Final answer:
DNA repair mechanisms involve base-excision and nucleotide-excision repair pathways. DNA glycosylase and AP endonucleases initiate the base repair, while in nucleotide repair, an excision nuclease recognizes bulky damage such as pyrimidine dimers. Both mechanisms use DNA polymerase to replace nucleotides and DNA ligase to seal the strand.
Step-by-step explanation:
Within the complex system of DNA repair, the base-excision repair pathway involves an enzyme called DNA glycosylase, which identifies and excises incorrect bases from the DNA. Following this, AP endonucleases and phosphodiesterase work to remove the remaining parts of the damaged nucleotides, allowing DNA polymerase to fill in with the correct base. The repair process is finalized by DNA ligase, which seals the nicks in the DNA backbone, completing the repair.
In the case of nucleotide-excision repair, which is notably responsible for correcting UV-induced pyrimidine dimers, the DNA is cut on both the 3' and 5' ends of the damage. This damaged section is then excised and replaced with correctly paired nucleotides synthesized by DNA polymerase. Again, DNA ligase is crucial for sealing the phosphodiester linkage, preserving the integrity of the DNA molecule.
Both base-excision and nucleotide-excision repair are essential for maintaining genetic stability by preventing mutations that can lead to diseases such as cancer. Indeed, defects in nucleotide excision repair processes can result in increased sensitivity to UV radiation and susceptibility to skin cancers.