Organisms Exchange Substances with their Environment: Mass Transport in Animals - Human Haemoglobin Flashcards
What is the role of haemoglobin?
- Its role is to load and unload oxygen around the body
- Found in red blood cells
Describe the structure of haemoglobin
- Protein with quaternary structure - four polypeptide chains
- Each chain has a haem group which contains an iron ion each
- Oxygen can bind to haem (Fe2+) group
- Can carry four oxygen molecules
Describe the reaction between haemoglobin and oxygen
- Oxygen can react with haemoglobin to form oxyhaemoglobin
- Reversible reaction
- When oxygen joins haemoglobin, it’s called association or loading
- When oxygen leaves oxyhaemoglobin, it’s called dissociation or unloading
Where does haemoglobin load and unload oxygen?
- Haemoglobin loads oxygen in the lungs
- Oxyhaemoglobin unloads near respiring cells
How do you measure the haemoglobin’s tendency to bind with oxygen?
- Affinity for oxygen means the tendency a molecule has to bind with oxygen
- Haemoglobin’s affinity for oxygen varies depending on conditions
What factors affect haemoglobin’s affinity for oxygen?
- Partial pressure of oxygen (pO2)
- Partial pressure of carbon dioxide (pCO2)
- Saturation of haemoglobin with oxygen
What is partial pressure of oxygen and how does it affect haemoglobin’s affinity for oxygen?
- pO2 is a measure of oxygen concentration
- The greater the concentration of dissolved oxygen in cells, the higher the pO2
- Haemoglobin has a high affinity for oxygen where pO2 is high (lungs)
- Haemoglobin has a low affinity for oxygen where pO2 is low (respiring tissues)
What is partial pressure of carbon dioxide an how does it affect haemoglobin’s affinity for oxygen?
- pCO2 is a measure of carbon dioxide concentration
- The greater the concentration of dissolved carbon dioxide in cells, the higher the pCO2
- As pCO2 increases from respiration, it dissolves in blood plasma
- This is acidic and lowers pH
- This changes haemoglobin’s shape and decreases its affinity for oxygen
- Called the Bohr effect
How does saturation of haemoglobin with oxygen affect haemoglobin’s affinity for oxygen?
- It is hard for the first oxygen molecule to bind
- Once it does, it changes the shape to make it easier for the second and third molecules to bind, known as positive cooperativity
- It is then slightly harder for the fourth oxygen molecule to bind because there is a low chance of finding a binding site
Explain why oxygen binds to haemoglobin in the lungs
- pO2 is high, so affinity is high
- pCO2 is low in the lungs, so affinity is high
- Positive cooperativity (after the first oxygen molecule binds, binding of subsequent molecules is easier)
Explain why oxygen is released from haemoglobin in respiring tissues
- pO2 is low, so affinity is low
- pCO2 is high, so affinity decreases
- Respiration produces CO2
What does an oxygen dissociation curve show?
- Saturation of haemoglobin with oxygen (in %), plotted against partial pressure of oxygen (in kPa)
- Curves further to the left show the haemoglobin has a higher affinity for oxygen
Describe the dissociation curve when pO2 is low and high
• Low pO2
- In respiring tissues
- Haemoglobin has low affinity for oxygen
- So it has a low saturation of oxygen
• High pO2
- In lungs
- Haemoglobin has a high affinity for oxygen
- So it has a high saturation of oxygen
Why are oxygen dissociation curves S-shaped?
- Due to positive cooperativity
- After the first oxygen molecule binds, binding of subsequent molecules is easier
- Curve has gradual slope at beginning and end
- It has hard to bind first and fourth oxygen molecules
- Curve is steep in between as it is easier to bind second and third oxygen molecules
How does pCO2 affect the oxygen dissociation curve?
- Increase in pCO2 shifts curve to the right, but shape remains the same
- Affinity for oxygen is lower so rate of oxygen unloading increases
- Advantage in respiring cells
