Quiz 5: Chapter 8: Motions of Biological Molecules Flashcards
Under what conditions does diffusion of molecules occur?
occurs if there is a concentration gradient dc/dx
What is net flux of molecules? (Diffusion)
- Flux is J, has units mol m^-2 s^-1
- it is the moles of molecules that moves through an area per second
What is Fick’s first law of diffusion?
- The net flux of molecules (J) is proportional to the gradient (dc/dx), the constant of proportionality is the diffusion coefficient D
What is the negative sign is Fick’s first law due to?
The negative sign is due to the flux being in the opposite direction of the gradient
What is the graph of a concentration gradient of a membrane between two reservoirs?
What is Fick’s second law of diffusion?
- relates the time dependent concentration change to the spatial variation of the concentration at that time point
What does Fick’s Second Law of Diffusion allow us to assume about this diagram?
- consider the slab with cross section A and thickness L (the slap extends from x to x + L)
- the number of molecules in moles that enter the slab in a time interval (dt) from the left is J(x)Adt
- Dividing this number by the volume AL gives the concentration change per time interval as:
dc/dt = (JAdt) / (ALdt) = J / L
*****What is the solution to Fick’s second law equation?
How does the solution to the diffusion equation change with time?
The solution of the equation for the diffusion from a point source is a Gaussian function that broadens with time
Describe Fick’s second law equation (order)?
Fick’s second law is a second-order differential equation in space and first order in time.
What is terminal velocity?
terminal velocity:
the limiting velocity due to friction with the air or for an object sinking in water
Why are calculated frictional coefficients lower than measured frictional coefficients?
- the hydrodynamic volume of macromolecules in the water (effective volume as they diffuse) is increased by tightly bound water molecules adhering to their surface (shell of hydration)
- spheriodal or ellipsoidal proteins have larger frictional coefficients than spheres of the same volume
- irregularities and clefts on the protein surface retard translational and rotational diffusion
What are the probability and average equations for a discrete variable?
What does a high diffusion coefficient mean?
diffuses quickly?
What is the average value of squared displacement for one dimensional diffusion?
x^2 = 2 D t
What is the average value of squared displacement for 3D diffusion?
d^2 = 6 D t
Flux is always___________
in the opposite direction of the gradient
What are the influx and outflux equations?
What does THE SOLUTION of Fick’s second law describe the behavior of?
diffusion of particles from a point source
What is Fick’s first law for?
steady state diffusion
What is Fick’s second law for?
time dependent concentration at position x
What is probability density?
probability of X falling in the interval between Xo to Xo + dx
What is the average equation for a continuous variable?
What is the friction coefficient equal to?
- r = radius of the sphere
- n = viscosity
What is a diagram illustrating stoke’s law?
How does the friction coefficient relate to force imbalance? For a pebble moving through water at CONSTANT velocity?
What is the equation for Ff?
Ff = (6 π n r) vt
Ff = f Vt
Force of friction = friction coefficient x terminal velocity
What is the equation for flux due to diffusion?