Figure 3.

Optimal regulation of a basic self-replicator, consisting of four enzymes and a membrane. The cell (A) consists of a pool of ribosomes that catalyze protein synthesis, including their own; a substrate transporter protein pool; a metabolic enzyme pool and a pool of enzymes that synthesize the lipid component of the membrane. The membrane consists of transporter protein and lipid. The cell accumulates a substrate from the environment and converts it into a metabolite that is used for protein synthesis and lipid synthesis. It can regulate the relative proportion of each of the protein pools by adjusting the amount of ribosomes that is engaged in the synthesis of each of the four proteins. (B, C) The results of numerical optimizations are shown. The individual protein pool fractions relative to total protein and the volume/surface ratio (cell shape parameter in the model description in the Supplementary information) were optimized (C) so as to maximize the growth rate (B) at different extracellular substrate concentrations. The points indicate the results of numerical simulations. (D) The experimental results of glucose uptake capacity in Klebsiella pneumoniae at different growth rates (Teixeira de Mattos and Neijssel, 1997). (E) The relative rate of synthesis of ribosomal protein to that of total protein (Gausing, 1977) in E. coli at different growth rates. Under balanced growth these relative rates directly translate into relative amounts of protein.