Provide a brief overview of nucleic acid metabolism: de novo synthesis vs salvage pathways for purines and pyrimidines.

• A. Purines are built from PRPP to IMP, then AMP/GMP; salvage via HGPRT; Pyrimidines synthesized via aspartate carbamoyl phosphate pathway and UDP/CTP formation; salvage for pyrimidines.
• B. Purines are synthesized from DHAP and rely on salvage; Pyrimidines are not salvaged.
• C. Purines are imported from diet; salvage is not used; Pyrimidines salvage only.
• D. Purine synthesis occurs in mitochondria exclusively; salvage occurs in cytosol.

Answer: (A)