Amino acids can be classified in two main ways

1. Based on whether they can be synthesized by our body or not they are classified into :

1. Essential Amino Acids - These are not synthesized in animal cells and hence their presence in the food is essential. These are Threonine, Leucine, Lysine, Tryptophan, Phenylalanine, Valine, Isoleucine, Methionine.
2. Semi Essential Amino Acids - Arginine and Histidine , are synthesized in animal cells but not in sufficient quantity and therefore their presence in food is essential.
3. Non- Essential Amino Acids - These amino acids are synthesized in animal cells and hence their presence in food is not essential. Remaining amino acids belong to this category.

2. Based on their structural properties they are classified into neutral, acidic and basic amino acids.

1. Neutral Amino Acids - These have equal number of amino and carboxylic groups.They can be further subdivided.

Neutral Amino Acids Are further Classified into

• Aliphatic Amino Acids - Glycine , Valine
• Aromatic Amino Acids - Phenylalanine , Tyrosine , Tryptophan
• Heterocyclic Amino Acids - Tryptophan
• Sulphur Containing Amino Acids -  Cysteine, Methionine

2. Acidic Amino Acids - They have greater number of carboxylic groups than amino groups. Eg - Glutamic Acid

3. Basic Amino Acids - They have greater number of amino groups than carboxylic groups. Eg - Lysine.