What is the function of hemoglobin?

Hemoglobin is an oxygen-binding protein found in the red blood cells of mammals and some other animals. It is responsible for transporting oxygen from the lungs to the rest of the body, and for transporting carbon dioxide from the body to the lungs.

Hemoglobin is a complex protein made up of four polypeptide chains, each of which is folded into a globin domain. Each globin domain contains an iron ion, which is the site at which oxygen binds. The four polypeptide chains are arranged in a tetrahedral shape, with the iron ions located at the corners of the tetrahedron.

Oxygen binds to hemoglobin in a cooperative fashion, meaning that the binding of one oxygen molecule to the protein increases the affinity of the remaining three oxygen-binding sites for oxygen. This cooperative binding allows hemoglobin to transport large amounts of oxygen efficiently.

When hemoglobin reaches the tissues, the oxygen concentration is lower than in the lungs. This causes some of the oxygen molecules bound to hemoglobin to dissociate from the protein and diffuse into the tissues. The carbon dioxide concentration is also higher in the tissues than in the lungs, which causes some of the carbon dioxide in the tissues to diffuse into the red blood cells and bind to hemoglobin.

The hemoglobin then transports the carbon dioxide back to the lungs, where the oxygen concentration is higher and the carbon dioxide concentration is lower. This causes some of the carbon dioxide molecules bound to hemoglobin to dissociate from the protein and diffuse into the lungs, while some of the oxygen molecules in the lungs bind to hemoglobin.

The process of oxygen and carbon dioxide transport by hemoglobin is essential for the survival of mammals. Without hemoglobin, mammals would not be able to get the oxygen they need to survive or to get rid of the carbon dioxide they produce.