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
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
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
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
5
Q
Mechanism for K+ passing through the channel
A
- K+-H20-K+ as if K+ occupied S1-4 would be unstable
2. All sites occupied w/ K+ + instability means ions move quickly
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