When wool fibers are stretched, these helical regions are elongated by the breaking of hydrogen bonds. Disulfide bonds between cysteine residues of neighboring alpha-keratin chains are too strong to be broken during stretching, however, and they limit the extent of distortion. After the stretching force is removed, the hydrogen bonds reform spontaneously and the wool fiber returns to its original shape. The tertiary structure is the overall shape of the folded protein chain. Quarternary structure describes the way several protein chains orient themselves in a multiple-polypeptide protein.
Fibrous proteins are long and narrow, and generally water insoluble.
A protein's shape is influenced by what is around it. Temperature and pH also affect the protein. Shape, or conformation, of a protein is important because that is what defines its function. In this way they promote certain processes to dominate to the virtual exclusion of others. The mechanism by which an enzyme acts has long been the subject of intense reserarch.