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๐Ÿฉบ USMLE Step 1 (Medical Biology & Basic Sciences): Official Syllabus & Linked Notes

๐Ÿฉบ United States Medical Licensing Examination

USMLE Step 1 (Medical Biology & Basic Sciences): Official Syllabus

United States Medical Licensing Examination Biomedical Sciences Curriculum Mapped to Lecture Notes. Every topic and subtopic below is directly mapped to in-depth university textbook lecture notes, interactive concept mind maps, and high-yield one-night exam cram sheets.

6 Units / Sections 22 Mapped Subtopics ๐Ÿ›๏ธ Federation of State Medical Boards (FSMB) & National Board of Medical Examiners (NBME) โœ… 100% Lecture Coverage
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Examination Format & Marking Scheme

Total MarksPass / Fail Benchmark (Three-digit diagnostic reporting)
Test Duration8-Hour Testing Session (Seven 60-minute blocks)
Negative MarkingNo negative marking
Basic Medical Principles & Foundation Disciplines
Up to 280 Multiple-Choice Questions (40 per block) (Pass/Fail Threshold: ~196 scale equivalent Marks)
Medical Biochemistry, Microbiology, Immunology, Pathology, Organ System Physiology, Pharmacology, and Behavioral Science.
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High-Yield Exam Strategy & Pro-Tips

  • Focus on mechanism-of-disease and clinicopathologic correlation rather than isolated biological trivia.
  • High-yield must-know areas: Inborn errors of metabolism, autosomal/X-linked pedigrees, immunodeficiency classifications, and cardiac/renal pressure-volume loops.
  • Link biochemical pathways directly to specific pharmacological inhibitors and deficiency syndromes (e.g., G6PD deficiency, statin targets, methotrexate mechanisms).
Target Eligibility: Medical students (allopathic and osteopathic) and International Medical Graduates (IMGs) registered with ECFMG
Unit 01

Medical Biochemistry & Inborn Metabolic Disorders

๐Ÿ”ฅ High Yield (~15-20% of Step 1 questions) 4 Subtopics

Molecular mechanisms of carbohydrate, lipid, and amino acid metabolism, inborn errors of metabolism, glycogen storage diseases, vitamin cofactors, and bioenergetics.

USMLE.1A

Glycogen Storage Diseases & Gluconeogenic Checkpoints

Von Gierke (Type I), Pompe (Type II), Cori (Type III), and McArdle (Type V) diseases; fructose intolerance and galactosemia enzymopathies.

USMLE.1B

Lipid Metabolism, Lysosomal Storage & Hyperlipidemias

Familial hypercholesterolemia, Gaucher disease (glucocerebrosidase), Tay-Sachs (hexosaminidase A), Niemann-Pick (sphingomyelinase), and Fabry disease.

USMLE.1C

Amino Acid Catabolism, Urea Cycle & Organic Acidemias

Phenylketonuria (PKU), Maple syrup urine disease (MSUD), Alkaptonuria, Homocystinuria, and hyperammonemia ornithine transcarbamylase (OTC) deficiency.

USMLE.1D

Vitamins, Cofactors & Micronutrient Deficiencies

Thiamine (B1 - Wernicke-Korsakoff, Beriberi), Niacin (B3 - Pellagra), Cobalamin (B12 - Subacute combined degeneration), Folate (B9 - Neural tube defects), and Vitamin D.

Unit 02

Medical Microbiology & Infectious Diseases

๐Ÿ”ฅ High Yield (~15-20% of Step 1 questions) 4 Subtopics

Bacterial classification, virulence factors, exotoxins vs. endotoxins, viral genetics and replication, fungal pathogens, and clinical parasitology.

USMLE.2A

Gram-Positive & Gram-Negative Bacteriology & Toxins

Staphylococcus, Streptococcus, Clostridium (tetani, botulinum, difficile), Neisseria, Enterobacteriaceae, Pseudomonas, and ADP-ribosylating toxins.

USMLE.2B

Clinical Virology & Viral Replication Cycles

Herpesviridae (HSV, VZV, EBV, CMV), Hepatitis viruses (HAV, HBV, HCV), HIV lifecycle and retroviral integration, Respiratory viruses (Influenza, RSV, Coronaviridae).

USMLE.2C

Medical Mycology & Dimorphic Systemic Fungi

Histoplasma, Blastomyces, Coccidioides, Paracoccidioides, Candida albicans, Cryptococcus neoformans, and Aspergillus fumigatus.

USMLE.2D

Antimicrobial Mechanisms & Resistance Determinants

Beta-lactams (PBP targets), aminoglycosides/macrolides (30S/50S ribosomal inhibition), fluoroquinolones (topoisomerase II/IV), and beta-lactamase resistance.

Unit 03

Medical Immunology & Hypersensitivity Reactions

๐Ÿ”ฅ High Yield (~12-15% of Step 1 questions) 4 Subtopics

Innate vs. adaptive immunity, T-cell activation, MHC restriction, primary immunodeficiencies, hypersensitivity types I-IV, and autoimmune pathology.

USMLE.3A

T & B Cell Development, Activation & Co-stimulation

Thymic positive/negative selection, TCR-CD3 complex, CD28-B7 co-stimulation, Th1/Th2/Th17/Treg subsets, and germinal center class-switch recombination.

USMLE.3B

Hypersensitivity Reactions: Types I, II, III & IV

Type I (IgE-mast cell anaphylaxis), Type II (cytotoxic antibody, Goodpasture, myasthenia), Type III (immune complex, SLE, post-strep GN), Type IV (delayed-type, TB test).

USMLE.3C

Primary & Secondary Immunodeficiency Syndromes

X-linked agammaglobulinemia (Bruton), Severe combined immunodeficiency (SCID), DiGeorge syndrome (22q11 deletion), Wiskott-Aldrich, and Chronic granulomatous disease.

USMLE.3D

Transplant Immunology & Rejection Mechanisms

Hyperacute (preformed antibodies), acute (cellular cytotoxic T-cell / humoral vasculitis), and chronic rejection (arteriosclerosis, interstitial fibrosis).

Unit 04

Cellular Pathology & Neoplasia

๐Ÿ”ฅ High Yield (~12-15% of Step 1 questions) 3 Subtopics

Cellular adaptations (hypertrophy, hyperplasia, metaplasia, dysplasia), reversible vs. irreversible cell injury, necrosis vs. apoptosis, oncogenes, and tumor biology.

USMLE.4A

Cell Injury, Free Radicals & Types of Tissue Necrosis

Ischemia-reperfusion injury, ATP depletion, coagulative, liquefactive, caseous, fat, and gangrenous necrosis; metastatic vs. dystrophic calcification.

USMLE.4B

Apoptosis Signaling: Extrinsic & Intrinsic Pathways

FasL-FasR/TNF-caspase 8 axis, mitochondrial cytochrome c release, Bcl-2/Bax regulation, Apaf-1 apoptosome assembly, and executioner caspases 3 and 6.

USMLE.4C

Molecular Hallmarks of Cancer, Oncogenes & Tumor Suppressors

p53, Rb (two-hit hypothesis), APC/beta-catenin, BRCA1/2, HER2/neu, BCR-ABL fusion (CML), telomerase reactivation, and immune evasion (PD-1/CTLA-4).

Unit 05

Human Organ Systems Physiology

๐Ÿ”ฅ Very High Yield (~20-25% of Step 1 questions) 4 Subtopics

Hemodynamics, cardiac electrophysiology, respiratory gas exchange, nephron transport kinetics, gastrointestinal motility, and endocrine feedback loops.

USMLE.5A

Cardiovascular Physiology, Pressure-Volume Loops & ECG

Preload, afterload, inotropy, pressure-volume loop changes in valvular defects, cardiac electrophysiology, and shock hemodynamics.

USMLE.5B

Respiratory Physiology: V/Q Mismatch & Acid-Base Dynamics

Ventilation-perfusion relationships, A-a gradient, shunt vs. dead space, metabolic/respiratory acidosis and alkalosis with Winter's formula compensation.

USMLE.5C

Renal Physiology, Electrolyte Transport & Acid-Base Secretion

Proximal tubule HCO3- reabsorption, thick ascending limb Na-K-2Cl symporter, distal tubule Na-Cl, collecting duct aldosterone/ADH action, and free water clearance.

USMLE.5D

Endocrine Axes: Thyroid, Adrenal & Calcium Homeostasis

Cushing syndrome, Addison disease, Conn syndrome (hyperaldosteronism), Graves disease, Hashimoto thyroiditis, and hyperparathyroidism.

Unit 06

Medical Genetics, Genomics & Neurobiology

๐Ÿ”ฅ High Yield (~10-14% of Step 1 questions) 3 Subtopics

Mendelian inheritance patterns, trinucleotide repeat expansion disorders, imprinting, chromosomal microdeletions, and neurobiology principles.

USMLE.6A

Trinucleotide Repeat Disorders & Genetic Imprinting

Huntington disease (CAG), Fragile X syndrome (CGG), Myotonic dystrophy (CTG), Friedreich ataxia (GAA); Prader-Willi vs. Angelman syndromes (15q11-13).

USMLE.6B

Chromosomal Aneuploidies & Microdeletions

Down syndrome (Trisomy 21), Edwards (Trisomy 18), Patau (Trisomy 13), Cri-du-chat (5p-), Williams syndrome (7q microdeletion), and Turner syndrome (45,XO).

USMLE.6C

Neurobiology: Action Potentials, Synapses & Neurotransmitters

GABA, glutamate, dopamine, acetylcholine, serotonin synthesis, myasthenia gravis vs. Lambert-Eaton syndrome, and demyelinating neuropathies.

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