Question

Mismatch repair mechanism in DNA deals with

• A. Deamination
• B. Adducts and cross-links
• C. Double stranded breaks
• D. Replication errors

Hint:

• Mismatch Repair (MMR) Corrects base-base mismatches and small insertions/deletions that arise during DNA replication and escape the proofreading activity of DNA polymerase.
• Base Excision Repair (BER) Repairs damage to single bases (e.g., deamination, oxidation, alkylation).
• Nucleotide Excision Repair (NER) Repairs bulky lesions that distort the DNA helix (e.g., pyrimidine dimers caused by UV, large chemical adducts).
• Double-Strand Break Repair (DSBR) Homologous Recombination (HR) and Non-Homologous End Joining (NHEJ).

Answer 1

The Correct Option is D

DNA repair mechanisms are crucial for maintaining the integrity of the genome. Different types of DNA damage are repaired by specific pathways. Mismatch Repair (MMR): This system corrects errors that occur during DNA replication when an incorrect nucleotide is inserted opposite a template nucleotide, resulting in a mismatched base pair (e.g., A paired with C instead of T, or G paired with T instead of C). It also corrects small insertions or deletions (indels) that can occur in repetitive DNA sequences during replication. The MMR system recognizes the mismatch, identifies the newly synthesized strand (which contains the error), excises the incorrect segment from the new strand, and then DNA polymerase and ligase fill in the gap with the correct nucleotides. Let's analyze the options: (a) Deamination (e.g., C to U): Often repaired by Base Excision Repair (BER). (b) Adducts and cross-links (bulky lesions): Often repaired by Nucleotide Excision Repair (NER) or other specialized pathways. (c) Double-stranded breaks: Repaired by Homologous Recombination (HR) or Non-Homologous End Joining (NHEJ). (d) Replication errors: This is precisely what mismatch repair deals with – errors made by DNA polymerase during replication that were not corrected by its proofreading activity. Therefore, the mismatch repair mechanism deals with replication errors. \[ \boxed{\text{Replication errors}} \]