Lipids isoprenoid structure

The most interesting new polyterpenoids are a series of C40 diols that form part of macrocyclic diglycerol tetraethers which constitute the major membrane lipids of the extremely thermo- and acido-philic bacterium Caldariella. These compounds, (196)—(200), which may be acyclic or may have from one to four isolated cyclopentane rings are formally dimers of C20 isoprenoid structures linked head-to-head rather than the conventional tail-to-tail linkage in, for example, carotenoids.The isoprenoid nature of these compounds has been shown by labelling. 

The chloracetamides and the thiocarbamates (chemical structure see Fig. 2) might also interfere with the metabolism of CoA. FLIrst (1987) proposed that the broad spectrum of effects such as inhibition of lipid, isoprenoid and flavonoid biosynthesis is caused by disrupting processes requiring CoA. 

The hydrophobic components of many lipids consist of either isoprenoids or fatty acids and their derivatives 34 Isoprenoids have the unit structure of a five-carbon branched chain 34 Brain fatty acids are long-chain carboxylic acids that may contain one or more double bonds 34... 

The three major classes of biopolymers found in eukaryotic systems are nucleic acids, proteins, and polysaccharides. The latter class is the most complex with respect to structural and stereochemical diversity. Polysaccharides indeed possess a massive information content. Furthermore, polysaccharides are commonly found in nature covalently attached (conjugated) to other biomolecules such as proteins, isoprenoids, fatty acids, and lipids.1... 

Carotenoids are lipid-soluble terpenoids derived from the isoprenoid pathway and are located in hydrophobic areas of cells. All have a 40-carbon isoprene backbone with a variety of ring structures at one or both ends (Fig. 8.2) [25]. The carbon skeleton is derived from five-carbon isoprenoid groups and contains alternating conjugated double bonds. There are two kinds of carotenoids (Fig. 8.2) carotenes composed of carbon and hydrogen and xanthophylls composed of carbon, hydrogen, and oxygen. 

One of the most impressive findings has been the discovery of lipid intermediates in the biosynthesis of polysaccharides (see Refs. 2 and 465.) At least two structurally different types of these compounds exist the intermediate may be an isoprenoid alcohol ester of the glycosyl pyrophosphate or the analogous derivative of the glycosyl phosphate. Derivatives of the first type are formed by reaction between the sugar nucleotide and the alcohol phosphate, for example, undecaprenyl phosphate (120), which participates in the biosynthesis of Salmonella lipopolysaccharide.466... 

The resin fractions of organic sulfur-rich bitumens are for a substantial part composed of monomers with linear, isoprenoid, steroid, hopanoid and carotenoid carbon skeletons connected to each other by (poly)sulfide linkages. These structural units may contain additional intramolecular sulfur linkages. This sulfur-rich geopolymer is also formed by sulfur incorporation into functionalised lipids in an intermolecular fashion during early diagenesis. 

Lipids are a complex group of substances, which include the long-chain fatty acids and their derivatives, sterols and steroids, carotenoids, and other related isoprenoids. It is evident that the term lipid denotes a wide range of compounds that appear to have little obvious interrelation. However, although these compounds possess widely different structures, they are derived in part from similar biological precursors and exhibit similar physical and chemical characteristics. Furthermore, most lipids occur naturally in close association with protein, either in membranes as insoluble lipid-protein complexes or as soluble lipoproteins of the plasma. 

Methanogen lipids have been intensively studied and characterized due to their structures being one of the most remarkable features that distinguish the Archaea from all other organisms (Woese et al., 1990). The polar lipids of methanogens comprise both di- and tetra-ethers of glycerol and isoprenoid alcohols with most compounds being based on the core lipids archaeol (12) or caldarchaeol (13). Minor core lipids are sn-2- and i -3-hydroxyarchaeol and macrocyclic... 

The fat-soluble vitamins share many properties despite their limited chemical similarity. They are absorbed into the intestinal lymphatics, along with other dietary lipids, after emulsification by bile salts. Lipid malabsorption accompanied by steatorrhea usually results in poor uptake of all the fat-soluble vitamins. Deficiency disease (except in the case of vitamin K) is difficult to produce in adults because large amounts of most fat-soluble vitamins are stored in the liver and in adipose tissue. The fat-soluble vitamins are assembled from isoprenoid units this fact is apparent from examination of the structures of vitamins A, E, and K cholesterol, the precursor of vitamin D, is derived from six isoprenoid units (Chapter 18). Specific biochemical functions for vitamins A, D, and K are known, but a role for vitamin E, other than as a relatively nonspecific antioxidant, remains elusive. 

It is unknown how the fatty chain carbonic acids of the lipids originally formed. It is noteworthy that fatty acids with up to six and seven C-atoms were detectable in the Murchison meteorite. Thus, it might be possible that membranes that were even more primitive existed in the past. However, dicarboxylic acids of chain lengths up to 17 were detectable after hydrothermal treatment. It is also remarkable that isoprenoid derivatives - more precisely, phytanyl and biphytanyl, that is CIO and C20 chains - linked to each other by monoether or diether bridges are part of membranes of the Archaea (Fig. 6.2, bottom structure). 

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