recombination and DNA damage Flashcards
genetic stability vs genetic diversity
stability: allows genome conservation, DNA repair and avoid cancer/genome disorders
Diversity: occurs through meiosis, antibody diversity, adaptation and evolution
both important
what are the 5 mechanisms of genetic recombination?
homologous recombination (HR)
non-homologous end joining (NHEJ)
transpositions
site-specific recombination
independent assortment
what 2 ways can Holliday junctions be resolved?
non-crossover- both cleaving points the same orientation
crossover - both cleaving points opposite orientation causes ‘start’ and ‘end’ parts of the new strands to be from different initial strands
what proteins aid (d.s DNA break repair) homologous recombination and explain their functions
RecBCD- nuclease which aid to generate s.s. DNA
Rec A- recombinase which coats s.s DNA to condense DNA
RuvABC- resolves Holliday junction by cleavage, causing the crossover or non-crossover arrangement
what protein aids s.s break repair in homologous recombination?
only recA. which coats the single-stranded DNA
explain recBCD process AND the function of each molecule
rec C- chi scanning
rec B- degrades the 3’ prime more that 5’ prime
recD is faster than recB
1) ATP-dependent binding at DS end and digests 3’ more than 5’
2) when chi sequence reached 3’ no longer degraded, but 5’ is
3) once recA loaded, it coats DNA until chi is reached and results in the 5’ having much larger fragments than 3’
explain each ruvABC molecules function
ruvC- cleavage
ruvA- holds strands in square planar formation
ruvB- catalyses migration of junction, pulling the strands
explain NHEJ process and molecules involved
non-homologous end joining
after DS break:
1) ku recognises and binds to broken ends to keep them in place
2)lig 4 ligates the two ends together, or sometimes they are directly ligated together
explain the two processes of site-specific recombination
head-to-head–> inversion
—–>—a—b—<——- ——>—b—a—-<—-
the strands fold together where arrows align and the sequence in between, is inverted, and new ‘arrows’ are comprised of half DNA of both initial ones.
head-to-tail—> deletion or integration
—–>–a–b—>——
forms a plasmid of circular DNA (comprising of a and b) and a linear DNA
- reversible process
- new ‘arrows’ are comprised of half DNA of both initial ones.
explain E.coli chromosome dimer resolution and the two possible outcomes.
ds circular DNA is broken and new DNA strands are formed by nucleotide pairing.
-when no crossover- 2 identical ds circular DNA molecules are produced, one with original DNA and one with new DNA, these can go into two separate daughter cells.
-when crossover, linked DNA formed, these cannot go into two separate daughter cells. needs to have one more crossover site– XerCD recombinase used (site-specific recombination used) now two separate daughter cells are formed, they both have new and original DNA.
what are the three ways DNA replication can cause damage?
- nicks/gaps lead to REPLICATION FORK COLLAPSE
- replication fork reversal and restart
- over replication
which are RuvABC dependent?
- nicks/gaps lead to REPLICATION FORK COLLAPSE
- replication fork reversal and restart
- over replication
only the replication fork reversal and re-start, but all use this even if not dependent
explain over replication and what molecules involved
occurs when DNA is re-started even though DNA forks are blocked and unfused
they run into Ter regions (unreplicated DNA) and continue replication
molecules: RecBC, recA and RuvABC (but is ruvABC independent)
what does priA do?
priA is the initiator of replication when away from ori
allows for replication re-start
it targets replication and recombination structures
what leads to replication fork collapse and what molecules are involved.
nick or gaps in DNA
when regulatory proteins fail to stabilize it
uses priA DNA repair enzyme to re-start replication once resolved
molecules: RecBC, recA and RuvABC (but is ruvABC independent)
