Haemoglobin Synthesis and Function & Haemoglobin Catabolism and Excretion

What are hemoglobins?

The hemoglobins are red globular proteins, which have a molecular weight of about 68,000 and comprise almost one third of the weight of a red cell. The haemoglobin is composed of haem and globin. The main function of red cells is to carry oxygen  to the tissues and to return carbon dioxide from tissues to the lungs. The red cells contain the specialised protein haemoglobin. Hemoglobin is a specialised protein. Each red cell contains approximately 640 million of Hb molecules.


           


WHAT HAPPENS DURING HAEMOGLOBIN SYNTHESIS?


Haemoglobin is synthesised in the erythroblasts. Haemoglobin synthesis is divided into two synthesis which is Haem Synthesis and Globin synthesis. Haem synthesis occurs  in the mitochondria and the globin synthesis occurs in the polyribosomes. Hemoglobin develops in cells in the bone marrow that become red blood cells. Each molecule of an adult haemoglobin (Hb-A) consists of four polypeptide chains [α2β2], each with its own haem group. Haem synthesis starts with the condensation of glycine and succinyl coenzyme A under the action of a rate limiting enzyme δ-aminolevulinic acid synthase.


       


Each haemoglobin molecule contains four globin chains and four haem. Each atom of iron can combine with an oxygen molecule,this means a single haemoglobin molecule can carry four molecules of oxygen. Iron is carried in the bloodstream bound to its transport protein, transferrin and stored in the liver. A red cell product requires supply in iron. Absorption of iron from the alimentary canal will be slow. This occur iron deficiency can occur if losses exceed intake.



WHAT HAPPENS DURING HAEMOGLOBIN CATABOLISM AND EXCRETION?


Haemoglobin catabolism occurs when red cell destruction after 120 days of life span. The cells are removed extravascularly by macrophage specially in the bone marrow and also liver and spleen. The breakdown of red cell occurs:


  • Iron for recirculation via plasma transferrin to marrow erythroblasts

  • Protoporphyrin will break down to bilirubin.

  • Globin will be converted into amino acids


Bilirubin is transported to the liver. Its conjugated to glucuronides which are excreted into the gut via bile and converted in relation to stercobilinogen and stercobilin which is known as faeces. Stercobilinogen and stercobilin are partly reabsorbed and excreted in urine as urobilinogen and urobilin. A small portion of protoporphyrin is converted into carbon monoxide (CO) and excreted via the lungs. Globin chains are broken down to amino acids which are reutilized for general protein synthesis in the  human body.


By: Thanusha A/P Tangavel Sritharan

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