Question

In resting stage, binding sites for myosin on actin filaments are masked by

• A. Troponin
• B. Light meromyosin
• C. Heavy meromyosin
• D. Calcium ions

Answer 1

The correct option is A Troponin

• Skeletal muscle fiber is made up of two types of filaments. They are thick filament (myosin) and thin filament (actin). Contraction of a muscle fiber takes place by the sliding of the thin filaments over the thick filaments.
  
• Myosin (thick) filament is also a polymerized protein. Many monomeric proteins called meromyosins constitute one thick filament.
  
• Each actin (thin) filament is made of two ‘F’ (filamentous) actins helically wound to each other. Each ‘F’ actin is a polymer of monomeric ‘G’ (Globular) actins. Two filaments of another protein, tropomyosin also run close to the ‘F’ actins throughout its length
• In the resting state a subunit of troponin masks the active binding sites for myosin on the actin filaments.
  
• So, the correct answer is 'Troponin'.