Membrane Permeability Flashcards
Is a membrane permeable to large uncharged polar molecules?
No
Can ions pass through the membrane?
No, only through specialised channels.
What two factors does the rate of passive transport depend on?
The permeability of the membrane to that molecule and the concentration gradient.
State 5 reasons why we need transport processes.
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.
What is a ligand gated ion channel?
This is where the binding of a ligand leads to opening of the channel so that there is influx or efflux of ions.
What is a gated pore and ping pong transport?
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.
What is active transport?
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.
What ion has a higher intracellular concentration than Extracellular?
Potassium. IC- 155mM, EX- 4mM
What are the conc of calcium inside and outside the cell?
10^-7 IC, 1.5mM outside of cell. Very small amounts of calcium need to enter the cell to produce a large response.
What ion has a concentration of 12mM IC and 145mM EC?
Sodium
What are the concentrations of Cl- in a cell?
IC - 4.2mM, EC - 123mM.
What is the difference between a symport and an anti port?
A symport transports two ions in the same direction whereas anti port transports them in opposite directions.
What is a primary active transporter?
These use ATP hydrolysis for ion transport directly.
What is moved by the sodium potassium pump?
3 Na+ out of cell, 2 K+ into cell. This uses ATP hydrolysis.
Remember this as drives against conc gradients.
What can inhibit the Sodium potassium pump?
Ouabin. Used for some cardiological conditions.
What is PMCA?
Plasma membrane calcium ATPase. It transports 1 calcium ion in to the cell for each ATP hydrolysis.
What type of transport is the Na Ca exchanger?
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.
What is the primary role of the NaH exchanger?
Maintenance of cellular pH. It pumps one Na in for one H out.
How is glucose taken into cells in the intestine or kidney?
By the Na Glucose co-transporter. This is another example of secondary active transport.
In conditions such as cystic fibrosis, what is the consequence for all ion levels?
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.
What does the cholera toxin do?
It causes phosphorylation of CFTR and so water follows leading to diarrhoea.
What two types of molecules is a cell membrane permeable to?
Hydrophobic molecules and small uncharged polar molecules.
Which calcium pump has a low affinity but a high capacity?
The NaCa exchanger. This means that when Ca levels are high, this will work to quickly remove calcium from the cell.
When calcium levels are close to resting, what pump will transport the last few ions?
PMCA which has high affinity but low capacity.
What is SERCA?
This is a pump of the sarcoplasmic recticulum which pumps Ca to act as a store in preparation for muscle contraction.
What action occurs with an organelle in the cell when Ca levels are potentially damaging?
The calcium uniporter on mitochondria operates to remove calcium from the cytosol.
In which direction does the Na Ca Exchanger operate?
It operates in the direction of the Na gradient. It can reverse which is a useful property for the cardiac action potential.
State the problem that occurs in ischaemia which causes toxic Ca levels in cells.
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.
What does the anion exchanger transport? What are its function in the cell?
Cl- into the cell and HCO3- out of the cell. Maintenance of cell volume and acidification of the cell.
What is done by pumps to combat cellular swelling?
Extrusion of ions.
When regulating cell volume, what is important about the ion movement?
It is important that the ion movement is neutral and doesn’t affect the polarisation of the membrane or acidity of the cell.
What two substances are reabsorbed by the proximal tubule in the kidney?
Na and HCO3-. bicarbonate is needed for pH buffers.
Water and carbon dioxide react to form carbonic acid in cells in the kidney. How does this assist Na and bicarbonate absorption?
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.
What is the importance of Na reuptake?
This means that water is also retained which maintains BP.
What does aldosterone up regulate? What problem can this cause?
It up regulates the sodium potassium pump. This can lead to too much sodium retention, and therefore high BP.
