The variety of life: Haemoglobin By the end of the lesson you should be able to: What haemoglobin is and how it is different in different living things What an oxygen dissociation curve is The impact of different adaptations on oxygen dissociation

Blood

Haemoglobins A family of molecules Protein Function: Oxygen transport Spelling haemoglobin (UK), hemoglobin (US)

Structure of haemoglobin Primary: Secondary: Tertiary: Quaternary:

Transport of Oxygen Oxygen + Haemoglobin ↔ Oxyhaemoglobin Haemoglobins Haem group combines with oxygen 4 O2 per molecule of haemoglobin Oxygen + Haemoglobin ↔ Oxyhaemoglobin 4O2 + Hb ↔ HbO8

Oxygen + Haemoglobin ↔ Oxyhaemoglobin Haemoglobin has a high affinity for oxygen in oxygen-rich situations and becomes saturated: haemoglobin is loaded with oxygen in the lungs. Oxyhaemoglobin dissociates in oxygen-poor situations: Oxygen Is unloaded in tissues.

Oxygen + Haemoglobin ↔ Oxyhaemoglobin The amount (%) of haemoglobin that is saturated with oxygen depends on the concentration (partial pressure) of oxygen in the environment. What is partial pressure? See ‘Hint’ box on page 152

Standard oxygen dissociation curve

Haemoglobin dissociation curve A small drop in oxygen (being used more in respiration) brings about a large decrease in % saturation Therefore, more oxygen available to tissues for respiration

Different types of haemoglobin Different organisms in different environments have different haemoglobins Some haemoglobins have a high affinity for oxygen: They take up oxygen more easily but release it less readily (e.g. organisms which live in a low oxygen environment) Some haemoglobins have a low affinity for oxygen: They take up oxygen less easily but release it quickly (e.g. organisms with a fast rate of respiration)

Effect of carbon dioxide on curve If you are exercising you need more oxygen for aerobic respiration. You want the haemoglobin to dissociate (give up its oxygen) at higher partial pressures / more readily This shift is known as the Bohr shift Due to acidity of carbon dioxide So, more exercise leads to Bohr shift

Some creatures need to grab hold of more oxygen… Hb becomes saturated at lower partial pressures of oxygen.

Summary

Example Questions

The graph shows the oxygen haemoglobin dissociation curves for three species of fish. Species A lives in water containing a low partial pressure of oxygen. Species C lives in water with a high partial pressure of oxygen. (a) Explain the advantage to species A of having haemoglobin with a curve in this position. (3 marks) Hb (in A) has greater affinity for O2; becomes saturated at low(er) ppO2 / more saturated at same ppO2 / unsaturated at very low ppO2; able to supply enough O2 to its tissues;

Species A and B live in the same place but B is more active Species A and B live in the same place but B is more active. Suggest an advantage to B of having an oxygen haemoglobin dissociation curve to the right of that for A. (2 marks) fish B has a greater rate of respiration (accept more O2 needed for respiration); Hb dissociates more readily (than A); more O2 supplied;

Shrews are small mammals Shrews are small mammals. Their tissues have a much higher respiration rate than human tissues. The graph shows the position of the oxygen haemoglobin dissociation curves for a shrew and a human. Explain the advantage to the shrew of the position of the curve being different from that of a human. (2 marks) high respiration rate means high demand for oxygen; shrew haemoglobin has lower affinity for oxygen / gives up O2 more readily; shrew Hb lower saturation rate than human Hb at same partial pressure / more O2 released at same pp;

Deer mice are small mammals which live in North America Deer mice are small mammals which live in North America. One population lives at high altitude and another at low altitude. Less oxygen is available at high altitude. The graph shows the oxygen haemoglobin dissociation curves for the two populations of deer mice. (a) Explain the advantage for mice living at high altitude in having a dissociation curve which is to the left of the curve for mice living at low altitude. (2 marks) (b) Suggest why it would be a disadvantage for the curve to be much further to the left. (1 mark) (a) high altitudes have a low partial pressure of O2; high saturation/affinity of Hb with O2 (at low partial pressure O2); sufficient/enough O2 supplied to cells / tissues; 2 max (b) difficult to unload/dissociate O2 (at tissues); 1 mark