Final answer:
DNA repair mechanisms include Base Excision Repair, Nucleotide Excision Repair, Mismatch Repair, Direct Reversal, Translesion Synthesis, Non-homologous End Joining, and Homologous Recombination, as well as proofreading during replication.
Step-by-step explanation:
The various types of DNA repair mechanisms that have been identified include:
- Base Excision Repair: This involves specific DNA glycosylases that recognize and remove damaged bases from the DNA, followed by end repair and resynthesis.
- Nucleotide Excision Repair: Removes bulky DNA damage, such as pyrimidine dimers caused by UV light, cutting out the damaged segment followed by resynthesis.
- Mismatch Repair: Corrects base-pairing mismatches left after DNA replication, identified by lack of methylation on the new strand, followed by excision and resynthesis.
- Direct Reversal: Some types of damage are directly reversed without breaking the DNA backbone, like the reversal of thymine dimers by photolyase.
- Translesion Synthesis: Uses specialized DNA polymerases that can synthesize DNA over the damaged region, likely introducing mutations.
- Non-homologous End Joining: Repairs double-strand breaks without the need for a homologous template, often leading to loss of nucleotide information at the break site.
- Homologous Recombination: Repair of double-strand breaks using a homologous sequence as a template, preserving the sequence information.
Additionally, DNA repair occurs through mechanisms like proofreading during DNA replication, which corrects most mistakes by the removal and replacement of incorrect bases.