Foundation
Biology Foundation
Nervous Control and coordination
Question
Read the statements regarding muscle proteins. Which of the following statement is correct?
(A) Actin is a thin filament and is made up of two F- actins.
(B) The complex protein, tropomyosin is distributed at regular intervals on the troponin.
(C) Myosin is a thick filament, which is also a polymerised protein.
D) The globular head of meromyosin consists of light meromyosin (LMM).
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Solution
Sarcomere forms the structural and functional unit of striated muscle fibre. Each sarcomere is a bundle of fine longitudinal myofilaments of two types :
(1). Primary myofilaments: They are thickened, confined to A - band only and free at both the ends. These are formed of protein myosin. Each myosin is a polymerised protein made of many monomeric proteins called meromyosin. Each meromyosin has two important parts- a globular head with a short arm and a tail, the former is called heavy meromyosin (HMM) and the latter is called (LMM).
(2). Secondary myofilaments: They are thinner, occur in I-band only but extend for some distance into A-band. They are composed of protein actin having with it two regulatory proteins: tropomyosin and troponin and are attached to Z-lines on one end and are free at the other. Each actin filament is a polymerised protein made up of two 'F' (fibrous) actin strands helically wound to each other. Each 'F' actin is a polymer of monomeric 'G' (globular) actins. Two filaments of tropomyosin proteins also run along the length of 'F' actins. Also. a complex troponin protein of three globular peptides is distributed at regular intervals on the tropomyosin.