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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.
a plasmid that can effect its own intercellular transfer by means of conjugation; this transfer is accomplished by a bacterium's being rendered a donor, usually with specialized pili.
Farlex Partner Medical Dictionary © Farlex 2012
con·ju·ga·tive plas·mid(kon'jŭ-gā-tiv plaz'mid)
A plasmid that can effect its own intercellular transfer by means of conjugation; this transfer is accomplished by a bacterium being rendered a donor, usually with specialized pili.
Medical Dictionary for the Health Professions and Nursing © Farlex 2012
conjugative plasmida self-transmissible PLASMID that carries genes promoting its own transfer by CONJUGATION. In GRAM-NEGATIVE BACTERIA conjugative plasmids contain a set of transfer (tra) genes, encoding the conjugation apparatus including the SEX PILUS and the gene products for processing and transfer of genetic material. Many conjugative plasmids can mediate the transfer of chromosomal genes between bacteria, which may involve a covalent association between the plasmid and chromosome as in Hfr STRAINS or PRIME PLASMIDS. Conjugative plasmids can also effect the transfer of certain NON-CONJUGATIVE PLASMIDS that are resident in the same cell. Compare NON-CONJUGATIVE PLASMID.
Collins Dictionary of Biology, 3rd ed. © W. G. Hale, V. A. Saunders, J. P. Margham 2005