12.11 Haemoglobin Flashcards
What structure does the protein Haemoglobin have?
- Quaternary structure
- Composed of four subunits each containing a haem group
- Complete the sentence: Haemoglobin has an ……… to oxygen.
Affinity
How many oxygen molecules does each haemoglobin combine with?
4
How does oxygen dissociate at respiring cells and tissues?
Haemoglobin must readily associate with oxygen at the gas exchange surface (lungs) and dissociate (unload) oxygen at respiring cells/tissues.
What is the equation for the uptake of oxygen by haemoglobin?
- Haemoglobin + Oxygen<–> Oxyhaemoglobin
- Hb + 4O2<–>HbO8
Give the formula for calculating the percentage saturation of haemoglobin with oxygen.
Percentage saturation of haemoglobin with oxygen= (oxygenated haemoglobin )/(maximum saturation) x100
What is the definition of partial pressure of oxygen (pO2/kPa)
Amount of oxygen in a mixture of gases/a solution.
What happens to the loading of oxygen when there is more oxygen in the blood?
The more oxygen there is in the blood, the more oxygen is loaded onto haemoglobin, and it becomes more saturated.
In the lungs, there is high oxygen partial pressure (concentration). So haemoglobin has a …………. for oxygen.
- 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.
In the tissue, there is a low partial pressure (concentration) of oxygen. So, Hb has a …….. for oxygen.
- 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.
If there is a high partial pressure of oxygen (concentration), is more or less oxygen loaded onto the Hb?
More
If there is a low partial pressure of oxygen (concentration), is more or less oxygen loaded onto the Hb?
Less
Explain the cooperative nature of oxygen loading and the S-shaped graph for the oxyhaemoglobin dissociation curve.
- 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.
What is the effect of increased respiration on oxygen dissociation?
- 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.
Why does haemoglobin have a lower affinity for O2 at higher CO2 levels?
- 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.
Explain the Bohr shift/effect
- 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.
Explain how haemoglobin is adapted for species that live in environments where the environmental PO2 is lower (lakes, mountains etc.)
- 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.
Explain how haemoglobin is adapted for species that have a higher metabolic rate (active animals like cheetahs/small mice with large SA: volume)
- Shifts to right
- Lower affinity for oxygen
- Dissociates from haemoglobin more readily
- Increased unloading at respiring cells/O2 more readily available.
The oxygen dissociation curve for a foetus is to the left of its mothers. Explain the advantage of this foetus
- Higher affinity for oxygen so loads more oxygen
- At lower partial pressures
- Oxygen moves from mother to foetus
Explain how oxygen is loaded, transported and unloaded in the blood.
- 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.
Binding of one molecule of oxygen to haemoglobin makes it easier for a second oxygen molecule to bind.
Explain why.
- Binding of first oxygen changes tertiary / quaternary (structure) of haemoglobin; [conformational shift caused]
- Creates / leads to / uncovers second / another binding site OR Uncovers another iron / Fe / haem group to bind to;
Describe and explain the effect of increasing carbon dioxide concentration on the dissociation of oxyhaemoglobin.
- Increases/more oxygen dissociation/unloading OR Deceases haemoglobin’s affinity for O2;
- (By) decreasing (blood) pH/increasing acidity;
The oxygen dissociation curve of the foetus is to the left of that for its mother. Explain the advantage of this for the foetus.
- Higher affinity / loads more oxygen;
- At low/same/high partial pressure/pO2;
- Oxygen moves from mother/to fetus;
The oxygen dissociation curve of the foetus is to the left of that for its mother. Explain the advantage of this for the foetus.
- Higher affinity / loads more oxygen;
- At low/same/high partial pressure/pO2;
- Oxygen moves from mother/to fetus;
The oxygen dissociation curve of the foetus is to the left of that for its mother. Explain the advantage of this for the foetus.
- Higher affinity / loads more oxygen;
- At low/same/high partial pressure/pO2;
- Oxygen moves from mother/to fetus;
Describe how haemoglobin normally loads oxygen in the lungs and unloads it in a tissue cell.
- 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;
