USMLE Step 1–Style Practice Questions
100% Verified
1.
A 65-year-old man presents with progressive memory loss and
confusion. Brain biopsy shows extracellular plaques composed
of β-amyloid. Which enzyme is responsible for generating β-
amyloid?
A. α-secretase
B. β-secretase
C. Acetylcholinesterase
D. Monoamine oxidase
Correct Answer: B. β-secretase
Rationale: β-secretase (and γ-secretase) cleave APP to form β-
amyloid → plaques in Alzheimer disease.
2.
A patient with chronic alcohol use presents with confusion,
ataxia, and ophthalmoplegia. Which vitamin deficiency is most
likely?
A. Vitamin B6
B. Vitamin B12
C. Thiamine (B1)
D. Niacin
,Correct Answer: C. Thiamine (B1)
Rationale: Classic triad = Wernicke encephalopathy due to B1
deficiency.
3.
A drug decreases heart rate by inhibiting funny (If) channels in
the SA node. Which drug is this?
A. Metoprolol
B. Ivabradine
C. Verapamil
D. Digoxin
Correct Answer: B. Ivabradine
Rationale: Selectively inhibits If channels → slows SA node
firing.
4.
A mutation causes defective collagen type I synthesis. Which
disease is most likely?
A. Ehlers-Danlos syndrome
B. Osteogenesis imperfecta
C. Marfan syndrome
D. Scurvy
Correct Answer: B. Osteogenesis imperfecta
Rationale: Type I collagen defect → brittle bones, blue sclera.
,5.
A 25-year-old woman has heat intolerance, weight loss, and
exophthalmos. Which antibody is responsible?
A. Anti-thyroglobulin
B. Anti-TPO
C. TSH receptor–stimulating antibody
D. Anti-TSH
Correct Answer: C. TSH receptor–stimulating antibody
Rationale: Graves disease → IgG stimulates TSH receptor.
6.
A researcher studies a drug that irreversibly inhibits an enzyme.
What happens to Vmax?
A. Increases
B. Decreases
C. Unchanged
D. Doubles
Correct Answer: B. Decreases
Rationale: Irreversible inhibition reduces total functional
enzyme → ↓ Vmax.
7.
, A patient presents with hematuria and hearing loss. Which
structure is affected?
A. Type I collagen
B. Type II collagen
C. Type III collagen
D. Type IV collagen
Correct Answer: D. Type IV collagen
Rationale: Alport syndrome affects basement membrane
collagen (type IV).
8.
Which electrolyte abnormality causes peaked T waves on ECG?
A. Hypokalemia
B. Hyperkalemia
C. Hypercalcemia
D. Hyponatremia
Correct Answer: B. Hyperkalemia
Rationale: Classic ECG change = tall, peaked T waves.
9.
A patient develops severe muscle rigidity after anesthesia.
Which condition is most likely?
100% Verified
1.
A 65-year-old man presents with progressive memory loss and
confusion. Brain biopsy shows extracellular plaques composed
of β-amyloid. Which enzyme is responsible for generating β-
amyloid?
A. α-secretase
B. β-secretase
C. Acetylcholinesterase
D. Monoamine oxidase
Correct Answer: B. β-secretase
Rationale: β-secretase (and γ-secretase) cleave APP to form β-
amyloid → plaques in Alzheimer disease.
2.
A patient with chronic alcohol use presents with confusion,
ataxia, and ophthalmoplegia. Which vitamin deficiency is most
likely?
A. Vitamin B6
B. Vitamin B12
C. Thiamine (B1)
D. Niacin
,Correct Answer: C. Thiamine (B1)
Rationale: Classic triad = Wernicke encephalopathy due to B1
deficiency.
3.
A drug decreases heart rate by inhibiting funny (If) channels in
the SA node. Which drug is this?
A. Metoprolol
B. Ivabradine
C. Verapamil
D. Digoxin
Correct Answer: B. Ivabradine
Rationale: Selectively inhibits If channels → slows SA node
firing.
4.
A mutation causes defective collagen type I synthesis. Which
disease is most likely?
A. Ehlers-Danlos syndrome
B. Osteogenesis imperfecta
C. Marfan syndrome
D. Scurvy
Correct Answer: B. Osteogenesis imperfecta
Rationale: Type I collagen defect → brittle bones, blue sclera.
,5.
A 25-year-old woman has heat intolerance, weight loss, and
exophthalmos. Which antibody is responsible?
A. Anti-thyroglobulin
B. Anti-TPO
C. TSH receptor–stimulating antibody
D. Anti-TSH
Correct Answer: C. TSH receptor–stimulating antibody
Rationale: Graves disease → IgG stimulates TSH receptor.
6.
A researcher studies a drug that irreversibly inhibits an enzyme.
What happens to Vmax?
A. Increases
B. Decreases
C. Unchanged
D. Doubles
Correct Answer: B. Decreases
Rationale: Irreversible inhibition reduces total functional
enzyme → ↓ Vmax.
7.
, A patient presents with hematuria and hearing loss. Which
structure is affected?
A. Type I collagen
B. Type II collagen
C. Type III collagen
D. Type IV collagen
Correct Answer: D. Type IV collagen
Rationale: Alport syndrome affects basement membrane
collagen (type IV).
8.
Which electrolyte abnormality causes peaked T waves on ECG?
A. Hypokalemia
B. Hyperkalemia
C. Hypercalcemia
D. Hyponatremia
Correct Answer: B. Hyperkalemia
Rationale: Classic ECG change = tall, peaked T waves.
9.
A patient develops severe muscle rigidity after anesthesia.
Which condition is most likely?
