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

Catecholamines, serotonin & the tyrosine tree · CNS and sympathetic ganglia (dopamine, NE); adrenal medulla only for epinephrine; melanocytes for melanin; liver for the degradation arm; serotonin in CNS raphe nuclei, gut enterochromaffin cells and platelets, with melatonin made from it in the pineal. Enzymes sit beside the arrows, ★ = rate-limiting, ⊕/⊖ = activators/inhibitors (toggle), −ATP +NADH = what the step spends and makes (toggle ⚡), dashed = allosteric signal, shaded bands = compartment. Drag to pan.

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Catecholamines, serotonin & the tyrosine tree

Maleylacetoacetate

Made from Homogentisic acid by Homogentisate oxidase (homogentisate 1,2-dioxygenase)

Homogentisate oxidase (homogentisate 1,2-dioxygenase) — Catecholamines, serotonin & the tyrosine tree

Cofactors: O₂, Fe²⁺

Deficiency: ALKAPTONURIA — homogentisic acid accumulates; urine darkens on standing, and over DECADES the pigment deposits in cartilage and connective tissue (ochronosis) causing arthritis that shows up around age 40. Blocked far downstream, so the damage is slow and mechanical — contrast PKU, blocked at the top, which harms the developing brain early

Ring-opening. The product is MALEYLacetoacetate — the cis isomer — not fumarylacetoacetate; that takes one more step (slides 5 and 10).

Condition cards:Alkaptonuria →

Becomes Fumarylacetoacetate via Maleylacetoacetate isomerase

Maleylacetoacetate isomerase — Catecholamines, serotonin & the tyrosine tree

Cofactors: Glutathione (GSH)

A cis → trans isomerisation, nothing more — the double bond flips so the next enzyme can hydrolyse it. No named disease sits here, which is exactly why it gets skipped in summaries; the deck still draws it (slides 5 and 10) and the two names are worth keeping straight.