The Bohr Effect

Question 1

How many haemoglobin molecules are there per erythrocytes?

Answer 1

300 million (roughly)

Question 2

Describe the structure of haemoglobin.

Answer 2

Four peptide chains, each with a iron containing haem prosthetic group.

Question 3

How many oxygen molecules can each haemoglobin molecule bind to?

Answer 3

4

Question 4

What is the reversible reaction including oxygen and haemoglobin?

Answer 4

Hb (Haemoglobin) + 4O2 (oxygen) <=> Hb(O2)4 (oxyhaemoglobin)

Question 5

Define positive cooperativity.

Answer 5

As soon as one oxygen molecule binds to a haem group, the molecule changes shape, making it easier for the next oxygen molecules to bind.

Question 6

How does oxygen gradient stay low as more oxygen binds?

Answer 6

Because the oxygen is focused on free oxygen concentration, which stays low in the erythrocyte.

Question 7

What does the oxygen dissociation curve show?

Answer 7

The affinity of haemoglobin for oxygen.

Question 8

How does partial pressure of oxygen effect the oxygen dissaciation curve?

Answer 8

At high partial pressure haemoglobin is rapidly loaded with oxygen, but this is limited by the free space available for haemoglobin to bind.

Question 9

Describe the Bohr effect.

Answer 9

As partial pressure of CO2 rises, haemoglobin gives up oxygen more easily.

Question 10

Why is the Bohr effect important? (Two reasons)

Answer 10

In tissues with high carbon dioxide concentrations, haemoglobin gives up oxygen more readily. In the lungs where carbon dioxide concentration is low, oxygen more readily binds to haemoglobin.

Question 11

What is the name of the compound formed from carbon dioxide and the polypeptide chains of haemoglobin?

Answer 11

Carbaminohaemoglobin.

Question 12

How is the majority of carbon dioxide transported in the body?

Answer 12

In hydrogen carbonate ions (HCO3-)

Question 13

What are the three ways Carbons dioxide is transported?

Answer 13

5% dissolved in the plasma
10-20% combined with haemoglobin to form carbaminohaemoglobin
75-85% converted to HCO3- ions in the cytoplasm of erythrocytes

Question 14

What is the process of forming hydrogen carbonate ions? (2 steps)

Answer 14

1. Carbon dioxide reacts slowly with water to form carbonic acid
2. Carbonic acid dissociates to form the hydrogen and hydrogen carbonate ions

Question 15

What is the enzyme that catalysed the reaction between water and carbon dioxide?

Answer 15

Carbonic anhydride, which forms carbonic acid.

Question 16

What happens to the hydrogen carbonate ions?

Answer 16

They diffuse out of the erythrocytes into the plasma across a concentration gradient.

Question 17

How does the erythrocytes maintain electrical integrity?

Answer 17

Chloride shift- negatively charged chloride ions move into erythrocytes as hydrogen carbonate ions move out of the

Question 18

What is the importance of converting carbon dioxide into hydrogen carbonate ions?

Answer 18

Erythrocytes maintain a concentration gradient for carbon dioxide to keep moving into them from respiring tissue.

Question 19

What happens to when erythrocytes reach the lung tissue? (3 points)

Answer 19

There is a low concentration of carbon dioxide in the lung tissue (so) hydrogen carbonate ions diffuse back into the erythrocytes and reforms carbonic acid.
Carbonic anhydrase catalyses the reverse reaction of carbonic acid to carbon dioxide and water.
Chloride ions diffuse back out.

Question 20

Which molecule acts as a pH buffer in this process and how?

Answer 20

Haemoglobin- accepts free hydrogen ions to form haeoglobinic acid