Role of Cofactors in Enzyme Activity — NEET Biology
📚 Practice ConceptCatalytic activity is lost when the co-factor is removed from the enzyme which testifies that they play a crucial role in the catalytic activity of the enzyme.
Which of the above statements are NOT correct? S1: The apoenzyme is the protein portion of an enzyme, becoming catalytically active only after binding with a non-protein cofactor. S2: Prosthetic groups, like haem in catalase, are organic compounds characterized by their tight and usually transient association with the apoenzyme. S3: Co-enzymes are organic compounds whose essential chemical components are often derived from vitamins, and they typically associate with the apoenzyme only transiently during catalysis. S4: Metal ions function as cofactors by forming coordination bonds exclusively with the enzyme's active site, without any direct interaction with the substrate. S5: The removal of any type of cofactor from its enzyme invariably results in a complete and irreversible loss of catalytic activity.
View solution & NCERT explanation
Correct answer: A — S2 and S4
The core concept tested is the nature and types of cofactors (apoenzyme, prosthetic groups, co-enzymes, and metal ions). S1: This statement is correct. The protein part of the enzyme is called the apoenzyme, and it requires a non-protein cofactor to become catalytically active, forming a holoenzyme. S2: This statement is incorrect. Prosthetic groups are organic compounds that are tightly bound to the apoenzyme, meaning their association is permanent, not transient. Haem in peroxidase and catalase is a classic example. S3: This statement is correct. Many co-enzymes, which are organic compounds, are indeed derived from vitamins (e.g., NAD and NADP contain niacin) and are characterized by their transient association with the apoenzyme during the catalytic process. S4: This statement is incorrect. Metal ions act as cofactors by forming coordination bonds with side chains at the active site *and* simultaneously forming one or more coordination bonds with the substrate, as seen with zinc in carboxypeptidase. S5: This statement is correct in its general assertion about catalytic activity loss but the irreversibility depends on the specific cofactor and enzyme. The NCERT states "Catalytic activity is lost when the co-factor is removed from the enzyme which testifies that they play a crucial role in the catalytic activity of the enzyme." It does not specify irreversibility for all cases, but clearly states loss of activity. Therefore, statements S2 and S4 are NOT correct. Cofactors are non-protein components essential for the catalytic activity of many enzymes, with different types (prosthetic groups, co-enzymes, and metal ions) exhibiting distinct characteristics regarding their chemical nature and mode of association with the apoenzyme.
What does NCERT say about Catalytic activity lost when?
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Through deep analysis of NEET and NTA, 176 of the 180 ReNEET 2026 (June 21) questions were already in the MedicNEET question bank before the exam.
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