Genetic Engineering

What’s it all about?

Genetic Engineering

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  

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.

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:– plant and animal food production,– industry,– and medicine.

How is this done?

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.

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.

If the bacterium is harmful, the harmful gene must be removed. Good idea!

Details:The scissors of DNA

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.

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

Plants and animals that develop from a cell into which new DNA has been introduced are called transgenic organisms.

Food Production

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

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

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 one-third larger than normal carp.

Examples in Industry  

Gene transfers also have been applied in the management of industrial wastes.– 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. – For example, naphthalene, an environmental pollutant

present in artificially manufactured soils, can be broken down by the bacterium Pseudomonas fluorescens.

Continued

To monitor this process, scientists transferred a light-producing 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

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

Since that time, the FDA has approved other genetically engineered proteins for use in humans, – 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?

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 (milk-producing) glands.

The egg of the animal is then injected with the linked genes.

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.

In this way, sheep's milk is used to produce alpha-1-antitrypsin, 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

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.

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

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?

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.

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.

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  

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.

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.

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.

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

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.

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.

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.

– "Genetic Engineering," Microsoft® Encarta® Encyclopedia 99. © 1993-1998 Microsoft Corporation. All rights reserved.

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.

© Microsoft Corporation. All Rights Reserved.

– "Correcting Genetic Diseases," Microsoft® Encarta® Encyclopedia 99. © 1993-1998 Microsoft Corporation. All rights reserved.