分子生物学英文版文档格式.docx
- 文档编号:19155681
- 上传时间:2023-01-04
- 格式:DOCX
- 页数:37
- 大小:179.62KB
分子生物学英文版文档格式.docx
《分子生物学英文版文档格式.docx》由会员分享,可在线阅读,更多相关《分子生物学英文版文档格式.docx(37页珍藏版)》请在冰豆网上搜索。
Hyperchromicity/ Hyperchromiceffect:
thestrikingincrease inabsorbanceofDNA(A260)causedbythedenaturationofthedouble-strandedDNAmolecule
Meltingtemperature(Tm):
thetemperatureatwhichhalfof the DNAstrands arein the double-helicalstate andhalfare denatured.The melting temperaturedependsonboth the length ofthemolecule,andthespecificnucleotidesequencecompositionofthat molecule.
FactorsAffecting Tm
●G-Ccontentof sample
●reagents that increase thesolubilityofthebases (anythingthatdisruptsH-bondsorbase stacking)
● Saltconcentration
●pH
●Length
5.Renaturation
Strandscan beinducedto renature(anneal)under properconditions.Factorstoconsider:
● Temperature
●Saltconcentration
●DNAconcentration
●Time
Repetitive Sequences
●Unique:
Single Copy Genes
●Slightlyrepetitive(2-10 copies)
●Middlerepetitive (10-hundreds)
--Clustered
--Dispersed
●Highlyrepetitive(hundreds tomillions)
--Shortsequences insatellite DNA
--Sequencesofnormallengthincertaingenesthat exist inverylarge numbers
C-value Paradox
Thereis apparentlyalack ofassociation betweenC-value(theamountof DNApresentin thehaploidgenomeofdifferent organisms)andthedegreeof organismalcomplexity ofvariousmulti-cellular organisms.In1971,Thomas namedthis phenomenon,“C-valueParadox”.
在每一种生物中其单倍体基因组的DNA总量是特异的,被称为C值(C Value)。
C值和生物结构或组成的复杂性不一致的现象称为C值悖论(C-valueparadox)。
6. Hybridization
Hybridization:
the technique whereinrenaturedDNAisformedfrom separatesingle-strandedsamples .
Heteroduplexing:
renaturationcombinedwith electronmicroscopyin aprocedure allowsthe localizationofcommon,distinct,andmissingsequencesin DNA.
DNA-RNAhybridization(Northernhybridization):
theuseoffilter hybridizationtodetectsequencecomplementaritybetweena single strandofDNAandanRNA molecule.
7.ThestructureofRNA
Types:
mRNA,tRNA,rRNA
Distinctions:
- ribose replaces deoxyribose;
-UreplacesT;
-Single-stranded
Conformation:
stem-loop orhairpin
8.Hydrolysisofnucleicacid
Thephosphodiesterbondsofboth DNAandRNA can bebrokenby hydrolysiseither chemically orenzymatically.
Ribozymes:
theRNAenzymes, areabletocleaveand form specificphosphodiesterbonds inamanneranalogoustoproteinenzymes.
Chapter6 Thegeneticmaterial
ThePathtotheWatsonand Crick Model
1928, Griffith, transformation inpneumococci(肺炎球菌)
1944,Avery, Griffith’stransformingprinciplewasDNA
1950,Chargaff,apatternintheamounts ofthefourbases
1952,HersheyandChase,DNAisthe genetic material
1953,Franklin, thex-ray pictureofDNA
Chargaff’srule
IntheDNAofall speciesexamined,A=T, G=C
Thetotal amountof purines(A+G)=pyrimidines(T+C)in DNA
Theration of (A+T)/(G+C)varies fromspeciestospecies
DNApropertiesandfunctions
1.DNA hastheabilitytostore geneticinformation,whichcanbeexpressedinthecellasneed.
2.This informationcanbe transmitted to daughter cellswith minimalerror. (Thisprocessrequirescomplexenzymesand repairmechanisms.)
3.DNApossessesboth physicaland chemicalstabilitysoinformationisnotlostoverlong periods oftime (years).
4.DNAhasthepotentialforheritablechange without majorloss ofparental information.
DNA-genetic material:
Double-strandedDNAhasevolvedasthegenetic material becauseitisespeciallywell-suitedforreplication, repair, occasionalchange,and long-time stability.
Gene:
Genescontain alltheinformationforthesynthesisandfunctioningofcellularcomponents.
Transcription:
the process ofsynthesizingRNAmolecules from a DNAtemplate.
Triplets/codons:
theRNAnucleotide sequenceis read(onribosomes)insequential groupsof threebases.
Mutation:
theprocessbywhichabase-sequencechanges.
Thecentraldogma:
DNAmakesRNA,makesprotein.
chapter7DNA replication
Semiconservativereplicationof double-strandedDNA
Untwistingof highlycoiledDNAisrequiredforDNAreplication
TopoisomeraseTypeI:
•Work aheadof replicatingDNA
•Mechanism
–Makesa cutinonestrand,passesotherstrandthroughit. Sealsgap.
–Result:
theDNAis“relaxed”somewhat
Gyrase--ATypeIITopoisomerase
–Introduces negativesupercoils
–breaks bothstrands
–Sectionlocatedawayfromactualcutisthen passedthroughcutsite.
Initiation of DNAreplication
•Replicaioninitiatedatspecificsites:
Originof Replication (ori)
•TwoTypesof initiation:
–Denovo–Synthesisinitiatedwith RNA primers.Mostcommon.
–Covalent extension—synthesis ofnewstrand asanextensionofan oldstrand(“RollingCircle”).Limited tocertainviruses.
DenovoInitiation
•Binding to Ori CbyDnaAprotein
•OpensStrands
•Replicationproceeds bidirectionally
Covalentextension initiationRolling Circle
Unwinding ofDNAforreplication
Helicase:
⏹ Breakshydrogenbondsandeliminateshydrophobicinteractions
⏹NeedsenergysuppliedbyATP
⏹EncodedbytheDnaBgenein E.coli
Single-strandDNAbinding proteins (SSB):
Bindto theexposedstrands,coatthemand blockthere-annealingprocess.
Elongation ofnewlysynthesized strands
1.The polymerization reactionand thepolymerases
Enzyme:
polymerase III
Needed:
substrates, template, primer
Direction:
5’→3’
2. Correctingmismatchedbases
The5’-3’exonucleaseactivityofpolI at a single-strandbreak (nick)canoccursimultaneouslywith polymerization----nick translation.
DNA polymeraseIII consists ofmultiplesubunits
⏹PolIand polIII arebothinvolved inE.coliDNAreplication.PolIII isthe major polymerase.
⏹BothpolyIandpolyIIIpossessaproofreadingoreditingfunction(3’-5’exonucleaseactivity).
⏹ The 5’-3’exonuclease activityof polI atasingle-strandbreak (nick) can occur simultaneouslywithpolymerization----nicktranslation.
⏹DNApolymerase IIIconsistsof multiple subunits.
⏹Allknownpolymerasescanworkonly in the5’-P→3’-OH direction.
PolI andpolIIIhavesomefeaturesincommon:
●5’-3’polymerizationactivity
Thefourdeoxynucleoside 5’-triphosphates
Aprimer witha free3’-OH
Atemplate
●3’-5’ exonucleaseactivity
AntiparallelDNAstrandsand discontinuousreplication
⏹Thetwostrands ofDNAisantiparalleland thereplication isdiscontinuoussynthesis.
⏹ Aprimer isrequiredforchaininitiationand twodifferentenzymes(RNApolymerase andprimase)are knowntosynthesizeprimerRNAmolecules.
⏹ DNAligasejoinsprecursorfragmentsandpolIas wellasRNaseHparticipatesin the removalofprimer.
RNApolymerase:
initiationofleading-strandsynthesis
Primase:
synthesisofprimers for lagging-strand
Primosome:
helicase/primase complex
PolI:
removaloftheprimerand replacementof DNA
DNAligase:
joining the fragment(gapsealed)
The complete DNAreplicationsystem
BidirectionalreplicationspeedsupDNA synthesis
Replication of eukaryoticchromosomes
1.Eukaryoteshave moreand largechromosomes.
2.Eukaryoticreplicationmay requireasmuchas 6-8hoursfor completionversus the 40 minutes neededby E.coli.
3.Therearemultiple,ratherthanasingle, replicationoriginsalongeukaryoticchromosomes. Theyarespaced about 20 kbapart.
4.EukaryoticDNAreplicationisattherate of about 10-100 nucleotides per secondasopposedtotheprokaryotic rateof about1500nucleotidesper second.
5.AtleastfivetypesofDNApolymeraseshavebeenfoundineukaryoticcells.
真生物DNA的复制有DNA聚合酶及多种蛋白质因子参与,DNA聚合酶也有多种类型。
其中DNAPolα及DNA Polδ在细胞核内DNA的复制中起主要作用。
DNAPolδ催化前导链及滞后链的合成,是主要负责DNA复制的酶。
DNAPolα的功能主要是引物合成。
DNA Polγ是线粒体中的复制酶。
Chapter8 Transcription
1.Enzymatic synthesisofRNA
E.Coli RNApolymerase
Holoenzyme:
coreenzyme:
α2ββ’ω
σfactor
(1)BindingofRNApol to atemplateatspecificsite
(2) Initiation
(3)Chainelongation
(4) Chainterminationandrelease
2. Transcriptionsignals
Inprokaryotes,thepromoterconsistsoftwoshortsequencesat-10 and-35positionsupstreamfrom thetranscription startsite.
●the-10element:
Pribnow box,usuallyconsistsTATAAT,is absolutelyessential tostarttranscriptionin prokaryotes.
●the-35 element:
usuallyconsistsofTTGACA.Itspresenceallows averyhightranscriptionrate.
Inprokaryotes:
Ineukaryotes:
Termination
Terminationof RNA synthesis occursatspecificbase-sequencesinthe DNAmolecule,calledterminators.
•Intrinsicterminators:
rho-independent terminators,theterminationsequencesallowRNA polymerasetoterminate elongationspontaneously.
•rho-dependent terminators:
it isdependentonaspecificprote
- 配套讲稿:
如PPT文件的首页显示word图标,表示该PPT已包含配套word讲稿。双击word图标可打开word文档。
- 特殊限制:
部分文档作品中含有的国旗、国徽等图片,仅作为作品整体效果示例展示,禁止商用。设计者仅对作品中独创性部分享有著作权。
- 关 键 词:
- 分子生物学 英文