Transport of Oxygen by Haemoglobin

This curve shows the relationship between saturation of Haemoglobin with Oxygen and the partial pressure of oxygen.

1.Shape of Haemoglobin makes it difficult for first Oxygen molecule to bind with one of the 4 polypeptide sites; low Oxygen concentration therefore means little amounts of Oxygen bind to Haemoglobin.

2.Binding of the first Oxygen molecule onto Haemoglobin:

Changes the quaternary structure of Haemoglobin and its shape

 Induces other subunits to bind to the Oxygen molecule.

 3.  Takes a smaller amount of partial pressure of Oxygen for the second molecule to bind with Haemoglobin; Positive Cooperativity. Gradient of curve steepens.

 4.   Gradient of curve reduces after the third Oxygen molecule has attached as the 4th Oxygen molecule is less likely to find an empty binding site.

The higher the CO2 concentration, the lower the affinity for O2 of Haemoglobin.

1.At gas exchange surfaces, CO2 concentration is low. This gives a higher pH to surrounding, causing Haemoglobin shape to change to readily load O2(Gain affinity). O2 concentration in the lungs is high, and therefore it is readily and easily loaded.

2.In respiring tissue, CO2 concentration is high. This gives a more acidic environment as CO2 is acidic. This changes the shape of Haemoglobin to more readily release O2 (Lose affinity). O2 concentration is low in the muscles, therefore it is readily unloaded.

Higher respiration rate in tissue -Higher CO2 production – Lower pH – Greater Haemoglobin shape change – Lower affinity for O2 – more O2 unloaded – more O2 available for respiration.

Overall saturation of Haemoglobin in atmospheric pressure is 97%

1. 1 oxygen molecule is released by Haemoglobin to lowly respiring tissue; this gives a 75% saturation of O2 in Haemoglobin when it returns to lungs.

2. 3 oxygen molecules are released by Haemoglobin to highly respiring tissue; this gives a 25% saturation of O2 in Haemoglobin when blood returns to lungs.

Species living in environment with lower partial pressure of Oxygen have Haemoglobin with higher affinity for O2.

1.Lugworm: Have no fresh supply of O2 when tide goes out.

               Water in burrow progressively contains less O2 as  lugworm uses it.

               Lugworm has higher affinity than humans in order to extract all possible oxygen from water in burrow to survive. 

2. Llama: Live in high altitude.

               Lower partial pressure of O2.

                Evolved to have higher O2affinity.