Functions of Channels and Transporters

Question 1

How do ion channels differ from aqueous pores?

Answer 1

• show ion selectivity

- NOT continuously open (can open and close)

Question 2

Where are ion channels found?

Answer 2

• ALL animal cells
• plant cells
• microorganisms

Question 3

What is the location and function of K+ leak channels?

Answer 3

• PM of most animal cells

- maintenance of RESTING membrane potential

Question 4

What gives the membrane high selective permeability?

Answer 4

lipids in the membrane

Question 5

A small flow of ions carries sufficient charge to cause a large change in the ____ _____.

Answer 5

membrane potential

Question 6

Where are the ions that give rise to the membrane potential?

Answer 6

thin (<1 nm) surface layer close to the membrane

Question 7

How are ions held on the surface layer near the membrane?

Answer 7

by their electrical attraction to their oppositely charged counterparts (counterions) on the other side of the membrane

Question 8

When is the membrane potential equal to zero?

Answer 8

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 9

What causes a nonzero membrane potential?

Answer 9

when few positive ions cross the membrane, leaving their negative counterions behind
(leak channels)

Question 10

Electrochemical gradients are measured based on what is (inside/outside) the cell.

Answer 10

inside

Question 11

The Na+/K+ pump helps maintain _____ _____ across the cell membrane.

Answer 11

osmotic balance

Question 12

The Na+ concentration inside the cell is (low/high).

Answer 12

low

Question 13

Which ion serves as the balancing role in the Na+/K+ pump?

Answer 13

K+

Question 14

Is K+ actively pumped (into/out of) the cell by the Na+/K+ ATPase?

Answer 14

into

Question 15

What is located on the PM and allows K+ to flow freely in and out of the cell?

Answer 15

K+ leak channels

Question 16

For every molecule of of ATP hydrolyzed inside the cell, the pumps move __ Na+ (in/out) and __ K+ (in/out).

Answer 16

3 out

2 in

Question 17

The equilibrium condition where there is no voltage gradient across the PM which causes K+ to flow out of cell (since there’s a high concentration of K+ inside the cell) and as it does, it leaves behind an unbalanced negative charge creating a membrane potential and once that potential reaches a certain point, K+ will no longer move out of the cell.

Answer 17

resting membrane potential

Question 18

How can the resting membrane potential be calculate?

Answer 18

Nernst Equation

Question 19

What do we need to know for the Nernst equation?

Answer 19

internal and external ion concentrations

Question 20

Which part of the neuron receive signals?

Answer 20

dendrites

Question 21

Where does the axon conduct signals from and to?

Answer 21

away from cell body and to the terminal branches of the axon

Question 22

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

Answer 22

neurotransmitter

Question 23

Which type of channel is involved in hearing?

Answer 23

mechanically gated channels

stress-activated

Question 24

Hereditary disease of ion channels and carrier proteins that involves mutations in the CFTR gene which is a chloride channel

Answer 24

cystic fibrosis

Question 25

Ion channel blocker that involves sodium channels

Answer 25

tetrodotoxin

Question 26

Ion channel blocker that involves voltage gated sodium channels

Answer 26

Saxitoxin

Question 27

Ion channel blocker that blocks sodium ion channels

Answer 27

Lidocaine and novocaine anesthetics

Question 28

Ion channel blocker that blocks potassium channels

Answer 28

Iberiotoxin (eastern indian scorpion)

Question 29

Ion channel blocker that blocks potassium channels (brown spider)

Answer 29

Heteropodatoxin

Question 30

What is tetrodoxin produced by?

Answer 30

puffer fish

Question 31

What type of drugs target molecules of the excitatory synapse?

Answer 31

Antiepileptic drugs

Question 32

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

Answer 32

ATP-binding cassette (ABC) transporters

Question 33

What are the 4 domains of ABC transporters?

Answer 33

2 hydrophobic

2 ATP-binding

Question 34

When is the interface between ATP-binding domains open?

Answer 34

when ATP is hydrolyzed

Question 35

When is the interface between ATP-binding domains closed?

Answer 35

when ATP is bound

Question 36

Clinical importance of ABC transporters: (3)

Answer 36

1. cause of drug resistance which develops in many human cancers
2. mutation in ABC chloride carrier = cause of CF
3. cause of drug resistance which frequently develops in malaria parasite

Question 37

Type of mechanism that gets proteins across a lipid bilayer membrane (inside –> outside) which are unable to pass through the bilayer directly themselves

Answer 37

exocytosis of secretory vesicles

Question 38

What are the 3 possible fates for transmembrane receptor proteins following endocytosis?

Answer 38

1. recycling
2. transcytosis
3. degradation

Question 39

What is the location and function of voltage-gated Na+ channels?

Answer 39

PM of nerve cell axon

generation of action potentials

Question 40

What is the location and function of voltage-gated K+ channels?

Answer 40

PM of nerve cell axon

return membrane to resting potential after initiation of action potential

Question 41

What is the location and function of voltage-gated Ca2+ channels?

Answer 41

PM of nerve terminal

stimulation of NT release

Question 42

What causes opening and closing of voltage gates channels?

Answer 42

changes in membrane potential

Question 43

Where are ATP-binding domains located?

Answer 43

cytosol

Question 44

purpose of sequestration of endocytosed proteins

Answer 44

recycle receptors

Question 45

Why is there antibiotic resistance?

Answer 45

mutations occurred in transporters repsonibsle for bringing antibiotics from outside to inside of bacterial cell (if it’s not inside, it won’t kill the cell bc it won’t have access to cellular machinery that it targets and tries to inhibit)