4.18. Catalytic RNA, siRNA, micro RNA

4.18.1. The RNA World

The RNA world hypothesis proposes that life based on ribonucleic acid (RNA) predates the current world of life based on deoxyribonucleic acid (DNA), RNA and protein. RNA is able to both store genetic information, like DNA, and catalyzes chemical reactions, like an enzyme protein. It may therefore have supported pre-cellular life and been the first step in the evolution of cellular life.
The RNA world is proposed to have evolved into the DNA, RNA and protein world of today. DNA is thought to have taken over the role of data storage due to its increased stability, while proteins, through a greater variety of monomers (amino acids), replaced RNA's role in specialized biocatalysis. The RNA world hypothesis suggests that RNA in modern cells is an evolutionary remnant of the RNA world.

• First proto-organisms had both genes and enzymes made of RNA
• DNA and proteins as specialized late-comers
• DNA took over information storage
• Proteins took over enzyme activity

Figure 4.23: The RNA world hypothesis