Lipid Chemistry : Definition & Classification PDF

Chemistry of lipids Dr/ Eman Abdelmaksoud Component: Def: Lipids are a heterogeneous group of organic compounds, mainly composed of hydrocarbon chains. Soluble in nonpolar (organic) solvents and insoluble in water. Lipids are the esters of fatty acids with alcohol. ...

Chemistry of lipids Dr/ Eman Abdelmaksoud Component: Def: Lipids are a heterogeneous group of organic compounds, mainly composed of hydrocarbon chains. Soluble in nonpolar (organic) solvents and insoluble in water. Lipids are the esters of fatty acids with alcohol.  Lipids ARE LIPIDS BAD? DO THEY HAVE ANY FUNCTION? Biological importance: Diet Depot fat Constant fat Signaling Highest source of -storage form energy (9.3 of energy -enter in structure of cell membrane and Supply bod KCal/g). -thermal cholesterol es insulator mitochondria for and bile -contain essential -Protect against hormone fatty acids trauma -enter in structure of -contain fat -support internal myelin sheath soluble vitamins organ Second (A, D, K and E). messanger 1-Fatty acids: FA Def: Fatty acids are water insoluble long chain hydrocarbons. having one carboxylic group at the end of the chain (-COOH). They are mostly aliphatic (not branched). Fatty acids present as free fatty FFA acids in the plasma. FA 10 carbon >10 carbon Lower FA higher FA Nomenclature of FA 4 3 2 1 (Arabic numbers) CH3-………CH2-CH2-CH2-COOH γ β α (Greek numbers) ω1 ω2 ω3 ω4 (Omega numbers) Fatty acids Classification: 1- Saturated fatty acids 2- Unsaturated fatty acids 3- Sulfur containing fatty acids 4- Hydroxy containing fatty acids 5- Branched chain fatty acids 6- Cyclic fatty acids IUPAC numerical multiplier 1- Saturated fatty acids: Have no double bonds in the chain. The general formula is CH3-(CH2)n-COOH (n) equals the number of methylene (-CH2) groups. CH3-………CH2-CH2-CH2-COOH Their systemic name ends by the suffix (-anoic) Stearic acid (18 C) Octadecanoic acid (Octa = 6, Deca = 10). Name Formulae Occurrence Acetic acid (2C) CH3-COOH vinegar Butyric acid (4C) CH3-CH2-CH2-COOH butter Caproic acid (6C) CH3-(CH2)4-COOH butter, palm oil, coconut Caprylic acid (8C) CH3-(CH2)6-COOH butter, palm oil Capric acid (10C) CH3-(CH2)8-COOH butter, palm oil, coconut Lauric acid (12C) CH3-(CH2)10-COOH cinnamon, palm, coconut oils Myristic acid (14C) CH3-(CH2)12-COOH nutmeg, palm oil, coconut oil Palmitic acid (16C) CH3- (CH2)14-COOH butter, palm oil Stearic acid (18C) CH3- (CH2)16-COOH butter, vegetable oils Arachidic acid (20C) CH3-(CH2)18-COOH peanut Behanic acid (22C) CH3-(CH2)20-COOH seeds Lignoceric acid (24C) CH3-(CH2)22-COOH peanut, cerebrosides 2- Unsaturated FA -General formula : CH3(CH2)nCH=CH(CH2)nCOOH. -Systemic name ends by the suffix (-enoic) oleic acid (18C) Octadecenoic acid (Octa=8, Deca =10). Linoleic acid (18C) Octadeca-9,12dienoic acid (cis,cis-9,12-octadecadienoicacid) Arachidonic acid all-cis-5,8,11,14-eicosatetraenoic acid  Unsaturated fatty acids A- Monounsaturated fatty acids B-Polyunsaturated fatty acids (PUFA) MUFA (monoethenoic, monoenoic) (polyethenoic, polyenoic) essential fatty acids containing one double bond containing two or more double bonds palmitoleic (16: 1 Δ9) linoleic (18:2Δ9,12) oleic acid (18: 1 Δ9) linolenic (18:3Δ9,12,15) nervonic acid (24: 1 Δ15). arachidonic acids (20:4Δ5,8,11,14) C-Eicosanoids: they are cyclic compounds which derived from arachidonic acid (20 C). Position of double bonds in unsaturated fatty acids A-The delta (Δ) numbering system: palmitoleic acid C 16:1Δ9 B-Omega (ω) numbering system: palmitoleic acid C 16:1 ω7 MUFA Palmitoleic (16: 1 Δ9) CH3-(CH2)5-CH=CH-(CH2)7-COOH Oleic acid (18: 1 Δ9) CH3-(CH2)7-CH=CH-(CH2)7-COOH Nervonic acid (24: 1 Δ15) CH3-(CH2)7-CH=CH-(CH2)13-COOH PUFA Linoleic (18:2Δ9,12): CH3-(CH2)4-CH=CH-CH2-CH=CH-(CH2)7-COOH Linolenic (18:3Δ9,12,15): CH3-CH2-CH=CH-CH2-CH=CH-CH2-CH=CH-(CH2)7-COOH Arachidonic acids (20:4Δ5,8,11,14): CH3-(CH2)4-CH=CH-CH2-CH=CH-CH2-CH=CH-CH2-CH=CH-(CH2)3-COOH Omega-3 fats: Eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) come mainly from fish, called marine omega-3s. Alpha-linolenic acid (ALA), found in vegetable oils and nuts. Function: -prevent heart disease and stroke -control lupus, eczema, and rheumatoid arthritis. Omega-6 fats: linoleic acid (LA), arachidonic acid come from vegetable oils (sunflower, corn, soybean, and cottonseed) -stimulate skin and hair growth, maintain bone health, reproductive system, regulate metabolism. -reduced rates of heart attacks and other heart diseases -has role in inflammation, fever promotion, blood pressure regulation. Most of us get 14 to 25 times more omega-6 mor than omega-3s. 3- Sulfur containing FA: Lipoic acid (6,8 dithiooctanic acid) is a water soluble vitamin and it is one of the hydrogen carriers that act as coenzyme in the body. CH2 – CH2 – CH – (CH2)4 – COOH SH SH 4- Hydroxy containing FA: OH group is attached to α-carbon atom of FA. Cerebronic acid (hydroxy Lignoceric acid): CH3 – (CH2)21 – CHOH – COOH  Function of essential fatty acids: Vegetable oils (corn seed, soybean and linseed oils) are rich in essential fatty acids -Normal growth. - Enter in the structure of phospholipids and cholesterol esters. -Treatment of atherosclerosis because they lower the blood cholesterol level. -Maintenance of normal structure and function of skin. Eicosanoids: comprise prostanoids and leukotriens. Prostanoids include prostaglandins, prostacyclins and thromboxanes.. -work like hormones, but they do not like to travel.. 'local hormones' -They act on the cells that produce them or on neighboring cells. can be classified as autocrine/paracrine hormones. -Prostaglandins: mediate the inflammatory response to infection and injury. -leukotriens play roles in acute and chronic inflammation and allergic diseases. 5- Branched chain FA: common constituents of the lipids of bacteria and to a much lesser extent of animals and plants. -primarily saturated fatty acids (FA) with a methyl branch or more on the carbon chain. branched chain fatty acid called phytanic acid (18 C). ▪ formed by bacterial degradation of chlorophyll in the intestinal tract of ruminants. ▪ Refsum′s disease is caused by inability of alpha oxidation of phytanic acid. This leads to accumulation of it in plasma and tissues. Cause neurodegeneration and muscle dystrophy. 6- Cyclic FA: -unusual class of minor fatty acids generally produced by bacteria and less frequently by plants. Bacteria (lactic acid bacteria) synthetize cyclopropane FA. -omega-cyclohexyl fatty acids, present in milk produced by rumen bacteria. Cyclopropane and omega-cyclohexyl fatty acids found in bovine meat and dairy products Classifying FA acc.to sources Non essential fatty acids Essential fatty acids -Synthesized in the body -Can't be synthesized in the -Can be synthesized from acetyl body. COA (active acetate) - not necessary to be obtained -They must be obtained from from the diet. the diet. ex: saturated, MUFA. Ex:PUFA Physical properties of fatty acids: A.Solubility: 1.Short chain fatty acids. (acetic acid and butyric acid) are soluble in water. 2.Long chain fatty acids are soluble in nonpolar solvents. B. Melting point: depends on the length of the chain of fatty acids and the degree of unsaturation 1. Short chain and unsaturated fatty acids are liquid at room temperature. 2. Long chain and saturated fatty acids are solid at room temperature. 11-Alcohols Include glycerol, cholesterol and higher alcohols (e.g. acetyl alcohol) usually found in the waxes. Glycerol: It is polyhydric alcohol containing 3 –OH groups. Numbering of carbons of glycerol is either: α, β and γ OR 1, 2 and 3  Simple lipid Def: it is esters of FA and alcohol. Classify acc.to type of alcohol Neutral fats or triacylglycerol Waxes (TAG) carry no charge. Fatty acids + glycerol Fatty acids + long chain alcohol (Storage form of fat in adipose (cholesterol ester) tissue) (bee wax)  Simple lipid: A-TAG -Human fat (TAG) is liquid at room temperature and contains high concentration of oleic acid. Dietary sources: Animals butter and lards. plants cotton seed oil, linseed oil, sesame oil and olive oil. Marine oils cod liver and shark liver oil. Types: Simple TAG: similar 3 fatty acids are attached to glycerol tripalmitin, tristearin, triolein. Mixed TAG: three different fatty acids are attached to glycerol 1-palmitodistearin, 1-2-distearopalmitin, 1-3-distearopalmitin. Physical properties of TAG: 1. Solubility: soluble in fat solvents. 2. Melting point: TAG rich (USFA) liquid at room temperature (oils). TAG rich (SFA) solid at room temperature (fats). lower fatty acids melt at lower temperature than those of higher fatty acids. N.B: -the membrane lipids must be fluid as it contains more unsaturated fat than storage lipids. -S/C fat is also softer than that serving as a protective layer around the internal organs. -Butter fat is softer than lard because butter contains large amount of short chain fatty acids which are butyric and Caproic. TAG Physical properties: 3. Specific gravity: it is less than 1 TAG float on the surface of water. 4. Grease stain test: TAG give positive grease stain test. 5. Pure fats are tasteless, odorless, colorless and neutral in reaction TAG Chemical properties: 1. Acrolein test: -all TAG contain glycerol, so all give positive acrolein test. -Glycerol give an aldehyde substance called acrolein by losing 2 water molecules. 2. Hydrolysis: lipase enzyme can hydrolyze TAG into fatty acids and glycerol TAG Chemical properties: 3. Saponification: Alkali +TAG glycerol and salts of fatty acids (soaps) -Soaps cause emulsification of oily material (i.e. breaking down large fat particles into small ones). helps easy washing the fatty materials away. Ordinary soap: Na and K salts of fatty acids are soluble in water. Hard soap: Ca and Mg salts of fatty acids are insoluble in water. hard water: Water containing calcium or magnesium ions. TAG Chemical properties: 4. Halogenations: presence of USFA in TAG. R – CH=CH – COOH I2 R – CH – CH – COOH I I 5. Hydrogenation: depends on the presence of USFA. Hydrogen is added at high temperature and this reaction is the base of conversion of oils into margarine (hardening of oils). TAG Chemical properties: 6. Oxidation or rancidity or rancidification:. this is a toxic reaction of TAG. It leads to unpleasant odor or taste of oils and fats developing after oxidation by oxygen of air, bacteria or moisture. small amount of unsaturated acids present in fats/oils gets oxidized by air to form peroxides which further break down into aldehydes having unpleasant smell and taste. Saturated fatty acids do not get rancid. Types of rancidity: 1- Oxidative rancidity: -by exposure to heat, light, moisture, copper, nickel and iron -The greater degree of unsaturation, the more liability to oxidative rancidity. -prevented by packing under vacuum, storage at low temperature Or using artificial antioxidants. Types of rancidity: 2. Ketonic rancidity: -oxidation of USFA by enzymes found in dry molds. give aldehyde and ketone with peculiar taste. R – CHO R – CH=CH –COOH R – C – CH2 – COOH It can be prevented by sterilization. Types of rancidity: 3. Hydrolytic rancidity: fats bacterial enzyme lipase glycerol and free fatty acids moisture,↑ temp -It occurs in butter due to high content of water. -prevented by inactivation of enzymes and keeping fats away from moisture. Fat constants Purity and composition of oil depends upon the degree of unsaturation, acidity on hydrolysis, and its molecular weight. Each fat has a certain constant value or numbers which detect adulteration and quality of fats. include: 1-Saponification value (number) 2-Acid value (number) 3-Iodine value (number) 4-Acetyl value (number) 1-Saponification value (number) Def: the number of mg of KOH necessary to saponify (combined) all fatty acids present in 1 gram of fats after complete hydrolysis. -Fats with a high percentage of short chain fatty acids have a greater saponification number than that with high percentage of long chain fatty acids. -Butter has greater saponification number than lard. -It is used for determination of adulteration. 2- Acid value (number): Def: the number of mg of KOH necessary to neutralize the free fatty acids present in 1 gram of fats. -Acid value is important for the detection of rancidity. -Normally, the acid number is zero but after rancidity free fatty acids are produced in excess. 4- Acetyl value (number): Def: the number of mg of KOH needed to neutralize the acetic acid produced by the saponification of 1 gram of completely acetylated fat or oil -used to detect the presence of hydroxyl fatty acids. -It is high in caster oil. 3- Iodine value (number): Def: the number of grams of iodine necessary to saturate all unsaturated fatty acids present in 100 grams of fats. -Iodine number gives an idea about the degree of unsaturation of the fatty acids present in fat (quality of fats). N.B: oils have high iodine number than fats. B-Waxes: Acetyl alcohol is most present in waxes. The fatty acids present are long chain acids. ▪ The commonest wax in human bodies is cholesterol ester. ▪ Bee wax is palmitic acid ester with myricyl alcohol. ▪ wool fat is oleic or stearic acid ester with cholesterol. It is useful in manufacture of cosmotic cream and ointments. Waxes Properties: ▪ They have the same physical properties as fats. ▪ Give negative acrolein test. ▪ Not digested by lipase enzyme. so not utilized by the body. ▪ They are solids at room temperature. Complex (compound) lipids: FA+ALCOHOL+ other substance 1-Phospholipids Ⅱ- Glycolipids Ⅲ- lipoproteins Ⅳ- Sulfolipids Ⅴ-Aminolipids.  Compound lipid 1-Phospholipids or phosphatides or lipoids: Fatty acids +alcohol + phosphoric acid residues and nitrogenous base. They are classified acc.to alcohol content into: A- Glycerophospholipids: alcohol is glycerol. B- Sphingophospholipids: alcohol is sphingosine. A- Glycerophospholipids B- Sphingophospholipids 1-Phosphatidic acid (diacylglycerol phosphate) Sphingomyelin 2- Lecithin (phosphatidylcholine) 3- Lysolecithin 4- Cephalin (phosphatidylethanolamine) 5- Phosphatidylserine and phosphatidyl threonine 6-Lipositol (phosphatidylinositol) or myo-inositol 7- Plasmalogens 8- Cardiolipin (diphosphatidylglycerol)  A-Glycerophospholipids Saturated FA ▪ It is Constant fat ▪ Identified by acrolein test. ▪ Amphipathic lipids Unsaturated FA Glycerol Pophoric Nitrogenous base acid  A-Glycerophospholipids: 1.Phosphatidic acid (DAG phosphate): Precursor of this group Saturated FA UnSaturated FA Phosphoric acid A-Glycerophospholipids: 2-Lecithin (phosphatidylcholine) The most abundant phospholipids in cell membrane. choline nerve transmission Dipalmitoyl lecithin: contain 2 palmitic acid act as surfactant in lung  A-Glycerophospholipids: 3- Lysolecithin: Formed by: -lecithin cholesterol acyl transferase (LCAT) -lecithinase enzyme (spreading factor) lecithinase enzyme lecithin lysolecithin A-Glycerophospholipids: 4- Cephalin (phosphatidylethanolamine) Saturated FA Glycerol Unsaturated FA Pophoric ethanolamine acid -It presents in cell membrane and myelin sheath of nerves. -Act as activator factor of coagulation mechanisms as it enters in composition of thromboplastin. 5- Plasmalogens -It is like cephalin but it contains unsaturated alcohol attached to glycerol at position 1 (α) by ether linkage instead of FA. -About 10% of the phospholipids present in brain, semen and muscles.  A-Glycerophospholipids: 6- Lipositol (phosphatidylinositol) or myo-inositol Saturated FA Glycerol Unsaturated FA Pophoric acid inositol It is present in cell membrane, brain, liver, heart and muscles. Diacylglycerol and inositol triphosphate both act as precursor of second messengers mediating hormonal action inside cells. A-Glycerophospholipids: 7- Phosphatidylserine and phosphatidyl threonine: 8- Cardiolipin:(diphosphatidylglycerol) -2 phosphatidic acids linked together by glycerol. -It is the major lipids in mitochondrial membrane of the heart.  B) Sphingophosphlipids: Sphingomyelin: Ceramide+ phosphoryl choline Niemann-Pick's disease: it is a genetic inborn error disease resulting from deficiency of sphingomyelinase enzyme lead to accumulation of sphingomyelin in liver and spleen which leads to hepatomegaly, splenomegaly, mental retardation and death in early life. II. Glycolipids (Glycosphingolipids) Fatty acid+ sphingosine+ carbohydrates. A) Neutral glycolipids (Cerebrosides): Ceramide + monosaccharide(glucose or galactose) Galactocerebroside: the major glycosphingolipids of the brain and other nervous tissues Glucocerebroside: the predominant simple glycosphingolipids of extra neural tissues (1) Nervon: the fatty acid is nervonic acid. (2) Kerasin: the fatty acid is lignoceric acid. (3) Oxynervon: the fatty acid is hydroxy nervonic acid. (4) Cerebron: the fatty acid is cerebronic acid. Functions of neutral glycolipids: Neutral glycosphingolipids are constituents of the outer plasma cell membrane, concerned with: ▪ Cell to cell communication and recognition. ▪ Tissue immunity. ▪ Species specificity. ▪ Blood group antigens. B) Acidic glycolipids (Gangliosides): Ceramide + glucose and galactose+ one or more sialic acid (NANA) Functions oF gangliosides: ▪ Highly concentrated ganglionic cell of nervous tissues especially nerve endings participate in transmission of nerve impulses across synapses. ▪ They are receptors to toxins (viruses and tetanus). ▪ They mediate cell-cell recognition. ▪ They act as tumor marker on surface of tumor cells. Tay-Sach's disease: It a genetic inborn error disease characterized by accumulation of large amount of gangliosides in brain and viscera due to absence of β-galactosidase enzyme leads to mental retardation, hepatomegaly, splenomegaly and death. IV. Lipoproteins lipids conjugated with protein. -The plasma lipids are TAG, phospholipids, free cholesterol , esterified cholesterol and free fatty acids. conjugated with proteins synthesized by the liver forming lipoproteins -This facilitates transport of lipids between blood and different tissues.  Composition of lipoproteins in human plasma Fraction Source Protein% Main contents Chylomicrons Intestine 1-2% Triacylglycerol from chyle Pre-β-lipoprotein Liver and intestine 7-10% Triacylglycerol from liver (VLDL) β-lipoprotein Chylomicrons and VLDL 22% 60% cholesterol (LDL) 40% phospholipid α-lipoprotein Liver and intestine 56% 60% phospholipid (HDL) 40% cholesterol NEFA Adipose tissue 99% 1% free fatty acids  Derived lipids Sterols and steroids: cyclic compound that contains cyclopentano perhydrophenanthrene ring or steroid nucleus The most important steroids ❑ Cholesterol (animal origin). ❑ Ergosterol (plant origin). ❑ Vitamin D group (D2 and D3). ❑ Bile salts. ❑ Steroid hormones (male and female sex hormones, adrenocortical hormones). ❑ Digitalis glycosides. ❑ Cholesterol (animal sterol): ▪ It is often found as cholesterol ester. Function: ▪ It enters in the structure of everybody cell. ▪ It is the major constituent of the plasma membrane. ▪ It is the precursor of all steroid hormones. ▪ It is oxidized in the liver to give cholic acid which forms bile salts. ▪ It is oxidized to give 7-dehydrocholesterol, a provitamin present under the skin which gives vitamin D3 by ultraviolet rays. ▪ High level of cholesterol in blood will lead to atherosclerosis and gall stone. ❑ Vitamin D group: Vitamin D3 (cholecalciferol) is derived from 7-dehydrocholesterol by the rupture of second ring by ultraviolet rays. Vitamin D2 (ergocalciferol) is derived from ergosterol by the rupture of second ring by ultraviolet rays. ❑ Bile acids and salts: Bile acids (cholic acid): They are the end products of cholesterol catabolism in the body Bile salts: are bile acids conjugated with glycine or taurine. types of bile salts: sodium or potassium glycocholate and sodium or potassium taurocholate. Functions of bile salts: ▪ They activate pancreatic lipase. ▪ They have emulsifying and hydrotropic action; help in lipid digestion and absorption. ▪ They have choleretic action i.e. they stimulate liver cells to secrete bile. ▪ They help absorption of fat soluble vitamins ❑ Hormones of steroid nature: 1. Female sex hormones: a-Estrogens: b-Progesterone: 2. Male sex hormones (testosterone): 3. Adrenal cortical hormones (corticoids):