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Biochemistry 304 > CH 13 Membrane Channels and Pumps P2 > Flashcards

CH 13 Membrane Channels and Pumps P2 Flashcards

1
Q

K+ Channel

A

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

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2
Q

Na+ Channel Purification

A

on basis of affinity to neurotoxin tetrodotoxin

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3
Q

Na+ Channel

A

4 repeated regions of similar seq.

each region has 5 hydrophobic segments, 1 hydrophilic segment.

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4
Q

Ca+ Channel

A

homologous to Na+ channel

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5
Q

Shaker

A

mutated version of K+ channel

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6
Q

K+ Channel reveals the basis of?

A

ion specificity

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7
Q

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

A

selectively

rapidly

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8
Q

K+ Channel does not transport?

A

larger ions - too big to enter channel.

smaller ions - cannot interact w/ selectivity filter.

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9
Q

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

A

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.

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10
Q

These 2 channels are homologous to the K+ Channel:

A

Na+ and Ca2+

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11
Q

Ca2+ Channels have what 4 residues?

A

(4) E - glutamate

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12
Q

Na+ Channels has what 4 residues?

A

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

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13
Q

K+ Channel Structure

A

4 ion-binding sites

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

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14
Q

Voltage Gating Channels

A

Na+ and K+ Channels.

change conf. w/ change in membrane potential.

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15
Q

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

A

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

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16
Q

How is the K+ inactivated?

A

physically blocking channel.

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

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17
Q

A channel can be inactivated by?

A

occlusion of pore

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18
Q

Mutants that do not inactivate lack?

A

ball and chain

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19
Q

Protease-Accessible

A

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

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20
Q

Depolarization opens?

A

channel.

creates binding site for ball, inactivates channel.

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21
Q

Acetylcholine Receptor

A

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

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22
Q

Acetylcholine Receptor Subnunits

A

4 w/ stoichiometry α2βγδ arranged in pentameric ring

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23
Q

Acetylcholine binding causes?

A

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

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24
Q

Equilibrium Potential

A

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

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25
Q

Equilibrium Potential: Nerst Eqn

A

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

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26
Q

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

A

tend to move down [gradient].

movement inhibited by accumulation of + charges.

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27
Q

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

A

-60 mV.

close to potential for K+ bc small # K+ channels open.

28
Q

Action Potential (APs)

A
  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.
29
Q

LQTS: Long QT Syndrome

A

recovery of action potential delayed.

loss of consciousness, heart arrhythmia, sudden death.

30
Q

QT

A

feature of electrical activity pattern measured by electrocardiography

31
Q

Most common mutation of LQTS:

A

inactivate K+ channels

prevent proper trafficking of channels to plasma membrane.

32
Q

The loss of K+ permeability _____.

A

slows repolarization of membrane, delays heart contraction.

33
Q

Gap Junctions

A

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

34
Q

What molecules can pass through gap junctions?

A

polar molecules w/ mass < 1kDa

35
Q

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

A

12 molecules of connexin

36
Q

Connexon / Hemichannel

A

6 hexagonally arranged connexins form this half-channel

37
Q

Connexons from ____ form ____.

A

adjacent cells

a gap junction

38
Q

Gap junctions traverse ____ to allow ____.

A

2 membranes

cytoplasm-to-cytoplasm communication.

39
Q

Cardiac Muscle Structure

A

elongated branching cells

1-2 centrally located nuclei

40
Q

Cardiac Muscle contains which filaments?

A

actin and myosin

41
Q

Intercalated Discs

A 
in cardiac muscle
specialized cell-cell contacts.
cell membranes interdigitate.
desmosomes.
gap junctions.
42
Q

Intercalated Discs: Desmosomes

A

hold cells together

43
Q

Intercalated Discs: Gap Junctions

A

allow action potentials to move from one cell to next

44
Q

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

A

atria and ventricles

45
Q

Aquaporins

A

allow rapid, specific movement of water across membranes.

hydrophilic residues that line water channel.

46
Q

What prevents the transport of protons through aquaporins?

A

specific positively charged residues toward center of channel

47
Q

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

A

membrane potential.

pumping of blood throughout body.

48
Q

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

A

pacemakers

49
Q

Pacemakers

A

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

50
Q

Funny Current

A

membrane permeability of pacemakers

51
Q

Pacemakers make up the?

A

SA Node

52
Q

SA Node Cells

A

spontaneously gen ~100 action potentials / second

53
Q

SA Node

A

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

54
Q

Conducting System

A
  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.
55
Q

Heart Valve Function: Blood Flow into Left Ventricle

A

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

56
Q

Heart Valve Function: Blood Flow out of Left Ventricle

A

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.

57
Q

The current is ___ during the action potential.

A

off

58
Q

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

A

on.

resting potential.

59
Q

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

A

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

60
Q

HCN Hyperpolarization-activated Cyclic Nucleotide-gated Channels

A

responsible for funny current.

HCN4 isomer highly expressed in SA node.

61
Q

The HCN Channels are opened by?

A

hyperpolarization

62
Q

The HCN Channels close when?

A

membrane is depolarized.

63
Q

Sick Sinus Syndrome

A

mutations in HCN4.

fewer HCN4 channels open at resting potential, slower depolarization.

64
Q

Sick Sinus Syndrome Symptoms:

A

abnormally low heart rate.
fainting.
fatigue.

65
Q

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

A

greater hyperpolarization

Biochemistry 304 (14 decks)

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