Aromatic amino acid has rings in their structures wile the aliphatic amino acids has carbon atoms joined in a branched or straight open chains.

There are three and they are called aromatic amino acids: tryptophan phenylalanine tyrosine. Proline also contains a ring but is not an aromatic compound

There are three and they are called aromatic amino acids: tryptophan phenylalanine tyrosine.

By their side chains. All amino acids have this structure:

HOOC- C - NH2

Attached to that middle C is the side chain. They can have many different properties-

They can be aromatic, polar, lipophilic, basic, acidic, Sulfur containing, among others

There are 20 amino acids inside the human body, each has a different structure and function, due to its properties.