7) Passive Transport Of Ions Flashcards
Driving force for the passive transport of ions
Facilitated diffusion
Diffusion through pores and channels in membrane
Simple non mediated diffusion through bilayer
Electrochemical potential
This is the sum of the chemical electrical and conc potentials
Magnitude and direction of ion flux density
Directed from high to low values of electrochemical gradient
Various models are used to calculate ionic currents
Facilitated diffusion
Ionophore is small hydrophobic molecules that shield the change of the ion and facilitate its diffusion
Ion binds to ioniphore
Ionophore ion complex forms and diffuses to other side of membrane
Facilitated diffusion carrier example
Valinomycin
Ring shaped proteins that facilities the diffusion of potassium ions by electrochemical gradient
Diffusion through ion pores and channels
Hey are transmembrane proteins and have hydrophilic and hydrophobic groups
Pore example
Gramacidin
Is a pore forming anntibiotic
Helical peptide chain of 15 AA
Electrically fates ion channel
Structure
Has 2 states open channel and closed channel
State is controlled by electric field and mechanical stress
Ligand gated ion channels
Drawing
Of bilayer with mesh
Ligand attaches and then the mesh splits down the middle
Mechanically gated channel
Light gated ions
Membrane proteins capable of responding to mechanical stress
Non specific is Na k and ca H
Limitation changes conformation and opens the passage
Electro diffusion model
Aim is to determine the flux density of ion through membrane
Assumptions
Membrane is a continuous homogenous medium
Ion flux density
J = cv = -cu du/dx
U is ion mobility
X is coordinate axis
Nernst plank equation
J= -D ( dc/dx + d / dx. C)
Goldman equation
P = lander D/d
P is permeability
d is membrane thickness
Input and output of ion flux densities
J = Ji- je
Input - output
Diffusion rate
The diffusion rate for cations through membrane of nerve desks is 10 times higher than that of the diffusion rate of anions
Due to layer of negative charge
Generation of diffusion potential
Conditions
2 neutral volumes separated by a membrane
Diffusion potential depends on conc and mobility of ions
Diffusion potential
Can be produced in bio membranes when there is damage
It usually reverts back to 0 bc then conc on both sides becomes equal
Nernst equation
Potential difference depends on the ion concentration ratio on both sides
Ion equilibrium in biological systems
In cells potassium is close to equilibrium
Sodium ions are far from equilibrium
