Ion Flux Through Membranes

Question 1

Passive Transport

Answer 1

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

Question 2

Active transport

Answer 2

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

Question 3

Extracellular/intracellular Concentrations of typical Neuron

Na

Answer 3

E: 145 mM
I: 15 mM

Question 4

Extracellular/intracellular Concentrations

K

Answer 4

E: 4 mM
I: 150 mM

Question 5

Extracellular/intracellular Concentrations

Cl

Answer 5

E: 50
I: 10

Question 6

Extracellular/intracellular Concentrations

Ca2+

Answer 6

E: 2mM
I: 10^-8 mM

10,000X times higher in the extracellular environment

Question 7

Simple diffusion

Answer 7

energy independent

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

Question 8

Facilitated diffusion

Answer 8

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

Question 9

Difference between Channels and Transporters

Answer 9

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

Question 10

How do transporters translocate molecules across membrane

Answer 10

either via a binding induced conformation change or through ATP hydrolysis

Question 11

Uniporter

Answer 11

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

same direction: cotransporters

Question 12

cotransport

Answer 12

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

same direction: cotransporters
opposite direction: antiporter

Question 13

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

which require facilitated diffusion and which will diffuse through simple means

Answer 13

benzene, ethanol, diethylether, O2, N2: simple

H20, urea, CO2, NH3: facilitated

Question 14

Name their channels

Na
H20
glucose

Answer 14

voltage gated - Na
aquaporins- H20
GLUTs - glucose

Question 15

Cystinuria

Answer 15

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

Question 16

what does cystinuria cause, and how does the patient present

Answer 16

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)

Question 17

Hartnup disease

Answer 17

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

Question 18

Ligand gated and voltage gated ion channels are classified as

Answer 18

facilitated diffusion channels

Question 19

Active transport

Answer 19

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

Question 20

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

Answer 20

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

Question 21

Examples of Primary active transporters

Answer 21

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

Ca ATPase

Question 22

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

Answer 22

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

Question 23

inhibitors of Na/K ATPase

Answer 23

oubain, digoxin

Question 24

secondary active transport

Answer 24

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

Question 25

examples of secondary transporters

Answer 25

Na-Glu transporters

Na-linked Ca2+ antiporters

Question 26

Na-Glu Transporter 1

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

Answer 26

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

Question 27

Na-Glu-transporter 1

Answer 27

symporter

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

Question 28

Na-Ca2+ Exchanger

Answer 28

called NCX antiporter

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

Question 29

Uptake of Dietary monosaccharides: cells involved and modes of transportation

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

Answer 29

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

Question 30

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

Answer 30

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

Question 31

Fructose is carried from intestinal lumen into blood…

Answer 31

only through facilitated diffusion

from apical surface via GLUT5
through basolateral surface via GLUT2

Question 32

Cardiotonic drugs

Answer 32

cause contraction

Question 33

Cardiac glycosides

Answer 33

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

Question 34

cystic fibrosis

Answer 34

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

Question 35

CFTR

Answer 35

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

Question 36

Facilitated diffusion

5 channels and how they work

Answer 36

polar molecules

Aquaporins - H20 (polar)

charged molecules

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

big molecules

GLUTs