核酸降解與和代謝

DegradationandBiosynthesis

ofNucleotidesNucleotides,Nucleoside.Thebaseofanucleotideisjoinedcovalently:N-9ofpurinesN-1ofpyrimidines1’-carbonofthepentose,N-beta-glycosylThephosphateisesterifiedtothe5’-carbon.Twotypesofpathwaysleadtonucleotides:Thedenovoandthesalvagepathways.Denovosynthesisofnucleotidesbeginswiththemetabolicprecursors:aminoacids,ribose5-phosphate,CO2,andNH3.Salvagepathwaysrecyclethefreebasesandnucleosidesreleasedfromnucleicacidbreakdown.DNA/RNAnucleotideNucleosidephosphatebasepentoseDNases,RNasesEndonuclease,ExonucleolasephospholipaseNucleosidase:NucleosidephosphorylaseNucleosidehydrolaseDNAandRNAdegradationGenomicDNAPlamidDNADnaseIdigestionofDNARNARNAdegradationbyRnaseDNADigestionbyRestrictionEnzymes1978NOBELPRIZE證明一種特別的限制酶的存在，它只分裂那些含有為噬菌體所特有的某種序列的核苷酸。流感嗜血桿菌從噬菌體接受DNA的機(jī)制時(shí)發(fā)現(xiàn)了一類新的限制酶，它們分別在特定部位切斷DNA分子一種限制酶只能識(shí)別一種特定的核苷酸序列，并在特定的切割點(diǎn)上將DNA分子切斷。目前已發(fā)現(xiàn)的限制酶有400～500多種。DNADigestionbyRestrictionEnzymesDNAfootprint基因重組與DNA克?。ɑ蚬こ蹋〥NADigestionbyRestrictionEnzymesAndDNAbinationPurineDegredation

DeaminationAdeninedeaminaseGuaninedeaminaseXanthineOxidaseXanthineOxidaseUrateOxidaseXanthineAdenineGuanineUricacidAllantoinAllantoinase尿酸尿囊素尿酸尿囊素尿囊酸尿素Uracil,CytosineThymineCytosineThymineUracilFinal：aminoacid,NH3,CO2PyrimidineDegradationBiogenesisofnucleotidesPentose戊糖phosphatepathwayBiogenesisofpurinesThisinformationwasobtainedfromisotopicexperimentswith14C-or15N-labeledprecursors.次黃嘌呤核苷酸Uniondeamination次黃嘌呤核苷酸腺苷琥珀酸黃嘌呤核苷酸AMPDNA/RNAnucleotideNucleosidephosphatebasepentoseDNases,RNasesEndonuclease,ExonucleolasephospholipaseNucleosidase:NucleosidephosphorylaseNucleosidehydrolaseDNAandRNAdegradationSalvagepathwayofpurinsSalvagepathwayofpurins腺嘌呤磷酸核糖轉(zhuǎn)移酶APRT次黃嘌呤鳥(niǎo)嘌呤磷酸核糖轉(zhuǎn)移酶HGPRTDefectinsalvagepathwayofpurinsLesch(/leski/)-Nyhansyndrome:NOHGPRTActivity!producedbymutationsintheHPRTgenelocatedontheXchromosomeRegulationofpurinenucleotideBiosynthesis:coordinationofdenovoandsalvagepathwayLesch(/leski/)-NyhansyndromePRPPSubstrateactivationTheGoutOverproductionofuricacidUricacidcrystalsprecipitateintojoints(GoutyArthritis痛風(fēng)性關(guān)節(jié)炎),kidneys,ureters(stones結(jié)石)AdeninedeaminaseGuaninedeaminaseXanthineOxidaseAdenineSalvagepathwaydeficiency,Cancertreatment,Allopurinol:hypoxanthineanalogXanthineoxidaseinhibitorsbindstoXanthineOxidaseinhibitproductionofuricacid別嘌呤醇次黃嘌呤缺乏次黃嘌呤-鳥(niǎo)嘌呤磷酸核糖轉(zhuǎn)移酶（HGPRT）HAT培養(yǎng)基含有次黃嘌呤(H)、氨基喋呤(A)和胸腺嘧啶核苷(T)具有次黃嘌呤-鳥(niǎo)嘌呤磷酸核糖轉(zhuǎn)移酶（HGPRT）雜交瘤細(xì)胞篩選在HAT培養(yǎng)基[屬于選擇性培養(yǎng)基，含有次黃嘌呤(H)、氨基喋呤(A)和胸腺嘧啶核苷(T)]中進(jìn)行選擇性培養(yǎng)，未融合的脾細(xì)胞因不能在體外長(zhǎng)期存活而死亡；未融合的骨髓瘤細(xì)胞合成DNA的主要途徑被培養(yǎng)基中的氨基蝶呤阻斷，又因缺乏次黃嘌呤-鳥(niǎo)嘌呤-磷酸核糖轉(zhuǎn)移酶（HGPRT），不能利用培養(yǎng)基中的次黃嘌呤完成DNA的合成過(guò)程而死亡。只有融合的雜交瘤細(xì)胞由于從脾細(xì)胞獲得了次黃嘌呤-鳥(niǎo)嘌呤-磷酸核糖轉(zhuǎn)移酶，因此能在HAT培養(yǎng)基中存活和增殖。經(jīng)過(guò)克隆選擇，可篩選出能產(chǎn)生特異性單克隆抗體的雜交瘤細(xì)胞，在體內(nèi)或體外培養(yǎng)，即可無(wú)限制地大量制備單克隆抗體。PyrimidinebiosynthesisCarbamoylphosphateAspartate門冬氨酸轉(zhuǎn)氨甲酰酶二氫乳清酸酶Orotate乳清酸orotidylateDecarboxylaseCarbamoylphosphateAspartateUMPN-CarbamoylaspartateaspartatetranscarbamoylasedihydroorotaseL-Dihydroorotatedihydroorotatedehydrogenaseorotatephosphoribosyl-transferaseOrotidylateUMP合成酶缺陷：遺傳性乳清酸尿癥ATPADPUMPKinaseUDPUDPKinaseATPADPUTPCTPsynthetaseGlnATPGluADP+PiAMP,GMP,UMP,CMPPurinebiosynthesisPyrimidinebiosynthesisPurinesalvagepathwaysOverviewofnucleotidebiosynthesisFormationofdeoxy-NucleotidesNucleoside5-diphosphatereductaseRNAAGCUDNAAGCUADP,GDP,UDP,CDPdADP,dGDP,dUDP,dCDP

UMPtodTMP

UMP→UDPdUDP→dUMPdTMP

-(O)+CH3(THF)RNAAGCUDNAAGCUTThymidylatesynthaseleadstomethylationofdUMPandproducesdTMP.ThymidylatesynthaseisespeciallyneededforDNAreplication/repair.ItisthusatargetforcancertreatmentlikefluoruracilBiogenesisofpurinesandpyromidine葉酸InhibitstheDNAsynthesisofBacterialbutnotofhuman.DrugsinterferingbiosynthesisofDNA