MCQs

1. Apart from proteins, one of the following molecules also 11. All the following coenzymes are derivatives of B-complex
exerts enzymatic function vitamins, except
a) DNA b) RNA a) S-adenosylmethionine b) NAD+
c) carbohydrates d) lipids c) pyridoxal phosphate d) coenzyme A
12. All the following coenzymes participate in the transfer of
2. All the following statements about the chemical reactions
hydrogen and electron, except
are correct, except
a) FAD b) PLP
a) the difference in the energy content of substrates and
products is equal to the energy released or added during a c) NAD+ d) NADP+
reaction 13. One of the following groups of enzymes does not exhibit
b) the energy released during a chemical reaction is either stereospecificity
released as heat or transferred to other molecules a) oxidoreductases b) isomerases
c) 
an increase or decrease in the concentrations of c) lyases d) transferases
substrates or products can alter the net direction of the
14. All the following statements regarding enzyme specificity
reaction
are correct, except
d) 
when large amounts of energy are released, all the
a) glucokinase phosphorylates only glucose
substrate molecules are converted to product molecules
making the reaction reversible b) hexokinase exhibits relative substrate specificity
c) glucose-6-phosphate undergoes multiple reactions, each
3. The enzymes engaged in the transfer of electrons are catalysed by a separate enzyme
known as d) human enzymes act only on D-amino acids
a) oxidoreductases b) transferases 15. Enzymes act by reducing the
c) lyases d) all the above a) activation energy b) binding energy
c) heat energy d) all the above
4. All the following enzymes are transferases, except
a) hexokinase b) alanine transaminase 16. Which one of the following forces contributes to binding
c) aspartate transaminase d) dioxygenase energy?
a) hydrophobic interactions b) van der Waals forces
5. Digestive enzymes belong the class of c) electrostatic interactions d) all the above
a) transferases b) lyases 17. Which one of the following statements about the
c) hydrolases d) ligases mechanism of enzyme action is true?
a) the binding of the substrate with the enzyme induces a fit
6. All the following enzymes are ligases, except in the enzyme
a) glycogen synthase b) acetyl CoA carboxylase b) the formation of non-covalent interactions between the
c) glutamine synthetase d) PRPP synthetase enzyme and the substrate increases the binding energy
c) 
substrate also undergoes some strain during enzyme–
7. All the following are multi-enzyme complexes, except substrate complex formation
a) LDH b) PDH d) all the above
c) a-KG dehydrogenase d) fatty acid synthase
18. Mechanism of enzyme catalysis involves
8. All the following statements about an active site are a) acid–base catalysis b) covalent catalysis
correct, except c) metal ion catalysis d) all the above
a) 
active sites occupy a small portion of the enzyme 19. All the following statements about enzyme kinetics are
structure true, except
b) the native structure of an enzyme must be intact for a a) enzymes increase the rate of reaction, but do not affect
functional active site the equilibrium
c) active site is rigid in conformation b) 
the velocity of reaction is directly proportional to the
d) substrates are bound at active sites by weak non-covalent enzyme concentration
bonds c) the substrate concentration required to produce maximum
9. Which one of the following amino acids occurs most velocity is known as Km
frequently in active sites? d) a low Km value indicates a high affinity of the enzyme for
a) threonine b) serine the substrate
c) glycine d) proline 20. In competitive inhibition of enzymes
10. All the following are metallo-enzymes, except a) Km increases whereas Vmax decreases
a) xanthine oxidase b) hexokinase b) Km increases whereas Vmax remains unchanged
c) carbonic anhydrase d) lactate dehydrogenase c) Vmax increases while Km decreases
d) Vmax decreases while Km remains unchanged

TB of Biochemistry.indb 116 4/19/2024 10:54:17 AM

 21. The Krebs cycle enzyme, succinate dehydrogenase, is 25. Which of the following mechanisms are associated with
inhibited by the following mechanism covalent modification?
a) competitive inhibition a) reversible phosphorylation b) acetylation
b) non-competitive inhibition c) ADP–ribosylation d) all the above
c) allosteric inhibition
26. The enzyme that adds phosphate to the regulatory protein
d) none of the above
is
22. Heavy metal ions are usually involved in the following type a) protein phosphatase b) protein kinase
of enzyme inhibition c) acetylase d) phosphotransferase
a) competitive inhibition
27. Which of the following enzymes are activated from the
b) non-competitive inhibition
zymogen form?
c) allosteric inhibition
a) trypsin b) pepsin
d) feedback inhibition
c) plasmin d) all the above
23. All the following statements about allosteric regulation 28. Which one of the following pathways occurs both in cytosol
are true, except and mitochondria?
a) allosteric enzymes exist in T and R conformations a) urea cycle b) gluconeogenesis
b) some allosteric enzymes act by cooperative binding c) heme synthesis d) all the above
c) 
allosteric enzymes produce a hyperbolic curve when
velocity is plotted against substrate concentration 29. The enzyme glucokinase is induced by
d) allosteric enzymes exist as two classes: K class and V class a) glucagon b) cortisol
c) insulin d) all the above
24. Which of the following molecules act as allosteric
modulators for the enzyme phosphofructokinase 30. Which one of the following enzymes is induced by cortisol?
a) acyl CoA and citrate a) pyruvate carboxylase b) tryptophan pyrrolase
b) CTP and UTP c) aminotransferase d) all the above
c) acetyl CoA and NAD+
d) ATP and fructose-2, 6-bisphosphate

Answers
1. b 2. d 3. a 4. d 5. c 6. a 7. a
8. c 9. b 10. d 11. a 12. b 13. b 14. d Scan QR code to access
15. a 16. d 17. d 18. d 19. c 20. b 21. a Riddles and Problems
22. b 23. c 24. d 25. d 26. b 27. d 28. d
29. c 30. d

Chapter 7 | Enzymes

TB of Biochemistry.indb 117 4/19/2024 10:54:17 AM