How does chromosomal replication differ from plasmid replication in bacteria?

How does chromosomal replication differ from plasmid replication in bacteria?

• A. Chromosome replication uses a rolling-circle mechanism.
• B. Chromosome replication does not have a defined origin.
• C. Chromosome replication follows a defined origin and cell-cycle program; plasmids often replicate via rolling-circle or theta mechanisms and can be more variable.
• D. Plasmids always integrate into the chromosome.

Answer: (C)

Chromosomal replication in bacteria is tightly organized: it starts at a specific origin of replication (oriC) and proceeds in a regulated way that is coordinated with the cell cycle so the chromosome is duplicated once per division. Plasmids, on the other hand, are extra-chromosomal DNA elements that replicate independently of the chromosome. They often use different replication modes—rolling-circle or theta type—and their replication is more variable, which means their copy number can differ between cells and is not as strictly tied to the cell cycle. This combination of a defined origin with cell-cycle control for the chromosome, plus the more flexible, origin-driven replication options for plasmids, best differentiates the two. The idea that chromosomes lack a defined origin is incorrect, and plasmids do not always integrate into the chromosome; they typically remain separate, though integration can occur in some cases.

Chromosomal replication in bacteria is tightly organized: it starts at a specific origin of replication (oriC) and proceeds in a regulated way that is coordinated with the cell cycle so the chromosome is duplicated once per division. Plasmids, on the other hand, are extra-chromosomal DNA elements that replicate independently of the chromosome. They often use different replication modes—rolling-circle or theta type—and their replication is more variable, which means their copy number can differ between cells and is not as strictly tied to the cell cycle. This combination of a defined origin with cell-cycle control for the chromosome, plus the more flexible, origin-driven replication options for plasmids, best differentiates the two. The idea that chromosomes lack a defined origin is incorrect, and plasmids do not always integrate into the chromosome; they typically remain separate, though integration can occur in some cases.