Lecture 7: Ion Channels Flashcards
Name the two major subclasses of ion channels
voltage and ligand gated
Ions have 3 important properties:
Conduct ions
Recognize and select for specific ions
They open and close in response to specific electrical, mechanical and chemical signals
Name the characteristics of voltage gated ion channels (Na+ and K+ channels)
show ion selectivity
both are voltage gated
Have voltage sensor
Na+ channel has mechanism, for inactivation
What does it mean when there is a decreased driving force?
Currents get smaller as the voltage approaches the equilibrium potential
Opening and closing of channels are __________.
voltage dependent
Tetdrotoxin blocks what kinds of Na channels
microscopic and macroscopic
T/F: Currents carried by Ca2+ are inward at potentials more negative than E(Na) and reverse their polarity above E(Na). The amplitude of current depends on Na concentration
False, currents are carried by Na not Ca
Name 3 characteristics of macroscopic K+ channels
Outward current
Do not inactivate during brief depolarizations
Depolarization increases probability of opening
The properties of a protein are determined by its amino acid sequence, aka the __________.
primary structure
Active proteins require the folding of polypeptide chains into 3-D shapes. Depending on nature and arrangement of the amino acids present, different parts of the molecule form secondary structure such as the __________ or ___________. The 3D structure is the thermodynamically most stable configuration.
alpha helices, beta sheets
What is tertiary structure?
Further folding of proteins that results in higher order
What is a heterooligomer?
moleculer structure that is constructed from distinct subunits
What is a homooligomer?
molecular structure that is constructed from a single type of subunits.
What is the structure of the single polypeptide chain?
organized into repeating motifs, each motif functioning like a subunit
In addition to the pore-forming alpha subunits, some channels contain _________ that modulate the gating characteristics of the central core.
auxillary subunits
What is the alpha subunit of Na+ channel do?
main component of Na channel, the ion conducting pore
What is the beta subunit of Na+ channel do?
accessory subunits, affect Na channel properties to target channel to membrane
What does the alpha subunit of the K+ channel do?
ion conducting pore, 4 subunits make functional channels
What does the alpha subunits of the K+ channel do?
Affect channel properties, target channels to membrance
Name the 3 Ca++ channel subunits and briefly describe their function
alpha1: ion conducting pore
alpha2δ, beta and y: ion channel properties, targeting to membrane
alpha2δ: target of anti-epileptic drugs
S4 is what part of the Na+ channel?
voltage sensor
___________ causes conformational change in channel
Depolarization
If ions are stable in solution, what does that mean in terms of it entering the pore of a channel?
it means that the ion must be equally stable in that pore. (The goal of a selective ion channel pore is to perfectly stabilize one ion while not adequately stabilizing others)
In Na+ channels, Na+ fits through a pore with a ___________ attached.
water molecule
In Na+ channels, _______ is too large to fit through with a water molecule
K+
In K+ channels, _______ is too small to be stabilized correctly withoutnwater and too large to fit with water
Na+
Na+ channels have two kinds of gates, what are they?
activation gate and inactivation gate
Describe the steps the activation/inactivation gates go thru in Na+ channels
rest: activation gate is closed, inactivation gate is open
at depolarization: activation gate opens and Na+ flows into cell
Inactivation gate closes
To reset, inactivation gate must open and activation gate must close
In K+ channel inactivation, what is n-type inactivation?
residues in the cytosolic part of the channel (the N terminus) plug the pore “ball and chain”
in K+ channel inactivation, what is c-type inactivation?
mediated by a collapse of the ion conducting pore near selectivity filter
Toxins like Tetrodotoxin and Saxitoxin block what?
Ion conducting pore of Na+ channel
Plant toxin, frog poison and rhododendron toxin, all cause what?
persistent activation of Na+ channels
Scorpion toxin, sea anemone toxin inhibit what?
inactivation of Na+ channel
Local anesthetics block ion channel from inside and are more effective on channels that open ________.
frequently
G protein coupled receptors contain what kind of protein, and what does this protein do?
can activate g proteins that can modulate channels
What can also phosphorylate channels and lead to different levels in function?
kinases
Phosphatases, which remove phosphate groups, can also _________
modulate ion channels.
