Question

What is the maximum number of $O_2$ molecules which one haemoglobin molecule can carry ?

Answer 1

Red blood cells are the most abundant of all the cells in blood. In humans red blood cells are devoid of nucleus and biconcave in shape. Red blood cells have a red coloured iron containing complex protein called haemoglobin hence the name and colour of the cells. Healthy individual has 12 to 16 grams of haemoglobin in every hundred ml of blood. Haemoglobin plays a significant role in transport of respiratory gases.

Complete Answer:
- Oxygen can bind with Haemoglobin in a reversible manner to form oxyhaemoglobin. Each haemoglobin molecule has 4 binding sites that means it can carry a maximum four molecules of oxygen.
- Binding of oxygen with haemoglobin is primarily related to partial pressure of $O_2$, Partial pressure of $CO_2$, hydrogen ion concentration and temperature are the other factors which can interfere with this binding.
- A sigmoid curve is obtained when percentage saturation of haemoglobin with $O_2$ is plotted against the $pO_2$. This curve is called oxygen dissociation curve.
- There are conditions due to which oxygen that’s bound to hemoglobin in the lungs surfaces and get dissociated at the tissues.
- Every hundred ml of oxygenated blood can deliver around 5 ml of $O_2$ to the tissue under normal physiological condition.

Note: In the alveoli, where is high $pO_2$, low $pCO_2$ lesser $H^+$ concentration and lower temperature are the factors all favourable for the formation of oxyhaemoglobin. Whereas in the tissue, low $pO_2$, high $pCO_2$, high $H^+$ concentration and higher temperature exist the conditions are favourable for dissociation of oxygen from the oxyhaemoglobin. Every 100 ml of deoxygenated blood delivers approximately 4 ml of $CO_2$ to the alveoli.