Polypeptides and proteins exhibit enormous structural diversity. The diverse three-dimensional organization of atoms within these macromolecules underlies the remarkable versatility in protein function. The protein biopolymer plays both structural and functional roles in living systems. For example, the molecular machines that convert light energy into chemical energy, coordinate the movement of muscle, transport oxygen in the blood, and catalyze chemical reactions are based primarily on protein biopolymers. In addition, the distinctive physical properties of proteins such as collagen and silk arise from their unique molecular structure.