How does mismatch repair function after DNA replication?

How does mismatch repair function after DNA replication?

• A. Mismatch repair identifies mispaired bases after replication, removes a DNA segment containing the error, and fills and ligates the gap.
• B. Mismatch repair duplicates the erroneous segment.
• C. Mismatch repair occurs only before replication.
• D. Mismatch repair uses RNA as a template.

Answer: (A)

Mismatch repair after replication fixes errors that escaped proofreading by recognizing mispaired bases, identifying the newly made strand, removing a short patch around the mismatch, and filling in the correct nucleotides before sealing the backbone. In bacteria, this starts when a mismatch is found by MutS, MutL helps coordinate, and MutH nicks the new strand at a nearby GATC site. An exonuclease then removes the patch containing the error, DNA polymerase fills in the correct bases, and DNA ligase seals the nick. In eukaryotes, similar players (like MSH2–MSH6 or MSH2–MSH3 for recognition and MLH1–PMS2 for coordination) carry out the same idea, using signals such as nicks or PCNA to distinguish the newly synthesized strand. The essential idea is removing the erroneous segment on the new strand and resynthesizing it using the old strand as a template, which is exactly what this option describes. The other statements don’t fit because they describe wrong timings or mechanisms: duplicating the erroneous segment would propagate the error, mismatch repair does not occur before replication, and the repair process does not use RNA as a template for fixing DNA.

Mismatch repair after replication fixes errors that escaped proofreading by recognizing mispaired bases, identifying the newly made strand, removing a short patch around the mismatch, and filling in the correct nucleotides before sealing the backbone. In bacteria, this starts when a mismatch is found by MutS, MutL helps coordinate, and MutH nicks the new strand at a nearby GATC site. An exonuclease then removes the patch containing the error, DNA polymerase fills in the correct bases, and DNA ligase seals the nick. In eukaryotes, similar players (like MSH2–MSH6 or MSH2–MSH3 for recognition and MLH1–PMS2 for coordination) carry out the same idea, using signals such as nicks or PCNA to distinguish the newly synthesized strand. The essential idea is removing the erroneous segment on the new strand and resynthesizing it using the old strand as a template, which is exactly what this option describes.

The other statements don’t fit because they describe wrong timings or mechanisms: duplicating the erroneous segment would propagate the error, mismatch repair does not occur before replication, and the repair process does not use RNA as a template for fixing DNA.