Functions of Channels and Transporters

Question 1

how do ion channels differ from aqueous pores? (2)

Answer 1

ion channels show ion selectivity

ion channels are not continuously open

Question 2

how many different types of ion channels are there?

Answer 2

more than 100

Question 3

in what types of cells are ion channels found? (3)

Answer 3

animal cells
plant cells
microorganisms

Question 4

ion channel: K+ leak channel
typical location:
function:

Answer 4

plasma membrane of most animal cells

maintenance of resting membrane potential

Question 5

ion channel: voltage gated Na+ channel
typical location:
function:

Answer 5

plasma membrane of nerve axon

generation of axon potentials

Question 6

ion channel: voltage gated K+ channel
typical location:
function:

Answer 6

plasma membrane of nerve cell axon

return of membrane to resting potential after initiation of action potential

Question 7

ion channel: voltage gated Ca2+ channel
typical location:
function:

Answer 7

plasma membrane of nerve terminal

stimulation of neurotransmitter release

Question 8

ion channel: Ach receptor (ach-gated Na+ and Ca2+ channel)
typical location:
function:

Answer 8

plasma membrane of muscle cell (at neuromuscular junction)

excitatory synaptic signaling

Question 9

ion channel: GABA receptor (GABA gated Cl- channel)
typical location:
function:

Answer 9

plasma membrane of many neurons (synapses)

inhibitory synaptic signaling

Question 10

ion channel: stress-activated cation channel
typical location:
function:

Answer 10

auditory hair cell in inner ear

detection of sound vibrations

Question 11

a small flow of ions carries sufficient charge to cause a large change in the

Answer 11

membrane potential

Question 12

the ions that give rise to the membrane potential lie in a thin, less than – nm, surface layer close to the membrane

Answer 12

1 nm

Question 13

the ions that give rise to the membrane potential are held there by their — on either side of the membrane

Answer 13

counterions

Question 14

for typical cell, 1 microcoulomb of charge (6x10^12 monovalent ions) per square centimeter of membrane, transferred from one side of the membrane to the other, changes the membrane potential by roughly

Answer 14

1V

Question 15

for example, that in a spherical cell of diameter 10 um, the number of K+ ions that have to flow out to alter the membrane potential by 100 mV is only about 1/100,000 of the total number of

Answer 15

k+ ions in the cytosol

Question 16

as k+ leaks out through leak channels, it leaves behind a

Answer 16

negative charge known as membrane potential

Question 17

when is the membrane potential at zero?

Answer 17

when there is an exact balance of charges on each side of the membrane so that each positive ion is balanced by a negative counterion

Question 18

when is there a nonzero membrane potential?

Answer 18

when a few of the positive ions cross the membrane from right to left, leaving their negative counterions behind

Question 19

electrochemical gradients are measured by the charge on the

Answer 19

inside of the membrane

Question 20

the Na+K+ ATPase pump helps maintain — — across the cell membrane

Answer 20

osmotic balance

Question 21

the Na+ concentration inside the cell is

Answer 21

low

Question 22

Na+K+ pumps – into the cell

Answer 22

K+

Question 23

the plasma membrane also has K+ leak channels, which allow

Answer 23

K+ to move freely in and out of the cell

Question 24

foe every molecule of ATP hydrolyzed inside the cell, the pump moves

Answer 24

3 Na+ out

2 K+ in

Question 25

ouabain

Answer 25

inhibitor of the Na+K+ ATPase

binds to the extracellular domain of the ATPase so K+ cant bind

Question 26

ouabain and K+ compete for

Answer 26

the same site on the extracellular side of the pump

Question 27

because of the leak channels, K+ comes almost to

Answer 27

equilibrium

Question 28

how does K+ come to almost equilibrium?

Answer 28

the electrical force exerted by the excess of negative charges attracting K+ into the cell is balanced by the tendency of K+ to leak out through the leak channels down its concentration gradient

Question 29

suppose there is no voltage gradient across the plasma membrane. the high intracellular concentration of K+ will cause it to flow out of the cell through the leak channels. as K+ moves out, this leaves behind an unbalanced negative charge creating a membrane potential. once the membrane potential reaches a certain point, K+ will

Answer 29

no longer move out of the cell

Question 30

the equilibrium condition defines the

Answer 30

resting membrane potential

Question 31

resting membrane potential is about

Answer 31

-70 mV

Question 32

which equation can we use to calculate the resting membrane potential?

Answer 32

the nerst equation

Question 33

for the nerst equation, we much know the ratio of

Answer 33

internal and external ion concentrations

Question 34

the nerst equation is dependent on the

Answer 34

inside and outside concentrations of the ion

Question 35

voltage gated channels open and close based on

Answer 35

changes in membrane potential

Question 36

ligand-ligand (extracellular and intracellular ligand) channels open and close based on

Answer 36

the binding of a particular molecule to the binding site of the channel

Question 37

stress activated channels open and close based on

Answer 37

physical force

ex. hair cells involved in hearing because of the movement of sound waves through the channel

Question 38

what is the axon length?

Answer 38

less than 1 mm to more than 1 m

Question 39

an action potential is triggered by a brief pulse of current, which

Answer 39

depolarizes the membrane

Question 40

the membrane cannot fire a second action potential until the Na+ channels have

Answer 40

returned to the closed conformation

until then, the membrane is refractory to stimulation

Question 41

an action potential can only travel away from the site of depolarization because

Answer 41

Na+ channel inactivation prevents the depolarization from spreading backward

Question 42

on myelinated axons, clusters of Na+ channels can be —- apart from each other

Answer 42

millimeters

Question 43

when the membrane potential is depolarized, the channel opens and begins to conduct ions. if the depolarization is maintained, the open channel adopts an — conformation

Answer 43

inactive

Question 44

inactive conformation

Answer 44

the pore is occluded by the N-terminal 20 amino acid “ball” which is linked to the channel proper by a segment of unfolded polypeptide chain that serves as the “chain”

Question 45

when an action potential reaches the nerve terminal in the presynaptic cell, it stimulates the terminal to release its

Answer 45

neurotransmitter

Question 46

the neurotransmitter molecules are contained in synaptic vesicles and are released to the cell exterior when the vesicles fuse with the — — of the nerve terminal

Answer 46

plasma membrane

Question 47

the released neurotransmitter binds to and opens the transmitter-gated ion channels concentrated in the plasma membrane of the postsynaptic target cell at the

Answer 47

synapse

Question 48

the resulting ion flows alter the — — of the target cell, thereby transmitting a signal from the excited nerve

Answer 48

membrane potential

Question 49

cystic fibrosis

Answer 49

mutations in CFTR gene which is a chloride channel

Question 50

hereditary disease of ion channels and carrier proteins mentioned in class

Answer 50

cystic fibrosis

Question 51

tetrodotoxin blocks

Answer 51

sodium channels

Question 52

saxitoxin blocks

Answer 52

voltage gated sodium channels

Question 53

lidocaine and novocaine anesthetics block

Answer 53

sodium ion channels

used in extracting teeth, fillings, etc

Question 54

iberiotoxin (eastern indian scorpion) blocks

Answer 54

potassium channels

Question 55

heteropodatoxin (brown spider) blocks

Answer 55

potassium channels

Question 56

— is produced by puffer fish, which are prepared and served in Japan

Answer 56

tetrodotoxin

Question 57

antiepileptic drugs target molecules of the

Answer 57

excitatory synapse

Question 58

ABC transporters

Answer 58

ATP-binding cassette

Question 59

ABC transporters are a superfamily of — membrane proteins

Answer 59

integral

Question 60

what are ABC transporters responsible for?

Answer 60

ATP-powered translocation of molecules such as sugars, amino acids, lipids, ions, polysaccharides, peptides, proteins, toxins, drugs, antibiotics, xenobiotics, and other metabolites

Question 61

what are the 4 ABC transporter domains?

Answer 61

2 hydrophobic

2 ATP binding

Question 62

when is the interface between ATP-binding domains closed? when is it open?

Answer 62

closed: when ATP is bound
open: when ATP is hydrolyzed

Question 63

instances of ABC transporters of clinical importance? (3)

Answer 63

1. cause of drug resistance which develops in many human cancers
2. mutations in ABC chloride carrier is a cause of cystic fibrosis
3. cause of drug resistance, which frequently develops in malaria parasite

Question 64

— of secretory vesicles is another mechanism to get material (proteins) across a lipid bilayer membrane which are unable to pass through the bilayer directly themselves

Answer 64

exocytosis

Question 65

receptor mediated endocytosis from class

Answer 65

LDL binds to the LDL receptor which leads to the clustering of clathrin to form a clathrin coated vesicle through endocytosis.
the vesicle is uncoated of clathrin
the vesicle fuses with an endosome
the endosome fuses with a lysosome
cholesterol is released inside of the cell

Question 66

how is the LDL receptor returned to the plasma membrane?

Answer 66

a vesicle containing the receptor pinches off as a secretory vesicle, which returns the LDL receptor to the plasma membrane

Question 67

what are the possible fates for transmembrane receptor proteins following endocytosis? (3)

Answer 67

1. recycling
2. transcytosis
3. degradation

Question 68

eventually, all of the internal membranes produced by the invaginations are digested by — and — in lysosomes

Answer 68

proteases

lipases

Question 69

the invagination is essential to achieve complete digestion of endocytosed — proteins

Answer 69

membrane

Question 70

if it were not for the invagination. lysosomal hydrolyases could not digest the cytosolic domains of transmembrane proteins (because of the outer membrane of the multivesicular body becomes continuous with the lysosomal membrane) such as the

Answer 70

EGF receptor

Question 71

if it werent for the pinching of the vesicles, we wouldnt be able to save

Answer 71

receptors

Question 72

the transferrin cycle

Answer 72

after endocytosis, iron is released from the receptor-ferrotransferrin complex in the acidic late endosome compartment. the apotransferrin protein remains bound to its receptor at this pH and they recycle to the cell surface together where the neutral pH of the exterior medium causes release of the iron-free apotransferrin

Question 73

many bacteria have developed resistance to antibiotics because there has been mutations in the —, which are responsible for

Answer 73

transporters

transporting the antibiotic into the cell