Describe the term solute fluxes?
What is a proteoliposome?
Artificial membrane with proteins embedded
Epithelial tissue is used as when looking at solute flux?
The best natural membrane vesicles.
Name the 2 radioactive labels?
3H and 14C
How is temp important when looking at diffusion?
The higher the temp the more diffusion that takes place.
Describe the term simple diffusion?
Random movement of solute molecules in solvent tending towards an equilibrium state.
How do solutes distribute themselves when undergoing diffusion?
Uniformly and independently of each other.
The net movement from region of greater concentration to region of lesser concentration.
Rate of diffusion (J)?
Is proportional to concentration gradient over distance ie J= k (dc/dx)
Name the 3 variables that the rate of diffusion is dependent on?
1) Physical properties of solute and solvent molecules (ie. size, electrical charge). 2) Temperature 3) Electric field Independent of the diffusion of other substances
Difference in dissolution between larger and small solutes?
Bigger solutes will dissolve slower than the smaller solutes
How to work out the concentration gradient
distance x the thickness of the membrane
How to measure the permeability?
Diffusion + partitioning
Describe the term partitioning?
The initial process of the solute getting into the bilayer.
How two processes is diffusion vital for?
1) Gas exchange 2) Lipophilic drug actions
What is ficks law of diffusion?
Quantitative description of solute movement across membrane
Why is there a concentration difference between the outside of the cell and inside of the cell?
There is a difference in concentration. Only in the membrane is diffusion taking place.
Foce- flow relationship?
Flow= energy gradient/resistance
Describes the concenrtation difference between the outside and inside of the cell
The equation of ficks law of diffusion?
J1->11= PA (S1-S11)
Why is partitiion coefficient important?
Some solutes try to get into the membrane but some are reflected back
However the net movment is towards the smaller concentration.
It is important in estimating the distribution of drugs within the body.
Define the lipid-water partition coefficient (Kp)?
Hydrophilic molecules (eg. glucose): Kp<1.
Hydrophobic molecules (eg. oxygen): Kp>1.
Hydrophilic molecules movement?
Hydrophilic molecules are water loving and have a low water parition coefficient- prefer to be in aqueous compartments such as blood serum.
Therefore does not readily pass the membrane barrier.
Hydrophobic molecules movement?
High water parititon coefficients are preferentially distributed to hydrophobic compartments such as the lipid bilayer.
Name the 4 factors that contribute to the diffusion coefficient?
Gas constant (8.3)
Viscosity of barrier
Radius of diffusing molecule
Why does the radius of the diffusing molecule effect its diffusion coefficient
Not all of them will be spherical.
the bilayer acts as a seive.
Smaller molecules will get through much quickly
What 3 things is the rate of solute diffusion proportional to?
- Permeability coefficient P
- Surface area A of membrane.
- Concentration difference.
What does J (rate of diffusion) relate to?
It is the net movement of molecules across the membrane.
If the concentration of both is equal. J=0
At equilbrium what is happening?
There is still a movement of molecules however there will be no net movement
What is the thickness of the membrane?
Name the 4 important factors for predicting passive permeability?
- Frictional effects ("mobility")
- Lipid solubility (Kp)
- Unstirred layers
- Charge effects
Name the 3 frictional effects on the passive permeability?
Lipid solubility effects on the passive permeability?
Kp high: permeability is high
Kp low: low permeability.
Unstirred layers effects on the passive permeability?
When the bilayer is unstirred the overall thickness is increased
Charge effects on the passive permeability?
Molecular charge affects Kp
Hydrogen-bonding alters effective molecular size/shape
Permeability differences have major effect on ion distribution across cell membrane.
If the bilayer has a very low ion permeability what can it be described as?
Net solvent flow
Water moves from a region of higher to lower water potential.
Zero for pure water: increasingly negative as solute concentration increases
Proportional to concentration of dissolved solutes.
Inversely proportional to osmotic potential.
Concentrated salt solution.
Normal salt concentration.
eg. red blood cells- will increase in water inside until it can no longer hold and burst