Enzymes MCQs (Quiz 10)By guishaqasif / April 29, 2026 1. The primary function of enzymes is to _______ Increase enthalpy change Alter Gibbs free energy permanently Increase equilibrium constant Lower activation energy of reactions 2. In enzyme repression (operon model), the operator region is _______ A region on mRNA involved in translation A protein-binding site on the enzyme The catalytic (active) site of the enzyme A DNA sequence that regulates transcription by binding regulatory proteins 3. Repression of enzyme synthesis at the genetic level primarily involves _______ Post-translational enzyme modification Increased mRNA translation efficiency Activation of transcription factors Binding of repressor proteins to operator regions 4. Which condition most strongly favors enzyme induction in metabolic systems? Presence of substrate (or inducer molecule) Low substrate concentration Already high levels of the enzyme High concentration of end product 5. In metabolic control, repression is most effective when applied to _______ Enzymes catalyzing the first committed step of the pathway All enzymes equally across the pathway Random enzymes within the pathway Terminal enzymes producing the final product 6. Which of the following regulatory mechanisms operates at the DNA (transcriptional) level? Gene repression controlling transcription Competitive inhibition at the active site Covalent phosphorylation of enzymes Allosteric control via effector binding 7. The lac operon in E. coli is an example of a _______ Inducible system activated in the presence of lactose (allolactose) Irreversible inhibition of enzyme activity Repressible system regulated by end-product accumulation Constitutive expression independent of regulatory control 8. Induction and repression together ensure _______ Maximum substrate accumulation Constant, unchanging enzyme levels Dynamic metabolic control in response to cellular needs Permanent inhibition of metabolic pathways 9. Which type of molecule typically functions as an inducer in inducible enzyme systems? The enzyme itself Cofactor required for enzyme activity End product of the pathway Substrate 10. The Michaelis–Menten equation describes how the initial reaction velocity varies as a function of _______ Temperature at optimal pH pH in the presence of a competitive inhibitor Enzyme concentration under saturating substrate conditions Substrate concentration at constant enzyme concentration Loading … Question 1 of 10
