Haemoglobin

Question 1

What does affinity mean

Answer 1

Chemical attraction

Question 2

Structure of haemoglobin

Answer 2

Complex protein with a quaternary structure
Compose of 4 subunits each containing a haem group

Question 3

Each haemoglobin molecule can attach to how many oxygens

Answer 3

4

Question 4

To be efficient at transporting oxygen, haemoglobin must….

Answer 4

…readily associate with oxygen at the lungs and dissociate oxygen at the respiring tissues

Question 5

What does saturation mean

Answer 5

How many oxygen are bound to haemoglobin

Question 6

Give the formula for calculating the percentage saturation of haemoglobin with oxygen

Answer 6

Percentage saturation
Of haemoglobin with oxygen =

oxygenated haemoglobin
—————————————— X100
Maximum saturation

Question 7

What is cooperative oxygen loading

Answer 7

First O2 changes tertiary structure of Hb molecule. It exposes the 2nd, 3rd O2 binding sites. Making it easier for 2nd, 3rd O2 molecules to bind/load.

Question 8

Define partial pressure

Answer 8

The amount of oxygen in a mixture of gases or a solution

Question 9

Lower pO2 means….

Answer 9

Less haemoglobin is saturated

Question 10

Shape of an oxygen dissociation curve

Answer 10

‘S’ shaped
Describes as sigmoid curve

Question 11

The effect of increased respiration on oxygen dissociation

Answer 11

Tissue cells respire aerobically so O2 is reduced rapidly
Reduces the pO2 to a level lower than normal
Oxygenated blood arriving with fully saturated haemoglobin will begin to unload more oxygen and more oxygen will be released from the haemoglobin to the tissue cells
Hb will have even lower affinity to oxygen

Question 12

Effect of carbon dioxide concentration - Bohr shift

Answer 12

Higher than usual pCO2, Hb’s affinity for oxygen is even lower
If pCO2 increases the saturation of haemoglobin decreases
This causes the ODC to move to the right

Question 13

Describe how haemoglobin normally loads oxygen in the lungs and unloads it in a tissue cell.

Answer 13

• Oxygen combines (reversibly) to produce oxyhaemoglobin;
• each haemoglobin molecule/ one haemoglobin may transport 4 molecules of oxygen;
• high partial pressure of oxygen / oxygen tension / concentration in lungs;
• haemoglobin (almost) 95% / 100% saturated;
• unloads at low oxygen tension(in tissues);
• presence of carbon dioxide displaces curve further to right / increases oxygen dissociation;
• allows more O2 to be unloaded;
• increase temp/ acidity allows more O2 to be unloaded;
• low pO2 / increase CO2 / increase term / increase acid occur in vicinity of respiring tissue;

Question 14

Explain how oxygen in a red blood cell is made available for respiration in active tissues.

Answer 14

• CO2 (increased) respiration;
• (increased) dissociation oxygen from haemoglobin;
• Low partial pressure in tissues/plasma;
• Oxygen diffuses from r.b.c. to tissues;

Question 15

The oxygen dissociation curve of the foetus is to the left of that for its mother. Explain the advantage of this for the foetus.

Answer 15

• Higher affinity / loads more oxygen;
• At low/same/high partial pressure/pO2;
• Oxygen moves from mother/to fetus;

Question 16

Explain how oxygen is loaded, transported and unloaded in the blood. (6)

Answer 16

• Haemoglobin carries oxygen / has a high affinity for oxygen / oxyhaemoglobin;
• In red blood cells;
• Loading/uptake/association in lungs at high p.O2;
• Unloads/ dissociates / releases to respiring cells/tissues at low p.O2;
• Unloading linked to higher carbon dioxide (concentration);

Question 17

Binding of one molecule of oxygen to haemoglobin makes it easier for a second oxygen molecule to bind.

Explain why.

Answer 17

1. Binding of first oxygen changes tertiary / quaternary (structure) of haemoglobin; [conformational shift caused]
2. Creates / leads to / uncovers second / another binding site OR Uncovers another iron / Fe / haem group to bind to;

Question 18

Describe and explain the effect of increasing carbon dioxide concentration on the dissociation of oxyhaemoglobin.

Answer 18

1. Increases/more oxygen dissociation/unloading OR Deceases haemoglobin’s affinity for O2;
2. (By) decreasing (blood) pH/increasing acidity;

Question 19

Explain a property of iron ions that enables these ions to carry out their role in red blood cellls

Answer 19

Is charged/polar or is part of haemoglobin

So binds with oxygen