Draw and explain structure of contractile …

Skeletal muscle is composed of muscle fibers which have smaller units called myofibrils. There are three types of proteins make up each myofibril; they are contractile, regulatory and structural proteins.

By contractile proteins, we mean actin (thin filament) and myosin (thick filament). Each actin filament is composed of two helical “F” actin (filamentous actin) and each ‘F’ actin is made up of multiple units of ‘G’ actin. Along with the ‘F’ actin, two filaments of regulatory proteins tropomyosin and troponin at regular intervals are present. During muscle relaxation, troponin covers the binding sites for myosin on actin filaments.

Each myosin is composed of multiple units of meromyosin which has two important parts- a globular head known as heavy meromyosin with a short arm and a tail known as light meromyosin. The head and arms project at regular distance and angle from each other from the surface of myosin filament and are known as the cross arm. The head bears binding sites for ATP and active sites for actin. Let us now try to understand the muscle contraction mechanism.