Comparison of TCA cycle of an uninfected and a MS2 phage-infected Escherichia coli cell. Thick flux arrows represent high reaction fluxes, whereas the thinner flux arrows represent low reaction fluxes. Biosynthesis of amino acids is upregulated in infected cells leading to the diversion of pyruvate to the biosynthesis of amino acids. As a result, the conversion of pyruvate to acetyl-CoA is downregulated. This severely downregulates the TCA cycle. The amount of α-ketoglutarate formed is just enough to act as the pre-cursor for the biosynthesis of amino acids. This is where the TCA cycle breaks leading to the deactivation of the reactions downstream (represented by red crosses). The activity of the last two reactions in the TCA cycle is only due to the formation of fumarate as a by-product of other reactions. Even so, these reactions are markedly downregulated.