DNA repair | Anatomy2Medicine
DNA damage

DNA repair


  • DNA repair
  • Single strand




  • Nucleotide excision repair


      • Specific endonucleases release the oligonucleotide-containing damaged bases; DNA polymerase and ligase fill and reseal the gap, respectively.
      • Repairs bulky helix-distorting lesions.
      • Defective in xeroderma pigmentosum, which prevents repair of pyrimidine dimers because of ultraviolet light exposure.



  • Base excision repair


        • Base-specific glycosylase recognizes altered base and creates AP site (apurinic/apyrimidinic).
        • One or more nucleotides are removed by APendonuclease, which cleaves the 5 end.
        • Lyase cleaves the 3 end.
        • DNA polymerase-b fills the gap and DNA ligase seals it.


  • Important in repair of spontaneous/toxic deamination.
  • Mismatch repair
  • Newly synthesized strand is recognized, mismatched nucleotides are removed, and the gap is filled and resealed.


        • Defective in hereditary nonpolyposis colorectal cancer (HNPCC).


  • Double strand
  • Nonhomologous end joining


        • Brings together 2 ends of DNA fragments to repair double-stranded breaks. No requirement for homology.


  • Mutated in ataxia telangiectasia.