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A gene library is the term for collections of deoxyribonucleic acid (DNA) fragments that have been cloned randomly from the genomes of organisms. They are cloned as plasmids which can replicate separately from their chromosomes and phages, which are a parasitic virus that feeds on bacteria. When cloned as plasmids the collection is of host cells and each of the cells contains a DNA fragment. Phage gene libraries are made up of what are called phage lysates, which are residues of destroyed cells with a DNA fragment inserted. When gene libraries contain a collection of all the genetic information on an organism, they are considered to be a representational gene library.
Additionally, libraries can use cellular recombinant nucleic acid (RNA) for berthing material, and this collection of host cells with the recombinant vectors is known as a cRNA gene library. Gene library screening finds particular cells containing cloning vectors with a particular gene being sought in a gene library and then uses one of many techniques of isolating and harvesting them. Once harvested, the cells are considered cloned. In order to have a reasonable chance of isolating and cloning a particular gene, usually only representational gene libraries are used as every gene and every original DNA fragment of a particular genome are collected therein. To reach a 99% chance of locating a particular human gene for cloning, more than 600,000 cloned cells would need to be screened to find the desired gene from a representational gene library.
DNA is extracted from an organism to start off a gene library. The library is structured to organize the DNA and its thousands of different genes. The library becomes a collection of tens of thousands of bacteria colonies, each modulated with a fragment of DNA from the organism that contains a gene of special interest. Libraries also contain restriction enzymes and a plasmid. The restriction enzymes are used to read the nucleotide information of the DNA and are used to cut the DNA into fragments by separating the nucleotides from each other.
The same restriction enzymes cut the bacterial plasmids and the fragments and plasmids are combined in a test tube to combine, making a new combination. These recombinant plasmids are then returned back to bacteria culture using either heat shock or electroporation. These steps are performed over and over until an entire gene library has been formed for a particular genome organism from all of the fragments of the original DNA extraction.