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The term plasmid was coined in 1952 by the American molecular biologist Joshua Lederberg to refer to "any extrachromosomal hereditary determinant." [14] [15] The term's early usage included any bacterial genetic material that exists extrachromosomally for at least part of its replication cycle, but because that description includes bacterial viruses, the notion of plasmid was refined over time ...
they play a role in the autonomous replication, conjugation, and ampicillin resistance genes. [citation needed] Genes in the resistance plasmids enable bacteria to produce Pilli and develop resistance to antibiotics. [7] MDR genes in bacteria are transmitted mainly through the resistance plasmids. [4]
For instance, if there are 2 copies of a plasmid in a cell, there is 50% chance of having one plasmid-less daughter cell. However, high-copy number plasmids have a cost for the hosting cell. This metabolic burden is lower for low-copy plasmids, but those have a higher probability of plasmid loss after a few generations.
Plasmids are almost always purified from liquid bacteria cultures, usually E. coli, which have been transformed and isolated. [5] [6] Virtually all plasmid vectors in common use encode one or more antibiotic resistance genes as a selectable marker, for example a gene encoding ampicillin or kanamycin resistance, which allows bacteria that have been successfully transformed to multiply uninhibited.
Plasmids can be further divided into mobilizable and non-mobilizable classes. Plasmids that use other genetic element MFPs in the cell are mobilizable. Plasmids that are not mobilizable but spread by transduction or transformation are termed non-mobilizable. [5] Plasmids can often inject genes that make bacteria resistant to antibiotics. [6] [5]
The bacteria containing the plasmids can generate millions of copies of the vector within the bacteria in hours, and the amplified vectors can be extracted from the bacteria for further manipulation. Plasmids may be used specifically as transcription vectors and such plasmids may lack crucial sequences for protein expression. Plasmids used for ...
Along with chromosomal DNA, most bacteria also contain small independent pieces of DNA called plasmids that often encode advantageous traits but are not essential to their bacterial host. Plasmids can be easily gained or lost by a bacterium and can be transferred between bacteria as a form of horizontal gene transfer.
It enhances plasmid DNA incorporation by the bacterial cell, promoting genetic transformation. Plasmid DNA can attach to LPS by being added to the cell solution together with CaCl 2. [12] Thus, when heat shock is applied, the negatively charged DNA backbone and LPS combine, allowing plasmid DNA to enter the bacterial cell. [13]