Biomolecules Survey Part 2: Lipids Lecture Supplement page 228 Myricyl cerotate Present in beeswax,...

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Transcript of Biomolecules Survey Part 2: Lipids Lecture Supplement page 228 Myricyl cerotate Present in beeswax,...

  • Biomolecules Survey Part 2: LipidsLecture Supplement page 228

  • Nonpolar: Hydrophobic (water hating) or lipophilic (fat loving)Polar: Hydrophilic (water loving) or lipophobic (fat hating)Found mostly in fatty tissues, membranes, and other nonpolar biological structuresLipidsDefinitionsExample: A phospholipidLipid solubility properties due to large nonpolar regions

  • LipidsEight General CategoriesFatty acidsWaxesTriacylglyceridesPhospholipidsSteroidsProstaglandinsLipophilic vitaminsTerpenesProduced mostly by plantsNot discussed in Chem 14C

  • Fatty AcidsFatty acid: Carboxylic acid with long unbranched hydrocarbon chainSaturated fatty acidsLauric acid (12 C)Myristic acid (14 C)Palmitic acid (16 C)Stearic acid (18 C)Arachidic acid (20 C)Most have even number of carbons: Two carbons added at a time during biosynthesis12-20 carbons most commonMost biologically-important fatty acids have 18 carbons: Stearic, oleic, and linoleic acidsMain biological function: Precursor to other lipidsCategorized by C=C in chain: Saturated (no C=C) or unsaturated (one or more C=C)

  • Fatty AcidsMonounsaturated: Contains one C=CPolyunsaturated: Contains more than one C=CCis C=C much more common than trans C=CUnsaturated fatty acidsSome important unsaturated fatty acids

  • WaxesMost natural waxes are esters derived from a fatty acid and a long-chain alcoholExample:Main biological function of waxes: Water barrier

  • TriacylglycerolsTriacylglycerol (triacylglyceride): Fatty acid triester of glycerol (glycerin)Triacylglycerol = fat if solid at room temperature; oil if liquidThe most abundant of the natural lipidsMain biological function: Energy storageHydrolysis (water breaking) of animal fats yields soap

  • TriacylglycerolsHow Does Soap Work?

    Hydrophilic CO2- groups attracted to d+ H-O-H d+Nonpolar (hydrophobic) hydrocarbon chains avoid waterNonpolar (lipophilic) hydrocarbon chains attracted to nonpolar dirt, other fatty acid chainsForms micelles (~spherical aggregates); suspends dirt in waterMicelles carry dirt away when wash water is removed

  • TriacylglycerolsSoapsHard water: Contains high levels of Fe3+, Mg2+, Ca2+Fatty acid salts of Fe3+, Mg2+, Ca2+ have low water solubilityResults in precipitates: Dull clothes, bathtub ringSolution: Synthetic soapsGood water solubility of Fe3+, Mg2+, Ca2+ sulfonatesAvoids dependency on animal fats (expensive; uncertain supply)Soap problems and solutions

  • Phosphate esterFatty acid estersPhospholipidsPhospholipid: Glycerol esterified with two fatty acids and one phosphate groupPhospholipid fatty acids usually palmitic acid, stearic acid, and/or oleic acidSecond most abundant group of natural lipidsMain biological function: Cell membranes (phospholipid bilayer)Generic phospholipid structureHydrophobic effect: Hydrophobic tails avoid water

  • Mayonaisse Oil and VinegarAn example of a phosphatidylcholine, a type of phospholipid in lecithin. Red - choline and phosphate groupBlack glycerolGreen - unsaturated fatty acid; Blue - saturated fatty acidOilVinegar or Lemon JuiceEgg!!!


  • ProstaglandinsProstaglandin: Molecule having the prostanoic acid skeletonNomenclature: Based on stereochemistry, number of OH, C=C, C=O groupsBiological functions: Mostly as regulators and signal molecules- cause constriction or dilatation in vascular and other smooth muscle cells- regulate aggregation and disaggregation of platelets- sensitize spinal neurons to pain- regulate inflammatory mediation, calcium movement, hormones- control cell growth

  • ProstaglandinsBiological origin: Prostaglandin cascadeMay occur at wound site, leading to inflammationIn vivo half-life typically 5 minutes or lessSimilar structures but wide range of functions

  • SteroidsSteroid: A molecule having the ring system shown belowShape: Core is approximately flat

  • SteroidsCategories and ExamplesSex hormones:Corticoid hormones:Synthesized in the adrenal complexRegulate metabolic processes

  • SteroidsCategories and ExamplesBile acids:Cholic acidAid in digestion by emulsifying fats in intestineSteroids have similar structures but wide range of functions

  • Steroid BiosynthesisMore than sixty steps from acetyl CoA cholesterolCholesterolBiological precursor to all other vertebrate steroids

  • Lipophilic VitaminsVitamin: An organic compound, other than fat, protein, or carbohydrate, required for the normal growth and maintenance of animalsBroad range of structures and functionsVitamin EMixture of stereoisomers; a-tocopherol most importantProtects against oxidative damage to cells from radicals

  • Lipophilic VitaminsVitamin A (retinol)Essential to visionIncorporated into rhodopsin (photon-harvesting protein)An answer to the question Do we have to memorize all of these structures?

    Expected skills:Categorize a structure according to its lipid categoryDraw generic examples from each lipid category