So here we have N number of ribonucleotide triphosphates but here we have N plus one. And in the process we build this phosphodiastor bond between the ribonucleotide triphosphate and the RNA chain and we release a single pyrophosphate molecule. So PP stands for a Pyrophosphate and in fact it's the breakdown of the Pyrophosphate that drives this transcription reaction forward as we'll discuss in much more detail when we'll discuss the process of transcription. So this is the general equation that describes RNA polymerase. Now, to actually work, what does RNA polymerase actually need? Well, it needs three different things.