E. phenylalanine hydroxylase and cystathionase. Phosphoribosyl pyrophosphate A. is required for both purine and pyrimidine synthesis. B. is a ribonucleotide. C. is synthesized from AMP and ribose. D. is a substrate for the first step of UMP biosynthesis.
E. synthesis is blocked by aminopterin.
Sulfa drugs such as sulfanilamide are effective against certain pathogenic bacteria because A. they block the synthesis of dihydrobiopterin. B. they block the synthesis of niacin. C. they block the synthesis of folate. D. they block the synthesis of pyridoxal. E. they block the synthesis of thiamine.