BCH 4053 Exam 3 V1 | BCH 4053 Biochemistry I | Actual Q&A with
Rationale (BCH4053 Exam 3) | University of Central Florida
1. Which enzyme catalyzes the primary rate-limiting and committed step of glycolysis?
A. Hexokinase
B. Aldolase
C. Pyruvate Kinase
D. Phosphofructokinase-1
Answer: D
Explanation: Phosphofructokinase-1 (PFK-1) is the most important regulatory enzyme in
the glycolytic pathway. It catalyzes the phosphorylation of fructose-6-phosphate to
fructose-1,6-bisphosphate using ATP. This step is irreversible and serves as the primary
flux-control point for the entire pathway.
2. In the Malate-Aspartate Shuttle, which molecule is transported into the mitochondrial
matrix while glutamate is transported out?
A. Oxaloacetate
B. Malate
C. Aspartate
D. Alpha-ketoglutarate
Answer: C
Explanation: The Malate-Aspartate shuttle is a mechanism used by cells to move reducing
equivalents from the cytosol into the mitochondria. Aspartate is moved out of the matrix in
exchange for glutamate moving in via an antiporter. This process is essential for
maintaining the high rate of aerobic glycolysis in heart and liver tissue.
3. What is the net yield of ATP molecules per molecule of glucose during anaerobic glycolysis
in a muscle cell?
A. 0
B. 2
C. 4
D. 32
Answer: B
,Explanation: Anaerobic glycolysis involves the conversion of glucose to lactate when
oxygen is limiting. Although four ATP are produced in the payoff phase, two ATP are
consumed in the preparatory phase, resulting in a net gain of two. This pathway allows for
rapid ATP production even in the absence of oxidative phosphorylation.
4. Which component of the Pyruvate Dehydrogenase (PDH) Complex utilizes Thiamine
Pyrophosphate (TPP) as a cofactor?
A. PDH Kinase
B. Dihydrolipoyl transacetylase (E2)
C. Dihydrolipoyl dehydrogenase (E3)
D. Pyruvate Dehydrogenase (E1)
Answer: D
Explanation: The E1 subunit of the PDH complex is responsible for the decarboxylation of
pyruvate. It requires TPP to stabilize the carbanion intermediate formed during the
reaction. Deficiency in thiamine leads to Beriberi because the PDH complex cannot function
effectively.
5. Which of the following citric acid cycle enzymes is also a member of the electron transport
chain?
A. Citrate Synthase
B. Isocitrate Dehydrogenase
C. Succinate Dehydrogenase
D. Malate Dehydrogenase
Answer: C
Explanation: Succinate dehydrogenase is unique among TCA cycle enzymes because it is
embedded in the inner mitochondrial membrane. It functions as Complex II in the electron
transport chain, transferring electrons directly to ubiquinone. This enzyme uses FAD as a
prosthetic group rather than NAD+.
6. The reaction catalyzed by which enzyme in the TCA cycle produces a molecule of GTP (or
ATP) via substrate-level phosphorylation?
A. Succinyl-CoA synthetase
B. Alpha-ketoglutarate dehydrogenase
C. Fumarase
D. Aconitase
Answer: A
, Explanation: Succinyl-CoA synthetase catalyzes the conversion of succinyl-CoA to
succinate. The energy released from the thioester bond cleavage is used to phosphorylate
GDP or ADP. This represents the only step in the citric acid cycle that directly generates a
high-energy nucleoside triphosphate.
7. Which molecule acts as a potent allosteric activator of Phosphofructokinase-1 (PFK-1) and
an inhibitor of Fructose-1,6-bisphosphatase?
A. ATP
B. Citrate
C. Fructose-2,6-bisphosphate
D. Glucose-6-phosphate
Answer: C
Explanation: Fructose-2,6-bisphosphate is a key regulatory molecule that signals high
blood glucose levels. It increases the affinity of PFK-1 for its substrate while simultaneously
inhibiting the gluconeogenic enzyme fructose-1,6-bisphosphatase. This reciprocal
regulation prevents futile cycling between glycolysis and gluconeogenesis.
8. What is the final electron acceptor in the mitochondrial electron transport chain?
A. NAD+
B. Oxygen
C. FAD
D. Water
Answer: B
Explanation: Molecular oxygen has the highest reduction potential in the electron
transport chain. It accepts four electrons at Complex IV to be reduced into two molecules of
water. Without oxygen, the entire electron transport chain backs up, and ATP production
ceases.
9. Which enzyme in gluconeogenesis bypasses the irreversible hexokinase step of glycolysis?
A. Pyruvate Carboxylase
B. Glucose-6-phosphatase
C. Fructose-1,6-bisphosphatase
D. PEP Carboxykinase
Answer: B
Explanation: Glucose-6-phosphatase is the enzyme responsible for the final step of
gluconeogenesis. It removes the phosphate group from glucose-6-phosphate, allowing free
Rationale (BCH4053 Exam 3) | University of Central Florida
1. Which enzyme catalyzes the primary rate-limiting and committed step of glycolysis?
A. Hexokinase
B. Aldolase
C. Pyruvate Kinase
D. Phosphofructokinase-1
Answer: D
Explanation: Phosphofructokinase-1 (PFK-1) is the most important regulatory enzyme in
the glycolytic pathway. It catalyzes the phosphorylation of fructose-6-phosphate to
fructose-1,6-bisphosphate using ATP. This step is irreversible and serves as the primary
flux-control point for the entire pathway.
2. In the Malate-Aspartate Shuttle, which molecule is transported into the mitochondrial
matrix while glutamate is transported out?
A. Oxaloacetate
B. Malate
C. Aspartate
D. Alpha-ketoglutarate
Answer: C
Explanation: The Malate-Aspartate shuttle is a mechanism used by cells to move reducing
equivalents from the cytosol into the mitochondria. Aspartate is moved out of the matrix in
exchange for glutamate moving in via an antiporter. This process is essential for
maintaining the high rate of aerobic glycolysis in heart and liver tissue.
3. What is the net yield of ATP molecules per molecule of glucose during anaerobic glycolysis
in a muscle cell?
A. 0
B. 2
C. 4
D. 32
Answer: B
,Explanation: Anaerobic glycolysis involves the conversion of glucose to lactate when
oxygen is limiting. Although four ATP are produced in the payoff phase, two ATP are
consumed in the preparatory phase, resulting in a net gain of two. This pathway allows for
rapid ATP production even in the absence of oxidative phosphorylation.
4. Which component of the Pyruvate Dehydrogenase (PDH) Complex utilizes Thiamine
Pyrophosphate (TPP) as a cofactor?
A. PDH Kinase
B. Dihydrolipoyl transacetylase (E2)
C. Dihydrolipoyl dehydrogenase (E3)
D. Pyruvate Dehydrogenase (E1)
Answer: D
Explanation: The E1 subunit of the PDH complex is responsible for the decarboxylation of
pyruvate. It requires TPP to stabilize the carbanion intermediate formed during the
reaction. Deficiency in thiamine leads to Beriberi because the PDH complex cannot function
effectively.
5. Which of the following citric acid cycle enzymes is also a member of the electron transport
chain?
A. Citrate Synthase
B. Isocitrate Dehydrogenase
C. Succinate Dehydrogenase
D. Malate Dehydrogenase
Answer: C
Explanation: Succinate dehydrogenase is unique among TCA cycle enzymes because it is
embedded in the inner mitochondrial membrane. It functions as Complex II in the electron
transport chain, transferring electrons directly to ubiquinone. This enzyme uses FAD as a
prosthetic group rather than NAD+.
6. The reaction catalyzed by which enzyme in the TCA cycle produces a molecule of GTP (or
ATP) via substrate-level phosphorylation?
A. Succinyl-CoA synthetase
B. Alpha-ketoglutarate dehydrogenase
C. Fumarase
D. Aconitase
Answer: A
, Explanation: Succinyl-CoA synthetase catalyzes the conversion of succinyl-CoA to
succinate. The energy released from the thioester bond cleavage is used to phosphorylate
GDP or ADP. This represents the only step in the citric acid cycle that directly generates a
high-energy nucleoside triphosphate.
7. Which molecule acts as a potent allosteric activator of Phosphofructokinase-1 (PFK-1) and
an inhibitor of Fructose-1,6-bisphosphatase?
A. ATP
B. Citrate
C. Fructose-2,6-bisphosphate
D. Glucose-6-phosphate
Answer: C
Explanation: Fructose-2,6-bisphosphate is a key regulatory molecule that signals high
blood glucose levels. It increases the affinity of PFK-1 for its substrate while simultaneously
inhibiting the gluconeogenic enzyme fructose-1,6-bisphosphatase. This reciprocal
regulation prevents futile cycling between glycolysis and gluconeogenesis.
8. What is the final electron acceptor in the mitochondrial electron transport chain?
A. NAD+
B. Oxygen
C. FAD
D. Water
Answer: B
Explanation: Molecular oxygen has the highest reduction potential in the electron
transport chain. It accepts four electrons at Complex IV to be reduced into two molecules of
water. Without oxygen, the entire electron transport chain backs up, and ATP production
ceases.
9. Which enzyme in gluconeogenesis bypasses the irreversible hexokinase step of glycolysis?
A. Pyruvate Carboxylase
B. Glucose-6-phosphatase
C. Fructose-1,6-bisphosphatase
D. PEP Carboxykinase
Answer: B
Explanation: Glucose-6-phosphatase is the enzyme responsible for the final step of
gluconeogenesis. It removes the phosphate group from glucose-6-phosphate, allowing free
