🐭 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:
- 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.
- Diffusion limitation: While the counterions are attracted, they cannot freely diffuse across the membrane to balance the charge of the impermeable molecule.
- 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.
- Compartment with impermeable anion:
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.