Chapter 22 Biosynthesis of amino acids nucleotides and related molecules Reduction (fixation) of N into ammonia (NH3 or NH 2.Synthesis of the 20 amino acids. 3. Synthesis of other biomolecules from amino acids 4. The de novo pathways for purine and pyrimidine biosynthesis 5. The salvage pathways for purine and pyrimidine reuse.Chapter 22 Biosynthesis of amino acids, nucleotides and related molecules 1. Reduction (fixation) of N2 into ammonia (NH3 or NH4 + ) 2. Synthesis of the 20 amino acids. 3. Synthesis of other biomolecules from amino acids 4. The de novo pathways for purine and pyrimidine biosynthesis. 5. The salvage pathways for purine and pyrimidine reuse