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Unformatted text preview: Biophysics 11b, Spring 2006 Solutions to Problem Set 5 1. Problem #1 Solution. (a) Total free energy cost to pump one Na + out: F ( Na + ) =- e V- V Nernst ( Na + ) = e [60 mV + 54 mV ] = 114 meV . (1) Total free energy cost to pump one K + in: F ( K + ) = + e V- V Nernst ( K + ) =- e [60 mV- 75 mV ] = 15 meV . (2) One cycle consists of pumping three Na + and two K + : F (cycle) = 3 F ( Na + ) + 2 F ( K + ) = 372 meV 15 k B T . (3) (b) 3 F ( Na + ) F (cycle) = 342 372 92% (4) of the energy expended in one cycle is used to pump Na + . (c) The energy of one ATP is 16 kcal mol 695 meV 28 k B T . (5) Based on this number the efficiency comes out to be 15 28 54% . (6) 1 2. Problem #2 Solution . Qualitative questions . (a) High selectivity means that the channel lets ions of one sort pass easily while effectively blocking those of another type. Imagine a simple selective mechanism based merely on the ions sizes: we cannot expect it to be very efficient, because the Pauling radii of...
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This note was uploaded on 09/21/2008 for the course BIPH 11 taught by Professor Kondev during the Spring '07 term at Brandeis.
- Spring '07