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Faculty of nursing CHEM 203 Biochemistry UNIT V Lipid chemistry and metabolism part 1 Dr.Ola Fouad Talkhan Slide 2 Lipids Lipids are water-insoluble organic substances found in cells which can be extracted by nonpolar solvent such chloroform, ether and benzen. All biological lipids are amphipathic (have both polar and nonpolar parts) Lipids are classified into three main groups as follow: Simple lipids Conjugated lipids Derived lipids Neutral fat waxes Liquids e.g.oils Solids fats -Phospholipids -Glycolipids -Lipoproteins This group is derived from the non saponifiable fraction (Compound lipids) Dr.Ola Fouad Talkhan Slide 3 Function of lipids 1- supply 20-25 % of daily caloric requirements 2- provides essentialfatty acids and fat soluble vitamins 3- render food palatable 4-preserve body temperature ( insulator for heat) 5- support of internal organs Dr.Ola Fouad Talkhan Slide 4 Lipids classified into : I ) Simple Lipids: esters of fatty acids with various alcohol : a) Neutral Fats : Esters of fatty acids with glycerol. b) Waxes: Esters of fatty acids with higher alcohols other than glycerol. II ) Complex lipids (Compound Lipids): Esters of fatty acids containing groups in addition to an alcohol and a fatty acid. a) Phospholipids: Lipids containing, in addition to fatty acids and an alcohol, a phosphoric acid residue. b) Glycolipids (glycosphingolipids): Lipids containing a fatty acid, sphingosine, and carbohydrate but no phosphoric acid and no glycerol. c) lipoproteins: Lipids attached to plasma protein. Dr.Ola Fouad Talkhan Slide 5 III)derived lipids: They are produced by hydrolysis of the above two groups or they are present in association with them in nature. These include: 1-fatty acids (both saturated and unsaturated). 2-alcohols: a) Glycerol. b) Sterols and other steriods, including vitamin D. c) Alcohols other than glycerol and sterol. d) Fatty aldehydes. Dr.Ola Fouad Talkhan Slide 6 Slide 7 1- Simple lipids a)Neutral fats(triacylglycerols): these are esters of fatty acids with the trihydroxy alcohol,glycerol. they include 2 types: -Solid at ordinary temperature and are called Fats. - Liquid at ordinary temperture and are called oils. Occurance of neutral fat: 1- in plants: Cotton seed oil, olive oil,lin seed oil oil,coconut oil,sesam oil and soya bean oil. 2- in animals: Butter,lard and mutton. 3- marin oils :(oils of see animals) Cod liver oil, halibut oil and shark oil.these oil are very rich in vitamin A and vitamin D. Dr.Ola Fouad Talkhan Slide 8 Triacylglycerols are a major energy source for many organisms. These have the most reduced form of carbon in nature which means that more energy is available on oxidation. They are stored in adipose tissue until metabolized for energy. They also have a role in insulation and act to cushion vital organs (liver, kidney,etc.). Dr.Ola Fouad Talkhan Slide 9 The chemical constituents of Triacylglycerols (TAG): They are esters resulting from the reaction of fatty acids(R-COOH) and glycerol(trihydroxy alcohol): The chemical constituents of Triacylglycerols (TAG): They are esters resulting from the reaction of fatty acids(R-COOH) and glycerol(trihydroxy alcohol): CH 2 -OH CH-OH CH 2 -OH R-COOH + CH 2 -O-C-R CH-O- C-R CH 2 -O- C-R O O O General formula of TAG Glycerol 3 molecules of fatty acids - 3 H 2 O Dr.Ola Fouad Talkhan Slide 10 Triacylglycerols are formed from glycerol and fatty acids by: ester bonds Dr.Ola Fouad Talkhan Slide 11 The carbon skeleton of fatty acids are numbered either from the carboxylic group or from the terminal methyl group Glycerol: It is trihydroxy alcohol cotains two terminal primary alcoholic groups and one second alcoholic group in the middle. Fatty acids:fatty acids found in nature have certain properties: 1-they are monocarboxylic acids ranging in chain length from 4 to about 34 carbon atoms. 2- the number of carbon atoms is even(with a few exceptions). 3- they may be saturated or unsaturated (contain one or more double bonds). Dr.Ola Fouad Talkhan Slide 12 Starting from the terminal methyl group or omega carbon () Starting from the carboxylic group: There are two systems as follows: a)By giving the carboxylic group the number 1 and proceed toward the CH 3 b)b) By using , , system, where -carbon is the first carbon adjust to the carbobylic group. Dr.Ola Fouad Talkhan Slide 13 1-Saturated fatty acids (common names): they contain an even number of carbons atoms.their general formula is: C n H 2n+1 COOH Common names and structures for fatty acids up to 20 carbons long - Butyric acid (4 C) Lauric acid (12 C) Myristic acid (14 C) Palmitic acid (16 C) Stearic acid (18 C) Arachidic acid (20 C) Dr.Ola Fouad Talkhan Slide 14 Saturated Fatty Acids Saturated fatty acids have single CC bonds. Dr.Ola Fouad Talkhan Slide 15 Palmitoleic acid (16:1), 9 Oleic acid (18:1), 9 Linoleic acid (18:2), 9,12 -Linolenic acid (18:3), 9,12,15 -Linolenic acid (18:3), 6,9,12 Arachidonic acid (20:4), 5,8,11,14 Most naturally occuring double bonds in lipids are cis. 2-Unsaturated fatty acids (common names): they contain an even number of carbons atoms and one or more double bonds. general formula C n H 2n - 1 COOH 2-Unsaturated fatty acids (common names): they contain an even number of carbons atoms and one or more double bonds. general formula C n H 2n - 1 COOH Dr.Ola Fouad Talkhan Slide 16 Unsaturated fatty acids are classified into four families according to the position of the first double bond in relation to the omega carbon (3, 6, 7 and 9 groups). Most of the double bonds in naturally present USFA are of the cis type. In case of polyunsaturated fatty acids (PUFA), each two double bonds are separated by methylene (CH 2 ) group Unsaturated fatty acids (USFA) Dr.Ola Fouad Talkhan Slide 17 The essential fatty acids: These acids are polyunsaturated fatty acids which contain more than one double bond,their essentiality is due to inability of the human body to form them so they must be taken in the diet. Structure of some unsaturated fatty acids. Dr.Ola Fouad Talkhan Slide 18 Omega-6 and Omega-3 Fatty Acids The first double bond: In vegetable oils is at carbon 6 (omega-6). In fish oils is at carbon 3 (omega-3). Dr.Ola Fouad Talkhan Slide 19 O CH 2 -OH CH 2 -O-C-C 17 H 35 - 3H 2 O O CH-OH + 3 C 17 H 35 COOH CH-O-C-C 17 H 35 O CH 2 -OH CH 2 -O-C-C 17 H 35 glycerol 3 stearic acid tristearin Types of triacylglycerols(TAG) There are 2 types: a)Simple triacylglycerols: in which the fatty acids attached to glycerol are similar e.g. tristearin: Dr.Ola Fouad Talkhan Slide 20 b)Mixed triacylglycerols : In which the fatty acids attached to glycerol are different, e.g.stearo-oleo-palmitin CH 2 -OH C 17 H 35 -COOH stearic acid CH-OH + C 17 H 33 -COOH oleic acid CH 2 -OH C 15 H 31 -COOH palmitic acid CH 2 -O-C-C 17 H 35 O CH- O-C-C 17 H 35 O CH 2 -O-C-C 15 H 35 Stearo-oleo-palmitin triacylglycerol O Dr.Ola Fouad Talkhan Slide 21 Slide 22 b)Waxes Waxes are: Esters of fatty acids with higher alcohols other than glycerol. Coatings that prevent loss of water by leaves of plants. Their importance are manufacture of lubericants,polishes,ointment and cosmotics Dr.Ola Fouad Talkhan Slide 23 Neutral fatwaxes 1)Contain glycerolContain higher monohydroxy alcohol 2) Cntain three fatty acidsCotain one fatty acids 3)May be solid or liquidUsually solid 4)Can be digestedCannot be digested 5)May get rancid.Do not become rancid 6)Utilised by the human body giving large amount of energy,so it is of high nutritional value. Not utilised by the human body so, it is not of nutritional value. Dr.Ola Fouad Talkhan Slide 24 2)Compound lipids or cojugated lipids: There are three types: 1)Phospholipids 2) glycolipids 3) lipoprotein 1- Phospholipids these cojugated lipids,their name indicate that contain phosphoric acid residue. they are abundant in all biological membranes. Phospholipids are derived from either glycerol,or sphingosine. Dr.Ola Fouad Talkhan Slide 25 Glycerophospholipids Glycerophospholipids are: The most abundant lipids in cell membranes. Composed of glycerol, two fatty acids, phosphate and an amino alcohol. Glycerol PO 4 Amino alcohol Fatty acid Dr.Ola Fouad Talkhan Slide 26 Phosphatidic acid: is parent compound of the phosphoglycerides,it occurs in only very small amounts in cells, but it is an important intermediate in the biosynthesis of the phosphoglycerides. It consists of: glycerol + 2 fatty acids + phosphoric acid CH 2 -OH CH-OH + 2 R-COOH + H 3 PO 4 CH 2 -OH -3H 2 O CH 2 -O-C-R O CH- O-C-R O CH 2 -O-P O OH Fatty acid Phosphoric acid Dr.Ola Fouad Talkhan Slide 27 Phosphoglycerides are derivatives of phosphatidic acid, in which the phosphate group becomes estrified to the hydroxyl group of several alcohols,e.g.; alcohol Phosphoglycerides name choline, phosphatidylcholine ( lecithins ) ethanolamine phosphatidylethanolamine ( cephalins ) serine phosphatidylserine ( cephalins ) inositol. Phosphatidylinositol ( lipositol) Phosphoglycerides:are polar lipids as it possess polar head in addition to their nonpolar hydrocarbon tails Dr.Ola Fouad Talkhan Slide 28 Polarity of Glycerophospholipids A glycerophospholipid has polar and nonpolar regions. Dr.Ola Fouad Talkhan Slide 29 Lecithin and Cephalin Lecithin and cephalin are glycerophospholipids: Abundant in brain and nerve tissues. Found in egg yolk, wheat germ, and yeast. Dr.Ola Fouad Talkhan Slide 30 1- Lecithins : - fatty acids present,one is saturated in position C-1, and the other in C-2 position is unsaturated. - is important in the metabolism of fat by the liver. -They may also be hydrolyzed by specific enzymes called lecithinases( is cobra venum can split off an unsaturated fatty acid,producing lysolecithin, a substance has the power of hemolyzing red blood corpuscles. Dr.Ola Fouad Talkhan Slide 31 2-Cephalin: resemble leithins in structure except that cholin is replaced by other components e.g.ethanolamine. Certain cephalins are constituents of lipoprotein 3-lipositol: consists of: - glycerol. - two fatty acids(saturated and unsaturated). - phosphoric acid. - inositol (six membered cyclic alcohol). 4-diphosphatidylglycerols: Lipositol and diphosphatidylglycerols are nitrogen free derivatives of phosphatidic acid. Dr.Ola Fouad Talkhan Slide 32 5-plasmalogen: resemble leithins and cephalins in structure but differ from them in that C-2 is esterified by along chain fatty acid and the fatty acid at C-1 is replaced by an - and -unsaturated ether. Choline or serine may be subsitituted for ethanolamine. 6- Cardiolipin: diphosphatidylglycerol found in the inner membrane of mitochondria,is the only phosphatidate with immunological Properties,and it utilized in the diagnosis of syphilis Dr.Ola Fouad Talkhan Slide 33 Phospholipids not containing glycerol Sphingolipids: contain sphingosine base instead of glycerol. sphingosine base is connected at its amino group by an amide linkage to a long saturated or monounsaturated fatty acid of 18 to 26 carbon atoms.the resulting compound is called ceramide. Ceramide : is the parent structure of all Sphingolipids. Sphingomyelin: One of Sphingolipids cosists of: sphingosine base. one fatty acid. phosphoric acid. choline. Dr.Ola Fouad Talkhan Slide 34 Biological importance of phospholipids: 1-they form the cell membrane, mitochodiria and golgi apparatus. 2-the brain and nerves are rich in cephalins and sphingomyelin. 3-cephalins are necessary for blood clotting. 4-phospholipids are necessary for absorption of lipids from the intestine. 5-phospholipids are necessary for transport of fat from the liver to the its stores. deficiency of choline, inositol and the amino acid methionine lead to accumulation of fat in the hepatic cells a condition called fatty liver. These substances are called lipotropic factors Dr.Ola Fouad Talkhan Slide 35 3)Derived lipids: These are substances derived from the simple and conjugated lipids by hydrolysis. Simple lipids derived lipids so drived lipids include: 1)fatty acids (saturated and un saturated). 2)glycerol. 3)polycyclic compound: e.g. sterols and steroids. Sterols and Steroids These are cyclic compound that contain perhydrophenantherene ring to which is attached with a cyclopentane producing nucleus known as: (cyclo-pentano-perhydrophenanthrene) or steroid nucleus hydrolysis. Dr.Ola Fouad Talkhan Slide 36 2 1 10 A B 5 6 7 8 17 4 9 11 12 13 14 16 15 C D 3 -if the derived compound has one or more OH groups and no carbonyl (-CHO or C=O) groups at carbon atom number 17, it is a sterol and its name is terminate by (OL) e.g. cholesterol. If drived compound has one or more carbonyl or carboxyl groups it is a steroid e.g.cortisone Sterols They are one of the non saponifiable fraction of fat. The most important one is the cholesterol. Dr.Ola Fouad Talkhan Slide 37 Cholesterol is: The most abundant sterols in the body. Composed of the steroid nucleus with methyl CH 3 groups, an alkyl chain, and a hydroxyl group OH attached. Cholesterol Dr.Ola Fouad Talkhan Slide 38 Cholesterol: Is considered elevated if plasma cholesterol exceeds 200-220 mg/dL. Is synthesized in the liver and obtained from foods. Cholesterol in Foods Dr.Ola Fouad Talkhan Slide 39 Biochemical derivatives of cholesterol: 1) 7-dehydrocholesterol: it gives vitamin D3 by irradiation with U.V.rays 2) Bile salts: these are sodium or potassium salts of glycocholic acid and tourocholic acid. the two acids derived from cholic acid. cholic acid is formed in the liver from cholesterol. Functions of bile salts: 1-Emulsification of fat. 2-Activate pancreatic lipase enzyme. 3- They essential for absorption of fat soluble vitamin. 4-They increase bile secrtion. 5- They anti putrification substances. Dr.Ola Fouad Talkhan