What roles do contractile, regulatory, and structural proteins play in muscle contraction and relaxation?
Skeletal muscles are composed of many individual cells known as muscle fibers. Each individual muscle fiber is in turn composed of a number of smaller myofibrils. Three types of proteins form myofibrils: contractile, regulatory, and structural.
Contractile proteins generate force for muscle contraction. The two contractile proteins in myofibrils are actin (part of the thin filament) and myosin (part of the thick filament). The regulatory proteins troponin and tropomysium, which are also part of the thin filament, are involved in allowing or inhibiting muscle contraction. The structural proteins (the most notable of which is titin) are involved in the stability and elasticity of the myofibrils.
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