What are hybrid muscle fibers?

What are the contractile protein fibers of a muscle cell?

• What are the contractile protein fibers of a muscle cell? a. ADH and PTH b. K and Ca c. actin and myosin d. lipase and amylase

• Answer:

  Actin, Myosin, Tropomyosin and Troponin. Actin In the native state, actin is a roughly globular protein with a molecular weight of approximately 46,000 called G actin. In the presence of ATP, G actin causes hydrolysis of the ATP and aggregates into a double helical structure called F-actin having a molecular weight of approximately 14,000,000. F actin can interact with troponin and tropomyosin (see figure 4). The bound ADP can interact with the head units of myosin. The interaction of actin with myosin can lead to motion in muscle. Tropomyosin and Troponin Two other proteins associate with actin to from the thin fliaments. Tropomyosin is compose of two polypeptides (a- and b-tropomyosin). Together they make up from 5 to 8% of the myofibrillar protein. These polypeptides aggregate to form long filaments that fit within the grove formed by the two chains of actin. Each molecule spans seven actin molecules and controls the reactivity of these actin molecules. Troponin is made up of three subunits. Troponin C conatins a calcium binding domain, troponin, T interacts with tropomyosin and tropinin I can block the actin binding site for myosin. One set of three troponin subunits is associated with each molecule of tropomyosin and is involved with the activity of seven actin molecules.