Computational model of carbon transitions in the TCA cycle. The numbered circles connected in a string represent single carbon atoms of the corresponding metabolite. Fluxes between carbon atoms of the metabolite pools are indicated by arrows. Blue and red dotted arrows stand for carbon atoms entering and leaving the system, respectively. Green dashed arrows indicate bidirectional exchange fluxes of carbon atoms with amino acids. The parameters determining the conversion rate are shown next to the arrows. Note that there are two possible transitions between α-ketoglutarate and succinate, indicated by arrows of different grey shade. The figure was adapted from Binsl et al. .