Lipids The term Lipid applies to a class of compounds that are soluble in organic solvent and nearly in soluble in water. Chemically: Lipids are either compounds that yield fatty acids on hydrolysis or complex alcohols that can combine with fatty acids to form esters.

 Some lipids contain non lipid groups such as sialic, phosphoryl, amino or sulphate groups.  These molecules gives lipid molecules an affinity for both water and organic solvents which is important in the formation of biological membranes.

Classification of clinically important lipids Sterol Derivatives: Cholesterol and Cholesterol esters. Steroid hormones. Bile acids Vitamin D. Fatty Acids: Short chain (2 to 4 carbon atoms). Medium chain (6to 10 carbon atoms). Long chain (12 to 26carbon atoms) {Prostaglandin}.

Glycerol Esters: Triglycerides, diglycerides, and monoglycerides (acyleglycerol). Phosphglycerides. Sphingosine Derivatives: Sphingomyellin. Glycosphing lipids. Terpenes (Isoprene Polymers): Vitamin A. Vitamin E. Vitamin K.

Cholesterol Is a steroid alcohol with 27 carbon atoms that are arranged in a tetracyclical perhydrocyclopentanophenantherene (sterane) skeleton. Sterols are steroid backbones that have a hydroxyl group at position 3 and a branched aliphatic chain of 8 or more carbons at position 17.

Cholesterol  It is found exclusively in animals, in which virtually all cells and body fluids contain some cholesterol.  Knowledge of the numbering system of carbon atoms found in cholesterol is important because it is the initial starting point in other metabolic pathways, including vit D, steroid hormones and bile acid synthesis.

Fatty acids RCOOH is a general chemical formula for a fatty acid where R is alkyl chain. Fatty acid chain lengths vary and commonly are classified according to the number of carbon atom present. The defined groups of fatty acids are:- Short chain (2 to 4 carbon atoms). Medium chain (6to 10 carbon atoms). Long chain (12 to 26carbon atoms). Those of importance in human nutrition and metabolism are of the long chain class containing.

Fatty acids are classified further according to their degree of saturation:  Saturated Fatty acids have no double bonds between carbon atoms.  Monounsaturated Fatty acids contain one double bond.  Polyunsaturated Fatty acids contain more than one double bond. The double bonds in polyunsaturated fatty acids of both animals and plant origin are usually three carbon atoms apart.

Fatty acids

Types of Lipids  Lipids with fatty acids Waxes Fats and oils (trigycerides) Phospholipids Sphingolipids  Lipids without fatty acids Steroids 11

Fatty Acids  Long-chain carboxylic acids  Insoluble in water  Typically carbon atoms (even number)  Some contain double bonds corn oil contains 86% unsaturated fatty acids and 14% saturated fatty acids 12

Saturated and Unsaturated Fatty Acids Saturated = C–C bonds Unsaturated = one or more C=C bonds 13

Structures Saturated fatty acids  Fit closely in regular pattern Unsaturated fatty acids  Cis double bonds 14

Properties of Saturated Fatty Acids  Contain only single C–C bonds  Closely packed  Strong attractions between chains  High melting points  Solids at room temperature 15

Properties of Unsaturated Fatty Acids  Contain one or more double C=C bonds  Nonlinear chains do not allow molecules to pack closely  Few interactions between chains  Low melting points  Liquids at room temperature 16

Fats and Oils Formed from glycerol and fatty acids 17

Triglycerides (triacylglcerols) Esters of glycerol and fatty acids 18

Properties of Triglycerides Hydrogenation  Unsaturated compounds react with H 2  Ni catalyst  C=C bonds C–Cbonds Hydrolysis  Split by water and acid or enzyme catalyst  Produce glycerol and 3 fatty acids 19

Hydrogenation 20

Product of Hydrogenation  Hydrogenation converts double bonds in oils to single bonds.  The solid products are used to make margarine and other hydrogenated items. 21

Hydrolysis Triglycerides split into glycerol and three fatty acids (H + or enzyme catalyst) 22

Saponification and Soap  Hydrolysis with a strong base  Triglycerides split into glycerol and the salts of fatty acids  The salts of fatty acids are “soaps”  KOH gives softer soaps 23

Saponification 24

Glycerol esters (acylglycerols) Glycerol is a three-carbon alcohol that contains a hydroxyl group on each of its carbon atom. Each hydroxyl can be esterified with a fatty acid. GlycerolTriglyceride The class of acyglycerol (glyceride) is determind by the number of fatty acyl-groups present; (monoglycerides,diglycerides and triglycerides)

Triglycerides In human nutrition, triglycerides constitute 95% of tissue storage fat and are the predominant form of glyceryl ester found in plasma. The fatty acid residues found in (monoglycerides, diglycerides, or triglycerides) vary considerably and usually include combinations of the long-chain fatty acids.

Triglycerides T riglycerides from plants tend to have large amount of C 18 :2 or linoleic residues and are liquid at room temperature (RT). T riglycerides from animals especially ruminants, tend to have C 12 :0 through C 18 :0 fatty- acid residues (saturated fats) and are solid at RT. Some plant triglyceride, such as coconut oil, are highly saturated and may be solid at RT.

Phospholipids are complex lipids, resembling triglycerides, but containing phosphate and a nitrogenous base in place of one of the fatty acids. They are important components of cell membranes and lipoproteins, maintaining the solubility of non-polar lipids and cholesterol. PHOSPHOLIPID