DNA Replication and Repair, Environmental Interaction, Adiations, Chemical Mutagens, Heat, Enzymatic Errors, Spontaneous Decay, Damage DNA

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	DNA Repair - DNA is constantly being subjected to environmental interaction that causes the alteration or removal of nucleotide bases. Radiations, chemical mutagens, heat, enzymatic errors, and spontaneous decay constantly damage DNA. If the damage is not repaired, a permanent mutation may be, introduced that can result in a number of deleterious effects including loss of control over the proliferation of the mutated cell. In the long evolutionary challenge to minimize mutation, cells have evolved numerous mechanisms to repair damaged or incorrectly replicated DNA.
Many enzymes, acting alone or in concert with other enzymes, repair DNA. Most of the repair enzymes are involved in recognizing the lesion, excising the damaged section of the DNA strand and using the sister strand as a template, filling the gap left by the excision of the abnormal DNA. Repair systems are generally placed in four broad categories: damage reversal, excision repair, double strand break repair and post-replicative repair. Enzymes of the repair system have been conserved during evolution. That is, enzymes found in E coli have homologues in yeast, fruitflies, etc.