Final answer:
The fidelity of DNA replication is maintained by three key mechanisms: proofreading by DNA polymerase, mismatch repair, and excision repair. These mechanisms help prevent, recognize, and correct errors to preserve genetic information across generations.
Step-by-step explanation:
Proofreading involves the DNA polymerase enzyme checking for errors as it assembles the DNA strand. If it detects an incorrectly paired nucleotide, it uses its 3' exonuclease activity to remove the incorrect base before continuing replication.
Mismatch repair is a post-replicative process where enzymes identify and fix mispaired nucleotides that were missed during proofreading. Specialized proteins recognize the unmethylated, newly synthesized strand and remove the incorrect section, which DNA polymerase then correctly resynthesizes.
Lastly, excision repair, such as nucleotide excision repair, targets damages like thymine dimers resulting from UV light exposure. Damaged nucleotides are excised, and the gap is filled in and sealed by DNA polymerase and DNA ligase, respectively.