Ribozyme

Ribozymes (from ribo(nucleic acid) (RNA) and (en)zyme), also known as catalytic RNA, are catalytically active RNA molecules which, like enzymes, catalyze chemical reactions.

Within the ribosome, the rRNA molecules control the catalytic steps of protein biosynthesis. Each cell contains several thousand rRNA molecules. For example, the 23S RNA of the ribosomes catalyzes the formation of the peptide bond during translation. Spliceosomes are also ribozymes, where the tight network of snRNAs catalyzes splicing. Both the ribosome and the spliceosome also contain proteins that do not participate in the actual reaction, but merely ensure that the RNA adopts the correct structure for catalysis. There are also ribozymes that manage completely without proteins, such as the Hammerhead ribozyme, which is used by various microorganisms and some viruses to cut their RNA to the correct length.

The main difference between an enzyme and a ribozyme lies in the reaction speed, but not in the variety of catalyzed reactions. The catalysis of a Diels-Alder reaction is currently of particular interest, as it could in principle have served to create further building blocks for RNAs in the very early phase of evolution. A big step towards an RNA that synthesizes its own building blocks and replicates itself - a possible origin of life with a transition from chemical to living evolution.

1. Blount KF et al (2002) The hammerhead ribozyme. Biochem Soc Trans 30:1119-1122.
2. Canny MD et al. (2004) Fast cleavage kinetics of a natural hammerhead ribozyme. J Am Chem Soc 126:10848-10849.