Figure 2

Monte Carlo simulation of a sugar-phosphate polymerization reaction in the presence of nitrogenous bases and under UV-illumination Sugar-phosphate polymerization reaction in the presence of nitrogenous bases and under UV-illumination was simulated using the following parameter set: The concentration of monomers in the reaction volume was kept on a constant level of 10^-3 M (comparable with their concentration in the cell). The second-order rate constant of polymerization k _poly was 3 M^-1 s^-1 and the first-order rate constant of re-dissociation k _mono was 10^-4 s^-1 that corresponded to the equilibrium constant = 30. The rate constants of nucleotide binding (k _bind ) and dissociation (k _diss ) were 3 × 10^-8 s^-1 and 10^-6 s^-1, respectively ( = 3 × 10^-2). Under the UV illumination, monomers decomposed with the rate constant of 3·10^-3 s^-1 irrespectively of their position in the chain. For simplicity, the UV protection factor U of 30 was used both for monomers and oligomers. The partial funneling of UV energy was assumed to increase the k _bind value from 3 × 10^-8s^-1 up to 1.2 × 10^-7 s^-1. a, Polymer length distribution at equilibrium. b, Fraction of monomers protected by nitrogenous bases as a function of time.