Each heme group of hemoglobin can carry how many oxygen molecules? O One O Four O Two O Six
The Correct Answer and Explanation is:
Correct Answer: One
Each heme group of hemoglobin can carry one oxygen molecule. This is a fundamental concept in respiratory physiology, directly linked to the specific molecular structure of the hemoglobin protein. Hemoglobin, the primary molecule responsible for transporting oxygen within red blood cells, is a large, complex protein. It is composed of four distinct polypeptide chains, known as globin subunits. In adult humans, a typical hemoglobin molecule consists of two alpha-globin chains and two beta-globin chains. Critically, each of these four protein subunits contains and protects a non-protein component called a heme group.
The structure of the heme group is the key to its oxygen-binding function. A heme group consists of a complex organic ring structure, called a porphyrin, which has a single iron atom (in the ferrous Fe²⁺ state) held at its center. This central iron atom is the precise location where an oxygen molecule (O₂) reversibly binds. The interaction is a 1:1 ratio: one iron atom binds to exactly one oxygen molecule. Since every individual heme group contains only one iron atom, it logically follows that each heme group has the capacity to carry only one molecule of oxygen.
It is important to distinguish this from the capacity of the entire hemoglobin molecule. A common point of confusion arises because the question asks about a single heme group, not the complete protein. Because a full hemoglobin molecule contains four subunits and, consequently, four heme groups, it can transport a total of four oxygen molecules when it is fully saturated. The option “Four” in the question refers to the total carrying capacity of the entire hemoglobin molecule. However, the question specifically isolates the function of “each heme group,” for which the correct answer is one
