Topic overview

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Cholesterol has a rigid four-ring steroid nucleus, a hydrocarbon side chain, and a single hydroxyl group. Cells synthesize it through a pathway in which HMG-CoA reductase converts HMG-CoA to mevalonate; this rate-limiting step is subject to metabolic and cholesterol feedback regulation. In blood, lipoproteins carry cholesterol between tissues, while LDL receptors mediate cellular uptake and excess intracellular cholesterol affects synthesis, uptake, and storage. Cholesterol also contributes to membrane fluidity and serves as a precursor for bile acids, steroid hormones, and vitamin D3. The liver converts it to primary bile acids, and biliary excretion provides its route of elimination. Elevated LDL cholesterol is associated with accelerated atherosclerosis, and the lesson introduces related genetic causes and medication approaches.