plasmid


plasmid
/plaz"mid/, n. Microbiol.
a segment of DNA independent of the chromosomes and capable of replication, occurring in bacteria and yeast: used in recombinant DNA procedures to transfer genetic material from one cell to another.
[1950-55; PLASM- + -ID3]

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Genetic element not contained within a chromosome.

It occurs in many bacterial strains. Plasmids are circular DNA molecules that replicate independently of the bacterial chromosome. They are not essential for the bacterium but may give it a selective advantage. Some plasmids determine the production of proteins that can kill other bacteria; others make bacteria resistant to antibiotics. Plasmids are extremely valuable tools in the fields of molecular biology and genetics, specifically in the area of genetic engineering.

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      in microbiology, an extrachromosomal genetic element that occurs in many bacterial strains. Plasmids are circular deoxyribonucleic acid (DNA) molecules that replicate independently of the bacterial chromosome. They are not essential for the bacterium but may confer a selective advantage. One class of plasmids, colicinogenic (or Col ) factors, determines the production of proteins called colicins, which have antibiotic activity and can kill other bacteria. Another class of plasmids, R factors, confers upon bacteria resistance to antibiotics. Some Col factors and R factors can transfer themselves from one cell to another and thus are capable of spreading rapidly through a bacterial population. A plasmid that is attached to the cell membrane or integrated into the bacterial chromosome is called an episome (q.v.).

      Plasmids are extremely valuable tools in the fields of molecular biology and genetics, specifically in the area of genetic engineering (q.v.). They play a critical role in such procedures as gene cloning, recombinant protein production (e.g., of human insulin), and gene therapy research. In such procedures, a plasmid is cut at a specific site (or sites) using enzymes called restriction endonucleases. A foreign DNA element (such as the gene for insulin) is then spliced into the plasmid. The resulting circular structure, a recombinant DNA molecule, is then introduced into bacterial cells (a process called transformation). The autonomous replication of the plasmid within the bacterial cells makes it possible to produce large numbers of copies of the recombinant DNA molecule for experimental manipulation or commercial purposes (such as the production of large amounts of insulin). Plasmids are well suited to genetic engineering in other ways. Their antibiotic resistance genes, for example, prove useful in identifying those bacterial cells that have taken up the recombinant DNA molecule in a high background of untransformed cells (transformation frequencies are only about 1 out of every 100,000 cells).

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Universalium. 2010.

Look at other dictionaries:

  • Plasmid — Plas mid, n. (Molecular genetics) A piece of DNA, usually circular, functioning as part of the genetic material of a cell, not integrated with the chromosome and replicating independently of the chromosome, but transferred, like the chromosome,… …   The Collaborative International Dictionary of English

  • plasmid — plasmid. См. плазмида. (Источник: «Англо русский толковый словарь генетических терминов». Арефьев В.А., Лисовенко Л.А., Москва: Изд во ВНИРО, 1995 г.) …   Молекулярная биология и генетика. Толковый словарь.

  • Plasmid — Plasmid, außerhalb des Bakterienchromosoms bei Protocyten in Ein oder Mehrzahl im Cytoplasma liegendes kleines, ringförmiges DNA Molekül, das ebenfalls genetische Information enthält und sich autonom repliziert. Ein P. kann z.B. Resistenzgene… …   Deutsch wörterbuch der biologie

  • plasmid — 1952, from PLASMA (Cf. plasma) + id …   Etymology dictionary

  • plasmid — [plaz′mid] n. [ PLASM(A) + ID] a small, DNA containing, self reproducing cytoplasmic element that exists outside the chromosome, as in some bacteria: because it can alter a hereditary characteristic when introduced into another bacterium, it is… …   English World dictionary

  • Plasmid — Figure 1: Illustration of a bacterium with plasmid enclosed showing chromosomal DNA and plasmids. In microbiology and genetics, a plasmid is a DNA molecule that is separate from, and can replicate independently of, the chromosomal DNA …   Wikipedia

  • Plasmid — Abb. 1: Schematische Darstellung eines Bakteriums mit chromosomaler DNA (1) und Plasmiden (2) …   Deutsch Wikipedia

  • Plasmid — A self replicating (autonomous) circle of DNA distinct from the chromosomal genome of bacteria. A plasmid contains genes normally not essential for cell growth or survival. Some plasmids can integrate into the host genome, be artificially… …   Medical dictionary

  • plasmid — (plaz mid) A double stranded DNA molecule that can exist and replicate independently of the chromosome or may be integrated with it. A plasmid is stably inherited, but is not required for the host cell s growth and reproduction …   Dictionary of microbiology

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