Preface
Genetically Modified Organisms (GMOs) are a particularly controversial topic. They bring out heated discussions at dinner tables, lab meetings and congressional hearings alike. These discussions and can (along with discussions of religion or politics) leave people with bruised egos and sometimes even strained relationships. This post is written for both those who support and oppose GMOs, as it is intended to be a purely fact based discussion of the science behind how GMOs are created. Understanding the principles behind these constructs leads to a more informed stance for or against the creation and use of these organisms (Plants, Bacterium etc.) I will not at any point in this article take a stance on the creation or use of these organisms, nor will I attempt in any capacity to sway your personal opinion on them. I only seek to increase your understanding of what they are, and how they are made. So, let us begin.
What is a GMO?
A GMO can be classified as any organism which genetic manipulation was performed on, resulting in the expression of a protein to cause a desired phenotypic change (phenotype is a physical property of an organism, size, color, sugar content, heat tolerance, smell, taste, metabolic rate, internal protein composition…etc). The very first example (1982) of a GMO approved for use in generation of a drug for humans was Escherichia Coli (E. coli, Figure 1).
Figure 1: An Electron Microscopy Image of E. coli
Source
Researchers used a technique called recombinant gene expression to create the human protein insulin (which you are likely familiar with as important in blood sugar regulation) artificially using the E. coli’s protein production machinery discussed in Science Lesson: DNA Part 3. Prior to the generation of the GMO E. coli, diabetics were provided with insulin from a pig as it is similar to human insulin. However now people who take insulin for their diabetes all use GMO produced insulin. It is sold under the brand name Humulin.
However, GMO bacteria are likely not why you are reading this article. You’re here for a discussion on GMO plants. GMO’s that may end up on your dinner plate. The very first genetically modified food approved for sale was the (ridiculously named) Flavr Savr tomato in 1994.
The Flavr Savr Tomato
The Flavr Savr tomato was one where an anti-sense gene was introduced which inhibited the production of the protein polygalacturonase (this is a protein which is responsible for breaking down a sugar called pectin in the cell wall of the tomato and aids in its ripening). How does this work? If you recall from Science Lesson: DNA Part 3 when discussing how proteins were made we talked about how the first step was the production of a single stranded RNA out of the DNA. The single RNA strand that is transcribed from a gene is the “sense” message for that gene and will allow for the ribosome to assemble the protein it encodes for. An anti-sense gene will also create an RNA molecule, however this one is the compliment to the “sense” message. The purpose of this RNA is not to code for a functional protein but rather to bind to the sense RNA resulting in the formation of a double stranded RNA molecule (Figure 2). As expression of a protein requires that the RNA be single stranded, this binding limits the amount of RNA available to create the protein. Effectively reducing the amount of that protein available (this sort of technique is referred to as RNA interference or RNAi for short).
Figure 2: Silencing Protein Expression with Anti-Sense Genes
Source: Self
What this means for the tomato is it will produce less polygalacturonase, and if less is produced then less is available to break down that pectin in the tomato’s cell wall and thus the fruit ripens more slowly.
Now let’s be science students and ask some pertinent questions! Where does this anti-sense gene come from? How does it get into the genome of the tomato? To answer the first question we should discuss what molecular biologists think it means to be a gene. As for how genes are manipulated that is answerable by discussing recombinant DNA technologies.
Getting Philosophical About Genes
The goal in the creation of the Flavr Savr tomato was to shut down the production of polyglactruonase, the easiest route to achieve that is to limit the amount of RNA generated from its gene. To a molecular biologist, a gene is just a set of instructions to code for a protein. It doesn’t have any inherent ties to the organism from which it was derived, it was just found there, performing a purpose for the cell. Bacteria pick up and lose genes from many sources over the course of their short lives. Let’s look at E. coli as an example. The core genome of E. coli is only 2200 genes, these are found in all known E. coli. However the pangenome (the list of all known genes in all known E. coli) contains over 13,000 genes. What this means is that while it takes 2200 genes to make all of the proteins necessary to be an E. coli cell, most cells have many other genes, and many of those genes are unique to certain E. coli and in all likelihood did not come from E. coli at all. To these cells, it would appear, that genes are also just a set of instructions that you pick up if you need it (in the cells case, to survive).
Back to the original question, where does the anti-sense gene for polyglactruonase come from? The answer is nowhere. It is not found in nature, it is an artificial construct assembled to cause a change in phenotype. Molecular biologists, like the E. coli just addressed a wanted change in phenotype by adding a gene. Is this okay to do or not okay? This is not a question which will be addressed, I will leave that debate to you and others.
Recombinant DNA Technology (producing a gene in an organism of interest)
One of the ways genes are artificially expressed in an organism of interest is through the use of plasmids in short these are small circular double stranded DNA constructs (Figure 3).
Figure 3: Bacterial Genomic DNA Vs. Plasmid DNA
Source: Self
They are readily taken into cells and are easy to assemble in the lab via use of various DNA replication enzymes in test tubes (I could make a whole blog post discussing molecular biology, PCR, gene assembly, etc. if you are interested). Into a plasmid the researchers gene of interest is placed, along with a promoter genes and promoters are discussed in Part 3 of my DNA series. The promoter needs to be the correct sequence for identification by the RNA polymerase of the cell type you wish to express the gene in. In the case of the Flavr Savr, a promoter specific for tomato RNA polymerase was used. The anti-sense gene was placed downstream (after the promoter) such that the RNA polymerase would generate a single stranded piece of RNA from the anti-sense gene. The plasmid is transformed into a bacterium (Agrobacterium) which then is allowed to infect the plant. The bacterium delivers the plasmid to the plant and the gene of interest is expressed. Agrobacterium does not infect all plants thus other methods have been developed to deliver genetic material including a “gene gun” which as you would expect, shoots the genetic material into the plants cells.
There are a few other ways which genes can be incorporated into an organism, not all require expression from a plasmid (but usually still involve the use of one for easy delivery). Molecular biologists can also hijack the homologous recombination pathway Science Lesson: DNA Part 5 and add homologous regions to a section of the genome found in the organism of interest to either side of a gene they would like to incorporate. A very small percentage of the time a cell will recombine those homologous regions into where they match in its genome via the error correction pathway that we previously discussed. When this happens the gene is carried along and becomes a part of the genome of the organism. What is unique about this is that the incorporation is more permanent, and will remain in the organism’s genetic code, rather than just sitting on a plasmid that may or may not be discarded by the cell.
Concluding Remarks
We have discussed a brief history of GMO’s and talked about some of the science behind their construction. I have utilized an older example the Flavr Savr tomato (a commercial flop) as a tool for discussing this technology. The logic behind this particular choice was its low level of controversially when compared to some other GMO food examples. The intention of this post was to discuss the science of the construction of genetically modified organisms, and provide you with a better understanding of what is done in the lab to produce them. Recombinant DNA techniques have been used to generate a multitude of different GMOs each with their own unique set of merits and/or concerns, a general understanding of the science is imperative to fully grasping what each unique set of modifications is being used for. I sincerely hope that my post and any subsequent discussion will allow you to engage in more informed discourse (whether that be in favor or against) about genetically modified organisms (and foods).
If you like my work, please consider giving me a follow: steemit.com/@justtryme90. I am a PhD holding biochemist with a love for science. My future science blog posts will cover a range of topics in the biology/chemistry fields.
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I'm not going into the GMO debate here. I wanted to say "good job!" explaining a very complex matter of generating a GMO to those without biology/biochemistry background. You would need a lot more posts to explain every detail, but this is pretty good. So, good job! :)
I would just add that the genetic engineering field has made considerable progress, some very recently (read about CRISPR-Cas system). However, there is a lot we do not understand about how the cells work, which is why scientists are extra careful when it comes to application which might affect humans or animals. Of course, mistakes can be (and were) made occasionally.
Oh I've used Cas9 in the past. ;)
This is also a blast from the past. I forgot I wrote this. :)
Man I could really have used some formatting lessons back here.
I realized the post was 2 years old, but the subject is still hot and I just had to say something :) I guess a little reminder won't hurt.
Cas9 is amazing, isn't it? When it works on your target sequence, that is. A real game changer for all of us in the lab.
Thank you for this, I am a tomato grower, If i had a bitcoin for every consumer who asks me if I grow GMO tomatoes, then doesn't know what GMO really is I would be a rich man!
Most of the public confuses GMO and hybrids. Thanks for the clear info!
Quite welcome. A basic working knowledge of prominent science related topics is basically a must in modern society. Will only become even more important as technology keeps getting more advanced. Hope to do my part to increase peoples general knowledge levels.
man, this one is a heated debate...
unfortunately, there's alot of misinformation that's spread via social media, and GMO's have gotten a pretty bad rep, based on what's probably alot of faulty "science." I was deep into the whole anti-GMO conspiracy camp; thankfully, I eventually cracked out to see the other side of the story...
I found this was one short, fun video in particular that really clarified alot:
Also found The Genetic Literacy Project to be a great source of balance, science-based info - both their website and Facebook group...
That is indeed a pretty nice video, and makes a convincing argument in favor of the technology. :)
I love GMOs! Yum Yums for my Tum Tum.
What a great article/post! High quality stuff here, so glad you're here to teach us!
Thank you! I appreciate the support, it truly means a lot to me. :)
GMO's could be a metaphor for what is being created thru socialism, communism... Things/ people look glossy and perfect on the surface, but are empty/ dead within! These contradictions also seem to be directly proportional!
I went into #science to post my article, to find by surprise that a VERY related post was also published there.
Nice approach to the topic, upvoted.
Upvoted yours as well. It's an important topic, and I think a significant amount of discussion on it is a good thing. Knowledge and being informed on these broad scientific topics is crucial going forward. Keep up the posting!
Your article is very complete and reliable. I am a new member
Thank you for your kind words.
same as sir, I liked your article
As usual, a very nice and complete post. Thanks a bunch!
Concerning GMOs debates, the main problem is in my opinion that one can find many pieces of information on the internet and it is not clear which is correct and which is wrong. Many people then build their opinion on wrong information. It is a bit like vaccines at the end... We are dealing with curate's eggs.
Thank you for your kind words @lemouth. I will stick to discussing the science and let others tackle the remaining good/bad type discussions. If someone wants to talk with me on some scientific evidence pertaining to this technology I will gladly read the material and give my take on what was trying to be done and whether I think the experiments were performed well.
Science is great. I like your approach of not having a bias, and presenting the facts.
Combining science with greed is not so great. I argue that Monsanto has little concern for the future of the planet or human health. I wrote this article about their pesticide roundup, and would love any scientific feedback:
https://steemit.com/california/@doyoueatdolphins/i-don-t-like-roundup-or-monsanto-do-you
Monsanto is not a monolith, I'd argue that the scientists there do have concern for the future of the planet and human health. Nothing is perfect, however the concerns over glyphosate are overblown IMO. Is it great for you? Probably not. But a lot of things aren't great and we go out of our way to ingest them.
Do you know or have you met any scientists working at Monsanto? You do raise an interesting point that there are certainly reasonable thinking people that work for Monsanto. Or at least we can hope. Your comment reminds me of thinking of the zoo as a place that is so bad for animals, meanwhile they employee so many biologists who love animals more than most folks.
I actually don't know on a personal basis anyone who is directly employed by Monsanto. I do know people who have collaborated on projects with them (like studying the enzymatic working of glyphosate, it inhibits the enzyme EPSP synthetase).