LIPIDS

DEFINITION

-          Lipids are heterogeneous group of compounds related to fatty acids.

-          These include fats acids and waxes.

                                      

-          These are insoluble in water but soluble in organic solvents such as chloroform.

-          All lipid molecules are amphiphatic which means they are both hydrophilic and hydrophobic.

-          These help in the formation of bio-membranes.

                                                 

FATTY ACIDS

-          These are long chain organic compounds containing 4-30 carbons.

-          These have a single carboxyl group and a long tail of non-polar hydrocarbon.

                                           

-          Fatty acids that occur in natural fats have a ‘mono carboxyl group’ with even number of carbon atoms.

-          These are usually straight chain derivatives.

-           Fatty acids with ring structure are called cyclic fatty acids.

-          Fatty acids are bounded to each other by ‘ester linkage’.
                                              

-          Fatty acids are used as energy reserves in humans and other animals.

-          Fatty acids are classified into two types: -

.       Saturated fatty acids
                         

.      Unsaturated fatty acids

SATURATED FATTY ACIDS

-          These are fatty acids in which only single bonds exist.

-          The general formula is CnH2n+1COOH.

-          These have even number of carbon atoms, fatty acids with odd number of carbon atoms is less than 1%.

                                      

-          Fatty acids present in animals are palmitic acid and steric acids.

UNSATURATED FATTY ACIDS

-          These are fatty acids with double and triple bonds.

-          These are classified on the basis of number of double and triple bonds present.

o   Monoethenoid acids: - these have only one double bond, CnH2n-1COOH.

o   Diethinoid acids: - two double bonds, CnH2n-3COOH.
                                    

o   Triethenoid acids: - three double bonds, CnH2n-5COOH.

o   Tetraethenoid acids: - four double bonds, CnH2n-7COOH.

-          Monoethenoids are called monounsaturated fatty acids and rest are called polyunsaturated fatty acids.

-          Some unsaturated fatty acids are not synthesised by our body and are called essential fatty acids. Example: - linoleic acid and linolenic acid.

-          These are found in vegetable oils and fish oil.

BIOLOGICAL ROLE OF LIPIDS

-          Food materials.

o   High calorific value.

o   One gram produces 9.8 Kcal of heat.

-          Food reserve.

o   Since these are insoluble, they are stored as food reserves in our body.

-          Structural component.

o   Important constituent of cell membranes.

-          Heat insulation.
                                  

-          Fatty acid absorption.

-          Hormone synthesis.

o   Many hormones are synthesised from lipids like cholesterol.

-          Vitamin carried.

o   These carry fat soluble vitamins like vitamin A, D, E and K.