10-7-09_lecture_transportA

10-7-09_lecture_transportA -...

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My father once told me that respect for the truth comes close to being the basis for all morality. "Something cannot emerge from nothing," he said. This is profound thinking if you understand how unstable "the truth" can be. -from "Conversations with "Muad'Dib" by the Princess Irulan (Dune) In the beginning the Universe was created. This has made a lot of people very angry and been widely regarded as a bad move. Douglas Adams
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Announcements Quiz 4 due Wednesday 10/14 at noon. Carol Greider, Elizabeth Blackburn, and Jack Szostak shared the 2009 Nobel Prize in Medicine for their discovery and characterization of telomeres, telomerases, and their roles in cancer and aging.
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Our respiratory and circulatory systems use very large areas, steep concentration gradients, and relatively short paths to transport oxygen via diffusion Our alveoli together form a surface area the size of a tennis court! For a solute s , the flux of s is given by Qs/ t=Ds x A x Cs/ x,
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Examples of osmosis Movement of water from lower [solute] to higher [solute] is osmosis Animal cells usually isotonic (a) Plant cells usually hypotonic, with higher internal [solute]. They are swollen and have an internal osmotic pressure called turgor . Turgor provides support for plants (b) If placed in a hypertonic solution so that they have lower internal [solute] (e.g. seawater), the cell will shrink away from the cell wall, or wilt, aka plasmolysis .
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Despite polar nature, water flows through membranes much faster than other polar solutes Water, as expected has a very low oil/water partition coefficient Its permeability is far above what would be expected based on this
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Like water for channels: Aquaporins Aquaporins are a family of water permeable channels discovered by Peter Agre’s group in the early 1990’s (Nobel Prize 2003) Left, one subunit, with multiple transmembrane portions Tetramers each with a specific, water permeable channel Very high flux rate, up to 1 billion waters/second King et al. 2004
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The free energy of solute movement Spontaneous movement from high to low concentration
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10-7-09_lecture_transportA -...

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