Arguably, the most interesting metabolic pathways from the perspective of regulation are those leading to the synthesis of nucleotides. We shall consider ribonucleotide synthesis from from scratch ( de novo synthesis). Deoxyribonucleotide synthesis from ribonucleotides will be considered separately.
Synthesis of ribonucleotides by the de novo method occurs in two pathways – one for purines and one for pyrimidines. What is notable about both of these pathways is that nucleotides are built from very simple building blocks.