Fig. 1.

Schematics of ED and energy partitioning for a metabolism in which the carbon source C is also used as the ED. After being taken up, a fraction $Y_C^{\mathit{cat}}$ of the ED is directed to the catabolic reaction to produce energy, $-Y_C^{\mathit{cat}}\mathrm{\Delta }{G}^{\mathit{cat}}$. The remaining ED is utilized in the anabolic reaction to create new biomass. Of the catabolic energy $-Y_C^{\mathit{cat}}\mathrm{\Delta }{G}^{\mathit{cat}}$, the anabolic reaction uses only an amount equal to $Y\mathrm{\Delta }{G}^{an}$, while the remaining is dissipated. The energy partitioning is characterized by the thermodynamic efficiency $\eta =Y\mathrm{\Delta }{G}^{an}/(-Y_C^{\mathit{cat}}\mathrm{\Delta }{G}^{\mathit{cat}})$.