Lipids
Lipids comprise very heterogeneous group of compounds which are insoluble in water but
soluble in non-polar organic solvents such us benzene, chloroform, and ether. They are present
in all living organisms. The group includes fats, oils, waxes and related compounds.
General Functions of Lipids
- They are efficient energy sources.
- Serve as thermal insulators.
- They are structural components of the cell membrane.
- Serve as precursors for hormones (steroid hormones).
- They also dissolve the vitamins, which are fat-soluble and assist their digestion.
Classification: - There are two ways of classification i.e.,
- Classification as storage and structural lipids and some other functional lipids.
- Classification based on lipid composition.
I. Simple lipids:- esters of fatty acids with different alcohols.
Fats and oils:- These are esters of fatty acids with glycerol.
Waxes:- Esters of fatty acids with high molecular weight monohydric alcohols
II. Complex lipids:- Esters of fatty acids and alcohols together with some other head
groups.
A. Phospholipids:- Esters of the above type containing phosphoric acid residue.
a) Glycerophospholipids:- The alcohol is glycerol
b) Sphingophospholipids:- The alcohol is shingosine.
B. Glycolipids:- Lipids containing fatty acid, sphingosine and carbohydrate residues.
C. Others:- Include sulfolipids, amino lipids and lipoproteins, which are modified forms of
lipids.
III. Derived lipids: include the hydrolytic products of the simple and complex lipids. Eg. Fatty
acids, cholesterol etc.
The simplest naturally occurring lipids are triacylglycerols formed by esterification of fatty acids
with glycerol. Biological membranes are made up of phospholipids, glycolipids and proteoglycans.