USMLE STEP 1 – 50 MCQs

1. Physiology

A decrease in arterial blood pressure is most likely to cause which of the following?
A. Decreased sympathetic tone
B. Increased baroreceptor firing
C. Increased renin release
D. Decreased aldosterone secretion
E. Decreased ADH release

2. Biochemistry

Which enzyme is deficient in classic galactosemia?
A. Galactokinase
B. Galactose-1-phosphate uridyltransferase
C. Lactase
D. Hexokinase
E. Aldolase B

3. Pathology

A child presents with edema, heavy proteinuria, and hyperlipidemia. Light microscopy is normal. What is the diagnosis?
A. FSGS
B. Membranous nephropathy
C. Minimal change disease
D. IgA nephropathy
E. Diabetic nephropathy

4. Pharmacology

Which drug is a noncompetitive NMDA receptor antagonist used in Alzheimer disease?
A. Donepezil
B. Rivastigmine
C. Memantine
D. Galantamine
E. Tacrine

5. Microbiology

Which organism is most likely to cause atypical pneumonia in young adults?
A. Streptococcus pneumoniae
B. Haemophilus influenzae
C. Mycoplasma pneumoniae
D. Klebsiella pneumoniae
E. Legionella pneumophila

6. Immunology

Which immunoglobulin crosses the placenta?
A. IgA
B. IgD
C. IgE
D. IgG
E. IgM

7. Genetics

A child has mental retardation, large ears, and macroorchidism. What is the mutation?
A. Trinucleotide repeat expansion in FMR1
B. Deletion of chromosome 5p
C. Point mutation in dystrophin
D. Deletion of chromosome 15
E. Robertsonian translocation

8. Anatomy

The nerve most commonly injured during thyroid surgery is:
A. Hypoglossal
B. Glossopharyngeal
C. Vagus
D. Recurrent laryngeal
E. Phrenic

9. Physiology

Which lung volume cannot be measured by spirometry?
A. Tidal volume
B. Inspiratory reserve volume
C. Expiratory reserve volume
D. Residual volume
E. Vital capacity

10. Biochemistry

Which vitamin deficiency causes Wernicke encephalopathy?
A. B1
B. B6
C. B12
D. Folate
E. Niacin

11. Pathology

A Reed–Sternberg cell is characteristic of:
A. Non-Hodgkin lymphoma
B. Burkitt lymphoma
C. Hodgkin lymphoma
D. Multiple myeloma
E. CLL

12. Pharmacology

Which drug causes gingival hyperplasia?
A. Warfarin
B. Phenytoin
C. Valproate
D. Carbamazepine
E. Phenobarbital

13. Microbiology

Which virus is associated with nasopharyngeal carcinoma?
A. HPV
B. EBV
C. CMV
D. HSV-1
E. HIV

14. Immunology

Type I hypersensitivity is mediated by:
A. IgG
B. IgM
C. IgE
D. IgA
E. IgD

15. Genetics

Marfan syndrome is caused by a defect in:
A. Collagen type I
B. Collagen type II
C. Collagen type IV
D. Fibrillin-1
E. Elastin

16. Physiology

Which hormone increases calcium levels in blood?
A. Calcitonin
B. Aldosterone
C. PTH
D. Vitamin D deficiency
E. Insulin

17. Biochemistry

Which enzyme is rate-limiting in cholesterol synthesis?
A. HMG-CoA synthase
B. HMG-CoA reductase
C. Acetyl-CoA carboxylase
D. LDL receptor
E. ACAT

18. Pathology

Which tumor marker is elevated in hepatocellular carcinoma?
A. PSA
B. CA-125
C. AFP
D. CEA
E. CA 19-9

19. Pharmacology

Which antibiotic inhibits bacterial DNA gyrase?
A. Penicillin
B. Vancomycin
C. Azithromycin
D. Ciprofloxacin
E. Linezolid

20. Microbiology

Which organism is acid-fast?
A. Nocardia
B. Streptococcus
C. Neisseria
D. Chlamydia
E. Mycoplasma

21. Immunology

MHC class I presents antigens to:
A. CD4+ T cells
B. CD8+ T cells
C. B cells
D. NK cells
E. Plasma cells

22. Anatomy

Which structure passes through the foramen rotundum?
A. Optic nerve
B. Maxillary nerve
C. Mandibular nerve
D. Facial nerve
E. Trigeminal ganglion

23. Physiology

Which electrolyte abnormality causes peaked T waves?
A. Hypokalemia
B. Hyperkalemia
C. Hypocalcemia
D. Hypercalcemia
E. Hyponatremia

24. Biochemistry

Which pathway is active in red blood cells?
A. TCA cycle
B. Pentose phosphate pathway
C. Urea cycle
D. Gluconeogenesis
E. β-oxidation

25. Pathology

Which cancer is associated with smoking?
A. Adenocarcinoma of lung
B. Small cell carcinoma of lung
C. Papillary thyroid carcinoma
D. Renal cell carcinoma
E. Colon cancer

26. Pharmacology

Which drug is used for acute gout?
A. Allopurinol
B. Probenecid
C. Colchicine
D. Febuxostat
E. Pegloticase

27. Microbiology

Which parasite causes malaria?
A. Leishmania
B. Trypanosoma
C. Plasmodium
D. Giardia
E. Entamoeba

28. Immunology

Which cells produce antibodies?
A. T lymphocytes
B. Macrophages
C. Plasma cells
D. NK cells
E. Dendritic cells

29. Genetics

Down syndrome is most commonly caused by:
A. Deletion
B. Mosaicism
C. Nondisjunction
D. Translocation
E. Point mutation

30. Anatomy

The appendix is supplied by:
A. Inferior mesenteric artery
B. Superior mesenteric artery
C. Celiac trunk
D. Renal artery
E. Gonadal artery

31. Physiology

Which acid-base disorder shows decreased pH and decreased HCO₃⁻?
A. Respiratory acidosis
B. Respiratory alkalosis
C. Metabolic acidosis
D. Metabolic alkalosis
E. Mixed disorder

32. Biochemistry

Phenylketonuria is caused by deficiency of:
A. Tyrosinase
B. Phenylalanine hydroxylase
C. DOPA decarboxylase
D. Tryptophan hydroxylase
E. Homogentisate oxidase

33. Pathology

Which disease shows “cobblestone” appearance?
A. Ulcerative colitis
B. Crohn disease
C. Celiac disease
D. IBS
E. Colon cancer

34. Pharmacology

Which drug causes lupus-like syndrome?
A. Digoxin
B. Procainamide
C. Propranolol
D. Atenolol
E. Amiodarone

35. Microbiology

Which bacteria is intracellular?
A. E. coli
B. Staphylococcus
C. Listeria
D. Pseudomonas
E. Vibrio

36. Immunology

Which cytokine activates macrophages?
A. IL-4
B. IL-5
C. IL-10
D. IFN-γ
E. TGF-β

37. Anatomy

The nerve injured in wrist drop is:
A. Ulnar
B. Median
C. Radial
D. Musculocutaneous
E. Axillary

38. Physiology

Which hormone is released from posterior pituitary?
A. TSH
B. ACTH
C. ADH
D. GH
E. Prolactin

39. Biochemistry

Which amino acid is aromatic?
A. Alanine
B. Valine
C. Phenylalanine
D. Glycine
E. Lysine

40. Pathology

Atherosclerosis primarily affects which layer?
A. Intima
B. Media
C. Adventitia
D. Endothelium
E. Pericytes

41. Pharmacology

Which drug is contraindicated in pregnancy?
A. Penicillin
B. Heparin
C. Warfarin
D. Insulin
E. Methyldopa

42. Microbiology

Which organism is a spirochete?
A. Borrelia
B. Staphylococcus
C. Bacillus
D. Clostridium
E. Corynebacterium

43. Immunology

Which complement component causes cell lysis?
A. C3a
B. C3b
C. C5a
D. C5b-9
E. C1

44. Anatomy

Which muscle abducts the arm from 15–90 degrees?
A. Deltoid
B. Supraspinatus
C. Infraspinatus
D. Teres minor
E. Subscapularis

45. Physiology

Which electrolyte imbalance causes muscle weakness?
A. Hyperkalemia
B. Hypokalemia
C. Hypercalcemia
D. Hypernatremia
E. Hypermagnesemia

46. Biochemistry

Which vitamin is required for collagen synthesis?
A. Vitamin A
B. Vitamin C
C. Vitamin D
D. Vitamin E
E. Vitamin K

47. Pathology

Which disease causes “owl eye” inclusions?
A. HSV
B. EBV
C. CMV
D. HIV
E. HPV

48. Pharmacology

Which beta-blocker is selective for β₁ receptors?
A. Propranolol
B. Nadolol
C. Metoprolol
D. Timolol
E. Labetalol

49. Microbiology

Which organism causes pseudomembranous colitis?
A. E. coli
B. Salmonella
C. Shigella
D. Clostridioides difficile
E. Campylobacter

50. Immunology

Which immune cells lack MHC I?
A. B cells
B. T cells
C. Macrophages
D. NK cells
E. Dendritic cells