When a skeletal muscle cell contracts and the muscle shortens,
A) myosin heads generate a single power stroke.
B) the position of an actin molecule relative to a myosin molecule does not change.
C) some myosin heads are forming crossbridges as others are releasing them.
D) the actin ATPase allows the actin molecule to swivel.
E) the actin molecule swivels during the power stroke.

Question

Quizplus · Accepted Answer

During muscle contraction, some myosin heads are forming crossbridges with actin filaments while others are releasing them. This allows for the repetitive cycling of crossbridge formation and release, leading to shortening of the muscle. Choice A is incorrect because myosin heads generate multiple power strokes during a contraction. Choice B is incorrect because the position of actin molecules does change during contraction as they are pulled closer to the center of the sarcomere by attaching to myosin heads. Choice D is incorrect because the actin ATPase is involved in breaking down ATP for energy, but it does not swivel the actin molecule. Choice E is also incorrect because while the actin molecule does undergo a conformational change during a power stroke, it does not swivel.

When a Skeletal Muscle Cell Contracts and the Muscle Shortens