分子生物学第五章ppt课件.ppt

Inprokaryotes transcriptionproducesanearlyexactmRNAcopyoftheDNA andthetranscriptisimmediatelytranslatedintoprotein Ineukaryotes aseriesofmodificationsoccurtomRNAduringandaftertranscription 在原核生物中 转录产生的mRNA几乎是DNA的准确拷贝 并且这一转录产物会立即被转译成蛋白质 在真核生物中 转录时以及转录后会对mRNA进行一系列修饰 Chapter5mRNAModificationsinEukaryotes第5章真核生物mRNA的修饰 5 1Capping5 2Polyadenylation5 3Splicing5 4mRNAEditing5 5Experiments 5 1加帽5 2聚腺苷酸化5 3剪接5 4mRNA编辑5 5实验研究 Chapter5mRNAModificationsinEukaryotes第5章真核生物mRNA的修饰 5 1Capping 加帽 AnmRNAthathasbeentranscribedbutisnotyetreadyfortranslationiscalledapre mRNA oraprimarytranscript Cappingistheprocessofaddingaderivativeofguaninenucleotidetothe5 endofthepre mRNA 一条已经转录出来但还没有准备好用于转译的mRNA称为前体mRNA或初级转录本 加帽是在前体mRNA的5 末端加上一个鸟嘌呤核苷酸衍生物的过程 Structureofthecap 帽的结构 5 3 phospho diesterbond 5 5 triphosphatebond RNApolymeraseII DiscussedinChapter4 Cappingtakesplacequiteearly 5 Cap RNApolymeraseII RNA DNA Cappingprocess 加帽过程 CTD C terminaldomain RNApolymeraseII DNA Methyltransferase Guanylyltransferase RNAtriphosphatase Functionsofthecapstructure帽结构的功能 1 Helpspreventdegradation帮助防止降解2 Helpstransportintocytoplasm帮助转运到细胞质中3 Enhancestranslation 增强转译4 Helpsremovethefirstintron帮助去除第一个内含子 1 Helpspreventdegradation帮助防止降解 RNase RNase 5 5 triphosphatebond 5 3 phosphodiesterbond 5 3 phosphodiesterbond 2 Helpstransportintocytoplasm帮助转运到细胞质中 DiscussedinChapter7 3 Enhancestranslation 增强转译 Cap bindingprotein Notranslationoccurs RNApolymeraseII RNA DNA 4 Helpsremovethefirstintron帮助去除第一个内含子 Thefirstintron AAAAAAA AAAA 5 2Polyadenylation 聚腺苷酸化 Poly A tail Polyadenylation Pre mRNA Polyadenylationisamodificationprocessinwhichastringofabout250adeninenucleotidesisaddedtothe3 endofthetranscript Polyadenylationdoesnotoccuratthenaturalend Thepolyadenylationsignal 聚腺苷酸化信号 AAAAAAA AAAA Poly A tail Polyadenylation Pre mRNA PolyadenylationsignalhasatypicaltypicalsequenceofAAUAAA Thissequencegivesaninstructionas tocutthemRNAabout20nucleotidesdownstream nearaGU richsequence AAUAAA GU Thecleavagecomplex 切割复合体 Cleavagecomplex CPSF cleavageandpolyadenylationspecificityfactor CstF cleavagestimulationfactor CFI cleavagefactorI CFII cleavagefactorsII Poly A BindingProtein CTD C terminaldomain ProteinsforcappingatCTD ProteinsforpolyadenylationatCTD Functionsofthepoly A tailpoly A 尾的功能 AAAAAAA AAAA AAAAAAA A A A A A A Themainfunctionofpoly A tailistoprotectthemRNAfromdegradationbyribonucleases Functionsofthepoly A tailpoly A 尾的功能 AAAAAAA AAAA Thereisalsosomeevidencethatthepoly AtailisinvolvedinsplicingandenhancestranslationofmRNAs 5 3Splicing 剪接 Exons Partsofagenethatareexpressedasprotein Introns Sequencesthatdonotcodeforproteinandinterruptthecodingregions Splicing Theprocessofremovingintronsfromapre mRNA 5 3 1TheBasicSplicingReaction基本的剪接反应 5 AG GUAUGU bodyofintron UACUAAC YAG 3 Splicesitesinyeast Splicesites Sequencesthatmarkthebeginningandendsofintronsandexons Thebasicsplicingreaction 5 3 2ProteinsinvolvedinSplicing在剪接中发挥作用的蛋白质 Spliceosome Thecollectionoffactors especiallysnRNPs thathelpwiththesplicingofintrons snRNPs smallnuclearribonucleoproteins snRNPsaresmallparticlesfoundinthenucleusandcontainbothproteinandRNA snRNPsfunctioninginsplicing U1 U2 U4 U5andU6 NowshowingmRNAsplicing File biophoto7 LehningerPrinciplesofBiochemistry mRNAsplicing 5 3 3Self Splicing 自我剪接 Tetrahymenathermophilia嗜热四膜虫 SplicingthatoccurswithoutthehelpofproteinsorsnRNPsiscalledself splicing Self splicingofgroupIintron Self splicingofgroupIIintronII类内含子的自我剪接 Withhelpofproteins Withouthelpofproteins Self splicing Normalsplicing 5 3 4Trans Splicing 反式剪接 MaturemRNA Protein RNApieceofseparateorigin DNA Trans Splicing 反式剪接 5 3 5ReasonsforIntrons内含子存在的原因 Introns earlytheory Introns latetheory Intron WhyamIhere Intron earlytheory 内含子早现说 E coli IheardsomebodysayE colioncehadintrons Isthattrue Couldbe Whoknows Intron latetheory 内含子后现说 E coli Wearetheoneshavingintrons Weareproudofit Alternativesplicing 可变剪接 Alternativesplicing akindofsplicingthatcanproducevariousproteinsfromonegene DrosophilaDscamgene Exon3 Exon5 4 14 24 34 44 54 64 74 84 94 104 114 12 Exon4Exon6Exon9 AlternativeSplicingGoesMainstream可变剪接成为主流TheScientist Volume17 24 28 Dec 15 2003 Alternativesplicing 可变剪接 5 4mRNAEditing mRNA编辑 Sleepingsicknessisoneofthemostneglectedhumandiseases andmainlyaffectsthemostdeprivedpeoplesofsomeAfricancountries Trypanosome锥虫 RNAeditingintrypanosome C