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Chapter 13

Chapter 13 - DNA Structure, Replication, and Organization.docx

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BIOL 204
Dr.Roland Treu

CHAPTER 13 DNA STRUCTURE REPLICATION AND ORGANIZATION131 Establishing DNA as the Hereditary Molecule131a Experiments Began When Griffith Found a Substance That Could Genetically Transform Pneumonia BacteriaStep 4 in some way living R bacteria had acqd ability to make polysacc capsule from dead S bacteria and transformed into virulent S cells permanently to be passed on to descendantsoConversiontransformation and the agent responsibletransforming principleoLikely molecule responsible were proteinsNAs131b Avery and His Coworkers Identified DNA as the Molecule That Transforms Rough Streptococcus to the Infective FormUsed heat to kill virulent S bacteria and then treated macromolecules extracted from cells w enzymes that break down each of 3 main candidate molecules for hereditary materialprotein DNA or RNAoDestroyed proteinsRNAno effecttransformation still occurred and cells produced smooth coloniesoDestroyed DNAeffectno transformation TF no smooth colonies seen131c Hershey and Chase Found the Final Evidence Establishing DNA as the Hereditary MoleculeNQ Is DNA or protein the genetic material35 35Expmt used phage T2 which consists of only DNA and protein labelled PphosphorusSsulphur respectively since component of those onlyStudied infection of bacterium E coli normally found in intestines of mammalsoBacteriophagesviruses that infect bacteriaoVirusinfectious agent that contains either DNARNA surrounded by protein coat cannot reproduce except in host cell Transformationconversion of cells hereditary type by uptake of DNA released by breakdown of another cell132 DNA Structure132a Watson and Crick Brought Together Information from Several Sources to Work Out DNA StructureDNA contains 4 nucleotides NTs each w o5C sugar deoxyribose C atoms d w primes 1 to 5oPhosphate PO4 groupo1 of 4 nitrogenous basesAdenine Apurines built from pair of fused rings of carbonnitrogen atomsGuanine Gpyrimidines built from single carbon ringThymine TCytosine C oChargaffs rules amount of purinespyrimidines AT GCDNA contains NTs joined to form polynucleotide chaindeoxyribose sugar linked by PO4 groups in altg sugarPO4sugarPO4 pattern forming sugarphosphate backboneoEach PO4 group acts as bridge btwn 3 carbon of one sugar and 5 carbon of next sugaroEntire linkage including bridgingphosphodiester bondPolynucleotide chain has polarity or directionalityo2 ends not the samePO4 bound to 5 and hydroxyl group bound to 3 5 end and 3 end respectively In Xray diffraction Xray beam directed at molecule in form of regular solid ideally crystalowin crystal regularly arranged rows and banks of atoms bend and reflect Xrays into smaller beams that exit crystal at definite angles determined by arrangement of atoms in crystaloif photographic film placed behind crystal exiting beams produce pattern of exposed spotsopatterns helps deduce positions of atoms in crystal 132b The New Model Proposed That Two Polynucleotide Chains Wind into a DNA Double HelixIn doublehelix model 2 sugarPO4 backbones separated from each other by regular distancesBases extend into and fill central spaceoPurinepyrimidine if paired tgh exactly wide enough to fill space btwn Purinepurine base pair too wide to fit space and pyrimidinepyrimidine too narrow
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