Gibbs-Donnan Effect

🐭 RAT series

Points to Ponder for NEET-PG, FMGE & NEXT

• The Gibbs-Donnan effect explains the unequal distribution of charged particles across a semi-permeable membrane.
• Gibbs-Donnan effect is important in maintaining cellular ion concentrations, shape, and volume.

Definition

• The Gibbs-Donnan effect describes the unequal distribution of charged particles across a semipermeable membrane due to the presence of impermeable charged molecules.

Key Concepts:

• Semipermeable membrane: Allows passage of some molecules (e.g., water, small ions) but restricts others (e.g., large proteins).
• Impermeable charged molecule: A charged molecule that cannot cross the membrane due to size or charge (e.g., proteins in cells) 

Mechanism:

1. Uneven distribution: When an impermeable charged molecule (e.g., protein) is present in one compartment, it attracts oppositely charged ions (counterions) to maintain electrical neutrality within that compartment.
2. Diffusion limitation: While the counterions are attracted, they cannot freely diffuse across the membrane to balance the charge of the impermeable molecule.
3. Equilibrium: A state called Gibbs-Donnan equilibrium is established:
   • Electrical neutrality: Both compartments maintain electrical neutrality (equal positive and negative charges).
   • Product equality: The product of diffusible ion concentrations (cations and anions) remains equal across the membrane.

Consequences of Equilibrium:

• Concentration differences:
  • Compartment with impermeable anion:
    • Higher concentration of total ions due to trapped anions and attracted cations.
    • Higher concentration of diffusible cations compared to the other compartment.
  • Compartment without impermeable anion:
    • Lower concentration of total ions.
    • Higher concentration of diffusible anions compared to the other compartment.

Physiological Significance:

• Cellular Environment: The Gibbs-Donnan effect plays a crucial role in maintaining the cellular environment.
  • Intracellular fluid (ICF): Contains high concentrations of non-diffusible anions like proteins and organic phosphates.
  • Extracellular fluid (ECF): Contains diffusible cations (e.g., K+) and anions (e.g., Cl-).
• Concentration Gradients: Due to the Gibbs-Donnan effect:
  • K+ concentration is higher inside cells (ICF) than outside (ECF).
  • Cl- concentration is higher outside cells (ECF) than inside (ICF).
  • Total ion concentration is higher inside cells (ICF) than outside (ECF).
• Cellular Functions: These concentration gradients created by the Gibbs-Donnan effect contribute to:
  • Maintaining cell shape and volume.
  • Generating electrical gradients for cell signaling and function.

Quiz