Transport of oxygen by haemoglobin Flashcards
What does the oxygen dissociation curve show?
The oxyhaemoglobin dissociation curve shows the relationship. between the saturation of haemoglobin with oxygen and the partial pressure of oxygen
Why does haemoglobin not bind oxygen evenly at different partial pressures?
Haemoglobin’s affinity for oxygen changes depending on the partial pressure, leading to the characteristic S - shape of the oxygen dissociation curve
What is the shape of the oxygen dissociation curve?
A sigmoid (S-shaped) curve
Why is the oxygen dissociation curve initially shallow at low partial pressures of oxygen?
The first oxygen molecule binds slowly because haemoglobin’s shape makes it difficult for oxygen to associate
Why is it difficult for the first oxygen molecule to bind to haemoglobin?
The polypeptide subunits are closely united, making it hard for the first oxygen molecule to bind
What happens at low oxygen concentrations, and how is this shown on the oxygen dissociation curve?
Little oxygen binds to haemoglobin, so the initial gradient of the oxygen dissociation curve is shallow
How does the bind of the first oxygen molecule affect the haemoglobin molecule?
It changes the quaternary structure, making it easier for the other subunits to bind oxygen
What is positive cooperativity in haemoglobin, and how does it affect the oxygen dissociation curve?
Positive cooperativity is when the binding of one oxygen molecule makes it easier for the next to bind, so a smaller increase in partial pressure is needed for the second oxygen molecule to bind
On the oxygen dissociation curve, the gradient of the curve steepens as oxygen binds more easily
Why does the binding of the fourth oxygen molecule become harder?
Most binding sites are already occupied, making it less likely that an oxygen molecule will find an empty site
Why does the curve level off at high partial pressures of oxygen?
Most haemoglobin molecules are already saturated , so additional oxygen molecules find fewer available binding sites
How does the difficulty of binding the fourth oxygen molecule affect the oxygen dissociation curve?
The gradient decreases, and the graph flattens off
How does the shape of haemoglobin change?
The shape of any one type of haemoglobin can change under different conditions, affecting its oxygen affinity
What does the existence of different types of haemoglobin result in?
A large number of different oxygen dissociation curves, each with a similar shape but differing positions on the axes
How does the position of the oxygen dissociation curve relate to haemoglobin’s affinity for oxygen?
- Left shifted curve?
- RIght shifted curve?
A left shifted curve results in haemoglobin having a higher affinity for oxygen, meaning it loads oxygen easily but unloads it less easily
A right shifted curve results in haemoglobin having a lower affinity for oxygen, meaning it can load oxygen less easily but unload it more easily
How does carbon dioxide affect haemoglobin’s affinity for oxygen?
Haemoglobin has a reduced affinity for oxygen in the presence of carbon dioxide, meaning it releases oxygen more readily
How does the Bohr effect explain haemoglobin’s behaviour at the gas exchange surface (lungs)?
At the lungs, where carbon dioxide concentration, hemoglobin’s affinity for oxygen increases, allowing oxygen to load rapidly. The oxygen dissociation curve shifts to the left
What is the Bohr effect?
The Bohr effect describes how the greater the concentration of carbon dioxide, the more readily haemoglobin releases its oxygen
How does the Bohr effect explain haemoglobin’s behaviour in rapidly respiring tissues (muscles)
In muscles, where carbon dioxide concentration is high, haemoglobin’s affinity for oxygen decreases, allowing oxygen to unload readily into the muscle cells. The oxygen dissociation curve shifts to the right
Why does increased carbon dioxide concentration reduce haemoglobin’s affinity for oxygen?
Dissolved carbon dioxide is acidic, and the lower pH causes haemoglobin to change shape, making it more likely to release oxygen
