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.
Cholesterol synthesis
Mevalonate
Made from HMG-CoA (cytosolic) by HMG-CoA reductase ★
HMG-CoA reductase ★ rate-limiting · irreversible — Cholesterol synthesis
Cofactors: 2 NADPH → 2 NADP⁺
Activated by: Insulin; Thyroid hormone; Low sterol → SREBP-2/SCAP to Golgi → ↑ transcription of reductase and LDL receptor
Inhibited by: Statins (competitive); AMPK phosphorylation (low energy); Glucagon, epinephrine, glucocorticoids; High sterol → INSIG retains SREBP-2 in ER and tags reductase for degradation
The PFK-1 of cholesterol synthesis. Statins lower intracellular cholesterol → SREBP-2 → more LDL receptors — that is the actual LDL-lowering mechanism.
Condition cards:Statins (HMG-CoA reductase inhibition) →
Becomes Isoprenoid units (IPP) via Mevalonate kinases / decarboxylase
Mevalonate kinases / decarboxylase — Cholesterol synthesis
Cofactors: 3 ATP
Isopentenyl pyrophosphate — also the source of dolichol, ubiquinone (CoQ) and prenyl groups (why statins can cause myopathy).