What is the function of tropomyosin in the actin filament?

The striated appearance of myofibrils is due to the distribution pattern of two important proteins - Actin and Myosin. The light bands contain actin and the dark bands contain myosin.The light bands in a myofibril contain actin and is called I-band or Isotropic bandThe actin filaments are thinner as compared to the myosin filaments Each 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) actinsTwo filaments of another protein, tropomyosin also run close to the "F" actins throughout its length.In the resting state a subunit of troponin masks the active binding sites for myosin on the actin filaments.Two filaments of tropomyosin run close to the "F" actins throughout its length.