Someone argues: "A regulatory protein is present at in a bacterial cell of volume
PHYSICS · Multi-part · Fermi University Physics · Mathematical Methods for Physics · Biophysics & Medical Physics · Genetic circuits, regulation and biological information
Forces, Machines and Signals, Ch Numbers and noise in a small system
Problem
Someone argues: "A regulatory protein is present at 0.05nM in a bacterial cell of volume 2fL. The mean copy number is nˉ=cNAV≈0.06, which is less than one molecule. Since a cell cannot hold a fraction of a molecule, this regulator must be completely absent from every cell."
((a)) Compute nˉ to check the arithmetic in this argument.
((b)) Find the actual percentage of cells that contain zero copies, and the percentage that contain at least one copy, treating the copy number as Poisson with mean nˉ. State whether the conclusion "absent from every cell" is correct.