Haemoglobin

Question 1

Where is haemoglobin found?

Answer 1

In erythrocytes.

Question 2

What is haemoglobin’s structure?

Answer 2

It is a globular, quaternary protein containing 4 polypeptide chains (=2 A subunit polypeptide chains and 2 B subunit polypeptide chains.)
Each polypeptide chain contains a haem group containing an iron ion.

Question 3

What is haemoglobin’s function?

Answer 3

To transport oxygen from the lungs to respiring tissues.

Question 4

What does affinity mean?

Answer 4

The likelihood of the one molecule associating with another.

Question 5

What does association mean?

Answer 5

Binding.

Question 6

What does dissociation mean?

Answer 6

Unbinding.

Question 7

What is anaemia?

Answer 7

When a person doesn’t produce enough haemoglobin, the body can’t produce enough erythrocytes. This results in the rate at which respiring tissues receive oxygen decreasing causing the person will feel lethargic due to a lack of energy.

Question 8

What does deoxyhaemoglobin mean?

Answer 8

A haemoglobin that is not associated to any oxygen.

Question 9

What does 1-oxyhaemoglobin mean?

Answer 9

The haemoglobin is bound to one oxygen molecule.

Question 10

What is percentage saturation of haemoglobin?

Answer 10

The number of iron ions in a group of haemoglobin molecules that are oxygenated/ associated with oxygen.

Question 11

What does pO₂ mean and what is this?

Answer 11

Partial pressure of oxygen. The concentration of oxygen.

Question 12

What is Hb’s affinity for O₂ in the lungs and why?

Answer 12

It is high because the pO₂ is high and the pCO₂ is low.

Question 13

What is Hb’s affinity for O₂ in the respiring tissues and why?

Answer 13

It is low because the pO₂ is low and the pCO₂ is high.

Question 14

How does the pO₂ of a tissue affect the saturation of Hb with O₂?

Answer 14

The lower the pO₂ of the tissue the lower Hb’s affinity to oxygen. This means less oxygen associates with the Hb molecules so the saturation of Hb with O₂ is lower.

Question 15

What is the Bohr affect?

Answer 15

When the concentration of CO₂ is high, Hb’s affinity for O₂ decreases because the CO₂ dissolves in the blood producing Hydrogen ions (which interact with hydrogen bonds in the haemoglobin’s tertiary structure) and the ion COOH₃‾ (which interacts with the ionic bonds in haemoglobin’s tertiary structure).
The interaction with bonds causes the haemoglobin to change shape resulting in the iron ion being less accessible to oxygen.

Question 16

Why is the Bohr effect advantageous?

Answer 16

It lowers Hb’s affinity for oxygen so the Hb is more likely to dissociate from the O₂.
This means the higher the rate of respiration, the higher the pCO₂, therefore the higher the concentration of O₂ released and made available for respiration.

Question 17

What is temperature’s effect on the deoxyhaemoglobin dissociation curve and why is this beneficial?

Answer 17

An increase in temperature causes it to shift to the right.
This is so more O₂ is released to the cells when respiring.
As the rate of respiration increases more heat is released so the temperature increases.

Question 18

What does the gradient of a deoxyhaemoglobin curve represent?

Answer 18

The rate that Hb binds to O₂.

Question 19

What causes a curve to be left shifted?

Answer 19

The percentage saturation of Hb with O₂ being higher than normal.

Question 20

What causes a curve to be right shifted?

Answer 20

There percentage saturation of Hb being lower than normal.

Question 21

What is the deoxyhaemoglobin curve for a tissue of high CO₂ concentration and can you explain why?

Answer 21

A high concentration of CO₂ decreases the affinity of Hb to O₂.
In the presence of CO₂, the percentage saturation of Hb with O₂ is lower than normal.
This means that the curve will be right shifted.

Question 22

What does the shifting of the curve mean for an organisms ability to associate with O₂?

Answer 22

Left shifted = Better at associating with O₂.
Right shifted = Better at dissociating from O₂.

Question 23

Can you give some examples of low oxygen environments?

Answer 23

• High altitudes.
• Underground.

Question 24

When living in what environments would an animal need a left shifted deoxyhaemoglobin curve and why?

Answer 24

• Low partial pressures of O₂.

They will need Hb that has a higher affinity for O₂, therefore can easily associate with O₂.

Question 25

At what level of activity would an animal need a right shifted deoxyhaemoglobin curve and why?

Answer 25

High level of activity. They need more energy so have a high respiration rate. This means they need haemoglobin that will dissociate from oxygen more quickly at the respiring tissues. ∴ Hb with a low affinity for O₂.

Question 26

What size animal needs a right shifted deoxyhaemoglobin curve and why?

Answer 26

Small animals. They have a larger SA:Vol resulting in them losing heat at a faster rate so they have a higher metabolic rate. This means they need haemoglobin that will dissociate from oxygen more quickly at the respiring tissues. ∴ Hb with a low affinity for O₂.

Question 27

What is the difference between fetal haemoglobin and maternal haemoglobin and what does this mean about their curves?

Answer 27

Fetal Hb has a different structure to maternal Hb. This gives it a higher affinity for O₂. Fetal Hb's curve is shifted to the left in comparison to maternal Hb.

Question 28

Why is fetal haemoglobin important for a fetus' survival?

Answer 28

It enables oxygen to be transferred from maternal Hb to fetal Hb at the low pO₂ found in the placenta. (Maternal dissociates more easily and fetal associates more easily so it is transferred from maternal to fetal)

Question 29

What is myoglobin?

Answer 29

A protein used for storing oxygen in muscle cells.

Question 30

What is the difference between myoglobin and haemoglobin?

Answer 30

Myoglobin has a much higher affinity for O₂ than haemoglobin.

Question 31

How can myoglobin be beneficial?

Answer 31

It has a very high affinity for O₂ so only releases O₂ when the partial pO₂ is very low and when haemoglobin has released almost all the O₂ it is carrying. This means myoglobin facilitates the continuation of aerobic respiration and can be an O₂ store.

Question 32

Where is myoglobin found in the body?

Answer 32

Muscle tissues ONLY.

Question 33

In what animals is myoglobin found in high concentrations?

Answer 33

Diving MAMMALS.

Question 34

Can you describe the oxyhaemoglobin dissociation curve for myoglobin?

Answer 34

It is left shifted in comparison to haemoglobin. This is due to it having a higher affinity for O₂ ∴ associating with O₂ more quickly and at lower pO₂'s ∴ having a higher percentage saturation of Hb with O₂ at lower pO₂'s.

Question 35

Can you describe cooperative binding?

Answer 35

1- An oxygen molecule binds to one of the four haem units. 2- This causes the quaternary structure of the Hb to change slightly. 3- The iron ions are more exposed so the affinity of Hb for O₂ has increased. 4- The 2nd O₂ molecule can associate more easily and the 3rd even more easily. 5- This binding causes the quaternary structure of the Hb to change again but now the last iron ion is less accessible. 6- This means the affinity of Hb for O₂ has decreased. 7- The 4th O₂ molecule binds much less easily.

Question 36

After going on a bike ride, would the curve be left or right shifted and why?

Answer 36

The curve would be shifted to the right because during the bike ride the respiration rate would be higher therefore the partial pressure of CO₂ is increasing in the muscle tissues. This increases the rate of Hb dissociating from oxygen.