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 NameC #Double Bonds (position) Myristate140 Palmitate160 Palmitoleate16 1 (  9) Stearate180 Oleate18 1 (  9) Linoleate18 2 (  9,  12) Linolenate18 3 (  9,  12,  15) Arachidonate20 4 (  5,  8,  11,  14 ) Common Fatty Acids

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 SourcePumpSubstanceDistribution Light BacteriorhodopsinH+H+ Halobacteria HalorhodopsinCl - PhotoredoxH+H+ Photosynthetic organisms Redox potential Electron transport chain NADH oxidase H+H+ Mitochondria, bacteria Decarboxlyation Ion-transporting decarboxlyases Na + Bacteria Pyrophosphate H + -pyrophosphataseH+H+ Plant vacuoles, fungi, bacteria ATPTransport ATPases various ions Universal

ATP-Driven Pumps PumpDistributionSubstrate 1  Function F0F1F0F1 Mitochondria, chloroplasts, bacteria, plasma membranes H+H+ ATP synthesis V0V1V0V1 eukaryotic endomembranes H+H+ ATP-driven H + pumping Na/K-ATPaseplasma membrane3 Na + for 2 K + Na/K gradient generation H/K – ATPasestomach & kidney cell plasma membranes 1 H + for 1 K + gastric & renal H secretion H-ATPaseplasma membrane in yeast, plants & protozoa 1 H + proton gradient CFTRrespiratory & 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