Gas transport - oxygen

Question 1

Describe the structure of haem.

Answer 1

A porphyrin ring with an iron (Fe2+) ion at its centre

Question 2

Which elements are present in the porphyrin ring of haem?

Answer 2

Carbon
Hydrogen
Nitrogen

Question 3

What colour is haem when it is saturated with oxygen?

Answer 3

Red

Question 4

What colour is haem when it is not saturated with oxygen?

Answer 4

Purple

Question 5

Describe the structure of haemoglobin.

Answer 5

A tetramer – consisting of 2 alpha and 2 beta globin polypeptide chains

Question 6

Each subunit of haemoglobin contains what?

Answer 6

A haem group

Question 7

What are the 2 main conformations that haemoglobin exists in?

Answer 7

Relaxed and tense

Question 8

How does the binding of oxygen change haemoglobins conformation state and how does this affect oxygen affinity?

Answer 8

Binding of oxygen causes haemoglobin to shift from the tense state to the relaxed state, increasing oxygen affinity and allowing for efficient loading of oxygen in the lungs

Question 9

What relationship does the oxygen dissociation curve describe?

Answer 9

The relationship between the partial pressure of oxygen in the blood and the amount of oxygen bound to haemoglobin

Question 10

When haemoglobin becomes saturated, what is the amount of oxygen bound then dependent on?

Answer 10

How much haemoglobin is available

Question 11

When considering oxygen saturation, it’s important to remember that it is independent of what?

Answer 11

Haemoglobin concentration

Question 12

Describe the meaning behind the S-shape of the oxygen dissociation curve.

Answer 12

Due to cooperative binding – as one molecule of O2 binds to haemoglobin, haemoglobin’s affinity for oxygen increases, making it easier for subsequent oxygen molecules to bind. This cooperative effect leads to a steep rise in the curve after the initial binding of O2 and then a plateau as haemoglobin becomes fully saturated

Question 13

Describe why there needs to be the right balance of partial pressure of oxygen in the tissues (extracellular).

Answer 13

It needs to be low enough to promote oxygen offloading by haemoglobin but high enough to maintain an oxygen gradient between the tissues (extracellular) and cells so that diffusion into cells is not compromised

Question 14

Which kind of tissues can tolerate greater falls in tissue oxygen partial pressure and why?

Answer 14

Tissues with high capillary density because diffusion is occurring across a shorter distance and higher surface area

Question 15

Describe the affinity of haemoglobin for oxygen as the oxygen dissociation curve shifts left and right.

Answer 15

Right shift – decreased affinity

Left shift – increased affinity

Question 16

List 4 things which shifts the oxygen dissociation curve to the right.

Answer 16

Increased temperature

Increased partial pressure of carbon dioxide

Decreased pH (increased acidity)

Increased 2,3-DPG

Question 17

List 4 things which shifts the oxygen dissociation curve to the left.

Answer 17

Decreased temperature

Decreased partial pressure of carbon dioxide

Increased pH

Decreased 2,3-DPG

Question 18

Which kind of tissues will have acidic / low pH conditions?

Answer 18

Metabolising tissues

Question 19

Describe when 2,3 diphosphoglycerate is produced, how it affects haemoglobins affinity for oxygen and how it does this.

Answer 19

2,3-DPG is produced by red blood cells in response to hypoxia. It decreases haemoglobins affinity for oxygen, therefore facilitating offloading, and it does this by stabilising its tense state

Question 20

What is the Bohr effect?

Answer 20

Haemoglobins affinity for oxygen decreases in response to lower pH and higher concentrations of carbon dioxide

Question 21

In regards to the Bohr effect, how does low pH and higher concentrations of carbon dioxide decrease haemoglobins affinity for oxygen?

Answer 21

The binding of hydrogen ions and carbon dioxide stabilises haemoglobin in the tense state

Question 22

How does increasing tissue metabolism affect tissue pH?

Answer 22

Tissue pH decreases progressively with increasing metabolism due to increased production of lactic acid and carbon dioxide