Select the correct statement about chromosomal DNA replication in Escherichia coli

Introduction / Context:E. coli replication is a textbook model: a single origin (oriC) fires to produce two replication forks that move in opposite directions around the circular chromosome.

Given Data / Assumptions:

• Organism: E. coli in normal growth (no specialized phage systems controlling replication).
• Genome: circular with one oriC and a defined terminus region.
• Fork movement: two forks in opposite directions.

Concept / Approach:Bidirectional replication halves the time needed to copy the chromosome compared with unidirectional synthesis. Phage infections can introduce their own polymerases for phage DNA replication, but chromosomal replication still relies on the host replisome and oriC regulation.

Step-by-Step Solution:Identify initiation site: oriC.Describe fork dynamics: two forks diverge and meet at terminus.Exclude phage-dependent or promoter-dependent misconceptions.

Verification / Alternative check:Marker frequency analysis and visualization of replication intermediates confirm two forks moving bidirectionally.

Why Other Options Are Wrong:

• Unidirectional (A): inconsistent with well-established bidirectionality.
• Use of T7 polymerase (C) pertains to phage genome replication, not host chromosome.
• Only during λ infection (D): false; cells replicate in normal cycles.
• Promoters (E) control transcription, not replication initiation.

Common Pitfalls:Conflating transcriptional promoters with replication origins and phage replication systems with host chromosomal replication.

Final Answer:Replication proceeds bidirectionally from the origin