Enzymes MCQs (Quiz 3)By guishaqasif / April 28, 2026 1. Feedback inhibition is most effective when the enzyme catalyzes the _______ First committed step unique to the pathway Equilibrium step near the end of the pathway Reversible step of a pathway Final step of product formation 2. Induction of enzyme synthesis primarily involves _______ Protein folding into active conformations Post-translational modification of existing enzymes Activation of gene expression leading to new enzyme production Direct binding of substrate to the enzyme 3. Which coenzyme is derived from niacin (vitamin B₃)? NAD⁺ FAD Coenzyme A Thiamine pyrophosphate 4. Histidine functions as a catalytic residue in many enzymes primarily due to its _______ Hydrophobic side chain Large molecular size Strong metal-binding property Imidazole group capable of proton transfer near physiological pH 5. An allosteric enzyme regulated by ATP and ADP exemplifies _______ Homotropic regulation Covalent regulation Irreversible inhibition Heterotropic regulation 6. The Michaelis–Menten equation describes the relationship between reaction velocity and _______ pH Substrate concentration Enzyme concentration Temperature 7. In metal ion catalysis (e.g., Zn²⁺ in carbonic anhydrase or Mg²⁺ in kinases), the primary role of the metal ion is to _______ Maintain enzyme tertiary structure without directly participating in catalysis Stabilize developing charges in transition states or reaction intermediates via electrostatic interactions Bind tightly to the substrate in its ground state to increase local concentration Form a stable covalent bond with the substrate to enhance reactivity 8. An enzyme characterized by a very high Km (low substrate affinity) and a high Vmax is best adapted for conditions of _______ Low substrate concentration Tight regulatory control at low substrate levels High substrate concentration Constant activity regardless of substrate levels 9. Rapid regulation of enzyme activity is primarily achieved through _______ DNA replication Allosteric interactions Gene transcription Protein synthesis 10. A patient with myocardial infarction shows elevated serum creatine kinase (CK) and troponin levels. The primary mechanism responsible for this increase is _______ Increased hepatic synthesis of these proteins Hormone-mediated active secretion into circulation Leakage of intracellular enzymes from necrotic cardiac myocytes Decreased renal clearance of circulating enzymes 11. Enzyme regulation mediated by Ca²⁺ ions primarily regulated through _______ Calmodulin Ligases Protein kinases Phosphatases Loading … Question 1 of 11
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