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2nd midterm full notes.docx

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DNARNA Structure General OverviewoMost basic structure is the DNA structure double stranded in cells most of the time Not double stranded during replicationoAdenine Guanine Thymine and Cytosine are the four common basesoDuring replication only taking about these four bases only found in natural DNAoRight after DNA synthesis these can be chemically modifiedSame thing happens in transcription when taking about RNAoUracil replaces Thymine in transcriptionoGuanine and Adenine are PURINESoThymine and Cytosine are PYRIMIDINESoAll of these are found in primary DNA and primary RNA the basesoBases are heterocyclic aromatic ringsBasic Experiments that DNA is the Genetic Information within CellsoTransformation experimentsoGriffiths ExperimentTwo strains S and R refers to how they looked under microscopeS cells are virulentlethal and R cells are nonvirulentnonlethalHeat and activated the lethal S cells release the contents it was no longer lethal Transforming Principle it is now called transformationRefer to Slide 6oExperiment of AveryMacLeodMcCartyDid a series of treatments with the transforming principleTook replicates of lysase and treated with extracts treat with protease degrade protein and if protein was transforming material loose transformation but it wasnt the caseConclusion was that the transforming principle was not protein and if it worked properly then it would degrade and you would not get transformationNext using RNAse which degrades RNA and still had transformationNext using DNAse which degrades DNA and lost transformationTherefore DNA is transforming principleToday transformation is taking up DNA DNA gets incorporated and is stable When cell reproduces it reproduces with the new DNA as welloChargaffs rulesoA with T and G with CoExperimentalist interested in DNA and components of the basesoDeveloped methods to degrade DNA to A C T G and look at there propertiesoGot ratios of how much there areoFound out A and T percentages are the same and C and G are the same percentagesoThen he looked at different organisms even percentages were different A and T matched up as well as C and GoHence base pairingoHowever occasionally Chargaff would make some DNA or some bring DNA to him he would find exceptions and Watson and Crick would have to ignore them so that their model would still be correct oPhage infection experimentoBacteriophages affect bacteriaChosen virus with this shapeWorks by binding to host it injects its DNA and protein part stays outside DNA alone codes for all the genes so that virus gets madeDNA leads to production of more viruses by getting replicated and transcribedoGrew a culture labeled S35 found in protein not in DNA grew another culture P32 found on the DNA DNA labeled with this can monitor the DNA and protein differently by labeling them differentlyoOnly find the radioactive P32 showing that the DNA got replicated and not the protein if protein would have been we would have seen S35 This suggests that the protein does not get insideoSupports the transformation experimentoHere you have viable phage and the DNA they inject is the only thing needed to replicate more viral phageoMain caveat if they have chosen virus with different properties this may not have workedoTransformationSeparate DNA from protein DNA can be transformed get same result for virusoXray analysisoOne of the most complicated to explaino Taken a picture of DNA thought it had to do with XRaysoMaurice Wilkins had a collaborator working in lab and she took DNA samples and blasted them with XRays and noticed a patternSomewhere diffracted noticed diffraction patternsoWatson and Crick recognized fiber diffraction picture was a helix looked at this and new immediately what it wasoFiber diffraction DNA being stretched outoMeasure distance from center works out to be a basetobase difference of 34 AngstromsPattern does not fall on x and yaxis fall on about axis of about 45oLooked like a helixoConclusion had a helix bases pairs separated by small distance and had 10 of them before it repeated againCould not tell any detail using this pictureoStandard model called BDNA and other DNA formsWhy do we need a standard modelWhen we say there is a standard human genome there is something we can refer to Natural DNA forms a righthand helixThe two strands are antiparallel read 5 to 3 but in opposite directionsNot a perfect spiral identify regions that are further apart Major Groove and regions that are closer together Minor GrooveAntiParallel plays a key role in storing information and replicationDNA structure is NOT always the sameMake different forms in the test tube but is it inside the cellA DNA is a bit thicker and grooves are a bit different still right handed angles differentZ DNA zigzag and not smooth and it is a lefthanded helix Still have major and minor groove but angles different from standard model Are the different forms inside the cell and is it inside the cell at different times of the cell cycle Some viruses have double stranded RNAWhen DNA being transcribed into RNA part will have DNA and RNA RNADNA hybrid at some partsA forms do occur inside the cell Z DNA associated with G C rich DNA People made antibodies that react with Z DNA and they found it in cells It could exist inside the cell MicroheterogeneityDifferent forms of DNA within cellsoModel BuildingoVariety of strange structures but do they exist in natureoCan cause DNA to transform into loop structureoG Tetraplex is hydrogen bonded All made up of G basesoDNA Aptamer can recognize specific parts of proteins Functions like protein oStructures are not fixed change on conditionsGoing to change during replication and transcriptions
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