Transport Through MembranesNecessity for TransportBiological MembranesMembrane LipidsTypes of Membrane LipidsGlycerophospholipids (Glycerol 3-phosphate)Phosphatidic Acid (1,2-diacylglycerol-3-P)Membrane GlycerophospholipidsFatty AcidsGlycerophospholipid AlcoholsAmphiphilicitySphingolipids (Sphingosine)Sphingolipids (Sphingomyelin)CholesterolProperties of CholesterolOccurrence of CholesterolProperties of Lipid AggregatesMonolayers (very dilute solutions)Micelles (single-tailed lipids)Cylindrical LipidsBilayersLiposomesProperties/Uses of LiposomesMembrane ProteinsPeripheral or Extrinsic ProteinsIntegral or Intrinsic ProteinsAsymmetric OrientationSlide 28Membrane CarbohydratesMembrane StructureFluid Mosaic ModelMembrane Permeability (Impermeable to Most Polar Substrates)Thermodynamics of TransportMove Toward EquilibriumMove from Higher Concentration to Lower ConcentrationKinetics and Mechanisms of TransportTypes of TransportTerminologyNon-mediated Transport (Permeability Coefficient)Mediated Transport (Transport Proteins)Mediated Transport PropertiesSlide 42Types of TransportersIonophoresValinomycinGramicidinStoichiometryElectrical CharacterPassive-Mediated Glucose TransportSlide 50Conformational ChangeInsulin Action (Muscle and Adipocytes)ATP-Driven Active TransportNa+-K+-ATPase of Plasma Membrane (Reaction)Electrogenic AntiportMechanismSlide 57Mechanistic StepsMechanistic EvidenceGroup TranslocationPEP-dependent Phosphotransferase System (PTS)EIIIgHpr: Histidine-containing phosphocarrier proteinIon Gradient-Driven Active TransportNa+-Glucose Symport (Mechanism)Na+-Glucose Symport (Function)Lactose PermeaseTransportThrough MembranesNecessity for Transport•Plasma Membranes•Intracellular Membranes (Organelles)Biological Membranes•Organized assemblies of lipids, proteins and small amounts of carbohydrates•Regulate composition of intracellular medium by controlling flow of nutrients, waste products, ions, etc. in and out of cell•Scaffolding–Oxidative phosphorylation–Photosynthesis–Nerve impulses–Hormone receptorsMembrane LipidsGenerally soluble in organic solventsTypes of Membrane Lipids•Glycerophospholipids•Sphingolipids•CholesterolGlycerophospholipids(Glycerol 3-phosphate)H2CCHH2C OPO32-OHHOGlycerolPhosphatePhosphatidic Acid(1,2-diacylglycerol-3-P)OCHH2C OPO32-C R1H2COOCR2OFatty AcidsMembrane GlycerophospholipidsOCHH2C OC R1H2COPOO–O R3AlcoholFatty AcidsOCR2OGlycerolFatty Acids•Saturated and unsaturated•AmphiphilicCOO–Glycerophospholipid Alcohols•Ethanolamine•Serine•CholineH O C H2C H2N H3+H O C H2C HN H3+C O O–H O C H2C H2N ( C H3)3+AmphiphilicityNonpolar Tail(Hydrophobic)Polar Head(Hydrophilic)AlcoholPGlycerolSphingolipids(Sphingosine)CH3(CH2)12CH CH CHOHCHCH2OHNH2Sphingolipids(Sphingomyelin)C H3( C H2)1 2C H C H C HO HC HC H2N H C R1OO POO–O C H2C H2N ( C H3)3C h o l i n e+F a t t y A c i dMyelin Sheath – defective in some metabolic diseasesCholesterolH OC H3C H3C HC H3C H2C H2C H2C HC H3C H3F l e x i b l e H y d r o p h o b i c T a i lH y d r o p h i l i c( P o l a r H e a d )R i g i d F u s e d R i n gProperties of Cholesterol•Highly hydrophobic (low solubility)•Lowers melting point of mixed lipids•Stiffens surface proximal region of bilayerOccurrence of Cholesterol•Animal plasma membranes•Organelle membranes (some)•Precursor to steroid hormonesProperties of Lipid AggregatesMonolayers, Micelles and BilayersMonolayers(very dilute solutions)WaterPolar Head GroupsHydrophobic TailsAirMicelles(single-tailed lipids)W e d g e - S h a p e d( V a n d e r W a a l s e n v e l o p e )Critical Micelle ConcentrationCylindrical LipidsNonpolar Tail(Hydrophobic)Polar Head(Hydrophilic)AlcoholPGlycerolBilayers6 0 ÅO u t e r L e a f l e tI n n e r L e a f l e tH y d r o p h o b i cT a i l sH y d r o p h i l i cH e a d sA q u e o u s P h a s eA q u e o u s P h a s eLiposomesP h o s p h o l i p i d B i l a y e rProperties/Uses of LiposomesSingle Bilayer(inner and outer leaflets)Delivery of Therapeutic AgentsMembrane ProteinsPeripheral or Extrinsic ProteinsIntegral or Intrinsic ProteinsPeripheral or Extrinsic Proteins•Easily dissociated–High ionic strength–pH chages•Free of attached lipid (dissociated)•Water-soluble (e.g. cytochrome c)•Normal amino acid compositionIntegral or Intrinsic Proteins•Not easily dissociated•Retain associated lipid (dissociated)•>average hydrophobic amino acds•Significant number hydrophilic amino acds•Asymmetrically oriented amphiphiles•Trans-membrane proteinsAsymmetric OrientationIntegral or Intrinsic ProteinsMembrane Carbohydrates•Mostly oligosaccharides•Variety of sugars•Often sialic acid•Glycolipids•GlycoproteinsMembrane StructureFluid Mosaic ModelCarbohydratePeripheral orExtrinsic ProteinIntegralorIntrinsicProteinIntegralorIntrinsicProteinOUTSIDEINSIDELipidBilayerMembrane Permeability(Impermeable to Most Polar Substrates)Aqueous solutionsWater-soluble compoundMembraneThermodynamicsofTransportMove Toward EquilibriumMove from Higher ConcentrationtoLower ConcentrationNo information about rate of movement!Kinetics and MechanismsofTransportTypes of Transport•Nonmediated Transport (Diffusion)•Mediated Transport (Transport Proteins)–Passive-mediated Transport(facilitated diffusion)–Active TransportTerminology•Carriers•Permeases•Porters•Translocases•Translocators•TransportersNon-mediated Transport(Permeability Coefficient)Rate[A]out – [A]inRate[A]out[A]out > [A]in[A]in = ConstantMediated Transport(Transport Proteins)Rate[A]Mediated Transport Properties•Saturation kinetics•Speed and specificity•Susceptibility to competitive inhibition•Susceptibility to chemical inactivationAsymmetric OrientationTypes of TransportersIonophoresValinomycinGramicidinStoichiometryElectrical Character•Electroneutral•ElectrogenicPassive-MediatedGlucose TransportErythrocyte Glucose TransporterAsymmetric OrientationConformational ChangeInsulin Action(Muscle and Adipocytes)ATP-Driven Active TransportAgainst a concentration gradientOften coupled to ATP hydrolysisNa+-K+-ATPase of Plasma Membrane(Reaction)3 Na+(in) + 2 K+(out) + ATP + H2O3 Na+(out) + 2 K+(in) + ADP + PiElectrogenic Antiport2 K+3 Na+OutsideInsideMechanism2 K+3 N a+2 K+3 N a+3 N a+3 N a+3 N a+2 K+ – P~ PA T PM g2 +M g2 +A T PA D P3 N a+2 K+ H2OA T PB i n d i n g~ PF o r m a t i o no fA s p a r t y l ~ PPiN a+T r a n s p o r tN a+R e l e a s eK+B i n d i n gP h o s p h a t e H y d r o l y