Diffusion and Osmosis Flashcards
Basic mechanisms for solute movement across the cell membrane ?
- simple diffusion ( bilayer ) down concentration gradient - until equilibrium….
- aqueous diffusion ( channels ) ( down concentration gradients
- facilitative transport ( passive ) (down concentration gradients )
- active transport ( with energy /ATP) against concentration gradients
What is diffusion?
net movement from greater concentration to lower concentration
J =(proportional) dc/dx
rate of diffusion is proportional to concentration gradient over disatnce
rate of diffusion —- proportional—- concentrations gradient/distance
Rate of diffusion is INDEPENDENT of diffusion of other substances but what is it related to?
- physical properties of the solute/ solvent molecules ( size/ electric charge )
- temperature
- electric field
Diffusion of solute across the membrane?
- membrane is a selective brarrier to diffusion
- concentration gradient lies within the membrane barrier
- measure Permeability ( diffusion and partitioning )
- vital for processes ( e.g. gas exchange (o2/co2, lipophillic drug actions )
- solute concentration difference also relevant for solvent ( water potential ) gradient:- osmotic water flow
what is Ficks Law of Diffusion ?
- Quantitative description of solute movement across membrane :- Ficks Law of Diffusion.
- high to low concentration depending on gradient and concentration …
What is Ficks Law equation ?
JI-II = P.A.(SI-SII)
J=Rate of Solute Diffusion (mol/sec)
P= Permeability coefficient of solute across membrane (m/sec)
A= membrane Area (m2)
S= concentration of Solute in each solution ( mol/m3)
—– concentration difference (SI-SII ) iss oftenn termed difference c
Force- Flow Relationships are extremely important in physiology
( what is the equation )
FLow= Energy Gradient /Resistance
includes Ficks law, Ohms Law , and Hagan -poiseuille equation !!!!
( refer to notes ! )
solute concentration witin membrane depends on Kp
permeability = diffusion and partioning
refer to page 6-9 lecture 2 notes???!!! - for all equations….. !!!)
hydrophobic lattice
The hydrophobic lattice structure of the bi layer acts as a viscous molecular ‘seive’
Important factors for predicting passive permeability ?
- *** frictional effects ( mobility)
- molecular size ( small =high permeability /large =low permeabilty )
- molecular shape - straight / snake like= high permeability /// globula = loow permeabiliy
- membrane viscosity - short R chains, c=c ( including temperature ) high permeability
***** lipid solubiliity (Kp)
if the lipid solubility is high ( high Kp) - eg O2/CO2 or lipophilic groups -high permeability !!!!
if liipid solubility is low (low Kp) e,g, sugars , amino acids , ions , polar/charged groups - low permeability !!!!
*** Unstirred layers - ( increases overall thickness of barrier )
-
*** Charge effects- molecular charge affects the Kp ( lipid solubility )
- hydrogen bonding alters effective molecular size/shape Kp
What are major solutes in cellular and external water pools ?
inorganic ions
what is a barrier to ion permeation ?
lipid cell membrane
- very low ion permeability ( electrical insulator )
- differential ion permeability ( usually K+, Cl- > Na+)
Pcl >Pk because of bilayer charge. PNa is 10-2
permeability differences have major effect on ion distributions across the cell membrane
what is the Donnan Equilibrium?
permeability differences have major effect on ion distributions across the cell membrane
failed equilibrium - due to charges !!!
What is Osmosis?
net solvent flow
water moves from region of higher to lower ( more negative ) water potential , showing bulk flow !
animal cells exert minimal turgor pressure !
