Children with xeroderma pigmentosum usually cannot carry out excision repair. Wh
ID: 96899 • Letter: C
Question
Children with xeroderma pigmentosum usually cannot carry out excision repair.
Why does this makes them so susceptible to developing cancer?
a) Carcinomas caused by epithelial cells that cover external and internal body surfaces lead to cancer, and one of the main mechanisms to destroy such cells is excision repair. b) Epstein-Barr virus damages DNA and leads to tumors, and one of the main mechanisms for repairing such damage is excision repair. c) Cancer is caused by many chemicals, that damage DNA , and one of the main mechanisms for repairing such damage is excision repair. d) Pyrimidine dimers caused by exposure to sunlight can create mutations that lead to cancer, and one of the main mechanisms for repairing such defects is excision repair.Explanation / Answer
d.Normally, damage to DNA in epidermal cells occurs during exposure to UV light. The absorption of the high-energy light leads to the formation of pyrimidine dimers, namely cyclobutane-pyrimidine dimers and pyrimidine-6-4-pyrimidone photoproducts. In a healthy, normal human being, the damage is first excised by endonucleases. DNA polymerase then repairs the missing sequence, and ligase "seals" the transaction. This process is known as nucleotide excision repair.This happens in the disease xeroderma pigmentosum.
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