Vectors Used in Biotechnology

2739 Words Sep 28th, 2011 11 Pages
1. Plasmids
Plasmids are closed circular, double-stranded, extrachromosomal DNA molecules which occur naturally in bacteria, yeast, and some higher eukaryotic cells, and exist in a parasitic or symbiotic relationship with their host cell (Lodish et al., 2000)
The main application of plasmids is as cloning vectors in gene cloning. In gene cloning, a fragment of DNA, containing the gene to be cloned is inserted into a circular molecule called the “vector” to produce recombinant DNA molecule. Plasmids are one of the most commonly used “vectors” for this purpose. They transport the gene into a host cell, such as a bacterium, which is said to be transformed with the recombinant molecule. Here, these plasmid vectors multiply, producing numerous
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2. Cosmids
Cosmid libraries are used for cloning genes with large introns and for sequencing larger chunks of the genome. Their main application is in the construction of genomic libraries, where the large insert capacity is an advantage in minimising the number of clones required for a complete representative gene library. Apart from this, they also enhance the likelihood that a cloned gene will be present as an intact copy in a cosmid library (because the gene is very long) (Brown, 2006; Lodish et al., 2000). Cosmid vectors have also been used for rapid genomic walking, gene transfer, restriction mapping and determining the functional and structural organization of complex eukaryotic genomes (Wahl et al., 1987).

Features of cosmids:
Cosmids are artificially constructed plasmids of about 40-50kb which combine the high efficiency of lambda transfection with the ability to clone large pieces of DNA into plasmid vectors (Brown, 2006; Lodge, Lund & Minchin, 2007). Thus cosmids are essentially plasmids which have had a small piece of bacteriophage lambda DNA including the cos site (that is, containing the single stranded cohesive/sticky endings of λ phage which are complimentary to each other) cloned into them (Lodge, Lund & Minchin, 2007). Their plasmid features enable the vectors to have an origin of replication, to replicate at a high copy number, a selectable marker such as an antibiotic resistant gene which can be amplified in the

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