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Membranes Membrane Models Fig 6-1 Membrane Lipids • Phosphoglycerides • AKA: Phospholipids Fig 6-2 Phosphoglycerides • Variety of alcohol head groups Fig 6-2 Phosphoglycerides • Variety of fatty acid tail groups Common Fatty Acids Name C # Double Bonds (position) Myristate 14 0 Palmitate 16 0 Palmitoleate 16 1 (9) Stearate 18 0 Oleate 18 1 (9) Linoleate 18 2 (9, 12) Linolenate 18 3 (9, 12, 15) Arachidonate 20 4 (5, 8, 11, 14 ) Sphingolipids • Sphingosine in place of glycerol & 1 fatty acid Glycolipids • Sphingolipids – glycosphingolipids are predominate glycolipid • Glycosylphosphatidylinositol – GPI – Sugar chain on inositol moiety of phosphatidylinositol – Used frequently as an anchor for peripheral membrane proteins Sterol Lipids • Cholesterol – Major animal membrane sterol lipid – Major contributor to fluidity of membranes – Precursor for steroid hormone and bile salt biosynthesis Physical Properties of Biological Membranes • Lipid Compositions PS = phosphotidylserine, PC= phosotidylcholine, SM = sphingomyelin, GS = glycosphingosine, PE = phosphotidylethanolamine Physical Properties of Biological Membranes • Computer generated atomic models predicting molecular arrangements in phospholipid bilayers Membrane Proteins • Integral proteins – Transmembrane domains • 25 aa -helix • -barrel • H-bonding of all amino & carbonyl groups • Hydrophobic residues – G, A, L, I, V – Hydropathy calculations predict TM domains from protein sequence Membrane Proteins • Peripheral proteins – Acylation • Farnesylation • Myristoylation – – – – GPI anchor Electrostatic interaction Partial insertion Association with integral protein Transport Complexes Control of Membrane Permeability • Selective permeability of membranes • Control of solute movement across membranes – Pumps • "active transport" • Require energy source to achieve movement – Carriers • "passive transport" • Movement of particles down concentration gradients result in conformational changes that can allow transport against gradient – Channels • "selective passive transport" • Opening and closing is regulated Types of Membrane Pumps Energy Source Pump Bacteriorhodopsin Substance Distribution H+ Halobacteria Halorhodopsin Cl- Photoredox H+ Photosynthetic organisms Redox potential Electron transport chain NADH oxidase H+ Mitochondria, bacteria Decarboxlyation Ion-transporting decarboxlyases Na+ Bacteria Pyrophosphate H+-pyrophosphatase H+ Plant vacuoles, fungi, bacteria ATP Transport ATPases Light various ions Universal ATP-Driven Pumps Pump Distribution Substrate 1 Function F0F1 Mitochondria, chloroplasts, bacteria, plasma membranes H+ ATP synthesis V0V1 eukaryotic endomembranes H+ ATP-driven H+ pumping Na/K-ATPase plasma membrane 3 Na+ for 2 K+ Na/K gradient generation H/K – ATPase stomach & kidney cell plasma membranes 1 H+ for 1 K+ gastric & renal H secretion H-ATPase plasma membrane in yeast, plants & protozoa 1 H+ proton gradient CFTR respiratory & pancreatic epithelial cell plasma membranes ATP, Cl- Cl- secretion Classes of Carriers F and V family ATPases Carrier Kinetics Channel Proteins Channel Complexes Chemiosmotic Cycles
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