About the National Institute on Drug Abuse (NIDA): The National Institute on Drug Abuse (NIDA) is a component of the National Institutes of Health, . Department of Health and Human Services. NIDA supports most of the world’s research on the health aspects of drug use and addiction. The Institute carries out a large variety of programs to inform policy, improve practice, and advance addiction science. Fact sheets on the health effects of drugs and information on NIDA research and other activities can be found at , which is now compatible with your smartphone, iPad or tablet. To order publications in English or Spanish, call NIDA’s DrugPubs research dissemination center at 1-877-NIDA-NIH or 240-645-0228 (TDD) or email requests to drugpubs@ . Online ordering is available at . NIDA’s media guide can be found at /publications/media-guide/dear-journalist , and its easy-to-read website can be found at . You can follow NIDA on Twitter and Facebook .
As indicated in the Figure above showing the pathway of cholesterol biosynthesis a molecule of geranylpyrophosphate (GPP) and a molecule of isopentenylpyrophosphate (IPP) are condensed into farnesylpyrophosphate (FPP) through the action of the farnesyl diphosphate synthase enzyme which is encoded by the FDPS gene. Through the action of the ER-localized enzyme, dehydrodolichyl diphosphate synthase (encoded by the DHDDS gene), farnesylpyrophosphate is elongated via the sequential head-to-tail addition of multiple isopentenylpyrophosphate groups in a reaction referred to as cis -prenylation. The number of IPP substrates added ultimately determines the overall number of isoprene units in dolichol which in humans ranges from 17 to 21. The DHDDS gene is located on chromosome and is composed of 10 exons that generate five alternatively spliced mRNAs each of which encode a distince protein isoform. The product(s) of the DHDDS reaction is referred to as a polyprenolpyrophosphate. The pyrophosphate is removed by an as yet uncharacterized enzyme activity that may be either a polyprenol pyrophosphate phosphatase or a polyprenol phosphatase resulting in the formation of a polyprenol.