Ion Channels

Question 1

What are the 4 electrical current terms and their units?

Answer 1

Potential (V) in volts
Current (I) in amperes
Resistance (R) in ohms
Conductance (G) in siemens

Question 2

What is current?

Answer 2

Movement of charge
Direction = movement of + charges from high to low potential

Question 3

What is the equation for voltage and conductance?

Answer 3

V=IR

G=1/R or G=I/V

Question 4

What is an ion channel?

Answer 4

• protein that forms pores for ions to transverse bilayer
• conduct ions, selective, open/close, sensor

Question 5

What are the components of an ion channel?

Answer 5

• selectivity filter (rigid)
• sensor and gate
• (-) residues at pore entrance to repel anions and attract cations

Question 6

What are 3 types of gating of channels?

Answer 6

Electrical = voltage-gated (depolarize membrane)
Chemical = ligand-gated (ligand bind)
Mechanical = mechanically-gated (channel stretches)

Question 7

How does the voltage sensor move?

Answer 7

the voltage sensor moves as the gate opens

Question 8

What is hydration?

Answer 8

• water stabilizes ions
• depends on charge + size
• determines ionic mobility in water
• MORE HYDRATION = LESS MOBILE

Question 9

How does hydration differ between Na+/K+/Cl-?

Answer 9

Na+: higher hydration number = lower mobility (carry H2O)
K+ and Cl-: lower hydration number = higher mobility (carries less H2O)

Question 10

How does hydration work in the channel?

Answer 10

The C=O bond of the selectivity filter replace water and stabilize ion through the pore
- Na+ too small to interact with all 4 chains of K+ channel
- not favoured