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Types of lipids

Types of lipids. Chemistry 256. Lipids. Basically, any biologically interesting nonpolar molecule Thus they are primarily hydrocarbons, with some (few) functional groups Generally built from small molecules such as acetyl-CoA or isoprene (below).

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Types of lipids

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  1. Types of lipids Chemistry 256

  2. Lipids • Basically, any biologically interesting nonpolar molecule • Thus they are primarily hydrocarbons, with some (few) functional groups • Generally built from small molecules such as acetyl-CoA or isoprene (below)

  3. Fatty acids – generally, even-numbered carbon chains • x:y notation indicates x carbons with y unsaturations • z notation indicates double bond at the z-carbon • -n notation indicates unsaturation at the nth carbon from the methyl end • Double-bond orientations alwayscis (puts 60° kink in chain).

  4. Fatty acid properties • More unsaturation = lower melting point (fewer London interactions to overcome due to the kinks in the chain) • Longer chain = higher melting point (more London interactions to overcome)

  5. Triacylglycerols = triglyceridesmain components of fats (solid) and oils (liquids)

  6. To make a triacylglycerol • Condense three fatty acids (they do not need to be the same fatty acid) onto the alcohol groups of glycerol. • Biodiesel, for instance, has this structure. • Energy storage

  7. Glycerophospholipids = phosphoglycerides, key membrane component X = H (phosphatidic acid), CH3CH2NH3+ (phosphatidyl-ethanolamine), CH3CH2N(CH3)3+ (phosphatidyl-choline)

  8. Polarity in glycerophospholipids • Note the “head” group (i.e., the phospho-X group) is charged, though overall neutral. This lends polarity to an otherwise fairly non-polar molecule

  9. Phospholipases hydrolyze glycerophospholipids, release fatty acids Problem: How does a nonpolar substrate get anywhere near a (polar) enzyme for a reaction to take place?

  10. One strategy that is found with phospholipase A2 is for the phosphate group head to interact deep in the active site, and the hydrophobic tail kept in place by hydrophobic interactions with side chain aromatic groups. (Barden, Darke, Deems and Dennis “Interaction of phospholipase A2 from cobra venom with Cibacron Blue F3GA” (1980) Biochemistry19)

  11. Plasmalogens have an ether linkage. Function of these molecules is not well-understood, though there is some evidence that they react with free radicals that prevents myelinization of nerves (for instance, see Gorgas, Teigler, Komljenovic and Just, “The ether lipid-deficient mouse: tracking down plasmalogen functions” (2006), Biochimica et Biophysica Acta 1763).

  12. Sphingolipids are amino alcohols – note the amide in R2 and vinyl group in R3 • Named in the 1920s, when Egyptology was all the rage (“Sphinx” = mysterious) and these compounds were discovered and their function not known at the time • Now known to have many functions, including nerve cell sheaths (electrical insulation), cell-cell recognition • The sphingomyelin shown is a type of sphingolipid called a ceramide.

  13. Sphingolipids can be quite complex - a ganglioside has an oligosaccharide attached

  14. Steroids – structure unlike the other lipids; basically, four fused rings, roughly planar

  15. Steroid carbon numbering system • The fused ring system is lettered A, B, C, D as shown • Numbering of carbons starts on ring A; C-18 is always a methyl off C-13, C-19 is always a methyl off C-10, and C-20 on up is always off of C-17 • Sterol alcohol is always on C-3

  16. Steroid synthetic history • Adolf Butenandt and G. Hamish (1935) “A method for preparing testosterone from cholesterol” was the first synthesis of a steroid hormone

  17. Steroid functions – mostly a eukaryote thing • Cholesterol changes fluidity of a membrane • Glucocorticoids are stress hormones regulating metabolism • Mineral corticoids regulate excretion by kidneys • Androgens and estrogens regulate sexual development and function

  18. Isoprenoids = terpenoids, contain isoprene units • Functions as diverse as pigments (beta-carotene), vitamins (retinol = vitamin A), pheromones

  19. In fact, when organisms decompose, isoprene and isoprenoid units are some of the most abundant compounds generated (Wallach, 1887). Fossil fuels (petroleum and coal) contain a great number of isoprenoids.

  20. Eicosanoids = icosanoids, which are mostly prostaglandins • Word derived from “eikos” = twenty; these compounds are derived from twenty-carbon fatty acids • “Local” hormones, work at or near site they were made and then are rapidly degraded • Key to inflammation and pain response

  21. The first prostaglandins were discovered by Ulf von Euler (Karolinska Institute, Stockholm) in 1935; he won the Nobel Prize in Medicine in 1970. Prostaglandins work at very low concentrations. fever pain inflammation

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