A plasmid is a separate intracellular fragment of DNA that can replicate independently of, chromosomal DNA within a cell. Plasmids are found primarily in bacteria, but may be present occasionally in archaea and eukaryotes. Plasmids are generally circular DNA molecules. Unlike the chromosomal DNA of bacteria, plasmids are typically not essential for bacterial growth. Plasmids provide an important additional dimension towards the flexibility of the body's response to changes in their environment, whether those changes are hostile or potentially favorable. A plasmid which is able to integrate into the chromosome of the bacterium is called episome.
Plasmids can be transferred to other bacteria or to plants in a process called "horizontal gene transfer". Bacterium to bacterium transmission is one way for bacteria to gain antibiotic resistance. Agrobacterium tumefaciens is able to infect plants and insert DNA from a plasmid into the plant genome, causing crown gall disease. This disease results in growths similar to tumors. Engineered plasmids known as "vectors" are used by scientists to introduce new or modified genetic in organisms.
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- What is a Plasmid? AddGene. Accessed 24 May 2016.