Haemoglobin And Myoglobin

Question 1

What is the difference in the shape of the oxygen binding curves between haemoglobin and myoglobin?

Answer 1

Myoglobin is HYPERBOLIC whereas haemoglobin is SIGMOIDAL

Question 2

Explain the changes that occur to the haemoglobin molecule when oxygen binds

Answer 2

• Binding of O2 causes a conformational change which pulls the Fe atom into the plane of the ring
• Stimulates COOPERATIVE BINDING of subsequent oxygen molecules to other subunits as binding promotes stabilisation of high affinity R state

Question 3

Describe the structure of haemoglobin

Answer 3

• TETRAMER consisting of 2 alpha and 2 beta globulin chains

- Contains 4 HAEM groups, each containing an Fe atom which is capable of binding 1 O2

Question 4

Explain why haemoglobin shows a sigmoidal binding curve for oxygen affinity

Answer 4

• Vinding of first O2 is difficult as HAEM groups are in the low affinity T state
• Binding of oxygen to one subunit makes subsequent binding to other subunits easier as it promotes the stabilisation of the high affinity R state

Question 5

Describe how oxygen affinity of haemoglobin differs at the lungs and tissues

Answer 5

• Al LUNGS there is a high pO2 therefore promotors the stabilisation of the high affinity R state of haemoglobin so O2 binds
• At the tissues there is a low pO2 which promotes stabilisation of the low affinity T state, therefore O2 dissociates from haemoglobin and is released to tissues

Question 6

What is the role of 2,3-bisphosohoglycerate?

Answer 6

• Decreases the affinity of haemoglobin for oxygen at the tissues
• Therefore oxygen is released at the tissues for respiring cells

Question 7

Why do talented train at high altitudes?

Answer 7

• Increases concentration of 2,3-BPG in blood

- Increased 2,3-BPG means haemoglobin has a decreased affinity for oxygen so more oxygen is released at the tissues

Question 8

What effect does the Bohr effect have on the oxygen affinity curve of haemoglobin?

Answer 8

Shifts to the RIGHT

Question 9

Describe the Bohr effect

Answer 9

• Metabolically active tissues produce CO2 and lactate (H+) under aerobic and anaerobic conditions respectively
• Increased concentrations of CO2 and H+ promote the low affinity T state of haemoglobin so affinity for oxygen is decreased at the tissues
• Therefore oxygen is released at the site of most need

Question 10

What are the advantages of the Bohr effect?

Answer 10

Ensures that oxygen delivery is coupled with demand from metabolically active tissues

Question 11

What are the effects of carbon monoxide on oxygen transport?

Answer 11

• Haemoglobin has a 200x greater affinity for CO than O2
• Acts as a competitive inhibitor with O2 for haemoglobin binding site
• Binding of CO promotes stabilisation of the high affinity R state therefore more O2 will be picked up at the lungs but not released at the tissues

Question 12

What is myoglobin?

Answer 12

Single polypeptide molecule present in muscles which can accept 1 O2 from haemoglobin

Question 13

What is the significance of fetal haemoglobin?

Answer 13

• Similar structure to that of haemoglobin (TETRAMER consisting of 2 alpha and 2 gamma chains)
• Has a higher affinity for O2 than haemoglobin so allows TRANSFER OF O2 to fetal blood supply from maternal blood

Question 14

What is meant by ‘thalassaemia’?

Answer 14

IMBALANCE between alpha and beta chains of haemoglobin

Question 15

What is β thalassaemia?

Answer 15

• Decreased or absent beta chain production
• Alpha chains cannot form stable tetramers
• Symptoms appear after birth

Question 16

What is α thalassaemia?

Answer 16

• Decreased or absent alpha chain production
• Beta chains cam form stable tetramers HOWEVER THEY HAVE AN INCREASED AFFINITY FOR O2 SO WILL BIND MORE TIGHTLY
• Symptoms appear before birth

Question 17

How is the binding of oxygen to haemoglobin regulated?

Answer 17

ALLOSTERICALLY

Question 18

Why must O2 be bound to carrier proteins?

Answer 18

NOT VERY POLAR so doesn’t dissolve easily in plasma