How does contraction of smooth muscle differ from that of skeletal muscle? Include the following in your answer : Ca2+ ions, troponin, tropomyosin, calmodulin, myosin-binding sites, light-chain region, actin, myosin, and cross bridge cycling
What will be an ideal response?
In skeletal muscle, tropomyosin covers up the binding sites on actin. Binding Ca2+ ions to troponin causes tropomyosin to move off the myosin-binding sites on actin, allowing myosin to grab hold of the actin to initiate cross bridge cycling. There is no troponin in smooth muscle. Instead, Ca2+ ions bind to a protein called calmodulin, which activates an enzyme that phosphorylates a light-chain region on the myosin. This allows the myosin to become phosphorylated with an additional Pi, which allows cross bridge cycling. The Ca2+ ions cause an effect on the actin in skeletal muscles, whereas they cause an effect on the myosin in smooth muscle.
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