And the way that we label that first amino acid is by reacting it with a special molecule known as pheny, or phenyl isothiocyanate. Now, the structure of phenol isotiocyanate is this structure here. Now, what's so special about this molecule? Well, it turns out that if you react this molecule with our polypeptide and the alpha amino group does not have a positive charge, then this will react with it to basically form a bond. It will attach to this uncharged terminal alpha amino group. So if we draw the structure of our six amino acid polypeptide, this is what we get.