Question

Which hemoglobin component is recovered for reuse following red blood cell destruction? a. heme c. iron b. globin d. Both b and c are correct.

Short answer

Option d. Both b (globin) and c (iron) are correct.

Step-by-step solution

Understanding hemoglobin and red blood cell destruction.

Hemoglobin is a protein complex found in red blood cells, responsible for carrying oxygen from the lungs to the body's tissues and exchanging it for carbon dioxide. Hemoglobin consists of four subunits, each containing a heme group and a globin chain. The heme group consists of a porphyrin ring surrounding an iron ion, which binds oxygen. The globin chains are proteins that support the structure of the molecule. During the breakdown of red blood cells (RBCs), the various components of hemoglobin are separated and processed differently.

Analyzing the fate of heme during RBC destruction

When red blood cells are destroyed, heme is released from the hemoglobin molecule. It is then broken down via complex enzymatic reactions into a substance called biliverdin, which is subsequently converted into bilirubin. Bilirubin is then transported to the liver to be metabolized and excreted as bile. Thus, heme is not reused in the body.

Analyzing the fate of globin during RBC destruction

Globin is also released from the hemoglobin molecule during red blood cell destruction. Globin chains are then broken down into their constituent amino acids, which can be reused by the body to generate new proteins, including new globin chains for hemoglobin synthesis.

Analyzing the fate of iron during RBC destruction

Iron ions are released from the heme group during red blood cell destruction. Instead of being excreted, the iron is conserved and reused by the body. It is either stored in specialized proteins, such as ferritin or hemosiderin, or transported by transferrin to be used for the synthesis of new heme groups and other iron-dependent processes.

Conclusion

Based on the analysis of heme, globin, and iron during red blood cell destruction, we can conclude that globin and iron are both recovered for reuse in the body. Therefore, the correct answer is option d. Both b (globin) and c (iron) are correct.

Key concepts

Red Blood Cell Destruction

Red blood cells, or RBCs, play a key role in the body's oxygen transport system. These cells have a lifespan of about 120 days, after which they are broken down in a process called red blood cell destruction. This process is crucial for recycling components that the body can use again.
When red blood cells are destroyed, hemoglobin, the protein that carries oxygen, is also broken down. Hemoglobin has two main parts—heme and globin.

• The heme part is where the iron is held.
• Globin is the protein chain portion.

Understanding what happens to each part during RBC destruction is important for grasping how the body recycles iron and proteins.

Heme

In the hemoglobin molecule, heme refers to a complex structure that holds an iron ion at its center. The heme component has a critical role in binding oxygen for transport through the bloodstream.
During the destruction of red blood cells, heme is released as the hemoglobin breaks down. However, unlike some other parts of hemoglobin, heme itself is not reused.
Instead, it undergoes transformation through several steps:

• First, it is broken down into a green pigment called biliverdin.
• Afterward, biliverdin is converted into bilirubin, a yellow compound.
• Bilirubin is sent to the liver, where it is processed and excreted in bile.

In this sense, heme is not a component that the body reuses directly.

Globin

Globin refers to the protein chains found in the hemoglobin molecule. These chains serve to support the heme group and are crucial for the overall structure and function of hemoglobin.
When RBCs are demolished, the globin chains are split from the heme group. They do not go to waste. Instead, they are broken down into amino acids.

• Amino acids are basic building blocks used by the body to construct new proteins.
• These include new globin chains for fresh hemoglobin molecules.

This ability to recycle globin into amino acids makes it a valuable resource for the body, ensuring that proteins continue to be available for crucial physiological functions.

Iron Reuse

Iron is an essential element found within the heme group of hemoglobin. It is crucial for oxygen transport and various metabolic reactions within the body. During the breakdown of red blood cells, the iron is carefully extracted and conserved.
Unlike heme, iron is not discarded. Instead, it undergoes a process of reuse:

• The body stores it in proteins like ferritin and hemosiderin. These proteins act as reserves for future iron needs.
• Iron is often transported via a protein called transferrin. This allows it to be distributed wherever required, including for new heme synthesis.

This conservation and reuse cycle ensures that the body's iron levels remain balanced and efficient, reducing the need for dietary iron intake.