The plots represent the result of the sensitivity analysis. We have computed the sensitivity coefficients matrix for the fluxes (panel a) and for the metabolite concentrations (panel b) with respect to parameters V
. We have considered choline incorporation via Kennedy pathway, namely C h o E=50 μ M, S e r E=0, E t n E=0. Fluxes and parameters are numbered from 1 to 17 that correspond to reaction labels from Figure 2. Metabolites are numbered from 1 to 8, which corresponds to species represented in Figure 2. Each bar has a size proportional to the value of the control coefficient (when this coefficient is negative the bars are oriented downwards). We can notice that the strongest effect on both the PC production (flux 8, panel a) and PC concentrations (species 6, panel b) is produced by changes of parameters of reactions 15 and 8, in this order. However, all the reactions in the CDP-choline pathway (with the exception of the fast, non-represented one, transforming CDP-choline into PC) have comparable sensitivity coefficients, meaning that this pathway has not an unique limiting step. The PC concentrations are also sensitive to the base exchange reaction R10 (panel b), which is normal, because this reaction consumes PC.