Figure 4

Chemotaxis pathway response and noise spectra in the full pathway model. (Left and Middle) Response upon impulse stimulation with attractant MeAsp. (Left) Time courses for MeAsp concentration c, total activity of receptors A _c , CheA-P and CheY-P, and motor bias X obtained from simulation of the full pathway model using the Euler method for integration of the differential equations without noise. (Middle) Fourier transformed ligand signal, as well as response functions. Symbols correspond to the numerical simulation in the left panel, and solid lines to analytically calculated functions. (Right) Analytically calculated noise spectra of ligand and for the total activity of receptors A _c , CheA-P and CheY-P, and motor bias X (thick black lines). Also shown are the contributions to the spectrum from ligand binding (L; thin solid black lines), receptor switching (RS; thin red lines and symbols), receptor methylation and demethylation (M; green lines), as well as phosphorylation and dephosphorylation of CheA, CheY and CheB (P; blue lines) and motor switching (MS; dashed grey line).