Physical limits of cellular sensing and information

4 problems

• Why E. coli encodes far less information than molecule counting allows

  Open

  The gut bacterium E. coli swims toward food by sensing chemical gradients, and it climbs them nearly as fast as the information it collects allows. Yet it collects about a hundred times less information than the random arrival of molecules at its receptors would permit, and the source of this loss is unknown.

• Energy cost of sensing beyond the Berg-Purcell limit

  Partially resolved

  In 1977 Berg and Purcell estimated how precisely a cell can measure a chemical concentration in a fixed time. Spending energy in the readout chemistry can do better than simple counting, and the exact trade-off between energy and precision is not settled.

• Origin of the extrinsic noise floor in gene expression

  Open

  Genetically identical cells contain different amounts of each protein. For highly expressed proteins this variation stops shrinking at a floor that random chemistry at a single gene does not explain.

• Are embryonic gene networks optimal encoders of position?

  Partially resolved

  In the fruit-fly embryo, a few genes switched on in graded patterns tell each cell where it is with about 1 percent precision. One hypothesis is that these networks are tuned to carry the most positional information possible given their noise.