Now that the sunny weather is almost here, it's timely to consider that mutations that inactivate nucleotide-excision repair (NER) have been associated with several genetic diseases, such as xeroderma pigmentosum (XP). In humans, NER is the sole repair pathway for cyclobutane pyrimidine photodimers, and thus people with XP are highly sensitive to light and are predisposed to sunlight-induced skin cancers.
A) In many microorganisms there is another pathway for repairing pyrimidine photodimers. What is it?
B) A consequence of the inability to repair UV-induced photodimers is stalled replication forks. What are the two ways to repair (or bypass) stalled/collapsed replication forks that were mentioned in class?
C) In a laboratory experiment cultures of fibroblasts from healthy individuals and from patients with type G XP (XPG) were irradiated with UV light. After the DNA was isolated and denatured, it was found that the samples from the normal, healthy patients showed a significant reduction in the average molecular weight of ssDNA after UV exposure, but the XPG fibroblasts did not show the same reduction in average ssDNA molecular weight. Explain this observation.
D) It has also been noted that XPG cells replicate normally in the absence of UV-induced DNA damage. Which step in the NER pathway is presumably defective in XPG patients?
A) Another pathway for repairing pyrimidine photodimers - Photoreactivation Process.
B) The two ways to repair stalled replication forks that were mentioned in class-
1. Sister Chromatid Recombination (SCR)
2. Re-priming of replication forks in human fibroblasts
D) Mutations in the XP genes
Now that the sunny weather is almost here, it's timely to consider that mutations that inactivate...
Now that the sunny weather is almost here, it's timely to consider that mutations that inactivate nucleotide-excision repair (NER) have been associated with several genetic diseases, such as xeroderma pigmentosum (XP). In humans, NER is the sole repair pathway for cyclobutane pyrimidine photodimers, and thus people with XP are highly sensitive to light and are predisposed to sunlight-induced skin cancers. A) In many microorganisms there is another pathway for repairing pyrimidine photodimers. What is it? B) A consequence of the...