a globular head that sticks out to form cross-bridges with actin on the thin filaments. When ATP is hydrolyzed, the myosin heads pull on actin, sliding the filaments past one another and generating contraction.

Actin, tropomyosin, and troponin play different roles. Actin is the primary component of thin filaments, not thick. Tropomyosin and troponin regulate whether myosin heads can bind to actin by blocking or exposing the binding sites in response to calcium, but they don’t drive contraction themselves.

So the principal contractile component found in thick filaments is myosin.