haemoglobin as an allosteric protein to transport oxygen

Question 1

What are the advantages of the shape of red blood cells?

Answer 1

Diffusion of oxygen and able to fit in capillaries

Question 2

What is the structure of haem?

Answer 2

Haem is porphyrin and iron. The porphyrin is a tetrapyrolle. There is a hydrophobic end and a hydrophilic end.

Question 3

What causes brown blood?

Answer 3

Redox state of the iron - Fe3+ is oxidised and gives dark brown blood - Met Hb

Question 4

What causes blue blood?

Answer 4

Cyanosis - cyanide binding instead of oxygen

Question 5

What causes cherry red blood?

Answer 5

Carbon monoxide binding instead of oxygen

Question 6

What causes dark red blood?

Answer 6

deoxyhaemoglobin

Question 7

What causes red blood?

Answer 7

oxyhaemoglobin

Question 8

What is the secondary structure of haemoglobin?

Answer 8

alpha helix

Question 9

What is the quaternary structure of haemoglobin?

Answer 9

tetramer

Question 10

What is myoglobin?

Answer 10

Myoglobin is found in the muscle and it stores oxygen - its structure is the same as the tertiary structure of haemoglobin

Question 11

What is the structure of myoglobin?

Answer 11

8 right handed alpha helices labelled A to H, hydrophilic on outside and hydrophobic on the inside which makes it very soluble

Question 12

Where does oxygen in the tissues go?

Answer 12

Either to myoglobin or to mitochondria

Question 13

What is the structure of haemoglobin in adults?

Answer 13

Two alpha subunits and two beta subunits

Question 14

What is the structure of foetal haemoglobin?

Answer 14

Two alpha subunits and two gamma subunits

Question 15

Where does the globin coordinate with the iron?

Answer 15

At the nitrogen on histamine residues E7 and F8 - F8 constantly locks on but E7 can be displaced by oxygen

Question 16

What is the difference between the oxygenated and deoxygenated structures of haemoglobin

Answer 16

In the oxygenated state the iron is in the haem plane. In the deoxygenated state iron is pulled out of the haem plane towards F8. The oxygenated state is the relaxed (R) state and the deoxygenated state is the tense (T) state

Question 17

Why is the deoxy-Hb form more rigid than the oxy-Hb form?

Answer 17

Because of the 8 salt bonds which are formed

Question 18

What pathway makes BPG?

Answer 18

1,3-bisphosphoglycerate from the glycolysis pathway is converted to 2,3-bisphosphoglycerate by mutase

Question 19

Where does BPG bind?

Answer 19

Binds to the deoxygenated Hb because BPG has 5 negative charges which fit in to a cavity between the beta subunits with 8 positive charges. It stabilises deoxy-Hb and prevents oxygen from rebinding in the tissues. It is dissociated when oxygen binds again in the lungs because they oxygen at a higher concentration can push its way in.

Question 20

What shape is the oxygen saturation curve for haemoglobin?

Answer 20

sigmoidal

Question 21

What shape is he oxygen saturation curve for myoglobin?

Answer 21

hyperbolic

Question 22

What pO2 gives 50% saturation for haemoglobin?

Answer 22

26 Torr

Question 23

What pO2 is in the tissues?

Answer 23

20-40 Torr

Question 24

What pO2 is in the lungs?

Answer 24

100 Torr

Question 25

In which direction does the oxygen saturation curve shift in acid?

Answer 25

To the right

Question 26

What is the Bohr effect?

Answer 26

Where active tissue produces acid and stimulates haemoglobin to yield more oxygen in the active tissue

Question 27

Why does the Bohr effect occur?

Answer 27

Because two histidine residues become positively charged in acid and lock deoxyHb more strongly

Question 28

What does an oxygen saturation curve that has been shifted to the right mean?

Answer 28

That deoxyhaemoglobin is more stable and that oxygen is more likely given up in the tissues

Question 29

What is subunit cooperativity?

Answer 29

Subunit cooperativity means when one oxygen binds it causes a conformational change in neighbouring haemoglobin allowing oxygen to more easily bind. The same happens when oxygen is released, when one leaves the rest foliow.

Question 30

What happens to the oxygen saturation curve when effectors (CO2 and BPG) are no longer present?

Answer 30

Haemoglobin has properties more like myoglobin (hyperbolic curve)

Question 31

Which has more affinity for oxygen, adult haemoglobin or foetal haemoglobin?

Answer 31

Foetal haemoglobin

Question 32

Why does foetal haemoglobin need more affinity for oxygen?

Answer 32

Because it needs to be able to take the oxygen from the adult circulation in the mother

Question 33

Why does foetal haemoglobin have more affinity for oxygen?

Answer 33

Because it binds BPG less strongly because there are only 6 instead of 8 negative charges in the cavity

Question 34

What happens in altitude?

Answer 34

There is more BPG which shifts the curve to the right - this means that the P50 is raised from 26 to 31 Torr so more oxygen is delivered to the tissue

Question 35

What is the cause of sickle cell anaemia?

Answer 35

A glutamic acid amino acid in haemoglobin is mutated to valine. The valine binds to a hydrophobic pocket in deoxy-haemoglobin to form insoluble crystalline structures.

Question 36

What percentage of dry red blood cell is haemoglobin?

Answer 36

97%