Recombinant DNA
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The
term "Recombinant DNA" refers to an important experimental
procedure allowing scientists to selectively take certain pieces of DNA
"code" from one organism, and transfer them to another. In order to do this, a specific gene,
coding for the appropriate protein is taken, with the help of restriction
enzymes. These enzymes recognize
certain patterns in the base pairs, and 'cut' the DNA when they reach
one. This piece of DNA is then
combined with other genes with different enzymes, forming what is known as a
plasmid. It can be imagined as a
circle of DNA. Often, genes for
antibiotic resistance are also added to the plasmid, so that when the cells
are cultured, the cells without the gene can be killed by the addition of
that antibiotic. |
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The
plasmid is inserted into bacteria from 'competent' cell lines- their cell
membranes are somewhat porous. This is
done be causing the bacteria to relax, and then to shock them with a
temperature. Much like a human
drowning in water, they will take in whatever is in their surroundings. If that is a plasmid, then that will be
taken into the cytoplasm. They are
then cultured, and the appropriate proteins will be produced. |
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The
ability to selectively add genes to cells has proved invaluable for producing
artificial replacements for enzymes and hormones in the case where the human
cannot. One of the most common uses
has been to produce human insulin in e.
coli cells. This is accomplished
when huge quantities of genetically engineered cells are cultured, and then
the insulin filtered out. Before this
breakthrough, insulin from pigs was used, not only requiring the slaughter of
many pigs, but also presenting problems with the purity of the derived
enzymes. Since e. coli are harmless, there is no problem, even if part of the
cell was to remain in the protein. |
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In
the future, some believe that techniques such as this will allow scientist to
control the development of plants and animals to an unprecedented level,
selecting only the most desirable traits for expression. Before modern genetic engineering, that
would involve many crosses until all of the desirable traits were contained
in one example. |
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