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Bioen 599 F, Autumn 2000 Bioengineering Principles of Physiology |
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Lecture Material and Notes Week 5, Lecture 15: Cell
water and viscosity Lecture theme and outline: 1. Anomalies: why is it that you can cut a cell in half, and notwithstanding the absence of "resealing," the cell does not die? Conclusion: cell membrane machinery may be less important than presumed. · Is the membrane really continuous? Conclusion: Not as clear as one presumes. · If the membrane is not a continuous barrier, and it doesn't matter if the cell is cut in half, then what keeps the "stuff" inside? Conclusion: It's a gel. · What's a gel like? Discussion of charged, hydrophilic surfaces and evidence that water is structured in multilayers around these surfaces. Discussion of Israelachvili/Granick evidence for layers at least 10 water molecules thick; Discussion of Pashley evidence for up to 600 layers. · Is water structuring characteristic of cell water? Demonstration that the average surface-to-surface gap between macromolecules in the cell is only 5 - 10 water molecules. This fits many estimates of structuring capacity. It also demonstrates that solutes of any size would have enormous difficulty penetrating through such narrow crevices. Conclusion: cell water is largely structured and therefore highly viscous. Reading: Pollack, 2001 book manuscript, Chapters 1-4. |
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Contact the instructor at: ghp@u.washington.edu
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