RNA

Nucleic acid involved in the process of translating the genetic material DNA into proteins. It is usually single-stranded, unlike the double-stranded DNA, and consists of a large number of nucleotides strung together, each of which comprises the sugar ribose, a phosphate group, and one of four bases (uracil, cytosine, adenine, or guanine). RNA is copied from DNA by the formation of base pairs, with uracil taking the place of thymine.

Traditionally, RNA has been known to occur in three major forms, each with a different function in the synthesis of protein molecules. Messenger RNA (mRNA) acts as the template for protein synthesis. Each codon (a set of three bases) on the RNA molecule is matched up with the corresponding amino acid, in accordance with the genetic code. This process (translation) takes place in the ribosomes, which are made up of proteins and ribosomal RNA (rRNA). Transfer RNA (tRNA) is responsible for combining with specific amino acids, and then matching up a special ‘anticodon’ sequence of its own with a codon on the mRNA.

With the discovery of RNAi (RNA interference), however, new kinds of RNA have emerged, including double-stranded RNA, and small interfering RNA (siRNA).

In 2007, the ENCODE (Encyclopedia of DNA Elements) consortium reported that the majority of what was previously considered junk DNA is transcribed into RNA, suggesting that there are further types of functional RNA yet to be discovered.

Although RNA is normally associated with the process of protein synthesis, it makes up the hereditary material itself in many viruses, such as retroviruses. Small RNA molecules have also been shown to have an important role in the silencing of genes (see RNA interference).