Inorganic cofactors are usually which type of substance?

• A. Organic molecules
• B. Metal ions
• C. Small peptides
• D. Carbohydrates

Answer: (B)

Metal ions serve as inorganic cofactors in many enzymes because they are small, non-organic elements that can participate directly in catalysis. Their ability to switch oxidation states and to coordinate with substrates and amino acid residues lets them stabilize charged transition states, polarize bonds, and facilitate electron transfer. This versatility enables a wide range of catalytic steps, from bond rearrangements to redox reactions. For example, magnesium helps stabilize ATP phosphates during energy transfer, zinc activates water for nucleophilic attack in certain hydrolases, and iron–sulfur clusters carry electrons in many respiratory enzymes. Organic cofactors, by contrast, are carbon-containing molecules such as vitamins or their derivatives and are not inorganic metal ions.