Stochastic approaches are needed for modelling many cellular processes to capture noise effects. The difficulty of solving the chemical master equation, the most common formulation of stochastic models, is circumvented by stochastic simulations and analytical approximations. The central theme here is one such approximation, the two-moment approximation (2MA) which represents the mean-covariance coupling. Our 2MA formulation allows non-elementary reactions and relative concentrations. The approach is applied to the fission yeast cell cycle model. The analytical model reproduces the relevant experimental data.
