Figure 7. Effect of the number of molecules on the behavior of the switch.

Stochastic simulations of the double-negative feedback loop, for distributive phosphorylation (Panel A: Ordered, and Panel B: Disordered), with N = 10 and q = 0. Top row: V = 20 (small cell); bottom row: V = 200 (large cell). In each panel, the left column corresponds to initializing the stochastic simulations in the lower steady state predicted by the deterministic equations, and the right column to initializing in the upper steady state. In each simulation H is held fixed at the number of molecules indicated on the abscissa. In panel A, the total time of each simulation is 10⁶ arbitrary time units; in panel B it is 10⁵ au. During each of these simulations, we record the total time, T_i, spent with a particular number, i, of kinase molecules, and we plot these times using a color code to indicate log₁₀(T_i). Parameter values: κ_s = 0.02, κ_d = 0.02, κ_a = 0.98