Haemoglobin And Myoglobin

Question 1

Oxygen binding in myoglobin

Answer 1

Shows a hyperbolic dependence on oxygen concentration

Question 2

Haemoglobin structure

- binds to 4O2 molecules

Answer 2

2 alpha and 2 beta polypeptide chains in a tetramer
Each chain contains the haem prosthetic group
Oxygen binding to on subunit causes a conformational change in the other subunits from low affinity T state to high affinity R state

Question 3

Oxygen binding in Haemoglobin

Answer 3

binding of 1 O2 increases the affinity of the other subunits to oxygen - cooperative binding gives a sigmoidal curve (T-R state)
This means O2 can efficiency be carried from the lungs to the tissues

Question 4

2,3-Bisphosphoglycerate

2,3-BPG

Answer 4

1 BPG per tetramer
Decreases the affinity for O2
BPG concentration increases at high altitudes - promotes the release of O2 at the tissues

Question 5

The BOHR effect

Answer 5

H+ and CO2 can bind to Hb - lowers the affinity of Hb for oxygen (curve shifts to the right)
Metabolically active tissues produce large amounts of H+ and CO2 - ensures delivery of O2 is coupled to demand

Question 6

Carbon Monoxide Poisoning

CO

Answer 6

Binds to Hb 250x more readily than O2 does
Increases the affinity for oxygen of the subunits it is not bound to - oxygen is not released at tissues
Irreversible binding - fatal if >50% of the subunits are bound to CO

Question 7

Foetal Haemoglobin

HbF

Answer 7

Has a higher binding affinity for O2 than HbA - allows the transfer of O2 into the foetal blood supply from the mother

Question 8

Myoglobin Structure

- binds to 1O2 molecule

Answer 8

153aa
75% alpha helical
Oxygen binding causes movement of Fe into the plane of the ring - small change in overall protein conformation

Question 9

Sickle cell anaemia

HbS

Answer 9

Mutation of Glutamate to Valine in beta globin
Hydrophilic aa to hydrophobic aa - they clump together
More prone to lyse - anaemia
More rigid - block microvascular

Question 10

Thalassaemias

Imbalance between number of alpha and beta chains

Answer 10

Beta thalassaemia - only has alpha chains - symptoms appear after birth (6 months when gamma chains supposed to change to beta chains) unable to form stable tetramers

Alpha thalassaemia - only has beta chains, onset before birth (severity depends on number of alpha chains) beta chains can form stable tetramers with and increased affinity for oxygen