Lipids – Definition, Classification and Properties

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Lipids – Definition, Classification and Properties

The term lipid was first used by the German biochemist Bloor in 1943

Definition of Lipid:
Chemically lipids are defined as esters of glycerol and fatty acids or as the triglycerides of fatty acids,

General formula of lipid = Glycerol + Fatty acid = Triglycerides


H2-C-OH                                    H2-C-OOC.C15H31
       I                                                          I
  H-C-OH + 3C15H31COOH                   H-C-OOC.C15H31 + 3H20
       I                                                   I
H2-C-OH                                    H2-C-OOC.C15H31

Glycerol         Palmitic Acid     Tripalmitine                                                                                                                                                                                                                             Water
(1 Mole)           (3 Moles)    (1 Mole)                           (3 Moles)

Classification of Lipid:

A) On the basic of Reaction with NaOH / KOH:

 i) Saponifiable
ii) Non saponifiable

B) On the basis to Products of Hydrolysis:

1) Simple Lipids:

On hydrolysis gives fatty acids and alcohol (trihydric or monohydric)

Oils: Unsaturated fatty acid + glycerol.
Fats: Saturated fatty acids + glycerol,
Waxes: Fatty acids + mono or dihydric alcohol.
Simple glyceride: Contains same fatty acids. .
Mixed glyceride: Contains different fatty acids.

2) Compound lipids: (Complex lipids):

On hydrolysis gives phosphoric acid, various sugars, sphingosine, ethanolamine and serine in addition to fatty acids and glycerol.


a) Phospholipid:  Fatty acids + glycerol + phosphoric acid + nitrogenous base.
e.g. Lecithin :Fatty acids + glycerol + phosphoric acid + choline
Cephalin: Fatty acids + glycerol + phosphoric acid + ethanolamine.

b) Glycolipids: Glycerol + fatty acid + Carbohydrates (on hydrolysis)

They are sub classified as galactosyl diglyceride, cerebrosides and sulpholipids.

c) Sphingophosphoiplds: Fatty acids + sphingosine + phosphoric acid + choline.

3) Derived Lipids: Hydrolytic products of simple and compound lipids

i) Alcohols: Glycerol and other sterol
ii) Fatty acids
iii) Terpenoids

Chemical Properties of Lipids:

i) Hydrolysis
ii) Hydrogenation
iii) Halogenation
iv) Saponification
 v) Oxidation
vi) Rancidity (oxidative and hydrolytic)

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