Protein folding determines the shape of the protein, and thuswhat it does, because it is the shape of the protein which enablesit to perform its function. For example, enzymes need to haveexactly the right shape to fit with the molecules they are workingwith to catalyze them. Also, hemoglobin is specifically folded withfour pocket like areas to allow oxygen to attach to it. The shapeof the protein is specific to the function that it is performing,and is different for each protein. If there is even a slight changein the make up of the protein, or a mutation (the amino acids aremessed up) then the protein will fold differently. Even a slightchange in the composition of the protein can disable the proteinfrom properly performing the function which it is meant to do.