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
2-MAG + 2 free fatty acids + free cholesterol
Made from Emulsified droplets — huge surface area by PANCREATIC LIPASE + COLIPASE (1:1; procolipase activated by trypsin)
PANCREATIC LIPASE + COLIPASE (1:1; procolipase activated by trypsin) · irreversible — Lipid digestion & absorption
Inhibited by: Orlistat (covalent inhibitor of gastric + pancreatic lipase)
Deficiency: Pancreatic exocrine insufficiency / cystic fibrosis — no lipase reaches the lumen. Orlistat reproduces this on purpose, and steatorrhoea is the expected side effect
Colipase anchors lipase to the droplet surface in the presence of bile salts, which would otherwise displace it. Cholesterol esterase and phospholipase A₂ (which cuts at C2) work alongside it, both activated by trypsin and enhanced by bile salts.
Condition cards:Pancreatic exocrine insufficiency →Cystic fibrosis →Orlistat (lipase inhibitor) — iatrogenic steatorrhea →
Becomes MIXED MICELLE (+ vitamins A, D, E, K) via Bile salts assemble MIXED MICELLES
Bile salts assemble MIXED MICELLES — Lipid digestion & absorption
Deficiency: Steatorrhoea with vitamins A, D, E and K all deficient together — a defect anywhere upstream (lipase, bile salts, or chylomicron assembly) takes all four down at once
Cargo: free fatty acids, 2-monoacylglycerol, free cholesterol, bile salts and the fat-soluble vitamins. Micelles diffuse to the brush border and release their contents for uptake.
Condition cards:Steatorrhea and fat-soluble vitamin (A, D, E, K) deficiency →
Becomes Short- & medium-chain FAs skip the micelle via Short- and medium-chain fatty acids need no micelle
Short- and medium-chain fatty acids need no micelle — Lipid digestion & absorption
Small and soluble enough to diffuse directly — the reason MCT oil is used when fat absorption is impaired.