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How is cholesterol made from acetate fragments?
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Steroid
Many important physiological functions of vertebrates are controlled by steroid hormones.
The biosynthesis of cholesterol from acetate fragments occurs in four primary stages:1
- Stage 1: Three two-carbon acetate units, in the form of acetyl-CoA, are converted into the six-carbon compound mevalonic acid.12
- Stage 2: Mevalonate undergoes a series of reactions to form the five-carbon molecule isopentenyl pyrophosphate.1
- Stage 3: Six molecules of isopentenyl pyrophosphate condense to form the 30-carbon terpenoid hydrocarbon known as squalene.12
- Stage 4: Squalene is oxidized to squalene 2,3-oxide, which then undergoes cyclization and structural rearrangement to yield lanosterol. Finally, lanosterol undergoes further structural modifications to produce the 27-carbon cholesterol molecule.21
This pathway is highly regulated; when tissue levels of cholesterol or bile acids are elevated, feedback mechanisms suppress the production of mevalonic acid to inhibit further cholesterol synthesis.2