Chem 452 - Lecture 8 Lipids and Cell Membranes Part 3 Question of the Day: What role do proteins play in biological membranes? Form vs. Function The membrane lipids give form to the cell membranes The membrane proteins provide the function 2 Membrane proteins function as Pumps (Chapter 13) Channels (Chapter 13) Signal transducers (Chapter 14) Energy transducers (Chapter 18 & 19) 3 Different membranes contain different proteins. They can visualized using SDS-Polyacrylamide electrophoresis. (Chapter 3, pp.71-75) 4
Different membranes contain different proteins 5 Different membranes contain different proteins RBC plasma membrane retinal rod cell photoreceptor membrane muscle cell sarcoplasmic membrane 6 Proteins can associate with membranes in different ways. 7 Proteins can associate with membranes in different ways. We will look a three different examples Bacteriorhodopsin (pump) Porin (channel) Prostaglandin H 2 synthase-1 (enzyme) 8
Archaeal Bacteriorhodopsin (Pump) Uses light energy to transport ions across the membrane. 9 Bacteriorhodopsin (7 -helical bundle) There are 7 non-polar stretches of amino-acids. 10 Bacteriorhodopsin (7 -helical bundle) There are 7 non-polar stretches of amino-acids. 10 Bacteriorhodopsin (7 -helical bundle) There are 7 non-polar stretches of amino-acids. 10
Hydropathy plots are used to look for membrane spanning -helicies Glycophorin 11 Hydropathy plots are used to look for membrane spanning -helicies Determining Transfer Energies Glycophorin 11 Hydropathy plots are used to look for membrane spanning -helicies Glycophorin 11 Hydropathy plots are used to look for membrane spanning -helicies Glycophorin 12
Porin (Channel) 13 Porin (Channel) 13 Porin (Channel) 13 Porin (Channel) 13
Porin (Channel) 13 Porin (Channel) Sequence alternates between polar and non-polar amino acid residues 14 Porin (Channel) Sequence alternates between polar and non-polar amino acid residues 15 Porin (Channel) Sequence alternates between polar and non-polar amino acid residues 15
Porin (Channel) Sequence alternates between polar and non-polar amino acid residues 15 Prostaglandin H 2 synthase-1 catalase (Enzyme) 16 Prostaglandin H 2 synthase-1 catalase (Enzyme) Promotes inflammation and modulates gastric acid secretion 16 Prostaglandin H 2 synthase-1 (Enzyme) 17
Prostaglandin H 2 synthase-1 catalase (Enzyme) 18 Prostaglandin H 2 synthase-1 (Enzyme) Inhibited by COX inhibitors (NSAID) 19 Peripheral proteins are often have hydrophobic lipids attached to them. 20 Lateral Diffusion in membranes can have a wide range of values. 21
Lateral Diffusion in membranes can have a wide range of values. S = (4Dt) 1/2 21 Lateral Diffusion in membranes can have a wide range of values. 21 Transverse diffusion is very slow. 22 Fluid Mosaic Model of Singer and Nicolson (1972). 23
Transverse diffusion is very slow. 24 Transverse diffusion is very slow. 24 Transverse diffusion is very slow. 24 25
Membranes are asymmetric 27 Bacterial cells 28 Eukaryotic cells 29
Eukaryotic cells 29 Eukaryotic cells 29 Next up Unit V, Lecture 9 - Membrane Channels and Pumps. (Chapter 13) 30