The variety of life continued

3.2.4

Haemoglobin continued

• On investigating how Haemoglobin joined with oxygen it was discovered that there were different types.

• The differences were to do with how they took up and released oxygen.

Haemoglobin continued

•Haemoglobins with a high affinity for oxygen. Take it up easily but release less readily.

•and Haemoglobins with a low affinity for oxygen. Not as easy to take up but release readily.

Why might this be?

Why different types?

• There is a correlation between the affinity for oxygen and factors such as environment in which the organisms lived or its metabolic rate.

• In an oxygen poor area the haemoglobin will need a much higher affinity for oxygen.

• If the metabolic rate is high oxygen needs to be given to the tissues very easily.

What causes these different affinities?

Different shaped caused by differences in the amino acid sequence.

Haemoglobin combining with oxygen is called loading or associating and in humans

happens in the lungs.

Haemoglobin releasing oxygen is called unloading or dissociating and in humans happens in the

tissues.

Oxygen dissociation curves.

Oxygen dissociation curves.

• Haemoglobin does not absorb oxygen evenly at all partial pressures.

• (The amount of gas is measured by how much pressure it contributes to the total pressure of the gas mixture, and is measured in kiloPascals (kPa))

• The shape of the molecule changes as the partial pressures of gases varies.

Oxygen dissociation curves.

• The shape of the molecule changes as the partial pressures of gases varies.

• At very low oxygen concentrations the 4 polypeptides are closely united making it difficult to absorb the first oxygen molecule.

• But once the first is loaded it becomes very easy to load the rest.

A very small decrease in the partial pressure of oxygen leads to a lot of oxygen becoming dissociated from the haemoglobin

Why does the graph tail off at very high concentrations?

The haemoglobin is almost saturated.

As there are many different types of haemoglobin and

respond to different conditions many oxygen dissociation curves exist but they all have the same

basic shape.

Effect of CO2 concentration

• Carbon dioxide reduces the affinity for oxygen (this helps oxygen get where it is needed)

• The greater the concentration of carbon dioxide the more readily it releases its oxygen (the Bohr effect)

Effect of CO2 concentration

• The greater the concentration of carbon dioxide the more readily it releases its oxygen (the Bohr effect)

•At the gas-exchange surface carbon dioxide levels are low and the affinity for oxygen is high. This combined with the high levels of oxygen means it is readily loaded by haemoglobin.

Effect of CO2 concentration•At the gas-exchange surface carbon dioxide levels are low and the affinity for oxygen is high. This combined with the high levels of oxygen means it is readily loaded by haemoglobin.

•In rapidly respiring tissues the levels of carbon dioxide is high. This reduces the affinity of haemoglobin for oxygen in the muscles, so the oxygen is readily unloaded.

Dissolved carbon dioxide is acidic and this low ph is what causes

the haemoglobin to change shape.

Loading, transport and unloading of oxygen

• Carbon dioxide is constantly being removed at gas exchange surfaces so the pH is higher

• As the pH changes the shape of the haemoglobin changes effecting oxygen affinity.

• At the respiring tissues carbon dioxide is produce lowering the pH.

• Haemoglobin changes shape of oxygen is lost.

This is useful as it makes sure each tissue gets the right amount of oxygen.More active tissue produces more carbon dioxide and needs more oxygen.

Other organisms

Where you live is important

• The Lugworm is not very active and spends most of its life in a U-shaped burrow.

• It is normally covered by sea water which it circulates through its burrow.

• Oxygen diffuses into the lugworm’s blood from the water and is transported by haemoglobin.

Lugworms• When the tide it out the lugworm can not circulate

fresh supply of oxygenated water through its burrow.

• The water has very little oxygen as the lugworm continues to use it up.

• So ALL the oxygen in the water needs to be extracted.

• Because of this the Lugworm can saturate its haemoglobin at a very low partial pressure of oxygen

Answer green question 1-6 on page 155

Size matters

• Mice has a large surface area to volume ratio (small animals).

• Consequently they lose body heat rapidly.

• To make up for this they have a high metabolic rate that generates heat and helps them to maintain their normal body temperature.

Because of this the curve is shifted to the right.

Activity counts.

• Flight in birds and swimming in fish are both energy demanding.

• Flight muscles have a high metabolic rate and during light, much of the blood pumped by the heart goes to these muscles.