More Exchange and Transport Systems - Haemoglobin Flashcards
What is haemoglobin made up of?
A large protein with a quarter army structure
— it’s made up four polypeptide chains.
Each chain has a haem group, which contains an iron ion, and gives haemoglobin its red colour.
Haemoglobin has a high affinity for oxygen. What does ‘affinity’ mean?
Tendency to combine with oxygen.
How many oxygen molecules can each haemoglobin carry?
4
What do oxygen and haemoglobin in the red blood cells combine to make?
Where does this occur?
Oxyhaemoglobin
This occurs in the lungs
What is the symbol equation for the reaction between haemoglobin and oxygen?
Hb + 4O2 ⇌ HbO8
This is a reversible reaction —
when oxygen leaves oxyhaemoglobin (dissociates from it) near the body cells, it turns back to haemoglobin.
What is partial pressure of oxygen (pO2) a measure of?
Oxygen concentration.
What is the partial pressure of carbon dioxide (pCO2)?
A measure of the concentration of CO2 in a cell.
Haemoglobin’s affinity for oxygen varies depending on what?
The partial pressure of oxygen.
Oxygen unloads onto haemoglobin to form oxyhaemoglobin where there’s a high pO2.
Oxyhaemoglobin unloads its oxygen where there’s a lower pO2.
——
Alveoli have a high pO2 so oxygen loads onto haemoglobin to form oxyhaemoglobin.
How does respiration affect pO2?
Respiration lowers pO2 because respiring cells use up oxygen.
Red blood cells deliver oxyhaemoglobin to respiring tissues, where it unloads it’s oxygen. The haemoglobin then returns to the lungs to pick up more oxygen.
What does 100% saturation on a dissociation curve?
What does 0% mean?
Every haemoglobin molecule is carrying the maximum of 4 molecules of oxygen.
0% means none of them are carrying any oxygen.
What does high pO2 mean?
Haemoglobin has a high affinity for oxygen, which means it will readily combine with oxygen, so it has a high saturation of oxygen.
Why is the dissociation curve S shaped?
When Hb combines with the first O2 molecule, it’s shape alters in a way that makes it easier for molecules to join too.
But as the Hb starts to become saturated, it gets harder for more oxygen molecules to join.
As a result, the curve has a steep bit in the middle where it’s really easy for oxygen molecules to join, and shallow bits at each end where it’s harder.
When the curve is steep, a small change in pO2 causes a big change in the amount of oxygen carried by the Hb.
When does Hb give away its oxygen most readily?
At higher partial pressures of carbon dioxide
as a way of getting more oxygen to cells during activity.
How does carbon dioxide concentration affect oxygen unloading?
What is this effect called?
Hb gives up its oxygen more readily at higher partial pressures of carbon dioxide (pCO2).
1) When cells respire they produce carbon dioxide, which raises the pCO2.
2) This increases the rate of the oxygen unloading
(i. e. the rate at which oxyHb dissociates to form Hb and oxygen)
- - so the dissociation curve ‘shifts’ right.
The saturation of blood with oxygen is lower for a gven pO2,
meaning that more oxygen is being released.
This is called the Bohr effect.
How does haemoglobin vary across different organisms?
Many animals are adapted to their environment
by possessing different types of haemoglobin with different oxygen transport properties.
Organisms that live in environments with a low concentraton of oxygen
have haemoglobin with a higher affinity for oxygen
than human haemoglobin – the dissociaton curve is to the left of ours.
Organisms that are very active and have a high oxygen demand
have haemoglobin with a lower affinity for oxygen
than human haemoglobin – the curve is to the right of ours.
