20 - Potassium Channels

whats the difference between chemical and electrical gradient ?

chemical = gradient that follows the concentration of solute

electrical = gradient that follows the electrical charge

what is the purpose of ion channels ?

allow passive diffusion of ions across the membrane by electrochemical gradient

what are the properties of ion channels?

1. ion selectivity → charge selectivity or ion selectivity
2. bi-directionality
3. conductance/ permeation rate → speed of ion travels (based on ion/channel interactions)
4. regulated/ gated

what are different ways that ion channels can be regulated?

1. ligand-gated → particular affinity
2. voltage-gated → certain charge threshold to cause open
3. temp-gated→ particular temp cause open
4. pressure-gated
5. light-gated

what occurs when a person puts a fire under their hand

1. temp-gated ion chennel cause open and local depolarization
2. cause votage gated response
3. allow for ligand gated response

why are ion channels thought to be enzymes?

ion selectivity → enzyme substrate specificity

both bi-directional

conductance → enzyme turnover rate/ catalytic rate

both regulated

how do ion channels discriminate between ions ?

based on the water coordination around different ions

the presence of a selectivity filter @ potassium channel pore

* TVGYG

what are the features of selectivity filters?

* the presence of hydration shells on K is isogenic in and out of the pore
* Na must shed the hydration shell to enter the pore, but not favourable

how do ion channels facilitate translocation of charged ions across hydrophobic lipid membrane ?

pore helix dipole, delta - position at the opening of the pore

* attract the ions in

water-filled cavity

* make the selectivity filter shorter so more Na get through

how are same charge ions able to translocate lipid membrane?

spacing of K+ and water

* avoid repulsion using knock off mechanism

how do diverse stimuli such as changes in

* transmembrane voltage
* chem ligand concentration

regulate activity of ion channels

different domains are present which all have different functions

which helices are related to the pore domains and voltage-sensing domains?

pore domain = S5 and S6

voltage-sensing domain = S1, S2, S3, and S4

how are the VSD and pore domain connected?

S4-S5 linker helix which interact in S6 helix packing causing switch

what are the characteristics of the VSD?

delocalization of (+) to disperse the positive charge

how does the VSD and pore domain perform conformational change?

VSD change conformation to R state 1 @ a time

once all switched, all pore domains switch @ same time

how is the conformational change in potassium channels related to a different concept in class?

VSD = KNF-like

Pore domain = MWC-like