COMLEX Level 1USMLE Step 1 Core Hub

Glycolysis: PFK-1 (inhibited by ATP, citrate; stimulated by AMP, F-2,6-BP). Gluconeogenesis: Fructose-1,6-bisphosphatase-1.

TCA Cycle: Isocitrate dehydrogenase (inhibited by ATP, NADH; stimulated by ADP).

Glycogen Storage: Von Gierke (Type I: Glucose-6-phosphatase defect → severe fasting hypoglycemia, hepatomegaly, lactic acidosis), Pompe (Type II: Lysosomal α-glucosidase → hypertrophic cardiomyopathy, "Pompe trashes the pump"), McArdle (Type V: Muscle glycogen phosphorylase → painful muscle cramps, myoglobinuria with exercise).

Lysosomal Storage: Tay-Sachs (Hexosaminidase A, GM2 ganglioside, cherry-red spot, NO hepatosplenomegaly), Niemann-Pick (Sphingomyelinase, cherry-red spot + hepatosplenomegaly, foam cells), Gaucher (Glucocerebrosidase, crumpled tissue paper macrophages, avascular necrosis).

Gram-Positive Cocci: Catalase-positive = Staph (Coagulase-pos = S. aureus; Coagulase-neg, Novobiocin-sens = S. epidermidis; Novobiocin-res = S. saprophyticus). Catalase-negative = Strep (α-hemolytic: Optochin-sens = S. pneumoniae; Optochin-res = Viridans; β-hemolytic: Bacitracin-sens = GAS; Bacitracin-res = GBS).

Bacterial Toxins: Inactivate EF-2 via ADP-ribosylation = Diphtheria & Pseudomonas (Exotoxin A). Increase cAMP = Cholera (Gs activation), Pertussis (Gi inhibition), Anthrax (EF). Cleave SNARE proteins = Tetanus (GABA/glycine inhibition → spastic paralysis) & Botulinum (ACh inhibition → flaccid paralysis).

Hypersensitivities: Type I (IgE, mast cells, anaphylaxis), Type II (IgG/IgM cytotoxic, Goodpasture, Graves, MG), Type III (Immune complexes, SLE, PSGN, serum sickness), Type IV (T-cell mediated, PPD, contact dermatitis, MS).

G-Protein Second Messengers: qiss and qiq till you are sik sqs: Gq = α1, M1, M3, V1, H1 (activates PLC → IP3/DAG → Ca2+/PKC). Gi = α2, M2, D2 (inhibits adenylyl cyclase → ↓cAMP). Gs = β1, β2, β3, D1, V2, H2 (stimulates adenylyl cyclase → ↑cAMP → PKA).

CYP450 Inducers: Ken Rides Greener Vans, Porches, Subarus: Carbamazepine, Rifampin, Griseofulvin, Chronic alcohol, Phenytoin, Phenobarbital, St. John's wort.

CYP450 Inhibitors: SICKFACES.COM: Sodium valproate, Isoniazid, Cimetidine, Ketoconazole, Fluconazole, Acute alcohol, Chloramphenicol, Erythromycin/Clarithromycin, Sulfonamides, Ciprofloxacin, Omeprazole, Metronidazole, Grapefruit juice.

PV Loops: Increased preload = width widens to the right (EDV increases). Increased afterload = loop gets taller and narrower (peak pressure increases, ESV increases). Increased inotropy = top-left corner shifts left (ESV decreases, EF increases).

Heart Sound Splits: Wide split (delayed pulmonic closure, e.g., pulmonic stenosis, RBBB; widens on inspiration). Fixed split (ASD, hemodynamically unchanged by respiration). Paradoxical split (delayed aortic closure, e.g., AS, LBBB; splits on expiration, fuses on inspiration).

Congenital Hearts: Right-to-Left (early cyanosis, "5 Ts"): Tetralogy of Fallot, Transposition of great arteries, Truncus arteriosus, Tricuspid atresia, TAPVR. Left-to-Right (late cyanosis, Eisenmenger): VSD (most common), ASD (fixed S2 split), PDA (machine murmur, indomethacin closes).

Nephron Segments: PCT (reabsorbs 65% Na/water, 100% glucose/amino acids via SGLT2; acetazolamide acts here). TAL (Na+/K+/2Cl- cotransporter; loop diuretics; impermeable to water; Bartter syndrome mimic). DCT (Na+/Cl- cotransporter; thiazides; Gitelman syndrome mimic). CD (ENaC, aldosterone, ADH via V2).

Metabolic Acidosis: Anion gap = Na - (Cl + HCO3). Normal = 8–12. High AG: MUDPILES / GOLDMARK (Methanol, Uremia, DKA, Propylene glycol, Iron/Isoniazid, Lactic acidosis, Ethylene glycol, Salicylates). Winter's Formula: Expected PaCO2 = 1.5 × [HCO3] + 8 ± 2.

Renal Tubular Acidoses: Type 1 (Distal, defect in H+ excretion, urine pH > 5.5, hypokalemia, nephrolithiasis). Type 2 (Proximal, defect in HCO3 reabsorption, urine pH < 5.5, hypokalemia, Fanconi syndrome). Type 4 (Hypoaldosteronism, hyperkalemia, urine pH < 5.5).

Brachial Plexus Injuries: Erb's palsy (C5–C6 upper trunk, "waiter's tip", loss of abduction/external rotation). Klumpke's palsy (C8–T1 lower trunk, "claw hand", intrinsic hand muscle paralysis, Horner syndrome). Saturday night palsy (Radial nerve in spiral groove → wrist drop, sensory loss over dorsal thumb webspace).

Lower Extremity Radiculopathy: L4 (patellar reflex, sensation medial calf, ankle dorsiflexion). L5 (sensation dorsal foot, big toe extension). S1 (Achilles reflex, sensation lateral foot, ankle plantarflexion).