Question

1. Fetal erythrocytes contain a structural variant of hemoglobin, HbF, consisting of two a and two y subunits (azy), whereas maternal erythrocytes contain HbA (022). Consider the oxygen saturation curve shown below and answer the questions that follow: a) Which hemoglobin has a higher affinity for oxygen? Explain how you made that interpretation. +BPG 0.5 -BPG b) What is the physiological significance of the different 02 affinities? 8 10 4 6 po, kPa) 2. In the context of O, binding to hemoglobin, describe the Bohr Effect and its significance to metabolism. 3. The O-binding curve for Hemoglobin is sigmoidal in shape. Explain the reasons and significance of this. 4. Draw the structure of 2,3 Bisphosphoglycerate. In 4-5 informative sentences, describe how 2,3-Bisphosphoglycerate regulates O, binding to Hemoglobin. Explain the physiological significance of this molecule.

Answer 1

1-a) HbF has greater binding affinity than HbA because HbA binds more with 2-3 DPG thus less available for binding with oxygen.

1- b) oxygen binds with HbA, HbF, myoglobin

2) factor ( fall in blood ph, increase in body temperature etc) which shift oxygen haemoglobin  dissociation curve to right decrease the affinity of Hb for oxygen. Therefore carbon dioxide enters blood from tissues and useful in unloading of oxygen. This phenomenon is known as Bohr effect

Significance - increase oxygen transport to tissues

3) Due to shifting affinity of Hb for oxygen.

All iron atoms (4) do not combine with oxygen immediately and simultaneously. Combination is a step wise process and affinity for oxygen is different at different steps. Eg combination of first heme in Hb molecule with oxygen increases affinity of second heme for oxygen and so on.

Significance - Hb saturated with oxygen.

4) 2-3 bisphosphoglycerate competes with oxygen for binding sites on Hb molecule

Significance - at given po2 percentage saturation of Hb with oxygen is reduced in presence of molecule.