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Biophysical Applications of the Physics of Diffusion



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Biophysical Applications of the Physics of Diffusion Sima Setayeshgar Department of Physics Indiana University 9 July 2007 Boulder Summer School Applications of Diffusion 1 Biochemical Signaling and the Physics of Diffusion 9 July 2007 Boulder Summer School Applications of Diffusion 2 Measurement of concentration of a diffusing signaling molecule by a receptor is a generic task RNAP In many cases signaling molecules are present in small copy numbers making fluctuations in their numbers significant CheY P CheY TF How reliably can biochemical reactions be carried out given inherent fluctuations in numbers of crucial molecules 9 July 2007 Boulder Summer School Applications of Diffusion 3 What is the physical limit in measuring the concentration of signaling molecules by biological receptors First addressed by H C Berg E M Purcell Physics of Chemoreception Biophysical Journal 1977 Measurement of chemoattractant by single celled organism limited by statistical fluctuations Least fractional error attainable set by physics of diffusion E coli chemotaxis machinery near optimal Outline Revisit BP result within general framework of statistical mechanics Generalize to cooperatively interacting receptor cluster Compare with recent experiments 9 July 2007 Boulder Summer School Applications of Diffusion 4 E coli as a Model Organism Workhorse of molecular biology most studied cell in all of science small genome 4300 genes normal lack of pathogenicity ease of growth in the lab Basis of recent developments in biotechnology and genetic engineering including living factory for producing human medicines Basis for understanding of fundamental cellular processes cellular sensory systems regulation of gene expression cell division etc Size 0 5 m in diameter 1 5 m in length Cell cycle 1 hour 9 July 2007 Boulder Summer School Applications of Diffusion 5 Sensory Mechanisms in Single Cells Chemotaxis in E coli 3D tracking microscope image of a single cell s motion From H C Berg Physics Today



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