New Delhi: A close examination of the samples returned from the asteroid Bennu by NASA’s OSIRIS-REx mission in 2023 has revealed that all the ingredients necessary to form ribonucleic acid (RNA). What is crucial here is that while ribose, the sugar needed to make RNA was discovered, deoxyribose, the sugar necessary to make deoxyribonucleic acid (DNA) was not. The RNA world hypothesis is a leading theory about the origin of life on Earth, proposing that the first self-replicating biological systems were based on RNA rather than DNA and proteins. This primordial RNA could store genetic information like DNA does today, and act as enzymes instead of proteins to catalyse chemical reactions.
As RNA could carry both hereditary information and speed up reactions, it could form a simple self-replicating system without DNA or proteins. These self-replicators would eventually evolve into the complex biochemistry seen on Earth today. The RNA molecules with dual-capabilities called ribozymes exist today, in modern cells, serving various biomolecular functions. In lab conditions, RNA molecules can replicate without proteins, and synthetic RNA molecules have been assembled to perform a number of protein-like functions. RNA also remains essential for translating DNA into proteins, which is another sign of a long-gone era dominated by RNA.
A number of competing paradigms
While the RNA World hypothesis is one of the leading theories, there are competing hypothesis. There are a number of theories on self-sustaining chemical cycles before genetic polymers such as RNA or DNA. These were autocatalytic networks that amplified the production of certain chemicals, with heredity and replication emerging later. Then there is the ribonucleoprotein (RNP) world, with the co-evolution of RNA and short peptides that help each other, with random amino acids stabilising RNA.
This last RNP World is a more advanced form of the RNA World hypothesis, and plugs in a few of the shortcomings of the older theory. The new research suggests that the conditions necessary for RNA worlds was present throughout the Solar System, and adds to an increasing amount of research that frames life as a astrochemical process that begins in the chemistry of the heat gradient of a protoplanetary disk and not a geochemical one requiring a warm little pond on a terrestrial surface.