plasmid /plas·mid/ (plaz´mid) an extrachromosomal self-replicating structure of bacterial cells that carries genes for a variety of functions not essential for cell growth and that can be transferred to other cells by conjugation or transduction. See also episome.
plasmid
plasmid,
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, to an F− (female) cell lacking such a plasmid.
R plasmid , resistance plasmid a conjugative factor in bacterial cells that promotes resistance to agents such as antibiotics, metal ions, ultraviolet radiation, and bacteriophages.
plas·mid (pl z m d)n. A circular, double-stranded unit of DNA that replicates within a cell independently of the chromosomal DNA and is most often found in bacteria; it is used in recombinant DNA research to transfer genes between cells. Also called extrachromosomal element. |
plasmid
[plaz′mid]
Etymology: Gk, plasma, something formed
in a bacterium, a small, circular molecule of DNA that is separate from the bacterial chromosome. Plasmids often carry genes that affect the ability of bacteria to respond to environmental challenges. For example, a bacterium containing the R (resistance) plasmid is able to resist many antibacterial drugs that act in different ways. Plasmids may be passed from one bacterium to another and are replicated in later generations of any bacterium carrying them. Molecular geneticists often use plasmids to insert specific genes into the chromosomes of bacteria and other organisms.
plasmid,
n a type of intracellular inclusion considered to have a genetic function.
plasmid
an extrachromosomal self-replicating genetic element of a cell. In bacteria, plasmids are circular DNA molecules that reproduce themselves and are thus conserved, apart from the chromosome, through successive cell divisions; they include the F factor and R factor.
R factor plasmid
see R factor.
relaxed plasmid
occurs in tens to several hundred copies per bacterium and are dependent solely on host enzymes for replication.
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