What do fine filaments consist of?

Globular monomers (G-actin) forming the F-actin filaments composed of two helically entwined polypeptide chains, G-actin is characterized by binding sites on which myosin heads bind during contraction. Tropomyosin consists of two alpha helical polypeptide chains located in the groove of F-actin, Troponin is composed of 3 globular subunits forming a complex: -tropnin T (Tnt) binding to the tropomyosin -troponin I (Tni) inhibiting the attachment of myosin heads to actin at rest -Troponin C (Tnc) binding sites for calcium.