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Semester 2 - Membranes and receptors > MnR S2 - Membrane Permeability, Cell Volume and pH Regulation > Flashcards

MnR S2 - Membrane Permeability, Cell Volume and pH Regulation Flashcards

1
Q

Define passive transport

A

Non-Polar molecules are able to enter and, therefore, diffuse across the hydrophobic domain of lipid bilayers down the concentration gradient, releasing free energy

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2
Q

What factors affect the rate of diffusion?

A

Permeability and concentration gradient

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3
Q

Define facilitated diffusion

A

Presence of specific proteins in the bilayer which increases the permeability for a polar substance

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4
Q

List the models for facilitated transport

A

Channel - Protein pore

Carrier - Ping pong

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5
Q

List the types of gated protein pore

A
  • Ligand-gated ion channels
  • Voltage-gated ion channels
  • Gap junctions
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6
Q

List the functions of transport systems for substances across the plasma membrane

A
  • Maintain intracellular ion composition, pH and metabolite concentration
  • Regulate cell volume
  • Extrusion of metabolism waste products and toxic substances
  • Generate ion gradients for electrical excitability of nerve and muscles
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7
Q

How are passive and active processes distinguished between?

A

Free energy change of the transported proteins

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8
Q

What is the purpose of active transport?

A

Overcome unfavourable concentration or electrochemical gradient by coupling to a thermodynamically favourable reaction

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9
Q

List the possible sources of energy to drive active transport

A
  • Directly or indirectly from hydrolysis of ATP
  • Electron transport
  • Light (photosynthesis)
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10
Q

What is co-transport?

A

Transport of more than one ion or molecule across the membrane per reaction cycle by linking the transport of one substance to the concentration of another

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11
Q

What is another name for co-transport?

A

Secondary active transport

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12
Q

Give an example of a co-transport system?

A
  • Sodium-glucose co-transporter
  • Found at small intestine and kidney
  • Entry of sodium provides the energy for entry of glucose
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13
Q

Define uniport

A

One solute molecule species is transported from one side of the membrane to the other

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14
Q

Define symport

A

Transfer of one solute molecule depends on the simultaneous or sequential transfer of a second solute molecule in the same direction

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15
Q

Define antiport

A

Transfer of one solute molecule depends on the simultaneous or sequential transfer of a second solute molecule in the opposite direction

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16
Q

How does a symport transporter differ from an antiport transporter?

A

Solute molecules are transferred in opposite directions in antiporters whilst in the same direction in symporters

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17
Q

Describe the structure of the Na+/K+-ATPase transport system

A

Alpha chains - Binding site for oubain, sodium and potassium

Beta chains - Glycoprotein directs pump to plasma membrane

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18
Q

List the secondary active transport processed driven by the Na+/K+-ATPase transport system

A
  • Ion homeostasis
  • Cell volume
  • Intracellular [Calcium]
  • Ion gradients underpinning membrane resting potential
  • Nutrient uptake
19
Q

List the intracellular concentrations of sodium, potassium calcium and chloride ions

A

Ca2+ 1 x 10-7mM

Cl 4.2mM

Na+ 12mM

K+ 155mM

20
Q

List the extracellular concentrations of sodium, potassium calcium and chloride ions

A

Ca2+ 1.5mM

Cl 123mM

Na+ 145mM

K+ 4mM

21
Q

List the intra and extracellular concentrations of sodium, potassium calcium and chloride ions

A

Ca2+ 1 x 10-7mM : 1.5mM

Cl 4.2mM : 123mM

Na+ 12mM : 145mM

K+ 155mM : 4mM

22
Q

What are the two primary active transport systems that control resting [calcium]?

A

PMCA - Expels calcium ions out of the cells, high affinity and low capacity

SERCA - Accumulates calcium ions in the SR/ER, high affinity and low capacity

23
Q

What is the secondary active transport system that controls resting calcium concentration?

A

Sodium-calcium exchanger (NCX)

Low affinity, high capacity

24
Q

Which of the calcium transport systems remove the majority of calcium and which removes residual calcium?

A

Majority - NCX

Residual - PMCA, SERCA and mitochondrial calcium uniports

25
Q

List the transport systems involved in acid extrusion

A

Sodium-Hydrogen exchanger (NHE)

Sodium bicarbonate co-transporter (NBC)

(NBC - Sodium and bicarbonate flow into the cell in exchange for hydrogen and chloride ions)

26
Q

List the transport system involved in alkali extrusion

A

Anion exchanger (AE) - Chloride ions move into the cell with bicarbonate ions moving out

Acidifies the cell

27
Q

How does Anion Exchange work?

A

Chloride ions move in as bicarbonate moves out

28
Q

What transport systems are activated by acidification?

A

Sodium bicarbonate co-transporter (NBC)

Sodium-hydrogen exchanger (NHE)

29
Q

What transport systems are activated by alkalisation?

A

Anion exchanger (AE)

30
Q

Describe the principles of regulating cell volume

A

Cell swelling - Extrude ions

Cell shrinking - influx of ions

(Water will follow the movement of ions)

31
Q

What must be taken into account when maintaining cell volume?

A

Ion transport must be electroneutral to ensure electrochemical gradient and pH is not affected

32
Q

What enzyme is involved in the reabsorption of bicarbonate in the kidney?

A

Carbonic anhydrase

33
Q

What reaction does carbonic anhydrase (reabsorption of bicarbonate in the kidney) catalyse?

A

Inter-conversion of water and carbon dioxide to hydrogen carbonate

34
Q

What is the main reason for reabsorption of bicarbonate in the kidney?

A

Retain base for pH buffer

35
Q

What is the function of aquaporin?

A

Increases membrane permeability to water in the cortical collecting duct

36
Q

What drugs increase the number of aquaporins in the membrane of the kidney lumen?

A

Anti-diuretics

37
Q

What are the main sites of sodium reuptake by the kidney?

A
  • Thick ascending limb
  • Distal convoluted tubule
  • Cortical collecting duct
38
Q

What is ROMK and where is it found

A

Potassium uniport channel moving potassium ions into the lumen in the thick ascending limb and cortical collecting duct

39
Q

To what tissue is ENaC specific and what is its function?

A
  • Reabsorption of sodium ions from the lumen

- Found in the epithelium of the distal convoluted tubule and cortical collecting duct of the kidney

40
Q

What is spironolactone and how does it work?

A

Potassium sparring diuretic

Interacts with mineralocorticoid receptors:

  • Enhances expression of Na+, K+-ATPase and the Na+ channel in the distal tubule
  • Blocks action of aldosterone on gene expression

Aldosterone is a hormone; its primary function is to retain sodium and excrete potassium in the kidneys

41
Q

What are loop diuretics and where do they act in the kidney?

A

Inhibits sodium uptake from the lumen in the thick ascending limb in the kidney

42
Q

What ion channels are found on the luminal border of the thick ascending limb and what is their function?

A

NKCC2 - Uptake of sodium, potassium and chlorine from the lumen

ROMK - Movement of potassium back into the lumen

43
Q

What ion channels are found on the capillary border of the thick ascending limb and what is their function?

A

KCICT - Potassium and chlorine into bloodstream

CIC-Kb - Chlorine into bloodstream

Na pump - 3 sodium pumped into bloodstream and potassium back into cells

Semester 2 - Membranes and receptors (11 decks)

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