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Semester 2 > M&R Session 2 > Flashcards

M&R Session 2 Flashcards

0
Q

What are the six roles of transport processes across cell membranes?

A

Maintenance of ionic composition
Maintenance of intracellular pH
Regulation of cell volume
Regulation of concentration of metabolic fuels and building blocks
Extrusion of waste products
Generation of ion gradients necessary for electrical excitability

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1
Q

What does the rate of passive transport increase linearly with?

A

Increasing concentration gradient

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2
Q

Name the four models of membrane transport proteins.

A

Ping-pong transport
Facilitated diffusion via ion channels
Ligand-gated ion channels
Voltage-gated ion channels

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3
Q

How does ping-pong transport work?

A

Conformational change allows binding of substance and its release on the other side

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4
Q

How does facilitated diffusion via ion channels function?

A

Pores which open and close in the plasma membrane allow selected ions to pass through

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5
Q

Describe the mechanism of ligand-gated ion channel function.

A

Ligand binds to receptor –> conformational change –> allows passage of molecule

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6
Q

How do voltage-gated ion channels function?

A

Membrane depolarisation moves sensor within the channel allowing passage of ions through

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7
Q

Are membrane transport protein mediated processes saturable?

A

Yes

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8
Q

What determines whether the transport process carried out by a transport protein is active or passive?

A

Concentration ratio

Membrane potential

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9
Q

What is linearly related to the natural log of the concentration gradient and the potential gradient?

A

Transport

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10
Q

Where is the energy for active transport derived?

A

Directly or indirectly from ATP hydrolysis

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11
Q

How much energy is released by the hydrolysis of one molecule of ATP?

A

-31 kJ per mole

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12
Q

Describe the direction of concentration gradients of sodium, potassium, chloride and calcium ions across the cell membrane.

A

Sodium in
Chloride in
Potassium out
Calcium in

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13
Q

What is a primary transporter?

A

A transporter directly involved in the hydrolysis of ATP

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14
Q

What is a cotransporter?

A

A transport protein which transports more than one type of ion/molecule per reaction cycle

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15
Q

Define uniport, symport and antiport.

A 
Uniport = one ion/molecule transported
Symport = 2 on same side
Antiport = one on each side
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16
Q

Which is the most important antiporter?

A

The sodium ion pump

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17
Q

What is the ionic movement of each cycle performed by the sodium pump?

A

3 sodium in

2 potassium out

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18
Q

What proportion of the BMR is used for the sodium pump?

A

25%

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19
Q

Why is the sodium pump called a P-type ATPase?

A

ATP phosphorylates aspartate which produces a phosphoenzyme intermediate so that the phosphate can be lost again freely within the cell

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20
Q

What is the function of the beta subunit of the sodium pump?

A

Directs it to cell surface

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21
Q

What is the function of the alpha subunit of the sodium pump?

A 
Provides binding sites for:
potassium
sodium
ATP
ouabain
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22
Q

What is ouabain?

A

A cardiac glycoside

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23
Q

Is the sodium pump electrogenic?

A

Yes

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24
Q

How does the sodium pump facilitate generation of the membrane potential?

A

Creates high intracellular potassium concentration

25
Q

Describe the calcium-magnesium-ATPase cotransporter.

A

Primary active transporter
High affinity
Low capacity

26
Q

Describe the sodium-calcium exchanger.

A

Secondary transporter
Low affinity
High capacity

27
Q

Which cotransporter contributes most to calcium extrusion in high calcium conditions?

A

Sodium-calcium exchanger

28
Q

Describe the sodium-hydrogen exchanger.

A

Secondary active transporter

Antiport

29
Q

Describe the sodium-glucose cotransporter.

A

Secondary active transporter

Found in small intestine and kidney

30
Q

How are cystic fibrosis and diarrhoea linked?

A

Same transport mechanism in a different cell gives a different effect:
CF - no efflux of chloride –> no water in lumen –> thick mucus
Diarrhoea - protein kinase A activated –> chloride efflux –> water follows

31
Q

What is the function of sodium-potassium-ATPase?

A

Electrical excitability
Drives secondary active transport for:
pH control, cell volume and calcium concentration regulation, absorption of sodium and nutrient uptake

32
Q

Describe the function of PMCA.

A

Expels calcium
High affinity
Low capacity

33
Q

Describe the function of the anion exchanger.

A

Acidifies cell
Hydrogen carbonate out
Chloride in

34
Q

Describe the function of SERCA.

A

Accumulates calcium into the SR/ER
High affinity
Low capacity

35
Q

Describe the ionic movements facilitated by the sodium-calcium exchanger.

A

Exchanges 3 sodium ions for 1 calcium ion

36
Q

How does current flow in the sodium-calcium exchanger?

A

In the direction of the sodium gradient

37
Q

What does the activity of the NCX depend on?

A

Membrane potential

38
Q

When the cell is depolarised, what happens to the mode of operation of the NCX?

A

It reverses - sodium out and calcium in

39
Q

How does ischaemia affect the function of the NCX?

A

Lack of oxygen = ATP depleted –> sodium pump inhibited –> sodium in and cell depolarises –> NCX reverses –> calcium necrosis

40
Q

Describe the function of the sodium-hydrogen exchanger.

A

Exchanges extracellular sodium for intracellular hydrogen 1:1
Regulates pH
Regulates cell volume

41
Q

What acts on the NHE to affect its function?

A

Activated by growth factors

Inhibited by Amiloride

42
Q

Why is calcium toxic to cells?

A

Reacts with key buffer - phosphate

Causes ‘ossification’ of cells

43
Q

What role do mitochondria have in cellular calcium regulation?

A

Act as a buffer when levels are dangerously high

Allow facilitated transport via uniports at high concentrations

44
Q

Which transporters act to alkalinise cells?

A

NHE
NBC (sodium bicarbonate cotransporter)
Sodium dependent chloride-hydrogen carbonate exchanger

45
Q

Which transporters are base extruders?

A

Chloride-hydrogen carbonate exchanger

Anion exchanger

46
Q

How is a drift away from the set pH of a cell corrected?

A

Transporters can move the set point

47
Q

How is cell volume regulated?

A

Transport of osmotic ally active ions which are followed by water

48
Q

What is the universal method for cell volume regulation?

A

There isn’t one - hah!

Different cell types use particular combinations of transporters to achieve the regulation they need

49
Q

Give the three methods of resisting cell swelling.

A

Efflux of potassium and chloride
Efflux of amino acids
Influx of hydrogen carbonate and hydrogen ions to form carbonic acid - carbon dioxide and water efflux

50
Q

Describe the three methods of resisting cell shrinking.

A

Influx of sodium, potassium, chloride and organic osmolytes
Efflux of hydrogen carbonate and hydrogen from dissociation of carbonic acid
Conductive influx of sodium and calcium

51
Q

How does the process of resisting cell swelling prevent depolarisation?

A

It is electroneutral

52
Q

Describe the reabsorption of filtered bicarbonate.

A

Normally all reabsorbed in proximal tubule
Needed to retain base for pH buffers
Carbonic anhydride acts in PCT lumen to dissociate bicarbonate for easy diffusion

53
Q

How does Amiloride act?

A

Blocks sodium uptake in PCT and DCT

Disrupts bicarbonate transporters

54
Q

What is hyperaldosterium?

A

High aldosterone –> excess sodium retention –> high blood pressure

55
Q

In what order would you try diuretics available for treatment?

A

Loop diuretics
Thiazide
Spirondactone

56
Q

What is Spirondactone?

A

Glucocorticoid receptor antagonist

57
Q

Which pumps are present in the thick ascending limb?

A

KClT
ClC-Kb
Sodium pump

58
Q

Which pumps are present in the distal convoluted tubule?

A

ClC-Kbps
KClCT
NCX
Sodium pump

59
Q

Which pumps are found in the cortical collecting duct?

A

ROMK
Sodium pump
ClC

60
Q

How does diuretic hormone work?

A

It acts on the cortical collecting duct to increase aquaporin expression

Semester 2 (45 decks)

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