How many oxygen molecules may bind to a single molecule of hemoglobin?
Multiple Choice
2
4
6
8
16
The correct answer and explanation is:
The correct answer is 4.
Hemoglobin is a protein found in red blood cells responsible for transporting oxygen throughout the body. It is made up of four subunits, each containing a heme group, which is where oxygen binds. Each heme group has an iron atom at its center, which can form a coordination bond with an oxygen molecule (O2). Since there are four heme groups in a hemoglobin molecule, it can bind a total of four oxygen molecules, one per heme group.
The binding of oxygen to hemoglobin is cooperative, meaning that the binding of one oxygen molecule increases the affinity of the remaining heme groups for oxygen. When the first oxygen molecule binds, it causes a conformational change in the hemoglobin structure, making it easier for the second, third, and fourth oxygen molecules to bind. This ensures efficient oxygen loading in the lungs, where oxygen concentration is high, and unloading in tissues, where oxygen concentration is low.
The process is reversible, and when oxygen levels decrease in tissues, hemoglobin releases the oxygen molecules, allowing for oxygen delivery to cells. The binding and release of oxygen is also influenced by factors such as pH (Bohr effect), carbon dioxide concentration, and temperature, which affect hemoglobin’s affinity for oxygen. For example, higher concentrations of carbon dioxide or lower pH in tissues signal that oxygen is needed more urgently, and hemoglobin releases oxygen more readily.
Thus, while a hemoglobin molecule can bind up to four oxygen molecules, it is the cooperative nature of the binding process that allows for efficient oxygen transport and delivery throughout the body.