Membranes and Transport Chapter 5 1 Biological membranes are phospholipid bilayers with proteins i Glycerol molecule connected to phosphate group a Phospholipids ii 2 fatty acids iii Amphipathic b Membrane fluidity is affected by temperature i Fatty acid chain length 1 Short chain increases fluidity ii Fatty acid saturation 1 Increase in unsaturated fatty acids double bonds are liquid at room temperature increase fluidity iii Cholesterol 1 Fluidity buffer 2 Keeping fatty acids fluid at low temperature 3 Stabilizing heads at high temperature c Integral proteins i Embedded in bilayer ii Trans membrane amphipathic d Peripheral proteins i Associated but not embedded in bilayer ii Bound to integral protein 2 Membrane fluidity a Proteins lateral movement within single layer i Can t flip flop between layer b Proteins anchor to cytoskeleton i Asymmetric distribution 3 Protein functions in cell membranes a Attached to cytoskeleton main cell shape b Enzymatic activity mones c Signal transduction proteins act as binding site for chemical messenger hor d Intercellular junction cell adhesion proteins attach membranes of adjacent cells e Cell recognition f Transport across membrane 4 Passive and active transport in cell membranes a Plasma membrane is selectively permeable b Passive transport c Active transport i Cells use metabolic energy ATP 5 Diffusion a Passive transport i Cell doesn t spend metabolic energy ATP ii Energy for transport is found from gradient concentration b Net movement of substance down concentration gradient i From higher concentration to low concentration c Rate of diffusion depends on temperature size of molecule electrical charge and concentration d Consider simple diffusion of CO2 across plasma membrane i What is the direction of net movement 1 Interior to exterior ii What is the source of energy 1 Concentration gradient 6 What substances readily diffuse across a lipid bilayer a Gases O2 CO2 N2 b Hydrophobic substances c Smaller polar molecules including water d Ions can t pass because of charge 7 Osmosis a Diffusion of water solvent across cell membrane b Direction of osmosis is determined by difference in solute concentration 8 Comparing 2 solutions a Isotonic solution i Same concentration b Hypotonic solution i Lower solute concentration ii Higher H2O concentration c Hypertonic solution i Higher solute concentration ii Lower H2O concentration a Animal cell i Hypotonic lysed ii Isotonic normal iii Hypertonic shriveled b Plant cell 9 Osmosis and water balance of animal and plant cells i Hypotonic turgid normal ii Isotonic flaccid iii Hypertonic plasmolyzed 10 Carrier mediated active transport a Integral membrane proteins b Examples i Aquaporin water transport ii Sodium potassium pump K ions 1 Animal cells 2 ATP required 3 Establish electrical gradient iii GLUT1 glucose transport 11 Endocytosis and exocytosis active transport a Endocytosis i Pinocytosis 1 Cell drinking ii Phagocytosis 1 Cell eating iii Process 1 Fold of plasma membrane surround particle to be ingested form ing small vacuole around it 2 Vacuole then pinches off inside cell 3 Lysosomes fuse with vacuole and pour potent hydrolytic enzymes onto ingested material b Exocytosis i Cell ejects waste products or secretions ii Growth of plasma membrane iii Process 1 Vesicle approaches plasma membrane 2 Fuses with it and 3 Release its contents outside cell 12 Receptor mediated Endocytosis a Main mechanism by which eukaryotic cells taken macromolecules b Plasma membrane with receptor proteins c Macromolecules bind to receptor proteins d Formation of coated vesicle e Vesicle fuses with lysosome f Vesicles recycled