Anaerobic Respiration

• Anaerobic Respiration

  • Sometimes cells experience conditions with little or no oxygen
  • There are several consequences when there is not enough oxygen available for respiration:
  • There is no final acceptor of electrons from the electron transport chain
  • The electron transport chain stops functioning
  • No more ATP is produced via oxidative phosphorylation
  • Reduced NAD and FAD aren’t oxidised by an electron carrier
  • No oxidised NAD and FAD are available for dehydrogenation in the Krebs cycle
  • The Krebs cycle stops
• • However, there is still a way for cells to produce some ATP in low oxygen conditions through anaerobic respiration
• Anaerobic pathways

  • Some cells are able to oxidise the reduced NAD produced during glycolysis so it can be used for further hydrogen transport
  • This means that glycolysis can continue and small amounts of ATP are still produced
  • Different cells use different pathways to achieve this
  • Yeast and microorganisms use ethanol fermentation
  • Other microorganisms and mammalian muscle cells use lactate fermentation
• Ethanol fermentation

  • In this pathway reduced NAD transfers its hydrogens to ethanal to form ethanol
  • In the first step of the pathway pyruvate is decarboxylated to ethanal
  • Producing CO2
  • Then ethanal is reduced to ethanol by the enzyme alcohol dehydrogenase
  • Ethanal is the hydrogen acceptor
  • Ethanol cannot be further metabolised; it is a waste product
• The pathway of ethanol fermentation

  A) ADP

  B) ATP

  C) glucose

  D) pyruvate

  E) co2

  F) ethanal

  G) ethanol

  H) 2h

  I) nadh + h+

  J) nad

  K) 2h

  
• Lactate fermentation

  • In this pathway reduced NAD transfers its hydrogens to pyruvate to form lactate
  • Pyruvate is reduced to lactate by enzyme lactate dehydrogenase
  • Pyruvate is the hydrogen acceptor
  • The final product lactate can be further metabolised
• The pathway of lactate fermentation

  A) ADP

  B) ATP

  C) glucose

  D) pyruvate

  E) lactate

  F) 2h

  G) nadh + H+

  H) nad

  I) 2h

  
• Metabolization of lactate

  • After lactate is produced two things can happen:1 .It can be oxidised back to pyruvate which is then channelled into the Krebs cycle for ATP production2.It can be converted into glycogen for storage in the liver
  • The oxidation of lactate back to pyruvate needs extra oxygen
  • This extra oxygen is referred to as an oxygen debt
  • It explains why animals breathe deeper and faster after exercise