Question

Hemoglobin levels in the blood samples of two persons A and B are found to be 9 gm/dL and 13 gm/dL respectively. Which statement is true with respect to the amount of oxygen supply in their body?
(a) More person B than in person A
(b) More in person A than in person B
(c) Equal in person A and person B
(d) No correlation between oxygen supply and the level of hemoglobin

Answer 1

In lungs, pressure of oxygen is high so it diffuses from outside the body to inside the body and binds with Hb. Bond of one oxygen to hemoglobin facilitates the binding of other oxygen molecules.

Complete step by step answer:
Hemoglobin is found exclusively in red blood cells (RBCs), where its main function is to transport oxygen from the lungs to the capillaries of the tissues. The tetrameric hemoglobin molecule is structurally and functionally more complex than myoglobin molecule. Hemoglobin can transport hydrogen ion and carbon dioxide from the tissues to the lungs, and can carry four molecules of oxygen from the lungs to the cells of the body. The oxygen- binding properties of hemoglobin are affected by interaction with allosteric effectors.
- In tissues, hemoglobin binds to 2,3 DPG and that causes an affinity of Hb to oxygen and releasing oxygen to the tissues.
- The haem pockets of α- subunits are of size just adequate for entry of an oxygen molecule, but the entry of oxygen into the haem- pockets of the β- subunits is blocked by a valine residue.
- Myoglobin can bind only a single molecule of oxygen, because it contains only one heme group. In contrast, hemoglobin can bind four oxygen molecules that are one at each of its four heme groups.
- Myoglobin consists of one polypeptide chain that’s structurally like the individual subunit polypeptide chains of the hemoglobin molecule.
- The Hb molecule and its subunits contain almost hydrophobic amino acids internally and hydrophilic amino acids on their surfaces. We can say that the Hb molecule is waxy inside and soapy outside that makes it impermeable to water but soluble in water.
- Cooperative binding of oxygen by the four subunits of hemoglobin which means that the binding of an oxygen molecule at one heme group increases the oxygen affinity of the remaining heme groups within the same hemoglobin molecule. This effect is mentioned as heme- heme interaction.
- It is harder for the first oxygen molecule to bind to hemoglobin, the subsequent binding of oxygen occurs with high affinity.
So, the correct answer is ‘(a) More person B than in person A.’

Note:
- Cyanide poisoning and carbon monoxide poisoning are fatal because they combine and inhibit heme protein cytochrome oxidase in the electron transport chain and stop cellular respiration.
- Conversion of Hb to methaemoglobin by sodium thiosulphate forms the basis of treatment of cyanide poisoning, as cyanide combines readily with methaemoglobin to form cyanmethemoglobin which is not toxic and thus spares the cytochrome oxidase.