Dna damage and repair (Photoreactivation)

Pyrimidine Dimer and DNA Repair- Photoreactivation

1. TOPIC : DNA Damage- Pyrimidine Dimer and DNA Repair- Photoreactivation NAME – V ivek kumar COURSE – Microbiology Bangalore University

2. DNA Damage – Pyrimidine Dimer Pyrimidine dimers are molecular lesions formed from thymine or cytosine bases in DNA via photochemical reactions . Ultraviolet light induces the formation of covalent linkages by reactions localized on the C=C double bonds . Two common UV products are cyclobutane pyrimidine dimers (CPDs, including thymine dimers) and 6,4 photoproducts . These lesions alter the structure of DNA and consequently inhibit polymerases and arrest replication.

3. Types of dimers Cyclobutane – A cyclobutane pyrimidine dimer (CPD) contains a four membered ring arising from the coupling of the C=C double bonds of pyrimidines. Such dimers interfere with base pairing during DNA replication, leading to mutations. 6,4-photoproducts – 6,4-photoproducts or 6,4 pyrimidine- pyrimidones , results from the formation of a bond between C6 of one pyrimidine base and C4 of the another pyrimidine base. Spore photoproduct lyase provides another enzymatic pathway for repair of thymine photodimers .

4. DNA Repair - P hotoreactivation Photoreactivation repair mechanism can be used to repair a specific DNA damage, called as Pyrimidine dimers . Those DNA who have their thymines as 3 H- labelled are ultraviolated -irradiated damaged. By this rule a repairable DNA is identified.

5. Reference Molecular Biology by David Freifelder , Narosa Publishing House, Page no.277-284 David S. Goodsell (2001). “The Molecular Perspective: Ultraviolet Light and Pyrimidine Dimers” PMID 11423677

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