What is the Difference Between Iron and Hemoglobin

The main difference between iron and hemoglobin is that iron is the metal ion bound to the hemoglobin whereas hemoglobin is the metalloprotein found in red blood cells. Furthermore, iron binds with oxygen while hemoglobin serves as an oxygen carrier molecule.

Iron and hemoglobin are two molecules related to oxygen transport by red blood cells. Both iron deficiency and deficiency of hemoglobin cause anemia.

Key Areas Covered

1. What is Iron
     – Definition, Structure, Function
2. What is Hemoglobin
     – Definition, Structure, Function
3. What are the Similarities Between Iron and Hemoglobin
     – Outline of Common Features
4. What is the Difference Between Iron and Hemoglobin
     – Comparison of Key Differences

Key Terms

Anemia, Hemoglobin, Iron, Oxygen Transport, Red Blood Cells

What is Iron

Iron is a metal ion, which is an essential micronutrient for the functioning of the body. Around 70% of the iron in the body occurs as a part of hemoglobin. Some amount of iron remains stored in the heart, liver, bone marrow by binding to ferritin. Also, myoglobin and some enzymes in muscles contain iron. A small amount of iron is transported through the blood by binding to transferrin. Moreover, the RDA (recommended dietary allowances) of iron in 8 mg per men and it is 18 mg for women.

Figure 1: Different Molecules Bound to Iron in the Porphyrin Ring

Furthermore, the main function of iron is to bind with oxygen. Generally, it occurs in its reduced state (Fe²⁺) in the porphyrin ring of hemoglobin. After binding to oxygen, it becomes oxidized (Fe³⁺). Iron can release oxygen at the metabolizing tissues based on the pH differences in the blood. Therefore, it is important for various respiratory and metabolic activities. Apart from that, iron is important for collagen synthesis and production of neurotransmitters. Also, the immunity of the body depends on the levels of iron in the body. In addition, low levels of iron lead to iron deficiency anemia.

What is Hemoglobin

Hemoglobin is the iron-containing metalloprotein in the red blood cells of vertebrates. Therefore, the main function of hemoglobin is to transport oxygen throughout the body. Also, it transports a small amount of carbon dioxide. In addition, the protein part of the hemoglobin molecule is made up of four globular proteins. Each subunit is tightly associated with a no-protein, prosthetic, heme group, consisting of an iron atom held by a porphyrin ring, which is a heterocyclic ring. Oxygen binding occurs at the iron atom.

Figure 2: Hemoglobin Structure

Moreover, the normal levels of hemoglobin in the blood are 13.5 to 17.5 g/dL in men and 12.0 to 15.5 g/dL in women. Deficiency of hemoglobin in the blood cause different stages of anemia. Malnutrition can lead to iron deficiency anemia. Active bleeding also causes anemia. It can occur due to heavy menstrual bleeding, wounds, gastrointestinal blood loss in men and post-menopausal women, and genitourinary blood loss in women in the reproductive age. Additionally, some other disease conditions including cancer, sickle cell anemia, kidney disease, etc. can lead to anemia.

Similarities Between Iron and Hemoglobin

• Iron and hemoglobin are two types of molecules related to oxygen transport in the blood.
• Their levels in the body are responsible for the amount of oxygen transported to the metabolizing tissues.
• Moreover, their deficiencies lead to anemia.

Difference Between Iron and Hemoglobin

Definition

Iron refers to an essential mineral necessary for the transport of oxygen while hemoglobin refers to the oxygen-carrying pigment of red blood cells that gives them their red color and serves to convey oxygen to the tissues. Thus, this is the main difference between iron and hemoglobin.

Type of Molecule

Moreover, iron is the metal iron present in the porphyrin ring of the hemoglobin molecule while hemoglobin is the iron-containing oxygen-transport metalloprotein in the red blood cells (erythrocytes) of almost all vertebrates.

Role

Another difference between iron and hemoglobin is that iron binds to oxygen by oxidizing the ion while hemoglobin is the protein, which serves as an oxygen carrier.

Conclusion

Iron is the metal iron found in the porphyrin ring of the hemoglobin molecule. Moreover, its reduced state binds to oxygen and becomes oxidized at the lungs and at the metabolizing tissues, the oxidized state gets reduced releasing oxygen. On the other hand, hemoglobin is the metalloprotein found in red blood cells. Therefore, it serves as the oxygen-carrier throughout the body. Hence, the main difference between iron and hemoglobin is their structure and function.

References: 

1. Abbaspour, Nazanin et al. “Review on iron and its importance for human health.” Journal of research in medical sciences: the official journal of Isfahan University of Medical Sciences vol. 19,2 (2014): 164-74. Available Here. 
2. “Hemoglobin and Functions of Iron.” UCSF Medical Center, Available Here.

Image Courtesy:

1. “Structures of Hemoglobin forms” By Gladissk – marvin sketch (CC BY-SA 3.0) via Commons Wikimedia   
2. “1904 Hemoglobin” By OpenStax College – Anatomy & Physiology, Connexions Web site. (CC BY 3.0) via Commons Wikimedia