Question

Read the statements regarding muscle proteins. Which of the following statement is correct?
(A) Actin is a thin filament and is made up of two F-actins.
(B) The complex protein, tropomyosin is distributed at regular intervals on the troponin.
(C) Myosin is a thick filament, which is also a polymerised protein.
D) The globular head of meromyosin consists of light meromyosin (LMM).

• A. (A), (B) and (C) are correct
• B. (A), (B) and (D) are correct
• C. (A) and (C) are correct
• D. (B) and (D) are correct
• E. (B), (C) and (D) are correct

Answer 1

The correct option is C (A) and (C) are correct

Sarcomere forms the structural and functional unit of striated muscle fibre. Each sarcomere is a bundle of fine longitudinal myofilaments of two types:

1. Primary myofilaments: They are thickened, confined to A- band only and free at both the ends. These are formed of protein myosin. Each myosin is a polymerised protein made of many monomeric proteins called meromyosin. Each meromyosin has two important parts- a globular head with a short arm and a tail, the former is called heavy meromyosin (HMM) and the latter is called (LMM).

2. Secondary myofilaments: They are thinner, occur in I-band only but extend for some distance into A-band. They are composed of protein actin having with it two regulatory proteins: tropomyosin and troponin and are attached to Z-lines on one end and are free at the other. Each actin filament is a polymerised protein made up of two 'F' (fibrous) actin strands helically wound to each other. Each 'F' actin is a polymer of monomeric 'G' (globular) actins. Two filaments of tropomyosin proteins also run along the length of 'F' actins. Also. a complex troponin protein of three globular peptides is distributed at regular intervals on the tropomyosin.

Thus, the correct answer is option C.