Final answer:
Mismatch repair in E. coli relies on the lack of base methylation in the newly synthesized DNA strand to identify and correct errors post-replication. Methylation serves as a marker for the repair enzymes to distinguish between the old and new strands of DNA. Therefore correct option is A
Step-by-step explanation:
Mismatch repair in E. coli is a crucial mechanism that corrects errors introduced during DNA replication. The question asks which process within mismatch repair depends on the recognition of the new DNA strand versus the parental strand. The correct answer is: a. base methylation within the newly synthesized DNA strand.
In E. coli, after DNA replication, the parental DNA strand will have methyl groups which are not yet present on the newly synthesized strand, as this strand has not been methylated. This temporal difference in methylation allows mismatch repair enzymes to discriminate between the older, parental strand and the new, daughter strand. Proteins such as MutS, MutL, and MutH bind to the DNA at mismatched sites, where MutH specifically cleaves only the newly synthesized strand due to its lack of methylation. Once the incorrect nucleotide is excised, DNA polymerase III and DNA ligase fill in the correct nucleotides and seal the strand.