1. Tardigrade
  2. Question
  3. Biology
  4. Read the following statements and select the correct option: I. In the skeletal muscle fibre, a large number of myofilaments are arranged in the sarcoplasm. II. The central part of an anisotropic band where the only thick filament is present and thin filament is absent is called 'A' band. III. In the resting state, a tropomyosin protein masks the active binding sites for myosin on the actin filaments. IV. The junction between a motor neuron and the sarcolemma of the muscle fibre is called motor-end plate.

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Q. Read the following statements and select the correct option:
I. In the skeletal muscle fibre, a large number of myofilaments are arranged in the sarcoplasm.
II. The central part of an anisotropic band where the only thick filament is present and thin filament is absent is called 'A' band.
III. In the resting state, a tropomyosin protein masks the active binding sites for myosin on the actin filaments.
IV. The junction between a motor neuron and the sarcolemma of the muscle fibre is called motor-end plate.

NTA AbhyasNTA Abhyas 2020Structural Organisation in Animals

Solution:

The light bands contain actin and is called I-band or Isotropic band, whereas the dark band called ‘A’ or Anisotropic band contains myosin. Both the proteins are arranged as rod-like structures, parallel to each other and also to the longitudinal axis of the myofibrils. Actin filaments are thinner as compared to the myosin filaments, hence are commonly called thin and thick filaments respectively.
The central part of anisotropic or A band where only thick or myosin filament is present and thin or actin filament is absent is called 'H' zone. In the middle of this zone a thin fibrous membrane 'M' line is present. In a resting state, the edges of thin filaments on either side of the thick filaments partially overlap the free ends of the thick filaments leaving the central part of the thick filaments. The H zone is not overlapped by the thin filaments.