Second mesenger production a gradient Dm 2-km+P(x) Dm- 1 umls"(membrane protein. lipid um2s-1 x D~100 P(x)=kR-△R (cytosolic small molecule) Images removed due to copyright considerations See Postma. M. andp.j. van hastert Diffusion flattens internal A diffusion-translocation model for gradient sensing by chemotactic cells. Biophys J.81, no. 3(Sep, 2001): 1314-23. gradient Gain is 1 ( the larger Dm the smaller the gain How to amplify⎟⎠⎞ ⎜⎝⎛ = − ∆ − + ∂ ∂ = − r x P x k R R k m P x x m D dt dm R m * * 2 1 2 ( ) ( ) Second mesenger production in a gradient Dm ~ 1 µm2s-1 (membrane protein. lipid) Dm ~ 100 µm2s-1 (cytosolic small molecule) Diffusion flattens internal gradient Gain is < 1 (the larger Dm the smaller the gain) How to amplify ? 3 Images removed due to copyright considerations. See Postma, M., and P. J. Van Haastert. "A diffusion-translocation model for gradient sensing by chemotactic cells." Biophys J. 81, no. 3 (Sep, 2001): 1314-23