,LEHNINGER PRINCIPLES OF BIOCHEMISTRY – TEST BANK
STRUCTURED WITH ACTUAL QUESTIONS AND RESPONSES
|USEFUL FOR QUICK REVISION |2026 UPDATED VERSION
ALREADY GRADED A+!!
1. (Protein Structure & Stability)
A mutation replaces a buried leucine with aspartate in the hydrophobic core of a globular protein. What is
the most likely effect?
A. Increased stability due to new ionic interactions
B. Decreased stability due to disruption of hydrophobic interactions
C. No effect on structure
D. Increased folding rate without affecting stability
Correct Answer: B
Rationale:
Hydrophobic cores stabilize proteins. Introducing a charged residue disrupts packing and creates
unfavorable energetics, reducing stability.
2. (Enzyme Kinetics)
A competitive inhibitor is added to an enzyme-catalyzed reaction. What is the expected effect on Km and
Vmax?
A. Km increases, Vmax unchanged
B. Km decreases, Vmax increases
C. Km unchanged, Vmax decreases
D. Both Km and Vmax decrease
Correct Answer: A
Rationale:
Competitive inhibitors increase apparent Km (lower affinity) but do not affect Vmax because inhibition
can be overcome with substrate.
3. (Thermodynamics)
Which statement best describes Gibbs free energy in biochemical reactions?
A. Negative ΔG always requires ATP hydrolysis
B. Positive ΔG indicates spontaneous reactions
C. Negative ΔG indicates thermodynamically favorable reactions
D. ΔG does not affect reaction direction
Correct Answer: C
Rationale:
A negative ΔG means the reaction is spontaneous under cellular conditions.
,4. (Carbohydrate Metabolism)
Which step of glycolysis is irreversible and highly regulated?
A. Glucose → Glucose-6-phosphate
B. Fructose-6-phosphate → Fructose-1,6-bisphosphate
C. 3-Phosphoglycerate → 2-Phosphoglycerate
D. Phosphoenolpyruvate → Pyruvate
Correct Answer: B
Rationale:
This step, catalyzed by PFK-1, is the committed and rate-limiting step of glycolysis.
5. (Bioenergetics)
Which process generates the most ATP?
A. Glycolysis
B. Citric acid cycle
C. Oxidative phosphorylation
D. Fermentation
Correct Answer: C
Rationale:
Most ATP is generated via electron transport chain and chemiosmosis.
6. (Lipid Metabolism)
Which molecule is the primary carrier of fatty acids into mitochondria?
A. Coenzyme A
B. Carnitine
C. NADH
D. ATP
Correct Answer: B
Rationale:
Carnitine transports long-chain fatty acids across the mitochondrial membrane.
7. (Amino Acid Metabolism)
Which pathway removes nitrogen from amino acids?
A. Glycolysis
B. Transamination
, C. β-oxidation
D. Gluconeogenesis
Correct Answer: B
Rationale:
Transamination transfers amino groups, a key step in nitrogen metabolism.
8. (DNA Structure)
Which interaction stabilizes the DNA double helix?
A. Covalent bonds between strands
B. Hydrogen bonds and base stacking
C. Ionic bonds only
D. Disulfide bridges
Correct Answer: B
Rationale:
DNA stability arises from hydrogen bonding and hydrophobic stacking interactions.
9. (Replication)
Which enzyme synthesizes RNA primers during DNA replication?
A. DNA polymerase
B. Primase
C. Helicase
D. Ligase
Correct Answer: B
Rationale:
Primase creates RNA primers needed for DNA polymerase.
10. (Transcription Regulation)
Which factor increases transcription rate?
A. Repressor binding
B. Enhancer sequences
C. DNA methylation
D. Histone deacetylation
Correct Answer: B
Rationale:
Enhancers increase transcription by promoting activator binding.
STRUCTURED WITH ACTUAL QUESTIONS AND RESPONSES
|USEFUL FOR QUICK REVISION |2026 UPDATED VERSION
ALREADY GRADED A+!!
1. (Protein Structure & Stability)
A mutation replaces a buried leucine with aspartate in the hydrophobic core of a globular protein. What is
the most likely effect?
A. Increased stability due to new ionic interactions
B. Decreased stability due to disruption of hydrophobic interactions
C. No effect on structure
D. Increased folding rate without affecting stability
Correct Answer: B
Rationale:
Hydrophobic cores stabilize proteins. Introducing a charged residue disrupts packing and creates
unfavorable energetics, reducing stability.
2. (Enzyme Kinetics)
A competitive inhibitor is added to an enzyme-catalyzed reaction. What is the expected effect on Km and
Vmax?
A. Km increases, Vmax unchanged
B. Km decreases, Vmax increases
C. Km unchanged, Vmax decreases
D. Both Km and Vmax decrease
Correct Answer: A
Rationale:
Competitive inhibitors increase apparent Km (lower affinity) but do not affect Vmax because inhibition
can be overcome with substrate.
3. (Thermodynamics)
Which statement best describes Gibbs free energy in biochemical reactions?
A. Negative ΔG always requires ATP hydrolysis
B. Positive ΔG indicates spontaneous reactions
C. Negative ΔG indicates thermodynamically favorable reactions
D. ΔG does not affect reaction direction
Correct Answer: C
Rationale:
A negative ΔG means the reaction is spontaneous under cellular conditions.
,4. (Carbohydrate Metabolism)
Which step of glycolysis is irreversible and highly regulated?
A. Glucose → Glucose-6-phosphate
B. Fructose-6-phosphate → Fructose-1,6-bisphosphate
C. 3-Phosphoglycerate → 2-Phosphoglycerate
D. Phosphoenolpyruvate → Pyruvate
Correct Answer: B
Rationale:
This step, catalyzed by PFK-1, is the committed and rate-limiting step of glycolysis.
5. (Bioenergetics)
Which process generates the most ATP?
A. Glycolysis
B. Citric acid cycle
C. Oxidative phosphorylation
D. Fermentation
Correct Answer: C
Rationale:
Most ATP is generated via electron transport chain and chemiosmosis.
6. (Lipid Metabolism)
Which molecule is the primary carrier of fatty acids into mitochondria?
A. Coenzyme A
B. Carnitine
C. NADH
D. ATP
Correct Answer: B
Rationale:
Carnitine transports long-chain fatty acids across the mitochondrial membrane.
7. (Amino Acid Metabolism)
Which pathway removes nitrogen from amino acids?
A. Glycolysis
B. Transamination
, C. β-oxidation
D. Gluconeogenesis
Correct Answer: B
Rationale:
Transamination transfers amino groups, a key step in nitrogen metabolism.
8. (DNA Structure)
Which interaction stabilizes the DNA double helix?
A. Covalent bonds between strands
B. Hydrogen bonds and base stacking
C. Ionic bonds only
D. Disulfide bridges
Correct Answer: B
Rationale:
DNA stability arises from hydrogen bonding and hydrophobic stacking interactions.
9. (Replication)
Which enzyme synthesizes RNA primers during DNA replication?
A. DNA polymerase
B. Primase
C. Helicase
D. Ligase
Correct Answer: B
Rationale:
Primase creates RNA primers needed for DNA polymerase.
10. (Transcription Regulation)
Which factor increases transcription rate?
A. Repressor binding
B. Enhancer sequences
C. DNA methylation
D. Histone deacetylation
Correct Answer: B
Rationale:
Enhancers increase transcription by promoting activator binding.
