How Are Plasmids Used in Molecular Cloning?
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What is Molecular Cloning?
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Molecular cloning is a process by which a specific DNA sequence is identified and replicated within a living cell. Unlike reproductive cloning, this makes use of cellular reproduction rather than sexual reproduction and is strictly small-scale, although because individual DNA segments can be isolated, this allows for much finer tuning.
What are Plasmids?
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A plasmid is a self-replicating DNA molecule that carries only a few genes of its own. In essence, it might be described as a type of virus, but without the negative connotations as they live in harmony with the cell rather than destroy it. They replicate themselves either autonomously or in time with the rate of reproduction of the surrounding cell. They have enormous value in genetic and biological research as they can be inserted into a cell and bond with its genetic code. If the plasmid were to already contain any genetic traits of its own, these genetic traits would be integrated into the cell's DNA seamlessly. In this way, the genome of living creatures can be subtly altered. However, they have a different use as they relate to the process of molecular cloning, in which they are referred to as vectors, not plasmids.
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How Are Plasmids Used in Molecular Cloning?
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Plasmids, or vectors for the remainder of this piece, are required for a type of molecular cloning known as ligation cloning. The DNA fragment of any living thing to be cloned is isolated using specialized enzymes. It is then inserted into a vector containing no other significant genetic information and marked with a chemical tag. The vector is introduced into a prolific, but non-pathogenic bacterium. The bacterium is encouraged to grow and reproduce by cellular division. The individual cells of the bacterium are then analyzed. As the vector should have combined with the genetic structure of the bacterium, the DNA fragment will have been copied to every new cell. The genome of something as small as a bacterium can still be very complex, and for that reason the chemical tag should indicate under a specialized microscope the exact placement of each cloned DNA fragment. The cloning is complete, and the DNA fragments can be isolated and used according to the needs of whoever did the cloning.
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