分子生物学英文版.docx
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分子生物学英文版.docx
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分子生物学英文版分子生物学英文版Chapter3NucleicAcid1.PhysicalandchemicalstructureofDNADouble-strandedhelixMajorgrooveandminorgrooveBasepairingThetwostrandsareantiparallelG+Ccontent(percentG+C)SatelliteDNASatelliteDNAconsistsofhighlyrepetitiveDNAandissocalledbecauserepetitionsofashortDNAsequencetendtoproduceadifferentfrequencyofthenucleotidesadenine,cytosine,guanineandthymine,andthushaveadifferentdensityfrombulkDNA-suchthattheyformasecondorsatellitebandwhengenomicDNAisseparatedonadensitygradient.2.AlternateDNAstructureTwobaseshavebeenextrudedfrombasestackingatthejunction.Thewhitelinegoesfromphosphatetophosphatealongthechain.Oisshownred,Nblue,PyellowandCgrey.3.CircularandsuperhelicalDNADNAcanalsoformadouble-stranded,covalently-closedcircle.Thesecircularmoleculesareoftencoiledintoasuperhelix,theformationofwhichiscatalyzedbyenzymescalledtopoisomerases.4.DenaturationofDNADenaturation:
AtransitionfromthenativetothedenaturedstateDNAdenaturation:
alsocalledDNAmelting,istheprocessbywhichdouble-strandedDNAunwindsandseparatesintosingle-strandedstrandsthroughthebreakingofhydrogenbondingbetweenthebases.Hyperchromicity/Hyperchromiceffect:
thestrikingincreaseinabsorbanceofDNA(A260)causedbythedenaturationofthedouble-strandedDNAmoleculeMeltingtemperature(Tm):
thetemperatureatwhichhalfoftheDNAstrandsareinthedouble-helicalstateandhalfaredenatured.Themeltingtemperaturedependsonboththelengthofthemolecule,andthespecificnucleotidesequencecompositionofthatmolecule.FactorsAffectingTmG-Ccontentofsamplereagentsthatincreasethesolubilityofthebases(anythingthatdisruptsH-bondsorbasestacking)SaltconcentrationpHLength5.RenaturationStrandscanbeinducedtorenature(anneal)underproperconditions.Factorstoconsider:
TemperatureSaltconcentrationDNAconcentrationTimeRepetitiveSequencesUnique:
SingleCopyGenesSlightlyrepetitive(2-10copies)Middlerepetitive(10-hundreds)-Clustered-DispersedHighlyrepetitive(hundredstomillions)-ShortsequencesinsatelliteDNA-SequencesofnormallengthincertaingenesthatexistinverylargenumbersC-valueParadoxThereisapparentlyalackofassociationbetweenC-value(theamountofDNApresentinthehaploidgenomeofdifferentorganisms)andthedegreeoforganismalcomplexityofvariousmulti-cellularorganisms.In1971,Thomasnamedthisphenomenon,“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(CValue)。
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.HybridizationHybridization:
thetechniquewhereinrenaturedDNAisformedfromseparatesingle-strandedsamples.Heteroduplexing:
renaturationcombinedwithelectronmicroscopyinaprocedureallowsthelocalizationofcommon,distinct,andmissingsequencesinDNA.DNA-RNAhybridization(Northernhybridization):
theuseoffilterhybridizationtodetectsequencecomplementaritybetweenasinglestrandofDNAandanRNAmolecule.7.ThestructureofRNATypes:
mRNA,tRNA,rRNADistinctions:
-ribosereplacesdeoxyribose;-UreplacesT;-Single-strandedConformation:
stem-looporhairpin8.HydrolysisofnucleicacidThephosphodiesterbondsofbothDNAandRNAcanbebrokenbyhydrolysiseitherchemicallyorenzymatically.Ribozymes:
theRNAenzymes,areabletocleaveandformspecificphosphodiesterbondsinamanneranalogoustoproteinenzymes.Chapter6ThegeneticmaterialThePathtotheWatsonandCrickModel1928,Griffith,transformationinpneumococci(肺炎球菌)1944,Avery,GriffithstransformingprinciplewasDNA1950,Chargaff,apatternintheamountsofthefourbases1952,HersheyandChase,DNAisthegeneticmaterial1953,Franklin,thex-raypictureofDNAChargaffsruleIntheDNAofallspeciesexamined,A=T,G=CThetotalamountofpurines(A+G)=pyrimidines(T+C)inDNATherationof(A+T)/(G+C)variesfromspeciestospeciesDNApropertiesandfunctions1.DNAhastheabilitytostoregeneticinformation,whichcanbeexpressedinthecellasneed.2.Thisinformationcanbetransmittedtodaughtercellswithminimalerror.(Thisprocessrequirescomplexenzymesandrepairmechanisms.)3.DNApossessesbothphysicalandchemicalstabilitysoinformationisnotlostoverlongperiodsoftime(years).4.DNAhasthepotentialforheritablechangewithoutmajorlossofparentalinformation.DNA-geneticmaterial:
Double-strandedDNAhasevolvedasthegeneticmaterialbecauseitisespeciallywell-suitedforreplication,repair,occasionalchange,andlong-timestability.Gene:
Genescontainalltheinformationforthesynthesisandfunctioningofcellularcomponents.Transcription:
theprocessofsynthesizingRNAmoleculesfromaDNAtemplate.Triplets/codons:
theRNAnucleotidesequenceisread(onribosomes)insequentialgroupsofthreebases.Mutation:
theprocessbywhichabase-sequencechanges.Thecentraldogma:
DNAmakesRNA,makesprotein.chapter7
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