NBME CBSE COMPREHENSIVE BASIC
SCIENCE EXAMINATION 2026/2027
QUESTIONS AND ANSWERS
1. A 24-year-old male presents with smoky-colored urine and facial puffiness two weeks after
recovering from a skin infection. Labs show decreased C3 and elevated antistreptolysin O
titers. What is the characteristic finding on electron microscopy for this patient?
A. Subendothelial deposits
B. Linear IgG deposits
C. Subepithelial humps
D. Tram-track appearance
Answer: C
Conceptual Explanation: Poststreptococcal glomerulonephritis (PSGN) presents with
nephritic syndrome after a GAS infection. Electron microscopy shows characteristic
subepithelial immune complex ‘humps’.
2. A 15-year-old boy develops jaundice and dark urine after taking primaquine for malaria
prophylaxis. A peripheral blood smear shows cells with ‘bite’ marks. What enzyme deficiency
is most likely?
A. Hexokinase
,B. Pyruvate kinase
C. Glucose-6-phosphate dehydrogenase
D. Glutathione reductase
Answer: C
Conceptual Explanation: G6PD deficiency leads to decreased NADPH production, making
RBCs susceptible to oxidative stress from drugs like primaquine, resulting in Heinz bodies
and bite cells.
3. A 65-year-old male is started on atorvastatin. What is the primary mechanism of action of
this drug?
A. Inhibition of cholesterol absorption in the small intestine
B. Irreversible inhibition of HMG-CoA reductase
C. Competitive inhibition of HMG-CoA reductase
D. Activation of PPAR-alpha
Answer: C
Conceptual Explanation: Statins are competitive inhibitors of HMG-CoA reductase, the
rate-limiting enzyme in cholesterol synthesis, which converts HMG-CoA to mevalonate.
, 4. An autopsy of a 60-year-old male who died from a myocardial infarction shows a wedge-
shaped area of pale tissue in the heart. What type of necrosis is most characteristic of this
finding?
A. Fat necrosis
B. Liquefactive necrosis
C. Caseous necrosis
D. Coagulative necrosis
Answer: D
Conceptual Explanation: Coagulative necrosis is typical of ischemia/infarction in most
solid organs (except the brain), where the architecture of the dead tissue is preserved for
some days.
5. A patient presents with high fever, hypotension, and a diffuse erythematous rash involving
the palms and soles after using high-absorbency tampons. The causative toxin acts as a
superantigen. What is the mechanism of this toxin?
A. Cross-links the Beta-region of TCR to MHC Class II
B. Inhibits protein synthesis by ADP-ribosylation of EF-2
C. Cleaves SNARE proteins to inhibit neurotransmitter release
D. Activates adenylate cyclase via Gs protein
Answer: A
SCIENCE EXAMINATION 2026/2027
QUESTIONS AND ANSWERS
1. A 24-year-old male presents with smoky-colored urine and facial puffiness two weeks after
recovering from a skin infection. Labs show decreased C3 and elevated antistreptolysin O
titers. What is the characteristic finding on electron microscopy for this patient?
A. Subendothelial deposits
B. Linear IgG deposits
C. Subepithelial humps
D. Tram-track appearance
Answer: C
Conceptual Explanation: Poststreptococcal glomerulonephritis (PSGN) presents with
nephritic syndrome after a GAS infection. Electron microscopy shows characteristic
subepithelial immune complex ‘humps’.
2. A 15-year-old boy develops jaundice and dark urine after taking primaquine for malaria
prophylaxis. A peripheral blood smear shows cells with ‘bite’ marks. What enzyme deficiency
is most likely?
A. Hexokinase
,B. Pyruvate kinase
C. Glucose-6-phosphate dehydrogenase
D. Glutathione reductase
Answer: C
Conceptual Explanation: G6PD deficiency leads to decreased NADPH production, making
RBCs susceptible to oxidative stress from drugs like primaquine, resulting in Heinz bodies
and bite cells.
3. A 65-year-old male is started on atorvastatin. What is the primary mechanism of action of
this drug?
A. Inhibition of cholesterol absorption in the small intestine
B. Irreversible inhibition of HMG-CoA reductase
C. Competitive inhibition of HMG-CoA reductase
D. Activation of PPAR-alpha
Answer: C
Conceptual Explanation: Statins are competitive inhibitors of HMG-CoA reductase, the
rate-limiting enzyme in cholesterol synthesis, which converts HMG-CoA to mevalonate.
, 4. An autopsy of a 60-year-old male who died from a myocardial infarction shows a wedge-
shaped area of pale tissue in the heart. What type of necrosis is most characteristic of this
finding?
A. Fat necrosis
B. Liquefactive necrosis
C. Caseous necrosis
D. Coagulative necrosis
Answer: D
Conceptual Explanation: Coagulative necrosis is typical of ischemia/infarction in most
solid organs (except the brain), where the architecture of the dead tissue is preserved for
some days.
5. A patient presents with high fever, hypotension, and a diffuse erythematous rash involving
the palms and soles after using high-absorbency tampons. The causative toxin acts as a
superantigen. What is the mechanism of this toxin?
A. Cross-links the Beta-region of TCR to MHC Class II
B. Inhibits protein synthesis by ADP-ribosylation of EF-2
C. Cleaves SNARE proteins to inhibit neurotransmitter release
D. Activates adenylate cyclase via Gs protein
Answer: A
