Ligand Gated Ion Channels

Question 1

How can multi-cellular organisms respond specifically to particular stimuli. (2)

Answer 1

Selective expression of certain receptors AND molecules involved in signal transduction

Question 2

What type of protein are ion channels

Answer 2

Transmembrane Proteins

Question 3

3 essential functions of ion channels- (Fluids, Nerve and muscles, muscle contraction and ..)

Answer 3

a) Transport ions across membranes- secretion and absorption
b) Regulate membrane potentials- Nerve and muscle cells
c) Ca2+ influx into the cytoplasm- Secretion and muscle contraction

Question 4

Alpha helices

Answer 4

a right hand helix conformation

Question 5

Beta sheets

Answer 5

Beta strands connected laterally by multiple backbone hydrogen cells- 2/3

Question 6

Subunits

Answer 6

Single protein that forms with others= forms protein complex

Question 7

Transmembrane domain (TM)

Answer 7

Protein that spans the width of the membrane from the extracellular to intracellular sides (usually helical)

Question 8

P-loop or pore

Answer 8

Pocket where ion will bind

Question 9

classification of ion channels

Answer 9

Gating mechanism- Voltage or ligand
Ion selectivity of the pore- physical size and aa lining pore

Question 10

main structural features of ALL ion channels
- how many a-helices make up a TM

Answer 10

2 or more

Question 11

In a simple K+ ion channel- which side of the gate is closed

Answer 11

Cytoplasmic gate

Question 12

Voltage Gated ion channels
-Two main functions

Answer 12

-Na+ and K+ create Active potentials in excitable cells
-Ca2+ transported into cytoplasm where 2nd messenger elicits cellular response

Question 13

What structurally is different between a ‘simple’ ion channel (3) and (for example) a voltage gated one

Answer 13

Additional helices S1 and S4 form separate ‘voltage sensing domain’ laterally
Large polypeptides- extend into cytoplasm
Plugging mechanism

Question 14

‘Transient’ Receptor potential (TRP) channels
-How are they similar to Voltage gated channels
-How do they differ
(unfinished)

Answer 14

1) similar structures…
2) Evolved to recept other stimuli- chemicals and chemical (tastes and smell?)

Question 15

When calcium binds to ‘calmodulin binding’ on the ligand gated channel what happens to the pore.

Answer 15

Pore closes

Question 16

-simple channels have how many subunits
-how many subunits per Voltage gated, TRP and ligand gated

Answer 16

-3
-4

Question 17

Helicies that cross the lipid bilayer-
in simple channels
voltage gated
TRP and ligand gated

Answer 17

. 2
. 6-24
. 6

Question 18

Which of the 4 channel types (simple, voltage, TRP and Ligand) have plugging mechanisms? (2)

Answer 18

Voltage gated and TRP

Question 19

What do extracellular ligand binding sites do?

Answer 19

(i think)? they can read neurotransmitters

Question 20

3 different amounts of subunits for extracellular ligand + gates-
Nicotenic etc

Answer 20

5, 4, and 3
Nicotenic have 5

Question 21

what do each neuronal nAChRs (nicotinic Acetylcholine receptors) display different levels of depending on alpha and beta subunits

Answer 21

Each have different affinity, depending on composition and location

Question 22

Where and what does the a4b2 subunits have a high affinity for

Answer 22

Cortex and hippocampus
high affinity to agonists, nicotine and varenicline

Question 23

what does the mutation in nAChR causing Autosomal Dominant Nocturnal Frontal Lobe Epilepsy entail? (what do the receptors do?)

Answer 23

Receptor the stimuli late, causing overloaded reaction to neurotransmitters

Question 24

REMEMBERING

A4B2

Answer 24

A= agonists (nicotine etc)
B= brain
2= structures in the brain

A4B2= agonists, 2 structures in brain
High affinity 4 agonists in the brain/ cortex and hippocampus