Question

Which protein is a contraction protein with site regulated by regulatory proteins

A sarcomere

B I band

C overlap zone

D H zone

E A band

Answer 1

Muscle Contraction
Contractile proteins of muscle are actin and myosin, the main components of the thin and thick filaments, respectively
. The two heads are called the myosin heads, or cross bridges. The tails point toward the center of the sarcomere (toward the M lines), while the head projects toward one of the thin filaments and contains an actin-binding site, an ATP binding site, and an ATPase.

The thin filaments extend from the Z lines; they are formed by the actin molecules twisted in a helix. Each molecule has a myosin-binding site for the myosin head.

The “regulatory” proteins troponin and tropomyosin are also part of the thin filament. Troponin has three subunits: TnT, which binds to tropomyosin; TnC, which binds calcium; and TnI, which inhibits the actin–myosin interaction.The binding of the myosin heads to the muscle actin is a highly-regulated process. When a muscle is in a resting state, actin and myosin are separated. To keep actin from binding to the active site on myosin, regulatory proteins block the molecular binding sites. Tropomyosin blocks myosin binding sites on actin molecules, preventing cross-bridge formation, which prevents contraction in a muscle without nervous input. The protein complex troponin binds to tropomyosin, helping to position it on the actin molecule

At rest, ATP binds ATPase and one myosin molecule; it is hydrolyzed very slowly. During this period, the actin-binding sites of the myosin molecules are blocked by the troponin-tropomyosin complex.