For a long time, RNA was only regarded as a messenger molecule, a mobile copy of DNA. Although this is necessary to produce proteins according to the gene sequence defined by the DNA, it also leads to a rather boring existence in the cell. Today, our view of RNA has completely changed: Countless research findings have led to the fact that RNA is now attributed a central role in a large number of important cellular processes. Of course, the messenger role of RNA remains important. However, RNA molecules take on a whole host of other vital functions in the cell. They are found in different lengths and structures. They act as messengers, as blueprints, as scaffolds for building complex structures, as interpreters and as biocatalysts for chemical reactions. In many viruses, RNA even fulfills the function that we normally attribute to DNA, i.e. RNA carries the viral genome. RNA is such a multi-talent because of its enormous flexibility and specific chemical properties. And nature, with its wealth of ingenuity, has taken advantage of this and devised RNA molecules for a multitude of biological tasks.
We can also make use of the properties of this multi-talent; as a tool for research or as a therapeutic drug in medicine. One example of its application as a tool is the "gene scissor" CRISPR, which allows targeted modification of sequences in the genome. RNA drugs are still in their infancy, but - as we, and many others, think - they have a great future ahead of them. One example is the recently approved RNA drug Spinraza®, which is used to treat a rare type of muscular atrophy called spinal muscular dystrophy.
RNA as messenger, blueprint and interpreter
For more than half a century it has been known that cells produce messenger RNAs (mRNAs) as mobile copies of specific DNA sequences - the genes. These mRNAs serve the cells as blueprints for the production of proteins. In order to be able to read this blueprint, the cells use a highly complicated molecular machine called a "ribosome". Ribosomes also consist of special RNA molecules and numerous proteins (we will discuss this in the next section). Ribosomes function as "molecular protein factories" by reading the nucleic acid sequence of the mRNAs and translating it into the language of the proteins. In this translation, a special type of RNA (the so-called transfer RNAs, tRNAs for short) acts as an interpreter. tRNAs understand both, the language of ribonucleic acids and that of proteins. They have a very characteristic structure. On one hand, tRNAs read the genetic language very precisely on the messenger RNA, and on the other hand they find the appropriate protein building blocks (these building blocks are called amino acids). You can read more about how this complicated process works here: Protein synthesis
RNAs not only play an important role as messenger molecules, but also as construction plans and interpreters for the retrieval and translation of all the information stored in our genes on the genome. By the way, messenger RNAs make up only about 5% of the total RNA of a cell. About 15% of all RNAs in a cell are tRNAs.
RNAs can catalyze chemical reactions - this was first observed in the early 1980s and was a real revolution at the time. It was assumed that catalytic reactions in the cell could only be carried out by certain proteins, the enzymes. RNAs that catalyze chemical reactions are called "ribozymes". This term derives from a combination of the two words ribonucleic acid and enzyme. To this day, many ribozymes have been identified, and we know, that without them, many processes within the cell would come to a complete standstill. One example for a ribozyme is the above-mentioned Ribosome. Ribosomes consist of a combination of proteins and ribosomal RNA (rRNA). Interestingly, it is mainly the rRNAs that carry out the catalytic tasks. For example, the so-called "28S rRNA" of the Ribosome catalyzes the assembly of the individual protein building blocks (i.e. the amino acids).