Base Excision Repair

DNA bases that have been modified by the addition or loss of a small chemical group as described above are repaired by the BER pathway (Figure 3). The BER pathway begins with the excision of a damaged base by an enzyme called DNA glycosylase (Figure 3, step 1). DNA glycosylases bind to chemically altered (damaged) bases and catalyze the cleavage (hydrolysis) of the

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Figure 3. Schematic diagram of the base excision repair pathway. The damaged base (in this case, guanine) is removed by a glycosylase enzyme. This creates an AP-site, which is recognized and cleaved by AP-endonuclease. DNA polymerase fills in the gap. DNA ligase links the broken strand together again.

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