protein channels Flashcards
do not require energy but rely on conformational changes
uniporter, symporter and anitporter
membrane permeability coefficient of large uncharged solutes and charged solutes
low membrane permeability coefficient
ion channesl
passive transport of ions
-down their electrochemical gradients (charge and concentration gradients)
why is the rate of ion movement thorugh an ion channels much faster than the rate via a uniporter
channles form a hydrophilic passageway through which multiple ions can move, simultaneously
forms a pore through membranes
membrane proteins
what are the two types of membrane channel
open- ex, porin
gated- closed channel that can be opened, is selective
what type of channels are most channels
gated
opening and closing triggered by change in membrane potential
voltage gated
opening and closing triggered by binding of a ligand to the channel protein
ligand gated
opennig and closing triggered by distortions in the cell shape (contraction)
mechanical or stretch gated
what type of gated channel is the sodium channel
voltage gated
channel structure of voltage gated channel
-hydrophobic R group on the outside interact with lipids
-polar peptide bond regions on the inside form aqueous channel
-cytoplasmic loop acts as a gate
-one helice in each segment acts as a voltage sensor
what do ion channesl consist of
-gate which opens and closes based on membrane potential
-sectivity filter that selects ion type
-voltage sensing helix detects change in membrane potential
operation of an ion channel
change in membrane potential causes shift in positively charged sensor helix which causes gate to open
voltage gated channels in an axon steps
1.membrane resting potential of -60mv
2. local depolarization/ change in membrane potential triggrers opening of nearby Na channesl leading na to flow in and membrane potential becomes +30mv
3. +30 potential cuases na channels to close and K channesl to open and k flows out and reestablishes negative potential of -75mv
4. -75mv potential caues k channesl to close and pump kick in to reestablish ion gradients
more na or k inside or outside
more na outside more k inside
T/F outside negative electric potential of 60-70 mv exists across all plast membranes
Flase bc its insdie thats negative
T/F- K resting channesl are nongated ion channels
true
the membrane potential in animal cells depends largely on resting k channels, how do these channesl achieve selectivity for k versus na which is actually smaller than k
k channels interact with 8 carbonyl oxygen atoms lining the channle resulting in a low activation energy to move into the channel
na ions cannot perfectly bind to the channl oxygen atoms
na remians hydrated and therefor needs a larger activation energy to move into the channel
what are ligand gated ion channles used for
in neurons when neurotransmitters are released at the synaptic cleft
where and when are stretch gated channels used
less common
used in sensory nerves
required the distortion in membrane that triggers opening of the gate
stretch gated channels
-tension in membrane casuses confrmational change
aquaporins
seelctive transport
-several narrow passages minimally larger than water
-pores form H bonds with water molecuels
-ions and solutes do not move through
there is a central pore and 4 pores
where does water move through in aquaporins
thorugh the narrow passages in each monomer not the central pore
