Hemoglobin: The Oxygen-Carrying Protein in Blood - Definition & Function

The oxygen-carrying compound in blood is hemoglobin. Hemoglobin is a protein molecule that contains iron atoms, each of which can bind to one oxygen molecule. Hemoglobin is found inside red blood cells, which are specialized cells that transport oxygen from the lungs to the rest of the body.

When red blood cells pass through the lungs, hemoglobin binds to oxygen molecules in the air sacs (alveoli). The oxygenated hemoglobin then travels through the bloodstream until it reaches the tissues, where the oxygen molecules are released from hemoglobin and taken up by the cells.

Hemoglobin also plays a role in transporting carbon dioxide from the tissues back to the lungs. Carbon dioxide is a waste product that is produced by the cells in the body. It is carried by hemoglobin in the form of a compound called carbaminohemoglobin.