Enzymes MCQs (Quiz 7)By guishaqasif / April 28, 2026 1. Feedback repression ensures that _______ Substrate concentration increases Energy is conserved by reducing enzyme synthesis Enzymes are permanently active All pathways remain active 2. Alanine aminotransferase (ALT) is considered more specific than aspartate aminotransferase (AST) for liver injury because it is _______ Lower in catalytic activity than AST Characterized by a shorter half-life in circulation Higher in molecular weight than AST Present in fewer tissues and predominantly localized in hepatocytes 3. The tryptophan (trp) operon in bacteria is best described as a _______ Repressible operon inhibited by end-product accumulation Post-translational regulatory mechanism Allosteric enzyme regulatory system Inducible operon activated by substrate presence 4. Inducible enzyme systems are typically activated in the presence of _______ Substrate (or its analog) acting as an inducer Enzyme inhibitor blocking activity Cofactor required for enzyme activity End product acting as a corepressor 5. Which interaction stabilizes enzyme–substrate complex? Covalent bonds only Disulfide bonds only Weak interactions (H-bonds, ionic, hydrophobic) Peptide bonds 6. Which mechanism enables the most rapid adaptation of enzyme activity to changing metabolic demand? Transcriptional repression of enzyme synthesis Gene repression at the transcriptional level Protein degradation and turnover Allosteric regulation via effector binding 7. An LDH isoenzyme “flip” (LDH₁ > LDH₂) in serum is indicative of _______ Liver disease Myocardial infarction (MI) Pancreatitis Kidney disease 8. The lac operon is an example of _______ Constitutive expression Irreversible inhibition Repressible system Inducible system 9. The proximity and orientation effect in enzyme catalysis enhances reaction rate by _______ Increasing the Gibbs free energy (ΔG\Delta GΔG) of the reaction Bringing substrates into close proximity and correct orientation to increase effective collisions Lowering the temperature of the system Reducing the amount of enzyme required 10. Serum amylase rises rapidly in acute conditions but is considered less specific as a diagnostic marker because it is _______ Not secreted into circulation Rapidly degraded before detection Characterized by inherently low enzymatic activity Also present in salivary glands and other tissues Loading … Question 1 of 10
