And this will be the amino acid found on the terminal carboxyl end of that growing polypeptide chain. So this is our group that will be attached onto the solid surface that will react with the carbon of the carboxyl group of this amino acid number one. Or let's call it amino acid number N, assuming that we have a number of amino acid in that eventual polypeptide chain. And notice we block our nitrogen, because we don't want this nitrogen to form any bonds with this molecule, we only want to form a bond with this carbon here. And so by reacting these two groups, we essentially form the following molecule. So now we have the initial amino acid at the terminal carboxyl end that is attached onto that solid surface.