Amino acids based on a number of NH2 and COOH groups can be classified into three types:
Neutral amino acids: The amino acids having an equal number of amino and carboxyl groups are called neutral amino acids. E.g. Glycine, alanine, valine, leucine, isoleucine, proline, methionine, tryptophan, phenylalanine, serine, threonine, cysteine, asparagine, glutamine, and tyrosine.
Acidic amino acids: The amino acids having more carboxyl groups as compared to amine groups are called acidic or negative amino acids. E.g. Aspartic acid and glutamic acid.
Basic amino acids: The amino acids having more amine groups as compared to carboxyl groups are called basic or negative amino acids. E.g. Lysine, arginine, and histidine.