And it forms a covalent bond between the oxygen and this phosphorus. Now eventually this H atom is removed and this Pyrophosphate molecule is kicked off. And so in the process when we form the phosphodieester bond and we form this polynucleotide chain, we essentially release a single pyrophosphate molecule and as we'll see in a future lecture the hydrolysis of the pyrophosphate molecule essentially drives this reaction forward. So RNA polymerase catalyzes the formation of phosphodiasta bond. It brings the complementary nucleotide triphosphate this nucleotide that is complementary to this base into the mixture and then our RNA polymerase holds this in place and it catalyzes the formation of this bond as shown in the following diagram and the pyrophosphate is released as a result. Now, as I mentioned before the RNA polymerase reads the DNA template from the three to five end but it synthesizes that polynucleotide chain in the five to three end and this is the same exact method that DNA polymerase uses.