3. Haemoglobin

Question 1

Haemoglobin structure

Answer 1

1. Quaternary: 4 polypeptide chains
2. Prosthetic group = Haem group
3. Each haem group can bind to 1 oxygen molecule
4. Globular: soluble in water

Question 2

Function of haemoglobin

Answer 2

To carry oxygen through the blood from lungs to respiring tissues

Question 3

How does the structure of haemoglobin relate to its function?

Answer 3

1. 4 haem groups: 4 oxygen molecules per haemoglobin molecule so more efficient transport of O2 throughout the body
2. Haemoglobin needs to be soluble so that it can be carried in the cytoplasm of the RBCs (the fact that it’s globular means it’s water-soluble)

Question 4

What is affinity?

Answer 4

How likely haemoglobin is to bind to oxygen

Question 5

What affects haemoglobin’s affinity for oxygen?

Answer 5

O2 & CO2 levels
The condition affects affinity, NOT LOCATION!
Association is a consequence of high O2 concentration, dissociation is a consequence of low O2 concentration

Question 6

Haemoglobin + oxygen =

Answer 6

Oxyhaemoglobin

Question 7

Where does association/loading occur?

Answer 7

In tissues with high oxygen content (i.e. lungs)

Question 8

Where does dissociation/unloading occur?

Answer 8

In tissues with low oxygen content (i.e. respiring tissues)

Question 9

X and y axes in an oxygen dissociation curve

Answer 9

X: partial pressure of oxygen (kPa)
Y: % saturation of haemoglobin with oxygen

Question 10

Explain why oxygen dissocation graphs are S shaped

Answer 10

• Shape of haemoglobin molecule makes it difficult for the 1st O2 molecule to bind: curve is shallow at low oxygen PP
• Once 1st O2 binds the quaternary structure changes: easier for 2nd and 3rd O2 to bind. Small changes in oxygen PP lead to larger changes in % saturation: positive cooperation
• After 3rd O2 binds it’s harder for last to bind because collisions between O2 molecules and final binding site are less likely: curve becomes shallow again

Question 11

Explain CO2’s effect on haemoglobin

Answer 11

• CO2 lowers pH (acidic when dissolved in blood plasma)
• Lower pH affects tertiary structure (H bonds) of haemoglobin
• Harder for O2 to bind to the haemoglobin

Question 12

Curve shifts to the left: increased or decreased affinity?

Answer 12

Increased

Question 13

Curve shifts to the right: increased or decreased affinity?

Answer 13

Decreased

Question 14

Lugworm: shifts left or right?

Answer 14

Left

Question 15

Mouse: shifts left or right?

Answer 15

Right

Question 16

Llama: shifts left or right?

Answer 16

Left

Question 17

Foetus: shifts left or right?

Answer 17

Left

Question 18

Myoglobin is found in muscles. It acts as an oxygen store, only releasing its oxygen if the oxygen levels in the muscle drop really low. Would myoglobin have a higher or lower affinity for oxygen than haemoglobin?

Answer 18

Higher

Curve shifts to the left