Passive transport of neutral particles. Flashcards Preview

Biophysics > Passive transport of neutral particles. > Flashcards

Flashcards in Passive transport of neutral particles. Deck (26):

Define passive transport.

It uses energy stored in gradients of; concentration, electric potential, chemical potential, osmotic pressure, hydrostatic pressure, to move atoms ions or molecules in a particular direction.


What is the formula and definition of flux density.

Flux density is a measure of transport.
Flux density J- the amount (of substance) that moves through a unit area normal to the direction of motion x during a unit time interval.


What is an exergonic(Spontaneous) process?

It reduces the free energy of a system.


What is simple diffusion?

Process by which the solutes move from a high concentration to a low concentration.


What is Ficks law?

J=-D dc/dx
D= diffusion constant m^2/s
C=Concentration, mol/m^3


What is the diffusion constant?

D=diffusion constant, T=absolute temperature, u= particle mobility.
For biological molecules, D is usually 10^-11 m^2/s to 10^-10 m^2/s


What is the diffusion constant for spherical particles in a liquid.

r= radius
(n)*= viscosity.


What is molecule mass of a spherical molecule and its relevance to the diffusion constant?

M~ r^3
At constant temperature and viscosity;
D~1/3(square root)M
D~1/(square root)M is the diffusion constant proportionality for small molecules.


What is Ficks second law?

Describes the variations of the concentration of the diffusing substance in time and space.
(t)*= diffusion time.


Describe the assumptions of diffusion across a membrane

Diffusion across a membrane is much slower than simple diffusion.
We can assume that the concentrations inside the membrane change linearly and that concentrations of both sides do not change over time.


How do you calculate the flux density of the membrane?

d= membrane thickness,m
P= permeablity, m/s


How do you calculate membrane permeability of Lipophilic substances?

P=(y)* D/d
dc/dx= (y)* (c1-c2)/d
(y)*= partition coefficient.


How do you calculate membrane permeability through pore?

P=n(pi)r^2 D/d
r= radius of pores
n=concentration of pores.


What is the definition of facilitated diffusion?

Passive transport facilitated by a transport protein. The protein is usually only adapted to transport a particular substance


How do you calculate flux density of facilitated diffusion?

J=c/c+Km J0
C= conc of diffusing substance
J0= maximum(saturated) flux density
Km= Michaelis-menten constant.


What are the jobs of inhibitors in facilitated diffusion?

Inhibitors; bond to the transporter, does not get transported, blocks transporter operation, their structure is similar to the transported molecules.


Explain co-transport facilitated diffusion.

The transport of 2 substances by one transporter.
The transport of one substance depends on the other.


Define osmosis.

The diffusion of the solvent(water) across a membrane separating areas with different concentrations of the solute.


What is the formula for osmotic pressure(pi)

i= number of particles obtained from the dissociation of one molecule of the solute.
c= solute concentration mol/m^3


Give the 3 forms of isotonicity.

Isotonic solutions have equal osmotic pressure.
Hypertonic solutions have a higher osmotic pressure.
Hypotonic solutions have a lower osmotic pressure.(Cells expand)


Define filtration.

Passive transport of the solvent acrosss a membrane due to hydrostatic pressure gradient.


Explain the conjugate process.

If the membrane is soluble to both the solvent and solute, the water flux changes the conc gradient and influences the solute flux.
The diffusing solute flux effects the osmotic pressure and influences the water flux.
The processes are conjugate as they both influence each other.


Define electroosmosis.

It is osmosis under the influence of an electric field. This osmosis can change the rate and even the direction of ordinary osmosis.


What is streaming potential?

A reverse phenomenon of electroosmosis caused by the ion flux conjugated to the water flux.
It is defined as the filtration of an electrolyte through a membrane results in a potential difference across the membrane.


What causes transport of water across membranes?

osmosis and electroosmosis.


How does hydrostatic pressure cause water transport in capillaries?

Filtration at the arterial end(water leaves capillaries) and osmosis at the venous end( Water enters the capillaries).