What is the purpose of adding urea? What does urea do in the dialysis sack?
The urea was added in the Anfinsen experiment to denature the protein (ribonuclease) in what turned out to be a reversible manner. The use of a dialysis sack was to allow the gradual change in the denaturing condition, especially in the removal of the urea. By letting the urea diffuse slowly out of the pores of the sack, its concentration gradually lessened, giving time for the polypeptide to explore different bonding possibilities, to settle on the most stable one, which turned out to be the one he started with, the native, functional form.