Bio211 lecture 9 (membrane structure)(1)
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Transcript of Bio211 lecture 9 (membrane structure)(1)
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