3.3.4 - Haemoglobin
Thursday 21st March ‘24
What are the adaptations of erythrocytes?
Bioconcave shape for large SA:V ratio for diffusion.
Flat and thin to decrease diffusion pathway.
Lots of haemoglobin.
What is haemoglobin?
Globular protein (spherical, soluble in water, hydrophobic centre, hydrophillic outer).
Quaternary structure - two alpha, two beta strands; haem group which contains Fe²⁺.
Each molecule can bind to 4 O2 groups. HOW DOES IT BIND FOR 4?
Fe³⁺ forms bright red blood cells.
Counter-example: Horseshoe crabs contain haemocyanin rather than haemoglobin which uses Cu²⁺ rather than Fe²⁺. Oxygenation of copper causes a colour change between the colourless Cu(I) deoxygenated form and the blue Cu(II) oxygenated form.
How does haemoglobin do its job?
To transport oxygen efficiently, haemoglobin must:
Readily associate with oxygen at gas exchange surface.
Readily dissociate at tissues needing oxygen.
Region of body | Oxygen concentration | Carbon dioxide concentration | Affinity of haemoglobin for oxygen | Result |
Gas exchange surface | high | low | high | Oxygen is associated |
Respiring tissues | low | high | low | Oxygen is dissociated. |
Haemoglobin’s affinity for oxygen is dependant on partial presssure of oxygen, haemoglobin saturation and partial pressure of carbon dioxide.