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
was 3 M-1 s-1 and the first-order rate constant of re-dissociation k
was 10-4 s-1 that corresponded to the equilibrium constant = 30. The rate constants of nucleotide binding (k
) and dissociation (k
) 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
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.