Edexcel A (SNAB) A Level Biology:复习笔记7.2.7 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 (oxygen) 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
    • The link reaction also 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
  • Certain types of micro-organisms and mammalian muscle cells use lactate fermentation

Lactate fermentation

  • In this pathway reduced NAD transfers hydrogen to pyruvate to form lactate
  • NAD can now be reused in glycolysis
  • Pyruvate is reduced to lactate by enzyme lactate dehydrogenase
  • Pyruvate is the hydrogen acceptor
  • The final product lactate can be further metabolised
  • A small amount of ATP is produced

The pathway of lactate fermentation

Processing Lactate

  • Lactate (lactic acid) can build up in the cells after a period of time
  • After lactate is produced two things can happen:
    • It can be oxidised back to pyruvate which is then channelled into the Krebs cycle for ATP production
    • It can be converted into glucose by the liver cells for use during respiration or for storage (in the form of glycogen)
  • 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