Lipid chemistry and metabolism Faculty of nursing CHEM 203 Biochemistry UNIT V Lipid chemistry and metabolism part 1 Dr.Ola Fouad Talkhan

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 (Compound lipids) This group is derived from the non saponifiable fraction -Phospholipids -Glycolipids -Lipoproteins Neutral fat waxes Liquids e.g.oils Solids fats Dr.Ola Fouad Talkhan

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

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

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

Dr.Ola Fouad Talkhan

a)Neutral fats(triacylglycerols): 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

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

The chemical constituents of Triacylglycerols (TAG): They are esters resulting from the reaction of fatty acids(R-COOH) and glycerol(trihydroxy alcohol): O CH2-OH CH-OH R-COOH CH2-O-C-R CH-O- C-R CH2-O- C-R - 3 H2O + O O Glycerol 3 molecules of fatty acids General formula of TAG Dr.Ola Fouad Talkhan

Triacylglycerols are formed from glycerol and fatty acids by: ester bonds Dr.Ola Fouad Talkhan

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). The carbon skeleton of fatty acids are numbered either from the carboxylic group or from the terminal methyl group Dr.Ola Fouad Talkhan

Starting from the terminal methyl group or omega carbon (ω) Starting from the carboxylic group: There are two systems as follows: By giving the carboxylic group the number 1 and proceed toward the –CH3 b) By using α, β, γ system, where α-carbon is the first carbon adjust to the carbobylic group. Starting from the terminal methyl group or omega carbon (ω) Dr.Ola Fouad Talkhan

1-Saturated fatty acids (common names): they contain an even number of carbons atoms.their general formula is: Cn H2n+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

Saturated Fatty Acids Saturated fatty acids have single C–C bonds. Dr.Ola Fouad Talkhan

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 Cn H2n - 1 COOH Palmitoleic acid (16:1), Δ9 Oleic acid (18:1), Δ9 Linoleic acid (18:2), Δ9,12 -Linolenic acid (18:3), Δ9,12,15 -Linolenic acid (18:3), Δ6,9,12 Arachidonic acid (20:4), Δ5,8,11,14 Most naturally occuring double bonds in lipids are cis. Dr.Ola Fouad Talkhan

Unsaturated fatty acids (USFA) Unsaturated fatty acids are classified into four families according to the position of the first double bond in relation to the omega carbon (ω3, ω6 , ω7 and ω9 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 (CH2) group Dr.Ola Fouad Talkhan

Structure of some unsaturated fatty acids. 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

In vegetable oils is at carbon 6 (omega-6). 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

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: O CH2-OH CH2-O-C-C17H35 - 3H2O O CH-OH + 3 C17H35COOH CH-O-C-C17H35 glycerol 3 stearic acid tristearin Dr.Ola Fouad Talkhan

Stearo-oleo-palmitin triacylglycerol b)Mixed triacylglycerols: In which the fatty acids attached to glycerol are different, e.g.stearo-oleo-palmitin CH2-OH C17H35-COOH stearic acid CH-OH + C17H33-COOH oleic acid CH2-OH C15H31-COOH palmitic acid O CH2-O-C-C17H35 O CH- O-C-C17H35 CH2-O-C-C15H35 Stearo-oleo-palmitin triacylglycerol Dr.Ola Fouad Talkhan

Dr.Ola Fouad Talkhan

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

Neutral fat waxes 1)Contain glycerol Contain higher monohydroxy alcohol 2) Cntain three fatty acids Cotain one fatty acids 3)May be solid or liquid Usually solid 4)Can be digested Cannot 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

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

Glycerophospholipids Glycerophospholipids are: The most abundant lipids in cell membranes. Composed of glycerol, two fatty acids, phosphate and an amino alcohol. Fatty acid Glycerol Fatty acid PO4 Amino alcohol Dr.Ola Fouad Talkhan

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 CH2-OH CH-OH + 2 R-COOH + H3PO4 -3H2O O Fatty acid Phosphoric acid CH2-O-C-R O CH- O-C-R CH2-O-P OH Dr.Ola Fouad Talkhan

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

Polarity of Glycerophospholipids A glycerophospholipid has polar and nonpolar regions. Dr.Ola Fouad Talkhan

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

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

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

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 α- and β-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

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

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

3)Derived lipids: Sterols and Steroids 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

-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 12 17 11 13 16 15 C D 14 1 10 A B 2 9 8 3 7 4 5 6 Sterols They are one of the non saponifiable fraction of fat. The most important one is the cholesterol. Dr.Ola Fouad Talkhan

Cholesterol Cholesterol is: The most abundant sterols in the body. Composed of the steroid nucleus with methyl CH3– groups, an alkyl chain, and a hydroxyl group –OH attached. Cholesterol Dr.Ola Fouad Talkhan

Cholesterol in Foods Cholesterol: Is considered elevated if plasma cholesterol exceeds 200-220 mg/dL. Is synthesized in the liver and obtained from foods. Dr.Ola Fouad Talkhan

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