Molecular Structure of Ion Channels

Question 1

What is the average number of subunits for specific ion channels?

Answer 1

Voltage-Gated Ion Channels ~ 4
Transmiter-Gated Ion Channels ~ 5
Gap Junction Hemichannel ~ 6

Question 2

What is the difference between homo-oligomeric and hetero-oligomeric?

Answer 2

Homo-oligomeric = all same subunits
Hetero-oligomeric = at least one different subunit

Question 3

What is the Nicotonic AChr comprised of?

Answer 3

• contains acetylcholine binding site
• negatively charged residues to filter for cations
• M2 region contributes to pore lining

Question 4

What is the K+ Channel comprised of?

Answer 4

• 4 homomeric subunits –> channel
• each subunit has 6 TM domains
• S4 = voltage-sensor region, moves upwards at depolarization
• a selectivity filter (pore loop) for blocking

Question 5

What is the Ca2+/Na+ Channel comprised of?

Answer 5

• one subunit (monomer)
• 4 domains each with 6 TM domains
• voltage sensor
• voltage-dependent inactivation

Question 6

What is N-Type Activation of K+ Channel?

Answer 6

Inactivation with prolonged membrane depolarization
- inactivation depends on N-terminus
- current closes at inactivation

Question 7

What is the Ball and Chain Model?

Answer 7

• membrane depolarization
• channel opens
• N-terminal binds and blocks the pore = inactive

Question 8

What is a Gap Junction?

Answer 8

pores between 2 cells
- 1 subunit = connexin
- 6 subunits = hemi-channel
- 12 subunits = channel

Question 9

What are the types of Gap Junctions?

Answer 9

Homomeric - hemi-channel of same subunits
Heteromeric - hemi-channel of diff subunits

Homotypic - channel of same subunits
Heterotypic - channel of diff subunits

Question 10

What are the 5 properties of Gap Junctions?

Answer 10

1) Cytoplasmic continuity
2) Electrical synapses with short synaptic delay
3) Synchronous activation
4) Pass small molecules between cells
5) Increase intracellular acidity or [Ca2+] – close junction