We have very good DNA machinery that replicates DNA to make many different copies. However, this machinery in our cells is not perfect. With so much DNA replication going on, there are bound to be some mistakes and errors made during this process. These errors lead to mutations and if not corrected, it may be detrimental to the cell. Even though these mistakes are rare (1/100,000,000 bases), it is still important that cells and DNA have a system to repair these errors; these are called DNA repair mechanisms. There are hundreds of enzymes made by our cells to repair damaged DNA.
Direct Repair
– Sometimes, the cell is able to reverse any damages in our DNA.
Example: DNA polymerase has a proofreading function that recognizes mismatched nucleotides and corrects it immediately during DNA replication. This undoes any damage to the DNA molecule.
Excision Repair
– The damaged section of DNA is recognized and replaced by a newly synthesized correct copy.
1) Repair enzymes recognizes an incorrect base or distortion in the DNA double helix and cuts out the damaged section.
2) A new section is synthesized by DNA polymerase, using the undamaged DNA strand as the template.
3) The new section is sealed into place by ligase.
Recombination Repair
– This happens when both strands of the DNA is damaged.
– The homologous portion of a sister chromatid is used as a template to construct new DNA.
– Although this method is likely to contain errors, there is more damage if no repair is made at all.
Sometimes when the damage to the DNA is severe, it may trigger suicide genes instead of DNA repair mechanisms. These genes cause the cell to die, preventing it from passing on the mutation to future daughter cells.
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This article was written for you by Samantha, one of the tutors with SchoolTutoring Academy.