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Definition

noun, plural: plasmids

A linear or circular double-stranded DNA that is capable of replicating independently of the chromosomal DNA.

Supplement

Certain plasmids are able to insert themselves into the chromosomes particularly in regions where there is a common sequence of nucleotides. Hence, they are used in recombinant DNA technology and research as means for transferring genes between cells or as cloning vectors.

Plasmids are important in certain bacteria since plasmids code for proteins, especially enzymes, which can confer resistance to antibiotics. Plasmids are ubiquitous in prokaryotes but they have also been found in a number of eukaryotes, e.g. Saccharomyces cerevisiae, which may contain a 2-micrometre-ring of plasmid.

Word origin: The term plasmid was first introduced by the American molecular biologist Joshua Lederberg in 1952.
Synonym: extrachromosomal element.
See also: DNA, chromosome.