Haemoglobin

Question 1

Describe the role of red blood cells & haemoglobin (Hb) in oxygen transport:

Answer 1

1. Red blood cells contain lots of Hb. No nucleus & biconcave → more space for Hb, high SA:V & short diffusion distance
2. Hb associates with / binds / loads oxygenat gas exchange surfaces (lungs) where partial
   pressure of oxygen (pO2) is high
3. This forms oxyhaemoglobin which transports oxygen. Each can carry four oxygen molecule, one at each Haem group
4. Hb dissociates from oxygen near cells / tissues where pO2is low.

Question 2

Describe the structure of haemoglobin:

Answer 2

1. Protein with a quaternary structure
2. Made of 4 polypeptide chains
3. Each chain contains a Haem group containing an iron ion (Fe2+)

Question 3

Areas with low pO2- respiring tissues:

Answer 3

1. Hb has a low affinity for oxygen
2. So oxygenreadily unloads / dissociates with Hb
3. So % saturation is low

Question 4

Areas with high pO2- gas exchange surfaces:

Answer 4

1. Hb has a high affinity for oxygen
2. So oxygenreadily loads / associates with Hb
3. So % saturation is high

Question 5

Explain how the cooperative nature of oxygen binding results in an S-shaped (sigmoid) oxyhaemoglobin dissociation curve:

Answer 5

1. Binding of first oxygen changes tertiary / quaternary structure of haemoglobin
2. This uncovers Haem group binding sites, making further binding of oxygens easier

Question 6

Describe evidence for the cooperative nature of oxygen binding:

Answer 6

1. A low pO2 as oxygen increases there is little / slow increase in % saturation of Hb with oxygen. When first oxygen is binding
2. At higher pO2, as oxygen increases there is a big / rapid increase in % saturation of Hb with oxygen. Showing it has got easier for oxygens to bind

Question 7

What is the Bohr effect?

Answer 7

Effect of CO2 concentration on dissociation of oxyhaemoglobin- curve shifts to right.

Question 8

Explain effect of CO2 concentration on the dissociation of oxyhaemoglobin:

Answer 8

1. Increasing blood CO2 eg. due to increased rate of respiration
2. Lowers blood pH (more acidic)
3. Reducing Hb’s affinity for oxygen as shape / tertiary / quaternary structure changes slightly
4. So more / faster unloading of oxygen to respiring cells at a given pO2

Question 9

Describe evidence for the Bohr effect:

Answer 9

At a given pO2 %, the saturation of Hb with oxygen is lower.

Question 10

Explain the advantage of the Bohr effect (eg. during exercise):

Answer 10

More dissociation of oxygen → faster aerobic respiration / less anaerobic respiration → more ATP produced.

Question 11

Explain why different types of haemoglobin can have different oxygen
transport properties:

Answer 11

1. Different types of Hb are made of polypeptide chains with slightly different amino acid sequences
2. Resulting in different tertiary / quaternary structures / shape
3. So they have different affinities for oxygen

Question 12

Curve shift left
Hb has higher affinity for O2:

Answer 12

1. More O2 associates with Hb more readily
2. At gas exchange surfaces where pO2
   is lower
3. Eg. organisms in low O2 environments - high
   altitudes, underground, or foetuses

Question 13

Curve shift right
Hb has lower affinity for O2:

Answer 13

1. More O2 dissociates from Hb more readily
2. At respiring tissues where more O2
   is needed
3. Eg. organisms with high rates of respiration /
   metabolic rate (may be small or active)