Each actin filament is made of two ‘F’  or filamentous actins. These are helically wound to each other. The ‘F’ actin is a polymer of monomeric
‘G’ (Globular) actins. Two filaments of another protein, tropomyosin are also present close to the ‘F’ actins throughout its length. Troponin a complex protein is found at regular intervals on the tropomyosin.