DNA repair Original Scenario-Based Download PDF

Questions

1. 1.

   In an orbital bio-dome exposed to unfiltered solar radiation, astrobiologists cultivate a synthetic microbe engineered to monitor ultraviolet-induced genome distortion. When intense ultraviolet photons strike the microbial chromosome, adjacent thymine residues fuse into covalent cyclobutane dimers that physically bend the double helix and stall replication forks. To preserve its genome, the organism deploys an endonuclease complex that cleaves the phosphodiester backbone on both sides of the distortion, releasing an oligonucleotide segment containing the lesion before resynthesis. Which DNA repair pathway carries out this recognition and excision of an oligonucleotide fragment encompassing the bulky structural distortion?

   • A) Base excision repair, which relies on DNA glycosylase to cleave solitary altered bases without initially releasing an intact oligonucleotide
   • B) Mismatch repair, which targets normal but non-complementary nucleotides that slipped past DNA polymerase proofreading
   • C) Nucleotide excision repair, which recognizes severe helical distortions and removes a short lesion-containing single-stranded fragment
   • D) Non-homologous end joining, which directly aligns and ligates broken chromosome ends resulting from double-strand fractures