Quiz 1 Material Lipids Membranes Permeability Transport Channels Membrane Poten9al Receptors as Channels GPCRs RTKs Phosphoinosi9des PIPs Fick s Law of Di usion di usion random con9nuous movement of molecules driven by kine9c energy Js L DA C X Js ux of substrate S D di usion coe cient A area C concentra9on X distance Permeability Constant P used when COMPLETE di usion is NOT occurring Js PA C units of P distance 9me distance X across membrane not known transport experiment on cell membranes 1 Measure permeability of di erent molecules 2 Vary concentra9on outside 3 Measure accumula9on inside cell ux Calculate P 4 di usion straight line through origin ALWAYS LINEAR carrierLmediated transport facilitated di usion approach to max value satura9on s9ll goes through origin b c no net ux if no conc gradient ac9ve transport ux w L conc gradient transport w either no conc gradient or a conc gradient moving in opposite direc9on CarrierOMediated Transport Mechanism of Carrier Mediated Transport glucose transport in RBCs AA transport in bacteria structure conserved 12 TM domains does conforma9onal change Glucose transport in red blood cell Amino acid transport in bacteria Structure conserved 12 transmembrane domains Active Transport Ac4ve Transport Na K ATPase Pump Active Transport Movement Of Molecules Against a Concentration Gradient maintains HIGH K LOW Na inside gradient 2 K go IN 3 Na go OUT transports Na K against Sodium Potassium ATPase Maintains high K inside Maintains low Na inside Transports Na and K against gradient Electrogenic electrogenic inside always Requires ATP more neg than outside Strict ordering of steps Similar pumps for H and Ca requires ATP similar pumps for H Ca2 no ATP hydrolysis w o No ATP hydrolysis without transport transport Transport Cycle Ac4ve Transport POType Pump Mechanism of P Type Active Transport Pumps phosphorylates step 1 dephosphorylates step 3 itself during transport nucleo9de binding to protein induces conforma9onal change nucleo9de state of enzyme controls conforma9on ion a nity P type pump is phosphorylated during transport Binding of nucleotide to protein induces a conformational change Nucleotide state of enzyme controls conformation and affinity for ion high or low Domains of Pump Ac4ve Transport Ca2 Pump changes in nucleo9de ligand induce conforma9onal change from E1 to E2 states E1 inwardLfacing HIGH a nity for Ca2 cytoplasmic ion access E2 outwardLfacing LOW a nity for Ca2 extracellular ion access Calcium Active Transport Pump Transmembrane Region Nucleotide Domain Phosphorylation Domain Activator Domain Changes in nucleotide ligand induce conformational change from E1 to E2 States E1 inward facing and high affinity for calcium E2 outward facing and low affinity for calcium 2 structures Coupled Transport Na Glucose Symport Na H An4port Coupled Transport electrochemical gradient drives transport SYMPORT Na Glucose ANTIPORT Na H Na gradient drives transport of other solutes energy supplied directly by Na K ATPase Electrochemical gradient drives transport Symport Na glucose Antiport Na H Sodium gradient drives transport of other solutes Energy supplied indirectly by Na K ATPase Lac permease Coupled Transport Lac Permease H gradient drives lactose uptake steps 1 H binds outside 2 Lactose binds outside 3 TM helices 9lt shiq 4 Lactose releases inside 5 H releases inside 6 TM helices 9lt shiq Rates of Pumps Transporters Channels pumps SLOW transporters moderate channels FAST Rate of Transporters Pumps and Channels Pumps slow Transporters moderate Channels fast Electrochemical Poten4al ion movement controlled by conc gradient electrical force membrane poten9al voltage across membrane chemical poten9al conc gradient across membrane res9ng L60 mV more neg inside G ZF V Z charge F Faraday s constant V voltage G RT ln Cout Cin R gas constant T temp oK electrochemical poten9al G ZF V RT ln Cout Cin Channels integral membrane proteins w a hydrophilic pore that provides a path for ion movement selec9ve passage of speci c ions can exist in open or closed states regulates ion movement patch clamp used to study channels Patch Clamp Method Patch Clamp Method Nobel Prize in 1992 measure channel proper9es dura9on of opening current voltage func9on conductance inverse of resistance 1 R higher conductance means bigger hole ion selec9vity regula9on structure func9on V IR I C CV Plot current vs voltage Slope gives conductance if not a simple straight line then voltage sensi9ve Measure Channel Properties Duration of Opening Current Voltage Function Conductance Ion Selectivity Regulation Structure Function V IR I C I CV Voltage V Resistance R Current I Conductance C Plot Current vs Voltage Slope gives conductance If not a simple straight line then voltage sensitive Units Volts pAmps pA pSiemens pS Nernst Nernst Equa4on K Leak Channel K Leak Channel always open sets membrane poten9al K ows un9l electrical chemical forces are in balance equilibrium Nernst Equa9on V RT ZF ln ion out ion in relates electrical chemical forces on ion can calculate membrane poten9al IF ionout in is known ion is at equilibrium revised form of equa9on can predict net movement of an ion not in equilibrium across a membrane membrane poten9al largely generated by K leak channels Ac4on Poten4al VG Na Channels Action Potential Voltage Gated Na Channels unidirec9onal propaga9on 3 structural states open closed inac9vated refractory period channel closes itself structural features pore voltage sensor ion selec9vity lter inac9va9on gate to close Unidirectional Propagation Three Structural States Open Closed Inactivated Channel Closes Itself Structural Features Pore Voltage Sensor Ion Selectivity Filter Inactivation Gate to Close 3 States 3 States of VG Na Channel During an Ac4on Poten4al 3 States of the Voltage Gated Na Channel During an Action Potential 1 Closed state in res9ng cell at L60 mV 2 Depolariza9on opens channel for short 9me 3 Open channel 4 inac9vates itself Inac9vated channel reverts to closed state Closed state in resting cell at 60 mV Depolariza tion opens channel for a short time Open Channel inactivates itself Inactivated channel reverts to the closed state Structure Structure Func4on of VG Channels VG Na Channels vs VG K Channels pore 24 TM spans Structure Function of Voltage Gated Channels 4 sets of 6 Pore 24 Transmembrane Spans 4 Sets of 6 Na 24 in 1 pep9de K 4 pep9des quaternary structure voltage sensor Lcharged M4 Voltage Sensor charges M4 Channel Closing Na channel 24 in 1