Haemoglobin Flashcards
What are haemoglobins?
A group of chemically similar molecules found in a wide variety of organisms
What is haemoglobin made up of?
4 polypeptide chains (protein) and each polypeptide chain has a haem group attached to it
What is a haem group?
A non protein which contains an Fe2+ ion to which one molecule of oxygen binds
How many oxygen molecules can one haemoglobin molecule carry?
4
What is the primary structure of a haemoglobin molecule?
A sequence of amino acids in the four polypeptide chains
What is the secondary structure of a haemoglobin molecule?
Each of the polypeptide chains is coiled into a helix
What is the tertiary structure of a haemoglobin molecule?
Each polypeptide chain is folded into a precise shape which is an important factor in its ability to carry oxygen
What is the quaternary structure of a haemoglobin molecule?
All 4 polypeptides are linked together to form an almost spherical molecule. Each polypeptide is associated with a haem group
What is the process called when haemoglobin binds with oxygen?
Loading / associating
Where does loading take place?
lungs
What is the process called when haemoglobin releases its oxygen?
Unloading / dissociating
Where does unloading take place?
tissues
What is loading?
the binding of oxygen to haemoglobin at the gas exchange surface e.g. lungs forming oxygaemoglobin
What is unloading?
the release of oxygen from haemoglobin at the tissues
What is partial pressure (tension)?
the pressure exerted by a gas if it alone occupied the space
When is partial pressure of oxygen the lowest?
During exercise
What does haemoglobin do?
-readily binds with oxygen at the surface where gas exchange takes place
-readily dissociates from oxygen at the tissues requiring it
Properties of haemoglobin
-changes its affinity for oxygen under different conditions
-has a high affinity for oxygen when the partial pressure of oxygen is high (e.g. the lungs)
-has a low affinity for oxygen when the partial pressure of oxygen is low (e.g. at the tissues)
Why are the properties of haemoglobin essential to its function?
As haemoglobin can load large amounts of oxygen as it passes through the lungs and unloads large amounts of oxygen as it passes through the tissues.
How does oxygen bind to haemoglobin?
co-operative binding
How does increasing carbon dioxide levels affect haemoglobin?
-The production of CO2 causes the formation of carbonic acid, which causes a fall in pH.
-The fall in pH causes a change in the structure of haemoglobin causing it to release its oxygen more readily
-Thus, the more CO2 being produced, the more oxygen being released for respiration
What is co-operative binding?
When the haemoglobin molecule binds to the first oxygen molecule it causes a change in its tertiary structure. This reveals more haem groups (binding sites) which makes it easier for the haemoglobin to bind to a second molecule of oxygen, then making it easier for the 3rd and 4th oxygens to bind.
How does oxygen dissociate from oxyhaemoglobin?
When oxyhaemoglobin moves into regions of low partial pressure of oxygen (in the tissues) , the 1st oxygen is readily released, but the 2nd, 3rd and 4th are given up successively less readily
What is the oxygen haemoglobin dissociation curve?
Shows the percentage saturation of oxygen in haemoglobin when in contact with different partial pressures of oxygen
What is the shape of an oxygen dissociation curve?
s-shaped (sigmoidal)
Why can the saturation of oxygen in haemoglobin never be 100%?
As it is always being released to cells
What is the partial pressure of oxygen in the lungs?
13kPa - 96% saturated, the highest it can be
Why is the gradient of the curve initially shallow on an oxygen dissociation curve?
As at low oxygen concentrations, little oxygen binds to haemoglobin.
What is significant about the s-shape on an oxygen dissociation curve?
-the steep gradient of the curve shows that large amount oxygen is being given up to the tissues
-As the partial pressure of oxygen in the air in the lungs is about 13 kPa, if we move into a lower oxygen environment (e.g. climb in altitude) the blood remains fully saturated until the partial pressure drops below 9kPa. This allows us to reach nearly 3000 m in height before our blood is no longer saturated at the lungs and we start to feel the effects of altitude
What is the Bohr shift?
a rightward shift of the oxygen dissociation curve due to increase in CO2 concentration
On an O2 dissociation curve, what does a curve that is closer to the right suggest?
That the haemoglobin has a lower affinity for oxygen, meaning it releases oxygen easier
Why is the % saturation of the blood lower after exercise than at rest at x kPa?
As more CO2 is in the blood during exercise, so more oxygen is being released
Why do different organisms have different types of haemoglobins?
As animals will adapt to their surroundings and their oxygen requirement
Why can haemoglobin be used to compare evolutionary relationships within organisms?
As they are found in many different organisms
