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1、1Chapter 6Mechanisms of DNA Damage and Repair6.2 Mismatch Repair and Direct Repair26.2.1 Mismatch RepairMismatch repair can correct DNA base mismatches that occur during DNA replication and recombination.3E.Coli Mismatch Repair45E.Coli Mismatch Repair6.2.2 Direct Repair(1).Single Strand Break Repair
2、If the 5 phosphate and 3-OH of the DNA are intact,DNA ligase can catalyze the formation of phosphodiester bonds at the break,directly repairing single strand break.6(2)Photoreactivation Cleaves Thymine DimersForming a Pyrimidine dimersPhotolyase binds to the injured siteEnzyme activated by visible l
3、ightRelease enzyme after repair7(3)Direct Repair of Alkylated BasesO6-Methylguanine methyltransferase8O6-methylguanine methyltransferase removes methyl from O6-methylguanine to repair DNA by transferring it to its own cysteine residue.(4)Direct Insertion of Purines9The shedding of purines on the DNA strand results in no purinesites,which can be recognized and bound by DNA purineinsertases,catalyzing the formation of glycosidic bonds betweenfree purine bases and the purine-free parts of DNA.Thank You!Thank You!