1. Lecture 14 Membranes continued Diffusion Membrane transport

2. From S. Feller Lipid Bilayers are dynamic distributions of phosphate and carbonyl groups and lateral pressure profiles

3. from S. White Distribution of groups along the z-axis

4. Electrostatic potential Electric Double Layer (EDL) Dipole Potential

5. surface pressure  = 70 dyne/cm compressed monolayer surface pressure of the crowding surfactant balances part of the surface tension, thus the apparent surface tension to the left of the barrier is smaller Lipids at air-water interface

6. Irving Langmuir  w -  surf =  surf  surf  w - surface tension of pure water  surf - surface tension in the presence of surfactant  surf  surf – surface pressure of the surfactant dipalmitoyl phosphatidylcholine (DPPC) monolayer-bilyer equivalence pressure 35-40 dyn/cm

7. Schematics for measuring surface potentials in lipid monolayers

8. what’s wrong?

9. Differential Scanning Calorimeter (DSC): Phase transition for DPPC (Dipalmitoyl phosphatidylcholine) http://employees.csbsju.edu/hjakubowski/classes/ch331/lipidstruct/oldynamicves.html For DOPC (oleyl)…-18°C For DPPC (palmytoyl)…+41°C  S =  H/T m

10. Mixtures of phospholipids Two phases www.mpikg-golm.mpg.de/th/people/jpencer/raftsposter.pdf

11. Increases short-range order Broadens phase transition Sizes are wrong?

12. Biochim Biophys Acta. 2005 Dec 30;1746(3):172-85. DOPC/DPPC POPC…palmitoyl, oleyl http://www.nature.com/emboj/journal/v24/n8/full/7600631a.html Phospholipid/ganglioside Lateral Phase Separation

13. Diffusion is a result of random motion which simply maximizes entropy Einstein treatment: c1c1 c2c2 ll but C distance negative slope therefore: but (Fick’s law) (one dimension)

14. y x z 1D 2D 3D l

15. Diffusion = random walk time X, distance Diffusion equation Fick’s law fluxgradient rate

16. Variance Normal distribution Random walk in one dimension D = diffusion coefficient t = time 0.060.040.020 0.040.06 0 20 40 60 80 100 p1x() p2x() p3x() x, cm t = 1 s t = 10 s t = 100 s D = 10 -5 cm 2 /s root-mean-square (standard) deviation x = deviation from the origin Replace: where

17. 01234 0 0.5 x,  1.0 0.607 area inside 1  = 0.68 If we step 1 sigma (  ) away from the origin, what do we see? concentration observer

18. x = x 1, x 2, x 3 t = t 1, t 2, t 3 t, s 00.0050.010.0150.020.025 0 20 40 60 80 100 x, cm  = 0.0045 cm  = 0.014 cm  = 0.045 cm t 1 = 1 s t 2 = 10 s t 3 = 100 s An observer sees that the concentration first increases and then decreases 1  is a special point where the concentration of the diffusible substance reaches its maximum 020406080100 0 10 20 30 40 50 60 t = 1 s t = 10 s t = 100 s x = 0.0045 cm x = 0.014 cm x = 0.045 D = 10 -5 cm 2 /s

19. Diffusion across exchange epithelium Einstein eqn: - mean square distance (cm 2 ) D – diffusion coefficient (cm 2 /s) t – time interval (s) “random walk”