Define a plasmid and name two features commonly found on cloning plasmids.

Define a plasmid and name two features commonly found on cloning plasmids.

• A. A small circular DNA molecule used for genetic manipulation; features: origin of replication and a selectable marker (e.g., antibiotic resistance)
• B. A large linear DNA molecule used for chromosomal integration
• C. A protein complex that binds DNA
• D. A virus used for gene delivery

Answer: (A)

Plasmids are small circular pieces of DNA that exist outside the bacterial chromosome and can be copied independently inside the host, making them ideal for genetic manipulation. On cloning plasmids, two common features are the origin of replication, which lets the plasmid be replicated as the cell divides, and a selectable marker, such as antibiotic resistance, which lets you identify cells that have taken up the plasmid by growing them under selective conditions. Together these features allow the plasmid to propagate in the host and to distinguish successful transformants from cells that didn’t obtain the plasmid. Many cloning plasmids also include a multiple cloning site for inserting foreign DNA and a promoter to drive expression, but the origin of replication and the selectable marker are the fundamental, defining elements. The other choices describe different genetic tools: a large linear DNA molecule wouldn’t function as a plasmid; a protein complex that binds DNA is not DNA itself; a virus used for gene delivery is a viral vector, not a plasmid.

Plasmids are small circular pieces of DNA that exist outside the bacterial chromosome and can be copied independently inside the host, making them ideal for genetic manipulation. On cloning plasmids, two common features are the origin of replication, which lets the plasmid be replicated as the cell divides, and a selectable marker, such as antibiotic resistance, which lets you identify cells that have taken up the plasmid by growing them under selective conditions. Together these features allow the plasmid to propagate in the host and to distinguish successful transformants from cells that didn’t obtain the plasmid. Many cloning plasmids also include a multiple cloning site for inserting foreign DNA and a promoter to drive expression, but the origin of replication and the selectable marker are the fundamental, defining elements. The other choices describe different genetic tools: a large linear DNA molecule wouldn’t function as a plasmid; a protein complex that binds DNA is not DNA itself; a virus used for gene delivery is a viral vector, not a plasmid.