Question

In the 1860s, Luis Pasteur noticed that when he added O2 to a culture of bacteria growing anaerobically on glucose, the rate of glucose consumption declined dramatically. Explan the basis for this effect, and make another prediction of something else you would expect to see under these same circumstances.

Answer 1

Ans:

Luis Pasteur noticed that when Oxygen (O2) is added to a culture of bacteria growing anaerobically on glucose, there was an unexpected decrease in the rate of glucose consumption. This effect can be explained as follows; If the bacteria is a facultative anaerobe, it can produce energy by using two different metabolic pathways. When the oxygen concentration is low, ethanol and carbondioxide will be produced as the product of glycolysis. The energy production efficiency is low (2moles of ATP per mole of glucose) in this cycle. If the concentration of oxygen concentration increases, pyruvate will be converted to acetyle CoA which can be used in citric acid cycle. This increases the efficiency to 29.5 moles of ATP per mole of glucose and therefore, about 15 times as less glucose only must be consumed aerobically as anaerobically to yield the same amount of ATP. This depends also on which shuttle is used for reducing the reducing equivalent, NADH that is formed in the cytosol. The Pasteur Effect will only occur when glucose concentration is low (<2 g/L) and if other nutrients, mostly nitrogen, are limited.