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mcb110_alber_transport

mcb110_alber_transport - ransport 1 MCB 110 Fall 2007 Albe...

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MCB 110 - Fall 2007 - Alber Transport 1 V Membrane Potential and Nerve Impulses Suggested Reading : Lodish, Chapter 7 Alberts, Chapter 11
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MCB 110 - Fall 2007 - Alber Transport 2
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MCB 110 - Fall 2007 - Alber Transport 5 E NERGETIC S O F S OLUTE M OVEMENT Movement into t he cell D G = RT ln C i [ ] C o [ ] = 2 . 3 RT log 10 C i [ ] C o [ ] At r oom t empera tu re , T = 2 5 ûC D G = 1 . 4 kcal / mol log 10 C i [ ] C o [ ] I f C i [ ] = C o [ ] Þ D G = 0 Equilibr ium!! I f C i [ ] < C o [ ] Þ D G < 0 Ter modynamical ly f avor able t o move into t he cell! Example: C i [ ] = 1 10 C o [ ] Þ D G = - 1 . 4 kcal / mol As solut e moves in C i [ ] -- unti l C i [ ] = C o [ ] Þ D G = 0 Equilibr ium!!
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MCB 110 - Fall 2007 - Alber Transport 6 I f th e solut e has charge: Electr ochemical Gradient D G = 2 . 3 RT log 10 C i [ ] C o [ ] + zF D E where : z is t he charg e numbe r F is a c onst ant , 23.06 kcal/ mol.V DE is t he ele ctr ic pote nti al (V) The el ect ric pot enti al at th e plasma membr ane is about Ð70 mV + + + + + + + + + + out + ____ _____ ___ ____ _____ ___ membra ne - - - - - - - - - - - in - I f Na + [ ] i = Na + [ ] o 10 t hen D G = - 1 . 4 kcal / mol + ( 1 )( 23 . 06 kcal / mol . V )( - 0 . 07 V ) = - 1 . 4 - 1 . 7 = - 3 . 1 kcal / mol +
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MCB 110 - Fall 2007 - Alber Transport 7
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MCB 110 - Fall 2007 - Alber Transport 8 I I C Ð Pores and I on Channels Solutes dif fus e t hrough hydr ophilic channels in int egral membrane prot eins Aquaporin Ð Water channel t hat e nhances wat er di f fusi on. Most abundant in ki dney wher e it i s regulat ed by t he hormone vasopressin. Tet r amer, wit h one wat er c hannel per monomer. The selectivi t y fi lt er is hydr ophobic except f or a f ew wat er-binding polar re sidues.
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MCB 110 - Fall 2007 - Alber Transport 9 I on Channels Ø Øss n e t ia l f or n e rv e i mpul s eD s e r ce t i onØ mu s c l ec ontr ac t o i nØ r e u g l a t o i n o f ce ll volum eD e t cD Ø Hi l ghD s e l ec t v ie D biD r di e t c on i a l ( d own e l ec tro che m ica l g r ad n ie tØØ r eg ul a t ed (volt ageD p h osp o h r°l a t i onØ l i ga n s dD Ø R ece nt t ech nolo gi ca l de v e lopm e nt n i t h s e tu u d o on f icha nn e l § Ølon n iD g s e qu n eceD stru c tur e pr edi c t i onØ mut age n s e i s § Øn c orpor a t on n i i to h ost ce ll s ( f ro g oo cD t e § Øtu d s n ie i l i posom s e ( c ontr oll e d n e v ron i m e nt°
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