[理学]第14章核苷酸的代谢.ppt

第十四章核苷酸的代谢 Key Terms nucleosidenucleotide pyrimidine carbamoyl phosphate synthetase (CSP) ATP-grasp fold 5-phosphoribosyl-1-pyrophosphate (PRPP) orotidylate purine salvage pathway inosinate hypoxanthine glutamine phosphoribosyl amidotransferase ribonucleotide reductase thymidylate synthase dihydrofolate reductase III. Synthesizing RNA Base Ribonucleoside Ribonucleotide (5 -monophosphate) Adenine (A) Adenosine Adenylate (AMP) Guanine (G) Guanosine Guanylate (GMP) Uracil (U) Uridine Uridylate (UMP) Cytosine (C) Cytidine Cytidylate (CMP) DNA Base Deoxyribonucleoside Deoxyribonucleotide (5 -monophosphate) Adenine (A) Deoxyadenosine Deoxyadenylate (dAMP) Guanine (G) Deoxyguanosine Deoxyguanylate (dGMP) Thymine (T) Thymidine Thymidylate (TMP) Cytosine (C) Deoxycytidine Deoxycytidylate (dCMP) Purines and Pyrimidines. Atoms within bases are numbered without primes. Uracil instead of thymine isused in RNA. Nucleotide Mono-, Di-, and Triphosphates Are Interconvertible How is the other major pyrimidine ribonucleotide, cytidine, formed? It is synthesized from the uracil base of UMP, but UMP is converted into UTP before the synthesis can take place. Recall that the diphosphates and triphosphates are the active forms of nucleotides in biosynthesis and energy conversions. Nucleoside monophosphates are converted into nucleoside triphosphates in stages. First, nucleoside monophosphates are converted into diphosphates by specific nucleoside monophosphate kinases that utilize ATP as the phosphoryl-group donor 。 For example, UMP is phosphorylated to UDP by UMP kinase. Nucleoside diphosphates and triphosphates are interconverted by nucleosi diphosphate kinase, an enzyme that has broad specificity, in contrast with the monophosphate kinases. X and Y can represent any of several ribonucleosides or even deoxyribonucleosides. de Novo Pathway for Pyrimidine Nucleotide Synthesis. The C-2 and N-3 atoms in the pyrimidine ringcome from carbamoyl phosphate, whereas the other atoms of the