Nucleotide synthesis and recycling

1 · Activate the sugar

Ribose-5-phosphate → PRPP

PRPP synthetase uses ATP. PRPP supplies activated ribose to synthesis and salvage.

2 · Build purine nucleotides

PRPP → IMP → AMP / GMP

Purine-ring assembly uses nitrogen donors, glycine, one-carbon units and energy. AMP and GMP are branches.

3 · Build pyrimidine nucleotides

Carbamoyl phosphate + aspartate

→ orotate; orotate + PRPP → OMP → UMP → UTP → CTP. The ring is built before ribose attachment.

4 · Recycle bases and nucleosides

Bases / nucleosides → nucleotides

Salvage enzymes recover usable material. Kinases and other enzymes adjust nucleotide pools.

5 · Supply DNA building blocks

Ribonucleotides → deoxyribonucleotides

Ribonucleotide reductase uses reducing power. Further reactions supply dATP, dGTP, dCTP and dTTP.

6 · Use the nucleotide pools

NTPs → RNA; dNTPs → DNA

Polymerases join the units. RNA/DNA synthesis is downstream of nucleotide metabolism.

Evidence and scope

Original explanatory diagram based on the sources below. These are selected documented biochemical routes or mechanisms, not a complete species-specific reconstruction. Each arrow can summarize several reactions; panels may represent branches or alternatives. Genome annotations, protein models and organism-specific evidence remain in the detailed system map.

• Aquifex metabolic reconstruction (Braakman & Smith, 2014)
• KEGG nucleotide interconversion reaction module