30.04.2008Physik der Lipide
hydrophobe Wechselwirkung kritische MizellkonzentrationPermeabilitätDiffusion
Biophysik der Zelle
Inhalt• The structure of the plasma membrane• Biochemistry of lipids• Hydrophobic effect, • Micelle formation• Packing Parameter and Tanford Modell• Transport across membranes• Diffusion in membranes
Literatur:„Structure and Dynamics of Membranes“, Sackmann, Lipowsky editors, Springer„Life-as a Matter of Fat“, O. Mouritsen, Springer 2005„Intermolecular & Surface Forces“, Israelachvili, Acad.Press, 2nd Ed. 2005Sackmann Skript: Kapitel Membranen
Fluid-Mosaic Model
Nicholson& Singer 1977
Proteins diffuse freelyin a fluid matrix of lipid
Lipid membranes ascomposite materials
The structure of the spectrin network
Lipide
Due to the amphipathic nature of phospholipids,these molecules spontaneously assemble to formclosed bilayers
Phospholipid structure
Bilder Membranes
Cholesterol
Fettsäuren
218CH3(CH2)4CH=CHCH2CH=CH(CH2)7COOH
Linolsäure
118CH3(CH2)7CH=CH(CH2)7
-COOHOleinsäure
020CH3(CH2)18COOHArchinsäuren -Eicodekansäure
018CH3(CH2)16COOHStearinsäuren -Octadekansäure
016CH3(CH2)14COOHPalmitinsäuren -Hexadekansäure
014CH3(CH2)12COOHMyristinsäuren -Tetradekansäure
A n z a h l d e rungesättigtenBindungen
Anzahl derC-Atome
StrukturTrivialnameName
Nomenclature
DMPC: Dimyristoyl-Phosphatidyl-Cholin
DPPC: Dipalmitoyl-Phosphatidyl-Cholin
DSPC: Distearoyl-Phosphatidyl-Cholin
Amphiphile Moleküle assoziieren zu Aggregaten
Lipid-Monolagen
Seifenfilm
Mizelle
Lipid-Doppelschicht
Solubility and partitition function
The critical micelle concentration, where further addition of solute moleculesresult in the formation of more aggregates, while leaving the momomerconcentration constant.
Thermodynamics of lipid aggregation
The hydrophobic effect
Morphologien von Lipidaggregaten
Mizelle
Stäbchenmizelle
Vesikel
Invertierte Mizelle
Bilayer
V: Volumea0: cross section of headgroupl: alcyl chain length
The Packing-Parameter
The Tanford Modell of opposing forces
Pulling a single lipid out of a membrane
Die Entbindungskraft ist für PC-C14:0 f*≈ 12 pN. Das entspricht einer Bindungsenergiepro Molekül von Δg*~5 kBT die ein Faktor 5 kleiner ist als nach dem hydrophobenEffekt erwartet.
H. Grubmüller, Göttingen
Forcefields
Lipid bilayer consisting of 512 POPC lipids.
Grubmüller group, MPI Göttingen
Efficient, robust and tunable solvent-free bilayer modelIra R. Cooke, Kurt Kremer, and Markus DesernoPHYSICAL REVIEW E 72, 011506 2005
Outcome of physical parameters: Observables
• Diffusion constant• orientational order parameter• flip-flop rate• bending modulus• compressibility modulus• rupture tension
TRANSPORT
A pure phospholipid bilayer acts as a selectivelypermeable barrier
Diffusive flux across a membrane
Flux across an energy barrier
Transepithelial movement of glucose and amino acidsrequires multiple transport proteins
Six ways in which membrane proteins associate with the lipid bilayer. Most trans-membrane proteins arethought to extend across the bilayer as a single α helix (1) or as multiple α helices (2); some of these"single-pass" and "multipass" proteins have a covalently attached fatty acid chain inserted in the cytoplasmicmonolayer (1). Other membrane proteins are attached to the bilayer solely by a covalently attached lipid -either a fatty acid chain or prenyl group - in the cytoplasmic monolayer (3) or, less often, via anoligosaccharide, to a minor phospholipid, phosphatidylinositol, in the noncytoplasmic monolayer (4). Finally,many proteins are attached to the membrane only by noncovalent interactions with other membrane proteins(5) and (6).
Overview of membrane transport proteins
Muscle Ca2+ ATPase pumps Ca2+ ions from thecytosol into the sarcoplasmic reticulum
Na+/K+ ATPase maintains the intracellular Na+ and K+
concentrations in animal cells
Sackmann script
Proposed model for operation of the two-Na+/one-glucose symporter
Aquaporin
http://www.mpibpc.gwdg.de/abteilungen/071/bgroot/gallery.html
Chemistry Nobel Prize 2003
Die Wasserleitfähigkeit eines Aquaporinkanals beträgt bis zu 3 Milliarden Moleküle pro Sekunde.
Peter Agre
Aquaporin-1 in action. Simulation fragment of 200 ps of aquaporin-1. Generated using Molscript/Bobscript and raster3d.
„Real time“ moleculardynamics simulation
Aquaglyceroporin tetramer (blue, cyan, orange, magenta), embedded within a POPElipid bilayer(yellow head groups and green tails) surrounded by water (red,white).The total system consists of about 101,000 atoms.
Overlaid snapshots from a trajectory of a water molecule passing through AQP1 (leftand middle panels, surface and ribbon representation of the same protein structure)and hydrogen bond energies per water molecule (right). The permeation eventshown on the left lasted 3.3 ns.
Molecular Dynamics of lipid bilayers
Random walks
from
Snap shots
Mobility in the plasma membrane
Jacobson, et al. Science 268 (1995) 5216
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