haemoglobin

• How is the majority of oxygen transported around the body?

  bound to the protein haemoglobin in red blood cells
• What does each molecule of haemoglobin contain?

  4 haem groups, each able to bond with 1 molecule of oxygen

  • This means that each molecule of haemoglobin can carry 4 oxygen molecules, or 8 oxygen atoms in total
• What is formed when oxygen binds to haemoglobin?

  oxyhaemoglobin

  Oxygen + Haemoglobin  Oxyhaemoglobin

  4O2 + Hb -> Hb4O2

  <-
• What occur during the binding of the first oxygen molecule to haemoglobin?

  it results in a conformational change in the structure of the haemoglobin molecule, making it easier for each successive oxygen molecule to bind: this is co-operative binding

  the reverse of this process happens when oxygen dissociates in the tissues
• What are the 3 main ways in which carbon dioxide is transported around the body?

  1 a small percentage of carbon dioxide dissolves directly in the blood plasma and is transported in solution

  2 carbon dioxide can bind to haemoglobin, forming carbaminohaemoglobin

  3 a large percentage of carbon dioxide is transported in the form of hydrogen carbonate ions (HCO3-)
• How do hydrogencarbonate ions form?

  carbon dioxide diffuses from the plasma into red blood cells

  inside red blood cells carbon dioxide combines with water to form

  red blood cells contain the enzyme carbonic anhydrase which catalyses the reaction between carbon dioxide and water

  without carbonic anhydrase this reaction proceeds very slowly

  the plasma contains very little carbonic anhydrase hence H2CO3 forms more slowly in plasma than in the cytoplasm of RBCs

  carbonic acid dissociates readily into H+ and HCO3- ions

  H+ ions can combine with haemoglobin, forming haemoglobinic acid
• How does haemoglobinic acid form?

  H+ ions combine with haemoglobin

  this prevents H+ ions from lowering the PH of the red blood cell

  haemoglobin is said to act as a buffer in this situation
• What do the hydrogen carbonate ions produced from the dissociation of carbonic acid do?

  diffuse out of the red blood cell into the blood plasma where they are transported in solution
• What is chloride shift?

  the movement of chloride ions into red blood cells that occurs when hydrogen carbonate ions are formed

  they're transported out of red blood cells via transport proteins in the membrane

  to prevent electrical imbalance, negatively charged chloride ions are transported into the red blood cells via the same transport protein
• What would happen if chloride shift didn't occur?

  red blood cells would become positively charged as a result of a build up of hydrogen ions formed from the dissociation of carbonic acid
• How are hydrogencarbonate ions formed?

  co2 diffuses into erythrocytes, carbonic anhydrase catalyses the combining of co2 and h2o to form h2co3 (carbonic acid)

  carbonic acid dissociates to form hydrogen carbonate ions (HCO3-) and hydrogen ions (H+)
• what is special about haemoglobin?


  it has a high affinity for oxygen

  when erythrocytes reach the lungs, oxygen diffuses into them and binds to haemoglobin

  four molecules of oxygen can bind to one molecule of haemoglobin
• what is formed when oxygen binds to haemoglobin?


  oxyhaemoglobin
• what is a haem group?


  a prosthetic group that is attached to the protein (haemoglobin)

  the haem group contains an iron ion

  the iron ion is what makes haemoglobin red

  each polypeptide chain in a haemoglobin molecule has a haem group
• when does dissociation occur?


  when erythrocytes reach the tissues in the body, oxygen is released from the oxyhaemoglobin in a process called dissociation
• why is haemoglobin a quaternary protein?


  it is made from 4 polypeptide chains
• what is p(O2)?


  oxygen partial pressure, this is the concentration of oxygen in the cells

  p(O2) is important in determining whether oxygen binds to haemoglobin
• what does p(O2) determine?


  the affinity of haemoglobin for oxygen

  if p(O2) is high, haemoglobin has a high affinity for oxygen and oxygen binds to haemoglobin
• what happens if p(O2) is low?


  e.g respiring muscle tissue

  haemoglobin has a low affinity for oxygen, and so oxygen dissociates from haemoglobin
• what is carbonic anhydrase?


  the enzyme that catalyses the reaction between carbon dioxide and water, forming carbonic acid in erythrocytes

  and then back into carbon dioxide when it reaches the lungs

  H2CO3 dissociates into HCO3- ions and H+ ions in the blood

  pH is maintained by haemoglobin acting as a buffer, reacting with H+ forming haemoglobinic acid to prevent a fall in pH
• what is chloride shift?


  HCO3- ions diffuse out of the red blood cells via a transport protein in the membrane

  to prevent an electrical imbalance, Cl- ions are transported into the red blood cell via the same transport protein
• what would happen if chloride shift didn't occur?


  red blood cells would become positively charged due to an accumulation of H+ ions formed from the dissociation of carbonic acid
• why are most HCO3- ions transported in blood plasma?


  to maximise the amount of carbon dioxide carried in the blood

  (for every HCO3- ion that moves out of a rbc, one Cl- ion moves in- Chloride shift)