A well known example of sterol is cholesterol, but there are over a hundred identified almost exclusively in animals, plants and fungi. Cholesterol synthesis occurs mainly towards the-hydroxymethyl-coenzyme A reductase (HMG-CoA reductase). This pathway allows the synthesis of squalene and lanosterol which derive many other sterols. Squalene is a lipid isoprenoid class of Prenol. The synthetic pathways of sterols and Prenol are partly common.

In fact, it seems that the metabolic pathways of synthesis of sterols are present in eukaryotes. However, it has been shown that the proteobacterium Methylococcus capsulatus and Planctomycetes Gemmata obscuriglobus possessed enzymes homologous to the monoxygénase squalene and oxidosqualene cyclase, two enzymes required for the initial synthesis of sterols from squalene. Moreover, the presence of lanosterol has been demonstrated in bacteria Methylococcus capsulatus and Methylosphaera hansoni. This could be explained by lateral gene transfer between an ancestor of these bacteria and eukaryotic cells or a phenomenon of endosymbiosis.

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