CellTour · a mode
CellBudget
A growing bacterium is mostly protein, and its protein comes in a fixed budget. Some of it is ribosomes, which make more protein. Some is food-uptake enzymes, which bring food in. The rest keeps the cell running. Too few ribosomes and the cell cannot build fast; too few enzymes and it runs out of food. Set the split, guess first, then run.
Toy model A simplified picture to show one idea. Not a measurement, and not a prediction. Of a measured law: the bacterial growth laws (Scott et al. 2010), with rounded numbers.
Your cell
Housekeeping stays at 50 of every 100. Ribosomes and food-uptake enzymes share the other 50.
The law behind it
Run all three foods. Where growth is fastest, the ribosome share and the growth rate fall on one straight line: richer food, faster growth, more ribosomes. That straight line was measured in real bacteria. Tick the antibiotic and run again: with slower ribosomes, the best share has more ribosomes for the same growth, so the points fall on a second, steeper line. That was measured too.
A real cell's split is set by its gene regulation, with no plan behind it. Here, you set it. The model's numbers are rounded so the shape is easy to see; published fits differ from study to study. The straight lines are the measured part.
About the numbers
Housekeeping 50 of 100; ribosomes that are not busy 7 of 100; busy ribosomes make protein at a rate of 6 per hour (3 with the antibiotic); food quality poor food 1.2, middling food 4, rich food 20 per hour. Growth is whichever runs short: what the busy ribosomes can build, or what the enzymes can bring in.
Sources: Scott, Gunderson, Mateescu, Zhang & Hwa (2010), Interdependence of cell growth and gene expression: origins and consequences, Science 330:1099. Scott, Klumpp, Mateescu & Hwa (2014), Emergence of robust growth laws from optimal regulation of ribosome synthesis, Molecular Systems Biology 10:747.