Evolutionary advantage of directional symmetry breaking in self-replicating polymers

TL;DR

This paper explores why unidirectional DNA replication, despite seeming less efficient than bidirectional, may have evolved due to physico-chemical advantages in primordial conditions, highlighting asymmetric self-replication benefits.

Contribution

It provides a theoretical explanation for the evolution of unidirectional replication based on physico-chemical constraints in early Earth conditions.

Findings

Unidirectional self-replicators have an evolutionary advantage at low monomer concentrations.

Asymmetric inter-strand bonds optimize formation and stability.

Primordial conditions favored unidirectional replication due to kinetic and stability factors.

Abstract

Due to the asymmetric nature of the nucleotides, the extant informational biomolecule, DNA, is constrained to replicate unidirectionally on a template. As a product of molecular evolution that sought to maximize replicative potential, DNA's unidirectional replication poses a mystery since symmetric bidirectional self-replicators obviously would replicate faster than unidirectional self-replicators and hence would have been evolutionarily more successful. Here we carefully examine the physico-chemical requirements for evolutionarily successful primordial self-replicators and theoretically show that at low monomer concentrations that possibly prevailed in the primordial oceans, asymmetric unidirectional self-replicators would have an evolutionary advantage over bidirectional self-replicators. The competing requirements of low and high kinetic barriers for formation and long lifetime of inter-strand bonds respectively are simultaneously satisfied through asymmetric kinetic influence of inter-strand bonds, resulting in evolutionarily successful unidirectional self-replicators.