Haemoglobin
Biology: Cambridge International A Level, topic 2.3.5
Haemoglobin
Haemoglobin is a globular protein found in red blood cells. Haemoglobin carries oxygen from the lungs around the body.
Quaternary stucture
- Haemoglobin is a protein made from four different polypeptide chains.
- The four chains give haemoglobin a quaternary structure.
- There are two alpha and two beta chains.
Haem groups
- Each polypeptide chain in a haemoglobin molecule has a haem group.
- A haem group is a prosthetic group that is attached to the protein.
- The haem groups contain an iron ion.
- The iron ion is what makes haemoglobin red.
Affinity
- Haemoglobin has a high affinity (attraction) for oxygen.
- When red blood cells reach the lungs, oxygen diffuses into the red blood cells and binds to haemoglobin.
- Four molecules of oxygen bind to one molecule of haemoglobin.
- When oxygen binds to haemoglobin, oxyhaemoglobin is formed.
Dissociation
- When the red blood cells reach the tissues in the body (e.g. muscle cells), oxygen is released from the oxyhaemoglobin in a process called dissociation.
Test yourself on Haemoglobin
What is the name given to haemoglobin that has bound to oxygen?
Which of the following statements about haemoglobin are true?