haemoglobin

• oxygen is carried around the body by haemoglobin in red blood cells
• red blood cells contain haemoglobin
• haemoglobin is a large protein with a quaternary structure
• it is made of four polypeptide chains
• each chain has a prosthetic haem group attached, which contains an iron ion (makes it red)
• haemoglobin has a high affinity for oxygen
• each haemoglobin molecule can carry four oxygen molecules
• in the lungs, oxygen joins to haemoglobin in red blood cells to form oxyhaemoglobin
• red blood cells are biconcave discs with a large surface area to volume ratio
• red blood cells do not contain a nucleus to provide more space inside the cell for haemoglobin so they can transport as much oxygen as possible
• the four globin subunits are arranged so the hydrophobic R groups are facing inwards, maintaining the 3D spherical shape, and the hydrophilic R groups are facing outwards, to maintain solubility
• each prosthetic haem group contains an iron ion which reversibly combines with oxygen to form oxyhaemoglobin
• red blood cells are also known as erythrocytes