Ionic Properties of Cells:
- Every cell maintains intracellular concentration of inorganic solute that are very different from those of the extracellular environment
- These ionic gradients across the cell membranes are so important to cell function that the cell spends a great deal of energy to maintain them (ex. Na+/K+ - ATPase)
Simple Diffusion
- Molecules more constantly and randomly
Over time, more molecules move at random from an area of high concentration to an area of low concentration. This process is passive (no energy needed)
Fick’s Law of Diffusion:
J = D x ((C1 - C2)/X)
J: rate of diffusion or quantity of solute diffusing per unit time
D: Diffusion coefficient
C1: Value of high concentration
C2: Value of low concentration
X: Distance between C1 and C2
Fick’s Law of Diffusion:
D= P/(square root)MW
D: Diffusion coefficient
P: Permeability
MW: Molecular weight
Electrochemical Gradients:
- Ionic charges separation occurs only with nanometers
- determines the movements of solutes across a permeable membrane
- when the chemical and electrical gradients are in the same way, diffusion is fast
Osmosis
Is the diffusion of water through a semipermeable membrane from a region of low solute concentration to a region of high solute concentration
Osmosis and Hydrostatic Pressure (water movement)
Water stops moving when the hydrostatic pressure equals the osmotic pressure
Osmotic Pressure
Property of a solution that allows you to predict which way water will move
Osmolarity
- Total dissolved entities per liter
- is the unit of measure or osmotic pressure
Tonicity
- The effect of a solution on cell volume
Effect of Tonicity
Depends on differences in osmolarity but also on the permeability of the membrane to the solutes
Ex. Whether or not the solute can enter the cell
Osmosis Vs. Tonicity
- Osmolarity considers the total concentration of penetratind of non- penetrating solutes
- Tonicity relates only to the total concentration or non-penetrating solutes
Donnan Equilibrium
- Predicts that the distribution of ions across a membrane will be unequal if the membrane is impermeable to one or more types of charged particles
- Animal cells tend towards this equation because they contain a high concentration of non-permeating avionics molecules (A-)
Rule #1: Donnan Equilibrium
Principle of Electroneutrality
Rule #2: Donnan Equilibrium
The product of the concentration of permeant ions inside the cell equals the product of the concentration of permeant ions outside the cell
Rule #3: Donnan Equilibrium
Osmolarity inside/outside the cell must balance
OLEK
Zabinski
