3: EXCHANGE SYSTEMS AND MASS TRANSPORT - HAEMOGLOBIN Flashcards
What is the role of haemoglobin?
carrying O2 around the body
Describe the structure of haemoglobin
- a large protein with a quaternary structure
- made up of 4 polypeptide chains
- each chain has a haem group which contains an iron ion Fe^2+ which gives Hb its red colour
How many molecules of O2 can each haemoglobin molecule carry?
4
What is association/loading?
when an O2 molecule joins to a Hb molecule
What is dissociation/unloading?
when an O2 molecule leaves oxyhaemoglobin
Give the equation for loading and unloading of O2 to haemoglobin/from oxyhaemoglobin
Hb + 4O2 ⇌ HbO8
haemoglobin + oxygen ⇌ oxyhaemoglobin
What is affinity for O2?
the tendency of a molecule to bind with O2
What is pO2?
- partial pressure of O2
- a measure of O2 conc.
- the higher the conc. of dissolved O2 in cells, the higher the pO2
How does pO2 affect Hb’s affinity for O2?
- as pO2 increases, Hb’s affinity for O2 also increases
- O2 loads onto Hb where there is a high pO2
- O2 unloads from HbO8 where there is a low pO2
Where does O2 load?
the alveoli
Where does O2 unload?
respiring tissue
Why does O2 load at the alveoli?
- high O2 conc.
- high pO2
- Hb has a high affinity for O2
- O2 loads onto Hb
Why does O2 unload at respiring tissue?
- low O2 conc.
- low pO2
- Hb has a low affinity for O2
- O2 unloads from HbO8
What does an O2 dissociation curve show?
how saturated Hb is with O2 at any given pO2
What is saturation of Hb?
measures % Hb binding sites occupied by O2
What is the usual saturation of Hb at a high pO2?
~96% saturation
Why is the O2 dissociation curve S-shaped?
affinity of Hb for O2 affects how saturated the Hb is but saturation of Hb can also affect its affinity for O2
What is pCO2?
- partial pressure of CO2
- measure of the conc. of CO2 in a cell
How does pCO2 affect O2 unloading?
- O2 unloads more readily at a higher pCO2 which is helpful for getting more O2 to cells during activity
- when cells respire they produce CO2 which increases the pCO2
- this increases rate of O2 unloading so the dissociation curve shifts right
- the saturation of blood is lower for a given pO2 meaning that more O2 is being released
What is the Bohr effect?
- when CO2 levels increase in tissues, it reacts with water to form carbonic acid (H2CO3), which then dissociates into HCO3 and H^+ ions, lowering the blood pH
- the increased acidity (lower pH) and the presence of CO2 cause Hb to release O2 more readily
- this allows tissues with high CO2 levels (and thus higher metabolic activity) to receive more O2, supporting their energy production
How do low O2 environments affect the O2 dissociation curve?
- organisms that live in environments with a low conc. of O2 have Hb with a higher affinity for O2
- this is because there isn’t much O2 available so the Hb has to be very good at loading any available O2
- dissociation curve shifts left
How do high activity levels affect the O2 dissociation curve?
- organisms that are very active and have a high O2 demand have Hb with a lower affinity for O2 than human Hb
- this is because they need their Hb to be ables to easily unload O2 so that it’s available for them to use
- dissociation curve shifts right
How does size affect the O2 dissociation curve?
- small organisms have a higher SA:V ratio than larger organisms
- this means that they lose heat quickly and so they have a higher metabolic rate to keep them warm which means they have a high O2 demand
- smaller organisms have Hb with a lower affinity for O2 as they need their Hb to easily unload O2 to meet their high O2 demand
- dissociation curve shifts right
Which way does the O2 dissociation curve shift for foetal Hb and why?
- curve shifts left
- Hb has higher affinity for O2
- O2 loads more readily than adults
