BCH 4053 Exam 3 V2 | BCH 4053
Biochemistry I | Actual Q&A with
Rationale (BCH4053 Exam 3) | University
of Central Florida
1. Which enzyme catalyzes the primary regulatory and committed step of glycolysis?
A. Hexokinase
B. Pyruvate Kinase
C. Aldolase
D. Phosphofructokinase-1
Answer: D
Rationale: Phosphofructokinase-1 (PFK-1) catalyzes the conversion of fructose-6-
phosphate to fructose-1,6-bisphosphate. This step is considered the committed step
because the product is used exclusively for the glycolytic pathway. The enzyme is tightly
regulated by allosteric effectors such as ATP, AMP, and fructose-2,6-bisphosphate to
maintain metabolic homeostasis.
2. In the liver, which molecule acts as a potent allosteric activator of PFK-1 and inhibitor of
Fructose-1,6-bisphosphatase?
A. Fructose-2,6-bisphosphate
B. Citrate
,C. ATP
D. Glucose-6-phosphate
Answer: A
Rationale: Fructose-2,6-bisphosphate is synthesized by PFK-2 in response to insulin
signaling. It serves to override the inhibitory effects of ATP on PFK-1, thereby promoting
glycolysis even when energy levels are relatively high. Simultaneously, it inhibits the
gluconeogenic enzyme fructose-1,6-bisphosphatase to prevent futile cycling.
3. Which of the following enzymes is unique to gluconeogenesis and is located within the
mitochondrial matrix?
A. Phosphoenolpyruvate carboxykinase
B. Glucose-6-phosphatase
C. Pyruvate carboxylase
D. Malate dehydrogenase
Answer: C
Rationale: Pyruvate carboxylase converts pyruvate into oxaloacetate, requiring biotin as a
cofactor and the consumption of one ATP. This reaction is the first bypass step in
gluconeogenesis and occurs exclusively in the mitochondria. Acetyl-CoA serves as an
essential allosteric activator for this enzyme, signaling that the TCA cycle is saturated and
precursors should be diverted to glucose synthesis.
, 4. Which cofactor is required by the E1 subunit of the Pyruvate Dehydrogenase Complex for
the decarboxylation of pyruvate?
A. FAD
B. Thiamine pyrophosphate (TPP)
C. Lipoamide
D. NAD+
Answer: B
Rationale: Thiamine pyrophosphate (TPP) is the prosthetic group for the pyruvate
dehydrogenase (E1) component. It facilitates the nucleophilic attack on the carbonyl
carbon of pyruvate, leading to the release of CO2. Deficiency in TPP can lead to metabolic
disorders like Beriberi because the oxidation of pyruvate is severely impaired.
5. The conversion of Succinyl-CoA to Succinate in the Citric Acid Cycle is unique because it:
A. Involves substrate-level phosphorylation
B. Produces the first CO2 of the cycle
C. Requires the input of ATP
D. Is the only reversible step in the cycle
Answer: A
Rationale: The reaction catalyzed by Succinyl-CoA synthetase cleaves a high-energy
thioester bond. This energy is harnessed to phosphorylate GDP (or ADP) to form GTP (or
Biochemistry I | Actual Q&A with
Rationale (BCH4053 Exam 3) | University
of Central Florida
1. Which enzyme catalyzes the primary regulatory and committed step of glycolysis?
A. Hexokinase
B. Pyruvate Kinase
C. Aldolase
D. Phosphofructokinase-1
Answer: D
Rationale: Phosphofructokinase-1 (PFK-1) catalyzes the conversion of fructose-6-
phosphate to fructose-1,6-bisphosphate. This step is considered the committed step
because the product is used exclusively for the glycolytic pathway. The enzyme is tightly
regulated by allosteric effectors such as ATP, AMP, and fructose-2,6-bisphosphate to
maintain metabolic homeostasis.
2. In the liver, which molecule acts as a potent allosteric activator of PFK-1 and inhibitor of
Fructose-1,6-bisphosphatase?
A. Fructose-2,6-bisphosphate
B. Citrate
,C. ATP
D. Glucose-6-phosphate
Answer: A
Rationale: Fructose-2,6-bisphosphate is synthesized by PFK-2 in response to insulin
signaling. It serves to override the inhibitory effects of ATP on PFK-1, thereby promoting
glycolysis even when energy levels are relatively high. Simultaneously, it inhibits the
gluconeogenic enzyme fructose-1,6-bisphosphatase to prevent futile cycling.
3. Which of the following enzymes is unique to gluconeogenesis and is located within the
mitochondrial matrix?
A. Phosphoenolpyruvate carboxykinase
B. Glucose-6-phosphatase
C. Pyruvate carboxylase
D. Malate dehydrogenase
Answer: C
Rationale: Pyruvate carboxylase converts pyruvate into oxaloacetate, requiring biotin as a
cofactor and the consumption of one ATP. This reaction is the first bypass step in
gluconeogenesis and occurs exclusively in the mitochondria. Acetyl-CoA serves as an
essential allosteric activator for this enzyme, signaling that the TCA cycle is saturated and
precursors should be diverted to glucose synthesis.
, 4. Which cofactor is required by the E1 subunit of the Pyruvate Dehydrogenase Complex for
the decarboxylation of pyruvate?
A. FAD
B. Thiamine pyrophosphate (TPP)
C. Lipoamide
D. NAD+
Answer: B
Rationale: Thiamine pyrophosphate (TPP) is the prosthetic group for the pyruvate
dehydrogenase (E1) component. It facilitates the nucleophilic attack on the carbonyl
carbon of pyruvate, leading to the release of CO2. Deficiency in TPP can lead to metabolic
disorders like Beriberi because the oxidation of pyruvate is severely impaired.
5. The conversion of Succinyl-CoA to Succinate in the Citric Acid Cycle is unique because it:
A. Involves substrate-level phosphorylation
B. Produces the first CO2 of the cycle
C. Requires the input of ATP
D. Is the only reversible step in the cycle
Answer: A
Rationale: The reaction catalyzed by Succinyl-CoA synthetase cleaves a high-energy
thioester bond. This energy is harnessed to phosphorylate GDP (or ADP) to form GTP (or
