1st

• Haemoglobin


  Group of chemically similar molecules found in many different organisms, protein with a quaternary structure
• Haemoglobin


  • Transports oxygen, readily associates with O₂ at surface where gas exchange takes place, dissociates from O₂ at tissues, changes affinity (chemical bonding) for O₂ under different conditions, contains substances that cause shape changes, binds more loosely to O₂ in different types of organisms with different affinities for oxygen
• Oxygen dissociation curve


  Shows the rate at which oxygen associates and dissociates at different partial pressures of oxygen (pO₂)
• Haemoglobin is saturated when all 4 oxygen binding sites are taken up with oxygen
• Haemoglobin's affinity for O₂ changes

  High affinity - binds oxygen easily and dissociates slowly (birds), Low affinity - binds oxygen slowly and dissociates easily (fish)
• Oxygen binding to haemoglobin

  Initial shallow increase in binding, then haemoglobin becomes fully saturated, haemoglobin has less affinity for O₂ which dissociates at low pO₂ (e.g. respiring tissues), subunits in haemoglobin molecule close up making it difficult to bind O₂, as O₂ concentration decreases the gradient of the curve steepens, binding the 1st O₂ molecule changes the shape of the haemoglobin molecule making it easier for subsequent O₂ molecules to bind, smaller increase in pO₂ required to bind 2nd O₂ molecule than 1st
• Cooperativity/Cooperative binding


  Binding the 1st O₂ molecule makes binding the 2nd molecule easier, gradient and curve reduces, harder for 4th O₂ molecule to bind because majority of binding sites occupied so less likely a single molecule will find enough space to bind