– Haemoglobin is a complex protein that is found in red blood cells and is responsible for transporting oxygen and carbon dioxide in the blood.

– It has a tetrameric structure, meaning that it consists of four subunits, each containing a heme group and a globin chain. The heme group is an iron-containing ring that can bind one molecule of oxygen The globin chain is a polypeptide that provides structural support and regulates the affinity of the heme group for oxygen.

🔅 Types of Haemoglobin:

– There are different types of haemoglobin, depending on the composition of the globin chains.

The most common type in adults is haemoglobin A, which has two alpha and two beta chains. Other types include haemoglobin F (fetal haemoglobin), which has two alpha and two gamma chains. and haemoglobin A2, which has two alpha and two delta chains.

🔅 Functions of Haemoglobin in the body:

1) Haemoglobin has several functions in the body. The main function is to transport oxygen from the lungs to the tissues, where it is used for cellular respiration. Haemoglobin binds oxygen reversibly, meaning that it can release it when needed. The binding of oxygen by one subunit of haemoglobin increases the affinity of the other subunits for oxygen, a phenomenon known as cooperativity. This allows haemoglobin to load oxygen efficiently in the lungs, where the oxygen pressure is high, and unload it in the tissues, where the oxygen pressure is low.

2) Another function of haemoglobin is to transport carbon dioxide from the tissues to the lungs, where it is exhaled. Carbon dioxide can bind to the amino groups of the globin chains, forming carbaminohaemoglobin. This reduces the affinity of haemoglobin for oxygen, facilitating its release in the tissues. This effect is known as the Bohr effect. Carbon dioxide can also react with water to form carbonic acid. which dissociates into bicarbonate and hydrogen ions. The bicarbonate can diffuse out of the red blood cells into the plasma, while the hydrogen ions can bind to haemoglobin, further reducing its affinity for oxygen. This effect is known as the Haldane effect.

3) Haemoglobin also plays a role in maintaining the acid-base balance of the blood. By binding or releasing hydrogen ions, haemoglobin can act as a buffer, preventing large changes in pH.

4) Haemoglobin can also bind nitric oxide, a vasodilator that regulates blood pressure and blood flow.

🔅 Adaptations of Haemoglobin:

– Haemoglobin has evolved to adapt to different environmental conditions and physiological needs. For example, some animals that live at high altitudes or have high metabolic rates have haemoglobins with higher affinity for oxygen than humans, allowing them to extract more oxygen from the air. Some animals that live in low-oxygen environments or have low metabolic rates have haemoglobins with lower affinity for oxygen than humans, allowing them to conserve oxygen and prevent oxidative damage. Some animals have multiple types of haemoglobins that can switch on or off depending on the oxygen level or temperature.

– Haemoglobin can be impaired by various factors that affect its structure, function, or production.

Some genetic disorders can cause abnormal haemoglobins that have altered affinity for oxygen or are prone to aggregation or oxidation. For example, sickle cell anaemia is caused by a mutation in the beta chain of haemoglobin A that makes it form long rods under low-oxygen conditions, deforming the red blood cells and causing them to block blood vessels.

– Thalassemia is caused by reduced or absent production of one or more globin chains of haemoglobin A, resulting in imbalanced synthesis and accumulation of excess chains that damage the red blood cells.

– Other genetic disorders can affect the synthesis of heme or globin, leading to reduced production or quality of haemoglobin.

Haemoglobin can also be impaired by environmental factors that affect its binding or release of oxygen or carbon dioxide. For example, carbon monoxide is a toxic gas that can bind to haemoglobin with much higher affinity than oxygen, preventing oxygen delivery to the tissues and causing hypoxia. Methaemoglobin is a form of haemoglobin that has oxidized iron that cannot bind oxygen, reducing its oxygen-carrying capacity.

– Some drugs or chemicals can also interfere with haemoglobin function by altering its structure or affinity for ligands.

Haemoglobin is a vital protein that enables life by facilitating gas exchange in the blood. It has a complex structure and function that are finely tuned to meet the demands of different organisms and situations. However, it can also be affected by various factors that impair its functionality and cause diseases or disorders.

References

• Hemoglobin | Definition, Structure, & Function | Britannica https://www.britannica.com/science/hemoglobin

• Haemoglobin: Structure, Function, Oxygen Transport and Saturation - BYJU'S https://byjus.com/neet/what-is-haemoglobin/

• Hemoglobin adaptations in animals: Examples and Explanations https://www.verywellhealth.com/importance-of-hemoglobin-2249107

• Sickle cell disease - Genetics Home Reference - NIH https://biochemden.com/hemoglobin/

• [Thalassemia - Genetics Home Reference - NIH]

• [Hemoglobinopathies - an overview | ScienceDirect Topics]

• [Carbon Monoxide Poisoning - an overview | ScienceDirect Topics]

• [Methemoglobinemia - an overview | ScienceDirect Topics]

• [Drugs and Chemicals That Can Cause Methemoglobinemia - PubMed]