Skeletal Structure and Muscle Filaments — NEET Biology
📚 Practice ConceptWrite true or false. If false change the statement so that it is true. (a) Actin is present in thin filament (b) H-zone of striated muscle fibre represents both thick and thin filaments. (c) Human skeleton has 206 bones. (d) There are 11 pairs of ribs in man. (e) Sternum is present on the ventral side of the body.
Which of the following statements about muscle structure and protein function are correct? S1: Each 'F' actin filament, a polymer of monomeric 'G' actins, is associated with two helical tropomyosin filaments that run throughout its length. S2: The heavy meromyosin (HMM) component, which includes the globular head and a short arm, projects outwards as the cross arm and has an active ATPase enzyme activity. S3: Troponin is a complex protein distributed at regular intervals on the F-actin filament, masking the myosin binding sites in a resting muscle. S4: The Z-line is an elastic fibre that bisects the 'I' band and serves as the anchoring point for the thick filaments. S5: In a resting state, the 'H' zone represents the central part of the 'A' band where the thick filaments are partially overlapped by the thin filaments.
View solution & NCERT explanation
Correct answer: B — S1 and S2 are correct
Let's evaluate each statement regarding muscle structure and protein function based on NCERT: S1: Each 'F' (filamentous) actin is made of two 'F' actins helically wound to each other, and two filaments of tropomyosin also run close to the 'F' actins throughout its length. This statement is correct. S2: The heavy meromyosin (HMM) component, consisting of the globular head and a short arm, projects outwards as the cross arm. The globular head is indeed an active ATPase enzyme. This statement is correct. S3: Troponin is a complex protein distributed at regular intervals on the *tropomyosin*, not directly on the F-actin filament. It masks the active binding sites for myosin on the actin filaments in the resting state. Therefore, this statement is incorrect. S4: The Z-line is an elastic fibre that bisects the 'I' band, and the *thin* filaments (actin) are firmly attached to the 'Z' line, not the thick filaments. Therefore, this statement is incorrect. S5: In a resting state, the 'H' zone is the central part of the thick filament *not overlapped* by thin filaments. Therefore, this statement is incorrect. Only S1 and S2 are correct.
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Through deep analysis of NEET and NTA, 176 of the 180 ReNEET 2026 (June 21) questions were already in the MedicNEET question bank before the exam.
176/180MedicNEET's Biology question bank is built from the same NCERT lines NTA picks repeatedly. Not random MCQs — questions crafted exactly like NTA crafts them.