Question

Sarcomere is the functional unit of contraction in a muscle fibre. Identify the portion of myofibril that constitutes a sarcomere

• A. Portion of myofibril between two successive Z-lines
• B. Portion of myofibril between two successive I-bands
• C. Portion of myofibril between two successive A-bands
• D. Portion of myofibril between two successive M-lines

Answer 1

The correct option is A Portion of myofibril between two successive Z-lines

• The ‘A’ and ‘I’ bands are arranged alternately throughout the length of the myofibrils. The light bands contain actin(thin filament) and are called I-band or Isotropic band, whereas the dark band called ‘A’ or Anisotropic band contains myosin(thick filament).
• In the centre of each ‘I’ band is an elastic fibre called ‘Z’ line which bisects it. The thin filaments are firmly attached to the ‘Z’ line. The portion of the myofibril between two successive ‘Z’ lines is considered as the functional unit of contraction and is called a sarcomere Sarcomere is considered as the functional unit of contraction in a muscle fibre.
  
• So, the correct answer is 'Portion of a myofibril between two successive Z-lines'.