Scitable explains that the central role of ribonucleic acid, or RNA, is to convert instructions written in the code of the organism's DNA into proteins. However, RNA is also involved in a number of other processes, such as signaling other cells and functioning as catalysts in cellular chemistry. Additionally, the ribosomes, which convert RNA into structural proteins, are themselves composed primarily of RNA.
RNA also plays an important role in the expression of genes coded for in the DNA, according to Scitable. This means that while some traits may be present in the genome of an organism, the trait is only expressed if it is activated by RNA.
Wikipedia explains that RNA is very similar to DNA. However, RNA molecules only bear a single strand of chained nucleotides, whereas DNA molecules are double-stranded. Along with DNA and proteins, RNA is one of the macromolecules that is necessary for all known forms of life.
According to the RNA Society, some organisms, particularly some types of viruses, store their genetic blueprint in the form of RNA rather than DNA. Scitable relates that some scientists now believe that because RNA is so ubiquitous and is known to be responsible for a variety of functions, it may have preceded the evolution of DNA and proteins.