DNA Repair Mechanisms Flashcards
1
Q
What are some examples of Single base alteration as a type of DNA damage ?
A
- depurination
- deamination of C –> U
- deamination of A
-Insertion/Deletion of nucleotides
2
Q
What are some examples of Two base alteration as a type of DNA damage ?
A
- UV light induced thymine-thymine dimer
- bifunctional alkylating agent cross-linkage
3
Q
What are some examples of chain breaks as a type of DNA Damage ?
A
- ionising radiation
- radioactive disintegration of backbone element
- oxidative free radical formation
4
Q
What are some examples of cross linkage as a type of DNA damage ?
A
- between bases in same or opposite strand
- between DNA and protein molecules
5
Q
Describe thymine dimers
A
- damage is introduced into DNA from cells from UV irradiation
- similar dimer will form between 2 neighbouring pyrimidine bases
6
Q
What’s the rate of damage for Depurination?
A
5000 purine bases (A & G) are lost everyday from the DNA of each human cell
7
Q
What are the main DNA repair pathways ?
A
- Base Excision repair
- nucleotide excision repair
- mismatch repair
- Double-strand break pair
8
Q
What is an example of genome surveillance ?
A
- DNA damage checkpoints
9
Q
What does the symmetry of the DNA helix allow ?
A
- easy & accurate replication and repair
10
Q
Explain proofreading
A
- as new bases are added DNA polymerase makes a proofreading check
- recognises errors, removes the wrong nucleotide and tries again
- error rate = 1/10,000
11
Q
Describe Excision repairs
A
- damage in 1 strand can be removed then the gap filled in and the remaining nick is ligated
- it uses the un-damaged strand as a template
- operates over life of a cell
12
Q
Describe Base Excision Repair
A
- damage is recognised by glycosylase
- common targets are deamination products
13
Q
Describe Nucleotide Excision Repair
A
- recognsises distortion in DNA
- removes most UV photoproducts, adducts
- most effective in transcribed regions
- more effective at repairing template strand than non-template
14
Q
Describe Mismatch Repair
A
- surpasses replication errors = substitution and slippage
- scans new DNA for mismatched pairs
- operates before new DNA strand is methylated
15
Q
How can you get double strand breaks?
A
- intentional = developmentally programmed
- by accident = radiation
- therapeutic = chemotherapy
- malicious intent = transposons
