Alternative Respiratory Substrates


  • both lipids and proteins can be used as repiratory substrates
  • only under certain conditions
  • do not enter the aerobic respiration cycle at the standard stages
  • respiration of lipids produces 2x as much energy as the same mass of carbohydrate
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Respiration of Lipids

  • lipids hydrolysed into glycerol and fatty acids

1st Stage

  • glycerol is phosphorylated
  • phosphorylated glycerol is converted into triose phosphate (3C)
  • enters glycolysis pathway and then the Krebs Cycle

2nd Stage

  • fatty acids broken down into 2 carbohydrate fragments via beta oxidation
  • converted into acetyl coenzyme A
  • enters the Krebs Cycle
  • H+ ions produced (used for ATP production)
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Respiration of Proteins

  • hydrolysed into amino acids
  • amino groups removed via deamination
  • enter the respiratory pathway at different parts, depending on the number of carbon atoms they contain

3 Carbon Molecules

  • converted into pyruvate
  • enter at the Links Reaction

4 + 5 Carbon Molecules

  • converted into intermediates in the Krebs Cycle
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