Class Note for BIOC 460 at UA 4
Class Note for BIOC 460 at UA 4
Popular in Course
Popular in Department
This 7 page Class Notes was uploaded by an elite notetaker on Friday February 6, 2015. The Class Notes belongs to a course at University of Arizona taught by a professor in Fall. Since its upload, it has received 12 views.
Reviews for Class Note for BIOC 460 at UA 4
Report this Material
What is Karma?
Karma is the currency of StudySoup.
You can buy or earn more Karma at anytime and redeem it for class notes, study guides, flashcards, and more!
Date Created: 02/06/15
BIOC 460 Spring 2008 Key Concepts Free energy of transporting material across membrane depends on concentration gradient across membrane Lectures 2021 For uncharged solutes 02 AG HTln Cl Membranes 34 solutes move spontaneously AG lt 0 from compartment of higher concentration to compartment of lower Cori centratlorl Membrane Transport Equilibrium uc Owheri c g Charged solutes presence of a membrane potential as well as the Readmg 599 Wmoczko amp Swen Chem 3 pp 351376 chemical concentration gradient influences the distribution of ions Problems intextboox chapter 13 pp 379380 1 3 14a 20 AG nrlr 72 ZFAV i Jmoi structure ofvalinomycin Passive transport spontaneous passage of solute down concentration WWW andor electrical potential gradient as no input of free energy required Jmol Structure 0 gramlCldl Simple diffusion no assistance t l Facilitated diffusion rate enhanced by carrier or channel generally Animations ufvalinumycin mobile carrier and gramicidin small molecule haririeie an integral rnernbrane protein transporter or perrnease former erapid diffusion quotdownquot a concentration gradient htt vWWvbluliierri allzurla educiassesbluc4BDs rlrl MBDWebiemuresLECZEL isaturable max velocity depends on transporter concentration William especific depends on interaction of solute With transporter eExampie GLUW glucose transporter in erythrocytes Key Concepts continued Key Concepts continued Passwe transport continued Active transport transport of solute against its concentration gradient GLUT1 transporter of erythrocytes t 7 Exampre of charmemm of amngponer mote requires an exergonlc process to drive the uphill transport works by conrormanonar changeg Wed to ngand bmdmg Primary active transport transport of solute against its concentration Raw quotMSW down concemmm game gradient coupled directlyto an exergonic chemical reaction eg saturable shows a maximum velocity can measure K1 analogous ATP Vd39 39ys39s to Ki 7 Examples specific Ptype ATPases Gated ion channels ligandgated or voltageegated e Caz ATPase of muscle cell sarcoplasmic reticulum e VERY rapid 401108 ionssec quotdownquot aconcentration gradient New ATPaSe or ammar cen magma membranes 7 got saturfable f r I f 1 ABC transporters Eegree 599 39 quotV 39 quot 5 9 quot V quot95 Secondary active transport transport flow of one solute down its WES concentration gradient is usedto drive transport of a different solute AcetVlChOllrle receptor or motor HeUrOHS against its concentration gradient energy badella WWWquot Channel 7 Concentration gradient of solute that drives the unfavorable process Euxaryotic sodium potassium and calcium channels comeg new Arp WWW Terminology applying to all transporter proteins passive or active 7 Examples Uniport system in which one solute transported E culi lactose permease Htlactose symporter Cotransport system in which transport of one solute is coupled to Natgiucose symporter in some animal cells transport of another solute e Symport different solutes transported in same direction Mechanisms oftransport processes involving membrane proteins 7 Antiport different solutes transported in opposite directions usually Involve protem conformational changes I Learning Objectives Learning Objectives continued Termmology membrane potential oassrve transport Simple dl USthi Explain whether ion channels mediate passive or active transport and feelitem diffusmh ionophore gated channel F rtvoe ATF esei active use the acetylcholine receptor to explain how one ion channel can Iranspnurt primary and secondary cutranspurt ayrnpurt antipurt mm me new or MS WW Describe the GLUTW erythrocyte glucose transporter with respect to What defines equilibrium for a transport process involving an uncharged 7 5 We Ca mam solute Express it in words and in terms of concentrations atthe 9 H H origin and at the destination 2 and c2 and also in terms of kinethS ottteh ooM Saturation oehawor olots otVa vs glucose mmquot and WW vs tglucose Explain free energy changes in biological transport reactions in terms of a proposed mode of action whetherthey are favorable solute is moving in direction to go towards Name 2 Prtype ATPases and briefly explain their biological functions equilibrium dempm lt 0 or unfavorable would have to go in other Which one consumes over 30 of the ATP in animal cells in order to direction to go towards equilibrium mum gt o establishmaintain the Na and K concentration gradients and Given the equation for free energy of transport be ableto calculate electrical potential across the plasma membrane Which one Ae mmn r0 an whammy 50W e g grume gwen me establishesmaintains the Caz gradient involved in control of muscle concentrations on both sides of the membrane and the direction of COWWWW transport Outlinethe proposed mechanism by which Petype ATPases couple ATP Explain the 2 terms involved in calculating AGWW for a chargedsolute hydrolv l wgh uphill transport of solutes With the sarcoplasmic under what conditions thefirst term concentration gradient term would tetlculuth Ce sATPeSe 65 the example be favorable and under what conditionsthe 2ndterm electrical gradient Briefly explain how the E culi lactose permease couples H transport term would be favorable and lactosetransport as an example of a membrane protein that Briefly explain ionophores and the difference between mobile carriers tunethhS 65 a Secondary actwetransoorteri coupling downhill transport and channeieformlng compounds with one example of each of one Solute to uohlll transport of another solute LEC 2021 Membranes 34 Membrane Transport corrected slides 3738 36 08 BIOC 460 Spring 2008 Thermodynamics of Transport Processes equilibrium for a transport process as for any process conditions under which AGt O uncharged solutes free energy change for transporting an uncharged solute across a membrane depends only on concentration gradient across the membrane 0 For uncharged solute C2 AG c 1 where C concentration at quotoriginquotand C2 concentration at quotdestinationquot Uncharged solutes move from region of higher concentration to region of lower concentration direction in which C1 gt C2 so AG 0 when C C2 Equal concentrations defines equilibrium for a transport process involving uncharged solutes Thermodynamics of Transport Processes continued charged solutes Electrical potential charge gradient across membrane in uences distribution of ions For ion of electrical charge 2 02 AGrRTIn 70 ZFAV 1 where F Faraday constant 96 5 kJVm ol AV membrane electrical potential charge gradient across membrane in Volts AV charge gradient electrical potential gradient can result from concentration differences across membrane for OTHER ions than the one you39re looking at Overall AGtrmspmis SUM of concentration gradient term and AV term AV term can work either with or against concentration gradient You have to draw a picture of the transport process to decide on the sign of the AV term decide whether that term favors or disfavors the direction of transport of the particular ion NOTE there39s no charge gradient term if solute is uncharged ZFAVOifZO Free Energy Change for Transport of Charged Solutes AG depends on signs and relative magnitudes of concentration gradient term and charge gradient term Sum of chemical potential term electrical potential term electrochemical potential AGt 0 AG FlT In 72 ZI AV rcI1123 mM c1 Does the concentration gradient of Cl ion across this cell membrane favor transport of the ion m or out ofthe cell Without domg a calculation what would be the sign on the first term of the equation for free energy of transport of Cl out ofthe cell 0 Ciquot gt 1 so transport outwould have this term gt 0 Le positive concentration gradient CZC1 term unfavorable to transport out of cell Does the charge gradient across this cell membrane favor transport of Cl ion m orout ofthe cell Without doing a calculation what would be the sign on the charge gradient term for free energy of transport of Cl out ofthe cell lfyou ve drawn a picture like the one above it s clear that there s more neg charge inside cell than outside so last term favors transport of a negative ion like C out of cell term would have a sign Another example Transport of Charged Solutes Suppose intracellular K 157 mM and extracellular K 4 mM Suppose plasma membrane AV 0 06 V inside negative relative to outside For transport of K ions mme cell 298K is chemical potential term concentration gradient favorable or unfavorable Its sign ls electrical potential term AV term favorable or unfavorable Its sign Draw picture CZ CELL AGgRTln 7 ZFAV C1 K1 4mM Plasma membrane Chemical potential term C1 4 mMC2157 mM so CZIC1 gt1 Thus sign of concentration term is positive chemical potential unfavorable for transport in Electrical potential term Inside of cell is negative relative to outside info given drawn on diagram so charge gradient means transporting a ion K in would be favorable from a charge point of view AV term 2nd term in equation must be negative electrical potential favors transport of a ion m cell Calculation is on posted sample problems PDF file Thermodynamics of Transport Processes Summary 1 thermodynamically favorable processes AGt39 lt O AGt39 is negative Uncharged solute transport direction is favorable ifmoving from area of higher concentration to area of lower concentration C1 gt C2 direction that would result in equalization ofconcentration distribution Charged solute ion overall AGquot depends on 2 terms concentration term chemical potential favorable if moving in direction that would give equalization of concentration distribution electrical potential term favorable if moving in direction that would result in equalization of charge distribution quotpassive transportquot any transport process in direction in which AGt39 lt 0 forthe process itself Passive transport goes spontaneously because its AGt39 is negative no free energy input required to make process proceed Favorable direction often referred to as quotdownhillquot direction AGt39 lt 0 Thermodynamics of Transport Processes Summary continued What if you need to move a solute in an unfavorable direction an quotuphillquot process 2 thermodynamically unfavorable processes AG39t gt O AG39t is positive forthe process itself Moving a solute across a membrane againstits concentration andor charge gradient ie moving from area of lower concentration to area of higher concentration andor in direction that would make charge gradient even steeper requires free energy coupling to another process with a greater negative free energy change so overall AG39t will be negative active transport Kinds of tranport 1 Passive transport solute moving in favorable direction from higher concentration to lower concentration andor for charged solutes in direction that would reduce charge gradient a simple diffusion solute moves freely across lipid bilayer no membrane protein needed to assist process ipophilic solutes passing freely across membrane don39t need help LEC 2021 Membranes 34 Membrane Transport corrected slides 3738 36 08 BIOC 460 Spring 2008 Passive Transport continued b facilitated diffusion specific protein required to quotassistquot solute to cross lipid bilayer solutes pass quotdownquot concentration or charge gradient but high activation energy to get them across membrane Polar or charged solutes have to lose HZO molecules solvating them in aqueous phase before they can cross hydrophobic lipid core of membrane Protein transporter quotassistingquot molecule in membrane reduces activation energy barrier to get polar solute eg glucose across by binding solute and transporting it across membrane but only in direction dictated by concentration or charge gradient OR by providing an opening a channel for solute to cross membrane Solute moves only in direction dictated by concentration or charge gradient Transporters and channels both display substrate speci city Some transporters and channels workingquotopenquot all the time others quotgatedquot opening regulated by some signal that opens or closes Energy changes as hydrophilic solute crosses membrane Hydrated solute Transporter protein reduces a high activation energy for hydrophilic solute to cross hydrophobic core simpledimsian of lipid bilayer by withoullransporter a Forming noncovalent u T interactions with solute G L Dl uslon simple to replace Interactions g wilhtransparler drumquot with lost H20 of g hydration t and b Providing a hydrophilic passageway across membrane 39A Nelson amp Cox LennngerPrncpes Transporter 1 728 OfBOcnemSlly 4th ed Fig 1 lonophores NonProtein Carriers and Pores passive compounds that work as transporters that dissipate essential ion gradients so work as poisonsantibiotics mobile carriers example valinomycin antibiotic a cyclic depsipeptide has some ester linkages as well as peptide bonds with both D and Lamino acids specifically binds K ions diffuses randomly from one side of membrane to the other binding Poreforming compounds form pores channels in membrane through which ions can diffuse in or out of cell example Gramicidin A a peptide antibiotic with alternating K where its concentration is higher 0 and Lamino adds and releasing it where its concentration is lower Monensin similar compound specific for Na ions forms a channel large enough for protons Na and K ions to pass through but is blocked by Ca Mobile carrier eg valinomycin Poreforming r compound eg gramicidin Protein Transporter Terminology uniport transport ofjust one kind of solute e g ion channels or GLUT1 glucose transporter both passive or Ca ATPase active transport COTRANSPORT processes that COUPLE transport of more than one solute Types of Cotransport a symport cotransport process in which 2 solutes are obligatorily transported in the same direction across membrane eg E coli lac permease protons and glucose both tranported into cell b antiport cotransport process in which 2 solutes are obligatorily tranported at the same time in opposite directions across membrane eg eukaryotic NaK ATPase Eggfsmlj Antiporter svaor39e39 quotnipo e39 Examples of Protein Transporters proteinmediated transport Passive Transport Solute is moving in favorable direction from higher concentration to lower concentration andor for charged solutes in direction that would reduce charge gradient Examples 1 gated ion channels acetyl choline receptor 2 glucose transporter GLUT1 1 Gated eukaryotic ion channels Background Animal cells maintain steep gradient of Na and K ions across their plasma membranes Na0UT gtgtgt NalN 39 Km gtgt KDUT Membranes with this large ion concentrationcharge gradient are in a state of polarization they have a difference in electrical potential across their membrane AV 0 Generating and maintaining transmembrane ion concentration gradients costs cell a LOT of energy by active transport NaK ATPase below lon channels mediate passive transport permit ions to dissipate gradient crossing membrane flowing DOWN their concentration gradient but only in the quotopenquot conformation specificity highly selective for particular ions though it may not be absolute Examples of Protein Transporters proteinmediated transport Gated channels have 2 conformational states open and closed Open ltgt closed transition for channels regulated by some signal an electrical potential change voltagegated channel or a ligand ligandgated channel Open states often spontaneously convert back to closed states a kind of builtin quottimerquot that determines duration of ion flow 1 voltagegated channels electrical potential changes cause conformational change that opens channel for ions to rush in quotdownquot their concentration gradient as in propagation of nerve impulses action potentials examples eukaryotic sodium channel potassium channel calcium channel 2 ligandgated channels chemical signal e g the neurotransmitter acetylcholine binds to channel to bring about conformational change example acetylcholine receptor a nonspecific cation channel pp 370373 in Berg et al LEC 2021 Membranes 34 Membrane Transport corrected slides 3738 36 08 BIOC 460 Spring 2008 Acetylcholine Receptor a ligandgated channel Acetvlcholine Receptor a pentameric ligandgated channel Acetylcholine is the gate that opens the channel V Acetylcholine ACh Extramllular neurotransmitter Direction of domain released from synaptic nerve impulse vesicles into synaptic cleft between nerve Presynaptic cells membrane Membranespanning binds to ACh receptors segments on postsynaptic Syniprquot cell membrane 0 O Vesrde 5 na tic cleft ACh binding to receptor 0 70000 y P Seaman triggers an action potential insidethecell by opening ion channel portion of receptor protein so posesynapti Na ions rush into cell down membrane A structure of single their concentration gradient where ACh subunit of ACh receptor and recaptors are B model of 0 en form of K i ns 15h Ut Ofcell down locateu pentameric Agh receptor their concentration gradient looking down channel from Berg et al Fig 1326 Berg et al Fig 1327 outside cell 8 Acetylcholine Receptor proposed gating mechanism Glucose Transporter GLUT1 Pr p sed structural basis for opening of channel in response to 2 Glucose transporter GLUT1 In erythrocyte red blood cell membranes acetylcholine binding Background Helices lining channel white in figure below change conformation 39 Prore39n39med39ated dl USIOH transporter that s NOT an Ion Channel when ACh binds rotating along their long axis to change What kind facilitates passive transport of glucose down its concentration gradient of residues are exposed to surface of channel 0 Closed conformation large nonpolar residues block channel Leu le Phe so ions can39t pass through 0 Open conformation with ACh bound small polar or neutral Aas face channel Ser Thr Gly so Na and K ions can pass through Other tissues have other isoforms of glucose transporters homologous but products of different genes with different affinities for glucose and rates of transport appropriate for their metabolic roles eg Neurons have GLUT3 with low Km high affinity for glucose so if blood glucose is low brain gets first quotdibsquot on scarce glucose Structure of pentameric Red bloodlcells depesnd hoIn constant supply of glucose from blood as fuel ACh receptor looking 0 asma g ucose m 39 down channel from Erythrocytes quottapquot glucose as energy source via glycolysis OUtSide Ge GLUT1 increases rate of glucose diffusion from blood across plasma M2 helices rotate when ACh binds membrane into erythrocyte by a factor of 50000 B open form A closed form reconstructed from GLUT1 example cryoelectron 1 Structure 7 micrograms 2 Kinetics Closed V 39 Berg etal Fig1328 3 Proposed mechanism N 2 Glucose Transporter GLUT1 Sequence known 3D structure isn t GLUT1 Kinetics of glucose transport from outside to inside of cells Glucose doesn39tjust quotflow inquot through an open channel GLUT1 binds Dglucose by hydrogen bonds to polar residues lining proposed aqueous channel Binding is specific other hexoses bind much more weakly GLUT1 binds Dglucose with high affinity and transport rate shows saturation hyperbolic kinetics as a function of external glucose concentration E coli lactose permease another transporter with 12 transmembrane amphipathic a helices gt GLUT1 structure is thought to be similar 2 halves surrounding binding pocket for V0 for transport vs extracellular glucose Som carbohydrate Berg et al a Fig 1311 5 E hydrophobic faces of helices on outer side face lipid core of membrane and Eng hydrophilic sides line a polar pocket that39s selective for glucose 3 Ser Leu Val Thr A5n Phe lle 395 gt example 1 amphipathic a 2 3 5 helix of GLUT1 quotHelical g wheelquot diagram looking down helix axis from its amino terminus so residues are going 1 y 1 Nelsonamp ox away from you quotinto the pagequot 9quot Extratellulargluzose 1 Slam mM gehnhingezfzizctfieg of I t m emS Iy e as numbers get higher quot equot aquot quot395omquotquotv K Fig Mesi Nelson amp Cox Lehninger Pn39nciples of Kt analogous to quotKmquot for an enzymecatalyzed reaction Biochemistry 4th ed Figl 130b 4quot 39 7 Kt solute concentration that gives 12 the maximal velocity of transport LEC 2021 Membranes 34 Membrane Transport corrected slides 3738 36 08 BIOC 460 Spring 2008 2 GLUT1 Proposed Transport Mechanism 2 alternating conformations th t tt Aetritvef Trans otrt th d H 1 open to outside and the other open to inside of cell u l gllgsrablgd ir gnu ranspo 0 some 5 u 65 m a ermo ynam39ca y Glucose binding pocket isn39t open to both sides of membrane at same time unfavorable transport coupled 0 a favorable DI39OCeSS bv conformational Conformational equilibrium 1 conformation open to outside and Changes 0 mm other conformation open to inside analogous to RltgtT for Hb or ATCase Net direction of transport bindingrelease depends on relative concentrations inside and out Glucose l I J l l l GLUT1 increases rate of u K Eerg13t2al ig transport In dlrectlon 0f Coniormalion1 Conformalionz 1 Elndlng eqUilibrium Source of quotdriving forcequot for active transportconformational change AGt 0 when inside and potential energy free energy quotstoredquot in outside concentrations of 1 primary active transportquot glucose are equal C2C Net hydrolysis of ATP provides free energy needed driven by changes in conformation linked to changes in ligand bindingdissociation and covalent modificationdemodification Lightdriven proton pumps are also primary active transport or No ATP needed light is the source of energy to drive the pump 2 some solutelion gradient secondary active transport Gradient can be quottappedquot when needed so quotuphillquot transport of one solute is driven by cotransport with some other solute moving r39 7 quotdownquot its concentration gradient We Wet amp pm driven by changes in conformation linked to changes in ligand All known transport proteins appear to be asymmetrically situated transmembrane proteins that alternate between 2 conformational states with ligand binding sites 3 Dissociation f l exposed on opposite sides FwdamemSS of ofmembrane Fig 1043 Biochemistry 3rd ed bindinqdissociation Active Transport continued 1 Primary Active Transport ion transport by ATPases 1 primary Active Transport Transport ATPases catalyze 2 coupled processes quotuphillquot ion transport ATPases common generic name for ATP hydrolasesy whole family of plus ATP hydrolysis via covalent modificationdemodification of enzyme enzymes all hydrolyze ATP Phosphorylationldephosphorylation gt conformational changes Membrane ATPases use free energy of net ATP hydrolysis to pump ions altering ligand ion binding affinities across membranes All use same basic catalytic mechanism transfer of terminal phosphoryl Coupling mechanism for ion movement against concentration gradient to group from ATP to Asp side chain on enzyme phosphoaspanate ATP hydr Y5i53 Saspartyl phosphate phosphoriccarboxylic anhydride linkage a covalent modi cation linked to conformational changes associated covalent intermediate covalent catalysis with changes in ligand binding af nities Control of intracellular ion concentrations very important physiologically eg Ca concentration regulated in cell and in intracellular organelles Ca2 a signal for many cellular processes Na and K primary active transport sets up ion gradients to drive other secondary active transport processes Examples of primary active transport processes Ptype ATPases large family of homologous ATPases including Sarcoplasmic Reticulum Ca2 ATPase of muscle cell NaK ATPase Na K pump ofanimal cell plasma membranes gastric HK ATPase pumps protons into out of parietal cells into stomach to generate pH lt 1 in lumen of stomach Phosphorylation of Asp triggers conformational change required for ion transport Hydrolytic cleavage of phosphoryl group off Asp residue triggers another conformational change also required for ion transport Example of uphill ion transport by an ATPase primary active transport Sarcoplasmic Reticulum Ca2 ATPase SERCA ATPase or SR ATPase sarcoplasmic reticulum specialized endoplasmic reticulum in muscle cells Sarcoplasmic Reticulum Ca2 ATPase SERCA ATPase or SR ATPase Sarcoplasmic Reticulum Ca2 ATPase SERCA ATPase or SR ATPase thlfSitQIOQicimaCkgr md conf o caf Algpize Physiological backgroundcontext of Ca ATPase continued m la Ion 0 use e on rac Ion on m y 3 Relaxation results from activity of the quotcalcium pumpquot 2 i Ca channels and SERCA ATPase SR Caz ATPase 3 Ptype ATPase Lume mSR Muscle contraction initiated by nerve impulse delivered to muscle producing electrochemical signal action potential Electrochemical signal spreads over sarcolemmal membrane plasma Calcium C3157 um Contraction ends when cytosolic release I I I I I I 2 pump membrane of indIVIdual muscle cell and into muscle fiberthrough special ca 395 rem9ved concentrat39on 395 r channel junctions to sarcoplasmic reticulum quotSRquot specialized endoplasmic lower d 39339 by bean Pumped reticulum in muscle cells for Ca storage back into sarcoplasmic reticulum A sacs by Ca2 ATPase ATPdriven Caz pumps in SR membrane Electrochemical signal triggers release of Ca ions from the SR where Ca2 1 mM through opening of Ca2 channels ion channels large Iliimiirl proteins in the SR membrane passive diffusion Ca2 ATPase transports 2 Ca2 ions 3 i Owning mm M Cytosolic concentration of Ca normally only about 10 7 M 01 pM too low into SR per ATP hydrolyzed l ugtlniggrrmiii v to trigger contraction 0 quotIquot WNW Ca2 released by SR by opening of Ca2 channels increases cytosolic 39 3212ir15i0le SR iS 10 3 M concentration to about 10 5 M 10 uM triggering muscle contraction bound to calsequestrin Ca ions in cytosol when concentration is high as result of nerve impulse N 0 bind to a regulatory protein troponin C TnC similar in structure to CaM Sieggg s fgtael gmseriqn 523 TnC is part of the troponin complex in muscle fibers pump Ca2 ATPase Cathound form of TnC changes conformation and interacts through other proteins of troponin complex TnT and Tnl and tropomyosin to let myosin interact with actin so muscle contraction occurs ewe em 5 05quot W 3rd ed Fig 16723 LEC 2021 Membranes 34 Memb BIOC 460 Spring 2008 353 gruiaizitgl gmipl a P gay zgg29 d main f 10 a SERCA ATPase Structure ATPase membranespanning domain of 10 a P domain has Asp residue that gets Ehosphorylated by ATP hellses plusa 39domam A P N cytosohc headp39ece Active site Asp 351 in P domain indicated by arrow data 0f Ca blndlng N domain binds Nucleotide ATP fLobm prevlo is g 134 After transfer ofphosphate from A Actuator domain communicates conformational changes in P amp N Eacgb 39 lgreoupsf39 77 gi gl flgsfgf gpdomam and domains to transmembrane Ca2 binding domain h conformational ohano e disrupts 2 Ca2 ions green bind in membranespanning domain 15304 05 A5quot793Hz l Ca2 binding sites in TM domain Ca2 ions lt 9 so Q dissociates L Transmembrane I I K s quotmsquot 768 l Caldumbinding domain 7 39 sites disrupted ll 7 Asp goo N and P domains have closed around the Cytosol 2 Gm 308 39ghorylaspartat C A H mm Adomain P dumain A domain Asp 351 Asp 351 1 Ndomain Ber et al Ber et al current 39 aging 135315ll edgFig133 Berg et aquot F39g39 13 5 SERCA ATPase Proposed Mechanism SERCA ATPase Proposed Mechanism Mechanism typical of Ptype ATPases in general Membrane 2 A 1 l 1 Enzyme interconverts between 2 different conformations E1 and E2 lumen 39 ca E39 3 HAW E39 a MAD 1 E1 conformation not phosphorylated binds 2 Ca ions 2 E1Ca22 binds ATP on cytosolic side of membrane and cytosolic domains rearrange trapping the two bound Ca ions in transmembrane domain c I 3 Phosphoryl group transfer Asp side chain carboxyl nucleophile of E1 W asquot Ca22 attacks terminal phosphate of bound ATP becoming phosphorylated to E1PCa22 4 ADP dissociates from E1P triggering conformational change to E2P quoteversionquot because in absence ofbound ADP the E1E2 conformational equilibrium favors E2 state E2P conformation has lower binding af nity for D Ca ions membrane domain39s Ca2binding site disrupted 66 ea In E2 conformation cytosolic quotentryquot for Ca binding is quotclosedquot no longer quot1 our accessible for Ca dissociation E2 state has quotescape routequot open for Ca dissociation on other side of membrane into the SR lumen so Ca ions go into SR lumen lon transport has been achieved ATP has been cleaved but no hydolysis has occurred yet 5 When Ca ions dissociate phosphate is hydrolyzed off Asp residue to release P E2 P gt E2 6 E2 without covalently attached phosphate quotevertsquot again back to E1 state NaK ATPase NaK pump in animal cell plasma membranes Importance of Eukaryotic Plasma Membrane NaquotK ATPase Animal cells high intracellular K and low intracellular Na relative to extracellular medlum Na and K gradients established by NaK ATPase are used to drive other cellular processes OppOSIte gradients of Na and K reqwre free energy Input to maintain Na and K gradients energy prOVIded by ATP hydrolySIS catalyzed by a speCIfic Ptype ATPase plasma membrane NaK ATPase quotNaK pumpquot 00mm Ge VOIUme couples export of 3 Na ions to import of 2 K ions and hydrolyzes 1 make neurons and muscle cells electrically eXCitable ATP t ADP Pi 2 drive active transport of other solutes like some sugars and amino acids coupling by conformationalchar1ges same mechanism as Ca ATPase Na and W gradients so important that more than 13 of theATP 39 E1 slate b39nds Na t39gh y and K weakly39 consumed by resting animal is used to pump these ions E2 binds Na weakly and K tightly I Reactlon c ole Digitalis drug a mixture of cardiotonic ster0ids from foxglove plants E1 binds 3 Na and then ATP inside cell trapping Na in binding sites 39eavesi d 9 quot 6 compoum abquot quotquot E139s active site Asp phosphorylated by ATP to give E1PNa3 Olfabaln pronounced quotWah39banequot from waa bayyol Somali for quotarrow ADP dissociates triggering conformational switch E1PNa 3 switches PO39Son 3 POtent and SPeCIfIC Inhlbltor 0f NTK ATPase c0nf0rmamns eVeltS to EZPNTh inhibits DEphosphoryation of E2P form of plasma membrane NaK E2P releases its 3 Na on outside of cells but then binds 2 K from ATPase outside cell extracellular medium ff f d f t t t f f h I l E2PKZ is dephosphorylated hydrolysis to reiease P E2PK2 gt 6 6 6 9 r rea me nges 9 ea 339 re E2K2 and E2 reverts quotevertsquot to E1 state strengthens heart muscle contractions without increasing heart rate and E1K 2 state dissociates the 2 K ions on inside of cell and binds 3 thus increases efficiency of the heart more Na ions ready to do another cycle Berg et al p 357 explains whyhow it has this effect if you39re interested LEC 2021 Membranes 34 Membrane Transport corrected slides 3738 36 08 BIOC 460 Spring 2008 Primary Active Transport continued ABC Transporters another family of ATP hydrolysisdriven transporters unrelated to P type ATPases 2 membranespanning domains 2 ATPbinding domains quotATP Binding Cassettesquot which give ABC transporters their name Examples human MultigrugLesistance MDR1 protein extrudes againsttheir concentration gradient a variety of hydrophobic molecules from cells that express this protein pumps drugs out of cells before drugs can exert their effects for example making tumor cells resistant to chemotherapeutic agents CFTR Cystic Eibrosis Iransmembrane egulator Channelfor Cl ions to flow down their conc gradient out of the cell ATP binding and hydrolysis controls openingclosing of channel by conformational change but doesn t quotpumpquot AGt already lt 0 Some prokaryotic ABC transporters confer antibiotic resistance on bacteria expressing them pumping the antibiotics out of the cell Mechanism One conformation binds solute from one side of membrane changes conformation and releases it on other side of membrane Familiar theme though details differ from Ptype ATPases no phosphorylated intermediate forABC transporters conformational changes mediated by solute bindingrelease ATP binding and hydrolysis and ADPIPi release result in solute transport against a concentration gradient Active Transport continued 2 Secondary Active Transport Ion gradients set up and maintained by ATP hydrolysis e g Na and K gradients require energy input expenditure of ATP to set up and maintain The RESULTING concentration and charge gradients represent potential energy That potential energy electrochemical potential can be quottappedquot to drive other unfavorable transport processes Proteins couple quotdownhillquot flow of one kind of ion eg letting Na ions flow back into cell with quotuphillquot transport of another ion or solute using energy quotstoredquot in concentrationcharge gradient originally paid for by ATP to drive another otherwise unfavorable process Cotransport in secondary active transport processes a symport cotransport process in which downhill flow of one species is used to drive uphill flow of another solute in the same direction across membrane eg lac permease protons flow down their conc gradient into cell bringing lactose into cell against its conc gradient b antiport cotransport process in which downhill flow of one species is used to drive uphill flow of another solute in the opposite direction across membrane eg eukaryotic Na Ca antiporter Na flows into cell down its conc gradient while Ca is pumped out of cell against its conc gradient 2 Secondary Active Transport examples Lactose permease of E coli symporter that uses H gradient across E coli membrane generated by fuel oxidation and electron transport to let protons flow down their concentration gradient back into the cell bringing lactose into the cell against a concentration gradient conformational changes linked to H binding by a specific carboxyl group and release and lactose binding and release Lactose Berg et al Fig 1312 Other examples of secondary active transporters Sodiumcalcium exchanger of animal cell membranes antiporterthat couples downhill flow of 3 Na into cell with uphill extrusion of 1 Ca out of cell Na gradient was generated by the NaK ATPase Natglucose symporter in some animal cells uses Na gradient generated by the NaK ATPase to drive import ofglucose into some cells against a concentration gradient permitting the cell to concentrate glucose to much higher concentrations than the extracellular glucose concentration Energy transduction by membrane proteins Natglucose symporter secondary active transport is driven by Na gradient that was generated by NaK ATPase primary active transport See figure below Na Nd Na Na la Nd Nd Nd 39 Na Nd gluwse WWW N Na Gmwse Berg et al M ATP A ll0 2 K ADP 39 Pi G39Umse Fig 1312 Glumst LEC 2021 Membranes 34 Membrane Transport corrected slides 3738 36 08
Are you sure you want to buy this material for
You're already Subscribed!
Looks like you've already subscribed to StudySoup, you won't need to purchase another subscription to get this material. To access this material simply click 'View Full Document'