分子生物学(英文版).doc

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1、Chapter3NucleicAcid1.PhysicalandchemicalstructureofDNAlDouble-strandedhelixlMajorgrooveandminorgroovelBasepairinglThetwostrandsareantiparallellG+Ccontent(percentG+C)lSatelliteDNASatelliteDNAconsistsofhighlyrepetitiveDNAandissocalledbecauserepetitionsofashortDN

2、Asequencetendtoproduceadifferentfrequencyofthenucleotidesadenine,cytosine,guanineandthymine,andthushaveadifferentdensityfrombulkDNA-suchthattheyformasecondor'satellite'bandwhengenomicDNAisseparatedonadensitygradient.2.AlternateDNAstructureTwobaseshavebeenextru

3、dedfrombasestackingatthejunction.Thewhitelinegoesfromphosphatetophosphatealongthechain.Oisshownred,Nblue,PyellowandCgrey.3.CircularandsuperhelicalDNADNAcanalsoformadouble-stranded,covalently-closedcircle.Thesecircularmoleculesareoftencoiledintoasuperhelix,thef

4、ormationofwhichiscatalyzedbyenzymescalledtopoisomerases.4.DenaturationofDNADenaturation:AtransitionfromthenativetothedenaturedstateDNAdenaturation:alsocalledDNAmelting,istheprocessbywhichdouble-strandedDNAunwindsandseparatesintosingle-strandedstrandsthroughthe

5、breakingofhydrogenbondingbetweenthebases.Hyperchromicity/Hyperchromiceffect:thestrikingincreaseinabsorbanceofDNA(A260)causedbythedenaturationofthedouble-strandedDNAmoleculeMeltingtemperature(Tm):thetemperatureatwhichhalfoftheDNAstrandsareinthedouble-helicalsta

6、teandhalfaredenatured.Themeltingtemperaturedependsonboththelengthofthemolecule,andthespecificnucleotidesequencecompositionofthatmolecule.FactorsAffectingTmlG-Ccontentofsamplelreagentsthatincreasethesolubilityofthebases(anythingthatdisruptsH-bondsorbasestacking

7、)lSaltconcentrationlpHlLength5.RenaturationStrandscanbeinducedtorenature(anneal)underproperconditions.Factorstoconsider:lTemperaturelSaltconcentrationlDNAconcentrationlTimeRepetitiveSequenceslUnique:SingleCopyGeneslSlightlyrepetitive(2-10copies)lMiddlerepetiti

8、ve(10-hundreds)--Clustered--DispersedlHighlyrepetitive(hundredstomillions)--ShortsequencesinsatelliteDNA--SequencesofnormallengthincertaingenesthatexistinverylargenumbersC-valuePar