Sterols structure-function

In general, the sterols perform a structural function, for example as components of the lipid layers of membranes. The Cis, C19 and C21 steroids mainly perform an endocrine function. In other words they are hormones. The bile salts (C24-steroids) fulfil a functional role in digestion in animals. 

Practically all plant steroid molecules are sterols. The function of plant sterols is still relatively unclear. They undoubtedly play an important role in membrane structure and function. Certain sterol derivatives, such as the cardiac glycosides, are known to protect plants that produce them from predators. Most plant sterols... 

One should expect sterols to function similarly In nematodes and other animals consequently, sterols should be Integral structural... 

William R. Nes was the first to propose that bacteria could have sterol-llke pentacycllc molecules [20]. Some years later these were found to be hopanolds by Ourlsson, Rohmer and Albrecht [21,22]. Hopanolds comprise a group of pentacycllc trlterpenolds for which some structures are shown In Fig. 2. Hopanolds are rigid, flat, amphlpathlc molecules with geometric dimensions similar to sterols. Their main structural differences are 1. The cyclic system contains 5 rings. As a consequence, the side chain is shorter. 2. The hydrophilic part Is the side chain, not the nucleus. 3. The side chain can be extended and further hydroxyl functions or other groups Introduced [23]. By mainly structural arguments. It was surmised by Ourlsson and Coworkers that hopanolds have a sterol-llke function [21]. 

Structure-Function Relati[Pg.252]

Phospholipids are essential components of membranes where they share a structural function with sterols. Phospholipids can be used to indicate freshly biosynthesized material [36] and individual ones may be used to distinguish... 

Sterols are also potentially excellent biomarker compounds due to their stability and the diversity of their structures. They are present in all eukaryotes, and in marine material such as sediments, detection of 25 sterols or more is common. They share with phospholipids a structural function in membranes where, because of their unique hydrophobic and steric properties, they act as specific internal regulators of membrane fluidity and influence various membrane functions and membrane associated enzymes [72]. 

Bloch, K., Sterol structure and membrane function, Curr. Top. Cell. Regul., 18, 289—299, 1981. 

Poly(c -l,4-isoprene) belongs to the family of polyisoprenoids, which are the most structurally diverse and abundant natural products known, with more than 23,000 primary and secondary metabolites. This huge family comprises, for example, sterols which display not only structural functions (control of biological membrane fluidity) but also hormonal functions (steroid hormones). Key phyto-hormones, such as abscisic acid, gibberellins and cytokinins, are isoprenoids too. Moreover, isoprenoids are used in protein prenylation, which is a key step in the activation and the localization of metabolic enzymes in many organisms. The first common step of all isoprenoid biosynthesis pathways is the formation of isopentenyl diphosphate (IPP). ... 

Sterol Structure and Membrane Function Konrad Bloch... 

Nes W D, Heupel R C, Le P H 1974 A comparison of sterol biosynthesis in fungi and tracheophytes and its phylogenetic and functional implications. In Siegenthaler P A, Eichenberger W (eds) Structure, function, and metabolism of plant lipids. Elsevier Amsterdam, 207-216... 

Recent mechanism studies involving incubations with stable isotopes (66,69,70) and studies by us on conformiational analysis (38-42), distribution (7), structure-function/metabolism relationships (54, 55) and mechanistic enzymology of sterol transformation (12,56), negate the otherwise attractive explanation hypothesized by Ourisson et al, (9,10) for evolution of the sterol pathway beginning with the cycloartenol-based pathway. The new data indicate that the lanosterol-based pathway may have evolved before cycloartenol-based pathway, the squalene-oxide cyclase and... 

Weete JD (1989) Structure and function of sterols in fungi. Adv Lipid Res 23 115 Morrissey JP, Osbourn AE (1999) Fungal resistance to plant antibiotics as a mechanism of pathogenesis. Microbiol Mol Biol Rev 63 708... 

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