Lecture 14 Membranes continued Diffusion Membrane transport Lipid

Lecture 14 Membranes continued Diffusion Membrane transport

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

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

Electrostatic potential Dipole Potential Electric Double Layer (EDL)

Lipids at air-water interface s = 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

dipalmitoyl phosphatidylcholine (DPPC) monolayer-bilyer equivalence pressure 35 -40 dyn/cm psurf Irving Langmuir sw- ssurf = psurf sw - surface tension of pure water ssurf - surface tension in the presence of surfactant psurf – surface pressure of the surfactant psurf

Schematics for measuring surface potentials in lipid monolayers

what’s wrong?

Differential Scanning Calorimeter (DSC): Phase transition for DPPC (Dipalmitoyl phosphatidylcholine) DS = DH/Tm For DPPC (palmytoyl)…+41°C For DOPC (oleyl)…-18°C http: //employees. csbsju. edu/hjakubowski/classes/ch 331/lipidstruct/oldynamicves. html

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

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

Lateral Phase Separation Phospholipid/ganglioside http: //www. nature. com/emboj/journal/v 24/n 8/full/7600631 a. html DOPC/DPPC Biochim Biophys Acta. 2005 Dec 30; 1746(3): 172 -85. POPC…palmitoyl, oleyl

Diffusion is a result of random motion which simply maximizes entropy Einstein treatment: c 1 c 2 l l negative slope C distance but therefore: but (Fick’s law) (one dimension)

1 D 2 D z 3 D l y x

Diffusion = random walk Fick’s law time flux gradient Diffusion equation rate X, distance

Normal distribution Random walk in one dimension Replace: 100 Variance 80 root-mean-square (standard) deviation D = 10 -5 cm 2/s t=1 s p 1(x) 60 p 2(x) p 3(x) 40 where D = diffusion coefficient t = time x = deviation from the origin t = 10 s 20 0 t = 100 s 0. 06 0. 04 0. 02 0 0. 02 x, cm 0. 04 0. 06

s If we step 1 sigma ( ) away from the origin, what do we see? concentration 1. 0 0. 607 area inside 1 = 0. 68 0. 5 s 0 0 1 observer 2 x, s 3 4

D = 10 -5 cm 2/s t = t 1, t 2, t 3 100 80 60 s = 0. 0045 cm s = 0. 045 cm t 3 = 100 s 20 0 40 t 2 = 10 s s = 0. 014 cm 40 0 0. 005 0. 01 x = 0. 0045 cm t=1 s 50 t 1 = 1 s 60 x = x 1, x 2, x 3 0. 015 0. 025 x, cm An observer sees that the concentration first increases and then decreases x = 0. 014 cm t = 10 s 30 20 x = 0. 045 t = 100 s 10 0 0 20 40 60 80 t, s 1 s is a special point where the concentration of the diffusible substance reaches its maximum 100

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