Ion Channels (E3)

Question 1

What is the general structure of an ion channel?

Answer 1

Many peptide subunits extending through the length of the bilayer; an H₂O-filled pore

Question 2

Why is the plasma membrane (PM) not very permeable to ions?

Answer 2

The hydrophobic tails of the phospholipid bilayer’s interior

Question 3

Why are ion channels not open at all times?

Answer 3

Because channels open and close in response to various stimuli

Question 4

What is an open probability?

Answer 4

The fraction of time that a channel is open

Question 5

List 2 varieties of ion channels. Mention the stimuli that their open probabilities depend on.

Answer 5

1) Voltage-gated: OP depends on membrane potential (V_m)

2) Ligand-gated: OP depends on ligand binding & concentration

Question 6

What is the function of the selectivity filter?

Answer 6

To prevent larger ions from passing through the aqueous pore

Question 7

How does the selectivity filter prevent larger ions from passing through?

Answer 7

The filter has a specific size and shape

Question 8

Describe the specific interactions between the ion and the selectivity filter.

Answer 8

Ions bind water molecules tightly, so they must shed some of that water to fit through the narrow selectivity filter. Additionally, carboxyl/carbonyl oxygens within the filter must interact with the ion to compensate for the loss of waters of hydration. Electronegativity & atomic radius size will play important roles here