Question

Discuss Xeroderma Pigmentosum in terms of DNA repair failure (Need to be thorough and specific. You may group the enzymes as to their specific functions such as helicase, endonuclease, ssDNA binding, etc.).

Answer 1

Xeroderma pigmentosum [XP] is a autosomally inherited skin and neurodegenrative disease . XP is highly cancer prone skin disorder .XP was the first nucleotide excision repair [NER] related disease.the NER related disease are associated predominantly with failures in DNA repair or replication in cells that contain UV induced photoproducts in their DNA. these include[5-5] and [6-6] cyclobutane pyrimidine dimers [CPDs] and [6-4] pyrimidine pyrimidinone dimers [PDs]  

There are eight complementation groups for XP [XP -A TO -G] .The product of XP genes are proteins involved in the different steps of NER, and comprises three damage recognition proteins, two helicase, and two nucleases. the two helicase , XPB and XPD are components of the basal transcription factor TFIIH, which has dual role in NER and initiation of transcription.different mutations in genes affects NER and trancription differentially. mutations resulting in defective repair without affecting transcription result in XP, whereas if transcription is also affected, TTD is the outcome.