DNA repair Original Scenario-Based Practice

Questions

1. 1.

   During a deep-space exploration mission, an autonomous bio-probe examines an extremophilic bacterium thriving under unshielded ultraviolet radiation on a barren moon. The probe's molecular sensors observe that whenever adjacent pyrimidine bases form covalent cyclobutane dimers that distort the double helix, a specialized multi-protein complex makes two distinct cuts in the damaged phosphodiester backbone flanking the lesion. A helicase then peels away a short single-stranded segment containing the distorted bases, allowing DNA polymerase to fill the resulting gap using the complementary strand as a template before DNA ligase seals the nick. Which biological pathway is this extraterrestrial microbe utilizing to rectify its UV-induced genetic damage?

   • A) Base excision repair, which employs a specific DNA glycosylase to excise solitary altered bases without removing surrounding intact nucleotides
   • B) Methyl-directed mismatch repair, which selectively recognizes unmethylated nascent strands to correct replication slippage and non-Watson-Crick pairings
   • C) Nucleotide excision repair, which hydrolyzes dual incisions to remove an oligonucleotide fragment bearing bulky helical distortions
   • D) Non-homologous end joining, which directly processes and ligates severed chromosome ends produced by double-strand breaks without a template

Answers and step-by-step solutions appear after you finish the test.