Understanding Donnan Membrane Equilibrium
Explore the concept of Donnan Membrane Equilibrium where the presence of non-diffusible ions alters the diffusion of diffusible ions across a membrane. Learn about passive distribution, Donnan Equilibrium mathematical expression, and the implications of impermeable negatively charged molecules in biological systems. Anil Gattani, Ajeet Kumar.
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Presentation Transcript
UNIT-I Donnan Membrane Equilibrium
Presence of a non diffusible ion on one side of the membrane alters the diffusion of diffusible ions is known as Donnan Membrane Equilibrium Anil Gattani, Ajeet Kumar
Passive distribution Donnan equilibrium The ratio of positively charged permeable ions equals the ratio of negatively charged permeable ions Start Equilibrium I II I II K+ [K+] = [K+] Cl- [Cl-] = [Cl-] Anil Gattani, Ajeet Kumar
Donnan Equilibrium Mathematically expressed: + [ [ ] ] [ [ ] ] K K Cl Cl = I II + II I Another way of saying the number of positive charges must equal the number of negative charges on each side of the membrane Anil Gattani, Ajeet Kumar
Passive Distribution BUT, in real cells there are a large number of negatively charged, impermeable molecules (proteins, nucleic acids, other ions) call them A- Start A- Equilibrium A- I II I II [K+] > [K+] K+ Cl- [Cl-] < [Cl-] Anil Gattani, Ajeet Kumar
The presence of impermeable negatively charged molecules requires more positively charged molecules inside the cell. Anil Gattani, Ajeet Kumar
Donnan Equilibrium Example Initial Concentrations I II A- = 0 A- = 100 K+ = 150 K+ = 150 Cl- = 150 Cl- = 50 Are these ions in electrochemical equilibrium? No, EK+ = 0 mV ECl- = -27 mV Anil Gattani, Ajeet Kumar
Application of Donna Membrane Equilibrium Difference in the ionic concentration of biological fluid Membrane hydrolysis Low pH in RBC Osmotic Imbalance Anil Gattani, Ajeet Kumar
