Gas Transport and Oxygen - Haemoglobin binding summary

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University of Toronto Scarborough
Biological Sciences
Stephen Reid

Gas Transport and Oxygen Haemoglobin Binding Haemoglobin Haemoglobin consists of 4 subunits 2 alpha subunits and 2 beta subunits. Each of these subunits consists of a globin molecule (alpha globin or beta globin) plus a heme group. The heart of the heme group is an iron (Fe) molecule that is the site of oxygen binding. The vast majority of the oxygen in blood is bound to haemoglobin. Only about 1.5% of the oxygen in blood is in the dissolved form within plasma. 98.5% is bound to haemoglobin. Haemoglobin only exists in red blood cells. It is not found in the plasma or any other tissues. Carbonic Anhydrase Carbonic anhydrase is an enzyme that catalyses the reversible CO hydrationd2hydration reaction. It is found within the red blood cells. + - H + HCO H 3 + CO 2 2 This reaction goes both ways depending upon the relative concentrations of the constituents on each side. Sometimes you see the intermediary carbonic acid (H CO appear 2n th3)equation. However, carbonic acid is so short-lived that it is impossible to ever quantify it. It is usually left out of the equation. + - H + HCO H 3O H 0 2 CO 3 2 2 Oxygen and Carbon Dioxide Transport in the Blood + Deoxygenated haemoglobin has a H ion (proton) bound to it. This is called a Bohr proton. When oxygen bind to haemoglobin (Hb) the H ion is released into solution. O + H Hb HbO + H + 2 2 + The H ion in the above equation links that equation to the CO hydration2ehydration reaction. It also means that oxygen transport in the blood is intimately linked to CO transport.2O transport 2 affects CO t2ansport and CO transp2rt affects O transport2 + - H + HCO H 3 + CO 2 2 In the lungs, oxygen diffuses from the lung gas into the plasma and then into the red blood cells. In the red blood cell, oxygen binds to deoxygenated haemoglobin. This causes haemoglobin to + become oxygenated but it also causes the release of a H ion (Bohr proton) from haemoglobin. This H ion reacts with a bicarbonate ion (carbonic anhydrase catalysis) to form water and CO . 2
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