And let's suppose we want to add one more nucleotide. We want to add one more ribonucleotide triphosphate. Now, what RNA polymerase does and we'll discuss this in much more detail in just a moment what RNA polymerase does is it essentially attaches the ribonucleocide triphosphate onto the RNA molecule to form an RNA molecule that is extended by one nucleotide. 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.