Lecture 7: Ion Channels

Question 1

Name the two major subclasses of ion channels

Answer 1

voltage and ligand gated

Question 2

Ions have 3 important properties:

Answer 2

Conduct ions
Recognize and select for specific ions
They open and close in response to specific electrical, mechanical and chemical signals

Question 3

Name the characteristics of voltage gated ion channels (Na+ and K+ channels)

Answer 3

show ion selectivity
both are voltage gated
Have voltage sensor
Na+ channel has mechanism, for inactivation

Question 4

What does it mean when there is a decreased driving force?

Answer 4

Currents get smaller as the voltage approaches the equilibrium potential

Question 5

Opening and closing of channels are __________.

Answer 5

voltage dependent

Question 6

Tetdrotoxin blocks what kinds of Na channels

Answer 6

microscopic and macroscopic

Question 7

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

Answer 7

False, currents are carried by Na not Ca

Question 8

Name 3 characteristics of macroscopic K+ channels

Answer 8

Outward current
Do not inactivate during brief depolarizations
Depolarization increases probability of opening

Question 9

The properties of a protein are determined by its amino acid sequence, aka the __________.

Answer 9

primary structure

Question 10

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.

Answer 10

alpha helices, beta sheets

Question 11

What is tertiary structure?

Answer 11

Further folding of proteins that results in higher order

Question 12

What is a heterooligomer?

Answer 12

moleculer structure that is constructed from distinct subunits

Question 13

What is a homooligomer?

Answer 13

molecular structure that is constructed from a single type of subunits.

Question 14

What is the structure of the single polypeptide chain?

Answer 14

organized into repeating motifs, each motif functioning like a subunit

Question 15

In addition to the pore-forming alpha subunits, some channels contain _________ that modulate the gating characteristics of the central core.

Answer 15

auxillary subunits

Question 16

What is the alpha subunit of Na+ channel do?

Answer 16

main component of Na channel, the ion conducting pore

Question 17

What is the beta subunit of Na+ channel do?

Answer 17

accessory subunits, affect Na channel properties to target channel to membrane

Question 18

What does the alpha subunit of the K+ channel do?

Answer 18

ion conducting pore, 4 subunits make functional channels

Question 19

What does the alpha subunits of the K+ channel do?

Answer 19

Affect channel properties, target channels to membrance

Question 20

Name the 3 Ca++ channel subunits and briefly describe their function

Answer 20

alpha1: ion conducting pore
alpha2δ, beta and y: ion channel properties, targeting to membrane
alpha2δ: target of anti-epileptic drugs

Question 21

S4 is what part of the Na+ channel?

Answer 21

voltage sensor

Question 22

___________ causes conformational change in channel

Answer 22

Depolarization

Question 23

If ions are stable in solution, what does that mean in terms of it entering the pore of a channel?

Answer 23

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)

Question 24

In Na+ channels, Na+ fits through a pore with a ___________ attached.

Answer 24

water molecule

Question 25

In Na+ channels, _______ is too large to fit through with a water molecule

Answer 25

K+

Question 26

In K+ channels, _______ is too small to be stabilized correctly withoutnwater and too large to fit with water

Answer 26

Na+

Question 27

Na+ channels have two kinds of gates, what are they?

Answer 27

activation gate and inactivation gate

Question 28

Describe the steps the activation/inactivation gates go thru in Na+ channels

Answer 28

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

Question 29

In K+ channel inactivation, what is n-type inactivation?

Answer 29

residues in the cytosolic part of the channel (the N terminus) plug the pore “ball and chain”

Question 30

in K+ channel inactivation, what is c-type inactivation?

Answer 30

mediated by a collapse of the ion conducting pore near selectivity filter

Question 31

Toxins like Tetrodotoxin and Saxitoxin block what?

Answer 31

Ion conducting pore of Na+ channel

Question 32

Plant toxin, frog poison and rhododendron toxin, all cause what?

Answer 32

persistent activation of Na+ channels

Question 33

Scorpion toxin, sea anemone toxin inhibit what?

Answer 33

inactivation of Na+ channel

Question 34

Local anesthetics block ion channel from inside and are more effective on channels that open ________.

Answer 34

frequently

Question 35

G protein coupled receptors contain what kind of protein, and what does this protein do?

Answer 35

can activate g proteins that can modulate channels

Question 36

What can also phosphorylate channels and lead to different levels in function?

Answer 36

kinases

Question 37

Phosphatases, which remove phosphate groups, can also _________

Answer 37

modulate ion channels.