资源描述
Information Transfer(in procaryotes)For Specialty of Biotechnology or Bioengineering at CSUMr.XIA JinlanContentnDNA replicationnTranscription and the regulation of gene expressionnProtein synthesisInformation transfer flowDNA replication in prokaryotesnMain pointsnReplication starts at a single originnReplication is bi-directional and semi-conservativenEach replication bubble(or eye)consists of two replication forksnGrowth at the replication forks is discontinuousnProteins involved in DNA replicationnPrimase nPolymerase I(Pol I),Pol II,Pol IIInLigasenhelicaseReplication is bidirectionalUnidirectional replication has been observed only in bacteriophages and some plasmidsp988Replication is semidiscontinuousOkazaki fragments冈崎片段冈崎片段p989nThe general reaction:n(DNA)n residues+dNTP (DNA)n+1+PPinRequirements for DNA synthesis nPolymerase I(or polymerase III+polymerase I)nAll four dNTPs nMg2+nA DNA template nA primer 启动子with a free 3-OH DNA replication:overviewRequirements for DNA synthesisBasic procedure of DNA replicationnPrimer binds to the DNA template strand by base pairing principlenPolymerase I recognizes the nucleotide A on the DNA template strandnPolymerase I directs the nucleotide T(pairing to A)n3-OH of the primer nucleophilic attacks to the a-phosphate group of the incoming nucleotidenThe primer extends in a 5 to 3 directionChain elongation reaction catalyzed by DNA polymeraseDNA polymerases-the enzymes of DNA replication in procaryotesPropertiesPol IPol IIPol IIIPolymerization 5320 bases4.6MegaBasesExonuclease 3 5Exonuclease 5 3DNA polymerase I and II function principally in DNA repair;DNA polymerase III is the chief DNA-replicating enzymep9913 5 exonuclease activity of DNA polymerase ITo correct the mismatched bases from 3 endThe 53 exomuclease activity of DNA polymerase IRemove the RNA primer from 5 endNick fillingGeneral features of a replication forkFigure 30.15 on p997Please find what kinds enzymes are included.Where are the Okazaki fragments and lagging strand?Where are the leading strand?Concept-check pointsTo which end of a newly synthesized strand of DNA does polymerase add a base?Why is a primer required for DNA replication?What are the leading and lagging strands?What is the function of primer?What are the differences in DNA replication between circular DNA in prokaryotes and linear DNA in eukaryotes?What is telomerase and what is its function?What is telomere?What are the typical DNA sequence repeats for telomeres among different species?Transcription in ProkaryotesnBinding of RNA polymerase to template DNAn(DNA-dependent)RNA polymerase(of E.coli):a2bbsnInitiation of polymerizationnChain elongationnChain terminationnOne depends on the termination factor:r nTypical bases segmentnInverted repeats(typically G:C rich)nA run of 6 to 8 As in the templateTranscriptionDNA-Dependent RNA polymeraseSequence of events in the initiation and elongationSee Fig.31.2p1017Within the Promoter are two consensus sequence elements 共有序列元件共有序列元件Fig.31.3p1019What are the two consensus elements?What is Pribnow box?Terminated by r r factorFig.31.8p1023Terminated by the inverted repeatsStem-loop structurep1022Transcription regulation in ProcaryotesnTranscription is regulated by operons操纵子nOperons consist of transcriptional control regions and a set of related structural genesnTranscription of operons is controlled by induction and repressionFig.31-13p 1029The general organization of operonsWhat are the typical structural elements of a operons?The lac OperonFig.31.16p1031The mode of action of lac repressorFig.31.17p1032Lac operon can be induced by either lactose or the analog of lactose,isopropyl b-thiogalactoside(IPTG)The analog of lactose:IPTGPositive control of the lac Operon by CAPnCAP:catabolite activator proteinThe mechanism ofcatabolite repression and CAP actionCAP-cAMPboundcan only be formedwhen glc=0 and lactose is available Relative cell densityRelative level of b-galactosidaseDiauxic growth on a mixture of glucose and lactoseIn this case,catabolite repression ensures that the cells useGlucose-the best source first.Positive control by catabolite activator protein(CAP)Only functions at the presence of lactose,otherwise repressed by lac repressorAlthough the presence of lactose removes the repressor,the presence of glucose lowers the level of cAMP in the cell and thus removes CAPConcept-check pointsnWhat is a promoter?nWhat is a transcription terminator?nWhat is a consensus sequence?nWhat is an intrinsic terminator?Protein synthesisnSome terms ncodons,Synonyms(同义密码子)Anticodon(反密码子),Wobble base-pairing(摆动碱基配对)nOpen reading framenrRNA,mRNA,and tRNA are required for protein synthesisnNewly synthesized protein needs to be folding to a correct conformationSome termsnCodon 密码子nA triplet of bases on the mRNAnSynonyms(同义密码子)：nCodons that specify the same amino acid(编码同一氨基酸的密码子)nAnticodon(反密码子):nA triplet of bases on the tRNA that pair with the bases in the corresponding codon on the messenger RNAnWobble base-pairing(摆动碱基配对):nthe pairing of the third base of a codon is less stringent than for the first two bases For example:nphenylalanine tRNA,which has the anticodon AAG,recognizes both of the codons UUU and UUC Open reading framenBegin with AUG,and end with UAA,UAG,UGArRNA,mRNA,and tRNA are required for protein synthesisA:acceptor siteP:peptidyl siteE:exit sitetRNAmRNArRNATypical structure of a tRNAThe conventional cloverleaf structure5 CCA-OHStructure of E.coli N-formyl-methionyl-tRNAfmetThe first codon translated in mRNA:AUG-3Anticodon in Trna:CAU-3p1096The cycle of events in peptide chain elongation on E.coli ribosomesp1100Aminoacyl-tRNA bindingPeptidyl transferVarious Shine-Dalgarno sequences recognized by E.coli ribosomesShine-Dalgarno sequence:purine-rich mRNA sequence,the ribosome-binding siteNewly synthesizedprotein needs to befolding to a correctconformation陪伴蛋白Concept-check pointsnWhy is it important for the ribosome to read“in frame”?nWhat is the function of the anticodon of a tRNA?nWhat is the function of the acceptor end of a tRNA?nWhat are the components of a ribosome?nWhat functional roles does rRNA play in protein synthesis?nWhat is a molecular chaperone?
展开阅读全文