We want to break down the non covalent interactions and the disulfide bonds that exist between those two polypeptide chains. So we need to expose the quadrinary structure to a denaturing solution. For example, we can use urea or guanidine hydrochloride to basically break down those non covalent interactions holding our two polypeptide chains. And then if we have disulfide bonds between our two polypeptide chains, we want to expose them to beta mercapto ethanol to basically break down those covalent interactions. So let's suppose we're dealing with a protein that consists of two individual subunits, two polypeptide chains. We have the green one and we have the blue one.