GENETIC ENGINEERING TECHNIQUES
There are a number of techniques
for moving genes artificially into recipient organisms. The
oldest of these is called recombinant DNA, a technique that
relies on biological vectors like plasmids or viruses. Other
newer gene transfer techniques are electro- and chemical poration,
microinjection, and bioballistics.
Recombinant DNA techniques use biological vectors
like plasmids and viruses to carry foreign genes into cells.
Plasmids are small circular pieces of genetic material found
in bacteria that have the ability to cross species boundaries.
The circles can be broken and new genetic material added to
them. Plasmids augmented with new genetic material can move
across microbial cell boundaries and place the new genetic
material next to the bacterium's own genes.
Often the bacteria will take up the gene and
begin to produce the protein for which the gene codes. Where
the new gene codes for insulin, for example, the bacterium
will begin to produce insulin along with its other gene products.
A large vat of bacteria engineered to produce insulin can
then become a sort of pharmaceutical factory.
Viruses can also act as vectors in genetic
engineering. Viruses are infectious particles that contain
genetic material to which a new gene can be added. The virus
can carry the new gene into a recipient cell in the process
of infecting that cell. The virus can also be disabled so
that while it can carry a new gene into a cell, it cannot
redirect the cell's genetic machines to make thousands of
copies of itself.
Other methods do not rely on biological vectors
like plasmids and viruses. One of these is called microinjection
and involves simply injecting genetic material containing
the new gene into the recipient cell. Where the cell is large
enough, as many plant and animal cells are, the injection
can be done with a fine-tipped glass needle. Somehow the injected
genes find the host cell genes and incorporate themselves
ELECTRO- AND CHEMICAL PORATION
Other methods for direct gene transfer
involve creating pores or holes in the cell membrane to allow
entry of the new genes. This can be done by bathing cells
in solutions of special chemicals--so-called chemical poration--or
subjecting cells to a weak electric current--so-called electroporation.