5 Ribosomes and the RNA World

Abstract

The hypothesis that all modern organisms are descendants of an ancient, self-replicating entity that depended on RNA both for its genetic material and for catalysis has gained a large following over the past decade, as the existence of this volume attests. This idea, also known as the RNA world hypothesis, has been around in various forms for almost 30 years, and it has been known for most of that time that RNA can serve a DNA-like function. The reason there is so much interest in the RNA world hypothesis today is that we now know something our predecessors did not, namely, that RNAs are capable of catalyzing biochemical reactions.

Boiled down to its essence, the RNA world hypothesis is a proposal for the origin of life that explains why RNA is so important for gene expression in modern organisms but has no role in any other aspect of metabolism. Ribosomes are important for two reasons in this context. First, because ribosomal RNA accounts for about 80% of the RNA in most modern cells, the RNA world hypothesis either makes sense of them or fails entirely. Second, again because the ribosome contains so much RNA, information about its structure and function has to be an important part of the input used for formulating all such theories.

This paper is intended to provide the reader with a broadbrush picture of the ribosome field that emphasizes the findings that bear most directly on evolutionary issues. Readers wishing to find out more about the...