💪 2. Myoglobin
📍 Where is it found?
- Myoglobin is found in muscle tissues – especially skeletal muscles and cardiac muscles (heart).
🧬 Structure of Myoglobin
- Myoglobin is simpler than haemoglobin
- It has only 1 polypeptide chain (a monomer)
- The chain has 153 amino acids
- It has one haem group, so it can carry only 1 oxygen molecule
🧠 Real-Life Example:
If haemoglobin is a delivery truck with 4 baskets, then myoglobin is a motorcycle with just one basket — but it’s fast and holds tightly to its cargo.
🔸 Function of Myoglobin
- Myoglobin’s job is to store oxygen in muscles
- It holds on to oxygen until the muscle is working hard and needs it
- When oxygen levels drop below 20 mm Hg, it releases the oxygen
🏋️♀️ During Exercise:
- Muscles use a lot of oxygen
- Oxygen levels drop
- Myoglobin releases its stored oxygen to keep muscles working
📊 Comparison Table – Haemoglobin vs. Myoglobin
| Feature | Haemoglobin | Myoglobin |
| Structure | 4 polypeptide chains | 1 polypeptide chain |
| Haem Groups | 4 | 1 |
| O₂ Carrying Capacity | 4 molecules | 1 molecule |
| Location | RBCs in blood | Muscle tissues |
| Function | Transports O₂ | Stores O₂ |
| O₂ Affinity | Lower (gives up O₂ easily) | Higher (holds O₂ tightly) |
| Releases O₂ at | PO₂ 60 mm Hg | PO₂ 20 mm Hg |
🔍 Important Concepts Explained
🔸 What is “Oxygen Affinity”?
Affinity means how strongly a molecule attracts or holds on to something.
- Myoglobin has high oxygen affinity – it holds on to oxygen tightly and only lets go when it’s really needed
- Haemoglobin has lower oxygen affinity – it easily picks up and drops oxygen during transport
🧠 Real-Life Example:
Imagine myoglobin is like a savings account — it keeps oxygen safe for emergencies.
Haemoglobin is like a delivery van — constantly picking up and dropping off oxygen.
🧾 Summary
- Respiratory pigments help carry and store oxygen in the body.
- Haemoglobin carries oxygen in the blood.
- Myoglobin stores oxygen in muscles.
- Haemoglobin has 4 chains and can carry 4 O₂ molecules; myoglobin has 1 chain and carries 1 O₂.
- Myoglobin helps during muscle activity, when oxygen is low.
- Both are vital for life — without them, your body wouldn’t get enough oxygen!
❓ Do You Know?
- The reason blood is red is because of haemoglobin.
- Whales and seals have lots of myoglobin, helping them hold their breath underwater for long periods.