structure and function of membranes

• name 3 functions of membranes?

  control movement of substances, production of vesicles, compartmentalisation
• hydrophilic phosphate heads
• hydrophobic fatty acid tails
• Intrinsic proteins: go through both layers of the membrane (either completely or partially). They have amino acids which have hydrophobic R-groups on their surface. They are held in place because these groups are able to interact with the hydrophobic fatty acids tails. E.g. channel proteins – these allow specific substances to move through the membrane by making spaces for molecules to move through, never requires energy. Carrier proteins – change shape to carry substances across the membrane, sometimes requires energy.
• Extrinsic proteins: only go through one layer of the membrane. They have amino acids with hydrophilic amino R-groups on their surface. Those on the outside are involved with cell signalling.
• Cholesterol – lipids, it stabilises the membrane and maintains fluidity - less fluid at high temperatures to prevent water leaving the cell.
• Glycoproteins (could be extrinsic or intrinsic)– proteins with carbohydrate chains attached. Can be receptors for messages received by the cell (cell signalling). Can be involved in joining cells together (cell adhesion). Can act as antigens to allow cells to be recognised as self or non-self.
• Glycolipids (neither extrinsic nor intrinsic) – carbohydrate chains attached directly to lipids. Used as cell markers which are recognised by the immune system.