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. And now we anchor our molecule in place. And so as we continually add our amino acids, as we'll see in just a moment, this growing polypeptide chain will essentially remain anchored onto this solid surface. And so we can easily wash our polypeptide many, many times over.