Enzymes and Co-factors — NEET Biology

Correct answer: A — A-iii, B-i, C-ii

The core concept is the different types of cofactors required for enzyme activity and their specific roles. Let's match each cofactor type from Column I with its characteristic feature from Column II as per NCERT Section 9.8.6 'Co-factors': A. Prosthetic groups: "Prosthetic groups are organic compounds and are distinguished from other cofactors in that they are tightly bound to the apoenzyme. For example, in peroxidase and catalase... haem is the prosthetic group and it is a part of the active site of the enzyme." This matches with (iii) Organic compounds that are tightly bound to the apoenzyme, forming part of the active site. B. Co-enzymes: "Co-enzymes are also organic compounds but their association with the apoenzyme is only transient, usually occurring during the course of catalysis. Furthermore, co-enzymes serve as co-factors in a number of different enzyme catalyzed reactions. The essential chemical components of many coenzymes are vitamins..." This matches with (i) Organic compounds that associate transiently with the apoenzyme during catalysis, often derived from vitamins. C. Metal ions: "A number of enzymes require metal ions for their activity which form coordination bonds with side chains at the active site and at the same time form one or more cordination bonds with the substrate, e.g., zinc is a cofactor for the proteolytic enzyme carboxypeptidase." This matches with (ii) Non-protein constituents that form coordination bonds with enzyme's active site side chains and simultaneously with the substrate. Thus, the correct match is A-iii, B-i, C-ii. The final answer is A, which correctly pairs each cofactor type with its distinguishing characteristic. Concept Recap: Enzyme cofactors are non-protein components essential for catalytic activity, classified into prosthetic groups (tightly bound organic), co-enzymes (transiently bound organic, often vitamins), and metal ions (form coordination bonds with enzyme and substrate).