Final answer:
Proofreading by DNA polymerase, DNA recombination, and nucleotide-excision repair are key mechanisms in maintaining DNA integrity by correcting replication errors and repairing substantial DNA damage like thymine dimers.
Step-by-step explanation:
The repair mechanisms responsible for maintaining the integrity of DNA include proofreading by DNA polymerase, DNA recombination, and nucleotide-excision repair. During the process of DNA replication, DNA polymerase can make mistakes. However, it also has a proofreading function that corrects errors by removing incorrect bases and replacing them with the right ones. If mismatched bases are left after replication, mismatch repair enzymes recognize the incorrect base, excise it, and fill the gap with the correct base. Finally, nucleotide excision repair is essential for fixing more substantial DNA damage such as thymine dimers caused by ultraviolet light, which can lead to mutations if not repaired.