mRNA – an acronym most people had never heard of 18 months ago - is now a household term thanks to news coverage of the vaccines developed to combat COVID-19. But what is mRNA and what does it have to do with vaccines?
Several current COVID-19 vaccines use the mRNA molecule to induce immunity. Image credit: Daniel Schludi on Unsplash
To explain the molecule, it is easiest to start at the beginning with a bit of background on how a cell works. Our body is made up of billions of microscopic cells which each perform a function to keep us alive. Cells do this by making proteins – enzymes which break things down like amylase in saliva, or structures which hold us together like collagen in skin. Every cell makes different proteins, and is directed by DNA. DNA (deoxy-ribose nucleic acid) is a long string of molecules that contains encoded information on how to make each protein in sections called genes. Similar to a folder in a hard drive, each gene contains all the “files” or instructions for a protein. However, DNA can be quite delicate and if anything damages it, normal healthy cells can develop into cancer, or can die. As a result, DNA is kept safely contained within a bubble called the nucleus inside a cell. So how does the DNA instructions get to the cell factory to be made into proteins?
Stained cells showing the nucleus in blue. The nucleus is where DNA can be found within a cell. Image credit: CDC on Unsplash.
This is where mRNA enters. mRNA stands for messenger RNA (RNA: ribonucleic acid) and is similar to DNA in that it encodes instructions, however it is meant to be a temporary messenger. It is a mirror-image replica of the gene sequence from the DNA that travels out of the safety of the nucleus and carries the instructions to the factory within the cell (the ribosome) that creates the proteins.
For a comparative explanation, I am a very messy cook. When I cook, I often splatter sauces, oil and juices all over the kitchen bench, and all over any cookbooks in the area. In this case, think of the cookbook as the DNA with instructions on how to bake my cake. The cake is the finished protein, ready to be eaten. To help protect my “master copy” of the recipe in the cookbook, I often copy the recipe onto a post-it note. This note is meant to be temporary - I can spill whatever I like on it because it will get thrown out after, and my cookbook is safe from stains.
mRNA is the post-it note. It is the sacrificial molecule whose sole purpose is carrying a message and then it is broken down. mRNA is a vital part of our cellular processes and without it, our cells would collapse and we would die.
The process called protein synthesis within a cell. The gene sequence on DNA is used to create an mRNA copy. This copy is used as a template to create proteins. Image created using BioRender.com
So what does this have to do with vaccines? Two of the recent COVID-19 vaccines produced by Pfizer and Moderna are termed “mRNA vaccines”. For anyone not familiar on how vaccines work, I will provide a more in-depth explanation in a future post. For now I will summarise like this: vaccines teach your body what a particular pathogen (virus/bacteria) looks like. Once your body knows how to recognise it, it will begin to defend against it much quicker; resulting in less severe symptoms and a more favourable outcome. Vaccines can be made in a few different ways, the most recent of which is the mRNA vaccine. These vaccines inject mRNA, the normal messenger molecule of all cells, but instead of carrying a gene sequence message from our DNA, the molecule carries a sequence mirroring part of the target virus (and thus imitating the regular mRNA that would normally be generated from our DNA). This means when the vaccine mRNA reaches the ribosome, instead of making a protein for our cells, it makes a viral protein. In the case of Moderna and Pfizer, it makes a protein called the spike glycoprotein – a protrusion from the surface of the virus. This is the first viral protein that an immune cell will encounter, so is a great choice to teach the body how to recognise the virus. Because of the unstable and temporary nature of mRNA, once it has delivered the message it degrades – that means the vaccine mRNA does not last in our body more than a few hours. It does it’s job of delivering the message and dissolves away.
Although mRNA vaccines are a relatively new technology, they are based on a deep understanding of the normal processes inside our cells. Hopefully this blog post helps you also understand a bit more about the role of mRNA and how we have repurposed it to help fight viruses.
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