Q50.According to Bohr effect the oxygen transport ability of hemoglobin is more when
(1) pH decreases
(2) pH increases
(3) pH remains stable
(4) It is not affected by pH

The Bohr effect enhances hemoglobin’s oxygen unloading in tissues when pH decreases due to CO₂ and H⁺ accumulation. The correct answer for Q50 is (1) pH decreases.

Option Breakdown

• (1) pH decreases: Correct. Lower pH (more acidic, from tissue CO₂ → H₂CO₃ → H⁺) stabilizes deoxyhemoglobin (T-state) via salt bridges (e.g., His146), shifting the O₂ dissociation curve right (↑P₅₀), reducing O₂ affinity, and promoting O₂ release where needed.

• (2) pH increases: Incorrect. Alkaline conditions (lungs) stabilize oxyhemoglobin (R-state), left-shifting curve (↓P₅₀), increasing O₂ affinity for loading.

• (3) pH remains stable: Incorrect. Bohr effect specifically requires pH change; stable pH shows standard sigmoid curve without modulation.

• (4) It is not affected by pH: Incorrect. pH is primary modulator alongside CO₂, temperature, 2,3-BPG.

Physiological Role

Tissues → ↑CO₂/H⁺ → ↓pH → ↑O₂ unloading (right shift). Lungs → ↓CO₂ → ↑pH → ↑O₂ loading (left shift).

Master Bohr effect oxygen transport ability of hemoglobin for CSIR NET Life Sciences: Oxygen delivery peaks when pH decreases in tissues (right-shifted O₂ curve). Q50 explained—why acidic pH enhances unloading, alkaline loads, with curve shifts, His146 role, exam tricks.

Bohr Effect Mechanism

Discovered 1904 (Christian Bohr): Hemoglobin O₂ affinity inversely proportional to blood [H⁺] and PCO₂.

• Low pH: Protonates His146β (C-terminus), forms salt bridge with Asp94β → stabilizes T-state → ↓O₂ affinity → O₂ release.

• ΔpH effect: Arterial pH 7.4 → venous ~7.2 = 0.2-0.4 log P₅₀ units shift.

Correct Answer: (1) pH Decreases

Tissue acidosis (CO₂, lactic acid) triggers unloading; ~10-15% extra O₂ released via Bohr.

Curve Illustration

• Normal: P₅₀ = 26 mmHg (pH 7.4).

• Acidosis (pH 7.2): P₅₀ ≈ 33 mmHg → more O₂ at tissue PO₂ (40 mmHg).

Exam Mastery

• Mnemonic: Bohr = Better O₂ delivery at low pH (Blood acidosis).

• CSIR trick: Confuses with Haldane (opposite: O₂ affects CO₂ binding).

• Quantify: ΔlogP₅₀/ΔpH = -0.48 (alkaline Bohr groups).

Nail Bohr effect oxygen transport ability hemoglobin pH decreases.