《分子生物学》5 chapter 10.ppt
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1、Chapter 10,Homologous recombination at the molecular level,All DNA is recombinant DNA. Genetic exchange works constantly to blend and rearrange chromosomes, most obviously during meiosis, when homologous chromosomes pair prior to the first nuclear division. During this pairing, genetic exchange betw
2、een the chromosomes occurs. This exchange, classically termed crossing over, is one of the results of homologous recombination.,Models for Homologous Recombination Homologous Recombination Protein Machines Homologous Recombination in Eukaryotes Mating-Type Switching,in prokaryotes,Alignment: Breaks:
3、 Strand invasionHolliday junction Branch migration: Movement of the Holliday junction Resolution: Cleavage of the Holliday junction,Models for homologous recombination,1.The Holliday Model,2.The Double-Strand Break Repair Model,Double-straned breaks in DNA arise quite frequently In bacteria, the maj
4、or biological role of homologous recombination is to repair DSBs In addition to repairing DSBs in chromosomal DNA, homologous recombination promotes genetic exchange in bacteria In eukaryotic cells, homologous recombination is critical for repairing DNA,Double stranded DNA breaks arise by numerous m
5、eans and initiate homologous recombination,Damage in the DNA template can lead To DSB formation during DNA replication,Homologous recombination protein machines,Homologous recombination in prokaryotes,The RecBCD helicase /nuclease processes broken DNA molecules for recombination RecA protein assembl
6、es on single-stranded DNA and promotes strand invasion Newly base-paired partners are established within the RecA filament RuvAB complex specifically recognizes Holliday junctions and promotes branch migration RuvC cleaves specific DNA strands at the Holliday junction to finish recombination,Steps o
7、f DNA processing by RecBCD,Polar action of chi,RecA Protein :strand-exchange protein The active form of recA is a protein-DNA filament many subunits + many strands Coated with RecA make DNA highly extended Polarity of RecA assembly,RecA Protein Assembles on Single-stranded DNA and Promotes Strand In
8、vasion,RecA Stabilises single stranded DNA,RecA prevents secondary structure within the single stranded DNA RecA forces the single stranded DNA to take on a helical shape, effectively lowering the energy barrier to recombination,RecA Protein Assembles on Single-stranded DNA and Promotes Strand Invas
9、ion,Polarity of RecA assembly,Newly base-paired partners are established within the RecA filament,cross-section of single DNA strand bound to RecA protein Homology search is promoted by RecA. DNA in secondary site is testes for complementarity Joint molecular: Base -paring between strands is switche
10、d RecA is prone to bind the DNA products after strand exchange.,RecA-catalyzed strand exchange can be divided into different stages,Model of two steps in search for homology and DNA strand exchange within the RecA filament,Homologous recombination in prokaryotes,The RecBCD helicase /nuclease process
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