Biochemistry

Michaelis-Menten kinetics, Km, Vmax, competitive vs non-competitive inhibition. The ETC enzyme poisons (cyanide, CO, rotenone) and how each halts the chain at a specific complex.

The three irreversible bypasses (pyruvate carboxylase, PEPCK, FBPase-1/FBPase-2) and the substrates that feed in. Why gluconeogenesis is liver + kidney only.

NADPH generation (G6PD route), ribose-5-phosphate for nucleotides, and the G6PD deficiency hemolysis trigger. Oxidative vs non-oxidative phases.

Carnitine shuttle, the four-step beta-ox cycle, ATP yield per palmitate, and the odd-chain fatty acid that feeds propionyl-CoA into the TCA. MCAD deficiency boards pattern.

Cytosol vs mitochondria, malonyl-CoA inhibits CPT-1, acetyl-CoA carboxylase as the rate-limiting step, and the NADPH requirement from PPP.

HMG-CoA reductase, statin mechanism, LDL receptor regulation, and familial hypercholesterolemia. Bile acid synthesis and the enterohepatic circulation.

Glycogenesis vs glycogenolysis, glycogen phosphorylase, branching enzyme, and the hormone control (glucagon/insulin/epinephrine). Muscle vs liver glycogen differences.

Von Gierke, Pompe, Cori, McArdle, Hers · enzyme, substrate that accumulates, and the clinical clue for each. The 'Very Painful Cramps' mnemonic.

Five enzymes, starting from NH3 + CO2, the two nitrogens in urea, and OTC deficiency (the boards favorite). Hyperammonemia labs and the orotic acid key.

One missing enzyme. A baby who never makes melanin, dopamine, or serotonin. The musty smell on the diaper that names the disease.

PKU, MSUD, alkaptonuria, homocystinuria, and the starvation timeline. Which metabolic disease smells like what and the lab pattern for each.

Iron absorption (Fe2+ absorbed, Fe3+ dietary), transferrin, ferritin, hepcidin, and the lab triad for IDA vs ACD vs hemochromatosis. Hemosiderin vs ferritin storage.

ALA dehydratase and ferrochelatase are the two targets of lead. Ringed sideroblasts, basophilic stippling, and the ABCs of lead effects (Anemia, Bones, CNS). Succimer/DMSA chelation.

Barbiturates and fasting raise hepatic heme demand; PBG deaminase deficiency backs up ALA and PBG. Board pattern: severe pain with a quiet abdomen, psych and autonomic symptoms, dark urine after standing.

Alpha (4-gene deletion, HbH, Hb Barts) vs beta (splice/nonsense, HbA2 and HbF compensation). Transfusion thresholds, iron overload, and deferoxamine.

Duchenne (dystrophin frameshift, pseudohypertrophy, Gowers sign) vs Becker (in-frame). EPO production at JGA, 2,3-BPG response, and erythropoiesis stages.

ATP depletion cascade: Na+/K+ ATPase fails, cell swells, calcium floods in, enzymes activate. Reversible vs irreversible injury threshold. Reperfusion injury mechanism.

What your gut bacteria synthesize (Vit K2, Biotin, Folate) vs. what must arrive from diet (B12). The IM Vitamin K newborn connection. The antibiotic coagulopathy trap.

De novo vs salvage pathways, PRPP as the backbone, HGPRT deficiency (Lesch-Nyhan), adenosine deaminase deficiency (SCID), and the drugs that poison these pathways (6-MP, methotrexate, hydroxyurea).

Leading vs lagging strand, Okazaki fragments, primase, DNA pol III (prokaryote), DNA pol alpha/delta/epsilon (eukaryote), and the five repair pathways: BER, NER, MMR, NHEJ, HR.

G1, S, G2, M phases; cyclins and CDKs; p53 and Rb checkpoints; intrinsic (cytochrome c/Bcl-2) vs extrinsic (death receptor) apoptosis. Oncogenes vs tumor suppressors.

Hexosaminidase A deficiency jams GM2 ganglioside into neurons. Cherry-red macula plus hyperacusis and rapid neuro regression without the bulky liver and spleen pair you frame against Niemann-Pick. Boards love Ashkenazi screening vignettes.

Sphingomyelinase loss (classic A/B picture) floods macrophages until they foam and blows up liver and spleen. Cherry-red macula overlaps Tay-Sachs, so boards hand you hepatosplenomegaly versus a quiet abdomen to split the lane.

A day-5 newborn with poor feeding, opisthotonos, and a sweet maple smell on the diaper. One broken enzyme complex (BCKD) backs up three amino acids and leucine poisons the brain.

MTTP mutation blocks chylomicron and VLDL assembly. Fat-soluble vitamins can't be absorbed. Acanthocytes, steatorrhea, and progressive ataxia from vitamin E deficiency.