THE BIRTH OF THE IRREPLACEABLE SIDEKICK OF ERYTHROCYTES

Last week, we already discussed on the obstacles that riddled the life of our red blood cells which also known as erythrocytes. So this week, we will be introducing the sidekick of erythrocytes that plays important roles in assisting them to carry out various exhausting tasks in our body. Haemoglobin is a crucial component of red blood cells. As the previous blog tells about how the blood cells produced, this time we want to share about the synthesis of haemoglobin that need to occur before the process of erythropoiesis done.

Haemoglobin is a protein in the red blood cells that responsible in binding with oxygen before erythrocytes carry the oxyhaemoglobin to various exhausted tissues. It also bind with carbon dioxide from the tissue back to the lungs. Basically, haemoglobin synthesis can be divided into two, haem and globin synthesis. Haem synthesis takes place in mitochondria meanwhile globin is at the cell cytosol. When both of them are ready, they will combine together and form the haemoglobin.

In the diagram above we can see the synthesis process of both haem and globin in a cell before they fused together to form haemoglobin. Let’s take a look at haem formation first.

Ø It starts with the condensation of succinyl CoA and glycine by ALA synthase to form 5-aminolevulic acid (ALA).

Ø The 5-aminolevulic acid or ɖ-ALA will then be transported into the cytosol. Two molecules of ɖ-ALA condense to form a pyrrole called as porphobilinogen (PBG).

Ø Later, four PBG will condense to form a tetrapyrrole uroporphyrinogen III (UPG III). UPG III then is converted to coproporphyrinogen (CPG).

Ø Next, iron is brought to the developing red cells by a carrier protein known as transferrin which attaches to special binding sites on the surface of these cells.

Ø CPG changes to protoporphyrin which ultimately combines with iron in the ferrous state (Fe²⁺) to form four molecules of haem.

On the other hand, globin synthesis is much simpler compared to the haem formation.

Ø Globin synthesised from the amino acid that then converted into α and β chain.

Ø The chains then combined and formed α₂β₂ globin.

The complete haem and globin will then fused together to form a perfect haemoglobin.

Ø To complete the haemoglobin synthesis, each molecule of haem combines with a globin chain.

Ø A tetramer of four globin chains each with its own haem group in a pocket is formed to make up a haemoglobin molecule.

Ø There are a few types of haemoglobin, HbF, HbA and HbA₂. These alpha, beta and gamma globin genes that determine the type of haemoglobin produce during erythropoiesis.

It’s almost impossible to accomplish important and crucial tasks without help. Just like us as human, blood also need various components to form a perfect team and play a flawless roles. After all, two heads are better than one. Well, with condition if both heads are not stupid!