CH 13 Membrane Channels and Pumps P2

Question 1

K+ Channel

Answer 1

four subunits - homologous to one of repeated units in Na+ channel.
cone-shaped.

Question 2

Na+ Channel Purification

Answer 2

on basis of affinity to neurotoxin tetrodotoxin

Question 3

Na+ Channel

Answer 3

4 repeated regions of similar seq.

each region has 5 hydrophobic segments, 1 hydrophilic segment.

Question 4

Ca+ Channel

Answer 4

homologous to Na+ channel

Question 5

Shaker

Answer 5

mutated version of K+ channel

Question 6

K+ Channel reveals the basis of?

Answer 6

ion specificity

Question 7

The K+ channel transports K+ across the membrane ____ and ____.

Answer 7

selectively

rapidly

Question 8

K+ Channel does not transport?

Answer 8

larger ions - too big to enter channel.

smaller ions - cannot interact w/ selectivity filter.

Question 9

What happens to the K+ ion in the K+ Channel?

Answer 9

Selectivity filter has 4 binding sites.
Hydrated K+ ions enter sites, 1 at a time, losing hydration shells.
when 2 ions occupy adj. sites - electrostatic repulsion forces them apart.
ions enter channel from one side, other ions pushed out other side.

Question 10

These 2 channels are homologous to the K+ Channel:

Answer 10

Na+ and Ca2+

Question 11

Ca2+ Channels have what 4 residues?

Answer 11

(4) E - glutamate

Question 12

Na+ Channels has what 4 residues?

Answer 12

D - aspartate
E - glutamate
K - lysine
A - alanine

Question 13

K+ Channel Structure

Answer 13

4 ion-binding sites

accounts for rapid transport of K+ ions down [gradient]

Question 14

Voltage Gating Channels

Answer 14

Na+ and K+ Channels.

change conf. w/ change in membrane potential.

Question 15

Which segments of the K+ channel are involved w/ voltage gating?

Answer 15

S1 - S4 - paddle domains.
-changes in membrane potential alter paddle conf. to open / close channel.
S4 - voltage sensor.

Question 16

How is the K+ inactivated?

Answer 16

physically blocking channel.

ball segment of channel tethered by polypeptide segment (chain).

Question 17

A channel can be inactivated by?

Answer 17

occlusion of pore

Question 18

Mutants that do not inactivate lack?

Answer 18

ball and chain

Question 19

Protease-Accessible

Answer 19

protease can be used to cleave chain provided chain is flexible.

Question 20

Depolarization opens?

Answer 20

channel.

creates binding site for ball, inactivates channel.

Question 21

Acetylcholine Receptor

Answer 21

ligand-activated channel tat acetylcholine binds to.
NT released into synaptic cleft.
opens channel for K+ and Na+.
triggers action potential.

Question 22

Acetylcholine Receptor Subnunits

Answer 22

4 w/ stoichiometry α2βγδ arranged in pentameric ring

Question 23

Acetylcholine binding causes?

Answer 23

conf. changes - rotate membrane-spanning helices so pore opens.
Na+ and K+ ions pass through.

Question 24

Equilibrium Potential

Answer 24

membrane potential.
equilibrium est’d.
driving force of [gradient] countered by charge repulsion (like charges).

Question 25

Equilibrium Potential: Nerst Eqn

Answer 25

Veq = −(RT/zF) ln([X]in/[X]out) R: gas constant F: Faraday constant z: ion charge

Question 26

If ion X+ is unequally distributed across a membrane it will?

Answer 26

tend to move down [gradient]. | movement inhibited by accumulation of + charges.

Question 27

In the absence of stimulation the resting potential for a typical neuron is?

Answer 27

-60 mV. | close to potential for K+ bc small # K+ channels open.

Question 28

Action Potential (APs)

Answer 28

1. acetylcholine receptor activated, K+ flows out, Na+ flows in. 2. membrane potential changes, Na+ channels activated. 3. voltage-gated K+ channels open. ball of Na+ inactivates Na+ channel. 4. K+ open - membrane potential drops to K+ equilibrium potential. 5. ball closes K+ channel. membrane potential to initial state. 6. propagates down nerve membrane as action potential.

Question 29

LQTS: Long QT Syndrome

Answer 29

recovery of action potential delayed. | loss of consciousness, heart arrhythmia, sudden death.

Question 30

QT

Answer 30

feature of electrical activity pattern measured by electrocardiography

Question 31

Most common mutation of LQTS:

Answer 31

inactivate K+ channels | prevent proper trafficking of channels to plasma membrane.

Question 32

The loss of K+ permeability _____.

Answer 32

slows repolarization of membrane, delays heart contraction.

Question 33

Gap Junctions

Answer 33

cell-to-cell channels allow ions, small molecules to flow btw communicating cells. intercellular communication

Question 34

What molecules can pass through gap junctions?

Answer 34

polar molecules w/ mass < 1kDa

Question 35

A cell-to-cell (gap) junction is composed of?

Answer 35

12 molecules of connexin

Question 36

Connexon / Hemichannel

Answer 36

6 hexagonally arranged connexins form this half-channel

Question 37

Connexons from ____ form ____.

Answer 37

adjacent cells | a gap junction

Question 38

Gap junctions traverse ____ to allow ____.

Answer 38

2 membranes | cytoplasm-to-cytoplasm communication.

Question 39

Cardiac Muscle Structure

Answer 39

elongated branching cells | 1-2 centrally located nuclei

Question 40

Cardiac Muscle contains which filaments?

Answer 40

actin and myosin

Question 41

Intercalated Discs

Answer 41

``` in cardiac muscle specialized cell-cell contacts. cell membranes interdigitate. desmosomes. gap junctions. ```

Question 42

Intercalated Discs: Desmosomes

Answer 42

hold cells together

Question 43

Intercalated Discs: Gap Junctions

Answer 43

allow action potentials to move from one cell to next

Question 44

In cardiac muscle, electrically, these behave as a single unit:

Answer 44

atria and ventricles

Question 45

Aquaporins

Answer 45

allow rapid, specific movement of water across membranes. | hydrophilic residues that line water channel.

Question 46

What prevents the transport of protons through aquaporins?

Answer 46

specific positively charged residues toward center of channel

Question 47

The heart uses coordinated changes in ____ to create efficient muscular contractions that allow effective ____.

Answer 47

membrane potential. | pumping of blood throughout body.

Question 48

How can the heart beat spontaneously w/o input from the rest of the body?

Answer 48

pacemakers

Question 49

Pacemakers

Answer 49

unusual capacity for mixed Na+/K+ conductance when membranes are hyperpolarized

Question 50

Funny Current

Answer 50

membrane permeability of pacemakers

Question 51

Pacemakers make up the?

Answer 51

SA Node

Question 52

SA Node Cells

Answer 52

spontaneously gen ~100 action potentials / second

Question 53

SA Node

Answer 53

sinoatrial node. most important region. where action potentials are gen'd.

Question 54

Conducting System

Answer 54

1. APs from SA Node to AV (atrioventricular) node. 2. Aps AV node along AC bundle. 3. AV bundle to right and left bundle branches. Aps to apex of each ventricle along bundle branches. 4. APs carried by Purkinje fibers from bundle branches to ventricular walls and papillary muscles.

Question 55

Heart Valve Function: Blood Flow into Left Ventricle

Answer 55

bicuspid valve open. valve cusps pushed by blood into ventricle. aortic semilunar valve overlap as pushed by blood in aorta toward vessicle.

Question 56

Heart Valve Function: Blood Flow out of Left Ventricle

Answer 56

bicuspid valve closed. cusps of valves overlap as pushed by blood toward left atrium. aortic semilunar valve open. cusps of valve pushed by blood toward aorta.

Question 57

The current is ___ during the action potential.

Answer 57

off

Question 58

The current is ___ when the membrane returns to its ___.

Answer 58

on. | resting potential.

Question 59

The current is only active at ____, leading to a gradual ____ to a level that ____.

Answer 59

rest. depolarization of the membrane. triggers initiation of an AP.

Question 60

HCN Hyperpolarization-activated Cyclic Nucleotide-gated Channels

Answer 60

responsible for funny current. | HCN4 isomer highly expressed in SA node.

Question 61

The HCN Channels are opened by?

Answer 61

hyperpolarization

Question 62

The HCN Channels close when?

Answer 62

membrane is depolarized.

Question 63

Sick Sinus Syndrome

Answer 63

mutations in HCN4. | fewer HCN4 channels open at resting potential, slower depolarization.

Question 64

Sick Sinus Syndrome Symptoms:

Answer 64

abnormally low heart rate. fainting. fatigue.

Question 65

What is req'd to open the mutant HCN4 receptor?

Answer 65

greater hyperpolarization