Write short notes on Potential uses of Recombinant DNA technology.
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I Introduction
In a brief note in Biochemical Education (1978, 6, 74) attention was
drawn to the importance of students, especially medical students,
obtaining a balanced view of both the potential and possible
hazards of recombinant DNA technology so that they could
formulate their opinions on a rational basis. It was suggested that
experts might be persuaded to submit articles to Biochemical
Education. In order to encourage others we have decided to try and
introduce the subject. The object is to state briefly the present state
of the art, then discuss its achievements and potential benefits and
finally to explain the potential hazards and the safeguards that are
being taken. We hope that the article will stimulate others to talk
about the subject to their students. With this in mind we have
prepared some simple figures which could be easily reproduced as
black and white slides.
II Recombinant DNA
The idea that DNA could be transferred from cells of one species to
another sprang from the observation concerning the development of
drug resistance by bacteria, particularly those that make up the
normal intestinal flora in man. Thus the pathogenic Salmonella
were found to acquire a resistance to several antibiotics and they
appeared to acquire this resistance from the non-pathogenic E coli.
The usual mechanism for this type of drug resistance arises from
the ability of the bacterium to synthesize an enzyme that breaks
down the drug to render it inactive. Thus penicillinase degrades
penicillin. The implication is that the bacterium in acquiring
resistance has acquired new information in the form of DNA to
allow it to synthesize a new enzyme, ie penicillinase. Fig 1 shows our
current understanding of this phenomenon. The information that
confers on E coil resistance to a variety of antibiotics resides in an
extra-chromosomal DNA molecule called a resistance factor or
R factor. Drug resistance is conferred on Salmonella by 'resistance
transfer' involving passage of the R factor from E coli via an R-
pilus.
R factors belong to a general class of DNA molecules normally
referred to as plasmids. These are relatively small extra-
chromosomal genetic elements capable of autonomous, self-
replication in the host cell without lowering its viability. Most
plasmids can be transmitted from cell to cell without killing the host
cell. Plasmids can be easily separated from host chromosomal DNA
by either isopycnic centrifugation, since their base compositions
and consequently buoyant densities usually differ, or by methods
designed to isolate supercoiled molecules as most plasmids are
circular.
Genetic manipulation is the process whereby a piece of foreign
DNA is inserted into the DNA of a plasmid or virus for subsequent