During the 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.

Solution & Explanation

Answer: C. During contraction the thin filaments slide over the thick filaments: the 'H' zone disappears (a) and the 'I' band reduces in width (c), while the 'A' band retains its length and does NOT widen, so (b) is wrong. The myosin head hydrolyses ATP, releasing ADP and Pi (d), and the 'Z' lines attached to the actins are pulled inwards (e). Hence the correct events are (a),(c),(d),(e). NCERT Ch 17, p.222, line 20: "The 'Z' line attached to these actins are also pulled inwards thereby causing a shortening of the sarcomere, i.e., contraction." NCERT Ch 17, p.222, line 22: "during shortening of the muscle, i.e., contraction, the 'I' bands get reduced, whereas the 'A' bands retain the length".