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Cell Biology and Disease > Membrane transport and ion channels > Flashcards

Membrane transport and ion channels Flashcards

1
Q

What is the lipid bilayer used for?

A

Communication
Cell growth
Adhesion
Morphology change
Division
Selective barrier

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2
Q

What is the function of channel proteins?

A

Passive transport

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3
Q

What is the function of a carrier protein?

A

Facilitated diffusion

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4
Q

What is the function of a pump on the lipid bilayer?

A

Active diffusion.

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5
Q

What are the protein classes at the plasma membrane?

A

Transporters
Linkers
Receptors
Enzymes

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6
Q

What are ion channels?

A

Transport ions across the plasma membrane.
Regulates membrane potential- the difference in electrical potential between interior and the exterior of a cell.

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7
Q

What is passive transport?

A

Moving down a concentration gradient, from high to low.
Energy expenditure (ATP hydrolysis) is not required.

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8
Q

What are the 3 types of passive transport?

A

Simple diffusion.
Osmosis.
Facilitated diffusion.

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9
Q

What is simple diffusion?

A

Movement of small or lipophilic molecules.

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10
Q

What is facilitated diffusion?

A

Movement of large or charged molecules via membrane proteins.

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11
Q

What is active transport?

A

The movement of materials against the concentration gradient, this requires energy expenditure (ATP hydrolysis) is needed.

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12
Q

What are the 2 main types of active transport?

A

Primary (direct) or Secondary (indirect)

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13
Q

What is the primary (direct) active transport?

A

Involves the direct use of metabolic energy to mediate transport.

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14
Q

What is secondary (indirect) active transport?

A

Involves coupling the molecule with another moving along an electrochemical gradient.

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15
Q

What is the process of the sodium-potassium pump?

A
  1. Cytoplasmic Na+ binds to the Na+/K+ pump.
  2. The Na+/K+ pump is phosphorylated by ATP.
  3. The pump changes its conformation, causing Na+ release.
  4. Extracellular K+ binds to the pump, leading to dephosphorylation.
  5. The pump returns to its original conformation.
  6. K+ is released from the pump.
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16
Q

What experimental methods are used to investigate ion channels?

A

Patch-clamp electrophysiology
Electron Microscopy

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17
Q

What does path clamp electrophysiology tell us about protein?

A

Function.

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18
Q

What does electron microscopy tell us about protein?

A

Structure

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19
Q

How does patch clamp electrophysiology work?

A

In patch clamp experiments, suction is used to attach a micropipette filled with electrolyte solution to the cell membrane. This forms a seal, isolating a patch of the membrane to enable the flow of currents across this section of the membrane to be measured.

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20
Q

How are ion channels regulated?

A

They are selective, ion movement requires the channel to be in an open state.
Ion movement is also governed by potential across the membrane and the concentration gradient for that ion.

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21
Q

What is ion channel gating?

A

Ion channels open/close in response to stimuli.

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22
Q

What type of gated ion channels are there?

A

Voltage gated
Ligand gated
Tension gated

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23
Q

What are voltage gated channels?

A

Confirmational change in structure due to change in membrane potential.

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24
Q

What are ligand gated channels?

A

Ligands bind to a receptor on the channel causing conformational change.

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25
Q

What is Vm?

A

Membrane potential, often the resting potential.

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26
Q

What is a membrane potential (Vm)?

A

Voltage difference between the inside and the outside of a cell.
Arises due to ion movement across the plasma membrane.

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27
Q

What is the resting membrane potential?

A

The phase between action potentials.

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28
Q

What is the resting potential in mammalian cells?

A

-50mV

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29
Q

How is the resting membrane potential maintained?

A

Leak potassium channels are open at rest meaning potassium has the highest permeability at rest.
Chloride and sodium leak channels are also open but in fewer numbers than potassium.
The sodium-potassium pump is responsible for maintaining the electrochemical gradients needed for neuron functioning.

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30
Q

What is a flux?

A

Ion moving across the membrane.

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31
Q

How to calculate the equilibrium potential?

A

Nernst Equation.

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32
Q

What is the Nernst equation?

A

Eion = (RT/zF)ln([ion1]/[ion2])
R= gas constant
T= absolute temperature (K)
z=valence of ion
F= faraday constant 96,485.33212

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33
Q

What is the faraday constant?

A

96,485.33212

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34
Q

What is valence of an ion?

A

Equal to the charge on the ion.

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35
Q

What is the normal concentration of potassium?

A

3.5 – 5.3 mmol/l

36
Q

What is hypokalaemia?

A

A higher than normal concentration of potassium.

37
Q

What is hyperkalaemia?

A

A lower than normal concentration of potassium.

38
Q

What effect do pufferfish have on ion channels?

A

Release tetrodotoxin (TTX) blocks sodium channels (pore).

39
Q

What effect does the deathstalker scorpion on ion channels?

A

Releases charybdotoxin (CTX) blocks potassium channels (pore)

40
Q

What effect does the funnel-web spider have on the ion channels?

A

Releases w-agatoxin which blocks calcium channels (voltage sensor).

41
Q

What is the first step to investigating ion channel structure?

A

Looking at the biochemical properties of specific amino acid side-chains allows you to make predictions about protein structure.

42
Q

How would you investigate ion structure experimentally?

A

X-ray crystallography
Electron microscopy

43
Q

What are the steps to x-ray crytallography?

A

Protein to crystal, x-rays allow us to study the diffraction patterns.
Out of these phases we can make electron density map which we can fit into an atomic model.
We can refine this by going back to the diffraction pattern stage.

44
Q

Why are ion channels hard to crystallise?

A

Transmembrane
Large proteins (high molecular weight)
Multiple subunits
Dynamic and disordered
Not very soluble

45
Q

What is cryo-EM?

A

You don’t need to crystallise proteins into a static state.
Proteins are purified and put onto a grid.
Using a very low means the proteins move much slower.
This allows us to study dynamic patterns.

46
Q

What is an alphafold?

A

Using protein structure databanks to predict structures using AI.

47
Q

What is the basic ion channel structure?

A

Alpha subunit
Ion channels can be composed of multiple alpha subunits.

48
Q

How many subunits does a typical potassium channel have?

A

4 (tetramer)

49
Q

How do voltage gated channels open/close?

A

Ion channels commonly have 6 arginine residues which is the voltage centre/sensor.

50
Q

What are the major extracellular cations?

A

Potassium
Magnesium

51
Q

What are the major extracellular anions?

A

Phosphate
Some amino acids

52
Q

What are the major intracellular cations?

A

Calcium
Sodium

53
Q

What are the major intracellular anions?

A

Chloride

54
Q

What is the resting membrane potential?

A

RMP is the voltage difference between outside and inside of the cell.

55
Q

What is the RMP voltage of the neuron?

A

-70mV

56
Q

What is an action potential?

A

Sudden reverse of membrane polarity which leads to the transmission of a signal.

57
Q

How is RMP maintained?

A

Through the flux of K+ ions by:
K+ ion channels “leak”
Na+/K+ ATPase “pump”

58
Q

What are the stages of action potential?

A
  1. Resting phase
  2. Depolarisation (slow rising phase and rapid rising phase)
  3. Repolarisation
  4. Hyperpolarisation (refractory)
59
Q

How does flux initiate action potential?

A

Voltage gated sodium channels open and Na+ ions enter the cell.
Voltage gated potassium channels open and K+ ion leave the cell.

60
Q

What is depolarisation?

A

Change from a (relatively) negative charge to a positive charge.
When the membrane reaches -55mV (due to stimulus), the voltage-gated Na+ channel open very rapidly allowing Na+ rushes into the cell.
The membrane potential is now +30mV.`

61
Q

What is repolarisation?

A

Restoration of membrane potential (after depolarisation).
Sodium channels close very slowly stopping the influx of Na+.
The potassium channels open in response however more slowly than Na+ channels.
Now the membrane potential is -80mV.

62
Q

What is the refractory (hyperpolarisation) period?

A

Period of time after an impulse before a cell can fire again.
Both the sodium an potassium gated channels are now closed.
The sodium potassium pump opens.
The membrane potential is now -70mV.

63
Q

What is the absolute refractory period?

A

Membrane cannot generate another action potential.
Sodium channels are completely innactive.

64
Q

What is the relative refractory period (hyperpolarization)?

A

Membrane could generate another action potential id given a larger than normal stimulus.
Sodium channels are recovered.
Potassium channels are still open.

65
Q

What is important about the axon initial segment?

A

At the AIS there is a clustering of voltage gated ion channels. This is where action potential is propagated.

66
Q

How does the action potential move down the axon?

A

Action potential travels via current loops. Nearby area becomes depolarised by the current AP to initiate the next AP. The refractory period prevents the AP from going backwards.

67
Q

What is the mode of action of TTX?

A

Inhibits the voltage dependent Na+ to channel.
Affects depolarisation.

68
Q

What is a channelopathy?

A

Pathology/disease arising from ion channel dysfunction.

69
Q

Why is neurone damage so serious?

A

Because neurones are fixed post mitotic cells, they cannot be replaced so the damage is long term.

70
Q

What is a phenotype?

A

An observable physical properties of an organism.

71
Q

What is genetic linkage?

A

Genetic channelopathies have been identified using linkage mapping.
Follows mendelian inheritance pattern.

72
Q

What is the mendelian inheritance pattern?

A

Follows the law of dominance and inheritance laws.

73
Q

What types of pain mechanisms exist?

A

Nociceptive
Inflammatory
Neuropathic

74
Q

What are the pain treatment options for inflammatory pain?

A

Cox2 inhibitors
Opioids

75
Q

What are the pain treatment options for neuropathic pain?

A

Tricyclic antidepressants
Anticonvulsants
Na+ channel blockers
NMDA receptor antagonists
Opioids

76
Q

What are the potential therapeutic strategies for pain?

A
  1. Inhibit the ion channel that senses the stimuli and initiates the AP.
  2. Inhibit the ion channels that propagate the AP.
  3. Inhibit the ion channel involved in DRG neurotransmission.
  4. Inhibit the ion channel that process the stimuli centrally within the brain.
77
Q

What is the main gene responsible for pain?

A

SCN9A 1.7

78
Q

What is primary erythromelalgia?

A

An autosomal dominant mutation in the SCN9A.

79
Q

What are the symptoms of Primary Erythromelalgia (PEM)?

A

Bilateral episodes of burning pain in feet and hands.

80
Q

What triggers the symptoms of primary erythromelalgia (PEM)?

A

Attacks triggered by exercise and/or heat.
Onset in childhood and continued through adult life.

81
Q

What is the mutation which causes PEM, primary erythromelalgia?

A

First mutation happens in L858H in the second domain.
The channel’s mutation leads shifts the activation voltage to 12mV in the hyperpolarising direction, resulting in a reduced threshold for channel opening and thus increased excitability.

82
Q

What is paroxysmal extreme pain disorder?

A

Mutation in SCN9A (AUTOSOMAL DOMINANT).

83
Q

What are the symptoms of paroxysmal extreme pain disorder?

A

Severe pain in the rectal, ocular and mandibular (jaw) areas.

84
Q

What triggers the symptoms of paroxysmal extreme pain disorder?

A

Attacks triggered by chewing and/or heat.
Onset in childhood and continued through adult life.

85
Q

What is complete insensitivity to pain (CIP)?

A

Mutation in SCN9A, autosomal recessive.

86
Q

What are the symptoms of complete insensitivity to pain (CIP)?

A

Loss of all sensations.

Cell Biology and Disease (6 decks)

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