Ion Channels

Question 1

What are the three types of ion channels?

Answer 1

~ voltage-gated
~ neurotransmitter-gated
~ 2nd messanger-gated

Question 2

Voltage-gated

Answer 2

e.g. action potential
~ Na+ channels (influx)
~ K+ channels (efflux)
~ Ca2+ channels (influx)
NOTE: in exam answer need to talk about equilibrium + nernst voltages

Question 3

Neurotransmitter-gated

Answer 3

e.g. synapse
~ controlled by extracellular substances
~ +ve ions = action potential e.g. ACh
~ -ve ions = inhibit

Question 4

2nd messenger-gated

Answer 4

~ open using a cytosolic 2nd messenger (cAMP or cGMP)

pathways: Ca2+ and rhodopsin

Question 5

Rhodopsin + dark state

Answer 5

~ more depolarisation as more +ve ions enter

~ +ve membrane voltage

Question 6

Rhodopsin + light state

Answer 6

~ decrease in cGMP = channel closes = hyperpolarisation

Question 7

IP3 receptors

Answer 7

Ca2+ selective and release Ca2+ form the ER to increase cytosolic Ca2+

Question 8

Basic structure of one subunit of a voltage-gated channels (5)

Answer 8

~ 6 TMS domains
~ 1 pore domain
~ voltage sensor = made of +ve a.a. residues
~ long N terminus which forms a ‘ball and chain’ arrangement
~ four subunits in total, p-domains in middle

Question 9

P-loop

Answer 9

forms the selectivity filter and pore region in voltage-gated channels
~ if P domain moved onto another channel, current changes

Question 10

Mechanism of ion selectivity and transport of K+ channels

Answer 10

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