Dr. Arrel Toews (say Tavz, like “waves”) 420 ME Jones Building atoews@med.unc - PowerPoint PPT Presentation

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Dr. Arrel Toews (say Tavz, like “waves”) 420 ME Jones Building atoews@med.unc

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  1. Dr. Arrel Toews (say Tavz, like “waves”) 420 ME Jones Building atoews@med.unc.edu 843-8727 Get UP To Speed (GUTS) Session on Lipids A primer on lipid structure, nomenclature, and function See also the GUTS session on Lipids notes (.doc) - self-assessment exam - additional lipid information

  2. Lipids Definition:biomolecules that are overall hydrophobic - very non-polar - insoluble in water/aqueous solutions (cellular environment) - soluble in “organic” (non-polar) solvents (CHCl3-MeOH) - operational rather than structural definition (water-fearing) - contrast this with definitions for: proteins nucleic acids carbohydrates

  3. Lipid Functions -energy source (dietary triglycerides)-energy stores (adipose tissue triglycerides) - triglycerides are completely hydrophobic highly reduced (energy-rich) compact, efficient energy storage -membranes – amphipathic lipids (both hydrophobic and hydrophilic portions) - phospholipids - sphingolipids - cholesterol -signaling molecules2nd messenger systems; eicosanoids; steroid hormones - fat-soluble vitamins: A (vision), D (bones/teeth), E (anti-oxidant; live forever), K (blood clotting) Fatty acids are basic building block of most lipids

  4. OllCH3CH2CH2CH2CH2CH2CH2CH2CH2CH2CH2CH2CH2CH2CH2CH2CH2C-O- * OllC-O- * Stearic acid CH3(CH2)16COOH Systematic: octadecanoic acid Shorthand: 18:0 (18C, no double bonds) Structure and nomenclature of fatty acids Long-chain carboxylic acids; building blocks of most lipids H H H H H H H H H H H H H H H H H Ol l l l l l l l l l l l l l l l l llH―C―C―C―C―C―C―C―C―C―C―C―C―C―C―C―C―C―C-O-l l l l l l l l l l l l l l l l lH H H H H H H H H H H H H H H H H * *All fatty acids ionized at physiological pH; pKa <5

  5. This is shorthand for a fatty acid with 18 carbons and 2 double bonds. The 6 indicates the double bond closest to the methyl end is 6 carbons from the  end. Structure and nomenclature of fatty acids Linoleic acid CH3(CH2)4CH=CHCH2CH=CH(CH2)7COOH Systematic: cis, cis 9,12-octadecadienoic acid Shorthand: 18:26 If more than one double bond, the configuration is always “methylene-interrupted” (-CH=CH-CH2-CH=CH-) with cisdouble bonds. Always 3C between C=C bonds So - the term18:26 completely defines the formula and structure of linoleic acid

  6. “biochemists”    no matter how long 3 2 1 “systematic” Trythisathome:writeshorthandnamesfortheFAbelow CH3(CH2)14COOHCH3(CH2)5CH=CH(CH2)7COOHCH3CH2CH=CHCH2CH=CHCH2CH=CH(CH2)7COOHCH3(CH2)4CH=CHCH2CH=CHCH2CH=CHCH2CH=CH(CH2)3COOHCH3(CH2)CH=CHCH2CH=CHCH2CH=CHCH2CH=CHCH2CH=CHCH2CH=CH(CH2)2COOH Write the chemical formulas for 18:19 and 20:53 Structure and nomenclature of fatty acids OllCH3―(CH2)n―CH2―CH―C-O- generic fatty acid 18orwhatever -designation important in nomenclature“-oxidation” of fatty acids

  7. H H H H C C COOH COOH C C cis-fatty acid H H HC HC 3 3 C C HC HC 3 3 C C COOH COOH trans - fatty acid H H HC HC 3 3 COOH COOH saturated fatty acid Fatty Acids: long-chain carboxylic acids Oll*really C―O- usually attached to glycerol as PL or TG Virtually all natural C=Cdouble bonds are cis “kinks”–less packing –morefluidGOODformembranes trans-FAareBAD!–nokinks,packtightly;LDL; HDL (partially hydrogenated vegetable oils, Crisco, margarine)

  8. Physiological functions of lipids–a problem hydrophobicity (long chain length) and fluidity (liquid at body temperature) both vitalrequired biophysical properties - cell membranes - storage depots of energy (adipose tissue) But melting point increases with chain length So FA long enough to be hydrophobic are solids!(mp is above body temp) How does Mother Nature handle this??

  9. 18Cfatty acids Stearic acid(18:0) Oleic acid(18:1) Linoleic acid(18:2) 18:4-57C — Linolenic acid(18:3) Melting points of fatty acids 90 80 70 Saturated fatty acids 60 50 Body temperature 40 Melting temperature (°C) 30 20 10 0 -10 -20 2 4 6 8 10 12 14 16 18 20 22 24 Number of carbon atoms

  10. Physiological functions of lipids The fatty acid composition of membrane lipids and adipose tissue triglycerides - chain length - degree of unsaturationis carefully regulated to maintain the appropriate fluidity

  11. fatty acid fatty acid glycerol fatty acid Most of the fatty acid in the body is esterified – much of it as triglyceride (mostly in adipose tissue) – also lots in phospholipids (major components of membranes) Fatty acid composition is regulated to maintain correct fluidity (both TG and PL) - critical to biological function OllCH2OC OllCHOC Triglycerideenergy sourcestorage form OllCH2OC

  12. polar head long hydrophobic tail e.g.,choline+ Phospholipids – vital components of membranes • glycerol backbone (like TG)- 2 FA in ester linkages- phosphate + X (choline, ethanolamine, serine, inositol) • amphipathic(amphi = both) F A T T Y A C I D GLYCEROL F A T T Y A C I D Remember kinks in cis-double bonds of unsat’d FA P THE defining components of biological membranes - make lipid bilayers (2 molecules thick)

  13. glycerol phosphate Choline(polar “X”) Phosphatidylcholine (PC) aka lecithina prominent phospholipidmajor membrane componentinvolved in cholesterol handling too 2 long-chain fatty acids FA heterogeneity means many molecular species of PC

  14. O O O ll ll ll fatty acid fatty acid fatty acid fatty acid - - - - - - CH CH CH O O O C C C 2 2 2 - - - - - - CH CH CH O O O C C C O O O fatty acid fatty acid fatty acid fatty acid ll ll ll ll ll ll + + + O O O - - - - - - - - - - - - HN HN HN - - - CH CH CH - - - CH CH CH O O O P P P O O O CH CH CH 3 3 3 2 2 2 2 2 2 2 2 2 l l l O O O - - - Phosphatidylethanolamine (PE) ethanolamine ethanolamine membranes 2nd messengersignalingsystems

  15. long hydrophobic tail polar head Sphingolipids Structures and properties are generally similar to phospholipids (amphipathic) Phospholipids sugar(s) O Long-chain amino alcohol (sphingosine) Glycosphingolipids (usually) F A T T Y A C I D (more on these in“Complex CH2O”GUTS session)

  16. water water water Lipid bilayer water water water Micelle Hydrophobic tails hide from water Amphipathic nature of PL and sphingolipids is vitalto life; makes membranes Polarhead Hydro-phobictail Phospholipidor glycolipid Lots more on this in Dr. Jacobson’s Membranes GUTS lecture

  17. polar - “a little bit” amphipathic Cholesterol - rigid ring structure - membrane component (affects fluidity) - lipid transport in blood (atherosclerosis, &c)

  18. Vocabulary – do you know the meaning of the following terms? lipidhydrophobic vs hydrophilicamphipathicfatty acid saturated vs unsaturated FA cis vs trans C=C double bondsshorthand nomenclature for FAtriglyceride (and mono- and diglyceride)phospholipidsphingolipidcholesterol