Myoglobin or Haemoglobin

Myoglobin and haemoglobin are both globular proteins that play important roles in transporting and storing oxygen in the body.

Structure of Myoglobin:
- Myoglobin is a single polypeptide chain consisting of 153 amino acids.
- It has a compact, globular structure.
- It contains a heme group, which is responsible for binding oxygen.
- The heme group consists of an iron atom coordinated with a porphyrin ring.
- The porphyrin ring is responsible for the red color of myoglobin.

Function of Myoglobin:
- Myoglobin is mainly found in muscle tissues and is responsible for storing oxygen and releasing it when needed.
- It has a higher affinity for oxygen compared to haemoglobin, allowing it to efficiently bind and retain oxygen in muscle tissues.
- During periods of low oxygen availability, such as during intense exercise, myoglobin releases oxygen to meet the increased demand of muscles.

Structure of Haemoglobin:
- Haemoglobin is a complex protein composed of four subunits: two alpha chains and two beta chains.
- Each subunit contains a heme group, similar to myoglobin.
- The four subunits come together to form a quaternary structure.
- The heme groups in haemoglobin are responsible for binding and transporting oxygen.

Function of Haemoglobin:
- Haemoglobin is found in red blood cells and is responsible for transporting oxygen from the lungs to the tissues.
- It binds to oxygen in the lungs, forming oxyhemoglobin, and releases oxygen in the tissues, forming deoxyhemoglobin.
- Haemoglobin also plays a role in buffering the pH of the blood by binding to and releasing hydrogen ions.

Conclusion:
In conclusion, myoglobin and haemoglobin are both globular proteins involved in oxygen transport and storage. Myoglobin is primarily found in muscle tissues and stores oxygen for muscle use, while haemoglobin is found in red blood cells and transports oxygen throughout the body.