Amino acids are the monomer units for protein biopolymers.
Amino acids are the "alphabets" of protein structures. There are 20 amino acids commonly found in biological systems. These amino acids can be divided into four classes, where R-groups are the side chains of the amino acids:
All amino acids have an amine and a carboxylic acid, as well as an R-group, attached to their alpha-carbon. The amino acids are zwitterions, and they can be represented by the three-letter abbreviation of their name. For example, anine is written as Ala, and aspartic acid is written as Asp .