Course: SAT 170 Introductory Biotechnology

Unit 7 Learning Module

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Page 4 of 5
DNA Technology Part 2 (continued)

Genetically Modified Organisms

Genetically modified organisms (GMO’s) are organisms that have had their DNA altered through genetic engineering. Genetic engineering is a type of biotechnology that results in the alteration of an organism’s genome. Often, these GMO’s are referred to as transgenic organisms because they have been modified to contain a gene that they did not previously have as part of their genome. These novel genes are often introduced from unrelated or distantly related organisms. An example that we discussed in unit 6 was the introduction of the human gene for insulin into a bacterial cell. The process of creating a GMO uses the following basic steps: isolate a gene of interest from one organism, insert that gene of interest into a vector, and finally, use that vector to introduce the gene of interest into a new organism. The isolation of the gene of interest and the subsequent incorporation of that gene into a vector relies on the recombinant DNA techniques that we discussed in our last unit. There are many types of vectors that are used for the production of GMO’s, most notably are plasmids and viruses. Plasmids are useful for these techniques because they are relatively small and can be easily manipulated to carry the gene of interest. However, not all cells will readily absorb plasmids into their cells. These can be introduced through a variety of techniques that attempt to make the cell membrane more permeable. In some cases, they can be injected directly into the cell using a very thin, glass hypodermic needle. This process is known as microinjection. The use of viruses as vectors can overcome this major hurdle of introducing foreign DNA into an organism by taking advantage of the inherent property of viruses that allows them to directly invade their host cells. Such viruses can be genetically altered to carry a gene of interest. They can then be allowed to “infect” their host cell. During the genetic manipulation, any of the genes that the virus carries for making their host cell sick are disabled, only the genes they require to invade the host cells are left intact. Retroviruses are excellent choices as vectors for the production of GMO’s. Such retroviruses are actually able to incorporate their own genetic information into the genome of their host cell. Thus, if a retrovirus were altered to carry a gene of interest into a cell of an organism, that gene of interest would become part of that cells genome. Often the cells of choice for genetic modification experiments are gametes (e.g. eggs). This allows the genetic modification to be present in every cell of the organism that develops from that gamete. There are many potential applications of such GMO’s in fields ranging from agriculture to medicine. We will be discussing these applications in more detail in future chapters.

One of the methods for introducing DNA into an organism for genetic modification is through electroporation which is illustrated in this figure. | DNA for genetic modification can also be introduced into cells directly through the use of a small, glass needle using a microscope. This method is known as microinjection.

This image shows a field of genetically modified food intended for human consumption.

Regulations on GMO research and the release of GMO’s vary from one country to another. A lot of the focus of regulation policies is on those GMO’s that are intended for human consumption, such a GM crops. There are many organizations that are involved in developing and implementing these policies including the Organisation for Economic Co-operation and Development (OECD), the Canadian Food Inspection Agency, Japan's Ministry of Health and Welfare, the U.S. Food and Drug Administration, the United Nation’s Food and Agriculture Organization, and the World Health Organization. Most of these organizations use a concept known as substantial equivalence when evaluating any potential risks of the consumption of GM foods. Substantial equivalence takes into account the fact that there is an inherent risk (usually due to the presence of toxins) to consuming many foods, including non-GM foods. Thus, the risks of GM foods must be compared to those risks that exist for non-GM foods. If the risk of the GM food does not exceed that of the non-GM food, it can be treated as safe for consumption and will not require further testing. However, when a GM food is substantially different than an existing food or if it has been modified with a gene produces a protein that has not previously been found in a food product, further investigation is performed. Another factor to consider when discussing the regulations of GM food is the labeling practices which are enforced to inform consumers of the presence of GM foods or food products. Generally speaking, if a food product has 1% or greater of GM content, it should be labeled as a GM food. This labeling, however, is currently voluntary in many countries including the United States and Canada.

One of the major hurdles to effective regulation of GM foods is the detection of GMO’s. Currently, the primary mechanism for detecting GMO’s is to use the polymerase chain reaction, or PCR (which we discussed in unit 6) to amplify a particular sequence of DNA that has been associated with a particular GMO or set of GMO’s. Examples of such target sequences would be the junction between the organisms natural DNA and the foreign DNA. If the PCR primers were able to amplify a specific sequence of DNA, that would indicate the presence of that DNA and, thus, the presence of that GMO. Another tactic for the detection of GMO’s is to detect the presence of a particular protein.  Recall from unit 5 that we employ methods such as western and eastern blot, chromatography and enzyme-linked immunosorbent assay (ELISA) to detect the presence of particular proteins. Part of the problem with such detection methods, is that this sequence or protein must be known in order for it to be detected. Additionally, it is time consuming and expensive to test large numbers of samples using these methods.