Question

In: Biology

Unlike adult hemoglobin (Hb) possessing two alpha-chains and two beta-chains, fetal hemoglobin expresses two alpha-chains and...

Unlike adult hemoglobin (Hb) possessing two alpha-chains and two beta-chains, fetal hemoglobin expresses two alpha-chains and two gamma-chains. Which experimentally established statement in connection with this observation is true?

a.

Fetal Hb has a higher oxygen affinity than maternal Hb due to both decreased 2,3-BPG binding affinity and a resistance to pH drop
b.

Fetal Hb has a higher oxygen affinity than maternal Hb due to increased resistance to pH drop
c.

Fetal Hb has a higher oxygen affinity than maternal Hb due to increased 2,3-BPG binding affinity (in fetal Hb)
d.

Fetal Hb has a higher oxygen affinity than maternal Hb due to decreased 2,3-BPG binding affinity (in fetal Hb)

Solutions

Expert Solution

The correct option is a

Fetal hemoglobin transports oxygen from mother to the growing foetus. For this transport to happen smoothly, the fetal hemoglobin must have more affinity for oxygen than the mother's hemoglobin.

The fetal oxygen has high oxygen affinity because of mainly two reasons-

The fetal hemoglobin (Hb F) possesses gamma subunits instead of beta subunits as is the case with adult hemoglobin Hb A).

The 2,3 bis phosphoglycerate is a glycolytic intermediate produced in RBCs. It binds to hemoglobin and decreases affinity of Hb for oxygen and hence helps in release or delivery of oxygen to the cells.

The 2,3 BPG has lesser affinity with fetal hemoglobin. The reason behind it is that 2,3, BPG is negatively charged molecule. The adult Hb (beta subunit) has more positively charged amino acids than fetal Hb ( gamma subunit)

Hb A- More positively charged- more affinity to 2,3 BPG- less affinity for oxygen- O2 is released to the cell

Hb F- less positively charged- lesser affinity to 2,3 BPG- more affinity for oxygen

The second reason is - The pH of fetal blood remains higher than adult blood. The reason behind it is that, more CO2 is dissolved in adult blood, means more H2CO3 (Weak acid) formation takes place in adult blood plasma. Therefore the pH drop happens in adult blood while such pH drop is not found in fetal blood and blood remains slightly more alkaline.

Less CO2- more alkaline - more O2 binding affinity - Fetal blood

More CO2- more acidic- O2 release is favored- Adult blood

Option B and C are not most appropriate- Because both options are not underlining simultaneous impact of 2,3 BPG as well as pH drop on oxygen affinity. Although, both sentences are correct yet incomplete.

Option C is incorrect- As Fetal hemoglobin (Hb F) has decreased or lesser binding affinity to 2,3 BPG. The reason is lack of positively charge in gamma subunit as compared to beta subunit of adults.

gladiator answered 2 years ago
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