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In1869,FriedrichMiescherdiscoveredDNA,frstnamedunuclein”żIn1918,
PhoebusLeveneidentifedthefourbases,adenine(A),cytosine(C),guanine
(G),andthymine(T),thebuildingblocksofDNA(Levene,1919)ż30years
later,ErwinChargaffoundthattheDNAbasecompositionvariedbetween
speciesbutdeterminedthatwithinaspeciesthebasesinDNAarealways
presentinfxedratios:thesamenumberofAsasTsandthesamenumber
ofCsasGs(Chargaf,1950)żHowever,thegreatcareerofDNAstartedin
1944withtheAvery,MacLeodandMcCartyexperiment(Averyetalż,1944),
provingthatnotproteinsorRNA,aspreviouslysuspected,butDNAisthe
substanceresponsibleforbacterialtransformationżTheprocessofbacterial
transformationwasfrstdescribedin1928byGrifth,whofoundthatan
extractfromthevirulentPneumococcuspneumoniaestraincouldinduce
theconversionofanonvirulentstrainintoavirulentone(Grifth,1928)ż
ThenextmilestoneinDNAstudieswasthemodelofDNAstructureand
replicationproposedbyWatsonandCrick(1953)żAfewyearslater,Crick
deliveredalectureduringasymposiumontheBiologicalReplicationof
MacromoleculesheldatUniversityCollegeLondonżThelecture,published
in1958underthetitleuOntheproteinsynthesis”(Crick,1958),isconsidered
asaveryimportantarticle,formulatingtheso-calledcentraldogmaof
molecularbiology:DNAmakesRNA,RNAmakesproteinżSincethen,genes
havenotbeenconsideredassomewhatmythicaluunitsofheredity”asit
wascommonafterGregorMendel’sdiscoveries,butasfragmentsofthe
DNAchainonwhichinformationontheRNAandproteinstructureiswrit-
tendownżThemainefortwasthendirectedtowardsdecipheringthe
modeofgenefunctioningż
