Final answer:
Hemoglobin is the iron-containing protein that is the principal component of red blood cells. It is responsible for transporting oxygen throughout the body and gives blood its red color. The iron in hemoglobin binds to oxygen, changing the protein's shape to release or capture oxygen as necessary.
Step-by-step explanation:
The protein that contains iron and is the main component of erythrocytes, or red blood cells, is hemoglobin. Hemoglobin is a complex protein with a quaternary structure, made up of four subunits: two alpha and two beta. Each subunit is associated with a heme group that contains an iron ion. This iron ion plays a critical role in hemoglobin's ability to bind and release oxygen. When oxygen binds to the iron ion, hemoglobin changes its shape to accommodate this binding, and it changes back upon the release of oxygen. This enables hemoglobin to capture oxygen in the lungs and deliver it to various parts of the body where it is needed.
Furthermore, it is the iron in hemoglobin that gives blood its characteristic red color. The process of iron absorption and its transportation in the body involves several proteins and storage sites. Iron absorbed from foods becomes part of the body's iron pool and is stored in the liver, spleen, or bone marrow in proteins like ferritin and hemosiderin. When new red blood cells are produced, stimulated by erythropoietin (EPO), iron is released from these stores, bound to transferrin, and transported to the red marrow to become part of hemoglobin in developing erythrocytes.