- The oxygen-haemoglobin dissociation curve illustrates the relationship between pO2 in blood and the number of O2 molecules bound to haemoglobin. The ‘S’ shape of the curve has been explained in the following proposed statements:
A. The quaternary structure of haemoglobin determines its affinity to O2.
B. In deoxyhaemoglobin, the globin units are tightly bound in a T-configuration.
C. The interactions between globin subunits are altered when O2 binds with deoxyhaemoglobin.
D. The affinity to O2 in T-conflguration of haemoglobin is increased.
E. In the relaxed configuration of haemoglobin, the affinity to O2 is reduced.
Choose one of the following combinations with both INCORRECT statements.
(1) A and B (2) B and C
(3) C and D (4) D and EIntroduction
The oxygen-hemoglobin dissociation curve demonstrates how oxygen binds to hemoglobin (Hb) as a function of oxygen partial pressure (pO2). Its characteristic sigmoidal (S) shape arises due to cooperative binding and the structural dynamics of hemoglobin. Several statements attempt to explain this mechanism, but some contain inaccuracies. This article clarifies these concepts and highlights the incorrect statements.
Explanation of the Statements
A. The quaternary structure of hemoglobin determines its affinity to O2.
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True.
Hemoglobin’s tetrameric quaternary structure (α2β2) is crucial; it allows cooperative oxygen binding where oxygen binding at one heme site influences others.
B. In deoxyhemoglobin, the globin units are tightly bound in a T-configuration.
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True.
Deoxyhemoglobin exists primarily in the Tense (T) state characterized by tighter globin subunit contacts and lower oxygen affinity.
C. The interactions between globin subunits are altered when O2 binds with deoxyhemoglobin.
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True.
Binding of oxygen induces conformational changes, weakening inter-subunit interactions in the T state and transitioning hemoglobin to the Relaxed (R) state, increasing affinity and facilitating further oxygen binding.
D. The affinity to O2 in T-configuration of hemoglobin is increased.
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False.
The T-state has lower affinity for oxygen; it is the deoxygenated form that resists additional oxygen binding.
E. In the relaxed configuration of hemoglobin, the affinity to O2 is reduced.
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False.
The R (Relaxed) state has increased affinity for oxygen, allowing hemoglobin to bind oxygen more readily.
Summary Table
Statement Correctness Explanation A True Quaternary structure governs affinity B True T-state = low affinity tight structure C True O2 binding shifts T → R state D False T-state actually has low affinity E False R-state actually has high affinity
Correct Choice for Both Incorrect Statements
The two incorrect statements explaining the S-shape are:
(4) D and E
Physiological Importance
Understanding the cooperative binding and related structural states (T and R) of hemoglobin is fundamental to grasping oxygen transport, delivery, and clinical scenarios affecting oxygen affinity.
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2 Comments
Kirti Agarwal
September 18, 2025Statement D and E is incorrect
Ankita Pareek
September 19, 2025Statement D and E is incorrect because affinity of oxygen binding in t state is actually low not high and r state has actually high affinity not low