BIOCHEM 210 BIOCHEMISTRY MODULE 3 EXAM ACTUAL
2026/2027 | Enzymes, Kinetics, Inhibition & Membrane
Transport | Portage Learning | Complete Questions & Verified
Answers | Pass Guaranteed - A+ Graded
Section 1: Enzyme Classification & Basic Concepts (Questions 1-12)
Q1. Which statement correctly defines an enzyme?
A. Enzymes are biological catalysts that increase reaction equilibrium constants
B. Enzymes are biological catalysts that are always proteins and function by changing
ΔG°'
C. Enzymes are biological catalysts that lower activation energy without changing Keq
or ΔG°'
D. Enzymes are biological catalysts that only function at 37°C and neutral pH
Correct Answer: C. Enzymes are biological catalysts that lower activation energy
without changing Keq or ΔG°' [CORRECT]
Rationale: Enzymes accelerate reactions by stabilizing the transition state and lowering
activation energy (ΔG‡), but they do not alter the equilibrium constant (Keq) or the
standard free energy change (ΔG°').
Q2. The active site of an enzyme typically contains:
A. Only hydrophobic amino acid residues that repel water
B. Substrate binding residues and catalytic residues that participate in the reaction
C. The entire polypeptide chain folded into an α-helix
D. Cofactors exclusively, with no amino acid involvement
Correct Answer: B. Substrate binding residues and catalytic residues that participate in
the reaction [CORRECT]
Rationale: The active site consists of a substrate-binding pocket and catalytic residues
that directly participate in bond making/breaking, often assisted by cofactors or
coenzymes.
,Q3. According to transition state theory, how does an enzyme increase reaction rate?
A. By increasing the energy of the substrate
B. By lowering the activation energy (ΔG‡) through transition state stabilization
C. By changing the standard free energy change (ΔG°') of the reaction
D. By increasing the equilibrium constant to favor product formation
Correct Answer: B. By lowering the activation energy (ΔG‡) through transition state
stabilization [CORRECT]
Rationale: Enzymes bind the transition state more tightly than the substrate, lowering
the activation energy barrier and exponentially increasing the reaction rate without
altering Keq.
Q4. Which enzyme class corresponds to EC number 3?
A. Oxidoreductases
B. Transferases
C. Hydrolases
D. Lyases
Correct Answer: C. Hydrolases [CORRECT]
Rationale: The Enzyme Commission (EC) numbering system classifies hydrolases as EC
3, which catalyze bond cleavage with water addition; oxidoreductases are EC 1,
transferases EC 2, and lyases EC 4.
Q5. Which of the following is correctly classified as a prosthetic group?
A. Mg²⁺ ion bound temporarily to the enzyme
B. NAD⁺ dissociating from the enzyme after each catalytic cycle
C. Heme group covalently and tightly bound to cytochrome c
D. Coenzyme A freely diffusing in the cytosol
Correct Answer: C. Heme group covalently and tightly bound to cytochrome c
[CORRECT]
Rationale: Prosthetic groups are tightly bound coenzymes or cofactors that remain
associated with the enzyme, unlike loosely bound coenzymes (NAD⁺, CoA) or inorganic
ions that may dissociate.
, Q6. Which enzyme class is responsible for catalyzing the transfer of electrons or
hydrogen atoms between molecules?
A. Transferases
B. Oxidoreductases
C. Hydrolases
D. Lyases
Correct Answer: B. Oxidoreductases [CORRECT]
Rationale: Oxidoreductases (EC 1) catalyze oxidation-reduction reactions involving
electron/hydrogen transfer; transferases (EC 2) move functional groups, hydrolases (EC
3) cleave bonds with water, and lyases (EC 4) cleave bonds without hydrolysis.
Q7. An enzyme binds its substrate and undergoes a conformational change that brings
catalytic residues into proper alignment. This best describes:
A. The lock-and-key model of rigid complementary binding
B. The induced fit model of dynamic conformational adaptation
C. The transition state theory of energy minimization
D. The Michaelis-Menten model of steady-state kinetics
Correct Answer: B. The induced fit model of dynamic conformational adaptation
[CORRECT]
Rationale: The induced fit model describes substrate-induced conformational changes
that optimize catalytic residue positioning, unlike the rigid lock-and-key model where the
active site is pre-formed.
Q8. Which of the following is a coenzyme rather than a prosthetic group or inorganic
cofactor?
A. Zn²⁺ bound to carbonic anhydrase
B. Heme covalently attached to cytochrome c
C. NAD⁺ dissociating from lactate dehydrogenase after reaction
D. Mg²⁺ required for kinase activity
Correct Answer: C. NAD⁺ dissociating from lactate dehydrogenase after reaction
[CORRECT]
2026/2027 | Enzymes, Kinetics, Inhibition & Membrane
Transport | Portage Learning | Complete Questions & Verified
Answers | Pass Guaranteed - A+ Graded
Section 1: Enzyme Classification & Basic Concepts (Questions 1-12)
Q1. Which statement correctly defines an enzyme?
A. Enzymes are biological catalysts that increase reaction equilibrium constants
B. Enzymes are biological catalysts that are always proteins and function by changing
ΔG°'
C. Enzymes are biological catalysts that lower activation energy without changing Keq
or ΔG°'
D. Enzymes are biological catalysts that only function at 37°C and neutral pH
Correct Answer: C. Enzymes are biological catalysts that lower activation energy
without changing Keq or ΔG°' [CORRECT]
Rationale: Enzymes accelerate reactions by stabilizing the transition state and lowering
activation energy (ΔG‡), but they do not alter the equilibrium constant (Keq) or the
standard free energy change (ΔG°').
Q2. The active site of an enzyme typically contains:
A. Only hydrophobic amino acid residues that repel water
B. Substrate binding residues and catalytic residues that participate in the reaction
C. The entire polypeptide chain folded into an α-helix
D. Cofactors exclusively, with no amino acid involvement
Correct Answer: B. Substrate binding residues and catalytic residues that participate in
the reaction [CORRECT]
Rationale: The active site consists of a substrate-binding pocket and catalytic residues
that directly participate in bond making/breaking, often assisted by cofactors or
coenzymes.
,Q3. According to transition state theory, how does an enzyme increase reaction rate?
A. By increasing the energy of the substrate
B. By lowering the activation energy (ΔG‡) through transition state stabilization
C. By changing the standard free energy change (ΔG°') of the reaction
D. By increasing the equilibrium constant to favor product formation
Correct Answer: B. By lowering the activation energy (ΔG‡) through transition state
stabilization [CORRECT]
Rationale: Enzymes bind the transition state more tightly than the substrate, lowering
the activation energy barrier and exponentially increasing the reaction rate without
altering Keq.
Q4. Which enzyme class corresponds to EC number 3?
A. Oxidoreductases
B. Transferases
C. Hydrolases
D. Lyases
Correct Answer: C. Hydrolases [CORRECT]
Rationale: The Enzyme Commission (EC) numbering system classifies hydrolases as EC
3, which catalyze bond cleavage with water addition; oxidoreductases are EC 1,
transferases EC 2, and lyases EC 4.
Q5. Which of the following is correctly classified as a prosthetic group?
A. Mg²⁺ ion bound temporarily to the enzyme
B. NAD⁺ dissociating from the enzyme after each catalytic cycle
C. Heme group covalently and tightly bound to cytochrome c
D. Coenzyme A freely diffusing in the cytosol
Correct Answer: C. Heme group covalently and tightly bound to cytochrome c
[CORRECT]
Rationale: Prosthetic groups are tightly bound coenzymes or cofactors that remain
associated with the enzyme, unlike loosely bound coenzymes (NAD⁺, CoA) or inorganic
ions that may dissociate.
, Q6. Which enzyme class is responsible for catalyzing the transfer of electrons or
hydrogen atoms between molecules?
A. Transferases
B. Oxidoreductases
C. Hydrolases
D. Lyases
Correct Answer: B. Oxidoreductases [CORRECT]
Rationale: Oxidoreductases (EC 1) catalyze oxidation-reduction reactions involving
electron/hydrogen transfer; transferases (EC 2) move functional groups, hydrolases (EC
3) cleave bonds with water, and lyases (EC 4) cleave bonds without hydrolysis.
Q7. An enzyme binds its substrate and undergoes a conformational change that brings
catalytic residues into proper alignment. This best describes:
A. The lock-and-key model of rigid complementary binding
B. The induced fit model of dynamic conformational adaptation
C. The transition state theory of energy minimization
D. The Michaelis-Menten model of steady-state kinetics
Correct Answer: B. The induced fit model of dynamic conformational adaptation
[CORRECT]
Rationale: The induced fit model describes substrate-induced conformational changes
that optimize catalytic residue positioning, unlike the rigid lock-and-key model where the
active site is pre-formed.
Q8. Which of the following is a coenzyme rather than a prosthetic group or inorganic
cofactor?
A. Zn²⁺ bound to carbonic anhydrase
B. Heme covalently attached to cytochrome c
C. NAD⁺ dissociating from lactate dehydrogenase after reaction
D. Mg²⁺ required for kinase activity
Correct Answer: C. NAD⁺ dissociating from lactate dehydrogenase after reaction
[CORRECT]
