Amino acids are biologically important organic compounds which perform critical roles in processes such as neurotransmitter transport and biosynthesis. They are containing amine (-NH2) and carboxylic acid (-COOH) functional groups as well as a side-chain (R group) specific to each amino acid usually. The key elements of an amino acid are carbon, hydrogen, oxygen, nitrogen and other elements which are found in the side-chains of certain amino acids. There are only 20 amino acids in the genetic code, and the 20 animo acids can be classified in many ways. They can be classified according to polarity(polar amino acids and no polar amino acids), pH level, and the type of side chain group, such as aliphatic, aromatic, containing hydroxyl or sulfur, etc. The amino acids reference charts are as follows.

• Hydrophobic Amino Acids
• Amino Acids with Hydrophobic Side Chain – Aliphatic
• Amino Acids with Hydrophobic Side Chain – Aromatic
• Polar Amino Acid
• Amino Acids with Polar Neutral Side Chain
• Amino Acids with Electricaly Charged Side Chains – Acidi
• Amino Acids with Electricaly Charged Side Chains – Basi
• Unique Amino Acid
• Properties of Common Amino Acid