Anaerobic Respiration

• anaerobic respiration

  glucose = lactic acid

  c6h12o6 = 2c3h6o3
• anaerobic respiration forms approx 2 ATP per glucose molecule
• obligate anaerobes - cannot survive in the presence of oxygen, almost all are prokaryotes
• facultative anaerobes - synthesise ATP by aerobic respiration when oxygen is present but, can switch to anaerobic in the absence of oxygen.

  for example - yeast
• obligate aerobes - can only synthesise ATP in the presence of oxygen

  for example - mammals
• ATP production still needs to happen but this can’t be done by oxidative phosphorylation due to the lack of oxygen to act as the final electron acceptor. In order for some ATP to be produced anaerobic respiration allows glycolysis to continue
• ways to re-oxidise NADH:

  • ethanol fermentation
  • lactate fermentation
• fermentation - process by which complex organic compounds are broken down into simpler inorganic compounds without the use of oxygen or involvement of the electron transport chain
• Lactate fermentation takes place in mammals
• Ethanol/Alcoholic fermentation takes place in starch
• lactate fermentation - occur in muscle tissue during physical activity, tissue has oxygen deficit
• lactate fermentation:

  • pyruvate is the acceptor rather than oxygen
  • Reduced NAD is oxidised and donates hydrogen to pyruvate, catalysed by lactate dehydrogenase
  • this forms lactic acid and regenerates NAD
  • lactic acid can be oxidised back to pyruvate to generate more ATP, or it can be stored as glycogen
  • ATP can continue to be made
• lactate fermentation:

  pyruvate = (lactate dehydrogenase) Lactate

  reduced NAD = NAD
• ethanol/alcohol fermentation:

  • Pyruvate is decarboxylated (loses a co2) and is converted into ethanal, catalysed by pyruvate decarboxylase
  • Ethanal accepts hydrogen from reduced NAD, which produces ethanol, and regenerates NAD.
  • Ethanol cannot be further metabolised so must be removed as a waste product.
• ethanol/alcohol fermentation

  pyruvate (removes co2)= (enzyme is pyruvate decarboxylase) = ethanal = (ethanol dehydrogenase) (reduced NAD becomes NAD) ethanol
• ethanol fermentation:

  ethanol is the acceptor

  co2 is produced

  no ATP is produced

  NAD is reoxidised

  ethanol and co2 are formed

  enzymes are pyruvate decarboxylase and ethanol dehydrogenase
• lactate fermentation:

  pyruvate is the acceptor

  co2 is not produced

  ATP is not produced

  NAD is re-oxidised

  lactate is formed

  enzyme used is lactate dehydrogenase