The rRNAs are folded into highly compact, precise three-dimensional structures that form the core of the ribosome. In contrast to the central positioning of the rRNAs, the ribosomal proteins are generally located on the surface, where they fill the gaps and crevices of the folded RN

The main role of the ribosomal proteins seems to be to help fold and stabilize the RNA core, while permitting the changes in rRNA conformation that are necessary for this RNA to catalyze efficient protein synthesis.

Not only are the three tRNA-binding sites (the A, P, and E sites) on the ribosome formed primarily by the rRNAs, but the catalytic site for peptide bond formation is formed by the 23S rRNA of the large subunit; the nearest ribosomal protein is located too far away to make contact with the incoming amino acid or with the growing polypeptide chain.

The catalytic site in this RNA—a peptidyl transferase—is similar in many respects to that found in some protein enzymes: it is a highly structured pocket that precisely orients the two reactants—the elongating polypeptide and the amino acid carried by the incoming tRNA—thereby greatly increasing the likelihood of a productive reaction.