BioChem 210 Module 3 Exam () | Portage Learning
Comprehensive 50-Question Examination with A+ Graded Rationales
Aligned with 2026-2027 Portage Learning / Geneva College CHEM 210 Curriculum Standards | Cognitive Distribution: 30% Recall, 50%
Application, 20% Analysis
Section 1: Enzyme Fundamentals (Definition, Classification, & Cofactors)
Questions 1-10 | Enzyme definition, EC classification, cofactors, coenzymes, apoenzyme vs holoenzyme, active site, catalysis
principles
Q1: A graduate student is designing an experiment to test how a novel biological catalyst affects the rate
of an endergonic biosynthetic reaction. He hypothesizes that the catalyst will allow the reaction to
proceed spontaneously. Based on the fundamental principles of enzyme catalysis, which statement best
describes what enzymes actually do?
A. Enzymes lower the activation energy of a reaction but do not change the free energy change (ΔG) of
the reaction or make a non-spontaneous reaction spontaneous [CORRECT]
B. Enzymes lower the activation energy and also make a non-spontaneous reaction spontaneous by reducing its
free energy change
C. Enzymes increase the free energy of the products, allowing unfavorable reactions to occur
D. Enzymes shift the equilibrium constant (Keq) of the reaction toward the products, driving non-spontaneous
reactions forward
Correct Answer: A
Rationale: Enzymes are biological catalysts that speed up chemical reactions by lowering the activation energy.
They do NOT change the free energy change (ΔG) of the reaction, cannot make a non-spontaneous reaction
spontaneous, and do NOT change the equilibrium constant (Keq). Enzymes only accelerate the rate at which
equilibrium is reached. Options B, C, and D all incorrectly attribute thermodynamic changes (ΔG or Keq) to
enzymes, which violates fundamental catalysis principles in the CHEM 210 Module 3 curriculum.
Q2: A biochemist isolates an enzyme that catalyzes the following reaction: pyruvate + NADH + H+ ->
lactate + NAD+. To which EC classification class does this enzyme belong, and what is the basis for the
classification?
A. Transferase, because it transfers electrons between molecules
B. Oxidoreductase, because it catalyzes an oxidation-reduction reaction involving the transfer of
electrons (NADH is oxidized to NAD+) [CORRECT]
C. Hydrolase, because it uses water to break bonds in pyruvate
D. Ligase, because it joins two molecules using ATP hydrolysis
Correct Answer: B
Rationale: Oxidoreductases (EC 1) catalyze oxidation-reduction reactions involving the transfer of electrons. In
this reaction, NADH donates electrons (becoming NAD+) while pyruvate is reduced to lactate, which is a clear
redox process catalyzed by lactate dehydrogenase, an oxidoreductase. Transferases move functional groups (not
electrons), hydrolases use water to cleave bonds, and ligases join molecules using ATP. The defining criterion is
electron transfer, distinguishing oxidoreductases from all other EC classes.
BioChem 210 Module 3 Exam (2026/2027) | Portage Learning - Page 1
,BioChem 210 Module 3 Exam - Enzymes
Q3: A researcher is studying hexokinase, which catalyzes the transfer of a phosphate group from ATP to
glucose, producing glucose-6-phosphate and ADP. Which EC classification correctly describes
hexokinase, and what is the defining feature of this class?
A. Hydrolase, because water is consumed in the reaction
B. Ligase, because ATP is hydrolyzed during the reaction
C. Transferase, because it transfers a functional group (phosphate) from one molecule (ATP) to another
(glucose) [CORRECT]
D. Isomerase, because it rearranges glucose into glucose-6-phosphate
Correct Answer: C
Rationale: Transferases (EC 2) catalyze the transfer of functional groups such as phosphate, methyl, or amino
groups from one molecule to another. Hexokinase transfers a phosphate group from ATP to glucose, which is a
hallmark transferase reaction, and kinases as a group are classified as transferases. Hydrolases require water
as a reactant to cleave bonds, ligases form new bonds with concomitant ATP hydrolysis (not merely transfer),
and isomerases rearrange atoms within a single molecule rather than transferring groups between two
molecules.
Q4: A pharmacologist is examining a protease that cleaves peptide bonds by adding water across the
bond, hydrolyzing it into two separate fragments. To which EC class does this protease belong, and what
distinguishes this class?
A. Lyase, because it cleaves bonds without water
B. Hydrolase, because it catalyzes hydrolysis reactions by breaking bonds with the addition of water
[CORRECT]
C. Transferase, because it transfers peptide fragments
D. Isomerase, because it rearranges the peptide backbone
Correct Answer: B
Rationale: Hydrolases (EC 3) catalyze hydrolysis reactions in which bonds are cleaved by the addition of water.
Proteases such as trypsin and pepsin are classic hydrolases that add water across peptide bonds, separating
them into fragments. Lyases cleave bonds by means other than hydrolysis or oxidation (e.g., elimination
reactions), transferases move functional groups between molecules, and isomerases rearrange atoms within a
single molecule. The defining feature of hydrolases is the use of water to break the bond.
Q5: A biochemist is studying an enzyme that catalyzes the reversible conversion of glucose-6-phosphate
to fructose-6-phosphate without breaking the carbon skeleton. To which EC class does this enzyme
belong, and what is the chemical basis for the classification?
A. Isomerase, because it catalyzes an isomerization reaction by rearranging atoms within the molecule
without changing its molecular formula [CORRECT]
B. Lyase, because it cleaves a carbon-carbon bond
C. Transferase, because it transfers a phosphate group within the molecule
D. Hydrolase, because it uses water to convert glucose to fructose
Correct Answer: A
BioChem 210 Module 3 Exam (2026/2027) | Portage Learning - Page 2
, BioChem 210 Module 3 Exam - Enzymes
Rationale: Isomerases (EC 5) catalyze isomerization reactions, which involve the rearrangement of atoms
within a molecule to produce an isomer with the same molecular formula but a different structure. The
conversion of glucose-6-phosphate to fructose-6-phosphate by phosphoglucose isomerase is a classic example of
an aldose-to-ketose isomerization. Lyases cleave bonds by elimination, transferases move functional groups
between molecules, and hydrolases use water to break bonds. None of these describe an intramolecular
rearrangement.
Q6: A molecular biologist is studying DNA ligase, which joins the 3'-hydroxyl end of one DNA strand to
the 5'-phosphate end of another, with the concomitant hydrolysis of ATP or NAD+. To which EC class
does DNA ligase belong, and what is the defining feature of this class?
A. Hydrolase, because ATP is hydrolyzed during the reaction
B. Ligase, because it joins two molecules together with the hydrolysis of ATP (also called a synthetase)
[CORRECT]
C. Transferase, because it transfers a phosphate group from ATP to DNA
D. Lyase, because it forms a new bond without water
Correct Answer: B
Rationale: Ligases (EC 6) are enzymes that join two molecules together by forming new chemical bonds
(typically C-O, C-N, or C-C bonds) with the concomitant hydrolysis of ATP or another high-energy phosphate.
They are also called synthetases. DNA ligase joins DNA strands while consuming ATP, which is a defining
ligase reaction. Hydrolases use water to cleave bonds (here, ATP hydrolysis is the energy source, not the
defining reaction), transferases move functional groups, and lyases form or break bonds without water or
oxidation but do not require ATP hydrolysis.
Q7: A researcher is studying an enzyme that requires zinc ions (Zn2+) for catalytic activity. When she
removes the zinc by dialysis, the protein loses all catalytic activity, but activity is restored when zinc is
added back. Which terms correctly describe the zinc ion, the protein without zinc, and the protein with
zinc?
A. Zinc is a coenzyme; the protein without zinc is a holoenzyme; the protein with zinc is an apoenzyme
B. Zinc is a cofactor; the protein without zinc is an apoenzyme (inactive); the protein with zinc is a
holoenzyme (active) [CORRECT]
C. Zinc is a substrate; the protein without zinc is a zymogen; the protein with zinc is an allosteric activator
D. Zinc is a coenzyme; the protein without zinc is a holoenzyme; the protein with zinc is a competitive
inhibitor
Correct Answer: B
Rationale: Zinc is a cofactor, defined as a non-protein chemical compound (often a metal ion such as Zn2+,
Mg2+, or Fe2+) required for enzyme activity. The protein portion without its cofactor is called an apoenzyme and
is inactive; the complete, active complex of apoenzyme plus cofactor is called a holoenzyme. Coenzymes are
organic cofactors often derived from vitamins (such as NAD+ or FAD), so zinc is not a coenzyme. Zymogens
refer to inactive protein precursors, and competitive inhibitors are unrelated to metal ion activation.
Q8: A nutritionist explains that vitamin B3 (niacin) is essential because it serves as a precursor for an
organic cofactor required by many dehydrogenase enzymes. Which term describes this organic cofactor,
and what is an example of such a cofactor derived from a vitamin?
BioChem 210 Module 3 Exam (2026/2027) | Portage Learning - Page 3
Comprehensive 50-Question Examination with A+ Graded Rationales
Aligned with 2026-2027 Portage Learning / Geneva College CHEM 210 Curriculum Standards | Cognitive Distribution: 30% Recall, 50%
Application, 20% Analysis
Section 1: Enzyme Fundamentals (Definition, Classification, & Cofactors)
Questions 1-10 | Enzyme definition, EC classification, cofactors, coenzymes, apoenzyme vs holoenzyme, active site, catalysis
principles
Q1: A graduate student is designing an experiment to test how a novel biological catalyst affects the rate
of an endergonic biosynthetic reaction. He hypothesizes that the catalyst will allow the reaction to
proceed spontaneously. Based on the fundamental principles of enzyme catalysis, which statement best
describes what enzymes actually do?
A. Enzymes lower the activation energy of a reaction but do not change the free energy change (ΔG) of
the reaction or make a non-spontaneous reaction spontaneous [CORRECT]
B. Enzymes lower the activation energy and also make a non-spontaneous reaction spontaneous by reducing its
free energy change
C. Enzymes increase the free energy of the products, allowing unfavorable reactions to occur
D. Enzymes shift the equilibrium constant (Keq) of the reaction toward the products, driving non-spontaneous
reactions forward
Correct Answer: A
Rationale: Enzymes are biological catalysts that speed up chemical reactions by lowering the activation energy.
They do NOT change the free energy change (ΔG) of the reaction, cannot make a non-spontaneous reaction
spontaneous, and do NOT change the equilibrium constant (Keq). Enzymes only accelerate the rate at which
equilibrium is reached. Options B, C, and D all incorrectly attribute thermodynamic changes (ΔG or Keq) to
enzymes, which violates fundamental catalysis principles in the CHEM 210 Module 3 curriculum.
Q2: A biochemist isolates an enzyme that catalyzes the following reaction: pyruvate + NADH + H+ ->
lactate + NAD+. To which EC classification class does this enzyme belong, and what is the basis for the
classification?
A. Transferase, because it transfers electrons between molecules
B. Oxidoreductase, because it catalyzes an oxidation-reduction reaction involving the transfer of
electrons (NADH is oxidized to NAD+) [CORRECT]
C. Hydrolase, because it uses water to break bonds in pyruvate
D. Ligase, because it joins two molecules using ATP hydrolysis
Correct Answer: B
Rationale: Oxidoreductases (EC 1) catalyze oxidation-reduction reactions involving the transfer of electrons. In
this reaction, NADH donates electrons (becoming NAD+) while pyruvate is reduced to lactate, which is a clear
redox process catalyzed by lactate dehydrogenase, an oxidoreductase. Transferases move functional groups (not
electrons), hydrolases use water to cleave bonds, and ligases join molecules using ATP. The defining criterion is
electron transfer, distinguishing oxidoreductases from all other EC classes.
BioChem 210 Module 3 Exam (2026/2027) | Portage Learning - Page 1
,BioChem 210 Module 3 Exam - Enzymes
Q3: A researcher is studying hexokinase, which catalyzes the transfer of a phosphate group from ATP to
glucose, producing glucose-6-phosphate and ADP. Which EC classification correctly describes
hexokinase, and what is the defining feature of this class?
A. Hydrolase, because water is consumed in the reaction
B. Ligase, because ATP is hydrolyzed during the reaction
C. Transferase, because it transfers a functional group (phosphate) from one molecule (ATP) to another
(glucose) [CORRECT]
D. Isomerase, because it rearranges glucose into glucose-6-phosphate
Correct Answer: C
Rationale: Transferases (EC 2) catalyze the transfer of functional groups such as phosphate, methyl, or amino
groups from one molecule to another. Hexokinase transfers a phosphate group from ATP to glucose, which is a
hallmark transferase reaction, and kinases as a group are classified as transferases. Hydrolases require water
as a reactant to cleave bonds, ligases form new bonds with concomitant ATP hydrolysis (not merely transfer),
and isomerases rearrange atoms within a single molecule rather than transferring groups between two
molecules.
Q4: A pharmacologist is examining a protease that cleaves peptide bonds by adding water across the
bond, hydrolyzing it into two separate fragments. To which EC class does this protease belong, and what
distinguishes this class?
A. Lyase, because it cleaves bonds without water
B. Hydrolase, because it catalyzes hydrolysis reactions by breaking bonds with the addition of water
[CORRECT]
C. Transferase, because it transfers peptide fragments
D. Isomerase, because it rearranges the peptide backbone
Correct Answer: B
Rationale: Hydrolases (EC 3) catalyze hydrolysis reactions in which bonds are cleaved by the addition of water.
Proteases such as trypsin and pepsin are classic hydrolases that add water across peptide bonds, separating
them into fragments. Lyases cleave bonds by means other than hydrolysis or oxidation (e.g., elimination
reactions), transferases move functional groups between molecules, and isomerases rearrange atoms within a
single molecule. The defining feature of hydrolases is the use of water to break the bond.
Q5: A biochemist is studying an enzyme that catalyzes the reversible conversion of glucose-6-phosphate
to fructose-6-phosphate without breaking the carbon skeleton. To which EC class does this enzyme
belong, and what is the chemical basis for the classification?
A. Isomerase, because it catalyzes an isomerization reaction by rearranging atoms within the molecule
without changing its molecular formula [CORRECT]
B. Lyase, because it cleaves a carbon-carbon bond
C. Transferase, because it transfers a phosphate group within the molecule
D. Hydrolase, because it uses water to convert glucose to fructose
Correct Answer: A
BioChem 210 Module 3 Exam (2026/2027) | Portage Learning - Page 2
, BioChem 210 Module 3 Exam - Enzymes
Rationale: Isomerases (EC 5) catalyze isomerization reactions, which involve the rearrangement of atoms
within a molecule to produce an isomer with the same molecular formula but a different structure. The
conversion of glucose-6-phosphate to fructose-6-phosphate by phosphoglucose isomerase is a classic example of
an aldose-to-ketose isomerization. Lyases cleave bonds by elimination, transferases move functional groups
between molecules, and hydrolases use water to break bonds. None of these describe an intramolecular
rearrangement.
Q6: A molecular biologist is studying DNA ligase, which joins the 3'-hydroxyl end of one DNA strand to
the 5'-phosphate end of another, with the concomitant hydrolysis of ATP or NAD+. To which EC class
does DNA ligase belong, and what is the defining feature of this class?
A. Hydrolase, because ATP is hydrolyzed during the reaction
B. Ligase, because it joins two molecules together with the hydrolysis of ATP (also called a synthetase)
[CORRECT]
C. Transferase, because it transfers a phosphate group from ATP to DNA
D. Lyase, because it forms a new bond without water
Correct Answer: B
Rationale: Ligases (EC 6) are enzymes that join two molecules together by forming new chemical bonds
(typically C-O, C-N, or C-C bonds) with the concomitant hydrolysis of ATP or another high-energy phosphate.
They are also called synthetases. DNA ligase joins DNA strands while consuming ATP, which is a defining
ligase reaction. Hydrolases use water to cleave bonds (here, ATP hydrolysis is the energy source, not the
defining reaction), transferases move functional groups, and lyases form or break bonds without water or
oxidation but do not require ATP hydrolysis.
Q7: A researcher is studying an enzyme that requires zinc ions (Zn2+) for catalytic activity. When she
removes the zinc by dialysis, the protein loses all catalytic activity, but activity is restored when zinc is
added back. Which terms correctly describe the zinc ion, the protein without zinc, and the protein with
zinc?
A. Zinc is a coenzyme; the protein without zinc is a holoenzyme; the protein with zinc is an apoenzyme
B. Zinc is a cofactor; the protein without zinc is an apoenzyme (inactive); the protein with zinc is a
holoenzyme (active) [CORRECT]
C. Zinc is a substrate; the protein without zinc is a zymogen; the protein with zinc is an allosteric activator
D. Zinc is a coenzyme; the protein without zinc is a holoenzyme; the protein with zinc is a competitive
inhibitor
Correct Answer: B
Rationale: Zinc is a cofactor, defined as a non-protein chemical compound (often a metal ion such as Zn2+,
Mg2+, or Fe2+) required for enzyme activity. The protein portion without its cofactor is called an apoenzyme and
is inactive; the complete, active complex of apoenzyme plus cofactor is called a holoenzyme. Coenzymes are
organic cofactors often derived from vitamins (such as NAD+ or FAD), so zinc is not a coenzyme. Zymogens
refer to inactive protein precursors, and competitive inhibitors are unrelated to metal ion activation.
Q8: A nutritionist explains that vitamin B3 (niacin) is essential because it serves as a precursor for an
organic cofactor required by many dehydrogenase enzymes. Which term describes this organic cofactor,
and what is an example of such a cofactor derived from a vitamin?
BioChem 210 Module 3 Exam (2026/2027) | Portage Learning - Page 3
