Portage Learning CHEM 210 Biochemistry
Module 4 Exam | Actual Enzymes Kinetics
Regulation and Catalysis Assessment with
Answers
DOMAIN: ENZYME CLASSIFICATION & NOMENCLATURE (10%)
Q1. Which enzyme class catalyzes the transfer of electrons (hydrogen atoms) from one
substrate to another?
A. Transferases
B. Hydrolases
C. Oxidoreductases
D. Lyases
Correct Answer: C
Rationale: C. [CORRECT] Oxidoreductases (EC Class 1) catalyze oxidation-reduction
reactions involving the transfer of electrons, hydrogen atoms, or hydride ions. Examples
include dehydrogenases, oxidases, and reductases. A is incorrect; transferases (EC
Class 2) transfer functional groups (e.g., methyl, phosphate, amino) between substrates,
not electrons. B is incorrect; hydrolases (EC Class 3) catalyze bond cleavage via
,addition of water (hydrolysis). D is incorrect; lyases (EC Class 4) add or remove groups
without hydrolysis or oxidation, often creating double bonds.
Q2. Which of the following enzymes belongs to the hydrolase class?
A. Hexokinase
B. Trypsin
C. Decarboxylase
D. Phosphoglucose isomerase
Correct Answer: B
Rationale: B. [CORRECT] Trypsin is a serine protease that catalyzes the hydrolysis of
peptide bonds, placing it in the hydrolase class (EC 3.4.21.4). A is incorrect; hexokinase
catalyzes phosphate transfer from ATP to glucose, making it a transferase (EC 2.7.1.1).
C is incorrect; decarboxylase removes CO₂ from substrates without hydrolysis, making it
a lyase (EC 4.1.1). D is incorrect; phosphoglucose isomerase catalyzes the
interconversion of glucose-6-phosphate and fructose-6-phosphate, making it an
isomerase (EC 5.3.1.9).
Q3. An enzyme that catalyzes the joining of two molecules using energy from ATP
hydrolysis belongs to which class?
A. Lyase
B. Isomerase
C. Ligase
,D. Oxidoreductase
Correct Answer: C
Rationale: C. [CORRECT] Ligases (EC Class 6) catalyze the joining of two molecules with
the concomitant hydrolysis of ATP or other nucleoside triphosphate. Examples include
DNA ligase and aminoacyl-tRNA synthetases. A is incorrect; lyases cleave bonds
without hydrolysis or oxidation, or add groups to double bonds. B is incorrect;
isomerases catalyze structural rearrangements within a single molecule. D is incorrect;
oxidoreductases catalyze electron transfer reactions.
Q4. Absolute specificity in enzyme catalysis refers to:
A. The enzyme catalyzes a reaction with only one specific substrate
B. The enzyme catalyzes reactions with a group of structurally related substrates
C. The enzyme distinguishes between stereoisomers
D. The enzyme requires a metal ion cofactor
Correct Answer: A
Rationale: A. [CORRECT] Absolute specificity means the enzyme catalyzes a reaction
with only one particular substrate and no others. For example, glucose oxidase acts
specifically on β-D-glucose and not on other sugars. B is incorrect; this describes group
specificity (relative specificity), where the enzyme acts on substrates with similar
functional groups. C is incorrect; this describes stereospecificity or stereochemical
specificity. D is incorrect; metal ion requirement refers to cofactor dependence, not
substrate specificity.
, DOMAIN: ENZYME KINETICS & MICHAELIS-MENTEN (25%)
Q5. In the Michaelis-Menten equation, v
0
=
K
m
+[S]
V
max
[S]
, what does K
m
represent?
A. The maximum velocity of the reaction
B. The substrate concentration at which the reaction velocity is half of V
Module 4 Exam | Actual Enzymes Kinetics
Regulation and Catalysis Assessment with
Answers
DOMAIN: ENZYME CLASSIFICATION & NOMENCLATURE (10%)
Q1. Which enzyme class catalyzes the transfer of electrons (hydrogen atoms) from one
substrate to another?
A. Transferases
B. Hydrolases
C. Oxidoreductases
D. Lyases
Correct Answer: C
Rationale: C. [CORRECT] Oxidoreductases (EC Class 1) catalyze oxidation-reduction
reactions involving the transfer of electrons, hydrogen atoms, or hydride ions. Examples
include dehydrogenases, oxidases, and reductases. A is incorrect; transferases (EC
Class 2) transfer functional groups (e.g., methyl, phosphate, amino) between substrates,
not electrons. B is incorrect; hydrolases (EC Class 3) catalyze bond cleavage via
,addition of water (hydrolysis). D is incorrect; lyases (EC Class 4) add or remove groups
without hydrolysis or oxidation, often creating double bonds.
Q2. Which of the following enzymes belongs to the hydrolase class?
A. Hexokinase
B. Trypsin
C. Decarboxylase
D. Phosphoglucose isomerase
Correct Answer: B
Rationale: B. [CORRECT] Trypsin is a serine protease that catalyzes the hydrolysis of
peptide bonds, placing it in the hydrolase class (EC 3.4.21.4). A is incorrect; hexokinase
catalyzes phosphate transfer from ATP to glucose, making it a transferase (EC 2.7.1.1).
C is incorrect; decarboxylase removes CO₂ from substrates without hydrolysis, making it
a lyase (EC 4.1.1). D is incorrect; phosphoglucose isomerase catalyzes the
interconversion of glucose-6-phosphate and fructose-6-phosphate, making it an
isomerase (EC 5.3.1.9).
Q3. An enzyme that catalyzes the joining of two molecules using energy from ATP
hydrolysis belongs to which class?
A. Lyase
B. Isomerase
C. Ligase
,D. Oxidoreductase
Correct Answer: C
Rationale: C. [CORRECT] Ligases (EC Class 6) catalyze the joining of two molecules with
the concomitant hydrolysis of ATP or other nucleoside triphosphate. Examples include
DNA ligase and aminoacyl-tRNA synthetases. A is incorrect; lyases cleave bonds
without hydrolysis or oxidation, or add groups to double bonds. B is incorrect;
isomerases catalyze structural rearrangements within a single molecule. D is incorrect;
oxidoreductases catalyze electron transfer reactions.
Q4. Absolute specificity in enzyme catalysis refers to:
A. The enzyme catalyzes a reaction with only one specific substrate
B. The enzyme catalyzes reactions with a group of structurally related substrates
C. The enzyme distinguishes between stereoisomers
D. The enzyme requires a metal ion cofactor
Correct Answer: A
Rationale: A. [CORRECT] Absolute specificity means the enzyme catalyzes a reaction
with only one particular substrate and no others. For example, glucose oxidase acts
specifically on β-D-glucose and not on other sugars. B is incorrect; this describes group
specificity (relative specificity), where the enzyme acts on substrates with similar
functional groups. C is incorrect; this describes stereospecificity or stereochemical
specificity. D is incorrect; metal ion requirement refers to cofactor dependence, not
substrate specificity.
, DOMAIN: ENZYME KINETICS & MICHAELIS-MENTEN (25%)
Q5. In the Michaelis-Menten equation, v
0
=
K
m
+[S]
V
max
[S]
, what does K
m
represent?
A. The maximum velocity of the reaction
B. The substrate concentration at which the reaction velocity is half of V
