Karen A. Beitler
Written as background for teachers and high school biology students, this unit assumes student knowledge of macromolecules, genes and how traits are passed from parent to offspring. Students should be aware of basic human needs and have explored food labels in terms of healthy choices of food intake. The narrative discusses the impact of genetic modification in the realm food production and effects on the environment as background for teachers of biology
A brief introduction into biotechnology will provide the reader with information for laboratory activities that simulate removal and replacement of genes to create recombinant organisms. The intention is to give the reader instruction in the processes and procedures of genetic modification as a precursor to the State of Connecticut Science and Technology embedded task; Genetically Modified Foods.
Are the foods we eat responsible for the high incidence of obesity and diabetes in this country, or is it merely the habits we have? What is a healthy diet, healthy lifestyle? Our national dependence on fast food has increased childhood obesity and diabetes to epidemic proportions. Is it the food itself that is causing these risk factors? In the fascinating world of genetic modification, Virginia Ursin, a senior scientist at Monsanto Corporation is experimenting with adding the fish gene for Omega-3 oil to soy bean crops to increase the available amount of this heart healthy oil enough to help improve cardiovascular health. How about a rice that provides essential vitamins and minerals, potatoes that absorb less oil, oil seed crops that have more unsaturated, than saturated fat, sugar beets engineered to contain lower calories sugars( McHughen,235)? Genetic modification is also being applied to produce chemicals, pharmaceuticals, cosmetics, cotton, flax and flowers. This is just the beginning; imagine what we will be able to do in the future. Just how does genetic engineering work? A brief look at the processes involved in cutting up genes( RFLP), duplication of genes( PCR), identification of genes (DNA fingerprinting) and transformation of genes, is provided here. And lastly, but most importantly, who has the right to know if a food is genetically modified and how do these "new" foods affect us, our bodies and our environment.
Many studies have been done to document the need for education of children on how they contribute to the health of their environment (Beech, 1999, Murphy, 1994, Russell 1994, Falciglia, 1997, Lin, 2001). Students who are informed about their environment are more likely to make smart choices that contribute to healthier bodies, healthier lifestyles and a healthier world (Guthrie, 2005). Schools can be identified as a key setting for promoting healthy choices for children. Many of the students in urban settings have little contact with the world outside their neighborhood and have no knowledge of where their food comes from outside the corner store. Some do not even know how a label describes the food within the package it is on. Our first order of business is education.
The National Restaurant Association estimates that more than 47% of the money spent on food will be in restaurants in 2005 that is almost double the 25% that was spent in 1955 (Horowitz, 2005). Our students eat out, or bring in food from take-out restaurants. They don't have a real connection with where foods come from or what requirements they have for growth or even how to put them together to make a meal (Pirouznia 2001). Because humans evolved over thousands of years in a world where salt, sugar and fat were difficult to come by, our bodies are programmed to seek out those ingredients (Schwader, 2005). Now that society has an overabundance of salt, sugar and fat available our brain doesn't know how to shut the cravings for these things off. We overindulge. If we want to have a healthy contributing society that is sustainable, we need to educate our young people; teach them how to eat and show them why, and shape responsible young adults that curb their own desires in favor of a healthy lifestyle. This is where genetic modification of foods comes in. Fresh fruits and vegetables don't have the appeal that a Big Mac with fries has, GM food companies seek to produce foods that have universal appeal and universal nutrition.
What are genes?
The central dogma of molecular biology describes the flow of the DNA message from the nucleus of our cells to a messenger called RNA which translates the message into proteins. What is that message? The message is how to replicate the order of the 20 amino acids that make up our cells. This genetic information determines what each cell will become determining our individual traits. Each trait is decided by a gene that has two alleles, inherited from each parent, which dictate what traits an organism will display. Much of agriculture today is based on Mendel's original principles of inheritance. Scientist and researches use these principles to cross breed plants to obtain desired characteristics. This process is time consuming, often many generations of a plant need to be bred to obtain the desired trait. Genetically engineering new types of plants is much faster and offers an advantage of transferring traits between species.
Understanding the structure of DNA is important to gaining insight into how foods are genetically modified. Deoxyribonucleic acid is found in the nucleus of cells. The shape is similar to a twisted ladder. The rungs of the ladder are called the sugar phosphate backbone of the structure. The pentose sugar, deoxyribose in each nucleotide is bound to the phosphate in the next by a strong covalent bond. A nucleotide is made of the sugar, phosphate and a nitrogen base. There are four nitrogen bases; two are double-ringed purines, Guanine and Adenine and two single-ringed pyrimidines; Thymine and Cytosine. The bases always pair up in the same way Adenine (A) with Thymine (T) and Cytosine (C) with Guanine (G). These bases are connected by hydrogen bonds and make up the rungs of the ladder. Each set of three nucleotide sequences is called a codon and translates to an amino acid. There are 20 amino acids that make up all the proteins (Campbell-Reece, 88-89). Amino acids make up the proteins that determine function. The pairs of bases, in triplets (codons) are put together in a specific order to make up genes. Genes are specific to the production of a particular protein (Holt, 187).
One way to think of DNA is to envision a story written on a long roll of parchment. The narrative chronicles the complete story (organism). Each chapter in the story is a chromosome with paragraphs (genes), words (codons) and letters (nucleotides). If a letter is out of place or missing, the word doesn't make sense - then the sentence may not make sense. This could cause confusion in the paragraph and the chapter, and the story may deliver the wrong message.
In eukaryotic cells, DNA seeks to avoid confusion by being semi-conserved; one half of the original molecule binds with a newly made second half to make a molecule that is half old and half new. The series of nucleotides that make up the DNA ladder matches each A with T and C with G. Theses nitrogen bases are joined by a weak hydrogen bond that can be 'unzipped' by the enzyme helicase to separate the ladder into two chains that are exactly opposite. New amino acids match up and reform the ladder and each half is 'zippered' by another enzyme called DNA polymerase. This is, of course, a brief over view of the process, the 'code' must be read by messenger RNA (mRNA), altered to leave the nucleus so that only exons (the sections of the molecule that code for proteins leave) and travel to the ribosome. At the ribosome, the exon code is translated and transcribed and the amino acids are linked together in chains three nucleotides long strung end to, which travel back to the nucleus.
One half of the 'unzippered' parent molecule is bound to new amino acid chains and introns( internal non-coding parts of DNA) in the 3' to 5' direction, using it as a template; this is called the leading strand. On the other strand, short discontinuous segments of polynucleotide called Okazaki fragments are bound and another enzyme, called DNA ligase, stitches them, with their introns, into the lagging strand. The short chains match up with the parent DNA in the nucleus and reform the ladder, when all the DNA is replicated the cell is ready to go through mitosis.
In prokaryotic cells, such as bacteria, all or most of an organism's genetic information is stored in one long, circular ring. DNA replication begins at a fixed location called replication origin and the process takes less than an hour to complete. Bacterial cells also contain circular rings of extra-chromosomal DNA called plasmids. Bacteria have a short replication time and duplicate exponentially making many new plasmids. Scientists often use bacterial cells as vectors to make copies of a gene they are interested in. This is one important process in genetic engineering and is used in forensic science, pharmaceuticals and modification of foods as well.
Genetic engineering or genetic modification is actually a collection of many technologies. Genetic modification changes the genetic content - the DNA sequence - of a cell, many cells, or a whole organism. Genetic modification is possible in bacteria, plants, and animals.
The process begins with identification of a gene, or gene sequence that determines a specific trait. Once the gene responsible for a trait is identified, then recombinant gene technology is used to artificially combine genetic material from one or more organisms (BIO, 1). Special enzymes are used to 'cut' the isolated gene from a chromosome. Many enzymes have been identified that will separate gene sequences at specific location on a chromosome. The set of technologies includes techniques for extracting genes, inserting them into a host DNA, cloning or multiplying them and the making of a unique new fingerprint to identify them.
If gene-splicing, cutting up the DNA into pieces, and then connecting the DNA back together, is probably the technique most people think of when referring to genetic modification. Imagine a long chain of pop beads of four different colors. Suppose a tool is needed to separate the pop beads, perhaps a different tool for each triplet sequence in a chromosome. Scientists have identified which tool will slice which gene sequence in a particular way. Now that the sequence is cut, it can be recombined in a bacterial plasmid's DNA and replicated many times or placed in a plant or organism's DNA to change the traits expressed. The application of these techniques to a cell that will later replicate and divide making a new and different organism is known as a transgenic or genetically transformed, or modified organism (BIO, 2).
Let's take a look at how genes are transferred. Imagine a chromosome containing thousands of genes and scientists have identified a gene that helps an organism break down fats in a fish. A researcher is looking to help fight the obesity challenge in the United States. The researcher learns of the gene that breaks down fats for fish. The process begins to extract the gene from the fish, perhaps using enzymes, known as restriction enzymes, and place the gene in a commonly available food that is easy to grow, like corn. The researcher will need to make many copies of the gene.
Restriction endonucleases are enzymes that protect the bacterial cell against intruding DNA from other organisms. Theses specific enzymes work by cutting up the foreign DNA, a process called restriction. Scientists have identified and isolated thousands of these enzymes and because each is specific and recognizes only one particular short sequence of DNA, they can be used to cut DNA into restriction fragments. A restriction enzyme cuts DNA in a reproducible way. The most useful restriction enzymes cleave the sugar-phosphate backbone of DNA in a staggered way resulting in restriction fragments that have at least one single-stranded end, called the sticky end. The short sticky ends can forms temporary hydrogen bonded base pairs with other sticky end on any other DNA strand with the complementary sticky end cut with the same enzyme. These temporary bonds can be made permanent with the addition of the enzyme called DNA ligase. This enzyme catalyzes the formation of a covalent bond that closes up the sugar phosphate backbone, thus joining DNA from two different molecules to produce a stable recombinant DNA molecule (Holt, 140).
An original DNA molecule is sometimes called a cloning vector because it can carry DNA from another molecule and clone it (Avise, 687). Bacteria make good cloning vectors because they have a circular DNA molecule, called a plasmid. The plasmid DNA can be easily isolated from bacteria, manipulated into forming recombinant DNA by insertion of a foreign gene, and reintroduced into a bacterial cell. Bacterial cells reproduce quickly and in the process multiply any foreign DNA that they carry.
Molecular biologists use a method called RFLP to trace a specific sequence of DNA as it is passed on to other cells. Sample DNA is cut (digested) with one or more restriction enzyme and resulting fragments are separated according to molecular size using gel electrophoresis (Avise, 688). Scientists can then calculate the genetic distance between two genes. RFLPs can be used to measure recombination rates.
Back to the fish gene, the scientist has isolated the gene and will now need to make many copies to experiment with. They may use the bacterial cell to make those copies or another method called polymerase chain reaction (PCR). A gene can be inserted into a plasmid that can replicate exponentially in a bacterium. The bacteria will duplicate its DNA with the newly inserted gene, cloning and purifying the gene. DNA molecules can also be quickly amplified in a three step cycle that brings about a chain reaction producing an exponentially growing population of identical DNA molecules. Using heating and cooling and providing the ample genetic material, the gene is quickly cloned. Students can practice PCR in an online tutorial at the website called Polymerase Chain Reaction (Cold Spring Harbor, 1). This website simulates rising and falling temperature, denaturing DNA, annealing and extending primers through all three cycles and then lets the students graph the exponential growth of the DNA fragment. An animated picture of PCR can be seen at Principle of the PCR (Vierstraete, 2). Now that we have the fragments multiplied many times, what do we do with them?
Electrophoresis is a means of separating proteins and purifying molecules by size using electricity and a porous medium. Because the phosphates of DNA have a negative charge, they will migrate towards the positive pole in an electrophoresis chamber. In a buffered solution, short strands move through the porous gel more quickly than the longer stands and thus are separated from each other. When stained, this makes a pattern that is unique. There is a logarithmic relationship between the distance a fragment travels and the molecular weight of the fragment (Campbell-Reese, 148)
The molecular size of unknown DNA fragments can be compared to a standard for identification Genes can be identified in this way, because each piece of DNA leave a unique fingerprint when separated by this method.
Three pictorial, manipulative gel electrophoresis websites;
Gel Electrophoresis for Separation of DNA molecules
(Hughes, 2) Graphics Text
, Learn Genetics
are available to practice gel electrophoresis.
Genetic engineering can be used to repair a genetic defect for example; gene therapy in humans or to increase growth rate or resistance to a disease or damage from an insect or to enable an organism to do something it doesn't ordinarily do. GMOs have enabled microorganisms to produce human insulin for diabetics and make blood clotting proteins for hemophiliacs (BIO, 3). The benefits of discovery can be applied to many industries that use biotechnology: pharmaceuticals, agriculture, the processing of food, and forestry. There are currently two broad categories where genetically modified organisms have created controversy; ethical issues (including political, social and religious concerns) and scientific issues.
GMO's; Ethical issues
Ethical issues currently in debate are based around whether it is acceptable or not to modify the genes or utilize any other the genetic transformation techniques we now have available. While most people will agree that we have developed the tools and therefore should utilize them, the debate begins when discussion centers on how and why we should utilize them. Altering genes to produce medicine to make better insulin for a diabetic is acceptable, but altering genes to produce oil with cholesterol lowering abilities is not. One is considered necessary medicine, the other is not. The issues seem to lie in changing living things that humans consume and in the product that is changed. The lack of knowledge about, and misunderstanding of the process of genetic modification, may be the reason for concern (McHughen, 32).
Traditional breeding methods have produce hybrid plants for generations, the difference today is in the method used to transfer genetic information. Early farmers would breed generation after generation of plants until they had breed out undesired traits and obtain a plant that contained just the characteristics they preferred. There are hundreds of varieties of tomatoes; each hybrid has specific qualities the farmer saw as desirable and lacks those that were unwanted. A hybrid plant is one that contains genes of two differing species of plants and is genetically a combination of the two but phenotypically different from both (Teitel, 15). A phenotype is how an organism looks, or its physical qualities. A genotype is the record of the actual genes in an organism, often represented by letters (Holt, 172). For hundreds of years local growers in each part of the world have breed the traditional plants of their forefathers, refining the character of the areas crops. These traditional practices have provided us with unique varieties of plants that often bare the name of their homeland. The unique flavor of a fruit from certain area is dependent on several factors that contribute to the amount of sugar the plant makes. Varieties of fruits and vegetables obtain their flavors from where they are grown, soil content, sunlight, rainfall and when a fruit is picked are all factors in plant flavor. Greenhouses and fertilizers and mechanical pickers can not imitate these conditions. Have you noticed that some 'fresh" fruits and vegetables just don't seem to have any flavor? We have gone from the individual farmer to large corporation farming - where a single variety of crop is grow on overused land with an abundance of fertilizers, pesticides and machinery to harvest the crop.
In the last half of the twentieth century the average crop yields of rice, corn, and wheat doubled or tripled and the number of tractors went from seven million to twenty-eight million (Ruse, 136). Large farm production drove down the prices of food while the farmer's costs rose. The hey-day of the family farm was over in developed nations and huge differences in food production exist between developed and undeveloped countries widened (Pringle, 3). The driving factor in the development of genetically modified food has been a desire to feed the worlds growing populations and the effort to keep down costs. Few people know how to farm today and are highly dependent on farmers to produce their food for them. As farming has become more and more industrialized, science has helped farmers reduce the difficulties of agriculture through development of machinery to reduce labor costs and through modification of the crop to reduce other factors. Breed varieties resistant to disease, produce larger yield and more flavorful varieties have been engineered to please the public.
The most famous GMO is the modification of corn to reduce pesticide use by inserting a gene that resists herbicides. Monsanto foods had developed a product called Round-up in the 1980"s containing a non-selective herbicide called glyphosate (Mchughen, 38). Glyphosate inhibits ESPS synthase, an enzyme, in almost all plants, except petunias. . Monsanto scientists were able to isolate and clone a petunia EPSP synthase gene, modify it and insert it - thus making the first herbicide-tolerant plant, a corn that could survive Round up (McHughen, 40). This began the competition for patented seeds which has substantially reduced the variety of seeds available in agriculture. Soon afterwards, a gene bank was formed. Here researchers could deposit seeds to grow specific types of plants. Deposits and withdrawals are free. The advent of genetic modification was upon us.
The most pressing issues early on in genetic modification were for producing high yield crops; early maturing crops, enhanced weed control and overall grain yield. However, managed environments can produce can produce herbicide resistant plants, the so-called 'superweeds'. Fortunately, these plants are usually resistant to only one herbicide, not all herbicides (MuHughen, 127).
All new products carry some degree of risk; developers of conventional products do not indicate their products are risk free either. We can only compare the products and make our own informed decision- GMO's are a matter of risk assessment.
GMO's; scientific issues
Genes change all the time and can affect the phenotype or the functional of an organism drastically. So what is the controversy in manipulating genes to produce better products?
Food produced on a large agricultural farm is consumed at our tables. What are the scientific issues that the public needs to be concerned with? The idea of being able to move genes between species initially caused alarm in the scientific community and a ban was recommended on experimentation that involved placing a gene from one species into another (Ruse, 34). The fear was that "super bugs" would take over naturally occurring organisms. After a few years of strictly controlled testing, the Institutes of Health in the mid 1980's lifted the ban because they found adding almost any gene to bacterial cells only weakened the organism. Top scientists agreed that modified bacteria cells were not dangerous (Ruse, 35). The Environmental Protection Agency (EPA) and Food and Drug Administration (FDA) took co-authority over the business of genetic modification. Research began on moving genes between species, bacteria were used to produce human insulin for diabetics and experimentation began on modifying foods. A major player in the business, Monsanto Foods, Inc. developed a plan to introduce biotechnology to the public. To solve political problems a document was drawn up encourage support for biotechnology from regulators around the world. Officials recognized early on that while public opinion regarding biotechnology used to develop new drugs for those in need would be acceptable. However, the modification of plants and animals, moving genes between species, would not go well with consumers. The leaders in biotechnology at the time agreed that keeping an open dialogue with consumer groups and important stake holders would be the best way to ensure support (Ruse, 37).
The government's position was loose and different aspects of genetic modification were shared by the FDA and EPA. Monsanto, under new leadership lobbied heavily in Washington and pushed through genetically modified food policies. As a result, many genetically modified foods made it to market ignoring religious, social, cultural, ethical and economic issues (Ruse, 37). Scientists at the FDA Center for veterinary medicine concluded that the move was premature to accept genetically modified foods and that toxicity studies were necessary. The industry dismissed the worries and stated that foods could be tested by the producers of GM foods and that labeling of GM foods would only mislead the public (Ruse, 38). The FDA's hands-off policy led to hundreds of groups protesting and began the movement against GM foods and biotechnology. By 1992 a petition reached the government offices that demanded a change in the GM food policy to include toxicity testing and specific labels on any food produced that had been modified in any way. GM foods had reached the market without any indication that they had been genetically modified. The public felt duped when they discovered that GM food had been in the marketplace without them knowing. There were many questions from a public that was naive about biotechnology. Questions like whether a genetically modified food makes a food product more allergenic remains to be answered. Until we fully understand the allergenic process we can not make this claim. Certainly, careful consideration and further monitoring needs to be continued. The controversy about genetically modified foods will endure and will keep the questions coming. Recombinant DNA technology will continue and will provide opportunity and scrutiny of practice and application. As we continue to try to provide food for all people we will learn more about how genes perform.
There have been many environmental concerns with the advent of GM Foods. Will superweeds be generated by gene flow when plants able to resist weeds are planted? Can the spread of pollen contaminate far-off fields making transgenic traits appear in other species of plants? In the organic way of farming cow manure is spread to fertilize plants. If the concern is use of massive tracks of land for organic farming, then shouldn't there be concern for the amount of land needed for cows to graze on to produce the manure to fertilize crops? What is the best way to produce food? The future of agriculture will need to be flexible and diverse in the technologies that are used today and those that can be developed in the future to bring to market safe and healthy foods.
To slow the ongoing loss of biodiversity we will have to be diligent in our monitoring of the preservation of wetlands, rivers, lakes and coral reefs. The destruction of tropical rainforests, mangroves and open spaces must be stopped (Ruse, 231). We do not yet know what we are destroying and we will never know what we have lost. Man must look to the whole biosphere and considers its preservation as well as its development.
Some scientists are working on a new method of improving crop yield; this is the science of Transgenomics. Transgenomics is a method halfway between the natural evolution of a plant and artificial genetic modification (Pringle, 196). The belief is that similar plants and animals have evolved to have certain traits, and then there must be a way to induce them to switch on or off certain traits to achieve the same type of results as we have by implanting genes from other species. Scientists have know for decades that corn has its own transposons, genes that appear when the plants is under stress and cause a genetic reorganization to help the plant survive (Pringle, 198). To manipulate a plant to cause a certain trait to appear is the aim of this new science. These new hybrids would theoretically have been forced to 'evolve' without insertion of a foreign gene. Perhaps this will be the farming method in the future. What label will be put on this type of foods- genetically evolved? The future of agriculture is still uncertain. What is certain is that we must continue to ask questions about the source of the goods we use and consume.