<P> 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 . 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 . 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 . Bacterial plasmids can also function in pigment production , nitrogen fixation and the resistance to heavy metals in those bacteria that possess them . </P>
<P> 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 . 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 . 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 . Bacterial plasmids can also function in pigment production , nitrogen fixation and the resistance to heavy metals in those bacteria that possess them . </P>
extra-chromosomal dna within a bacterial cell is known as
extra-chromosomal dna within a bacterial cell is known as
plasmids
plasmids