The transport of oxygen in living organisms

Question 1

Describe the structure and role of haemoglobin

Answer 1

Globular + water soluble, present in RBC’s
4 polypeptide chains (quaternary structure) , each has iron haem group which combines with oxygen
Role: oxygen binds to haem groups + are carried around body to respiring tissues

Question 2

Name the 3 factors that affect oxygen-haemoglobin binding

Answer 2

-Partial pressure of oxygen (PO2)
-Partial pressure of carbon dioxide (PCO2)
-Saturation of haemoglobin with
oxygen
High affinity: takes up oxygen more easily but releases it less easily
Low affinity: takes up oxygen less easily but releases it more easily
RIGHT- RELEASES MORE, low affinity
LEFT-LOADS MORE, high affinity

Question 3

How does partial pressure of oxygen affect oxygen-haemoglobin binding?

Answer 3

As PO2 increases, affinity for O2 also increases so O2 binds tightly to haemoglobin
Low partial pressure- O2 is released

Question 4

How does saturation of haemoglobin with oxygen affect oxygen-haemoglobin binding?

Answer 4

Hard for first O2 to bind as polypeptides are closely united. Once it binds it changes shape so easier for 2nd and 3rd to bind (positive cooperativity). Then slightly harder for 4th molecule to bind as low chance of finding binding site.

Question 5

How does partial pressure of carbon dioxide affect oxygen-haemoglobin binding?

Answer 5

As PCO2 increases, conditions become acidic causing haemoglobin to change shape. Affinity decreases so O2 is released (advantage as unloaded at respiring tissues) - BOHR EFFECT
-Low PCO2 curve shifts left, increases affinity, uploads more O2
-High PCO2 curve shifts right, decreases affinity, unloads more O2

Question 6

Explain why oxygen binds to haemoglobin in the lungs

Answer 6

PO2 is high
There is a low conc of CO2 in lungs so affinity is high
positive cooperativity

Question 7

Explain why oxygen is released from haemoglobin in respiring tissues

Answer 7

PO2 is low
High conc of CO2 in respiring tissues so affinity is low

Question 8

What do oxyhaemoglobin dissociation curves show?

Answer 8

Saturation of haemoglobin with O2 plotted against partial pressure of O2 (kPa). Curves further to left show haemoglobin has higher affinity for O2