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.
Sphingolipid degradation & the sphingolipidoses
Lactosylceramide (Glc-Gal-ceramide)
Made from GM2 ganglioside (globoside + NANA) by Hexosaminidase A
Hexosaminidase A · irreversible — Sphingolipid degradation & the sphingolipidoses
Deficiency: Tay-Sachs disease (AR, HEXA) — GM2 ganglioside accumulates in neurons: developmental regression, blindness, CHERRY-RED MACULA, exaggerated startle. No hepatosplenomegaly (the discriminator from Niemann-Pick)
Removes the terminal N-acetylgalactosamine (GM2 → GM3); a neuraminidase then removes NANA to give lactosylceramide. The lecture and the board compress these two steps into one arrow.
Condition cards:Tay-Sachs disease →
Made from Globoside / ceramide trihexoside (Gb3) by α-Galactosidase A
α-Galactosidase A · irreversible — Sphingolipid degradation & the sphingolipidoses
Deficiency: Fabry disease (X-LINKED, GLA) — globosides/ceramide trihexoside accumulate: angiokeratomas, burning neuropathic pain in hands and feet, hypohidrosis, corneal whorls, progressive kidney failure and cardiomyopathy
Removes the terminal galactose from globotriaosylceramide (Gb3). The only X-linked sphingolipidosis.
Condition cards:Fabry disease →
Becomes Glucocerebroside (Glc + ceramide) via β-Galactosidase
β-Galactosidase — Sphingolipid degradation & the sphingolipidoses
The convergence point: both the ganglioside arm (Tay-Sachs enzyme above it) and the globoside arm (Fabry enzyme above it) come through here on the way down to ceramide.