Module 3. Haemoglobin (set 1)

Question 1

Describe the role of red blood cells and haemoglobin in oxygen transport

Answer 1

● **Red blood cells **contain lots of haemoglobin (Hb) - no nucleus, biconcave, high SA:V, short diffusion path
● Haemoglobin associates with / binds / loads O₂ at gas exchange surfaces where partial pressure of O₂ (pO₂) is high
● This forms oxyhaemoglobin which transports O₂ (each can carry 4O₂ - one at each Haem group)
● Haemoglobin dissociates from / unloads O₂ near **cells **/ tissues where pO₂ is low

Question 2

Describe the structure of haemoglobin

Answer 2

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

The haemoglobins are a group of **chemically similar **molecules found in many different organisms.

Question 3

Describe the loading, transport and unloading of oxygen in relation to the oxyhaemoglobin dissociation curve

Answer 3

Areas with low partial pressure of O₂ (respiring tissues):
● Hb has a low affinity for O2
● So O2 readily unloads / dissociates with Hb
● So % saturation is low

Areas with high partial pressure of O₂ (gas exchange surfaces):
● Hb has a high affinity for O2
● So O2 readily loads / associates with Hb
● So % saturation is high

Question 4

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

Answer 4

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 5

Describe evidence for the cooperative nature of oxygen binding

Answer 5

● A low pO2 as oxygen increases there is **little / slow increase in % saturation **of Hb with oxygen
→ When first oxygen is binding
● 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 6

Describe the advantage of the Bohr effect during intense exercise
(2 marks)

Answer 6

1. Increases dissociation of oxygen;
   (Accept unloading/release/reduced affinity for dissociation)
2. For aerobic respiration at the tissues/muscles/cells
   OR
   Anaerobic respiration delayed at the tissues/muscles/cells
   OR
   Less lactate at the tissues/muscles/cells;

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

How the curve provides evidence for this:
at a given pO2 % saturation of Hb is lower

Question 9

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

Answer 9

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

Question 10

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

Answer 10

● Different types of Hb are made of polypeptide chains with slightly different amino acid sequences
● Resulting in different tertiary / quaternary structures / shape → different affinities for oxygen

Question 11

Explain how organisms can be adapted to their environment by having different types of haemoglobin with different oxygen transport properties

Answer 11

Curve shift left → Hb has higher affinity for O2
● More O2 associates with Hb more readily
● At gas exchange surfaces where pO2 is lower
● Eg. organisms in low O2 environments - high altitudes, underground, or foetuses

Curve shift right → Hb has lower affinity for O2
● More O2 dissociates from Hb more readily
● At respiring tissues where more O2
is needed
● Eg. organisms with high rates of respiration /metabolic rate (may be small or active)