The central dogma of biology states that the genetic information is hard-wired into DNA which is transcribed into individual transportable cassettes, composed of messenger RNA and each mRNA cassette contains the program for the synthesis of a particular protein—or “DNA makes RNA and RNA makes protein.”
It’s less complicated than it sounds, DNA has the information on how to make an organism and proteins are the functional and structural molecules of cells—with a type of RNA (messenger or mRNA) playing the middle man. And for decades that’s how we thought molecular biology worked: as a one-way street.
However, we have since learned that the relationship between DNA and RNA is more complicated than the central dogma originally described.
There are many RNA molecules in the cell that do not encode proteins. These are categorized as non-coding RNA (ncRNA), or functional RNA, which means that their job in the cell is performed by the RNA molecule itself.
Within this family of non-coding RNA are the newly discovered small RNAs, a key component of epigenetics that can alter change gene expression. There are multiple different types of small RNAs. The two broad categories are microRNA (miRNA) (which can be broken down further into small interfering RNA (siRNA) and piwi-interacting RNAs (piRNA)) and long noncoding RNA(lncRNA).
Because this family of RNA was discovered so recently (small RNAs were chosen as the “Breakthrough of the year” by Science magazine in 2002), there is still much to be understood about how they work. The first time that it was realized that small RNAs may be shutting down the transcription of genes was through work done in petunia flowers by Rich Jorgensen in 1990. The process of RNA silencing was further understood a few years later in the model organism C. elegans in the labs of Victor Ambrose, Andrew Fire, and Craig Mello and was the basis of the Nobel Prize awarded in 2006.
The process that microRNAs use to turn off a gene is incredibly complicated. They work primarily by blocking a protein-encoding mRNA so that it can no longer make protein. In order to prevent this process, they bind to the target mRNA, with the help of a protein complex called RISC, and break up the mRNA into small pieces.
This process is being utilized by researchers who want to shut down or silence genes simply by introducing pieces of double-stranded RNA to the cell. By doing this, the expression of almost any gene can be shut down. Since their discovery, these RNAs have been at the center of the study of promising new ideas for drugs and therapeutics.