Genetic Engineering

DNA Technology Applications

The use of recombinant DNA technology has become commonplace as new products from genetically altered plants, animals, and microbes have become available for human use. In 1997, Dolly made headlines as the first successfully cloned large mammal (sheep). Since then there have been many similar advances in medicine, such as treatments for cancer; many advances in agriculture, such as transgenic insect-resistant crops; and many advances in animal husbandry, such as growth hormones and transgenic animals (an animal that has received recombinant DNA).

Most biotechnologists envision DNA technological applications as one of the new frontiers in science with tremendous growth and discovery potential.

Medicine

Genetic engineering has resulted in a series of medical products. The first two commercially prepared products from recombinant DNA technology were insulin and human growth hormone, both of which were cultured in the E. coli bacteria. Since then a plethora of products have appeared on the market, including the following abbreviated list, all made in E. coli:

• Tumor necrosis factor. Treatment for certain tumor cells
• Interleukin-2 (IL-2). Cancer treatment, immune deficiency, and HIV infection treatment
• Prourokinase. Treatment for heart attacks
• Taxol. Treatment for ovarian cancer
• Interferon. Treatment for cancer and viral infections

In addition, a number of vaccines are now commercially prepared from recombinant hosts. At one time vaccines were made by denaturing the disease and then injecting it into humans with the hope that it would activate their immune system to fight future intrusions by that invader. Unfortunately, the patient sometimes still ended up with the disease.

With DNA technology, only the identifiable outside shell of the microorganism is needed, copied, and injected into a harmless host to create the vaccine. This method is likely to be much safer because the actual disease-causing microbe is not transferred to the host. The immune system is activated by specific proteins on the surface of the microorganism -e. DNA technology takes that into account and only utilizes identifying surface features for the vaccine. Currently vaccines for the hepatitis B virus, herpes type 2 viruses, and malaria are in development for trial use in the near future.

Agriculture

Crop plants have been and continue to be the focus of biotechnology as efforts are made to improve yield and profitability by improving crop resistance to insects and certain herbicides and delaying ripening (for better transport and spoilage resistance). The creation of a transgenic plant, one that has received genes from another organism, proved more difficult than animals. Unlike animals, finding a vector for plants proved to be difficult until the isolation of the Ti plasmid, harvested from a tumor-inducing (Ti) bacteria found in the soil. The plasmid is “shot” into a cell, where the plasmid readily attaches to the plant's DNA. Although successful in fruits and vegetables, the Ti plasmid has generated limited success in grain crops.

Creating a crop that is resistant to a specific herbicide proved to be a success because the herbicide eliminated weed competition from the crop plant. Researchers discovered herbicide-resistant bacteria, isolated the genes responsible for the condition, and “shot” them into a crop plant, which then proved to be resistant to that herbicide. Similarly, insect-resistant plants are becoming available as researchers discover bacterial enzymes that destroy or immobilize unwanted herbivores, and others that increase nitrogen fixation in the soil for use by plants.

Geneticists are on the threshold of a major agricultural breakthrough. All plants need nitrogen to grow. In fact, nitrogen is one of the three most important nutrients a plant requires. Although the atmosphere is approximately 78 percent nitrogen, it is in a form that is unusable to plants. However, a naturally occurring rhizobium bacterium is found in the soil and converts atmospheric nitrogen into a form usable by plants. These nitrogen-fixing bacteria are also found naturally occurring in the legumes of certain plants such as soybeans and peanuts. Because they contain these unusual bacteria, they can grow in nitrogen-deficient soil that prohibits the growth of other crop plants. Researchers hope that by isolating these bacteria, they can identify the DNA segment that codes for nitrogen fixation, remove the segment, and insert it into the DNA of a profitable cash crop! In so doing, the new transgenic crop plants could live in new fringe territories, which are areas normally not suitable for their growth, and grow in current locations without the addition of costly fertilizers!

Animal Husbandry

Neither the use of animal vaccines nor adding bovine growth hormones to cows to dramatically increase milk production can match the real excitement in animal husbandry: transgenic animals and clones.

Transgenic animals model advancements in DNA technology in their development. The mechanism for creating one can be described in three steps:

1. Healthy egg cells are removed from a female of the host animal and fertilized in the laboratory.
2. The desired gene from another species is identified, isolated, and cloned.
3. The cloned genes are injected directly into the eggs, which are then surgically implanted in the host female, where the embryo undergoes a normal development process.

It is hoped that this process will provide a cheap and rapid means of generating desired enzymes, other proteins, and increased production of meat, wool, and other animal products through common, natural functions.

Ever since 1997 when Dolly was cloned, research and experimentation to clone useful livestock has continued unceasingly. The attractiveness of cloning is the knowledge that the offspring will be genetically identical to the parent as in asexual reproduction. Four steps describe the general process:

1. A differentiated cell, one that has become specialized during development, with its diploid nucleus is removed from an animal to provide the DNA source for the clone.
2. An egg cell from a similar animal is recovered and the nucleus is removed, leaving only the cytoplasm and cytoplasm organelles.
3. The two egg cells are fused with an electric current to form a single diploid cell, which then begins normal cell division.
4. The developing embryo is placed in a surrogate mother, who then undergoes a normal pregnancy.

Excerpted from The Complete Idiot's Guide to Biology © 2004 by Glen E. Moulton, Ed.D.. All rights reserved including the right of reproduction in whole or in part in any form. Used by arrangement with Alpha Books, a member of Penguin Group (USA) Inc.

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