A8- Haemoglobin

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

• Red blood cells contain lots of Hb

→ No nucleus & biconcave → more space for Hb, high SA:V & short diffusion distance

• Hb associates with / binds / loads oxygen at gas exchange surfaces (eg. lungs) where partial pressure of oxygen (pO2) is high

• This forms oxyhaemoglobin which transports oxygen

• Each can carry four oxygen molecules, one at each Haem group

• Hb dissociates from / unloads oxygen near cells / tissues where pO2 is low

describe the structure of haemoglobin

• protein with a quaternary structure

• made of 4 polypeptide chains

• each chain contains a Haem group contain and iron iron

describe the loading, transport and unloading of oxygen in areas of low partial pressure of oxygen ( low pO₂)

• Hb has a low affinity for oxygen

• SO oxygen readily dissociates

• so % saturation of Hb with oxygen is low

describe the loading, transport and unloading of oxygen in areas of high partial pressure of oxygen ( high pO₂)

• Hb has a high affinity for oxygen

• so oxygen readily associates

• so % saturation of Hb with oxygen is high

give an example of an area in the body with low partial pressure of oxygen

respiring tissue

give an example of an area in the body with a high partial pressure of oxygen

gas exchange surfaces

• e.g. lungs

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

• binding of first oxygen changes the tertiary / quaternary structure of haemoglobin

• this uncovers Haem group binding sites, making further binding of oxygen easier

Describe evidence for the cooperative nature of oxygen binding

● At 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 oxygen to bind

what is the Bohr effect?

• Effect of CO₂ concentration on dissociation of oxyhaemoglobin

• Oxyhaemoglobin dissociation curve shifts right

Explain the effect of CO2 concentration on the dissociation of oxyhaemoglobin

1. Blood CO₂ increases eg. due to increased rate of respiration

2. This lowers blood pH (more acidic)

3. Reducing Hb’s affinity for oxygen as its shape / tertiary / quaternary structure changes slightly

4. So more / faster unloading of oxygen to respiring cells at a given pO2

describe evidence for the Bohr effect

At a given pO2 %, the saturation of Hb with oxygen is lower - DONT GET THIS ASK ABT

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

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

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

• Different types of Hb are made of polypeptide chains with slightly different amino acid sequences

• Resulting in different tertiary / quaternary structures / shapes

• So they have different affinities for oxygen

explain what an oxyhemoglobin curve looks like for an organism which lives in a low oxygen environment

e.g. high altitude

• Oxyhaemoglobin dissociation curve shifts left

• Hb has a higher affinity for O2

• more O₂ associates with Hb more readily

• at gas exchange surfaces

explain what an oxyhemoglobin curve looks like for an organism which lives in a high oxygen environment

Eg. organisms with high rates of respiration /

metabolic rate (may be small or active)

• oxyhameoglobin curve shifts right

• Hb has a lower affinity for O2

• more O2 disassociates from Hb more readily

• at respiring tissues

Give the formula for calculating the percentage saturation of Hb with oxygen

Oxygenated haemoglobin / maximum saturation x100