MnR S2 - Membrane Permeability, Cell Volume and pH Regulation

Question 1

Define passive transport

Answer 1

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

Question 2

What factors affect the rate of diffusion?

Answer 2

Permeability and concentration gradient

Question 3

Define facilitated diffusion

Answer 3

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

Question 4

List the models for facilitated transport

Answer 4

Channel - Protein pore

Carrier - Ping pong

Question 5

List the types of gated protein pore

Answer 5

• Ligand-gated ion channels
• Voltage-gated ion channels
• Gap junctions

Question 6

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

Answer 6

• 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

Question 7

How are passive and active processes distinguished between?

Answer 7

Free energy change of the transported proteins

Question 8

What is the purpose of active transport?

Answer 8

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

Question 9

List the possible sources of energy to drive active transport

Answer 9

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

Question 10

What is co-transport?

Answer 10

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

Question 11

What is another name for co-transport?

Answer 11

Secondary active transport

Question 12

Give an example of a co-transport system?

Answer 12

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

Question 13

Define uniport

Answer 13

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

Question 14

Define symport

Answer 14

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

Question 15

Define antiport

Answer 15

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

Question 16

How does a symport transporter differ from an antiport transporter?

Answer 16

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

Question 17

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

Answer 17

Alpha chains - Binding site for oubain, sodium and potassium

Beta chains - Glycoprotein directs pump to plasma membrane

Question 18

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

Answer 18

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

Question 19

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

Answer 19

Ca2+ 1 x 10-7mM

Cl 4.2mM

Na+ 12mM

K+ 155mM

Question 20

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

Answer 20

Ca2+ 1.5mM

Cl 123mM

Na+ 145mM

K+ 4mM

Question 21

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

Answer 21

Ca2+ 1 x 10-7mM : 1.5mM

Cl 4.2mM : 123mM

Na+ 12mM : 145mM

K+ 155mM : 4mM

Question 22

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

Answer 22

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

Question 23

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

Answer 23

Sodium-calcium exchanger (NCX)

Low affinity, high capacity

Question 24

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

Answer 24

Majority - NCX

Residual - PMCA, SERCA and mitochondrial calcium uniports

Question 25

List the transport systems involved in acid extrusion

Answer 25

Sodium-Hydrogen exchanger (NHE) Sodium bicarbonate co-transporter (NBC) (NBC - Sodium and bicarbonate flow into the cell in exchange for hydrogen and chloride ions)

Question 26

List the transport system involved in alkali extrusion

Answer 26

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

Question 27

How does Anion Exchange work?

Answer 27

Chloride ions move in as bicarbonate moves out

Question 28

What transport systems are activated by acidification?

Answer 28

Sodium bicarbonate co-transporter (NBC) Sodium-hydrogen exchanger (NHE)

Question 29

What transport systems are activated by alkalisation?

Answer 29

Anion exchanger (AE)

Question 30

Describe the principles of regulating cell volume

Answer 30

Cell swelling - Extrude ions Cell shrinking - influx of ions (Water will follow the movement of ions)

Question 31

What must be taken into account when maintaining cell volume?

Answer 31

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

Question 32

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

Answer 32

Carbonic anhydrase

Question 33

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

Answer 33

Inter-conversion of water and carbon dioxide to hydrogen carbonate

Question 34

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

Answer 34

Retain base for pH buffer

Question 35

What is the function of aquaporin?

Answer 35

Increases membrane permeability to water in the cortical collecting duct

Question 36

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

Answer 36

Anti-diuretics

Question 37

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

Answer 37

- Thick ascending limb - Distal convoluted tubule - Cortical collecting duct

Question 38

What is ROMK and where is it found

Answer 38

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

Question 39

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

Answer 39

- Reabsorption of sodium ions from the lumen | - Found in the epithelium of the distal convoluted tubule and cortical collecting duct of the kidney

Question 40

What is spironolactone and how does it work?

Answer 40

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

Question 41

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

Answer 41

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

Question 42

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

Answer 42

NKCC2 - Uptake of sodium, potassium and chlorine from the lumen ROMK - Movement of potassium back into the lumen

Question 43

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

Answer 43

KCICT - Potassium and chlorine into bloodstream CIC-Kb - Chlorine into bloodstream Na pump - 3 sodium pumped into bloodstream and potassium back into cells