Question

During the resting state, the myosin binding sites on actin filaments are blocked by

• A. none of these
• B. tropomyosin
• C. troponin-tropomyosin complex
• D. troponin

Answer 1

The correct option is B tropomyosin

During the resting state, the myosin binding sites on actin filaments are blocked by tropomyosin. Each actin (thin) filament is made up of 2 F (filamentous) actins helically wound to each other. 2 filaments of tropomyosin also run close to the F actins throughout its length. They block the myosin binding sites on actin filaments.
Troponin is another protein which is distributed along regular intervals. It holds the tropomyosin in place.