MR 2 Membrane Permeability

Question 1

What kinds of molecules can pass through membranes?

Answer 1

hydrophobic and small, uncharged, polar molecules

Question 2

What kinds of molecules cannot pass through membranes?

Answer 2

Large, uncharged, polar molecules and ions

Question 3

What is passive diffusion?

Answer 3

Dependent on permeability and concentration, rate of passive transport increasing linearly with increasing concentration gradient

Question 4

What is faciliatated diffusion?

Answer 4

Where permeability of membrane for a substance increased by incorporation of a specific protein in the bilayer. Models include carrier molecules(ping-pong) and protein channels.

Question 5

What is active transport?

Answer 5

Transport of ions or molecules against concentration and or electrical gradient, requiring energy from the hydrolysis of ATP

Question 6

What type of free energy change do active processes have?

Answer 6

positive

Question 7

What are co-transporters?

Answer 7

Transporters that transport more than one molecule?

Question 8

What is a uniport?

Answer 8

transports 1 molecule in 1 direction

Question 9

What is a symport?

Answer 9

Transports more than one molecule in the same direction

Question 10

What is an antiport?

Answer 10

Transports more than one molecule in opposite directions

Question 11

What are the extra and intracellular Na+ concentrations?

Answer 11

outside- 145mM inside- 12mM

Question 12

What are the extra and intracellular K+ concentrations?

Answer 12

outside- 4mM inside- 155mM

Question 13

What are the extra and intracellular Ca2+ concentrations?

Answer 13

outside-1.5mM inside 10-7M= 0.1um

Question 14

What are the extra and intracellular Cl- concentrations?

Answer 14

outside- 123mM inside- 4.2mM

Question 15

What does Na+/K+ ATPase do?

Answer 15

antiport using energy from ATP to move 2K+ into the cell and 3Na+ out of the cell to form Na+ and K+ gradients necessary for electrical excitability and to drive secondary active transport

Question 16

For what processes does the sodium potassium pump drive secondary active transport?

Answer 16

pH control regulation of cell volume Na+ absorption in epithelia Nutrient uptake e.g glucose from small intestine

Question 17

What are K+ channels mainly responsible for?

Answer 17

Diffusion down conc grad set up by the sodium potassium pump, K+ moving out of cell, is mainly responsible for the resting membrane potential of -70mv

Question 18

What does Plasma Membrane Ca2+-ATPase(PMCA) do?

Answer 18

Uses ATP to expel residual Ca2+ from the cell in exchange for H+ (antiport). high affinity, low capacity

Question 19

What does Sarco(endo)plasmic Reticulum Ca2+-ATPase(SERCA) do?

Answer 19

Accumulates Ca2+ into SR/ER in exchange for H+ using ATP (antiport) High affinity, low capacity

Question 20

What is secondary active transport?

Answer 20

Facilitated diffusion using a concentration gradient set up by an active transport process

Question 21

What does the sodium calcium exchanger (NCX) do?

Answer 21

Expels 1 Ca2+ in exchange for 3Na+(antiport) via secondary active transport using the Na+ gradient set up by the sodium potassium pump. Responsible for removing most Ca2+. Activity is membrane potential dependent

Question 22

Is NCX electrogenic?

Answer 22

Yes, current flows in direction of Na+ gradient

Question 23

What happens in ischaemia relating to NCX?

Answer 23

ATP depleted Sodium potassium pump therefore inhibited Na+ accumulates in cell leading to depolarisation NCX reverses Na+ moves out and Ca2+ moves in High Ca2+ is toxic

Question 24

What happens to CFTR in diarrhoea?

Answer 24

In gut epithelial cells its activated by protein kinase A, it pumps out more Cl- into the lumen causing water to follow causing diarrhoea

Question 25

What are the acid extruders in cell pH control?

Answer 25

Na+/H+ exchanger (NHE) Na+ dependent Cl-/HCO3- exchanger (NBC- sodium bicarbonate cotransporter) note: uses Na+ grad

Question 26

What is the alkali extruder?

Answer 26

Cl-/HCO3- exchanger (AE-anion exchanger) (Band 3)

Question 27

What transporters cause alkali influx?

Answer 27

NBC Na+/HCO3- co transporter (symport)

Question 28

How is cell volume regulated?

Answer 28

Transport of osmotically active ions e.g Na+, K+, Cl- or organic osmolytes (amino acids) in and out of cell causing water to follow

Question 29

What are the mechanisms to resist cell swelling?

Answer 29

Question 30

What are the mechanisms to resist cell shrinking?

Answer 30

Question 31

Outline bicarbonate resorption by the proximal tubule

Answer 31

Question 32

What transporter do loop diuretics block and where is this in the kidney?

Answer 32

NKCC2

thick ascending limb

Question 33

What transporter to thiazides block and where in the kidney does this occur?

Answer 33

NCCT Na+/Cl- co-transporter

distal convoluted tubule

Question 34

What protein does amiloride block and where in the kidney does this occur?

Answer 34

Epithelial sodium channel

distal convoluted tubule

Question 35

Why do you get hypertension in hyperaldosteronism?

Answer 35

aldosterone stimulates the reuptake of ions in the cortical collecting duct by binding with glucocorticoid receptors so too many ions are taken back

Question 36

How does spironolactone act?

Answer 36

glucocorticoid receptor antagonist blocking aldosterone from activating receptors in the cortical collecting duct and so reducing ion reuptake and hypertension.

Question 37

What transporters raise intracellular Ca2+

Answer 37

Facilitated diffusion:

Receptor operated Ca2+ channels (ROC)

Voltage operated/gated Ca2+ channels (VOCC/VGCC)

IP3 gated Ca2+ channels

Ca2+ induced Ca2+ release (CICR)

Store operated Ca2+ channels (SOC)

Mitochondrial Ca2+ uniporters

Secondary active transport: NCX in reverse in depolarised cells