Membrane lecture 3 Flashcards

1
Q

Biological roles of ion channels

A
  • Axons have Na+ + K+ that are switched on/off

- Action potential activates Ca2+ channels → release Ca2+ → neurotransmitter fusion

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2
Q

Key properties of channel

A
  • TM protein that forms pore
  • Some selectivity
  • Filter that interacts w/ favoured ions only
  • Switch btw open + closed w/ gate or ligand
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3
Q

K+ channel topology

A
  • Conserved core topology
  • Central pore-forming region - M1, loop that goes in + out of membrane, M2
  • 4 subunits come together, M2 form lining of core pore
  • TVGYG
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4
Q

Selectivity

A
  • M2 close off channel + positions
  • All carbonyl O point the same way
  • As K+ enters, encounters 8O (S4), 8O(S3), 8O(S2), 8O(S1) and 4O(So)
  • In solution, K+ surrounded by 8H20
  • Replaced by 8O in protein = selective = no E lost
  • Na+ is smaller so H20 have stronger interaction, x fit as well, more expensive to dehydrate
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5
Q

Mechanism for K+ passing through the channel

A
  1. K+-H20-K+ as if K+ occupied S1-4 would be unstable

2. All sites occupied w/ K+ + instability means ions move quickly

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6
Q

Voltage gating

A
  • TVGYG in filter
  • Conserved Glycogen in inner helix → bend/hing in middle of helix, opens channel
  • S4 has repeat of R (+ve charge)
  • S1-4 move when change voltage
  • Pulls S4 helix down when membrane changes voltage, pulls on S4/5 linker → opens channel
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