Which of the following statements about myosin and actin is CORRECT?
A) The binding of calcium to troponin is necessary for the dissociation of the actin-myosin complex.
B) Actin has ATPase activity.
C) The binding of ATP to the actin-myosin complex promotes the formation of the complex.
D) The binding of ATP to the actin-myosin complex promotes the dissociation of the complex.
E) Tropomyosin has ATPase activity.
IMAT 2025 · Question 17
Q17 - Muscle contraction
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The correct answer is D) The binding of ATP to the actin-myosin complex promotes the dissociation of the complex.
ATP binding makes myosin let go of actin. Hydrolysing the ATP then cocks the myosin head ready for the next stroke.
Without ATP, myosin stays stuck to actin, which is why muscles go stiff after death (rigor mortis). The ATPase activity belongs to myosin, not actin or tropomyosin, and calcium is needed for binding, not for letting go.
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