In allosteric interactions, the binding of a molecule to one site on the protein leads to conformational changes that affect a distant site on the protein. In hemoglobin, O2 binding is cooperative (the first binding enhances additional binding by the other heme groups nested in the other polypeptide chains). Cooperative binding in hemoglobin has found its way onto many MCATs. Additionally, the binding of H+ or CO2 allosterically alters the binding of O2. The allosteric changes in hemoglobin occur through subunit interaction. Most allosteric changes occur by means of quaternary structure. O2 binding relaxes the hemoglobin tetramer, promoting additional binding. The molecule BPG decreases affinity by stabilizing the deoxyhemoglobin quaternary structure. CO2 binding occurs at the terminal amino groups which take up carbamate to form salt bridges which stabilize deoxyhemoglobin. Furthermore, with deoxyhemoglobin, a certain histidine side chain gains affinity for H+, so acidic conditions stabilize deoxyhemoglobin.

These effects are summarized in the MCAT favorite discussion of the Bohr effect. Basically, an increase in blood carbon dioxide level, a decrease in pH or increase in temperature leads hemoglobin to bind oxygen less strongly. The Bohr effect supports the oxygen transport function of hemoglobin. Hemoglobin binds to oxygen in the lungs, but then releases it in the tissues, where carbon dioxide levels are high and pH is low.

The WikiPremed MCAT Course is a comprehensive course in the undergraduate level general sciences. Undergraduate level physics, chemistry, organic chemistry and biology are presented by this course as a unified whole within a spiraling curriculum. Please read our policies on Privacy and Shipping & Returns.  Contact Us. MCAT is a registered trademark of the Association of American Medical Colleges, which does not endorse the WikiPremed Course. WikiPremed offers the customers of our publications or our teaching services no guarantees regarding eventual performance on the MCAT.

Creative Commons License
WikiPremed is a trademark of Wisebridge Learning Systems LLC. The work of WikiPremed is published under a Creative Commons Attribution NonCommercial ShareAlike License. There are elements of work here, such as a subset of the images in the archive from WikiPedia, that originated as GNU General Public License works, so take care to follow the unique stipulations of that license in printed reproductions.