Amino acids are classified as acidic, basic or neutral depending upon the relative number of amino and carboxyl groups in their molecule.
Equal number of amino and carboxyl groups makes it neutral, more number of amino than carboxyl groups makes it basic and more carboxyl as compared to amino groups makes it acidic.
Essential amino acids : The amino acids which cannot be synthesised in the body and must be obtained through diet, are known as essential amino acids.
Example : Valine, Leucine.
Non-essential amino acids : The acids, which can be synthesised in the body are known as non-essential amino acids.
Exmple : Alanine, Aspartic acid.