As a follow-up to question 13 regarding urea, what would happen if the urea diffused extremely quickly or somehow instantaneously from the dialysis sack? Would there be a difference in renaturation of the protein compared to what happens with slow diffusion of the urea? or can the urea only diffuse slowly due to the pores in the dialysis bag?
The urea diffuses slowly into or out of the dialysis sack, as the molecules must find the pores by random motion. The slow diffusion out during renaturation is thought to be important, as it would allow the polypeptide, through random motions, to explore different bonding possibilities while it is still partially denatured and settle on the strongest combinations. Thus when the urea finally gets to zero, the polypeptide has found its most stable state, presumably the native form.