12) Surface Electric Charge Of Cells Flashcards
Origin of the electric charge of the cell surface
Cellular membrane is composed of
Proteins
Lipids
Hydrocarbons
The surface of the membrane builds up electric charge due to
Dissociation of atomic groups
Adsorption of ions from the surrounding fluid from surface membrane
Electric charge of proteins
Adsorption is weak because of the hydration of protein molecules
Dissociation can be acidic or basic
Proteins in acidic soloutions
The basic OH dissociates from the protein molecule
Protein cations are obtained
E+ HCl= E+ H20 cl-
Proteins in basic solutions
Acidic H dissociated from the protein
Anions are obtained
e + NaOH= e_ Na h20
Electric charge of lipids and hydrocarbons
Lipids and hydrocarbons have no dissociating atomic groups
The adsorption of ions prevails
Anions are adsorbed more readily than cations because their hydrate shell is thinner
Potential determining ions
The ions which remain on the cell surface on dissociation
Are attached to cell surface by adsorption
Counterions
Dissolve in the liquid phase due to dissociation
Remain in liquid phases due to adsorption
Electric charge on native cell surface
The surface of intact cells in w medium with normal Ph builds up a negative charge
The surface change of cells indices the voltage gated ion channels mainly the sodium ones
Electrical double layer definition and structure
The system of the surface charge and then neutralising charge of the counterions close to the surface
The screening charge consist of 2 layers
Stern adsorption layer
Diffuse layer 2
Stern layer and the diffuse layer
The ions of the stern layer are attached to the surface by adsorption forces
The ions of the diffuse layer are attracted by the coulomb
The gouy chapman model for the double layer
Approximations
Flat solid surface
In contact with ionic solution
Uniformly distributed electric charge on the surface
Equilibrium of counterions
The electrochemical potential does not change with the distance x from the solid surface
Equilibrium distribution of electrical potential
Additional assumption
The total charge of the system is zero
The electrical energy of the counterions is much less than its thermal energy
Electrical potential decays exponentially away from the surface
The Debye screening length lander
The distance lander from the surface at which the potential is e times less than on the surface
Lander = root of ktę/z2e2c infinity
Electrical potential inside thin membrane
If the electrical potential on both sides of the membrane are equal the potential inside the membrane has the same value as the outside
If the electrical potential on both sides are not equal then the potential inside changes linearly between 2 values
Electrical potential inside thick membrane
The electrical potential inside the membrane changes nonlineerly even if the potential on both sides is the same
The transmembrane potential
The potential difference between the inner and outer surface of the membrane
Cell Morrison in an electrical field
Some of the counterions move with the cell
The interface between double layers is the slipping plane
The electrokinetic potential is the electric potential at the slipping plane
Also called zeta potential t
