Plasmids are used in genetic engineering to reproduce recombinant genetic material. When a plasmid is inserted into a bacterium, the bacterium is encouraged to multiply, creating more copies of the recombinant DNA.
In addition to portions that allow the plasmids to be cloned, plasmids contain expression vectors and promoter sequences that drive that expression. Genetic markers let researchers know that the plasmid is present. Some plasmids include antibiotic resistance; after a plasmid is applied to a population of bacteria, antibiotics are added. Whatever bacteria survive the antibiotics must contain the plasmid. Sometimes, the plasmids express proteins that glow in the dark, allowing researchers to readily identify how much of the population contains the plasmid.
Some plasmids reproduce through conjugation, which is the exchange of genetic material between bacteria. This method is faster because bacteria spread the plasmid without needing to reproduce.
The ultimate goal of recombinant DNA in bacteria is usually to produce proteins for human use. Therefore, plasmids frequently contain purification tags that make this process easier, such as increasing their solubility.
Plasmids are applicable to not only bacteria. While it uses a bacterial (prokaryotic) vector, gene therapy for human beings is often performed through the use of plasmids.