Which of the following statements about the molecular arrangement of actin and mysin In myofibre is/are incorrect ?
(i) Each actin (thin filament) is made of 2F (filamentous) actins.
(ii) F-actin is the polymer of G (globular) actin.
(iii) 2F0actins are twisted into a helix.
(iv) Two strands of tropomyosin (protein) lie in the grooves of F-actin.
(v) Troponin molecules (complex proteins) are distributed at regular intervals on the tropomyosin.
(vi) Troponin forms the head of the myosin molecule.
(vii) The myosin is a polymerised protein.

Options

A. (i), (iii) and (vii)
B. (ii), (iv) and (v)
C. Only (vi)
D. Only (iii)

Answer

C

Explanation

A complex troponin protein of three globular peptides (Troponin T-Binding to tropomyosin as well as to the other two troponin components, troponin l-inhibiting the F-actin - myosin interaction, also binding to other components of troponin, Troponin C-calcium binding polypeptide) is distibuted at regular intervals on the tropomyosin. In the resting stage of muscle fibre, a sub-unit of troponin masks the active sites for myosin on the actin filaments.