Hemoglobin

Hemoglobin

1. Structure

   • tetramer, made up of two alpha subunits and two beta subunits. each binds a heme
   • subunit has similar structure to myoglobin

2. Myoglobin

   • made up of alpha helices with connecting loops with heme sitting in a pocket
   • Heme contains iron which can bind to oxygen at one of its six ligand sites
   • only unloads oxygen when levels become unusually low.

3. Binding of Oxygen

   • four oxygen molecules bind per hemoglobin, one per subunit.
   • binding curve = sigmodial
     • binding of one oxygen molecule makes it easier for a second to bind
     • homotrophic positive cooperative effect = affinity of binding of oxygen for the fourth oxygen is 20 fold greater than the affinity for the first oxygen

4. Allosteric change

   • alpha and beta subunit are more associated with each other than the other two subunits
     • when oxgen binds, the subunits change their position. this is due to the change of shape of heme when oxygen binds.
       • When oxygen isnt bound iron doesnt fit in the planar structure but when bound it becomes smaller and can fit
   • this change results in the molecule shifting from low affinity (T) to high affinity (R) state.