a Plasmid is an extrachromosomal DNA molecule within a cell that is physically separated from chromosomal DNA and can replicate independently. They are most commonly found as small circular, double-stranded DNA molecules in bacteria; however, plasmids are sometimes present in archaea and eukaryotic organisms. In nature, plasmids often carry genes that benefit the survival of the organism and confer selective advantages such as antibiotic resistance. While chromosomes are large and contain all the essential genetic information for living under normal conditions, plasmids are usually very small and contain only additional genes that may be useful in certain situations or conditions. Artificial plasmids are widely used as vectors in molecular cloning, serving to drive the replication of recombinant DNA sequences within host organisms. In the laboratory, plasmids may be introduced into a cell via transformation.
Scientists have taken advantage of plasmids to use them as tools to clone, transfer, and manipulate genes. Plasmids that are used experimentally for these purposes are called vectors. Researchers can insert DNA fragments or genes into a plasmid vector, creating a so-called recombinant plasmid. This plasmid can be introduced into a bacterium by way of the process called transformation. Then, because bacteria divide rapidly, they can be used as factories to copy DNA fragments in large quantities.
- They are extrachromosomal and not essential. They are useful but not necessarily present in every organism of the species
- Plasmids are not a part of the genome and the same plasmid can exist in different species and gets transferred from one another
- Plasmids have their own origin of replication (ORI) and they replicate along with the cell so that each daughter cell possesses a copy of the plasmid also
- Apart from the origin of replication, often it contains genes for antibiotic resistance, for the production of toxins, and other useful genes, that may be required for the survival of cells
The word Plasmid was first coined by Joshua Lederberg in 1952. The term was first described in a research paper he published describing the experiments carried out by himself and his student Norton Zinder. The experiment was conducted on salmonella bacteria and its virus P22.
Types of Plasmids
- Resistance Plasmids
- Virulence Plasmids
- Degradative Plasmids
- Col Plasmids
- Fertility F Plasmids