Repair MechanismWhen does it happen?How does it work?What is the outcome?Lesion BypassDuring replication- have to keep going! WIll replicate through Thymine dimerSwitches normal Pol for special Pols that can blow through the damage. Are good at recognizing TdimerOften causes mutation-- but lets cell live (replication doesn’t stall)Direct ReversalWhen bases are chemically damaged (thymine dimer, methylation damage)Photoreactivation: reverses Tdimer with visible light.Methyltransferase: reverse met damageNo mutations-- just reverses base damageDamage Removal:When you need to correct mistakes the Pol made or DNA damageExcise damaged area and repolymerize fresh DNAGenerally corrects damage, no mutations (excepting ds Break repair non-homologous)1. Base excision repairSingle base is damaged or converted to U1-2 base removed then residue removed, polymerase adds new NTPCorrects damage, no mutation-- uses other un-damaged strand as template2. Mismatch excision repairProofreading after
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DNA Damage, DNA damage Single, template Corrects mismatch, met damage Excise