the ribozyme
/ RYE-bo-zyme /
For decades, biology taught a simple division of labour: DNA stores information, and proteins do the work — especially the work of enzymes, the catalysts that speed up the cell's chemistry. RNA was just the messenger in between. A ribozyme breaks that division: it is an RNA molecule that itself acts as an enzyme, folding into a precise shape that catalyzes a chemical reaction.
How can a strand of just four kinds of base do an enzyme's job? The trick is the same one proteins use: shape. An RNA can fold back on itself, pairing distant regions, to build a compact three-dimensional structure with a pocket that grips a target and lines up reacting groups, often using a metal ion such as magnesium as a helper. The negatively charged backbone and the chemically reactive 2'-OH of ribose (which DNA lacks) give RNA tools that DNA does not have. Known natural ribozymes cut RNA, join RNA, and most importantly form the peptide bonds of proteins.
The discovery of ribozymes in the early 1980s, by Tom Cech and Sidney Altman, won a Nobel Prize and reshaped the field, because it removed a paradox about life's origin. If you need proteins to copy genes, but genes to make proteins, which came first? A molecule that is both information and catalyst — RNA — could break the deadlock. And the deepest example is right inside you: the ribosome that builds every one of your proteins is itself a ribozyme, its peptide-bond-forming center made of RNA, not protein.
The ribosome's peptidyl transferase center — where amino acids are stitched into a chain during translation — contains no protein at its active heart; it is built of ribosomal RNA. The largest and most essential catalyst in your cells is a ribozyme.
RNA can be a catalyst — the ribosome that builds proteins is itself a ribozyme.
Ribozymes are real but limited: natural RNA catalysts are far slower and chemically less versatile than protein enzymes, which is widely thought to be why proteins took over most catalysis. RNA catalysis is a remarkable proof of principle, not evidence that RNA is as good a catalyst as protein.