What is a plasmid?

What is a plasmid?

• A. A large linear chromosome.
• B. A small circular DNA molecule capable of replicating; usually double stranded.
• C. A protein that carries genetic information.
• D. RNA molecule that encodes enzymes.

Answer: (B)

Plasmids are small circular DNA molecules that replicate independently of the bacterial chromosome. They are usually double-stranded and exist outside the main chromosomal DNA, carrying extra genes such as those for antibiotic resistance or specialized metabolisms. Their autonomous replication lets them persist in the cell and, in many cases, they can be transferred between bacteria, which is a key feature in horizontal gene transfer. They are not large linear chromosomes, not proteins, and not RNA molecules, which is why the description of a small circular, self-replicating DNA element best fits plasmids.

Plasmids are small circular DNA molecules that replicate independently of the bacterial chromosome. They are usually double-stranded and exist outside the main chromosomal DNA, carrying extra genes such as those for antibiotic resistance or specialized metabolisms. Their autonomous replication lets them persist in the cell and, in many cases, they can be transferred between bacteria, which is a key feature in horizontal gene transfer. They are not large linear chromosomes, not proteins, and not RNA molecules, which is why the description of a small circular, self-replicating DNA element best fits plasmids.