So what the RNA polymerase does is it essentially hovers around this section and it brings that complementary ribonucleocide triphosphate which is complementary to this base that is found on the DNA template. Now, how do we know when it's complementary? Well, basically when the bonding is just perfect, this molecule will stay in this location for long enough for this bond to actually take place. So it will stay long enough for the bond to form. And the way that the bond forms is so we can label these carbon atoms as carbon atom one, carbon atom two, carbon atom three, carbon atom four, and carbon atom five on this sugar molecule. And we have the three prime hydroxyl group acts as a nucleophile and attacks this innermost phosphorus atom of this incoming nucleuside triphosphate.