[7.2] transport of oxygen by haemoglobin

Question 1

what does cooperative binding explain?

Answer 1

the oxygen dissociation curve ie. the graph of the relationship between the saturation of haemoglobin with oxygen and the partial pressure of oxygen

Question 2

describe the shape of the oxygen dissociation graph

Answer 2

• x-axis is partial pressure of oxygen (kPa) ie. concentration
• y-axis is % saturation of haemoglobin ie. how much oxygen haemoglobin is carrying, going from 0-100%
• s-shaped curve which starts at 0 and levels off close to 100% saturation

Question 3

what happens to the affinity further to the left of the curve?

Answer 3

• greater affinity of haemoglobin for oxygen
• therefore, loads oxygen readily but unloads it less easily

Question 4

what happens to the affinity further to the right of the curve?

Answer 4

• lower affinity of haemoglobin for oxygen
• release oxygen more readily and at higher partial pressure of oxygen than previously
• therefore, more oxygen is supplied to respiring muscles to maintain aerobic respiration

Question 5

what causes the bohr shift?

Answer 5

• curve shifts to the right when intense respiration in respiring muscles produces a lot of carbon dioxide
• this dissolves in water in the plasma of the blood, which produces carbonic acid
• carbonic acid lowers the pH of the surroundings so the tertiary structure of the protein (hgb) changes and it loses its function

Question 6

what is the effect of carbon dioxide concentration at the gas-exchange surface (eg. lungs)?

Answer 6

• low carbon dioxide concentration because it diffuses across the exchange surface and is excreted from the organism
• increased affinity of haemoglobin for oxygen and high concentration of oxygen in the lungs means oxygen is readily loaded by haemoglobin
• reduction in carbon dioxide concentration shifts oxygen dissociation curve to the left

Question 7

what is the effect of carbon dioxide concentration in rapidly respiring tissues (eg. muscles)?

Answer 7

• high carbon dioxide concentration since it is released during aerobic respiration
• decreased affinity of haemoglobin for oxygen and low concentration of oxygen in the lungs means oxygen is readily unloaded from haemoglobin into the muscle cells
• increase in carbon dioxide concentration shifts oxygen dissociation curve to the right

Question 8

process which explains why the more active a tissue, the more oxygen is unloaded

Answer 8

1. higher rate of respiration
2. more carbon dioxide is produced by tissues
3. lower pH
4. greater haemoglobin shape change
5. oxygen is unloaded more readily
6. more oxygen is available for respiration

Question 9

which animals would have a curve which is shifted to the left and why?

Answer 9

• animals living at high altitude
• animals that live in water with a low oxygen content

> need to hold onto whatever oxygen is available and use it only when necessary

• human foetal haemoglobin

> good at taking oxygen from maternal hgb

Question 10

which animals would have a curve which is shifted to the right and why?

Answer 10

• small animals
• animals that have a high metabolic rate

> higher SA:V ratio so loses heat more easily so high metabolic rate is needed to replace that lost heat

> oxygen is released more readily to give to tissues as easily as possible to increase rate of respiration, so hgb has lower affinity for oxygen

Question 11

what would the curve for myoglobin look like?

Answer 11

• shifted to the left but very extreme, only letting go when there is almost 0 kPa of oxygen
• this is because myoglobin is found in muscles and is used as an emergency store of oxygen
• this means it holds onto oxygen for a long time then suddenly drops it to the muscle

> myoglobin has higher affinity for oxygen and therefore releases it less readily