The secondary, tertiary, and quaternary structures of a protein are collectively termed as the “higher order structure” (HOS) of a protein. HOS is responsible for the correct folding and 3-dimensional shape of proteins, including therapeutic proteins such as monoclonal antibodies (mAbs). This interactive scrollable describes the general relationship between a molecule's structure and its function, examines the 4 levels of protein structure and how they relate to HOS, and describes how circular dichroism spectroscopy can be used to study the HOS of a mAb therapeutic protein.