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.
PDH & TCA cycle · Mitochondrial matrix. 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.
Zoom
PDH & TCA cycle
Fumarate
Made from Succinate by Succinate dehydrogenase (Complex II)
Succinate dehydrogenase (Complex II) — PDH & TCA cycle
Cofactors: FAD → FADH₂
Inhibited by: Malonate (competitive)
Sits in the inner membrane — it is Complex II of the ETC, so its FADH₂ feeds CoQ directly (only 1.5 ATP).
Becomes Malate via Fumarase
Fumarase — PDH & TCA cycle
Fumarate also arrives from the urea cycle (argininosuccinate lyase) — the link between the two cycles.