Session 10: Haemoglobin and Myoglobin

Question 1

Where does oxygen bind on the molecule?

Answer 1

Haem group

Question 2

How many molecules of O2 can bind to the haem group in myoglobin and haemoglobin?

Answer 2

1

Question 3

How many molecules of O2 can myoglobin bind?

Answer 3

1

Question 4

How many molecules of O2 can haemoglobin bind?

Answer 4

4

Question 5

How is the heam group bound to the protein?

Answer 5

Via a proximal histidine residue

Question 6

Name 3 structural features of myoglobin.

Answer 6

• single chain polypeptide
• 153 aa
• 75% alpha helix

Question 7

Where does the iron atom of the haem group sit in a deoxymyoglobin molecule? Why?

Answer 7

Just below the plane of the ring structure as the atom is too big to sit in the centre of the haem group

Question 8

Why does the binding of oxygen cause the movement of the iron atom into the plane of the ring of a haem group?

Answer 8

Causes a conformational change

Question 9

Describe the graph of myoglobins affinity for oxygen.

Answer 9

Hyperbolic

Question 10

What is on the Y axis of an oxygen binding curve?

Answer 10

Fractional Saturation (percentage saturation of how many O2 molecules are bound to the protein)

Question 11

What is on the X axis of an oxygen binding curve?

Answer 11

pO2 (partial pressure of oxygen)

Question 12

Name the shape of a haemoglobin oxygen binding curve.

Answer 12

Sigmoidal

Question 13

Name 2 structural features of haemoglobin.

Answer 13

• 2 polypeptides

- tetramer (4 subunits, two alpha, two beta)

Question 14

Which state of deoxyhaemoglobin has the highest affinity for O2?

Answer 14

R state

Question 15

What affect does the binding of O2 have on the state of deoxyhaemoglobin?

Answer 15

Stabilises the R state

Question 16

Why is the oxygen binding curve for haemoglobin sigmoidal in shape?

Answer 16

Mixture of T and R state to allow either release of oxygen into tissues or acceptance of oxygen in the lungs respectively.

Question 17

What is cooperative binding of oxygen?

Answer 17

When the binding of one oxygen molecule promotes the binding of subsequent molecules

Question 18

TRUE OR FALSE: the binding of BPG powers the binding affinity of oxygen for haemoglobin.

Answer 18

TRUE

Question 19

How many molecules of BPG bind per haemoglobin tetramer?

Answer 19

1

Question 20

What’s the affect of an increase in BPG concentration?

Answer 20

Lowers the affinity of oxygen to haemoglobin hence releasing more oxygen into tissues

Question 21

How does the binding of protons and carbon dioxide affect the affinity of haemoglobin for oxygen.

Answer 21

It lowers the affinity of haemoglobin for oxygen.

Question 22

What is the Bohr effect?

Answer 22

When protons or carbon dioxide binds to haemoglobin, lowering the affinity for oxygen. It is important to ensure the delivery of O2 is coupled to demand.

Question 23

Which binds more strongly to haemoglobin, carbon dioxide or oxygen?

Answer 23

Carbon dioxide

Question 24

Does carbon dioxide contribute to cooperative binding of oxygen?

Answer 24

Yes

Question 25

TRUE OR FLASE: CO poisoning is irreversible.

Answer 25

TRUE

Question 26

TRUE OR FALSE: HbF has a higher binding affinity for oxygen than HbA?

Answer 26

TRUE

Question 27

Why is it important that HbF has a higher binding affinity for oxygen than HbA?

Answer 27

Allows oxygen transfer to foetal blood from adult blood supply

Question 28

What is the as mutation in sickle cell?

Answer 28

Glutamate to valine

Question 29

What is the affect of the aa mutation within sickle cell?

Answer 29

Sticky hydrophobic pocket cause multiple sickle cells to stick together

Question 30

What are thalassaemias?

Answer 30

A group of genetic disorders which have an imbalance of the alpha and beta subunits