Fidelity of Dna replication:
Dna must be replicated with minimal error.
Failure to maintian _______ fidelity of dna replication causes ________.
High
Mutations(cancer/diseases)
Dna repair mechanisms:
mediated by enzyme complexes ti ensure that the replication error rate is low.
Proofreading of dna polymerase:
Optimum confirmation of DNA polymerization 3 active sitre and the incoming dNTP allows for addition of correct base pairs, but mistakes are still made.
What is the process of proofreading?
dna polymerase 3 detects the error and stalls then uses its 3’-5’ exonuclease activity to remove the most recently added nucleotides.
Dna mismatch repair(MMR):
Covers for replication errors not covered by proofreading.
What is the first step in the process of MMR:
- MutS and MutL recognize and bind the dna at the site of the mismatch.
What is the second step in the process of MMR:
- MutH endonuclease nicks the daughter strand several nucleotides away from the mismatch.
What is the third step in the process of MMR:
- Exo5’-3’ exonuclease removes nucleotides on the daughter strand around the mismatch.
What is the fourth step in the process of MMR:
- dna polymerase 3 fills the gap and repairs the mismatch.
What is the fifth step in the process of MMR:
DNA ligase seals the nick to complete the repair.
What is DNA damage?
mutagens are chemical agents that alter DNA bases.
What are the 3 main ways that dna bases are altered?
1) UV exposure
2) Radiation(x-rays and radioactive decay).
3) Chemical damage(Acetylation-the addition of carbons, oxidation, and damination-removal of NH2).
Base excision repair:
A mechanism to correct damage made to nitrogenous bases that are damaged by chemical modification.
What is the first step of the process of base excision repair:
- DNA glycosylase removes the modified base forming an AP sit (spot on the back bone without a base).
What is the second step of the process of base excision repair:
- AP endonuclease removes the Ap site.
What is the third step of the process of base excision repair:
DNA polymerase 1 adds the correct nucleotide.
What is the fourth step of the process of base excision repair:
- DNA ligase seals the nick.
Thymine dimer:
UV lights covalently links adjacent pyrimiadines along the DNA strand, results in a buldge in the DNA double helix.
Nucleotide excision repair:
A mechanism to correct dna damage made from exposure to UV radiation or chemical mutagens.
What is the first step in the process of nucleotide excision repair?
- repair enzymes recognize distortions in the double helix, excise the distorted segments and replace it.
What is the second step in the process of nucleotide excision repair?
- Uvr ABC excinuclease cuts the damage at 2 sites.
What is the third step in the process of nucleotide excision repair?
- DNA polymerase 1 adds the correct nucleotides.
What is the fourth step in the process of nucleotide excision repair?
- DNA ligase seals the nick.
