What is the difference between mRNA and miRNA?

Why have you heard of mRNA?

At this point everyone has heard of mRNA. With the advent of the novel vaccines against COVID-19 produced by Pfizer and Moderna, the verbal usage of mRNA has spread outsize of biology classrooms and into the common parlance of everyday life. This is no surprise as mRNA, which stands for messenger RNA, is the key ingredient in producing the new vaccines and charging one’s immune system against COVID-19. But we are not here to get into the nitty-gritty of how the vaccine works. We are here to discuss the fact that there exists another very important type of RNA that you may not know much about.

It is called microRNA (miRNA). As the name implies, miRNA is very small. On the other hand, mRNA is very large. Let’s discuss the key points of each molecule.

What does mRNA do?

mRNA is directly involved in the synthesis of proteins and can be thousands of nucleotides in length. It is made from an enzyme reading a cell’s DNA and then transcribing it into a chain of new building blocks called mRNA. This mRNA is the message that is sent to biological machines in the cell called ribosomes, that read the message of the mRNA and translate it into a protein. Therefore, mRNA uses the coding portion of a gene to produce a protein product.

How are miRNAs different from mRNA?

When comparing mRNA to miRNA there are many differences. miRNAs are significantly shorter at 18-22 nucleotides in length and also are of completely different biological significance. miRNAs are a type of non-coding RNA, because they do not contain information from the cell’s DNA that codes for and consequently produces protein. These tiny non-coding RNA molecules function to regulate the way certain genes are expressed. This interplay occurs through multiple ways: the miRNA can bind to specific mRNA and block them from being read and turned into protein through physical sitting on the mRNA; the miRNA can bind to mRNA and subsequently send the mRNA to be degraded and therefore not turned into a protein.

As you can see miRNA functions as a negative regulator of gene expression through its ability to base-pair in a complementary fashion to target mRNA. Of note, one single miRNA can have many mRNA targets, and one single mRNA may be targeted my many miRNAs. Therefore, there is an incredible amount of gene expression control from many levels of miRNA-mRNA dynamics.