26/10/18
Professor Kenneth Linton
Cell Membranes
• Separates contents from outside
• Useful for concentration and electrochemical gradients
• Amphiphilic – hydrophilic and hydrophobic properties
o Permeability barrier to prevent most solutes from crossing – only non-polar gases
and small solutes can diffuse through
• 5nm (50Å) thick lipid bilayer
Stearic acid = saturated fatty acid
Oleic acid = unsaturated kinky fatty acid
• Inflexible and makes molecule bulkier
Amphiphilicity means they readily self-associate in water
Cylindrical shape means it favours a bilayer structure rather than a micelle
• Usually forms sheets but this means fatty acids are exposed to
water on the side so self-seals to form sphere and cut this off
Liposomes
• Can insert proteins into the membranes
• Used to deliver things to cells e.g. drugs
• Fuses with plasma membrane to release cargo
• Exosomes – little liposomes made by the cell for communication
Fluid Mosaic Model
• Implies 2D fluid
• Lateral diffusion occurs – movement of lipids through the membrane
• Rotation, flexion and flip flop can occur
o Flip flop is very rare because of hydrophilic/phobic barriers
o They can be stimulated to do this by protein mediation
Cholesterol
• Steroid ring, polar hydroxyl head group, non-polar hydrocarbon tail
• Inserts itself into membrane
• Glycerophospholipid membrane
o There is a kink in the phospholipids so not usually densely packed
o Addition of cholesterol allows tighter packing and a stiffer, gel-like membrane
• Sphingolipid membrane
o Longer, straighter fatty acid chains that are already packed tightly
o With cholesterol it packs less tightly and increases fluidity
Professor Kenneth Linton
Cell Membranes
• Separates contents from outside
• Useful for concentration and electrochemical gradients
• Amphiphilic – hydrophilic and hydrophobic properties
o Permeability barrier to prevent most solutes from crossing – only non-polar gases
and small solutes can diffuse through
• 5nm (50Å) thick lipid bilayer
Stearic acid = saturated fatty acid
Oleic acid = unsaturated kinky fatty acid
• Inflexible and makes molecule bulkier
Amphiphilicity means they readily self-associate in water
Cylindrical shape means it favours a bilayer structure rather than a micelle
• Usually forms sheets but this means fatty acids are exposed to
water on the side so self-seals to form sphere and cut this off
Liposomes
• Can insert proteins into the membranes
• Used to deliver things to cells e.g. drugs
• Fuses with plasma membrane to release cargo
• Exosomes – little liposomes made by the cell for communication
Fluid Mosaic Model
• Implies 2D fluid
• Lateral diffusion occurs – movement of lipids through the membrane
• Rotation, flexion and flip flop can occur
o Flip flop is very rare because of hydrophilic/phobic barriers
o They can be stimulated to do this by protein mediation
Cholesterol
• Steroid ring, polar hydroxyl head group, non-polar hydrocarbon tail
• Inserts itself into membrane
• Glycerophospholipid membrane
o There is a kink in the phospholipids so not usually densely packed
o Addition of cholesterol allows tighter packing and a stiffer, gel-like membrane
• Sphingolipid membrane
o Longer, straighter fatty acid chains that are already packed tightly
o With cholesterol it packs less tightly and increases fluidity
