PowerPoint PresentationSlide 2Slide 3Slide 4Slide 5Slide 6Slide 7Slide 8Slide 9Slide 10Slide 11Slide 12Slide 13Slide 14Slide 15Slide 16Slide 17Slide 18Slide 19Slide 20Slide 21Slide 22Slide 23Slide 24Slide 25Slide 26Slide 27Slide 28Slide 29Slide 30Slide 31Slide 32Slide 33Slide 34Slide 35Slide 36Slide 37Slide 38Slide 39Slide 40Slide 41Slide 42Slide 43Slide 44Slide 45Slide 46Slide 47Slide 488-1MCB 450Lecture 8Fatty Acids and LipidsMembranesOutline1. Fatty acids: structure, nomenclature, properties2. Lipids: components, structure, properties3. Functions of lipids:•energy storage•components of cell membranes4. Membrane lipids•phospholipids: phosphoglycerides & sphingolipids•cholesterol5. Lipid bilayers•why they form•bilayer fluidity•lipid mobility and asymmetry8-2Five classes of lipids1. Fatty acids:Major building blocks of membranesMain sources of fuelCan be saturated or unsaturated fatty acids2. Triglycerides:Storage form of fatty acids, source of glycerol3. Phospholipids:Main component of cell membranes4. Glycolipids:Important constituents of membranes5. Sterols: = Polycyclic hydrocarbonsMembrane componentsVariety of functions(e.g. component of electron carriers, hormones)8-31. Carboxylic acids with l o n g hydrocarbon chains2. Chain can be fully saturated, or contain one or more double bonds (a few have 3-C rings, -OH groups, or methyl group branches)8-4 Major membrane components: fatty acids (FA)C-atom closest tocarboxyl C = -carbonC-atom most distant fromcarboxyl C = -carbonCARBOXYL HEADGROUP IONIZED AT PHYSIOLOGICAL pH35791113152468101214161Unsaturated fatty acids8-5Double bondintroducesrigid 30° bendDouble bonds almost always have cis configuration18:1 Oleic acid 18:2 Linoleic acidFatty acid nomenclature-18-6Specifies...Chain length, # double bonds, separated by colon:16-C saturated palmitic acid = 16:0 CH3(CH2)14COOH18-C oleic acid (w. 1 double bond) = 18:1) CH3(CH2)7CH=CH(CH2)7COOHPosition of double bond specified by superscript #s following 18-C oleic acid has its double bond between C-9 & C-10 = 18:1(9)20-C FA w. double bonds between C-9 & C-10 & C-12 & C-13 = 20:2(9,12)Carboxyl C= carbon #1DO NOT include C=O when asked for the number of double bondsThe most commonly occurring FA have even #s of carbons in unbranched chains(even #s result from biosynthesis from C2 units)8-7 Fatty acid nomenclature-2n = normal, unbranchedFA have systematic names, and many have common names too:Chain length, # double bonds, separated by colon:12:0 laurate n-dodecanoate14:0 myristate n-tetradecanoate16:0 palmitate acid n-hexadecanoate18:1(9) oleate cis-9-octadecenoate18:2(9,12) linoleate cis,cis-9,12-octadecadienoateconfiguration of eachdouble bond is indicatedFatty acid nomenclature is important, because it also tells us about thephysical properties of fatty acids and lipids that contain them18:3 (∆9,12,15)8-8 Cis-polyunsaturated fats are essential componentsof our dietFROM VEGETABLE OILFROM FISH & SHELLFISHLast C=C bond is 3 bondsin from -C, hence:-3 fatty acids20:5 (∆5,8,11,14,17)Physical properties of fatty acids-18-9Physical properties of FA and compounds that contain themare largely determined by their........• hydrocarbon chain length and• degree of saturation, which influence….1. Solubility: the longer the fatty acyl chainand the fewer double bonds, the lowerthe solubility in H2O.2. “Melting” temperature.*Sat. Tm Fatty acids: solubility and melting point trends8-10Carbon skeleton Melting point (°C) Solubility in water (mg/g solvent, 30°C)12:014:016:018:016:1 (9)18:1 (9)18:2 (9,12)18:3 (9,12,15)44546370-113-5-110.0630.0240.0080.003***Common nameSystematic namelauric aciddodecanoic/atemyristictetradecanoatepalmitichexadecanoatestearicoctadecanoatepalmitoleiccis-9 hexadecenoicoleiccis-9 octadecenoiclinoleiccis-,cis-9,12-octadecadienoic-linoleniccis-,cis-,cis-9,12,15-octadecatrienoicMORE DOUBLE BONDS,LOWER MELTING TEMPPhysical properties of fatty acids-28-11Hydrocarbon chain length and degree of saturation influence….Melting temperatures: higher for saturated FA:•Free rotation about each C-C bond allows each chain to adopt a fully extended form.FA chains can pack together tightly, stabilized by hydrophobic interactions,with many atoms all along one molecule in van der Waals contact withatoms in neighboring chains.•FAs with double bonds can't pack together as tightly:interactions between them are weaker.• It takes less thermal energy to disorder arrays consisting of or containingunsaturated fatty acids, hence they have lower melting points.Classes of fatty acid-containing lipids8-20glycerolTriacylglycerols• 3 FA ester-linked to glycerol• FA can vary8-13Tristearin (3 x C18:0)http://chemistry2.csudh.edu/rpendarvis/ester-fats.htmlEster linkage issusceptible toalkaline hydrolysis(“saponification”)Saponification8-148-15 Most natural plant and animal fats triacylglycerolsTriacylglycerols are the storage form of fatty acids8-16Triacylglycerols accumulate in lipid dropletsin adipocytes (= fat cells)in adipose tissue.Glycogen & glucose stores can maintain biological activity for ~ 18-24 hrs Triacylglycerol stores allow survival for several weeksTriacylglycerols are a major energy reserve8-171. Fatty acids are richer in energy (more reduced) than carbohydrates.Complete oxidation of Tg yields 38 kJ energy/1g(compared to 17 kJ/g from protein or carbohydrate)2. Tg can be stored more efficiently.Tg are hydrophobic & stored in anhydrous formGlycogen, a polar carbohydrate, binds 2 x its weight in water1 g fat stores ≥ 6 x as much energy as 1 g hydrated glycogen3. Tg provides enough stored energy to last for weeksTrivia:The typical 70-kg man has 11 kg in fat storage. The equivalent amount of energy in the form of glycogen would add an extra 55 kg! Why are triacylglycerols (Tg) such a good fuel reserve?8-18Octane C8H18Saturated C8:0 fatty acidHYDROCARBON TAILSCARBOHYDRATECarbon-containing fuel molecules8-19Membrane lipids1. Three common types…phospholipidsglycolipidscholesterol8-202. Amphipathic: one end of molecule ishighly hydrophobic, the other, hydrophilicinsoluble in watersoluble in waterClasses of fatty acid-containing lipids8-21L-glycerol-3-phosphate& others8-22The simplest phosphoglyceride8-23PhosphoglyceridesNEGATIVE CHARGE!Major constituents of cellular membranesHH- 1InositolPEPCPSPI8-24PhosphoglyceridesSphingolipids-18-25Fatty acyl chain amide-linked to NH2 on C-2BOTH
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