Final answer:
Hemoglobin is a protein with four globin chains; each chain binds to one oxygen molecule thanks to the iron ion in its heme group, allowing hemoglobin to carry four oxygen molecules in total.
Step-by-step explanation:
The molecule of interest here is hemoglobin, a complex protein found in red blood cells. Hemoglobin consists of four globin proteins, each bound to a molecule of heme. The heme group contains iron, which is capable of binding to one oxygen molecule. Consequently, since there are four heme groups in a single hemoglobin molecule, it can bind to and transport four oxygen molecules. An individual erythrocyte, which is a red blood cell, contains about 300 million hemoglobin molecules, potentially binding to up to 1.2 billion oxygen molecules.
In summary, a four-chain globin, known as hemoglobin, can bind four oxygen molecules, with each iron ion in the heme attaching to one oxygen molecule. This binding process is vital for transporting oxygen throughout the body.