Different types of haemoglobin
- Haemoglobin is a quaternary protein made up of four globin polypeptides and four haem groups
- The structure of haem is identical in all types of haemoglobin but the globin chains can differ substantially between species
- The globin polypeptides determine the precise properties of haemoglobin
- Haemoglobin types vary in their oxygen-binding properties, meaning that they bind to and release oxygen in different conditions
- Environmental factors can have a major impact on the evolution of haemoglobin within a species
Effects of altitude
- The partial pressure of oxygen in the air is lower at higher altitudes
- Species living at high altitudes have haemoglobin that is adapted to these conditions, e.g.
- Llamas have haemoglobin that binds much more readily to oxygen
- This is beneficial as it allows them to obtain a sufficient level of oxygen saturation in their blood when the partial pressure of oxygen (pO2) in the air is low
Species that live at high altitudes have evolved haemoglobin with a higher affinity for oxygen; this means that at any given partial pressure of oxygen the high altitude haemoglobin has a higher percentage saturation than lower altitude haemoglobin
- The haemoglobin of a developing foetus has a higher affinity for oxygen than adult haemoglobin
- This is vital as it allows a foetus to obtain oxygen from its mother's blood at the placenta
- Fetal haemoglobin can bind to oxygen at low pO2
- At this low pO2 the mother's haemoglobin is dissociating with oxygen
- On a dissociation curve graph, the curve for foetal heamoglobin shifts to the left of that for adult haemoglobin
- This means that at any given partial pressure of oxygen, foetal haemoglobin has a higher percentage saturation than adult haemoglobin
- After birth, a baby begins to produce adult haemoglobin which gradually replaces foetal haemoglobin
- This is important for the easy release of oxygen in the respiring tissues of a more metabolically active individual
Foetal haemoglobin has a higher affinity for oxygen than adult haemoglobin. This means that at any given pO2, foetal haemoglobin will have a higher percentage saturation than adult haemoglobin.
You may be shown the oxygen dissociation curves of different types of haemoglobin and asked to explain how they are adapted to the environment the animal is living in. Remember that the curve furthest to the left represents the haemoglobin with the highest affinity for oxygen.