Small peptides

Dipeptides

There are two possible dipeptides that can be formed from the combination of two different amino acids. In this example, the dipeptides formed from the combination of the two amino acids alanine and serine are shown. it can be seen that Ser-Ala is not the same as Ala-Ser

Tripeptide

Glutathione is an important antioxidant in the blood. This tripeptide can be abbreviated as $\gamma$Glu-Cys-Gly.

The bond between cysteine and glycine is a normal peptide bond. However, the bond between glutamate and cysteine is through the carboxylic acid on the glutamate side chain (the $\gamma$ carbon).