Plasmids

Plasmids are small, circular, double-stranded DNA molecules of mostly bacterial origin. A plasmid is often present episomally in the cell, which means that it replicates independently of the cell's genome. This usually results in a high plasmid copy number. Plasmids are primarily used as cloning vectors for the amplification and expression of recombinant DNA. Moreover, plasmids can also be utilized as expression vectors for the biotechnological production of proteins in cell culture. Many plasmids carrying cDNA fragments are commercially available for molecular cloning and plasmids as well as backbones optimized for various expression systems and species have been developed.