Lab - Week 1 Content - Membrane Transport Flashcards
What does the plasma membrane of most cells separate?
Intracellular and extracellular compartments
T/F: the plasma membrane does permit the movement of certain substances between the ICF and ECF
True
Have you revised membrane transport from week 1?
Yes
Osmosis is the term given to the movement of any ___________ across a __________________________
Solvent
Selectively permeable barrier
What kind of solutions are the ICF and ECF?
Aqueous solutions
For our purposes what does osmosis refer to?
The movement of water across the plasma membrane
What are a good model system in which to study osmosis?
Why?
Erythrocytes
Their plasma membrane is permeable to water but fairly impermeable to salts
If erythrocytes are placed in a hypotonic solution then water will flow…?
What will happen if the process continues?
What is the name of the resulting process?
Into the cell, DOWN it’s concentration gradient and the cell will increase in volume.
The cell will eventually burst, expelling the haemoglobin into the surrounding fluid
Haemolysis
If erythrocytes are placed in a hypertonic solution water will move…?
What will happen if the process continues?
What is the name of the resulting process?
Out of the cell
This will cause the cell to shrink
Process known as CRENATION
If erythrocytes are placed in a hypertonic solution water will move…?
What will happen if the process continues?
What is the name of the resulting process?
Out of the cell
This will cause the cell to shrink
Process known as CRENATION
What is the goal of the lab?
What kind of blood did we use?
To determine which aqeuous solutions are which
Sheeps blood
What is the rough osmolarity of sheep erythrocyte ICF?
Roughly 300 mOsm/L
How much of a drop of blood can we place on a slide with how much of the unknown, diluting solution?
1/10 of a drop of sheeps blood
1 drop of unknown solution
It is very important that only a very small volume of blood is applied to the slide so that you can observe…?
Why?
How long do you have to examine the cells within?
The shape of the cells
If when you look down the microscope and see clumps of cells your results will be meaningless
1-2 minutes of applying the solution in order to observe the changes (crenation or haemolysis etc)
If red blood cells are suspended in a solution containing a foreign substance to which the membrane is readily permeable, then this substance will…?
How long will this continue?
Rapidly diffuse into the cells down it’s concentration gradient.
This diffusion will continue until its concentration inside the cells is the same as its concentration outside the cells.
What will the addition of extra solute to the normal intracellular constituents of the cells mean?
The effective concentration of water inside the cells is now less than it was previously.
As a result, water will move into the cell by osmosis and may cause haemolysis.
The rate at which water moves into the cell depends on…?
the permeability of the cell membrane to the foreign substance.
The time for haemolysis to occur will give an indication of…?
The permeability of the membrane to the substance
What is the procedure to determine haemolysis?
- Put 2mL of the solution into a plastic vial
- Add two drops (only) of sheep blood to the vial, start the timer and mix gently
- Note the time taken for the suspension to become translucent, due to haemolysis of the cells
When is the end point of the haemolysis experiment?
How is the experiment facilitated?
When the solution changes from being a cloudy suspension to being translucent (not transparent).
By holding the tube against some text.
Practice as many times as you’d like with the Practice solution provided - make sure you’re comfortable at determining this end point before you continue
What is the maximum cut off time for the haemolysis experiment we are recommended to use?
12 minutes
What is the effect of the size of the solute on haemolysis time?
Why is this the case?
The result of these findings suggest that smaller molecules hemolysis faster as compared to larger molecules (extra: and the stronger the lipid-water partition coefficient the fast hemolysis can occur regardless of the size of the molecule)
This is due to the simple fact the plasma membrane is generally more permeable to smaller molecules as compared to larger one as they enter the cell effortlessly. So, the hemolysis rate is dependent on the size of the molecules
How does relative lipid solubility effect haemolysis time?
The lipid solubility increases the permeability of the membrane, which increase hemolysis. This is because the formation of longer carbons will make lipids more soluble, thus reducing the molecular size of the lipid, which will then be easily passed out.
What effect does temperature have on haemolysis time?
The rate of hemolysis was rapid at 5–10° and above 40°, but slow at around 25°. The results suggest the importance of membrane fluidity in hemolysis and the occurrence of phase separations of membrane lipids.
Determine the haemolysis time for the 1M solution of urea at the different temperatures provided and enter the results in the table below (Temperature in celsius by haemolysis time)
What is the effect of temperature on haemolysis time?
How do you explain this result?
Determine the haemolysis time for each of the solutions in the table below.
From your observations, identify each of the numbered solutions and explain why you came to this conclusion:
What is the effect of the size of the solute on haemolysis time?
How do you explain these observations?
