Final answer:
Protein folding is the process by which a polypeptide chain assumes a three-dimensional shape. When a protein loses its shape, it becomes denatured and may no longer be functional.
Step-by-step explanation:
The process by which a polypeptide chain assumes a large-scale, three-dimensional shape is called protein folding. Folded proteins that are fully functional in their normal biological role are said to possess a native structure. When a protein loses its three-dimensional shape, it may no longer be functional. These unfolded proteins are denatured, implying the loss of the secondary structure and tertiary structure without the loss of the primary structure.