Haemoglobin (AQA)

• Conjugated (proteins joined to non-proteins) protein with quarternary structure (more than one polypeptide joined together.

• Found in red blood cells

• Contains a haem group (prosthetic group) - this is an iron atom enclosed in a ring

• Each haem can bind with one oxygen molecule

• Four oxygens can bind with one haemoglobin molecule

In the lungs - oxygen and haemoglobin form oxyhaemoglobin

Near the body cells - oxyhaemoglobin unloads oxygen

The pressure exerted by each gas in a gas mixture.

The partial pressure of oxygen is simply the measure of the concentration of oxygen.

Haemoglobins affinity for oxygen depends on partial pressure.

High p.p = oxygen loads easily onto haemoglobin

Low p.p = oxygen unloads easily from oxyhaemoglobin

Oxygen enters the blood capillaries in the alveoli of the lungs.

p.p of oxygen is high

oxygen loads onto haemoglobin

respiring cells use up oxygen

p.p of oxygen us low

oxygen is unloaded from the oxyhaemoglobin to the cells

This shows how saturated haemoglobin is at various partial pressures.

When p.p is high (e.g. in the lungs) haemoglobin has a high affinity.

This means it can easily bind so has a high saturation of oxygen.

When p.p is low (e.g. at respiring tissues) haemoglobin has a low affinity.

This means oxygen is unloaded so has a low saturation of oxygen.

At partial pressure = 0 - no oxygen is bound to the haemoglobin.

At low partial pressures = 

Polypeptide chains are tightly bound together.

This makes it difficult for oxygen molecules to reach haem and bind.        = curve rises gently

As 1 oxygen bonds to 1 haem group, the polypeptide chains open up.

This reveals the other haem groups.                                                            = curve rises steeply

At high partial pressures =

The haemoglobin is fully saturated.                                                             = curve levels off

loading = the process by which haemoglobin binds to oxygen

unloading = when haemoglobin releases oxygen.

Haemoglobin gives up oxygen more readily at high partial pressures of CO2.

This is a way to get more oxygen to already respiring cells.

• cells respire and produce co2
• high p.p of co2
• Oxygen unloads easily
• Dissociation curve shifts right
• Saturation of oxygen will be lower

= Bohr effect

• CO2 diffuses into red blood cells
• Converted into carbonic acid
• This dissociates to form hydrogen carbonate & hydrogen ions
• Hydrogen carbonate ions diffuse into the plasma
• Hydrogen ions remain in red blood cells
• These bind with haemoglobin to form haemoglobinic acid

This acid decreases pH.

Less oxygen available.

Low partial pressures.

Dissociation curve is to the left.

Haemoglobin has a higher affinity for oxygen.

(oxygen will bind more easily at lower partial pressures.)

Human foetus is to the left of the normal curve.

Higher affinity for oxygen

More oxygen can be loaded to supply the cells.

Oxygen levels are low.

Dissociation curve to the left.

Haemoglobin has a higher affinity for oxygen.

(Fast moving, oxygen-rich areas)

Lower affinity for oxygen.

Dissociation curve to the right