extra-chromosomal dna within a bacterial cell is known as
Extrachromosomal DNA Although prokaryotic organisms do not possess a membrane bound nucleus like the eukaryotes, they do contain a nucleoid region in which the main chromosome is found. Extrachromosomal DNA exists in prokaryotes outside of the nucleoid region as circular or linear plasmids. Bacterial plasmids are typically short sequences, consisting of 1 kilobase (kb) to a few hundred kb segments, and contain an origin of replication which allows the plasmid to replicate independently of the bacterial chromosome.[4] The total number of a particular plasmid within a cell is referred to as the copy number and can range from as few as two copies per cell to as many as several hundred copies per cell.[5] Circular bacterial plasmids are classified according to the special functions that the genes encoded on the plasmid provide. Fertility plasmids, or f plasmids, allow for conjugation to occur whereas resistance plasmids, or r plasmids, contain genes that convey resistance to a variety of different antibiotics such as ampicillin and tetracycline. There also exists virulence plasmids that contain the genetic elements necessary for bacteria to become pathogenic as well as degradative plasmids that harbor the genes that allow bacteria to degrade a variety of substances such as aromatic compounds and xenobiotics.[6] Bacterial plasmids can also function in pigment production, nitrogen fixation and the resistance to heavy metals in those bacteria that possess them.[7]