Learn / Metabolism
Metabolic pathways
Every FMK pathway as a clickable map. Pick one pathway to hammer it — next step, enzyme, regulator, cofactor, and the facts that get tested (NADPH and who needs it, rate-limiting steps, deficiencies) — or set it to all pathways for a mixed drill. Every answer says which enzyme and which pathway.
Lipid digestion & absorption
CHYLOMICRON (apo B-48)
Made from Re-esterified: TAG, cholesteryl esters, phospholipids by MTP (microsomal triglyceride transfer protein) loads lipid onto apo B-48
MTP (microsomal triglyceride transfer protein) loads lipid onto apo B-48 · irreversible — Lipid digestion & absorption
Deficiency: ABETALIPOPROTEINEMIA — no MTP, so neither chylomicrons nor VLDL can be assembled. Lipid and fat-soluble vitamins pile up inside enterocytes and hepatocytes: steatorrhoea, failure to thrive, vitamin E deficiency (ataxia, areflexia), ACANTHOCYTES on smear. The drug lomitapide inhibits MTP deliberately, and risks hepatic steatosis for the same reason
Chylomicrons (intestine, apo B-48) and VLDL (liver, apo B-100) are assembled by the same mechanism — MTP serves both.
Condition cards:Abetalipoproteinemia →
Becomes Lymphatic lacteal → thoracic duct → blood via Golgi → secretory vesicle → exocytosis into a LYMPHATIC LACTEAL
Golgi → secretory vesicle → exocytosis into a LYMPHATIC LACTEAL · irreversible — Lipid digestion & absorption
Chylomicrons are too large for the capillary; they enter lymph and reach the blood at the thoracic duct, bypassing the liver's first pass.