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.

Pathway

Pyrimidine synthesis (& thymidylate) · Cytosol, essentially all cells (CAD, UMP synthase); dihydroorotate dehydrogenase on the inner mitochondrial membrane. Enzymes sit beside the arrows; a ★ marks the rate-limiting step. The map scrolls inside its panel.

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Pyrimidine synthesis (& thymidylate)

OMP

Made from Orotate (free base) by Orotate phosphoribosyltransferase (UMP synthase, activity 1)

Orotate phosphoribosyltransferase (UMP synthase, activity 1) — Pyrimidine synthesis (& thymidylate)

Cofactors: PRPP → PPi

Deficiency: Hereditary orotic aciduria (AR, UMP synthase) — orotic acid crystals in urine, megaloblastic anemia that does NOT respond to B12/folate, failure to thrive, NORMAL ammonia; treat with oral uridine

Condition cards:Hereditary orotic aciduria (UMP synthase deficiency) →

Becomes UMP via OMP decarboxylase (UMP synthase, activity 2)

OMP decarboxylase (UMP synthase, activity 2) — Pyrimidine synthesis (& thymidylate)

Either UMP synthase activity lost → orotic aciduria. Orotic aciduria WITH hyperammonemia is OTC deficiency instead (mitochondrial carbamoyl phosphate overflows into this pathway).

Condition cards:Ornithine transcarbamylase (OTC) deficiency →