Myoglobin has a hyperbolic oxygen dissociation curve (non-cooperative, Hill n=1) while hemoglobin shows sigmoidal cooperative binding. The structural basis for cooperativity in hemoglobin is:

• A Hemoglobin has a heme group with two iron atoms versus myoglobin's single iron
• B Myoglobin lacks 2,3-BPG binding site
• C Hemoglobin is purely a beta-barrel structure unlike myoglobin's globin fold
• D Hemoglobin has 4 subunits; oxygen binding in one subunit induces conformational T→R state changes that alter affinity of remaining subunits ✓

Explanation

Hemoglobin's cooperativity arises from its tetrameric (alpha2beta2) quaternary structure. In the deoxy (T) state, salt bridges and hydrophobic contacts constrain the four subunits in a low-affinity conformation. Binding of O2 to one subunit breaks these constraints, shifting the entire tetramer toward the high-affinity R state — markedly increasing affinity of remaining subunits (positive cooperativity). Myoglobin is monomeric and has no conformational partners, so it binds O2 in a simple hyperbolic fashion with constant affinity. This tetrameric allostery is fundamental to efficient O2 loading in lungs and unloading in tissues.

Reference: Harper's Illustrated Biochemistry, 32nd ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.