RNA World

A living cell typically contains roughly ten times as much RNA as DNA, a striking imbalance explained by the sheer variety of jobs RNA performs inside the cell beyond simply storing genetic information. Historically, RNA's credentials as a genetic material in its own right were established by Heinz Fraenkel-Conrat and Beatrice Singer in 1957, who separated the RNA from the protein of Tobacco Mosaic Virus (TMV) and showed that the RNA component alone carried the infectious, heritable information. Building on this and related findings, three molecular biologists working independently in the early 1980s, Leslie Orgel, Francis Crick and Carl Woese, proposed that life on Earth began with an 'RNA world': an early stage of evolution in which RNA molecules alone catalysed all of the chemical reactions necessary for their own survival and replication, without any help from DNA or protein enzymes. The phrase 'RNA world' itself was coined slightly later, in 1986, by Walter Gilbert. There is now substantial evidence that fundamental life processes such as metabolism, translation and RNA splicing evolved originally around RNA, and that RNA is capable of acting as both genetic material and biological catalyst at the same time; catalytic RNA of this kind is given the special name ribozyme. However, being reactive enough to act as a catalyst also makes RNA chemically unstable, which is thought to have driven the evolutionary shift toward the more stable, double-stranded DNA molecule, whose two complementary strands allow damage to be detected and repaired far m …