Question

outline the steps involved in nucleotide excision repair which of these steps is affected in the disease Xeroderma

Answer 1

In base excision repair mechanism, the damaged DNA is spliced out, the new DNA base pairs are synthesized and ligated with the help of DNA ligase. The step-by-step process is given below:

1. Identifying the damage
2. Binding of a multi-protein complex to the site of damage
3. Incision of nucleotides away from the damaged site in both 5’ and 3’ sides (double incision)
4. Removal of damaged strand
5. The gap is filled by DNA polymerase and ligated by the DNA ligase

For example, the pyrimidine dimers can be repaired by this process. Exposure to sunlight causes the formation of several dimers, which are removed and repaired by the base excision repair.

In Xeroderma, the enzymes needed to remove the nucleotide dimers from the affected region. So, these mutations accumulate and increase the risk of cancer.