What roles do contractile, regulatory, and structural proteins play in muscle contraction and relaxation?

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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...

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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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Proteins are composed of amino acids and most proteins are enzymes, enzymes are organic substances that act as a catalyst to change the rates of biochemical reactions, speed them up. I think when you say "contractile and regulatory proteins", you are really saying contractile and regulatory enzymes.

There is a structural protein called collagen which is mainly found in connective tissue like bone, ligaments, tendons, and fascia.

Having said this, enzymatic processes have a major role in all body processes including muscular contraction and relaxation. In other words, enzymes control and are responsible for other processes that cause muscles to contract and relax. Because collagen is found in structures that connect to bones and bones are pulled when muscles contract, theoretically collagen plays a role in muscular actions because they give strength to connective tissues that are attached to bone and muscle tissue.

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