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What is Defect in xeroderma pigmentosum (Repeat) and explain in detail?
Ans: C (Nucleotide excision repair) Ref: Robbins Pathologic Basis of Disease, 8th edition, Pg: 275 & Frosiius G Commentary: DNA base excision repair defects in human pathologies Free Radic Res. 2004 Oct:38(10): 1037-54.Explanation:Types of defects in DNA-repair systems and conditions associatedDNA Repair MechanismsDiseases associatedMismatch repair* Hereditary Nonpolyposis Colon Cancer Syndrome* Muir-Torre SyndromeNucleotide excision repair* Xeroderma pigmentosum* Cockayne's syndrome* T richothiodystrophyBase excision repair* Gross defects - Not compatible with life* Partial defects -Colorectal cancer & LungRecombinational repairCancers* Ataxia Telangiectasia (ATM gene, genome instability syndrome)* Bloom syndrome (RecQ DNA helicase; BLM gene)* Fancont anemia (BRCA-2)* Werner syndrome (WRNp protein- RecQ DNA helicase)Direct Repair-- DNA damaging agent X-raysoxygen radicals (internal/external) alkylating agents spontaneousUV-light oxygen radicals (internal/external)X-raysoxygen radicals (internal/external) UV-lightanti-tumor agentsreplicationerrorsnon-enzymatic methylation of DNA by cellular S-adenosyl- methionine||Lesions|||Uracilabasic site 8-oxoguanme single-strand break6-4 photoproduct bulky adducts cyclobutane pyrimidine dimerdouble-strandbreakinterstrand-crosslinkA-G mismatchT-C mismatch insertiondeletionO-6-methyl-guanine||Repairprocess|||Base excision repair (BER)Nucleotide excision repair (NER)Recombinational repair (HR/NHEJ)Mismatch repair (MMR)Direct reversal (DR)