Excision repair - If uracil is not repaired, it will base...

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Excision repair : Most important repair mechanism. Damaged DNA is recognized, removed either as free bases or as nucleotides, and the gap is filled by synthesis of new DNA using the complementary strand as a template. Types of excision repair: 1) base excision repair 2) nucleotide excision repair 3) mismatch repair One example for base excision repair is the removal of uracil from DNA. Most uracil in DNA arises from the deamination of cytosine which directly leads to the structure of uracil (Fig. 5.19 A). In humans it occurs at a frequency of about 100 times a day in each cell.
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Unformatted text preview: If uracil is not repaired, it will base pair with adenine during the next round of replication and thus cause a mutation. The general use of thymine instead of uracil in DNA allows the repair system to recognize deaminated cytosine as incorrect. In general, the excision of a base is catalyzed by DNA glycosylase , which cleaves the bond between the base and the deoxyribose (called glycosidic bond). The result is an apyrimidinic or apurinic (AP) site : a sugar with no base attached....
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