Haemoglobin

• Association

  Oxygen binding to haemoglobin
• Dissociation

  Oxygen being released from haemoglobin
• Affinity

  Attraction towards
• Haemoglobin

  • Protein with a quaternary structure consisting of 4 polypeptides with a haem group attached to each containing a Fe atom where one molecule of oxygen can bind to, allowing 4 molecules of oxygen to bind to one haemoglobin to form oxyhaemoglobin
• Positive cooperativity

  • As each molecule of oxygen binds onto haemoglobin the quaternary structure changes to make it easier for the next oxygen molecule to bind to by uncovering the iron atom in the haem groups
  • The same the other way round, as one oxygen leaves the structure changes for it to be easier for other oxygen molecules to dissociate
• Function of haemoglobin

  Found in erythrocytes and responsible for transporting oxygen as oxygen binds to it
• Oxygen always travels down the pressure gradient: Lungs → blood and blood → respiring tissues
• Concentration of carbon dioxide present in the blood

  Can shift the oxyhaemoglobin dissociation curve left or right as when there is:

  
  

  high conc of CO2: the conditions of the blood become acidic as there is more H+ ions which change the structure of haemoglobin to dissociate with oxygen more readily hence the curve shifts to the right

  
  

  low conc of CO2: the conditions of the blood become more basic as there are less H+ ions again changing the structure of haemoglobin to dissociate less readily and shifts the curve to the left
• Bohr effect

  Shifts in the oxyhaemoglobin dissociation curve due to factors like concentration of carbon dioxide
• Transporting carbon dioxide

  1. CO2 produced via respiration diffuses into erythrocytes

  2. CO2 reacts with water in erythrocyte cytoplasm to form carbonic acid, catalysed by carbonic anhydrase

  3. Carbonic acid dissociates into H+ and HCO3-

  4. HCO3- diffuses out erythrocyte into blood plasma due to concentration gradient, chloride ions diffuse in to maintain electrical balance (Chloride shift)

  5. In lung tissue, carbonic anhydrase reverses the reaction converting H2CO3 back into H2O +CO2 which causes more HCO3- to diffuse back into the erythrocyte and react with H+ to go through that process again

  6. Once CO2 is produced and released out the lungs, Chlorine ions diffuse out the erythrocyte down the electrochemical gradient and Hb acts as a buffer to prevent pH change by accepting H+ ions
• The oxyhaemoglobin dissociation curve shows the proportion of haemoglobin that binds to oxygen at certain partial pressures
• why is there a sudden steep increase in the oxyhaemoglobin dissociation curve

  Due to positive cooperativity, as oxygen binds to a haem group, the quaternary structure changes to make it easier for further oxygen to bind
• where is a plateau in the oxyhaemoglobin dissociation curve?


  It is hard for oxygen to locate the final haem groups
• Fetal haemoglobin has a higher oxygen affinity than adult haemoglobin
• Why does fetal haemoglobin have a higher oxygen affinity than adult haemoglobin?

  Partial pressure of oxygen is low in the placenta so oxygen dissociates from the maternal haemoglobin and diffuses to the fetal blood and increases the oxygen saturation of the fetal haemoglobin
• In areas of low pO2, oxygen will dissociate from haemoglobin
• What is the bohr effect?

  where haemoglobins affinity for oxygen decreases in areas where the concentration of CO2 increases.

  allows for haemoglobin to release oxygen into respiring tissues that need it
• what causes the Bohr effect?

  The effect of pH altering the quaternary structure of haemoglobin
• Factors that can affect the Bohr effect curve

  • Shift to the left (acidic conditions)
  • Shift to the right (basic conditions)
• Shift to the left (acidic conditions)

  1. Concentration of carbon dioxide (CO2 released in respiring tissues)

  2. Carbon dioxide + water → carbonic acid

  3. Carbonic acid → H+ + carbonic acid ion(-)

  4. Protons released make the blood more acidic

  5. Acidic conditions alter the structure of haemoglobin to lower its affinity with oxygen

  6. Oxyhaemoglobin dissociation curve shifts to the left (easier for oxygen to dissociate as there is less saturated haemoglobin at that pressure)
• Shift to the right (basic conditions)

  1. Low concentration of carbon dioxide (small amount of H+ ions present)

  2. Higher pH of the blood

  3. Alkaline conditions alter the structure of haemoglobin to have a high affinity for oxygen
• What is the structure of haemoglobin?

  a globular conjugated protein consisting of 4 polypeptides with 4 haem prosthetic group