Inner organization of the cellStructure

BarriersMaintenance of the inner structure of the cell

FunctionTransportSignal transmission

Unity of structure and functionMembrane structureMembrane transportCell compartmentalization and protein sortingVesicle transportSignal transmission

Structur & organization of the main components of biological membranes

Lipid bilayerMembrane proteins

Membrane lipids are amphipatic and form bilayers in watery milieu

Lipid bilayer behaves like a two dimensional liquid

2mm/s

Fluidity depends on the composition of the lipid bilayer

Fatty acidssaturatedunsaturated

Lipid compositionCholesterol Different phospholipidsGlycolipids

CholesterolA B

Stabilizes lipid bilayerPrevents transport of small water soluble moleculesSeparates CH-chains to prevent cristallisation

Phospholipids are two-dimensional solvents for membrane proteins

Lipid bilayer is assymetrical

Lipid bilayers are not permeable for solvents and ions

Membrane proteins have different functions

Structure of membrane proteinsAssociation with lipid-bilayer

Membrane proteins can be linked to lipid bilayer in different ways

Most transmembrane proteins span the lipid bilayer with an αlpha-helix

Transmembrane proteins can water-filled transmembrane channels

Hydrophilic side chains are directed towards the inner core of the pore which is formed by hydrphobic single chains

Maximisation of hydrogen bond formation through „beta-Barrel“

Example: Porines

16 beta-sheets form a transmembrane water-filled channel

Plasma membrane proteinsA B

GlycocalixProtectionSurface recognitionCell-Cell contacts

Cell-cell adhesion in blood

Membran proteins can be solved and purified with detergents

The plasma membrane is enforced by a cytoskeleton

Membrane proteins diffuse within the membrane

Fluorescence recoveryafter light bleaching

Cells can limit protein and lipid movement to certain membrane domains

Example: Epithelial cells