Enzymes MCQs

81 MCQs with clinical pearls · MBBS Biochemistry · Prof Jariya

Topics covered (11)

Cofactors and Coenzymes — 16 MCQs
Enzyme Inhibition Clinical — 14 MCQs
Enzyme Classification — 10 MCQs
Serum Enzymes in Diagnosis — 8 MCQs
Enzyme Kinetics — 8 MCQs
Cardiac Biomarkers — 6 MCQs
Enzyme Inhibition — 4 MCQs
Enzyme Regulation — 4 MCQs
Clinical Enzymology and Isoenzymes — 4 MCQs
Enzyme Fundamentals — 4 MCQs
Regulatory Enzymes — 3 MCQs

Sample MCQs with clinical pearls

During glycolysis, glucose-6-phosphate is converted to fructose-6-phosphate without addition or removal of atoms. Which class of enzyme catalyses this reaction?

A) EC1 Oxidoreductases

B) EC2 Transferases

C) EC3 Hydrolases

D) EC4 Lyases

E) EC5 Isomerases ✔

PHOSPHOGLUCOSE ISOMERASE = ISOMERASE (EC5). Rearranges bond structure without adding or removing atoms. Types: MUTASES (move phosphate between atoms), RACEMASES (interconvert D and L forms), EPIMERASES (interconvert epimers). Glucose-6-phosphate → fructose-6-phosphate = aldose → ketose conversion. No net change in molecular formula.\ \ 📹 [VIDEO LINK]

During fatty acid activation before beta-oxidation, a fatty acid is joined to coenzyme A using energy from ATP hydrolysis. Which class of enzyme catalyses this bond formation?

A) EC1 Oxidoreductases

B) EC2 Transferases

C) EC3 Hydrolases

D) EC4 Lyases

E) EC6 Ligases ✔

FATTY ACYL CoA SYNTHETASE = LIGASE (EC6). Synthesises C-S bond COUPLED TO ATP HYDROLYSIS. EC6 types: CARBOXYLASES (biotin-dependent, add CO₂ — pyruvate carboxylase, ACC), SYNTHETASES (ATP-requiring — fatty acyl CoA synthetase), AMINOACYL-tRNA SYNTHETASES. Ligases differ from SYNTHASES (EC4) which do NOT require ATP.\ \ 📹 [VIDEO LINK]

Luciferase catalyses the oxidation of luciferin in the presence of oxygen and ATP, enabling fireflies to emit light. Luciferase belongs to which of the following enzyme classes?

A) EC1 Oxidoreductases ✔

B) EC2 Transferases

C) EC3 Hydrolases

D) EC4 Lyases

E) EC5 Isomerases

LUCIFERASE = OXIDOREDUCTASE (EC1) — specifically a monooxygenase. Catalyses: luciferin + O₂ + ATP → oxyluciferin + CO₂ + AMP + PPi + LIGHT. O₂ reduced, luciferin oxidised = oxidoreductase. Used in reporter gene assays in molecular biology. The excited-state oxyluciferin releases energy as light upon returning to ground state.\ \ 📹 [VIDEO LINK]

These are three of 81 MCQs in this section. Every question carries a clinical pearl explaining the reasoning.

Open MCQ Arena →