Transport of Oxygen (Haemoglobin)

Adaptations of Erythrocytes (RBCs)

• Biconcave shape maximizes SA for gas exchange

• Small and flexible to pass through narrow capillaries

• No nucleus - more room to carry respiratory gases (O₂)

• Packed with Haemoglobin (Hb)

Haemoglobin (Hb)

• Made up of 4 globular proteins (amino groups)

• 4 Fe²⁺

• allows RBCs to carry respiratory gases (especially O₂)

• It has an affinity (attraction) for oxygen (can carry 4 O₂ molecules)

• When Hb becomes oxygenated, it’s known as oxyhaemoglobin

The structure of Hb

O₂ Transport: Capillaries in the lungs and respiring tissues

Describe the quaternary structure of Hb

Haem group is added to each polypeptide and the 4 chains link together to form a spherical molecule

Explain how DNA leads to different Hb molecules having different affinities for O₂

Different primary structure resulting in a different secondary, tertiary and quaternary structure

When the body is at rest only 1 of the 4 O₂ molecules carried by Hb is normally released into the tissues. Suggest why this could be an advantage when the organisms becomes more active.

• Faster rate of respiration;

• More CO₂ produces and so more O₂ dissociated at respiring tissues to meet the increased demands

Formula for % saturation of Hb with O₂

O₂ Dissociation Curve

• After the 1st O₂ molecule associates, the conformation (shape) of Hb changes

• Conformational changes makes it easier for the 2nd and 3rd O₂ molecule to associate

• It’s difficult to associate a 4th O₂ molecule . This is because the Hb becomes full and O₂ struggles to find a free binding site - curve plateaus below 100%

The effect of exercise in muscle tissue

• More CO₂ produced

• More Carbonic Acid (H₂CO₃) formed

• More H⁺ dissociated - RBC is more acidic

• Greater the shape change of Hb

• More O₂ dissociation

• Meets the demand of the respiring muscle cells

CO₂ effect on O₂ dissociation - Bohr effect

• In a CO₂ - rich environment (all respiring tissue) more O₂ dissociates from oxyhaemoglobin

• O₂ dissociation curve shifts to the right

Low pCO₂ vs High pCO₂ effect on graph