A Polyaddition Model for the Prebiotic Polymerization of RNA and RNA-like Polymers

TL;DR

This paper develops a mathematical model for prebiotic RNA polymerization, explaining how long RNA chains could form without catalysts, and connects the model to experimental data.

Contribution

It introduces a polyaddition model based on step-growth polymerization, linking rate dynamics, thermodynamics, and polymer length distribution in prebiotic conditions.

Findings

Polymer length distribution follows a geometric Flory-Schulz distribution.

Closed-form solutions for dynamics with specific initial conditions.

Imposition of maximum polymer length affects distribution and error bounds.

Abstract

Implicit in the RNA world hypothesis is that prebiotic RNA synthesis, despite occurring in an environment without biochemical catalysts, produced the long RNA polymers which are essential to the formation of life. In order to investigate the prebiotic formation of long RNA polymers, we consider a general solution of functionally identical monomer units that are capable of bonding to form linear polymers by a step-growth process. Under the assumptions that (1) the solution is well-mixed and (2) bonding/unbonding rates are independent of polymerization state, the concentration of each length of polymer follows the geometric Flory-Schulz distribution. We consider the rate dynamics that produce this equilibrium; connect the rate dynamics, Gibbs free energy of bond formation, and the bonding probability; solve the dynamics in closed form for the representative special case of a Flory-Schulz initial condition; and demonstrate the effects of imposing a maximum polymer length. Afterwards, we derive a lower bound on the error introduced by truncation and compare this lower bound to the actual error found in our simulation. Finally, we suggest methods to connect these theoretical predictions to experimental results.