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Plasmids are extrachromosomal DNA replicons that replicate independently of the chromosome and often carry accessory genes that help hosts survive under particular conditions.
A plasmid is a small, extrachromosomal DNA molecule found in cells that is physically separate from the chromosomal DNA and can replicate independently. They are most commonly small circular, double-stranded DNA molecules in bacteria and archaea, but plasmids can also occur in eukaryotes. Plasmids often carry genes that provide advantages under specific conditions—such as antibiotic resistance, virulence factors, genes for secondary metabolism, and functions for bioremediation—while chromosomes generally contain the essential genes needed for normal growth. Plasmids are considered replicons, meaning they contain an origin of replication (and related replication elements) that allows autonomous copying in a suitable host. They vary widely in size (from <1 kbp to over 400 kbp) and in copy number per cell (from one to thousands), with low-copy-number plasmids often using partition systems to ensure inheritance during cell division. Some plasmids can integrate into the host chromosome; in prokaryotes these integrative forms are sometimes called episomes. Plasmids can be transferred between bacteria—often across species—mainly via conjugation, and they are part of the mobilome; unlike viruses, they are typically “naked” DNA and do not encode a protective capsid for transfer (though some conjugative plasmids encode transfer machinery such as sex pili).
Plasmids are extrachromosomal DNA replicons that replicate independently of the chromosome and often carry accessory genes that help hosts survive under particular conditions.
Key plasmid features include an origin of replication, variable size and copy number, and sometimes partition systems for stable inheritance; some plasmids can integrate as episomes.
Plasmids are commonly transferred between bacteria via conjugation and contribute to horizontal gene transfer, including the spread of traits like antibiotic resistance.
A small extrachromosomal DNA molecule separated from chromosomal DNA that can replicate independently within a cell.
A DNA unit (including an origin of replication and associated elements) that enables autonomous DNA replication in a suitable host.
A DNA sequence that allows plasmid DNA to initiate replication independently of the chromosome.
The number of plasmid molecules present in a single cell, influenced by how replication initiation is regulated and by plasmid size.
A plasmid maintenance mechanism that helps distribute plasmid copies to daughter cells during cell division, especially for low-copy-number plasmids.
An integrative plasmid form that can exist by integrating into the host chromosome in prokaryotes.
A process of host-to-host transfer of plasmids (often via sex pili) that enables horizontal gene transfer between bacteria.
The collection of mobile genetic elements and their associated transfer capabilities, in which plasmids play a major role.
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