Module 3 Section 2 : Haemoglobin

Question 1

Red blood cells contain…

Answer 1

Haemoglobin

Question 2

What is haemoglobin

Answer 2

• A large protein with a quaternary structure - made up of one or more polypeptide chain (four of them)
• Each chain has a haem group which contains iron and gives haemoglobin its red colour
• Haemoglobin has a high affinity for oxygen each molecule can carry four oxygen molecules

Question 3

How is oxyhemoglobin formed

Answer 3

• joins in the lungs
• oxygen joins to the iron in haemoglobin to form oxyhemoglobin
• reversible reaction - when oxygen leaves oxyhemoglobin near the body cells it turns back to haemoglobin

Question 4

What is the word equation for how oxyhemoglobin is formed

Answer 4

Haemoglobin (Hb) + Oxygen (4O₂) = oxyhemoglobin (HbO₈)

Question 5

What does haemoglobin saturation depend on

Answer 5

The partial pressure of oxygen

Question 6

What is partial pressure of oxygen

Answer 6

• Partial pressure of oxygen is a measure of oxygen concentration
• the greater the concentration of dissolved oxygen in cell, the higher the partial pressure

Question 7

What is the symbol of partial pressure of oxygen

Answer 7

pO₂

Question 8

What is the partial pressure of Carbon dioxide

Answer 8

• the partial pressure of carbon dioxide is a measure of concentration of CO₂ in a cell
• the greater the concentration of dissolved carbon dioxide in cells the higher the pressure

Question 9

Haemoglobins affinity for oxygen varies depending on…..

Answer 9

Partial pressure of oxygen:
Oxygen loads into haemoglobin to form oxyhaemoglobin where there’s a high pO₂
Oxyhaemoglobin disassociates it’s oxygen where there’s a lower pO₂

Question 10

Give a situation when oxygen loads into haemoglobin

Answer 10

When oxygen enters blood capillaries at the alveoli in the lungs. Alveoli have a high pO₂ so oxygen loads into haemoglobin to form oxyhemoglobin

Question 11

Give a situation when oxygen disassociates from oxyhemoglobin

Answer 11

When cells respire they use up oxygen - this is a lower pO₂. Red blood cells deliver oxyhemoglobin to respiring tissues where it disassociates its oxygen

Question 12

After disassociation what happens to the haemoglobin

Answer 12

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

Question 13

What shows how saturated the haemoglobin is with oxygen at any given partial pressure

Answer 13

An oxygen dissociation curve

Question 14

Where the pO₂ is high haemoglobin has….

Answer 14

A high affinity for oxygen (it will readily combine with oxygen), so it has a high saturation of oxygen

Question 15

Where pO₂ is low haemoglobin has a….

Answer 15

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 16

Why is the oxygen dissociation curve an s-shape

Answer 16

• Because when haemoglobin combines with the first O₂ molecule it’s shape alters in a way that makes it easier for other molecules to join too.
• But as Hb starts to become saturated, it gets harder for more oxygen molecule to join
• the curve has a steep bit in the middle where it’s really easy for oxygen molecules to join
• the curve has shallow bits at each end where it’s harder for oxygen molecules to join.

Question 17

What is the meaning when the curve is steep

Answer 17

When the curve is steep a small change in pO₂ causes a big change in the amount of oxygen carried by Hb

Question 18

What has a higher affinity for oxygen Fetal haemoglobin or adult haemoglobin

Answer 18

Fetal haemoglobin has a higher affinity for oxygen than adult haemoglobin

Question 19

Why does Fetal haemoglobin have a higher affinity for oxygen than adult haemoglobin

Answer 19

Fetal haemoglobin has a higher affinity for oxygen because the fetus’s blood is better at absorbing oxygen than it’s mothers blood at the same partial pressure of oxygen

Question 20

How does a fetus get oxygen from its mothers blood

Answer 20

Across the placenta

Question 21

What happens to the oxygen saturation by the time the blood reaches the placenta

Answer 21

It has decreased by the time it reaches the placenta. This is because some has been used up by the mother’s body

Question 22

Why does a fetus need to have a higher affinity for oxygen

Answer 22

It needs a higher affinity because the fetus needs to get enough oxygen to survive

Question 23

What would happen if Fetal haemoglobin had the same affinity for oxygen as adult haemoglobin

Answer 23

If the Fetal haemoglobin had the same affinity for oxygen as adult haemoglobin it’s blood wouldn’t be saturated enough

Question 24

What affects oxygen unloading

Answer 24

Carbon dioxide concentration

Question 25

When does haemoglobin give up its oxygen more readily and why does it happen

Answer 25

• At higher partial pressures of carbon dioxide (pCO₂)

Question 26

Where does most of the CO₂ diffuse into

Answer 26

Most of the CO₂ from the respiring tissues diffuses into red blood cells

Question 27

What does the CO₂ react with, produce and what is it catalysed by

Answer 27

• Reacts with water
• Forms Carbonic acid
• Catalysed by the enzyme carbonic anhydrase
• the rest of the CO₂, around 10% binds directly to haemoglobin and is carried to the lungs

Question 28

What happens to carbonic acid after it’s formed

Answer 28

The carbonic acid dissociates (splits up) to give hydrogen (H⁺) ions and hydrogencarbonate (HCO₃^-) ions

Question 29

What does the increase in H⁺ ions cause

Answer 29

• This increase in H⁺ ions causes oxyhemoglobin to unload its oxygen so that haemoglobin can take up the H⁺ ions
• This forms a compound called Haemoglobinic acid.
• This process also stops the hydrogen ions from increasing the cell’s acidity

Question 30

What happens to the hydrogencarbonate ions

Answer 30

The HCO ₃^- ions diffuse out of the red blood cells and are transported in the blood plasma

Question 31

How does the red blood cells compensate from the loss of HCO₃^- ions

Answer 31

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

Question 32

What does the chloride shift do

Answer 32

The chloride shift maintains the balance of charge between the red blood cells and the plasma

Question 33

What happens to the blood when it reaches the lungs

Answer 33

• The low pCO₂ causes some of the HCO₃^- and H⁺ ions to recombine into CO₂ (and water).
• The CO₂ the diffuses into alveoli and is breathed out

Question 34

What is the Bohr Effect

Answer 34

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).

Question 35

How does CO₂ affect oxygen unloading

Answer 35

• Most CO₂ from respiring tissues diffuses into red blood cells
• reacts with water to form carbonic acid
• which is catalysed by carbonic anhydrase
• carbonic acid dissociates to give hydrogen ions and hydrocarbonate ions
• increase in H⁺ cause oxyhemoglobin to unload its oxygen so Hb can take up the H⁺ ions
• hydrogencarbonate ions diffuse out of RBC and are transported in the blood plasma
• to compensate for loss is hydrogencarbonate ions in RBC, Cl ions diffuse into the RBC
• Called the chloride shift
• chloride shift maintains the balance of charge between RBC and the plasma
• When blood reaches lungs the low pCO₂ causes some of the hydrogen carbonate and hydrogen ions to recombine into CO₂
• the CO₂ then diffuses into the alveoli and is breathed out