Oxygen Transport

Question 1

Explain the physiological role of haemoglobin

Answer 1

Oxygen transporter
As oxygen is non polar so not water soluble therefore oxygen transporters are required to transport oxygen to tissues further away from the cell surface

Also to transport carbon dioxide from tissues to the lungs as carbaminohaemoglobin

Question 2

Explain the role of myoglobin

Answer 2

As a temporary store
So once oxygen dissociates from haemoglobin in tissues it can associated to myoglobin and stored in some tissues for future use

Question 3

Explain how the structure of haemoglobin relates to its function

Answer 3

Fe2+ group in the middle can make two additional bonds to oxygen one on either side of the plane to but still only binds to ONE oxygen molecule.
So above and below it.
On the sides it’s bound to 4 N atoms of the ring

Question 4

Why does only one oxygen bind to haemoglobin

Answer 4

As the haem group isn’t acc free

It’s bound to a histidine via the Fe2+ so it can only make one bind to one oxygen molecule

Question 5

What is a haem group

Answer 5

Porphyrin ring system which includes an Fe2+

Question 6

Give some important structural features of myoglobin

Answer 6

Single chain sub unit
Tertiary structure with majority 2° structure of alpha helices
Small
Compact- folded loads showing its globular
Haem group in the middle

Question 7

Explain what happens when oxygen binds to myoglobin

Answer 7

Fe in deoxymyoglobin is slightly below the plane of the porphyrin ring (haem group)
Oxygen binding causes Fe to move into the plane of the ring
Which drags the histidine attached to the Fe up too
Doesn’t have much effect on conformational change in myoglobin

Question 8

What curve does a myoglobin binding to oxygen give and what does this mean?

Answer 8

Hyperbolic
It shows a hyperbolic dependence on oxygen concentration
This means the affinity of oxygen binding to myoglobin always remains the same

Question 9

What’s on the axis of the graph

Answer 9

Y- % saturation with oxygen = p02/(p02+p50) and p50= partial pressure giving 50% saturation
X - p02

Question 10

What is the shape of the curve for haemoglobin

Answer 10

Sigmoidal which tells us it binds to oxygen differently

Question 11

Give some important structural features of haemoglobin

Answer 11

Made of 4 subunits
2 alpha subunits and 2 beta subunits
Both types of subunits are of similar shape
Each subunit contain a haem group so a haemoglobin molecule can bind to 4 oxygen molecules
Each polypeptide (a subunit) has a similar conformation to myoglobin

Question 12

What different conformations does haemoglobin have?

Answer 12

Deoxyhaemoglobin can exist in a low affinity for oxygen T state or a high affinity for oxygen R state.

Question 13

What are the structural differences between the T and R state?

Answer 13

Haem groups packed closer together and space in the middle - T
Haem groups more exposed so oxygen can bind more easily and no space in the middle - R

Question 14

What affect does oxygen binding to a haem group have on haemoglobin?

Answer 14

Causes conformational change that promotes the stabilisation of the R state

Question 15

What shape is the oxygen binding curve for haemoglobin and what does its shape tell us?

Answer 15

Sigmoidal

That the binding affinity of haemoglobin to oxygen changes

Question 16

Why is the curve sigmoidal?

Answer 16

Due to co-operative binding of oxygen to haemoglobin
The binding affinity increases each time an oxygen molecule binds to a subunit
as the binding causes a conformational change that exposes haem groups
This means it becomes easiest to bind by the 4th molecule