And this is the same molecule that is used as a reaction reactin in step number five. Now in this reaction, this is actually the only step of the citric acid cycle in which we generate a high energy purine nucleuside triphosphate molecule. We generate a GTP. So what we ultimately want to do in this process is we want to attach a phosphoryl group onto the GDP, the guanitine diphosphate, to form the guanosine triphosphate GTP. The problem with carrying out this step is it requires an input of energy. So the process by which we attach the pi onto the GDP to form the GTP is an endergonic process.