I'm sure you've heard the term GMO being thrown around a lot lately. It seems like every week there's a new story about GMO crops. Some want to ban them completely, others want to label any foods that use them. Obviously there are a lot of strong opinions out there, and a lot of unclear or even false information to boot. Nevertheless we all will be faced with important decisions about GMOs sooner or later. Whether it’s at the polls or in the grocery store, you need the best information you can get in order to make the right choice for you. Our goal at FeedtheDataMonster is to educate and inform. To that extent I’d like to try to clear up some of the misconceptions. I'm not writing this to advocate for or against the use of GMO crops. I'm not here to tell you about the companies or institutions that make them. I am writing this piece to give you the most accurate information I can. I will leave you to form your own opinions.
What exactly is a GMO?
Let's start with the basics. The term stands for Genetically Modified Organism; that's a pretty vague phrase. It can refer to fish that have pigmentation from corals and jellyfish, bacteria that have been modified to produce human insulin, or mouse cells that make monoclonal antibodies (which are used in a wide variety of medical treatments). Most of the time, however, the controversy is around the plants that we grow for food.
Ever since the invention of agriculture – some 12,000 years ago – humans have been modifying the plants we use for food. Farmers save the seeds from the biggest and most fruitful plants and use those the next year, creating larger and more successful crops. Some people also breed select individuals together in order to produce offspring with a combination of traits. Corn (Zea mays) is perhaps the best example. What we eat today is nothing like natural corn. In fact scientists aren’t entirely sure what corn was like before humans got involved (you can read more about that here). Not only is modern corn a lot bigger, we have different varieties (or cultivars) for different purposes. There’s sweet corn that we eat, feed corn that livestock eats, and even specific varieties that are best for popcorn. Beyond just food uses, some cultivars may be more resistant to drought, more cold tolerant, or grow better in a particular soil type. What was one single species in nature can yield an astounding variety of cultivars. Vitis vinifera (the most popular grape for winemaking) has thousands of varieties. This process has even led to seedless fruits like bananas and watermelons. People have bred plants that can no longer breed, pretty amazing when you think about it.
* DNA – Deoxyribonucleic acid. This is the molecule responsible for storing genetic information.
* Gene – A specific sequence of DNA that holds the code for a specific protein.
* Protein – A large molecule that is produced by translation of a gene.
* Enzyme – A specific class of protein that acts a catalyst for chemical reactions.
* Genome – The entire collection of genes that an organism possesses.
* Plasmid – A small circular DNA molecule that can be passed between cells.
All of those foods are modified from their natural state (also called wild type), but that's still not the kind of modification that I'm here to talk about. For the purpose of this article, when I refer to GMOs, I'm talking about transgenic food crops, or plants that have DNA from other organisms. That’s generally where the controversy lies.
Now that we’re on the same page, let’s get to know a bit about GMOs, starting with the methods used to modify an organism.
How are they made?
One of the most common methods of modification is the use of the gene gun. With this method, microscopic slivers of gold are coated with plasmids containing the desired gene. These are shot (usually with pressurized air) at a culture of embryonic cells of the target organism. Some of the gold may hit a cell, land in the nucleus, and deposit their DNA coating. Those cells will then carry the new trait. Needless to say this approach is very random and doesn’t always work. Most of the cells don’t get the new DNA, some of them are destroyed by the gold, and some are scattered and lost by the impact. When the process works, then the researchers only have individual cells. Those then need to be treated with hormones to get them to divide, differentiate, and grow into fully developed plants that can pass their new trait on to their offspring. This process has also given rise to my new favorite science term: biolistic gene transfer.
Another common method uses the same strategies that a virus uses to hijack a cell. When a virus infects a cell it inserts its own DNA into the host’s DNA. The basic process (there are actually a few different mechanisms) uses a restriction enzyme. This enzyme finds a specific DNA sequence and cuts the strand along that sequence, leaving an attachment site that another piece of DNA can stick to. The viral DNA has a matching attachment site so it can easily be incorporated into the host’s genome. The new genes contain the instructions for making copies of the virus, and the infected cell becomes a virus factory. If one were to replace the viral DNA with DNA that codes for a desired gene, then the virus becomes a very precisely targeted method for creating transgenic organisms (a scalpel to the gene gun’s shotgun). As you may have guessed, this method is a lot more expensive and more technically difficult than the gene gun, so both methods are still widely used.
This list is by no means all-inclusive, and as time goes on, scientists will undoubtedly develop even more methods for altering the DNA of an organism. The thing to remember about any method of genetic modification is that it inserts one or more genes into the target organism. Genes are sequences of DNA that contain the information needed to produce proteins. Proteins are large molecules which can have a very wide range of functions in a cell. It’s hard to overstate just how many things in a cell are accomplished by proteins. They can be structural: giving a cell its shape (tubulin), or keeping strands of DNA neatly coiled (histones). They can be used as signals, and released by one cell to activate or deactivate functions in another cell. Insulin, for instance, is released by the pancreas and tells muscle and fat cells how to process and store blood sugar. Hemoglobin is the protein in our blood that carries oxygen from our lungs to wherever it is needed. Actin and myosin work together to produce our muscle movements. Some of the most common genes are the ones that produce enzymes. Enzymes are like molecular machines. They can break other molecules apart (like digestive enzymes) or combine them into new compounds. That’s why genetic modification is such a potentially powerful tool (and such a hotly debated subject). Just about everything that any cell can do comes from a protein that is encoded in a gene which is made of DNA.
Be sure to come back and read the next post in the series. I’ll be looking at some specific transgenic crops to see just what genetic modification can do.
Some further interesting reading for you.
- Genetic Science Learning Center. "The Evolution of Corn." Learn.Genetics 29 April 2015 http://learn.genetics.utah.edu/content/selection/corn/
- Gene Guns http://www.bio.davidson.edu/Courses/Molbio/MolStudents/spring2003/McDonald/Gene_gun.html
- Transformation Methods (University of Nebraska Lincoln) http://passel.unl.edu/pages/informationmodule.php?idinformationmodule=958077244&topicorder=1&maxto=7&minto=1