Plasmid
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Introduction
A plasmid is an extra-chromosomal genetic element found in the cells of most organisms, but particularly in Prokaryotes. Plasmids consist of double-stranded, usually circular DNA. They can generally replicate autonomously with their own molecular machinery, starting at an "origin" or ori sequence, and can be considered to be "mini-chromosomes". Plasmids are typically between 1,000 and 250,000 base pairs, and there may be several copies of each plasmid in a cell.
Gene transfer in Bacteria
- Main article: gene transfer.
Plasmids and episomes (plasmids which can integrate themselves into chromosomes) are an important part of prokaryotic evolution, as they can transfer genes between cells. Such activity usually takes place in a process of conjugation, in which two cells come together and "mate" by transfering plasmids (gene transfer). Plasmids are notable as they often carry genes for resistance to antibiotics.
Plasmids in genetic research and biotech
Plasmids are the most common way of introducing foreign genes into a cell, used mainly for amplifying (replicating) genes on the plasmid, and for genetic engineering. By adding a gene for a useful product, for example human insulin for diabetics, to a plasmid, scientists can hijack the molecular machinery of a bacterial cell for use as their own factory machinery.
References
- Wikipedia: Plasmid
- Russel, P.J., 2003. iGenetics, San Francisco: Benjamin Cummings
- Suzuki, D., A. Griffiths, J. Miller & R. Lewontin, 1989. An Introduction To Genetic Analysis, W.H. Freeman.
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This page is part of the EvoWiki encyclopedia of genetics and molecular biology. Topics: Genetics - Transmission genetics - Molecular genetics - Population genetics - Quantitative genetics - Molecular biology - Genomics |
