Haemoglobin

Question 1

Haemoglobin is a complex protein with a quaternary structure (4°), composed of four polypeptide subunits, each containing a haem group. Haemoglobin has an affinity to oxygen

Question 2

Each haem (Fe2+) group can combine with one molecule of oxygen; Therefore, each haemoglobin molecule can combine with four oxygen molecules (O2).

Question 3

To be efficient at transporting oxygen, haemoglobin MUST readily associate (load) with oxygen at the gas exchange surface (e.g. lungs) and dissociate (unload) oxygen at the respiring cells / tissues.

Question 4

When oxygen combines with haemoglobin, it forms oxyhaemoglobin.

Question 5

The amount of oxygen combined is described in terms of the percentage saturation of the haemoglobin.

Question 6

% saturation does not always apply to just one haemoglobin molecule; it is the combination of many. Therefore, % saturation is not always a multiple of 25

Question 7

Partial pressure of Oxygen (pO2 / kPa):

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

Question 8

The more oxygen there is in the blood, the more the oxygen is LOADED onto haemoglobin. The haemoglobin becomes more saturated.

Question 9

Loading / association: When oxygen is taken up by haemoglobin.

Question 10

Unloading / dissociation: When oxygen is released/given up by haemoglobin

Question 11

Affinity – ‘a natural/chemical attraction to something’

Hb loads oxygen as it has a high affinity to it

Question 12

Loading:
High O2 Concentration (High pO2) – More oxygen loaded onto Hb

Low O2 Concentration (Low pO2) – Less oxygen loaded onto Hb

Question 13

Unloading:
If oxyhaemoglobin moves to an area of low O2 concentration, then oxygen will be unloaded to the surroundings

Question 14

An oxygen dissociation curve is always ‘S’ shaped and is described as a ‘sigmoid curve’ The first O2 molecule alters the tertiary structure of the Hb molecule. This exposes the 2nd and 3rd O2 BINDING sites. This makes it EASIER for 2nd & 3rd O2 molecules to bind & load.

Question 15

pO2 in lungs

The partial pressure of O2 (pO2) is high in the capillaries (about 13.16kPa)

Hb has a higher affinity for O2 at a high pO2.

Haemoglobin becomes (almost) fully saturated as the red blood cells pass through the pulmonary capillaries (LUNGS).

The haemoglobin has bound its maximum amount of oxygen and is 98%+ saturated.

Question 16

pO2 in respiring tissues

The pO2 in the tissue capillaries is LOWER, only about 5.0 kPa.

Haemoglobin now has a lower affinity for O2 at a lower pO2 and so the oxyhaemoglobin starts to break down and unloads oxygen.

The oxygen released is then available to the tissue cells to be used in aerobic respiration.

Question 17

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

Answer 17

1. (Is) charged/polar OR (Is) part of haem(oglobin);
2. (So) binds/associates/loads (with) oxygen OR (So) forms oxyhaemoglobin OR (So) transports oxygen;

Question 18

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

Answer 18

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

Question 19

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

Answer 19

· 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 20

The Effect of Increased Respiration RATE on Oxygen Dissociation

1. Tissue cells respire aerobically, quickly reducing the dissolved O2 in the surrounding the tissue fluid.
2. This reduces the pO2 to a lower level than normal
3. The oxygenated blood arriving with fully saturated haemoglobin will begin to unload more oxygen (become less saturated) and more oxygen will be released from the haemoglobin to the tissue cells. This is because the surrounding pO2 is lower and so haemoglobin will have an even lower affinity to oxygen.

Question 21

If a question asks what happens to % saturation at either a low or high pO2, then draw a line from a low or high pO2 up the sigmoid curve and across to the Y axis to see the effect on Hb % saturation. Calculate the difference between these 2 points
Lungs – tissues = % of oxygen unloaded

Question 22

Effect of Carbon Dioxide concentration - Bohr Shift

In higher-than-normal pCO2, Haemoglobins affinity for Oxygen is even lower.
If pCO2 increase the saturation of haemoglobin decreases.
This causes the haemoglobin-oxygen dissociation curve to shift to the right (Bohr shift)

Question 23

When CO2 dissolves in the blood it makes the blood more acidic, thus lowering the pH.
As Hb is a protein, a change in pH slightly alters its tertiary structure (R group interactions)
That’s why it has a lower affinity to O2 at higher levels of CO2

Question 24

The more that tissue cells respire, the more the carbon dioxide concentration will increase and cause a shift to the right in the oxyhaemoglobin dissociation curve.

Hb now has a lower affinity to oxygen at the respiring cells.

As a result, more oxygen is unloaded from the haemoglobin, at the same pO2, as it becomes less saturated.

MORE oxygen is now available to meet the oxygen demands of the respiring cells/tissues.

Question 25

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

Answer 25

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

Question 26

Heat from respiration helps mammals to maintain a constant body temperature. Use this information to explain the relationship between the surface area to volume ratio of mammals and the oxygen dissociation curves of their haemoglobins.

Answer 26

Smaller mammal has greater surface area to volume ratio; Smaller mammal/larger SA:Vol ratio more heat lost (per unit body mass);
Smaller mammal/larger SA:Vol ratio so has greater rate of respiration/metabolism;
Oxygen required for aerobic respiration;
(Haemoglobin) releases more oxygen / oxygen released more readily / haemoglobin has lower affinity;

Question 27

Adaptation to Environment

Different species and different populations of the same species, live in different environments with varying pO2.

Genetic differences between species and populations leads to different haemoglobin affinities.

Mutations causes the variation in Hb affinity (based on alterations to tertiary structures of Hb) which alters the position of their dissociation curve.

As mutations accumulate (over longer periods of time) the more the primary, secondary, tertiary structures are altered and so different Hb molecules are produced. Different Hb have different affinities to Oxygen.

Question 28

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 28

1. Higher affinity / loads more oxygen;
2. At low/same/high partial pressure/pO2;
3. Oxygen moves from mother/to foetus;

Question 29

High Altitude/ Foetus / Lug worm
(Left)

1) Partial Pressure of O2 (pO2) at lungs/of environment is low
↓
2) Haemoglobin has a higher affinity for oxygen
↓
3) More O2 is loaded (associates) at lower partial pressures of oxygen
↓
4) This is then transported to the tissues
↓
5) For use in aerobic respiration

Question 30

Bohr Shift
(Right)

1) Increase in partial pressure of CO2 in the blood
↓
2) Oxygen dissociation curve shifts to the right
↓
3) Haemoglobin has a lower affinity for oxygen
↓
4) More O2 is unloaded (dissociates) at the tissue
↓
5) For use in aerobic respiration

Question 31

Small mammals and Birds (Right)

1) Large SA:Vol ratio, so loses heat more readily to the environment
↓
2) Must increase rate of respiration to maintain body temperature
↓
3) Haemoglobin has a lower affinity for oxygen
↓
4) More O2 is unloaded (dissociates) at the tissue
↓
5) For use in aerobic respiration