Membrane Permeability

Question 1

Is a membrane permeable to large uncharged polar molecules?

Answer 1

No

Question 2

Can ions pass through the membrane?

Answer 2

No, only through specialised channels.

Question 3

What two factors does the rate of passive transport depend on?

Answer 3

The permeability of the membrane to that molecule and the concentration gradient.

Question 4

State 5 reasons why we need transport processes.

Answer 4

Exclusion of waste production, generation of ion gradients for electrical activity, maintenance of cell volume, maintenance of pH, conc of metabolic fuels and building blocks.

Question 5

What is a ligand gated ion channel?

Answer 5

This is where the binding of a ligand leads to opening of the channel so that there is influx or efflux of ions.

Question 6

What is a gated pore and ping pong transport?

Answer 6

This is where the molecule enters the pore, and then it causes a conformational change and so it opens on the other side of the membrane, releasing the molecule.

Question 7

What is active transport?

Answer 7

This is where there is a positive change in free energy. It is a process which requires energy either directly or indirectly from ATP and is where ions are moved against their concentration gradient.

Question 8

What ion has a higher intracellular concentration than Extracellular?

Answer 8

Potassium. IC- 155mM, EX- 4mM

Question 9

What are the conc of calcium inside and outside the cell?

Answer 9

10^-7 IC, 1.5mM outside of cell. Very small amounts of calcium need to enter the cell to produce a large response.

Question 10

What ion has a concentration of 12mM IC and 145mM EC?

Answer 10

Sodium

Question 11

What are the concentrations of Cl- in a cell?

Answer 11

IC - 4.2mM, EC - 123mM.

Question 12

What is the difference between a symport and an anti port?

Answer 12

A symport transports two ions in the same direction whereas anti port transports them in opposite directions.

Question 13

What is a primary active transporter?

Answer 13

These use ATP hydrolysis for ion transport directly.

Question 14

What is moved by the sodium potassium pump?

Answer 14

3 Na+ out of cell, 2 K+ into cell. This uses ATP hydrolysis.

Remember this as drives against conc gradients.

Question 15

What can inhibit the Sodium potassium pump?

Answer 15

Ouabin. Used for some cardiological conditions.

Question 16

What is PMCA?

Answer 16

Plasma membrane calcium ATPase. It transports 1 calcium ion in to the cell for each ATP hydrolysis.

Question 17

What type of transport is the Na Ca exchanger?

Answer 17

This is an example of secondary active transport as it uses the Na gradient, 3 Na enter the cell and one Ca is pumped out.

Question 18

What is the primary role of the NaH exchanger?

Answer 18

Maintenance of cellular pH. It pumps one Na in for one H out.

Question 19

How is glucose taken into cells in the intestine or kidney?

Answer 19

By the Na Glucose co-transporter. This is another example of secondary active transport.

Question 20

In conditions such as cystic fibrosis, what is the consequence for all ion levels?

Answer 20

All the pumps work together to maintain a cellular environment so if there is a lack of Cl- pumping then this will have a knock on effect on all other ion concentrations.

Question 21

What does the cholera toxin do?

Answer 21

It causes phosphorylation of CFTR and so water follows leading to diarrhoea.

Question 22

What two types of molecules is a cell membrane permeable to?

Answer 22

Hydrophobic molecules and small uncharged polar molecules.

Question 23

Which calcium pump has a low affinity but a high capacity?

Answer 23

The NaCa exchanger. This means that when Ca levels are high, this will work to quickly remove calcium from the cell.

Question 24

When calcium levels are close to resting, what pump will transport the last few ions?

Answer 24

PMCA which has high affinity but low capacity.

Question 25

What is SERCA?

Answer 25

This is a pump of the sarcoplasmic recticulum which pumps Ca to act as a store in preparation for muscle contraction.

Question 26

What action occurs with an organelle in the cell when Ca levels are potentially damaging?

Answer 26

The calcium uniporter on mitochondria operates to remove calcium from the cytosol.

Question 27

In which direction does the Na Ca Exchanger operate?

Answer 27

It operates in the direction of the Na gradient. It can reverse which is a useful property for the cardiac action potential.

Question 28

State the problem that occurs in ischaemia which causes toxic Ca levels in cells.

Answer 28

In ischaemia, the Na K pump cannot operate due to depleted ATP and so Na accumulates in the cell the membrane becomes depolarised. NCX reverses and pumps calcium into the cell as it pumps Na out down its conc gradient.

Question 29

What does the anion exchanger transport? What are its function in the cell?

Answer 29

Cl- into the cell and HCO3- out of the cell. Maintenance of cell volume and acidification of the cell.

Question 30

What is done by pumps to combat cellular swelling?

Answer 30

Extrusion of ions.

Question 31

When regulating cell volume, what is important about the ion movement?

Answer 31

It is important that the ion movement is neutral and doesn’t affect the polarisation of the membrane or acidity of the cell.

Question 32

What two substances are reabsorbed by the proximal tubule in the kidney?

Answer 32

Na and HCO3-. bicarbonate is needed for pH buffers.

Question 33

Water and carbon dioxide react to form carbonic acid in cells in the kidney. How does this assist Na and bicarbonate absorption?

Answer 33

Carbonic acid then dissociates into a H ion and a bicarbonate ion. The NaH exchanger means Na is taken up into the cell as H moves out, and also the bicarbonate ion is taken into the capillary from the cell by the anion exchanger.

Question 34

What is the importance of Na reuptake?

Answer 34

This means that water is also retained which maintains BP.

Question 35

What does aldosterone up regulate? What problem can this cause?

Answer 35

It up regulates the sodium potassium pump. This can lead to too much sodium retention, and therefore high BP.