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Plasmids, commonly found in small, double-stranded, DNA molecules inside bacteria. They can be present in archea and eucaryotic organisms, but are mostl just foud in bacteria. Plasmids are an essential tool for gene transfer due to their ability to transfer essential genetic information or information that has been spliced in withthe usage of restriction enzymes. Like viruses, plasmids are not classified as life, but merely a tool used by life. Plasmids allow the scientists to, for the most part, control an otherwise purely natural process.
plasmids are usually found in bacteria as well as archaebacteria. Plasmids themselves only have a few genes and they exist independently of chromosomes. organisms use there own plasmids to get through stressful conditions. Plasmids are very easy to genetically modify and have a relatively small DNA sequence, between 1000 and 20000 DNA base pairs. Plasmids are easy to work with. They can be cut open and put back together with ease. As a result, new DNA can be easily inserted into plasmids. By far the most important use of plasimds is their use as a vector. They can introduce foreign DNA into bacteria. These qualities have made plasmids a very important tool in genetics a bio-technology. 
in 1952, Joshua Lederberg coined the word plasmid described as any extrachromosomal hereditary element. Joshua Lederberg discovered that virus particles could pick up bacterial genes and transfer them elsewhere. After the discovery of the double-helix DNA structure, scientists determined that plasmids were made up of smaller DNA sequences. Joshua Lederberg got the name plasmid by creating a hybrid of the word cytoplasm and id(latin for it). Plasmids, although discovered in 1952 did not become commonly used untill the 1970s. Now, plasmids are an essential tool for gene transfer.
Plasmids are usually about 1000 to 100000 nucleotides in length and are self-acting and self-replicating. plasmids preform DNA recombination and offer a way to transfer certain DNA from bacteria to bacteria. For example, a bacteria that has become immune to a certain antibiotic can use a plasmid to transfer this immunity to other bacteria. Scientists can also use restriction enzymes to cut a piece out of a plasmid and replace it with another, they can then expose this modified plasmid to the bacteria so that is can multiple into many genetically modified bacteria. 
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- Authorlastname, Firstname. History of Plasmids The Virtual Genome Project. Web. January 2002.