Final answer:
The mismatch repair mechanism in bacteria uses the absence of methyl groups on the new DNA strand to identify and correct errors by cutting the non-methylated strand, excising the incorrect nucleotide, and then filling in the gap with the correct nucleotide.
Step-by-step explanation:
In bacteria, the mismatch repair mechanism distinguishes between the parent strand and the newly synthesized strand by identifying the methylation pattern present only on the parent strand. After DNA replication, the parental strand is already methylated; however, the new strand lacks these methyl groups initially.
Mismatch repair enzymes such as MutS, MutL, and MutH take advantage of this temporary difference to recognize and repair errors on the unmethylated, new strand by excising the misplaced nucleotide and replacing it with the correct one.
The MutH enzyme specifically makes a cut in the newly synthesized strand, signaling other repair proteins to remove a portion of this strand including the mismatched nucleotide. Afterwards, DNA polymerase III and DNA ligase work to fill in the gap with the correct nucleotide, thus restoring the DNA to its proper sequence.
The proteins Muts, MutL, and MutH bind to the hemimethylated site where the incorrect nucleotide is found. MutH cuts the nonmethylated strand, and an exonuclease removes the portion of the strand with the mistake. The gap is then filled in by DNA pol III and ligase.