Haemoglobin

• What is haemoglobin?


  Large protein with quaternary structure- made of 4 polypeptide chains. Each chain has haem group which contains an iron ion (gives hb red colour). Each hb can carry 4 O2 molecules.
• Oxyhaemoglobin:

  In lungs O2 joins to hb in red blood cells. (Association/loading).
• Affinity for oxygen:


  Tendency a molecules has to bind with oxygen. Hb's affinity for O2 varies depending on conditions it's in.
• What is the partial pressure of oxygen (pO2)?

  Measure of oxygen concentration. Greater conc. of O2, higher partial pressure. As pO2 increases, hb's affinity for O2 increases.
• In lungs, hb has a...

  high affinity for O2
• In respiring tissues, hb has a...

  low affinity for O2
• What does an oxygen dissociation curve show?

  How saturated the hb is with O2 at any given partial pressure.
• Why is the dissociation curve S-shaped for hb?


  When hb combines with first O2 molecule, its shape alters so easier for other O2 molecules to join too. As hb starts to become saturated, it gets harder for more O2 to join.
• Partial pressure of carbon dioxide (pCO2):

  Measure of CO2 concentration in cell. Hb gives up O2 more readily at higher pCO2. Dissociation curve shifts right. (Bohr effect)
• The further left the curve...

  the higher the hb's affinity for O2.
• Low oxygen environments:


  Hb has higher affinity for O2 than human hb. (underground, high altitudes or seabed)
• High activity levels:


  Hb has lower affinity for O2 than human hb
• Size:


  Small mammals have higher surface area to volume ratio- lose heat quickly so have high metabolic rate to keep them warm ( high O2 demand). Hb has lower affinity for O2 than human hb.