Question

troponin is activated by the presence of

o ach

o ca²+

o cl-

o k+

o na+

Explanation:

Troponin is a complex of three proteins (troponin C, troponin I, troponin T) that plays a crucial role in muscle contraction. Calcium ions (\(Ca^{2+}\)) bind to troponin C. This binding causes a conformational change in the troponin - tropomyosin complex. As a result, the binding site on actin for myosin becomes exposed, allowing muscle contraction to occur. Acetylcholine (ACh) is a neurotransmitter involved in the initiation of muscle contraction at the neuromuscular junction but does not directly activate troponin. Chloride ions (\(Cl^{-}\)), potassium ions (\(K^{+}\)), and sodium ions (\(Na^{+}\)) are involved in maintaining the resting membrane potential and action potential propagation in muscle cells but are not the specific ions that activate troponin.

Answer:

B. \(Ca^{2+}\)