試題詳解

40. Which one of the following descriptions about the biosynthesis of nucleotides is       correct      ?
(A) The ribosyl phosphate moiety needed for the synthesis of orotidylate, inosinate, and guanylate is provided most directly by ribose 5-phosphate.
(B) Deoxyribonucleotides are derived from the corresponding ribonucleotides by direct reduction at the 3'-carbon atom of the D-ribose.
(C) The immediate precursor of thymidylate (dTMP) is dUMP. The conversion of dUMP to dTMP is a reaction of deamination.
(D) The enzyme xanthine oxidase plays a critical role in the salvage pathways for the formation of nucleotides.
(E) Formation of deoxyribonucleotides is catalyzed by ribonucleotide reductase, in which its substrates are ribonucleoside diphosphates.