Haemoglobin

How Haemoglobin transport oxygen:

1. Red blood cells contain Haemoglobin, which had 4 haem groups.

2. In the capillaries in the lungs, oxygen binds to iron in haem groups forming oxyhaemoglobin

3. Each Haemoglobin molecule can carry 4 oxygen molecules, one per haem group.

4. Oxyhaemoglobin can be transported via blood to repairing body tissues.

5. At body cells, oxygen dissociates from Haemoglobin.

Haemoglobin:

• Globular protein

  • Makes it spherical and water soluble

    • Allowing it to be easily transported by blood plasma

• Complex protein

• Conjugated protein

• Haem group

  • Prosthetic group

    • Non-protein

• Can bind to 4 oxygen molecules

• 4 Subunits

  • 2 alpha globin chains

  • 2 beta globin chains

• Quarternary structure

  • Enables cooperative binding

    • When one O₂ binds

    • it changes the proteins shape

      • Making it easier for subsequent O₂ molecules to bind.

Factors affecting Haemoglobin saturation

• Haemoglobin saturation with oxygen depends on the oxygen concentration or partial pressure of oxygen.

• The units for partial pressure are kilo pascals (kPa)

• Partial pressure cna be shown on a graph called an oxygen dissociation curve.

Partial pressure of edge affects Haemoglobin saturation:

• higher partial pressure

  • Haemoglobin has a high affinity for oxygen and binds with it

  • in the lungs

• lower partial pressure

  • Haemoglobin has a low affinity for oxygen and releases it

  • At the repairing body cells

Transport of oxygen

• When oxygen binds to Haemoglobin, oxyhaemoglobin is formed.

• The binding of teh first oxygen molecule causes a change in the structure of the Haemoglobin molecule making it easier for each successive oxygen to bind

  • This is called cooperative binding

• The reverse of this process happens when oxygen dissociates in the tissues

Carbon dioxide transport

• Waste CO2 produced during restoration diffuses from the tissues into teh blood.

• There are 3 ways in which carbon dioxide is transported around the body:

  1. Small percentage of carbon dioxide dissolves directly in the blood plasma and is transported in solution

  2. Carbon dioxide can bind to Haemoglobin forming carbominohaemoglobin

  3. Large percentage of CO2 is transported in teh form of hydrogen carbonate ions (HCO^3-)

     • CO2 diffuses form teh plasma into teh RBC

     • Inside the RBC CO2 combines w H2O to form (carbon acid) H₂CO₃

       • Which is catalysed by the enzyme carbonic anhydrase

         • Without this enzyme the reaction would be very slow

         • The plasma contains veyr little carbonic anhydrase so H₂CO₃ forms faster in the the RBC

     • Carbonic acid dissociates readily into H⁺ and HCO₃^- ions

     • The hydrogen ions combine w Haemoglobin to form Haemoglobinic acid

       • preventing H+ ions form lowering teh pH of the RBC

       • Haemoglobin acts as a buffer

     • The hydrogen carbonate ions diffuse out of teh RBC into the blood plasma where they are transported.

The Chloride Shift

• The chloride shift is the movement of chloride ions into RBC when hydrogen carbonate ions are formed.

• This exchange helps to maintain electrical neutrality within the cell, allowing for effective gas exchange during respiration.

• Negatively charged hydrogen carbon ions formed from the dissociation of carbonic acids are transported out of the RBC via a transport protein

• to prevent electrical imbalance, negatively charge chloride ions ar extrapolated in the RBC via the same transport protein

  • If this doesn't happen then RBC would become positively charged as a result of a buildup of hydrogen ions formed form te dissociation of carbonic acid

The oxygen dissociation curve

• It shows the arte at which the oxygen associates and also dissociates with a hemoglobin at Differnet article pressure of oxygen

  • Haemoglobin is referred to as being saturated when al of its oxygen binding sites are taken up with oxygen: so when it contains four oxygen molecules.

• The ease w which Haemoglobin binds and dissociates w oxygen can be described as it's affinity for oxygen

  • when Haemoglobin has a high affinity it binds easily and dissociates slowly

  • when Haemoglobin has low affinity for oxygen it binds slowly and dissociates easily

• With haemoglobin oxygen binds at different rates as the pO2 changes

  • Haemoglobin affinity for oxygen changes at different partial pressure of oxygen.

Explaining the shape of the curve

• Due to the shape of the Haemoglobin molecule it is difficult for the first oxygen molecule to bind to the Haemoglobin

  • Meaning the binding of the first oxygen occurs slowly

  • Explaining the relatively shallow curve at the bottom left corner of the graph

• After the first oxygen molecule binds to Haemoglobin, the Haemoglobin protein changes shape, or conformation, making I easier for the next oxygen molecules to bind

  • This speeds up the binding of the remains oxygen molecules

  • Explains stepper part of the curve in teh middle of the graph

  • The shape change of Haemoglobin eating to easier oxygen binding is known as cooperative binding

• As Haemoglobin molecule approaches saturation it takes longer for the further oxygen molecules to bind due to the shortage of remains binding sites

  • Explaining the levelling off of the curve in the top right corner of the graph

Interpreting the curve

• When the curve is read or left to right it provides information about the rate at which Haemoglobin binds to oxygen at different partial pressures of oxygen.

• At low pO2, in the bottom left corner of the graph, oxygen binds slowly to haemoglobin

  • This means that Haemoglobin cannot pick up oxygen and become saturated as blood passes through the body's oxygen-depleted tissues.

  • Haemoglobin has a low affinity for oxygen at low pO2 so saturation percentage is low.

• At medium pO2, in the central region of the graph, oxygen binds more easily to Haemoglobin and saturation increases quickly

  • At this point on teh graph a small increase in pO2 causes a large increase in Haemoglobin saturation .