Final answer:
Mismatch repair corrects replication errors by excising incorrect nucleotides and replacing them with the correct base. Mutations in mismatch repair enzymes can lead to permanent damage.
Step-by-step explanation:
Mismatch repair corrects the errors after the replication is completed by excising the incorrectly added nucleotide and adding the correct base. If any mutation occurs in the mismatch repair enzyme, it would lead to more permanent damage. The enzymes involved in this mechanism recognize the incorrectly added nucleotide, excise it, and replace it with the correct base.
One example is the methyl-directed mismatch repair in E. coli. The DNA is hemimethylated, the parental strand is methylated while the newly synthesized daughter strand is not.
Proteins Muts, MutL, and MutH bind to the hemimethylated site, where the incorrect nucleotide is found. MutH cuts the nonmethylated strand (the new strand), then an exonuclease removes a portion of the strand (including the incorrect nucleotide). The gap formed is then filled in by DNA pol III and ligase.
The enzymes recognize the incorrect nucleotide, excise it, and replace it with the correct base using a hemimethylated mechanism in E. coli.