Question

How are errors that occur during DNA replication repaired?

Answer 1

DNA replication errors are corrected through a multi-step “quality control” system that ensures genetic accuracy:

• Proofreading: This happens instantly during replication. As DNA polymerase adds nucleotides, it checks each one. If it detects a mismatch, it immediately swaps its activity to “reverse,” removes the wrong base, and inserts the correct one before continuing.
• Mismatch Repair (MMR): Some errors sneak past the polymerase. Shortly after replication is finished, a dedicated set of proteins scans the new DNA for “bumps” caused by mispaired bases. They snip out the incorrect segment on the new strand and let DNA polymerase fill it in correctly using the original parental strand as a template.
• DNA Damage Repair: If DNA is damaged later (by things like UV light or chemicals), the cell uses Excision Repair. Specialised enzymes “cut and paste” by removing the damaged section and replacing it with fresh, accurate nucleotides.