So basically, in this process, the protein kinase catalyze the transfer of a terminal phosphoryl group, shown in red from that ATP molecule, onto a hydroxyl containing group, hydroxyl containing side chain found on that protein, the target protein. And because serine 13 and Tyrosine all contain hydroxyl groups on the side chains of these amino acids, these are the three residues that are capable of actually using the hydroxyl group to accept that transfer, that phosphoryl group. So in this process, on the reactant side, we have an ATP molecule and the target enzyme of protein. And then on the product side, we basically have the ADP molecule adenosine diphosphate. We have a single H plus ion that comes from this oxygen here. And we have this modified residue that is part of that target enzyme, the target protein.