AQA Biology (as level) - Haemoglobin (exchange and transport systems)
what is the Bohr effect?
- cells respire and release CO2 - this raises the pCO2 - increasing rate of oxygen unloading (the rate at which oxyhaemoglobin dissociates from oxygen to form Hb and O2) - this causes the dissociation curve to shift to the right meaning that more oxygen is being released.
draw a dissociation curve with partial pressure of oxygen on x axis and annotate
1. where there's a high pO2 ie in the lungs Hb has a high affinity for oxygen ie it will readily combine with oxygen so it has a high saturation of oxygen 2. where there's a low pO2 ie in respiring tissue Hb has a lower affinity for oxygen so it releases oxygen rather than combines with it so it has a lower saturation of oxygen
How many oxygen molecules can each haemoglobin molecule carry?
4 O2 molecules
What happens to the curve for an earthworm living in low pO2?
Curve shifts to the left of the human curve Low pO2 So Hb has a higher affinity for oxygen than human Hb
What adaptation do haemoglobin have that helps organisms to survive in a particular environment ?
Different organisms have different types of haemoglobin with different oxygen transporting capacities Organisms that live in environments with a low concentration of oxygen
what is the reversible reaction for oxygen and haemoglobin binding and unbinding?
HB + 4O2 >< HbO8 (reversible reaction) (remember each haemoglobin molecule can carry four oxygen molecules)
Why are oxygen dissociation curves S shaped ?
Hb combines with the first O2 molecule its shape alters in a way that makes it easier for other oxygen molecules to join too but as the Hb starts to become saturated it becomes harder for more oxygen molecules to join as a result, the curve has a steep area, in the middle where it's easy for the O2 molecules to join a shallow parts at each end, where its harder. (when the curve is steep, a small change in the pO2 causes a big change in the amount of oxygen carried by the Hb)
What is the oxygen transporting capacity for haemoglobin of organisms that live in environments with a low concentration of oxygen ? And where is the dissociation curve compared to human Hb
Hb had a higher affinity for oxygen than human haemoglobin The dissociation curve is to the left of ours
What is the oxygen transporting capacity for haemoglobin of organisms that are very active and has a high oxygen demand ? And where is the dissociation curve compared to human Hb
Hb with s lower affinity for oxygen than humans because they need oxygen for respiration The dissociation curve is to the right of the human one
Hb is a proteins with a quaternary structure Explains what this means .
Jb has more than polypeptide chain (4 polypeptide chains 2 alpha and 2 beta)
What happens to the dissociation curve of a human in a high concentration of carbon dioxide environment ?
The curve shifts to the right This is the Bohr effect High concentration of Co2 Increases rate of oxygen unloading Saturation of blood with oxygen is lower for a given pO2 More O2 molecules unbound to Hb
what is haemoglobin?
a group of chemically similar molecules found in many different organisms a protein with a Quaternary structure
what is the structure of a haemoglobin molecule?
a large protein made up of four polypeptides each chain contains a haem group each haem group contains an Fe2+ ion each molecule of haemoglobin carries four O2 molecules.
what do dissociation curves show?
by showing how saturated the haemoglobin is with oxygen (thus its affinity for oxygen) at any given partial pressure.
what affects oxygen unloading?
carbon dioxide concentration Hb unloads its oxygen more readily at higher partial pressures of carbon dioxide pCO2 this allows cells to get more oxygen to cells during activity
hat does 100% saturation mean ?
every haemoglobin molecule is carrying the maximum of 4 molecules of O2
does haemoglobin have a high/low affinity for oxygen?
high affinity for oxygen each molecule can carry four O2 molecules
where in the body would you find a high partial pressure of oxygen and what does haemoglobin form in these areas, give equations?
in the lungs haemoglobin in the red blood cells and oxygen join forms oxyhaemoglobin
what is the partial pressure of carbon dioxide?
measure of concentration of CO2 in a cell
what is the partial pressure of oxygen?
measure of oxygen concentration pO2 higher concentration of dissolved oxygen in cells = higher partial pressure
what does 0% saturation mean?
none of the haemoglobin molecules are carrying any oxygen molecules.
How is oxygen carried around the body ?
oxygen enters blood capillaries at the alveoli in the lungs alveoli have a high pO2 so oxygen loads onto haemoglobin to form oxyhaemoglobin when cells respire, they use up oxygen this lowers the pO2 RBC deliver oxyhaemoglobin to respiring tissues where haemoglobin unloads its oxygen haemoglobin returns back to the lungs to pick up more oxygen
Where in the body would you find a low partial pressure of oxygen and what does haemoglobin form ?
respiring muscles haemoglobin and oxygen are unbound and forms oxygen + haemoglobin
what affects haemoglobin's affinity for oxygen thus its saturation?
the partial pressure of oxygen
what does affinity mean?
the tendency to combine with oxygen
when does oxygen load onto haemoglobin to form oxyhaemoglobin?
when there's a high partial pressure of oxygen (ie the lungs)
when does oxyhaemoglobin unload its oxygen to form haemoglobin + oxygen ?
when there's a low partial pressure of oxygen (ie respiring cells)
