Lipids

The features that characterize lipids include the following:

1. They are either liquids or non-crystalline solids at room temperature.
2. They are less dense than water.
3. They are hydrolyzed by alkalis into their respective constituent compounds. This process is called saponification.
4. They contain either saturated or unsaturated hydrocarbon chains.
5. In the presence of water and alcohol, they form an emulsion.

They are esters of higher aliphatic alcohols.

All lipids are insoluble in water but soluble in organic compounds or solvents, e.g., ether, chloroform, and hot alcohol.

They occur in adipose tissues of animals and some are a component of the protoplasm of all living cells.

Lipids have an ester linkage.

i.e.

Because of unsaturated bonds which are easy to break, they are liquid at room temperature; solids contain saturated bonds.

Simple lipids are oils and fats, which are esters of glycerol (higher alcohols). Glycerol forms esters called waxes.

Oils and fats are formed by the combination of fatty acids and glycerol, e.g., oleic acid, which are widely distributed in many fats and oils.

They are also known as triglycerides.

They are a mixture of glycerides (esters) of fatty acids and glycerol.

Oils: contain a greater proportion of unsaturated fatty acids; they are liquid at 20°C.

Fats: contain a greater proportion of saturated fatty acids; they are solids at 20°C.

1. They form an insulation material, thus preventing heat loss in organisms and animals particularly.
2. Prevent water loss, form waterproof coatings in organisms, plants, and insects.
3. Can be a stored form of energy in the body of an organism, e.g., amoeba and seeds.
4. Form the basic constituent of the cell membrane as well as cell components, e.g., phospholipids.
5. Enable large aquatic organisms like whales to have buoyancy.
6. Contain basic fat-soluble vitamins A, D, E, and K.
7. Form natural rubber.
8. Are a constituent of hormones like steroids, e.g., oestrogen, progesterone; also ecdysone hormone in insects and crustaceans are made up of lipids.
9. Provide more energy in metabolism.
10. Are used to make bile salts (sodium taurocholate and sodium glycocholate) for emulsification in the duodenum.
11. Limit the linkage of small molecules across the plasma membrane (cholesterol).
12. Are a constituent of the myelin sheath; this helps to prevent outward flow of ions which would short circuit the movement of ions along the nerve, also enhancing saltatory conduction.