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A circular extrachromosomal genetic element that is ubiquitous in prokaryotes and has also been identified in a number of eukaryotes. In general, bacterial plasmids can be classified into two groups on the basis of the number of genes and functions they carry. The larger plasmids are deoxyribonucleic acid (DNA) molecules of around 100 kilobase (kb) pairs, which is sufficient to code for approximately 100 genes. There is usually a small number of copies of these plasmids per host chromosome, so that their replication must be precisely coordinated with the cell division cycle. The plasmids in the second group are smaller in size, about 6–10 kb. These plasmids may harbor 6–10 genes and are usually present in multiple copies (10–20 per chromosome). See Gene

Plasmids have been identified in a large number of bacterial genera. Some bacterial species harbor plasmids with no known functions (cryptic plasmids) which have been identified as small circular molecules present in the bacterial DNA. The host range of a particular plasmid is usually limited to closely related genera. Some plasmids, however, are much more promiscuous and have a much broader host range.

The functions specified by different bacterial plasmids are usually quite specialized in nature. Moreover, they are not essential for cell growth since the host bacteria are viable without a plasmid when the cells are cultured under conditions that do not select for plasmid-specified gene products. Plasmids thus introduce specialized functions to host cells which provide versatility and adaptability for growth and survival. Plasmids which confer antibiotic resistance (R plasmids) have been extensively characterized because of their medical importance. Plasmids have played a seminal role in the spectacular advances in the area of genetic engineering. Individual genes can be inserted into specific sites on plasmids in cell cultures and the recombinant plasmid thus formed introduced into a living cell by the process of bacterial transformation. See Genetic engineering



a generic term for any intracellular hereditary factor that is not located within the chromosomes. Plasmids include genetic factors in cell organelles, for example, mitochondria and plastids, as well as genetic factors that are not found in any essential components of cells. Of the plasmids that are not associated with any permanent structure, the most extensively studied are the kappa-particle in paramecia (which produces the antibiotic paramecin), the sensitivity factor for CO2, and the agent that inhibits the occurrence of male Drosophila. In addition, several bacteria possess plasmids. Bacterial plasmids control resistance to medicines and regulate the synthesis of bacteriocin, enterotoxin, hemolysin, and certain antigens. The plasmids that are called sex factors control sexual differentiation in bacteria. It has been shown that many plasmids consist of ring molecules of double-stranded deoxyribonucleic acid with a molecular weight that ranges from 106 to 108 daltons.



An extrachromosomal genetic element found among various strains of Escherichia coli and other bacteria.
References in periodicals archive ?
The plasmids were then extracted and digested with restriction enzyme EcoRI.
The expected sizes for the linear forms of plasmids gWiz- blank & gWizHbs after complete digestion by the endonuclease Hind III below are respectively 5060bp and 6435bp.
Other technologies rely on either integrating the synthetic gene(s) into the bacterial chromosome or using antibiotics and antibiotic resistance genes to amplify plasmids containing the new genes.
Also each of the known curing agents is effective against only a limited number of plasmids in a limited number of hosts.
Other than the Plasmids and Tonics, the sense of morality that Bioshock 2 places on the player is also what makes it so different.
The precipitation of plasmids in alcohol followed by centrifugation can be demonstrated by using fingers to push the washers to the side of the carpet away from the marbles and twine (Figure 1E; Steps 10 and 11 of the Appendix).
The Woodlands, TX) ("VGXI") to supply the plasmid portion of the company's combination therapy consisting of the Factor 5A gene and siRNA against Factor 5A.
The team input the genetic code for 3,799 known artificial plasmids into the software, which compared the sequences and found hundreds of matching stretches, each with about 20 "letters" of genetic code.
larvae strains tested from across the United States and 1 from Canada, all 21 OTC-resistant strains possessed this plasmid and all 15 OTC-sensitive strains did not.
9%--of the plasmid in some labeled strains grown for five consecutive subcultures in the absence of selective pressure.
Although some strains exhibited different antibiotic resistance patterns, some of their plasmids had similar migration patterns on agarose gel electrophoresis.