Transgenics | Research & Encyclopedia Articles

Transgenics

The term transgenics refers to the process of transferring genetic information from one organism to another. By introducing new genetic material into a cell or individual, a transgenic organism is created that has new characteristics it did not have before. The genes transferred from one organism or cell to another are called transgenes. The development of biotechnological techniques has led to the creation of transgenic bacteria, pants, and animals that have great advantages over their natural counterparts and sometimes act as living machines to create pharmaceutical therapies for the treatment of disease. Despite the advantages of transgenics, some people have great concern regarding the use of transgenic plants as food, and with the possibility of transgenic organisms escaping into the environment where they may upset ecosystem balance.

All of the cells of every living thing on Earth contain DNA (deoxyribonucleic acid). DNA is a complex and long molecule composed of a sequence of smaller molecules, called nucleotides, linked together. Nucleotides are nitrogen-containing molecules, called bases that are combined with sugar and phosphate. There are four different kinds of nucleotides in DNA. Each nucleotide has a unique base component. The sequence of nucleotides, and therefore of bases, within an organism's DNA is unique. In other words, no two organisms have exactly the same sequence of nucleotides in their DNA, even if they belong to the same species or are related. DNA holds within its nucleotide sequence information that directs the activities of the cell. Groups, or sets of nucleotide sequences that instruct a single function are called genes.

Much of the genetic material, or DNA, of organisms is coiled into compact forms called chromosomes. Chromosomes are highly organized compilations of DNA and protein that make the long molecules of DNA more manageable during cell division. In many organisms, including human beings, chromosomes are found within the nucleus of a cell. The nucleus is the central compartment of the cell that houses genetic information and acts as a control center for the cell. In other organisms, such as bacteria, DNA is not found within a nucleus. Instead, chromosomes are free within the cell. Additionally, many cells have extrachromosomal DNA--DNA that is not found within chromosomes. The mitochondria of cells, and the chloroplasts of plant cells have extrachromosomal DNA that help direct the activities of these organelles independent from the activities of the nucleus where the chromosomes are found. Plasmids are circular pieces of extrachromosomal DNA found in bacteria that are extensively used in transgenics.

DNA, whether in chromosomes or in extrachromosomal molecules, uses the same code to direct cell activities. The genetic code is the sequence of nucleotides in genes that is defined by sets of three nucleotides. The genetic code itself is universal, meaning it is interpreted the same way in all living things. Therefore, all cells use the same code to store information in DNA, but have different amounts and kinds of information. The entire set of DNA found within a cell (and all of the identical cells of a multicellular organism) is called the genome of that cell or organism.

The DNA of chromosomes within the cellular genome is responsible for the production of proteins. The universal genetic code simply tells cells which proteins to make. Proteins, in turn have many varied and important functions, and in fact help determine the major characteristics of cells and whole organisms. Proteins have structural functions, which give shape and strength to cells and tissues and they also act as hormones. Insulin, for example, is a protein hormone. Proteins can act as neurotransmitters, enabling nerve cells to relay signals. As enzymes, proteins carry out thousands of kinds of chemical reactions that make life possible. Proteins also act as cell receptors and signal molecules, which enable cells to communicate with one another, to coordinate growth and other activities important for wound healing and development. Proteins also have contractile functions involved in motion. Thus, many of the vital activities and characteristics that define a cell are really the result of the proteins that are present. The proteins, in turn, are determined by the genome of the organism.

Because the genetic code with genes is the same for all known organisms, and because genes determine characteristics of organisms, the characteristics of one kind of organism can be transferred to another. If genes from an insect, for example, are placed into a plant in such a way that they are functional, the plant will gain characteristics of the insect. The insect's DNA provides information on how to make insect proteins within the plant because the genetic code is interpreted in the same way. That is, the insect genes give new characteristics to the plant. This very process has already been performed with firefly genes and tobacco plants. Firefly genes were spliced into tobacco plants, which created new tobacco plants that could glow in the dark. This amazing artificial genetic mixing, called recombinant biotechnology, is the crux of transgenics. The organisms that are created from mixing genes from different sources are transgenic. The glow-in-the-dark tobacco plants in the previous example, then, are transgenic tobacco plants.

One of the major obstacles in the creation of transgenic organisms is the problem of physically transferring DNA from one organism or cell into another. It was observed early on that bacteria resistant to antibiotics transferred the resistance characteristic to other nearby bacterial cells that were not previously resistant. It was eventually discovered that the resistant bacterial cells were actually exchanging plasmid DNA carrying resistance genes. The plasmids traveled between resistant and susceptible cells. In this way, susceptible bacterial cells were transformed into resistant cells.

The permanent modification of a genome by the external application of DNA from a cell of different genotype is called transformation. Transformed cells can pass on the new characteristics to new cells when they reproduce because copies of the foreign transgenes are replicated during cell division. Transformation can be either naturally occurring or the result of transgenics. Scientists mimic the natural uptake of plasmids by bacterial cells for use in creating transgenic cells. Certain chemicals make transgenic cells more willing to take-up genetically engineered plasmids. Electroporation is a process where cells are induced by an electric current to take up pieces of foreign DNA. Transgenes are also introduced via engineered viruses. In a procedure called transfection, viruses that infect bacterial cells are used to inject the foreign pieces of DNA. DNA can also be transferred using microinjection, which uses microscopic needles to insert DNA to the inside of cells. A new technique to introduce transgenes into cells uses liposomes. Liposomes are microscopic spheres filled with DNA that fuse to cells. When liposomes merge with host cells, they deliver the transgenes to the new cell. Liposomes are composed of lipids very similar to the lipids that make up cell membranes, which gives them the ability to fuse with cells.

Humankind has been beneficially manipulating the genomes of organisms for a long time. Historically, the manipulations involved interbreeding of plants and animals to give new variations of useful characteristics. Such a practice is called artificial selection--the purposeful manipulation of reproduction to select for a particular genetic characteristic. It is the intentional counterpart to the more random process of natural selection. Examples of artificial selection used to create organisms with new and desirable characteristics include unusual breeds of dogs for pets, larger breeds of horses for work, and new corn varieties developed to withstand dry conditions or improve productivity. With the aid of new scientific knowledge, scientists can now use transgenics to accomplish the same results as selective breeding.

By recombining genes, bacteria that metabolize petroleum products are created to clean-up the environment, antibiotics are made by transgenic bacteria on mass industrial scales, and new protein drugs are produced. By creating transgenic plants, food crops have enhanced productivity. Transgenic corn, wheat, and soy with herbicide resistance, for example, are able to grow in areas treated with herbicide that kills weeds. Transgenic tomato plants produce larger, more colorful tomatoes in greater abundance. Transgenics is also used to create influenza immunizations and other vaccines.

Despite their incredible utility, there are concerns regarding trangenics. The Human Genome Project is a large collaborative effort among scientists worldwide that announced the determination of the sequence of the entire human genome in 2000. In doing this, the creation of transgenic humans could become more of a reality, which could lead to serious ramifications. Also, transgenic plants used as genetically modified food is a topic of debate. Some people believe transgenic food is a consumer safety issue since not all of the effects of transgenic