The Third Stage of Synthesis

Formation of Squalene

Squalene is formed by the condensation of 6 activated isoprene units

1. Head to tail condensation of Isopentyl pyrophosphate and Dimethylallyl pyrophosphate. A 10 carbon chain is formed. Elimination of 1 pyrophosphate.Geranyl pyrophosphate
2. Head to tail condensation of geranyl pyrophosphate with isopentenyl pyrophosphate gives a 15 carbon intermediate. Farnesyl pyrophosphate
3. Head to head joining of two molecules of Farnesyl pyrophosphate and elimination of 2 pyrophosphate groups gives a 30 carbon chain. Squalene.

Squalene

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Synthesis of Cholesterol

Second Stage of Synthesis

Fourth Stage of Synthesis