L4 - Ion channels

Question 1

What are the essential functions of ion channels? (3)

Answer 1

1) Transport ions across membrane: secretion/absorption of fluids
2) Regulate membrane potentials: nerve and muscle cells
3) Calcium influx into the cytoplasm: secretion and muscle contraction

Question 2

What are ion channels classified into groups based off? (2)

Answer 2

-Gating mechanism: voltage or ligand

-Ion selectivity of the pore – defined by physical size of filter and amino acids lining the pore

Question 3

Describe the structure of a simple (K+) ion channel? (3)

Answer 3

-Two helices with P-loop in the middle
-Has 4 subunits

Question 4

What are the 2 main functions of a voltage gated ion channel? (2)

Answer 4

1) Na+ and K+ create action potentials in excitable cells

2) Calcium ions transported into cytoplasm where secondary messenger elicits a cellular response

Question 5

Describe the difference in structure of a voltage gated ion channel? (2)

Answer 5

-Additional helices s1 and s4 that have a voltage sensing domain lateral to subunits
-Large polypeptides that extend into the cytoplasm

Question 6

What are TRP channels?
and what do they do?

Answer 6

-Transient Receptor Potential (TRP) channels

-Have evolved to sense chemicals and physical stimuli

Question 7

Describe the structure of a ligand gated ion channel? (2)

Answer 7

-They have 6 transmembrane domains which have 4 subunits
-The P loop does through the middle

Question 8

Describe the mechanism of a ligand gated ion channel? (3)

Answer 8

• Controlled by binding of a ligand (intra/extracellular)
  -Ligand bound to 3 subunits to have a response
  -Channels evolved to sense either cAMP or cGMP

Question 9

Describe the structure of an extracellular ligand gated ion channel? (2)

Answer 9

-Trimeric has 2 transmembrane domains (etc tetrameric, pentameric)

Question 10

What do extracellular ligand gated channels do? (2)

Answer 10

-Channels gated by extracellular ligands identifies distinct families of ‘ionotropic receptors’

-Na+/K+ selective channels control membrane excitability and depolarise cells

Question 11

Describe the structure of a cystic-loop receptor (nicotine’s acetycholine receptor - nAChr)?

Answer 11

-Made up of 5 transmembrane domains
(nicotine receptors)

Question 12

What is the gene a4b2 linked to?
and what are CHRNA4 (a4) and CHRNA6 (a6) linked to ?

Answer 12

-High affinity to agonists nicotine and varenicline
-Linked to tobacco dependance

Question 13

What mutation is associated with Autosomal Dominant Nocturnal frontal lobe epilepsy (mutation in nAChR)?
Why is this?

Answer 13

-Associated with mutation in CHRNA4 (a4)
-Receptors aren’t being recycled so if there’s a sudden increase in inputs it triggers seizures because the delay is blocking receptors

Question 14

What is the main neurotransmitter in the brain?

Answer 14

Glutamate

Question 15

How many transmembrane domains in glutamate receptors?

Answer 15

Tetrameric so 3 transmembrane domains

Question 16

What are the functions of the following glutamate receptors?
AMPA -
NMDA -
Kainate -

Answer 16

AMPA – mediate fast excitatory synaptic transmission in the CNS
NMDA – involved in learning and memory. Slower than other isoforms
Kainate – similar to AMPA but lesser tole at synapses and linked to schizophrenia, depression and Huntingtons

Question 17

Describe the structure of a P2X receptor? (2)

Answer 17

-2 transmembrane domains
-3 subunits

Question 18

Describe the mechanism of a P2X receptor?

Answer 18

• It is an ATP gated ion channel, 3 subunits for 3 ATPs

Question 19

P2X receptors have 7 subtypes of subunits, how is this useful?

Answer 19

-Diversity of subunits gives potential for drug treatments