Final answer:
In E. coli, the mismatch repair machinery distinguishes between the template and the new strand by recognizing the maternal strand's methylation status where adenines in GATC sequences are methylated. The newly synthesized strand, lacking this methylation, is identified and corrected by the repair enzymes.
Step-by-step explanation:
The enzyme machinery responsible for mismatch repair in a bacterial cell, such as E. coli, distinguishes between the template strand and the newly synthesized strand by looking at methylation markers. After replication in E. coli, the parental DNA strand is methylated, which means that the adenines in the sequence GATC have acquired methyl groups. In contrast, the newly synthesized strand initially lacks these methyl groups. This allows repair enzymes, including MutS, MutL, and MutH, to recognize and fix errors on the non-methylated, newly synthesized strand by excision and resynthesis. The correct answer to the multiple-choice question is B. For a short period after replication, the sequence GATC is methylated at the A only on the template strand. The key factor is the methylation status of the adenine in this sequence, which occurs on the template strand and not on the newly synthesized strand immediately after replication. This difference in methylation provides a signal for the mismatch repair machinery to identify the correct strand to repair.