RNA in evolution: a review

There are two main groups of molecules in the cell as it exists today: nucleic acids which transmit genetic information and participate directly in reproduction; and proteins which are responsible for the metabolic functions and chemical and structural relations within the cell. What interests evolutionary biochemistry is how these first molecules came to exist, their original replication and how the different classes of molecules relate to one another. What was the first system enabling information to be transferred? Were the first autoreplicative molecules, the same as those we know today, or did they only have certain similarities to our nucleic acids? How did relations between molecules come about so as to construct the first metabolic pathways? Chemical reactions have to be selective, rapid, therefore catalysed, to be efficient. Were the very first catalysts which played a role in the first appearance of metabolism made up of enzymes such as we know them today, i.e. complex and highly organised proteins? Or were they quite simply mineral supports or reactive compounds? From the point of view of molecular evolution i.e. before the appearance of cellular life when prebiotic chemistry furnished the basic building-blocks of the living organism we can suggest a number of hypotheses to answer these questions. Today, of all known organic molecules, the nucleic acids alone are capable of self-replication. Thus, one of the key stages in the origin of life on earth was the appearance of primitive molecules similar to nucleic acids.