Gas transport (O2)

Question 1

How many ATP molecules does each glucose molecule produce in the presence of oxygen (aerobic)?

Answer 1

36-38

Question 2

How many ATP molecules does each glucose molecule produce in the absence of oxygen (anaerobic)?

Answer 2

2

Question 3

What is the oxygen cascade?

Answer 3

The oxygen cascade describes the transfer of oxygen from air to mitochondria. In each step of the cascade the PaO2 falls. It demonstrates that oxygen delivery to tissues relies on the passive transfer of gas down partial pressure gradients.

Question 4

What is a typical resting oxygen consumption?

Answer 4

250ml/min

Question 5

Describe the structure of heam

Answer 5

Haem is a porphyrin compound coordinated to a single iron ion. Iron is in its ferrous form (Fe2+).

Question 6

Describe the structure of haemoglobin

Answer 6

A tetramer - 2 alpha and 2 beta globin polypeptide chains

Haemoglobin A - main adult form

Each coiled polypeptide chain has one haem group attached

Overall molecule has a complex quaternary structure

Structure influenced by various factors and its modification alters the oxygen affinity of the molecule – cooperative binding.

Question 7

Compare the differences between relaxed and tense haemoglobin

Answer 7

Relaxed haemoglobin has a much higher oxygen affinity – an open and receptive conformation allows oxygen access to haem groups

Tense haemoglobin has a conformation that inhibits oxygen binding and thus binds oxygen ~500 times less strongly than in the relaxed state

These conformations are influenced by the environment (surrounds pO2), binding of oxygen and binding of other molecules

Question 8

What is meant by cooperatively between the oxygen binding sites in haemoglobin?

Answer 8

As haemoglobin binds oxygen to one haem group, the conformation of the whole tetramer changes and becomes more open

This change in conformation makes binding the next oxygen molecule much easier – there is cooperativity between the oxygen binding sites

Binding becomes progressively easier as more oxygen molecules are bound

Question 9

Describe why the dissociation curve of oxygen has its shape

Answer 9

Initially the curve of oxygen binding as pO2 increases is shallow

Binding changes conformation, increases oxygen affinity and facilitates further binding

The curve steepens rapidly as pO2 rises until saturation where it levels out

These changes in affinity with binding create a sigmoid dissociation curve

Question 10

At what pO2 does the dissociation curve reach a plateau?

Answer 10

~8kPa and is ~90% saturated

Question 11

What is the oxygen saturation (%) of haemoglobin below 1kPa?

Answer 11

Virtually unsaturated

Question 12

At what pO2 is haemoglobin half saturated (50%)?

Answer 12

~3.5 kPa

Question 13

What is alveolar pO2 and what does this mean?

Answer 13

Alveolar pO2 is 13.3.kPa and therefore haemoglobin is almost fully saturated at ~95%

Question 14

*What is the typical oxygen concentration for fully saturated haemoglobin?

Answer 14

~200ml/L

So or calculations, you would multiply change in oxygen saturation x 200

Amount of oxygen delivered per litre of blood = (change in oxygen saturation as a decimal) x 200

Question 15

What is the typical pO2 of tissues at rest?

Answer 15

~6kPa and haemoglobin is not ~65% saturated

Question 16

What factors cause the dissociation curve to shift to the right?

Answer 16

Acidity, increased temperature, increased CO2 and increased 2,3-DPG cause a shift to the right and thus decrease oxygen affinity

Major shift occurs at tissues favouring oxygen being offloaded where it is needed

2,3 diphosphoglycerate (2,3-DPG) levels increase in red blood cells in response to hypoxia – stabilises tense state

Question 17

What is the Bohr effect?

Answer 17

This refers to the fact that in acid conditions the oxygen dissociation curve shifts along the pO2 axis

This is due to hydrogen ion and carbon dioxide binding which both stabilise haemoglobin in the tense state

Result is that at any given pO2 haemoglobin binds less oxygen

Oxygen is thus released more easily in the tissues where the pH is more acidic and CO2 in higher concentration

Question 18

What is the Haldane effect?

Answer 18

Conversely to the Bohr effect….

Increasing oxygen binding to haemoglobin (in lungs) reduces the affinity for carbon dioxide and hydrogen ions by modifying the haemoglobin conformation

This is effective at the level of the pulmonary capillaries and results in more CO2 being offloaded at the lungs

Question 19

What are some adaptations to chronic hypoxia?

Answer 19

1) Increased erythropoietin (EPO) production
2) Increased tissue capillary density
3) Increased 2,3-DPG levels
4) Increased ventilation