We use them for energy conversion and we also use them in many different types of signal transduction pathways. So there are two types of nucleotides we have permitted and we have purines. And in this lecture, we're going to focus on primidines. So how do we synthesize primidines within our cells? Well, our cells use two different pathways. The first pathway is what we call the salvage pathway, and the second pathway is called the novosynthesis of primidines.