What is a plasmid?

What is a plasmid?

• A. A large linear chromosome found in bacteria.
• B. A ribosomal RNA molecule essential for translation.
• C. A small ring of DNA independent from the bacterium's main genome and is commonly used in genetic engineering.
• D. A protein that carries genetic information.

Answer: (C)

Plasmids are small, circular DNA molecules that exist inside bacteria separate from the main chromosome and replicate independently. They typically carry genes that aren’t essential for everyday growth but can provide advantages, such as antibiotic resistance. In genetic engineering, plasmids are used as cloning vectors: they’re designed with an origin of replication, a site to insert a gene of interest, and a selectable marker so cells that take up the plasmid can be identified. This combination makes them the standard tool for introducing new genes into a bacterial cell. The other descriptions refer to the bacterial chromosome, ribosomal RNA, or incorrectly describe how genetic information is stored, so they don’t fit as well.

Plasmids are small, circular DNA molecules that exist inside bacteria separate from the main chromosome and replicate independently. They typically carry genes that aren’t essential for everyday growth but can provide advantages, such as antibiotic resistance. In genetic engineering, plasmids are used as cloning vectors: they’re designed with an origin of replication, a site to insert a gene of interest, and a selectable marker so cells that take up the plasmid can be identified. This combination makes them the standard tool for introducing new genes into a bacterial cell. The other descriptions refer to the bacterial chromosome, ribosomal RNA, or incorrectly describe how genetic information is stored, so they don’t fit as well.