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