Vectors Used in Biotechnology
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 identical copies of itself and the gene that it carries. Like the host-cell chromosomal DNA, plasmid DNA is duplicated before every cell division; they replicate independent of the chromosomal DNA. During cell division, at least one copy of the plasmid DNA is segregated to each daughter cell, assuring continued propagation of the plasmid through successive generations of the host cell. Thus after a number of successive cell divisions, various identical host cells are produced, thus, the gene carried by the plasmid is “cloned” (Brown, 2006; Lodish et al., 2000). Furthermore, the transformed bacterial host cells may have the ability to express the gene, thus producing proteins encoded by the gene included in the recombinant plasmid. This application can be used for producing proteins in large quantities which can be purified further, as is done for the production of recombinant insulin. Also, plasmids could be used in gene therapy, for delivery of therapeutic gene of interest into human host cells, without causing cell injury, oncogenic mutations and an immune response (Daugherty, 2007; Lipps, 2008).
Various features of plasmid that make it a suitable cloning vector are:
1. Plasmids contain an “Origin of replication” sequence
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 identical copies of itself and the gene that it carries. Like the host-cell chromosomal DNA, plasmid DNA is duplicated before every cell division; they replicate independent of the chromosomal DNA. During cell division, at least one copy of the plasmid DNA is segregated to each daughter cell, assuring continued propagation of the plasmid through successive generations of the host cell. Thus after a number of successive cell divisions, various identical host cells are produced, thus, the gene carried by the plasmid is “cloned” (Brown, 2006; Lodish et al., 2000). Furthermore, the transformed bacterial host cells may have the ability to express the gene, thus producing proteins encoded by the gene included in the recombinant plasmid. This application can be used for producing proteins in large quantities which can be purified further, as is done for the production of recombinant insulin. Also, plasmids could be used in gene therapy, for delivery of therapeutic gene of interest into human host cells, without causing cell injury, oncogenic mutations and an immune response (Daugherty, 2007; Lipps, 2008).
Various features of plasmid that make it a suitable cloning vector are:
1. Plasmids contain an “Origin of replication” sequence