Question 9 10 pts Hemoglobin is a protein that carries oxygen in the blood. Exam

Question

Question 9 10 pts Hemoglobin is a protein that carries oxygen in the blood. Examine the O2-hemoglobin binding curve for H 7.4 and tell which statement is false? 100--- 02 unloaded to tissues at rest 02 unloaded to tissues during exercise D 60 40 20 0 0 20 40 60 80 100 Lungs Tissues during Tissues exercise at rest Po2 (mm Hg) (a) Po2 and hemoglobin dissociation at pH 7.4 In normal metabolism, the body uses only the upper 1/4th of its oxygen-binding capacity The blood normally carries an enormous reserve of O2 The steepest part of the O2 binding curve results in a great release of O2 for only a modest drop in PO2 0 Hemoglobin releases about 70% of bound oxygen in tissues at rest. The PO2 of blood drops below about 40 mm Hg only during exertion

Explanation / Answer

4th option which says hemoglobin releases about 70%of bound oxygen at rest was false because -

As hemoglobin molecule has the capacity to carry four oxygen molecules(which is 100% binding) .These molecules of oxygen bind to the iron of HEME group.

While loading of oxygen molecules by binding of 1st molecule induces a conformational change in hemeoglobin that increases the affinity for the remaining three oxygen molecules.In this scenerio there is presence of high partial pressure of oxygen P02.oxygen carrying is done majorly by heme and liitle about 2% by plasma in the form of dissolved oxygen.

BUT as the blood continues to circulate towards periphery ,the small amount of dissolved oxygen is consumed first due to reduced partial pressure and increased carbondioxide levels.This release in pressure makes available the much larger reserviour of hem-bound oxygen,which begans a sequential unloading of its four(100%) oxygen molecules.AT THE MOST,UNDER NORMAL CIRCUMSTANCES ONLY 3 MOLECULES OF OXYGEN i.e.,75% ARE UNLOADED.

During oxygen unloading,the hemoglobin tetramer undergoes subtle intramolecular conformational changes called cooperativity.

As a result of cooperativity ,once the first oxygen has been unloaded ,the unloading of the second oxygen is facilitated.The second oxygen can dissociate after amuch smaller change in oxygen pressure than was needed to unload the first.

Another conformational change facilitates dissociation of 3rd oxygen molecule which finally ends up in 75%(3 out of 4) ,NOT 70% AS MENTIONED IN OPTION.

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