Tropomyosin and troponin prevent muscle contractions in the absence of Ca²⁺ because they: A) block the myosin head binding sites on actin filaments. B) prevent the hydrolysis of ATP by myosin. C) degrade the actin filaments. D) increase the release of P_i by myosin. E) block the "power stroke" conformational change of actin filaments.

Question

Quizplus · Accepted Answer

Tropomyosin and troponin bind to actin filaments and block the myosin binding sites in the absence of Ca²⁺. This prevents muscle contractions because myosin cannot bind to actin and perform the "power stroke" necessary for muscle contraction.

Tropomyosin and Troponin Prevent Muscle Contractions in the Absence of Ca2+

Tropomyosin and Troponin Prevent Muscle Contractions in the Absence of Ca²⁺