1. 1- Based on structure
1.1. A- Aliphatic amino acids
1.1.1. a. Mono amino mono carboxylic acids
1.1.1.1. Simple amino acids
1.1.1.1.1. 1.Glycine
1.1.1.1.2. 2.Alanine
1.1.1.2. Branched chain amino amino acids
1.1.1.2.1. 3.Valine
1.1.1.2.2. 4.Leucine
1.1.1.2.3. 5.Isoleucine
1.1.1.3. Hydroxy amino acids
1.1.1.3.1. 6.Serine
1.1.1.3.2. 7.Threonine
1.1.1.4. Sulphur containing
1.1.1.4.1. 8.Cysteine
1.1.1.4.2. 9.Methionine
1.1.1.5. Having amide group
1.1.1.5.1. 10.Aspargine
1.1.1.5.2. 11.Glutamine
1.1.2. b. Mono amino dicarboxylic acids
1.1.2.1. 12.asparticacid
1.1.2.2. 13.Glutamicacid
1.1.3. c. Di basic mono carboxylic acids
1.1.3.1. 14.Lysine
1.1.3.2. 15.Arginine
1.2. B. Aromatic amino acids
1.2.1. 16.Phenylalanine
1.2.2. 17.Tyrosine
1.3. C. Hetero cyclic amino acids
1.3.1. 18.Tryptophan
1.3.2. 19.Histidine
1.4. D. Imino
1.4.1. 20.Proline
1.5. E. Derived amino acids
1.5.1. found in proteins
1.5.1.1. hydroxy proline
1.5.1.2. hydroxy lysine
1.5.2. not seen in proteins
1.5.2.1. .Ornithine
1.5.2.2. Citrulline
1.5.2.3. Homocysteine
2. 2. side chain
2.1. A Amino acids having non polar side chain
2.1.1. Alanine ,Valine. Leucine , Isoleucine , Methionine, Proline, Phenylalanine and Tryptophan
2.2. B Amino acids having uncharged or non ionic polar side chains
2.2.1. Glycine ,Serine, Threonine, Cysteine ,Tyrosine, Glutamine and Asparagine belong to this group
2.3. C-Amino acids having charged or ionic polar side chains
2.3.1. a. Acidic amino acids
2.3.1.1. Aspartic acid
2.3.1.2. Glutamic acid
2.3.1.3. Tyrosine is mildly acidic
2.3.2. b. Basic amino acids
2.3.2.1. Lysine
2.3.2.2. Arginine
2.3.2.3. Histidine
3. 3- based on metabolic fate
3.1. A- Purely Ketogenic
3.2. B- Ketogenic and Glucogenic
3.2.1. Lysine, Isoleucine ,Phenylalanine ,Tyrosine and Trptophan
3.3. C- Purely Glucogenic
3.3.1. All the remaining 14 amino acids are purely glucogenic as they enter only into the glucogenic pathway
4. 4- based on nutritional requirements
4.1. A-Essential or indispensable
4.1.1. Leucine, Threonine ,Lysine, Methionine, Phenylalanine, Tryptophan and Valine are essential amino acids.
4.2. B-Partially essential or Semi-essentia
4.2.1. Histidine and Arginine are semi essential amino acids
4.3. C-Non-essential or dispensible
4.3.1. The remaining 10 amino acids are non-essential