Identify A,B and C in the above diagram:

The correct answer is A: Troponin, B: F - actin,  C: Tropomyosin

Explanation:

• Each actin (thin) filament is made of two ‘F’ (filamentous) actions 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.
• A complex protein Troponin is distributed at regular intervals on the tropomyosin.
• In the resting state a subunit of troponin masks the active binding sites for myosin on the actin filaments

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