plasmid

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plasmid

 [plaz´mid]
an extrachromosomal self-replicating structure found in bacterial cells that carries genes for a variety of functions not essential for cell growth. Plasmids consist of cyclic double-stranded DNA molecules, replicating independently of the chromosomes and transmitting through successive cell divisions genes specifying such functions as antibiotic resistance (R plasmid); conjugation (F plasmid); the production of enzymes, toxins and antigens; and the metabolism of sugars and other organic compounds. Plasmids can be transferred from one cell to another by conjugation and by transduction. Some plasmids may also become integrated into the bacterial chromosome; these are known as episomes.
conjugative plasmid a plasmid that is transferred from one bacterial cell to another during conjugation.
F plasmid a conjugative plasmid found in F+ (male) bacterial cells that leads with high frequency to its transfer and much less often to transfer of the bacterial chromosome. A cell possessing the F plasmid (F+, male) can form a conjugation bridge (F pilus) to a cell lacking the F plasmid (F, female), through which genetic material may pass from one cell to another.
F′ plasmid a hybrid F plasmid that contains also a segment of the host chromosome.
R plasmid a conjugative factor in bacterial cells that promotes resistance to agents such as antibiotics, metal ions, ultraviolet radiation, and bacteriophage.
Miller-Keane Encyclopedia and Dictionary of Medicine, Nursing, and Allied Health, Seventh Edition. © 2003 by Saunders, an imprint of Elsevier, Inc. All rights reserved.

plas·mid

(plaz'mid),
A genetic particle physically separate from the chromosome of the host cell (chiefly bacterial) that can function and replicate stably and usually confer some advantage to the host cell; not essential to the cell's basic functioning.
[cytoplasm + -id]
Farlex Partner Medical Dictionary © Farlex 2012

plasmid

(plăz′mĭd)
n.
A circular, double-stranded unit of DNA that replicates within a cell independently of the chromosomal DNA. Plasmids are most often found in bacteria and are used in recombinant DNA research to transfer genes between cells.
The American Heritage® Medical Dictionary Copyright © 2007, 2004 by Houghton Mifflin Company. Published by Houghton Mifflin Company. All rights reserved.

plas·mid

(plaz'mid)
A genetic particle physically separate from the chromosome of the host cell (chiefly bacterial) that can stably function and replicate; not essential to the basic functioning of the cell.
Synonym(s): extrachromosomal element, extrachromosomal genetic element.
[cytoplasm + -id]
Medical Dictionary for the Health Professions and Nursing © Farlex 2012

plasmid

A ring-shaped, double-stranded, piece of DNA in bacterial cells that contains genes extra to those in the chromosome. Plasmid genes code for characteristics such as toxin production and the factors that cause antibiotic resistance. Plasmids are convenient vehicles for the introduction of new genes into organisms in recombinant DNA technology (genetic engineering).
Collins Dictionary of Medicine © Robert M. Youngson 2004, 2005

plasmid

an extrachromosomal genetic element of DNA or RNA that is capable of replicating independently of the host chromosome. Plasmids are generally circular molecules, although some linear plasmids have been found. They occur in both prokaryotic and eukaryotic cells, often in the cytoplasm. Plasmids can be important in public health since some types possess genes for antibiotic resistance, and can be quickly transferred to different types of host cell, thus spreading resistance very rapidly. Plasmids form the basis of many cloning vectors used in GENETIC ENGINEERING. See also EPISOME, CONJUGATIVE PLASMID, NON-CONJUGATIVE PLASMID.
Collins Dictionary of Biology, 3rd ed. © W. G. Hale, V. A. Saunders, J. P. Margham 2005

plas·mid

(plaz'mid)
Genetic particle physically separate from chromosome of host cell (chiefly bacterial), which can function and replicate stably and usually confer some advantage to the host cell.
[cytoplasm + -id]
Medical Dictionary for the Dental Professions © Farlex 2012