Question

Read the statement regarding myofibril and choose the correct option:
1. Each myofibril has alternate dark and light bands.
2. In the center of each A band is an elastic fiber called Z-line.
3. A and I bands are arranged alternately throughout the length of myofibril.
4. The sarcomere is the functional unit of contraction.
5. The central part of thick filament not overlapped by a thin filament is the M line.

• A. 1, 3 and 5 alone are correct
• B. 2 and 5 alone are correct
• C. 2 and 3 alone are correct
• D. 1, 3 and 4 alone are correct.
• E. 1, 3 and 2 alone are correct.

Answer 1

The correct option is D 1, 3 and 4 alone are correct.

1. Each myofibril has alternate light and dark bands due to the presence of contractile proteins actin and myosin.
2. Z line is present in the center of each I band but not A band. So, this option is incorrect.
3. As shown in the diagram, A and I bands are arranged alternatively throughout the length of the myofibril.
4. The functional unit of muscle contraction is the sarcomere which shortens and lengthens during muscle contraction and relaxation.
   
5. The central part of the thick filament which is not overlapped by the thin filament is H zone and not the M line (Refer Diagram).

So, the correct option is '1, 3 and 4 alone are correct'.