Which of the following ions binds to the troponin complex, initiating muscle contraction?
A.
Potassium.
B.
Calcium.
C.
Phosphorus.
D.
Sodium.
The correct answer is:
B. Calcium
Explanation:
Calcium ions play a crucial role in muscle contraction. When a muscle cell is stimulated, calcium ions are released from the sarcoplasmic reticulum into the cytoplasm. These calcium ions bind to the troponin complex, which is part of the thin filament in muscle fibers. This binding causes a conformational change in the troponin-tropomyosin complex, exposing binding sites on actin for myosin, thereby initiating muscle contraction.
Potassium (A) and Sodium (D) are important for generating and propagating electrical signals in muscle cells but do not directly initiate muscle contraction.
Phosphorus (C) is involved in the energy transfer processes within cells, such as ATP production, but does not directly bind to the troponin complex.
Therefore, calcium is the ion responsible for binding to the troponin complex and initiating muscle contraction.