Diffusion in cells

Diffusion in cells- been teaching the course bio435 - biophysics II or Physical Biology of the Cell or what i really do for a living or...
The fascinating part about diffusion is that it binds both historically and scientifically energy, matter and living-systems. Brown who discovered the motion named after him, was looking at pollen grains. And in order to convince himself it was not 'vital' force, he even went to the extent of grinding pieces of the pyramids of egypt, to see if they.moved (guaranteed to be dead). Einstein who described the relation between macroscopic viscosity and molecular movement is "the physicist". In his Wunderjahr (miracle year) of 1906 papers one of them, less popularly known as compared to the mass energy relations, was the relation between heat (Wärme) and molecular movement (Bewegung).

In the lab, we have been using fluorescence recovery after photobleaching (FRAP), an experimental technique, combined wirh some simple imageJ data extraction and loads of attempts at analyzing the data, to estimate molecular diffusion coefficients inside cells. Currently we find a few odd things.

A FRAP profile of an E. coli cell expressing GFP

1_ GFP diffuses faster in E. coli than we can bleach it out.
2_ Reducing the number of bleach pulses doesn't allow any measurable bleaching, i.e. our scanning system is too slow
3_ The recovery kinetics show heavy amounts of imaging-dependent bleaching. 

Did we not turn down the laser after the bleach?

More on this when i get to it.