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

Purine synthesis & salvage · Cytosol — de novo mainly liver; salvage matters most in brain, marrow and RBCs. Enzymes sit beside the arrows; a ★ marks the rate-limiting step. The map scrolls inside its panel.

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Purine synthesis & salvage

PRPP

Made from Ribose-5-phosphate (HMP shunt) by PRPP synthetase

PRPP synthetase — Purine synthesis & salvage

Cofactors: ATP → AMP

Deficiency: PRPP synthetase superactivity (gain of function) — primary hyperuricemia and gout from purine overproduction

Shared by purine synthesis, pyrimidine synthesis AND purine salvage. Gain-of-function → more PRPP → more purine flux.

Condition cards:PRPP synthetase superactivity (primary hyperuricemia from overproduction) →

Becomes 5-Phosphoribosylamine via Glutamine:PRPP amidotransferase (GPAT) ★

Glutamine:PRPP amidotransferase (GPAT) ★ rate-limiting · irreversible — Purine synthesis & salvage

Cofactors: Glutamine → glutamate

Activated by: PRPP (substrate availability)

Inhibited by: AMP; GMP (end-product feedback)

The committed step of purine biosynthesis. Three layers of control: PRPP supply, end-product inhibition here, branch-specific feedback below.

Condition cards:6-Mercaptopurine (6-MP) →