Respiratory substrates                         ALBIO9700/2006JK
• Glucose is the essential respiratory substrate  for some cells such as neurones in the  brains, red blood cells and lymp...
Energy values of respiratory substrates• Most of the energy released in aerobic respiration comes  from oxidation of hydro...
Calorimeter              ALBIO9700/2006JK
Energy values           Food component     Energy density                              kcal/g     kJ/gFat                 ...
Respiratory quotient (RQ)• The overall equation for the aerobic  respiration of glucose shows that the  number of molecule...
• However, when other substrates are  respired, the ratio of the volumes of  O2 used and CO2 given off differ• Measuring t...
• For the aerobic respiration  – Glucose RQ    = 1.0  – Lipid RQ      = 0.7  – Protein RQ    = 0.9• For anaerobic respirat...
Respirometer               ALBIO9700/2006JK
• CO2 produced in respiration is absorbed (by  soda-lime/potassium hydroxide/sodium  hydroxide)• Decrease in volume of sur...
•       RQ of an organism can be measured using the same        apparatus:    –     O2 consumption at a particular tempera...
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03 Respiratory Substrates

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03 Respiratory Substrates

  1. 1. Respiratory substrates ALBIO9700/2006JK
  2. 2. • Glucose is the essential respiratory substrate for some cells such as neurones in the brains, red blood cells and lymphocytes• Other cells can oxidise lipids and amino acids• When lipids are respired, C atoms are removed in pairs, as acetyl CoA, from the fatty acid chains and fed into the Krebs cycle• The carbon-hydrogen skeletons of amino acids are converted into pyruvate or into acetyl CoA ALBIO9700/2006JK
  3. 3. Energy values of respiratory substrates• Most of the energy released in aerobic respiration comes from oxidation of hydrogen to H2O when NADH and FADH are passed to the ETC• The greater the number of hydrogen in the structure of the substrate molecule the greater the energy value• Lipids have a greater energy value per unit mass (energy density) than carbohydrates and proteins• The energy value of a substrate is determined by burning a known mass of the substrate in oxygen in a calorimeter• Energy released by oxidising substrate can be determined from the rise in temperature of a known mass of water in the calorimeter ALBIO9700/2006JK
  4. 4. Calorimeter ALBIO9700/2006JK
  5. 5. Energy values Food component Energy density kcal/g kJ/gFat 9 37Ethanol (alcohol) 7 29Proteins 4 17Carbohydrates 4 17Organic acids 3 13Sugar alcohols (sweeteners) 2.4 10 ALBIO9700/2006JK
  6. 6. Respiratory quotient (RQ)• The overall equation for the aerobic respiration of glucose shows that the number of molecules, and hence the volumes, of oxygen used and carbon dioxide produced are the same: C6H12O6 + 6O2 → 6CO2 + 6H2O + energy• So the ratio of O2 taken in and CO2 released is 1:1 ALBIO9700/2006JK
  7. 7. • However, when other substrates are respired, the ratio of the volumes of O2 used and CO2 given off differ• Measuring the ratio (RQ) shows what substrate is being used in respiration• It can also show whether or not anaerobic respiration is occurring• RQ = volume of CO2 given out in unit time volume of O2 taken in in unit time• RQ = moles or molecules of CO2 given out moles or molecules of O2 taken in ALBIO9700/2006JK
  8. 8. • For the aerobic respiration – Glucose RQ = 1.0 – Lipid RQ = 0.7 – Protein RQ = 0.9• For anaerobic respiration – Alcoholic fermentation of glucose, RQ = ∞• High values of RQ indicate anaerobic respiration is occurring• No RQ can be calculated for muscle cells using lactate pathway since no CO2 is produced glucose (C6H12O6) → 2 lactic acid (C3H6O3) + energy• O2 uptake during respiration can be measured using respirometer ALBIO9700/2006JK
  9. 9. Respirometer ALBIO9700/2006JK
  10. 10. • CO2 produced in respiration is absorbed (by soda-lime/potassium hydroxide/sodium hydroxide)• Decrease in volume of surrounding air results from organisms’ O2 consumption• O2 consumption in unit time can be measured by reading the level of the manometer fluid against the scale• Once measurements have been taken at a series of temperatures, a graph can be plotted of O2 consumption against temperature – Temperature of the surroundings must be kept constant whilst readings are taken – Presence of a control tube containing an equal volume of inert material to the volume of the organisms used helps to compensate for the changes in atmospheric pressure ALBIO9700/2006JK
  11. 11. • RQ of an organism can be measured using the same apparatus: – O2 consumption at a particular temperature is found (x cm3min-1) – Then respirometer is set up with the same organism at the same temperature but with no chemical to absorb CO2 – Manometer scale will show whether the volumes of O2 absorbed and CO2 produced are the same – When volumes same, level of manometer fluid will not change and RQ = 1 – When more CO2 produced than O2 absorbed, scale will show increase in the volume of air in the respirometer (by y cm3min-1) – RQ = CO2 = x + y O2 x – When less CO2 produced than O2 absorbed, volume of air in the respirometer will decrease (by z cm3 min-1) – RQ = CO2 = x – z O2 x ALBIO9700/2006JK

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