Question

Describe the role of specific proteins involved in the muscle contraction process.

Answer 1

Muscles contraction occurs by the action of two proteins actin and myosin. Myosin is a motor protein which produces the force in a muscle contraction as the stroke. It consists of a head and a tail region. The tails of three hundred myosin molecules form the shaft of the thick filament. The myosin heads of these molecules project outward toward the thin filaments.

Actin is a spherical protein, which forms the thin filament in muscle cells. Thin filaments are composed of two long chains of actin molecules, which are twisted around one another. Each actin molecule has a myosin-binding site where a myosin head can bind.

Skeletal muscle is composed of a repeating structure of myosin and actin fibers. Each myosin thick filament, which is surrounded by actin thin filaments and each thin filament is surrounded by thick filaments. These filament bundles form the functional portion of a muscle cell. During the process of contraction, myosin heads in the thick filaments bind actin in the thin filaments and pull the thin filaments in towards the center. There are many sites at which myosin binds actin and runs the entire length of the thin filament or thick filament overlap. This process is similar to pulling on a rope, with each pull , the rope (or thin filament) is pulled inward more. During this contraction, the ends of the sarcomeres are pulled closer together, therefore shortening the length of the muscle fiber.

The regulatory proteins tropomyosin and troponin, which control voluntary movements.

Tropomyosin and troponin are two other proteins found in small quantities in muscle. They help regulate muscle contraction. Troponin is combined with the thin filaments and can bind to the actin molecules.

Tropomyosin is a long thin protein, which enlarges between and binds to the troponin molecules. When troponin is bound to actin, the tropomyosin is positioned so it prevents the myosin heads from contacting actin, therefore they prevent contraction.