Thin Filament Structure and Regulation — NEET Biology
📚 Practice ConceptEach actin (thin) filament is made of two 'F' (filamentous) actins helically wound to each other. Each 'F' actin is a polymer of monomeric 'G' (Globular) actins. Two filaments of another protein, tropomyosin also run close to the 'F' actins throughout its length. A complex protein Troponin is distributed at regular intervals on the tropomyosin. In the resting state a subunit of troponin masks the active binding sites for myosin on the actin filaments.
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.
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