分子生物学英文版.docx

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