These assemblies may contain as few as two units, as in an enzyme complex, or hundreds, as in a virus. Often quaternary structure is organized symmetrically. This allows the formation of large complexes with only a few different tertiary units. In some cases, the monomer must change its conformation in order to make these contacts. Insulin illustrates how the tertiary structure can be influenced by the quaternary organizational requirements.
Enzymes exemplify the advantages of multimeric complexes that combine different functions.
Multiple functionality is enhanced by forming multi-enzyme complexes. Finally, large assemblies play not only functional but structural roles on the cellular level. While studying this section, bear in mind the interplay between tertiary and quaternary structure. Also consider the advantages, both functional and structural, that are provided by the assemblies of tertiary structures. To best appreciate the material in this chapter, you should have your WWW browser configured to invoke RasMol as the helper application for chemical MIME type files.