Nomenclature of enzymes MCQs With Answer

Nomenclature of enzymes MCQs With Answer is an essential topic for B. Pharm students studying enzyme classification, naming rules, EC numbers and practical applications. This introduction covers systematic vs common names, the EC (Enzyme Commission) numbering system, enzyme classes (oxidoreductases, transferases, hydrolases, lyases, isomerases, ligases), cofactors, zymogens, isoenzymes and examples important in pharmacology. Learning enzyme nomenclature helps interpret literature, enzyme assays and drug–enzyme interactions. These SEO-focused keywords — nomenclature of enzymes, enzyme classification, EC number, enzymes MCQs with answers — will guide your exam and revision. Now let’s test your knowledge with 50 MCQs on this topic.

Q1. What suffix is most commonly used in trivial enzyme names to indicate enzymatic activity?

• -ase
• -in
• -ose
• -ine

Correct Answer: -ase

Q2. How many parts are there in a full EC (Enzyme Commission) number?

• Two
• Three
• Four
• Five

Correct Answer: Four

Q3. Which EC class includes enzymes that catalyze oxidation-reduction reactions?

• EC 1 — Oxidoreductases
• EC 2 — Transferases
• EC 3 — Hydrolases
• EC 4 — Lyases

Correct Answer: EC 1 — Oxidoreductases

Q4. Kinases, which transfer phosphate groups from ATP to substrates, belong to which EC class?

• Oxidoreductases
• Transferases
• Hydrolases
• Isomerases

Correct Answer: Transferases

Q5. Which EC class comprises enzymes that catalyze hydrolysis reactions (breaking bonds with water)?

• EC 2 — Transferases
• EC 3 — Hydrolases
• EC 5 — Isomerases
• EC 6 — Ligases

Correct Answer: EC 3 — Hydrolases

Q6. Which enzyme class is characterized by cleavage of bonds without hydrolysis, often forming double bonds (e.g., decarboxylases)?

• Hydrolases
• Lyases
• Ligases
• Oxidoreductases

Correct Answer: Lyases

Q7. Ligases (EC 6) catalyze which type of reaction?

• Isomerization only
• Bond formation with ATP consumption
• Direct electron transfer to oxygen
• Hydrolysis of peptide bonds

Correct Answer: Bond formation with ATP consumption

Q8. The systematic name of an enzyme typically describes which two aspects?

• Enzyme color and origin
• Reaction catalyzed and substrates/donors/acceptors
• pH optimum and molecular weight
• Inhibitor sensitivity and distribution in tissue

Correct Answer: Reaction catalyzed and substrates/donors/acceptors

Q9. Alcohol dehydrogenase has a systematic name that indicates its substrates and cofactors. Which of the following is that systematic name?

• Alcohol oxidase
• Alcohol:NAD+ oxidoreductase
• Alcohol hydrolase
• Alcohol transferase

Correct Answer: Alcohol:NAD+ oxidoreductase

Q10. Hexokinase, which phosphorylates glucose using ATP, has which EC number?

• 1.1.1.1
• 2.7.1.1
• 3.2.1.1
• 6.3.4.1

Correct Answer: 2.7.1.1

Q11. Which of these describes a prosthetic group?

• A non-protein cofactor tightly and often covalently bound to the enzyme
• A generic term for all metal ions in the cell
• A transient substrate analog
• A reversible competitive inhibitor

Correct Answer: A non-protein cofactor tightly and often covalently bound to the enzyme

Q12. The difference between an apoenzyme and a holoenzyme is:

• Apoenzyme is active; holoenzyme is inactive
• Apoenzyme lacks its cofactor; holoenzyme includes the cofactor and is active
• Apoenzyme contains the prosthetic group; holoenzyme is only protein
• They are synonyms for the same thing

Correct Answer: Apoenzyme lacks its cofactor; holoenzyme includes the cofactor and is active

Q13. What term describes the inactive precursor form of an enzyme that requires proteolytic cleavage for activation?

• Isoenzyme
• Zymogen (proenzyme)
• Holoenzyme
• Allosteric enzyme

Correct Answer: Zymogen (proenzyme)

Q14. Isoenzymes are best defined as:

• Same gene product in different species
• Different enzymes that catalyze different reactions
• Different molecular forms of an enzyme that catalyze the same reaction
• Inactive precursor enzymes

Correct Answer: Different molecular forms of an enzyme that catalyze the same reaction

Q15. Which international body maintains and updates the EC (Enzyme Commission) classification?

• WHO
• IUBMB (International Union of Biochemistry and Molecular Biology)
• FDA
• ISO

Correct Answer: IUBMB (International Union of Biochemistry and Molecular Biology)

Q16. EC class 3.4 indicates which subgroup of hydrolases?

• Glycosidases
• Peptidases (proteases)
• Lipases
• Phosphatases

Correct Answer: Peptidases (proteases)

Q17. Which of the following enzyme names is an example of a trivial/common name rather than a systematic one?

• ATP:glucose 6-phosphotransferase
• Glucose-6-phosphate isomerase
• Invertase
• Alcohol:NAD+ oxidoreductase

Correct Answer: Invertase

Q18. Dehydrogenases typically transfer electrons to which type of cofactors?

• NAD+/NADP+
• Heme only
• ATP
• CoA

Correct Answer: NAD+/NADP+

Q19. What distinguishes a kinase from a phosphorylase?

• Kinase removes phosphate; phosphorylase adds phosphate using ATP
• Kinase transfers phosphate from ATP; phosphorylase uses inorganic phosphate (Pi)
• Kinase is a hydrolase; phosphorylase is an oxidoreductase
• There is no difference; they are synonyms

Correct Answer: Kinase transfers phosphate from ATP; phosphorylase uses inorganic phosphate (Pi)

Q20. Which EC class includes racemases and epimerases that change stereochemistry within a molecule?

• EC 2 — Transferases
• EC 3 — Hydrolases
• EC 5 — Isomerases
• EC 6 — Ligases

Correct Answer: EC 5 — Isomerases

Q21. The EC subclass number (the second digit) provides information about:

• The specific organism that produces the enzyme
• The type of bond or group acted upon within the main class
• The enzyme’s molecular weight range
• The enzyme’s optimal pH

Correct Answer: The type of bond or group acted upon within the main class

Q22. Which enzyme systematic name component indicates the acceptor in an oxidoreductase reaction?

• First substrate listed
• Suffix -ase
• The part after the colon (:) in names like donor:acceptor oxidoreductase
• EC class number only

Correct Answer: The part after the colon (:) in names like donor:acceptor oxidoreductase

Q23. Which resource is commonly used by researchers to look up enzyme nomenclature and EC numbers?

• BRENDA enzyme database
• PubChem exclusively
• WebMD
• Amazon

Correct Answer: BRENDA enzyme database

Q24. Enzymes ending in -ase that hydrolyze carbohydrate glycosidic bonds are commonly called:

• Proteases
• Glycosidases (or carbohydrases)
• Lipases
• Ligases

Correct Answer: Glycosidases (or carbohydrases)

Q25. Which EC main class acts on CH-OH group of donors with NAD+ or NADP+ as acceptor (e.g., alcohol dehydrogenase)?

• EC 1 (Oxidoreductases)
• EC 2 (Transferases)
• EC 3 (Hydrolases)
• EC 4 (Lyases)

Correct Answer: EC 1 (Oxidoreductases)

Q26. The enzyme name “alanine aminotransferase” indicates it belongs to which general enzyme family?

• Hydrolases
• Transferases
• Isomerases
• Oxidoreductases

Correct Answer: Transferases

Q27. Which of the following is an example of a lyase activity?

• Formation of peptide bonds using ATP
• Decarboxylation producing CO2 and an alkene
• Hydrolysis of ester bonds
• Electron transfer to NAD+

Correct Answer: Decarboxylation producing CO2 and an alkene

Q28. Proteases that cleave peptide bonds by hydrolysis are classified under which EC main class?

• EC 1
• EC 2
• EC 3
• EC 4

Correct Answer: EC 3

Q29. The enzyme classification number 3.2.1.x typically refers to which type of enzyme?

• Peptidases
• Glycosidases (carbohydrate hydrolases)
• Ligases forming C–C bonds
• Oxidases acting on oxygen

Correct Answer: Glycosidases (carbohydrate hydrolases)

Q30. The term “flavoenzyme” indicates an enzyme that uses which cofactor?

• Heme
• FAD or FMN (flavin adenine dinucleotide or flavin mononucleotide)
• Metal ion only
• ATP

Correct Answer: FAD or FMN (flavin adenine dinucleotide or flavin mononucleotide)

Q31. Which enzyme name indicates specificity for sucrose hydrolysis?

• Sucrase (invertase)
• Amylase
• Cellulase
• Lipase

Correct Answer: Sucrase (invertase)

Q32. Which statement about trivial/common names versus systematic names is correct?

• Common names always include EC numbers
• Systematic names describe the chemical reaction in a standardized way while common names may be historical or simpler
• Systematic names are shorter than trivial names
• Common names are created by the IUBMB only

Correct Answer: Systematic names describe the chemical reaction in a standardized way while common names may be historical or simpler

Q33. Which EC number prefix denotes enzymes that form C–C bonds by lyase activity (carboxy-lyases)?

• 1.1
• 2.7
• 4.1
• 6.1

Correct Answer: 4.1

Q34. DNA polymerase belongs to which general enzyme EC class based on its transfer of nucleotidyl groups?

• EC 1 — Oxidoreductases
• EC 2 — Transferases (nucleotidyltransferases)
• EC 3 — Hydrolases
• EC 5 — Isomerases

Correct Answer: EC 2 — Transferases (nucleotidyltransferases)

Q35. Which of the following best describes a recommended name in enzyme nomenclature?

• A name chosen arbitrarily by individual laboratories
• An IUBMB-sanctioned common name recommended for general use
• A deprecated historical name no longer in use
• A trade name given by pharmaceutical companies

Correct Answer: An IUBMB-sanctioned common name recommended for general use

Q36. Which EC main class includes enzymes that catalyze group transfer to water (e.g., phosphatases)?

• EC 1
• EC 2
• EC 3
• EC 5

Correct Answer: EC 3

Q37. What does the third digit in an EC number represent?

• Specific enzyme name
• Subclass related to the type of chemical group transferred or acted upon
• Organism of origin
• Enzyme molecular weight range

Correct Answer: Subclass related to the type of chemical group transferred or acted upon

Q38. An enzyme annotated as EC 1.1.1.x acts on which donor and which acceptor type?

• Donor: CH-OH group; Acceptor: NAD+ or NADP+
• Donor: phosphate group; Acceptor: sugar
• Donor: peptide bonds; Acceptor: water
• Donor: CO2; Acceptor: ammonia

Correct Answer: Donor: CH-OH group; Acceptor: NAD+ or NADP+

Q39. Which term refers to non-protein small molecules required for enzyme activity but not tightly bound?

• Prosthetic group
• Coenzyme (diffusible cofactor)
• Apoenzyme
• Zymogen

Correct Answer: Coenzyme (diffusible cofactor)

Q40. Which enzyme naming convention indicates the direction of reaction by listing donor and acceptor (e.g., donor:acceptor transferase)?

• Trivial name
• Systematic name
• Brand name
• Abbreviated gene symbol

Correct Answer: Systematic name

Q41. The enzyme term “dehydratase” suggests what type of reaction and EC class?

• Hydrolysis reaction, EC 3
• Removal of water (dehydration), often a lyase (EC 4)
• Transfer of phosphate, EC 2
• Oxidation by oxygen, EC 1

Correct Answer: Removal of water (dehydration), often a lyase (EC 4)

Q42. Which unit defines one International Unit (IU) of enzyme activity?

• Amount of enzyme converting 1 gram of substrate per hour
• Amount of enzyme catalyzing the conversion of 1 micromole of substrate per minute under defined conditions
• Number of enzyme molecules per cell
• Mass of enzyme equivalent to 1 mg

Correct Answer: Amount of enzyme catalyzing the conversion of 1 micromole of substrate per minute under defined conditions

Q43. The name “glucose-6-phosphate isomerase” tells you what about the reaction?

• It hydrolyzes glucose
• It transfers a phosphate from ATP to glucose
• It converts glucose-6-phosphate between isomeric forms (aldose-ketose isomerization)
• It ligates glucose to another sugar

Correct Answer: It converts glucose-6-phosphate between isomeric forms (aldose-ketose isomerization)

Q44. Which enzyme class would include pyruvate decarboxylase?

• Oxidoreductases (EC 1)
• Lyases (EC 4)
• Hydrolases (EC 3)
• Ligases (EC 6)

Correct Answer: Lyases (EC 4)

Q45. The name “alcohol oxidase” vs “alcohol dehydrogenase” differs mainly in what mechanistic detail?

• Oxidase uses molecular oxygen as electron acceptor, dehydrogenase uses cofactors like NAD+
• Oxidase hydrolyzes alcohols, dehydrogenase ligates alcohols
• There is no mechanistic difference
• Dehydrogenase always uses oxygen

Correct Answer: Oxidase uses molecular oxygen as electron acceptor, dehydrogenase uses cofactors like NAD+

Q46. Which of the following is true about EC numbers and enzyme nomenclature updates?

• EC numbers are permanent and never change
• IUBMB may revise classifications and add or obselete EC numbers as knowledge advances
• EC numbers are assigned by pharmaceutical companies
• EC numbers only apply to human enzymes

Correct Answer: IUBMB may revise classifications and add or obselete EC numbers as knowledge advances

Q47. Which name indicates an enzyme that removes phosphate groups from substrates?

• Kinase
• Phosphatase
• Transferase
• Ligase

Correct Answer: Phosphatase

Q48. A recommended systematic name for a transferase often follows which pattern?

• Substrate:cofactor oxidoreductase
• Donor:acceptor grouptransferase
• Proteinase hydrolase
• Substrate hydratase

Correct Answer: Donor:acceptor grouptransferase

Q49. Which EC subclass would you expect for enzymes that cleave C–N bonds other than peptide bonds?

• EC 3.4 (peptidases)
• EC 3.5 (hydrolases acting on C–N bonds other than peptides)
• EC 2.7 (phosphotransferases)
• EC 4.2 (lyases acting on C–O bonds)

Correct Answer: EC 3.5 (hydrolases acting on C–N bonds other than peptides)

Q50. Why is understanding enzyme nomenclature and EC numbers important for B.Pharm students in pharmacology and drug development?

• It helps correlate enzyme names with molecular weight only
• It enables identification of enzyme function, reaction mechanism, cofactor needs, and potential drug targets or metabolic interactions
• It is useful only for biochemistry trivia
• It replaces the need to know enzyme kinetics

Correct Answer: It enables identification of enzyme function, reaction mechanism, cofactor needs, and potential drug targets or metabolic interactions

G S Sachin

I am a Registered Pharmacist under the Pharmacy Act, 1948, and the founder of PharmacyFreak.com. I hold a Bachelor of Pharmacy degree from Rungta College of Pharmaceutical Science and Research. With a strong academic foundation and practical knowledge, I am committed to providing accurate, easy-to-understand content to support pharmacy students and professionals. My aim is to make complex pharmaceutical concepts accessible and useful for real-world application.

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