DONNANS EQUILIBRIUM and Bohar's effect (mushtaq ahmed and lippincott) biochemistry

1. SOURCE: MUSHTAQ AHMED
Maryam Fida (o-1827)

2.  The Gibbs–Donnan effect (also known as
the Donnan's effect, Donnan law,
Donnan equilibrium, or Gibbs–Donnan
equilibrium) is a name for the behaviour
of charged particles near a semi
permeable membrane that sometimes fail
to distribute evenly across the two sides of
the membrane.

3.  Semipermeable membrane.
 Permits the passage of crystalloids but not
of colloids.

4. • There are two main types of volume
expanders: crystalloids and colloids.
• Crystalloids are aqueous solutions of
mineral salts or other water-soluble
molecules.
• Colloids contain larger insoluble
molecules, such as gelatin; blood itself is a
colloid.

6.  If we take two solutions of a simple
electrolyte such as KCl of different conc.
then K1Cl1=K2Cl2
 Suppose we add a colloid (KPr) on side 1
while on side 2 we add a solution of KCl
then K2=Cl2 while K1 > Cl1
 The presence of colloid Pr on one side of
the membrane will affect the distribution of
K and Cl on two sides differently.

9. Source: Lippincott - Biochemistry

10.  The release of oxygen from hemoglobin is
enhanced when the pH is lowered or when
the hemoglobin is in the presence of an
increased pCO2.
 Decrease O2 affinity of Hb
 Shift to the right in oxygen dissociation
curve
 Stabilize T state (deoxy form of Hb)
 This change in oxygen binding is called
Bohr effect.

12. Source of the protons that lowers the pH
Bicarbonate buffer system
 CO2+H2O H2CO3
 H2CO3 H+HCO3

13. Mechanism of bohr effect
 Deoxy form of Hb has greater affinity for
protons than oxy form
 Histidine residues on side chains of Hb
become protonated releasing O2 easily