Explain the mechanism of oxygen binding to haemoglobin.

Oxygen binds to haemoglobin through a process called cooperative binding at the heme group of the protein.

Haemoglobin is a protein molecule found in red blood cells, responsible for transporting oxygen from the lungs to the body's tissues and cells. It is composed of four subunits, each containing a heme group. The heme group is a ring-like structure with an iron atom at its centre. It is this iron atom that oxygen binds to.

The process of oxygen binding to haemoglobin is known as cooperative binding. This means that the binding of one oxygen molecule to a heme group increases the likelihood of other oxygen molecules binding to the remaining heme groups. This is due to the conformational changes that occur in the haemoglobin molecule upon the binding of the first oxygen molecule.

When an oxygen molecule binds to the iron atom in a heme group, the iron atom is pulled into the plane of the heme, causing the attached protein chain to shift. This shift changes the shape of the haemoglobin molecule, making it easier for other oxygen molecules to bind to the remaining heme groups. This is why haemoglobin can carry up to four oxygen molecules at once.

The binding of oxygen to haemoglobin is also influenced by environmental factors such as pH and carbon dioxide concentration. In areas of high carbon dioxide concentration and low pH, such as actively respiring tissues, haemoglobin is more likely to release its bound oxygen. This is known as the Bohr effect. Conversely, in areas of low carbon dioxide concentration and high pH, such as the lungs, haemoglobin is more likely to bind oxygen.

In summary, the binding of oxygen to haemoglobin is a complex process involving cooperative binding at the heme groups of the protein, influenced by conformational changes in the protein structure and environmental conditions. This mechanism allows haemoglobin to efficiently transport oxygen from the lungs to the body's tissues and cells.