Enzymes MCQs (Quiz 4)By guishaqasif / April 28, 2026 1. A holoenzyme refers to the catalytically active form of an enzyme consisting of _______ Protein part (apoenzyme) Apoenzyme + cofactor/coenzyme Protein + product complex Substrate + enzyme 2. Heme in catalase is an example of a ________ Apoenzyme Prosthetic group Coenzyme Free cofactor 3. A low Km value indicates that the enzyme _______ Has low affinity for substrate Has high affinity for substrate Is saturate Is inactive 4. Covalent phosphorylation regulates enzyme activity primarily by _______ Changing the chemical nature of the substrate Altering the protein’s conformation and active site properties Irreversibly destroying the enzyme Changing gene expression levels 5. Transition state stabilization by enzymes primarily lowers _______ Gibbs free energy (ΔG) of the reaction Activation energy of the reaction Enthalpy of the reactants Entropy of the system 6. Repression of enzyme synthesis in metabolic pathways is primarily caused by _______ End product Cofactor availability Enzyme concentration Substrate accumulation 7. An enzyme regulated by both covalent phosphorylation and allosteric effectors exhibits _______ Irreversible regulation only Dual regulation through covalent and allosteric mechanisms Single regulatory control mechanism No regulatory control 8. The Michaelis constant (Km​) is best defined as the substrate concentration at which _______ The reaction velocity is half of the maximum velocity (Vmax/2) Product formation ceases Reaction velocity is maximum The enzyme is fully saturated with substrate 9. Oxidoreductases are a class of enzymes that catalyze _______ Hydrolytic cleavage of chemical bonds using water Oxidation–reduction (redox) reactions involving electron transfer Transfer of functional groups between molecules Intramolecular rearrangement of atoms within a molecule 10. A Lineweaver–Burk plot becomes unreliable at low substrate concentrations because ______ Experimental error is magnified due to reciprocal transformation The slope approaches zero Km increases artificially Vmax decreases at low substrate levels Loading … Question 1 of 10
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