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LIPIDS. By Henry Wormser, Ph.D. PSC 3110 – Fall semester 2008. Introduction. Definition: water insoluble compounds Most lipids are fatty acids or ester of fatty acid They are soluble in non-polar solvents such as petroleum ether, benzene, chloroform Functions Energy storage
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LIPIDS By Henry Wormser, Ph.D. PSC 3110 – Fall semester 2008
Introduction • Definition: water insoluble compounds • Most lipids are fatty acids or ester of fatty acid • They are soluble in non-polar solvents such as petroleum ether, benzene, chloroform • Functions • Energy storage • Structure of cell membranes • Thermal blanket and cushion • Precursors of hormones (steroids and prostaglandins) • Types: • Fatty acids • Neutral lipids • Phospholipids and other lipids
Fatty acids • Carboxylic acid derivatives of long chain hydrocarbons • Nomenclature (somewhat confusing) • Stearate – stearic acid – C18:0 – n-octadecanoic acid • General structure:
Fatty acids • Common fatty acids n = 4 butyric acid (butanoic acid) n = 6 caproic acid (hexanoic acid) n = 8 caprylic acid (octanoic acid) n = 10 capric acid (decanoic acid)
Fatty acids • common FA’s: n = 12: lauric acid (n-dodecanoic acid; C12:0) n = 14: myristic acid (n-tetradecanoic acid; C14:0) n = 16: palmitic acid (n-hexadecanoic acid; C16:0) n = 18; stearic acid (n-octadecanoic acid; C18:0) n = 20; arachidic (eicosanoic acid; C20:0) n= 22; behenic acid n = 24; lignoceric acid n = 26; cerotic acid
Less common fatty acids iso – isobutyric acid anteiso odd carbon fatty acid – propionic acid hydroxy fatty acids – ricinoleic acid, dihydroxystearic acid, cerebronic acid cyclic fatty acids – hydnocarpic, chaulmoogric acid
PHYTANIC ACID A plant derived fatty acid with 16 carbons and branches at C 3, C7, C11 and C15. Present in dairy products and ruminant fats. A peroxisome responsible for the metabolism of phytanic acid is defective in some individuals. This leads to a disease called Refsum’s disease Refsum’s disease is characterized by peripheral polyneuropathy, cerebellar ataxia and retinitis pigmentosa
Less common fatty acids These are alkyne fatty acids
Fatty acids • Fatty acids can be classified either as: • saturated or unsaturated • according to chain length: • short chain FA: 2-4 carbon atoms • medium chain FA: 6 –10 carbon atoms • long chain FA: 12 – 26 carbon atoms • essential fatty acids vs those that can be biosynthesized in the body: • linoleic and linolenic are two examples of essential fatty acid
Unsaturated fatty acids • Monoenoic acid (monounsaturated) Double bond is always cis in natural fatty acids. This lowers the melting point due to “kink” in the chain
Unsaturated fatty acids • Dienoic acid: linoleic acid
Unsaturated fatty acids • Various conventions are in use for indicating the number and position of the double bond(s)
Unsaturated fatty acids • Polyenoic acid (polyunsaturated)
Unsaturated fatty acids • Monoenoic acids (one double bond): • 16:1, 9 w7: palmitoleic acid (cis-9-hexadecenoic acid • 18:1, 9 w9: oleic acid (cis-9-octadecenoic acid) • 18:1, 9 w9: elaidic acid (trans-9-octadecenoic acid) • 22:1, 13 w9: erucic acid (cis-13-docosenoic acid) • 24:1, 15 w9: nervonic acid (cis-15-tetracosenoic acid)
Unsaturated fatty acids • Trienoic acids (3 double bonds) • 18:3;6,9,12 w6 : g-linolenic acid (all cis-6,9,12-octadecatrienoic acid) • 18:3; 9,12,15 w3 : a-linolenic acid (all-cis-9,12,15-octadecatrienoic acid) • Tetraenoic acids (4 double bonds) • 20:4; 5,8,11,14 w6: arachidonic acid (all-cis-5,8,11,14-eicosatetraenoic acid)
Unsaturated fatty acids • Pentaenoic acid (5 double bonds) • 20:5; 5,8,11,14,17 w3: timnodonic acid or EPA (all-cis-5,8,11,14,17-eicosapentaenoic acid)* • Hexaenoic acid (6 double bonds) • 22:6; 4,7,10,13,16,19 w3: cervonic acid or DHA (all-cis-4,7,10,13,16,19-docosahexaenoic acid)* Both FAs are found in cold water fish oils
Properties of 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)
Examples of oils • Olive oil – from Oleo europa (olive tree) • Corn oil – from Zea mays • Peanut oil – from Arachis hypogaea • Cottonseed oil – from Gossypium • Sesame oil – from Sesamum indicum • Linseed oil – from Linum usitatissimum • Sunflower seed oil – from Helianthus annuus • Rapeseed oil – from Brassica rapa • Coconut oil – from Cocos nucifera
Non-drying, semi-drying and drying oils • 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 oils • Corn, sesame, cottonseed oils • Drying oils • Soybean, sunflower, hemp, linseed, tung, oiticica oils
Fatty acid reactions • salt formation • ester formation • lipid peroxidation
Soaps • Process of formation is known as saponification • 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)
Lipid 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
Hydrogenated fats • hydrogenation leads to either saturated fats and or trans fatty acids • the purpose of hydrogenation is to make the oil/fat more stable to oxygen and temperature variation (increase shelf life) • example of hydrogenated fats: Crisco, margarine
Neutral lipids • Glycerides (fats and oils) ;glycerides • Glycerol • Ester of glycerol - mono glycerides, diglycerides and triglycerides • Waxes – simple esters of long chain alcohols
GLYCERIDES Function: storage of energy in compact form and cushioning
Stereospecific numbering • carbon 2 of triglycerides is frequently asymmetric since C-1 and C-3 may be substituted with different acyl groups • by convention we normally draw the hydroxyl group at C-2 to the left and use the designation of sn2 for that particular substituent • C-1 and C-3 of the glycerol molecule become sn1 and sn3 respectively
Analytical methods to evaluate lipids • saponification number • iodine value (Hanus method) • free fatty acids • acetyl number • Reichert-Meissl number • HPLC/GC (for more precise analysis)
Saponification number • gives some clue as to the average size of fatty acids in a given sample of fat • defined as the number of milligrams of KOH needed to neutralize the fatty acids in 1 Gm of fat • butter (large proportion of short chain FAs) sap. no. 220 – 230 • oleomargarine (long chain FAs) sap. No is 195 or less
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
Acetyl number some fatty acids have hydroxyl groups The acetyl number gives the proportion of these hydroxyl-containing fatty acids in a given sample of fat or oil
Acetyl number • the acetyl number is the number of milligrams of KOH needed to neutralize the acetic acid of 1 Gm of acetylated fat • examples: • castor oil – 146 –150 • cod liver oil – 1.1 • cottonseed oil – 21 – 25 • olive oil – 10.5 • peanut oil – 3.5
Reichert – Meissl 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
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
Spermaceti source Carnauba wax source Bee’s wax
Waxes Examples of long chain monohydric alcohols found in waxes
Phospholipids • the major components of cell membranes • phosphoglycerides Phospholipids are generally composed of FAs, a nitrogenous base, phosphoric acid and either glycerol, inositol or sphingosine
Phosphatidyl inositol Commonly utilized in cellular signaling
Sphingolipids Based on sphingosine instead of glycerol
Sphingomyelin (a ceramide) It is a ubiquitous component of animal cell membranes, where it is by far the most abundant sphingolipid. It can comprise as much as 50% of the lipids in certain tissues, though it is usually lower in concentration than phosphatidylcholine
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,b-unsaturated ethers • The alpha/beta unsaturated ether can be hydrolyzed more easily
glycolipids There are different types of glycolipids: cerebrosides, gangliosides, lactosylceramides
GLYCOLIPIDS • Cerebrosides • One sugar molecule • Galactocerebroside – in neuronal membranes • Glucocerebrosides – elsewhere in the body • Sulfatides or sulfogalactocerebrosides • A sulfuric acid ester of galactocerebroside • Globosides: ceramide oligosaccharides • Lactosylceramide • 2 sugars ( eg. lactose) • Gangliosides • Have a more complex oligosaccharide attached • Biological functions: cell-cell recognition; receptors for hormones
Gangliosides • complex glycosphingolipids that consist of a ceramide backbone with 3 or more sugars esterified,one of these being a sialic acid such as N-acetylneuraminic acid • common gangliosides: GM1, GM2, GM3, GD1a, GD1b, GT1a, GT1b, Gq1b
Ganglioside nomenclature • letter G refers to the name ganglioside • the subscripts M, D, T and Q indicate mono-, di-, tri, and quatra(tetra)-sialic-containing gangliosides • the numerical subscripts 1, 2, and 3 designate the carbohydrate sequence attached to ceramide
Ganglioside nomenclature • Numerical subscripts: • 1. Gal-GalNAc-Gal-Glc-ceramide • 2. GalNAc-Gal-Glc-ceramide • 3. Gal-Glc-ceramide