Genetically Engineered Foods

General schematic of GM crop production

Genetically modified foods (GM foods or GMO foods) are foods derived from genetically modified organisms (GMOs). Genetically modified organisms have had specific changes introduced into their DNA by genetic engineering techniques.

Generally, this term refers to food crops that have been altered using a variety of molecular biology techniques in order to provide them with either new or enhanced characteristics. Examples of such enhancements of modifications are herbicide tolerance, pesticide resistance, greater nutritional content or increased tolerance of cold temperatures. Genetically modified organisms (GMOs) can also be referred to as transgenic organisms. Transgenic simply means that the organism’s genes come from more than one source.

Method

Genetic modification involves the insertion or deletion of genes. In the process of transgenesis, genes from a different species are inserted, which is a form of horizontal gene transfer. In nature this can occur when exogenous DNA penetrates the cell membrane for any reason. To do this artificially may require transferring genes as part of an attenuated virus genome or physically inserting the extra DNA into the nucleus of the intended host using a microsyringe, or as a coating on gold nanoparticles fired from a gene gun. However, other methods exploit natural forms of gene transfer, such as the ability of Agrobacterium to transfer genetic material to plants, and the ability of lentiviruses to transfer genes to animal cells.

The method to introduce new genes into plants requires several important factors such as specific promoter, codon usage of the gene and how to deactivate the gene. The specific promoter must pertain to area that we want the gene to express. For instance, if we want the gene to express only in the rice instead of the leaf than we would only use an endosperm specific promoter. The reason is because we only want our transgenic genes to express only in the rice and not the leaves. The codon usage of the gene must also be more optimize for the rice since there are several different codons for each of the 20 amino acid. The transgenic genes should also be able to be denatured by heat in order for human consumption.

Transferring the gene

Let us use the insertion of B. thuringiensis genes into corn as an example. In order to cut out the gene of interest in the bacteria, its total DNA is isolated. Special enzymes, called restriction endonucleases, act as scissors to cut out the desired gene. These enzymes are sensitive to the DNA sequence and will only cut DNA at specific spots. There are many different enzymes that cut in different places, so the enzyme used depends on the sequence of DNA surrounding the desired gene.

Once the gene is cut out, scientists must make an “expression cassette.” This consists of additional DNA surrounding the gene so that the corn cell knows where the gene of interest begins and ends. The part that tells the corn cell where the gene begins is called the promoter and the end, the terminator. Once the expression cassette has been made, it is inserted into a plasmid. The plasmid is a parasitic circle of DNA present in bacteria. By putting the cassette into a plasmid, millions of copies of it can be made. These copies are then introduced into the host cell and get inserted into the genome. Cells which have successfully incorporated the foreign gene into their genome are then expanded in cell culture and used to generate new plants.

Development

The first commercially grown genetically modified whole food crop was a tomato (called FlavrSavr), which was modified to ripen without softening, by Calgene, later a subsidiary of Monsanto. Calgene took the initiative to obtain FDA approval for its release in 1994 without any special labeling, although legally no such approval was required. It was welcomed by consumers who purchased them at a substantial premium over the price of regular tomatoes. However, production problems and competition from a conventionally bred, longer shelf-life variety prevented the product from becoming profitable. A tomato produced using similar technology to the Flavr Savr was used by Zeneca to produce tomato paste which was sold in Europe during the summer of 1996. The labeling and pricing were designed as a marketing experiment, which proved, at the time, that European consumers would accept genetically engineered foods. Currently, there are a number of food species in which a genetically modified version exists.