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LIPIDS What are Lipids? Class of biomolecules that are all water insoluble No defining characteristic except that all of them share the same trait: non-polar Most common are fatty acids and esters of fatty acids Functions Energy Storage Cell membrane Thermal blanket and cushion Precursors of hormones Fatty Acids Fatty acids consist of a hydrocarbon chain with a carboxylic acid at one end. A 16-C fatty acid: CH3(CH2)14-COONon-polar polar General Structure: CH3 (CH 2)n COOH n = 0 : CH 3COOH n = 1 : propionic acid n is almost always even Fatty Acids Double bonds in fatty acids usually have the cis configuration. Most naturally occurring fatty acids have an even number of carbon atoms. IUPAC naming: COOH carbon as C1 Farthest carbon is ω Total carbons/# double bonds/Δdouble bond position Fatty Acids Some fatty acids and their common names: 14:0 myristic acid; 16:0 palmitic acid; 18:0 stearic acid; 18:1 cisD9 oleic acid 18:2 cisD9,12 linoleic acid 18:3 cisD9,12,15 a-linonenic acid 20:4 cisD5,8,11,14 arachidonic acid 20:5 cisD5,8,11,14,17 eicosapentaenoic acid (an omega-3) Essential fatty acids ALA- ω-3 FA precursor for EPA and DHA LA – ω-6 FA precursor of AA Fatty Acid Chemistry Peroxidation a non-enzymatic reaction catalyzed by oxygen may occur in tissues or in foods (spoilage) the hydroperoxide formed is very reactive and leads to the formation of free radicals which oxidize protein and/or DNA (causes aging and cancer) principle is also used in drying oils (linseed, tung, walnut) to form hard films Drying Oils: Application of Peroxidation based on the ease of autoxidation and polymerization of oils (important in paints and varnishes) the more unsaturation in the oil, the more likely the “drying” process Non-drying oils: Castor, olive, peanut, rapeseed oils Semi-drying Corn, sesame, cottonseed oils Drying oils oils Soybean, sunflower, hemp, linseed, tung, oiticica oils Fatty Acid Chemistry Transesterification Acid-catalyzed exchange betweein R groups of esters Frequently-used in polyester, methanolysis and biodiesel industries Fatty Acid Chemistry Hydrogenation Reduces double bonds on unsaturated fatty acids Prevents oils from going rancid Fatty Acid Chemistry Saponification Base hydrolysis of triglycerides to produce fatty acid salts 𝑠𝑎𝑝𝑜𝑛𝑖𝑓𝑖𝑐𝑎𝑡𝑖𝑜𝑛 𝑛𝑢𝑚𝑏𝑒𝑟 = High 𝑚𝑔 𝐾𝑂𝐻 𝑔 𝑓𝑎𝑡 saponification number, shorter chain length Soaps Types of soaps: Sodium soap – ordinary hard soap Potassium soap – soft soap (shaving soaps are potassium soaps of coconut and palm oils) Castile soap – sodium soap of olive oil Green soap – mixture of sodium and potassium linseed oil Transparent soap – contains sucrose Floating soap – contains air Calcium and magnesium soaps are very poorly water soluble (hard water contains calcium and magnesium salts – these insolubilize soaps) Fatty Acid Chemistry Iodine Number measures the degree of unsaturation in a given amount of fat or oil the iodine number is the number of grams of iodine absorbed by 100 grams of fat Cottonseed oil: 103 –111 Olive oil: 79 – 88 Linseed oil: 175 –202 frequently used to determine adulteration of commercial lots of oils H H I2 I H I H Fatty Acid Chemistry Acetyl Number the number of milligrams of KOH needed to neutralize the acetic acid of 1 g of acetylated fat acetic anhydride fatty acid OH fatty acid fatty acid O C OH CH3 + O acetylated fatty acid titrate with standardized KOH H3C COOH Fatty Acid Chemistry Reichert-Meisl Number measures the amount of volatile fatty acids (low MW and water soluble Fas) the R-M number is the number of milliliters of 0.1N alkali required to neutralize the soluble fatty acids distilled from 5 Gm of fat butter fat has a high R-M number Indicator of non-fat compounds in edible fats, or volatile fatty acids Fats and Oils fats are solids or semi solids oils are liquids melting points and boiling points are not usually sharp (most fats/oils are mixtures) when shaken with water, oils tend to emulsify pure fats and oils are colorless and odorless (color and odor is always a result of contaminants) – i.e. butter (bacteria give flavor, carotene gives color) Waxes simple esters of fatty acids (usually saturated with long chain monohydric alcohols) Beeswax – also includes some free alcohol and fatty acids Spermaceti – contains cetyl palmitate (from whale oil) – useful for pharmaceuticals (creams/ointments; tableting and granulation) Carnauba wax – from a palm tree from brazil – a hard wax used on cars and boats O H3C (CH 2)14 C O CH 2 (CH 2)28-CH 3 fatty acid long chain alcohol Spermaceti source Carnauba wax source Bee’s wax Glycerides Function Storage of energy Cushions O O O O O R O OH OH OH O R R R O MONOGLYCERIDE DIGLYCERIDE O R O R O O TRIGLYCERIDE Triglycerides Esters of fatty acids and glycerol Constituent of fats and oils Phosphoglycerides aka glycerophospholipids Major constituent of cell membranes Structure Glycerol backbone with esterifies fatty acids at C1 and C2 Fatty acids are usually nonidentical Phosphate group attached to C1 A polar group is usually esterified to Pi (usually serine, choline, ethanolamine, glycerol, or inositol X = H (phosphatidic acid) - precursor to other phospholipids X = CH2-CH2-N+(CH3)3 phosphatidyl choline X = CH2-CH(COO-)NH3+ phosphatidyl serine X = CH2-CH2-NH3+ phosphatidyl ethanolamine Phosphoglycerides Structure=Function region – glycerol, phosphate group, X Nonpolar region – fatty acid Amphiphatic character Ideal for forming bilayers polar Polar "kink" due to double bond non-polar Phosphoglyceride Phosphatidyl inositol Inositol as a polar head group Has roles in cell signaling as well as a cell membrane component O O R1 C H2C O O CH H2C C R2 O O P O O H OH OH H OH phosphatidylinositol OH H H H H OH Ether glycerophospholipids Possess an ether linkage instead of an acyl group at the C-1 position of glycerol PAF ( platelet activating factor) - a potent mediator in inflammation, allergic response and in shock (also responsible for asthma-like symptom The ether linkage is stable in either acid or base Plasmalogens: cis a,bunsaturated ethers The alpha/beta unsaturated ether can be hydrolyzed more easily Sphingolipids derivatives of the lipid sphingosine, which has a long hydrocarbon tail, and a polar domain that includes an amino group Like phosphoglycerides, are also constituents of cell membranes Can be reversibly phosphorylated and utilized as signaling molecule Sphingolipid Derivatives Ceramide - amino group of sphingosine forms an amide bond with a fatty acid carboxyl Sphingomyelin has a phosphocholine or phosphethanolamine head group. common constituent of plasma membranes similar in size and shape to the glycerophospholipid phosphatidyl choline OH H2C O OH H C CH NH CH C R ceramide HC (CH2 )12 CH3 Sphingolipid Derivatives Cerebroside a sphingolipid (ceramide) with a monosaccharide such as glucose or galactose as polar head group. Ganglioside – a ceramide with polar head group that is a complex oligosaccharide, including the acidic sugar derivative sialic acid Both are collectively known as glycosphingolipids and are commonly found on the outer leaflet of the cell membrane CH2OH O OH H OH H H H OH O H H2C OH O cerebroside with -galactose head group H C CH NH CH C R HC (CH2 )12 CH3 Ganglioside Structure Ganglioside Cerebrosides One sugar molecule Sulfatides or sulfogalactocerebrosides A sulfuric acid ester of galactocerebroside Globosides: ceramide oligosaccharides Lactosylceramide Galactocerebroside – in neuronal membranes Glucocerebrosides – elsewhere in the body 2 sugars ( eg. lactose) Gangliosides Have a more complex oligosaccharide attached Biological functions: cell-cell recognition; receptors for hormones Cardiolipids A polyglycerol phospholipid; makes up 15% of total lipid-phosphorus content of the myocardium – associated with the cell membrane Cardiolipids are antigenic and as such are used in serologic test for syphilis (Wasserman test) O O R2 C O H2C O C C H O H2C O P OH O R1 R4 H O CH 2 C CH 2 O OH C O CH 2 O H C P O CH 2 O O C R3 OH glycerol glycerol glycerol Sulfolipids also called sulfatides or cerebroside sulfates contained in brain lipids sulfate esters of cerebrosides present in low levels in liver, lung, kidney, spleen, skeletal muscle and heart function is not established Lipid Storage Diseases Lipid Storage Diease a group of inherited metabolic disorders in which harmful amounts of fatty materials (lipids) accumulate in various tissues and cells in the body also known as sphingolipidoses genetically acquired due to the deficiency or absence of a catabolic enzyme Tay Sachs disease Gaucher’s disease Niemann-Pick disease Fabry’s disease Tay Sachs Disease Fabry’s Disease Niemann Pick Disease Cholesterol and related compounds Cholesterol an important constituent of cell membranes, has a rigid ring system and a short branched hydrocarbon tail. HO Cholesterol serves as a component of membranes of cells (increases or moderates membrane fluidity) precursor to steroid hormones and bile acids storage and transport –cholesterol esters Cholesterol is largely hydrophobic. But it has one polar group, a hydroxyl, making it amphipathic. PDB 1N83 cholesterol Steroid Ring System 18 11 19 1 2 A 3 17 C 13 D 14 9 10 8 B 7 5 4 12 6 16 15 Eicosanoids Includes prostaglandins and related compounds Derivatives of arachidonic acid Serves as local hormones and intercellular signaling Key hormones in inflammation response 9 8 COOH 20 11 12 15 prostanoic acid Eicosanoids Types of Eicosanoids Prostaglandins Prostacyclins Thromboxanes Leukotrienes epoxyeicosatrienoic acids. Biological Functions Inflammation Fever regulation of blood pressure blood clotting immune system modulation control of reproductive processes and tissue growth regulation of the sleep/wake cycle Terpenes simple lipids, but lack fatty acid component formed by the combination of 2 or more molecules of 2methyl-1,3-butadiene (isoprene) monoterpene (C-10) – made up of 2 isoprene units sesquiterpene (C-15) – made up of 3 isoprene units diterpene (C-20) – made up of 4 isoprene units CHO OH menthol citronellal limonene HO H squalene lanosterol camphene Terpenes tetraterpenes (C-40) are not as common as mono, di, and triterpenes include the carotenoids such as beta-carotene (precursor of vitamin A) and lycopene found in tomatoes usually colorful compounds due to highly conjugated system polyisoprenoids or polyprenols consist of numerous isoprene adducts (8 – 22) examples include dolichol phosphate, undecaprenyl alcohol (bactoprenol) and the side chains of vitamins K, vitamin E and coenzyme Q Lipid-linked proteins and Lipoproteins Lipid-linked proteins Proteins that have lipids covalently bonded to them Usually found in cell membranes 3 types are most common: Prenylated proteins Farnesylated proteins (C15 isoprene unit) Geranylgeranylated proteins (C20 isoprene unit) Fatty acylated proteins Myristoylated proteins (C14) Palmitoylated proteins (C16) glycosylphosphatidylinositol-linked proteins (GPI-linked proteins) occur in all eukaryotes, but are particularly abundant in parasitic protozoa located only on the exterior surface of the plasma membrane Fatty acylated proteins Prenylated proteins GPI-linked proteins Lipoproteins particles found in plasma that transport lipids including cholesterol lipoprotein classes chylomicrons: take lipids from small intestine through lymph cells very low density lipoproteins (VLDL) intermediate density lipoproteins (IDL) low density lipoproteins (LDL) high density lipoproteins (HDL) Lipoprotein Lipoprotein class Density (g/mL) Diameter (nm) Protein % of dry wt Phospholip Triacylglycerol % id % of dry wt HDL 1.063-1.21 5 – 15 33 29 8 LDL 1.019 – 1.063 18 – 28 25 21 4 IDL 1.006-1.019 25 - 50 18 22 31 VLDL 0.95 – 1.006 30 - 80 10 18 50 chylomicrons < 0.95 100 - 500 1-2 7 84