Direct Repair - DNA Photolyases
DNA Damaged by UV light
- Environmental & chemical agents can generate mutation - UV light
- UV irradition promotes pyrimidine dimer formation (cyclobutyl ring -covalent bond) between 2 adjacent thymines (as shown in pic2)
- Distorts DNA and interferes with replication
Concept of Direct Repair: Reverse damage --> Photoreactivation and DNA Photolyases
- Many types of repair repaired without removing a base or nucleotide.
- The best example of this is --> direct photoreactivation of cyclobutane pyrimidine dimer, catalysed by DNA Photolyases
- Pyrimidine dimers result from a UV-induced reaction (as talked about above) and photolyases use energy derived from absorbed light to reverse damage.
- Photolyases contain 2 cofactors, that serve as light-absorbing agents, or chromophores
- One of the chromophore is --> always FADH- (in E.coli and yeast)
- Other chromophore is --> Folate
- DNA photolyases are not present in cells of placental animals (e.g. humans)
Steps of Direct Repair
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