Which of the following statements is TRUE regarding skeletal-muscle contraction? A) Only one cross-bridge cycle can occur when the [Ca²⁺] is elevated in the cytosol; in order to undergo a second cycle, [Ca²⁺] must be sequestered in the sarcoplasmic reticulum and released again. B) ATP hydrolysis products must be removed from myosin before it can bind to actin. C) Binding of myosin to actin takes place when [Ca²⁺] increases in the cytosol. D) A single twitch in skeletal muscle lasts the same length of time as the action potential that causes it. E) The powerstroke of the cross-bridge cycle occurs simultaneously with ATP being hydrolyzed into ADP and P_i.

Question

Quizplus · Accepted Answer

The binding of myosin to actin occurs when the concentration of [Ca²⁺] increases in the cytosol. This initiates the cross-bridge cycle and leads to muscle contraction. Option A is incorrect because multiple cross-bridge cycles can occur as long as [Ca²⁺] remains elevated. Option B is incorrect because ATP hydrolysis products do not need to be removed from myosin before it can bind to actin. Option D is incorrect because a twitch lasts longer than the action potential that causes it. Option E is incorrect because the powerstroke of the cross-bridge cycle occurs after ATP is hydrolyzed into ADP and P_i.

Which of the Following Statements Is TRUE Regarding Skeletal-Muscle Contraction