BIOC 385 METABOLIC
BIOCHEMISTRY EXAM 1 – 230
LATEST REAL EXAM QUESTIONS
WITH CORRECT DETAILED
ANSWERS | UNIVERSITY OF
ARIZONA | 2025/2026 EDITION
1. If the Gibbs free energy change (ΔG) of a reaction is less than zero, then this
reaction is ______.
A. Endergonic
B. Exergonic
C. At equilibrium
D. Cannot be determined
Answer: B
Explanation: A negative ΔG indicates that the reaction releases free energy and can
proceed spontaneously, i.e., an exergonic reaction.
2. How can an unfavorable reaction (ΔG > 0) still occur in a metabolic pathway?
A. By increasing the temperature
B. By coupling it to a favorable reaction
C. By removing the enzyme
D. By decreasing substrate concentration
Answer: B
Explanation: Endergonic reactions can be driven forward by coupling with exergonic
reactions (such as ATP hydrolysis), and the overall ΔG of the coupled reaction is
negative.
3. The binding of glucose to hexokinase causes a conformational change in the
enzyme. This is an example of which model?
A. Lock-and-key model
B. Induced fit model
C. Allosteric model
D. Cooperative model
,Answer: B
Explanation: The induced fit model holds that the enzyme active site is not a rigid
structure, but rather undergoes conformational adjustment upon substrate binding to
achieve complementary fit.
4. Which of the following statements about enzymes is correct? (Select two)
A. Enzymes increase reaction rates without changing the equilibrium constant
B. Enzymes lower the activation energy of reactions
C. All proteins are enzymes
D. Enzymes change the ΔG of reactions
Answer: A, B
Explanation: Enzymes accelerate reactions by lowering the activation energy, but do
not change the equilibrium constant or the overall free energy change of the reaction.
Not all proteins are enzymes.
5. Where does the O₂ produced in photosynthesis come from?
A. CO₂
B. H₂O
C. Glucose
D. ATP
Answer: B
Explanation: Photosystem II (PSII) obtains electrons by splitting water molecules, with
O₂ released as a byproduct.
6. Where does the Calvin-Benson cycle occur?
A. Thylakoid membrane
B. Chloroplast stroma
C. Cytoplasm
D. Mitochondrial matrix
Answer: B
Explanation: The enzymes of the Calvin cycle are located in the chloroplast stroma,
utilizing ATP and NADPH generated by the light reactions.
7. Which metabolites produced by the light reactions are required for the
Calvin cycle?
A. ATP and NADH
B. ATP and NADPH
C. GTP and FADH₂
D. NADH and FADH₂
,Answer: B
Explanation: The light reactions generate ATP and NADPH, both of which are
consumed during the reduction phase of the Calvin cycle.
8. Why does the O₂ side reaction of rubisco become significant under certain
conditions?
A. When CO₂ concentration is high
B. When O₂ concentration is higher than CO₂ concentration
C. When light is insufficient
D. When temperature is low
Answer: B
Explanation: Rubisco has a dual affinity for CO₂ and O₂. When soluble O₂
concentration exceeds CO₂ concentration, the oxygenase activity predominates, leading
to wasteful photorespiration.
9. What is the advantage of glycogen having more branch points compared to
amylopectin?
A. Higher energy density
B. More non-reducing ends, facilitating rapid glucose release and addition
C. Better solubility
D. Easier to degrade completely
Answer: B
Explanation: Branching creates more non-reducing ends, allowing glycogen
phosphorylase and synthase to act simultaneously at multiple sites, thereby
accelerating glucose mobilization and storage.
10. Why are raffinose-series oligosaccharides difficult for humans to digest?
A. They are too large in molecular size
B. Humans lack the enzymes needed to hydrolyze the relevant glycosidic bonds
C. They are not soluble in water
D. They are bound by proteins
Answer: B
Explanation: Humans do not possess α-galactosidase, which is required to hydrolyze
the α-1,6 glycosidic bonds in raffinose-series oligosaccharides, so these sugars pass
through the small intestine to the colon where they are fermented by bacteria to
produce gas.
11. What are the products of the oxidative phase of the pentose phosphate
pathway?
A. 2 NADH + 1 hexose phosphate
B. 2 NADPH + 1 pentose phosphate
, C. 2 NADP⁺ + 1 pentose phosphate
D. 2 NADPH + 1 hexose phosphate
Answer: B
Explanation: The oxidative phase converts glucose-6-phosphate to ribulose-5-
phosphate, while generating 2 molecules of NADPH and releasing 1 molecule of CO₂.
12. What is the main reason the Biosphere 2 project had to be interrupted?
A. The humans ran out of food
B. CO₂ levels rose to dangerous levels
C. Photosynthesis rate was too high
D. Plants stopped producing oxygen
Answer: B
Explanation: The balance between heterotrophs (humans and animals) and autotrophs
(plants) in the sealed system was disrupted, causing CO₂ concentration to rise to levels
that threatened the health of the inhabitants.
13. Which enzyme do penicillin-resistant bacteria produce to inactivate
penicillin?
A. Peptidase
B. Transpeptidase
C. β-Lactamase
D. α-Galactosidase
Answer: C
Explanation: β-Lactamase hydrolyzes the β-lactam ring of penicillin, rendering it
inactive and unable to inhibit transpeptidase (a cell wall synthesis enzyme).
14. What is the probability that a child will have type AB blood when one
parent is homozygous for GTA glycosyltransferase and the other is homozygous
for GTB?
A. 0%
B. 25%
C. 75%
D. 100%
Answer: D
Explanation: Both parents are homozygous (GTA/GTA and GTB/GTB), and all offspring
will inherit one GTA allele and one GTB allele, expressing both enzymes and thus
producing both A and B antigens, i.e., type AB blood.
15. Which glucose homopolymer would the human body use when rapid
sprinting is needed?
A. Sucrose
BIOCHEMISTRY EXAM 1 – 230
LATEST REAL EXAM QUESTIONS
WITH CORRECT DETAILED
ANSWERS | UNIVERSITY OF
ARIZONA | 2025/2026 EDITION
1. If the Gibbs free energy change (ΔG) of a reaction is less than zero, then this
reaction is ______.
A. Endergonic
B. Exergonic
C. At equilibrium
D. Cannot be determined
Answer: B
Explanation: A negative ΔG indicates that the reaction releases free energy and can
proceed spontaneously, i.e., an exergonic reaction.
2. How can an unfavorable reaction (ΔG > 0) still occur in a metabolic pathway?
A. By increasing the temperature
B. By coupling it to a favorable reaction
C. By removing the enzyme
D. By decreasing substrate concentration
Answer: B
Explanation: Endergonic reactions can be driven forward by coupling with exergonic
reactions (such as ATP hydrolysis), and the overall ΔG of the coupled reaction is
negative.
3. The binding of glucose to hexokinase causes a conformational change in the
enzyme. This is an example of which model?
A. Lock-and-key model
B. Induced fit model
C. Allosteric model
D. Cooperative model
,Answer: B
Explanation: The induced fit model holds that the enzyme active site is not a rigid
structure, but rather undergoes conformational adjustment upon substrate binding to
achieve complementary fit.
4. Which of the following statements about enzymes is correct? (Select two)
A. Enzymes increase reaction rates without changing the equilibrium constant
B. Enzymes lower the activation energy of reactions
C. All proteins are enzymes
D. Enzymes change the ΔG of reactions
Answer: A, B
Explanation: Enzymes accelerate reactions by lowering the activation energy, but do
not change the equilibrium constant or the overall free energy change of the reaction.
Not all proteins are enzymes.
5. Where does the O₂ produced in photosynthesis come from?
A. CO₂
B. H₂O
C. Glucose
D. ATP
Answer: B
Explanation: Photosystem II (PSII) obtains electrons by splitting water molecules, with
O₂ released as a byproduct.
6. Where does the Calvin-Benson cycle occur?
A. Thylakoid membrane
B. Chloroplast stroma
C. Cytoplasm
D. Mitochondrial matrix
Answer: B
Explanation: The enzymes of the Calvin cycle are located in the chloroplast stroma,
utilizing ATP and NADPH generated by the light reactions.
7. Which metabolites produced by the light reactions are required for the
Calvin cycle?
A. ATP and NADH
B. ATP and NADPH
C. GTP and FADH₂
D. NADH and FADH₂
,Answer: B
Explanation: The light reactions generate ATP and NADPH, both of which are
consumed during the reduction phase of the Calvin cycle.
8. Why does the O₂ side reaction of rubisco become significant under certain
conditions?
A. When CO₂ concentration is high
B. When O₂ concentration is higher than CO₂ concentration
C. When light is insufficient
D. When temperature is low
Answer: B
Explanation: Rubisco has a dual affinity for CO₂ and O₂. When soluble O₂
concentration exceeds CO₂ concentration, the oxygenase activity predominates, leading
to wasteful photorespiration.
9. What is the advantage of glycogen having more branch points compared to
amylopectin?
A. Higher energy density
B. More non-reducing ends, facilitating rapid glucose release and addition
C. Better solubility
D. Easier to degrade completely
Answer: B
Explanation: Branching creates more non-reducing ends, allowing glycogen
phosphorylase and synthase to act simultaneously at multiple sites, thereby
accelerating glucose mobilization and storage.
10. Why are raffinose-series oligosaccharides difficult for humans to digest?
A. They are too large in molecular size
B. Humans lack the enzymes needed to hydrolyze the relevant glycosidic bonds
C. They are not soluble in water
D. They are bound by proteins
Answer: B
Explanation: Humans do not possess α-galactosidase, which is required to hydrolyze
the α-1,6 glycosidic bonds in raffinose-series oligosaccharides, so these sugars pass
through the small intestine to the colon where they are fermented by bacteria to
produce gas.
11. What are the products of the oxidative phase of the pentose phosphate
pathway?
A. 2 NADH + 1 hexose phosphate
B. 2 NADPH + 1 pentose phosphate
, C. 2 NADP⁺ + 1 pentose phosphate
D. 2 NADPH + 1 hexose phosphate
Answer: B
Explanation: The oxidative phase converts glucose-6-phosphate to ribulose-5-
phosphate, while generating 2 molecules of NADPH and releasing 1 molecule of CO₂.
12. What is the main reason the Biosphere 2 project had to be interrupted?
A. The humans ran out of food
B. CO₂ levels rose to dangerous levels
C. Photosynthesis rate was too high
D. Plants stopped producing oxygen
Answer: B
Explanation: The balance between heterotrophs (humans and animals) and autotrophs
(plants) in the sealed system was disrupted, causing CO₂ concentration to rise to levels
that threatened the health of the inhabitants.
13. Which enzyme do penicillin-resistant bacteria produce to inactivate
penicillin?
A. Peptidase
B. Transpeptidase
C. β-Lactamase
D. α-Galactosidase
Answer: C
Explanation: β-Lactamase hydrolyzes the β-lactam ring of penicillin, rendering it
inactive and unable to inhibit transpeptidase (a cell wall synthesis enzyme).
14. What is the probability that a child will have type AB blood when one
parent is homozygous for GTA glycosyltransferase and the other is homozygous
for GTB?
A. 0%
B. 25%
C. 75%
D. 100%
Answer: D
Explanation: Both parents are homozygous (GTA/GTA and GTB/GTB), and all offspring
will inherit one GTA allele and one GTB allele, expressing both enzymes and thus
producing both A and B antigens, i.e., type AB blood.
15. Which glucose homopolymer would the human body use when rapid
sprinting is needed?
A. Sucrose
