Haemoglobin

Question 1

Describe the structure of a haemoglobin.

Answer 1

• water soluble
• globular protein
• has 4 polypeptide chains, each containing a haem group
• has a quarternary structure

Question 2

What is the structure of the 4 polyptide chains in the haemoglobin?

Answer 2

1. two are beta pleated sheets
2. two are alpha helixes

Question 3

How many molecules of oxygen can a haemoglobin carry?

Answer 3

4

Question 4

What is the reaction between haemoglobin and oxygen?

Answer 4

Hb + 4O2 ⇌ Hb(O2)4

Hb(O2)4 is oxyhaemoglobin

Question 5

What is the partial pressure of oxygen?

pO2

Answer 5

the measure of oxygen concentration

Question 6

Where in the body is pO2 is high?

Answer 6

the lungs

Question 7

Where in the body is pO2 is low?

Answer 7

the body tissues (muscles)

Question 8

What is pO2 measured in?

Answer 8

kPa or kilopasclas

Question 9

What is another word for pO2?

Answer 9

oxygen tension

Question 10

What does affinity mean?

Answer 10

a tendency to attract

Question 11

How does the levels of pO2 affect affinity?

Answer 11

• where there is a high pO2 (lungs) there is a high oxygen affinity (more oxygen uptake/binding)
• where there is a low pO2 (body tissues) there is a low oxygen affinity (more oxygen unloading/bonds breaking)

Question 12

What graphs shows how pO2 affects Hb saturation?

Answer 12

Oxygen Dissociation Curve

Question 13

What is the shape of a Oxygen Dissociation Curve?

Answer 13

S shape

Question 14

Explain the S shape of the Oxygen Dissociation Curve.

Answer 14

• beginning there is a low pO2 but not much change to Hb saturation (not a very steep curve)
• middle there is a small change in pO2 and a large change (steep curve)
• end there is a high pO2 but not much change to Hb saturation (not a very steep curve)

Question 15

Explain the S shape of the Oxygen Dissociation Curve.

using what is happening in the Haemoglobin

Answer 15

• beginning of the graph, first molecule of oxygen binds to an Hb, which distorts the shape and takes a long time
• middle of the graph, change of shape means that it’s easier for first and second oxygen to bind
• more difficult for fourth oxygen to bind so line flatterns

Question 16

Why is it more difficult for the fourth oxygen molecule to bind?

Answer 16

all the other oxygen-binding sites are are occupied so it’s less likely that it will find one

Question 17

How does the haemoglobin exchange oxygen with the lungs?

Answer 17

• when blood has a lower pO2 than the lungs
• this creates a concentration gradient for oxygen to move into the blood from the alveoli
• when the oxygen moves out of the alveoli it is uploaded onto the Hbs until 96% full to produce oxyhaemoglobin

this process is the forward reaction

Question 18

How does the haemoglobin exchange oxygen with body tissues (muscles)?

Answer 18

• cells are constantly respiring which means that there is a low pO2
• Hb will unload oxygen which will diffuse into the tissue for aerobic respiration

Question 19

Why does carbon dioxide cause oxygen to be unloaded at the tissue?

Explain The Bohr Effect

Answer 19

• when the cells respire they produce CO2 which creates a high pCO2
• carbon dioxide is slighly acidic which affects the H+ bonds that make up the haemoglobin’s tertiary structure, causing a conformational change
• this decreases Hb’s affinity for oxygen so more oxygen is given up readily (more dissociation)

Question 20

How does carbon affect the Oxygen Dissociation Curve?

Answer 20

• it makes the curve shift to the right
• this is because saturation decreases as more oxygen is released

Question 21

What does it mean if the Oxygen Dissociation Curve shifts to the left?

Answer 21

• there is a greater affinity for oxygen
• more oxygen is taken from the lungs (alveoli)

occurs for animals who live in an area with less oxygen (high up, underground ect)

Question 22

What does it mean if the Oxygen Dissociation Curve shifts to the right?

Answer 22

• there is a lower affinity for oxygen
• more oxygen is given out into the tissues (for examples the muscle tissue)

occurs for animals who are very active (like animals who fly or run a lot) because they need it for respiration

Question 23

Explain the difference between an adult and fetal haemoglobin.

Answer 23

fetal haemoglobin has a higher affinity for oxygen because by the time blood has reached the placenta (for the fetus to absorb) oxygen saturation has decreased

*this allows them to survive in an area of low pO2 *

*their S curve shifts to the left *