List the main steps of bacterial DNA replication and the roles of DNA polymerases I and III.

• A. Initiation at origins, unwinding, primer synthesis by primase, elongation by DNA polymerase III, removal of RNA primers and replacement with DNA by DNA polymerase I, and ligation; Pol III synthesizes the bulk of DNA.
• B. Initiation at origins and direct ligation of DNA without primers.
• C. Helicase alone carries out DNA synthesis.
• D. Primers are synthesized by ligase, and Pol II carries out synthesis.

Answer: (A)

Bacterial DNA replication relies on a coordinated handoff between enzymes, with one polymerase doing the heavy lifting and another handling finishing touches. The process starts at the origin where the DNA is unwound and the replication machinery assembles. Short RNA primers are laid down by primase to provide starting points for DNA synthesis. The bulk of synthesis is carried out by DNA polymerase III, which extends the new DNA on both strands. On the leading strand, synthesis is continuous; on the lagging strand, it proceeds in short segments called Okazaki fragments, each starting from a new primer. Once a fragment is completed, those RNA primers must be removed and replaced with DNA. This job is done by DNA polymerase I, which has 5' to 3' exonuclease activity to remove RNA primers and a 5' to 3' polymerase activity to fill in the gaps with DNA. Finally, DNA ligase seals the remaining nicks to create a continuous DNA strand. Pol III is responsible for the majority of DNA synthesis, while Pol I handles primer removal and DNA replacement (and some repair). The roles described—primers made by primase, synthesis by Pol III, primer removal and gap filling by Pol I, and ligation by ligase—are essential for efficient and accurate bacterial DNA replication.