C785 Biochemistry Week 4 Study Guide 2026 |WGU
1. Which enzyme is the primary rate-limiting step of glycolysis?
A. Hexokinase
B. Pyruvate Kinase
C. Phosphofructokinase-1 (PFK-1)
D. Aldolase
Answer: C
Rationale: PFK-1 is the key regulatory enzyme of glycolysis and is inhibited by ATP and
citrate.
2. Under anaerobic conditions, pyruvate is converted into which molecule in
human muscle cells?
A. Lactate
B. Acetyl-CoA
C. Ethanol
D. Oxaloacetate
Answer: A
Rationale: Lactate dehydrogenase reduces pyruvate to lactate to regenerate NAD+ for
glycolysis to continue.
3. Where does the Citric Acid Cycle (Krebs Cycle) take place in the cell?
A. Cytosol
B. Inner Mitochondrial Membrane
C. Mitochondrial Matrix
D. Intermembrane Space
Answer: C
,Rationale: The enzymes for the Citric Acid Cycle are located within the mitochondrial
matrix.
4. Which molecule acts as the final electron acceptor in the Electron Transport
Chain (ETC)?
A. Water
B. Carbon Dioxide
C. Oxygen
D. NAD+
Answer: C
Rationale: Oxygen accepts electrons at Complex IV and combines with protons to form
water.
5. How many net ATP molecules are produced during the aerobic oxidation of
one glucose molecule via substrate-level phosphorylation only?
A. 4
B. 2
C. 32
D. 36
Answer: A
Rationale: Substrate-level phosphorylation produces 2 ATP in glycolysis and 2 GTP/ATP in
the Citric Acid Cycle.
6. Which hormone promotes glycogenesis (glycogen synthesis)?
A. Insulin
B. Epinephrine
C. Cortisol
D. Glucagon
Answer: A
, Rationale: Insulin is released in response to high blood glucose and stimulates the storage
of glucose as glycogen.
7. Which enzyme is responsible for the ‘bypass’ step in gluconeogenesis that
converts Pyruvate to Oxaloacetate?
A. Pyruvate Kinase
B. Pyruvate Carboxylase
C. PEP Carboxykinase
D. Glucose-6-Phosphatase
Answer: B
Rationale: Pyruvate carboxylase adds a CO2 to pyruvate to form oxaloacetate in the
mitochondria.
8. Which complex in the Electron Transport Chain does NOT pump protons
across the inner mitochondrial membrane?
A. Complex II
B. Complex I
C. Complex III
D. Complex IV
Answer: A
Rationale: Complex II (Succinate Dehydrogenase) transfers electrons but does not have
the machinery to pump protons.
9. The Cori Cycle involves the transport of which substance from the muscle to
the liver?
A. Glucose
B. Lactate
C. Alanine
D. Pyruvate
Answer: B
1. Which enzyme is the primary rate-limiting step of glycolysis?
A. Hexokinase
B. Pyruvate Kinase
C. Phosphofructokinase-1 (PFK-1)
D. Aldolase
Answer: C
Rationale: PFK-1 is the key regulatory enzyme of glycolysis and is inhibited by ATP and
citrate.
2. Under anaerobic conditions, pyruvate is converted into which molecule in
human muscle cells?
A. Lactate
B. Acetyl-CoA
C. Ethanol
D. Oxaloacetate
Answer: A
Rationale: Lactate dehydrogenase reduces pyruvate to lactate to regenerate NAD+ for
glycolysis to continue.
3. Where does the Citric Acid Cycle (Krebs Cycle) take place in the cell?
A. Cytosol
B. Inner Mitochondrial Membrane
C. Mitochondrial Matrix
D. Intermembrane Space
Answer: C
,Rationale: The enzymes for the Citric Acid Cycle are located within the mitochondrial
matrix.
4. Which molecule acts as the final electron acceptor in the Electron Transport
Chain (ETC)?
A. Water
B. Carbon Dioxide
C. Oxygen
D. NAD+
Answer: C
Rationale: Oxygen accepts electrons at Complex IV and combines with protons to form
water.
5. How many net ATP molecules are produced during the aerobic oxidation of
one glucose molecule via substrate-level phosphorylation only?
A. 4
B. 2
C. 32
D. 36
Answer: A
Rationale: Substrate-level phosphorylation produces 2 ATP in glycolysis and 2 GTP/ATP in
the Citric Acid Cycle.
6. Which hormone promotes glycogenesis (glycogen synthesis)?
A. Insulin
B. Epinephrine
C. Cortisol
D. Glucagon
Answer: A
, Rationale: Insulin is released in response to high blood glucose and stimulates the storage
of glucose as glycogen.
7. Which enzyme is responsible for the ‘bypass’ step in gluconeogenesis that
converts Pyruvate to Oxaloacetate?
A. Pyruvate Kinase
B. Pyruvate Carboxylase
C. PEP Carboxykinase
D. Glucose-6-Phosphatase
Answer: B
Rationale: Pyruvate carboxylase adds a CO2 to pyruvate to form oxaloacetate in the
mitochondria.
8. Which complex in the Electron Transport Chain does NOT pump protons
across the inner mitochondrial membrane?
A. Complex II
B. Complex I
C. Complex III
D. Complex IV
Answer: A
Rationale: Complex II (Succinate Dehydrogenase) transfers electrons but does not have
the machinery to pump protons.
9. The Cori Cycle involves the transport of which substance from the muscle to
the liver?
A. Glucose
B. Lactate
C. Alanine
D. Pyruvate
Answer: B
