Chapter 13 lecture (Homologous recombination) Flashcards
why is Homologous recombination Essential in bacteria and in eukaryotic mitosis
to repair DNA damage and stalled replication forks
why is homologous recombination essential in eukaryotic meiosis
for generating diversity and for chromosome segregation
Recombination enzymes can use … as substrates
any pair of identical or nearly identical sequences
how is homologous recombination initiated
a double stranded break
in homologous recombination, how is the DbSB enlarged?
exonuclease will Degrade the 5’ end of both strands flanking the gap to form 3’-single stranded overhangs
A 3’ overhang will perform a … of the other duplex to make …
stand invasion
heteroduplex DNA
what will be used as template to synthesize new DNA through DbSB region
undamaged copy of DNA
after the DNA is synthesized in homologous recombination, what happens next?
The invading strand is released and base pairs with the single strand from the original duplex
in homologous recombination, High fidelity DNA polymerases will
fill in remaining gaps and all strands will be ligated
If it occurs after S phase
there will be identical sister chromatids to use as a template
If it occurs in G1,
it will have to use a non-identical homologous chromosome as a template
Meiotic recombination uses a homologous sequence as a template, even though
a sister chromatid is present
what is a key component of the homologous recombination mechanism in E. coli
RecA protein
RecA protein is similar to what in eukaryotes
Rad51
RecA binds to
the single stranded 3’ overhang produced after DbSB
RecA forces ssDNA into a
“double stranded” helical conformation
The RecA/ssDNA complex can displace
single strands from duplexes
If RecA/ssDNA finds a complimentary sequence of >15 nt
Complimentary strand will pair with ssDNA to form heteroduplex
Homologous recombination is necessary in eukaryotes
for
DNA repair
Restarting of collapsed replication forks
Needed for successful pairing of homologous chromosomes in prophase I
failure of homologous pairing leads to
nondisjunction in anaphase 1
Meiotic recombination begins in the same way as with general homologous recombination, except
The DbSB is induced by the Spo11 protein complex
The undamaged copy that is used as a template is a nonidentical homologous chromosome
what two proteins coat ssDNA overhangs and promote strand invasion
dmc1 and rad51
dcm1 is only active in
meiosis and has specificity for homologous chromosome
Prevents invasion of sister chromatid
rad51 is active
throughout the cell cycle for all DsDB recombination in eukaryotes
Loaded onto the ssDNA by the Brca2 protein
Loss of Brca2 function leads to reduced DsDB repair