Q44. In the plot given below, the solid line represents oxygen binding to hemoglobin
under physiological conditions. The broken line represents the condition(s) of
(A) High CO2 concentration
(B) Increase in 2,3– Bisphosphoglycerate concentration
(C) High pH
(D) Loss of cooperativity
Hemoglobin Oxygen Dissociation Curve Shift: High CO2 and BPG Effects
The solid line shows the standard sigmoid oxygen-hemoglobin dissociation curve under physiological conditions, while the broken line represents a rightward shift due to high CO2 concentration, increased 2,3-bisphosphoglycerate (BPG), or loss of cooperativity. This shift decreases hemoglobin’s oxygen affinity, promoting unloading in tissues.
Option Analysis
High CO2 concentration triggers the Bohr effect, where elevated PCO2 lowers pH and directly binds hemoglobin, stabilizing its deoxy (T) state and shifting the curve rightward for better oxygen release. Increased 2,3-BPG (bisphosphoglycerate), produced in RBC glycolysis under hypoxia, binds deoxyhemoglobin’s beta chains, further reducing oxygen affinity and causing a right shift. Loss of cooperativity eliminates the sigmoidal shape’s steepness from allosteric O2 binding changes, yielding a hyperbolic curve like myoglobin with lower tissue unloading efficiency.
Physiological Impact
Right shifts from high CO2 or BPG enhance oxygen delivery during exercise or hypoxia by increasing P50 (PO2 at 50% saturation). The steep curve portion ensures small PO2 drops unload substantial oxygen to tissues. Cooperativity loss impairs this, as seen in hyperbolic binding without subunit interactions.
Introduction to Hemoglobin Oxygen Dissociation Curve Shift
The hemoglobin oxygen dissociation curve shift is crucial in physiology, plotting % saturation against PO2 to show how factors like high CO2 and BPG modulate oxygen binding. Under physiological conditions, the sigmoid curve reflects cooperativity for efficient lung loading and tissue unloading. High CO2 or BPG causes a rightward hemoglobin oxygen dissociation curve shift, decreasing affinity to match metabolic demands.
Causes of Rightward Shift
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High CO2 Concentration: Via Bohr effect, CO2 forms carbonic acid (lowering pH) and carbaminohemoglobin, stabilizing T-state deoxyhemoglobin.
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Increased 2,3-BPG: Binds deoxyhemoglobin cavity, forming salt bridges that favor oxygen release; levels rise in hypoxia or anemia.
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Loss of Cooperativity: Disrupts allosteric transitions, flattening the curve to hyperbolic, reducing unloading efficiency.
| Factor | Curve Shift | Effect on Oxygen Affinity | Example Condition |
|---|---|---|---|
| High CO2 | Right | Decreased | Exercise, hypercapnia |
| High BPG | Right | Decreased | High altitude |
| Cooperativity Loss | Hyperbolic (effective right) | Altered | Pathological mutations |
Clinical Relevance for CSIR NET
Right shifts optimize oxygen delivery: at tissue PO2 ~40 mmHg, saturation drops from ~75% to lower, unloading more O2. For exams, recall “CADET right”: CO2, Acid, DPG/BPG, Exercise, Temperature. Fetal Hb shows left shift due to low BPG binding.
Keywords
Primary: hemoglobin oxygen dissociation curve shift
Secondary: high CO2 effect BPG, oxygen affinity hemoglobin, Bohr effect cooperativity, CSIR NET physiology.
