MRNA Vaccines

Messenger RNA, or mRNA, is a single-stranded molecule that carries the genetic instructions needed to build proteins in our cells, according to Wikipedia ^[3]. Think of it as a temporary copy of genetic code that tells your body's machinery exactly what to make. Understanding how this process works is essential to understanding how these new vaccines function in your body.

Here's where it gets fascinating. mRNA is created during a process called transcription, where an enzyme named RNA polymerase converts a gene into a primary transcript ^[3]. This is exactly what your cells do naturally every day — they're constantly making mRNA copies of genes to build the proteins they need. But once that mRNA is created, the real work begins.

Translation is the biological process that converts those genetic instructions carried by messenger RNA into chains of amino acids linked together by peptide bonds, according to the Science Education Resource Center at Carleton College ^[1]. This is where the magic happens — where genetic code becomes actual, working proteins. And the star of this show? The ribosome. The ribosome is the site of translation, matching the base sequence just as RNA polymerase matched sequences during mRNA synthesis.

But ribosomes don't work randomly. They read mRNA instructions in a specific direction, starting from the five-prime end and moving toward the three-prime end, translating that genetic code into proteins. This directional reading ensures your cells produce exactly the right proteins in the correct order.

The genetic code itself works like a language with three-letter words. Each codon—a three-nucleotide sequence—corresponds to a specific amino acid, defined by the universal genetic code that is the same across all living organisms. And here's the crucial part: transfer RNA, or tRNA, molecules carry amino acids to the ribosome and match them with mRNA codons during translation, according to Khan Academy ^[2].

When this process kicks off, three special proteins called IF1, IF2, and IF3 attach to the ribosome's small subunit to form what's called the translation initiation complex near the start codon, according to Learn Science at Scitable ^[4]. This setup positions the ribosome correctly to begin reading the genetic instructions.

Here's what makes this system remarkably efficient: according to the NIH, multiple ribosomes translate each mRNA molecule simultaneously, spacing themselves about 100 to 200 nucleotides apart. It's like an assembly line, allowing cells to produce proteins quickly and in large quantities. And that efficiency becomes crucial when we're talking about how mRNA vaccines work in your body.

The vaccine delivers messenger RNA instructions that teach your cells to produce the spike protein, which is the unique, recognizable part of the SARS-CoV-2 virus that causes COVID-19 ^[5]. After vaccination, this mRNA enters muscle cells and uses the cells' machinery to produce a harmless piece of the spike protein found on the surface of the virus ^[9]. This is why your arm might feel sore after the shot—your cells are essentially working overtime to create these protein pieces.

Once your cells produce the spike protein, something fascinating happens at the cellular level. The spike protein binds to a receptor called ACE2 on the cell surface, and the cell's own protease, TMPRSS2, then cuts open this spike protein. This crucial step mimics exactly what happens when the actual virus tries to enter cells naturally, which is precisely what your immune system needs to see in order to build a strong defense.

Some of these spike protein molecules get stuck on the cell's outer membrane, creating a training ground for your immune defenses. This positioning helps your immune system learn to attack SARS-CoV-2-infected cells directly and pump out antibodies that neutralize the virus before it spreads. Your immune cells spring into action, producing the spike protein and displaying it on their surfaces, which triggers your body to generate antibodies specifically designed to fight the COVID-19 virus ^[7].

The spike protein itself contains special markers—B-cell and T-cell epitopes—that trigger immune cells to create these protective antibodies ^[11]. This dual defense system is crucial because it means your body can stop the virus at multiple points in its attack. COVID-19 mRNA vaccines show good tolerance and may be better at eliciting a rapid antibody response compared to other vaccine types ^[8]. This rapid protection matters enormously—if you're later exposed to the actual virus, your immune system can recognize and attack it before it infects healthy cells or causes illness ^[6].

Both the mRNA-1273 vaccine and BNT162b2 encode the spike protein as their target antigen ^[11]. By focusing on this shared target, both vaccines help protect millions of people against the same coronavirus threat.

Thanks for listening to this VocaCast briefing. Until next time.