Transport of oxygen by haemoglobin Flashcards
Under what conditions do haemoglobin not combine with oxygen evenly?
When the haemoglobin is exposed to the different partial pressure of oxygen.
What is an oxygen dissociation curve?
The relationship between the saturation of haemoglobin with oxygen(how many oxygens is picked up) and the partial pressure of oxygen.
Explain the shape of the oxygen dissociation curve.
- The shape of the haemoglobin makes it hard for the 1st oxygen molecule to bind to one of the sites on its 4 polypeptide subunits because they are tightly packed. Therefore at a low O2 concentration, little oxygen binds to haemoglobin so the gradient of the curve is shallow at first.
- But the binding of the first O2 molecule changes the quaternary structure of the haemoglobin so it changes shape. This change means that it’s easier for other subunits to bind to other oxygens.
- Therefore it only takes a small increase in the partial pressure of oxygen to bind to the second oxygen molecule than it did to bind with the first one. This is known as positive cooperativity because the binding of the first molecule makes the binding of the second easier and so on. The gradient of the curve steepens.
- After the binding of the third molecule, it will be harder to bind the 4th one because there’s less probability, with the majority of the binding sites occupied, it is less likely that single oxygen will find an empty site to bind to so the gradient of the curve reduces and graph levels off.
Why are there different oxygen dissociation curves?
Because there are different types of haemoglobin so different shape and hence different affinity for oxygen.
Also, the shape of any one type of haemoglobin can change under different conditions so it means that there are different types of oxygen dissociation curves.
What are the 2 factors which associate with all oxygen dissociation curve?
- The further to the left of the curve, the greater the affinity of haemoglobin because there’s a higher concentration of oxygen at the start of the curve so it loads oxygen readily but unloads it less easily.
- The further to the right of the curve, the lower the affinity of haemoglobin because there’s a lower concentration of oxygen at the start of the curve so loads less oxygen readily but unload it more easily.
How can haemoglobin reduce its affinity for oxygen?
Under the presence of CO2.
Greater the concentration of CO2, more readily the haemoglobin releases its oxygen (Bohr effect).
How does haemoglobin behave at the gas exchange surface?
At gas exchange surface e.g. lungs, The concentration of CO2 is low as it diffuses across the exchange surface and is excreted from the organism. Therefore the affinity of haemoglobin for oxygen is increased and because there’s a high concentration of O2 in the lungs, oxygen is readily loaded by haemoglobin. The reduced CO2 concentration will shift the curve to the left.
How does haemoglobin behave at respiring tissues?
At respiring tissues e.g. muscles, the concentration of CO2 is high. Therefore the affinity for oxygen is reduced and as there’s a low concentration of oxygen in the muscles, oxygen is readily unloaded from the haemoglobin into the muscle cells. The increase of CO2 concentration means that the curve will shift to the right.
Why does a high concentration of CO2 make haemoglobin to release its oxygen?
Because dissolved CO2 is acidic and the low pH causes the haemoglobin to change shape.
How is oxygen been loaded, transported and unloaded from the gas-exchange surface to respiring tissues?
1) At gas exchange surfaces, CO2 is constantly being removed.
2) The pH will slightly increase due to the lower concentration of CO2.
3) The higher the pH changes the shape of the haemoglobin making it more able to load with oxygen readily.
4) This shape also increases the affinity of haemoglobin for oxygen so it is not released during the transportation from the surface to the tissue.
5) In the tissues, CO2 is produced by respiring cells.
6) CO2 is acidic in solution so the pH of the blood within the tissue in lowered.
7) The lower pH changes the shape of haemoglobin into one with a lower affinity for oxygen.
8) Haemoglobin releases its oxygen into respiring tissues.
How can haemoglobin provide more oxygen to be unloaded for highly respiring cells?
- Higher the rate of respiration
- More CO2 produced
- Lower the pH
- Greater the haemoglobin shape change
- More readily oxygen is unloaded
- More oxygen for respiring tissue
How does the unloading molecules of oxygen change due to different respiratory tissues?
When haemoglobin passes through the lungs to be saturated with O2, not all molecules are loaded with maximum 4 oxygen molecules so most haemoglobins contain only 97% of overall saturation.
When haemoglobin reaches a low respiratory tissue, it may only release one of the oxygen molecules and the haemoglobin may still contain with 75% of O2 but if it’s a highly respiring tissue, e.g. exercising tissue, then 3 molecules of O2 might be released.
How might different species have different adaptations for their haemoglobins?
Due to different environments and conditions, species of animals that live in an environment with a low partial pressure of oxygen are evolved to have haemoglobins with high affinity for oxygen than haemoglobins of animals that live where there’s a high partial pressure of oxygen.
Why do lungworms have haemoglobins with higher affinity than human?
- Lungworms are not very active.
- They are covered by sea water.
- Oxygen diffuses into the lungworm’s blood from the water and it uses haemoglobin to transport oxygen to its tissues.
- When the tide goes out, there’s a low concentration of O2, so it means that lungworms need to extract as much oxygen when there’s water so they need haemoglobins with high affinity to maintain the most oxygens as possible.
