What is a plasmid and why is it used in cloning?

• A. A circular DNA molecule used as a vector to move genes into cells for propagation
• B. A linear DNA fragment that carries antibiotics
• C. A protein that binds DNA
• D. A carbohydrate used for energy

Answer: (A)

Plasmids are circular DNA molecules that exist and replicate independently of the bacterial chromosome, and they act as vehicles to move genes into cells for propagation. They’re used in cloning because they can carry a gene of interest, be easily introduced into host cells, and then amplify to yield many copies of the gene. Features like an origin of replication ensure they replicate inside the host, a multiple cloning site lets researchers insert the gene, and selectable markers (such as antibiotic resistance) help identify cells that have taken up the plasmid. In cloning workflows, the gene is inserted into the plasmid, the plasmid is introduced into bacteria, and the bacteria replicate the plasmid to produce large amounts of the gene or its protein product. They’re DNA, not proteins or carbohydrates, and their circular form helps stability and efficient propagation.