12.11 Haemoglobin

Question 1

What structure does the protein Haemoglobin have?

Answer 1

• Quaternary structure
• Composed of four subunits each containing a haem group

Question 2

2. Complete the sentence: Haemoglobin has an ……… to oxygen.

Answer 2

Affinity

Question 3

How many oxygen molecules does each haemoglobin combine with?

Answer 3

4

Question 4

How does oxygen dissociate at respiring cells and tissues?

Answer 4

Haemoglobin must readily associate with oxygen at the gas exchange surface (lungs) and dissociate (unload) oxygen at respiring cells/tissues.

Question 5

What is the equation for the uptake of oxygen by haemoglobin?

Answer 5

• Haemoglobin + Oxygen<–> Oxyhaemoglobin
• Hb + 4O2<–>HbO8

Question 6

Give the formula for calculating the percentage saturation of haemoglobin with oxygen.

Answer 6

Percentage saturation of haemoglobin with oxygen= (oxygenated haemoglobin )/(maximum saturation) x100

Question 7

What is the definition of partial pressure of oxygen (pO2/kPa)

Answer 7

Amount of oxygen in a mixture of gases/a solution.

Question 8

What happens to the loading of oxygen when there is more oxygen in the blood?

Answer 8

The more oxygen there is in the blood, the more oxygen is loaded onto haemoglobin, and it becomes more saturated.

Question 9

In the lungs, there is high oxygen partial pressure (concentration). So haemoglobin has a …………. for oxygen.

Answer 9

• Hb has a high affinity for oxygen and so it loads readily
• It is almost fully saturated as the red blood cells pass through the pulmonary capillaries.

Question 10

In the tissue, there is a low partial pressure (concentration) of oxygen. So, Hb has a …….. for oxygen.

Answer 10

• Hb has a low affinity for oxygen and so unloads readily.
• Oxyhaemoglobin starts to break down and unload readily.
• Oxygen is released and is available to tissue cells to be used in aerobic respiration.

Question 11

If there is a high partial pressure of oxygen (concentration), is more or less oxygen loaded onto the Hb?

Answer 11

More

Question 12

If there is a low partial pressure of oxygen (concentration), is more or less oxygen loaded onto the Hb?

Answer 12

Less

Question 13

Explain the cooperative nature of oxygen loading and the S-shaped graph for the oxyhaemoglobin dissociation curve.

Answer 13

• Proteins often change shape when they bind to other substances.
• An oxygen dissociation curve is always an ‘S’ shape and is described as a ‘sigmoid’ curve’.
• The first O2 molecule alters the tertiary structure of the Hb molecule.
• This exposes the 2nd and 3rd binding sites, making it easier for the O2 molecules to bind and load.
• This is referred to as the cooperative nature of oxygen loading.

Question 14

What is the effect of increased respiration on oxygen dissociation?

Answer 14

• Tissue cells respire aerobically, quickly reducing oxygen is the surrounding tissue.
• Reducing the PO2 level lower than normal.
• Oxygenated blood arriving with fully saturated haemoglobin begins to unload more oxygen (become less saturated)
• More oxygen will be released from the haemoglobin to the tissue cells.
• The surrounding PO2 is lower and so haemoglobin will have an even lower affinity to oxygen.

Question 15

Why does haemoglobin have a lower affinity for O2 at higher CO2 levels?

Answer 15

• When CO2 dissolves in the blood it makes the blood acidic, thus lowering the pH.
• As Hb is a protein, a change in pH slightly alters the tertiary structure.
• More oxygen is unloaded from haemoglobin at tissues meaning it becomes less saturated.
• This O2 is unloaded at the tissues so more aerobic respiration can occur.

Question 16

Explain the Bohr shift/effect

Answer 16

• In higher than normal PCO2 levels, haemoglobins’ affinity for oxygen is even lower.
• If PCO2 increases, the saturation of haemoglobin decreases.
• This causes the haemoglobin-oxygen dissociation curve to shift to the right.

Question 17

Explain how haemoglobin is adapted for species that live in environments where the environmental PO2 is lower (lakes, mountains etc.)

Answer 17

• Curve shifts to left
• Higher affinity for O2
• Fully saturated at lower PO2
• Increased loading in lungs at lower PO2
• Similar to human foetal curve.

Question 18

Explain how haemoglobin is adapted for species that have a higher metabolic rate (active animals like cheetahs/small mice with large SA: volume)

Answer 18

• Shifts to right
• Lower affinity for oxygen
• Dissociates from haemoglobin more readily
• Increased unloading at respiring cells/O2 more readily available.

Question 19

The oxygen dissociation curve for a foetus is to the left of its mothers. Explain the advantage of this foetus

Answer 19

• Higher affinity for oxygen so loads more oxygen
• At lower partial pressures
• Oxygen moves from mother to foetus

Question 20

Explain how oxygen is loaded, transported and unloaded in the blood.

Answer 20

• Haemoglobin carries oxygen in red blood cells.
• It has a high affinity for oxygen.
• Loading occurs in the lungs
• At a high PO2
• Unloading releases oxygen to respiring tissues
• At low PO2
• Unloading occurs quicker at higher carbon dioxide concentrations.

Question 21

Binding of one molecule of oxygen to haemoglobin makes it easier for a second oxygen molecule to bind.

Explain why.

Answer 21

1. Binding of first oxygen changes tertiary / quaternary (structure) of haemoglobin; [conformational shift caused]
2. Creates / leads to / uncovers second / another binding site OR Uncovers another iron / Fe / haem group to bind to;

Question 22

Describe and explain the effect of increasing carbon dioxide concentration on the dissociation of oxyhaemoglobin.

Answer 22

1. Increases/more oxygen dissociation/unloading OR Deceases haemoglobin’s affinity for O2;
2. (By) decreasing (blood) pH/increasing acidity;

Question 23

The oxygen dissociation curve of the foetus is to the left of that for its mother. Explain the advantage of this for the foetus.

Answer 23

• Higher affinity / loads more oxygen;
• At low/same/high partial pressure/pO2;
• Oxygen moves from mother/to fetus;

Question 24

The oxygen dissociation curve of the foetus is to the left of that for its mother. Explain the advantage of this for the foetus.

Answer 24

• Higher affinity / loads more oxygen;
• At low/same/high partial pressure/pO2;
• Oxygen moves from mother/to fetus;

Question 24

The oxygen dissociation curve of the foetus is to the left of that for its mother. Explain the advantage of this for the foetus.

Answer 24

• Higher affinity / loads more oxygen;
• At low/same/high partial pressure/pO2;
• Oxygen moves from mother/to fetus;

Question 25

Describe how haemoglobin normally loads oxygen in the lungs and unloads it in a tissue cell.

Answer 25

• Oxygen combines (reversibly) to produce oxyhaemoglobin;
• each haemoglobin molecule/ one haemoglobin may transport 4 molecules of oxygen;
• high partial pressure of oxygen / oxygen tension / concentration in lungs;
• haemoglobin (almost) 95% / 100% saturated;
• unloads at low oxygen tension(in tissues);
• presence of carbon dioxide displaces curve further to right / increases oxygen dissociation;
• allows more O2 to be unloaded;
• increase temp/ acidity allows more O2 to be unloaded;
• low pO2 / increase CO2 / increase term / increase acid occur in vicinity of respiring tissue;