Lipids are organic molecules that are insoluble in water but soluble in non-polar solvents. They provide structure to cell membranes, store energy, and function as signaling molecules. Lipids include fats, oils, waxes, phospholipids, glycolipids, steroids, terpenes, and carotenoids. Fats and oils are triglycerides made of glycerol bonded to three fatty acids, and are solid or liquid depending on temperature. Phospholipids contain fatty acids, glycerol, and a phosphate group, giving them a polar structure. Steroids do not contain fatty acids and are nonsaponifiable.

2. • Definition : Lipids are organic molecule of biological origin
that are insoluble in water and soluble in non-polar
solvents.
• The chemical composition of these molecules includes
hydrogen, carbon, and oxygen.
• They provide high energy and perform three important
biological functions in the body: to provide structure to cell
membranes, to store energy, and to function as signalling
molecules.
• They include fats and oils – mostly triglycerides
– Fat: solid at room temperature
– Oil: liquid at room temperature

3. Classification Of Lipids

4. • Simple lipids are esters of fatty acid linked with various
alcohols.
• Fats and oils (triglycerides)
• These esters of fatty acid have glycerol, a trihydroxy alcohol.
• Triglycerides are abundant and constitute about 98 percent of
all dietary lipids.
• Waxes
• Waxes are long-chain saturated and unsaturated fatty acid
esters with monohydroxy alcohols, which have high molecular
weight.
• Waxes are produced naturally by skin glands as a protection,
to keep it lubricated and water-proof.

6. • Heterolipids are fatty acid esters with alcohol and additional groups.
• Phospholipids (phosphatids)
• Phospholipids contain fatty acids, glycerol, nitrogen bases, phosphoric acid,
and other substituents. As their name implies, phospholipids contain
phosphorus in the form of phosphoric acid groups. Their molecular
structure is polar, consisting of one hydrophilic head group and two
hydrophobic tails.
• Glycolipids (cerebrosides)
• Glycolipids are fatty acids with carbohydrates and nitrogen but without
phosphoric acid. Glycolipids also include some compounds like sulfolipids,
gangliosides, and sulfatids which are structurally-related.

8. • These substances are derived by hydrolysis from compound and
simple lipids. These fatty acids include carotenoids, steroids, and
terpenes.
• Steroids
• The steroids are the most studied types of fat. They contain no fatty
acids and unlike fats, are nonsaponifiable (cannot be hydrolyzed to
yield soap).
• Cholesterol
• Cholesterol is a well-studied lipid, because of its strong correlation
with the incidence cardiovascular disease. It is an important
component of cell membranes and plasma lipoproteins, and is an
important precursor of many biologically important substances like
bile acids and steroid hormones.

10. • Terpenes
They are large group of volatile unsaturated
hydrocarbons found in the essential oils of plants,
especially conifers and citrus trees.
• Carotenoids
They are a class of mainly yellow, orange, or red fat-
soluble pigments, including carotene, which give
colour to plant parts such as ripe tomatoes and
autumn leaves.