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)

dTMP

Made from dUMP by Thymidylate synthase

Thymidylate synthase · irreversible — Pyrimidine synthesis (& thymidylate)

Cofactors: N⁵,N¹⁰-methylene-THF → dihydrofolate (DHFR + NADPH regenerates THF)

Inhibited by: 5-Fluorouracil (irreversible, via FdUMP); Methotrexate (indirect — no THF regeneration)

5-FU inactivates the enzyme; methotrexate starves it of cofactor — combined in chemotherapy because they attack the same reaction from two angles.

Condition cards:5-Fluorouracil (5-FU) - thymidylate synthase inhibitor →