K
channel animation*
Let's look at role channel proteins...
CHANNEL PROTEINS
form a hydrophilic pore across a membrane and allow
small seelect
molecules or ions to cross membranes & establish gradients and electrical potentials.
channel proteins allow movement via
passive diffusion [
12.2* ]
|
K
channel animation* |
|
ION CHANNELS and
Transport
an ion channel is a trans-membrane aqueous pore
formed by a…
CHANNEL PROTEIN - membrane transport proteins which
forms a
hydrophilic pore
allowing small molecules and
ions
to move
ions via passive
uniport
[in/out].
ex:
Na /
K
/ Cl /
Ca
[ figure* ]
ROLE of Ion Channels -
makes membranes transiently permeable to charged ions
opening of a channel allows rush
(pulse) of electrical charge
in/out
ions & small hydrophilics
can move thru a membrane hydrophilic PORE
ion channels are
responsible for... Action Potentials
[
12.36* Na
& K ion channels]
...
Synaptic Transmissions [
12.39*
Ca ion channels]
PROPERTIES
of Ion Channels ("ionophores" = ion mover)
SELECTIVE - permits only some ions to pass,
and exclude others
PORE SIZE - based upon distance between & distribution of
polar charged aa's (glu, asp, his, lys, arg)
on channel protein [figure*]
often
the sphere of hydration of the ions is shed to facilitate transport
-
positive channels: allow
- ions to flow & vice versa
Gramacidin model:
cationic bacterial antibiotic ionophore
[ Na+ ]
GATED -
channels exist in OPEN/CLOSED conformation states [
figure*]
VOLTAGE Gated - open state controlled via
cell's electricl potential
LIGAND Gated
- controlled by binding of
solute [
as neurotransmitter acetylcholine* ]
STRESS ACTIVATED- as
with a
mechanical force [
auditory hair cells*
&
movie* ]
Observing Ion Channels in Action
PATCH CLAMP Recording... Procedures & Equipment & [ ecb4e 12.24* ]
microelectrode [μm meter glass tube] contacts membrane surface
