This document provides an overview of lipids, including: 1. Lipids are organic compounds that are insoluble in water and soluble in organic solvents. They serve as concentrated energy stores and play roles in cellular structure and biochemical functions. 2. Lipids can be broadly classified into simple lipids, complex lipids, derived lipids, and miscellaneous lipids. Simple lipids include fats, oils, and waxes. Complex lipids contain additional groups like phosphate and nitrogenous bases. 3. Key functions of lipids include serving as concentrated fuel reserves, constituting cell membranes, being a source of fat-soluble vitamins, and acting as cellular metabolic regulators like steroid hormones.

1. Lecture 6
Lipids

2. Introduction
 Lipids (lipos-fat) are of great importance to the
body as the chief concentrated storage form
of energy, besides their role in cellular
structure and various other biochemical
functions
 Lipids are heterogeneous group of
compounds

3. Definition
 Organic substances relatively insoluble in water,
soluble in organic solvents ( alcohol, ether etc),
actually or potentially related to fatty acids and
utilized by the living cells
 They are not polymer unlike proteins and nucleic
acid
 They are mostly small molecules

4. Classification
Broadly classified into
 Simple lipids
 Complex lipids
 Derived lipids
 Miscellaneous lipids
They are subdivided into different groups

5. a)Simple lipids
 Esters of fatty acids with alcohol
 They are of two types
1. Fats and oils: these are esters of fatty acids with
glycerol.The difference is only physical
between them
2. Waxes: esters of fatty acids (long chain) with
alcohol other than glycerol. They may be
aliphatic or alicyclic. Cetyl alcohol is most
commonly found in waxes. They are used in the
preparation of candles, lubricants, cosmatics,
polishes etc

6. b)Complex or compound lipids
 These are esters of fatty acids with alcohol
containing additional groups such as phosphate,
nitrogenous base, carbohydrates, proteins etc
 They are further subdivided as:
1. Phospholipids: they contain phosphoric and
frequently a nitrogenous base. This is in addition
to alcohol and fatty acids

7. 2. Glycerophospholipids: these phospholipids
contain glycerol as the alcohol
Eg. Lecithin, cephalin
3. Sphingophospholipids: these lipids contain a
fatty acid , carbohydrate and nitrogenous base.
The alcohol is sphingosine hence also called
glycosphingolipids. Glycerol and phosphate are
absent eg. Cerebrosides, gangliosides

8. 4. lipoproteins: macromolecules complexes of lipids
with proteins
5. Other complex lipids: sulfolipids, aminolipids and
lipopolysaccharides are among the other
commplex lipids

9. c) Derived lipids
 These are the derivatives obtained on the
hydrolysis of group 1 and group 2 lipids which
possess the characteristics of lipids
 These include glycerol and other alcohols, fatty
acids, mono and diacylglycerol, lipid (fat) soluble
vitamins, steroid hormones, hydrocarbons and
ketone bodies

10. d) Micellaneous lipids
 These include a large number of compounds
possessing the characteristics of lipids
 For example: carotenoids, squalene,
hydrocarbons , terpenes etc
 Neutral lipids: the lipids which are uncharged
are referred to as neutral lipids.
e.g. mono-, di, and triacylglcerol, cholesterol.

11. Functions of lipids
Lipids perform several important functions
1. They are the concentrated fuel reserve of the
body (triacylglycerol)
2. They are the constituents of the membrane
structure and regulate the membrane
permeability (phospholipids and cholesterol)
3. They serve as a source of fat soluble vitamins
(A, D, E and K)

12. 4. Lipids are important as cellular metabolic
regulators (steroid hormones)
5. Lipid protect internal organs, serve as an
insulating materials and give shape and smooth
appearance to the body