Haemaglobin And Erythrocyte Function

Front 1

Structural adaptions of erythrocytes to function

Back 1

1. Small size and biconcave disc to move through capillaries
2. Membrane composed of flexible cytoskeleton and outer lipid bilayer, maintaining shape with maximum flexibility and hydrophobic skin.
3. Lack of nucleus or organelles, allowing the biconcave disc for maximum surface area.

Front 2

Oxygen transport by erythrocyte

Back 2

Oxygen from lungs is transported bound to Hb then released to the tissues.

Front 3

Carbon dioxide transport by erythrocyte

Back 3

CO2 diffuses into the bloodstream - 93% into RBCs, 7% dissolved in plasma
- 23% binds to Hb forming carbaminohaemoglobin
- 70% converted to H2CO3 by carbonic anhydrase
- H2CO3 dissociates
- H+ removed by buffers, esp Hb
- HCO3- leaves RBC in exchange for Cl-

Front 4

Structure of haemoglobin

Back 4

Haemaglobin = haem + globin
- 4 protein globin chains, each centered around a heme group
- The active site is non-protein haem

Front 5

Structure of globin

Back 5

Globular protein each composed of 8 helices, which form a hydrophobic pocket protecting haem from H2O

Front 6

Structure of haem

Back 6

Contains a porphyrin ring with iron in the middle
- Iron binds O2

Front 7

Changes to Hb during oxygenation

Back 7

- Binding of oxygen to the iron ion rearranges the electrons within the iron so that it becomes smaller
- This allows the iron to move into the plane of the porphyrin
- On oxygenation, the pair of ab subunits shifts with respect to the other by a rotation of 15 degrees: T to R transition

Front 8

Foetal Hb

Back 8

- The structure of Hb gives it a higher affinity for O2 than normal Hb
- This allows the foetus to obtain adequate oxygen from the maternal bloodstream

Front 9

Myoglobin

Back 9

- Found in muscle
- Only 1 chain with 1 haem group
- Much higher affinity for O2 than Hb

Front 10

The Bohr Effect

Back 10

The Bohr effect is the effect of pH on the Hb saturation curve.
- When pH drops, Hb releases O2 more readily
CO2 + H2O = H2CO3 = H+ + HCO3-

Front 11

Hb and Le Chatelier's Principle

Back 11

Hb (2.5H+) + 4O2 = Hb (O2)4 + 2.5H+
Hb (CO2)n + 4O2 = Hb (O2)4 + n(CO2)

Front 12

Effects of 2,3-BPG

Back 12

2,3-biphosphoglycerate
- Formed in RBCs as a byproduct of glycolysis
- Decreases Hb's affinity for oxygen, returning it to its tense form ready to deliver oxygen.

Front 13

Oxygen binding in anaemia

Back 13

- Hb conc reduced by 50% or more, shifting oxygen dissociation curve to the right
- Binding to O2 is still sigmoid and cooperative
- Hb adapts and is still able to deliver more O2 than expected

Front 14

Oxygen binding in CO poisoning

Back 14

- CO binds irreversibly to haem, with 200x greater affinity than O2.
- CO + Hb = COHb bright red carboxyhaemaglobin