Haemoglobin structure and function Flashcards
What is the structure of haemoglobin? [3 marks]
- Globular haemoglobin
- Contains haem as a prosthetic group
- Haem is a complex of protoporphyrin IX and Fe2+
How does iron fit into haem? [1 mark]
It is held in the centre of the haem molecule by coordinate bonds to 4 nitrogens in a porphyrin ring.
Does haem and globin synthesis occur in the same place? [1 mark]
NO - they occur separately
Where is haemoglobin synthesised? [2 marks]
- 65% in erythroblasts
- 35% in reticulocytes
What happens in kidneys in hypoxia? [2 marks]
- Kidneys increase production of erythropoietin.
- This increases erythrocytes and haemoglobin synthesis.
Where is haem synthesised? [1 mark]
In mitochondria
How haem synthesised? [3 marks]
- Transferrin carries iron to the transferrin receptor of a reticulocyte.
- Protoporpyrins are synthesised (mediated by EPO and vit. B6)
- Protoporphyrin + iron = haem
What is the rate limiting enzyme in haem synthesis? [1 mark]
Ala-synthase
Where does globin synthesis occur? [1 mark]
Polyribosomes
What is thalassaemia caused by? [1 mark]
Reduced rate of synthesis of normal α or β chain.
Which chromosome are the B-cluster (β, γ, δ and ε globin) genes found in? [1 mark]
Chromosome 11 (in its short arm)
Which chromosome are the Α-cluster (α and ζ globin) genes found in? [1 mark]
Chromosome 16 (in its short arm)
What are the forms of embryonic haemoglobin? [3 marks]
- Gower I (ζ2ε2)
- Gower II (α2ε2)
- Portland (ζ2γ2)
What is foetal haemoglobin? [1 mark]
α2γ2
What are the forms of adult haemoglobin? [3 marks]
- HbA (α2β2): makes up 96-98% of blood
- HbA2 (α2δ2): makes up 1.5-3.2% of blood
- HbF (α2γ2): makes up 0.5-0.8% of gene
What are the functions of haemoglobin? [3 marks]
- Carrying oxygen from lungs to tissue
- Removing CO2
- Buffering action, maintains pH by changing from oxyhaemoglobin to deoxyhaemoglobin
How many molecules of oxygen can haemoglobin bind to? [1 mark]
4
What happens to 2,3-diphosphoglycerate (2,3-DPG) when haemoglobin is oxygenated? {2 marks]
- 2,3-DPG gets pushed out.
- β-chains move closer
What happens to 2,3-diphosphoglycerate (2,3-DPG) when haemoglobin is deoxygenated? [3 marks]
- β-chains get pulled apart
- 2,3-DPG enters
- There’s a lower affinity of haemoglobin to oxygen
What happens if there’s more 2,3-DPG in the red blood cell? [1 mark]
More oxygen is released from the red blood cell to tissues
What does the amount of oxygen bound to haemoglobin and released depend on? [3 marks]
- PO2
- PCO2
- Affinity of haemoglobin for O2
What is oxygen affinity and what does it determine? [2 marks]
- The ease with which haemoglobin binds and releases oxygen
- It determines the proportion of O2 released to the tissues or loaded onto the cells at a given oxygen pressure
What is the Bohr effect? [3 marks]
- When there’s an increase in CO2 production and drop in blood pH.
- Results in dissociation curve shifting to the right
- O2 is released from haemoglobin
What is P50? [1 mark]
The partial pressure of oxygen where Hb is 50% saturated.
How does P50 affect haemoglobin’s affinity to oxygen? [2 marks]
LOW: increased affinity to O2
HIGH: decreased affinity to O2
What does the normal position of the dissociation curve depend on? [4 marks]
- Concentration of 2,3-DPG
- Blood pH
- CO2 in red blood cells
- Structure of haemoglobin
What are the standard conditions? [3 marks]
- Temperature: 37 degrees Celsius
- pH: 7.4
- Base excess: 0
What is base excess? [1 mark]
The amount of H+ required to keep blood pH at 7.4
