Question

30.1 A 10-year-old girl is brought by her parents to the
dermatologist. She has many freckles on her face,
neck, arms, and hands, and the parents report that
she is unusually sensitive to sunlight. Two basal cell
carcinomas are identified on her face. Based on the
clinical picture, which of the following processes is most
likely to be defective in this patient?
A. Repair of double-strand breaks by error-prone homol-
ogous recombination
B. Removal of mismatched bases from the 3-end of
Okazaki fragments by a methyl-directed process
C. Removal of pyrimidine dimers from DNA by nucleo-
tide excision repair
D. Removal of uracil from DNA by base excision repair​

Answer 1

Answer:

B is the answer for above question

Answer 2

Answer:

The correct answer is option C, D

Explanation:

• The sensitivity to sunlight, extensive freckling on parts of the body exposed to the sun, and presence of skin cancer at a young age indicate that the patient most likely suffers from xeroderma pigmentosum (XP). These patients are deficient in any one of several XP proteins required for nucleotide excision repair of pyrimidine dimers in ultraviolet light–damaged DNA. Double-strand breaks are repaired by nonhomologous end-joining (error-prone) or homologous recombination (error-free).
• Methylation is not used for strand discrimination in eukaryotic mismatch repair.
• Uracil is removed from DNA molecules by a specific glycosylase in base excision repair, but a defect here does not cause XP.