Question

8. Comparison of Fetal and Maternal Hemoglobins Studies of oxygen transport in pregnant mammals show that the Oy-saturation curves of fetal and maternal blood are markedly different when measured under the same conditions. Fetal erythrocytes contain a structural variant of hemoglobin, HbF, consisting of two a and two y subunits (2972), whereas maternal erythrocytes contain HbA (292). HbF +BPG o 0.5 i HbA +BPG 2 4 6 8 10 pOg (kPa) (a) Which hemoglobin has a higher affinity for oxygen under physiological conditions, HbA or HbF? Explain. (b) What is the physiological significance of the different 0, affinities? When all the BPG is carefully removed from samples of HbA and HbF, the measured Og-saturation curves and consequently the O2 affinities) are displaced to the left. However, HbA now has a greater affinity for oxygen than does HbF. When BPG is reintroduced, the Oy-saturation curves return to normal, as shown in the graph. What is the effect of BPG on the 0, affinity of hemoglobin? How can the above information be used to explain the different o, affinities of fetal and maternal hemoglobin?

Answer 1

Part (a).

According to the given O₂-saturation curves, fetal hemoglobin (HbF) has a higher affinity for oxygen binding.

Part (b).

Higher the affinity for oxygen bonding for a molecule, greater is the oxygen transport from the lungs to the tissues.

Smaller the affinity for oxygen bonding for a molecule, lesser is the oxygen transport from the lungs to the tissues.