Joe over at The View from North Central Idaho asks how mRNA works. Let me give a quick and simplified explanation of how DNA and mRNA work with each other. Let me reach way back to my undergrad classes on cellular and molecular biology to explain this a bit.
Please excuse me if I make minor errors. It’s been a few years since I took these classes. This is also a greatly simplified Cliff’s notes version of several semesters of college biology classes. Even though simplified, the subject is complex and will make for a bit of a long post.
DNA and RNA are nucleic acids. They are long, chainlike molecules that can encode information that allows the manufacture of proteins and are required for all life as we know it. Think of them like incredibly dense storage drives that hold all of the information needed to build a living organism. Everything from how tall you are, to what foods you like, to what subject you enjoy studying in school is affected by what is encoded in your DNA. Every trait that is you is saved on this biological hard drive. With the exception of identical twins, no two people have the same DNA.
DNA is a template from which RNA can be made. The process where RNA is created is called transcription. The entire process is controlled by enzymes called RNA polymerases and occurs in the cell’s nucleus. Since the nucleus in eukaryotes is enclosed in a membrane, the DNA cannot leave that nucleus, so messenger RNA needs to be created in order for a cell to manufacture proteins.
The RNA molecule that is produced is a near mirror image of whatever part of the DNA molecule was used as a template. When a messenger RNA (mRNA) molecule is made, that mRNA molecule then leaves the nucleus of the cell and enters the portion of the cell where proteins are made. The process of using RNA to make a protein is called translation.
One of the basic tenets of biology is that this is a one way process. DNA makes RNA, but RNA cannot change or make DNA. There has been one exception to this: a virus.
A virus is not a living organism. A virus (to simplify things) is essentially just an RNA molecule wrapped in an envelope made of other molecules. By itself, it cannot do anything, not even reproduce. The way that a virus replicates is that the virus uses an enzyme called reverse transcriptase to replace a part of the host cell’s DNA with a copy of itself. That corrupted DNA then causes the cell to create copies of the virus, which then go on to infect other cells.
If this change to DNA happens in a reproductive cell, the change in DNA can be passed on to that organism’s offspring. If it doesn’t happen in a reproductive cell, it isn’t passed on. It was that simple when I went to college.
That was how things were believed to work until about a year and a half ago. Then scientists made a new discovery. There are circumstances where DNA can be modified by RNA molecules.
When a new cell needs to be made so that an organism can grow in size, or a cell is needed to replace a damaged one, a copy of the original cell’s DNA must be made. There are 14 polymerases which control this process in mammals.
When DNA is copied, there is a built in error correction system that allows mistakes in the copying process to be corrected. The enzyme that controls this process is called polymerase theta. Polymerase theta can correct errors and damage that occurs to DNA inside of the cell.
It turns out that polymerase theta also has the ability to take pieces of RNA and use those pieces to rewrite parts of the DNA. The paper describing this was just published in June. This is huge- for the first time ever, we now know that human cells can rewrite DNA using RNA as a template.
So to answer Joe’s question:
It sounds like the DNA of a plant is being modified so that the plant cells themselves manufacture mRNA vaccines. Thus, a person eating the plant will ingest mRNA that will act as a vaccine. I don’t think the mRNA in the plant will rewrite the DNA of the person who consumes it.