haemoglobin Flashcards
(14 cards)
What is the structure of haemoglobin? (3)
Haemoglobin is a water-soluble, globular protein
It consists of two alpha and two beta polypeptide chains, each with a haem group containing Fe²⁺
Each haemoglobin molecule can bind up to 4 oxygen molecules
How does oxygen bind to haemoglobin? (2)
In the lungs, oxygen binds to the iron in haemoglobin to form oxyhaemoglobin
This is a reversible reaction:
Hb + O₂ ⇌ HbO₈
How does partial pressure affect haemoglobin’s affinity for oxygen? (2)
As partial pressure of oxygen (ppO₂) increases, haemoglobin’s affinity for oxygen increases, and it binds more oxygen tightly
As ppO₂ decreases, haemoglobin’s affinity for oxygen decreases, and it releases oxygen
Where does oxygen loading and unloading occur in the body? (2)
Loading: In the lungs, where partial pressure of oxygen is high, oxygen binds to haemoglobin
Unloading: In respiring tissues, where ppO₂ is low, oxygen is released
What does the haemoglobin dissociation curve show? (3)
It shows how haemoglobin saturation changes with partial pressure of oxygen
At high ppO₂, haemoglobin is highly saturated, and at low ppO₂, it is less saturated
The curve is S-shaped due to the ease of oxygen binding after the first molecule binds
What is the Bohr effect? (2)
- When CO₂ levels increase (and pH decreases), the dissociation curve shifts to the right
- More oxygen is released because haemoglobin has a lower saturation and releases oxygen more readily in respiring tissues
How is carbon dioxide transported in the blood? (2)
- Most CO₂ diffuses into red blood cells and reacts with water to form carbonic acid, catalysed by carbonic anhydrase
- Some CO₂ binds directly to haemoglobin and is carried to the lungs
What happens to carbonic acid in red blood cells? (3)
- Carbonic acid dissociates into hydrogen ions (H⁺) and hydrogencarbonate ions (HCO₃⁻)
- The H⁺ ions cause oxyhaemoglobin to unload oxygen, and haemoglobin takes up H⁺ ions
- To form haemoglobinic acid, preventing pH changes
What is the chloride shift? (2)
To maintain the charge balance when HCO₃⁻ ions leave the red blood cells;- Cl⁻ ions diffuse into the red blood cells
What happens to carbon dioxide when blood reaches the lungs? (2)
In the lungs, H⁺ and HCO₃⁻ ions recombine to form CO₂ and water
The CO₂ diffuses into the alveoli and is exhaled
How is the oxygen dissociation curve for fetal haemoglobin different from adult haemoglobin? (2)
Shifted to the left
How does the fetus receive oxygen from the mother’s blood? (1)
Across the placenta
Why does fetal haemoglobin need a higher affinity for oxygen? (4)
By the time the mother’s blood reaches the placenta
Its oxygen saturation has decreased because her cells have used some oxygen
Fetal haemoglobin must have a higher affinity for oxygen
To absorb enough oxygen at the lower partial pressures, ensuring the fetus survives
What would happen if fetal haemoglobin had the same affinity for oxygen as adult haemoglobin? (2)
The fetus’s blood wouldn’t be saturated enough with oxygen
The fetus might not survive
