Enzymes MCQs (Quiz 5)By guishaqasif / April 28, 2026 1. Covalent catalysis in enzymatic reactions involves the formation of _______ A permanent covalent bond between enzyme and substrate No bond formation during the reaction A transient covalent intermediate between enzyme and substrate Only hydrogen bonding interactions 2. A mutation in the regulatory subunit of an enzyme primarily affects _______ Enzyme control and regulation by effectors Catalytic activity at the active site Release of product after catalysis Direct substrate binding at the catalytic site 3. In enzyme kinetics, a sigmoidal (S-shaped) velocity–substrate curve is indicative of _______ Simple Michaelis–Menten kinetics Irreversible inhibition of enzyme activity Allosteric (cooperative) behavior of the enzyme Competitive inhibition at the active site 4. Which pair is incorrectly matched? Coenzyme – vitamin-derived organic molecule Holoenzyme – active enzyme complex Apoenzyme – inactive protein component Prosthetic group – loosely bound cofactor 5. End-product repression differs from feedback inhibition because it primarily operates at the level of _______ Enzyme activity Gene transcription Substrate binding Protein folding 6. Allosteric enzymes deviate from Michaelis–Menten kinetics because they _______ Consist of multiple subunits exhibiting cooperative interactions Lack the ability to bind substrate Possess a single active site with independent substrate binding Do not form an enzyme–substrate (ES) complex 7. Serum enzyme levels increase due to _______ Increased synthesis Cell damage Hormonal action Decreased degradation 8. If the Michaelis constant (Km) increases, this indicates that _______ The reaction has stopped Maximum reaction velocity (Vmax) has increased Enzyme affinity for the substrate has increased Enzyme affinity for the substrate has decreased 9. Acid–base catalysis in enzymes requires amino acid residues with _______ pKa values near physiological pH, enabling proton donation and acceptance Very low pKa values far below physiological pH No ionizable groups (no pKa) Very high pKa values far above physiological pH 10. Transferases are enzymes that catalyze _______ Transfer of functional groups from one molecule to another Intramolecular rearrangement of atoms within a molecule Hydrolytic cleavage of bonds using water Cleavage of bonds without the involvement of water Loading … Question 1 of 10
