But normally you're not going to know the sequence of your proteins. So let's begin with step one. So, in the first step of the evidengration, we want to basically label that first amino acid. 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?