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Unformatted text preview: Probing the Interior of Living Cells with Fluorescence Correlation Spectroscopy M ATTHIAS W EISS Cellular Biophysics Group (BIOMS), German Cancer Research Center, Heidelberg, Germany To a large extent the cellular interior is occupied by two complex fluids, the cytoplasm and the nucleoplasm, both of which show a considerable degree of macromolecular crowding. While it is easy to imagine that the chromosomal DNA provides the nucleoplasm with properties similar to a polymer melt, the material properties of the cytoplasm are also affected by the high amount of dissolved macromolecules, the cytoskeletal network, and dispersed organelles. By virtue of the strongly obstructed random motion, reactions in the cytoplasm and nucleoplasm are not comparable to the aqueous conditions commonly used in biochemical experiments. To overcome this gap, a thorough understanding of the material properties of intracellular fluids, and hence transport properties within the cell, is mandatory. Here, we review some recent results on bulk diffusion in living cells and some generic consequences that arise from these observations. Key words: fluorescence correlation spectroscopy; anomalous diffusion; subdiffusion; viscoelas- ticity; macromolecular crowding; diffuse-to-capture Introduction The interior of living cells is an amazingly complex microscosm in which myriad proteins and lipids act in concert to sustain vital cellular processes. 1 During the last decades, molecular biology has boosted our under- standing of cellular dynamics and reaction networks by making virtually any protein accessible to genetic ma- nipulations, be it by silencing or knocking out specific genes or by attaching genetically encoded fluorescent tags to the protein of interest. Despite these advances that have shaped our current thinking in terms of well- defined cellular pathways and networks, one must not forget that cells lack an organizing mastermind but rather have to self-organize on the molecular level due to the fundamental laws of physics and chemistry. A particular aspect of this self-organization is the molec- ular communication within the cell, that is, proteins have to sample their environment for interaction part- ners to be able to establish a reaction network. Char- acterizing cellular pathways solely by kinetic equations (which indeed is a frequent approach in many systems biology studies 2 , 3 ) neglects this important spatial aspect Address for correspondence: Dr. Matthias Weiss, Cellular Biophysics Group (BIOMS), B085, German Cancer Research Center, BIOQUANT Center, BQ0019, Im Neuenheimer Feld 267, D-69120 Heidelberg, Germany. Voice: + 49 6221 5451304. email@example.com and may therefore fall short in giving an appropriate decription of the cells behavior on the molecular scale....
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This note was uploaded on 07/11/2010 for the course SPECTOGRAP 545 taught by Professor Gdf during the Spring '10 term at AIB College of Business.
- Spring '10