Discussion section 0429

Discussion section 0429 - Discussionsection#4...

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Discussion section#4 DNA repair(cont.) DNA recombination genome 05/02/08
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Prediction:   replication should be semi-conservative Meselson-Stahl experiment     DNA containing "heavy nitrogen" (N15) can be distinguished form DNA containing "light nitrogen" (N14) by CsCl density-gradient  centrifugation . 1. Make a gradient (e.g. sucrose gradient of 20-70%) 2. Add sample 3. High speed centrifuge 4. Sample will move up or down until density reaches buoyancy/density of sucrose 5. visualize bands under UV (DNA will fluoresce) and photograph. 6. Take measurements over many generations.
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GENERATI ON N N / N N 15 0 1.1 1.9 N 14 N 15 Result from the original paper Created diagram
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DNA repair Single step Multiple steps O6-alkylguanine-DNA alkyltransferase photo lyases Base Excision Repair (BER) Nucleotide Excision Repair (NER) Mismatch repair Double stranded break repair
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double stranded break repair Caused by?      ionizing radiation/free radicals What is ionizing radiation?       highly-energetic  particles  or  waves  that can detach ( ionize ) at least one electron from an  atom  or  molecule What is free radicals?       free radicals are  atomic  or  molecular  species with unpaired  electrons  on an otherwise  open shell   configuration. These unpaired electrons are usually highly  reactive , so radicals are likely to take  part in chemical reactions.  repaired by?      non homologous end-joining (NHEJ) and recombination repair ends are aligned by Ku70 and Ku80    
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Mechanism of endjoining Error prone Ku80/KU70 appear to be the cell’s broken-DNA sensor DNA-dependent protein kinase (DNA-PK )
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E.Coli SOS response  (when repair system fails) upon DNA damage cells stop dividing LexA and RecA DNA binding proteins regulate the SOS response
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This note was uploaded on 10/30/2010 for the course CHEM 114C taught by Professor Alexanderhoffmann during the Spring '08 term at UCSD.

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Discussion section 0429 - Discussionsection#4...

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