Dna repair systems

Base excision repair, nucleotide excision repair, mismatach repair and double strand break repair

1. DNA Repair Systems R. C. Gupta Professor and Head Department of Biochemistry National Institute of Medical Sciences Jaipur, India

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3. E M B - R C G Chemotherapeutic agents Ultraviolet light Ionizing radiation Mutagenic chemicals

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8. E M B - R C G Mismatch repair system

9. E M B - R C G Mismatch repair system has to: Recognize the newly synthesized strand Scan the strand rapidly

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12. E M B - R C G MutS scans the new strand from one GATC sequence to another If it finds a mispaired base, it binds to it Then, MutL binds to MutS In E.coli , the system is made up of three proteins − MutS, MutL and MutH

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15. E M B - R C G Base excision repair system This system recognizes modified bases that are not normally found in DNA Such bases may be formed by deamination of: Cytosine to uracil Adenine to hypoxanthine Guanine to xanthine

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17. Nucleotide excision repair system

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20. Thymine dimer distorts the helix

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28. E M B - R C G Two additional proteins are required in transcription-coupled nucleotide excision repair These are CS-A and CS-B An inherited defect in either of these causes Cockayne syndrome

29. E M B - R C G Double strand break repair system

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31. E M B - R C G Double-strand breaks are repaired by homologous recombination (HR) or non-homologous end joining (NHEJ) In HR, a sister or homologous chromo-some is used as a template for repair In NHEJ, overhanging pieces of DNA adjacent to the break are joined

32. E M B - R C G Homologous recombination

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35. E M B - R C G Non-homologous end joining

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37. Thank you