What is the function of the plasmid origin of replication?

• A. Binds transcription factors to enhance expression.
• B. Allows plasmid to replicate within host cells.
• C. Terminates transcription.
• D. Encodes a selectable marker.

Answer: (B)

The key idea here is that a plasmid’s origin of replication is the starting point for copying the plasmid inside the bacterial host. This sequence is recognized by the host’s replication machinery, so the plasmid can be duplicated and passed on to daughter cells during cell division. Without this origin, the plasmid wouldn’t replicate and would be lost over generations, which is why the origin determines whether the plasmid can exist inside the host and how many copies appear in each cell.

This is why the function described is to allow the plasmid to replicate within host cells. Other features like promoters influence gene expression, termination signals stop transcription, and selectable markers let you identify cells carrying the plasmid—but none of those enable the plasmid to replicate on its own.