Question

Read the following statements and find out the incorrect statements.

a. Each actin (thin) filament is made of two ‘G‘ (Globular) actins helically wound to each other.
b. Each ‘G‘ actin is a polymer of monomeric ‘F’ (Filamentous) actins.
c. Two filaments of another protein, troponin also run close to the ‘F' actin throughout its length.
d. In the resting state, tropomyosin masks the active binding sites for myosin on the actin filaments.
e. Each meromyosin has two parts, a globular head with a short arm (HMM) and a tail (LMM).

• A. a, b and c
• B. b, c and d
• C. a, b and e
• D. c, d and e

Answer 1

The correct option is A a, b and c

Incorrect statements

Statement a: Each actin (thin) filament is made of two ‘G‘ (Globular) actins helically wound to each other.

Elaboration: Each actin (thin) filament is made of two ‘F’ (filamentous) actin helically wound around each other.
Each ‘F’ actin is a polymer of monomeric ‘G’ (globular) actins.

Statement b: Each ‘G‘ actin is a polymer of monomeric ‘F’ (Filamentous) actins.

Elaboration: The thin filament consists of the proteins: actin, troponin, and tropomyosin.
The actin protein that makes up most of the thin filament is filamentous in form and hence is called F actin. F actin is a polymer of G (globular) actin monomers.

Statement c: Two filaments of another protein, troponin also run close to the ‘F' actin throughout its length.

Elaboration: Two filaments of another protein, tropomyosin, also run close to the ‘F’ actin throughout their lengths. Troponin is a complex protein, which is distributed at regular intervals on tropomyosin.

Final answer: (A) a, b and c