Oxygen transport n Haemoglobin is a conjugated protein

Oxygen transport n Haemoglobin is a conjugated protein attached to a prosthetic group n The prosthetic group is called haem and contains iron n There are four haem groups in each haemoglobin molecule each of which can bind to an oxygen molecule.

Oxygen transport Hb + 4 O 2 haemoglobin + oxygen in lungs in tissues Hb. O 8 oxyhaemoglobin

Oxygen transport n The partial pressure of oxygen (p. O 2) is a measure of the amount of oxygen concentration n The greater the concentration of dissolved oxygen, the higher its partial pressure

Oxygen transport n RBC pick up oxygen in the capillaries that cover the alveoli of the lungs n Here the partial pressure of oxygen is high and the haemoglobin becomes saturated with oxygen.

Oxygen transport n The rbc carry the oxyhaemoglobin to respiring tissues. n Here the partial pressure of oxygen is low as the oxygen is being used up in respiration. n Under these conditions, oxyhaemoglobin gives up its oxygen to the respiring cells.

Oxygen transport We say that the oxygen dissociates.

Oxygen transport Haemoglobin n In high concentrations of oxygen it will combine with large amounts of the gas. n In low concentrations it dissociates with the gas, giving it up.

Oxygen transport n Samples of haemoglobin can be exposed to different partial pressures of oxygen n The amount of oxygen combining at the different partial pressures can then be estimated n The percentage saturation of each sample can then be plotted against the partial pressure to give and oxygen dissociation curve.

p. O 2 in human lung alveoli

p. O 2 in human lung alveoli p. O 2 in human muscle capillaries

Oxygen transport Look at the graph n Hb becomes almost fully saturated with oxygen at high partial pressures such as is found in the lungs n Oxyhaemoglobin dissociates under low partia pressures such as found in respiring tissue.

Oxygen transport Why is the curve S shaped? n Each molecule of Hb has four haem groups n When the first oxygen combines with the first haem group the shape of the Hb molecule becomes distorted n This makes it easier for the other three oxygen molecules to bind to the other haem groups