Haemoglobin (pages 86 - 87)

Question 1

What is the name for Oxygen carried round the body?

Answer 1

Oxyhaemoglobin

Question 2

Red blood cells contain what?

Answer 2

Haemoglobin (Hb)

Question 3

What is Haemoglobin?

Answer 3

Haemoglobin is a large protein with a quaternary structure (see pages 27 and 28) - it is made up of more than one polypeptide chain (four of them).

Question 4

Each polypeptide chain has a haem group which contains what?

Answer 4

conatins iron, and this gives haemoglobin its red colour.

Question 5

Haemoglobin has a high affinity for oxygen, what do this mean?

Answer 5

each molecule can carry four oxygen molecules

(affinity for oxygen means tendency to combine with oxygen)

Question 6

In the lungs, oxygen joins to the iron in haemoglobin to form what?

Answer 6

oxyhaemoglobin.

Question 7

Is Oxyhaemoglobin a reversible reaction, and why?

Answer 7

Yes it is a reversible reaction because when sxygen leaves oxyhaemoglobin (dissociates from it) near the body cells, it turns back to haemoglobin.

see diagram 1 on reaction.

Hb + 4O² 》》》》 《《《《 HbO⁸

Haemoglobin + oxygen&raquo_space;>«< oxyhaemoglobin.

Question 8

Haemoglobin Saturation depends on what?

Answer 8

on the Partial Pressure of Oxygen.

Question 9

What is the partial pressure of oxygen (pO2) a measure of?

Answer 9

Oxygen concentration. The greater the concentration of dissolved oxygen in cells, the higher the partial pressure.

Question 10

What is the partial pressure of carbon dioxide (pCO2) a measure of?

Answer 10

a measure of the concentration of CO2 in a cell.

Question 11

Haemoglobin’s affinity for oxygen varies depending on the partial pressre of oxygen, explain why?

Answer 11

Oxygen loads onto haemoglobin to form oxyhaemoglobin where there’s a high pO2.
Oxyhaemoglobin unloads its oxygen where there’s a lower pO2.

Question 12

Where do Oxygen enter the blood capillaries?

Answer 12

at the Alveoli in the lungs.

Alveoli have a high pO2 so oxygen loads onto haemoglobin to form oxyhaemoglobin.

Question 13

When cells respire, they use up oxygen - this lowers the pO2. Explain how?

Answer 13

Red blood cells deliver oxyhaemoglobin to respiring tissues, where it unloads its oxygen.

The haemoglobin then returns to the lungs to pick up more oxygen.

Question 14

Dissociation Curves show what on a graph?

Answer 14

how Affinity for oxygen varies

An oxygen dissociation curve shows how saturated the haemoglobin is with oxygen at any given partial pressure.

Question 15

Looking at graph 1 on page 86, what do the 100% saturation mean?

Answer 15

it means every haemoglobin molecule is carrying the maximum of 4 molecules of oxygen.

Where the pO2 is high (e.g. in the lungs), haemoglobin has a high affinity for oxygen (e.e. it will readily combine with oxygen), so it has a high saturation of oxygen.

Question 16

Looking at graph 1 on page 86 explain what 0% saturation means?

Answer 16

it means none of the haemoglobin molecules are carrying any oxygen.

Where pO2 is low (e.g. in respiring tissues), haemoglobin has a low affinity for oxygen, which means it releases oxygen rather than combines with it. That’s why it has a low saturation of oxygen.

Question 17

Looking at graph 1 on page 86, why is the graph ‘S’ shaped?

Answer 17

1) because when haemoglobin (Hb) combines with the first O2 molecule, its shape alters in a way that makes it easier for other molecules to join too.

2) but as the Hb starts to become saturated, it gets harder for more oxygen molecules to join.

3) As a result, the curve has a steep bit in the middle where it’s really easy for oxygen molecules to join, and shallow bits at each end where it’s harder. When the curve is steep, a small change in pO2 causes a big change in the amount of oxygen carried by the Hb.

Question 18

Adult haemoglobin and fetal haemoglobin have different affinities for oxygen why?

Answer 18

Fetal haemoglobin has a high affinity for oxygen (the fetus’s blood is better at absorbing oxygen than its mother’s blood) at the same partial pressure of oxygen.

Question 19

This is really important:

Where do the fetus get oxygen from?

Answer 19

from its mother’s blood accross the placenta.

Question 20

This is really important:

By the time the mother’s blood reaches the placenta, its oxygen saturation has decreased, why?

Answer 20

because some has been used up by the mother’s body.

Question 21

This is really important:

For the fetus to get enough oxygen to survive what do its haemoglobin have to have?

Answer 21

the fetus haemoglobin has to have a higher affinity for oxygen (so it takes up enough)

Question 22

This is really important:

If the fetus’s haemoglobin had the same affinity for oxygen as adult haemoglobin, would its blood be saturated enough?

Answer 22

No the blood wouldn’t be saturated enough.

look at graph 1 on page 87

Question 23

Carbon Dioxide concentration affects what?

Answer 23

oxygen unloading.

Question 24

To complicate matters, haemoglobin gives up its oxygen more readily at high partial pressures of carbon dioxide (pCO2), why?

Answer 24

Its a cunning way of getting more oxygen to cells during activity. When cells respire they produce carbon dioxide, which raises the pCO2, increasing the rate of oxygen unloading. The reason for this is linked to how CO2 affects blood pH.

Question 25

What happens to most of the CO2 from respiring tissues?

Answer 25

diffuses into red blood cells. Here it reacts with water to form carbonic acid, catalysed by the enzyme carbonic anhydrase. (the rest of the CO, around 10%, binds directly to haemoglobin and is carried to the lungs).

Question 26

Why do carbonic acid dissociates (splits up)?

Answer 26

this happens to give hydrogen (H+) ions and hydrogencarbonate (HCO3) ions.

This increase in H+ ions causes oxyhaemoglobin to unload its oxygen so that haemoglobin can take up the H+ ions. This forms a compound called haaemoglobinic acid. (this precess also stops the hydrogen ions from increasing the cells acidity).

Question 27

The HCO3 ions diffuse out of the red blood cells and are transported in the blood plasma, why?

Answer 27

to compensate for the loss of HCO3 ions from the red blood cells, chloride (Cl-) ions diffuse into the red blood cells. This is called the chloride shift and it maintains the balance of charge between the red blood cell and the plasma.

Question 28

When the blood reaches the lungs the low pCO2 causes what?

Answer 28

it causes some of the HCO3 and H+ ions to recombine into CO2 (and water)

The CO2 then diffuses into the Alveoli and is breathed out.

Question 29

Look at graph 2 on page 87, Explain what the Bohr Effect means?

Answer 29

When carbon dioxide levels increase, the dissociation curve ‘shifts’ right, showing that more oxygen is released from the blood (because the lower the saturation of haemoglobin with O2, the more O2 is released) This is called the Bohr effect.

Question 30

How many Oxygen molecules can each haemoglobin molecule carry?

Answer 30

four oxygen molecules

Question 31

What is carbon dioxide converted to in red blood cells?

Answer 31

Most of the carbon dioxide diffusing through the capillaries and ultimately into the red blood cells combines with water via a chemical reaction catalyzed by the enzyme carbonic anhydrase, formingcarbonic acid. Carbonic acid almost immediately dissociates into a bicarbonate anion (HCO3-) and a proton.

Question 32

Which statement correctly described the Bohr effect?

a) when pCO2 increases, less O2 is released from the blood and the O2 dissociation curve shifts right.
b) when pCO2 increased, more O2 is released from the blood and the O2 dissociation curve shifts right.
c) when pCO2 increases, less O2 is released from the blood and the O2 dissociation curve shifts left.
d) when pCO2 increases, more O2 is released from the blood and the O2 dissociation curve shifts left (mark).

Answer 32

The answer is ‘B’

you know that the Bohr effect means that as pCO2 increases, more O is released from the blood, so this removes A and C. If the curve shifts right this means that a particular pO2 the haemoglobin will be less saturated with O2 at hight pCO2. (this is true so the curve shifts right and the correct answer is B). Try doing a sketch of the O2 dissociation curve and experiment with the movement of the curve to help you remember this.

(dissociation graphys can be a bit confusing - but basically, whe tissues contain lots of oxygen (i.e. pO2 is high), haemoglobin readily combines with the oxygen, so the blood has a high saturation of oxygen (and vice versa, when pO2 is low). Simple. Also make sure you get the lingo right, like ‘partial pressure’ and ‘affinity’ .