4. DNA Repair Flashcards
What happens during a cell cycle checkpoint?
Temporary arrest
Where are the 3 cell cycle check points?
End of G1
G2
Mitosis
What happens in the first checkpoint at the end of G1?
Checks environment - cell size, nutrients, growth factors, etc
What happens during the checkpoint in G2?
After DNA replication, so checks that it has been replicated successfully and all damage has been repaired before M phase.
What happens in the mitosis checkpoint?
Checks that spindles are attached to chromosomes
If DNA damage levels in a cell are too high, what could happen?
Apoptosis or senescence - permanent cell cycle arrest
Following DNA damage, what repair pathways are there?
- Base excision repair
- Nucleotide excision repair
- Recombinational repair
- Mismatch repair
Describe base excision repair.
When the base of a nucleotide is damaged, it is removed and replaced by DNA polymerase and the strand is resealed by DNA ligase .
What type of damage is nucleotide excision repair used for?
Remove bulky addicts or dimerisation
E.g UV induced thymine dimers
What type of damage does recombinational repair method repair?
Interstrand cross-link
Double-strand break
When would mismatch repair be a suitable repair method?
Mismatched bases
Insertions
Deletions
How can a double- break in DNA be repaired?
- Non homologous end joining
2. Homology -directed repair
Which of the 2 double strand repair mechanisms is error-prone?
Non-homologous end joining
What gene is commonly mutated in many cancers?
P53
Which type of double strand break repair is cell-cycle limited?
Homology-directed repair
S + G2/M phase
