transport of oxygen and carbon dioxide

• RBCs are aka erythrocytes
• what part of erythrocytes carry oxygen?

  haemoglobin
• what biological molecule is haemoglobin?

  globular conjugated protein
• haemoglobin is made up of 4 peptide chains meaning it has a quaternary structure, each with an iron containing haem prosthetic group
• how many oxygen molecules can one haemoglobin molecule bind to?

  4
• word: haemoglobin + oxygen <--> oxyhaemoglobin

  symbol: Hb + 4O2 <--> Hb(O2)4
• cooperative binding - when one oxygen molecule binds to a haem group, haemoglobin changes shape making it easier for the next oxygen molecule to bind
• what is on the y-axis of an oxygen dissociation curve?

  Percent saturation of haemoglobin with oxygen
• what is on the x-axis of an oxygen dissociation curve?

  Partial pressure of oxygen
• C?

  C

  
• why is there a faster rate of saturation after a little while on the oxygen dissociation curve?

  Cooperative binding
• where will there be a low saturation of haemoglobin with oxygen in the body?

  respiring tissues
• where will there be a high saturation of haemoglobin with oxygen?

  Lungs
• at low ppO2 haemoglobin has a low affinity for oxygen
• as the partial pressure of carbon dioxide increases, haemoglobin gives up oxygen more readily
• the bohr effect is important because in active tissues haemoglobin gives up oxygen more readily, in the lungs - where CO2 concentration is low - oxygen binds easilt
• fetal haemoglobin has higher affinity for oxygen than adult haemoglobin
• what enzyme catalyses the reaction between carbon dioxide and water to form carbonic acid?

  Carbonic anhydrase
• what is the formula of carbonic acid?

  H2CO3
• carbon dioxide is transported to the lungs in the form of hydrogen carbonate ions
• carbon dioxide to hydrogen carbonate ions?

  CO2 + H2O <-(carbonic anhydrase)-> H2CO3 <--> H+ + HCO3-
• transporting CO2: carbon dioxide and water react, with the catalysts carbonic anhydrase, to form carbonic acid which dissociates into hydrogen ions and hydrogen carbonate ions (HCO3-). the HCO3- leave the RBC into the plasma by diffusion and Cl- ions enter the RBC to balance the charges. this is known as the chloride shift.
• why is it beneficial to convert CO2 to HCO3-?

  maintain concentration gradient for CO2 to diffuse into erythrocytes
• when the blood reaches the lung tissue, carbonic anhydrase catalyses the reverse reaction of carbonic acid into carbon dioxide and water. hydrogen carbonate ions diffuse back into the RBC to form more carbonic acid. the carbon dioxide diffuses out of the blood into the lungs and chloride ions diffuse out of the RBC down an electrochemical gradient
• haemoglobin acts as a buffer by accepting the free hydrogen ions, forming haemoglobinic acid