A
plasmid is a small
DNA molecule within a cell that is physically separated from a
chromosomal DNA and can replicate independently. They are most commonly found in
bacteria as small, circular, double-stranded DNA molecules; however, plasmids are sometimes present in
archaea and
eukaryotic organisms. In nature, plasmids often carry genes that may benefit the survival of the organism, for example
antibiotic resistance. While the chromosomes are big and contain all the essential information for living, plasmids usually are very small and contain only additional information. Artificial plasmids are widely used as
vectors in
molecular cloning, serving to drive the replication of
recombinant DNA sequences within host organisms.