Describe the use of plasmids as vectors in biotechnology?

Answer 1

Plasmids are often used as expression vectors in biotechnology. Plasmids are small, circular or linear pieces of DNA containing non-essential genes that are found in all life, although much more common in prokaryotes, especially bacteria. These genes confer abilities such as metabolizing a previously unusable compound, building an amino acid previously unbuildable, or even antibiotic resistance. Plasmids are used in research to induce the expression of a gene usually not found in the given organism. For example, you can construct a plasmid with a bacterial promoter connected to the gene for a human protein through a process called 'cloning'. The plasmid with the human gene can then be introduced into bacteria by transforming a competent gram-negative with the plasmid. Usually the plasmid also has an antibiotic resistance gene in addition to the target gene. This antibiotic resistance can be used to select for bacteria containing the plasmid. For example, the most common resistance gene is ampicillin resistance gene. If you grow the transformed bacteria in a culture containing ampicillin, only bacteria containing the antibiotic resistance, and therefore containing the plasmid, can survive. This will ensure that what you have is a pure culture of bacteria containing the plasmid. After selection, these bacteria can be cultured in suitable media to increase their numbers to a point that their production of the human protein becomes appreciable. Then these bacteria are usually lysed (killed) to extract the protein. Sometimes, however, these bacteria can also be made to secrete the protein into the medium.