BIOCHEM 210 MODULE 7 EXAM 2026/2027 | Metabolism:
Glycolysis, Citric Acid Cycle & Oxidative Phosphorylation |
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Q1: Which of the following best describes the relationship between catabolism and
anabolism in cellular metabolism?
A. Catabolism builds complex molecules while anabolism breaks them down
B. Catabolism releases energy through exergonic reactions, while anabolism requires
energy input through endergonic reactions [CORRECT]
C. Both pathways occur simultaneously in the same cellular compartment with identical
enzymes
D. Catabolism only occurs during fasting states, while anabolism only occurs during fed
states
Correct Answer: B
Rationale: Catabolism involves the breakdown of complex molecules (glucose, fatty
acids) into simpler compounds, releasing free energy (exergonic, ΔG < 0). This energy is
captured in ATP and reduced cofactors (NADH, FADH₂). Anabolism builds complex
molecules (proteins, nucleic acids, lipids) from simpler precursors, requiring energy
input (endergonic, ΔG > 0), often coupled to ATP hydrolysis. Option A reverses the
definitions. Option C is incorrect because pathways are compartmentalized (glycolysis
in cytosol, TCA in mitochondria) and use distinct enzymes. Option D is incorrect
because both pathways operate continuously, though their rates shift based on
metabolic state.
,Q2: In glycolysis, which enzyme catalyzes the first committed step and is the primary
regulatory point of the pathway?
A. Hexokinase
B. Phosphofructokinase-1 (PFK-1) [CORRECT]
C. Pyruvate kinase
D. Glyceraldehyde-3-phosphate dehydrogenase
Correct Answer: B
Rationale: PFK-1 catalyzes the phosphorylation of fructose-6-phosphate to
fructose-1,6-bisphosphate using ATP. This is the first irreversible step unique to
glycolysis (committed step), making it the primary flux-control point. PFK-1 is
allosterically inhibited by ATP and citrate, and activated by AMP and
fructose-2,6-bisphosphate. Hexokinase (A) catalyzes the first step but
glucose-6-phosphate can enter other pathways (glycogen synthesis, pentose phosphate
pathway). Pyruvate kinase (C) regulates the final step but is not the primary control
point. GAPDH (D) is not a regulatory enzyme.
Q3: Under anaerobic conditions, pyruvate is converted to lactate in human muscle cells.
What is the primary purpose of this conversion?
A. To produce additional ATP through substrate-level phosphorylation
B. To regenerate NAD⁺ to allow glycolysis to continue [CORRECT]
C. To produce lactate as the primary energy source for the cell
D. To prevent the accumulation of acetyl-CoA in the cytosol
Correct Answer: B
Rationale: During anaerobic glycolysis, NADH produced at the
glyceraldehyde-3-phosphate dehydrogenase step must be reoxidized to NAD⁺ to sustain
glycolytic flux. When oxygen is absent, the electron transport chain cannot accept
, electrons, so pyruvate serves as the electron acceptor, forming lactate via lactate
dehydrogenase. This regenerates NAD⁺, allowing glycolysis to produce 2 ATP per
glucose continuously. No additional ATP is produced in the lactate step (A). Lactate is
not an energy source for the producing cell (C). Acetyl-CoA accumulation (D) is not
relevant as pyruvate dehydrogenase requires oxygen for the ETC.
Q4: Calculate the net ATP yield from one molecule of glucose undergoing complete
aerobic oxidation through glycolysis, the pyruvate dehydrogenase complex, the citric
acid cycle, and oxidative phosphorylation. Assume the malate-aspartate shuttle
operates (NADH from glycolysis yields 2.5 ATP).
A. 30 ATP
B. 32 ATP [CORRECT]
C. 36 ATP
D. 38 ATP
Correct Answer: B
Rationale: Complete oxidation yields: Glycolysis: 2 ATP (substrate-level) + 2 NADH → 5
ATP (via malate-aspartate shuttle). Pyruvate dehydrogenase: 2 NADH → 5 ATP. Citric
acid cycle: 2 GTP (2 ATP) + 6 NADH (15 ATP) + 2 FADH₂ (3 ATP) = 20 ATP. Total: 2 + 5 +
5 + 20 = 32 ATP. Option A (30) uses glycerol-3-phosphate shuttle (1.5 ATP/NADH from
glycolysis). Option C (36) and D (38) are outdated values from older P/O ratio
assumptions (3 ATP/NADH, 2 ATP/FADH₂).
Q5: Which of the following is NOT a cofactor required by the pyruvate dehydrogenase
complex?
A. Thiamine pyrophosphate (TPP)
B. Lipoamide
C. Biotin [CORRECT]
Glycolysis, Citric Acid Cycle & Oxidative Phosphorylation |
Latest Q&A Verified | Portage Learning | Pass Guaranteed -
A+ Graded
Q1: Which of the following best describes the relationship between catabolism and
anabolism in cellular metabolism?
A. Catabolism builds complex molecules while anabolism breaks them down
B. Catabolism releases energy through exergonic reactions, while anabolism requires
energy input through endergonic reactions [CORRECT]
C. Both pathways occur simultaneously in the same cellular compartment with identical
enzymes
D. Catabolism only occurs during fasting states, while anabolism only occurs during fed
states
Correct Answer: B
Rationale: Catabolism involves the breakdown of complex molecules (glucose, fatty
acids) into simpler compounds, releasing free energy (exergonic, ΔG < 0). This energy is
captured in ATP and reduced cofactors (NADH, FADH₂). Anabolism builds complex
molecules (proteins, nucleic acids, lipids) from simpler precursors, requiring energy
input (endergonic, ΔG > 0), often coupled to ATP hydrolysis. Option A reverses the
definitions. Option C is incorrect because pathways are compartmentalized (glycolysis
in cytosol, TCA in mitochondria) and use distinct enzymes. Option D is incorrect
because both pathways operate continuously, though their rates shift based on
metabolic state.
,Q2: In glycolysis, which enzyme catalyzes the first committed step and is the primary
regulatory point of the pathway?
A. Hexokinase
B. Phosphofructokinase-1 (PFK-1) [CORRECT]
C. Pyruvate kinase
D. Glyceraldehyde-3-phosphate dehydrogenase
Correct Answer: B
Rationale: PFK-1 catalyzes the phosphorylation of fructose-6-phosphate to
fructose-1,6-bisphosphate using ATP. This is the first irreversible step unique to
glycolysis (committed step), making it the primary flux-control point. PFK-1 is
allosterically inhibited by ATP and citrate, and activated by AMP and
fructose-2,6-bisphosphate. Hexokinase (A) catalyzes the first step but
glucose-6-phosphate can enter other pathways (glycogen synthesis, pentose phosphate
pathway). Pyruvate kinase (C) regulates the final step but is not the primary control
point. GAPDH (D) is not a regulatory enzyme.
Q3: Under anaerobic conditions, pyruvate is converted to lactate in human muscle cells.
What is the primary purpose of this conversion?
A. To produce additional ATP through substrate-level phosphorylation
B. To regenerate NAD⁺ to allow glycolysis to continue [CORRECT]
C. To produce lactate as the primary energy source for the cell
D. To prevent the accumulation of acetyl-CoA in the cytosol
Correct Answer: B
Rationale: During anaerobic glycolysis, NADH produced at the
glyceraldehyde-3-phosphate dehydrogenase step must be reoxidized to NAD⁺ to sustain
glycolytic flux. When oxygen is absent, the electron transport chain cannot accept
, electrons, so pyruvate serves as the electron acceptor, forming lactate via lactate
dehydrogenase. This regenerates NAD⁺, allowing glycolysis to produce 2 ATP per
glucose continuously. No additional ATP is produced in the lactate step (A). Lactate is
not an energy source for the producing cell (C). Acetyl-CoA accumulation (D) is not
relevant as pyruvate dehydrogenase requires oxygen for the ETC.
Q4: Calculate the net ATP yield from one molecule of glucose undergoing complete
aerobic oxidation through glycolysis, the pyruvate dehydrogenase complex, the citric
acid cycle, and oxidative phosphorylation. Assume the malate-aspartate shuttle
operates (NADH from glycolysis yields 2.5 ATP).
A. 30 ATP
B. 32 ATP [CORRECT]
C. 36 ATP
D. 38 ATP
Correct Answer: B
Rationale: Complete oxidation yields: Glycolysis: 2 ATP (substrate-level) + 2 NADH → 5
ATP (via malate-aspartate shuttle). Pyruvate dehydrogenase: 2 NADH → 5 ATP. Citric
acid cycle: 2 GTP (2 ATP) + 6 NADH (15 ATP) + 2 FADH₂ (3 ATP) = 20 ATP. Total: 2 + 5 +
5 + 20 = 32 ATP. Option A (30) uses glycerol-3-phosphate shuttle (1.5 ATP/NADH from
glycolysis). Option C (36) and D (38) are outdated values from older P/O ratio
assumptions (3 ATP/NADH, 2 ATP/FADH₂).
Q5: Which of the following is NOT a cofactor required by the pyruvate dehydrogenase
complex?
A. Thiamine pyrophosphate (TPP)
B. Lipoamide
C. Biotin [CORRECT]
