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10 Cards in this Set
- Front
- Back
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Types of recombination involved with ds breaks |
Non homologous end joining Homology directed repair using homologous chromosome Homologous recombination |
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Homologous recombination |
Double stranded breaks can induce homo recomb- results in reciprocal exchange of large segments of dna between DNA duplexes. Can occur between any dna molecules with extensive regions of identical (sister chromatids) or similar sequences (homologous chromosome), generates diversity by reshuffling segments of the genome to make new combinations of existing characteristics. Often occurs during meiosis and production of haploid gametes. Contributed to the diversity of bacterial genomes. |
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Holiday junctions |
Formed by reciprocal exchange of dna strands between two duplexes to form regions of heteroduplex dna. Formed via RecA-like recombinases that mediate D-loop formation |
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HJ- resolution |
HJ-separation of the two joined duplexes in the HJ need to be separated by resolution- cleaves DNA strands at the point where the molecules are joined, occurs by resolvase enzymes (E. coli: RuvC) Horizontal-cut dna strand originally broken and exchanged to form junction; parent DNA molecules are regenerated almost exactly (A and B; a nd b still on the same duplex), nonrecombinant. Vertical-cuts two DNA strands not originally cleaved and a physical exchange of DNA between two molecules occurs (A nd b and b^b and A) recombinant product
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Experiment by robin holiday |
Junction proposed by Robin Holliday to explain products of fungal meiosis A) domestic and monomer is plasmids were produced in an experiment using E. Coli, suggesting that holiday junctions could be resolved in two directions in coco B)Holiday junctions can be made in vitro by annealing four oligonucleotides. |
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Branch migration of HJ |
Duplexes joined at HJ can move along DNA without any net change in base pairing Can occur spontaneously in either direction. RuvA tetramer binds at HJ keeping unfolded and recruits RuvB RuvB is a helicase that uses ATP hydrolysis to move junction along DNA RuvC(resolvase) recruited by interaction with RuvAB |
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Ds break with homo recomb |
Homo recomb can be initiated by ds breaks Ds is respected by uncleared similarly to HDR and a 3’ end strand is bound by rec A(E. Coli) and Rad51 or Dmc1 (eukaryotes) to initiate strand invasion and D loop formation |
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HJ resolution determines whether recomb occurs |
1) if the two junctions are resolved in the same direction, no recombination occurs (a and b still on the same molecule) 2) resolution in different directions creates recombinant molecules (a and b now on different molecules, they’re linked instead) |
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Homologous directed repair vs homologous recombination |
Homology dependent repair - newly synthesized strand pairs with the other broken strand. The second end of the double- strand break captures the newly synthesized dna primer from the first end- the two duplexes do not become linked Homologous recombination - displaced template strand pairs with the other broken strand. The second end of the double-strand break captures the displaced strand of the D-loop -the two duplexes are linked |
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Recombination can lead to deletions duplications and translocations |
Intra- chromosomal deletion, unequal crossing over between sister chromatids, unequal crossing over between homologs, translocation between non-homologous chromosomes |
