This is a common structural motif in biological systems. The terpenes (for example, the carotenes are tetraterpenes) are derived from isoprene, as is Coenzyme Q. Also derived from isoprene are phytol, retinol (vitamin A) , tocopherol (vitamin E), dolichols, 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 terpenes and lanosterol derivatives.