Messenger RNA (mRNA) serves as the messenger between the DNA and the ribosomes – the cell’s protein factories. Within the nucleus, a section of DNA coding for a protein is used as a template to create a strand of mRNA in a process called transcription. This mRNA then exits the nucleus and travels to the ribosome, where it is used to build the protein encoded by the original DNA sequence.
DNA is transcribed into mRNA, which is then translated into proteins at the ribosome.
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Ribosomal RNA (rRNA) is the RNA that forms an essential component of the ribosomes – the cell’s protein factories. rRNA makes up about 80% of all cellular RNA. Unlike mRNA, rRNA is non-coding RNA, meaning that it is never translated into a protein. Rather, it plays a structural role within the ribosome, and serves to bring the messenger RNA and the transfer RNA together so that proteins can be built.
Transfer RNA (tRNA) is responsible for bringing the amino acids – the building blocks of proteins – to the ribosome to be joined together in a process called translation. Every three letters (or codon) of messenger RNA sequence encodes a specific amino acid. Each tRNA molecule comes attached to an amino acid at one end. At the other end, there is a three letter sequence that is complementary to the triplet which encodes that amino acid. rRNAs line up with the triplets of the mRNA, bringing their amino acids together to be joined into a protein by the ribosome.
Translation of mRNA into a protein at the ribosome.
An Introduction to Ribosomes: Nature’s busiest molecular machines
Viral RNA is found within RNA viruses. Some viruses (such as those that cause influenza, measles and COVID-19) encode their genetic information within RNA rather than DNA. Most viral RNA is single-stranded RNA, though this is not always the case.
Micro RNA (miRNA) and Small Interfering RNA (siRNA) are small RNAs which don’t code for proteins, but instead have the ability to neutralise complementary mRNA molecules by binding to them in a process called silencing, making them a form of post-transcriptional regulation of gene expression.