Haemoglobin and Oxygen Transport

• What are the haemoglobins?

  A group of chemically similar molecules that are formed in many different organisms
• Where is haemoglobin carried?


  In red blood cells
• What are the adaptations of red blood cells?

  Biconcave shape, being flat and thin, being enucleated
• Why do red blood cells have a biconcave shape?

  It creates high surface area to volume ratio, so the diffusion of gases can occur faster
• Why are red blood cells flat and thin?


  It allows a short diffusion pathway for the exchange of gases across its membrane
• Why are red blood cells enucleated?


  It provides more space inside the cell for haemoglobin so that they can transport as much oxygen as possible
• What is the function of haemoglobin?


  It is responsible for binding oxygen in the lungs and transporting it to tissues in the body to be used in anaerobic metabolic pathways
• Why does oxygen bind to haemoglobin?


  Oxygen is not very soluble in water, but haemoglobin is, this means that the oxygen can be carried more efficiently around the body when bound to haemoglobin
• Haemoglobin is a large globular protein which is an oxygen carrying pigment found in vast quantities in red blood cells
• What is the structure of haemoglobin?


  It is quaternary, as it is made up of four polypeptide chains known as globin proteins and each subunit has a prosthetic haem group
• Haemoglobin contains two alpha globins and two beta globins
• What is a prosthetic haem group?


  A permanent, non protein part of a protein molecule
• How many globin subunits are present in haemoglobin?


  Four
• How many alpha globin subunits are present in haemoglobin?


  Two
• How many beta globin subunits are present in haemoglobin?


  Two
• What holds together the globin subunits in haemoglobin?


  Disulphide bridges
• How are the globin subunits arranged in haemoglobin?


  The hydrophobic R groups are facing inwards and the hydrophilic R groups are facing outwards
• The hydrophobic R groups of the globin subunits in haemoglobin face inwards in order to preserve the 3D spherical shape
• The hydrophilic R groups of the globin subunits in haemoglobin face outwards in order to maintain solubility
• If changes occur to the sequence of amino acids in the globin subunits in haemoglobin, the arrangement of the R groups (and thus the function of the protein) could be changed
• The prosthetic haem group in haemoglobin contains an iron 2+ ion
• What is the function of the iron ion in haemoglobin?

  It can reversibly combine with an oxygen molecule to form oxyhaemoglobin
• What is formed when oxygen binds with haemoglobin?

  Oxyhaemoglobin
• The presence of oxyhaemoglobin causes blood to appear red in colour
• Each haemoglobin contains four haem groups, which can therefore carry four oxygen molecules
• How many oxygen molecules can a single haemoglobin carry?

  Four
• How many oxygen atoms can a single haemoglobin carry?

  Eight
• When oxygen binds to haemoglobin, oxyhaemoglobin is formed in a reversible reaction, this process can be described as the loading and unloading of oxygen
• The binding of the first oxygen molecule to haemoglobin results in a change in its structure, making it easier for each successive oxygen molecule to bind
• What is cooperative binding?


  When an oxygen molecule binds to a haem group, the affinity of another oxygen molecule binding to one of the three remaining haem groups increases
• Oxygen is more likely to bind to a haemoglobin bound it one oxygen than to an unbound haemoglobin
• Haemoglobin has a higher affinity for oxygen when it is already carrying some oxygen (cooperativity)
• Why is the formation of oxyhaemoglobin a reversible reaction?


  In respiring cells, the oxygen dissociates, turning the haemoglobin into deoxyhaemoglobin
• How is deoxyhaemoglobin formed?


  When an oxygen molecule dissociates from haemoglobin
• What is oxygen affinity?


  The ease with which haemoglobin binds and dissociates with oxygen
• When haemoglobin has a high affinity, oxygen binds easily and dissociates slowly
• When haemoglobin has a low affinity, oxygen binds slowly and dissociates easily
• Haemoglobin is referred to as being saturated when all of its oxygen binding sites are taken up with oxygen (contains four oxygen molecules)
• What factors affect haemoglobins affinity for oxygen?


  Haemoglobin saturation and the partial pressure of oxygen and carbon dioxide
• What is the partial pressure of oxygen?


  The pressure exerted by oxygen within a mixture