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.
Lipolysis, carnitine shuttle & β-oxidation
Acylcarnitine
Made from Fatty acyl-CoA (cytosol) by Carnitine palmitoyltransferase I (CPT I, outer membrane) ★
Carnitine palmitoyltransferase I (CPT I, outer membrane) ★ rate-limiting — Lipolysis, carnitine shuttle & β-oxidation
Cofactors: Carnitine
Inhibited by: Malonyl-CoA
Deficiency: CPT I deficiency (liver isoform) — fasting hypoketotic hypoglycemia, hepatomegaly, LOW acylcarnitines; muscle spared
Rate-limiting step of β-oxidation. Fed state: ↑malonyl-CoA → CPT I off. Fasting: ↓malonyl-CoA → fatty acids enter. Medium/short-chain fatty acids skip the shuttle.
Condition cards:CPT I deficiency →
Becomes Fatty acyl-CoA (matrix) via Carnitine-acylcarnitine translocase → CPT II (inner membrane)
Carnitine-acylcarnitine translocase → CPT II (inner membrane) — Lipolysis, carnitine shuttle & β-oxidation
Cofactors: Carnitine regenerated
Deficiency: CPT II deficiency (muscle isoform, adult) — exercise/fasting/cold-induced myalgia, rhabdomyolysis, myoglobinuria, ↑CK, long-chain acylcarnitines high; infantile form has cardiomyopathy
CPT II regenerates acyl-CoA inside the matrix.
Condition cards:CPT II deficiency →