Exchange and transport - HAEMOGLOBIN

Question 1

Explain how cooperative binding of oxygen can occur in haemoglobin

Answer 1

Tertiary structure is changed when oxygen binds, making it easier for the second oxygen to bind…

Question 2

How are erythrocytes (RBCs) adapted?

Answer 2

• No nucleus; more haemoglobin can be stored for increased oxygen transportation
• Biconcave shape; increased surface area

Question 3

What is the process by which haemoglobin binds with oxygen called?

Answer 3

Loading or associating

Question 4

What is the process by which haemoglobin releases oxygen called?

Answer 4

Unloading or dissociation

Question 5

What is positive cooperativity?

Answer 5

• Relaxed state
• Haem groups are exposed making it easier for subsequent oxygens to bind

Question 6

Explain the oxygen dissociation curve in 3 stages

Answer 6

1. Initial shallow gradient - shape of haemoglobin makes it difficult for 1st oxygen molecule to bind
2. Steep gradient - Binding of 1st oxygen molecule changed quaternary structure of haemoglobin so the next are easier to bind
3. Flattening of gradient - majority of binding sites full so less likely a 4th oxygen will collide with the 4th empty site.

Question 7

Why doesn’t the haemoglobin unload oxygen before reaching the respiring tissues?

Answer 7

• Walls of veins/arteries are too thick to allow oxygen to escape
• Therefore partial pressure remains the same

Question 8

What is the bohr effect?

Answer 8

• Decrease in pH reduces affinity of haemoglobin for oxygen
• Haemoglobin changes shape
• Curve shifts right

Question 9

A rise in temperature shifts the oxygen dissociation curve to the right. Suggest how this enables an exercising muscle to work more efficiently.

Answer 9

• Dissociation occurs more easily as temperature has altered tertiary structure of haemoglobin
• Reduced affinity for oxygen so it dissociates more readily for muscles (high rate of aerobic respiration)

Question 10

The oxygen dissociation curve of the fetus is to the left of that for its mother. Explain the advantage of this for the fetus. (PPQ 2 marks)

Answer 10

• Fetus has a higher affinity of oxygen
• Therefore oxygen moves from mother to fetus

Question 11

Describe the relationship between the size of mammals and the oxygen dissociation curves of their haemoglobins (PPQ 1 mark)

Answer 11

The larger the mammal, the more to the left the curve is

Question 12

The tissues of the shrew have a higher rate of oxygen consumption per gram of body tissue than the elephant. There is an advantage to the shrew in having haemoglobin with a dissociation curve shifted right. Explain this advantage (PPQ 3 marks)

Answer 12

• Shrew haemoglobin is less saturated with oxygen
• Oxyhaemoglobin dissociates more readily
• Oxygen more readily released
• Allowing greater demand/respiration rate