Which feature enables a plasmid to replicate independently within a bacterial host?

• A. Promoter region.
• B. Cloning site.
• C. Origin of replication.
• D. Antibiotic resistance gene.

Answer: (C)

The key idea is autonomous replication. A plasmid can make extra copies in a bacterial cell because it contains an origin of replication, a specific DNA sequence that signals the host’s replication machinery to start copying the plasmid. This origin, sometimes with a plasmid-encoded initiator protein, initiates replication and ensures the plasmid is duplicated and passed on to daughter cells during division. Without this origin, the plasmid wouldn’t initiate replication on its own and wouldn’t be stably maintained.

The other features don’t enable independent replication: a promoter region is where transcription starts; a cloning site is simply a location to insert foreign DNA; an antibiotic resistance gene helps with selection but doesn’t drive replication.