1. transporting O2

HAEMOGLOBIN

• made of 4 globular polypeptide chains (globin)

• each w/ an iron ion (haem prosthetic group)

• the molecule that allows erythrocytes to carry respiratory gases (esp O2)

• has an affinity for O2 (can carry up to 4 O2 molecules)

• Hb + 4O2 —> Hb(O2)4

• when haemoglobin becomes oxygenated, known as oxyhaemoglobin

OXYGEN TRANSPORT- LUNGS

• in lungs, O2 diffuses into blood plasma

• then passes down conc gradient and into erythrocytes

• O2 binds to haemoglobin to maintain this conc gradient

• O2 binds to haem Fe²+ group of haemoglobin

OXYGEN TRANSPORT- RESPIRING TISSUE

• in respiring tissues, O2 disassociates (releases) from oxyhaemoglobin

• O2 can then diffuse out of erythrocytes and to respiring cells

OXYGEN TRANSPORT- LUNGS (pO2)

• amount of O2 in tissue is referred to as its partial pressure for O2 (pO2) or O2 tension

• measured in kPa

• ventilation allows lung tissue to have high pO2

• where pO2 is high, more O2 can associate w/ haemoglobin molecules to be transported

• % of haemoglobin saturation highest here

OXYGEN TRANSPORT- RESPIRING TISSUES (pO2)

• in respiring tissue, pO2 is low

• at low pO2, O2 dissociates from oxyhaemoglobin and can diffuse to respiring cells

OXYGEN ASSOCIATION

• after first O2 molecule associates, the conformation of haemoglobin changes

• conformational change makes it easier for 2nd and 3rd O2 molecules to associate

• difficult to associate a 4th O2 molecule

• bc haemoglobin molecule becomes full

• why curve plateaus below 100%

OXYGEN DISSOCIATION CURVE

• s-shape

• % Hb saturation w/ oxygen not directly proportional to pO2

• difficult to achieve 100% saturation

• conformation of haemoglobin molecule changes as O2 molecules become associated with/ it

• changes haemoglobin ability to associate w/ further O2 molecules

OXYGEN DISSOCIATION CURVE- SECTIONS

• curve going up

  • as deoxygenated blood approaches lungs, the steep part of curve means that small increase in partial pressure cause large increase in % saturation

• curve going down

  • as oxygenated blood approaches tissues, steel part of curve means small decrease in partial pressure causes large decrease in % saturation

MYOGLOBIN

• made of single globular polypeptide chain w/ 1 iron ion (haem prosthetic group)

• stores O2 in muscle cells and has higher affinity for O2 than haemoglobin in same partial pressure

• means that as blood passes through muscles, O2 more readily binds to myoglobin so is transferred to muscle cells

• supplies the O2 working muscles need for aerobic respiration, providing energy required for them to contract

OXYGEN DISSOCIATION CURVE 2

• O2 dissociation curve compares % saturation of haemoglobin and myoglobin at diff partial pressures

• at partial pressure similar to that at the tissues (muscles) myoglobin is significantly more saturated than haemoglobin

• must have a higher affinity for O2 for this to be true

FOETAL HAEMOGLOBIN

• foetal and maternal blood is kept separate in placenta

• to get O2 from maternal to foetal blood, foetal haemoglobin needs a higher affinity for O2 than maternal haemoglobin

• foetal haemoglobin O2 dissociation curve are left of adult curves- their stronger affinity means they can become saturated at lower pO2