Membrane Transport System

This slide focuses on the channel and carrier protein, passive and active transport.

1. CHAPTER TWO
Membrane Transport System
Topic:MembraneTransportSystem
Outline:
•Membrane transport
•Membrane Transport Proteins
•Classes of carrier proteins
•Types of transport
•Passive transport
•Active transport

2. Teachingandlearningmethods:Lectures,visualaid,interactiveforms,assignmentand
groupdiscussion.
Attheendofthislecturestudentshouldbeabletoanswerfollowingquestions.
•What do you mean by Membrane transport?
•Explain the Membrane Transport Proteins.
•Explain the Carrier proteins and ion channel.
•Differentiate between Passive and active transport.
Referencebooks:
1.LehningerPrinciples of Biochemistry, 6
th
Edition-Nelson DL & Cox MM, Chapter 11;
page: 389-395
2.Bacterial Metabolism, 2
nd
Edition-Gottschalk G; Chapter five; page: 104-109

3. Membranetransport
•Incellularbiologythetermmembranetransportreferstothe
collectionofmechanismsthatregulatethepassageofsolutessuch
asionsandsmallmoleculesthroughbiologicalmembranes,which
arelipidbilayersthatcontainproteinsembeddedinthem.
•Theregulationofpassagethroughthemembraneisdueto
selectivemembranepermeability-acharacteristicofbiological
membraneswhichallowsthemtoseparatesubstancesofdistinct
chemicalnature.Inotherwords,theycanbepermeabletocertain
substancesbutnottoothers.
•Themovementsofmostsolutesthroughthemembraneare
mediatedbymembranetransportproteinswhicharespecialized
tovaryingdegreesinthetransportofspecificmolecules.

4. Figure-1: Fluid mosaic model for membrane structure.

5. Membrane Transport Proteins
•Manymoleculesmustmovebackandforthfrominsideand
outsideofthecell.
•Mostcannotpassthroughwithouttheassistanceofproteinsin
themembranebilayer.
•Eachcellhasmembranehasaspecificsetofproteinsdepending
onthecell.
2kindsofproteinsinvolved
1.Carrierproteins
2.Ionchannels

6. 1.CARRIERPROTEINS
Carrierproteinsfacilitatethediffusionofdifferentmolecules
Carrierproteinsareintegral/intrinsicmembraneproteins;theyexist
withinandspanthemembraneacrosswhichtheytransportsubstances.
Bindtoaspecifictypeofdiffusing
molecule.
Haveahighlyspecifichydrophilic
regiontowhichthesolute
moleculebinds.
Bindingcausetheproteinto
undergoachangeinshapethat
movesthesoluteacrossthebilayer
andreleaseitontheotherside

7. Classes of carrier proteins:
Uniport(facilitateddiffusion)carriersmediatetotransportasingle
solute.
Symport(cotransport)carriersbindtwodissimilarsolutes
(substrates)&transportthemtogetheracrossamembrane.
Transportofthetwosolutesisobligatorilycoupled.
Antiport(exchangediffusion)carriersexchangeonesolutefor
anotheracrossamembrane.

8. 2. ION CHANNELS:
Channelproteinsareinvolvedinthe
movementofions,smallmolecules,or
macromolecules(suchasanother
protein)acrossabiologicalmembrane
Formedbyproteinswithacentralpore
thatislinedwithchargedgroups.
Helpthediffusionofchargedparticles
suchasCa
2+,
Na
+
,K
+
,HCO
3-
andCl-ions.
Somechannelsaregatedandallow
cellstoregulatetheflowofionsfrom
onecelltoanother

9. ImpermeableMembranes
•Ionsandhydrophilicmoleculescannot
easilypassthroughthehydrophobic
membrane.
•Smallandhydrophobicmoleculescan
easilypassthroughthehydrophobic
membrane.

10. Typesoftransport
A.Passivetransport
—Simplediffusion
—Facilitateddiffusion
—Osmosis
Activetransport
A.Primary active transport
B.Secondary active transport
Passive transport
a)SimpleDiffusion
—Noenergyrequired
—Downconcentrationgradient
—Moleculesequallydistributeacrossavailableareabytype
—Non-polarmolecules(steroids,O
2,CO
2)

12. b)Facilitateddiffusion
—Noenergyrequired
—Downconcentrationgradient
—Moleculesequallydistributebutcrossmembranewiththehelpof
achannelproteinorcarrierprotein.

13. a)Osmosis:
—Movementofwateracrosscellmembrane
—Watercrossescellmembranesviaspecialchannelscalled
aquaporins
—Solutesareimpermeabletocellmembrane.
—Movesinto/outofcelluntilsoluteconcentrationisbalanced.

15. •Hypotonic solution –fewer solutes in solution
•Isotonic solution –equal solutes in solution
•Hypertonic solution –more solutes in solution

17. Activetransport
Activetransportisthemovementofmoleculesacrossacellmembraneinthe
directionagainsttheirconcentrationgradient,i.e.movingfromanareaof
lowerconcentrationtoanareaofhigherconcentration.
Activetransportisusuallyassociatedwithaccumulatinghighconcentrations
ofmoleculesthatthecellneeds,suchasions,glucoseandaminoacids.
Iftheprocessuseschemicalenergy,suchasfromadenosine
triphosphate(ATP),itistermedprimaryactivetransport.
Secondaryactivetransportinvolvestheuseofanelectrochemical.
Activetransportusescellularenergy,unlikepassivetransport,whichdoes
notusecellularenergy.
Examplesofactivetransportincludetheuptakeofglucoseintheintestinesin
humansandtheuptakeofmineralionsintoroothaircellsofplants.

19. Primaryactivetransport
—Primaryactivetransport,alsocalleddirectactivetransport,directlyuses
metabolicenergytotransportmoleculesacrossamembrane.
—Mostoftheenzymesthatperformthistypeoftransportaretransmembrane
ATPases.OthersourcesofenergyforPrimaryactivetransport
areredoxenergyandphotonenergy(light).
—AnexampleofprimaryactivetransportusingRedoxenergyisthe
mitochondrialelectrontransportchainthatusesthereductionenergy
ofNADHtomoveprotonsacrosstheinnermitochondrialmembraneagainst
theirconcentrationgradient.
—Anexampleofprimaryactivetransportusinglightenergyaretheproteins
involvedinphotosynthesisthatusetheenergyofphotonstocreateaproton
gradientacrossthethylakoidmembraneandalsotocreatereductionpower
intheformofNADPH.

20. Secondary active transport
—Insecondaryactivetransport,alsoknownascoupledtransportorco-
transport,energyisusedtotransportmoleculesacrossamembrane;
however,incontrasttoprimaryactivetransport,thereisnodirectcoupling
ofATP;insteaditreliesupontheelectrochemicalpotentialdifferencecreated
bypumpingionsin/outofthecell.
—Permittingoneionormoleculetomovedownanelectrochemicalgradient,
butpossiblyagainsttheconcentrationgradientwhereitismoreconcentrated
tothatwhereitislessconcentratedincreasesentropyandcanserveasa
sourceofenergyformetabolism(e.g.inATPsynthase).

21. Process
Therearetwotypesofactivetransport:primaryandsecondary.Inprimaryactivetransport,
specializedtrans-membraneproteinsrecognizethepresenceofasubstancethatneedstobe
transportedandserveaspumps,poweredbythechemicalenergyATP,tocarrythedesired
biochemicalacross.Insecondaryactivetransport,pore-formingproteinsformchannelsinthe
cellmembraneandforcethebiochemicalacrossusinganelectromagneticgradient.Often,this
energyisgainedbysimultaneouslymovinganothersubstancedowntheconcentration
gradient
Exampleofprimaryactive
transport,whereenergyfrom
hydrolysisofATPisdirectly
coupledtothemovementof
aspecificsubstanceacrossa
membraneindependentof
anyotherspecies.

22. Active transport:
Na
+
K
+
Pump (Na
+
K
+
ATPase)
3 Na
+
out
2 K
+
in

23. Active Transport PassiveTransport
Definition
ActiveTransportusesATPtopumpmolecules
AGAINST/UPtheconcentrationgradient.Transport
occursfromalowconcentrationofsolutetohigh
concentrationofsolute.Requirescellularenergy.
MovementofmoleculesDOWNtheconcentration
gradient.Itgoesfromhightolowconcentration,in
ordertomaintainequilibriuminthecells.Doesnot
requirecellularenergy.
Types of
Transport
Endocytosis,cellmembrane/sodium-potassiumpump&
exocytosis
Diffusion,facilitateddiffusion,andosmosis.
Types of
Particles
Transported
Proteins,ions,largecells,complexsugars. Anythingsoluble(meaningabletodissolve)inlipids,
smallmonosaccharides,water,oxygen,carbondioxide,
sexhormones,etc.
Examples
Phagocytosis,pinocytosis,sodium/potassiumpump,
secretionofasubstanceintothebloodstream(processis
oppositeofphagocytosis&pinocytosis)
Diffusion,osmosis,andfacilitateddiffusion.
Importance
Ineukaryoticcells,aminoacids,sugarsandlipidsneedto
enterthecellbyproteinpumps,whichrequireactive
transport.Theseitemseithercannotdiffuseordiffuse
tooslowlyforsurvival.
Itmaintainsequilibriuminthecell.Wastes(carbon
dioxide,water,etc.)diffuseoutandareexcreted;
nutrientsandoxygendiffuseintobeusedbythecell.
Functions
Transportsmoleculesthroughthecellmembraneagainst
theconcentrationgradientsomoreofthesubstanceis
insidethecell(i.e.anutrient)oroutsidethecell(i.e.a
waste)thannormal.Disruptsequilibriumestablishedby
diffusion.
Maintainsdynamicequilibriumofwater,gases,
nutrients,wastes,etc.betweencellsandextracellular
fluid;allowsforsmallnutrientsandgasestoenter/exit.
NoNETdiffusion/osmosisafterequilibriumis
established.