Plasmids have no replication machinery of their own and are reliant upon the host for duplication.
Examples of plasmids include the puC18, or the F plasmid. Note that the F plasmids are unusually large. This property allows large scale genetic exchange between bacteria.
Plasmids exist in three forms: Open circle, supercoiled and linear. Supercoiled is when the plasmid has is tightly wound round itself in order to fit inside the cell. Open circle is when there is a nick in the outer ring of the plasmid and linear is when the plasmid is cut with a restriction enzyme.
When run on an agarose gel, linear runs the fastest down the gel, then supercoiled then open cirlce.
- ↑ Maloy (1987), Microbial Genetics, 2nd edition, Jones and Bartlett Publishers.