Editing Isoprene (section)

===Isoprenoids===
The isoprene skeleton can be found in naturally occurring compounds called [[terpenes]] and [[terpenoid]] (oxygenated terpenes), collectively called isoprenoids. These compounds do not arise from isoprene itself. Instead, the precursor to isoprene units in biological systems is [[dimethylallyl pyrophosphate]] (DMAPP) and its isomer [[isopentenyl pyrophosphate]] (IPP). The plural 'isoprenes' is sometimes used to refer to [[terpene]]s in general.

Examples of isoprenoids include [[carotene]], [[phytol]], [[retinol]] ([[vitamin A]]), [[tocopherol]] ([[vitamin E]]), [[dolichol]]s, and [[squalene]]. [[Heme]] A has an isoprenoid tail, and [[lanosterol]], the sterol precursor in animals, is derived from squalene and hence from isoprene. The functional isoprene units in biological systems are [[dimethylallyl pyrophosphate]] (DMAPP) and its isomer [[isopentenyl pyrophosphate]] (IPP), which are used in the biosynthesis of naturally occurring isoprenoids such as [[carotenoid]]s, [[quinone]]s, lanosterol derivatives (e.g. steroids) and the [[prenyl]] chains of certain compounds (e.g. phytol chain of chlorophyll). Isoprenes are used in the cell membrane monolayer of many [[Archaea]], filling the space between the diglycerol tetraether head groups. This is thought to add structural resistance to harsh environments in which many Archaea are found.

Similarly, [[natural rubber]] is composed of linear [[polyisoprene]] chains of very high [[molecular weight]] and other natural molecules.<ref name=Ullmann>{{Cite book |doi=10.1002/14356007.a23_225 |chapter=Rubber, 2. Natural |title=Ullmann's Encyclopedia of Industrial Chemistry |year=2000 | vauthors = Greve HH |isbn=978-3527306732 }}</ref>

[[Image:Sterol synthesis.svg|thumb|left|350px|Simplified version of the steroid synthesis pathway with the intermediates [[isopentenyl pyrophosphate]] (IPP), [[dimethylallyl pyrophosphate]] (DMAPP), [[geranyl pyrophosphate]] (GPP) and squalene shown. Some intermediates are omitted.]]
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