What are the steps in de novo synthesis of the purine ring?
• ribose-5-phosphate is used as the foundation on which other components are added to form the purine ring; • R5P + ATP yields PRPP (by PRPP synthetase); • PRPP + glutamine (adds amine) to form 5-phosphoribosylamine (committed step; inhibited by AMP, GMP, and IMP = end products) • then glycine (entire molecule) • then formyl-THF (adds carbonyl) • then glutamine (adds amine) • then first ring forms (5-member) • then CO2 (adds carboxylic acid) • then aspartate (converts acid to amide) • then formyl-THF (adds carbonyl) • then second ring forms (6-member) –> IMP • then aspartic acid (adds amine at 6) –> AMP • OR glutamine (adds amine at 2) –> GMP • then ATP (adds phosphate esters); most high-energy phosphate bonds are derived from ATP since it is used in oxidative phosphorylation reactions. They are then transferred to other nucleotides by various kinases. 5. Know the mechanism of sulfonamide antibiotics. A: Sulfonamides are structural analogs of PABA that inhibit bacterial synthesis of
