Most enzymes are proteins but a few are RNAs. That is, there are some RNAs that can increase the rates of exergonic reactions; such RNAs are termed Ribozymes. The discovery of ribozymes, for which Petes and Altman received the Nobel prize, is interesting both in terms of enzymic catalysis and evolution. There are different classes or ribozymes that can carry out different kinds of reactions. Most of the reactions involve the cleavage, modification or polymerization of RNA. In evolutionary terms, the ability or RNA to make a copy of itself suggests that RNA and not necessarily DNA may have been the first replicating polymer to carry information to have evolved.
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