8.5: Plasmids and Vectors

Plasmids are small, circular, self-replicating DNA molecules that scientists manipulate to carry and clone other DNA pieces. They function as vectors—DNA molecules that carry foreign DNA into host cells, replicate there, and produce many copies. Because of their small size and ability to replicate independently, plasmids are extremely useful tools in genetic engineering.

Scientists can modify plasmids to carry additional DNA fragments, such as genes from other organisms. When plasmids are used to transfer foreign DNA into host cells, they are called vectors. A vector is any DNA molecule that acts as a carrier to introduce foreign genetic material into another cell. Once the plasmid vector enters the host cell, it replicates along with the cell's own DNA, producing many copies of the inserted gene. This process allows researchers to clone genes, study gene function, or produce large amounts of specific proteins. Plasmid vectors often contain special features, such as selectable marker genes, that help scientists identify cells that have successfully taken up the recombinant DNA.

Image credit: National Cancer Institute on Unsplash Link to image described above [unsplash.com]

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