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What is mRNA? Definition, Structure, and Function

If you're wondering, "What is mRNA?" you've come to the right place! In simple terms, if the DNA is the master blueprint of life located in the nucleus, mRNA serves as a disposable copy that gets smuggled out into the cytoplasm. It's like a little messenger, if you will.

In this article, we'll break down the science behind mRNA by answering the following questions:

  • What is the definition of mRNA?
  • What does mRNA do to keep you alive?
  • What is the chemistry behind mRNA?
  • What base is found in mRNA but not in DNA?
  • What is an mRNA vaccine?

Let's get started!

To understand the definition of mRNA, we first have to consider the flow of information that makes life possible: DNA → RNA → Protein.

Your DNA contains precise instructions for your body. To protect this data, your cells keep the DNA safe inside the nucleus; however, ribosomes, which play a crucial part in protein synthesis, are located outside the nucleus.

So, what is the function of mRNA? "mRNA" stands for "messenger ribonucleic acid," and it carries the genetic code from the nucleus to the ribosomes. Unlike DNA, which can last for centuries (given the right conditions), mRNA is temporary: once it delivers its message, the cell destroys it.

If you look under the microscope, the structure of mRNA seems quite similar to that of DNA, but there are a few differences.

  • One singular strand
    While DNA forms a double helix, mRNA is made of a single strand, so it's much more flexible and unstable.
  • The sugar
    DNA uses deoxyribose, whereas RNA uses ribose, which is more prone to breaking down because it has one extra oxygen atom.
  • The letters
    DNA is composed of A, C, G, and T. RNA also uses four letters, but it substitutes T with U!

What base is found in mRNA but not in DNA?

The answer is uracil (U).

In DNA, adenine (A) pairs with thymine (T). In mRNA, adenine pairs with uracil (U) because producing thymine is energetically expensive for the cell.

Another significant difference lies in quantity. A typical human cell contains approximately six picograms of DNA, a number that remains relatively constant. DNA concentration fluctuates a lot — a cell might have zero copies of mRNA for a gene it doesn't need, but thousands of them for another gene.

🙋 To get an idea of what these codes look like when translated, head over to our DNA to mRNA converter.

Let's take a look at the life cycle of mRNA, shall we?

  1. Transcription
    Everything begins in your cell's nucleus. RNA polymerase, a type of enzyme, unwinds part of your DNA to read it, then it copies that genetic information onto mRNA. If it reads A in your DNA, it writes U; if it reads G, it writes C.

  2. Processing
    The non-coding regions, known as introns, are removed, and protective caps and tails are added to protect the coding regions.

  3. Translation
    The mature mRNA molecule moves to the cytoplasm to find a ribosome, which marks the beginning of protein synthesis. The ribosome reads sequences of three letters (codons) from mRNA, while transfer RNA (tRNA) carries amino acids to it. The ribosome then combines these amino acids to form a protein.

🔎 Do you want to learn more about transcription and translation? Go to our dedicated article about this topic, "Is DNA to mRNA Transcription or Translation​?"

What is an mRNA vaccine?

Conventional vaccines come in the form of injecting a weakened version of a virus or just part of it to boost your immune defenses. In contrast, mRNA doesn't contain the virus or protein; it carries instructions, allowing your body to learn to recognize and fight the virus.

Here's how it works:

  1. Researchers build an mRNA molecule to code for a benign piece of the virus.

  2. They package this mRNA in a lipid bubble called a lipid nanoparticle (LNP), which shields this mRNA from your body breaking it down after it's injected.

  3. LNPs enter the cell and release the mRNA into the cytoplasm.

  4. Your ribosomes read the mRNA and start manufacturing copies of part of the virus.

  5. Your immune system launches a defense mechanism and creates antibodies.

Think of mRNA as a hardworking courier. While DNA stays locked in the nucleus, mRNA carries the instructions to your ribosomes, it substitutes thymine for uracil, and disappears once the job is complete. Thanks to mRNA, your cells can efficiently export information about your genetic code to wherever it's needed.

No. mRNA sits in the cytoplasm, whereas DNA is confined to the nucleus. In general, mRNA lacks the "key" to enter the nucleus and the enzymes to write itself back into the genome.

The presence of the extra oxygen atom in the ribose sugar allows it to attack its own structure, causing the strand to break. This instability is crucial because it prevents the cell from making too much of a protein it no longer needs.

Uracil (U). DNA uses thymine instead for greater stability, but uracil is good enough for temporary molecules like mRNA and saves energy. Thanks to this smart substitution, our genetic code can be transported outside of the nucleus of our cells.

This article was written by Agata Flak and reviewed by Steven Wooding.