C785 Biochemistry: Glycolysis, Krebs Cycle & ATP Production Practice
Pack 2026/2027 WGU
1. Where does glycolysis occur within a eukaryotic cell?
A. Mitochondrial matrix
B. Nucleus
C. Inner mitochondrial membrane
D. Cytosol
Answer: D
Rationale: Glycolysis is a metabolic pathway that takes place in the cytosol of the cell,
where glucose is broken down into pyruvate.
2. Which enzyme is considered the primary rate-limiting step of glycolysis?
A. Hexokinase
B. Phosphofructokinase-1 (PFK-1)
C. Pyruvate kinase
D. Aldolase
Answer: B
Rationale: PFK-1 is the key regulatory enzyme in glycolysis, inhibited by ATP and citrate,
and activated by AMP and fructose-2,6-bisphosphate.
,3. What is the net gain of ATP molecules from the breakdown of one molecule
of glucose during glycolysis?
A. 1 ATP
B. 36 ATP
C. 4 ATP
D. 2 ATP
Answer: D
Rationale: Although 4 ATP are produced, 2 ATP are consumed in the preparatory phase,
resulting in a net gain of 2 ATP.
4. In the absence of oxygen, what is pyruvate converted to in human muscle
cells to regenerate NAD+?
A. Ethanol
B. Acetyl-CoA
C. Oxaloacetate
D. Lactate
Answer: D
Rationale: Under anaerobic conditions, lactate dehydrogenase reduces pyruvate to lactate,
which regenerates the NAD+ needed for glycolysis to continue.
5. Which molecule acts as a feedback inhibitor of Hexokinase in most tissues?
A. Fructose-6-phosphate
B. Citrate
C. ATP
D. Glucose-6-phosphate
Answer: D
Rationale: Hexokinase is inhibited by its product, glucose-6-phosphate, preventing the
accumulation of phosphorylated glucose when it is not needed.
, 6. The conversion of pyruvate to acetyl-CoA is catalyzed by which enzyme
complex?
A. Pyruvate dehydrogenase complex
B. Pyruvate kinase
C. Citrate synthase
D. Lactate dehydrogenase
Answer: A
Rationale: The pyruvate dehydrogenase complex (PDC) links glycolysis to the Krebs cycle
by converting pyruvate into acetyl-CoA in the mitochondria.
7. Which of the following is NOT a product of the Krebs cycle (per turn)?
A. 3 NADH
B. 2 Pyruvate
C. 1 GTP/ATP
D. 1 FADH2
Answer: B
Rationale: Pyruvate is a reactant that enters the mitochondria to be converted to Acetyl-
CoA; it is not a product of the Krebs cycle.
8. Where in the mitochondria does the Krebs Cycle take place?
A. Intermembrane space
B. Outer membrane
C. Cristae
D. Mitochondrial matrix
Answer: D
Rationale: The enzymes of the Krebs cycle are located within the mitochondrial matrix,
except for succinate dehydrogenase which is in the inner membrane.
Pack 2026/2027 WGU
1. Where does glycolysis occur within a eukaryotic cell?
A. Mitochondrial matrix
B. Nucleus
C. Inner mitochondrial membrane
D. Cytosol
Answer: D
Rationale: Glycolysis is a metabolic pathway that takes place in the cytosol of the cell,
where glucose is broken down into pyruvate.
2. Which enzyme is considered the primary rate-limiting step of glycolysis?
A. Hexokinase
B. Phosphofructokinase-1 (PFK-1)
C. Pyruvate kinase
D. Aldolase
Answer: B
Rationale: PFK-1 is the key regulatory enzyme in glycolysis, inhibited by ATP and citrate,
and activated by AMP and fructose-2,6-bisphosphate.
,3. What is the net gain of ATP molecules from the breakdown of one molecule
of glucose during glycolysis?
A. 1 ATP
B. 36 ATP
C. 4 ATP
D. 2 ATP
Answer: D
Rationale: Although 4 ATP are produced, 2 ATP are consumed in the preparatory phase,
resulting in a net gain of 2 ATP.
4. In the absence of oxygen, what is pyruvate converted to in human muscle
cells to regenerate NAD+?
A. Ethanol
B. Acetyl-CoA
C. Oxaloacetate
D. Lactate
Answer: D
Rationale: Under anaerobic conditions, lactate dehydrogenase reduces pyruvate to lactate,
which regenerates the NAD+ needed for glycolysis to continue.
5. Which molecule acts as a feedback inhibitor of Hexokinase in most tissues?
A. Fructose-6-phosphate
B. Citrate
C. ATP
D. Glucose-6-phosphate
Answer: D
Rationale: Hexokinase is inhibited by its product, glucose-6-phosphate, preventing the
accumulation of phosphorylated glucose when it is not needed.
, 6. The conversion of pyruvate to acetyl-CoA is catalyzed by which enzyme
complex?
A. Pyruvate dehydrogenase complex
B. Pyruvate kinase
C. Citrate synthase
D. Lactate dehydrogenase
Answer: A
Rationale: The pyruvate dehydrogenase complex (PDC) links glycolysis to the Krebs cycle
by converting pyruvate into acetyl-CoA in the mitochondria.
7. Which of the following is NOT a product of the Krebs cycle (per turn)?
A. 3 NADH
B. 2 Pyruvate
C. 1 GTP/ATP
D. 1 FADH2
Answer: B
Rationale: Pyruvate is a reactant that enters the mitochondria to be converted to Acetyl-
CoA; it is not a product of the Krebs cycle.
8. Where in the mitochondria does the Krebs Cycle take place?
A. Intermembrane space
B. Outer membrane
C. Cristae
D. Mitochondrial matrix
Answer: D
Rationale: The enzymes of the Krebs cycle are located within the mitochondrial matrix,
except for succinate dehydrogenase which is in the inner membrane.
