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Flashcards in Ion Flux Through Membranes Deck (36):

Passive Transport

Energy independent mechanism that moves molecules down their concentration gradients (from areas of high concentration to areas of low concentration)


Active transport

energy dependent mechanism that moves molecules against their concentration gradient (from area of low concentration to region of high concentration


Extracellular/intracellular Concentrations of typical Neuron


E: 145 mM
I: 15 mM


Extracellular/intracellular Concentrations

E: 4 mM
I: 150 mM


Extracellular/intracellular Concentrations

E: 50
I: 10


Extracellular/intracellular Concentrations

E: 2mM
I: 10^-8 mM

10,000X times higher in the extracellular environment


Simple diffusion

energy independent
molecules are small, non-polar. uncharged molecules diffuse freely


Facilitated diffusion

passive transport

molecules that are large and charged are unable to cross the membrane

such molecules need a facilitator i.e. proteins that can facilitate the membrane

proteins function as transporters or channels

these increase rate of transport


Difference between Channels and Transporters

channels contain core of polar residues that allow charged and polar molecules to move against membranes (WATER and ions)

transporters bind molecule on one side, undergo conformational change, translocating molecule to other side of the membrane


How do transporters translocate molecules across membrane

either via a binding induced conformation change or through ATP hydrolysis



passive transport, transports a substance in one direction (downhill)
cotransporter: transports two different substances

same direction: cotransporters



passive transport, transports two substance in one direction (downhill)

same direction: cotransporters
opposite direction: antiporter


O2, H20, CO2, N2, ethanol, urea, diethylether, NH3, benzene

which require facilitated diffusion and which will diffuse through simple means

benzene, ethanol, diethylether, O2, N2: simple
H20, urea, CO2, NH3: facilitated


Name their channels


voltage gated - Na
aquaporins- H20
GLUTs - glucose



autosomal recessive disease

defect in the transport system for DIMERIC amino acid Cystine and DIBASIC amino acids Lysine, Arginine, Ornithine

results in Cystine crystals or "stones" building in the kidneys

can be identified via a +nitroprusside test


what does cystinuria cause, and how does the patient present

results in Cystine crystals or "stones" building in the kidneys

presents with renal cholic (abdominal pain that comes in waves and is linked to kidney stones)


Hartnup disease

autosomal recessive disorder caused by a defect in a transporter for non-polar or neutral amino acids

found primarily in kidneys and intestine

discovered in infancy: failure to thrive, nystagmus (repetitive eye movement), intermittent ataxia (lack of muscle coordination), tremor, and photosensitivity


Ligand gated and voltage gated ion channels are classified as

facilitated diffusion channels


Active transport

protein assisted, energy dependent, and moves molecules against their concentration gradient

mediated by transmembrane protein transporters

bind to a specific molecule on one side of the membrane


What kind of transporters are involved, and what kind of gradients do they establish

they're transmembrane proteins that move molecules against their own gradients

they hydrolyze ATP in this process in order to induce conformation changes, allowing molecule to be released on the other side of the membrane


Examples of Primary active transporters

Na/K ATPase (2 Na's in/3 K's out): Antiporter that uses ATP

Ca ATPase


What is the charge distribution created by Na/K ATPase and what ions cause this

The Na/K ATPase moves Na against its con gradient into the extracellular matrix, and potassium against its con gradient into the intracellular cytosol

this creates an overall positive charge on the exterior surface of the cell and a negative one interiorly


inhibitors of Na/K ATPase

oubain, digoxin


secondary active transport

moves molecules against concentration gradient in an energy dependent, protein assisted manner

energy does not come ATP hydrolysis: comes from facilitated diffusion of a different molecule down its concentration gradient: this gradient is established/maintained by primary active transport mechanism


examples of secondary transporters

Na-Glu transporters
Na-linked Ca2+ antiporters


Na-Glu Transporter 1

where are they located
mediates what?
what provides the energy?
how is the gradient reset?

intestine and kidneys

mediates unidirectional movement of Na and glu across small intestine and renal tubules

movement of Na DOWN its gradient

provides energy to move glu against gradient (uphill)

gradient is established by Na/K ATPase


Na-Glu-transporter 1


moves Na-Glu from lumen of intestine into cells
Na down its gradient, glu against its gradient


Na-Ca2+ Exchanger

called NCX antiporter


function is to maintain love levels of intracellular calcium in cells

imports 3Na down their concentration gradient and exports 1 Ca against its gradient


Uptake of Dietary monosaccharides: cells involved and modes of transportation

mono, di, and polysaccharides can be transported from intestinal lumen....

across ENTEROCYTE into the blood stream through facilitated diffusion and active transport


D-glucose and D-galactose transport from the intestinal lumen into the blood stream (apical surface to basolateral surface)

both enter enterocytes at the apical surface through SGLT1 (secondary active transport) along with Na

both diffuse via facilitated diffusion out of enterocyte into the blood via GLUT2 channels

Na diffuses back into blood via PRIMARY active transport process mediated by Na/K ATPase in the basolateral membrane


Fructose is carried from intestinal lumen into blood...

only through facilitated diffusion

from apical surface via GLUT5
through basolateral surface via GLUT2


Cardiotonic drugs

cause contraction


Cardiac glycosides

ouabain and digoxin

inhibit Na/K ATPase on cardiac myocytes, causing great Na build up intracellularly, causing the NCX to stop (Calcium isn't transported out of cell): increased sarcoplasmic Ca results in stronger excitation contraction of heart muscle with each action potential


cystic fibrosis

defective chlorine chnnel

disease causes mutation in CFTR gene

CFTR is the chloride channel that mediates the active transport of Cl- from inside cells to the outside in airways and sweat ducts



chloride channel that mediates active transport of Cl from inside cells to outside in airways and sweat ducts

defect in channels causes build up of Cl and salts in airway epithelia

decrased water content of the surface mucous layer surrounding the airway epithelial cells leads to thicker mucous and leaves airway susceptible to bacterial infections


Facilitated diffusion

5 channels and how they work

polar molecules

Aquaporins - H20 (polar)

charged molecules

symporter: 2Cl/Na/K
Uniporter: voltage gated Na
Antiporter: Cl-HCO3 exchanger

big molecules