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Flashcards in CK L2 DNA Repair Deck (23)
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what is spontaneous deamination

the removal of an amino group from a molecule


DNA Replication Stress

Inefficient replication that leads to replication fork slowing, stalling and/or breakage


why is it imortant that spontaneous mismatches get repaired straight away?

because it will have a knock on effect during replication where a single mismatch will effect lots once its has been replicated


how can DNA replication stress occur?

if there is any machinery defects


why can lots of errors cause DNA replication stress?

because it causes delays which in turn causes stress


Types of DNA replication stress

> Replication machinery defects
> Replication fork progression hindrance
> defects in response pathways


how can repetitive DNA slow down DNA machinery and cause DNA replication stress

Repetitive DNA can lead to fork slippage


Fork slippage leads to...?



trinucleotide repeat disorders

Huntingtons disease


trinucleotide repeat disorders- some info on Huntingtons disease

> CAG repeats
> polylgutamine repeats
> normal protein function still unknown
Mutant protein aggregates in neurons
> progressive, late onset disease


3 different outcomes of DNA damage response

> Senescence
> Proliferation
> Apoptosis


Senescence is...?

permanent cell cycle arrest



Cell death


if DNA damage levels too high or persist what are the two outcomes

> Senescence
> Apoptosis



DNA repair


what do cell cycle checkpoints do?

slow dow the cell cycle to allows for DNA repair


the 4 steps in base excision repair

1) deamination converts one base into another e.g C into U (this is the error)

2) U is detected and removed leaving base-less nucleotide

3) Base-less nucleotide is removed leaving small hole in DNA backbone

4) The hole is filled with the right base by a DNA polymerase and the gap is sealed by ligase


what is a dimer

two identical subunits


4 steps of Nucleotide excision repair

1) UV radiation produces a thymine dimer

2) once the dimer has been detected the surrounding DNA is opened to form a bubble

3) enzymes cut the damaged DNA region out of the bubble

4) a DNA polymerase replaces the excised (cut-out) DNA and a ligase seals the backbone


4 steps of mismatch repair

1) a mismatch is detected in newly synthesised DNA e.g G paired with T.

2) the new DNA strand is cut and the mispaired nucleotide and its neighbours are removed by exonuclease activity

3) the missing patch is replaced with correct nucleotides by a DNA polymerase

4) a DNA ligase seals the gap in the DNA backbone


info on single strand breaks

> relatively simple
> many diff mechanisms
> integrity of DNA molecule intact
> damage removed on one strand only
> homology of other strand used to repair
> not error-free but not error prone either


info in double strand breaks

> complex
> integrity of DNA molecule lost
> more likely to be error prone
> use of homology may be possible


what are the two ways of repairing a double strand break?

1) non-homologous end joining

2) homologous directed repair