Transportation of Oxygen

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  • Transportation of Oxygen
    • Red blood cells
      • Transport oxygen around the body
      • Have many adaptations to increase the efficiency of oxygen transportation;
        • This includes large surface area to volume ratio because;
          • They are very small
          • They don't have a nucleus which gives them a biconcave shape and increases the amount of space available for oxygen in the cytoplasm
      • Contain haemoglobin
    • Haemoglobin
      • Globular protein
      • Quarternary structure - 4 polypeptide chains, each has a tertiary structure
      • Specific 3D shape
      • Each polypeptide chain contains a prosthetic group, a non protein part called a haem group
        • Haem group contains iron ions (Fe2+). This forms loose association with oxygen
          • The 3D shape of the haemoglobin provides a specific shaped bonding site for the oxygen
            • As there are 4 haem groups, each molecule of haemoglobin can transport 4 moleucles of of oxygen
              • When oxygen combines with haemoglobin, it is called oxyhaemoglobin
                • The reaction is reversible, and when the oxygne leaves the haemoglobin it is said to dissociate
    • Red blood cells can be thought of as an oxygen taxi
      • They pick up oxygen in the lungs where the partial pressure is high, and drop off/unload in the tissues, where the partial is low and where the oxygen is needed for respiration
        • They can only pick up and drop off at one site
          • As they are only loosely associated with the oxygen, they can pick up and drop off easily and therefore association is reversible
    • The oxygen dissociation curve
      • This shows the relationship between the partial pressure of the oxygen and the percentage saturation of the haemoglobin with oxygen
        • The graph forms a sigmoid shaped curve. This is because the 4 oxygen molecules do not attach to the haem groups at the same time
          • It is difficult for the first o2 molecules to bind to the haem group, but each time an O2 attaches,it makes it easier for the next O2 to bind to a haem group
      • The shape of the curve is significant
        • The s shape indicates that haemoglobin is efficient at loading oxygen and can become fully saturated at a lower pO2 than if the relationship is linear
          • Hb has a higher affinity for O2 at a relatively high partial pressure of O2 and will therefore load O2 to form oxyhaemoglobin
            • This occurs in the capillaries of the tissues
              • The steep part of the curve shows that for a relatively small decrease in pO2, there will be a large decrease in the % saturation of Hb with O2. This means more O2 will be unloaded to the tissues to carry out aerobic respiration
      • Dissociation curve shifts to the left
        • These show a higher affinity for O2 and that at any given pO2, the % saturation of haemoglobin is higher than for normal adult haemoglobin
          • Advantage is that more O2 can be loaded at a lower pO2
            • Foetal haemoglobin
              • Foetal haemoglobin has a higher affinity for O2 than normal Hb
                • Therefore, at any given pO2, the % saturation of foetal Hb is higher than for normal adult Hb
                  • The significance of this is that the maternal Hb will unload approximately 70% of it's O2 to the tissues in the placenta. The foetal haemoglobin will then load O2 from the placenta to become approximately 80% saturated
            • Myoglobin
              • Respiratory pigment found in muscle fibres - it has a very high affinity for O2
                • This means that at any pO2, the % saturation of myoglobin is higher than normal Hb
                  • The significance of this is that;
                    • Myoglobin will retain it's O2 until very low pO2 levels occur for example, during intense exercise
                      • In this way, it delays the onset of anaerobic respiration
    • Other respiratory pigments
      • Some animals live in habitats with low O2 levels
        • The lug worm lives in sand on the sea shore. It pumps sea water through it's burrow, giving access to the limited amount of  dissolved oxygen present
          • It's Hb has a high affinity for O2
            • The advantage of this is that it can pick up more O2 and become fully saturated at lower pO
      • Llamas
        • Live at high altitudes where O2 levels are low
          • It's Hb has a high affinity for O2
            • The advantage of this is that it can pick up more O2 and become fully saturated at a lower pO2
              • At high altitudes, the number of red blood cells in the blood of mammals increases
    • Dissociation curve shifts to the right (Bohr effect)
      • During exercise, muscles work harder, so they need more ATP . Therefor , the rate of respiration increases
        • This also produces more CO2, which lowers the pH of the blood
          • The causes the dissociation curve to shift to the right, known as the Bohr effect
            • The Hb now has a lower affinity for O2
              • At any given pO2, the % saturation of the Hb is lower than for normal adult Hb
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