BIOL 271 Microbiology w/ Lab | Module 2 Exam Review v2.0:
Advanced Mastery in Microbial Metabolism, Enzymology,
Bioenergetics, and Metabolic Integration — A Comprehensive
150-Question Assessment for LockDown Browser Examination
QUESTIONS 1–50: METABOLIC FOUNDATIONS, THERMODYNAMICS,
AND ENZYME KINETICS
🟢 1. A facultative anaerobe is cultured under strictly anaerobic conditions for 24 hours, then shifted
to aerobic conditions. Which of the following best describes the immediate metabolic adjustment that
occurs at the molecular level?
🔴 A) Glycolysis is permanently inactivated due to oxygen toxicity
🔴 B) The electron transport chain is rapidly assembled from pre-existing subunits in the plasma
membrane
🔴 C) The organism switches from substrate-level phosphorylation to oxidative phosphorylation,
increasing ATP yield per glucose
🔴 D) Fermentation pathways are upregulated to compete with respiration
Rationale: Facultative anaerobes preferentially use aerobic respiration when oxygen is available
because it yields significantly more ATP (approximately 36–38 ATP per glucose) compared to
fermentation (2 ATP per glucose). The switch involves activation of the electron transport chain and
oxidative phosphorylation, not de novo assembly of the ETC.
🟢 2. A newly discovered extremophilic bacterium exhibits optimal growth at 85°C and pH 2.0. Which
structural feature would most likely be observed in its enzymes to maintain catalytic activity under
these conditions?
🔴 A) Increased glycine content to enhance flexibility
🔴 B) Extensive disulfide bridges and increased hydrophobic core interactions
🔴 C) Reduced overall net charge on the protein surface
🔴 D) Decreased number of salt bridges between domains
Rationale: Thermophilic and acidophilic enzymes require enhanced stability. Extensive disulfide
bridges provide covalent stabilization, while increased hydrophobic interactions in the protein core
resist thermal denaturation. Glycine would increase flexibility (detrimental), and surface charge
modifications are more relevant to acidophily than thermostability.
,🟢 3. During the oxidative decarboxylation of pyruvate, the carbon that is released as CO₂ originates
from which position of the original glucose molecule?
🔴 A) Carbon 1 and carbon 6
🔴 B) Carbon 3 and carbon 4
🔴 C) Carbon 2 and carbon 5
🔴 D) Carbon 1 only
Rationale: During glycolysis, glucose (carbons 1–6) is split into two pyruvate molecules. Pyruvate
dehydrogenase removes the carboxyl group (originally carbons 3 and 4 of glucose) as CO₂. The
remaining acetyl groups (carbons 1–2 and 5–6) become acetyl-CoA. This is why the CO₂ released in the
Krebs cycle ultimately comes from specific positions of the original glucose.
🟢 4. A researcher measures the Vₘₐₓ of an enzyme in the presence and absence of a potential
inhibitor. In the presence of the inhibitor, Vₘₐₓ remains unchanged but Kₘ increases significantly. This
inhibitor is best classified as:
🔴 A) Non-competitive inhibitor
🔴 B) Competitive inhibitor
🔴 C) Uncompetitive inhibitor
🔴 D) Irreversible inhibitor
Rationale: Competitive inhibitors bind at the active site, competing with substrate. This increases Kₘ
(apparent lower affinity) but does not affect Vₘₐₓ because excess substrate can overcome the inhibition.
Non-competitive inhibitors decrease Vₘₐₓ without affecting Kₘ; uncompetitive inhibitors decrease both.
🟢 5. In a suspension of isolated mitochondria, the addition of 2,4-dinitrophenol (DNP) causes a
dramatic increase in oxygen consumption while ATP synthesis ceases. This effect is best explained by:
🔴 A) DNP inhibiting cytochrome c oxidase directly
🔴 B) DNP dissipating the proton gradient, causing the ETC to work maximally without generating
ATP
🔴 C) DNP blocking the ATP/ADP translocase
🔴 D) DNP uncoupling substrate-level phosphorylation from the Krebs cycle
Rationale: DNP is a protonophore that makes the inner mitochondrial membrane permeable to
protons. The proton gradient dissipates, so ATP synthase can no longer function. However, the
electron transport chain continues to pump protons (consuming oxygen), but the energy is released as
heat rather than used for ATP synthesis.
,🟢 6. Which of the following correctly describes the net stoichiometry of the Krebs cycle per molecule
of acetyl-CoA oxidized?
🔴 A) 3 NADH, 1 FADH₂, 1 GTP, 2 CO₂
🔴 B) 3 NADH, 1 FADH₂, 1 GTP, 2 CO₂
🔴 C) 2 NADH, 2 FADH₂, 1 GTP, 2 CO₂
🔴 D) 3 NADH, 1 FADH₂, 1 ATP, 2 CO₂
Rationale: Per acetyl-CoA entering the Krebs cycle, the net products are 3 NADH (from isocitrate
dehydrogenase, α-ketoglutarate dehydrogenase, and malate dehydrogenase), 1 FADH₂ (from
succinate dehydrogenase), 1 GTP (from succinyl-CoA synthetase), and 2 CO₂ (from isocitrate
dehydrogenase and α-ketoglutarate dehydrogenase). GTP is equivalent to ATP.
🟢 7. A bacterial strain is isolated that can grow on minimal medium containing only glucose,
ammonium sulfate, and trace minerals. However, it cannot grow when glucose is replaced by acetate
as the sole carbon source. The most likely explanation is:
🔴 A) The organism lacks the enzymes for acetate transport
🔴 B) The organism lacks the glyoxylate cycle, preventing net conversion of acetate to
carbohydrate precursors
🔴 C) Acetate is toxic to this organism
🔴 D) The organism cannot perform β-oxidation
Rationale: Organisms that can grow on acetate as the sole carbon source require the glyoxylate cycle
to convert acetyl-CoA (from acetate) into oxaloacetate and other intermediates for biosynthesis. If the
organism lacks the glyoxylate cycle (as most animals do), acetyl-CoA carbons are lost as CO₂ in the
Krebs cycle and cannot be used for net synthesis of carbohydrates or other biomass.
🟢 8. The standard reduction potential (E°') of NAD⁺/NADH is -0.32 V, while that of O₂/H₂O is +0.82 V.
What is the theoretical ΔE°' for the transfer of electrons from NADH to oxygen?
🔴 A) +0.50 V
🔴 B) +1.14 V
🔴 C) -1.14 V
🔴 D) +0.32 V
Rationale: ΔE°' = E°'(acceptor) - E°'(donor) = +0.82 V - (-0.32 V) = +1.14 V. This positive value
indicates a thermodynamically favorable electron transfer. The free energy change can be calculated
from ΔG°' = -nFΔE°', where n = 2 (electrons transferred) and F = Faraday's constant.
, 🟢 9. Which of the following statements about the role of cytochrome c in the electron transport
chain is CORRECT?
🔴 A) Cytochrome c is a membrane-bound protein that directly reduces oxygen
🔴 B) Cytochrome c is a mobile electron carrier that shuttles electrons from Complex III to Complex
IV
🔴 C) Cytochrome c accepts electrons from NADH dehydrogenase (Complex I)
🔴 D) Cytochrome c contains a copper center instead of a heme group
Rationale: Cytochrome c is a small, water-soluble protein located in the intermembrane space that
shuttles electrons from Complex III (cytochrome bc₁) to Complex IV (cytochrome c oxidase). It contains
a heme c prosthetic group (iron), not copper. It does not directly reduce oxygen; Complex IV does.
🟢 10. In the malate-aspartate shuttle, the conversion of aspartate to oxaloacetate in the cytosol is
coupled to which of the following?
🔴 A) The reduction of NAD⁺ to NADH
🔴 B) The transamination reaction that regenerates α-ketoglutarate from glutamate
🔴 C) The direct transport of electrons across the mitochondrial membrane
🔴 D) The hydrolysis of ATP
Rationale: In the malate-aspartate shuttle, cytosolic aspartate is transaminated with α-ketoglutarate to
form oxaloacetate and glutamate. This reaction is catalyzed by aspartate aminotransferase and
regenerates α-ketoglutarate for the next cycle. The shuttle ultimately transfers electrons from cytosolic
NADH to mitochondrial NAD⁺.
🟢 11. A patient presents with symptoms of beriberi, including peripheral neuropathy and cardiac
dysfunction. Which enzyme complex is most directly affected by the underlying deficiency?
🔴 A) Succinate dehydrogenase
🔴 B) Pyruvate dehydrogenase complex
🔴 C) ATP synthase
🔴 D) Cytochrome c oxidase
Rationale: Beriberi is caused by thiamine (vitamin B₁) deficiency. Thiamine pyrophosphate (TPP) is a
cofactor for pyruvate dehydrogenase, α-ketoglutarate dehydrogenase, and transketolase. Pyruvate
dehydrogenase deficiency leads to accumulation of pyruvate and lactate, with neurological and
cardiovascular manifestations characteristic of beriberi.
🟢 12. The enzyme fumarase catalyzes the reversible hydration of fumarate to malate. This reaction is
classified as which type of enzymatic reaction?
Advanced Mastery in Microbial Metabolism, Enzymology,
Bioenergetics, and Metabolic Integration — A Comprehensive
150-Question Assessment for LockDown Browser Examination
QUESTIONS 1–50: METABOLIC FOUNDATIONS, THERMODYNAMICS,
AND ENZYME KINETICS
🟢 1. A facultative anaerobe is cultured under strictly anaerobic conditions for 24 hours, then shifted
to aerobic conditions. Which of the following best describes the immediate metabolic adjustment that
occurs at the molecular level?
🔴 A) Glycolysis is permanently inactivated due to oxygen toxicity
🔴 B) The electron transport chain is rapidly assembled from pre-existing subunits in the plasma
membrane
🔴 C) The organism switches from substrate-level phosphorylation to oxidative phosphorylation,
increasing ATP yield per glucose
🔴 D) Fermentation pathways are upregulated to compete with respiration
Rationale: Facultative anaerobes preferentially use aerobic respiration when oxygen is available
because it yields significantly more ATP (approximately 36–38 ATP per glucose) compared to
fermentation (2 ATP per glucose). The switch involves activation of the electron transport chain and
oxidative phosphorylation, not de novo assembly of the ETC.
🟢 2. A newly discovered extremophilic bacterium exhibits optimal growth at 85°C and pH 2.0. Which
structural feature would most likely be observed in its enzymes to maintain catalytic activity under
these conditions?
🔴 A) Increased glycine content to enhance flexibility
🔴 B) Extensive disulfide bridges and increased hydrophobic core interactions
🔴 C) Reduced overall net charge on the protein surface
🔴 D) Decreased number of salt bridges between domains
Rationale: Thermophilic and acidophilic enzymes require enhanced stability. Extensive disulfide
bridges provide covalent stabilization, while increased hydrophobic interactions in the protein core
resist thermal denaturation. Glycine would increase flexibility (detrimental), and surface charge
modifications are more relevant to acidophily than thermostability.
,🟢 3. During the oxidative decarboxylation of pyruvate, the carbon that is released as CO₂ originates
from which position of the original glucose molecule?
🔴 A) Carbon 1 and carbon 6
🔴 B) Carbon 3 and carbon 4
🔴 C) Carbon 2 and carbon 5
🔴 D) Carbon 1 only
Rationale: During glycolysis, glucose (carbons 1–6) is split into two pyruvate molecules. Pyruvate
dehydrogenase removes the carboxyl group (originally carbons 3 and 4 of glucose) as CO₂. The
remaining acetyl groups (carbons 1–2 and 5–6) become acetyl-CoA. This is why the CO₂ released in the
Krebs cycle ultimately comes from specific positions of the original glucose.
🟢 4. A researcher measures the Vₘₐₓ of an enzyme in the presence and absence of a potential
inhibitor. In the presence of the inhibitor, Vₘₐₓ remains unchanged but Kₘ increases significantly. This
inhibitor is best classified as:
🔴 A) Non-competitive inhibitor
🔴 B) Competitive inhibitor
🔴 C) Uncompetitive inhibitor
🔴 D) Irreversible inhibitor
Rationale: Competitive inhibitors bind at the active site, competing with substrate. This increases Kₘ
(apparent lower affinity) but does not affect Vₘₐₓ because excess substrate can overcome the inhibition.
Non-competitive inhibitors decrease Vₘₐₓ without affecting Kₘ; uncompetitive inhibitors decrease both.
🟢 5. In a suspension of isolated mitochondria, the addition of 2,4-dinitrophenol (DNP) causes a
dramatic increase in oxygen consumption while ATP synthesis ceases. This effect is best explained by:
🔴 A) DNP inhibiting cytochrome c oxidase directly
🔴 B) DNP dissipating the proton gradient, causing the ETC to work maximally without generating
ATP
🔴 C) DNP blocking the ATP/ADP translocase
🔴 D) DNP uncoupling substrate-level phosphorylation from the Krebs cycle
Rationale: DNP is a protonophore that makes the inner mitochondrial membrane permeable to
protons. The proton gradient dissipates, so ATP synthase can no longer function. However, the
electron transport chain continues to pump protons (consuming oxygen), but the energy is released as
heat rather than used for ATP synthesis.
,🟢 6. Which of the following correctly describes the net stoichiometry of the Krebs cycle per molecule
of acetyl-CoA oxidized?
🔴 A) 3 NADH, 1 FADH₂, 1 GTP, 2 CO₂
🔴 B) 3 NADH, 1 FADH₂, 1 GTP, 2 CO₂
🔴 C) 2 NADH, 2 FADH₂, 1 GTP, 2 CO₂
🔴 D) 3 NADH, 1 FADH₂, 1 ATP, 2 CO₂
Rationale: Per acetyl-CoA entering the Krebs cycle, the net products are 3 NADH (from isocitrate
dehydrogenase, α-ketoglutarate dehydrogenase, and malate dehydrogenase), 1 FADH₂ (from
succinate dehydrogenase), 1 GTP (from succinyl-CoA synthetase), and 2 CO₂ (from isocitrate
dehydrogenase and α-ketoglutarate dehydrogenase). GTP is equivalent to ATP.
🟢 7. A bacterial strain is isolated that can grow on minimal medium containing only glucose,
ammonium sulfate, and trace minerals. However, it cannot grow when glucose is replaced by acetate
as the sole carbon source. The most likely explanation is:
🔴 A) The organism lacks the enzymes for acetate transport
🔴 B) The organism lacks the glyoxylate cycle, preventing net conversion of acetate to
carbohydrate precursors
🔴 C) Acetate is toxic to this organism
🔴 D) The organism cannot perform β-oxidation
Rationale: Organisms that can grow on acetate as the sole carbon source require the glyoxylate cycle
to convert acetyl-CoA (from acetate) into oxaloacetate and other intermediates for biosynthesis. If the
organism lacks the glyoxylate cycle (as most animals do), acetyl-CoA carbons are lost as CO₂ in the
Krebs cycle and cannot be used for net synthesis of carbohydrates or other biomass.
🟢 8. The standard reduction potential (E°') of NAD⁺/NADH is -0.32 V, while that of O₂/H₂O is +0.82 V.
What is the theoretical ΔE°' for the transfer of electrons from NADH to oxygen?
🔴 A) +0.50 V
🔴 B) +1.14 V
🔴 C) -1.14 V
🔴 D) +0.32 V
Rationale: ΔE°' = E°'(acceptor) - E°'(donor) = +0.82 V - (-0.32 V) = +1.14 V. This positive value
indicates a thermodynamically favorable electron transfer. The free energy change can be calculated
from ΔG°' = -nFΔE°', where n = 2 (electrons transferred) and F = Faraday's constant.
, 🟢 9. Which of the following statements about the role of cytochrome c in the electron transport
chain is CORRECT?
🔴 A) Cytochrome c is a membrane-bound protein that directly reduces oxygen
🔴 B) Cytochrome c is a mobile electron carrier that shuttles electrons from Complex III to Complex
IV
🔴 C) Cytochrome c accepts electrons from NADH dehydrogenase (Complex I)
🔴 D) Cytochrome c contains a copper center instead of a heme group
Rationale: Cytochrome c is a small, water-soluble protein located in the intermembrane space that
shuttles electrons from Complex III (cytochrome bc₁) to Complex IV (cytochrome c oxidase). It contains
a heme c prosthetic group (iron), not copper. It does not directly reduce oxygen; Complex IV does.
🟢 10. In the malate-aspartate shuttle, the conversion of aspartate to oxaloacetate in the cytosol is
coupled to which of the following?
🔴 A) The reduction of NAD⁺ to NADH
🔴 B) The transamination reaction that regenerates α-ketoglutarate from glutamate
🔴 C) The direct transport of electrons across the mitochondrial membrane
🔴 D) The hydrolysis of ATP
Rationale: In the malate-aspartate shuttle, cytosolic aspartate is transaminated with α-ketoglutarate to
form oxaloacetate and glutamate. This reaction is catalyzed by aspartate aminotransferase and
regenerates α-ketoglutarate for the next cycle. The shuttle ultimately transfers electrons from cytosolic
NADH to mitochondrial NAD⁺.
🟢 11. A patient presents with symptoms of beriberi, including peripheral neuropathy and cardiac
dysfunction. Which enzyme complex is most directly affected by the underlying deficiency?
🔴 A) Succinate dehydrogenase
🔴 B) Pyruvate dehydrogenase complex
🔴 C) ATP synthase
🔴 D) Cytochrome c oxidase
Rationale: Beriberi is caused by thiamine (vitamin B₁) deficiency. Thiamine pyrophosphate (TPP) is a
cofactor for pyruvate dehydrogenase, α-ketoglutarate dehydrogenase, and transketolase. Pyruvate
dehydrogenase deficiency leads to accumulation of pyruvate and lactate, with neurological and
cardiovascular manifestations characteristic of beriberi.
🟢 12. The enzyme fumarase catalyzes the reversible hydration of fumarate to malate. This reaction is
classified as which type of enzymatic reaction?
