Only proteins can act as enzymes or biological catalysts.

A catalyst speeds up a chemical reaction without being consumed by that reaction.

In living cells, catalysts are usually called enzymes, and for much of twentieth-century biochemistry enzymes were assumed to be proteins. That expectation made sense. Proteins can fold into complicated three-dimensional shapes and contain many different chemical groups that help reactions occur.

RNA seemed to have a different job: carrying or helping interpret genetic information.

Two discoveries in the early 1980s broke that division.

Thomas Cech studied an RNA molecule from the microorganism Tetrahymena. Part of the RNA could remove itself from a longer RNA molecule and join the remaining pieces together without a protein enzyme doing the chemistry.

Sidney Altman’s work on another system, RNase P, showed that its RNA component could also perform catalytic chemistry.

RNA molecules with catalytic activity became known as ribozymes.

The discovery did not make proteins unimportant as enzymes. Proteins remain the overwhelmingly diverse and common biological catalysts. But RNA can combine two properties once thought to belong to different molecular classes: it can carry information and it can catalyze reactions.

That combination also helped motivate ideas about an early “RNA world,” although the existence of ribozymes by itself does not prove any single origin-of-life scenario.