Before life emerged on Earth, many physicochemical processes on our planet were highly chaotic. A plethora of small compounds, and polymers of varying lengths, made up of subunits (such as the bases found in DNA and RNA), were present in every conceivable combination. Before life-like chemical processes could emerge, the level of chaos in these systems had to be reduced. In a new study, LMU physicists led by Dieter Braun show that basic features of simple polymers, together with certain aspects of the prebiotic environment, can give rise to selection processes that reduce disorder.
In previous publications, Braun’s research group explored how spatial order could have developed in narrow, water-filled chambers within porous volcanic rocks on the sea bottom. These studies showed that, in the presence of temperature differences and a convective phenomenon known as the Soret effect, RNA strands could locally be accumulated by several orders of magnitude in a length-dependent manner. “The problem is that the base sequences of the longer molecules that one obtains are totally chaotic“, says Braun.
Evolved ribozymes (RNA-based enzymes) have a very specific base sequence that enable the molecules to fold into particular shapes, while the vast majority of oligomers formed on the Early Earth most probably had random sequences. “The total number of possible base sequences, known as the ‘sequence space’, is incredibly large,” says Patrick Kudella, first author of the new report. “This makes it practically impossible to assemble the complex structures characteristic of functional ribozymes or comparable molecules by a purely random process.” This led the LMU team to suspect that the extension of molecules to form larger ‘oligomers’ was subject to some sort of preselection mechanism.