DNA Replication Excision Repair System The first type of repair system we will discuss is the excision repair system. To excise simply means to remove, so this repair systems works by removing the area of damage. Special enzymes recognize damaged DNA. This repair system comes in two forms: Base-excision repair and short-patch nucleotide excision. Base-pair Excision Repair In base-pair excision, single base-pairs are identified and removed. The resultant gap is then filled with a DNA polymerase and the nick is sealed by a DNA ligase. Short-patch Excision Repair Short-patch excision varies from base-pair excision in that its enzymes will recognize and remove "short patches" of DNA that are damaged. These short patches of damage arise from bulky lesions such as thymine dimers. This form of damage is radiation-induced and leads to the formation of a bond between adjacent thymine bases on the same strand of DNA. This bond
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