What are lipids
Bloor in 1943
proposed the term lipid for those naturally occurring compounds which are
insoluble in water but soluble in organic solvent. These are also the compounds
containing carbon, hydrogen and oxygen like carbohydrate but contain much
lesser ration of oxygen than carbohydrates.
Lipids are
important diverse group of biological molecules widely distributed among plants
and animals.
(i) Acyl
glycerol (fats and oil)
(ii) Waxes
(iii)
Phospholipids
(iv) Terpenoids
(i) ACYL GLYCEROL
These are found
in plants and provide energy for different metabolic activity and are very rich
in chemical energy. When compared an equal amount of acyl glycerol contains
over twice the energy content than carbohydrate. It consists of glycerol
molecule linked to three fatty acids. This condensed molecule is also called a
Tetracyl glycerol (Trigly ceride). They
are two types
(a) Saturated
acyl glycerol: They contain saturated fatty acids i.e. they do not contain any
double bond between carbon atom. They solid at ordinary temperature, mostly
found in animals e.g. stearin.
(b) Unsaturated
acyl glycerol: They are liquid at ordinary temperature. They are found in plant
also called oil e.g. Linolin found in cotton seed contains Linoleic acid.
(ii) WAXES
Waxes are simple
lipids with one molecule of fatty acids forming bond with one molecule of long
chain alcohol e.g. Bee’s wax.
Waxes are found
as protective coating on stems, stalks, leaves, petals, fruit waxes are water
repellent and non reactive.
(iii) PHOSPHOLIPIDS
Phospholipids is
most important class of lipids from biological point of view. Phospholipid is
similar to Triacyl glycerol or an oil except that one fatty acid is replaced by
phosphate group. Phospholipid molecule consists of two end which are called
hydrophilic (water loving) end (heat) and hydrophobic (water fearing) end
(tail).
Phospholipids are
present in all living cells frequently associated with membranes and are
related to vital functions such as regulations of cell permeability and
transport processes. Proteins of cell membrane depend on their phospholipids
component.
(iv) TERPENOIDS
Terpenoid is a
large and important class of lipids built up of isoprenoid (C5H8)
units. Steroids, carotenoids and terpens are important classes of it. They help
in oxidation reduction processes as terpens, some are components of essential
oils of plants e.g. Menthal, camphor, mint etc. Plant pigments like carotene,
xanthophylls are also form of terpenoids.
(a) Terpenses: They
are volatile in nature produce special fragrance. Some of them are used in
perfumes e.g. Myrcene from oil of bay Geraniol from rose, limonene from lemon
oil and Menthol from peppermint oil.
(b) Carotenoids:
They consist of fatty acids like carbon chain which are conjugated by double
bonds and carrying 6 membrane carbon ring at each end. These compounds are
pigments producing red, orange, yellow, cream and brown colours in plants.
Another group of
pigmented compounds are Tetra phyrrol which are present as an important part of
familiar chlorophyll and cytochromes pigments.
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