Final Exam

Question 1

How many transmembrane regions does a K ion channel need?

Answer 1

6 transmembrane regions

Question 2

How many transmembrane regions does a Ca/Na ion channel need?

Answer 2

24 transmembrane regions

Question 3

What are some K channel subtypes and how many transmembrane domains do they have?

Answer 3

Inward rectifier - 2 TMD
Two pore K - 4 TMD

Question 4

What are the three families of ligand-gated ion channels?

Answer 4

1. Cys-loop - nACh, GABA(A), glycine, 5HT and ZAC (zinc)
2. Glutamate - NMDA, AMPA and kainate
3. P2X

Question 5

What are the stoichiometric subunits in neuronal vs muscular ACh?

Answer 5

Muscle – a, b, y/E, d

Neuronal
a2 – a6
b2 – b4
a7 – a10

Question 6

Where is the highest concentration of voltage-gated sodium channels?

Answer 6

Initial segment

Question 7

What produces neuron resting potential?

Answer 7

Sodium, potassium and chlorine leak channels

Question 8

How do Na+/K+ ATPases maintain the concentration gradient through ATP hydrolysis?

Answer 8

3 Na+ ions out
2 K+ ions in

Question 9

How does the electrochemical driving force (Vm – Eion) affect ion flux?

Answer 9

Negative = positive ions into the cell
Positive = negative ions into the cell

Question 10

What is Ohm’s Law?

Answer 10

V = I x R

Question 11

What is membrane capacitance?

Answer 11

Ability to store charge Q when a voltage difference V occurs between two surfaces

Question 12

What are some features of capacitors?

Answer 12

Material properties – lipid bilayer
Areas of two conducting surface
–> Larger area – increases capacitance
Thickness of insulating layer
–> Greater thickness – decreases capacitance

Question 13

What is the time constant equal to?

Answer 13

t = Rm x Cm

Question 14

What is the difference between electrical and chemical synapses?

Answer 14

Electrical - gap junctions (hemichannels built from connexin proteins)

Chemical - neurotransmitter release and ion flow through postsynaptic channels

Question 15

How does a voltage-clamp amplifier work?

Answer 15

Keeps the membrane potential constant by pumping current into the cell to counteract movement of current across the membrane

Question 16

What experiment was conducted by Labarca et al.?

Answer 16

Mutations of Leucine9’ to Serine on M2 of nAChRs

Question 17

Where is L9’ facing when channel is opened?

Answer 17

Facing away from the pore

Question 18

What is the significance of mutating Leucine to Serine?

Answer 18

Leucine is very hydrophobic whereas serine is hydrophilic

Question 19

What happened to EC50 with the Leu9’Ser mutation?

Answer 19

EC50 decreased 10-fold with each subunit mutation (1-4 mutations)

Question 20

What was the wild type EC50 compared to the 4* mutation type?

Answer 20

WT = 24uM
4M* = 2.0-2.3nM

Question 21

What happened to channel opening and bursting with the mutations?

Answer 21

Channel opened longer and bursting lasted longer

Question 22

What are the effects of hydropathy on channel opening?

Answer 22

More hydrophobic (Leu) = harder to open

Question 23

What happens when MTSEA and ACh are applied to nAChR together with a L251C mutation?

Answer 23

Leads to smaller response (inhibited)

Question 24

What does it mean when every second residue of M2 is accessible by MTSEA?

Answer 24

Every second residue must face the pore, so M2 must be a beta-strand structure

Question 25

What does it mean when every fourth residue of M2 is accessible by QX-222?

Answer 25

Every fourth residue must face the pore, so M2 must be an alpha-helix structure

Question 26

Where does L251 face when the channel is open?

Answer 26

Faces the toward the pore (opposite of Labarca et al)

Question 27

What is different about pentameric ligand-gate ion channels?

Answer 27

Doesn’t have a cys-loop

Question 28

Where was L251 pointing in the Cyro EM structure of torpedo nAChR?

Answer 28

Pointed toward adjacent subunits, not towards the pore

Question 29

What type of interactions was determined play a role in gating in the Cyro EM structure of torpedo nAChR?

Answer 29

Hydrophobic-hydrophobic interactions

Question 30

What form the two hydrophobic rings that act as the effective gate of the channel in the Cyro EM structure of torpedo nAChR?

Answer 30

Leu9’ and Val13’

Question 31

What would happen with disruption of the hydrophobic-hydrophobic interactions?

Answer 31

Subunits no longer interact, channel would open more easily

Question 32

What does Leu9’ make side-to-side hydrophobic interaction with to produce a tight “hydrophobic girdle”?

Answer 32

Neighboring alanine

Question 33

What happens to the conformation of M2 when it moves to the open position?

Answer 33

M2 straightens