Lecture20CMFall2009FINAL

Lecture20CMFall2009FINAL - CM Office Hour Today 3:30-5:00...

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CM Office Hour Today 3:30-5:00 A446 CLSL Additional Office Hour Tuesday (tomorrow) 12:00 – 1:00
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MAPS  MINORITY ASSOCIATION FOR PRE-HEALTH STUDENTS General Meeting + Social!! Thursday, October 15 th 6pm @ COCOMERO Meet other members and learn more about  upcoming events including: Med-School Student Panels Volunteer Opportunities + Much More!!
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MCB 250 Lecture 20 DNA Repair
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Misincorporated base becomes a mutation when it’s replicated Text Fig. 9-2 Friday Clicker Question ERROR
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Clicker Question The mutation depicted in the last slide (A-T G-C) is an example of A. a transition mutation. B. a transversion mutation. C. an insertion mutation. D. a deletion mutation. This should have read A-T C-G A-T to C-G (as depicted in the previous slide) is a transversion. A-T to G-C (as indicated in this question) is indeed a transition.
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Lecture Outline DNA repair Excision repair Base excision repair Nucleotide excision repair Photoreactivation SOS response, translesion synthesis Homologous Recombination Double strand break repair Proteins that catalyze recombination
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DNA Repair in Prokaryotes Base Excision Repair Removes modified bases Ung - uracil N-glycosylase - removes U from DNA. One example of base excision repair. Other glycosylases remove other damaged bases. Nucleotide Excision Repair Remove the bad base along with neighboring nucleotides. SOS – Translesion DNA Synthesis When all else fails, put in something. Alternative DNA polymerases - “error prone” replication. Recombinational Repair
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Base Excision Repair - Ung Text Fig. 9-13 A glycosylase removes U (Ung = uracil N-glycosylase). An AP (apurinic, apyrimidinic = abasic) endonuclease cuts the backbone, an exonuclease removes the abasic nucleoside. PolI fills in the gap and ligase seals the nick. This is an AP site.
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Excision Repair Base excision repair fixes “small” lesions - lesions that don’t distort the backbone. “Large” lesions (“bulky” adducts on bases, for example) that distort the backbone are repaired by nucleotide excision repair. Both types of repair processes take place in both prokaryotes and eukaryotes. Uracil is not the only target of base excision repair. There are other glycosylases that can remove other bases that shouldn’t be in DNA.
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UvrA-UvrB scan DNA for mismatches that distort the backbone. UvrB melts a region
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Lecture20CMFall2009FINAL - CM Office Hour Today 3:30-5:00...

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