Choose the correct statements regarding muscle proteins I. Actin is a thin filament and made up of two F-actins II. The complex protein, tropomyosin is distributed at regular intervals of troponin III. Myosin is a thick filament which is not a polymerized protein IV. The globular head of meromyosin consists of Light Meromyosin (LMM) Option containing correct statement is
a)	I, II and III	b)	I, II and IV	c)	Only I	d)	II and IV

(c)

Actin is thin filament and made up of f-actin.

Each myosin (thick filament) is a polymerized protein. Many monomeric proteins called meromyosin constitutes one thick filament. Each meromyosin has two important parts, a globular head with a short arm and a tail, the former being called heavy meromyosin and the later is called light meromyosin.

The HMM component, i.e., the head and short arm projects outwards at regular distance and angle from each other from the surface of polymerized myosin filament and is called cross arm. The globular head is an active ATPase enzyme and has binding sites for ATP and active sites for actin

Each actin (thin) filament is made up of two ‘F’ (filamentous) actins which are 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 sub-unit of troponin masks the active binding sites for myosin on the actin filaments