Home Tools Sign In L211 SP18 Proble...x 1 16 119% DNA Repair Questions Q1 A) The

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Home Tools Sign In L211 SP18 Proble...x 1 16 119% DNA Repair Questions Q1 A) The human disease known as xeroderma pigmentosum (XP) arises from mutations in at least seven different genes. The resulting deficiencies are generally in enzymes involved in some part of the pathway for nucleotide excision repair James Cleaver, a scientist was reading an account of the genetics of XP and clinical descriptions and realized that the disease might be the sought-after connection to the UV repair pathway that had been characterized in bacteria. To obtain support for his hypothesis he needed to first establish an assay to observe repair replication in mammalian cells He obtained skin biopsies from patients with XP and developed cell lines that could be grown in petri dishes. Cultures of fibroblasts (skin cells) from healthy (normal) individuals and from patients with XP were irradiated with UV light. DNA was isolated from samples, denatured and the resulting single-stranded DNA was analyzed using density gradient centrifugation The results are shown below Normal XP (+UV) (+UV) Samples from normal fibroblasts show a lower molecular weight single-stranded DNA after irradiation, but samples from the XP fibroblasts do not. What does the lower molecular weight DNA band represent? Why do the XP cells not show that band? [3 points]

Explanation / Answer

In normal NER always damaged and some normal nucleotides removed from DNA strands so when it treated with UV it will give two bands. In case of XP, NER process is inhibited due to lack of enzymes so no breakage of nucleotide will occur and only one band will be produced.

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