Haemaglobin Vocab Flashcards
What are haemaglobins?
A group of chemically similar molecules found in a wide variety of organisms. Protein molecules with a quaternary structure that has evolved to make it efficient at unloading oxygen under one set of conditions but unloading it under a different set of conditions. It has four polypeptide chains which are linked together to form a spherical molecule - each polypeptide is associated with a haem group which contains a ferrous (Fe2+) ion which can combine with an oxygen molecule (O2).
What is oxygen loading?
The process by which haemoglobin binds with oxygen is called loading or associating. In humans this takes place in the lungs.
What is oxygen unloading?
The process by which haemoglobin releases its oxygen is called unloading or dissociating. In humans this takes place in the tissues.
What is high affinity?
Haemoglobins with this for oxygen take up oxygen more easily, but release it less easily.
What is low affinity?
Haemoglobins with this for oxygen take up oxygen less easily, but release it more easily.
What is an oxygen dissociation curve?
The graph of the relationship between the saturation of haemoglobin with oxygen and the partial pressure of oxygen. Shows how at low oxygen concentrations little oxygen binds to haemoglobin (shallow gradient initially). After the first oxygen molecule binding, the quaternary structure of the haemoglobin molecule changes, making it easier for the other sub-units to bind an oxygen molecule, therefore it takes a smaller increase in the partial pressure of oxygen to bind the second and third molecule, so the gradient steepens. After the binding of the third molecule, it is less likely that a single oxygen molecule will find an empty site to bind to, so the gradient of the curve reduces and the graph flattens off.
What is the positive co-operativity of the oxygen dissociation curve?
The binding of the first molecule makes binding of the second molecule easier and so on, so the gradient of the curve steepens.
What is the partial pressure of a gas?
The amount of gas that is present in a mixture of gases is measured by the pressure it contributes to the total pressure of the gas mixture.
What is the Bohr shift?
The greater the concentration of carbon dioxide, the more readily haemoglobin releases its oxygen because the more carbon dioxide there is, the lower the pH, the greater the haemoglobin shape change, the more readily oxygen is unloaded and the more oxygen is available for respiration.
