FAT Presented by Dr Sabbir Ansari Department of

FAT Presented by Dr. Sabbir Ansari Department of Zoology

INTRODUCTION: The word lipid is derived from a Greek word “lipos” which means FAT. These are heterogenous group of compounds Unlike proteins, nucleic acids, polysaccharides, lipids are not polymers rather they are small molecules. They are the chief storage form of energy, besides their role in cellular structure and other biochemical functions.

DEFINITION: Lipids may be regarded as organic substances relatively insoluble in water, soluble in organic solvents, actually or potentially related to fatty acids and utilized by the living cells.

FUNCTIONS: ØFat is stored in adipose tissue, where it also serves as a thermal insulator in the subcutaneous tissues. Ø Fatty acid derivatives serve as vitamins(A, D, E&K) or hormones. ØIt act as energy/food reservoir (Triacylglycerol). ØSeveral proteins are covalently modified by fatty acids. Ø Structural components of biological membranes (lipoprotein, phospholipids &sphingomyelins).

CLASSIFICATION: Lipids are broadly classified into 3 types which are the following: I. Simple lipids II. Complex lipids III. Derived lipids

� � � I. SIMPLE LIPIDS: Esters of fatty acids with glycerol. Mainly of two types: i. Fats and oils: -These are esters of fatty acids and glycerol. Fats have saturated fatty acids with high melting point, so solid. E. g. animal fats Oils have unsaturated fatty acid with low melting point so liquid. E. g. Plant oils ii. Waxes : -Esters of long chain fatty acids and long chain high molecular weight monohydroxy alcohol but not glycerol. E. g. Beewax, sperm whale wax

II. COMPLEX OR COMPOUND LIPIDS: �Esters of fatty acids+Alcohol+other groups like phosphate, Nitrogenous base, carbohydrate , Protein, etc. Based on the group present they are further classified into: 1. PHOSPHOLIPIDS: - • F. A+Alcohol+phosphoric acid as nitrogenous base. • Based on the type of alcohol present they are again divided into a. Glycerphospholipids: Contain Glycerol as alcohol. Eg: lecithin &cephalin b. Sphingophospholipids : Contain sphingosine as alcohol. Eg: sphingomyelin

2. GLYCOLIPIDS: • Fatty acids+alcohol+carbohydrate as nitrogenous base. • They contain sphingosine as alcohol and hence also known as GLYCOSPHINGOLIPIDS. Eg: Cerebrosides and Gangliosides. 3. LIPOPROTEINS: • Macromolecular complexes of lipids with proteins. • Eg: LDL, VLDL, Chylomicrons, HDL, etc

III. DERIVED LIPIDS: These are the derivatives of hydrolysis of simple and complex lipids which possess the characteristics of lipids. These include: • Lipid soluble vitamins • Steroid hormones • Terpenes • Ketone bodies • Carotenoids , etc

FATTY ACIDS �Carboxylic acids with hydrocarbon side chains. �� Occur in esterified form �� They occur in even and odd carbon forms �� Saturated and unsaturated. �� Essential and non essential fatty acids. �� Essential fatty acids are: �Linoleic acid �Linolenic acid �Arachidonic acid.