Introduction

Question 1

Describe the two states of Hb

Answer 1

Taut (T) State- unable to bind O2

Relaxed (R) State- able to bind O2

Question 2

Describe the concept of cooperative binding

Answer 2

Hb has multiple ligand binding sites, allosteric effects generate cooperative ligand binding behaviour.

Binding of O2 increases the affinity of successive ham groups to O2. It is caused by a conformational change.

Question 3

Outline the three determinants of O2 binding

Answer 3

1. Partial pressure of O2 drives O2 saturation
2. Cooperative binding
3. Factors altering O2 affinity and have allosteric effects

Question 4

Explain the difference between homo-trophic allosteric effects and hetero-trophic allosteric effects

Answer 4

Homo-trophic allosteric effects refer to when the same ligand is binding. Binding of oxygen increases affinity for Hb to bind other O2 molecules. LOADING OF OXYGEN

Hetero-trophic allosteric effects refer to when the ligands binding are different. For example, binding of CO2, H+, 2-3 DPG to non-harm groups decreases affinity for Hb to bind o2. These molecules stabilise T state thus causing the RELEASE OF OXYGEN. In this case P50(Pao2 at 50% saturation) increases and the curve shifts to the right. Temp and Cl- have the same effect

Question 5

Why does foetal Hb have a greater affinity for O2 than adult Hb?

Answer 5

Unable to bind 2.3-DPG so T state is less stable. Instead the R state is favoured which increases oxygen loading.

The curve shifts to the left and oxygen loaded from maternal blood at the cost of unloading in foetal tissues.

Question 6

Describe the binding of Carbon Monoxide with Hb and symptoms of CO poisoning

Answer 6

Hb has an affinity for CO which is 200x greater than that of O2. When Co binds Hb it stabilises the R state of remaining sites which means O2 is not released.

When CO binds Hb, the PaO2 may still read normal

Symptoms -

1. Headache because brain is affected first
2. Nausea/vomit
3. Dizziness
4. Lethargy
5. Weakness, confusion, coma, death ( CO-Hb >40%)

Question 7

What is cyanosis?

Answer 7

Blueish discolouration of skin evident in hypoxaemia. It occurs at a critical threshold of deoxygenated-Hb

Question 8

There are two steps in the reaction between water and CO2.

How does each step occur?

What happens to the final products?

Answer 8

CO2+ H20–> H2CO3 is catalysed by Carbonic Anhydrase in Hb

H2CO3–> H+ + HCO3- occurs spontaneously

HCO3- diffuses out of the cell and plasma Cl- diffuses in to maintain extra-neutrality

H+ is unable to diffuse out so is buffered by Hb. De-oxy-Hb is a better proton acceptor than OxyHb

Question 9

How does the concentration of Cl- in RBC’s differ in veins and arteries?

Answer 9

Venous Hb contains more Cl-

Question 10

How is CO2 transported in the blood?

Answer 10

90%- as bicarbonate
5% as CO2 gas
5% as carbamino compounds