Amino acid are organic compounds made up of carbon, hydrogen, oxygen and nitrogen. They consist of an amino group and an acidic group attached to the the same carbon called α-carbon. Thus, they are also known as α-amino acids. They are substituted methanes. Four groups occupy the four valency positions. The four groups being an amino group, a hydrogen, A carboxylic group and a variable R group. The R group could be a hydrogen(the amino acid is called glycine), a methyl group (alanine) etc. There are 20 amino acids that occur in proteins.

1. Lipids act as important storage compounds. 

2. They form membranous structures of the cell.

3. Lipids are rich source of energy and the energy produced by 1 gram of fat is more than twice than that produced from 1 gram of glucose.

4. They serve as main parts of cell wall in plants and form exoskeleton of insects.

5. In certain animals such as whale, polar bear etc. they form an insulating layer.

6. They are also used in the synthesis of steroid hormones and bile salts.

7. Fats from cushion like structures below vital organs such as brain, heart, kidneys, eyes etc. and protect them from mechanical shocks.

8. Fats insulate the nerve fibres electrically.

The resulting  linkage is called a peptide linkage and the product is called dipeptide. The C–N bond in the peptide linkage is called a peptide bond.