Respiratory substances

  • Created by: portia
  • Created on: 17-04-17 12:52

Respiratory Substrates

  • glucose is the essential respiratory substrate for some cells such as neurones, red blood cells and lymphocytes
  • however other cells can oxidise lipids and amino acids
    • when lipids are respired, carbon atoms are removed in pairs as, acetyl CoA, from fatty acid chains and fed into the Krebs cycle
    • the carbon-hydrogen skeletons of amino acids are converted to pyruvate or acetyl CoA

Energy values of respiratory substrates

  • most energy liberated in aerobic respiration comes from oxidation of hydrogen to water when reduced NAD and reduced FAD are passed to the ETC
  • hence, the greater the number of hydrogens in the structure of a substrate molecule, the greater the energy value
  • fatty acids have more hydrogens per molecule than carbohydrates so lipids have a greater energy value per unit mass or energy density, than carbohydrates or proteins

The energy value of a substrate is determined by burning a known mass of the substrate in oxygen in a calorimeter

  • the energy liberated by oxidising the substrate is determined from the rise in temperature of a known mass of water in the calorimeter

Respiratory quotient (RQ)

  • the overall aerobic respiration equation of glucose shows that the ratio of oxygen taken in and carbon dioxide released is 1:1
  • when other substrates are respired the ratio of volumes of oxygen used and carbon dioxide released differ
  • therefore measuring this ratio, RQ, shows which substrate is being used in respiration
  • it can also show wheter or not anaerobic respiration is ocurring
    • the RQ will be slightly less than…


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