chapter 11 part 3 Flashcards
(77 cards)
2 mechanisms for carrying out double-stranded break repair
- non-homologous end joining
- synthesis-dependent strand annealing
when is non-homologous end joining used
when the double-stranded break occurs during G1 and before replication
is replication resumed after non-homologous end joining?
yes, but the process inevitably leads to mutation
4 steps of non-homologous end joining
- double-stranded break produced in DNA
- recognized by proteins PKcs, Ku70, and Ku80 that attach to the broken ends
- complex trims back the free ends of the break (loss of genetic information)
- blunt ends produced by resection are ligated by ligase IV
when is genetic information lost during non-homologous end joining
when the complex trims back the free ends of the break
when does synthesis-dependent strand annealing occur
when the double-stranded break occurs after replication
does synthesis-dependent strand annealing create mutations?
no - error-free process
another name for synthesis-dependent strand annealing
homology dependent repair
process of synthesis-dependent strand annealing (SDSA)
- begins with trimming of broken ends
- attachment of protein Rad15
- Rad51 facilitates invasion of intact sister chromatid by the resected end of the broken strand
strand invasion process of SDSA
displaces on strand of the DNA duplex on the sister chromatid to form a displacement loop
how do sister chromatids reform
by dissociation and annealing of the new strand to the other side of the break
- results in replacement of the excised DNA with a duplex identical to the sister chromatid
homologous recombination
exchange of genetic material between homologous DNA molecules
when does homologous recombination occur in bacteria/archaea
conjugation - consequence of double-strand break repair
when does homologous recombination occur in eukaryotes
prophase I of meiosis
in eukaryotes, homologous recombination is initiated by controlled _______________
double-stranded DNA breaks
proper chromosome segregation during meiosis depends on
homologous recombination
what is the system of homologous recombination in bacteria
RecBCD pathway
RecBCD pathway
- double-strand breaks attract RecA protein
- RecBCD then attaches to region where RecA is bound
- leads to single-strand invasion and D loop formation
- RuvAB and RuvC proteins bind and complete homologous recombination
what does RecBCD pathway rely on to initiate process
DNA double-strand breaks
what is RecA protein a homolog of
human Rad51 protein
double-stranded break model of meiotic recombination
- recombination initiated by Spo11
- Spo11 degrades, Mrx resect single strands of cut chromatin
- proteins Rad51 and Dmc1 help facilitate strand invasion and D loop formation
- 2 strands that appear to cross over one another form Holliday junction
- heterduplex forms
- invading strand extended, with DNA synthesis guided by intact template strands, assisted by Rad52 and Rad59
- 3’ end of invading strand joins to 5’ end of strand segment that was initially part of the invading strand (ligation)
- non-sister chromatids now connected by double Holliday junctions
where was Spo11 first discovered
yeast
Spo11
dimeric protein that generates an asymmetric double-stranded cut in one chromatid (both strands)
what proteins associate with Spo11
Mrx and Exol
