1
TheNeedforEnergyinAc1veTransport
• Ac1vetransport
– movessubstancesagainsttheirconcentra2ongradient
– Requiresenergy
• intheformofATP
– Performedbyspecificproteins
embeddedinthemembranes
Animation: Active TransportAnimation: Active Transport
• Ac2vetransport
– allowscellstomaintainconcentra2ongradientsthatdifferfromtheirsurroundings
• Sodium‐potassiumpump
Ac1veTransport
2
EXTRACELLULARFLUID
[Na+] high[K+] low
[Na+] low[K+] high
Na+
Na+
Na+
Na+
Na+
Na+
CYTOPLASMATP
ADPP
Na+
Na+
Na+
P
3
K+
K+
6
K+
K+
5 4
K+
K+
PP
1
Fig. 7-16-7 Fig. 7-17Passive transport
Diffusion Facilitated diffusion
Active transport
ATP
2
IonPumpsMaintainMembranePoten1al
• Membranepoten1al
– voltagedifferenceacrossamembrane
– Voltageiscreatedbydifferencesinthedistribu2onofposi2veandnega2veions
• Electrochemicalgradient
– Twocombinedforcesdrivediffusionofionsacrossamembrane
• chemicalforce(theion’sconcentra2ongradient)
• electricalforce(theeffectofthemembranepoten2alontheion’smovement)
MembranePoten1al
• Electrogenicpump
• transportproteinthatgeneratesvoltageacrossamembrane
• sodium‐potassiumpump
• majorelectrogenicpumpofanimalcells
• Themainelectrogenicpumpofplants,fungi,andbacteriaisaprotonpump
MembranePoten1alFig. 7-18
EXTRACELLULARFLUID
H+
H+
H+
H+
Proton pump
+
+
+
H+
H+
+
+
H+
–
–
–
–
ATP
CYTOPLASM
–
3
Cotransport:CoupledTransportbyaMembraneProtein
• Cotransport
– occurswhenac2vetransportofasoluteindirectlydrivestransportofanothersolute
• Plantscommonlyusethegradientofhydrogenionsgeneratedbyprotonpumpstodriveac2vetransportofnutrientsintothecell
Fig. 7-19
Proton pump
–
–
–
–
–
–
+
+
+
+
+
+
ATP
H+
H+
H+
H+
H+
H+
H+
H+
Diffusionof H+
Sucrose-H+
cotransporter
Sucrose
Sucrose
BulkTransport:ExocytosisandEndocytosis
• Smallmoleculesandwaterenterorleavethecellthroughthelipidbilayerorbytransportproteins
• Largemolecules,suchaspolysaccharidesandproteins,crossthemembraneinbulkviavesicles
• Bulktransportrequiresenergy
Exocytosis
• Exocytosis
– Transportvesiclesmigratetothemembrane,fusewithit,andreleasetheircontents
– Usedbymanysecretorycellstoexporttheirproducts
Animation: Animation: ExocytosisExocytosis
4
Endocytosis
• Endocytosis
– celltakesinmacromoleculesbyformingvesiclesfromtheplasmamembrane
– reversalofexocytosis,involvingdifferentproteins
• Threetypesofendocytosis:
– Phagocytosis(“cellularea2ng”)
– Pinocytosis(“cellulardrinking”)
– Receptor‐mediatedendocytosisAnimation: Animation: Exocytosis Exocytosis and and Endocytosis Endocytosis IntroductionIntroduction
• Phagocytosis
– Cellengulfsapar2cleinavacuole
– Vacuolefuseswithalysosometodigestthepar2cle
Animation: Animation: PhagocytosisPhagocytosis
TypesofEndocytosis
Fig. 7-20a
PHAGOCYTOSIS
CYTOPLASMEXTRACELLULARFLUID
Pseudopodium
“Food” orother particle
Foodvacuole Food vacuole
Bacterium
An amoeba engulfing a bacteriumvia phagocytosis (TEM)
Pseudopodiumof amoeba
1 µm
• Pinocytosis
– moleculesaretakenupwhenextracellularfluidis“gulped”into2nyvesicles
Animation: Animation: PinocytosisPinocytosis
TypesofEndocytosis
5
Fig. 7-20b
PINOCYTOSIS
Plasmamembrane
Vesicle
0.5 µm
Pinocytosis vesiclesforming (arrows) ina cell lining a smallblood vessel (TEM)
• Receptor‐mediatedendocytosis
– bindingofligandstoreceptorstriggersvesicleforma2on
– Ligand
• anymoleculethatbindsspecificallytoareceptorsiteofanothermolecule
Animation: Receptor-Mediated Animation: Receptor-Mediated EndocytosisEndocytosis
TypesofEndocytosis
Fig. 7-20cRECEPTOR-MEDIATED ENDOCYTOSIS
ReceptorCoat protein
Coatedpit
Ligand
Coatprotein
Plasmamembrane
0.25 µm
Coatedvesicle
A coated pitand a coatedvesicle formedduringreceptor-mediatedendocytosis(TEMs)
Youshouldnowbeableto:
1. Definethefollowingterms:amphipathicmolecules,aquaporins,diffusion
2. Explainhowmembranefluidityisinfluencedbytemperatureandmembranecomposi2on
3. Dis2nguishbetweenthefollowingpairsorsetsofterms:peripheralandintegralmembraneproteins;channelandcarrierproteins;osmosis,facilitateddiffusion,andac2vetransport;hypertonic,hypotonic,andisotonicsolu2ons
6
4. Explainhowtransportproteinsfacilitatediffusion
5. Explainhowanelectrogenicpumpcreatesvoltageacrossamembrane,andnametwoelectrogenicpumps
6. Explainhowlargemoleculesaretransportedacrossacellmembrane
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