Comprehensive Exam Questions with
Answers
EXAM
Q1. Glycolysis Net Equation
Question: Write the net equation for glycolysis starting from one molecule of glucose.
Answer: Glucose + 2 NAD⁺ + 2 ADP + 2 Pᵢ → 2 Pyruvate + 2 NADH + 2 ATP + 2 H⁺ + 2
H₂O
Rationale: Glycolysis consumes 2 ATP in the investment phase (hexokinase, PFK-1) and
produces 4 ATP in the payoff phase (phosphoglycerate kinase, pyruvate kinase), yielding
a net of 2 ATP. Two molecules of NAD⁺ are reduced to NADH during the oxidation of
glyceraldehyde-3-phosphate.
Q2. Irreversible Steps of Glycolysis
Question: Name the three irreversible, regulated enzymes in glycolysis.
Answer: Hexokinase (or glucokinase), Phosphofructokinase-1 (PFK-1), Pyruvate kinase
Rationale: These steps are highly exergonic and serve as control points. They are
bypassed by distinct enzymes during gluconeogenesis, allowing reciprocal regulation of
the two pathways.
Q3. Anaerobic vs. Aerobic ATP Yield
Question: Why does anaerobic glycolysis yield only 2 ATP per glucose while aerobic
oxidation yields approximately 30–32 ATP?
Answer: Under anaerobic conditions, NADH cannot enter the electron transport chain
,and is instead reoxidized by reducing pyruvate to lactate, capturing no additional ATP.
Aerobic conditions allow NADH and FADH₂ to donate electrons to the ETC, driving
oxidative phosphorylation.
Rationale: The 2 NADH from glycolysis alone can generate 3–5 ATP depending on the
shuttle system (glycerol-3-phosphate shuttle yields ~1.5 ATP/NADH; malate-aspartate
yields ~2.5 ATP/NADH).
Q4. Von Gierke Disease
Question: A child presents with fasting hypoglycemia, lactic acidosis, and
hepatomegaly. Which enzyme is deficient?
Answer: Glucose-6-phosphatase
Rationale: Glucose-6-phosphatase catalyzes the final common step of glycogenolysis
and gluconeogenesis in the liver. Deficiency prevents glucose export, causing
hypoglycemia. Accumulated glucose-6-phosphate drives glycolysis and lactate
production, causing lactic acidosis and glycogen storage hepatomegaly.
Q5. Cori Cycle
Question: Describe the Cori cycle.
Answer: Lactate produced by anaerobic glycolysis in muscle is transported to the liver,
converted back to glucose via gluconeogenesis, and returned to muscle.
Rationale: This cycle allows the body to recycle lactate and regenerate glucose without
net ATP gain; it consumes 6 ATP per glucose regenerated but maintains blood glucose
during exertion.
, Q6. Pasteur Effect
Question: What is the Pasteur effect?
Answer: The inhibition of glycolysis in the presence of oxygen.
Rationale: Oxygen promotes oxidative phosphorylation, increasing ATP production.
Elevated ATP and citrate allosterically inhibit PFK-1, slowing glycolysis. This spares
glucose for more efficient energy production.
Q7. Warburg Effect
Question: What is the Warburg effect?
Answer: Cancer cells preferentially use aerobic glycolysis (fermentation of glucose to
lactate even in the presence of oxygen).
Rationale: This phenomenon supports rapid biosynthesis by diverting glycolytic
intermediates into nucleotide, amino acid, and lipid synthesis pathways. It also maintains
redox balance and supports proliferation.
Q8. Hexokinase vs. Glucokinase
Question: Compare hexokinase and glucokinase.
Answer:
Hexokinase: Low Km (high affinity), present in most tissues, inhibited by glucose-
6-phosphate
Glucokinase: High Km (low affinity), liver and pancreas, not inhibited by glucose-
6-phosphate, induced by insulin
Rationale: Glucokinase allows the liver to take up glucose only when blood
glucose is high, storing it as glycogen. Hexokinase ensures glucose trapping even
at low concentrations in tissues like brain and muscle.
Answers
EXAM
Q1. Glycolysis Net Equation
Question: Write the net equation for glycolysis starting from one molecule of glucose.
Answer: Glucose + 2 NAD⁺ + 2 ADP + 2 Pᵢ → 2 Pyruvate + 2 NADH + 2 ATP + 2 H⁺ + 2
H₂O
Rationale: Glycolysis consumes 2 ATP in the investment phase (hexokinase, PFK-1) and
produces 4 ATP in the payoff phase (phosphoglycerate kinase, pyruvate kinase), yielding
a net of 2 ATP. Two molecules of NAD⁺ are reduced to NADH during the oxidation of
glyceraldehyde-3-phosphate.
Q2. Irreversible Steps of Glycolysis
Question: Name the three irreversible, regulated enzymes in glycolysis.
Answer: Hexokinase (or glucokinase), Phosphofructokinase-1 (PFK-1), Pyruvate kinase
Rationale: These steps are highly exergonic and serve as control points. They are
bypassed by distinct enzymes during gluconeogenesis, allowing reciprocal regulation of
the two pathways.
Q3. Anaerobic vs. Aerobic ATP Yield
Question: Why does anaerobic glycolysis yield only 2 ATP per glucose while aerobic
oxidation yields approximately 30–32 ATP?
Answer: Under anaerobic conditions, NADH cannot enter the electron transport chain
,and is instead reoxidized by reducing pyruvate to lactate, capturing no additional ATP.
Aerobic conditions allow NADH and FADH₂ to donate electrons to the ETC, driving
oxidative phosphorylation.
Rationale: The 2 NADH from glycolysis alone can generate 3–5 ATP depending on the
shuttle system (glycerol-3-phosphate shuttle yields ~1.5 ATP/NADH; malate-aspartate
yields ~2.5 ATP/NADH).
Q4. Von Gierke Disease
Question: A child presents with fasting hypoglycemia, lactic acidosis, and
hepatomegaly. Which enzyme is deficient?
Answer: Glucose-6-phosphatase
Rationale: Glucose-6-phosphatase catalyzes the final common step of glycogenolysis
and gluconeogenesis in the liver. Deficiency prevents glucose export, causing
hypoglycemia. Accumulated glucose-6-phosphate drives glycolysis and lactate
production, causing lactic acidosis and glycogen storage hepatomegaly.
Q5. Cori Cycle
Question: Describe the Cori cycle.
Answer: Lactate produced by anaerobic glycolysis in muscle is transported to the liver,
converted back to glucose via gluconeogenesis, and returned to muscle.
Rationale: This cycle allows the body to recycle lactate and regenerate glucose without
net ATP gain; it consumes 6 ATP per glucose regenerated but maintains blood glucose
during exertion.
, Q6. Pasteur Effect
Question: What is the Pasteur effect?
Answer: The inhibition of glycolysis in the presence of oxygen.
Rationale: Oxygen promotes oxidative phosphorylation, increasing ATP production.
Elevated ATP and citrate allosterically inhibit PFK-1, slowing glycolysis. This spares
glucose for more efficient energy production.
Q7. Warburg Effect
Question: What is the Warburg effect?
Answer: Cancer cells preferentially use aerobic glycolysis (fermentation of glucose to
lactate even in the presence of oxygen).
Rationale: This phenomenon supports rapid biosynthesis by diverting glycolytic
intermediates into nucleotide, amino acid, and lipid synthesis pathways. It also maintains
redox balance and supports proliferation.
Q8. Hexokinase vs. Glucokinase
Question: Compare hexokinase and glucokinase.
Answer:
Hexokinase: Low Km (high affinity), present in most tissues, inhibited by glucose-
6-phosphate
Glucokinase: High Km (low affinity), liver and pancreas, not inhibited by glucose-
6-phosphate, induced by insulin
Rationale: Glucokinase allows the liver to take up glucose only when blood
glucose is high, storing it as glycogen. Hexokinase ensures glucose trapping even
at low concentrations in tissues like brain and muscle.
