Explore the quaternary interactions of hemoglobin which is composed of four subunits. (Note: to view ribonuclease interactively on your Web browser, the free Chemscape Chime plug-in viewer must be installed in your browser's plug-in folder.) Select chains from the color menu to view the four separate subunits. Display the structure as sticks and look for the heme molecule associated with each subunit. Be sure to select the options and view the hydrogen and disulfide bonds. This will show how the helicies and sheets are held together in three dimensional space.