Plasmid | Autonomously replicating, extrachromosomal circular DNA molecules, distinct from the normal bacterial genome and nonessential for cell survival under nonselective conditions. Some plasmids are capable of integrating into the host genome and are used as a cloning vector for small pieces of DNA (typically 50 to 5000 base pairs) by insertion into the plasmid. A number of artificially constructed plasmids are used as cloning vectors. |