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Genetic Engineering
What’s it all about?
Genetic Engineering
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Genetic Engineering, the alteration of an
organism's genetic material to eliminate
undesirable (bad) characteristics or to produce
desirable (good) new ones.
Genetic engineering is used to:
1.
increase plant and animal food production;
2.
to diagnose disease
3.
improve medical treatment,
4.
produce vaccines and other useful drugs;
5.
and to help dispose of industrial wastes.
RECOMBINANT DNA
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Over the past 20 years, genetic engineering has
been revolutionized with a technique called
recombinant DNA, or gene splicing, with which
scientists alter genetic material.
Genes consist of the molecule deoxyribonucleic acid
(DNA).
In recombinant DNA, one or more genes of an
organism are introduced to a second organism.
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If the second organism incorporates the new DNA
into its own, recombined DNA results.
In humans, recombinant DNA is the basis of gene
therapy, in which the DNA is introduced into
body, or somatic cells, where it may alter their
genetic makeup.
These alterations cannot be passed to future
generations since sperm and eggs, or germ cells,
are not affected.
Techniques
Recombinant DNA technology alters the
characteristics of an organism by
changing its protein makeup.
 Recombinant DNA techniques have
transformed genetic engineering in:
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plant and animal food production,
industry,
and medicine.
How is this done?
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In most cases, DNA cannot be transferred
directly from its original organism, known as
the donor, to the recipient organism, known
as the host.
Instead, the donor DNA must be cut and
recombined with a matching fragment of
DNA from a vector—that is, an organism that
can carry the donor DNA into the host.
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The host organism is often a rapidly multiplying
microorganism such as a harmless bacterium, which
serves as a factory where the recombined
(recombinant) DNA can be cloned (that is, duplicated)
in large quantities.
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If the bacterium is harmful, the harmful gene must be
removed. Good idea!
Details:The scissors of DNA
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Restriction enzymes are
used to cut DNA
molecules at specific
sequences.
Some restriction
enzymes make blunt
end cuts, others
generate “sticky ends”.
Ligase is the enzyme
used to “glue” the DNA
molecule into the new
plasmid.
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Viruses are also used as vectors.
A gene gun may also be used.
The naked DNA may also be introduced directly into
an organism by techniques such as injection through
the cell walls of plants or into the fertilized egg of an
animal.
Transgenic Organisms
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Plants and animals that develop from a cell into
which new DNA has been introduced are called
transgenic organisms.
Food Production
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Recombinant DNA has been used to combat one of
the greatest problems in plant food production: the
destruction of crops by plant viruses.
For example, by transferring the protein-coat gene of
the zucchini yellow mosaic virus to squash plants
that had previously sustained great damage from the
virus, scientists were able to create transgenic
squash plants with immunity to this virus.
More Examples: Plants
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Scientists also have developed:
transgenic potato and strawberry plants that are
frost-resistant,
transgenic tomato plants containing a gene that
slows the ripening process of the fruit, which slows
spoilage once the tomatoes are off the plant.
More Examples: Animals
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Similarly, in animal food production, the growth
hormone gene of rainbow trout has been transferred
directly into carp eggs.
The resultant transgenic carp produce both carp and
rainbow trout growth hormones and grow to be onethird larger than normal carp.
Examples in Industry
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Gene transfers also have been applied in the
management of industrial wastes.
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Genetically altered bacteria can be used to decompose many
forms of garbage and to break down petroleum products.
Recombinant DNA technology also can be used to
monitor the breakdown of pollutants.
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For example, naphthalene, an environmental pollutant present
in artificially manufactured soils, can be broken down by the
bacterium Pseudomonas fluorescens.
Continued
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To monitor this process, scientists transferred a lightproducing enzyme called luciferase, found in the
bacterium Vibrio fischeri, to the Pseudomonas
fluorescens bacterium.
The genetically altered Pseudomonas fluorescens
bacterium produces light in proportion to the amount
of its activity in breaking down the napthalene, thus
providing a way to monitor the efficiency of the
process. Cool!!
Medical Examples
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In 1982 the United States Food and Drug
Administration (FDA) approved for the first time the
medical use of a recombinant DNA protein, the
hormone insulin, which had been cloned in large
quantities by inserting the human insulin gene in
Escherichia coli bacteria.
Previously, this hormone, used by insulin-dependent
people with diabetes, had been available only in
limited quantities from hogs.
Continued
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Since that time, the FDA has approved other
genetically engineered proteins for use in
humans,
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including two cloned in hamster cell cultures:
tissue plasminogen activator (tPA), an enzyme
used to dissolve blood clots in people who have
suffered heart attacks,
and erythropoetin, a hormone used to stimulate
the production of red blood cells in people with
severe anemia.
Got Milk?
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Scientists also have employed recombinant DNA
techniques to produce medically useful human
proteins in animal milk.
In this procedure, the human gene responsible for
the desired protein is first linked to specific genes of
the animal that are active only in its mammary (milkproducing) glands.
The egg of the animal is then injected with the linked
genes.
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The resulting transgenic animals will have these
linked genes in every cell of their body but will
produce the human protein only in their milk.
The human protein is finally extracted from the
animal's milk for use as medicine.
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In this way, sheep's milk is used to produce alpha-1antitrypsin, an enzyme used in the treatment of
emphysema;
cow's milk is used to produce lactoferrin, a protein
that combats bacterial infections;
and goat's milk is used as yet another way to
produce tPA, the blood-clot-dissolving enzyme also
cloned in hamster cell cultures.
Vaccines
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Recombinant DNA technology also is used in the
production of vaccines against disease.
A vaccine contains a form of an infectious organism
that does not cause severe disease but does cause
the body's immune system to form protective
antibodies against the organism.
When a person is vaccinated against a viral disease,
the production of antibodies is actually a reaction to
the surface proteins of the coat of the virus.
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With recombinant DNA technology, scientists have
been able to transfer the genes for some viral-coat
proteins to the vaccinia, or cowpox, virus, which was
used against smallpox in the first efforts at
vaccination, and which gave the process its name.
Vaccination with genetically altered vaccinia is now
being used against hepatitis, influenza, and herpes
simplex viruses.
Genetically engineered vaccinia is considered safer
than using the disease-causing virus itself and is
equally as effective.
Gene therapy
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Gene therapy, in which a healthy gene can be
directly inserted into a person with a
malfunctioning gene, is perhaps the most
revolutionary and promising of recombinant DNA
technologies, but many problems remain to be
solved in getting the healthy gene into human cells.
Although the use of gene therapy has been
approved in more than 100 clinical trials for diseases
such as cystic fibrosis, emphysema, and muscular
dystrophy, there have as yet been no cures.
How Much does this cost?
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It takes an average of seven to nine years and an
investment of about $55 million to develop, test, and
market a new genetically engineered product.
Because of this great cost, companies have sought to
patent the results of their discoveries.
In 1980 the Patent and Trademark Office of the U.S.
Department of Commerce issued its first patent on an
organism that had been produced with recombinant
DNA.
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The patent was for a so-called oil-eating bacterium
that could be used in the bioremediation (that is, the
cleaning up by natural means) of oil spills from ships
and storage tanks.
Since then, hundreds of patents have been granted
for genetically altered bacteria, viruses, and plants.
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In 1988 the first patent was issued on a transgenic
animal, a strain of laboratory mice whose cells were
engineered to contain a cancer-predisposing gene.
The mice are used to test low doses of suspected
carcinogens, or cancer-causing substances, and to
test the effectiveness of anticancer therapies.
CONTROVERSIES
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Public reaction to the use of recombinant DNA in
genetic engineering has been mixed.
The production of medicines through the use of
genetically altered organisms has generally been
welcomed.
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However, critics of recombinant DNA fear that the
pathogenic, or disease-producing, organisms used in
some recombinant DNA experiments might develop
extremely infectious forms that could cause worldwide
epidemics.
In an effort to prevent such an occurrence, the National
Institutes of Health (NIH) has established regulations
restricting the types of recombinant DNA experiments
that can be performed using such pathogens.
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Transgenic plants also present controversial issues.
Environmentalists fear that the transgenic plants
could spread and eliminate existing species.
In addition, it has now been proved that allergens
(cause allergies) can be transferred from one food
crop to another through genetic engineering.
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In an attempt to increase the nutritional value of
soybeans, a genetic engineering firm experimentally
transferred a Brazil nut gene producing a nutritious
protein into the soybean plant.
However, when a study found that the genetically
engineered soybeans caused an allergic reaction in
people sensitive to Brazil nuts, the project was
canceled.
More Questions
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Questions also have been raised concerning the
morality of producing transgenic organisms.
In addition, some critics object to the patenting of
genetically altered organisms because it makes the
organisms the property of particular companies.
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The lack of a completely successful gene therapy
program has concerned many people, including a
number of scientists.
They feel that, before additional clinical trials are
conducted, more must be understood about the
factors that control whether a particular vector can
enter a given type of cell and become incorporated
into its genetic material.
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However, the wishes of many people awaiting gene
therapy, as well as the commercial interests of
companies, have created great pressure both to
continue existing programs and to begin new ones.
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"Genetic Engineering," Microsoft® Encarta® Encyclopedia
99. © 1993-1998 Microsoft Corporation. All rights reserved.
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Gene therapy may someday be able to
cure hereditary diseases, such as
hemophilia and cystic fibrosis, which are
caused by missing or defective genes. In
one type of gene therapy, genetically
engineered viruses are used to insert new,
functioning genes into the cells of people
who are unable to produce certain
hormones or proteins necessary for the
body to function normally.
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© Microsoft Corporation. All Rights
Reserved.
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"Correcting Genetic Diseases,"
Microsoft® Encarta® Encyclopedia
99. © 1993-1998 Microsoft
Corporation. All rights reserved.