Metalloproteins require a metal ion cofactor for function.

• A. False
• B. True
• C. Sometimes
• D. Only in plants

Answer: (B)

Metalloproteins incorporate a metal ion into their active site or overall structure, and that metal is essential for the protein’s function. The metal ion acts in several key ways: it can activate a bound water molecule or substrate, stabilize negative charges during catalysis, participate in redox chemistry, or help hold the protein’s three-dimensional shape in the correct arrangement. Because this metal is required for the protein to perform its role, the statement is true across biological systems, not limited to a subset of organisms. For example, zinc in carbonic anhydrase helps activate water for CO2 hydration, iron in heme groups enables oxygen binding and electron transfer, and magnesium often coordinates ATP in kinases to enable phosphate transfer. Without the metal cofactor, many metalloproteins lose activity or proper structure.