Ion channels

Question 1

4 examples of natural substances that are dangerous and

• where they come from,
• what they block

Answer 1

1. omega-conotoxin GVIA : Conus geographus : blocks Ca+2 channels
2. Ryanodine (RyRs) : Ryania speciosa : stuffs
3. tetrodotoxin : Fugu fish : blocks VG Na+ channels
4. alpha-bungarotoxin: sea krait : blocks nicotinic AchRs

Question 2

Kv, Nav, and Cav channels have what structure?

Answer 2

Each have 4 membrane spanning domains
     -each of the 4 domains have   
       6 alpha helices (S1-S6).
     - 4 domains are linked -->  
        single polypeptide

Question 3

Every __#?__ position on the ______ helices sense voltage. How?

Answer 3

Third, s4

• they have positively charged residues (lys or arg)

Question 4

How do K and NA/Ca channels differ?

Answer 4

In K channels, each domain is a separate pp.

Nav and Cav have the four domains linked into a single pp

Question 5

Which helices do the ‘p loop’ connect?

Answer 5

s5 and s6

Question 6

Pentamer ligand-gated channels consist of what structures?

Answer 6

1. 5 subunits combine as a heteropentamer
   
   • each subunit consists of 4
     transmembrane alpha helices
2. the 5 subunits form a selective ion conducting pathway

Question 7

ionotropic glutamate receptors are what type of ligand gated channels? (shape)

Answer 7

tetrameric ligand gated channels

Question 8

describe structure of tetrameric ligand gated channels

using NMDA receptors as an example

Answer 8

4 subunits 
      -each consists of 3 alpha   
        helices 
-two subunits bind glutamate,
-two subunits bind glycine

Question 9

Cl- channels are important for what regarding membrane potential??

Answer 9

important for stabilizing the resting membrane potential

Question 10

What is the structure of chloride channels in the CLC family?

Answer 10

Dimers

- each subunit has ion permeation pathway

Question 11

aquaporin channels

-structure

Answer 11

tetramer

• each subunit has a water permeation pathway (anti ion)
• the four water channels produces central pore

Question 12

central pore of aquaporins allow what to pass through?

Answer 12

ions and water

Question 13

channel selectivity (not gating) depends on what 5 factors?

Answer 13

1. selectivity varies between different ions
2. size
3. charge
4. dehydration
5. multiple binding sites

Question 14

Describe how dehydration can affect selectivity.

Answer 14

ion size can be affected by waters of hydration.

-ions must be substantially dehydrated (get smaller) before they pass through the channel pore

Question 15

process of activation

Answer 15

opening of channel

-caused by inside of cell being made positive

Question 16

process of deactivation

Answer 16

closing of channel

-caused by inside of cell being made negative

Question 17

typical K channels typically have activation gate/deactivation gate

Answer 17

activation gate

Question 18

what types of gates do the Na channels have?

Answer 18

activation gate
and
inactivation gate

Question 19

depolarization opens/close activation gate

Answer 19

opens activation gate

Question 20

inactivation gate is open when?

Answer 20

at the resting membrane potential

Question 21

What two processes can close the Na channel?

Answer 21

deactivation and inactivation

Question 22

repolarization opens/closes activation gate

Answer 22

closes activation gate

Question 23

activation gates and inactivation gates are near intracellular/extracellular side

Answer 23

intracellular:

- demonstrates sideness and state-dependence of agents acting on Nav and Kv

Question 24

sort channel selectivity from high to low

Answer 24

Kv>Cav>Nav>naAChR

Question 25

inactivation gate contains which repeats?

Answer 25

cytoplasmic loop region which links repeats III and IV (III-IV linker)