Variations of Haemoglobin (PK6)

Question 1

Components of adult Hb

Answer 1

• 98% HbA (2 alpha + 2 beta chains)
• 2% HbA2 (2 alpha + 2 delta chains)

Question 2

Components of foetal Hb

Answer 2

2 alpha chains + 2 gamma chains

Question 3

Why is foetal Hb necessary for foetuses?

Answer 3

• Slightly less affinity for O2 than HbA but considerably less affinity for 2,3-DPG
  > Curve shifted left of HbA
• Overall foetal Hb has higher affinity for O2 than HbA, so can take O2 from maternal blood

Question 4

Other variants of Hb

Answer 4

• Haemoglobin S
• Methemoglobinaemia
• Myoglobin

Question 5

Components of haemoglobin S

Answer 5

2 alpha chains + 2 beta* chains

Question 6

What does haemoglobin S cause and how?

Answer 6

• Sickle cell anaemia
• Crystalised out in low PO2/pH to form rod-shape which distorts shape of RBCs (sickling)
  > Shifts curve to the right

Question 7

Why is methemoglobinaemia bad?

Answer 7

• Contains Fe3+ instead of usual Fe2+
• Cannot bind or transport O2

Question 8

What is myoglobin?

Answer 8

O2 store in muscle used at onset of exercise

Question 9

How does myoglobin differ from normal Hb?

Answer 9

• Only 1 haem group
• Hyperbolic rather than sigmoidal curve
• Curve to left of Hb
• No Bohr effect

Question 10

What is the P50 value of myoglobin and why is this significant?

Answer 10

• 1kPa
• 100% saturated at 2.5kPa