Protein Function

Question 1

How is oxygen transported around the body?

Answer 1

Oxygen binds to the Haem group on red blood cells

Binds to the Fe2+

Question 2

How does the Fe bind to the Haem group?

Answer 2

Histidine Residue

Question 3

What is Myoglobin’s structure?

Answer 3

153 aa
compact
mainly Alpha helix
His 93 in 8th Alpha helix is covalently linked to Fe

Question 4

What does binding of oxygen do to the Fe in myoglobin?

Answer 4

Moves from slightly below the plane of the ring to in the plane of ring changing the conformational shape

Question 5

What does oxygen binding to myoglobin show?

Answer 5

A hyperbolic dependence on oxygen concentration

Question 6

What are the features of haemoglobin structure?

Answer 6

2 polypeptide chains

2 alpha and 2 beta

Question 7

What does oxygen binding to haemoglobin promote?

Answer 7

Stabilisation of the R state

Question 8

What is the T state?

Answer 8

Low affinity state

Question 9

What is the R state?

Answer 9

High affinity state

Question 10

Why is the oxygen binding curve for haemoglobin sigmoidal?

Answer 10

Due to cooperative binding of oxygen as affinity increases as more oxygen molecules bind to the Hb subunit e.g. 1st O2- low affinity
4th O2- High affinity

Question 11

What does cooperative binding mean for oxygen transport?

Answer 11

O2 can be efficiently carried from lungs to tissues and more sensitive to small change in O2 concentrations

Question 12

What is BPG?

Answer 12

2,3- Biophosphoglycerate

Question 13

What does BPG do?

Answer 13

Decreased the affinity for Oxygen

Question 14

When does BPG concentration increase?

Answer 14

At high altitudes so O2 is released from tissues

Question 15

What is the Bohr effect?

Answer 15

Binding of H+ and CO2 lowers the affinity for oxygen
Metabolically active tissues produce lots of H+ and CO2
this ensures delivery of O2 is coupled with demand

Question 16

Why is CO poisonous?

Answer 16

Combines with Ferromyoglobin and Ferrohaemoglobin and blocks oxygen transport

Question 17

How much more readily for CO bind to Haemoglobin than O2?

Answer 17

250x

Question 18

When would CO levels become fatal?

Answer 18

When COHb is more than 50%

Question 19

What does CO binding to for unaffected subunits?

Answer 19

increase affinity for oxygen

Question 20

What is the different between Adult and Foetal Haemoglobin?

Answer 20

Adult contains 2 alpha and 2 beta

Foetal contains 2 alpha and 2 gamma

Question 21

Why is Foetal haemoglobin so important?

Answer 21

Allows transfer of oxygen to Foetus from the mother due to higher affinity

Question 22

What is the mutation in Sickle Cell anaemia?

Answer 22

Glutamate to Valine in Beta Globin

Question 23

Why does the Sickle cell mutation cause a problem?

Answer 23

Sticky hydrophobic posted form by the Valine which allow deoxygenated HbS to polymerize causing sickle shape- prone to anaemia and more rigid so cause blockages

Question 24

What is Thalassaemia?

Answer 24

Inbalance between number of alpha and beta chains

Question 25

What is a- Thalassaemia?

Answer 25

decreased or absent alpha globin chain
shows before birth
Beta chains can form stable tetramers with increased affinity for oxygen

Question 26

What is B- Thalassaemia?

Answer 26

Decreased or absent beta globin chains
alpha chains cannot form stable tetramers
shows after birth

Question 27

What do activators do to the curve?

Answer 27

Shift to left and enhance high affinity R state

Question 28

What do allosteric inhibitors do to the curve?

Answer 28

Shift to the right and enhance low affinity T state