M&R Session 2

Question 0

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

Answer 0

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

Question 1

What does the rate of passive transport increase linearly with?

Answer 1

Increasing concentration gradient

Question 2

Name the four models of membrane transport proteins.

Answer 2

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

Question 3

How does ping-pong transport work?

Answer 3

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

Question 4

How does facilitated diffusion via ion channels function?

Answer 4

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

Question 5

Describe the mechanism of ligand-gated ion channel function.

Answer 5

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

Question 6

How do voltage-gated ion channels function?

Answer 6

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

Question 7

Are membrane transport protein mediated processes saturable?

Answer 7

Yes

Question 8

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

Answer 8

Concentration ratio

Membrane potential

Question 9

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

Answer 9

Transport

Question 10

Where is the energy for active transport derived?

Answer 10

Directly or indirectly from ATP hydrolysis

Question 11

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

Answer 11

-31 kJ per mole

Question 12

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

Answer 12

Sodium in
Chloride in
Potassium out
Calcium in

Question 13

What is a primary transporter?

Answer 13

A transporter directly involved in the hydrolysis of ATP

Question 14

What is a cotransporter?

Answer 14

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

Question 15

Define uniport, symport and antiport.

Answer 15

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

Question 16

Which is the most important antiporter?

Answer 16

The sodium ion pump

Question 17

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

Answer 17

3 sodium in

2 potassium out

Question 18

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

Answer 18

25%

Question 19

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

Answer 19

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

Question 20

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

Answer 20

Directs it to cell surface

Question 21

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

Answer 21

Provides binding sites for:
potassium
sodium
ATP
ouabain

Question 22

What is ouabain?

Answer 22

A cardiac glycoside

Question 23

Is the sodium pump electrogenic?

Answer 23

Yes

Question 24

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

Answer 24

Creates high intracellular potassium concentration

Question 25

Describe the calcium-magnesium-ATPase cotransporter.

Answer 25

Primary active transporter High affinity Low capacity

Question 26

Describe the sodium-calcium exchanger.

Answer 26

Secondary transporter Low affinity High capacity

Question 27

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

Answer 27

Sodium-calcium exchanger

Question 28

Describe the sodium-hydrogen exchanger.

Answer 28

Secondary active transporter | Antiport

Question 29

Describe the sodium-glucose cotransporter.

Answer 29

Secondary active transporter | Found in small intestine and kidney

Question 30

How are cystic fibrosis and diarrhoea linked?

Answer 30

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

Question 31

What is the function of sodium-potassium-ATPase?

Answer 31

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

Question 32

Describe the function of PMCA.

Answer 32

Expels calcium High affinity Low capacity

Question 33

Describe the function of the anion exchanger.

Answer 33

Acidifies cell Hydrogen carbonate out Chloride in

Question 34

Describe the function of SERCA.

Answer 34

Accumulates calcium into the SR/ER High affinity Low capacity

Question 35

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

Answer 35

Exchanges 3 sodium ions for 1 calcium ion

Question 36

How does current flow in the sodium-calcium exchanger?

Answer 36

In the direction of the sodium gradient

Question 37

What does the activity of the NCX depend on?

Answer 37

Membrane potential

Question 38

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

Answer 38

It reverses - sodium out and calcium in

Question 39

How does ischaemia affect the function of the NCX?

Answer 39

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

Question 40

Describe the function of the sodium-hydrogen exchanger.

Answer 40

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

Question 41

What acts on the NHE to affect its function?

Answer 41

Activated by growth factors | Inhibited by Amiloride

Question 42

Why is calcium toxic to cells?

Answer 42

Reacts with key buffer - phosphate | Causes 'ossification' of cells

Question 43

What role do mitochondria have in cellular calcium regulation?

Answer 43

Act as a buffer when levels are dangerously high | Allow facilitated transport via uniports at high concentrations

Question 44

Which transporters act to alkalinise cells?

Answer 44

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

Question 45

Which transporters are base extruders?

Answer 45

Chloride-hydrogen carbonate exchanger | Anion exchanger

Question 46

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

Answer 46

Transporters can move the set point

Question 47

How is cell volume regulated?

Answer 47

Transport of osmotic ally active ions which are followed by water

Question 48

What is the universal method for cell volume regulation?

Answer 48

There isn't one - hah! | Different cell types use particular combinations of transporters to achieve the regulation they need

Question 49

Give the three methods of resisting cell swelling.

Answer 49

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

Question 50

Describe the three methods of resisting cell shrinking.

Answer 50

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

Question 51

How does the process of resisting cell swelling prevent depolarisation?

Answer 51

It is electroneutral

Question 52

Describe the reabsorption of filtered bicarbonate.

Answer 52

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

Question 53

How does Amiloride act?

Answer 53

Blocks sodium uptake in PCT and DCT | Disrupts bicarbonate transporters

Question 54

What is hyperaldosterium?

Answer 54

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

Question 55

In what order would you try diuretics available for treatment?

Answer 55

Loop diuretics Thiazide Spirondactone

Question 56

What is Spirondactone?

Answer 56

Glucocorticoid receptor antagonist

Question 57

Which pumps are present in the thick ascending limb?

Answer 57

KClT ClC-Kb Sodium pump

Question 58

Which pumps are present in the distal convoluted tubule?

Answer 58

ClC-Kbps KClCT NCX Sodium pump

Question 59

Which pumps are found in the cortical collecting duct?

Answer 59

ROMK Sodium pump ClC

Question 60

How does diuretic hormone work?

Answer 60

It acts on the cortical collecting duct to increase aquaporin expression