Final answer:
Purine synthesis involves two main pathways: de novo synthesis and salvage pathway. De novo synthesis builds purine nucleotides from scratch, while the salvage pathway recycles free purine bases. The overall process is regulated to maintain balance.
Step-by-step explanation:
In purine synthesis, there are two main pathways involved: de novo synthesis and salvage pathway. In the de novo synthesis, purine nucleotides are synthesized from scratch, with the purine ring being built up step by step using various precursors. On the other hand, the salvage pathway involves recycling of free purine bases from dietary sources and tissue breakdown to synthesize purine nucleotides. The regulation of purine nucleotide biosynthesis is important to prevent overproduction. Feedback inhibition is one mechanism that regulates purine biosynthesis, where the process is inhibited at the committed step, which is generally irreversible. The big picture in purine synthesis is the overall process by which purine nucleotides are synthesized in living organisms, either through de novo synthesis or salvage pathway, and how their biosynthesis is regulated to maintain balance.