Anaerobic Respiration

Question 0

Explain the alcoholic fermentation pathway

Answer 0

1. Pyruvate is decarboxylated into ethanal (releasing CO2), catalysed
   by Pyruvate decarboxylase
2. Ethanal is reduced into ethanol with the H+ from NADH. NADH is
   reoxidised into NAD, catalysed by ethanol dehydrogenase

• DOESN’T take place in mammals as they don’t have the enzyme Pyruvate decarboxylase

Question 1

When does anaerobic respiration take place?

Answer 1

• oxygen is the final electron acceptor in the final stage of aerobic
respiration
–> if oxygen is not present, oxidative phosphorylation, link
reaction and Krebs cycle cannot take place
–> in these circumstances anaerobic respiration takes place
–> this is also the case in organisms or cells which do not
contain the machinery to carry out these stages e.g. RBC
have no mitochondria so only carry out glycolysis
• the purpose of anaerobic pathways is to re-oxides NAD so that
glycolysis can continue thus generating a small amount of ATP

Question 2

Explain the lactate fermentation pathway

Answer 2

1. • Pyruvate is reduced into lactate using the 2H+ from
   NADH
   • NADH is reoxidised into NAD, catalysed by lactate
   dehydrogenase

Question 3

Explain why mammals only use lactate fermentation when it is necessary

Answer 3

• a build up of lactate forms lactic acid in muscles, which lowers muscle pH, causes pain and reduces enzyme activity in muscles
• lactate is carried away from the muscles to the liver by the blood and is converted back to glucose, glycogen or Pyruvate
- this requires oxygen which is why breathing after exercise
continues to repay oxygen debt
• Pyruvate enters the Link reaction and Krebs in the presence of oxygen