1028 CHAPTER TWENTY-SIX Lipids PROBLEM 26.7 Locate the isoprene units in each of the monoterpenes, sesquiterpenes, and diterpenes shown in Figure 26.6. (In some cases there are two equally correct arrangements. Tail-to-tail linkages of isoprene units sometimes occur, especially in the higher ter- penes. The C(12)-C(13) bond of squalene unites two Cis units in a tail-to-tail manner. Notice, however, that isoprene units are joined head to tail within each Cis unit of squa Isoprene units in squalene PROBLEM 26.8 Identify the isoprene units in B-carotene(see Figure 26.6) Which carbons are joined by a tail-to-tail link between isoprene units? The German chemist Otto Wallach(Nobel Prize in chemistry, 1910) established the structures of and is credited wit viewed as collections of isoprene units. Leopold Ruzicka of the Swiss Federal Institute of Technology(Zurich), in his studies of sesquiterpenes and higher terpenes, extended and refined what we now know as the isoprene rule. He was a corecipient of the Nobel Prize in chemistry in 1939. Although exceptions to it are known, the isoprene rule is a useful guide to terpene structures and has stimulated research in the biosynthetic origin of these compounds. It is a curious fact that terpenes contain isoprene units but isoprene does not occur naturally. What is the biological isoprene unit, how is it biosynthesized and how do individual isoprene units combine to give terpenes? 26. 8 ISOPENTENYL PYROPHOSPHATE: THE BIOLOGICAL ISOPRENE UNIT Isoprenoid compounds are biosynthesized from acetate by a process that involves sev The first stage is the formation of mevalonic acid from three molecules of 3CH COH -PS> HOCCh.OH In the second stage, mevalonic acid is converted to 3-Imethyl-3-butenyl pyrophosphate CH Oo symbol -oPP to represent HOCCH,CCH,,OH ->CH-CCHCHOPOPOH OPP Mevalonic acid Isopentenyl pyrophosphate Back Forward Main MenuToc Study Guide ToC Student o MHHE Website1028 CHAPTER TWENTY-SIX Lipids PROBLEM 26.7 Locate the isoprene units in each of the monoterpenes, sesquiterpenes, and diterpenes shown in Figure 26.6. (In some cases there are two equally correct arrangements.) Tail-to-tail linkages of isoprene units sometimes occur, especially in the higher ter￾penes. The C(12)±C(13) bond of squalene unites two C15 units in a tail-to-tail manner. Notice, however, that isoprene units are joined head to tail within each C15 unit of squa￾lene. PROBLEM 26.8 Identify the isoprene units in -carotene (see Figure 26.6). Which carbons are joined by a tail-to-tail link between isoprene units? The German chemist Otto Wallach (Nobel Prize in chemistry, 1910) established the structures of many monoterpenes and is credited with recognizing that they can be viewed as collections of isoprene units. Leopold Ruzicka of the Swiss Federal Institute of Technology (Zürich), in his studies of sesquiterpenes and higher terpenes, extended and refined what we now know as the isoprene rule. He was a corecipient of the Nobel Prize in chemistry in 1939. Although exceptions to it are known, the isoprene rule is a useful guide to terpene structures and has stimulated research in the biosynthetic origin of these compounds. It is a curious fact that terpenes contain isoprene units but isoprene does not occur naturally. What is the biological isoprene unit, how is it biosynthesized, and how do individual isoprene units combine to give terpenes? 26.8 ISOPENTENYL PYROPHOSPHATE: THE BIOLOGICAL ISOPRENE UNIT Isoprenoid compounds are biosynthesized from acetate by a process that involves sev￾eral stages. The first stage is the formation of mevalonic acid from three molecules of acetic acid: In the second stage, mevalonic acid is converted to 3-methyl-3-butenyl pyrophosphate (isopentenyl pyrophosphate): O CH3 OH HOCCH2CCH2CH2OH Mevalonic acid several steps Isopentenyl pyrophosphate CH2 CCH2CH2OPOPOH OH O HO CH3 O OPP O 3CH3COH Acetic acid O CH3 OH HOCCH2CCH2CH2OH Mevalonic acid several steps tail tail 12 13 Isoprene units in squalene It is convenient to use the symbol ±OPP to represent the pyrophosphate group. Back Forward Main Menu TOC Study Guide TOC Student OLC MHHE Website