I wrote the following in response to someone on social media who said Round-Up gets into the DNA of GM crops. Several other people in the same thread made the same claim. I know a great number of people out there believe a whole host of things about genetically modified organisms for one reason or another. In most cases, the people don’t have a basic background in the issues at hand. That would be fine if the topic stayed on safety – we can all read the summaries of scientific papers – but time and time again, people insist on making outlandish claims that betray an ignorance of biology. Here’s what I wrote:
DNA is composed of four nucleotides: guanine, cytosine, adenine, and thymine (plus a few things to help glue it all together). These are the molecules that compose that double-helix structure we all know so well. Guanine (G) and cytosine (C) bond while adenine (A) and thymine (T) bond. Each strand of the double helix has some given order of these letters (GAACATTAC) that goes on for some time. The corresponding strand has the matching letters (CTTGTAATG). These are called base pairs. Every three base pairs correspond to an amino acid. TGG, for example, corresponds to the familiar tryptophan we find in our turkey every Thanksgiving.
That’s a crash course in what DNA is. Next, it’s necessary to understand what a gene is (on a biological level). Knowing that DNA is composed of nucleotides that form an amino acid every three base pairs, we can understand what a gene is. Those base pairs continue to form a double helix structure between start and stop codons. These are specific sequences of 3 base pairs which indicate where a gene begins and ends:
AUG GAC TGA AAA GCG TAG
The start codon is AUG and the stop codon is TAG here. All the letters in between code for amino acids. (Those letters tend to get into the hundreds or thousands.) These amino acids are folded into a specific 3D shape that catalyzes reactions. If there is some sort of error anywhere along the line, the 3D shape won’t form correctly and thus won’t work. That’s what Round-Up does to most plants. If you spray it on some weeds in the cracks of your driveway, you’ve inhibited the synthesis of necessary amino acids plants use. Without those amino acids, the ultimate 3D structure is mal-formed, if it forms at all.
I’ve bored you with all this because I want to be clear: Round-Up is not present in the DNA of GMOs. GMOs are able to synthesize the aforementioned amino acids via a naturally occurring gene that has been inserted into them.
In other words, the active ingredient in Round-Up is glyphosate. This is not a nucleotide and it does not attach to or compose DNA. It attaches to a specific enzyme (which is produced by DNA) and inhibits a pathway that is only found in plants. (That is, a given enzyme is needed to catalyze a given process, but it is inhibited from doing so. It’s similar to a key being needed to open a door, but someone has stuffed the keyhole with other junk. You aren’t opening that door.) As a result, a number of necessary amino acids cannot be synthesized, causing the plant to die. GM crops have a slightly different enzyme, however. Recall that enzymes form specific 3D shapes. The enzyme in GM crops form a different shape than the enzyme in other crops. That means the glyphosate cannot attach, and thus it cannot inhibit the synthesis of those amino acids.
At no point is Round-Up a part of anything’s DNA. It couldn’t be. The double helix structure works with nucleotides. That’s just what DNA is. Glyphosate is a synthesized molecule which interrupts the enzymatic process of plants. Those interrupted enzymes are products of genes and they also contribute to the production of amino acids which are necessary for the replication of more genes.
Nothing But Science 