Most proteins are globular, essentially spherical.
They posses both secondary structure and are folded into compact Tertiary Structures . From x-ray diffraction studies we know the details of the three dimensional structure of many globular proteins. Every protein has a unique three dimensional structure made up of a variety of helices, beta-sheets and nonregular regions, which are folded in a specific manner. Combinations of secondary structural elements are often found in proteins. These combinations are called motifs .