When deoxyhemoglobin crystals are exposed to oxygen, they shatter. On the other hand, deoxymyoglobin crystals are unaffected by oxygen. Explain. (Myoglobin is made up of only one of the four subunits, or polypeptide chains, in hemoglobin.)

Understanding the intricate structure of hemoglobin is fundamental in comprehending how oxygen transport occurs in the body. Hemoglobin, a vital protein found in red blood cells, adopts a quaternary structure comprised of four polypeptide subunits: two alpha chains and two beta chains. Each subunit contains an iron-loaded heme group, which is the actual site where oxygen binds.

The sophisticated configuration of these subunits allows the protein to carry out its primary function - transporting oxygen from the lungs to various tissues and carrying carbon dioxide back to the lungs for exhalation. Hemoglobin’s tetrameric form is not just for stability but is crucial for its functionality, particularly the unique characteristic of cooperative oxygen binding, which is absent in its myoglobin counterpart.

In contrast to hemoglobin, myoglobin’s structure is comparatively straightforward. Residing mainly in muscle tissue, myoglobin’s role is to store and facilitate the diffusive transport of oxygen within muscles. The protein is composed of a single polypeptide chain along with one heme group, mirroring one of the subunits of hemoglobin.

Myoglobin's simplicity of being a monomer with only one binding site for oxygen eliminates the capability for cooperative binding and dictates its behavior in oxygen absorption and release. Its structure remains consistent whether or not it binds oxygen, which explains its stability as crystals when exposed to oxygen and is why, unlike hemoglobin, myoglobin crystals do not shatter upon oxygen exposure.

The phenomena of cooperative binding is a defining property of hemoglobin that distinguishes it dramatically from myoglobin. Cooperative binding refers to the mechanism wherein the binding of oxygen to one subunit of hemoglobin significantly increases the affinity for oxygen of the remaining subunits. This is also described as positive cooperativity.

When the first oxygen molecule binds, it induces a conformational change in the hemoglobin subunit, making it easier for subsequent oxygen molecules to attach to the other subunits. The result is a sigmoidal or 'S-shaped' oxygen dissociation curve, reflecting a more effective oxygen delivery system which is responsive to varying oxygen levels. This adaptability, attributable to the tetrameric structure, underpins the reason for the fragility of hemoglobin crystals in the presence of oxygen as opposed to the unaffected myoglobin crystals.