Cards (15)

  • When haemoglobin is exposed to different partial pressures of oxygen, it doesn't bind to the oxygen evenly.
  • The graph of the relationship between the saturation of haemoglobin with oxygen and the partial pressure of oxygen is known as the oxygen disassociation curve.
  • The shape of the oxygen disassociation curve can be explained. Firstly, at low oxygen concentrations, little oxygen binds to haemoglobin because the shape of the haemoglobin makes it difficult to bind to the first oxygen molecule. This makes the gradient of the curve shallow initially.
  • The binding of the first oxygen molecule to haemoglobin causes it to change shape. This makes it easier for the other subunits to bind to the oxygen molecules. Therefore, the curve steepens.
  • Once the third oxygen has bound to the haemoglobin, it becomes more difficult for the last oxygen to bind. This is because 3/4 of the binding sites are already occupied, so it is harder to find a binding site. As a result, the gradient of the curve flattens off.
  • The further to the left the oxygen disassociation curve is, the greater the affinity for oxygen.
  • The further to the right the oxygen disassociation curve is, the lower the affinity for oxygen.
  • After the binding of the first oxygen to haemoglobin, a smaller increase in partial pressure is required to bind the second oxygen molecule. This is known as positive cooperativity. This causes the gradient of the curve to steepen.
  • Haemoglobin has a reduced affinity for oxygen in the presence of carbon dioxide.
  • The Bohr effect describes how as the concentration of carbon dioxide increases, the readiness of haemoglobin to release its oxygen also increases (reduced oxygen affinity).
  • At gas exchange surfaces, the concentration of carbon dioxide is low because it diffuses across the exchange surface and is excreted from the organism. As a result, oxygen affinity increases and because of the high oxygen concentration, more oxygen is readily loaded by haemoglobin.
  • In rapidly respiring tissues, the concentration of carbon dioxide is high. This reduces oxygen affinity and alongside low oxygen concentration, more oxygen is readily unloaded/released by the haemoglobin.
  • In humans, haemoglobin usually becomes saturated with oxygen as it passes through the lungs. However, not all haemoglobin molecules are fully loaded with four oxygen molecules.
  • When haemoglobin reaches a tissue with a low respiratory rate, only one oxygen molecule will be released.
  • When haemoglobin reaches a tissue with a high respiratory rate, three oxygen molecules will be released.