Lipids are waxy, greasy molecules found in the body that are water-insoluble and can be extracted from cells using non-polar solvents. They serve several general functions like as structural components of membranes, storage forms of metabolic fuel, and transport forms of metabolic fuel. Lipids are a heterogeneous group classified based on chemical composition including fatty acids, triacylglycerols, steroids, and fat-soluble vitamins. They also combine with sugars and proteins.

1. Lipids general properties
Lipids are the waxy, greasy, oily molecules found in the body. They are water-
insoluble (hydrophobic), and this property is put to great use in the organization of
cells and tissues. Lipids can normally be extracted from cells using non-polar solvents
such as chloroform or benzene.
They appear to serve several general functions in plants and animal cells.
(1) As structural component of membranes.
(2) As storage forms of metabolic fuel e.g. fats.
(3) As transport forms of metabolic fuel e.g. fatty acids.
(4) As protection against shock and insulation agents in cells/tissues.
The lipids are a very heterogeneous group of structural types, and the most prominent
members are grouped on the basis of chemical composition.
Steroids and fat soluble vitamins have no structural resemblance to fatty acids or
triacylglycerols, but they are grouped under lipids on the bases of their solubility in
organic solvents. As in other groups lipids form combinations with sugars
(glycolipids) and proteins (proteolipids).
Function
 Prostaglandin, cytokine synthesis
 Cell differentiation and growth
 Cell membrane structure, myelination
 Signal transmission
 Hormone synthesis
 Bile acid synthesis