Haemoglobin and oxygen

Question 1

What does partial pressure of oxygen mean? What are the units?

Answer 1

concentration of oxygen, measured in kPa

Question 2

Where can low and high partial pressures of oxygen be found?

Answer 2

low: respiring tissues
high: lungs

Question 3

What is haemoglobin?

Answer 3

a pigment in the blood of mammals which helps transport respiratory gases

Question 4

Describe the quaternary structure of haemoglobin

Answer 4

-has 4 haem groups in each molecule
-oxygen binds with the atom of Fe2+ in each haem group

Question 5

Why is it important that oxygen dissociates from haemoglobin at tissues?

Answer 5

-oxygen must dissociate and diffuse to respiring cells down concentration gradient, as oxygen is being used up by these tissues

Question 6

Why is it important that oxygen associates in the lungs?

Answer 6

-more oxygen can associate with haemoglobin and be transported

Question 7

How does oxygen move into the erythrocyte?

Answer 7

-oxygen diffuses into blood plasma and then into the RBC, down a concentration gradient
-binds to ‘haem’ Fe2+ group of haemoglobin to maintain the concentration gradient and form oxyhaemoglobin

Question 8

How is oxygen transported to tissues?

Answer 8

oxygen dissociates from oxyhaemoglobin at respiring tissues and diffuses out of the RBC

Question 9

What is on the X and Y axis of the oxygen dissociation curve?

Answer 9

X: partial pressure of oxygen (kPa)
Y: % saturation of haemoglobin

Question 10

How would you describe the curve?

Answer 10

-S shaped curve (sigmoidal)
-X is not directly proportional to Y
-does not reach 100% as this is very difficult to achieve

Question 11

Why does the curve have an initially low gradient?

Answer 11

conformational changes have not yet happened as the 1st oxygen molecule has not associated with the haemoglobin

Question 12

What happens after the 1st oxygen molecule associates?

Answer 12

-conformation of the Hb molecule changes which makes it easier for the 2nd and 3rd O2 molecules to associate,

Question 13

How is this seen on the graph?

Answer 13

-curve is steeper as saturation of Hb quickly increases, and so does oxygen partial pressure

Question 14

What happens with the 4th oxygen molecule?

Answer 14

Hb molecule becomes full as there are only 4 haem groups, so 4th oxygen struggles to associate and curve plateaus below 100%

Question 15

Why is it a benefit to respiring tissue that at low partial pressures of oxygen, there is low saturation of haemoglobin?

Answer 15

-haemoglobin can become more saturated and will do so due to the diffusion gradient
-oxygen binds in order to supply the respiring tissue

Question 16

Describe and explain the affinity of foetal haemoglobin compared to maternal haemoglobin

Answer 16

-fetal HB needs a stronger affinity for oxygen so that maternal Hb with dissociate

Question 17

Why must the foetal curve be to the left of the maternal curve?

Answer 17

-placenta has a low pO2
-foetal Hb has higher affinity for O2 (lower pO2 can saturate same % of Hb)
-maternal Hb will dissociate its O2 and follow stronger affinity to foetus

Question 18

Why is it an advantage that the maternal curve is sigmoid?

Answer 18

-low pO2 in respiring tissue so O2 can dissociate
-high pO2 in the lungs so O2 associates with Hb

Question 19

How do you know where to draw the dissociation curve for different organisms?

Answer 19

shifts to the left if there’s a struggle for oxygen-organism must have a high affinity for oxygen under low partial pressures