1.3.7 The Molecular Structure of Haemoglobin

Structure of Haemoglobin:

• Quaternary Structure:
  • Haemoglobin is made up of four polypeptide chains: two alpha (α) chains and two beta (β) chains. These chains are tightly folded into a compact, spherical shape.
  • The quaternary structure allows the polypeptide chains to work together to enhance oxygen-carrying efficiency.
• Haem Group:
  • Each polypeptide chain in haemoglobin contains a haem group. This haem group includes an iron ion (Fe²⁺), which can bind to one molecule of oxygen.
  • With four haem groups, a single haemoglobin molecule can carry up to four oxygen molecules.

• Binding and Release of Oxygen:
  • When oxygen levels are high, such as in the lungs, haemoglobin binds oxygen, forming oxyhaemoglobin.
  • In tissues with lower oxygen levels, haemoglobin releases oxygen to supply cells.

Importance of Haemoglobin's Structure:

• The globular shape makes haemoglobin soluble, allowing it to travel easily through the bloodstream.
• The presence of iron ions in the haem groups enables haemoglobin to bind oxygen reversibly, essential for oxygen transport and release in tissues. Haemoglobin's structure allows it to efficiently transport oxygen from the lungs to tissues, playing a critical role in respiration and cellular energy production.