Until recently, prokaryotes did not contain linear plasmids or chromosomes, but they have since been discovered in spirochaetes, Gram-positive bacteria, and Gram-negative bacteria. Bacterial linear DNA has been classified into two structural kinds. Each end of linear plasmids from the spirochaete Borrelia has a covalently closed hairpin loop, while each end of linear plasmids from the Gram-positive filamentous Streptomyces has a covalently connected protein. In eukaryotic cells, replicons with comparable structures are more common than in prokaryotes. However, linear genomic architectures are likely more widespread in bacteria than previously thought, and some replicons may be able to switch between circular and linear isomers. The molecular biology of these widely scattered pieces reveals information about the origins of linear DNA in bacteria, including evidence of prokaryote-eukaryotes genetic exchange.
Because humans and all other organisms use some combination of these elements. if we lost a whole species everything would be out of balance and we would slowly lose everything and in the in, causing a global scale extinction event. <span />
