BCH4024 - McKenna Lecture 57

BCH4024 - McKenna Lecture 57 - Information Restructuring...

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1 Information Restructuring Homologous Recombination New combination of alleles - Does not change the arrangement of the entire loci . Larger scale genetic rearrangements are mediated by a Mobile Genetic Elements = Transposable elements a Gene Re-arrangements Gene Amplification Variation and Evolution DNA RECOMBINATION AND REPAIR 5. RECOMBINATION GENERAL RECOMBINATION : - Breaking and joining of chromosomes -ds DNA molecules align at regions of similar sequence -New DNA molecules form by exchange of region DNA repair (ds damage and ssDNA breaks) Genetic recombination Transposition : -Movement of gene to a new site, on same or a different chromosome Does not require extensive homology Transposons : Mobile genetic elements that enable genes to move between non-homologous sites in DNA – Transposable elements. Altered expression of genes in new environments Site-specific recombination - integration of viral DNA - Antibody formation/switching Genetic recombination is mediated by breakage and joining of DNA strands In Ecoli- requires RecA ATP driven Catalyses strand exchange at site of homology Limited homology Specific DNA-protein interactions Requires Integrase enzymes
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2 Recombination Repair Holliday model for genetic recombination – Proposed ‘64 1 Endonuclease nicking 2 Strand invasion 3 Ligation 4 Branch migration Two homologous sequences align Cleavage of one strand of each duplex Base pairing with unbroken strand Joining of adjacent bases Branch migration – duplex unwinding and rewinding HJ LINEAR DNA
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3 5. Isomerization 4 Holliday model of genetic recombination ctd. Hybrid middle region Strands broken in step 1 Strands not broken in step 1 Recombinant Non Recombinant Model Being refined 6 7 8 9 10 9 Recombination of circular DNA duplexes : = to 5 Recombinant Nonrecombinant 1 2 3 Invasion Ligation Isomerisation 5 Nicking 6 9 Seen in micrographs
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4 Micrographs of DNA Molecules undergoing Recombination Two DNA molecules at an intermediate stage of recombination Holliday junction created during recombination between two plasmid DNA Molecules – generated by Endonuclease cleavage of Figure 8 structure Plasmid DNA Rec A protein (38 kD) binds to ss DNA -forms polymeric filament – Helical, 6 monomers/turn -has binding site b for ssDNA that alsoaccommodates ds DNA near b for invasion at regions of homology -ATP drives strand displacement (branch migration) ATPase function Additional genes involved in recomb: a 328 kD recBCD (exonuclease V)
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This note was uploaded on 03/15/2010 for the course BCH 4024 taught by Professor Allison during the Spring '08 term at University of Florida.

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BCH4024 - McKenna Lecture 57 - Information Restructuring...

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