Before revision:  Bistability induced by the small-number effect in a two-component model is analyzed and excellent agreement with the simulated mean switching time is demonstrated. A novel transition involving the reversal of the chemical reaction flow is also found in a three-component model and quantified analytically using the proposed method .
After revision:  Bistability induced by the small-number effect in a two-component model is analyzed and excellent agreement with the simulated mean switching time between the bistable states are analytically calculated in agreement with numerical simulations. In addition, a novel transition involving the reversal of the chemical reaction flow is also found in a three-component model and quantified analytically using the proposed method .