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Solution


Q.

During muscular contraction which of the following events occur
(A) ‘H’ zone disappears.
(B) ‘A’ band widens.
(C) ‘I’ band reduces in width.
(D) Myosine hydrolyzes ATP, releasing the ADP and Pi.
(E) Z-lines attached to actins are pulled inwards.

Choose the correct answer from the options given below:                     [2021]
1 (B), (D), (E), (A) only  
2 (A), (C), (D), (E) only  
3 (A), (B), (C), (D) only  
4 (B), (C), (D), (E) only  

Ans.

(2)

During muscle contraction, the thin myofilaments i.e., actin slide inwards towards the H-zone. As the thin myofilaments move past the thick myofilaments, the H-zone narrows and even disappears during contraction. Utilising the energy from ATP hydrolysis, the myosin head now binds to the exposed active sites on actin to form cross bridge. The ‘Z’ line attached to these actins are pulled inwards thereby causing shortening of the sarcomere. Size of I-bands shorten, but the width of the A-band remains constant.