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Membranes and receptors > Session 2 > Flashcards

Session 2 Flashcards

1
Q

How can a lipid bilayer be observed?

A

Use of a black film

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2
Q

Which molecules can cross the plasma membrane freely?

A

Hydrophobic molecules, and small uncharged polar molecules

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3
Q

What is the name of channels that facilitate the flow of water across the plasma membrane?

A

Aquaporins

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4
Q

Which molecules cannot freely cross the plasma membrane and hence require transport proteins?

A

Large uncharged molecules and ions

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5
Q

What is a permeability coefficient?

A

The ease with which a molecule can dissolve across a phospholipid bilayer

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6
Q

What to key things does the rate of passive transport depend on?

A

Permeability and concentration gradient

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7
Q

How does the rate of passive transport vary with increasing concentration gradient?

A

Increases linearly

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8
Q

List three mechanisms by which membrane transport proteins work

A

Protein pores (channels), carrier molecule model (ping-pong), flip-flop and rotating carrier model (unlikely)

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9
Q

Describe the basis of the functioning of facilitated diffusion by ion channels

A

The ion channel is closed/open at rest, a stimulus arrives and this causes the opening/closing of the channel

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10
Q

Name three mechanism of ion channels involved in facilitated diffusion

A

Ligand-gated, voltage-gated, gap junction

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11
Q

What are ‘saturable’ transport processes?

A

Those with a maximum rate; they can be modelled in michaelis-menten style plots

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12
Q

Give approximate values for the extracellular and intracellular concentrations of sodium ions

A

E: 145mM
I: ~10mM

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13
Q

Give approximate values for the extracellular and intracellular concentrations of potassium ions

A

E: 4.5mM
I: 160mM

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14
Q

Give approximate values for the extracellular and intracellular concentrations of chloride ions

A

E: 110-120mM
I: 3-4mM

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15
Q

Give approximate values for the extracellular and intracellular concentrations of calcium ions

A

E: 1-2mM
I: ~100nM

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16
Q

What is co-transport? What are the two types?

A

More than one ion or molecule transported on a membrane transporter per reaction cycle; symport and antiport (uniport is for only one molecule/ion)

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17
Q

What type of co-transport if the Na+ pump? In what ratio do the ions move?

A

Antiport; 3 Na+ out, for 2 K+ in

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18
Q

Why is the Na+ pump described as a ‘P-type ATPase’?

A

Transport requires the hydrolysis of ATP; it self-phosphorylates an aspartate residue on its structure

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19
Q

What does the molecule Ouabin do to the sodium pump?

A

Inhibits it

20
Q

How much charge does the sodium pump generate through electrogenic pump activity?

A

About -5 to -10 mV

21
Q

What does the PMCA do?

A

Exports calcium from the cell, with hydrolysis of ATP (needs Mg2+)

22
Q

Describe the affinity and capacity of the PMCA and NCX

A

PMCA: high affinity, low capacity, good at low concentrations
NCX: low affinity, high capacity, good at high concentrations

23
Q

What is the NCX?

A

Sodium calcium exchanger; uses gradient from Na+ to export 1 Ca2+ for every 3 Na+ in (antiport)

24
Q

Why is the NCX described as a secondary active transport?

A

Needs the action of the sodium pump to generate the sodium gradient

25
Q

What direction does the NCX work in when the cell is polarised?

A

NCX acts to export calcium and import sodium

26
Q

What direction does the NCX work in when the cell is depolarised?

A

NCX is reversed; calcium in, sodium out

27
Q

Which direction does the NCX work in during ischemia?

A

Lack of ATP results in no sodium pump activity; hence sodium builds up inside the cell, and the NCX acts to removing, bringing calcium into the cell; the high concentration of calcium is toxic

28
Q

What effect cystic fibrosis have on the sodium pump?

A

The faulty CFTR results in a lack of movement out of the cell; in order to keep electroneutrality, the cell retains sodium by decreasing the activity of the sodium pump

29
Q

How is the CFTR transporter affected by the cholera toxin?

A

Protein kinase A stimulates an increase in the activity of the CFTR transport protein, resulting in chloride ions flowing out of the cell; other ions follow to retain electroneutrality, and water follows

30
Q

Why must the intracellular calcium concentration be tightly regulated?

A

Used in cell signalling

31
Q

What is the SERCA? In what conditions does it act?

A

Sarco(endo)plasmic reticulum Ca2+-ATPase; accumulates calcium into the SR/ER using ATP and the expulsion of H+; it is high affinity, low capacity (removes residual Ca2+)

32
Q

When do mitochondrial Ca2+ uniports operate?

A

High calcium concentrations, to buffer potential damage

33
Q

Name the two acid extruders of the cell membrane

A

Na+/H+ exchanger (NHE), and Na+ dependent Cl-/HCO3- exchanger

34
Q

Why is the NHE described as electroneutral?

A

It exchanges an extracellular Na+ for an intracellular H+, in a 1:1 ratio, which hence has no effect on membrane potential

35
Q

What does the NHE regulate?

A

Intracellular pH and cell volume

36
Q

What inhibits the NHE?

A

Amiloride

37
Q

Describe the sodium dependent Cl-/HCO3- exchanger

A

Exchanges H+ and Cl- out for Na+ and HCO3- in; it is electroneutral

38
Q

Which transporter regulates alkali influx?

A

Na+-HCO3- cotransporter; sodium and bicarbonate travel into the cell together, and this can be 1,2, or even carbonate molecules (only found in some cells)

39
Q

Which membrane protein is responsible for alkali extrusion?

A

Anion exchanger (band 3); removes HCO3-, whilst taking in Cl-; this acidifies the cell

40
Q

What are conductive system mechanisms to resist cell swelling?

A

K+ and Cl- ion channels (voltage gated)

41
Q

What are cotransport system mechanisms to resist cell swelling?

A

Cotransport systems: bicarbonate intake for Cl- release, H+ intake for K+ release (loss of bicarbonate as CO2), amino acid efflux and K+ and Cl- efflux via carrier proteins

42
Q

What are conductive system mechanisms to resist cell shrinkage?

A

Sodium and calcium ion channels open, allowing their influx into the cell (chloride actively trasnsported in, to keep electroneutrality)

43
Q

What are the cotransport system mechanisms to resist cell shrinkage?

A

Bicarbonate efflux, resulting in Na+ and Cl- influx, in place of K+; cotransport influx of: (Na+, K+ and 2Cl-; NKCC2), (Na+ and organic osmolytes), and (Na+ and Cl-)

44
Q

Which transporters are present in the thick ascending limb of the kidney, between the lumen of the ascending limb and epithelial cells?

A

NKCC2 (takes up K+, Na+, and 2Cl-), and K+ leaves by ROMK channel (into the lumen)

45
Q

Which transporters are present in the thick ascending limb of the kidney, between the lumen capillaries and epithelial cells?

A

K+ and Cl- enter the capillary via the symport KCICT, Cl- enter the capillary by the CIC-Kb channel, and the sodium pump also operates

46
Q

Which ions flow between cells from the lumen of the thick ascending limb of the kidney to the lumen of the capillary?

A

Ca2+, Mg2+

47
Q

How do loop diuretics act to treat hypertension?

A

Inhibit NKCC2; prevents sodium reuptake, reducing the amount of water reuptake

Membranes and receptors (4 decks)

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