3.4.1 Haemoglobin

Question 1

what is haemoglobin

Answer 1

a globular protein with a quaternary structure
- consists of 4 PPchains

Question 2

where is the haem group associated

Answer 2

each PPchain - where the oxygen molecule binds irreversibly, forming oxyhaemoglobin

Question 3

why is haemoglobin required

Answer 3

oxygen has low solubility in water (plasma) as body temperature

Question 4

how are RBC specialised to maximise transport and exchange of oxygen

Answer 4

• minimal organelles, so more space for haemoglobin
• biconcave shape maximises SA:V, increasing the rate of diffusion
• diameter of 7-10µm - short diffusion distance

Question 5

what is cooperative binding

Answer 5

when the first oxygen molecule binds to haemoglobin it causes a change in the protein’s shape
- this makes it easier for other oxygen molecules to bind to it
- so the affinity of haemoglobin for oxygen has increased

Question 6

what is the affinity for oxygen in the lungs like

Answer 6

• high affinity for oxygen
• because haemoglobin will be close to 100% saturated with oxygen
• so association will occur

Question 7

what will the affinity for oxygen be in active tissues

Answer 7

• lower affinity for oxygen
• because haemoglobin will be around 25% saturated with oxygen
• oxygen will dissociate from haemoglobin

Question 8

how is carbon dioxide transported

Answer 8

• Carbon dioxide diffuses from respiring tissues into the blood plasma and then into the red blood cells.
• majority of carbon dioxide reacts with water to form carbonic acid. catalysed by the enzyme carbonic anhydrase.
• Carbonic acid partially dissociates to form H+ and hydrogen carbonate ions.
• The H+ binds to haemoglobin to form haemoglobinic acid.

Question 9

what is the effect of carbon dioxide on haemoglobin

Answer 9

• haemoglobinic acid has a different quaternary than haemoglobin so has a lower affinity for oxygen
• oxygen dissociates more readily and supplies more oxygen to respiring tissue
• shift to the right (Bohr effect)

Question 10

what does the Bohr shift look like

Answer 10

Question 11

what has a higher affinity to oxygen than regular haemoglobin

Answer 11

foetal haemoglobin so oxygen dissociation curve would shift left
- this makes oxygen transfer from mother to foetus at placenta

Question 12

what has a lower affinity for oxygen than regular haemoglobin

Answer 12

mouses haemoglobin as it has a smaller SA:V so needs to respire to maintain body temp- curve would shift right